Exposures from the Uranium Series With Emphasis on Radon and Its Daughters

NCRP Report No. 77

Exposures From the Uranium Series With Emphasis on Radon and I t s Daughters

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Recommendations of the NATIONAL COUNCIL O N RADIA'TION PROTECTION A N D MEASUREMENTS

Issued March 15,1984 First Reprinting January 15,1987 Second Reprinting April 30, 1991 National Council on Radiation Protection and Measurements 7910 WOODMONT AVENUE 1 BETHESDA, MD 20814

LEGAL NOTICE This report was prepared by the National Council on Radiation Protection and Measurements (NCRP). The Council strives to provide accurate, complete and useful information in its reports. However, neither the NCRP, the members of NCRP, other persons contributing to or assisting in the preparation of this report, nor any person acting on the behalf of rny of these parties (a) makes any warranty or representation, express or implied, with respect to the accuracy, completeness or usefulness of the information contained in this report, or that the use of any information, method or process disclosed in this report may not infringe on privately owned righta; or (b) assumes any liability with respect to the use of, or for damages resulting from the use of, any information, method or process disclosed in this report.

L i b r a r y of Congress Cataloging i n Publication D a t a National Council on Radiation Protection and Measurements. Exposures from the uranium series with emphasis on radon and ita daughters. (NCRP report, ISSN 0083-209X; no. 77) "Issued March 15, 1984." Includes bibliographical references and index 1. Radiation-Safety measures. 2. Uranium-Physiological effect. 3. Radon-Physiological effect. 4. Radiation-Measurement. I. Title. 11. Series. RA 569.N353 1984 363.1'79 84-3420 ISBN 0-913392-67-7.

Copyright 8 National Council on Radiation Protection and Measurements 1984 All rights reserved. This publication is protected by copyright. No part of this publication may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotation in critical articles or reviews.

Preface In 1981, the National Council on Radiation Protection and Measurements (NCRP) gave consideration to the potential exposure of the U.S. population from elevated levels of natural background or from the redistribution by man's activities of naturally occurring radionuclides. Brief examination led to the conolusion that the potential for significant exposure justified an in-depth study and a scientific committee was established to evaluate the situation and, if necessary, formulate recommendations. The effort was focused on exposures from the principal sources of possible concern, the radionuclides of the uranium series, particularly radon and its daughters. The work of the committee culminated in this report. The report surveys the sources of radon, assesses the levels of exposure and their probable distribution, and estimates the risks attributable to these exposures. This makes it evident that while information on levels and number of individuals exposed in the U.S. is incomplete and needs to be improved, radon daughter exposure potentially constitutes the most significant exposure of the U.S. population. As a result, the report goes on to specify a level of exposure at which remedial measures need to be considered and suggests possible remedial measures. In this report levels for remedial action are specified to include exposure from natural background (but not medical exposure). This report constitutes an important adjunct to the Council's work on basic radiation protection criteria, which has recently resulted in a draft report which is before the Council members for review. The draft report specifies permissible levels of exposure for workers and members of the population in terms of risk. It too specifies remedial action levels to include natural background (but not medical exposure), as distinct from the specification of limits for exposure of the public from sources other than background The Council has noted the adoption by the 15th General Conference of Weights and Measures of special names for some units of the Systkme International &Unites (SI) used in the field of ionizing radiation. The gray (symbol Gy) has been adopted as the special name for the SI unit of absorbed dose, absorbed dose index, kerma, and specific energy imparted. The becquerel (symbol Bq) has been adopted iii

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Preface

as the special name for the SI unit of activity (of a radionuclide). One gray equals one joule per kilogram; and one becquerel is equal to one second to the power of minus one. Since the transition from the special units currently employed-rad and curie-to the new special names is expected to take some time, the Council has determined to continue, for the time being, the use of rad and curie. T o convert from one set of units to the other, the following relationships pertain: 1 rad = 0.01 J kg-' = 0.01 Gy 1 curie = 3.7 X 10'O.s-l = 3.7 x 10" Bq (exactly). Serving on Scientific Committee 73 on Exposures from The Uranium Series with Emphasis on Radon and its Daughters were John H. Harley, Chairman P.O. Box M 268 Hoboken, NJ 07030 Members

Naomi H. Harley Department of Environmental Medicine New York University Medical Center 550 First Avenue New York, NY 10016

John W. Healy H-1, University of California Los Alamos National Laboratory P.O. Box 1663 Los Alamos, NM 87544

George V. LeRoy 171 N. Rutledge Street Pentwater. MI 49449

Ernest G. Letourneau Director Radiation Protection Bureau Department of National Health and Welfare Brookfield Road Ottawa, Ontario, KIA 1C1 Canada

NCRP Secretariat, William M. Beckner E. Ivan White

The Council wishes to express its gratitude to the members of the Committee for the time and effort devoted to the preparation of this report. Bethesda, Maryland November 7, 1983

Warren K. Sinclair President, NCRP

Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Natural Background Radiation . . . . . . . . . . . . . . . . . . . . 1.2 Elevated and Enhanced Natural Radioactivity . . . . . . 1.3 Exposure to Enhanced Natural Radiation . . . . . . . . . . 1.4 Remedial Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Characteristics of the Uranium Series . . . . . . . . . . . . . . . 3 Soil Content and Transport . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 General Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Normal Concentrations in the United States . . . . . . . . 3.3 Examples of Enhanced Concentrations . . . . . . . . . . . . . 4 External Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Indoor Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Elevated Natural Background Areas . . . . . . . . . . . . . . . 4.4 Enhanced Natural Activity Areas . . . . . . . . . . . . . . . . . . 5 Inhalation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Outdoor Radon and Radon Daughters . . . . . . . . . . . . . . 5.2 Indoor Radon and Radon Daughters . . . . . . . . . . . . . . . 5.3 Origins of Radon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Sources of Radon in Buildings . . . . . . . . . . . . . . . . . . . . 5.5 Variations of Radon Concentrations Within the Home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6 Remedial Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Measurement of Exposure and Estimation of Dose . . . 5.8 Inhalation of Other Series Members . . . . . . . . . . . . . . . 5.9Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Drinking Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Uranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Radium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Radon in Drinking Water . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Lead-210 and Polonium-210 in Drinking Water . . . . . 6.5 Remedial Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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...

111

1

2 4 5 7 7 9 12 12 15 16 19 19 20 22 23 25 25 26 32

32 33 35 41 42 43 44 45 47 52 54 55 55

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CONTENTS

7 Dietary Intake and Body Content . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Natural Uranium (U.238. 234) . . . . . . . . . . . . . . . . . . . . 7.3 Radium-226 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Lead-210 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Uranium. Radium and Lead in Human Tissues . . . . . . 7.6 Skeletal Dose from Alpha Irradiation . . . . . . . . . . . . . . 7.7 Lung Dose Due to Inhaled Lead-210 and Polonium-

56 56 57 59 61 63

65

210 in Cigarette Smoke . . . . . . . . . . . . . . . . . . . . . . . . . . 67 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 8 Dose Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 8.1 Radon Daughters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 8.2 External Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 8.3 Ingested Radionuclides . . . . . . . . . . . . . . . . . . . . . . . . . . 71 8.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 9 Basis for Recommendatione . . . . . . . . . . . . . . . . . . . . . . . . . 73 9.1 Risk Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 9.2 Dose Limitation Approach . . . . . . . . . . . . . . . . . . . . . . . 79 9.3 Exposure Distribution Approach . . . . . . . . . . . . . . . . . . 81 9.4 Additivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 9.5 Existing Recommendations . . . . . . . . . . . . . . . . . . . . . . . 84 9.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 10 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 10.1 Inhalation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 10.2 External Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 10.3 Ingestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 10.4 Land Use for Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . 90 10.5 Land to be Used for Housing . . . . . . . . . . . . . . . . . . . . . 90 10.6 Use of the Recommendations . . . . . . . . . . . . . . . . . . . . . 91 10.7 Need for Additional Data . . . . . . . . . . . . . . . . . . . . . . . . 92 10.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 APPENDIX A-Regulatory Status . . . . . . . . . . . . . . . . . . . . . 95 APPENDIX B-Measurements for Assessing Exposures . 98 APPENDIX C-Derivation of Soil Guid-Uranium, Radium and Lead-2 10 . . . . . . . . . . . . . . . . . 101 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 The NCRP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 NCRP Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

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7.8 Summary

1. Introduction This report is intended to present an evaluation of the exposures and an estimation of the risks from enhanced natural or elevated natural radioactivity of the uranium series. Recommendations are made on remedial action levels for exposure of individuals in the population to elevated and enhanced radioactivity. Enhancement of natural radioactivity results, most notably, from the mining of uranium ore and phosphate rock. These operations cause material that is more radioactive than the average soil to reach the accessible environment, exposing local populations to increased external radiation and to possible increases in the amounts of radionuclides inhaled and ingested. Elevated natural radioactivity, on the other hand, refers in this report to levels which are well above the average, but which do not result from human activities. The principal decay chain for the uranium series is shown in Figure 1.1. The most striking feature of the chain is that 222Rnis a gas and that a fraction of this gas can escape to the atmosphere after formation. The resulting atmospheric transport and the inhalation of radon and its short-lived daughter products give a very different exposure pattern than that for radionuclides that are not airborne. The solid members of the series, including isotopes of uranium, thorium, radium, bismuth and lead are all heavy metals and tend to accumulate in bone, while polonium is also distributed in soft tissues. The polonium in bone is essentially all from decay of the lead parent present in the skeleton. Externally, 214Biand 214Pb,which emit virtually all the gamma rays from the series (Table 2.1),contribute about one-quarter of all the natural terrestrial background gamma radiation. Internally, the alpha emitters are most significant, both for inhaled and for ingested materials. The three potentially deleterious health effects considered in this report are lung cancer from the short-lived daughters of radon, bone cancer from the other members of the uranium series in the body and total cancers from whole body exposure to external gamma radiation. This report describes the various modes of exposure to members of the uranium series and indicates the range of values for natural background, elevated natural background and enhanced natural back-

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1. INTRODUCTION

U-238 (UI) 4.2 MeV

2.51 1O'y 47-4.8 MeV

Princ~pal Decay Scheme of the Uranium Series

Th-234 (UXJ 0.2,O.l MeV

8.0 r 10' y 4.6-47 MeV

Rn-222 5.5 MeV Po-218 (RoA) 3.05m 6.0 MeV 01-214 I Beta Decay 07.10 MeV

Po-2IO(RaF) 138 d

Po-214 (Roc? 1.6xIO-*s 2 7.7 MeV

7 5.3 MeV

R~c~

1

01-210(RaEI 5.0 d

7 1.2 MeV

Pb-210 (ROD)' 2 2 ~ < 0.1 MeV

'

1

Pb-206 (RoG) STABLE

Fig. 1.1. Principal decay scheme of the uranium series.

ground levels. As a final step, recommendations are made for remedial action levels for exposure to radiation from the uranium series. In preparing this report, it became apparent that the present data are not adequate for describing the mean and distribution of radiation exposures for the population of the United States. Since natural sources give rise to the largest human exposures under most conditions, an additional recommendation is made that the necessary radiation surveys be carried out.

1.1 Natural Background Radiation The NCRP published a review in 1975, Report NO. 45, Natural Background Radiation in the United States (NCRP, 1975). which described the sources of natural radiation exposure and their variability. Since that report was issued, some additional data on average indoor radon exposures have become available. This results in a large increase in the estimated dose equivalent to lung from radon daughters because the original report considered only the lower average outdoor values. Table 1.1 compares the two sets of figures and includes gonad and bone doses as well. It should also be noted that the International

1.1 NATURAL BACKGROUND RADIATION

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TABLE1.1-Summary of average dose equwalent rates in mremly from uarious sources of natural background radiation in the United States. (Values are from NCRP Report No. 45. Present best estimates are given inparentheses.) Gonads Bone surfaces Bronchial epithelium Cosmic radiation" Cosmogenic radionuclides External terrestrialb Inhaled radionuclides Radionuclides in the body Rounded totals

28 1 26 27 (35)d 80 (90)

28 1 26 60 (105)~ 120 (160)

28 1 26 450 (3000)' 24 ( 4 0 ) ~ 500 (3000)

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'Allowing for 10% shielding by buildings. Allowing for 20% shielding by buildings and 20% by the body. ' Does not include thoron and its daughters. The modified value allows for indoor exposure to radon daughter inhalation and a change in quality factor from 10 to 20 for alpha radiation. Allows for a change in quality factor from 10 to 20 for alpha radiation. Note: These values are the same as the values in NCRP Report No. 45 and have not been reassessed except as noted above and except in the case of inhaled radionuclides. The average value 3000 mremly, to bronchial epithelium is discussed and derived in Chapter 5 of this report.

Commission on Radiological Protection (ICRP) recommended, as an approximation, a quality factor for alpha radiation of 20 (ICRP, 1977a). The NCRP is involved in an extended study of this question and the present report uses the value of 20 as an interim measure. A quality factor of 10 was used in NCRP Report No. 45. Geographical differences in natural background were also estimated in NCRP Report No. 45 for external gamma radiation, cosmic radiation and radiation from radionuclides in the body. Three levels of external gamma dose equivalent rate were noted-15 mrem/y for the Gulf and Atlantic coastal plains, 30 mrem/y for most of the United States, and 55 mrem/y for a rather undefined area along the Eastern slopes of the Rocky Mountains. Cosmic-ray variation is primarily a function of altitude, other factors such as latitude and the solar cycle causing a variation in dose equivalent rate of only about 10%. The sea-level dose equivalent rate of 26 mrem/y is doubled at about 2000 meters; only a small fraction of the population would have this higher exposure. The whole-body dose equivalent rate from radionuclides in the body is dominated by the 20 mrem/y from the body potassium, which is under homeostatic control and does not vary strongly with diet. There is some variation with age and sex, but this does not affect the considerations in this report. The dose equivalent rate to bone surfaces is controlled by the internal alpha emitters. This quantity is subject to some variability but present data, except for '"jRa, are not adequate

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1. INTRODUCTION

to give an estimate of the range. Similar deficiencies exist in the data for the dose equivalent rate to the lung from inhaled radon daughters, although the limited data available indicate that the range is large. In most cases, the geographic differences in total dose equivalent rate from natural background are limited to a factor of less than two from the average. This is because the three sources-external terrestrial radiation, cosmic radiation and radiation from internal emittersdo not all change in the same direction at the same place. If the detailed data were available, however, it is probable that small areas, small groups, and individuals in particular would show a much greater range. For the present purpose, the evaluation of exposures from elevated and enhanced sources, the average dose equivalent rates shown in Table 1.1 are an adequate basis for comparison. It is these values that are meant when "average naturaln or "normaln levels are referred to in this report.

1.2 Elevated and Enhanced Natural Radioactivity

The term elevated natural radioactivity is used in this report to describe radioactivity that results in exposures which are several times the average values shown in Table 1.1, but which are natural in origin. At present, these are not subject to regulation but the recommendations of this report should apply to such exposures. It is to be expected that more widespread measurements of the terrestrial component of natural background in the United States will bring to light areas of elevated natural exposure. Such areas have already been described for Brazil (Penna-Franca et al., 1972)and India (Gopal-Ayengar et al., 1975) where the thorium mineral monazite occurs and for the uraniferous areas of Canada (Richardson et al., 1972). The data on levels of radon and its daughters are also limited. Some measurements of elevated natural levels indoors and outdoors have been reported for the United States but much of the effort has been spent on enhanced levels. Surveys of thousands of houses are available for Canada (Letourneau et al., 1979; McGregor et al., 1980)and surveys are in progress in some European countries. Elevated natural levels will undoubtedly be found and these will have to be dealt with along with enhanced levels. The term enhanced natural radioactivity has come to mean the increase over natural background that occurs when an area is disturbed

1.3 EXPOSURE TO ENHANCED NATURAL RADIATION

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by human activities. No new radioactivity is produced, but the radionuclides are redistributed in a way that increases the real or potential human exposure. Typical examples appear when uranium ore, thorium ore and phosphate rock are mined or extracted. Residues from the mining or the ore treatment are left on the surface and their radioactivity is the source of the exposure. In addition to bringing the radioactive material physically closer, it is likely that the ore processing may change the chemical availability of the radionuclides with respect to water solubility, plant uptake and metabolic behavior. While it is possible that the availability might be decreased, the nature of most chemical processes is such that solubility and similar factors are generally increased. The increased exposures from mining and processing appear to be local rather than global. For example, mining of the world's known and probable reserves of uranium ore would allow the added release of about lo7 Ci of mRn per year. Present global releases from radium present in surfgce soil are more than 100 times as great. Exposures resulting from ingestion of enhanced radium in soil are also confined to local areas because the transport mechanisms are limited. Radium and other radionuclides released to water could be ingested downstream. Radon, of course, travels farther in air but measurable increases above background levels seem to be confined to a kilometer or so from the source (Shearer and Sill, 1969).

1.3 Exposure to Enhanced Natural Radiation As with average natural background radiation, the modes of exposure are external irradiation from gamma rays and internal irradiation from ingestion and inhalation of radionuclides. In most cases, we can make direct comparisons with the natural levels in the environment as a basis for predicting the doses from enhanced radiation. In a few cases, it is necessary to use transport or metabolic models and, of course, dose models are required for internal emitters.

1.3.1 External Radiation. Enhanced external radiation comes largely from the soil. Buildings provide shielding to some extent from the terrestrial component; in NCRP Report No. 45 an overall reduction of 20% from the outdoor dose rate was assumed. Building materials contain some radionuclides that may influence the indoor dose rate, with frame houses being lower

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1. INTRODUCTION

than masonry structures. These latter usually exhibit radium concentrations quite comparable with those-of the average soil (1 pCi/g), so any shielding is offset by the intrinsic radioactivity. Building materials with enhanced radioactivity can contribute to exposure in some areas, both when used as structural blocks or bricks and when sand with higher than average radionuclide content is used in mixing concrete or for fill. An additional factor to consider for external radiation is the shielding of various organs by the body itself. This produces an additional reduction in dose to the gonads of about 20% and is included in the dose equivalent rates given in this report.

1.3.2

Ingestion.

Ingestion of food and water containing 226Raand it, long-lived daughters, 'lOPb and "OPo, results in a significant dose equivalent to bone surfaces. These sources were estimated in NCRP Report No. 45 to contribute an average of about 30 mrem/y. This is about half the total dose equivalent to bone surfaces, the other half being split between 'OK and the thorium series. Some of the radon daughters come from inhalation but the two intakes cannot be readily separated. In areas of elevated or enhanced radioactivity, the intake could be increased above average natural levels by the consumption of locallygrown foods and by contamination of the water supply. Because the known areas of high radium content do not appear to have large numbers of people engaged in subsistence farming, the radionuclide content of the local food supply is diluted considerably by foods from other areas. Such dilution would not occur in the case of the water supply and this source is more likely to produce local variability in dietary intake.

1.3.3 Inhalation. Inhalation of the short-lived radon daughters produces a dose equivalent rate to the lungs larger than that to any other human organ from natural background. As will be discussed later in detail, the average indoor radon concentrations lead to exposures to members of the public that are about 5% of the presently allowed occupational level for miners. By contrast, the average body radium content of about 30 pCi is a very small fraction of the allowed occupational level of 100,000 pCi. It is obvious that a relatively small enhancement for radon daughters can lead to exposures that are a significant fraction of recommended levels.

1.5

UNITS

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7

Indoor radon concentrations are ordinarily several times those observed outdoors. A major source in houses is emanation of radon from the ground under and around the house, so that basements tend to be highest and upper floors the lowest in a particular house. The level can be reduced markedly by ventilation-essentially dilution by outside air-so that it is likely to vary both diurnally and seasonally. The outdoor radon concentration also shows diurnal and seasonal patterns, some of which are due to atmospheric ventilation and some to changes in the rate of radon emanation from the ground. These latter factors, in turn, can affect indoor concentrations. Indoor radon levels can also be increased by the release of dissolved radon during household water usage, burning of natural gas and by radon emanation from materials of construction. The relative importance of these and the ground source vary from place to place and are considered further in Section 5. 1.3.4 Summary of Exposures. In summary, it is necessary to consider all of the sources of exposure in each area of elevated or enhanced natural radiation to evaluate possible risk to the population. It is likely that inhalation is the most significant factor and ingestion the least, but the relative importance can conceivably be altered a t specific sites. 1.4 Remedial Actions When the levels of exposure are found to exceed recommended values, it is generally possible to reduce them by various techniques. These are addressed in more detail in the chapters on the various modes of exposure. All remedies have some cost, for example not using contaminated foods, increasing home ventilation or removing contaminated material from or around houses require the expenditure of money or effort. Research is being conducted on new remedial techniques and on increasing their efficiency, so the actual remedies used will change with time and circumstances. The primary requirements before remedial action can be effective are that the source be definitely identified and then either removed or mitigated. General efforts to reduce exposure without locating the source are likely to be inefficient. 1.5 Units Since the exposures to radiation from the uranium series have a long history and an extensive literature, the traditional units for activity, absorbed dose and dose equivalent will be used in this report.

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1. INTRODUCTION

In the case of radon daughter inhalation, all of the air concentrations to which uranium miners were exposed are given in terms of the Working Level (WL). It is thus necessary to continue its use in this report, although it is not truly descriptive of any radiation dose. The WL is defined as that concentration of radon daughters which has a potential alpha energy release of 1.3 x lo5 MeV per liter of air. The unit of exposure is the Working Level Month (WLM) which is defined as exposure to an average of one WL for a working month of 170 hours. For annual exposures, a miner exposed a t an average concentration of 1 WL during his working hours (170 hlmonth) would accumulate 12 WLM/y. In the case of members of the population exposed continuously (730 hlmonth) to 1 WL, they would accumulate a rounded value of 50 WLM in a year.

2. Characteristics of the Uranium Series Uranium-238 is the first member of one of the three primordial radioactive series that occur in nature. The principal decay scheme of the series is shown in Figure 1.1 and the energies released in decay of the various members are listed in Table 2.1. If the series has been undisturbed by chemical or physical changes, there will be radioactive equilibrium, where each member of the series has a decay rate essentially equal to that of the parent 238U.Actually, in the environment, a number of processes take place which tend to separate the series into groups. Thus a given environmental sample may not be in radioactive equilibrium, although the global radioactivity of each series member must be equal. The degree of separation depends not only on the process efficiency but also on the relative time scales of the radioactive half-lives and the particular geological, meteorological or biological process. For example, slow processes cannot separate the parent nuclide from daughter products that have short half-lives, since the daughters will grow back into equilibrium very rapidly. The uranium series may be divided into four major groups: 1. 238U,234Th,234mPa,n4U and 230Th generally behave as a group, which is formed by the with two exceptions. An atom of decay of mmPa may recoil sufficiently to displace it from the original crystal lattice. The free atom may then be oxidized to a more soluble form. Thus, water samples have been found with a 238Uf34Uratio as low as 0.1 (UNSCEAR, 1977). Thorium-230 follows the group in terrestrial and fresh water environments but in the oceans it tends to precipitate preferentially and is enriched in the sediments. In the body, uranium accumulates in bone, although inhaled material is only translocated from the lung very slowly, since the naturally-occurring element is usually in an insoluble form. Soluble uranium that is ingested is regarded as a chemical toxin affecting the kidney. The n4Th and 234mPaare short-lived and decay in place, while the long-lived 230Th also tends to be taken up by bone. 9

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2. CHARACTERISTICS OF THE URANIUM SERIES

TABLE2.1-Energies of the principal emissions in the natural umnium series. (Only emissions appearing in at least 5% of the decays aregioen.) Radionuclide

Alphe energy

Maximum beta energy

Gamma energy

(MeV)

(MeV)

(MeV)

2. Radium-226 is readily separated from earlier members of the series and is distributed differently in nature. It is an alkaline earth and follows calcium and barium in its chemical reactions and metabolism. Radium also accumulates in bone, with more than 90% of the body content being found in the skeleton. Some of the resultant bone dose comes from decay of 222Rnand its short-lived daughters, since about one-third of the gaseous radon formed in the body is not exhaled (UNSCEAR, 1977). 3. Radon-222 is an inert or noble gas, having no natural chemical compounds. As a gas, it may separate from its parent radium and enter the atmosphere. In an unventilated, enclosed space, it will be close to equilibrium with its solid, short-lived daughters 218P~, 2'4Pb, 21'Bi and 2 1 4 P ~but , some separation of the solid products from the parent is common in nature. The alpha radiation from the short-lived radon daughters gives the significant dose to the lung, while the gamma rays from the '14Pb and '14Bi in soil give essentially all of the external terrestrial

CHARACTERISTICS OF THE URANIUM SERIES

/

11

gamma radiation dose from the uranium series. Radon is soluble in body fluids and in fats but the resulting doses are negligible compared with those to the respiratory system from the inhaled daughter products. 4. The longer-lived decay products of radon, 210Pb,'lOBi and 210Po, are also subject to physical and chemical processes in the environment that can cause disequilibrium, although it is still convenient to consider them as a group. In the body, lead accumulates in bone, and its short-lived bismuth daughter decays in place. Polonium is distributed in soft tissues as well as bone. Inhalation and ingestion contribute some 210Poto the body content but the primary source of 210Pois the decay of 210Pbin the body. This is because the 22-year half-life 210Pbcan build up a much larger body content than the 138-day half-life 'loPo. The significant bone dose equivalent comes from the alpha emission of 210Po,this being almost ten times the beta dose equivalent from the 'I0Bi. to the extent It should be noted that natural uranium contains 235U of 0.7%. This isotope is the parent of another primordial series with a This similarity and the low decay chain very similar to that of 238U. allows US to avoid considering possible contriconcentration of 235U butions separately. In summary, the uranium series contains seven chemical elements that are important. The metabolic behavior of each of these follows its own chemistry although the similarity of the group, as heavy metals, means that some generalizations are possible. The dose contributions of emission, half-life and energy. These properties are included in the dose factors used in this report which have been adopted from other sources.

3. Soil Content and Transport The rocks, and the soils derived from them, are the repositories of the primordial radionuclides. Immediately ~€ter formation, a large number of radionuclides was present. However, all except those with very long half-lives or those that are daughters of long-lived parents have disappeared. In this report, the primary interest is in the series headed by 238U, the uranium series.

