Ionizing Radiation: Exposure to the Population of the U.S., Report 93 (N C R P Report)

NCRP REPORT No. 93

IONIZING RADIATION EXPOSURE OF THE POPULATION OF THE UNITED STATES Recommendations of the NATIONAL COUNCIL O N RADIATION PROTECTION AND MEASUREMENTS

Issued September 1,1987 First Reprinting April 15,1998 National Council on Radiation Protection and Measurements 7910 W O O D M O N T AVENUE I 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 reporta. 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 any 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 rights; 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, under the Cwil Rights Act of 1964, Sectton 701 et seq. as amended 42 U.S.C. Section 2000e et seq. (Title VII) or any other statutory or common law theory governing linbility.

Library of Congress Catploging-in-PublicationData National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. (NCRP report ;no. 93) Bibilography: p. Includes index. 1. Ionizing radiation-Dosage. 2. Ionizing radiation-Environmental aspectsUnited States. 3. Health risk assessment-United States. I. Title. II. Series. fDNLM: 1. Environmental Exposure. 2. Radiation Injuries-prevention & control. 3. Radiation Monitoring. WN 650 N279il RA569.N353 1987a 363.1'79 87-22062 ISBN 0-913392-91-X

Copyright O National Council on Radiation Protection and Measurements 1987 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. Library of Congress Catalog Card Number International Standard Book Number

Preface The NCRP has recognized for some time the need for a clear assessment of the magnitude of the doses from various sources of radiation to which the population of the U.S. is exposed In anticipation of the need to gather basic data for input into this process five assessment committees, each addressing a different source category, were established in 1971. NCRP reports assessing exposures from natural background and from consumer products were produced (NCRP 1975, 1977), but no attempt was made to develop a comprehensive account of all sources of exposure. In 1985, the NCRP reconsidered its overall effort in this area and, with the further support and stimulation of the Committee on Interagency Radiation Research and Policy Coordination (Office of Science and Technology Policy, Executive Office of the President of the United States), undertook to evaluate the exposure of the U.S. population from all sources. Six organizational groups were constituted or reconstituted to address different phases of the task and the results of their work are summarized in this document, which describes the exposure of the U.S. population from all known sources. The six organizational groups and their members are:

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PREFACE

Scientific Committee 28Radiation Exposure from Comurner Products

D.W. Moeller, Chairman R.J. Guimond J.W.N. Hickey E. Miller G.D. Schmidt

Scientific Committee 43Natural Background Radiation J.H. Harley, Chru'rman RB. Holtzman W.M.Lowder D.P.Meyerhof A.B. Tanner N.A. Wogman Consultants: B.S. Pasternack J.K.Soldat J.A. Young

Scientific Committee 44Radiation Associated with Medical Examinations RD. Moseley, Jr.7. Chairnun (19761987) F. A. Mettler. Jr., Chairman (1987J.S. Acarese W.W. Burr, Jr. R.O. Gorson S. Marks A. Raventos M. Rosenstein E.L. Saenger B. Shleien Advisors: D.L. Abernathy R.E. Bunge L.A. Selke Consultant: J.G. Kereiakes

Scientific Committee 45Radiation Received by Radiation Employees D.E.Barber, Chairman B.G. Brooks L.H.Lanzl R.E.Shore P.S. Stansbury R.A. Wynveen

scientific Committee 64, Task Group 5*Public Exposure from Nuclear Power B. Kahn, ChairM.J.BelJ ILL. Blanchard E.F. Branagan, Jr. K.Cowser K.F.Eckerman J.M. Hardin R.E. Luna E.Y.S. Shum C. W i l l s J.F. Wing

Scientific Committee 64, Special Group*MisceUaneow Environmental Sources W.E. Kreger, Co-Chairman W.A. Mills, Co-Chairman

t Deceased. *Subgroups of Scientific Committee 64 on Radionuclides in the Environment; Chairman, M.W. Carter, M. Eisenbud, J.W. Healy, W.E. Kreger, W.A. Mills, J.N. Stannard, J.E. Till and M.E. Wrenn

PREFACE

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These groups, except for the Special Group on Miscellaneous Environmental Sources, are in the course of producing separate NCRP reports. This summary report was prepared by the NCRP's Scientific Committee 48, Assessment of Exposures of the Population Contributed by Various Sources. Serving on Scientific Committee 48 during the preparation of this report were: W.K. Sinclair, Chairman National Council on Radiation Protection and Measurements Bethesda, Maryland

S.J. Adelstein

J.H. Harley Hoboken, New Jersey

Haward Medical School Boston, Maesachusetta M.W. Carter Georgia Institute of Technology Atlanta, Georgia

D.W. Moeller Haward School of Public Health Boston, Massachusetts

NCRP Secretariat-T.M. Koval

The NCRP is grateful to all who not only contributed their expertise in developing the contents of these reports but also made extraordinary efforts in managing their schedules of work to make this coordinated comprehensive report possible. Dr. F.A. Mettler, Jr. and Dr. D.E. Barber made important contributions to this text. Tom Koval served as the NCRP staff member providing support for all of these organizational groups. The International System of Units (SI) is used in this report followed by conventional units in parentheses in accordance with the procedure set forth in NCRP Report No. 82, SI Units in Radiation Protection and Measurements. Warren K. Sinclair President, NCRP

Bethesda, Maryland 11 June 1987

Contents .

1 Introduction 1.1 Sources of Population Exposure . . . . . . . . . . . . . . . . . . . 1.2 Earlier Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Quantities and Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 The Present Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Public Radiation Exposure from Natural Background 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Sources of Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Naturally Occurring Radionuclides . . . . . . . . . . 2.2.2 External Radiation . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Radionuclides in the Body . . . . . . . . . . . . . . . . . 2.3 Exposure Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Cosmic Radiation . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Terrestrial Gamma Radiation . . . . . . . . . . . . . . . 2.3.3 Cosmogenic Radionuclides . . . . . . . . . . . . . . . . . 2.3.4 Inhaled Radionuclides . . . . . . . . . . . . . . . . . . . . . 2.3.5 Radionuclides in the Body . . . . . . . . . . . . . . . . . 2.3.6 Total Exposure from Natural Background . . . . 2.4 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Occupational Exposure 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Sources of Data and Estimates . . . . . . . . . . . . . . . . . . . . 3.3 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Public Radiation Exposure from Nuclear 'Power Generation 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Sources of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Estimates and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Public Radiation Exposure from Consumer Products 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Sources of Data and Estimates . . . . . . . . . . . . . . . . . . . . 5.3 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . .

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CONTENTS 5.4 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Public Radiation Exposure from Miscellaneous Environmental Sources 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 SourcesofData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Estimates and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Fallout from Nuclear Weapons Testing . . . . . . . . . . . . . 6.6 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Public Radiation Exposure from Medical Diagnosis and Therapy 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Sources of Data for Diagnosis . . . . . . . . . . . . . . . . . . . . . 7.3 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Estimates and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Radiation Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Summary and Conclusions 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 The Exposure of the U.S . Population to All Sources . . 8.3 The Most Significant Exposures . . . . . . . . . . . . . . . . . . . 8.4 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1 Recommendations for Dose Reduction . . . . . . . 8.5.2 Recommendations for Improved Data in the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.2.1 Natural Background . . . . . . . . . . . . . . 8.5.2.2 Occupational . . . . . . . . . . . . . . . . . . . . 8.5.2.3 Nuclear Fuel Cycle . . . . . . . . . . . . . . . 8.5.2.4 Consumer Products . . . . . . . . . . . . . . . 8.5.2.5 Miscellaneous Environmental Sources . . . . . . . . . . . . . . . . . . . . . . . 8.5.2.6 Medical Sources . . . . . . . . . . . . . . . . . . 8.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The NCRP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NCRP Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction 1.1 Sources of Population Exposure All members of the public in the United States are inevitably exposed to sources of ionizing radiation, some to a wide variety of such sources, others to only a few. The sources involved are of three general types, those of natural origin, unperturbed by human activities, those of natural origin but affected by human activities (termed enhanced natural sources), and man-made sources. Natural sources include cosmic radiation from outer space, terrestrial radiation from natural radioactive sources in the ground, radiations from radionuclides naturally present in the body and inhaled and ingested radionuclides of natural origin. Each of these natural sources has certain characteristics which lead to varying human exposures depending on locality and other special circumstances. When these exposures are substantially above the average they are referred to as "elevated." Enhanced natural sources include those for which human exposures have been increased as a result of man's actions, deliberate or otherwise. For example, air travel, especially at very high altitudes, increases the exposure to cosmic radiation, whereas movement of radionuclides on the ground, as in phosphate mining, can increase the terrestrial component to persons living in houses built on phosphate and other waste landfills. Radon exposures indoors might be considered, in some instances at least, to be due to elevated natural levels and also to be "enhanced natural" since the exposure can be increased by the characteristics of the home. In a sense also, all the operations of the nuclear fuel cycle, starting with mining, could be considered to be enhanced exposures from natural materials but these are generally included with "man-maden exposures. A variety of exposures results from man-made materials and devices, e.g., radiopharmaceuticals and x rays in medicine, and consumer products containing radioactive materials such as some smoke detectors or static eliminators. Exposures may also result from episodic events due to man's activities, such as atmospheric nuclear weapons testing, accidents in nuclear power plants, etc. Although some previous attempts have been made to determine the dose from all sources (as noted below), none of these has been fully 1

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1. INTRODUCTION

comprehensive for the United States. It is therefore timely to make as accurate an assessment as possible of the overall exposure of the U.S. population from all sources of ionizing radiation. It is convenient to categorize these sources according to the origin of the exposure, namely: natural radiation, occupational, the nuclear fuel cycle, consumer products, miscellaneous environmental sources connected with human activities, and medical diagnosis and therapy. Unfortunately, there are limitations in the accuracy of the data available in each of these categories, which will become clear in the discussion below. Nevertheless, this Report provides a comprehensive account of the exposure of members of the U.S. public to all sources of ionizing radiation.

1.2 Earlier Surveys Selected surveys of one or more sources of radiation, especially medical, have been made from time to time but few of these have attempted to be comprehensive. Furthermore, assessment activities at the international level, as exemplified by the earlier reports of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (UNSCEAR, 1958), and by joint groups of the International Commission on Radiological Protection (ICRP) and the International Commission on Radiation Units and Measurements (ICRU) (ICRP-ICRU, 1957, 1961) on medical exposure, have tended to emphasize global considerations rather than assessments of population exposure in individual countries. However, the UNSCEAR reports, which continue to provide global assessments of population exposures from a variety of sources, inevitably rely, to a substantial degree, on well-documented critical assessments of exposures at the national level (UNSCEAR, 1982). One early assessment of the exposure of the population in the U.S. was made by Moeller, Terrill, and Ingraham (1953). This pioneering report drew attention to natural background radiation and to medical diagnostic radiation. The former was estimated to result in an exposure of about nine roentgens in a 70-year lifetime and for the latter, the average annual dose to a limited region of the body was estimated to be about two roentgens to a "large portion" of the U.S. population. Other less important sources treated in that report included medical therapy, dental x rays, x rays in industry and research, radioisotopes in medicine, radium in luminous paints, static eliminators, the shipping of radioactive materials, nuclear reactors, and particle accelerators. It was noted that it was not possible to reach definitive conclu-

1.2 EARLIER SURVEYS

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sions on the magnitude of the radiological health problem occasioned by these sources of ionizing radiation because of the extremely fragmentary nature of much of the data In 1960 the Federal Radiation Council published a document which contained a section on sources of radiation exposure (FRC, 1960). This report concluded that the exposure of human beings from natural sources led to average annual dose equivalents to bone marrow, gonads and soft tissue of between 0.8 mSv (80 mrem) and 1.7 mSv (170 mrem), while from medical sources the annual genetically significant dose (GSD) was from 0.8 mSv (80 mrem) to 2.8 mSv (280 mrem) and the mean bone marrow dose was of the same order. Weapons testing fallout was identified as an important contributor, resulting in an average genetically significant dose of 0.53 mSv (63 mrem) over the following 30 years if atmospheric nuclear testing were not resumed after the cessation in 1958, but eight times this dose if atmospheric testing were resumed and continued at the same rate as in the previous five years. The mean bone marrow dose over 70 years would be 3.3 mSv (330 mrem) and 26.5 mSv (2,650 mrem), respectively, for these two circumstances. The nuclear fuel cycle was not believed to release radioactivity sufficient to cause a significant cnntribution to the population dose. A new effort was initiated by the Federal Radiation Council in 1970, and resulted in a report being produced by the Environmental Protection Agency (EPA, 1972) on the exposure of the U.S. population for the years 1960-1970 with predictions to the year 2000. Only environmental sources were considered, and the average annual natural background exposure was found to be about 1.3 mSv (130 mrem) in 1960, while fallout from earlier atmospheric tests of nuclear devices contributed an additional ten percent. All other sources were minor. The annual dose from fallout was expected to decline to about three percent of the natural background by 1970 and to stay at about that level until the year 2000. A few years later the EPA again reviewed the sources of ionizing radiation exposure to the population (EPA, 1977). The conclusions of this report were that the four major source categories contributing to the collective exposure of the United States population to ionizing radiation were environmental radiation, medical and dental radiation, the application of radiopharmaceuticals in medicine, and technologically enhanced natural radiation. However, the largest doses on an individual basis were identified as those from technologically enhanced natural radiation, medical radiation, environmental radiation, consumer products, occupational and industrial operations, and federal nuclear facilities. A particular source responsible for high individual doses in the category of technologically enhanced natural radiation

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1. INTRODUCTION

was radon from uranium mill tailings that had been used in the construction of residences. I t was noted that' the dose received by the patient from the limited use of radionuclide-powered cardiac pacemakers was significant to the individual but the report considered that this should be weighed against the benefit derived from these devices. The report also noted that there were many gaps in the dose data discussed in the report and the resulting observations and comments were necessarily restricted by this fact. The report emphasized that there was a need for major improvements in the data base for dose assessment in the United States. 1.3 Quantities and Units At the low doses likely to be received by members of the public, the effects of concern are assumed to be the small probabilities of stochastic effects such as the induction of cancer and/or severe genetic defects. In general, nonstochastic effects are presumed not to occur because the expected doses will be below the threshold for any such effects. This is true in all cases with the exception of some nonstochastic side effects in patients receiving radiation therapy. These side effects, however, are beyond the scope of this Report. The dosimetric quantities used in this Report include the absorbed dose, the dose equivalent, the effective dose equivalent, the collective effective dose equivalent, and the genetically significant dose equivalent. The absorbed dose, D, is the energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest. The dose equivalent, H, is a quantity used for radiation protection purposes that expresses on a common scale for all radiations, the irradiation incurred by exposed persons. It is defined as the product of the absorbed dose, D, and the quality factor, Q, which accounts for the variation in biological effectiveness of different types of radiation. For the purpose of relating exposure to risk, a convenient quantity is the effective dose equivalent, HE, which is either Hwb, the dose equivalent when the whole body is irradiated uniformly, or the weighted sum of the dose equivalents, HT, to each of the tissues (T) of the body, i.e., HE = C HTwT = H w b . By such weighting, one obtains a value of HEwhich is estimated to be proportional to the radiationinduced risk (somatic and genetic) even though the body is not uniformly irradiated. In this Report, the effective dose equivalent and the weighting factors (w,) defined by the International Commission on Radiological Protection (ICRP) (ICRP, 1977, 1978) will be used (see Glossary). Both the dose equivalent and the effective dose equivalent are expressed in sieverts (hundreds of rem). (It should be noted that

1.3 QUANTITIES

AND UNITS

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the uncertainties in risk estimates are considerable and information on both somatic and genetic risks continues to develop. Consequently, both the total magnitude of the risk and the weighting factors are subject to modification.) Among the exposures to be described in this Report are some that result in the irradiation of specific organs or tissues only (such as the lung in the case of radon), others that result in partial irradiation of the body (as in many medical procedures), and some that irradiate the entire body more or less uniformly (such as cosmic radiation). To account for these differing circumstances the effective dose equivalent is appropriate. For the irradiation of selected organs, the dose equivalent to the organ will be specified in this text and the appropriate weighting factors will be used to obtain HE.For "whole-body irradiation," the dose equivalent, Hwb,will be the same as the effective dose equivalent for that circumstance. Measurements of the dose equivalent to the whole body are usually only approximations to H,b which are, however, considered acceptable for the purposes of this Report. These approximations vary with the circumstances and, in the case of photons, are more accurate for high energies than for low energies (ICRU, 1985). For each source and source category, the number of people involved and the average effective dose equivalent to those exposed will be presented. The collective effectivedose equivalent is obtained by multiplying the average effective dose equivalent to the exposed population by the number of people exposed. This collective effective dose equivalent is then divided by the entire U.S. population (230,000,000 in 1980) to obtain the average effective dose equivalent for a member of the U.S. population. This quantity is, in some circumstances, such as occupational exposure, a highly artificial number but it is nevertheless useful for comparison purposes. It will be the quantity used in this report to describe population exposure from the various sources. For purposes of expressing the genetic risk, a convenient quantity is the genetically significant dose equivalent (GSD). This is the dose equivalent to the gonads weighted for the age and sex distribution of the irradiated population, i.e., to take into account the expected number of future children for each sex and age category (see Glossary). The GSD is expressed in sieverts (hundreds of rem). The gonadal dose equivalent is an upper limit to the GSD and when the dose equivalent is small, the gonadal dose equivalent itself may be used for the GSD. Additionally, when the exposure is to the entire U.S. population, the average gonadal dose equivalent and the GSD are equal. In some instances, the dose equivalent to some specific organ will be the quantity of interest for deriving the HE or the GSD. These organ dose equivalents are listed in the tables where appropriate.

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1. INTRODUCTION

Most of the exposures to be discussed below arise from radiation having low linear energy transfer (LET) (see Glossary); where highLET alpha-ray sources are involved, a quality factor, &, of 20 will be applied to absorbed doses to estimate the dose equivalents. For neutrons, the quality factor will be specified where appropriate. Throughout this Report, SI units will be shown first followed by the value in present conventional units in parentheses [see NCRP Report No. 82 (NCRP, 1985)l. Conventional prefixes in the SI system (pico, femto, atto, etc., see Glossary) will also be used. The terms "dose" and "exposure" will also be used throughout the text in their general sense.