3.1.1 Environmental Behavior. For purposes of analyzing environmental behavior, the series may be divided into four parts a little different from those given in Section 2; the group from ='U to ='Us 230Th,226Raand its short-lived daughters to '14Po, and 210Pbthrough 210P~. Each of these groups is headed by a relatively long-lived radionuclide that controls the quantity and the behavior of its immediate daughters. In the fvst grouping, the important radiological constituents are the 238Uparent and the 234Udaughter, because both are long-lived alpha emitters. The two intermediate products (234Thand 234mPa)are relatively short-lived (24.1 days and 1.17 minutes) beta emitters. In the environment, the can be separated from the 238Uby chemical processes involving the intermediate members or by a change in water solubility of the daughter radionuclide following decay of the parent (NCRP, 1975). Thus, the 234U f "U ratios in natural uranium from 16 sources are reported as 0.914 to 0.985, while in ocean water the ratio is 1.14 -1 0.01. This shows a preferential solubility of 234Uand movement from the land to the oceans over a long period of time. This has little significance in estimating human radiation dose because of the wide variations in the quantities of uranium from place to place on the earth and the uncertainties inherent in calculating such doses. Thorium-230 has a half-life of about 80,000 years. The NCRP (1975) reports that *?h can be enriched or depleted in natural situations by about a factor of two compared to or 234U.Thorium is, in general, less soluble under environmental conditions than uranium so that its movement in water is of lesser importance. Radium-226 and its.short-lived daughters are of the greatest interest

3.1 GENERALBEHAVIOR

/

13

in assessing hazards, primarily because of the mobility of 222Rn,the immediate daughter of 226Ra.Radium-226 is soluble in water, however, and can be a source of internal exposure from drinking water, particularly if the water is from deep formations that contain higher than average concentrations of uranium and radium. Radium can also be taken up from the soil by plants to produce internal exposure when the plants are eaten. Radium is chemically similar to calcium and will tend to follow calcium in the environment. Radon-222 is the direct daughter of nsRa and each disintegration of ='Ra produces one atom of radon. Because radon is a noble gas (in the same chemical family as helium and argon) it does not undergo chemical reaction in the environment. Thus, each atom of radon as it is formed is released from any chemical combination of the 226Raand can diffuse through materials to the extent allowed by its 3.82-day half-life and the porosity of the medium. When the radon atom disintegrates, it forms an atom of polonium which is a solid and can be trapped in the diffusing medium. Because a gas diffuses slowly through solid materials, only that radon produced near enough to the surface of a solid to diffuse to the surface before the atom decays will escape. (An alternative method of escape from the near surface of a solid is by the recoil energy obtained by the nucleus from the decay of 226Ra.)Thus the fraction escaping will depend upon the size of the object in which it is formed. For massive rocks, only a small fraction of the radon formed will escape. For soils, the fraction escaping to the air through the pore spaces between the particles is higher, and can reach 0.6. This high emanating fraction occurs in clays which have small particle sizes. In soils, which are the main source of radon moving to the atmosphere, the radon escapes from the soil grains into the air contained in the pore spaces of the soil. From this position it can move to the surface of the ground by diffusion or by movement of air in the pore spaces caused by changes in barometric pressure. Once again, the movement to the surface must be complete before the radon atom decays if it is to enter the atmosphere. This limits the depth of the soil layer that contributes to the radon leaving the surface to a few meters, depending on the type of soil and its moisture content. Once the radon leaves the surface of the ground, it is transported downwind and decays to produce the short-lived daughters that are the source of the radiation exposure from radon. Radon may also be dissolved in ground water as a result of release from rock or soil containing the aquifer. The quantity of radon released is dependent upon the radium content of the formation while the quantity remaining in the water is a function of the time required for the ground water to reach the surface.

14

/

3. SOIL CONTENT AND TRANSPORT

The gamma radiation from the 226Ragroup is emitted by the shortlived daughters of *"Rn. This is mostly from the '14Bi (19.7 minutes) with some contribution from 214Pb(26.8 minutes) (Table 2.1). Thus, in areas where the radon daughters have been depleted by movement of radon away from the site, the gamma radiation is reduced from the equilibrium level accordingly. The last segment of the uranium series starts with 'lOPb and ends with stable '"'jPb. Lead-210 is a low-energy beta emitter with a halflife of 22 years, and it can accumulate in the environment as a separate source if separated from its radium predecessor by diffusion and transport of radon gas. Lead-210 decays through "OBi, another beta emitter, to 2'0Powhich is an alpha emitter with a half-life of 138 days. This section of the series may be subjected to separation processes throughout all the preceding steps in the series decay, in particular the release of radon to air or water. As a result, "Opb may often occur in situations where the parents, uranium or radium, are not present. This is particularly true in air, as demonstrated by Hill (1965)who showed a direct correlation between alpha activity in grass and in rainfall because of the washout of radon daughters from the atmosphere. Francis et al., (1968) have also indicated that the fallout of 21"Pbis a mechanism for the entry of 210Pointo plants.

3.1.2 Routes of Exposure. There are five routes of human exposure to members of the uranium series. These are: (1) gamma radiation from the radon daughters in soil, rocks and air resulting in external exposure to penetrating radiation; (2) uptake of radionuclides by plants which are eaten by humans or by animals used subsequently for meat or to provide dairy products; (3) dissolution of radionuclides in water that is used for drinking, cooking or irrigation; (4) emanation of radon into the atmosphere with inhalation of the daughters; (5) resuspension of dust containing the solid radionuclides with inhalation of the dust. The first four routes of exposure will be considered in detail in the next sections. Resuspension of dust containing any of the nuclides can occur under the influence of winds or mechanical disturbance. Unfortunately, the estimation of air concentrations resulting from resuspension is an empirical process with inadequate information to allow any detailed

3.2

NORMAL CONCENTRATIONS IN T H E UNITED STATES

/

15

estimate of air concentrations. In a review of present resuspension concepts and models, Healy (1980) recommends the use of a dust loading model that combines the dust content in the air with the findings of Anspaugh et al., (1975) that the concentration in soils could be related to the concentration in air by assuming that the dust loading is 100 micrograms of the soil per cubic meter. Healy (1980) recommended an increase to 200 micrograms/m3 to allow for increased inhalation by those people working outdoors in dusty occupations. Radon daughter products provide the highest radiation exposure to man from the uranium series. This exposure can arise from a number of sources: (1) Soils are a continuing source of radon emanation depending on their radium content. The NCRP (1975) estimated an average emanation rate of 0.42 pCi/m2 per second from the soils in the United States. This emanation rate is variable, even a t any one place, depending upon changes in barometric pressure, and conditions such as soil moisture, freezing of the soil and snow cover. In the atmosphere, diurnal changes in radon concentration occur at many places because of the formation of a capping inversion that keeps the radon emanating from the surface of the ground from mixing into the upper layers of the atmosphere. The most important indoor source of radon is radium in soil under buildings or in the materials used in building construction. Here, the radon may be released directly into the building where it remains for a time that varies with the ventilation rate of the building. The concentrations of radon and radon daughters in the home are not constant but will change with time, particularly with the season of the year and the accompanying change in the ventilation rate. The number and type of surfaces available for plating out of the radon daughters is also important. (2) Another source for entry of radon into the home is its release during domestic use of water. If the water contains radon, it can be released, totally or partially, during such activities as taking a shower or washing dishes. (3) A third source of radon in houses is the burning of natural gas. This fuel contains varying amounts of radon, depending on the source and the time that the gas spends in transit and storage.

3.2 Normal Concentrations in the United States The NCRP (1975) presented a table showing the average concentrations of uranium in various types of rocks and soils. The data are

16

/

3. SOIL CONTENT AND TRANSPORT

TABLE3.1-Uranium in mks and soih (NCRP, 1975). Material

Igneous rocks Basalt (crustal average) Mafic' Salic" Granite (cnletal average) Sedimentary rocks Shale Sandatones Clean quartz Dirty quartz Arkose Beach eands (unconsolidated) Carbonate rocks Soils

Minograms per mam

0.5-1 0.5.0.9 3.9,4.7 3.0

Pieocurie8

mad

per

0.2-0.3 0.2,0.3 1.3. 1.6 1.0

3.7

1.0

4.0 2-3 1-zb 3.0 2.0 1.8

<0.3 l.Ob 0.3-0.7~ 1.0 0.7 0.6

"To obtain the series equilibrium radioactivity for total alpha, beta or approximate gamma emissions (excluding bremestrahlung and x rays). multiply by 8.6 or 3, reepectively. Indicatee that the values are not well defined. "Themedian and mean value are given.

reproduced in Table 3.1. There can be wide variations from the values shown, particularly in regions where uranium minerals are present. The radioactivity in soils is related to the activity in the rocks from which the soil was formed. While this is frequently the bedrock in a particular area, there are cases where the soils have migrated from mountains having relatively high concentrations of radionuclides to cover bedrock that contains low concentrations. 3.3 Examples of Enhanced Concentrations A large number of situations occur where the natural radioactivity in soils or rocks is altered in position, chemical form or availability so that radiation exposures to people can be increased over those normally encountered with these materials. These situations can range from the small additional amounts of radon released when soil is plowed or otherwise tilled, to the movement of large amounts of ores containing the uranium series. When these ores are taken from a position deep in the earth, where the radon decays before reaching the surface, to the surface of the earth, a fraction of the radon is released to the atmosphere. In this section, the discussion is primarily on the enhancement of uranium and radium in several specific areas where the more important exposures may occur.

3.3 EXAMPLES OF ENHANCED CONCENTRATIONS

/

17

3.3.1 Uranium Mining and Milling. Uranium is mined either in underground mines or in open pits. The ore in the United States contains up to 1000 times the concentration of uranium found in average soils. The primary effluent from mining is the release of radon. While good estimates of the total amount of radon released are not available, Jackson et al., (1980) reported measurements on 27 underground mines. The average emission rate was 5700 Ci/y with a range from 170 to 30,000 Ci/y. After mining, the ore is taken to a mill for extraction of the uranium. and its daughters. The ore itself is close to equilibrium between the 238U Thus an ore containing 0.2% UaOs will have about 560 microcuries of each of the daughters per metric ton of ore or about 560 pCi of each per gram. After separation, a large part of the uranium (both 238Uand 234U) will be in the product, but the other daughters remain in the residue, known as tailings. The tailings are discharged from the mill as a slurry and are placed on a tailings pile. Because the radium is in the tailings, the radon emanation from the tailings pile is considerably greater than that from normal soil in the area. However, Shearer and Sill (1969) have shown that, for at least three tailings piles, the radon from the pile cannot be measured above local background at distances of 1 km or more. The radon emanation rate from a tailings pile will continue for very long periods of time because the long-lived 230Th, the immediate predecessor of 226Ra,remains in the residue and will continue to generate radium. An important source of enhanced radiation associated with tailings was the past use of the material under foundations and as backfill for buiidings. These tailings are a very clean sand and are attractive for such uses. The high radium content, however, results in increased gamma radiation and, more importantly, increased levels of radon and its daughters in buildings.

3.3.2 Phosphate Production. A principal source of phosphate for fertilizers and other products is rock that contains high concentrations of phosphate. Currently, there are mines in Florida, Tennessee, Idaho, Montana, Utah,North Carolina and Wyoming. About one-half of the mines is located in central Florida. These phosphate rock ores contain above-average uranium concentrations. Mining of the ore is usually by strip mining. The mined rock

18

/

3. SOIL CONTENT AND TRANSPORT

TABLE 3.2-Uranium in coal 1979). - and ash IEPA. -

Uranium concentration

T y p of coal

-

(micrograms/gmm)

Coal

Asb

Anthracite

1.5

9

Eastern bituminous Western bituminous

1.9 1.9 2.3

38

Lienite

16

22

is crushed and separated from sand and clay by a series of screening and flotation steps. Following this, the ore is dried and sorted according to particle size. This material is then used to produce products such as phosphoric acid and fertilizers. The sand, clay and/or fines are returned to mined out areas as fill. The radioactivity in the unmined phosphate rock, which is usually near the surface, also results in areas of higher than average concentrations of radioactivity in the surface soils. This can result in elevated gamma radiation from the soils as well as increased radon concentrations in the homes. Also, land reclaimed after strip mining can have higher radium concentrations, leading to enhanced radon concentrations in buildings. For example, in 12 Florida houses built on reclaimed land, four were above 0.05 WL, while none of nine houses on natural land exceeded this value (DHRS,1978).

3.3.3 Electricity Generated from Coal. Coals contain uranium in various amounts depending on the source. This uranium and many of its daughters tend to stay with the ash when the coal is burned. Thus any fly ash escaping to the atmosphere will carry some radioactivity that will be inhaled or deposited on plants or on the soil. The concentrations of uranium vary widely, but some indications of mean values are given in Table 3.2. The Environmental Protection Agency (EPA, 1979) estimated that a modern coal-fired electricity generating plant of 550 MWe would have a coal input of about 1.5 million tons per year. This amount of coal with a uranium content of 1.9 micrograms per gram will contain about 3 tons of uranium. The emissions will depend on the design of the combustion chamber and on the air-cleaning equipment used for the off-gas air. The EPA (1979) estimated emissions from a model coal-fired plant of about 0.06-0.2 Ci of 238Uand 234U,and 0.02-0.7 Ci of '*'Ra per year.

4. External Radiation 4.1 Introduction

The overall population-weighted absorbed dose rate in air in the United States from external terrestrial radiation is estimated to be about 40 mrad/y. The absorbed dose is corrected by a housing shielding factor of 0.8 and a body-shielding factor of 0.8 to obtain a dose equivalent rate of 26 mrem/y (NCRP 1975). The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 1982) has adopted a body shielding factor of 0.7, but the values in this report (Table 1.1) have not been modified from those in the 1975 NCRP report. This dose is essentially from gamma rays and X rays and the dose equivalent is considered to be uniform throughout the body. This is not strictly correct for skin and other surface organs; however, it is within 210% for gonads, lung, bone marrow and the gastrointestinal tract. At a particular location, the primary determinant of the absorbed dose rate is the soil concentration of the primordial radionuclides: potassium-40, uranium-238 and its daughters and thorium-232 and its daughters. The radioactivity of surface soil is that of the rock from which it derived as modified by a number of geological and meteorological factors. Human activities can also alter surface radioactivity: these include tillage, importation of soil, addition of fertilizer, construction work and the like. The mining and processing of uranium ores and the mining of phosphate deposits that contain uranium can produce significant local variations in the external terrestrial radiation field. A soil layer about 0.25 m thick furnishes the external gamma radiation from the ground (NCRP, 1975) and can mask bedrock of substantially greater or lesser activity. The variability in terrestrial radiation from the primordial radionuclides is larger than that from the other external source of human exposure: cosmic radiation. The latter is not considered in any detail in this report. Approximately one-fourth of the average background absorbed dose rate in air-about 10 to 12 mrad/y-is contributed by the uranium series. This is largely determined by the '14Bi daughter of 226Rain the soil and the concentration of the atmospheric daughters of gaseous 2nRn that escapes the soil. Since the 214Biactivity builds up toward equilibrium with 226Ra 19

20

/

4.

EXTERNAL RADIATION

quite rapidly, the soil concentration of 226Rais an indicator of the expected gamma dose from the uranium series. At 1 m above the surface, the gamma radiation absorbed dose rate from the daughters of radon in the atmosphere is a function of meteorological conditions. Beck (1974) has calculated the expected external absorbed dose rate outdoors for four different conditions of atmospheric stability and estimates 0.4, 1.0, 2.3, and 11 mrad/y for strong mixing, normal turbulence, weak mixing and strong inversion conditions, respectively. These correspond to concentrations of approximately 30, 70, 200 and 1000 pCi/m3, respectively for the daughters. For a typical time-averaged radon daughter concentration of 150 pCi/m3, the resulting absorbed dose rate in air would be about 1.7 mrad/y. This is approximately 20% of the total gamma dose from the uranium series and less than 5% of the total external gamma dose under typical conditions. The alpha absorbed dose rate in air from radon and its daughters in the lower atmosphere varies in a similar fashion, and is typically estimated to be 10-50 mrad/y. The external whole body dose from the accompanying gamma radiation is negligible. Note, however, that the dose equivalent to the respiratory tract from inhaled radionuclidesprincipally radon and its short-lived daughters-may be far from negligible. There are two basic sources of experimental data from which we can infer absorbed dose rates in air due to natural background radiation from terrestrial sources. The first is the measurement of external dose rates in air through surveys a t ground level, conventionally at 1 m above the surface-The second is the estimation of ground-level dose through aerial surveys, generally conducted a t about 150 m above the surveyed terrain, with traverses spaced about 1.6 km apart. Both of these systems include gamma radiation from radionuclides in the ground and in the atmosphere. Results from the two methods have been found to be compatible. Either system can be used to identify regions where the radioactivity deviates significantly from the average, but only a small fraction of the United States has been mapped. Bogen and Goldin (1981) have published estimates of extemal gamma radiation and cosmic-ray exposures on a state-by-state basis, interpolating from the available data.

4.2

Indoor Exposuree

A considerable portion of the introductory material in this section has described the situation for the average natural background expo-

4.2

INDOOREXPOSURES

/

21

sure to external radiation from the uranium series. This description was mostly devoted to outdoor exposures, with a note that the average shielding factor for housing has been taken as 0.8 (NCRP, 1975). Some additional detail on building materials is included in this section. Radiation exposure from building materials may arise from gammaemitting nuclides in the material itself. The exposure is different from that outdoors, since the geometry is nearly 4 pi steradians, that is the occupants are almost completely surrounded by the source rather than being on a plane surface. This geometric effect is limited to less than 4 pi by the fact that not all of the building materials or furniture are equally radioactive and that windows, doors and the like are relatively non-radioactive. Any structure gives some shielding against terrestrial radiation and, of course, may increase the separation of the occupants from the ground source. Thus the indoor gamma exposure is a balance between those factors tending to decrease the exposure levels and the concentrations of radionuclides in the building materials. The range of exposure for normal buildings seems to be about +30% compared with normal outdoor exposure. The lower values are associated with wooden buildings, while the higher values are found in masonry structures. In the case of multistory masonry buildings, virtually all of the gamma radiation on the upper floors comes from the materials and not from the ground. The exposure is still close to the outdoor value because many building materials have radioactivity contents close to that of soils. Cameras and Rickards (1973) reported some measurements on shielding. General conclusions from their data indicate that a 12Y2 cm wood frame wall would reduce outdoor gamma dose rates by a factor of 2, a brick wall by a factor of 4, and a 20 cm solid concrete wall by a factor of 20. It should be noted that windows and doors have little shielding value. Investigators in a number of countries have begun to measure building materials or buildings constructed with different materials to assess radiation exposures. Table 4.1 has been adapted and simplified from the 1977 UNSCEAR Report, using the data where the same materials were measured in different countries. The Table shows the concentrations of the radionuclides and the calculated absorbed dose rates in air, using 4 pi geometry with the dose conversion factors of Beck (1972).The calculated dose rates are higher than those measured in actual houses by factors of 2 or 3, for the reasons discussed above. Eichholz et al., (1980) conducted a series of measurements on building materials, estimated the indoor gamma exposure rates, then measured the actual gamma radiation dose rates in the finished

22

/

4. EXTERNALRADIATION

TABLE 4.1-Concentrations of radionuclides i n building materiak, with an estimate of the resulting absorbed dose rate i n air. (Ade~tedfrom UNSCEAR. 1977.)

Material

Country

*)K

(PC~/P)

=Ra

(&i/g)

Brick

FR Germany Sweden USSR UK

16 25 20 17

2.6 2.6 1.5 1.4

Concrete

FR Germany Sweden' USSR' UK

15 19 15 14

1.8 1.3 0.9 2.0

Cement

FR Germany Sweden USSR UK

5 6 6

1.2 1.5 1.2

-

-

Plaster

FR Germany Sweden USSR UK

2 0.6 10 4

Granite

FR Germany Sweden USSR UK

33

Yh

(pcllg)

Absorbed dqse rate ~n a ~ r (mrad/y)

<0.5 0.1 0.2 0.6 2.6

-

-

40 28

3 2.4

Soilb Us 12 0.6 ' Heavy concrete. LOwder et a1 (1964), 200 samples. 'Calculated to 4 pi geometry for comparison purposes.

buildings. These buildings were one-story houses of brick, wood and concrete built in Atlanta, GA. By assuming only 2 pi geometry, they found the estimates agreed quite well with subsequent measurements in houses. The indoor absorbed dose rates in air for 23 houses ranged from about 20 to 100 mrad/y.

4.3 Elevated Natural Background Areas The limited distribution of external radiation measurements in the United States leaves open the possibility that undiscovered areas of

4.4 ENHANCED NATURAL RADIOACTIVITY AREAS

/

23

elevated natural exposure exist. On the other hand, many of the aerial surveys were intended for mineral exploration and the states where elevated exposures might be expected have been covered. In the United States, elevated localities include the Denver area where outdoor values ranging from 75 to 140 mrad/y have been found over undisturbed land. Surveys in the Florida phosphate region showed that residents in about 5% of the houses on undisturbed land had exposures greater than 120 mrad/y. As a matter of interest, gamma radiation measurements in Kerala, India, in villages located on monazite deposits, have been reported to range from 130 to 2800 mrad/y. Elevated natural levels or enhanced levels in building materials have been reported and were summarized by UNSCEAR (1977) and by the Nuclear Energy Agency (NEA, 1979). The amount of information is not large and little of it refers to the United States. Concrete containing alum shale that is high in radium, as used in Sweden, gave a calculated dose of 1300 mrad/y. Phosphosgypsum (also high in radium) gave values of 600 mrad/y as calculated in the United Kingdom and 1100 mrad/y in the United States. Red slime bricks, using a by-product of the aluminum industry, are high in thorium and gave a dose rate of 500 mrad/y as calculated in the Federal Republic of Germany. As in previous cases mentioned, doses measured in dwellings are considerably lower than the calculated values.

4.4 Enhanced Natural Radioactivity Areas The enhanced levels of external radiation observed in the United States and Canada are mostly caused by the high levels of radium in mining and processing residues. Average soil in the United States contains 0.5-1 pCi of 226Raper gram of soil, although there is considerable variability. The mining and milling of uranium ore bodies produces uranium that is relatively free of other elements of the series, while the other radionuclides are in the waste streams. For example, some tailings piles in the Western States have been found to have '"Ra concentrations ranging from 100 to 500 pCi/g. Soil samples from the site a t Canonsburg, PA where wastes from the extraction of radium from carnotite ores have collected for several decades and where wastes from some operations of the Manhattan Project were accumulated, have been found to have 226Ra concentrations as high as 14,000 pCi/g. In one swampy area a t the site, 226Raconcentrations of 4000 pCi/g are present a t a depth of 3-4 meters.

24

/

4.

EXTERNALRADIATION

The situation in the phosphate mining areas of Florida is quite different from the Western sites. When measurements are made over debris, overburden, slimes, and soil from the leach zone, the external gamma dose rates are variable but high. On reclaimed land, dose rates range from 90 to 350 mrad/y in air, at 1 meter above ground. Very approximately, such rates should be associated with 226Raconcentrations of 6-22 pCi/g. When phosphate rock is treated with sulfuric acid to produce phosphoric acid, gypsum (calcium sulfate) is a by-product. The 228Raconcentration in the gypsum may be 30-40 pCi/g. The ammonium phosphate fertilizer may have coneentrations on the order of 5-6 pCi/g. The amounts of these wastes from uranium and phosphate processing are large. A national inventory of uranium tailings is maintained by Oak Ridge National Laboratory: in 1980 there were 25 million tonnes of tailinge a t 24 inactive mills in the Western states and 150 million tonnes a t 21 active mills. New tailinge are accumulating a t the rate of about 25 million tonnes per year. The volumes are equally impressive: there are now about 100 million cubic meters of uranium tailings with a yearly increment of about 15 million cubic meters. In Florida, the gypsum piles are accumulating a t the rate of 11 million tonnes per year and the amount on hand is approaching a billion tonnes. The total area affected by mining and milling operations is not great-several thousand acres-and most of it is in regions where relatively few people live. These vast piles, however, have been considered as presenting local problems in addition to their external gamma radiation fields. Heavy storms have caused piles to collapse and contaminate water courses; rains leach out the radioactivity and toxic chemicals into ground waters and aquifers, and winds blow away an unknown amount every year. As far as building materials are concerned, some of those described in the section on elevated natural areas might really be classified as enhanced radioactivity, but separation of the two in this case ie difficult. The problem with uranium b$-products has generally been the use of mill tailings as fill under and around houses rather than with building materials as such. In Port Hope, Ontario, actual building materials coming from the demolition of a radium refinery were reused (Spurgeon, 1976).Other enhanced exposures to external radiation have resulted from the use of land reclaimed following phosphate mining and milling operations in Florida and the use of phosphate slag in road-building and construction around Butte, Montana.

Inhalation The major exposure of the population to radiation from the uranium series arises by inhalation of the short-lived daughter products of "'Rn. Most of the early measurements that were applied to population exposures were made outdoors for other purposes. During the last few years, it has become apparent that indoor concentrations are generally several times higher than those outdoors. Combining this with the fact that people in western countries spend only about 15% of their time outdoors, indoor concentrations are the more significant concern. This section will, therefore, emphasize the indoor levels as a basis for dose estimates and for the recommendation of limits.

5.1 Outdoor Radon a n d Radon Daughters The average outdoor radon concentration was given in NCRP Report No. 45 (1975) as 150 pCi/m3 for land areas of the northern hemisphere, while UNSCEAR (1982) gives a value of 100 pCi/m3 over the continents. The data on geographic variability are very limited, but diurnal and seasonal variations reach factors of two or three. A few measurements on daughter product equilibrium outdoors indicate that the daughters average about 60% of equilibrium, while measurements close to the radon source show a lower degree of equilibrium. A very rough value for the average outdoor Working Level (defined in Section 1.5) would be 0.0006 to 0.0009 W L corresponding to 100 and 150 pCi/m3, assuming 60% equilibrium. Elevated and enhanced levels of radon outdoors may be as high as 1000 pCi/m3 over sizeable areas. Even higher values of radon may be measured directly on tailings piles. The concentration falls off rapidly with distance from the source while the degree of equilibrium increases with time. Elevated or enhanced outdoor air concentrations may also contribute to indoor exposures in the ventilation of houses that have low inherent concentrations. High outdoor concentrations could then reduce or even reverse the normal dilution effect. 25

26

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5. INHALATION

5.2 Indoor Radon and Radon Daughters T h e most important factor in assessing the exposure and in estimating the risk from natural radioactivity of the uranium series is the actual measurement of radon and radon daughter concentrations in the specific house. As has been shown, estimates derived from a few measurements in the same area lead to dose and risk figures which may be unrelated to actual exposures. The purpose of this section is to describe the relevant measurements that have been made. These measurements have been directed towards determining: (1) the concentrations of radon and radon daughters present in the home; (2) the means of radon entry into the home; (3) the pathways followed by the radon in the home; (4) the source of the levels measured-in nature, human activity or a combination of both; (5) the variation of radon concentration by area in the home, by season, by ventilation practices, by household activities, and by occupancy and other factors; (6) the means of reducing radon daughter concentrations in the home; (7) the doses and risks that can be expected from this radioactivity. There are many studies of radon and radon daughter concentrations in progress around the world. It has been necessary to be selective in order to present relevant data for the purposes of this report.

Surveys for radon and radon daughter concentrations were started in Canada in 1975 in response to the concern over radioactive contamination resulting from past operations and disposal practices in the uranium and radium refining industry. The surveys were then extended to uranium mining communities and finally to other areas in Canada to determine the so-called "normaln or average background levels of radon and radon daughters in homes. Surveys of uranium miningproperties showed that 18% of the homes had radon daughter levels greater than 0.02 WL. The highest value measured was in Uranium City, Saskatchewan, where 2.5 WL was found. These communities showed high radon daughter levels due to elevated or enhanced natural background. In some cases, rock removed in the development of one or more of the mines was used as a construction aggregate. In other cases, the houses were built directly

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5.2 INDOOR RADON AND RADON DAUGHTERS

27

on top of the ore bodies. The communities of South March, Ontario and Castlegar, British Columbia are not associated with uranium mining but are located in geological areas with elevated uranium. A large number of measurements are available from these communities as shown in Tables 5.1-5.3 (Eaton, 1982; Knight and Makepeace, 1980; McGregor, 1979; Taniguchi, 1977; Taniguchi and Vasudev, 1978). Another survey was carried out over a period of three summers to determine the radon and radon daughter levels in homes in major Canadian cities (Letourneau et al., 1979; McGregor et al., 1980). Nineteen cities were sampled during the summer, using a statistically proven sampling technique on a grab sample basis. Most samples were taken in basements with doors and windows left as they were when the inspectors arrived. The purpose of this survey was to determine the geographical distribution of radon and radon daughter levels for a majority of the population. Approximately 4% of the homes had radon daughter concentrations greater than 0.02 WL, with a maximum of 0.23 WL. The results for these cities, for both radon and radon daughters, are indicated in Table 5.4. It is worth noting that the prairie provinces of Manitoba, Saskatchewan and Alberta would be expected t o show low radon concentrations, on the basis of geology, but the table indicates that they are the highest in Canada. Other studies were done in Canada with repeated samplings in the TABLE5.1.wRadon daughter concentratwns in houses in Canado suspected of having enhanced natural background. (Knight and Makepeace, 1980.) Number of Geometric Location housea mean WL Port Hope (radiumluranium refinery) Cobourg (reference area-spring) -autumn) Uranium City (uranium mining) Elliot Lake (uranium mining) Bancroft Area (uranium mining) Deloro (metallur~caloperations)

2961 106 97 632 1921 1162 68

0.0029' 0.0014' 0.0015' 0.013 0.008 0.007 0.006

Estimated from radon concentrations using an equilibrium factor of 0.3. TABLE5.2-Houses requiring remedial action in four areas of Canoda. (radon daughter , levels >0.02 W Lor excessive external gamma.) f ~ a t o n1982.) Number of Houses Port How Elliot Lake Bancroft Uranium City Initially surveyed Requiring remedial action Proportion Source

3500 450 13% Contamination

1920 120

1170 140

545 100

6% 12% 18% Largely natural with some surface contamination

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TABLE5.3.-Distribution of indoor rodon daughter concentrations in selected

Location

communities. Distribution of Rn daughter (WL) concentrations in 96 Number of properties m.01 M.02 C0.01 4.02 4.16 M.15

Geometric reference mean

Bancroft, Ont. Elliot Lake, Ont. Uranium City, Sask. South March, Ont.