1.4

The Present Report

This Report provides, from the source material in the six categories described earlier, a comprehensive data base and dose assessment for the population of the United States. These six categories are natural sources, occupational exposure, the nuclear fuel cycle, consumer products, miscellaneous environmental sources, and medical diagnosis and therapy. Each of these categories is treated in a separate Section of this Report and each Section represents a summary of a separate detailed NCRP Report (except for that on miscellaneous environmental sources). One of these Reports is NCRP Report No. 92, Public Radiation Exposure from Nuclear Power Generation in the United States ( N C R P , 1987a). The others are in the course of publication. In the Sections to follow, the present estimates of the effective dose equivalent and the gonadal dose equivalent (and/or the GSD) for each source category are described. The contributions of each source to the average effective dose equivalent and genetically significant dose to the U.S. population are discussed in the summary. Some indication of the range of uncertainties in the estimates is also given. The limitations in the accuracy of the data are substantial, and it is to be hoped that more accurate data will become available in the future. Specific suggestions for improvement are made in this document. Some of the sources turn out to be minor in significance and certainly sources producing an annual dose equivalent of less than 0.01 mSv (1 mrem) to an individual can be dismissed from further consideration (NCRP, 1987b). In applying this criterion it is, of course, necessary to examine all sources before determining which of them can subsequently be neglected. It is also possible that some individuals

1.4 THE PRESENT REPORT

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may be exposed to more than one of these sources, but in considering the problem the NCRP concluded that it is most unlikely that many persons would be exposed to more than ten such sources (NCRP, 198%). Other sources result in appreciable exposure for which efforts a t dose reduction are considered warranted. Obviously, the higher exposures justify more effort. The Report addresses methods of dose reduction in those instances. It also identifies existing gaps in our information on exposure and the research or other steps needed to obtain better information.

2.

Public Radiation Exposure from Natural Background 2.1 Introduction

Natural radiation and naturally occurring radioactive materials in the environment provide the major source of human radiation exposure. For this reason, natural radiation is frequently used as a basis of comparison for various man-made sources of ionizing radiation. In addition, numerous epidemiological studies have attempted to relate health effects to exposures from elevated natural radiation. None has provided definitive results but such epidemiological uses of the data make it highly desirable to quantify the average exposure of the population and to determine the distribution of natural exposures expected under various conditions. In 1975, the National Council on Radiation Protection and Measurements (NCRP) issued Report No. 45, Natural Background Radiation in the United States (NCRP, 1975). That Report presented a comprehensive picture of exposure to natural background radiation in the United States. The recognition more recently of the high exposures from indoor radon decay products (NCRP, 1984a) and additional data on exposures from other sources led t o an updating of the Report (NCRP, 1987~). Useful summary reports on exposures to natural radiation are available from a number of sources. The most comprehensive are those prepared by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 1966, 1972, 1977, 1982). Oakley (1972) authored a report, Natural Radi~tionExposure in the United States, which dealt with external natural radiation. This was published by the Environmental Protection Agency and was used extensively in the preparation of the 1975 NCRP Report. Also, the Committee on the Biological Effects of Ionizing Radiation of the National Academy of Sciences included data on natural background radiation in its 1972 and 1980 reports (NAS-NRC, 1972,1980). In deriving the effective dose equivalent, HE, and the GSD, it is useful first to express the results in terms of the annual dose equivalent, in mSv (or mrem), in specific tissues. HE is the sum of the dose 8

2.1 INTRODUCTION

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equivalents to these tissues, each weighted by the appropriate ICRP factors. For whole body irradiation (external) HE is taken to be the same as the dose equivalent to whole body. The GSD is equal to the gonadal dose equivalent. Absorbed doses are converted to dose equivalents using quality factors (Q) of 20 for alpha radiation, a mean of 5 for neutrons from cosmic rays1 and 1 for photons, electrons and muons (NCRP, 1987~).All of the radiation doses discussed here are low and most are delivered a t low dose rates.

2.2 Sources of Exposure Exposures to natural background radiation may be classified in several ways, but in this Report they will be divided into those from external sources and those from radionuclides in the body. The dose estimates for external source irradiation used in this Report are based on measurements, while those for internal sources must be calculated from limited analyses of radionuclide concentrations in individual organs, often from autopsy specimens. 2.2.1

Naturally Occurring Radionuclides

All the exposures treated in this section, except those due to direct cosmic radiation, are produced by radiation coming from the natural radionuclides in the environment. These radionuclides are of two general classes, primordial and cosmogenic. Most primordial radionuclides are isotopes of the heavy elements of the three radioactive series headed by uranium-238, thorium-232 and uranium-235. The radiation from these are significant contributors to the average effective dose equivalent to members of the population. The major primordial radionuclides which decay directly to stable nuclides are potassium-40 and rubidium-87. The relatively constant isotopic abundance of 40Kin potassium is only 0.0118 percent, but potassium is so widespread that 40Kcontributes about one-third of both the external terrestrial and the internal whole-body dose arising from natural sources. The isotopic abundance of "Rb is considerably higher, but rubidium's abundance in the earth's crust is two orders of magnitude less than potassium, and thus its contribution to the HE from natural background is much lower than that of 40K.

' Thii is a calculated value for the known energy spectrum of cosmic riiy neutrons (NCRP,1975).

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2. RADIATION EXPOSURE FROM NATURAL BACKGROUND

Most cosmogenic radionuclides are beta, gamma or x-ray emitters with low to intermediate atomic numbers, and are produced by interactions of cosmic nucleons with target atoms in the atmosphere or in the earth. The four radionuclides of dosimetric interest are 'H,'J3e, "C, and 22Na.Three of these, 3H, l4C, and nNa, are isotopes of major elements in the body. A number of other radionuclides are of scientific interest in tracing atmospheric processes but are not of significance with respect to population doses.

2.2.2

External Radiation

External radiation comes from two sources of approximately equal magnitude, the cosmic radiation from outer space and terrestrial gamma radiation from radionuclides in the environment, mainly the earth. The external radiation field consists of energetic penetrating radiations and may be considered, as a first approximation, to irradiate the whole body uniformly. In the case of cosmic radiation, the charged particles, primarily protons from extra-terrestrial sources that are incident on the earth's atmosphere, have sufficiently high energies to generate secondary particles. These are mostly high-energy muons and electrons, commonly referred to as the ionizing component, and a smaller number of neutrons. These neutrons are strongly absorbed in the atmosphere, so they are not important a t sea level, but are significant at higher altitudes. There is some shielding by housing and, to account for this, indoor exposures from cosmic radiation are assumed in this Report to be 80 percent of outdoor exposures. The three contributors to the terrestrial gamma radiation field are 40 K, and the members of the thorium and the uranium series. Most of the gamma radiation comes from the top 20 cm of soil, with a small contribution from airborne radon decay products. The absorbed dose in air is converted to dose equivalent in the whole body using a factor of 0.7 to allow for self-shielding (UNSCEAR, 1982). It appears that the amount of indoor exposure from radionuclides in the environment is close to that outdoors, due to a balance between shielding by housing materials and the geometry of exposure from radionuclides in the walls when the individual is within a structure (NCRP, 1987~).

2.2.3 Radionuclides in the Body For the case of irradiation by radionuclides within the body, where measurement of dose equivalent is difficult, it is necessary to calculate

2.2 SOURCES OF EXPOSURE

/

11

the annual dose equivalents. For all cases except radon decay products in the lung, this calculation is based on measured concentrations of radionuclides, e.g., ?K, in the specific organs of interest. For radon decay products, it is necessary to use atmospheric characteristics and a lung deposition model to convert concentrations in air to tissue doses. The primordial radionuclides considered include the series isotopes and 232Thseries, plus *K, of U, Th, Ra, Rn, Po, Bi, and Pb of the 238U "Rb, and the only cosmogenic nuclide of importance, 14C.These enter the body by ingestion of food, milk, and water or by inhalation. The isotopes follow the normal chemical metabolism of the element and the long-lived radionuclides are usually maintained a t an equilibrium concentration or increase slowly with age. The shorter-lived radionuclides disappear by decay, but concentrations in the body are continually renewed by fresh intake.

2.3 Exposure Estimaters 2.3.1

Cosmic Radiation

The average cosmic-ray annual dose equivalent is about 0.26 mSv (26 mrem) at sea level. This essentially doubles with each 2,000 m increase in altitude in the lower atmosphere. Latitude, solar cycle variations and other factors modify these exposures by about ten percent. In the United States, cities such as Denver (at 1,600 meters) have an annual external exposure from cosmic radiation of 0.5 mSv (50 mrem) (NCRP, 1987~). The earlier NCRP Report on natural background (NCRP, 1975) noted that air travel at an altitude of 12 km (39,000 feet) gave an enhanced cosmic-ray exposure of 5 p9v/h (0.5 mrem/h). A more recent study (NAS-NRC, 1986), which considered additional sources of information, came to a similar conclusion. Air travel statistics (U.S. Bureau of the Census, 1986) indicate that the average time in the air is about 1.5 hours per trip and that there were 340 million revenue passengers in 1984. This would give an annual collective dose equivalent of about 2,500 person-Sv (250,000 person-rem) or an average annual individual effective dose equivalent of about 0.1 mSv (1 mrem).

2.3.2 Terrestrial Gamma Radiation The average annual gamma-ray effective dose equivalent is about 0.28 mSv (28 mrem) derived from airborne radiation measurements.

12

/

2. RADIATION EXPOSURE FROM NATURAL BACKGROUND

This varies geographically. The annual effective dose equivalent (to the whole body) on the Atlantic and Gulf coastal plain is 0.16 mSv (16 mrem), for a region on the eastern slopes of the Rockies i t is 0.63 mSv (63 mrem), and for the remainder of the country it is about 0.30 mSv (30 mrem). A ground-based survey of four countries, including the United States, showed a normal distribution with 95 percent of the measurements within 50 percent of the mean value and thus the variability seems small. There are a few areas known to have elevated exposures but even aerial surveys do not have broad enough coverage to define the extent of such exposures.

This source gives a n annual effective dose equivalent of about 0.01 mSv (1 mrem) to the whole body, mostly from 14C in tissues. This exposure is uniform on a global basis, since the source is atmospheric carbon dioxide, which is uniformly distributed a t ground level. 2.3.4

Inhaled Radionuclldes

The annual dose equivalents for various inhaled radionuclides are listed in Table 2.1 The p,rimary tissue of concern involving these radionuclides is the bronchial epithelium in the upper airways which is the site of most lung cancers whether or not the lung cancer was induced by radiation (NCRP, 1984b). The major contributors are the short-lived decay products of radon. TABLE 2.1-Annual dose eouivalents to hna tissue from inholed radionuclides Radionuclides

Assumed air concentration

Average annual dose eauivalent (rsv)' Whole lung

w-22BRa "'Rn P1ap0-214p0 210Po ZS2Th-rURa mRn z12pb-Z1Zpo

700 n13q/m3 40 Bq/m3 8 x lo-' J/m3 70 pBq/m3 400 nBq/m3 200 mBq/m3 70 mBq/m3

Bronchial eDithelium

0.1 200 24,000 8 0.2 0.1 400

Note: The conversion coefficients between air concentrations and annual dose equivalents are given in NCRP, 1987c. '1 pSv = 0.1 mrem. 1 J/m3 = 0.5 X lo6 WL (see Glossary).

2.3 EXPOSURE ESTIMATES

/

13

Surveys of homes show an apparent log-normal distribution of concentrations of these decay products in indoor air. The distribution cannot be well defined with the present data but the NCRP (NCRP, 1984a) estimated that more than one percent of the population would be exposed to concentrations greater than five times the average and smaller numbers of people to higher concentrations. Note that inhalation exposures due to a natural radionuclide (21"Po) in tobacco products are discussed in Section 5.

2.3.5 Radionuelidesinthe Body Except for 40K, there are very few data to assess the dose equivalent from these radionuclides, and the annual dose equivalents given in Table 2.2 provide no information on the distribution of exposures. The doses are dominated by 40Kand 'loPo and, while the former is under homeostatic control and is directly proportional to lean body mass, the latter is a function of intake and may vary widely.

2.3.6 Total Exposure from Natural Background The exposures resulting from the various sources described in this Section are summarized in Table 2.3. The dominant annual dose equivalent is that to the bronchial epithelium from the decay products TABLE 2.2-Average annual dose equiualents to various tissues from natural mdionuelides contained in the body (pSu)" Radionuclide

"C 'OK "Rb W-='U ='lh %.a

'9, 210pb-2"Jpo 532Th 228Ra-mRa mRn Rounded total

Soft tissue

10 180 10 5 0.1 3 7 140 0.1 2 1 360

Bone surfaces

8 140 14 3 6 90 14 700 2 120 1,100

Bone marrow

30 270 7 0.4 1 15 14 140 0.4 22 -

500

Note: 1. Individual organs may sometimes receive an annual dose equivalent from individual radionuclides up to twice those shown for "Soft Tissues." 2. These dose equivalents include those estimated in Table 2.1. " 1 pSv = 0.1 mrem.

14

/

2. RADIATION EXPOSURE FROM NATURAL BACKGROUND

TABLE 2.3-Estimated average annual dose equivalents to various tissuea for a member of the population in the United States from vario1t.s sources of natuml background radiation (u.Svlm Bone Other soft Bone Bronchial Source

evithelium

timum

Cosmic Coamogenic

270 10

270 10

Terrestrial Inhaledb h the body'

280

280

24,000

-

360 26.000

360

Rounded total

900

surfaces

marow

270 10 280

270 30 280

1,100 1,700

600 1,100

-

-

'1 pSv = 0.1 mrem. D m s to other tissues from inhaled radionuclides are included under "In the Body." 'This includes all radionuclides in the body (seeTable 2.2) excluding the cosmogenic component shown separately in this Table.

of radon. The differences in the dose equivalent rate reported here and those in the earlier NCRP Report (NCRP, 1975)are quite marked. The major change is in the annual dose estimate to the bronchial epithelium from inhaled radon decay products, which increased from 4.5 to 24 mSv (450 to 2,400 mrem). The increases in the estimated dose equivalent from internal emitters were due to the higher quality factor for a radiation, to data showing higher concentrations of the 210Pb-210Po pair in bone, to a higher estimate for the tissue dose from radon decaying in the body, and to higher radon levels indoors as compared to outdoors. The dose equivalent values for cosmic radiation, cosmogenic radionuclides and terrestrial gamma radiation are very little changed from the previous estimates. The annual dose equivalents have been converted to effective dose equivalent using the weighting factors (WT)of the ICRP (ICRP, 1977, 1981). The individual contributions are shown (in PSV)in Table 2.4, and their sum is a total of HEof 3.0 mSv (300 mrem). This estimate of average effective dose equivalent is considered to apply to both sexes and all ages. In the case of irradiation of the entire public (such as by natural background), the GSD is equal to the gonadal dose equivalent. The value of the gonadal dose equivalent is the same as that for other soft tissues shown in Table 2.3, viz 0.9 mSv/y (90 mrem/y). We assume that the average effective dose equivalents given in Table 2.4 apply to all members of the U.S. population (230,000,000) and therefore the collective effective dose equivalent from natural sources is 69 X lo4person-Sv (69 million person-rem).

2.3 EXPOSURE ESTIMATES

/

15

TABLE 2.4-Estimated total werage a n d effectwe dose equivalents to various tissues for a member of the population in the United States from varwua sources of natural backround radiation (LSD)' Bone Bone Other HE Source surfaces

Lung

Cosmicb Cosmogenic Terrestrial Inhaled' In the body Rounded total

30 1 30 ~.'JOO 40 2.100

70 2 70 90 230

8 10 30 50

marrow

tissues

130

30 4 30

140

60 120

170 440

-

3

-

270 10 280 2,000 390d -3.000

-

'1pSv = (1.1mrem.

Includes 1x lod Sv population dose from air travel. 'Derived from calculations of ICRP Publication 32 (ICRP. 1981). The ICRP cites a w~ of 0.12 for whole lung and 0.06 each for bronchial epithelium and pulmonary tissue, respectively. Radon and its daughters irradiate the tracheobronchial region mainly. In ICRP Publication 32, the ICRP uses the James-Birchall model to establish dose equivalents to the bronchial basal cell layer in the range 0.06 to 0.18 Sv per WLM (Table 2) for an average of 0.12 Sv/WLM. This, combined with the ICRPconversionfactor (derived in equation 16)of 0.01 Sv/WLM, yields an effective weighting factor of 0.08. It is clear that weighting factors for use in these circumstances are debatable, as indeed are the conversion factors for effective dose equivalent (in sievert) from the a particle concentration (measured in WLM). Uncertainties of *50% derive from this source alone. dThis is an approximation derived by assuming that the rest of the organs (w = 0.48) had the same annual dose equivalent as soft tissue, namely 360 pSv, thus adding 170 ~ S for V a total of 390 pSv.

2.4 Recommendations The components of natural background include external cosmic and terrestrial radiation, radionuclides &I the body, and inhaled radon and its decay products. External cosmic radiation varies to some degree with altitude but is otherwise essentially constant over the U.S. External terrestrial radiation varies little over the surface of the U.S. in normal (undisturbed) circumstances. Radionuclides in the body, are essentially constant. None of these is amenable to mainly 40K, dose reduction in any obvious and simple way. Radon as a source is not only the largest component of natural background, but also the most variable. It may be responsible for a substantial number of lung cancer deaths annually (NCRP, 1984b), but its actual concentration indoors is still not well known in all parts of the country. Consequently, NCRP Reports No. 77 and No. 78 (NCRP, 1984a, 198413) recommended actions relative to the control of indoor radon sources. This Report draws attention to these actions

16

1

2. RADIATION EXPOSURE

FROM NATURAL BACKGROUND

which included conducting a nationwide survey of radon levels, the recommendation of remedial action levels at concentrations above about 400 mBq/m3 (actually specified was 2 WLM/y) (NCRP, 1984a), and the introduction of mitigation techniques to reduce radon levels indoors (NCRP, 1987g). The radon problem is now receiving significant attention nationally and the Environmental Protection Agency has set guidance at about 150 mBq/mS (actually specified was 4 pCi/ 1) (EPA, 1987). We can hope that as a result of these activities, the true extent of the problem will become better known and the higher indoor radon levels reduced.

3. Occupational Exposure 3.1 Introduction It has long been appreciated that the health risks of ionizing radiation are most likely to be faced by those who use ionizing radiation and/or radioactive materials in their work. Consequently, recommendations and standards to control exposure were first applied to radiation workers (by the NCRP and the ICRP in 1934, for example) and have constantly been re-examined and revised, as the need arose, to provide adequate worker protection. The principal areas which involve radiation workers have varied over the years but now include medical radiology, industrial applications such as radiography, nuclear power, and some research activities. The exposure of workers contributes to the collective effective dose equivalent of the entire population and hence to the somatic and genetic detriment in the population. Thus, the level of exposure of radiation workers, the number exposed and the average exposure have been a matter of considerable general interest. Recently, trends in these levels in given occupations have also been studied (EPA, 1984a). In this Section, the doses presented will be those resulting exclusively from occupational exposures to ionizing radiation. Many accounts of the exposure of selected worker populations have been published over the years, and such reports are cited and discussed in a forthcoming NCRP Report on the subject (NCRP, 1987d). Fewer comprehensive accounts of the exposure of workers in all occupational categories have been published, however. The Federal Radiation Council in 1960, in preparing guidance for occupational exposure, developed the first estimates of the number of radiation workers in the U.S. and their doses (FRC, 1960). The principal occupations considered at that time related to medical applications of x rays, industrial radiography and the activities of the Atomic Energy Commission (AEC). In AEC facilities, the average exposure of the 66,000 radiation workers for the year 1958 was of the order of 2 to 4 mSv (200 to 400 mrem). For the 250,000 medical workers and industrial radiographers, exposures were in the range of 5 to 50 mSv (500 to 5,000 mrem). (A specific year was not stated but presumably these exposures were for the mid-to-late 1950s.) In a 1972 report by the EPA (EPA, 1972), 771,800 workers were identified with a mean annual exposure of 2.1 mSv (210 mrem) for the

18

/

3. OCCUPATIONAL EXPOSURE

year 1970, and the contribution to the average dose equivalent to a member of the U.S. population was estimated to be 8 PSV(0.8 mrem) for that year. The report included workers in the medical and dental field, the armed services, other federal workers, AEC licensees and licensees in agreement states. In 1980, the EPA (EPA, 1980) published a follow-up report on occupational exposures in the U.S. in the year 1975. This report stated that about 1.1 million workers were potentially exposed to ionizing radiation of which 370,000 received measurable doses. The average annual "dose" to all workers was 1.2 mSv (120 mrem) and their annual collective "dosen was 1,300 person-Sv (130,000 person-rem). A comprehensive report was prepared recently by the EPA (EPA, 1984). This report finds 1.32 million people in the U.S. in 1980 engaged in radiation work with an average dose equivalent of 1.1 mSv (110 mrem). Of these persons, only about one half had measurable exposures and for these the average dose equivalent was 2.3 mSv (230 mrem). The collective dose equivalent was 1,500 person-Sv (150,000 person-rem) and the occupational contribution to the average dose equivalent to a member of the 1980 U.S. population of 230 million people was thus about 7 &v (0.7 mrem).

3.2 Sources of Data and Estimates The NCRP Report on occupational exposure is intended to be comprehensive (NCRP, 1987d). Not only does it take into account the data in the EPA report, but it also considers individual studies of selected occupational groups that supplement and elaborate on those data. The EPA report is not specific -about how workers are defined. In addition to the nominal 1.32 million workers referred to as "all U.S. workers," the EPA report discusses some additional workers, such as uranium and other miners and personnel in aircraft, totalling 115,000 persons who were exposed on the average to about 1.7 mSv (170 mrem) in 1980. Yet another group, 155,000people who were not workers but visitors to facilities and potentially exposed in occupational circumstances, were exposed on the average to about 0.3 mSv (30 mrem) in 1980. Another source of exposure among miners noted in the EPA report is due to radon decay products. The miners totalled 18,000 persons with a mean annual exposure of 0.4 WLM (see Glossary) or about 4 mSv (400 mrem) annual effective dose equivalent (ICRP, 1981). Thus, the total number of persons exposed occupationally, as identified by the EPA in 1980, was actually 1.59 million, the total collective dose was about 1,740 person-Sv (174,000 person-rem), and

3.2

/

SOURCES OF DATA AND ESTIMATES

19

TABLE 3.1-Exposures of radiation workers to ~OWTLET radiation for year I980 Occupational category

Number of workers (thousands) All

Medicine Industry Nuclear fuel cycle Government Miscellaneous Other workers Others (e.g., visitors) Rounded subtotal Additional Industrial' Uranium minin$ Well loggers DOE contractors USPHS Rounded total

Exposed

Average annual effective dose equivalent (mSv). All

Exposed

Collective effective dose equivalent

[per~on-sv)~

584 305 151 204 76 1b5 155

277 156 91 105 31 107 42

0.7 1.2 3.6 0.6 0.7 1.7 0.25

1.5 2.4 6.0 1.2 1.6 1.8 0.9

410 380 540 120

1,590

810

1.1

2.1

1,700

1.56 3.50 0.07

5.2 1.15 4.2 1.8 0.47

1.24

2.2

6.9 8.7 4.6 1,610+

2.1 10 7.3 81 0.7 911

60 200 40

11' 12' 3V l6oh 0.3b 2,000

" 1mSv = 100 mrem. 1 person-Sv = 100 person-rem. Ten states only. External effective dose equivalent based on sample of 47 open pit miners. Population exposed based on underground mining population. " 1970-75. '1975-76. '1979. 1983.

the average effective dose equivalent for those actually exposed was 2.1 mSv (210 mrem). In this Section, the measurements of the occupational exposure of individuals will be taken to represent the dose equivalent to the whole body of those individuals. The effective dose equ~valent,HE,will be taken to be the same as the dose equivalent. Inaccuracies resulting from the use of these assumptions will be discussed later. The main categories of exposure to low-LET radiation are listed in Table 3.1, which separately identifies those nominally exposed (all) and those actually exposed. The Table includes not only the EPA data but additional data identified in the NCRP Report on occupational exposure (NCRP, 1987d). There may be some small unavoidable overlap in these summations which only a separately undertaken al.djr could be expected to resolve. These data yield an overall total (see Table 3.1) of 1.61 x 10' persons nominally exposed, an average effective dose equivalent to these persons of 1.24 mSv (124 mrem), a

20

/

3. OCCUPATIONAL EXPOSURE

collective dose equivalent of 2.0 x 10"erson-Sv (200 x lo3 personrem), and an annual effective dose equivalent per exposed worker of 2.2 mSv (220 mrem). As indicated in Table 3.2, workers exposed to high-LET radiation include miners exposed to airborne radon decay products, certain workers employed by U.S. Department of Energy contractors, and other workers exposed to neutrons. In the nuclear power industry, the dose equivalents from occupational exposure to high-LET radiations are probably not more than about 10 percent of those from gammaray exposures. The total number of workers involved in all of these occupations is 60,000, the annual collective dose equivalent is 140 person-Sv (14,000 person-rem) and the annual effective dose equivalent for all these workers is 2.3 mSv (230 mrem). Presumably, the Q used for neutrons in these situations was 10, since the data are for 1984 or earlier. For exposures to both low and high-LET radiation, a total of about 1.7 x lo6 persons are nominally exposed occupationally and of these about 930,000 actually receive measurable doses. (There could be some further overlap because some of the workers exposed to high-LET radiation also have low-LET exposures.) The total collective effective dose equivalent is about 2,100 person-Sv (210,000 person-rem) and the average annual effective dose equivalent for those exposed for the year 1980 is about 2.3 mSv (230 mrem).

TABLE 3.2-Exposures of radiation workers to high-LETradiation for 1980 Number of workers (thousands)

Type of radiation and occupational category

All

Exposed

Average annual effective dose equivalent (mSvP All

Exposed

Collective effective dose equivalent (person-SV)~

a Particles

Underground mining'

18

Neutrons (using Q = 10, presumably) DOE contractorsd Nuclear powef Nawl

25

Rounded total

-

10

1.1

1.5

12

60+

23+

'1 mSv = 100 mrem. 1 person-Sv = 100 person-rem. 1977,1980. 1979. " 1984.

2.3

-5.0

140

3.3 SPECIAL CONSIDERATIONS

/

21

3.3 Special Considerations The NCRP Report on occupational exposures (NCRP, 1987d), has the aim of determining to what extent reasonably reliable values of average dose for each occupational category can be established at the present time. The Report notes the problems inherent in data of these types, especially those concerned with dosimeter location, dosimeter accuracy and the relationship of the dosimeter reading to the effective dose equivalent to the person. However, while it is concluded that personnel monitoring can be used for dose determination and risk assessment, a t the present time, occupational exposure values can only be considered approximate. Some improvements in personnel dosimetry are proposed in the Report which, if undertaken, will eventually improve the quality of occupational data. The Report notes the value of using the collective dose equivalent ratio (i.e., the ratio of annual collective dose equivalent resulting from annual dose equivalents above 15 mSv (1.5 rem) to the total annual collective dose equivalent) as an indicator of the probable spread in the distribution of dose equivalents to individuals in different groups. It also notes that dose equivalents to some individuals can be quite high even when averages are low. However, efforts at reducing the exposure to the more highly exposed personnel both in nuclear power plants (INPO, 1986) and in DOE facilities have resulted with time in the virtual elimination of annual dose equivalents above 50 mSv (5 rem) and a decrease in the number of those above 10 mSv (1 rem). The EPA report and the NCRP evaluation of those data clearly show average occupational dose equivalent values declining by a factor of about two over the period 1960 to 1985. The systematic errors in personnel dosimetry include a t least the error associated with the dosimeter measurements, the location of the dosimeter on the body, and the direction, nature and energy of the radiations involved. These are all intrinsically amenable to evaluation, but in most protection services, approximations which tend to overestimate the true values are accepted Consequently, these systematic uncertainties usually far outweigh the statistical errors for both internal and external exposures. For that reason, uncertainties in the numbers are difficult to assess. As noted, the uncertainties depend on the energy of the radiation because the measured dose on the surface of the body will be a better approximation to the effective dose equivalent to the individual a t high gamma ray energies than at low energies (ICRU, 1985). When the dosimeter is calibrated for a specified depth in the body, this energy dependence is reduced. At higher photon energies (>0.5 MeV), the systematic errors in the estimate of effective dose equivalents probably should not exceed a

22

/

3. OCCUPATIONAL EXPOSURE

factor of 2 or 3 overall (provided that the personal dosimeter is placed on the same side of the body as that most frequently struck by the incident radiation). Furthermore, these e m r s will usually be on the side of overestimation of the effective dose equivalent. Comparisons with Canadian data (Fujimoto et al., 1984) indicate average occupational exposures similar to those in the U.S. Exposures are somewhat better documented in Canada and the existence of a central registry makes them more accessible. The highest -effectivedose equivalents are recorded by underground uranium miners followed by certain workers in the nuclear fuel cycle (for example, commercial nuclear power plant operators and maintenance workers), industrial radiographers and well-loggers. Workers in hospitals and in government contractor facilities have the lowest exposures of the larger groups. Relatively few individuals are exposed to high doses and consequently the distribution of doses among worker groups is often approximately log normal. 3.4

Discussion

Workers in radiation-related occupations are increasing in number but the time trends continue to show decreasing average values of dose equivalent. With the average dose for those exposed being about 2.3 mSv (230 mrem) for the year 1980, a figure comparable with exposures from natural background and other sources, progress in the control of occupational exposures can be considered satisfactory. Nevertheless, efforts must continue to be made to reduce doses to the more highly exposed individuals and indeed that continues to be an aim of the NCRP. In the radiation occupations, the application of radiation protection principles, including ALARA (see Glossary), and the presence of knowledgeable radiation protection personnel tend to ensure good practice and decreasing exposures. More care in measurement specification and recording, and development of a better understanding of the relationship between dosimeter reading and dose to the individual, would improve our ability to interpret dose information, and thus, to use the information for risk assessment. The contribution of the average effective dose equivalent from occupational exposure to the total average effective dose equivalent for the U.S. population is estimated to be less than 10 PSV (1 mrem) [actually -9 PSV (0.9 mrem)] annually. This somewhat artificial distribution of occupational exposure across the whole population constitutes only a small source of detriment to society as a whole. The GSD will be less than the average effective dose equivalent, perhaps of the order of 6 pSv (0.6 mrem). However, occupational exposures are unquestionably important to the individuals involved and to the fields of endeaver in which these exposures occur.

4. Public Radiation Exposure from Nuclear Power Generation 4.1 Introduction

Operation of nuclear power plants results in the irradiation of some members of the public from releases of radionuclides to the atmosphere and to bodies of water, and from direct gamma radiation emitted from those facilities. Various regulations promulgated by the Environmental Protection Agency and the Nuclear Regulatory Commission require that releases be controlled to very low levels. The air- and water-borne radionuclides deliver radiation doses by various pathways such as external exposure, intake from breathing or drinking, and intake of foods contaminated by these radionuclides. The most exposed persons are usually those in the immediate vicinity of a facility, and in the following discussion, the dose to the regional population within 80 km (50 miles) will be specified. The entire fuel cycle must be considered in evaluating the radiation dose due to nuclear power production. In the United States, the nuclear fuel cycle consists of uranium mining, uranium milling, uranium hexduoride production, uranium-235 enrichment, uranium oxide fuel fabrication, power production, fuel reprocessing (currently limited to military operations), and low- and high-level radioactive waste management. Some radiation exposure to the public occurs at facilities for each of these fuel cycle components, and also during transportation of radioactive materials between the facilities. In the United States, the fuel cycle is focused almost entirely on the operation of light-water moderated reactors, specifically Boiling Water Reactors (BWRs) and Pressurized Water Reactors (PWRs). The fuel cycle for power generation in the United States is not complete, however; there is no commercial fuel reprocessing, and no permanent high-level waste disposal (spent fuel-elements are now stored in special facilities at nuclear power plant sites). Uranium is also mined, milled, and enriched for the purposes of the military nuclear fuel cycle. Fuel reprocessing and high-level waste storage facilities exist to serve the purposes of the military fuel cycle in the United States. 23

24

/

4. EXPOSURE FROM NUCLEAR POWER GENERATION

Low-level radioactive wastes from the nuclear industry and other sources (e.g., medical applications) are shipped to designated sites for shallow land burial.

4.2 Sources of Data Non-occupational radiation exposures from the nuclear fuel cycle are calculated for the most exposed persons and for the population within 80 km (50 miles) of a facility. Beyond this distance, exposures are too small to warrant consideration. Data to calculate public exposures are obtained by facility operators in response to requirements by the regulatory agencies-the U.S. Nuclear Regulatory Commission (NRC)and the U.S. Environmental Protection Agency (EPA)-or by the U.S. Department of Energy (DOE),which is responsible for some of these facilities. A typical approach is to monitor or estimate annual radionuclide releases to air and to water, consider the various pathways by which persons may be exposed, and calculate the doses using selected computational models. Environmental radiological monitoring is performed, among other reasons, to assure that regulatory limits are not exceeded.

4.3 Special Considerations

In this Section, the effective dose equivalent, HE,is determined from the dose equivalent rates to various body organs resulting from the release of radionuclides to air, water and via the food chain (NCRP, 1987a). These permit comparison of maximum exposures and the addition of collective doses, but it must be realized that the dose values were not derived by uniform methods for each phase of the fuel cycle. Differences exist in the amount of effort expended in determining radionuclide release rates and radiation exposure rates, in the calculational models used to estimate individual and collective effective dose equivalents, and in computation at the point of exposure of doses from calculated radionuclide concentrations. As mentioned previously, collective effective dose equivalents from airborne (and waterborne) radionuclides were calculated only to the population within 80 km (50 miles) of a facility, and only during the life of the persons currently exposed.

4.4 ESTIMATES AND DISCUSSION

4.4

/

25

Estimates and Discussion

The Tables in this Section summarize the annual radiation dose estimates presented in the NCRP Report on public exposures from nuclear power generation (NCRP, 1987a). Sources of information were NRC, EPA, and DOE compilations and selections of available effluent and dose reports by facility operators. In some instances, a range of values was given and a typical value selected. In other instances, a model facility was assumed, based on the range of operating characteristics and a model transportation network. Table 4.1 indicates the annual doses to maximally exposed persons due to airborne effluents; doses due to liquid effluents were generally low. Subsequent Tables (4.2 and 4.3) give annual collective doses and the annual collective dose per nuclear power plant (normalized to one gigawatt electric (1 GWe) power production operating during 80 percent of the year). The essence of these data is that both maximum and collective effective dose equivalents from the nuclear fuel cycle are relatively low. Among the highest annual effective dose equivalents to the maximally exposed individual are (1)values up to about 2.6 mSv (260 mrem) for milling but much smaller values apply to some mills, (2) TAELE4.1-Summary of average annual effective dose equivalents to the mawinally exposed individual member of the public due to airborne radioactive effluents from fuel cycle facilities Average annual Facility effective dose Basis of estimate equivalent Mining Open pit Underground Milling Conversion Wet Dry Enrichment Fabrication Nuclear power plants PWR BWR Low-level waste storage Transportation

" 1 mSv = 100 mrem.

0.26 0.61 0.004-2.6

Model mine Model mine 8 Typical mills

0.008 0.032 <0.001-0.004 <0.001-0.007

Plant, calculation Plant, calculation All 3 plants All 7 plants

0.006 0.001 <0.01

Model reactor Model reactor Maxey Flats, KY facility To support 1 model reactor

0.2

26

/

4. EXPOSURE FROM NUCLEAR POWER GENERATION

T ~ L4.2-Summary E of annual collective effective dose equivalents to regional populations due to radioactive effluents i n the air and water pathways from fuel cycle facilities Facility

Mining Open pit-air Open pit-water Underground-air Underground-water Milling

Conversion Wet

Enrichment

Fabrication

Nuclear power plant Air Water Low-level waste storage

Annual collective effective dose equivalent (~erson-Sv)'

Basis of estimate

Model mine Model mine Airborne effluent from model mill Plant airborne effluent in 1980 Plant airborne effluent in 1980 3 plants, airborne effluents in 1981 7 plants, airborne effluents in 1980 47 plants in 1980 47 plants in 1980 Maxey Flats, KY facility (estimate)

' 1person-Sv = 100 person-rem.

values up to about 0.6 mSv (60 mrem) due to uranium mining, and (3) values due to transporting radioactive material, about 0.2 mSv (20 mrem) for which it was assumed that the amounts of radionuclides and the exposure rates were a t the maximum level within compliance, although, in practice, much lower exposures are usually experienced. The annual collective effective dose equivalent per model nuclear power plant from the entire fuel cycle was estimated to be 1.36 personSv (136 person-rem), considerably less than earlier estimates. This is due to improved effluent treatment practices (NCRP, 1987a). With approximately 100 nuclear power plants operating in the U.S., this yields a total collective effective dose equivalent of 136 person-Sv (13,600 person-rem) from nuclear electricity generation.

4.4 ESTIMATES AND DISCUSSION

/

27

TABLE4.3-Summry of annual collective effective dose equivalents to the regwnal populations normalized to a 1 GWe reactor operating at fd capaci~y80 percent of the time Annual collective effective dose equivalent (person-Sv).