1162 1921 632 343

61.7 63.3 50.5 75.2

21.6 20.4 19.7 11.7

12.9 15.4 25.7 12.0

0.9 0.9 4.0 1.2

0.007' 0.00s' 0.01" 0 . W

C&legar/"I'rail, B.C. Trail, B. C. Port Hope,Ont. Cobowg, Ont. (Spring)

135 118 2961 106 97

52.6 85.6 -

14.1 8.5 -

24.4 5.1

2.2 0.8

-

-

-

-

0.009d 0.0032~ 0.0029U 0.0014w 0.0015U

[Autumn)

-

-

-

'Knight and Makepiece, 1980. Taniychi, 1977. 'Taniguchi and Vasudev, 1978. McGregor. 1979. 'Estimated from radon concentrations aseuming an equilibrium factor of 0.3.

same home to determine the diurnal and seasonal variations in the radon and radon daughter concentrations (Case, 1979; Scott, 1979). The results of these studies established that, even in the absence of known high uranium concentrations and in the absence of contamination, there is still a wide spread of radon and radon daughter values in Canadian homes. Generally, all cities show a log-normal distribution of the radioactivity, while the curve is shifted from one geographic area to another. There is a statistically significant difference between the cities. 6.2.2 United States

While no generalized survey of the United States has been undertaken, a number of local measurements have been made in response to specific problems or to study diurnal or seasonal variations in radon and radon daughter concentrations in homes. The results of these measurements are summarized in Table 5.5. A large portion of west central Florida is underlain with deposits of phosphate rock. In general, the deposits are covered with a layer of topsoil measuring from 3 to 20 meters thick. Immediately above the phosphate ore, there may be a leach zone measuring up to 3 meters thick which contains a relatively high concentration of 226Raand its decay products. When the phosphate ore is removed by strip mining, the overburden and leach zone may well be mixed, resulting in more

5.2 INDOOR RADON AND RADON DAUGHTERS

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29

TABLE 5.4.-Radon and radon k h t e r concentrations in Canadian homee. ( ~ c ~ r e &etr4 1980.') Radon, (pCil m9 m

mean

i

Radon daughters, (WL) ,metric

devlat~on

mean

d?dard denetaon

Brandon, Man. Calgary, Alta. Charlottetown, P. E. I.

840 310 410

5.0 3.6 5.3

0.0034 0.0019 0.0018

2.7 2.3 2.6

Edmonton, Alta. Fredericton, N. B. Halifax, N. S.

460 660

4.5 4.0

-

0.0028 0.0032 0.0031

2.3 2.9 3.1

Montreal, P. Q. Quebec, P. Q. Regina, Sask. St. John, N. B.

290 280

3.3 3.8 3.8 5.7

0.0014 0.0013 0.0044 0.0018

2.5 2.7 2.9 3.0

0.0015 0.0017 0.0034

2.7 4.6 2.5

-

1330 270

St. John's. Nfld. St. Lawrence, Nfld. Saskatoon, Sask.

880

420

4.4 6.8 4.3

Sherbrooke, P. Q. Sudbury, Ont. Thunder Bay, Ont.

360 580 540

5.4 4.0 4.4

0.0023 0.0036 0.0025

33 3.0 2.6

310 140 1540

2.8 3.0 4.6

0.0018 0.0009 0.0058

2.6 2.0 3.1

Toronto, Ont. Vancouver, B. C. Winniwe. Man.

300

'Data from Brandon, Edmonton, Regina, Saskatoon and Winnipeg-R. G. McGregor, peraonal communication.

radioactive material being left on the surface. The ore itself is mined and, after a series of refining operations, the slimes and sand tailings are returned to the site where the ore was removed Approximately half of the radionuclide content of the phosphate rock is returned to the mined areas with the slimes and about 12% ends up in the sand tailings. The radium removed from the ore ends up in the gypsum byproduct, with a typical 226Raconcentration in the gypsum of 30-40 pCi/g. No structures are built on the gypsum piles a t this time. It is apparent, therefore, that houses built on reclaimed mined lands where the radioactive soil is at or near the surface and houses built on non-mined lands where the phosphate deposits are near the surface may contain relatively high concentrations of radon and radon daughters. Actual measurements in central Florida show that radon daughter

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TABLE5.5-Indoor radon and radon daughter product concentrations i n the United States, (R PC, 1980.) -Average Average Measurement Location radon number of conditions (*it m3) WL houses New York/New Jersey basements first floors Grand Junctionb Background houses Florida phosphate areaC backgroundd background' backgroundr Montanaa Butte Anaconda Alabama, othersh phosphate slag-basements phosphate slag-first floors background basements San Francisco Fkgion'

Soda Springs, Idahd

Year-round Year-round Year-round Year-round Year-round Year-round Year-round Year-round Year-round Jan-May Jan-May Jan-May Grab/Closed house. Grab/Closed house Grab/Closed house

" Environmental Measurements Laboratory-median values. Colorado Dept. of Health.

'EPA and Florida Dept. of Health and Rehabilitative Services. EPA. "Florida Dept. of Health and Rehabilitative Services. University of Florida. a EPA and Montana Dept. of Health and Environmental Services. Tennessee Valley Authority. ' Lawrence Berkeley National Laboratory. ' Idaho Dept. of Health and Welfare.

'

concentrations within the homes range from 0.001 to 0.1 WL (DHRS, 1978). Results show that there is a significant difference in the radon levels between homes built on reclaimed land and those built on undisturbed, unmineralized land. Significantly, the same factors appear in these measurements as have been found in other areas where homes have been built on soils containing relatively high levels of 226 Ra. The mean WL of homes built on reclaimed land was 0.015, while on undisturbed, unmineralized land the mean was 0.004. Another significant difference was the distribution of values. No values above 0.011 were found on unmineralized land, while homes on reclaimed

5.2 INDOOR RADON AND RADON DAUGHTERS

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31

land showed what appeared to be a bimodal distribution, with a significant portion of the homes above 0.02 WL. In 1978, the Montana Department of Health and Environmental Sciences (Lloyd, 1981b) found that phosphate slag had been used aa concrete aggregate for construction in Butte. The Department suspected that enhanced radon levels might be found in homes and commercial buildings using this material. A group of 121 homes in the area plus a group of control homes were checked for gamma radiation and radon daughters, and it was found that radon daughter levels were elevated equally above average background levels in both groups. The data are indicated later in Table 8.1 which shows that 7% of the homes were above 0.1 WL. This is a case of elevated natural, rather than enhanced exposure. Rundo et al. (1982) measured radon concentrations in houses in the Chicago area. They found a geometric mean of 0.5 pCi/l for first floors (44 houses) and 0.7 pCi/l for second floors (26 houses). Assuming 50% equilibrium, the WL's would be 0.0025 and 0.0035. They also found a geometric mean for basements and crawl spaces of 1.6 pCi/l (91 houses), or a WL of about 0.008. A study of 26 dwellings in New York and New Jersey over a 2-year period indicated a range of mean radon daughter concentrations from 0.002 to 0.01 WL (George and Breslin, 1980). In basements, concentrations tended to be about twice the concentrations on main floors. For lack of more definitive data, their median value of 0.004 WL has been used to describe average indoor radon daughter exposures in the United States. 5.2.3

Sweden

The majority of the studies in Sweden has been on houses built of aerated concrete based on alum shale and tailings from shale workings. These materials have an average radium content of 20 to 65 pCi/g (Swedjemark, 1980; 1981). Studies on elevated natural radon concentrations in homes have not yet been reported.

Eighty-seven dwellings were measured by an indirect method in England and Scotland. The mean radon daughter concentration was found to be 0.0035 WL (Cliff, 1978; 1980). Further studies are in progress.

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6.2.6 Finlund

Castren et d ,(1977) and Castren (1980) have investigated the radon and radon daughter levels in homes due to radon emanating from water drawn from private drilled wells. They estimate that some individuals are exposed to between 20 and 25 WLM per year and that a cumulative exposure of 200 WLM has been exceeded by a few. More than 10,000 people in Helsinki are estimated to be exposed to more than 2 WLM/y. Radon concentrations in air have been found to be as high as 100,000 pCi/m3. 6.2.6 Austria

Four hundred houses in Salzburg and about 100 houses in the Gastein area were measured for radon and radon daughters. The distribution of radon values in homes was typical for elevated natural background areas with evidence of multiple distributions. The range was from 100 to 5200 pCi/m3, with a median of 400 pCi/m3 (Steinhaueler et al., 1975). 6.3 Origins of Radon

Radon-222 is the gaseous daughter product of '=Ra and is therefore, formed wherever '=Ra is present. The majority of the radon found in homes comes from the soil air, which moves to the atmosphere by diffusion. A complicating factor is that this radon in soil air often dissolves in ground water, which then transports the radon to sites distant from where it was formed. The radon will emanate from the ground water when the water reaches the surface near foundations or near sumps. Drinking water from wells (or potable ground water) can also be the source of radon to the air as has been shown in Finland (Castren et al., 1977; Caetren, 1980) and Halifax (McGregor and Gourgon, 1980). Emanation of radon from building materials follows the same diffusion pattern as that from soil. Surface contamination with from commercial operations has been responsible for elevated indoor radon daughter concentrations in a few areas such as Port Hope in Canada. 6.4 Sources of Radon in Buildings

It has been customary to describe radon levels indoors as average natural, elevated natural, and enhanced or man-made. It is easy to

5.5 RADON CONCENTRATIONS WITHIN THE HOME

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33

describe some enhanced sources when the radon concentrations result from radium contamination due to refined products. However, the distinction is blurred between elevated and enhanced sources in the case of uranium mining areas where waste mine rock with an uneconomic grade of uranium concentration is indistinguishable from the normal bedrock throughout the building areas. Also, it is difficult to define natural as applying to anything except outside air, since the building of a home and the digging of a basement can be considered causes for elevated or even enhanced levels. There are a number of primary pathways by which radon enters homes. It is now known that poured or solid concrete is not readily permeable to radon. In this case, the pathway would be diffusion of radon emanating from the radium-containing aggregate in the concrete. In areas of high natural radioactivity, the aggregate can have a high radium content, but studies have shown that the amount of radon emanating from concrete is low. Thus, diffusion of radon from solid concrete is not a serious problem, except in well-sealed modem homes. Cracks in the concrete basement walls or basement slabs are the most common source of radon diffusion into the home. These cracks can be microscopic and still be very effective. The joint between the wall and the floor is the next most common pathway. Other sources are loose-fitting pipes through walls or floors and floor drains connected to weeping tiles providing a direct pathway into the basement. In the case of water-borne radon gas, the most common entrance pathway has been a sump without a cover or with a loose-fitting cover. In many cases in Canada, placing a tight-fitting cover on the sump has reduced the radon levels in basements to ambient levels.

5.5 Variations of Radon Concentrations Within the Home

Radon concentrations within the home vary enormously according to different factors which are described below (McCullough et al., 1981).Generally speaking, the concentrations decrease from the basement to the first floor and from the first floor to the higher floors for times of normal human activity. However, other situations have been described which involve the so-called chimney effect, mostly occurring in winter, whereby radon concentrations on the first or second floor are higher than in the basement. This can occur whenever there is a vertical channel which brings up air from the basement through pressure or temperature differentials. The chimney effect can be an entry route in houses built with hollow block basement walls which

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can funnel soil gases up through the walls to the first floor. The same effect has been observed in one house in Deloro, Ontario, where the levels in the kitchen were consistently higher than than those in the basement. In this case, the source of radon was radioactive fill against the basement walls. Diurnal variations indicate that the radon concentrations are generally higher in the early morning. Barometric pressure is also a cause of variations of radon concentration in homes where a decrease in barometric pressure is followed by an increase in radon concentration. The rate of change of pressure seems to be more important than the actual value of the pressure. Seasonal variations in radon concentrations in homes have been recorded (Case, 1979; Scott, 1979). However, these seasonal variations are different depending on the area in North America where the measurements have been made and on the type of heating system used. In temperate climates, it often appears that the indoor radon concentrations are greater in summer than in winter. Other studies in the same area show the opposite effect and, in Canada, both effects have been measured. It would apear that during the heating season, the basic factor is increased or decreased ventilation. In homes with electric heating, radon concentrations tend to increase in winter with the sealing of the house. Homes with fossil fuel heating often show a decrease as air is sucked in through the basement and up the chimney for combustion purposes. There is also another factor that depends on the type of heating system used. With radiators or convectors, radon concentrations tend to increase in winter. With forced air systems, radon daughter concentrations tend to decrease because of the plating out effect caused by movement of air through the ducts. Recently, there is also the suggestion of the "snow effect" in winter. Rio Algom has discovered in Elliot Lake that snow piled up against the houses increases the indoor radon levels and removal of the snow lowers the levels. The hypothesis is that the snow traps radon emanating at the soil interface on the outside of the foundation, thus allowing it to diffuse into the basement. Family activity within the home is also responsible for variations in radon concentrations. Opening and closing of doors and windows, which is frequent in homes with many occupants or with children, tends to decrease the concentration. A word of warning on artificial measurement conditions is in order here. In many areas, measurements for regulatory or legal purposes have been made in closed homes when the inhabitants are absent. This creates a dead air space where levels of radon and radon daughters are artificially increased. The same homes measured under conditions of normal activity show much lower concentrations.

5.6 REMEDIALMEASURES

/

35

In summary, no general statement can be made concerning the variations of radon and radon daughter concentrations in homes for a whole continent. Representative, long-term measurements for each locality and type of home are required before an assessment can be made of these variations. 5.6 Remedial Measures

Radon and radon daughter concentrations may be reduced by the following general procedures, many of which are illustrated in Figures 5.1-5.6 (illustrations are reproduced here by courtesy of the Canada Mortgage and Housing Corporation (CMHC, 1981)): (1) Removing the source of radon; (2) Diverting the radon before it enters the structure; (3) Placing a barrier between the source and the open living space; (4) Installing air cleaning equipment; (5) Increasing the ventilation rate. Examples of these may be detailed as follows:

weeplng t~le footlnq floor-wall join1 from weeplng tile

to sewer

double trapping of drams

.. P P penetration ~

crack sealtng and taping

Standard Remed~alAct~ons

I

Fig. 5.1. General techniques for reducing radon and radon daughter concentrations

in buildings.

5.6 REMEDIAL MEASURES

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37

38 / 5.

INHALATION

5.6 REMEDIAL MEASURES

I

39

40

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5. INHALATION

MlLQ A N D SEWER SLPVICL ENTPANCL DETAIL:

Fig. 6.6. Details of water and sewer entrance sealing.

(1) In some cases, extraneous high-radium material, such as development rock from mines, tailings or active gravel, has been placed against the foundation or under the basement floor or slab foundation. This material can be removed, thus solving the problem. Replacing radioactive concrete walls or floors with

5.7 EXPOSURE AND ESTIMATION OF DOSE

/

41

concrete made from aggregate which is low in radium also constitutes removal of the source. Contaminated material such as lumber or concrete blocks can also be removed. (2) Radon can be diverted by the installation of sub-floor ventilation systems made of weeping tiles (see Figure 5.1) connected to. either passive or active ventilation ducts and a chimney. Emanated radon is thereby drawn away from the sub-basement space and vented to outside air. (3) Placing a barrier between the radon source and the living space is done by either sealing cracks in concrete floors and walls and around pipe penetrations, by adding traps and trap primers to underfloor drains, by filling concrete block walls or by total sealing of concrete walls. (4) Radon daughter concentrations in houses may be reduced by domestic air treatment. Various methods have been tried, but the most effective has been the use of electrostatic precipitators or electronic air cleaners. Such systems are already in common use in Canada in homes with forced air heating. The levels of radon daughters may be reduced by factors of 6 to 19 depending on the conditions in the room. (5) The last method is increasing the ventilation rate by increasing the number of house air changes per hour. This may be by a passive or active system. In northern climates it entails an extra cost for heating the air. Air-to-air heat exchangers have been designed to reduce this cost, and these heat exchangers are becoming available commercially. Comparable considerations for cooling incoming air would arise in southern climates. All of these methods have been used and proven but no one technique has shown itself to be universally applicable or the most cost effective. In many cases, in older Canadian homes, a combination of techniques is required to bring the radon levels down to the Canadian regulatory standards. Similar systems have been developed for new housing construction. Essentially, when the source of radon cannot be removed, solid poured basements with special reinforcements to prevent cracking and special sealants for floor-wall joints and pipe penetrations are required. Finally, hollow concrete blocks are not allowed because of the chimney effect.

5.7 Measurement of Exposure and Estimation of Dose The indoor exposure of individuals to radon and radon daughters is difficult to eetimate, due to the variations in the concentrations with

42

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INHALATION

season, time of day and ventilation for different floor levels in the house. Added to these factors are the differing occupancy times for the various occupants, who in turn have different breathing and exposure patterns due to their age. In general, calculations with rounded-off occupancy times tend to overestimate the exposure. The exposure is usually derived from one or at most a few grab samples. This is not satisfactory since the calculation of risk derived from exposure to a group of individuals should be based on realistic measurements and calculations of exposure. The factor for converting radon daughter exposure to dose used in this report is the one developed by Harley and Pasternack (1982). While there are some variations in the model due to age and sex, a single factor of 0.7 rad/WLM is satisfactory for our estimates of dose to the bronchial epithelium. Using a quality factor of 20 for alpha radiation, the dose equivalent factor is 14 rem/WLM. This is in reasonable agreement with other estimates made for environmental conditions and is also the value adopted by UNSCEAR (1982). The dose equivalent rate from the assumed average exposure rate in the United States (0.2 WLM/y) is about 3 rem/y to the bronchial epithelium. Some of the Canadian cities listed in Table 5.4 show a higher average, but not by a factor of two. The distribution of values in Canada is such that a few percent of the population is above 1 WLM/y or 14 rem/y. A few houses in the United States with enhanced radium levels show similar concentrations and a broader survey should uncover a larger number.

5.8 Inhalation of Other Series Members

Uranium and radium in airborne dust appear to result from the resuspension of soil and show the same concentrations as soil particles. With an average dust loading of 100 micrograms/m3, the daily intakes would be a few femtocuries each, much smaller than the dietary intakes. Air samples taken near a uranium mill tailings pile showed a uranium concentration of 1 pCi/m%nd a radium concentration of 0.2 pCi/m3 (Breslin and Glauberman, 1970). Both of these were down by a factor of 10 at 1 km from the pile. The concentrations depend, of course, on the levels in the resuspendable portion of the tailings and on the dust loading generated by the winds. The airborne long-lived daughters of radon, "'OPb and "'Po are largely formed in the atmosphere and the long half-life of the 'IOPb means that they have an existence independent of the parent radon.

5.9

SUMMARY

/

43

Like the short-lived daughters, they are attached to the ambient aerosol so their lung deposition is similar. The longer half-lives mean, however, that they have time to be metabolized before radioactive decay occurs. The average ground level concentrations were given in NCRP Report No. 45 (1975) as 10 and 1 fCi/m3 for 210Pband 210Po, respectively. Geographic variability for 210Pbis about a factor of two from the average. While the 210Pb,210Po combination gives an average lung dose that is only a few percent of that from the short-lived radon daughters, the skeletal dose from the inhaled short-lived radionuclides is about one-fourth that from ingested 2'0Pb,210Po. The average airborne concentrations of 210Pband *loPo do not contribute large fractions of the average natural lung or bone dose. Data from elevated or enhanced areas are almost entirely lacking, but might be roughly estimated as being proportional to the relative radon concentrations.

5.9

Summary

The significant inhalation exposures and consequent lung doses from the uranium series arise from the short-lived daughter products of 222Rn.Radon itself, as well as its precursors and its long-lived daughters, does not contribute markedly to the average natural lung dose. The available data for indoor radon daughter concentrations in the United States are inadequate to determine either an average exposure or a distribution of exposures for the country. The most complete data set, from Canada, indicates that the range of exposures is wide and that there are a number of areas where elevated natural concentrations of radon daughters occur. Areas of enhanced natural background also exist in both Canada and the United States. These sites involve relatively small population groups but usually show the highest exposure rates of those measured. Dose rates and dose equivalent rates for the exposures described are summarized in Section 8.

6. Drinking Water The discussion of radioactivity in drinking water has been separated from that for the diet, chiefly because water is almost always of local origin. Thus it is expected to vary more from place to place than foods which tend to be distributed nationally. In addition, water supplies are generally more easily contaminated by human activity than are large blocks of agricultural land. The type of water supply ranges from wells used by a single family to large municipal systems furnishing water to millions of people. The sources may be surface water, such as rivers, lakes and reservoirs or ground water, where sub-surface waters feed springs and wells. Ground water sources are usually referred to as aquifers, which are geologic formations containing water. Ground water, of course, was surface water at one time although the time underground may have been hundreds of years. Durfer and Becker (1962) noted that about threequarters of the U.S. population use surface water supplies. Some ground waters are saline or mineralized sufficiently not to be potable. Such sources also tend to have higher radioactivity than the potable waters. The high usage of water in many areas has led to a reduction in quality as nearby saline waters intrude into the depleted fresh water source. Salinity, and possibly natural radioactivity, also tend to increase as the waters of rivers are used and reused in their course downstream. Water treatment in municipal systems usually removes suspended solids by filtration, while flocculation plus additional filtration is required to reduce hardness in some supplies. The latter operation also reduces radium, lead and polonium contents to some extent. Home water softeners are also effective in removing the same radionuclides. Exposure of the population, thus, can only be assessed by measuring the actual domestic supplies and data on raw waters are only of scientific interest. The relevant material is presented in order of the radionuclides involved. In each case, the exposures are considered under the headings of average natural, elevated natural and enhanced levels. Following that, the doses from each element are considered. 44

6.1

URANIUM

I

45

6.1 Uranium 6.1.1 Average Natural Exposure. Until recently, uranium in drinking water has been measured rarely, except when contamination was suspected. Welford and Baird (1967) found a concentration of 0.02 pCi/l in New York City tap water. This would contribute about 8 pCi/y to intake compared with almost 400 pCi/y from the total diet. UNSCEAR (1977) noted that tap water usually contains less than 0.03 pCi/l and would be a minor contributor to human exposure. It would appear, however, that this conclusion is based on the uranium content of surface waters, which are not universally used. A large study, involving data from the National Uranium Resource Evaluation (NURE) program plus data from the literature was prepared for the EPA (Drury et al., 1981) and covered 90,000 water samples. The 28,000 samples considered to be domestic supplies averaged 1.7 pCi/l and a population-weighted mean value for finished waters, based on 100 measurements was 0.8 pCi/l. The total data included about 35,000 surface water samples which averaged 1.1pCi/ 1 and 55,000 ground water samples which averaged 3.2 pCi/l. The population mean of 0.8 pCi/l would indicate that the uranium intake from water is about equal to the total from other diet components and is thus not a negligible quantity.

6.1.2 Elevated Exposures. Cline et al., (1981) measured 1400 public water supplies (90% ground water) in the State of Georgia and found that 14 exceeded 10 pCi/l of uranium. In these areas, the intake from drinking water would exceed that in food. In other countries, Asikainen and Kahlos (1980) found a mean of 15 pCi/l for drilled wells in Helsinki, Finland. All of these wells also contained elevated levels of radium. The U. S. Geological Survey carried out an extensive survey of 226Rain wells in Sarasota County, FL (Sutcliffe and Miller, 1981). A few of these samples were also analyzed for uranium, which showed concentrations about half that of the radium. Similar ratios were also found by Scott (1962) in studies of wells in the Midwest. On the other hand, Miyake et al., (1964) indicated that Japanese rivers give U/Ra activity ratios of about 5, while continental ground waters tend toward an equilibrium ratio. The New York City diet data (Welford and Baird,

46

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6. DRINKING WATER

1967; Fisenne and Keller, 1970) showed a U/Ra ratio of 5 for water. This difference between ground and surface water is reasonable but, considering the relative toxicities of uranium and radium, the radium would still be the controlling factor in risk assessment. Scott and Barker (1962) reviewed data collected between 1954 and 1957 on total radium (226Raplus 228Ra)and uranium in water. Their individual data on wells and springs used for drinking water have been rearranged by geographical region for two concentration ranges of each element. The data are shown in Table 6.1. It is worth noting that the wells high in radium are usually not high in uranium, indicating that the sources for the two elements may not be the same. The data show that over 40% of the samples have readily measurable concentrations of uranium. Few values higher than 5 pCi/l are found in the Atlantic and Gulf Coastal Plains which also have low terrestrial gamma radiation. The original report covered 561 samples including industrial, stock watering and unused wells not included in the Table. Many of these showed high levels of uranium, radium or both. The wells in the Table included 270 municipal supplies, none of them serving large cities, while the other wells and springs serve small groups. TABLE 6.1--Total radium and uranium in wells according to geographic region. (Adapted from Scott and Barker, 1962.) Region

New England (ME, NH, VT, MA, CT, RI) Middle Atlantic (NY, NJ, PA) South Atlantic (DE. MD, WV, NC, SC, GA, FL) East North Central (OH, IN, IL, MI, WI) West North Central (MN, IA, MO, ND, SD, NE, KS) East South Central (KY, T N , AL, MS) West South Central (AR, LA, OK, T X ) Rocky Mountain (MT, ID, WY, CO, NM, AZ, UT, NV) Pacific Coast" (WA, OR, CA) Total

Total Radium-% with Uranium-% with Number Ra of Wells Ra above between U above U between 5 PC'A 1 & 5 pCi/, 5 'Lgll 1 & 5 'LgIl

19

10

0

20

23

13

0

44

58

10

0

27

40

30

2

30

55

39

4

58

38

18

5

11

44

29

11

32

88

8

5

68

44

14

7

39

409

19

4

42

"All but two of the wells showing detectable activity were in California.

6.2 RADIUM

/

47

The EPA study mentioned earlier (Dmry et al., 1981) showed that several western states had domestic water supplies that averaged 2 pCi/l or above, with South Dakota having the maximum value of 7 pCi/l. This compares with the population-weighted mean of 0.8 pCi/l estimated in the same report. 6.1.3 Enhanced Exposures.

Enhanced exposures to uranium in water were first noted following contamination of the Animas River (Tsivoglou et al., 1959) when uranium wastes were allowed to wash into the river. Since the wastes were depleted in uranium compared to radium, the uranium did not receive a great deal of attention. The radium picture will be presented later. Kaufmann et ad., (1976) reviewed the effects of uranium operations around Grants, NM on the local ground water. Their preliminary findings indicated that no adverse impacts had been observed, but that longer-term studies were probably required. Some private wells contained up to a few hundred pCi/l of uranium, but these did not seem to be related to mine or mill effluents. The authors concluded that 226Rameasurements would be more significant following a contaminating incident. 6.1.4 Radiation Doses.

The data in Chapter 7 indicate that average U. S. background diet concentrations of uranium would deliver a dose equivalent of about 0.2 mrem/y to bone surfaces. These doses are based on measured skeletal concentrations. On the average, the contribution from water should be equal to or less than that from food intake. Higher dose equivalent rates have been reported (NCRP, 1975; UNSCEAR, 1977), but these were based on skeletal concentrations which now seem to have been too high.

6.2 Radium

Radium in drinking water presents a potential hazard t o the population and has been subject to loose regulation in several countries for many years. The permissible level has usually been set in the range of 3 to 5 pCi/l. Many supplies that furnish drinking water to sizeable groups in these countries do not meet such a standard but there has

48

/

6. DRINKING WATER

been no concerted effort a t enforcement. In addition, most of the municipal supplies have not been measured and the average population exposure cannot be estimated. A study camed out in Illinois (Lucas, 1960) showed that the radium in water was about twice as available for uptake as that in food. In the early part of this chapter it was indicated that water was one of the few dietary items that was generally of local origin. This means that the body burdens of radium should vary with the concentration of radium in drinking water from place to place. Unfortunately, radium concentrations in bone specimens have only been reported for a few locations where the water concentrations are known.

6.2.1 Average Natural Exposure. There are insufficient data on which to base an estimate of the in water. While many average exposure to the population from 22BFh measurements have been made, most of them have been directed toward elevated or enhanced levels, with no attention to the lower concentrations. in the United States has The broadest program for measuring 226Ra been developing under the guidance of the Environmental Protection Agency. The intent has been to analyze the radioactivity in every municipal supply in the country. Under the Safe Drinking Water Act (Public Law 93-523) supplies are to be screened for total alpha activity. If this is above 5 pCi/l, 226Fb is to be determined and if the latter is above 3 pCi/l, then 228Rais to be measured. Most of the samples pass the total alpha requirement so no radiochemical analyses are required. Thus the program is not helpful in developing an average population exposure, although it does point out areas with elevated exposure. The analyses for this program are being performed by the states and a full report has not yet been published. Cothern et al., (1981) summarized the situation by noting that 400 to 800 public water supplies out of about 60,000 measured exceed 5 pCi/l for 226Ra. Measurements of 226Fhin water were made in connection with diet studies for 3 cities using surface water supplies, New York (0.006 pCi/l), San Francisco (0.008 pCi/l) and San Juan (0.006 pCi/l) as reported by Fisenne and Keller (1970) and Hallden and Harley (1964). Emrich and Lucas (1963) measured 28 surface water sources in Illinois and reported a mean concentration of 0.04 pCi/l. Thus the ingestion of water from surface supplies would contribute little to the normal dietary intake of a few pCi/day. About three-fourths of the population uses surface water supplies in the United States (Durfer and Becker, 1962). Some other surveys had a broader aim. Perhaps the first was that of Hursh (1953) who analyzed samples from 35 cities and found a

6.2

RADIUM

/

49

mean of 0.03 pCi/l. The high value was 6.5 for Joliet, IL.Durfer and Becker (1962)reported on the water supplies of the 100 largest cities in the United States, noting that these served 60 million people. Only Rockford, IL (2.5),Houston, TX (1.3)and Lubbock, TX (1.9)showed concentrations greater than 1 pCi/l. A few data are available for other countries. Muth et d., (1960) reported on '%Ra in drinking water and showed values of 0.2 pCi/l for 7 tap waters, 0.4 for 4 river watere, 0.2 for 5 shallow wells and 13 for 3 deep wells in Germany. Miyake et al., (1964)reported 0.08 pCi/l for '"Ra in 10 rivers in Japan. Asikainen and Kahlos (1980)found a mean value of 0.1 pCi/l for tap waters in Finland. These were mostly from surface sources-dug wells and springs averaged 0.2,while drilled wells averaged 2.4 pCi/l with a maximum of 200.

TABU 6.2-Summary of radium-226 analyses of public water supplies, 1966. (Hickey and campbell, I&%.) State

Number of water supplies analyzed

Alaska Arizona Arkansas

5 41 42

Colorado Hawaii Kansas

43 17 92

Louisiana Maine Michigan Minnesota Missouri Nebraska

Total population served- 1963 (thousands)

Supplies with >3pCi/l of

=Ra

Number

Highest

Ra

Population

(pCi/l)

10 242 178

0 0 0

0 0 0

0.1 2.0 1.4

107 428 287

4

1 2

3 16 1

15.7 8.9 5.0

44 25 8

300 74 115

1 0 0

9 0 0

4.0 0.3 0.9

64 67 79

304 175 226

13 5 2

46 18 10

24.1 8.7 3.8

New Hampshire New Mexico North Dakota

19 30 33

80 24 1 61

0 0 0

0 0 0

2.5 2.3 0.7

Oklahoma South Dakota Texan

67 42 97

203 89 540

3 5 5

7 12 23

10.3 6.9 9.7

Utah Wyoming

58 18

143 84

0 0

0 0

0.9 0.8

Total

891

3,864

41

144

.

50

1

6. DRINKING WATER

6.2.2 Elevated Exposures. Ground water supplies may range up to 100pCi/l of 226Rafor potable waters. Many of the studies performed were designed to seek out high values. For example, Edgar (1963) found total radium concentrations of >3 pCi/l in the 11 wells he selected in the Savannah River area. Smith et al. (1961) measured 226Rain 85 wells in Maine and New Hampshire, reporting means of 65 and 5 pCi/l, respectively. Hickey and Campbell (1968) tried to identify population groups consuming water that contained >3 pCi/l of "'Ra. Twenty states were selected and about 1000 supplies using untreated ground water were measured. The results are shown in Table 6.2. Emrich and Lucas (1963) summarized some of the earlier data and presented new measurements for Illinois. Their paper was oriented toward characterizing geologic formations and aquifers, but the data are of interest for our purposesshowing a range of 0.5 to 100 pCi/l for active wells. Mineral water springs are also expected to show high activity. Remy and Pellerin (1968) tested the 250 principal sources in France and found that 77 had 226Racontents >5 pCi/l. The U.S. Geological Survey carried out a study in Sarasota County, FL (Sutcliffe and Miller, 1981). They reported on 200 samples from 92 wells. Radium-226 was measured in 161 of the samples and half of these showed concentrations >5 pCi/l with a maximum of 110 pCi/l. Very few samples showed less than 1 pCi/l.

6.2.3 Enhanced Exposures. Kaufmann and Bliss (1977) studied the effects of both phosphate mineralization and the phosphate industry on the ground water in Central Florida. They found a range of 1 to 15 pCi/l for the geometric means for various areas, but could see no evidence of contamination by the industry. The report cautions, however, that continuing monitoring and review are necessary. The maximum of 15 pCi/l was found in Sarasota County, which is almost completely outside the mineralized area. Other parts of the state having no phosphate deposits showed a mean of 1 pCi/l in the ground water, which the authors compared with a national geometric mean, calculated from available data, of 0.15 pCi/l. The Polk County (Florida) Health Department (Keaton et al., 1981) surveyed 325 wells, about 113within the area of the phosphate deposits and 213 outside. About 6% of the wells inside and 20% of those outside had 226Racontentg greater than 3 pCi/l. The authors concluded that the higher levels are a natural phenomenon, although local contamination of the shallow aquifer is still possible. It was notable that,

6.2 RADIUM

/

51

unlike other areas, the shallow wells tended to have higher concentrations than the deep wells. The Florida Department of Health and Rehabilitative Services (DHRS,1981) surveyed about 50 private wells in each of 7 counties where there were shallow phosphate deposits of the Hawthorne formation. Polk County was not covered as it was the subject of the survey discussed in the preceding paragraph. The private wells tend to be shallower than public or municipal wells and from 4 to 30% of the wells in different counties exceeded total radium concentrations of 5 pCi/l. For the wells requiring 226Raanalysis (total alpha activity >10 pCi/l), private wells averaged 7 pCi/l, while the public wells had averaged 4.5 pCi/l. Also, the northern Florida counties showed lower concentrations than those in the central part of the state. Kaufmann et al., (1976) reviewed uranium operations in the Grants mineral belt of New Mexico. No effect on the 226Racontent of the water could be shown. In this case, however, both the private and municipal wells were generally below 1 pCi/l of 226Ra. Myers and Stewart (1979) reported on the Elliot Lake mining area in Ontario. The 226Rain waters from adjacent drainage basins was in the range of 1-2 pCi/l, but the municipal supply for the town of Elliot Lake was only 0.4 to 0.6 pCi/l. The Animas River incident mentioned under uranium is the only documented case of long-term contamination of a water supply by uranium processing operations. Before 1959, effluents from the Durango, CO mill were discharged to the river. It is estimated that the liquid wastes contained 0.2 mCi/d of dissolved and 30 mCi/d of suspended 226Ra.Measurements by the Public Health Service showed 13 pCi/l in river water a t the mill and 3 pCi/l at a distance of 100 km downstream. These values may be compared with analyses showing 0.3-0.6 pCi/l upstream. Measurements reported in 1972 showed no measurable water contamination (EPA, 1972) but the change with time was not fully documented.

6.2.4 Radiation Doses. Radium-226 in drinking water is at low concentrations in surface waters, which supply about 314 of the population. No definite increases appear in areas where enhanced levels might be expected but elevated natural levels do exist in the water supplies for large numbers of people. If the fractional uptake from water is higher than that from foods, then intake with water would be the controlling factor in these areas (Lucas, 1960). Therefore, there should be many thousands of people with several times the body burden of people from areas using surface waters and where intake is controlled by foods. The dose

52

/

6. DRINKING WATER

equivalent rate to bone surfaces for these people from 226Raand its retained daughters would be over 100 mrem/y compared to 10 mrem/y estimated in Section 7 for average background areas. This could be confirmed by analysis of autopsy bone specimens from these areas.

6.3 Radon in Drinking Water 6.3.1 Average Natural Exposure. Radon in water may expose populations through ingestion in drinking water or by the contribution of domestic water usage to indoor radon concentrations. The latter contribution has been described in Section 5. There have been many measurements of high radon levels in water, made either in seeking out high exposures or in looking at special water sources such as spas and springs with high levels of radionuclides. On the other hand, there have not been any broad surveys designed to develop an average exposure picture for a sizeable population group. Certain generalizations may be made. Rainwater is low as it has little time in the lower troposphere-the region of highest atmospheric concentration-to absorb radon. Surface waters also exhibit low concentrations, most of the radon originally present having transferred to the atmosphere. Ground water and well water concentrations depend on the type of rock involved in the aquifer. Acidic rocks such as granite usually contain more radium and produce higher radon concentrations, while basic rocks, limestone and sandstone tend to produce lower concentrations. It is worth noting here that there is no correlation between the concentrations of radium and of radon in waters. Radon will decay on storage, although this is seldom a factor in water supplies. The major removal occurs if the water supply is aerated as a purification process. Heating, and particularly boiling, of water in open vessels transfers the radon to the atmosphere so any ingestion exposure must result from direct water consumption and not from hot beverages or the water used in cooking. No estimate of average ingestion exposure is made here, due to lack of information, but it is definitely small compared to the other radionuclides. 6.3.2 Elevated Exposures. A number of surveys in individual states demonstrate high values and some of these have also quoted radon levels for "normalwareas in the state. Some of the data are listed in Table 6.3. Hess et al., (1980) showed that the average radon content of deep wells in northern New England was a function of the bedrock. Granite areas gave a mean of

6.3 RADON IN DRINKING WATER

/

53

TABLE 6.3-Radon concentratwns in water Location

Maine Central Florida North Carolina Nova Scotia Finland

Number of sources

Mean pCi/l (range)

Reference

128 Drilled wells 76 Dug wells 80 Ground water 210 Wells 11 Drilled wells 39 Drilled wells 625 Dug wells/springs 172 Wells

88oW (2OOO-W,000) 8OW (0-32,000) 3000 (20-47.000) 2700 ( -46,000) 170000 (43,000-370,000) 17000 ( -1,200,000) 16000 ( -44,000) 500 ( -3,600)

(a)

-

Sweden

-

(b) (c) (d) (4 (0

References (a) Smith et al, 1961. (b) DHRS, 1981-quoting earlier work. (c) Sasser and Watson, 1978. (d) McGregor and Gourgon, 1980. (e) Asikainen and Kahlos, 1980. ( 0 UNSCEAR, 1982.

24,000 pCi/l, sillimanite 18,000 and chlorite 1,300. It is apparent that there is a considerable range of exposures and, even given a particular source, the actual ingestion exposure of the population group will depend on many factors which control whether or not the water actually contains the radon when taken in.

Exhunced Exposures. There are some areas in North America where the concentration of radon in drinking water may have been enhanced by human activities. This is not as likely to affect drinking water as the longer-lived radionuclides since mine, mill and plant effluents are not directly potable and, by the time these waters can enter domestic supplies, the radon will have decayed. Enhanced exposures are not considered further. 6.3.3

Radiation Doses. Suomela and Kahlos (1972) estimated the relevant doses from ingested radon based on a series of measurements on human subjects. They derived an alpha dose equivalent range of 240-440 mrem to the stomach per microcurie of ingested 222Rn,using a quality factor of 10. This is in line with calculated values obtained by others. The authors considered the intake of unboiled water to be from 300 to 1200 ml/d. An earlier estimate of von Dobeln and Lindell (1964) also included a whole-body dose equivalent factor of 4 mrem per microcurie of ingested radon (this value was given in their paper as 2 mrem, using a quality factor of lo), with the stomach receiving about 100 times more. The whole-body dose is considered to be more pertinent for our purposes. The range of radon concentrations in Table 6.3 can be converted to whole-body dose equivalents if we assume an intake-say 0.5 1 of 6.3.4

54

/

6. DRINKING WATER

unboiled water a day. As an example, the mean value for Central Florida (3000 pCi/l) would give a whole-body dose equivalent rate of 2 mrem/y.

6.4 Lead-210 and Polonium-210 in Drinking Water In the group containing 'lOPb,2'%i and 210Po,the first two are beta emitters and contribute only about 10% of the dose from the group to any organ. The 210Pbis important, however, since its 22-year half-life controls much of the group's environmental behavior. The 'loPo alpha emission delivers most of the dose equivalent and the polonium is sufficiently long-lived to redistribute in the body after formation.

6.4.1 Average Natural Exposure. The major source of 2L0Pband its daughters in the environment is from the decay of atmospheric radon. While the majority of the global radon decays in the soil or soil air, this material is not as available to the biosphere as is the natural fallout of "OPb. The typical 'lOPb content of rain is 3 pCi/l in the Northern Hemisphere, with the Po/ Pb ratio being 0.1 to 0.5. Some of the radionuclides in rainfall are absorbed in soil and the like, since surface waters usually contain less than 0.1 pCi/l. UNSCEAR (1977) states that well water could approach the same concentrations as rain but gives no data. They also indicate that drinking water contributes only a few percent to the dietary intake. Holtzman (1964) presented the largest body of data for 'lOPb and 21"0 in water. Eighteen treated supplies showed 0.02f 0.01 pCi/l while 4 raw waters showed 0.13~k0.05pCi/l of 210Pb.Twenty-five untreated well supplies showed 0.05f 0.04 pCi/l for 210Pband 0.02+0.03 pCi/l for 21"P~. He concluded that water was not an important source for these radionuclides. For comparison, the 226Racontent of the wells was 5 pCi/l and the 222Rncontent about 100 pCi/l. Bogen et aL, (1976) reported a dietary intake of 210Pbof 1.2 pCi/d for New York City with the water making only a small contribution at 0.04 pCi/l. Similar, but higher data were reported by UNSCEAR (1977) with the further indication that the dietary ratio of Po/Pb is close to unity in ordinary circumstances. 6.4.2 Elevated Exposures. No elevated exposures to 210Pbor 2 1 0 P have ~ been reported for the United States. UNSCEAR (1977) summarized data for the Lapps in Finland and for the Japanese with a high intake of seafood. The former derive their 210Pband 'loPo from the lichen-reindeer-human chain and have intakes an order of magnitude higher than usual. It is to be expected that the Eskimos of Canada and the United States

6.6

SUMMARY

/

55

would have exposures similar to those of the Lapps. Elevated dietary intake of 'lOPb and 2 1 0 Pis~discussed in Section 7. In none of these cases is water a real contributor to intake. It would appear that finding noteworthy elevated concentrations of these radionuclides in water is a remote possibility. 6.4.3

Enhanced Exposures.

Lead2'' and 210Pohave not been measured in effluents to any degree and their possible contaminating effects cannot be evaluated directly. McDowell et al., (1979) reviewed the models for transport of 226Raand 210 Pb to humans and predicted that the 50-year dose equivalent commitments per microcurie released would be the same within a factor of two. Thus the significance of industrial operations on 'lOPb and "OPo contamination of water supplies is indeterminate. Radiation Doses. The alpha dose equivalent rate estimates for normal dietary intake of 'lOPb and 210Poare given in section 7 as 50 mrem/y to bone surfaces. As mentioned earlier, 90% of the dose comes from the alpha emission of the 210Po.Water intake gives only a few percent of the dose for normal exposures. 6.4.4

6.5 Remedial Action

Techniques are available for reducing the concentrations of members of the uranium series in drinking water. In municipal supply systems, aeration will remove radon and alum treatment with flocculation and filtration will decrease the heavy metal concentrations. Uranium present as an anionic complex is a possible exception. In the home, water softeners would have the same effect on the heavy metals. The preferred alternative to water treatment is the use of other supplies, if available. 6.6 Summary

In all cases, the contribution of drinking water to the total intake for members of the uranium series is small for average background conditions. This is particularly true for surface supplies which furnish water to most of the population. For elevated and enhanced exposures, the water intake of 226Rais of some interest, but the increase of dose equivalent rate to bone surfaces is less than 100 mrem/y for forseeable conditions.

7. Dietary Intake and Body Content 7.1 Introduction The members of the uranium series found in the body that arise primarily from dietary intake are 238U, 234U, 226Raand 'lOPb. Lead210, the predominant series radionuclide in the body, decays to the alpha emitter 210Po,while the others are alpha emitters themselves. While 'I0Pb primarily enters the body through diet, inhalation must also be considered, especially in smokers. The primary site of deposition for these nuclides is the skeleton and the dose t~ bone is the critical factor. Most other naturally-occurring alpha emitters that appear in the diet and that have long enough half-lives to deliver a significant dose to tissues are poorly absorbed from the gut. For example, the adopted value (ICRP, 1979) of gut uptake for thorium is 2 x as compared with about 0.2 for 226Raand *lOPb.Measurements of naturally-occurring 232Thin the skeleton confirm this low uptake (Lucas et al., 19701, the majority of the body 232Tharising through inhalation (Harley and Pasternack, 1979). Radium-228 follows the same uptake pattern as 226Raand some data on this radionuclide are included in this chapter for comparison. Extensive worldwide measurements of uranium series radionuclides in the diet are not available. The data that exist on the skeletal content of uranium and radium in different countries are perhaps the best information for inferring the effect of variation in normal diet. These skeletal contents appear to vary by about a factor of 10 in locations where no significant elevated sources are suspected. This most probably reflects variation in individual dietary and water intakes. Including areas of elevated or enhanced radioactivity could increase this variability to a factor of 100. In this section, the average background, elevated natural and enhanced dietary intakes of the uranium series radionuclides are discussed. Human skeletal levels and consequent alpha doses are summarized.

7.2 NATURAL URANIUM (-U)

1

57

7.2 Natural Uranium (2s8.2S4U) 7.2.1 Average Background Levels of Uranium,

Measurement of normal levels of dietary 2=234U indicate that they

are about 0.3 to 0.5 pCi/d for each isotope, which is 0.9 to 1.5 microgram of natural uranium per day (Welford and Baird, 1967). The isotopic measurements that have been performed on skeletal ash (Fisenne et al., 1981b) indicate radioactive equilibrium between 238U and 234U, so equilibrium in the normal diet can be inferred. Welford and Baird (1967) measured 19 individual food categories in a typical diet sampled in New York, Chicago and San Francisco. These results are shown in Table 7.1 and will be considered as baseline values.

TABLE 7.1-Measured uranium intake with 19 food categories in the United States'. Food category

kg/~

Bakery products Whole grain products Egs~ Freeh vegetables

Root vegetables Dairy producte Poultry Fresh fish

Micmgmma uraniumly

Food intake

New York

San

Francium

Citv .--

58

44 11 15 48

66 16

25

25

10

12 16 2.7

31

200 20 8

3.4

16 3.4

9.4

58 16 3.4 44

12 62

3.4

8.4 6.8

4.2

6.4

4.0

1.1 4.0

1.1

3.4 4.0

5.6 4.5

Flour Macaroni

Rice Meat Shellfish Dried beam Fresh fruit Potatoes Canned fruit Fruit juices Canned vegetables Annual Intake (micrograms)

22 28 22

Daily intake (micromameldav)

'Data from Welford and Baird (1967).

464

2.0 523

462

58

/

7 . DIETARY INTAKE AND BODY CONTENT

Although soil was not measured in this study, the produce measured is thought to be associated with soil containing average background levels of uranium, that is 1.8 micrograms/g, or 0.6 pCi of 238U/g (NCRP, 1975). The mean dietary intake was 1.3 micrograms of uranium, or about 0.4 pCi of '%U, per day.

7.2.2 Eleuated and Enhanced Levels of Uranium. Tracy et al., (1982) measured uranium in garden produce grown in soil in Port Hope, Ontario, a location that has been contaminated with uranium tailings. The soil concentration in a "low" contamination area averaged about 33 micrograms of uranium per gram of soil compared with average background values of about 2 micrograms per gram (Fisenne et al., 1978). Uranium concentrations in 11 types of root and leafy vegetables grown in this soil were factors of 10 to 20 higher than for normal soil. Tracy et al., (1982) also reported mean vegetable concentrations for several different soil uranium levels and found a direct linear relationship. A 100-fold increase in soil uranium resulted in about a 100-fold increase in the uranium content of the vegetation. They calculated an average uptake coefficient for uranium micrograms/kg fresh weight per microgram/kg dry soil. of 8 x This value is lower than the factor observed for the average background levels described above and additional data are required to resolve the difference. The average background soil concentration of about 1.8 micrograms/g gives uranium concentrations in vegetable foods of about 1 microgram/kg. This gives an uptake factor of 6 x For value will be used, since the other the present report, the 8 x TABLE 7.2-Daily radionuclide intake from standard diets in the U. S. (Adapted from Holtzman. 1980.) City

New York, NY

Infant San Francisco, C A Infant Chicago, IL Infant San Juan. P R

Year (approx)

1966 1968 1963 1970 1972-3 1965 1966 1968 1965 1963 1965 1963

"'PO pCi/day

Calcium g/hy

1.1 1.0

figure does not come from vegetation and soil that are definitely linked. Uptake by vegetables from soil is dependent upon many factors including soil pH and the concentrations of stable nutrient ions (ScottRussell, 1966).The direct relationship of soil concentration and uptake should probably hold for most agricultural areas where food is produced for large-scale consumption, since soil conditions are controlled within broad limits. Under these circumstances, and especially if the mean of a variety of vegetables is considered, the linear relationship should be a reasonably accurate predictor of levels in vegetation.

7.3.1 Average Background Levels of 226Ra. Radium-226 in the diet has been more widely studied than any other natural alpha emitter. The first report of 226Rain food appeared in 1929 (Burkser et al., 1929) and their results are in good agreement with present data. Holtzman (1980) has summarized both dietary 226Raand 228Rafor the United States and these values are shown in Table 7.2. Although 228Rais a beta emitter, its daughter 228This an alpha emitter which is retained in the skeleton. Few dietary data exist, but in areas with average background levels of the uranium and thorium series, the 226Raf28Ra activity ratio in diet is near unity (Petrow et al., 1965). One comprehensive study of 226Rain diet that is included in Table 7.3 is that of Fisenne and Keller (1970). They measured 19 individual food categories to obtain normal daily intakes for New York City and San Francisco. The concentrations measured are shown in Table 7.3 and will be considered baseline values. Holtzman (1980) also summarized worldwide 226Rameasurements and these are shown in Table 7.4. In areas where no unusual conditions exist, the average 226Raintake can be considered to be about 1 pCi/ day.

7.3.2 Elevated and Enhanced Levels of 226Ra Certain selected foods offer the potential for elevated 226Raintake if they are consumed in quantity. Van Middlesworth (1980) and Wogman et al., (1977), for example, measured 0.5 to 25 pCi/g in cattle

60

/

7. DIETARY INTAKE AND BODY CONTENT

thyroids. These are eaten as a delicacy in some areas. Brazil nuts are also known to contain elevated levels of '26Ra and values up to 3 pCi/g have been reported (Turner et al., 1958). Individual odd items such as these are unlikely to cause a major change in dietary intake. Tracy et al., (1982) measured n6Ra in 11 types of root and leafy vegetables grown on soil contaminated with uranium tailings in Port Hope, Ontario. Data from a "lown contamination area showed a measured soil concentration of 12 pCi 226Ra/gcompared with an average background level of 2.5 for the region. Based on their analyses, they calculated an average uptake coefficient of 1 x pCi/kg fresh weight per pCi/kg dry soil. As in the case of uranium, they found a TABLE7.3-Measured

-Ra and 2'0Pb intakes with 19 food categories in the United States.

Food cntegory

Food intake

kg/y

Bakery producta Whole grain producte Eggs Fresh vegetables Root vegetables Dairy products Poultry Fresh fish

44 11 15 48

pCi/JT =Ra New York

City

101 28 150 53

San Francisco

pCi/$ "Tb New York City

62 24 27 32

78 24 3.9 52

10 200 20 8

13 50 8.8 7.1

14 18 8.2 2.1

2.1 58 9.0 3.1

22 28 22

1.8 18

4.8 16 7.9

22 6.4 9.7

0.8

1.2

Flour Macaroni Rice Meat Shellfish Dried beans Fresh fruit Potatoes Canned fruit h i t juices Canned vegetables

15

Annual intake (picocuries) Daily intake (pieocuries/day)

'From Fisenne and Keller (1970). From M o m and Welford (1971).

1.7

linear relationship between 226Raconcentrations in vegetation and soil. If we consider that the average background soil contains from 0.5 to 1 pCi 226Ra/g (NCRP,1975), the above value for the uptake coefficient would predict a level of 0.5 to 1 pCi/kg for fresh vegetables. This is in good agreement with the individual measured values in Table 7.3.

7.4.1 Average Background Levels of 210Pb.

Holtzman (1980) has summarized worldwide measurements of "OPb dietary intake and his compilation is shown in Table 7.4. Values range from 1.4 to 40 pCi/d. Lead-210 is not an alpha emitter, but the 210Po daughter decays by emission of a 5.3 MeV alpha particle. Polonium210 is also present in the diet (normally to about the same extent as ''OPb) and its fractional uptake from food is thought to be similar to TABLE 7.4-Compilation of dady intake of &nuclides. (Adapted from Hdtzmw 1980). -Ra "OPb 'loPo Year City or region

Country United States United Kingdom Germany USSR Cmhdovakia Italy Bulgaria France Belgium Netherlande Argentina Brazil Japan India Canada Finland Alaska

USSR India Brazil

Central Asla Leningrad Romtov-on-Don Southern Bohemia Varene B ~ s a e l (teen--) s %it

Buenos A i m Rio de Janeim Entire Country Bombay

Special area8 Arctic dwellers Arctic dwellers Arctic dwellers 300 g/d caribou 500 g/d caribou

Arctic dwellers Monazitearea Monazite area From excreta meaaurementu.