Facility

Mining

0.94

Basis of estimate

Weighted for 2 types of model mines ('h open pit 3 underground) 0.4 Model mill Weighted for 2 plants (65%wet) Paducah plus Oak Ridge Weighted for 7 plants 1980 data for 47 plants No estimate available

+

Milling Conversion

0.25 0.0003

Enrichment

0.01

Fabrication Nuclear power plant

0.004 0.048

Low-level waste storage Transportation Incident-free Accidents Total

" 1 person-Sv

=

-

0.071 0.054 1.36

Excludes decommissioning wastes

100 person-rem.

The reliability of the values differs for the various fuel cycle components, and the individual values are not necessarily comparable because those who made the estimates used different pathway models and different approaches to dose calculations. For example, the doses estimated for nuclear power plants are based on relatively detailed examinations of effluent data and pathways; those for conversion and fabrication are in some instances based on detailed concentration measurements at the points of maximum exposure; at mills, on the other hand, many values are predictions based on calculations (often maxima) reported in environmental impact statements.

4.5

Comments

Off-site doses arising from normal operations in the nuclear fuel cycle are evidently small and, therefore, dose reduction for the various phases of these operations is not presently a priority item. A more consistent approach to determining these doses is highly recommended, however. This effort would include compiling effluent and environmental monitoring data in a uniform format for each compo-

28

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4.

EXPOSURE FROM NUCLEAR POWER GENERATION

nent of the fuel cycle, using similar dispersion and transfer models, applying site-specific factors to these models, and converting radionuclide concentrations to collective effective dose equivalents by the same method. This Report has not attempted to treat the exposure of the U.S. population from nuclear accidents. The most notable of these, as far as the U.S. population is concerned, was the accident at the Three Mile Island Nuclear Plant on March 28, 1979. Although that accident ,was a serious event in nuclear engineering terms, the radioactive releases from it were relatively small. The collective dose estimated to the population within 50 miles ranged from 16 to 53 person-Sv (1,600 to 5,300 person-rem) with a most probable value of 33 persons-Sv (3,300 person-rem). The maximum individual dose was less than 1 mSv (100 mrem) while the average dose to individuals living within a 16 km (10 mile) radius was 0.8 mSv (8 mrem) and within an 80 km (50 mile) radius it was 15 $ 3 (1.5 ~ mrem) (Behling and Hildebrand, 1986). These doses are small compared with the average annual effective dose equivalent to members of the U.S. Population from the other sources covered in this Report. The accident at Chernobyl in the U.S.S.R on April 26, 1986, although a much worse accident in every respect, had virtually no impact on the population of the United States. Nonetheless, the potential doses to the U.S. population from a major nuclear power plant accident in this country could be significant. Continued attention to the prevention of accidents in such facilities is, of course, mandatory.

5. Public Radiation Exposure from Consumer Products 5.1 Introduction

During the last several decades, there has been a great increase in the types and quantities of products commercially available to the general public within the United States. Many of these involve novel materials that have properties and behaviors with which the average individual is not familiar. One such property is the emission of ionizing radiation. In many cases, such emission is essential to the performance of the task for which the device was designed. Examples include radioluminous products containing 3H, 147Pmor "'Ra, gas and aerosol (smoke) detectors containing 241Am,static eliminators containing 'loPo, and airport x-ray baggage inspection systems. In other cases, such emissions are incidental or extraneous to the purpose for which the consumer product was designed. Examples include television receivers (potential sources of low energy x rays), tobacco products containing 210Pband 'loPo, combustible fuels and building materials containing members of the U and T h decay series, and gas mantles, camera lenses and welding rods containing thorium In 1977, the NCRP issued a report that presented detailed information on doses to the U.S. population from consumer products (NCRP, 1977). That report is in the process of being updated (NCRP, 1987e). In the course of that update, the Council identified additional consumer products (such as domestic water supplies and video display terminals) that can be sources of ionizing radiation, and deleted coverage of some products (such as shoe-fitting fluoroscopes) that are either no longer available or whose use has been essentially discontinued. For each source, an effort was made to provide data on the number of products currently in use and the range of typical dose equivalents being received from that source by the general public. Because of the variety of products considered and differences in the degree to which the radiation doses from each of these had been evaluated, however, the quality of the data relating to these sources proved to be extremely variable. 29

30

/

5. RADIATION EXPOSURE FROM CONSUMER PRODUCTS

5.2 Sources of Data and Estimates Presented in Table 5.1 is a summary of information on a wide range of consumer products which are sources of ionizing radiation. For each source, the Table includes a summary of the number of people exposed, an estimate of the effective dose equivalent (HE) to the exposed individuals, an estimate of the average annual collective effective dose equivalent to the U.S. population and finally an estimate of the average annual effective dose equivalent to a member of the U.S. population. The effective dose equivalent to those exposed was estimated by weighting the dose equivalent to one or more organs when selective organ irradiation was involved or by taking it as equivalent to the whole-body dose equivalent when whole-body irradiation was involved. In many cases, these estimates are very approximate but suffice for purposes of comparison. The data are arranged in three groups according to the importance of the individual consumer products as contributors to the population dose. Details of the nature of the products, the tissues exposed, and the doses involved will be available in the previously cited forthcoming NCRP Report (NCRP, 1987e). Group I: As may be noted from the data presented in Table 5.1, the dominant contributors to the population dose equivalent from consumer products are tobacco products and domestic water supplies. For reasons cited later, however (see Section 5.3), it is not possible at the present time to accurately estimate the collective effective dose equivalent from tobacco products. Domestic water supplies, depending on their origin, contribute appreciable quantities of radon to the indoor air and thus irradiate the lungs. This is the same body organ that receives the major impact of the dose from tobacco products. These two sources are followed, in turn, by the contributions to the average effective dose equivalent in the population from materials used in the construction of buildings. The contribution to the effective dose equivalent from all other sources in this group is small in comparison to these three sources. Group 11: As may be noted from the data presented in Table 5.1, none of the sources in this group compares in terms of collective dose contribution to those in Group I. A possible exception is the contribution from television receivers for which the collective effective dose equivalent appears to be relatively large because the number of people involved includes virtually the entire U.S. population. Group 111: Again, as may be noted from the data in Table 5.1, the two sources in this group represent only a small contribution to the overall collective effective population dose equivalent. In terms of overall impact. the total annual collective effective dose

TABLE5.1-Radiation

Source

exposures from consumer products arranged in accordance with their significance Average Number of annual Annual collective Average annual HE' to the effective dose HE' in the U.S. people exposad equivalent population exposed (&Wb (thousands) population (person-Sv)' (..sv\b

Group I-involves

many people and the dose equivalent is relatively large

Tobacco products Domestic water supP~Y Building materials Mining and agricultural products Combustible fuels Coal Natural gas heaters Natural gas cooking ranges Dental prostheses Ophthalmic glass Rounded total

(See Section 5.3) 2,300-14,000

Group 11-involves many people but the dose equivalent is relatively small or is limited to a verv small portion of the body Television receivers Luminous watches and clocks Airport inspection systems Gas and aerosol (Smoke) detectors Highway and road construction materials Electron tubes Thorium products Fluorescent lamp starters Gas mantles Rounded total Group 111-both the number of people involved and the dose equivalent fmm these sources are relatively small Thorium products Tungsten welding rods Check sources" Rounded total

300

160

50

800


<8 50

0.2 <4 x 1 0 P 0.2

" H e is the effective dose equivalent. 1p S = ~ 0.1 mrem. ' 1person-Sv = 100 person-rem. Of this number, the predominant exposure is to that portion of the population using groundwater sources, insufficient data are available to specify the numbers of people most affected or the exposures they receive. "Sources used to check the performance of radiation monitoring instruments.

32

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5. RADIATION EXPOSURE FROM CONSUMER PRODUCTS

equivalent to the U.S. population from consumer products ranges from 12,000 person-Sv (1,200 x 10"erson-rem) to 29,000 person-Sv (2,900 x lo3 person-rem), and the average annual effective dose equivalent to a member of the U.S. population ranges from about 60 to 120 PSV (6 to 12 mrem). However, not all of the members of the U.S. population are exposed to all of these sources.

5.3 Special Considerations Although it is recognized that there is considerable uncertainty in some of the estimates of the dose equivalents associated with the use of consumer products, it is believed that the estimates presented in Table 5.1 are not in error by a factor of more than ten. The effective dose equivalent resulting from the use of tobacco products is impossible to estimate in the present state of knowledge. The annual average dose to a small region of the bronchial epithelium is estimated to be about 0.008 Gy (0.8 rad) (Little et al., 1965; Cohen et al., 1980). An upper limit to the annual HE could be obtained by multiplying by a quality factor of 20 which would yield 160 mSv (16 rem). Applying an effective weighting factor, WT, of 0.08 (see Table 2.4) yields an effective dose equivalent of about 13 mSv (1,300 mrem) for the average smoker. This wT is derived by weighting the dose to the bronchial epithelium and the pulmonary region as described in ICRP Publication 32 (ICRP, 1981). Whether such a value of W T is reasonable is a matter of considerable conjecture since only a small percentage of the bronchial epithelium is actually exposed to this dose. There is a question also whether a weighting factor derived on the basis of the deposition of airborne radon decay products is applicable to the bronchial deposition of 210Poand the particulates in tobacco smoke. However, even if this effective dose equivalent should be two orders of magnitude less (taking into account the small size of the area irradiated), tobacco products would still represent the largest contributor from the consumer product group. In view of the relatively high potential doses involved, more investigation of these matters would seem to be warranted. Regardless of our inability to calculate a meaningful effective dose equivalent from this source, there is widespread recognition that a high risk of lung cancer is associated with smoking. Indeed, studies indicate that smokers face a risk of fatal lung cancer of about 3 to 9 percent, while for non-smokers the risk is only about 0.5 percent (Boice and Blot, 1986). The risk associated with the upper limit value of an annual HE of 13 mSv (1.3 rem) estimated above would, in 50

5.3 SPECIAL CONSIDERATIONS

/

33

years, using a nominal risk coefficient of 2 x 10-~/Sv (2 x 10-4/rem) (Sinclair, 1984), amount to about one percent. It is obvious, therefore, that radiation contributes only a portion of the total risk of lung cancer to smokers, the larger portion of the risk presumably being due to the chemical or physical nature of tobacco products. The average effective dose equivalent estimates for all the remaining consumer products, with the exception of domestic water supplies, appear to be so far below the recommended limits of exposure for the general population that additional refinements in the data are not considered necessary at this time. As will be noted, however, domestic water supplies are estimated to contribute an annual average effective dose equivalent to the U.S. population in the range of 0.01 to 0.06 mSv (1 to 6 mrem). For this reason, it would appear that further analyses of this dose estimate would be justified.

6.4 Recommendations

As stated above, tobacco products probably contribute the highest dose to the U.S. population of all consumer products. Although no estimates have been made of the exposure resulting from so-called passive smoking, presumably the largest doses are those to the smokers. Of the remaining consumer products, those that represent the major sources of collective effective dose equivalent to the general population are domestic water supplies, building materials, mining and agricultural products, and the use of natural gas in heaters and cooking ranges. With regard to dose reduction, the NCRP believes the most important consideration is the level of exposure which results from a given consumer product source. The NCRP has defined a negligible individual risk level (NCRP, 1987b) which corresponds to a source producing no more than 0.01 mSv/y (1 mrem/y) to the exposed individual. Sources delivering lower doses can be dismissed from consideration. Reduction in the use of tobacco products would, of course, produce a significant reduction in dose to the exposed individual. As a result, the NCRP encourages and supports the many societal efforts already underway to limit and to reduce the use of cigarettes by the general population. Although domestic water supplies are not a major contributor to the total exposure of the U.S. population to indoor radon, they can be a significant source of exposure if their concentrations of radon are unusually high. In those cases, this source would appear to be worthy

34

1

5. RADIATION EXPOSURE

FROM CONSUMER PRODUCTS

of dose reduction techniques. Recommendations on the implementation of a variety of radon mitigation techniques are being developed in a report being prepared by NCRP Scientific Committee 82. Since building materials are a significant contributor of dose from consumer products, some thought might be given to actions that would reduce the contribution from this source. However, while it might seem that the use of construction materials containing low concentrations of naturally occurring radionuclides should be encouraged, the associated economic and logistic problems would probably prove to be over-riding. Much the same considerations would apply to the application of mitigative measures to mining and agricultural products. Much of the population dose equivalent due to the use of natural gas in heaters and cooking ranges is due to the associated radon gas. Techniques are available for properly venting such units and these techniques are generally effective in controlling the associated radon releases. For tungsten welding products, the exposures are primarily from external radiation and are limited to a small group of people not usually classified as radiation workers. The usual principles of radiation protection and ALARA should be applied to reduce the dose to the individuals involved. For the other sources cited in Table 5.1, no additional efforts at dose reduction appear to be warranted at the present time.

6. Public Radiation Exposure from Miscellaneous Environmental Sources 6.1 Introduction

Most environmental sources of exposure of the public are accounted for in the foregoing Sections. However, radiation exposures to the U.S. population due to air emissions from three categories of sources and from transportation of radioactive materials (except in the nuclear fuel cycle) were not accounted for earlier and will be examined in this Section. The declining doses resulting from fallout from nuclear weapons testing will also be examined here. The three air emission categories are (1) Department of Energy (DOE) facilities not accounted for earlier, (2) Nuclear Regulatory Commission (NRC) licensed and non-DOE federal facilities, excluding nuclear fuel cycle facilities, and (3) certain mineral extraction industry facilities. Emissions through the liquid release pathway are not examined but are known to be either small or inconsequential for these source categories. These categories were examined by the Environmental Protection Agency in order to determine whether national emission standards for hazardous air pollutants were needed. Experience related to the determination of the exposures from the sources in these categories is reviewed in two major references (EPA, 1984b, 1984-c).The NCRP has not previously reported on radiation exposures due to these source categories. The collective effective dose equivalent received by the U.S. population, as well as the corresponding average individual effective dose equivalent from the transportation of radioactive materials in the U.S. is also examined. These have been determined from data on the number of packages of radioactive materials transported by various modes (Javitz et al., 1985), and combined with data from an earlier Nuclear Regulatory Commission report (NRC, 1977) which estimates collective dose equivalents per unit of Transport Index (TI) and expected size of the population potentially exposed.

36

/

6. EXPOSURE FROM ENVIRONMENTAL SOURCES

6.2 Sources of Data

Most of the results for air emissions from the facilities considered in this Section were obtained by combining measured radioactive emissions data with the characteristics of a reference facility and receptor locations, and calculating dispersion, deposition, and dose data for individuals and population groups typical of the reference facilities. These methods and the input data are described in detail in the references cited. For the transportation doses, a Sandia report (Javitz et d.,1985) provides estimates of the quantity of radioactive materials transported. This was combined with additional information obtained from the NRC and Agreement States and from DOE sampling of licensee sites and other facilities. The data from the sampling are given as the Transport Index (TI), which is either the highest measured dose equivalent rate at 1 meter from the external surface of the package or a number assigned for criticality control purposes. From this information, total TI can be estimated, and using the NRC models for conversions to dose, individual and population effective dose equivalents can be estimated.

6.3 Special Considerations While the dose estimates provided for these source categories are not measured, and are not calculated for every emitting facility and transport situation of concern, it should be noted that most of the calculations have been made on a relatively conservative basis, as explained in the referenced documents. However, a large uncertainty still exists in the application of environmental models to these situations, possibly of the order of one, or even two, orders of magnitude depending on circumstances. These sources may require more complete evaluation in the future.

6.4 Estimates and Discussion

The doses due to air emissions from typical facilities in the three categories listed above are given in Table 6.1. Listed in the Table are the organs of importance for each source, the annual average dose equivalent to those organs and the annual collective effective dose equivalent obtained by using the ICRP weighting factors (see Glossary). In the EPA reports (EPA, 1984a, 1984b), uncertainties are discussed at considerable length, and the EPA estimated an overall

/

6.4 ESTIMATES AND DISCUSSION

37

TABLE6.1-Effective dose equivalents to nearby individuals and to regional populrrhbns from air emissions

Facility

Number Of

pel.fJ'Jns

exposed

Organ or tissue'

effective dose

wluivalent

to nearby

individuals (''SV)~ DOE facilities Oak Ridge reservation Savannah River plant

4,200 24,000

Lung Thyroid

NRC licensed facilities and non-DOE federal facilities 340,000 Average all Research and test reactors organs Accelerator" 6,000 Average all organs Radiopharmaceutical 30,000 Thyroid suppliers AFRRIf 400 Average all organs U.S. Army facilities (two 6,000 Spleen reactors) U.S. Navy facilities 4,000 Average all (nine shipyards) organs 40,000 Average all Radiation source manufacturers organs Mineral extraction industry Aluminum reduction plants Copper smelters Zinc smelters Lead smelters

3,400

4,800 125,000 14,000

Kidney Lung Bone surface Lung

500d 50

Annual

collective

effective dose equivalent (person-Svy

0.21 0.04 0.25

10 0.001 3 0.05 0.3 0.2 2

12 2 0.2 50

0.002 0.001 0.007 0.08 0.1

Rounded total

4.0

"Organ with highest annual dose. 1 P S =~ 0.1 mrem. 1 person-Sv = 100 person-rem. *Recent surveys indicate much smaller values (ORNL, 1986). '6 MeV Van de Graaff. 'Armed Forces Radiobiology Research Institute.

uncertainty of about a factor of ten, but in some circumstances this could be larger, as noted above. Redundancies with other parts of this report have been eliminated as far as possible. While not all facilities are included here, those with the greatest impact are, and given the small overall contribution to the collective dose from these sources, omissions are probably unimportant.

/

38

6. EXPOSURE FROM ENVIRONMENTAL SOURCES

The contribution to the annual collective effective dose equivaIent received by the U.S. population from these air emission sources is about 4 person-Sv (400 person-rem). The transportation doses are derived from estimates of the number of packages carried, the average TI per package and the collective effective dose equivalent per TI given in Table 6.2. The total annual collective effective dose equivalent is 160 person-Sv (16,000 personrem). Uncertainties in these results were not discussed in the original references but estimates are almost certainly conservative. The estimates of Table 6.2 include shipments relating to the nuclear fuel cycle. Some doses from transportation were also included in Section 4, and may amount (derivable from Table 4.3) to about 13 person-Sv (1,300 person-rem). Since the extent of the overlap in the two estimates is not clear, the estimate given here has not been reduced by that amount. The total, 160 person-Sv (16,000 person-rem), is believed to result from the exposure of about 25 million people, for whom the average annual effective dose equivalent is, therefore, about 0.006 mSv (0.6 mrem). This makes a contribution of about 0.0006 mSv (0.06 mrem) to the average effective dose equivalent of the U.S. population. It is noteworthy that these estimates are for 1983, and that in 1975, the corresponding figure was less than 100 person-Sv (10,000 personrem), and for 1985, it had risen to about 250 person-Sv (25,000 personrem). Thus, this may be a source of exposure that is worthy of continuing attention.