(appmr) 1963-77 1963 1466 1959 1965 1965 1968 1973 1977 1970 1975

1965 1966 1971 1972 1972 1968 1966 1976

pCiIday 1.4 1.2

pCVday 1.4

pcilday 1.6

3.2' 3 4.6

4.6

6.2

2.8 4.0

7.9 3

1.4

0.5 I.€-21

1.0-1.4 1.2 2.0 0.70

1.1 0.77 1.3

3

17 0.72

1.65

1967 1966 1966

8.6

100 69

10

100

10

100 40.

60

1963 1972 1966 1970

Calcium g/day 1.0

2

40'

2.85 10-120

62

/

7. DIETARY INTAKE AND BODY CONTENT

the factor of about 0.2 found for 210Pb(Bernard, 1979). The short halflife of 210Po(138 d) relative to that of 210Pb(22 y), as well as its short biological half-life of 50 days (Bernard, 1979), makes the 210Pbin the body the most important source of 'loPo under normal conditions. The "OPo remains in the skeleton long enough to produce the highest skeletal dose of any natural radionuclide under conditions of average background exposure. Morse and Welford (1971) measured 210Pbin 19 different food categories for New York City and the individual values are shown in Table 7.3. The daily intake of 210Pbthat they estimated was 1.2 pCi. Spencer et al., (1977) measured 2'0Pb and 210Poin institutional diets in Chicago and found intakes of 1.3 and 1.6 pCi/d, respectively. 7.4.2

Elevated and Enhanced ~ e v e lofs "OPb.

Although the origin of most of the 210Poin the body is normally through ingestion of 210Pb,some special diets must be considered. It is well-known that high concentrations of 'loPo exist in the edible portions of many aquatic organisms, and the Po/Pb ratio has been measured as greater than unity (Cherry and Shannon, 1974). The concentration of "'Po in the edible portion of fish was measured as approximately 20 pCi/kg of dry tissue (very roughly, 4 pCi/kg wet), with a Po/Pb ratio of about 4 (Parfenov, 1974). The 210Poconcentrations in Mollusca are normally higher than in fish and attain about the same levels as the diatoms and phytoplankton upon which they feed. Polonium-210 levels ranging from 200 to 1000 pCi/kg wet weight have been reported in Mollusca (Hill, 1965; Beasley et aL, 1969; Holtzman, 1967; Kauranen and Miettinen, 1970). Beasley et al. (1969) reported 140 pCi/kg wet in prawns and Hill (1965) measured up to 1400 pCi/kg wet in crabs. Diets high in seafood are thus able to introduce substantial quantities of 'loPo into the body. UNSCEAR (1977) has reviewed the elevated 'loPo intake of tens of thousands of Lapps and Eskimos that consume reindeer and caribou in the arctic and subarctic regions of the northern hemisphere. The animals consume 3 to 4 kg of lichens per day. Lichens are a combination of a fungus and an alga living in a symbiotic relationship and their large surface area accumulates the natural fallout of both 'lOPb and 210Po.Levels of 7000-9000 pCi/kg were listed for lichens in the UNSCEAR summary. Reindeer and caribou meat from northern Canada, Alaska and Lapland (Finland, Sweden and the USSR)average 20 pCi/kg and 200 pCi/kg for "OPb and 'loPo, respectively. The animal livers, consumed in some areas, are considerably higher in concentration.

7.5 URANIUM, RADIUM AND LEAD IN HUMAN TISSUES

/

63

Tracy et al., (1982) measured 'lOPb in 11 varieties of root and leafy vegetables grown in Port Hope, Ontario. The soil was known to be contaminated with uranium tailings and contained 9 pCi of 'lOPb/g compared with average background levels of 1 to 3 pCi/g (NCRP, 1975). They calculated an average uptake coefficient of 4 x pCi/ kg fresh weight per pCi/kg dry soil. As with uranium and 226Ra, they found a linear relationship of 'lOPb contamination in vegetation with soil concentration. Using their uptake coefficient and the value of 13 pCi 210Pbin average soil (Fisenne et al., 1978) yields a value of 0.4 to 1 pCi/kg for fresh vegetables, in reasonable agreement with the reported levels in Table 7.3. 7.4.3 Elevated levels of 'lOPbfrom Cigarette Smoking.

The content of 210Pband 'loPo in cigarette tobacco is well-known (Tso et al., 1964, 1966a. 1966b; Harley et al., 1978). The total 'loPo in human lung due to normal dietary intake and inhalation is about 3 pCi. This is increased by a factor of 3 as a direct result of inhalation of 'lOPb and 'loPo in cigarette smoke (Cohen et al., 1979; Parfenov, 1974). Holtzman and Ilcewicz (1966) measured skeletal tissue of smokers and non-smokers with the results shown in Table 7.5. The higher values in smokers result from translocation of 'lOPb deposited in lung to the skeleton. The two-fold difference indicates that smoking is .a significant source of 'lOPb in the body. No data are available on inhalation of side-stream smoke by non-smokers.

7.5 Uranium. Radium and Lead in Human Tissues The majority of the uranium, radium and lead found in the human body resides in the skeleton. Some data exist for other organs and these are mentioned in the following sections, but the emphasis is on the skeletal data. 7.5.1 Uranium in Human Tissues. Few measurements have been made on the uranium content of human tissues. These are summarized in Table 7.6. The difference among locations, for example the 7 pCi 238U/kg ash in the total skeleton for the U. K. (Hamilton, 1972) compared with 1.2 for Australia undoubtedly represents a difference in dietary intake.

64

/

7. DIETARY INTAKE AND BODY CONTENT

TABLE 7.5-Skeletal l'OPband "OPo in smokers and nonsmokers. %'a Smokers Non-smokere

"OPo

(pCi/g ash)

(pCi/g aeh)

Po/Pb Ratio

0.285 + .025 0.135 f ,016

0.25 & .04 0.09 f .0%

0.87 + .10 0.62 f .14

7.5.2 Radium in Human Tissues. Greater than 90% of the body radium content is thought to reside in the skeleton (Schlencker et ad., 1982). The published values for 226Rain human bone were summarized by Fisenne et al., (1981a). The means of the measured values for 26 countries give a median value of 0.03 pCi/g Ca. The 26 nations sampled represent 35% of the world population. The cumulative frequency distribution of the fCi 226Ra/g Ca in bone against the cumulative population probability (percentage of the world population) is shown in Figure 7.1. The median for the population distribution is 0.023 pCi/g Ca with a geometric standard deviation of 1.6. The tange by country is 0.008 to 0.10 pCi/g Ca, presumably representing the differences in their "normal" dietary intakes. Assuming.1000 g of calcium in the human skeletoh, the total skeletal content would range from 8 to 100pCi for the different countries with a global population median of 23 pCi. TABLE 7.6-Memud in h u m tissue samples. Soft tiesue values in pCi %/kg wet weight, bone valuea in pCi =U/kg ash. (number of samples). Skeleton of bow

U.S.

Mlreclc

Lung

Liver

0.17 (27)

0.07 (27)

0.28 (21)

7 (63)

Nepal

Fat

0.8 (63) vertebrae

U.K.

Australia

Blood

Skull, rib. femur, vertebra 1.2 (8) Crania, rib femur, vertebra 5 (9)

vertebra References Welford et al.. (1976). Hamilton (1970). 'Hamilton (1972). F i n n e et a1 (1881b).

Kidney Ref.

0.14 (12)

a b

0.20 (2)

0.06 (8)

0.0s

c

(2)

d

d

7.6 SKELETAL DOSE FROM ALPHA IRRADIATION

100 -

S .-0

3

60 40 I

r

-

U

65

ISRAfL 1

I

ma-,

*O- c u u o q m n c o .

-

m u . VMZUL.

g.-

/

41

-

-

2-

b.01QI 1.0

10

50

90

99

99.99

Cumulative Population Probnbil~ty

Figure 7.1. bone.

Geographic dietribution of measured mRa concentration in human

Radium-226 is sometimes considered to be analogous to calcium in its uptake from diet. In the case of low dietary calcium, it is possible that the fractional radium uptake could be higher than with the "normal" 1 g Ca/d. The data for New York City and for Puerto Rico (Hallden and Harley, 1964), Table 7.7, indicate that this is not the case. Only in the case of severe calcium deficiency would higher ''%a uptake be a consideration. 7.5.3 Lead-210in Human Tissues.

UNSCEAR (1977) has summarized the ""Pb measurements in human bone ash from 10 countries. They found an average of 0.14 pCi/g ash with a range of 0.06 to 0.32. These values were reported without regard to the smoking history of the individuals included in the averages and so do not necessarily represent only dietary differences. Assuming 0.37 g Ca/g bone ash and a calcium content of 1000 g in the skeleton, this corresponds to a mean of 380 pCi ""Pb in the total skeleton with a range of 160 to 860. Blanchard and Moore (1970) found 0.3 and 0.2 pCi/g ash respectively for 'lOPband 21"Poin one Alaskan whose diet contained caribou meat. This is about a factor of 2 higher than the data for "normal" areas.

7.6 Skeletal Dose from Alpha Irradiation Harley and Pasternack (1976) have reported dose factors for the absorbed alpha dose to cells lying close to bone surfaces. These are thought to be the critical sites in the production of osteogenic sarcoma. A summary of their factors is shown in Table 7.8. The factors are

66

/

7. DIETARY INTAKE AND BODY CONTENT

TABLE 7.7-The relationship of dietary colcium levels with uptake of dietarymRa. Dietary calcium

Skeletal =Ra

(Pcilday)

(glday)

(pCilg Ca)

N e w York City

1.7

Puerto Rico

0.68

1.0 0.51

0.029 0.016

Dietary

given for bone uniformly labelled with 23BU, 234U,22BRa(including %d of its alpha-emitting daughters) and ''OPo. The alpha dose is calculated at 1,10,20 and 40 micrometers from the bone surface. Osteoprogenitor cells, which are the stem cells involved in accumulation (accretion) and removal (resorption) of bone are located throughout adult bone marrow but are more numerous near bone surfaces (Owen, 1980). Lloyd (1981a) states that, "Approximately half of those (stem cells) documented lay outside the 0 to 10 micrometer thickness commonly used for calculation of relevant carcinogenic dose." From these considerations, the absorbed dose a t 10 micrometers is taken in this report to represent the relevant quantity. The dose factors in Table 7.8 are used in combination with a few of the average skeletal values for uranium, radium and lead discussed in =Ra TABLE 7.8-Alpha bone dose factors for and "O PO to ceUr lying - - clase to bone surfaces. Radionuclides assumed to be mixed homoaeneously throughout bone. Radionuclide

Distance

from bone surface

(micrometers)

mu

1 10

20 40

=Fte plus H of daughters, including Z'OPo.

1 10 20 40

mrad/y per pCi/g of

wet. defatted bone

60 20 4.4

-

7.8 SUMMARY

/

67

Section 7.5 to calculate an average annual absorbed alpha dose. The skeletal content of each nuclide in pCi/g wet defatted bone is estimated assuming 5000 g of wet defatted bone in the adult male skelr;ton, 1000 g Ca in the skeleton and 0.37 g Ca/g bone ash. The calculated skeletal contents are given in Table 7.9. The annual alpha dose for 238U,234Uranges from 0.01 to 0.07 mrad, with the 0.01 value representing the United States. The dose rate from 226Raaverages about 0.5 mradly and that from the 'lOPb ( 2 1 0 Pabout ~) 2.5 mrad/y. If a quality factor of 20 is applied for alpha radiation, the dose equivalent rates become 0.2, 10 and 50 mrem/y for uranium, 226Raand 210Pb(210Po), respectively. The 'lOPb (210Po)dose equivalent rate to bone surfaces thus approximates the whole-body external dose from terrestrial gamma and cosmic radiation of 54 mremly (NCRP, 1975). It should be noted that the occupational limits for intake of soluble natural uranium are controlled by the chemical toxicity of the element. It is expected that any significant exposures to soluble uranium can only come from areas of enhanced radioactivity under regulatory control and this aspect of uranium toxicity will not be considered further. 7.7 Lung Dose Due to Inhaled Lead-210 a n d Polonium-210 in Cigarette Smoke

Although other alpha emitters such as 232Thand 226Raare present in cigarette tobacco (Joyet, 1971; Tso et al., 1966a and b), measurements indicate that only 'lOPb and 210Poare transferred to cigarette smoke (Cohen et al., 1980a). In one study, the alpha activities on the tracheob~nchialmucosa in fresh autopsy specimens from smokers, ex-smokers and non-smokers were found to be 0.1, 0.08 and 0.02 fCi/cm2 (Cohen et d.,1980b). The corresponding dose equivalent rates to shallow basal cells (22 micrometers below the surface of the bronchial epithelium are 12, 10 and 2 mrem/y). One elderly female smoker had a single area with an elevated activity of 180 fCi/cm2 and a consequent dose of 20 rem/y, if the activity remained at that spot. Measured 'lOPb and 210Poburdens in the lower lung (parenchyma) of ex-smokers who had ceased smoking 3 to 5 years prior to death were found to be nearly equal to those in current smokers, indicating that 'lOPb can be retained in this portion of the lung for long times.

7.8 Summary The average background dietary intakes for uranium, "'Ra and the 210Pb,21"P~ combination have been presented. Measurements of con-

68

/

7. DIETARY INTAKE AND BODY CONTENT

TABLE 7.9-Absorbed alpha dose to cells on bone surfaces fmm average concentrations of uranium, ne Ra andz1' P b in the human sheleton. Alpha dose Reference for bone conSkeleton Skeleton tent PCilk~ mradlyenf total pCi Uranium U. K. New York City Nepal

Hamilton (1970) Welford et ai., (1976) Fisenne el al., (1981b)

234U

Australia

Fisenne et al., (1981b)

="u

Radium-226

u. S.

Fisenne et al., (1981a) F i n n e et al.,(1981a)

"World" average (26 countries) Lead-zrob U. S. (non-smokers)

Holtzman end Ilcewicz (1966) UNSCEAR (1977)

"World" average (4 countries)

'Alpha dose ie that to cells 10 micrometers distant from the bone surface for bone uniformly contaminated with the specified radionuclide. Assumes 5000 grams of wet, defatted skeleton and that "U and are in equilibrium unless measured. Assume ""Po is in equilibrium with the 'l~pb. TABLE7.10-Absorbed dose rates and dose equivalent rates to tk skeleton resulting from the ingestwn of a n auerage diet for uranium. %Ra and ""Pb (1''Pol. Absorbed dose Dose equivalent rate imradlv) rate (mremlv) Uranium 2'oPb(210Po)

0.01 0.5 2.5

0.3 10 50

centrations in vegetables grown on soil contaminated with various levels of these radionuclides show that the uptake is linear with soil concentration, and that the corresponding uptake factors may be used to predict the levels in vegetation grown on a particular soil. These factors are useful for predictive purposes but have not been used for the dose estimates made in this section. The uranium, radium and 2'0Po in the body reside in the skeleton, and the significant dose is from alpha irradiation of cells near bone surfaces. Typical absorbed dose rates and dose equivalent rates calculated for measured skeletal concentrations arising from ingestion of an average background diet containing 1.3 micrograms of uranium, 1.7 pCi of and 1.2 pCi of 'lOPb per day are given in Tables 7.10 and 8.3. Lead-210 is clearly the governing radionuclide that limits the allowable intake of the uranium series.

8.

Dose Summary

Previous chapters on the modes of exposure indicated the absorbed dose rates that appear in normal and in elevated and enhanced background situations. This chapter summarizes the data and presents the relevant dose equivalent rates. The latter calculation uses a quality factor of 20 to convert from rads to rems for alpha particle irradiation. The values developed here are only approximations, since the data are not always complete or in comparable forms. However, this is not a serious drawback in indicating the magnitude of the situation.

8.1 Radon Daughters Table 8.1 presents representative values for the indoor exposure rates, absorbed dose rates and dose equivalent rates produced in bronchial epithelium by the short-lived daughter products of radon. The absorbed dose rates have been obtained on the basis that continuous exposure to 1WL results in 50 WLM/y and that 1WLM equals 0.7 rad (Harley and Pasternack, 1982). The table entries have not been rounded as severely as might be justified as they serve for further calculations.

8.2 External Radiation Table 8.2 lists the total dose rates from external gamma radiation. The absorbed dose rates in air are for indoor exposure. The dose equivalent rates are numerically equal to the absorbed dose rates in tissue, except for a correction for shielding by the body itself. The cosmic-ray component (about 28 mrem/y) is not included in the tabulated values. As in Table 8.1, the entries are probably good to only one significant figure. 69

70

1

8. DOSE SUMMARY

TABLE 8.1-Indoor absorbed dose rates and dose equivalent rates to the bronchial epithelium from normal, elevated and enhanced levels of the short-bed dwghter ~roductsof *2Rn Absorbed dose rate Dose equivalent rate Ex ure (radly)' (remly)' Auerage background New York/New Jersey Median 0.004 0.14 3 Grand Junction Mean 0.004 0.14 3 Florida 0.14 3 Mean 0.004 Canada' 4%> 0.02 0.7 14

(EL)

Elevated Florida Montanab Canadac Enhanced Grand Junction Florida Canada '

Mean 2%> 10% lo%>

0.1 0.05 0.03 0.02

3.5 1.8 1 0.7

70 35 20 14

10,000houses in 14 cities 179 houses in Butte ' 600 houses in two towns houses on tailings ' 7000 houses in four towns 'Absorbed dose and dose equivalent rate8 are for the WL values shown.

TABLE 8.2-Indoor dose rates lo the whole body from e x t e r d terrestrial narnma radiation. Doae equivalent rate Absorbed dose rate In air lmradlv)' (mremlv)' Average Buckground U. S. Average Coastal Plain Rocky Mountain Slopes Elevated Florida Phosphate Areao Enhanced Florida Phosphate Areab Grand Junction

5%>

50

33%> 50 7%> 120 I%> 400

40 100 320

Mineralized but unmined areas Reclaimed land area ' Absorbed do* and dose equivalent rates are for gamma radiation only and do not include the cosmic-ray contribution.

/

8.4 SUMMARY

71

8.3 Ingested Radionuclides

Table 8.3 lists the exposures and dose equivalent rates to bone surfaces for normal background and for some projected levels that might apply to ingested materials in areas of elevated or enhanced natural activity. Subsistence farming in such areas is assumed, with no dilution by national food supplies. The simplifying assumptions are made that the dietary intake is directly proportional to local soil content and that the uptake of 226Rafrom drinking water follows the predictions of Lucas (1960). The soil levels were taken from the work of Tracy et al., (1982) at Port Hope, Ontario. Water levels were taken as representative values of elevated ground waters from section 6.

8.4 Summary

This section compared the dose equivalent rates .to relevant tissues from exposure to normal background with those measured or projected for exposure to elevated or enhanced levels. The information on radon daughters and on external radiation is reasonably realistic, although a larger amount of data would allow better estimates. The ingestion exposures are overestimates for most of the population, being based on subsistence farming without outside foods. The dose equivalent rates to bronchial epithelium in the few percent TABLE 8.3-Dose

equivalent rates to bone surfaces from ingestion of members of the uranium series.

Food

intake (pCiId) Water

0.8 1.7 1.2

0.03-1' 0.01-0.2' 0.02

Total skeletal eontent (pCi)

Dose equivalent

4 30 360

0.3 10 50

raw (mremly)

Average Background

2ylU + 23IU 2"Ra 2'0Pb(2'oPo)

Rounded Total

60

Elevated or Enhanced

2"U + mu '=Ra 2'0Pb(2'0Po)

20 15 10

10 10 Low

Rounded Total

150 400 3000

10 150 400 600

'The minimum figures apply to the skeletal contents shown, while the higher values may be a better representation of average intake.

72

/

8.

DOSE SUMMARY

of the population that are exposed to elevated or enhanced levels can be an order of magnitude above those from normal background. The dose equivalent rates to the whole body from external radiation in elevated or enhanced areas do not exceed those from normal background by a large factor. Also, in this case, the higher doses are received by only a small fraction of the population group involved The dose equivalent rates to bone surfaces from ingestion are shown in Table 8.3 as an order of magnitude higher for the elevated and enhanced areas. This is probably a greater difference from average levels than actually exists, but the difference cannot be evaluated until dietary or bone data become available from some of the special areas. The relative magnitude of the dose equivalent rates and the known relative radiation sensitivities of lung, whole body and bone indicate that the controlling factor in elevated or enhanced exposures is the inhalation of the short-lived daughter products of radon.

Basis for Recommendations Three general methods for developing recommendations about levels of exposure from the uranium series will be discussed. These involve: 1)selecting a level of risk that is appropriate for the exposure circumstances; 2) using previously established limits on radiation dose equivalent; or 3) specifying levels on the basis of the distribution of radiation exposures normally encountered from natural background radiation. The preceding chapters have described some of the levels that exist and some of the features that will affect the dose or risk to humans from members of the uranium series. Exposure limits developed in the past have applied to exposures above natural background. From the data presented in this report, it is apparent that background has considerable variability especially for radon daughters. Thus it is difficult to establish a meaningful background for use in assessing elevated or enhanced exposures. In addition, some exposures to elevated natural background may be high enough that remedial action is desirable. As a result, it seems appropriate to consider the total exposure, including background, in making recommendations for individual members of the public. This procedure should not interfere with the present system of regulating potential increments in exposures around nuclear facilities and other sources by controlling effluent releases. The resulting dose increments are ordinarily estimated from release quantities using accepted environmental and biological models without reference to existing background. Thus the two systems, one addressing all existing exposures regardless of the source and the other addressing exposure increments from planned operations are independent.

9.1 Risk Approach Selecting a level of risk that is appropriate for the circumstances requires estimation of factors relating health effects to exposure as well as judgements about the impacts of these levels on the population concerned. In this section, we will estimate the risks associated with 73

74

/

9. BASIS FOR RECOMMENDATIONS

various exposures and indicate levels of risk that are considered acceptable in given circumstances. In this report, only the carcinogenic risk of radiation is considered, specifically the probability that a specified amount of radiation will cause fatal cancer in some fraction of the people exposed. This may be expressed as an annual or a lifetime mortality risk per unit of radiation. For the purpose of making risk estimates, we have made the following assumptions: 1. In the dose range of interest here, the probability that an individual will develop radiation-induced cancer is a direct linear function of the total dose. 2. The probability is independent of whether the dose is delivered continuously, intermittently or in a single exposure. 3. The risk factors obtained at high doses and high dose rates are valid down to doses and dose rates approaching average background levels' and there is no threshold for radiation effects. It is recognized that these assumptions have uncertainties relating to limitations on the data and their applicability at low dose levels. It should be emphasized that calculated risks for radiation exposure are not the same as the risks which actuaries cite to predict the number of highway deaths over a holiday weekend or the number of homicides expected in a particular city the following year. The latter risk estimates are based on past experience with events of relatively high incidence and definite attribution and no extrapolation is involved. In the ideal case, for determining a risk factor for exposure to radiation, two populations-identical except for the known radiation exposure-would be followed from birth to death. In fact, none of the populations being followed today are near closure (all participants dead) and the total mortality must be estimated by projection into the future. In addition, none of the possible effects from low level irradiation have actually been observed and hence they must be estimated by extrapolation from high dose exposures. For modelling lifetime exposure effects, data from acute exposures mainly is available in the case of external radiation, but in the case of radon daughters, data on extended exposures over a working lifetime for miners is available. There is presently some disagreement on the form of the models used for the projection required to express risks over a lifetime, in addition to the other uncertainties noted above. The absolute risk model assumes that the risk of cancer mortality

' In the case of alpha radiation, this is strictly true, but for gamma radiation the estimates are reduced by a factor of 2-2% between high and low doses.The resulting low dose value is applicable for 10 rads and below.

9.1 RISK APPROACH

/

75

is only a function of the radiation dose received, while the relative risk model assumes, in addition, that the risk is proportional to the natural mortality in the population from the particular cancer. If the lifetime risk were derivable as described for the ideal case above, a projection would not be necessary, since the actual mortality by cause, age and sex would be available for the two populations. An example of the difference resulting from the two methods of projection is that given in the calculations set out by the Committee on the Biological Effects of Ionizing Radiation (NAS, 1980), where their concensus model for total excess cancer mortality per million people exposed t o 1 rem uniform whole body radiation gives 67 with the absolute and 169 with the relative risk projection. The value for low doses used by UNSCEAR (1977) and ICRP (1977a) and adopted in this report is 100. In the consideration of radon risks in this report, the extent of future projection is rather minimal, because there has been more than 50% mortality in some of the miner populations. Furthermore, increased lung cancer mortality has been found in groups of miners exposed t o less than 100 WLM, which is less than 10 times the lifetime background level of more than 10 WLM, and since the assumption of linearity is believed t o be valid for alpha particles, the error in considering low exposures should be small. The NCRP will publish risk limits in a forthcoming report (NCRP, 1984a). For the public, an average risk level in the range of 10-6/y t o 10-5/y was considered by ICRP t o be one likely to be acceptable to individuals (ICRP, 1977a). The specification that critical groups be limited to 0.5 rem/y (risk = 0.5 x 10-4/y for somatic effects only) is deemed by ICRP to be adequate to yield an average risk a t or below the desired level. It is necessary now to -consider separately the risk incurred as a result of inhalation, external exposure and ingestion from components of the uranium series. 9.1.1 Inhalation

The estimate of lifetime risk of lung cancer for a given exposure to radon daughters, as used here, is based on the model of Harley and Pasternack (1981). Their model includes a 5-year latent period, no lung cancer appearing before age 40 and a 20-year half-time for an apparent reduction in effect with time which may be attributable to cellular repair or to some other cause. It is used in conjunction with a life table to account for competing risks. The total epidemiological

76

/

9. BASIS FOR RECOMMENDATIONS

per WLM. Using this experience of miners points to a risk of value with the model gives a lifetime risk factor of 9100 lung cancer deaths in one million people exposed to 1WLM/y from birth (NCRP, 1984a). The mortality estimates for various levels of exposure are shown in Table 9.1. The annual risks are obtained by dividing the lifetime risk by 45, the number of years over which lung cancer is likely to be expressed, and thus 1 WLM/y corresponds to an annual risk of 2 x 10-4/y. The tabulated data also suggest that, because of the high incidence of lung cancer, any incremental effects of environmental radiation exposure would be difficult to detect epidemiologically. On the other hand, the failure of the data of Letourneau and Wigle (1980) and Letourneau et al (1983) to show any relationship between environmental exposure and lung cancer incidence in Canadian cities indicates that the risk from radon daughters cannot be appreciably higher than has been estimated. It is apparent that the model predicts a risk comparable with an accepted occupational risk of 1 x 10-'/y (ICRP,1977a) at an exposure of about 0.5 WLM/y. The average background exposure of 0.2 WLM/y derived in this report is associated with a risk of 4 x 10-5/y. A risk of 10-~/ymight have been a reasonable choice (see above) in considering a limit for the population but obviously it cannot be approached in practice since it is equivalent to 0.05 WLM/y, only l/r of the average background. TABLE 9.1-Expected excess lung cancer mortality rates in individuals exposed to various levels of radon daughters and a comparison with the observed lung cancer mortulihr. Radon daughter Lifetime risk Annual r W Conditions Death per Deaths/y per million exposed million exposed

&EM"/;

Average background Possible limiting levels Occupational limit Observed mortality from lung cancer in a U.S.population of 10 million male female

0.2 0.5 1.O 2.0

4.0

1800 4600

40 100

9100

200 400 800

lsooo

36000 Deaths per million Lifetimeb Annuar

'After age 40. Lifetime risk from Zdeb (1977),annual riak obtained by dividing by 45 years at risk.

9.1 RISK APPROACH

/

77

TABLE9.2-Probability of living to a given age with and without radon daughter exposures.

,,

-

Exposure

1975 L ife

Tab'e'

0.2 WLM/y

1 WLMh

2 WLM/y

5 WLM/y

'Vital statistics of the United States-1975 (NCHS, 1979). Note: The life table necessarily includes lung cancer deaths from average background levels of radon daughters. This is a small difference, as indicated by the effect of an added 0.2 WLM/y shown in the table.

Another way of looking at the risk from radon daughters is to consider the potential loss in life expectancy caused by exposure. This is shown in Table 9.2, where the 1975 life table, or the probability that a child born in 1975 will survive to a given age, is compared with the probabilities calculated to include various lifetime exposures from birth. This comparison should be less sensitive to smoking vs. nonsmoking habits, because the other causes of death outweigh those caused by smoking. The decrease in probability of living to any given age is apparent from Table 9.2. Exposure at a level of 2 WLM/y would reduce the probability of living to age 70 by 1.5% and exposure a t a level of 5 WLM/y for a lifetime would reduce the probability by about 4%. Evidently, at the average background level of 0.2 WLM/y, the effect on the probability of a given individual living to a given age is minimal.

9.1.2 External Exposure The ICRP (1977a), UNSCEAR (1977) and the NCRP (1984b) consider the lifetime mortality risk to be about 1 x 10-4/rem for all cancers from whole-body exposure to gamma radiation. The total lifetime risk of 2 x 10-4/rem used by ICRP (197%) includes genetic effects for all generations. The lifetime cancer risk coefficient of rem can be compared with the risk of lung cancer from radon daughter inhalation, which has no genetic component. Table 9.3 lists the estimated cancer risks for various levels of exposure. The average external radiation background includes external terrestrial gamma dose and the cosmic radiation dose. The average whole-

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TABLE9.3-Expected excess total cancer mortality rates in indiuiduals elposed to various levels of external whole-body radiation and a comparison with the observed cancer martakty. Conditions

Average external background including cosmic Possible limiting levels

Occupational limit Observed cancer mortality in a U.S. population of 10 million male female

equivalent (mrem/y)

Lifetime rink Deaths per Million exposed

Annual risk Deathsly per Million exposed

54

300

5

200 500 lo00

1200 3000 6000

20 50 100

5000

30000

500

Deaths per million'

Average annual risk

270000 280000

'Lifetime risk from Zdeb (1977).Annual risk obtained by dividing by 60.

body dose, including internal radionuclides is about 80 mrem/y, with a lifetime risk of about 500 deaths per million exposed. This may be compared with the lifetime risk for average background radon daughter exposure of 1800 per million which is 4 times greater. Comparing Table 9.3 and Table 9.1 it can be seen that the risks associated with the occupational limits are about the same for external radiation and for radon. 9.1.3 Ingestion The members of the uranium series (except radon) are all heavy metals and most of the elements metabolized after inhalation or ingestion tend to concentrate in bone. Our basis of comparison for these elements has been the skeletal content without specifying the route of intake. The corresponding dose rates were developed in Section 7. The risk for fatal bone cancer (UNSCEAR, 1977) is given as 2-5 x lO-'j/rad for gamma radiation with the statement that alpha radiation is comparable in this case, i.e., 2-5 x 10 -6/rem. The dose calculated by UNSCEAR (1982) is that t o a surface layer 10 micrometers thick. The dose factor per unit concentration of radionuclide in bone is higher than that calculated with the assumptions given in Section 7. Because of this difference, the higher risk factor of 5 x 10-6/rem is used here.

9.2 DOSE LIMITATION APPROACH

1

79

TABLE9.4-Expected excess bone cancer mortality rates in individuals exposed lo radiation from members of the uranium series in their skeleton and a comparison with the observed bone cancer mortality. Skeletal content Lifetime risk deaths Annual risk deaths/ Conditions (di) v e r million exwsed v e r million e x w e d Average background

2"U

+ mu

2%tl

ZlOpb 210p0 Occupational limit 226Ra

Observed bone cancer Mortality in U.S. population of 10 million' male female

Deaths per million

200 Annual risk

' Lifetime risk from Zdeb (1977). Annual risk obtained by dividing by 60.

Table 9.4 gives the estimated excess bone cancer mortality rates for a few levels of the uranium series deposited in bone. Clearly the average background levels are quite low and correspond to risks less than lO-'j/yr.

9.2 Dose Limitation Approach The current NCRP dose limitations are given in NCRP Report No. 39 Basic Radiation Protection Criteria (NCRP, 1971). For individual members of the public, the dose limit for the critical organs, (whole-body) is 0.5 rem in any one year-in addition to radiation from natural sources and from medical and dental exposures. No limit is given for other organs or tissues, although it is stated that: "To have no organ or tissue exceed 0.5 rem/y is a reasonable target, but it is arbitrary, of course, and may not always be achievable." A limit of dose equivalent to the population is given as an average of 0.17 rem/y per person in the United States. As mentioned previously, new NCRP criteria are being provided in another report (NCRP, 198413).

9.2.1 Inhalation The radiation dose in tissue from inhaled radon daughters cannot be measured and must be calculated. Table 9.5 gives the dose rates to the bronchial epithelium calculated for various exposure rates of radon daughters, based on the average conversion factor for all ages of 0.7

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TABLE 9.5-Dose rate to the bronchial epithelium of the lung from exposure to rodon daughter products.

,

Conditions -

-

Absorbed done rate (mred/y)

t h e equivalent rate (mrem/y)

-

Average background

0.2

140

2800

Possible limiting levels

0.5

14000

2.0

350 700 1400

28000

4.0

2800

56000

Occupational limit

1O .

7000

rad/WLM developed by Harley and Pasternack (1982) for environmental exposures and a quality factor of 20. If the aim cited above of no organ or tissue exceeding 0.5 rem/y were applied to the bronchial epithelium only exposures below 0.036 WLM/y of radon daughters would be permissible. As this is only 116th of the average background level it is unachievable. The ICRP uses a dose factor of about 12 rem/WLM (ICRP, 1981) for the tracheobronchial dose. The dose equivalent obtained is then multiplied by a factor of 0.08 (ICRP 32) to give the regional effective dose equivalent. Thus a limit of 0.5 WLMIy for radon daughters would correspond to an effective dose equivalent limit of 500 mrem/y, according to ICRP. 9.2.2 External Radiation

The external whole body doses have already been given in Table 9.3. In this case, 500 mremly is well above the average external background, approximately ten times, and can be considered as a practical limit.

9.2.3 Ingestion Table 9.6 lists the dose equivalent rates for bone surfaces from ingested radionuclides. These doses, with the assumptions given in Section 7, are calculated for cells at 10 micrometers from the bone surface. Both UNSCEAR (1982) and ICRP (1979) calculate the dose to a layer from the surface to 10 micrometers. The UNSCEAR calculated doses would be about 50% higher, and the ICRP calculated doses a few percent higher, than the rounded totals given in Table 9.6. Such differences are not considered to be significant. A 500 mrem/y limit

9.3 EXPOSURE DISTRlBUTION APPROACH

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81

TABLE9.6-Dose mte to bone surfaces from members of the umniwn series in the skeleton. (Doses calculated as described in Section 7). Skeletal content Absorbed doae Done equivalent (&i) rate (rnradly) rate (mrem/y)

Average background

mu+

=Ra nopb zropo Rounded total Occupational limit '=Ra

4 30 360

100OOO

0.01 0.6 2.6

1700

0.2 10 60 60

34000

would be practical because the average background rates are lower by a factor of about 10 than this limit. In the ICRP system (ICRP, 1977a), the calculated dose equivalent for bone surfaces is multiplied by a factor of 0.03 to obtain the effective dose equivalent, which would then be compared with the 500 mrem/y allowed for whole body irradiation.

9.3 Exposure Distribution Approach A broad survey of measured values of natural background is required to allow adequate estimates of the average population exposure and the statistical distribution of these exposures. This distribution can then be used to predict the exposure level that will include all but some small fraction of the population. This fraction of the population would then be classed as having elevated natural exposure and remedial action might be required. Thus, while the average natural background may not be of concern, the higher end of the range may be. The situation with the inhalation of radon and its daughters, especially indoors, appears to be such a case even though data for radon daughter exposures in the U.S. are not fully adequate to develop the required distribution curve. Areas with elevated and enhanced exposures to radon daughters (and external radiation) have been sufficiently studied that limited distribution curves can be developed for houses in parts of Colorado, Florida and Montana. Some of the relevant data were listed in Tables 8.1 and 8.2. The houses in these groups are selected examples which probably represent only the upper end of the total distribution curve, which is not helpful on its own as a basis for judgements or recommendations. The distribution approach was used in Canada (see Appendix A) to assess the situation for radon daughter exposure in uranium mining

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communities. Their survey of a large number of houses (Letourneau et d.,1979) led to the adoption of a limit of 0.02 WL for the average annual exposure (1WLM/y). The limits selected for external exposure were 0.05 mR/h indoors and 0.1 mR/h outdoors, which would result in about 500 mrem/y if 80%of the time is spent indoors. As examples, the distributions of radon daughter concentrations for the highest and lowest Canadian cities are shown in Figure 9.1. It must be remembered that the values measured are not necessarily representative of annual population exposures, since the data are for spot samples taken in cellars during the summer months. Concentrations will probably be higher in winter, when the houses have less ventilation. On the other hand, average concentrations in living areas should be lower than in cellars. The distributions in the figure may be compared with the concentrations of radon daughters found in a Montana mining community, as given in Table 8.1. In this case, about 7% of the houses exceeded 5 WLM/y. The radon involved arises. from the natural mineralization of the area and not from mining or milling residues near the houses. The data are not representative of the full community because all of the measurements were taken in a small portion of the city thought

90

50

10

1.0

0.1 001

Percent Exceeding Working LHel Shown

Fig. 9.1. Distribution of working level measurements in the highest and lowest Canadian cities, as described in Section 5.

9.3 EXPOSURE DISTRIBUTION APPROACH

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83

TABLE9.7-Cukulated distribution for the lifetime risk of &ath from lung cancer for a populatwn of one million having an average exposure of 0.2 WLM/y and a geometric standard deviation of 2.5. Average % of Deaths per Pooulation million WLMIV C0.2 0.2-0.5 0.5-1.0 1.0-2.0 2.0-4.0 >4.0

Total

69.3 23.6 5.7 1.2 0.14

100.0

594 658 348 143 35 22 1800

to have the highest radon in the homes. The data serve, however, to show that elevated natural levels of radon can exist in U.S. buildings that have not been influenced by activities that lead to enhanced levels. If a radon daughter exposure of 0.2 WLM/y, assumed here as the U.S. average, is combined with the mean geometric standard deviation of 2.5 found for the Canadian cities, a tentative distribution for the U.S. can be calculated. This distribution predicts that about 6% of the houses would exceed 0.5 WLM/y, 1.2% would exceed 1 WLM/y and that 0.14% would exceed 2 WLM/y. It is of interest to estimate the distribution of cancer deaths within the various exposure categories. This is shown in Table 9.7. While the tentative distribution may not describe actual exposure and risks in the U.S. accurately, the relative values may be reasonable. The majority of the population risk is incurred by the large number of people in the lower exposure categories, rather than the small number of individuals with high exposures. Thus, any limit on radon daughter exposure will reduce the individual risk for a few people but will not markedly reduce the population risk. In summary, there are not enough data to provide a full exposure distribution for the United States. However, the Canadian data have been utilized to establish a distribution for the U.S. (Table 9.7). It is recognized that there are significant geological differences which point to the pressing need for the acquisition of more comprehensive data for the U.S. Information on external radiation is not as extensive as one would wish but the levels are about 50 mrem/y external, Table 9.3, and the variations are within only about a factor of 2 in either direction, (NCRP, 1975). Thus large groups of people exposed at high external

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background levels are not expected. UNSCEAR (1982) combined the available external gamma radiation data for Italy, Japan, the United States and West Germany and found that the distribution was normal with a median value of 30 mremly. Only about 1% of this population is exposed at a level 50% above the median. Levels of exposure from ingestion, Table 9.6 and earlier, are also unlikely to lead to high exposures of groups of people.

9.4 Additivity The foregoing indicates that exposure to members of the uranium series depends on the physical and chemical behavior of the particular element and is by three main routes, inhalation, external irradiation and ingestion. The short-lived daughters of radon are an inhalation hazard and deliver the significant dose to the bronchial epithelium. The external gamma emitters, and to some extent the 210Poin the body, irradiate the whole body. Internal deposition of the long-lived daughters of radon and from ingested uranium and radium tends to concentrate in bone and the dose is delivered to bone surfaces. These varied doses to different organs are not directly additive, but one might wish to consider some form of summation in order to evaluate mixed exposures. One way is to express each exposure as a fraction of a permissible limit and require that the sum of these fractions not exceed unity. The ICRP, in its Publication 26 (ICRP, 1977a), used weighting factors for various organs to convert the organ doses to effective whole body doses, which are then additive because they represent risks. The weighting factors were set to be in proportion to the health risk for exposure of the individual organs. Although such a summation is possible for the three routes of exposure to the uranium series, it does not appear to be necessary. The ingestion route delivers only a small dose compared with external whole body radiation and inhalation. Further, in most circumstances, the external whole body dose is significantly less than the dose to lung resulting from inhalation. Therefore, it seems appropriate to treat these independently.

9.5 Exieting Recommendations Before making any recommendations, it is necessary to review the existing dose limits recommended by bodies such as the NCRP and

9.6 SUMMARY

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85

the ICRP for public exposures. These are often adopted by regulatory groups, usually with modifications. Some of the regulatory standards have been mentioned in this report and a brief summary is provided in Appendix A. The NCRP, in its Report No. 39 (NCRP, 1971), recommended a dose limit of 500 mrem/y for the critical organs (whole body) for an individual in the population. The ICRP in its Publication 26 (ICRP, 1977a) gives the same dose limit for the whole body but derives higher limits for the irradiation of individual organs through use of the effective dose equivalent. Neither NCRP nor ICRP in these reports specifically addressed the radon daughter problem for populations. For occupational circumstances, the ICRP (1981) has recalculated the occupational limit as 4.8 WLM/y which is somewhat higher than the 4 WLM/y used for miners in the United States. Applying the customary factor of onetenth to the 4 WLM/y would give a limit for individuals of 0.4 WLM/y. This limit, like all of those discussed, is for the incremental exposure above natural background. Adding the average background of 0.2 WLM/y assumed here would give a total of 0.6 WLM/y. Like most of the values derived in the three approaches in this chapter, the limit would be exceeded by a large number of individuals (Table 9.7). The Surgeon General's guidelines for the Grand Junction houses (CFR, 1972) required consideration of remedial action a t a radon daughter exposure rate of 0.01 WL above background and mandated remedial action at 0.05 WL. These would translate to 0.5 and 2.5 WLM/y above background, respectively. 9.6 Summary

In this section, three approaches have been utilized to evaluate exposure of individuals to elevated or enhanced environmental radiation from the uranium series. These are the risk approach, dose limitation approach and the distribution of exposures from background radiation approach. Within each approach, the relative contribution from inhalation, external exposure and ingestion was evaluated. The significant dose results from inhalation of radon and its daughters and only rarely, in special geographical locations, does external exposure provide a significant fraction of the total dose or constitute the most significant component. Ingestion is not of special concern because the resulting doses are so low. The derivation of recommendations for radon and its daughters presents difficult choices because the exposure distribution (Table 9.7)

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BASIS FOR RECOMMENDATIONS

is broad and ranges up to high values. Furthermore, the average radon background level of 0.2 WLM/y leads to risks substantially greater than from other background sources; thus, natural radon background probably constitutes the most significant exposure of the U. S. population. External radiation exposure and ingestion from the uranium series do not represent the same risks. This section has presented the relevant dose limits previously recommended by the NCRP and the ICRP. They offer guidance for external radiation exposure and ingestion but were not intended to address the special case of radon daughters.

10. Recommendations This Section will present recommendations for controlling exposure to individuals in the population from members of the uranium series. They are intended to indicate the point at which some form of remedial action to reduce exposure is advisable. They are all, therefore, termed remedial action levels. They apply to annual exposures to individuals and are not intended to apply to shorter periods. The remedial action levels are for total exposures, including background and are not intended to be applied separately to individual components of the total. Setting remedial action levels based on the distribution of natural background involves considerations of both risk and practicality. A choice must be made at a level where the remedial action required is reasonable given the costs involved and other factors. It is desirable to minimize the impact by placing the remedial action level at a point where as few buildings as possible require remedial action. However, in view of the possibility of very high exposures in some circumstances, remedial action levels are necessary to limit the health risks to the people involved. Remedial action levels based on considerations developed earlier and especially in Section 9 are presented for inhalation and for external exposure circumstances. Other circumstances relating to ingestion and to land use are discussed but no specific levels are developed. The Section concludes with one subsection on the use of the recommendations and another on the need for additional data.

10.1 Inhalation Inhalation of the short-lived daughter products of 222Rnpresents the greatest exposure to individuals from members of the uranium series in the environment. The estimated risk and calculated dose from average background levels, as shown in Section 9, are about 1/20 of the present occupational limits and the distribution is such that a considerable number of people are exposed to levels 10 times the average in areas of elevated natural background. It is believed that 87

88

1

lo. RECOMMENDATIONS

the risk and dose estimates of Section 9 are reasonable derivations from the available data, although there are no human epidemiological data that show increases in lung cancer at the radon daughter levels considered here. However, the epidemiologic data indicate that the risk from radon daughters cannot be appreciably higher than has been estimated. The remedial action level selected must be based on consideration of the probable distribution of natural exposures and of the calculated risk associated with exposures at that level. In particular, recommendation of a low level to minimize the risk is not warranted if the impacts are excessive. Thus, the selection will inevitably involve a risk greater than the average to those individuals exposed near the remedial action level. In this report, it is considered that an excess risk of death from lung cancer of 2% or more over a lifetime for the individual exposed to elevated or enhanced levels of radon daughters should be avoided. This would correspond to an annual exposure of 2 WLM which is now specified as the remedial action level for radon daughter inhalatioa2 This is about 10 times the average background exposure assumed for the United States. The associated annual risk is 4 X lo-' for a 45y period of expression and the cancers would appear after age 40. It must be emphasized that the lung cancer risk expressed here is for those exposed at the remedial action level (2 WLM/y) and that the population risk depends on the average background exposure (0.2 WLM/y) which is approximately one tenth of this level. The recommendation is that exposures beyond the remedial action level s h o d be reduced by appropriate remedial action. Exposures below this level may not be acceptable to some individuals and they are free to reduce their exposures as they see fit. For the purposes of protection from environmental radiation, a remedial action level based on lifetime exposure is not practical. Adherence to the annual level of 2 WLM/y will mean that the average lifetime exposure rate for individuals must necessarily be lower than 2 WLM/y and that their average risk of lung cancer will actually be less than 4 x 10-4/y. Table 9.2 indicates that a lifetime exposure to the recommended 'This report discusses concentrations of radon and its daughters only, however, thoron is often present also and may contribute appreciably, perhaps, 20% to the dose (UNSCEAR, 1982). There are no data to assess population exposures to thoron daughters in the United States and radon daughter memuring equipment does not make the necessary separate measurement of thoron or its daughters. When adequate information is available, it may be advisable to include thoron daughter exposures in the recommendations.

10.2 EXTERNAL RADIATION

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89

remedial action level for radon daughters would reduce the probability of living to age 70 from 65.5% to 64.1% and the probability of living to age 85 from 24.5% to 22.6%. The reduction a t age 45 would be from 92.7% to 92.4%. The annual average exposure rate of 2 WLM/y can be translated into an average WL of 0.04. The recommendation is specifically not given in these terms because occupancy factors may allow higher WL values in the home, if these are compensated for by lower WL values outdoors, in work places and in other buildings.

10.2 External Radiation

The dose equivalent rate to the whole body from natural external radiation averages about 50 mrem/y, including cosmic and terrestrial gamma radiation, with the two sources contributing about equally. The consequent cancer mortality risk would be about 5 x 1OW6/y.This may be compared with the calculated risk from average background exposure to radon daughters of 40 x 10-6/y. Areas with elevated or enhanced levels of the uranium series may have higher external radiation exposures than 50 mrem/y (see Section 4), but the dose rates that have been recorded for elevated or enhanced levels of the uranium series have not exceeded the limit for individuals in the population of 500 mrem/y (NCRP, 1971). NCRP recommendations in preparation (NCRP, 198413) for exposures to individual members of the public for occasional and continuous exposures are as follows: 1. a maximum limit of 500 mrem in any one year (other than medical and natural background) to an individual member of the public is still recommended, but not for continuous or repeated exposures; 2. it is recommended that continuous exposures (other than medical and natural background) resulting in a dose equivalent of 100 mrem/y or more to individual members of the public be avoided; 3. in situations where continuous exposures resulting in dose equivalents of 100 mrem/y cannot be avoided, such as from elevated or enhanced natural sources, NCRP recommends a remedial action level of 500 mrem/y from external radiation from all sources except medical. When elevated or enhanced exposures involve a combination of radon daughter inhalation and external radiation, the former is expected to be the controlling factor. The added risk from the accom-

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panying gamma radiation should be small enough that any attempt to recommend reduced remedial action levels for the combined exposure is not warranted. The recommended total external gamma radiation limit of 500 mrem/y may be a controlling factor in some exposures which are not accompanied by high levels of radon daughters but such cases should be rare.

10.3 Ingestion The contribution of dose from ingested radionuclides in areas of elevated or enhanced natural activity is usually much less than that from the inhaled short-lived radon daughters or even that from external radiation (see Section 9). Thus there is no need for either a separate remedial action level or for establishing a remedial action level which includes dietary intake. Occasional monitoring may be desirable nevertheless. Attention might be paid to water supplies, since water concentration is most indicative of local conditions.

10.4 Land Used for Agriculture It would appear that some consideration of the soil content of radionuclides whether elevated or enhanced is desirable for land that is to be used for agricultural purposes. A practical solution is to recommend use of such land for crops that have minimal uptake of radionuclides of the uranium series or for crops that are not directly consumed by humans. Such consideration should be given to soils with concentrations of 2000 pCi/g (3000 micrograms/g) of natural uranium, 40 pCi/g of 226Ra,or 20 pCi/g of 2'0Pb in the rooting zones of crops to be grown. Note that this is not a recommended remedial action level but merely a guide for land use. The derivation of these values is given in Appendix C.

10.5 Land to be Used for Housing It would be most useful to be able to predict with certainty what radon daughter concentrations will appear in a new house built on land with elevated or enhanced uranium series activity because action is almost always more expensive after construction than before. Un-

10.6 USE OF T H E RECOMMENDATIONS

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91

fortunately this is usually not possible. Certain features described in Section 5 can minimize radon influx into a building and the installation of a sub-slab ventilation system could almost ensure that the new house would result in exposure levels below those requiring remedial action. Although it is not possible to make broad general recommendations for soil concentration limits, local authorities may find that adequate predictions are possible for specific areas. In any case, the actual gamma radiation levels and working levels in the finished buildings are the final criteria for evaluating exposures to people.

10.6 Use of the Recommendations The remedial action levels recommended in this report are intended to apply to those individuals in the population subject to elevated or enhanced radiation exposures from members of the uranium series. Exposures above the recommended action levels should be the basis for remedial action, but the extent and timing of the action obviously depends on the magnitude of the exposure. Since the recommendations do not make a sharp division into safe and unsafe levels, but merely mark a reference point in the gradation of risk, a degree of judgement on the speed and extent of the response should be applied in individual cases. As noted in the Introduction, the recommendations are intended t o apply to measured total exposures. In particular, the recommendation on radon daughter exposures is not readily applicable to the control of effluents from operating facilities, since the prediction of the relevant annual indoor exposures from release quantities is not considered to be practical. The recommended action levels are based on the exposure of individuals and most often action will be necessary only in local areas with above-average exposures. Remedial action levels are not to be multiplied for example, by the population of the United States to obtain an apparent permissible collective dose. No remedial action should be taken based on information that is inadequate for estimating annual exposure. As mentioned before, radon daughter evaluations, in particular, require integrated or extended measurements, covering a year under representative living conditions. Occupancy time in different buildings or even in different rooms becomes critical if exposures vary markedly from place to place. External radiation can be evaluated with measurement periods of a

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RECOMMENDATIONS

few months and ingestion exposure need be evaluated only infrequently. As noted above, the remedial action levels recommended in this report are associated with the estimated values of risk. If a n individual feels that this risk is excessive, the person is free to take remedial measures to reduce the risk to any desired level.

10.7 Need for Additional Data

Without a knowledge of the actual exposure distribution and a further knowledge of the extent of the remedial action required to reduce exposures t o specific levels, a comprehensive cost benefit analysis is not feasible. It is apparent that a broader data base on exposures, particularly for radon daughters, would provide mean values and distributions more adequate for assessing the impact of exposure limits. T h e present data may be sufficient for development of a statistical sampling plan that could provide the needed information. Also, the statistical methodology and experience from the Canadian survey and other studies might be valuable in planning for a U.S. study. A preliminary range-finding survey should be designed to cover perhaps 1000 homes within 10 of the 100 largest Standard Metropolitan Statistical Districts. The Districts should be selected to give geographical coverage and, within Districts, the homes should be selected to represent the distribution of urban vs. non-urban, single family vs. multifamily, and modern vs. older structures. Two consecutive six-month integrated measurements, a s described in Appendix B, should be made in the living room a t each location. Passive monitors for radon daughter concentration would be desirable but, if this is not feasible, radon measurements would be acceptable. The overall value of the survey would be increased if thermoluminescent dosimeters were included to measure the external radiation exposure. The results of this study should allow decisions to be made as to whether a larger measurement program is necessary to characterize exposures in the United States. The NCRP recommends that such a program be undertaken without delay.

10.8 SUMMARY

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93

10.8 Summary The recommendations are1. Remedial action is advisable if the total exposure to radon daughter products for an individual in the population exceeds an annual average of 2 WLM, including background, which is defined as the remedial action level for inhalation3 2. Remedial action is advisable if the total exposure from all sources, except medical, to penetrating external radiation for an individual in the population subject to elevated or enhanced radiation exposures from members of the uranium series exceeds an annual average of 500 mrem including background. Thus 500 mrem/y is the remedial action level for external radiatiom4 These recommendations indicate that continuous exposure of individuals in the population to 2 WLM/y of short-lived radon daughters for a lifetime should be avoided. The external gamma radiation associated with such exposures is not considered to present enough added risk to require a summation technique for exposure assessment. In special cases where external radiation becomes a controlling factor, 500 mrem/y from all sources except medical is the recommended remedial action level. The practical result of limiting individual annual exposures at 2 WLM or at 500 mrem is that the average lifetime exposure for any individual will usually be lower than the product of age and the limit, with a consequent smaller risk. The average exposure of population groups in the area should be smaller yet. No specific limit is recommended here for exposure to ingested radionuclides of the uranium series. The risk is minimal. relative to inhalation. In Section 9, two ways of expressing the risk were given, the reduction in life expectancy and the calculated risk of developing cancer from exposure to specific levels of radon daughters or to external radiation. Table 9.2 indicates that a lifetime exposure to the recommended limit for radon daughters would reduce the probability This report discusses concentrations of radon and its daughters only, however, thoron is often present a180 and may contribute appreciably, perhaps, 20% to the dose (UNSCEAR, 1982).There are no data to assess population exposures to thoron daughters in the United States and radon daughter measuring equipment does not make the necessary separate measurement of thoron or its daughters. When adequate information is available. it may be advisable to include thoron daughter exposures in the recommendations. 'As indicated in Section 10.2 NCRP recommendations in preparation make three distinct recommendations about external exposure and individual members of the public.