TABLE 6.2-Annual collective effective dose equwa!ents for U.S. transportation of radtoactiue materials in the U.S. (1983)" Transportation mode

Aii Highway

Rail Other unspecified Rounded total

Number of packages

604,000 2,190,000 6,900 14,400

$ : ; package

0.34 0.70 0.74 0.24

Tl's carried

202,000 1,530,000 5,100 34,400

Average annual collective

(~erson-Sv/TIY

Annual cOuective effective dose equivalent (,,erson-~v)=

0.000081 0.000089 0.000018 0.00M)2

16 140 0.1 0.7

160

'Javitz et al. (1985),NRC (1977). TI = Transport index, defined as the highest radiation dose rate (in mrem/h) at 3 f t from any external aurface of the package. 'Iperson-Sv = 100 person-rem.

6.5 FALLOUT FROM NUCLEAR WEAPONS TESTING

/

39

6.6 Fallout from Nuclear Weapons Testing Another miscellaneous environmental source of exposure of the public is fallout from nuclear weapons tests. The radiation dose from atmospheric nuclear weapons testing is delivered over a period of years at changing dose rates, depending on factors such as the time since the tests occurred and the nature of the fallout field. For this reason, the UNSCEAR developed the dose commitment concept as the best means of expressing possible detriment from this type of source. Dose commitment is the dose that could ultimately be delivered from a given intake of radionuclide. It may also be used as a commitment over a defined period. Accurate estimation of the total annual dose from fallout is not possible, since the necessary measurements were never made. The dose commitment is estimated by use of a series of approximations and simplistic models that are subject to many uncertainties. They are probably adequate, however, for the rather small doses delivered on a global basis (UNSCEAR, 1982). In the revision of NCRP Report No. 45 (NCRP, 1975), fallout is discussed in an Appendix (NCRP, 1987~).There has been no atmospheric nuclear testing since 1980. The estimates have changed little since 1975, partly because there are no longer many measurements being made. Many of the radionuclides have decayed significantly. The mean dose commitment estimated in the revision of Report No. 45 is shown in Table 6.3 and it should be noted at once that only a few percent of these doses (except for 14C) are yet to be received. A T ~ L6.3-Mean E dose equivalent commitments to the year 2000 in the United States from nuclear testing through 1970' Dose equivalent Source commitment ( ~ S V ) ~

External Whole body Internal 'OSr marrow endosteal 13'Cs, whole body 239.uaP" lung bone 'H,whole body "C. whole bodv

"Most of this dose has already been received, see text. 1p S = ~ 0.1 mrem. 'This is the dose commitment to the year 2000. The total dose commitment, to be delivered over many generations, is 1.4 mSv (140 mrem).

40

/

6. EXPOSURE FROM ENVIRONMENTAL SOURCES

subjective estimate of the dose still to be delivered is about 0.1 mSv (10 mrem) to the whole body from external radiation, perhaps the same from the internal deposition of "Sr in bone, and very little from internally deposited 13'Cs, inhaled Pu, and from tritium. That leaves over 1 mSv (100 mrem) to the whole body from I4C which will be delivered at a decreasing rate over the next few thousand years. None of these doses, even when combined, gives rise to an effective dose equivalent to an exposed individual of as much as 0.01 mSv/y (1 mrem/y) now. Consequently, fallout is no longer a significant source of exposure of the public. The UNSCEAR (1982) calculated the effective dose equivalent commitment (in this case, the effective dose equivalent delivered in a defined time) for the northern hemisphere. They determined a total commitment of 4.5 mSv (450 mrem), with 2.1 mSv (210 mrem) delivered from the start of testing up to the year 2000.

6.6 Recommendations

For the sources other than fallout considered in this Section, the total annual collective effective dose equivalent is approximately 160 person-Sv (16,000 person-rem) (Table 6.2). There are no examples of relatively high doses in the results given here, and all of the facilities involved are under continuous observation and control. Therefore, no recommendation to initiate dose reduction efforts for these sources appears to be warranted, and no research needs have been identified in this review. In the case of fallout from nuclear weapons testing, while there still remains an effective dose equivalent commitment from long-lived sources, the annual effective dose equivalent is less than 0.01 mSv (1 mrem) and will continue to decline assuming no resumption of testing which releases radioactivity to the atmosphere. Consequently, it is no longer necessary to include this source in estimating the total exposure of the U.S. population.

Public Radiation Exposure from Medical Diagnosis and Therapy 7.1 Introduction The use of radiation in medicine and dentistry has been recognized in earlier reports (Moeller et al., 1953; DHEW, 1979; NAS-NRC, 1980) as an important source of radiation exposure to the U.S. population. Radiation is one of the principal tools of diagnostic medicine and of cancer treatment. Thus, the exposure of patients is deliberate and the motivation for medical and dental use is to benefit directly the individuals exposed. X rays were first used in medical practice, especially in orthopedics, shortly after their discovery by Roentgen in 1895. Many early x-ray generators, including the portable generators used in World War I, were not well shielded, and some of these exposed their operators to considerable radiation. X rays were very quickly adapted to hospital practice and considerable experience and literature developed; for example, with radiographic examinations of the chest and abdomen and films of the long bones, skull and spine. The fluoroscope made it possible to assess the severity of valvular heart disease and respiratory dynamics. The introduction of barium salts as contrast agents allowed radiologists to examine the activity of the gastrointestinal tract and to infer lesions on its inner surfaces. Iodinated contrast agents permitted the study of gall bladder and kidney function, the anatomy of the spinal canal, and, ultimately, the patency of blood vessels leading to and from various organs. There has been an impressive progression in the technology of diagnostic imaging; some aimed at or resulting in dose reduction (e.g., image intensifiers, faster film-screen combinations), some to obtain more and better diagnostic information (e.g., digital subtraction methods, computed x-ray tomography, ultrasound, nuclear magnetic resonance imaging). In the case of ultrasound and magnetic resonance imaging, no ionizing radiation is involved. After World War 11, the general availability of artificially produced radionuclides encouraged their use in medicine. Starting with radioi41

42

/

7. EXPOSURE

FROM MEDICAL DIAGNOSIS AND THERAPY

odine in the study of thyroid function, agents and instruments were developed to examine kidneys, lungs, brain, liver and bones. Nuclear medicine procedures are presently important in the study of heart disease and biliary function as well. The dosimetry of administered radionuclides has been closely examined, particularly by the Medical Internal Radiation Dose (MIRD) Committee of the Society of Nuclear Medicine (Loevinger et al., 1987) and in documents such as NCRP Reports No. 70 and No. 73 (NCRP, 1981, 1983) and ICRU Report 32 (ICRU, 1979). Longer-lived radionuclides with highly absorbed particulate radiations (e.g., iodine-131, gold-198, mercury-203) have been replaced by shorter-lived radionuclides with little particulate radiation (technetium-99m, iodine-123). More photons are available for diagnostic purposes with these because larger activities, delivering the same or lower doses to tissues, can be administered. Lastly, radiation has long been used for medical treatments. X rays were used at the turn of the century for treatment of breast cancer and, not long after the isolation of radium by the Curies working in Becquerel's laboratory, 226Rawas employed in treating cancer of the uterine cervix. External-beam therapy began with high intensity xray machines. Nuclear and high-voltage accelerator technology has enabled the development of devices capable of delivering high doses to specific body sites with much less dose to surrounding normal tissues. Until 1958, most radiation protection groups were interested primarily in exposures relevant to the risk of hereditary effects and calculated a genetically significant dose (GSD). The major contribution to the GSD is from relatively few medical procedures (see Section 7.4). Recently, interest has shifted to estimating the doses to other tissues, particularly those regarded as more susceptible to the induction of cancer (e-g.,bone marrow, breast, thyroid). In the following parts of this Section, emphasis will be placed on estimates of the effective dose equivalents (HE)calculated for various procedures, the number of procedures performed each year, and the importance of knowing the distribution of ages in the exposed populations.

7.2 Sources of Data for Diagnosis

The available data on dosimetry and usage in diagnostic radiology and nuclear medicine are reviewed extensively in a forthcoming NCRP Report (NCRP, 1987f). For its estimates of diagnostic x-ray exposures,

7.2 SOURCES OF DATA FOR DIAGNOSIS

/

43

the Report drew upon the large medical literature, but especially upon the sources described below. A. Extensive x-ray exposure studies were carried out by the Food and Drug Administration (FDA, 1966, 1973, 1976). In 1964 and 1970, the U.S. Public Health Service surveyed x-ray exposures of the entire U.S. population. These surveys provided information on the frequency of diagnostic and therapeutic medical and dental x-ray procedures, the amount of x-ray exposure, technical machine parameters, age of patients receiving examinations or treatment, and their anthropometric characteristics. Nuclear medicine procedures were not included. B. Comprehensive data on diagnostic imaging procedures were collected by J. Lloyd Johnson Associates in 1973, 1979, 1980 and published in 1983 (Johnson and Abernathy, 1983). These were stratified, random-sample and facility (not population)-based surveys conducted by mail questionnaire. C. In 1980 and 1981, the Bureau of Radiological Health (now the Center for Devices and Radiological Health) conducted a hospital-based survey of radiological procedures (FDA, 1985). Information on the age and sex of patients as well as the types of procedure was collected. In 1982, a larger number of hospitals was surveyed by mail, but no demographic data were collected. D. A study carried out in cooperation with 40 state radiation health programs, including exposure data from hospitals and outpatient facilities, has been published (Johnson and Goetz, 1986). Based upon data accumulated in 1973 and 1981, the study provides information for seven common diagnostic procedures. In addition to these large surveys, data on the number of operational diagnostic x-ray machines were supplied by individual state radiation control programs and compiled by the U.S. Food and Drug Adrninistration. Information on the sale of x-ray film was also available, as well as information on chiropractic and podiatric practices. Because it takes a long time to gather and process such data, useful information for very recent times is not available. Recently, in preparation for the evaluation of collective dose to the British population from medical exposures, the National Radiological Protection Board (U.K.) has published tabular data on doses to individual organs for certain types of x-ray examinations (Shrimpton et al., 1986). For nuclear medicine exposures, information is available from several sources. A. The American College of Radiology performed regional surveys in 1972,1973 and 1975 (ACR, 1975, 1982).

44

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7. EXPOSURE FROM MEDICAL DIAGNOSIS AND THERAPY

B. The Food and Drug Administration collected data from 26 hospitals for 12 months during 1977-1978. C. J. Lloyd Johnson Associates collected additional material in 1980 (Johnson and Abernathy, 1983). D. In 1980, 1981 and 1982, the Bureau of Radiological Health conducted a hospital-based survey (FDA, 1985) and reported a relative standard error of 2.6 percent in estimating the number of nuclear medicine procedures. It is believed that hospital-based data are a sufficient estimator of general nuclear medicine practice since more than 99 percent of all nuclear medicine procedures are performed in hospitals.

7.3 Special Considerations

In general, medical exposures from diagnostic or therapeutic x rays result from radiation beams directed to specific areas of the body, so that not all organs are uniformly irradiated, and many are not within the field of irradiation. In the case of nuclear medicine examinations, the distribution of radionuclides throughout the body is quite heterogeneous, and the agents are deliberately chosen to concentrate in particular organs. For these reasons, the concept of effective dose equivalent is particularly useful when describing doses from medical exposures. The dose rates from medical exposures are considerably higher and, generally, less protracted than those from environmental or routine occupational sources. For external-beam exposures, doses are delivered intermittently and at a relatively high dose-rate. For radionuclides, while the doses are delivered at relatively lower rates and extend over longer periods of time than for external beams, these exposures generally last for a shorter time than environmental exposures. TABLE 7.1-Distribution of x-ray and nuclear medicine exnminatiom among various age groups in the U.S.population in I980 Percent of age group receiving Age range

Percent of U.S. population in w e group

X-Ray

examinations (Mettler, 1987)

Nuclear medicine examinations (Mettler et d, 1982)

7.3 SPECIAL CONSIDERATIONS

/

45

The population exposed to medical radiation has a different demographic composition than that exposed to environmental or occupational sources. In addition to suffering from some form of illness, the members are usually older. Hence, any estimate of the radiation detriment to the entire U.S. population should include an age and possibly a sex correction factor, see Table 7.1 (NCRP, 1987~;Mettler et al., 1986).

7.4

Estimates and Discussion

The number of examinations for the year 1980, the effective dose equivalent per examination, and the collective effective dose equivalents from certain diagnostic medical procedures are given in Table 7.2. The entries in Table 7.2 are taken from the forthcoming NCRP Report treating this subject (1987f).The values of HE for the specified TABLE7.2-CoUectiue

Examination

effective dose equwalent for the U.S.in 1980 from diagnostic medical x-ray examinations Average Annual effective collective Annual dose effective number of equivalent examinations dose 9er (in thousands) examination equivalene (person-Sv)' (PSV)~

Computed tomography (head and body) Chest Skull and other head and neck Cervical spine Biliary tract Lumbar spine Upper gastrointestinal tract Kidney, ureters, bladder Barium enema Intravenous pyelogram Pelvis and hip Extremities OtheP Rounded total "Numbers obtained from product of two previous columns but using unrounded @a. 1 /lSv = 0.1 mrem. 1person-Sv = 100 person-rem. Estimated from the average of all examinations.

46

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7 . EXPOSURE FROM MEDICAL DIAGNOSIS AND THERAPY

examinations are calculated from tables of absorbed doses to organs (Rosenstein, 1976) and the ICRP weighting factors. For the examinations denominated as "Other" (including thoracic spine, full spine, mammography, etc.), the HE was estimated from the mean value of the specified procedures. The greatest contributors to the collective effective dose equivalent are lumbar spine, upper gastrointestinal and barium enema examinations; these three procedures provide more than 50 percent of the total collective effective dose equivalent. Dental examinations have been omitted since they are estimated to contribute less than 0.01 mSv (1mrem) to the total average annual effective dose equivalent (see Wall and Kendall, 1983). The collective effective dose equivalents from nuclear medical procedures are given in Table 7.3. The numbers of testa performed annually are from Mettler et al. (1985). The greatest contributors to the collective effective dose equivalent are bone, cardiovascular and brain examinations which contribute about 60 percent of the total effective dose equivalent. Effective dose equivalents from diagnostic medical exposures are summarized in Table 7.4 (NCRP, 1987f). Dose equivalents to the gonads and the bone marrow are given in Table 7.5 (NCRP, 1987f). The GSDs derived from the gonad doses have been estimated for diagnostic x rays to be 40 to 100 jtSv (4 to 10 mrem) for males and 180 to 200 CISv(18 to 20 mrem) for females, totalling 220 to 300 WSV TABLE 7.3-Collective effective dose equivalent from diagnostic nuclear medicine tests in the U.S. in 1982

Examination

Brain Hepatobiliary Liver Bone Lung Thyroid Kidney Tumor Cardiovascular Rounded total

Annual number of examinations (thousands)

810 180 1,400 1,800 1,200 680 240 120 950 7,400

Average effective dose equivalent

98'

exammation (PSV)~

6,500 3,700 2,400 4,400 1,500 5,900 3,100 12,000 7,100 4,300

Average annual collective effective dose equivalentm (person-Svr

5,300 700 3,400 8,000 1,800 4,000 700 1,500

6,700 32,000

'Number obtained from product of previous two columns but using unrounded figures. 1 FSV = 0.1 mrem. ' 1 person-Sv = 100 person-rem.

7.4 ESTIMATES AND DISCUSSION

47

/

(22 to 30 mrem). For nuclear medicine, the GSD has been estimated to be about 20 ~ S (2Vmrem) (NCRP,1987f). As would be expected, the greatest contributors to the genetically significant dose are diagnostic x-ray examinations. During the decade 1970-1980, the GSD has increased, reflecting an increase in the total number of x-ray examinations (Table 7.6). The recorded annual GSD of 220 to 300 pSv (22 to 30 mrem) is probably an overestimate because TABLE 7.4-Annual

effectiue dose equivalents from aU medical exurninations in the

Annual collective effective dose equivalent (wrson-Sv)'

Modality

U.S.

Average annual effective dose equivalent in the U.S. population (rSvIb

Diagnostic x-rays (1980) Nuclear medicine (1982)

'1 person-Sv = 100 person-rem. 1 ~ S=V0.1 nmm.

TABLE 7.5-Annual dose equivalent to gonads and bone marrow from medical emminations in the U.S. Modality and target tissue

Diagnostic x-rays Gonads Bone marrow Nuclear medicine Gonads Bone marrow

Annual collective dose equivalent (oerson-Sv)'

Average annual dose equivalent (ILSV)~

50,000-70,000 160,000-250,000

750-1,100 140

4,400 32.000

'1 person-Sv = 100 person-rem. 1 &V

= 0.1 mrem.