94

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10. RECOMMENDATIONS

of living to age 70 from 65.5% to 64.1%. The reduction a t age 45 would be from 92.7% to 92.4% and at age 85 from 24.5% to 22.6%. Lifetime exposures to radon daughters and to external gamma radiation at the recommended remedial action levels lead to total calculated risks of 4 X and 0.5 x radiation-induced cancer deaths per year, respectively. These risks might be compared with the risk of 0.4 x 10-4/y for average radon daughter background, and 0.05 X 10-4/y for the average external radiation background.

APPENDIX A

Regulatory Status Three countries, Canada, Sweden and the United States have found levels of environmental radon that are high enough that some form of regulation has been considered. The status of their actions is given in this Appendix. A. 1 Canada Under the Atomic Energy Control Act, for all radon contamination arising from the nuclear industry and for houses built in uranium mining areas or those contaminated by refined radium or contaminated fill, the primary clean-up criterion for radon daughter products indoors is 0.02 WL based on an annual average concentration. Remedial measures start with a detailed survey of the building and its surroundings in order to locate and identify the source of radon. Any radioactive material found will be removed to an appropriate waste management site or, if this is not practicable, other measures may be taken such as improving the ventilation or sealing the walls and floors of the basement. Once remedial measures have been started, they will continue until the radon levels have been reduced below the primary criterion. The second criterion is a guideline for all other areas in Canada and involves natural radiation not associated with the nuclear industry. This is for areas under provincial jurisdiction. The guideline is as follows: "A single grab sample measured in the most critical area of less than 0.1 WL shall require no further action. If the working level is greater than or equal to 0.1, then a realistic estimate of the annual effective dose equivalent must be determined. Should this estimate exceed 5 millisieverts (500 mrem), then remedial measures shall be undertaken."

A.2 Sweden A provisional limit for radon daughter concentrations where remedial action shall be undertaken within 2 years is set a t 0.27 WL and 95

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APPENDIX A

for remedial action within 5 years at 0.11 WL. (It is estimated that 5000 to 15000 dwellings are affected.) For existing buildings undergoing major alterations, an upper limit of 0.06 WL is proposed.

A.3 United States

The specific case of buildings constructed on or with mill tailings in Grand Junction, CO was covered by guidelines issued by the U. S. Surgeon General (CFR, 1972). These recommended that remedial action be considered at 0.01 WL and mandated remedial action at 0.05 WL above background. There is currently no federal legislation which might be invoked as the statutory basis for a generalized program of regulating the radon levels in homes. Section 112 of the Clean Air Act, 42 USC, Section 7412, could be used by listing radionuclides as hazardous air pollutants. However, the thrust of the Clean Air Act is towards prevention of atmospheric pollution and the maintenance of ambient air quality. The regulations implementing the Act specifically define the term ambient air as "that portion of the atmosphere external to buildings to which the general public has accessn. There does exist a basis for the regulation of indoor radon levels in certain limited circumstances under current federal legislation. Certain waste materials known to be radon sources are subject to regulation under the Atomic Energy Act (uranium mine tailings) and the Resource Conservation and Recovery Act (waste from uranium and phosphate mining). In the case of uranium mine tailings, regulation by the Nuclear Regulatory Commission is now specifically mandated pursuant to an amendment to the definition of the term "by-product materialn in the Atomic Energy Act accomplished by the Uranium Mill Tailings Radiation Control Act of 1978. Similarly, radon-emitting wastes from uranium and phosphate mining activity are subject to regulation as hazardous waste pursuant to the Resource Conservation and Recovery Act of 1976. Regulation of radon in inhabited structures under either of these two Acts is limited to situations involving the utilization of material which emits radon and otherwise meets the respective statutory definitions of by-product material or hazardous waste. Another regulatory basis may be found under the Toxic Substances Control Act (TSCA) of 1976. However, it is clear that the principal thrust of the Act is aimed at chemical substances or mixtures subsequent to manufacture or processing. This limits its utility in regulating

REGULATORY STATUS

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naturally-occurring radon. In addition, the TSCA authorizes regulation to prevent "an unreasonable risk to injury and health". This standard for triggering statutory coverage may well require more rigorous evidence of adverse health effects than is currently possible with naturally-occurring radon. Under the Safe Drinking Water Act, EPA has authority to establish maximum contaminant levels for radioactive pollutants in the finished drinking water furnished by community water systems to their customers. Private wells are unregulated. No maximum contaminant level for radon has been promulgated The Department of Housing and Urban Development (HUD) has authority to issue regulations to implement the National Housing Policy goal of "a decent home and suitable living environment for every American family". The Department takes the view that, under this authority, it could issue regulations which, on a prospective basis (e.g., applicable to mortgages refinanced or entered into after the effective date of such regulations) could establish radon exposure limits with respect to public housing and to private housing financed in whole or in part with federal financial assistance. In Montana, HUD convinced the state that it should adopt the EPA recommendations for HUD projects. The 0.02 WL number is used for remedial action, with the level being based on a four-season grab sample system. In January 1981, the NRC amended 10CFR20-Standards for Protection Against Radiation-to delete Section 20.304 which provided general authority for disposal of radioactive materials by burial. Under the amended regulations, licensees must obtain specific NRC approval to dispose of thorium or uranium wastes from past operations by onsite burial. A similar authority is provided to the Secretary of Agriculture but again it is fairly certain that the regulation of radon exposure levels would be possible only on a prospective basis. Accordingly, while there is apparent authority for the development of regulations, no regulatory scheme is in place at present. In conclusion, no current legislation provides any particularly useful guidance with respect to a workable approach to the regulation of radon daughter concentrations in inhabited structures.

APPENDIX B

Measurements For Assessing Exposures It is not the purpose of this report to describe in detail the various methods of measurement that may be used for assessment purposes. It is worth noting, however, a few points that should be considered in planning a measurement program or in weighing the validity of reported results. These will be noted under the headings for the three modes of exposure. In general, when exposures are well below any recommended limits, the accuracy of the techniques is not as critical. At levels where decisions have to be made by a regulatory body, an accuracy of perhaps +20% would be desired. In reality, for health protection, there is no sharp dividing line between safe and unsafe. Since the limit is not sharply defined, a decision based on experience is required for each case.

B. 1 Radon Daughter Inhalation It must be stressed repeatedly that the only relevant measurement for radon daughter exposure is the annual average exposure under actual living conditions. Many factors, not detailed here, cause significant variations on a diurnal or seasonal basis. Thus, single or even multiple grab samples are not truly valid for exposure evaluation. They are useful for screening purposes, that is for indicating whether a building requires detailed study or whether it can be considered acceptable. This approach is noted in Appendix A, as it is used in Canada. Continuous samples, integrated samples or even repeated grab samples are expensive. A number of integrating monitors that measure 98

MEASUREMENTS FOR ASSESSING EXPOSURES

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99

total exposure over weeks or months are available, but the cheapest costs over $1000 to purchase and operating costs must be added. Several groups have used commercial track detector monitors for radon daughters. They are less costly-perhaps $300 for a series of four quarterly measurements-but there are still questions as to their accuracy for environmental levels. The data from the radon detectors seem to be better than the data for the daughter detectors. This system might be adequate for screening purposes. True continuous monitors for radon or radon daughters give data, for example, on an hourly basis which is useful in many scientific studies but is not needed for monitoring. There is considerable variability from house to house, depending on construction and living pattern, and using a single structure to typify an area is not valid. Thus, each house has to be monitored when elevated or enhanced levels are suspected. Multistory apartment buildings should be more amenable to generalization within a given structural type but there are few data.

B.2 External Exposure The measurement of personal external gamma exposure by thermoluminescent dosimeters (TLD) is adequate for monitoring. The dosimeters can be worn for three months which should be adequate for evaluation. External exposure is less variable than that for radon daughters so even a one-month measurement might be sufficient for screening. It is also possible to use TLD for area monitoring, for example, to measure different rooms in a house, outdoors, work areas and so on, but the estimation of individual dose from these data becomes a complex bookkeeping job. Thus, area TLD's are generally only used for checking the location of radiation sources, although instantaneous measurements with radiation survey instruments are more efficient for this purpose. Survey meter readings are not adequate for exposure assessment, both because extended measurements are needed and because the energy response of most survey instruments is not suitable. It must be pointed out that measuring external gamma radiation as a substitute for radon daughter measurements is invalid. Many field studies have failed to reveal any correlation between the two.

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B.3 Ingestion Expsoure Skeletal burdens of uranium series radionuclides at environmental levels are not measurable in uivo. An estimate of population exposure can be obtained by radiochemical analysis of autopsy specimens. The skeletal content is a stable quantity, so a series of analyses perhaps once a decade is sufficient for an area. If local contamination is suspected, a more rapid evaluation is possible by analysis of dietary samples. The measurement of soils involves an additional modelling step to estimate human exposure and requires information on the fraction of the diet coming from the contaminated area, so it is not usually helpful in exposure evaluation. Soil analysis is most helpful for predictive purposes, that is for making decisions on future land use for agriculture.

B.4 Summary The assessment of external and ingestion exposures does not require frequent measurement since the sources are quite stable. Contamination levels should be detected by other means than population studies. Radon daughters, on the other hand, are so variable that only an annual average exposure estimate is adequate. Suitable instruments and analytical methods exist but the required effort and the costs are high. It is apparent that less valid techniques will often be substituted, but it should be realized that the resulting decisions may not be soundly based.

APPENDIX C

Derivation of Soil Guides-Uranium, Radium and Lead-210 The NCRP (1971) states, "The dose limit for critical organs (whole body) of an individual not occupationally exposed shall be 0.5 rem in any one year, . .. ." If the reasonable target of no organ or tissue receiving 0.5 rems annually (NCRP, 1971) is applied to bone, it can be utilized for deriving an agricultural guide. A dose limit of 500 mrem/ y to bone is used as the dose limit for deriving an agricultural guide for radium, uranium and 'lOPb. In Section 7, the dose rates to bone surfaces for 1 pCi/g of the nuclides are given. For these derivations, the representative distance from bone surface for the absorption of alpha energy is taken to be 10 micrometers. Thus, the dose rates for 1 pCi/g of bone are 20 mrads/y for 234U, 13 mradsly for 'W, 84 mrads/y for 226Ra,including one-third of the daughters, and 34 mradsly for 210Pb.

C.1 Uranium Because natural uranium consists of 23aUand 234U,both will conin one microgram of natural uranium tribute to the bone dose. The 238U has an activity of 0.33 pCi. The 234Uactivity, when in equilibrium, is also 0.33 pCi but its mass is negligible. Thus one microgram of natural uranium has a total activity of 0.66 pCi. This latter conversion is used here and 1 pCi of natural uranium refers to 238Uplus 234U,Thus, the dose factor from Table 7.5 to be used is the average of those for the two isotopes or 16.5 mrad/y per pCi/g bone for natural uranium. The weight of the marrow-free skeleton in reference man is 5000 g, so the dose rate given is for 5000 pCi in the skeleton. A quality factor of 20 is used here to convert absorbed dose rate in bone surfaces to 101

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dose equivalent rate. The amount of uranium in the skeleton to give 500 mremly is, then, 7600 pCi. Hursh and Spoor (1973) have reviewed much of the information available on administrations of uranium to humans. In their review, they reported pertinent data on the uptake by humans upon continued ingestion of uranium. A summary of the uranium in the diet and in tissue for the U.S. and the U.K. is given in Table C.1. The significant quantities are in reasonable agreement for the two countries. The data for daily dietary intake are also supported by measurements in Japan. The urinary output for the U.S. is based on 37 subjects and the output for the U. K. is based on 300 samples. From Table C.l, the number of days intake equivalent retained in the bone can be estimated by assuming that all of the bone samples were taken from subjects at equilibrium with their diet. If the ratio of bone ash to mineral bone is 0.4, then mineral bone in the U. S. contains 8 ng of U/g of bone and a skeleton with 5000 g bone contains about 40 micrograms. Thus, the quantity in bone represents a 31-day intake by ingestion. The U. K. data indicate an accumulation of 40 days of intake in the bone. In the following, an accumulation in the bone equal to that ingested in 35 days will be used. Thus, the daily intake to arrive a t 500 mreml y is 7600135 = 220 pCi/d. (This is 330 micrograms per day.) Another calculation can be made using the ICRP Publication 30 (1979) scheme of 20% of that taken into the blood going to bone with a 20-day halflife and 2.3% with a 5000-day half-life. Using an absorption from the gut of 20%, in accordance with the findings of Adams and Spoor (1974), also results in an estimated intake limit of 220 pCi/d. To convert this intake limit to concentration in foodstuffs, it is necessary to know how much an individual eats from the uraniumcontaining area. Table 7.1 provides estimates of the average amounts of different types of foods consumed along with the measured concenTABLE C.l-Natural uranium in diet and tissue Description

Tissue concentration (ng/g) Blood Lung Liver Bone Ash Dietary intake (nglday) Urinary excretion (ng/day) Tap water concentration (ng/liter) Air concentration (ng/m3) Total estimated body content (micrograms)

U.S. Values

U.K. Values

DERIVATION O F SOIL GUIDES

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103

tration of uranium in each type of foodstuff. The total intake, excluding fish, is about 1750 g/d. An argument can be made that a given individual will not grow all of the food that is eaten, so the total intake from the local area should be lower. Also, there are undoubtedly significant differences in the concentration ratios in different foodstuffs. For lack of detailed information on the land and its uses and the actual food to soil concentration ratios, however, it was assumed that the 1750 g/d intake was appropriate. (Note that weighting the amount of foodstuffs eaten by the ratio of the concentration to the average gives the same result.) Using the 1750 g/d intake and the intake limit of 220 pCi of natural uranium per day, the average food concentration limit would be 130 pCi/kg. The concentration ratio of vegetation to dry soil from Section 7 is 8 x for uranium. Thus, the soil concentration guide is 1600 pCi/g which is rounded to 2000 pCi/g. The rounded figure for the mass concentration is 3000 micrograms of uranium/g soil. The problem of inhaling soil at these concentrations was also considered. Using an effective dust loading of 200 micrograms/m3, the whole lung dose equivalent at equilibrium is 360 mrem/y if the uranium is in a class D compound (retained in the lung for days) or 3600 mrem/ y if it is in a class Y compound (retained in the lung for weeks). Thus, inhalation can be a controlling factor at high soil concentrations.

C.2 Radium

The Federal Radiation Council (FRC, 1961) indicated that the 226Ra in the skeleton of individuals drinking water with a higher than normal content of radium does not exceed about 50 times the daily intake from all sources. Wrenn (1975), using data from 3 continental U. S. cities and from San Juan, Puerto Rico, the U. K. and Kerala, India, derived values for the skeletal content of from 7 to 96 times the daily intake. The values for the 3 continental cities were 14,15 and 16, with San Juan being 24. The U. K. values ranged from 7 to 17, while the Kerala burden was 96 times the daily intake. Kerala is a high background area and Wrenn questioned whether the intake may have been underestimated or the skeletal content overestimated. Stehney and Lucas (1950) measured the ratio as 24 for adult controls, 17 for adult prisoners in Stateville, 22 for Chicago boys and 45 for boys in Lockport, an area where the radium concentration in water is known to be high. From their data they tentatively concluded that a greater fraction of

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the radium is retained in childhood than after maturity is reached and that the retention of radium ingested in water is greater than that ingested in food. From these data, a ratio between skeletal burden and daily intake of 25 was assumed. This is one-half of the value for the ratio that the FRC said "-does not exceed-", but is higher than the majority of measurements made in the U. S., particularly for those where the primary intake was with food. The dose rate for radium in bone is 84 mrad/y to bone surfaces for a concentration of 1 pCi/g. The dose equivalent rate is 1700 mrem/y for a total skeletal content of 5000 pCi, so 500 mrem/y corresponds to a skeletal content of 1500 pCi. This may be divided by 25 to give the average dietary intake of 60 pCi/d. Table 7.1 indicates that meat is very low in radium. This contribution is therefore omitted and an intake of 1500 g/d is assumed. This gives an average concentration limit of 40 pCi/kg in foodstuffs. From Section 7, the plant/soil concentration ratio is 1 x which leads to a soil concentration guide of 40 pCi/g.

The data for 'lOPb are not quite as good as those for uranium and radium, but a similar derivation is possible. The dose rate factor from Table 6.6 is 34 mrad/y for 1pCi/g bone, so the skeletal burden required to give 500 mrem/y would be 3700 pCi. From ICRP Publication 30 (1979), it is possible to derive a value of 320 days of intake to represent the skeletal burden. The maximum daily intake would then be 11pCi/ d or 6 pCi/kg. Using the plant/soil concentration ratio of 4 x from Section 7, the soil concentration corresponding to a dose equivalent of 500 mrem/y would be 15 pCi/g. This is rounded to 20 pCi/g for simplicity.

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KAURANEN, P., AND MIETTINEN,J. K. (1970). "Polonium and radiolead in some aqueous ecosystems in Finland," in Radioactive Foodchains in the Subartic Environment, New York Operations Office Report NYO-3445-14 (National Technical Information Service, Springfield, Va.). KEATON,H., NALL,J., A N D MCNALLY,W. (1981). Radiological Analysis of Public Drinking Water Wells in a Phosphate Mining Region, Polk County (Florida) Health Department. C.E. (1980). "Modifications of the natural KNIGHT,G . B., AND MAKEPEACE, radionuclide distribution by some human activities in Canada," page 1494 in Natural Radiation Environment IZI, Gesell, T. and Lowder, W., Eds., United States Department of Energy Symposium Series 51 CONF 780422 (National Technical lnformation Service, Springfield, Va.). E. G., MAO,Y., MCGREGOR,R. G., SEMENCIAW, R., SMITH, LETOURNEAU, M. H., WIGLE, D. T. (1983). "Lung cancer mortality and indoor radon concentrations in 18 Canadian cities," Presented at the 16th Midyear Topical Meeting of the Health Physics Society-Epidemiology Applied to Health Physics, Albuquerque, NM., January 9-13,1983. LETOURNEAU, E. G., AND WIGLE,D. T. (1980). "Mortality and indoor radon daughter concentrations in 13 Canadian cities," presented a t Specialists Meeting on the Assessment of Radon and Daughter Exposures and Related Biological Effects, Rome, March, 1980. R. G., AND TANIGUCHI, H. (1979). "BackLETOURNEAU, E. G., MCGREGOR, ground levels of radon and radon daughters in Canadian homes," page 167 in Proceedings of the Specialists Meeting on Personal Dosimetry and Area Monitoring Suitable for Radon and Daughter Products (Nuclear Energy Agency, Organization for Economic Cooperation and Development, Paris). LLOYD,E. (1981a). "Radiation dose to the cells at risk for the induction of bone tumors by bone-seeking radionuclides," in USDOE Report ANL-80115, Radiological and Environmental Research Division Annual Report Center for Human Radiobiology, July 1979 - June 1980. LLOYD,L. L. (1981b). Butte Radiation Study, Montana Department of Health and Environmental Sciences, Report to the 1981 Montana Legislature. LOWDER,W. M., CONDON,W. J., A N D BECK,H. L. (1964). "Field spectrometric investigations of environmental radiation in the United States." Natural Radiation Environment, Adams, J. A. S. and Lowder, W. M., Eds. (Univ. of Chicago Press, Chicago). L u c ~ s H. , F., JR. (1960). "Correlation of the natural radioactivity of the human body to that of its environment," page 55 in Argonne Nationol Laboratory Radiological Physics Division Semi-Annual Report, Argonne National Laboratory Report ANL6297 (National Technical Information Service. Springfield, Va.). D. N., AND MARKUM, F. (1970). "Natural LUCAS,H. F., JR., EDGINGTON, thorium in human bone," Health Phys. 19,739. R. S., LETOURNEAU, E. G., A N D WAIGHT,P. J. (1981). "A four MCCULLOUGH, factor model for estimating human radiation exposure to radon daughters in the home," Health Phys. 40,299.

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MCDOWELL-BOYER, L. M., WATSON, A. P., A N D TRAVIS,C. C. (1979). Review and Recommendations of Dose Conversion Factors and Environmental Transport Parameters for 2'0Pband 22BRa, United States Nuclear Regulatory Commission Report NUREG/CR-0574 (National Technical Information Service, Springfield, Va.). R. G. (1979). "Background levels of radon and radon daughters MCGREGOR, in homes in the Castlegar-Trail area of British Columbia," (unpublished report). MCGREGOR, R. G., A N D GOURGON, L. A. (1980). "Radon and radon daughters in homes utilizing deep well water supplies, Halifax County, Nova Scotia," J. Environ. Sci. Eng. 15, 25. E. G., MCCULLOUGH, R. S., MCGREGOR, R. G., VASUDEV, P., LETOURNEAU, PRANTL,F. A., AND TANIGUCHI, H. (1980). "Background concentrations of radon and radon daughters in Canadian homes," Health Phys. 39,285. MIYAKE, Y., SUGIMURA, Y., A N D TSUBOTA,H. (1964). "Content of U, Ra and Th in river waters in Japan," Natural Radiation Environment, Adams, J. A. S. and Lowder, W. M., Eds. (Univ. of Chicago Press, Chicago). MORSE,R. S., AND WELFORD,G. A. (1971). "Dietary intake of '''Pb," Health Phys. 21.53. MUTH,H., RAJEWSKY, B., HANTKE, J. H., AND AURAND, K. (1960). "Normal radium content and the '=Ra/Ca ratio of various foods, drinking water and different organs and tissues," Health Phys. 2, 239. MYERS,D. K., A N D STEWART, C. G. (1979). "Some health aspects of Canadian uranium mining," page 368 in Conference/ Workshop on Lung Cancer Epidemiology and Industrial Applications of Spectrum Cytology (Colorado School of Mines Press, Golden, Colorado). NAS/NRC (1980). Committee on the Biological Effects of Ionizing Radiations of the National Academy of Sciences/National Research Council. The Effects on Populations of Exposure to Low Levels of Ionizing Radiations: 1980. (National Academy of Sciences, Washington). NCHS (1979). National Center for Health Statistics. Vital Statistics of the United States-1975, United States Public Health Service Report 79-1114 (Government Printing Office, Washington). NCRP (1971). National Council on Radiation Protection and Measurements. Basic Radiation Protection Criteria, NCRP Report 39 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1975). National Council on Radiation Protection and Measurements. Natural Background Radiation in the United States, NCRP Report No. 45 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1984a). National Council on Radiation Protection and Measurements. Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters, NCRP Report No. 78 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). (In press). NCRP (1984b). National Council on Radiation Protection and Measurements, The Risk System for Radiution Protection, Report of NCRP Scientific

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The NCRP The National Council on Radiation Protection and Measurements is a nonprofit corporation chartered by Congress in 1964 to: 1. Collect, analyze, develop, and disseminate in the public interest information and recommendations about (a) protection against radiation and (b) radiation measurements, quantities, and units, particularly those concerned with radiation protection; 2. Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units, and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations; 3. Develop basic concepts about radiation quantities, units, and measurements, about the application of these concepts, and about radiation protection; 4. Cooperate with the International Commission on Radiological Protection, the International Commission on Radiation Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units, and measurements and with radiation protection. The Council is the successor to the unincorporated association of scientists known as the National Committee on Radiation Protection and Measurements and was formed to carry on the work begun by the Committee. The Council is made up of the members and the participants who serve on the eighty one Scientific Committees of the Council. The Scientific Committees, composed of experts having detailed knowledge and competence in the particular area of the Committee's interest, draft proposed recommendations. These are then submitted to the full membership of the Council for careful review and approval before being published. The following comprise the current officers and membership of the Council: 115

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President Vice President Secretary and Treasurer Assistant Secretary Assistant Treasurer

Members

SEYMOUR ABRAHAMSON ADELSTEIN S. JAMES ROY E. ALBERT EDWARD L. ALPEN JOHNA. AUXIER WILLIAM J. BAIR JOHND. BOICE,JR. VICTORP. BOND ROBERTL. BRENT ANTONEBROOKS F. BROWN REYNOLD F. BUDINGER THOMAS MELVIN W. CARTER GEORGEW. C A S A R ~ RANDALLS. CASWELL ARTHURB. CHILTON GERALD DODD PATRICIA W. DURBIN JOEA. ELDER MORTIMER M. ELKIND THOMAS S. ELY EDWARD R. EPP R. J. MICHAELFRY ROBERTA. GOEPP BARRY B. GOLDBERG ROBERT0.GORSON DOUGLAS CRAHN ARTHURW. GUY ERICJ. HALL JOHNH. HARLEY NAOMIHARLEY JOHNW. HEALY JOHNM. HESLEP SEYMOUR JABLON DONALD G. JACOBS A. E v e m JAMES, JR. BERNDKAHN

JAMESG. KEREIAKES CHARLESE. LAND THOMAS A. LINCOLN RAYD. LLOYD ARTHURC. LUCAS CHARLES W. MAYS ROGER0.MCCLELLAN JAMESMCLAUGHLIN J. MCNEIL BARBARA CHARLES B. MEINHOLD MORTIMER L. MENDELSOHN WrLLUM E. MILLS DADEW. MOELLER A. ALANMOGHISSI PAULE. MORROW JR ROBERTD. MOSELEY, JAMESV. NEEL WESLEY NvBoRG FRANK PARKER ANDREWK. POZNANSKI NORMAN C. RASMUSSEN WILLIAMC. REINIG CHESTERR. RICHMOND JAMEST. ROBERTSON LEONARD A. SAGAN GLENNE. SHELINE ROYE. SHORE WARRENK. SINCLAIR LEWISV. SPENCER JOHNB. STORER ROYC. THOMPSON JAMESE. TURNER ARTHURC. U ~ N GEORGEL. VOELZ EDWARD W. WEBSTER GEORGEM. WILKENING H. RODNEY WITHERS

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Honorary Members LAURISTON S. TAYLOR, Honorary President

Currently, the following subgroups are actively engaged in formulating recommendations: SC-1: SC-3: SC-16: SC-18: SC-38:

SC-42: SC-44: SC-45: SC-46:

Basic Radiation Protection Criteria Medical X-Ray. Electron Beam and Gamma-Ray Protection for Energies Up to 50 MeV (Equipment Performance and Uae) X-Ray Protection in Dental OEces Standards and Measurements of Radioactivity for Radiological Use Waste Disposal Task Group on Krypton-= Task Group on Carbon-14 Task Group on Disposal of Accident Generated Waste Water Task Group on Disposal of Low-Level Wante Task Group on the Actinides Task Croup on Xenon Biological Aspects of Radiation Protection Criteria Task Group on Atomic Bomb Survivor Dosimetry Subgroup on Biological Aspects of Dosimetry of Atomic Bomb Survivors Industrial Applications of X Rays and Sealed Sources Radiation Associated with Medical Examinations Radiation Received by Radiation Employees Operational Radiation Safety Teak Group 1 on Warning and Pemnnel Security Systems Task Group 2 on Uranium Mining and Milling-Radiation Safety Programs Task Group 3 on ALARA for Occupationally Exposed Individuals in Clinical Radiology Task Group 4 on Calibration of Instrumentation Instrumentation for the Determination of Dose Equivalent Apportionment of Radiation Exposure Conce~tualBasis of Calculations of Dose Distributions ~iolo&calEffects and Exposure Criteria for Radiofrequency Electromagnetic Radiation Bioassay for Assessment of Control of Intake of Ftadionuclides Experimental Verification of Internal Dosimetry Calculations Internal Emitter Standards

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Task Group 2 on Respiratory Tract Model Task Group 3 on General Metabolic Models Task Group 4 on Radon and Daughters Tmk Group 6 on Bone Problems Task Group 7 on Thyroid Cancer Risk Task Group 8 on Leukemia Risk Task Group 9 on Lung Cancer Risk Task Group 10 on Liver Cancer Risk Task Group 11 on Genetic Risk Task Group 12 on Strontium Task Group 13 on Neptunium SC-59: Human Radiation Exposure Experience SC-60: Dosimetry of Neutrons from Medical Accelerators SC-61: Radon Measurements SC-62: Priorities for Dose Reduction Efforts SC-63: Control of Exposure to Ionizing Radiation from Accident or Attack SC-64: Radionuclides in the Environment Task Group 5 on Public Exposure to Nuclear Power Task Group 6 on Screening Models SC-65: Quality Assurance and Accuracy in Radiation Protection Measurements SC-67: Biological Effects of Magnetic Fields SC-68: Microprocessors in Dosimetry SC-69: Efficacy Studies SC-70: Quality Assurance and Measurement in Diagnostic Radiology SC-71: Radiation Exposure and Potentially Related Injury SC-72: Radiation Protection in Mammography SC-74: Radiation FZeceived in the Decontamination of Nuclear Facilities SC-75: Guidance on Rediation Received in Space Activities SC-76: Effects of Radiation on the Embryo-Fetus SC-77: Guidance on Occupational and Public Exposure Resulting from Diagnostic Nuclear Medicine Procedures SC-78: Practical Guidance on the Evaluation of Human Exposures to Radiofrequency Rsdiation SC-79: Extremely Low-Frequency Electric and Magnetic Fields SC-80: Radiation Biology of the Skin (Beta-RayDosimetry) SC-81: Assessment of Exposure from Therapy Committee on Public Education Committee on Public Relations Ad Hoc Committee on Policy in Regard to the International System of Units Ad Hoc Committee on Comparison of Radiation Exposures Study Group on Comparative Risk Task Croup on Comparative Carcinogenicity of Pollutant Chemicals Task Force on Occupational Exposure Levels

In recognition of its responsibility to facilitate and stimulate cooperation among organizations concerned with the scientific and related aspects of radiation protection and measurement, the Council has created a category of NCRP Collaborating Organizations. Organizations or groups of organizations that are national or international in

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scope and are concerned with scientific problems involving radiation quantities, units, measurements and effects, or radiation protection may be admitted to collaborating status by the Council. The present Collaborating Organizations with which the NCRP maintains liaison are as follows: American Academy of Dermatology American Association of Physicists in Medicine American College of Nuclear Physicians American College of Radiology American Dental Association American Industrial Hygiene Association American Institute of Ultrasound in Medicine American Insurance Association American Medical Association American Nuclear Society American Occupational Medical Association American Podiatry Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Society of Therapeutic Radiology and Oncology Association of University Radiologists Atomic Industrial Forum Bioelectromagnetics Society College of American Pathologists Federal Emergency Management Agency Genetics Society of America Health Physics Society National Bureau of Standards National Electrical Manufacturers Association Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Air Force United States Army United States Department of Energy United States Department of Labor United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission United States Public Health Service

The NCRP has found its relationships with these organizations to be extremely valuable to continued progress in its program. Another aspect of the cooperative efforts of the NCRP relates to the special liaison relationships established with various governmental

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organizations that have an interest in radiation protection and measurements. This liaison relationship provides: (1) an opportunity for participating organizations to designate an individual to provide liaison between the organization and the NCRP; (2) that the individual designated will receive copies of draft NCRP reports (at the time that these are submitted to the members of the Council) with an invitation to comment, but not vote; and (3) that new NCRP efforts might be discussed with liaison individuals as appropriate, so that they might have an opportunity to make suggestions on new studies and related matters. The following organizations participate in the special liaison program: Defense Nuclear Agency Federal Emergency Management Agency National Bureau of Standards Office of Science and Technology Policy Office of Technology Assessment United States Air Force United States Army United States Coaat Guard United States Department of Energy United States Department of Health and Human Services United Statee Department of Labor United States Department of Traneportation United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission

The NCRP values highly the participation of these organizations in the liaison program. The Council's activities are made possible by the voluntary contribution of time and effort by its members and participants and the geilerous support of the following organizations: Alfred P. Sloan Foundation Alliance of American Insurere American Academy of Dental Radiology American Academy of Dermatology American Aesociation of Phyeicists in Medicine American College of Radiology American College of Radiology Foundation American Dental Asmiation American Industrial Hygiene Association American Insurance Association American Medical Association American Nuclear Society American Occupational Medical h i a t i o n

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American Osteopathic College of Radiology American Podiatrv Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Society of Therapeutic Radiologiste American Veterinary Medical Aseociation American Veterinary Radiology Society Association of University Radiologists Atomic Industrial F O N ~ Battelle Memorial Institute College of American Pathologists Commonwealth of Pennsylvania Defense Nuclear Agency Edison Electric Institute Edward Mallinckrodt, Jr. Foundation Electric Power Research Institute Federal Emergency Management Agency Florida Institute of Phosphate Research Genetics Society of ~ m e i c a Health Physics Society Jamea Picker Foundation National Association of Photographic Manufacturers National Bureau of Standards National Cancer Institute National Center for Medical Devices and Radiation Health National Electrical Manufacturers Association Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Department of Energy United States Department of Labor United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission

To all these organizations the Council expresses its profound appreciation for their support. Initial funds for publication of NCRP reports were provided by a grant from the James Picker Foundation and for this the Council wishes to express its deep appreciation. The NCRP seeks to promulgate information and recommendations based on leading scientific judgment on matters of radiation protection and measurement and to foster cooperation among organizations concerned with these matters. These efforts are intended to serve the public interest and the Council welcomes comments and suggestions on its reports or activities from those interested in ita work.

NCRP Publications NCRP publications are distributed by the NCRP Publications' office. Information on prices and how to order may be obtained by directing an inquiry to: NCRP Publications 7910 Woodmont Ave., Suite 800 Bethesda, Md 20814 The currently available publications are listed below.

Proceedings of the Annual Meeting No. 1 2 3 4

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Title Perceptions ofRisk, Proceedings of the Fifteenth Annual Meeting, Held on March 14-15, 1979 (Including Taylor Lecture No. 3) (1980) Quuntitative Risk in Stundurds Setting, Proceedings of the Sixteenth Annual Meeting, Held on April 2-3, 1980 (Including Taylor Lecture No. 4) (1981) Critical Iss7les in Setting Radiation Dose Limits, Proceedings of the Seventeenth Annual Meeting, Held on April 8-9, 1981 (Including Taylor Lecture No. 5) (1982) Radiation Protection and New Medical Diagnostic Procedures, Proceedings of the Eighteenth Annual Meeting, Held on April 6-7, 1982 (Including Taylor Lecture No. 6) (1983) Environmental Radioactivity, Proceedings of the Nineteenth Annual Meeting, Held on April 6-7, 1983 (Including Taylor h c t u r e No. 7) (1984) Some Issues Important in Developing Basic Radiation Protection Recommendations, Proceedings of the Twentieth Annual Meeting, Held on April 4-5, 1984 (Including Taylor lecture No. 8) (1985) Radioactive Waste, Proceedings of the Twenty-first Annual Meeting, Held on April 3-4, 1985 (Including Taylor Lecture No. 9) (1986)

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Nonionizing Electromagnetic Radiation and Ultrasound, Proceedings of the Twenty-second Annual Meeting, Held on April 2-3,1986 (Including Taylor Lecture No. 10) (1988) New Dosimetry at Hiroshima and Nagasaki and Its Implications for Risk Estimates, Proceedings of the Twenty-third Annual Meeting, Held on April 5-6, 1987 (Including Taylor Lecture No. 11)(1988). Radon, Proceedings of the Twenty-fourth Annual Meeting, Held on March 30-31,1988 (Including Taylor Lecture No. 12) (1989). Radiation Protection Today-The NCRP at Sixty Years, Proceedings of the Twenty-fifth Annual Meeting, Held on April 5-6, 1989 (Including Taylor Lecture No. 13) (1990). Symposium Proceedings

The Control of Exposure of the Public to Ionizing Radiation i n the Event of Accident or Attack, Proceedings of a Symposium held April 27-29, 1981 (1982) Lauriston S. Taylor Lectures No. 1

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The Squares of the Natural Numbers i n Radiation Protection by Herbert M. Parker (1977) Why be Quantitative About Radiation Risk Estimates? by Sir Edward Pochin (1978) Radiation Protection-Concepts and Trade Offs by Hymer L. Friedell (1979:)[Available also in Perceptions of Risk, see above] From "Quantity of Radiation" and "Dose" to "Exposure" and "Absorbed Dosey'-An Historical Review by Harold 0.Wyckoff (1980) [Available also in Quantitative Risks i n Standards Setting, see abovel How Well Can We Assess Genetic Risk? Not Very by James F. Crow (1981) [Available also in Critical Issues i n Setting Radiation Dose Limits, see abovel Ethics, Trade-offs and Medical Radiation by Eugene L. Saenger (1982) [Available also in Radiation Protection and New Medical Diagnostic Approaches, see abovel

NCRP PUBLICATIONS

The Human Environment-Past, Present and Future by Merril Eisenbud (1983) [Available also in Environmental Radioactivity, see abovel Limitation and Assessment in Radiation Protection by Harald H. Rossi (1984) [Available also in Some Issues Important in Developing Basic Radiation Protection Recommendations, see above] Truth (and Beauty) in Radiation Measurement by John H. Harley (1985) [Available also in Radiwctive Waste, see above] Nonionizing Radiation Bioeffects: Cellular Properties and Intemctwns by Herman P. Schwan (1986) [Available also in Nonionizing Electromagnetic Radiations and Ultrasound, see abovel How to be Quantitative about Radiation Risk Estimates by Seymour Jablon (1987) [Available also in New Dosimetry at Hiroshima and Nagasaki and its Zmplicatwns for Risk Estimates, see abovel How Safe is Safe Enough? by Bo Lindell(1988) [Available also in Radon, See above] Radiobiology and Radiation Protection: The Past Century and Prospects for the Future by Arthur C. Upton (1989) [Available also in Radiation Protection Today-The NCRP at Sixty Years, See abovel Radiation Protection and the Internal Emitter Saga by J . Newel1 Stannard (1990)

NCRP Commentaries No. 1

Title Krypton-85 in the A tmosphere-With Specific Reference to the Public Health Significance of the Proposed Controlled Rekase at Three Mile Island (1980) Preliminary Evaluation of Criteria fir the Disposal of Transumnic Contaminated Waste (1982) Screening Techniques for Determining Compliance with Environmental Standards (19861, Rev. (1989) Guidelines for t h Rekase ~ of Waste Water from Nuclear Facilities with Special Reference to the Public Health Significance of the Proposed R e h e of Twated Waste Waters at Three Mile Island (1987) Living Without Landfills (1989) Radon Exposure of the U.S. Population-Status of the Problem (1991)

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Control and Removal of Radioactive Contamination in Laboratories (1951) Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides in Air and in Water for Occupational Exposure (1959) [Includes Addendum 1 issued in August 19631 Measurement of Neutron Flux and Spectra for Physical and Biological Applications (1960) Measurement ofAbsorbed Dose of Neutrons and Mixtures of Neutrons and Gamma Rays (1961) Stopping Powers for Use with Cavity Chambers (1961) Safe Handling of Radioactive Materials (1964) Radiation Protection in Educational Institutions (1966) Dental X-Ray Protection (1970) Radiation Protection in Veterinary Medicine (1970) Precautions in the Management of Patients Who Have Received Therapeutic Amounts of Radionuclides (1970) Protection Against Neutron Radiation (1971) Protection Against Radiation from Brachytherapy Sources (1972) Specifications of Gamma-Ray Brachytherapy Sources (1974) Radiological Factors Affecting Decision-Making in a Nuclear Attack (1974) Krypton-85 in the Atmosphere-Accumulation, Biological Significance, and Control Technology (1975) Alpha-Emitting Particles in Lungs (1975) Tritium Measurement Techniques (1976) Structural Shielding Design and Evaluation for Medical Use of X Rays and Gamma Rays of Energies Up to 10 MeV (1976) Environmental Radiation Measurements (1976) Radiation Protection Design Guidelines for 0.1 -1 00 MeV Particle Accelerator Facilities (1977) Cesium-137 fhom the Environment to Man: Metabolism and Dose (1977) Review of NCRP Radiation Dose Limit for Embryo and Fetus in Occupationally Exposed Women (1977) Medical Radiation Exposure of Pregnant and Potentially Pregnant Women (1977)

NCRP PUBLICATIONS

Protection of the Thyroid Gland in the Event of Releases of Radioiodine (1977) Instrumentation and Monitoring Methods for Radiation Protection (1978) A Handbook of Radioactivity Measurements Procedures, 2nd ed. (1985) Operational Radiation Safety Progmm (1978) Physical, Chemical, and Biological Properties of Radiocerium Relevant to Radiation Protection Guidelines (1978) Radiation Safety Training Criteria for Industrial Radiography (1978) Tritium i n the Environment (1979) Tritium and Other Radionuclide Labeled Organic Compounds Incorporated i n Genetic Material (1979) Influence of Dose and Its Distribution in Time o n DoseResponse Relationships for Low-LET Radiations (1980) Management of Persons Accidentally Contaminated with Radionuclides (1980) Mammography (1980) Radiofreqency Electromagnetic Fields-Properties, Quantities and Units, Biophysical Interaction, and Measurements (1981) Radiation Protection i n Pediatric Radiology (1981) Dosimetry of X-Ray and Gamma-Ray Beams for Radiation Therapy in the Energy Range 10 keV to 50 MeV (1981) Nuclear Medicine-Factors Influencing the Choice and Use of Radionuclides i n Diagnosis and Therapy (1982) Operational Radiation Safety-Training (1983) Radiation Protection and Measurement for Low Voltage Neutron Generators (1983) Protection i n Nuclear Medicine and Ultrasound Diagnostic Procedures in Children (1983) Biological Effects of Ultrasound: Mechanisms and Clinical Implications (1983) Iodine-129: Evaluution of Releases from Nuclear Power Generation (1983) Radiological Assessment: Predicting the Transport, Bioaccumulation, and Uptake by Man ofRadionuclides Released to the Environment (1984) Exposures from the Uranium Series with Emphasis on Radon and its Daughters (1984)

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Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States (1984) Neutron Contamination from Medical Electron Accelerators (1984) Induction of Thyroid Cancer bylonizing Radiation (1985) Carbon-14 in the Environment (1985) SI Units in Radiation Protection and Measurements (1985) The Experimental Basis for Absorbed-Dose Calculations in Medical Uses of Radionuclides (1985) General Concepts for the Dosimetry of Internally Deposited Radionuclides (1985) Mammography-A User's Guide (1986) Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields (1986) Use of Bioassay Procedures for Assessment of Internal Radionuclide Deposition (1987) Radiation Alarms and Access Control Systems (1987) Genetic Effects of Internally Deposited Radionuclides (1987) Neptunium: Radiation Protection Guidelines (1987) Recommendations on Limits for Exposure to Ionizing Radiation (1987) Public Radiation Exposure from Nuclear Power Generation in the United States (1987) Ionizing Radiation Exposure of the Population of the United States (1987) Exposure of the Population in the United States and Canada from Natural Background Radiation (1987) Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources (1987) Comparative Carcinogenesis of Ionizing Radiation and Chemicals (1989) Measurement ofRadon and Radon Daughters in Air (1988) Guidance on Radiation Received in Space Activities (1989) Quality Assurance for Diagnostic Imaging (1988) Exposure of the U.S. Population from Diagnostic Medical Radiation (1989) Exposure of the U.S. Population From Occupational Radiation (1989) Medical X-Ray, Electron Beam and Gamma-Ray Protection For Energies Up To 50 MeV (Equipment Design, Performance and Use) (1989)

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Control of Radon in Houses (1989) The Relative Biological Effectiveness ofRadiutiolbs ofDifferent Qualities (1990) 105 Radiation Protection for Medical and Allied Health Personnel (1989) 106 Limits of Exposure to "Hot Particles" on the skin (1989) 107 Implementation of the Principle ofAs Low As Reasonably Achievable (ALARA) For Medical and Dentul Personnel (1990) 108 Conceptual Basis for Calculations of Absorbed-Dose Distributions Binders for NCRP Reports are available. Two sizes make it possible to collect into small binders the "old series" of reports (NCRP Reports Nos. 8-30) and into large binders the more recent publications (NCRP Reports Nos. 32-108). Each binder will accommodate from five to seven reports. The binders c a n y the identification "NCRP Reports" and come with label holders which permit the user to attach labels showing the reports contained in each binder. The following bound sets of NCRP Reports are also available: 103 104

Volume I. NCRP Reports Nos. 8,22 Volume 11. NCRP Reports Nos. 23,25,27,30 Volume ID.NCRP Reports Nos. 32,35,36,37 Volume IV. NCRP Reports Nos. 38,40,41 Volume V. NCRP Reports Nos. 42,44,46 Volume VI. NCRP Reports Nos. 47,49,50,51 Volume VII. NCRP Reports Nos. 52,53,54,55, 57 Volume VIII. NCRP Reporta No. 58 Volume IX. NCRP Reports Nos. 59,60,61,62,63 Volume X. NCRP Reports Nos. 64,65,66,67 Volume XI. NCRP Reports Nos. 68,69,70,71,72 Volume XII. NCRP Reports Nos. 73,74,75,76 Volume XIII. NCRP Reporta Nos. 77,78,79,80 Volume XIV. NCRP Reports Nos. 81,82,83,84, 85 Volume XV. NCRP Reports Nos. 86,87,88,89 Volume XVI. NCRP Reports Nos. 90,91,92,93 Volume XVII. NCRP Reports Nos. 94,95,96,97 Volume XVIII. NCRP Reports Nos. 98,99,100 Volume XIX. NCRP Reports Nos. 101, 102,103,104 (Titles of the individual reports contained in each volume are given above). The following NCRP Reports are now superseded andlor out of print:

NCRP PUBLICATIONS

No. 1

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Title X-Ray Protection (1931). [Superseded by NCRP Report No. 31 Radium Protection (1934). [Superseded by NCRP Report No. 41 X-Ray Protection (1936). [Superseded by NCRP Report No. 61 Radium Protection (1938). [Superseded by NCRP Report No. 131 Safe Handling of Radioactive Luminous Compounds (1941). [Out of Printl MedicalX-Ray Protection Up to Two Million Volts (1949). [Superseded by NCRP Report No. 181 Safe Handling of Radioactive Isotopes (1949). [Superseded by NCRP Report No. 301 Recommendations for Waste Disposal of Phosphorus32 and Iodine-131 for Medical Users (1951). [Out of Printl Radiological Monitoring Methods and Instruments (1952). [Superseded by NCRP Report No. 571 Maximum Permissible Amounts of Radioisotopes in the Human Body and Maximum Permissible Concentrations in Air and Water (1953). [Superseded by NCRP Report No. 221 Recommendations for the Disposal of Carbon-14 Wastes (1953). [Superseded by NCRP Report No. 811 Protection Against Radiations from Radium, Cobalt-60 and Cesium-137 (1954). [Superseded by NCRP Report No. 241 Protection Against Betatron-Synchrotron Radiations Up to 100 Million Electron Volts (1954). [Superseded by NCRP Report No. 511 Safe Handling of Cadavers Containing Radioactive Isotopes (1953). [Superseded by NCRP R e p r t No. 211 Radioactive Waste Disposal in the Ocean (1954). [Out of Printl Permissible Dose from External Sources of Ionizing Radiation (1954) including Maximum Permissible Exposure to Man, Addendum to National Bureau of Standards Handbook 59 (1958). [Superseded by NCRP Report No. 391 X-Ray Protection (1955). [Superseded by NCRP Report No. 261 Regulation of Radiation Exposure by Legislative Means (1955). [Out of Printl

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NCRP PUBLICATIONS

Protection Against Neutron Radiation Up to 30 Million Electron Volts (1957). [Superseded by NCRP Report No. 381 Safe Handling of Bodies Containing Radioactive lsotopes (1958). [Superseded by NCRP Report No. 371 Protection Against Radiations from Sealed Gamma Sources ( 1960). [Superseded by NCRP Report Nos. 33, 34, and 401 Medical X-Ray Protection Up b Three Million Volts (1961). [Superseded by NCRP Report Nos. 33,34,35, and 361 A Manual of Radioactivity Procedures (1961). [Superseded by NCRP Report No. 581 Exposure to Radiation in a n Emergency (1962). [Superseded by NCRP Report No. 421 Shielding for High Energy Electron Accelerator Installations (1964). [Superseded by NCRP Report No. 511 Medical X-Ray and Gamma-Ray Protection for Energies up to 10 MeV-Equipment Design and Use (1968). [Superseded by NCRP Report No. 1021 Medical X-Ray and Gamma-Ray Protection for Energies U p to 10 MeV-Structural Shielding Design and Evaluution (1970). [Superseded by NCRP Report No. 491 Basic Radiation Protection Criteria (1971). [Superseded by NCRP Report No. 911 Review o f t h e Current State of Radiation Protection Philosophy (1975). [Superseded by NCRP Report No. 911 Natural Background Radiation i n the United States (1975). [Superseded by NCRP Report No. 941 Radiation Protection for Medical and Allied Health Personnel [Superseded by NCRP Report No. 1051 Radiation Exposuref?om ConsumerProducts and Miscellaneous Sources (1977). [Superseded by NCRP Report No. 951 A Handbook on Radioactivity Measurement Procedures. [Superseded by NCRP Report No. 58, 2nd ed..] Other Documents The following documents of the NCRP were published outside of the NCRP Reports and Commentaries series: "Blood Counts, Statement of the National Committee on Radiation Protection," Radiology 63, 428 (1954)

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"Statements on Maximum Permissible Dose from Television Receivers and Maximum Permissible Dose to the Skin of the Whole Body," Am. J. Roentgenol., Radium Ther. and Nucl. Med. 84, 152 (1960) and Radiology 75, 122 (1960) Dose Effect Modifying Factors In Radiation Protection, Report of Subcommittee M-4 (Relative Biological Effectiveness) of the National Council on Radiation Protection and Measurements, Report BNL 50073 (T-471) (1967) Brookhaven National Laboratory (National Technical Info~~nation Service, Springfield, Virginia). X-Ray Protection Standards for Home Television Receivers, Interim Statement of the National Council on Radiation Protection and Measurements (National Council on Radiation Protection and Measurements, Washington, 1968) Specification of Units of Natural Uranium and Natural Thorium (National Council on Radiation Protection and Measurements, Washington, 1973) NCRP Statement on Dose Limit for Neutrons (National Council on Radiation Protection and Measurements, Washington, 1980) Control 0fAirEmission.s ofRadionuclides (National Council on Radiation Protection and Measurements, Bethesda, Maryland, 1984) Copies of the statements published in journals may be consulted in libraries. A limited number of copies of the remaining documents listed above are available for distribution by NCRP Publications.

Index Additivity, 84 Agricultural Uae of Land. 90,101 Air Cleaning, 41 Body Content, Uranium, 63, 64 Table, 64 Body Content, Radium. 64 Table, 66 Body Content, Lead-210.65 Bone Cancer Risk, 78 Bone Dosimetry, 65,66 Building Materials. Radioactivity, 21,22 Table, 22 0x11 Burning, Releases. 18 Table. 18 Cosmic Radiation, 3

Drinking Water, 44-47,49,51,53,54 Lead-210,54 Radium, 47 Tables, 46, 49 Radon, 51 Table, 53 . Uranium, 45 Table, 46

Elevated Natural Radioactivity, 4, 22, 23, 26,31, 32,45, 49,58, 59, 62

Dietary Intake, 58,59,62 External Radiation, 22 Radon, 26.31.32 Water, 45,49,52 Enhanced Natural Radioactivity, 4,23.26. 28,47,50,52,58,59,62

Dietary Intake. 6 , 6 6 4 1 Lead-210.61 Tables, 58,60,61 Radium, 59 Tablee, 58, 60.61 Uranium, 57 Table, 57 D w , Bone. 65-68. 71,81 Tables, 66,68, 71, 81 Dose, Lung, 42, 79,80 Table, 80

Dose, Natural Background, 2 , 3 Table, 3 Dose, Whole Body, 3, 5, 69, 70 Body Potamium, 3 h m i c Radiation, 3 Terrestrial Gamma Radiation, 69 Table, 70 Doee Factors, Bone, 66.81 Table, 66 Factors, Lung, 42,79 Dose Limitation, 79.84.89 Approach to Standard-Setting, 79 External Radiation, 89 ICRP,84 NCRP, 84

Dietary Intake, 58.59.62 External Radiation, 23 Radon, 26,28 Water, 47,50,52 Exposure Distribution, 81.83 Approach to Standard-Setting, 81 External Radiation, 83 Radon Daughters, 81 Table, 83 External Radiation, 3,5, 19,20,22,23, 78, 83

Dose, 3,78 Tables, 3, 78 Dose Distribution, 83 Elevated, 22 Enhanced, 23 Indoor. 20 Outdoor, 19

Half-Lives, Uranium Series, Chart, 2 Ingestion see Dietary Intake Inhalation, 6,25,42 Radon Daughters, 25 Lead-210.42

Land line,Agriculture, 90, 104 Land Uee. Houeing. 90 Lead-210 (Polonium-2101, 11, 14, 53, 61, 62 Environmental Behavior, 11, 14 in Bone, 61 in Diet, 61 in Water. 53 Plant Uptake. 62 Soid Content, 62 Life Shortening, 76-78 Radon Daughter Exposure, 76,813 Table, 77 Lung Cancer Riek, 75 Table, 76 Lung Doemetry, 41.79 Measurements, 98 Natural Backgraund, 2 Averega. 2.19 Elevated, 4 2 2 Phosphate Rock, 17,24,28 Mining Areas, 24,28 Reeiduee, 24.28 Plant Uptake, 14.68.59.63.101 Lead-210.62 Radium. 59 Uranium, 68 Polonium-210 See Lead-210

Radium, 10,13,22,47,49,59,60,63,64 Environmental Behavior, 10, 13 in Bone. 63 Graph, 64 in Diet, 58 Tablee, 59, 60 in Water, 47 Table, 49 Plant Uptake, 59 Soil Content, 22.59 Rsdon con cent ratio^, 25.26.29.30, 33, 51 in Indoor Air, 26 Table, Canada, 29 Table, United States, 30 in Outdoor Air, 25

Radon Concentratione (Continued) in Water. 51 Variatione, 33 Radon Sources, 13, 15,32 in Buildings, 15,32 Radon Daughters (Short-Lived), 10, 25, 26, 42,79 Dosimetry. 42.79 Indoor Concentrationa, 26 Outdoor Concentratione, 25 Recommendatione, 87 Regulations, 95 Remedial Action, 7.34.55.87.93 Radon. 34 Drinking Water, 55 Riek, 71 Approach to Standard-Setting, 71, 75-79 Bone Cancer. 78 Table, 79 Lung Cancer. 75 Table, 76 Total Cancer, 77 Table, 78 Rock,Uranium Content, 15.16 Table. 16 Smoking and Lung D m ,67 Smoking and Lead-210 in the Body,62,63 Table, 63 Soil, 12, 15, 16,22 Radionuelide Content, Table, 22 Uranium Content, 15 Table, 16 Units, 7 Uranium, 9,12,16,46,46,57,58,63,64 Environmental Behavior. 9.12 in Bone. 63 Table, 64 in Diet, 57 Table. 57 in Soil and Rock. Table. 16 in Water, 45 Table. 46 Plant Uptake, 58 Uranium Mining and Milling, 5,17,23 Releaees, 17 Tailings. 17.23

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INDEX

Uranium Seriea, 2.9, 10,12 Decay Energies, Table, 10 Decay Scheme, Chart, 2 Environmental Behavior, 12 Half-Lives, Chart, 2 Ventilation, 41

Water see Drinking Water Whole Body Radiation D m ,3.78, 80 Tables. 3,78 Whole Body Radiation Exposure. 19 Whole Body Radiation Risk, 77.78 Table, 78