TABLE 7.6-Estimated

Medical Dental Total Frequency

medical and dental x-ray procedures in the United States Number of examinntiom (in thousands)

total diagnostic

lO9,ooO

Woo 163,000

136,000 67,OOO 203,000

180.000 101,000 281,000

Frequency per 1,000 population 870 990 1,240

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7. EXPOSURE FROM MEDICAL DIAGNOSIS AND THERAPY

no account has been taken of gonadal shielding. The greatest contributors to the GSD are x-ray examinations of the hips and pelvis of men, and of the lumbar spine and lower gastrointestinal tract of women; these three examinations account for more than 50 percent of the dose. The annual GSD for most developed countries is reported in the range of 0.2 to 0.3 mSv (20 to 30 mrem). The average annual bone-marrow dose equivalent from diagnostic x rays is estimated as 0.75 to 1.1 mSv (75 to 110 mrem) (NCRP, 1987f). The lower figure is calculated by Monte Carlo methods and is probably more reliable. Older calculational methods yield the higher value. It was not possible to provide data on the actual number of persons exposed in medical procedures (and hence the average annual effective dose equivalent to those exposed) because frequency data are provided for the number of films utilized and the number of procedures performed, but not on the average number of x-ray examinations performed per person exposed. There is considerable uncertainty in estimating the radiation dose to the population exposed to diagnostic x-ray procedures. First, absorbed doses for a given procedure vary among institutions due to differences in equipment, type of film used, number and size of views, and other variables. Second, the absorbed doses for the same procedure in the-same institution vary among patients due to differences in body size and type. Third, several approaches need to be used in estimating the total number of procedures performed: sample surveys, film utilization rates, etc. Fourth, the practice of diagnostic radiology is undergoing a revolutionary change which derives from the introduction of new technologies: computed tomography (CT), ultrasound, digital methods including subtraction, and nuclear magnetic resonance imaging. Some of these methods substitute a different dose distribution of ionizing radiation for techniques that they displace; others deliver no ionizing radiation at all. In some instances, the new procedures are replacing older ones; in others, they add a new dimension to the diagnostic process. The estimated average annual effective dose equivalent from diagnostic x rays to the U.S. population is 0.39 mSv (39 mrem). This is a calculated value which does not include allowance for age distribution such as suggested by Beninson and Sowby (1985). If such allowance is made, the value of the new "weighted dose" is reduced by about 40 percent to about 0.25 mSv (25 mrem) (Beninson and Sowby, 1985). [In the case of nuclear medicine the comparable reduction would be about 60 percent (NCRP, 1987f).] On the other hand, there are reasons discussed in the forthcoming NCRP Report (NCRP 19870 which

7.6 RECOMMENDATIONS

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49

indicate that 0.39 mSv (39 mrem) for diagnostic x rays is an underestimate and that the true average annual effective dose equivalent may be as high as about 0.55 mSv (55 mrem). Thus, the range about the 0.39 mSv (39 mrem) value may be from about 0.25 to 0.55 mSv (25 to about 55 mrem). This range is not out of line with reports from other countries, although different authors do not always utilize all the same elements in the calculations. For France (1982), a value of 0.4 mSv (40 mrem) has been reported; for Japan (1979), 1.3 mSv (130 mrem); for the U.K. (1977), 0.3 mSv (30 mrem); and for the U.S.S.R. (19801981), 1.5 mSv (150 mrem) (NCRP, 19870.

7.5 Recommendations

In medical imaging, minimization of exposure is limited by the number of photons required to obtain optimal diagnostic information. Often, absorbed dose has to be increased in order to improve diagnostic quality. While there is the possibility of dose reduction without decreasing associated benefits, substantial dose reduction for a specific examination is generally not possible without technological advances. Modest dose reduction, however, is possible with adherence to good radiological or nuclear medicine practice and the use of state-of-theart equipment and materials. Such procedures as the introduction of quality assurance programs, the use of rare earth screens in radiography, changing from photofluorography to chest radiography, and the use of CT tomograms for pelvimetry can lead to dose reduction. Similarly, the exclusion of the eyes from the primary beam in CT examinations can be very helpful in avoiding nonstochastic effects in the eye (NCRP, 19870. In addition, some steps should yield immediate results. First, gonadal shielding should be more widely employed; this would significantly reduce the male contribution to the GSD. Second, the use of iodine-131 for diagnostic nuclear medicine studies should be limited and iodine-123 or technetium-99m used in its place; both of these measures have already been implemented, a t least in part. Some studies should be directed at the possibilities of dose reduction via the substitution of newer modalities for older ones, if it is known that the result is a net reduction in risk. For example, considerable reduction in GSD would be achieved if magnetic resonance imaging could be substituted, in the long run, for x-ray examinations of the lumbar spine (in much the same way that ultrasound has reduced fetal dose by substituting for x-ray pelvimetry and radionuclide placentography).

50

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7. EXPOSURE FROM MEDICAL DIAGNOSIS AND

THERAPY

Other efforts should be directed to reducing the number of fdms and procedures without compromising the informational requirements. Cost-containment practices have led to the development of algorithms and other devices for obtaining an optimal number and sequence of examinations for a particular clinical task (McNeil and Abrams, 1986). If changes occur with regard to malpractice litigation, it is possible that some x rays taken principally for defensive medicolegal reasons would also be eliminated.

7.6 Radiation Therapy

The highest individual doses are provided by radiation therapy and are specified by prescription. Careful treatment planning can minimize the radiation doses to tissues away from the target region, but there are limits to what may be achieved and still deliver tumoricidal doses. As a result, second cancers are a complication of radiation therapy but currently must be seen as costs, in the same patient, for benefits gained. Doses in the treatment field are generally so high as to sterilize the tissue with a consequent reduction in carcinogenic risk as compared with more moderate doses (Boice et al., 1985). On the other hand, nonstochastic effects due to vascular and other tissue damage are not uncommon, especially to lung, kidneys and gastrointestinal tract. There are few reliable surveys of therapeutic practice with regard to the doses to tissues outside the treatment fields (Boice et ul., 1985). Moreover, the life-expectancy and age of therapy patients differs from those undergoing diagnostic procedures so that the demographics of the patient population are of considerable importance. The situation with regard to the use of the effective dose equivalent may be even more unsatisfactory. First, few data are available with regard to dose distribution outside the target volume. Second, above a few gray (ie.,a few hundreds of rads), the concept of effective dose equivalent as an indicator of risk may no longer be reasonable, considering that thresholds for nonstochastic effects, Le., nonmalignant tissue damage, may be exceeded. These facts plus the uncertainties in life expectancy have made this a formidable problem, which will be addressed in a separate future NCRP study of radiation received due to therapeutic radiation procedures. For the present, the UNSCEAR (1982) estimates the average effective dose equivalent in the whole population to be 7 &v (0.7 mrem)

7.6 RADIATION THERAPY

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51

for Europe and, from an older U.S. study (Terpilak et al., 1971), 23 pSv (2.3 mrem) for this country. From the absorbed doses per organ outside of the field per unit of exposure given by the UNSCEAR (1982) and from estimates of the frequency of these treatments in the US., it seems likely that the individual annual effective dose equivalent is below 0.01 mSv (1 mrem) for the U.S. population.

8. Summary and Conclusions 8.1 Introduction Radiation exposure of members of the U.S. population can result from radiation that is natural in origin, sometimes enhanced by man for useful or incidental purposes, and from man-made sources. However, the most convenient categorization of source exposure is by specific origin as indicated by the sectional organization of this Report. The categories treated include exposures of the public from natural radiation, occupational practices, the nuclear fuel cycle, consumer products, miscellaneous environmental sources, and medical diagnosis and therapy.

8.2 The Exposure of the U.S. Population to all Sources

The number of people exposed to these sources, the effective dose equivalent to those exposed, the effective collective dose equivalent and the average effective dose equivalent (HE)in the U.S. population are given in Table 8.1. The contributions to the GSD are listed separately in Table 8.2. These are for various years within the period 1977-1984, with most of the data being for 1980-1982. The average annual effective dose equivalent from all sources in the entire U.S. population is obtained by summing the annual collective effective dose equivalents and dividing by 230,000,000 taken as the U.S. population in 1980. The result is approximately 3.6 mSv (360 mrem) annually for all people in the U.S. from all sources, exclusive of tobacco products, i.e., about 0.01 mSv/day (1 mrem/day). For the 50,000,000 smokers, there is an additional exposure to the lungs from the naturally occurring radionuclides in tobacco products. The effective dose equivalent from this source is difficult to estimate and may not be meaningful. A small segment of the bronchial epithelium appears to receive about 0.16 Sv/y (16 rem/y) on the average and this is probably dependent on the number of cigarettes smoked (for further discussion see Section 5.3 and NCRP, 1987e). The GSD (Table 8.2) is about 1.3 mSv/y (130 mrem/y) from all sources, including a small contribution from consumer products which irradiate the whole body.

8.3 THE MOST SIGNIFICANT EXPOSURES

TABLE 8.1-And

Source

Natural sources Radon Otherd Occupational Nuclear fuel cycle Consumer products Tobaccog Other Miscellaneous envimnmental sourxes Medical Diagnostic x rays Nuclear medicine Rounded total

1

53

effech'uedose eouiuaknt in the U.S. population circa 1980-82 Average Annual Average Number of annual HB. collective annual Hea people effedivedose in the U.S. exposed population (thousands) population (person-Sv)' (mSvIb (~SV)~

230,000 230,000 930"

-f

50,000 120,000 -25,000 -h

-i

230,000 " H Eis the effective dose equivalent.

2.0 1.0 2.3

-

0.05-0.3

0.006 -

-

460,000 230,000 2,000 136

2.0 1.0 0.009 0.0005

-

12,000-29,000 0.05-0.13 160 0.0006

91,000 32,000 835,000

0.39 0.14 3.6

1 mSv = 100 mrem. 1 person-Sv = 100 person-rem. See Table 2.4. " Those nominally exposed total 1.68 x lo6. 'Collective doses were calculated to the regional population within 80 km (50miles) of each facility. gEffective dose equivalent difficult to determine; dose to a segment of bronchial epithelium estimated to be 0.16 Sv/y (16rem/y), see Section 5.3. Number of persons exposed is not known. Number of examinations was 180 million and HEper examination 500 pSv. Number of persons exposed is not known. Number of examinations was 7.4 million and HE per examination 4,300 pSv.

"

'

8.3 The Most Significant Exposures The data of Table 8.1 indicate that natural sources make the greatest contribution to the average annual effective dose equivalent for members of the U.S. population. Among these natural sources, radon and radon decay products indoors are the largest contributors to the average annual effective dose equivalent, and they make a small contribution to the annual GSD. The estimates for the exposure resulting from radon and its decay products are higher than those presented in NCRP Report No. 45 which was issued in 1975. The increase in the dose equivalent to the bronchial epithelium, 4.5 mSv (450 mrem) to 24 mSv (2,400 mrem), is due to two principal factors, the use of a higher quality factor for alpha

54

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8. SUMMARY AND CONCLUSIONS

TABLE8.2-Annwl GSD in the U.S. ~ o ~ u h t w circa n 1980-82 Contributions to GSD Source (mSv)' Natural sources Radon Other Occupational Nuclear fuel cycle Consumer products Tobacco Other Miscellaneous environmental sources Medical Diagnostic x rays Nuclear medicine -Rounded total

O.lb 0.9' -0.006 <0.0005 -

-0.05 <0.001 0.2-0.3 - 0.02 -1.3

" 1 mSv = 100 mrem. See Table 2.2. 'See Table 2.3.

particle radiation, and higher estimates of radon levels indoors as compared with outdoors. The use of the effective dose equivalent enables the exposure from radon and its decay products to be combined with exposures from other sources irradiating the whole body.2 These latter sources, cosmic radiation, cosmogenic radionuclides, and terrestrial gamma radiation, result in exposures little changed from those given in 1975. Among man-made or enhanced sources, medical exposures contribute the largest exposure. These exposures are different in character however, from inadvertent exposures, in that they contribute to the benefit of the specific individual receiving them. Other people are affected only through the GSD to the population. Furthermore, medical exposures as a source appear to be smaller than formerly estimated. This is mainly due to the method of dose calculation utilizing the effective dose equivalent which accounts for the fact that many medical exposures are only to part of the body. When age and sex are taken into account also, the new quantity, the "weighted dose," is even smaller than the effective dose equivalent (Beninson and Sowby, 1985). On the other hand, the bone marrow dose equivalents given in Table 7.5 are in a range similar to those of earlier studies (DHEW, 'However, it should be noted (see Table 2.4, Footnote c) that conversion factors from a particle concentration to effective dose equivalent are subject to considerable uncertainty.

8.4 SPECIAL CONSIDERATIONS

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55

1979; NAS-NRC, 1980), about 1 mSv (100 mrem) annually. These bone marrow doses are relevant primarily to the possible induction of leukemia. For all cancers, the more relevant quantity is the effective dose equivalent. For all medical procedures, the effective dose equivalent amounts to only about 0.5 mSv (50 mrem) (Table 7.4) or about 15percent of the present exposure of the nonsmoking population from all radiation sources. The contribution to the population dose from most of the other sources, including nuclear power and consumer products (with the possible exception of tobacco), are minor. For illustrative purposes, the percentage contributions of the various radiation sources described here to the total average effective dose equivalent to members of the U.S. population are represented in Figure 8.1.

8.4

Special Considerations

The data in the summary Table 8.1 are subject to various uncertainties which are noted in the individual sections of this Report. These are stated in several cases to be of the order of a factor of two or three.

-

OTHER <1%

Fuel Cycle Miscellaneous

Fig. 8.1. The percentage contribution of various radiation sources to the total average effective dose equivalent in the U.S. population.

56

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8. SUMMARY AND CONCLUSIONS

For some of the better documented external radiation exposures, such as cosmic and terrestrial radiation in given locations, the uncertainties are much less. On the other hand, for exposures from some consumer products the uncertainties are greater. For the most important exposure, namely that of the lungs to radon and its decay products, many uncertainties exist. These include our limited knowledge of both the average and the distribution of radon concentrations indoors in the United States, and problems concerned with the dosimetry of alpha particles in the lungs and the assessment of an actual effective dose equivalent from this source. In the case of smokers, additional uncertainties arise because of the small region of bronchial epithelium exposed to a relatively high dose and the difficulty of assigning a meaningful weighting factor to obtain an effective dose equivalent. The exposure circumstances resulting from smoking tobacco should continue to be the subject of further examination. The use of the effective dose equivalent has made it possible to combine the exposures from the several different source categories and thus to determine an average annual effective dose equivalent in the U.S. population, which, presumably, has some meaning with respect to the overall somatic risk. Similarly, the GSD enables estimates from different sources to be combined into an average GSD that presumably has some meaning for overall genetic risk. However, additional uncertainties are introduced with these combinations. For example, the weighting factors used for effective dose equivalent were specified by ICRP in 1977 on the basis of the relative risks between different organs. It is possible that at least slightly different weighting factors would be chosen today. Another difficulty arises in combining data from the different sources. The data are not all for the same years. The occupational exposures are mainly, but not entirely, for the year 1980 as noted in Section 3. The medical exposures from diagnostic x rays are for the year 1980, while those for nuclear medicine are for 1982. Transportation data included in miscellaneous environmental sources are for the year 1983. Exposures from sources such as consumer products and natural radiation have been assessed over a period of years while the nuclear fuel cycle estimates are for the early 1980's. These, among other factors, render very difficult the definition of an accurate average exposure for members of the U.S. population in any given year and thus the observation of precise trends from year to year. Nevertheless, it seems that a firmer base for these exposures is beginning to be established. Thus, if a similar survey were to be done, for example, in about ten years, it should be possible to establish general, if not precise, trends.

8.5 RECOMMENDATIONS

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57

8.5 Recommendations 8.5.1

Recommendations for Dose Reduction

Natural background is the largest contributor to the average effective dose equivalent to individuals in the U.S. population. Its components include external cosmic and terrestrial radiation, radionuclides in the body, and inhaled radon and its decay products. External cosmic radiation varies to some degree with altitude but is otherwise essentially constant over the United States. External terrestrial radiation varies little over the surface of the United States in normal (undisturbed) circumstances. Radionuclides in the body (other than radon), mainly *K, are essentially constant. None of these three is amenable to dose reduction in any obvious and simple way. Radon as a source is not only the largest component of natural background, it is also the most variable. It may be responsible for a substantial number of lung cancer deaths annually (NCRP, 1984b), but its actual concentration indoors is still not well known in all parts of the country. Consequently, NCRP Reports No. 77 and No. 78 (NCRP, 1984a, 198413) recommended actions relative to the control of indoor radon sources. These actions included conducting a nationwide survey of radon levels, the recommendation of remedial action levels (NCRP, 1984a), and the introduction of mitigation techniques to reduce radon levels indoors (NCRP, 1987g). The radon problem is now receiving significant attention nationally and we can hope that, as a result of these activities, the true extent of the problem will become better known and the higher indoor levels reduced. This should result in a reduction in overall population exposure from this source in the course of time. Among the man-made sources, the most important is the use of x rays and radionuclides for medical diagnosis. In recent years, this has become well known and techniques for dose reduction are widely recommended (see Section 7.5). The NCRP supports these efforts strongly. However, it is also appreciated that the benefits of these procedures accrue mainly to the person being exposed and dose reduction at the expense of important diagnostic information is not warranted. Thus, while every effort should be made to minimize the dose, the overall welfare of the patient must be the over-riding consideration. Consumer products also contribute a small fraction of the total average effective dose equivalent to individuals in the U.S. population. Dose reduction is discussed for these products in Section 5.4 and would seem not to be feasible or cost effective in the case of building materials or mining and agricultural products. It may have some value in

58

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8. SUMMARY AND CONCLUSIONS

connection with the removal of radon from domestic water supplies, along with other means of reducing indoor radon and proper venting procedures which can be helpful with natural gas heaters. The NCRP considers that exposures below 10 &v/y (1 mrem/y) correspond to a negligible individual risk level (NCRP, 1987b) and should not be considered further. Therefore, additional dose reduction procedures would not appear to be warranted in the case of other consumer products, for the nuclear fuel cycIe, or for miscellaneous sources including transportation. In occupational circumstances, the application of ALARA principles, the dose limits, and a recent NCRP guideline (NCRP, 1987b) are aimed a t minimizing exposures to radiation workers. 8.5.2 Recommendations for Improved Data for the Future 8.5.2.1 Natural Background. External cosmic and terrestrial radiation and internal radionuclides in the body appear to be quite well documented for the purpose of assessing population exposure. If, a t some time in the future, other sources become better documented and assessments are made on a regional basis, more detail of a regional nature might then be warranted and useful. Radon information is clearly still much too limited and the following recommendations are made. 1. A national survey of radon levels in homes is needed; first, to obtain a general overall scope of the problem, followed probably by more detailed regional surveys. 2. Better identification is required of the factors controlling indoor levels. 3. Development of mitigation techniques to reduce radon in homes with higher levels is necessary. 4. Building codes need to be modified to limit radon concentrations in future home construction. 5. Improved understanding should be sought of the deposition of radon and decay products in the lungs and the a-radiation dosimetry associated with it. 6. Better (more assured) estimates of the risk of lung cancer from a given exposure to radon and its decay products are needed. 8.5.2.2 Occupational. Again, the information on this source of exposure seems to suffer from important uncertainties. 1. The number of people actually involved in radiation work is not easily determined. Improved methods for defining and ascertaining the number of workers need to be developed.

8.6 CONCLUSIONS

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59

2. As far as possible, individual radiation measurements should be made on all radiation workers. 3. If the exposure is above a minimum value [about 1 mSv/y (100 mrem/y)] consideration should be given to interpreting the exposure in terms of the effective dose equivalent. 8.5.2.3 Nuclear Fuel Cycle. A more consistent procedure for translating effluent and environmental monitoring data into collective effective dose equivalents for different portions of the fuel cycle is needed. 8.5.2.4 Consumer Products. The most important problem here is to establish the number of people actually exposed to the more important sources, such as domestic water supplies (whether from ground water or surface water supplies) and building materials. Knowledge of the actual doses to which people are exposed from these sources also needs improvement. Further study of the circumstances of exposure to 'loPo in tobacco smoke is necessary to properly evaluate the magnitude of this exposure. 8.5.2.5 Miscellaneous Environmental Sources. Although this is currently a very small contributor, the problem of determining all the sources to be assessed and the number of people exposed to them needs further study. 8.5.2.6 Medical Sources. Presumably the assessment of the number of examinations is reasonably accurate, but the number of people exposed to each medical procedure is not known precisely. Possibly, the average number of examinations per individual could be determined in a limited sample. More information on the dose range for each procedure, and the effective dose equivalent resulting from it would be very useful.

8.6

Conclusions

The average annual effective dose equivalent to individuals in the

U.S.population is estimated to be 3.6 mSv (360 mrem), about 10 pSv/ day (1 mrem/day). The major part of this, 3 mSv (300 mrem), is from natural background radiation and includes 2 mSv (200 mrem) from radon and its decay products. The largest man-made source is medical diagnosis and amounts to about 0.5 mSv/y (50 mrem/y). Consumer products contribute the remaining 0.1 mSv/y (10 mremly). The nuclear fuel cycle, occupational practices, and miscellaneous other sources, including transportation and fallout from weapons tests, are essentially negligible. Smoking results in additional exposure from

60

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8. SUMMARY AND CONCLUSIONS

''!Po in the lungs but the exposure from this source is difficult to estimate and thus to compare with the others. The most important source of exposure, radon and its decay products, is variable and can range to high values. Recommendations have been provided for better characterization of this source and dose reduction. Additional recommendations treat improved data acquisition in the future. It would seem highly desirable t o unclertake another assessment of the exposure of the U.S. population in about ten years.

APPENDIX A

Glossary absorbed dose: The energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest. In SI units, the unit of absorbed dose is the gray (Gy), defined as 1joule per kilogram. Still in use temporarily is the tad; one rad equals 0.61 joules per kilogram. agreement states: any state with which the U.S. Nuclear Regulatory Commission or the U.S. Atomic Energy Commission has entered into an effective agreement under subsection 274b of the Atomic Energy Act of 1954, as amended (73 Stat. 689) concerning licensing of by-product materials ALARA: system of dose limitation based on keeping exposures "as low as reasonably achievable," economic and social factors being taken into account. collective effective dose equivalent (SE)for : a given source, the integrated product of the effective dose equivalent to those exposed and the number of individuals in the exposed population:

where P (HE)dHEis the number of individuals receiving an effective dose equivalent between HE and HE + HE from the given source. dose equivalent (H): A quantity used for radiation protection purposes that expresses on a common scale for all radiations, the irradiation incurred by exposed persons. It is defined as the product of the absorbed dose and quality factor (ICRU, 1986). In SI units, the unit of dose equivalent is the sievert (Sv). Still in use temporarily is the rem; 1 rem = 0.01 Sv. effective dose equivalent (HE):The sum over the tissues of the product of the dose equivalent HT in a tissue (T) and the weighting factor WT representing its proportion of the total stochastic (cancer and genetic) risk resulting from irradiation of tissue (T) to the total risk when the whole body is irradiated uniformly, i-e.,HE = C;TUITHT = H*.

62

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APPENDIX A

genetically significant dose (GSD): The GSD is "that dose which, if received by every member of the population, would be expected to produce the same genetic injury to the population as do the actual doses received by the individuals irradiated" (UNSCEAR, 1972). Thus, the GSD is the dose equivalent to the gonads weighted for the age and sex distribution in those members of the irradiated population expected to have offspring. The GSD is expressed in sieverts (or rem). gray (Gy): The SI unit of absorbed dose (see absorbed dose). GWe: Gigawatts electrical. linear energy transfer (L): Is the quotient of dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl due to those collisons with electrons in which the energy loss is less than A,

maximally exposed individual: An individual whose location and habits tend to maximize his or her radiation dose from a particular source, resulting in a dose higher than that received by other individuals in the general population. nonstochastic effects: Effects for which the severity of the effect varies with the dose, and for which a threshold may therefore exist. nuclide: A species of atom having a specified number of neutrons and protons in its nucleus. quality factor (Q): The quality factor, which appears in the relation H = QD between dose equivalent and absorbed dose, weights the absorbed dose for the biological effectiveness of the type of radiation producing the absorbed dose. The quality factor is chosen after surveying measured values of the relative biological effectiveness (RBE) for low absorbed doses and/or low dose rates, including those on human material when available. It is independent of the organ and tissue or of the biological endpoint under consideration. The quality factor represents a judgment for use in radiation protection, and it is not a direct result of radiobiological experimentation as is RBE. rad: A unit of absorbed dose being replaced by the gray (see absorbed dose). relative biological effectiveness (RBE): A ratio of the absorbed dose of a reference radiation to the absorbed dose of a test radiation to produce the same level of biological effect, other conditions being equal. rem: a unit of dose equivalent being replaced by the sievert (see dose equivalent).

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SI: The International System of Units ("Le Systeme International &Unitesn). sievert (Sv): The SI unit of dose equivalent (see dose equivalent). stochastic effects: Effects for which the probability of an effect occurring, rather than its severity, is a function of dose without threshold. Examples would include malignant or hereditary disease. More generally, stochastic means random in nature. weighting factor (w):A factor which represents the proportion of the total stochastic (cancer plus genetic) risk resulting from irradiation of tissue (T) to the total risk, when the whole body is irradiated uniformly. Values of WT recommended by ICRP (ICRP, 1977) and used in this report are: Tissue

WT

Gonads Breast Red bone marrow

0.25 0.15 0.12 0.12 0.03 0.03 0.30

Lwz Thyroid Bone Surfaces Remaindef

" A W T of 0.06 is to be assigned to each of the five remainder tissues receiving the highest dose equivalents and the other remainder tissues are to be neglected. (When the gastrointestinal tract is irradiated, the stomach, small intestine, upper large intestine and lower large intestine are to be treated as four separate organs and each may therefore be included in the five remainder tissues depending on the magnitude of the dose equivalent they receive when compared to the dose equivalent received by other remainder tissues and organs.)

whole-body dose equivalent (Hd): The dose equivalent that results when the whole body is irradiated and taken, when the irradiation is uniform, as equivalent to the effective dose equivalent,

HE. working level (WL): A unit of air concentration of potential alpha energy released from radon and its daughters. One Working Level is that concentration of radon daughters which has a potential alpha energy release of 1.3 x lo6 MeV per liter of air or 2.08 x lo-' J/m3. working level month (WLM): A unit of exposure to air concentrations of potential alpha energy released from radon daughters. One Working Level Month is defined as the exposure to an average of 1 Jh/m3. WL for a working month of 170 hours or 3.5 x

References ACR (1975). American College of Radiology, Survey on Regionalization in Nuclear Medicine (American College of Radiology, Reston, Virginia). ACR (1982). American College of Radiology, Manpower III: A Report of the ACR Committee on Manpower (American College of Radiology, Reston, Virginia). J. E. (1986). Radiation a d Health Effects: BEHLING,U. H. AND HILDEBRAND, A Report on the TMZ-2Accident and Related Health Studies (GPU Nuclear Corporation, Middletown, Pennsylvania). BENINSON,D. AND SOWBY,D. (1985). "Age and sex dependent weighting factors for medical irradiation," Radiat. Prot. Dosimetry 11,57. BOICE,J. D. AND BLOT,W. J. (1986) Private Communication. BOICE,J. D.,DAY,N.E.,ANDERSEN, A., BRINTON,L. A., BROWN,R.,CHOL, N. W., CLARKE,E. A., COLEMAN, M. P., CURTIS,R. E., FLANNERY, J. T., HAKAMA, M., HAKULINEN, T., HOWE,G. R., JENSEN, 0. M., KLEINERMAN, R. A., MAGNIN,D., MAGNUS,K., MAKELA,K., MALKER,B., MILLER,A. B., NELSON,N., PAITERSON, C. C., PE'ITERSSON, F., POMPE-KIRN,V., PRIMIC-ZAKEIJ, M., PRIOR,P., RAVNIHAR, B., SKEET,R. G.,SKJERVEN,J. E., SMITH,P. G., SOK,M., SPENGLER,R. F., STORM,H. H., STOVALL, M., TOMKINS,G. W. 0.A N D WALL, C. (1985). "Second cancers following radiation treatment for cervical cancer. An international collaboration among cancer registries," J. NCI 74, 955. COHEN,B. S., EISENBUD, M. A N D HARLEY,N. H. (1980). "Measurement of the a-radioactivity on the mucosal surface of the human bronchial tree," Health Phys. 39,619. COTHERN,C. R., LAPPENBUSCH, W. L. AND MICHEL,J. (1986). "Drinkingwater contribution to natural background radiation," Health Phys. 50,33. DHEW (1979). Department of Health, Education and Welfare, Report of the Interagency Task Force on the Health Effects of Ionizing Radiation, (Libassi Report) Report of the Interagency Task Force on the Health Effects of Ionizing Radiation (National Technical Information Service, Springfield, Virginia). EPA (1972). Environmental Protection Agency, Estimutes of Ionizing Radiation Doses in the United States 1960-2000, A. W. Klement, C.R. Miller, R. P. Minx and B. Shleien, Eds. ORP-CSD 72-1 (Environmental Protection Agency, Washington, D.C.). EPA (1977). Environmental Protection Agency. The Radiological Quality of the Environment in the United States 1977, EPA 52011-77-009 (Environmental Protection Agency, Washington, D.C.). EPA (1980). Environmental Protection Agency, Occupational Exposure to

Ionizing Radiation i n the United States: A Comprehensive Summary for the Year 1975, EPA 52014-80-001 (Environmental Protection Agency, Washington, D.C.). EPA (1984a). Environmental Protection Agency, Occupational Exposure to Ionizing Radiation i n the United States. A Comprehensive Review for the year 1980 and a Summary of Trends for the years 1960-1985, EPA 5201184-005 (Environmental Protection Agency, Washington, D.C.). EPA (1984b). Environmental Protection Agency, Radionuclides: Background Information Document for Final Rules, EPA 52011-84-022-1, Vol. 1 (Environmental Protection Agency, Washington, D.C.). EPA ( 1 9 8 4 ~ )Environmental . Protection Agency, Radionuclides: Background Information Document for Final Rules, E P A 52011-84-022-1, Vol. 2 (Environmental Protection Agency, Washington, D.C.). EPA (1987). Environmental Protection Agency, Radon Reference Manual, (Office o f Radiation Programs, Environmental Protection Agency, Washington, D.C.) In Press. FDA (1966). Food and Drug Administration, Population Exposure to X-rays: United States 1964. A Report on the Public Health Service X-ray Exposure Study, Department o f Health, Education and Welfare,DHEW Publication (FDA) 66-1519 (U.S. Government Printing Office,Washington, D.C.). FDA (1973).Food and Drug Administration, Population Exposure to X-rays: United States 1970. A Report o n Public Health Service X-ray Exposure Study, Department of Health, Education and Welfare,DHEW Publication (FDA) 73-8047 (U.S. Government Printing Office,Washington, D.C.). FDA (1976). Food and Drug Administration, Gonad Doses and Genetically Significant Dose from Diagnostic Radiology, U.S., 1964 and 1970, DHEW Publication (FDA)76-8034 ( U S . Government Printing Office,Washington, D.C.). FDA (1985). Food and Drug Administration, Radiation Experience Data, (RED) 1980, Survey of U.S. Hospitals, Department o f Health and Human Services, DHHS Publication (FDA) 86-8253 ( U S . Government Printing Office,Washington, D.C.). FRC (1960). Federal Radiation Council, Background Material for the Development of Radiation Protection Standards, S t a f f report o f the Federal Radiation Council (Federal Radiation Council, Washington, D.C.). FUJIMOTO, K., W I L S O NJ. , A., ASHMORE,J. P. A N D GROGAN,D. (1984). Occupational Radiation Exposures i n Canada-1983, Environmental Health Directorate Publication No. 85-EHD-115 (Department o f National Health and Welfare, Ottawa, Canada). ICRP (1977). International Commission on Radiological Protection, Recommendations of the ICRP, Publication 26, Annals o f the ICRP, 1, NO. 3 (Pergamon Press, New York). ICRP (1978). International Commission on Radiological Protection, Statement from the 1978 Stockholm Meeting of the ICRP, Publication 28, Annals o f the ICRP, 2, No. 1 (Pergamon Press, New York). ICRP (1981). International Commission on Radiological Protection, Limits for Inhalrrtion of Radon Daughters by Workers, Publication 32, Annals o f

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MET~LER,F. A., CHRISTIE,J. H., WILLIAMS,A. G., MOSELEY,R. D. AND KELSEY,C. A. (1982). "Population characteristics and absorbed dose to the population from nuclear medicine in the United States-1982," Health Phys. 5 0 , 619. M ~ L E RF.,A., DAVIS,M., MOSELEY,R. D. AND KELSEY,C. A. (1986). "The effect of utilizing age and sex dependent factors for calculating detriment from medical irradiation," Rad. Prot. Dosimetry 15, 269. METTLER,F. A., WILLIAMS,A. G., CHRISTIE,J. H., MOSELEY,R. D. AND KELSEY,C. A. (1985). "Trends and utilization of nuclear medicine in the United States: 1972-1982," J. Nucl. Med. 26,201. MOELLER,D. W., TERRILL,J. G., JR. AND INGRAHAM, S. C., 11, (1953). "Radiation exposure in the United States," Public Health Reports 68.57. NAS-NRC (1972). National Academy of Sciences-National Research Council, The Effectson Populations of Exposure to Low Levels of Ionizing Radiation, Report of the Advisory Committee on the Biological Effects of Ionizing Radiations (BEIR I) (National Academy of Sciences, Washington, D.C.). NAS-NRC (1980). National Academy of Sciences-National Research Council, The Effects on Populations of Exposure to Low Levels of Ionizing Radiation: 1980, Report of the Advisory Committee on the Biological Effects of Ionizing Radiations (BEIR 111) (National Academy of Sciences, Washington, D.C.). NAS-NRC (1986). National Academy of Sciences-National Research Council, The Airliner Cabin Environment. Air Quality and Safety (National Academy Press, Washington, D.C.). NAZAROFF, W. W., DOYLE,S. M., NERO,A. V. A N D SEXTRO,R. G. (1987). "Potable water as a source of airborne 222Rnin U.S. dwellings; A review and assessment," Health Phys. 52, 281. 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 (1977). National Council on Radiation Protection and Measurements, Radiation Exposure from Consumer Products and Miscellaneous Sources, NCRP Report No. 56 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1981). National Council on Radiation Protection and Measurements, Nuclear Medicine-Factors Influencing the Choice and Use of Radionuclides in Diagnosis and Therapy, NCRP Report No. 70 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1983). National Council on Radiation Protection and Measurements, Protection in Nuclear Medicine and Ultrasound Diagnostic Procedures in Children, NCRP Report No. 73 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1984a). National Council on Radiation Protection and Measurements, Exposures from the Uranium Series with Emphasis on Radon and Its Daughters, NCRP Report No. 77 (National Council on Radiation Protection and Measurements, Bethesda, Maryland).

NCRP (1984b). National Council on Radiation Protection and Measurements, Evaluation of Occyxrtionul and Environmental Exposures to Radon and Radon Daughters i n the United States, NCRP Report No. 78 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1985). National Council on Radiation Protection and Measurements, SI Units i n Radiation Protection and Measurements, NCRP Report No. 82 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987a). National Council on Radiation Protection and Measurements, Public Radiation Exposure from Nuclear Power Generation i n the United States, NCRP Report No. 92 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987b). National Council on Radiation Protection and Measurements, Recommendations on Limits for Ionizing Radiation Exposure, NCRP Report No. 91 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987~).National Council on Radiation Protection and Measurements, Exposure of the U.S. Population from Natural Background Radiation, Report of Scientific Committee 43, to be published (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987d). National Council on Radiation Protection and Measurements, Radiation Exposure of the U.S. Population from Occupationul Radiation, Report of Scientific Committee 45, to be published (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987e). National Council on Radiation Protection and Measurements, Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources, Report of Scientific Committee 28, to be published (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (19870. National Council on Radiation Protection and Measurements, Radiation Exposure of the U.S. Population from Medical Examinations, Report of Scientific Committee 44, to be published (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987g). National Council on Radiation Protection and Measurements, Mitigation of Radon Levels Indoors, Report of Scientific Committee 82, to be published (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987h). National Council on Radiation Protection and Measurements, Guidance on Radiation Received in Space Activities, Report of Scientific Committee 75, to be published (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NIH (1985). National Institutes of Health, Report of The National Institutes of Health Ad Hoc Working Group to Develop Radioepidemiological Tables, Department of Health and Human Services, NIH Publication 85-2748 (Government Printing Office, Washington, D.C.). NRC (1977). Nuclear Regulatory Commission, Final Environmental Statement on the Transportation of Radioactive Material by Air and Other Modes,

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NUREG-0170, Vol. 1 (National Technical Information Service, Springfield, Virginia). OAKLEY,D. T. (1972). Natural Radiation Exposure in the United States, Report ORP/SID 72-1 (U.S. Environmental Protection Agency, Washington, D.C.). ORNL (1986). Oak Ridge National Laboratory, Enviionmntal Surveillance of the Oak Ridge Reservation and Surrounding Environs during 1985, Report ORNL-6271 (Oak Ridge National Laboratory, Oak Ridge, Tennessee). M. (1976). Organ Doses in Diugnostic Radiology, DHEW PubliROSENSTEIN, cation (FDA) 76-8030 (Government Printing Office, Washington, D.C.). SHLEIEN, B., TUCKER, T. T. AND JOHNSON, D. W. (1978). &Themean active bone marrow dose to the adult population of the United States from diagnostic radiology," Health Phys. 34, 587. SHRIMPTON, P. C., WALL,B. F., JONES, D. G., FISHER,E. S., HILLIER,M. C., KENDALL, G. M. AND HARRISON, R. H. (1986). "Doses to patients from routine diagnostic x-ray examinations in England," Brit. J. Radiol. 69, 749. M. S., WEAVER,C. L. AND WIEDER,S. (1971). "Dose assessment TERPILAK, of ionizing radiation exposure to the population," Radiol. Health Data Rep. 12,171. UNSCEAR (1958). United Nations Scientific Committee on the Effects of Atomic Radiation, Report of the United Nations Scientific Committee on the Effects of Atomic Radiation. Document A3838 (United Nations, New York). UNSCEAR (1966). United Nations Scientific Committee on the Effects of Atomic Radiation, Report of the United Nations Scientific Committee on the Effectsof Atomic Radiation. General Assembly, Official Records, XXI Session, Supplement No. 14 (Al6314) (United Nations, New York). UNSCEAR (1972). United Nations Scientific Committee on the Effects of Atomic Radiation, Ionizing Radiation: Levels and Effects, No. E.72.IX.17 and 18 (United Nations, New York). UNSCEAR (1977). United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation, No. E.77.IX.1 (United Nations, New York). UNSCEAR (19821, United Nations Scientific Committee on the Effects of Atomic Radiation, Ionizing Radiation: Sources and Biological Effects, No. E.82. IX.8.. 06300P (United Nations, New York). OF THE CENSUS(1986). Statistical Abstracts of the United States, U.S. BUREAU 106th ed. (U.S. Government Printing Office, Washington, D.C.). WALL,B. F. AND KENDALL, G. M. (1983). "Collective doses and risks from dental radiology in Great Britain," Brit. J. Radiol. 56, 511.

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 C o u ~ c i is l made up of the members and the participants who serve on the eighty-two 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: Officers President Vice President Secretary and Tr-urer Assistant Secretary Assistant Treasurer

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Members

ARTHURC. LUCAS CHARLES W. WYS ROGER0. MCCLELLAN JAMES E. MCLAUGHLIN BARBARA J. MCNELL THOMAS F. MEANEY B. MEINHOLD CHARLES MORTIMER L. MENDELSOHN FREDA. METTLER WILLIAM A. MILLS DADEW. MOELLER A. ALANMOGHISSI WESLEYNYBORG MARYELLENO'CONNOR ANDREWK. POZNANSKI NORMAN C. RASMUSSEN WILIAMC. REINIG CHESTERR. RICHMOND JAMES S. ROBERTSON N. ROTHENBERG LAWRENCE LEONARD A. SAGAN WILLIAMJ. SCHULL GLENNE. SHELINE ROYE. SHORE WARREN K. SINCLAlR PAULSLOVIC LEWIS V. SPENCER WILLIAM L. TEMPLETON J. W. THIESSEN ROYC. THOMPSON JOHN E. TILL ARTHURC. UPTON GEORGEL. VOELZ EDWARD W. WEBSTER GEORGEM. WILKENING H. RODNEY WITHERS MARVIN ZISKIN Honorary Members LAURI 'STON S. TAYLOR, Honorary President RICHARD F. FOSTER WILPRIDB. MANN EDGAR C. BARNES KARL2.MORGAN HYMERL. FRIEDELL VICTORP. BOND ROBERTD. MOSELEY JR.* REYNOLD F. BROWN ROBERT0 . GORSON ROBERTJ. NELSEN AUSTINM. BRUES JOHNH. HARLEY HARALD H. Ross1 GEORGEW. CASARETT JOHNW. HEALY LOUISH. WILLIAM L. RUSSELL FREDERICK P. COWAN JAMESF. CROW HEMPELMANN, JR. JOHNH. RUST EUGENEL. SAENGER PAULC. HODGES MERRILLEISENBUD J. NEWELLSTANNARD ROBLEYD. EVANS GEORGEV. LEROY HAROLD 0. WYCKOFP *Elected posthumously

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Currently, the following subgroups are actively engaged in formulating recommendations: SC-I: SC-3:

Basic Radiation Protection Criteria Medical X-Ray, Electron Beam and Gamma-Ray Protection for Energies Up to 50 MeV (Equipment Performance and Use) X-Ray Protection in Dental Offices Standards and Measurements of Radioactivity for Radiological Use Radiation Exposure from Consumer Products Biological Aspects of Radiation Protection Criteria Task Group on Atomic Bomb Survivor Dosimetry Subgroup on Biological Aspects of Dosimetry of Atomic Bomb Survivors Natural Background Radiation Radiation Associated with Medical Examination Radiation Received by Radiation Employees Operational Radiation Safety 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 Task Group 5 on Maintaining Radiation Protection Records Task Group 6 on Radiation Protection for Allied Health Personnel Task Group 7 on Emergency Planning Task Group 8 on Radiation Protection Design Guidelines for Particle Accelerators Task Group 9 on ALARA at Nuclear Power Plants Instrumentation for the Determination of Dose Equivalent Conceptual Basis of Calculations of Dose Distributions Internal Emitter Standards Task Group 2 on Fkspiratory Tract Model Task Group 5 on Gastrointestinal Models Task Group 6 on Bone Problems Task Group 8 on Leukemia Risk Task Group 9 on Lung Cancer Risk Task Group 10 on Liver Cancer Risk Task Group 12 on Strontium Task Group 14 on Placental Transfer Task Group 15 on Uranium Human Radiation Exposure Experience Radon Measurements Radiation Exposure Control in a Nuclear Emergency Task Group on Public Knowledge About Radiation Criteria for Radiation Instruments for the Public Task Group on Exposure Criteria for Specialized Categories of the Public Environmental Radioactivity and Waste Management Task Group 6 on Screening Models Task Group 7 on Contaminated Soil as a Source of Radiation Exposure Task Group 8 on Ocean Disposal of Radioactive Waste Task Group 9 on Biological Effects on Aquatic Organisms

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Task Group 10 on Low Level Waste Task Group 11 on Xenon Quality Assurance and Accuracy in Radiation Protection Measurements Biological Effects and Exposure Criteria for Ultrasound Biological Effects of Magnetic Fields Microprocessors in Dosimetry Efficacy of Radiographic Procedures Quality Assurance and Measurement in Diagnostic Radiology Radiation Exposure and Potentially Related Injury Radiation Received in the Decontamination of Nuclear Facilities Guidance on Radiation Received in Space Activities Effects of Radiation on the Embryo-Fetus Guidance on Occupational and Public Exposure Resulting from Diagnostic Nuclear Medicine Procedures Practical Guidance on the Evaluation of Human Exposures in Radiofrequency Radiation Extremely Low-Frequency Electric and Magnetic Fields Radiation Biology of the Skin (Beta-Ray Dosimetry) Assessment of Exposure from Therapy Control of Indoor Radon Study Group on Comparative Risk Task Group on Comparative Carcinogenicity of Pollutant Chemicals Ad Hoc Group on Medical Ebaluation of Radiation Workers Ad Hoc Group on Video Display Terminals 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 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 Medical Physics 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

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American Occupational Medical Association American Podiatric Medical Association American Public Health Association American Radium Society American Roentgen b y Society American Society of Radiologic Technologists American Society for Therapeutic Radiology and Oncology Association of University Radiologists Atomic Industrial Forum Bioelectromagnetics Society College of American Pathologists Conference of Radiation Control Program Directors Federal Communications Commission 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 1Jnited States Department of Energy United States Department of Housing and Urban Development 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 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 a n 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: Commission of the European Communities Cornmisariat a 1'Energie Atomique (France)

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Defense Nuclear Agency Federal Emergency Management Agency Japan Radiation Council National Bureau of Standards National Radiological Protection Board (United Kingdom) National Research Council (Canada) Office of Science and ~ e c h n k l policy o~~ Office of Technology Assessment United States Air Force United States Army United States Coast Guard United States Department of Energy United States De~artmentof Health and Human Services United States ~epartrnentof Labor United States Department of Transportation 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 generous support of the following organizations: Alfred P. Sloan Foundation Alliance of American Insurers American Academy of Dental Radiology American Academy of Dermatology American Association of Physicists in Medicine American College of Nuclear Physicians American College of Radiology American College of ~adiolo&Foundation American Dental Association American Hospital Radiology Administrators American Industrial Hygiene Association American Insurance Association American Medical Association American Nuclear Society American Occupational Medical Association American Osteopathic College of Radiology American Podiatric Medical Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Society for Therapeutic Radiology and Oncology American Veterinary Medical Association American Veterinary Radiology Society Association of Univemity Radiologists

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Atomic Industrial Forum Battelle Memorial Institute Center for Devices and Radiological Health 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 America Health Physics Society Institute of Nuclear Power Operations James Picker Foundation National Aeronautics and Space Administration National Association of Photographic Manufacturers National Bureau of Standards National Cancer Institute 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 of 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 its work.

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Title Perceptions of Risk, Proceedings of the Fifteenth Annual Meeting, Held on March 14-15, 1979 (Including Taylor Lecture No. 3) (1980) Quantitative Risk in Standurds Setting, Proceedings of the Sixteenth Annual Meeting, Held on April 2-3, 1980 (Including Taylor Lecture No. 4) (1981) Critical Issues 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 Lecture No. 7) (1984) Some Issues Important in Developing Basic Radiation Protection Recommendutions, Proceedings of the Twentieth Annual Meeting, Held on April 6 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) 77

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Symposium Proceedings The Control of Exposure of the Public to Ionizing Radiation in the Event of Accident or Attack, Proceedings of a Symposium held April 27-29,1981 (1982)

Lauriston S. Taylor Lectures No. 1

Title and Author The Squares of the Natural Numbers in Radiation Protection by Herbert M. Parker (1977) Why be Quantitative About Radiation Risk Estimates? by Sir Edward Pochin (1978) Radiation Protection-Concepts and Trade Offsby Hymer L. Friedell (1979) [Available also in Perceptions of Risk, see above] From "Quantity of Radiation" and "Dose" to "Exposure" and "Absorbed Dose"-An Historical Review by Harold 0. Wyckoff (1980) [Available also in Quuntitative Risks in Standards Setting, see above] How Well Can We Assess Genetic Risk? Not Very by James F. Crow (1981) [Available also in Critical Issues in Setting Radiation Dose Limits, see above] Ethics, Trade-offs and Medical Radiation by Eugene L. Saenger (1982) [Available also in Radiation Protection and New Medical Diagnostic Approaches, see above] The Human Environment-Past, Present and Future by Merril Eisenbud (1983) [Available also in Environmental Radioactivity, see above] 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) Nonionizing Radiation Bioeffects: Cellular Properties and Interactions by Herman P. Schwan (1986) How to be Quantitative about Radiation Risk Estimates by Seymour Jablon (1987)

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NCRP Commentaries Commentary No. 1 2

3

4

Title

Krypton-85 in the Atmosphere- With Specific Reference to the Public Health Significance of the Proposed Controlled Release at Three Mile Islnnd (1980) Preliminary Evaluation of Criteria for the Disposal of Transuranic Contaminated Waste (1982) Screening Techniques for Determining Compliance with Environmental S t a h r d s (1986) Guidelines for the Release of Waste Water from Nuclear Facilities with Special Reference to the Public Health Significance of the Proposed R e h e of Treated Waste Waters at Three Mile Island (1987)

NCRP Reports No.

Title Control and Removal of Radioactive Contamination in Laboratories (1951) Radioactive Waste Disposal in the Ocean (1954) Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides i n 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 of Absorbed 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 i n Educational Institutions (1966) Medical X-Ray and Gamna-Ray Protection for Energies Up to 10 MeV-Equipment Design and Use (1968) Dental X-Ray Protection (1970) Radiation Protection i n Veterinary Medicine (1970) Precautions in the Management of Patients Who Have Received Therapeutic Amounts of Radionuclides (1970) Protection against Neutron Radiation (1971)

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Protection Against Radiation from Brachytherapy Sources (1972)

Specificationof 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) Natural Background Radiation in the United States (1975) Alphu-Emitting Particles in Lungs (1975) Tritium Measurement Techniques (1976) Radiation Protection for Medical and Allied Health Personnel (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-I37 From 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) Protection of the Thyroid Gland in the Event of Releases of Radioiodine (1977) Radiation Exposure From Consumer Products and Miscel2aneous Sources (1977) Instrumentation and Monitoring Methods for Radiation Protection (1978) A Handbook of Radioactivity Measurements Procedures, 2nd ed. (1985) Operational Radiation Safety Program (1978) Physical, Chemical, and Biological Properties of Radiocerium Relevant to Radiation Protection Guidelines (1978) Radiation Safety Training Criteria for Industrial Radiography (1978) Tritium in the Environment (1979) Tritium and Other Radionuclide Labeled Organic Compounds Incorporated in Genetic Material (1979) Influence of Dose and Its Distribution in Time on DoseResponse Relationships for Low-LET Radiations (1980)

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Management of Persons Accidentally Contaminated with Radionuclides (1980) Mammography (1980) Radiofrequency Electromagnetic Fields-Properties, Quantities and Units, Biophysical Interaction, and Measurements (1981) Radiation Protection in 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 in Diagnosis and Therapy (1982) Operational Radiation Safety-Training (1983) Radiation Protection and Measurement for LAW Voltage Neutron Generators (1983) Protection in Nuclear Medicine and Ultrasound Diagnostic Procedures in Children (1983) Biological Effects of Ultrasound: Mechanisms and Clinical Implications (1983) Iodine-129: Evaluation of Releases from Nuclear Power Generation (1983) Radiological Assessment: Predicting the Transport, Bioaccumulation, and Uptake by Man of Radionuclides Released to the Environment (1984) Exposures from the Uranium Series with Emphasis on Radon and its Daughters (1984) Evaluution of Occupatioml and Environmental E~posures to Radon and Radon Daughters in the United States (1984) Neutron Contamination from Medical Electron Accelerators (1984) Induction of Thyroid Cancer by Ionizing Radiation (1985) Carbon-14 in the Environment (1985) S I Units in Radiation Protection and Measurements (1985) The Experimental Bask 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)

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NCRP PUBLICATIONS

88

Radiation Alarms and Access-Control Systems (1987) Genetic Effects of Internally Deposited Radionuclides (1987) 90 Neptunium: Radiation Protection Guidelines (1987) 91 Recommendations on Limits for Exposure to Ionizing Radiation (1987) 92 Public Radiation Exposure from Nuclear Power Generation in the United States (1987) 93 Ionizing Radiation Exposure of the Population of the United States (1987) 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. 32-93). Each binder will accommodate from five to seven reports. The binders carry the identification "NCRP Reports" and come with label holders which permit the user to attach labels showing the reports contained in each binder. 89

The following bound sets of NCRP Reports are also available: Volume I. NCRP Reports Nos. 8, 16, 22 Volume 11. NCRP Reports Nos. 23,25,27,30 Volume 111. NCRP Reports Nos. 32, 33, 35, 36, 37 Volume IV. NCRP Reports Nos. 38,40,41 Volume V. NCRP Reports Nos. 42,44,45,46 Volume VI. NCRP Reports Nos. 47,48,49,50,51 Volume VII. NCRP Reports Nos. 52, 53, 54, 55, 56, 57 Volume VIII. NCRP Reports 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 Reports Nos. 77, 78, 79, 80 Volume XIV. NCRP Reports Nos. 81,82,83, 84,85. (Titles of the individual reports contained in each volume are given above). The following NCRP Reports are now superseded and/or out of print: No. 1

Title X-Ray Protection (1931). [Superseded b y NCRP Report No. 31

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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 o f Print] Medical X-Ray Protection U p 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 Phosphorus-32 and clodine-131 for Medical Users (1951).[0ut of Print] Radiological Monitoring Methods and Instruments (1952). [Superseded by NCRP Report No. 571 Maximum Permissible Amounts of Radioisotopes i n the Human Body and Maximum Permissible Concentrations i n 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 U p to 100 Million Electron Volts (1954). [Superseded by NCRP Report No. 511 Safe Handling of Cadavers Containing Radioactive Isotopes (1953). [Superseded by NCRP Report No. 211 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 Print] Protection Against Neutron Radiation U p to AU 1vic;lLun Electron Volts (1957). [Superseded by NCRP Report No. 381 Safe Handling of Bodies Containing Radioactive Isotopes

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(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 to 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 an Emergency (1962). [Superseded by NCRP Report No. 421 Shielding for High Energy Electron Accelerator ZnstaUatiom (1964). [Superseded by NCRP Report No. 511 Medical X-Ray and Gamma-Ray Protection for Energies Up to 10 MeV-Structural Shielding Design and Evaluation (1970). [Superseded by NCRP Report No. 491 Basic Radiation Protection Criteria (1971). [Superseded by NCRP Report No. 911 Review of the Current State of Radiation Protection Philosophy (1975). [Superseded by NCRP Report No. 911 -

26 28

29 31 34

39 43

Other Documents The following documents of the NCRP were published outside of the NCRP Reports series: "Blood Counts, Statement of the National Committee on Radiation Protection," Radiology 63, 428 (1954) "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) 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) Specifitation 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 of Air Emissions of Radionuclides (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 Consumer products (Continued) Absorbed dose. 4,61 Accident, 28 combustible fuels, 29,31 Three Mile Island Nuclear Plant, 28 coal, 31 Chernobyl, 28 natural gas heaters, 31.33, 34 Aerosol (smoke) detectors, 29,31 natural gas cooking, 31,33,34 Airport x-ray baggage inspection systeme, dental prostheses, 31 29,31 domestic water supplies, 31,33.58 Air travel, 11 electron tubes. 31 enhanced cosmic-ray exposure, 11 gas (smoke) detectors, 31 Annual effective dose equivalent, 5,12,15, gas mantles. 29,31 highway and road construction mate19,20,25,31,45-48,50-53,56 all sources, 52,53.56 rials, 31 average, 5, 12, 15, 19,20,25, 31,45-48, luminous watches, 31 mining and agricultural products, 31,33, 50-53,56 consumer products, 31,53 57 diagnostic x-rays, 45,47,48,53 ophthalmic glass, 31 medical, 45-47,50,51,63 radioluminousproducts, 29,31 miscellaneous environmental sources, static eliminators, 29 37,40,53 television receivers, W 3 1 natural sources, 12,15,53 thorium products, 31 nuclear fuel cycle. 25,53 check sources, 31 occupational, 19,20,53 fluorescent lamp starters, 31 Annual GSD, 14,22,42,46-49,52,54,56 tungsten welding rods, 29,31,34 consumer products, 54 tobacco products, 29-33,62,53 medical, 42.46-49,54 Cosmic radiation, 1,10,11,15,54 miscellaneous environmental sources, Cosmogenic radionuclides, 10.12, 54 54

natural sowcea, 14.M nuclear fuel cycle, 54 occupational, 22.64 ~ v e r & eeffecti1e dose equivalent (See Annual effective dose equivalent) Chernobyl, 28 Collective effective dose equivalent, 5, 19, 20,269 27,31,37,38,45-47,63,61 Consumer producta, 29-34,55,57,69 aerosol (smoke) detectare, 29,31 airport x-ray baggage inspection systems, 29,31 building materials, 29,31,33 camera lenses, 29

Diagnostic medical x-ray examinations, 42-45 Diagnostic nuclear medicine tests, 46 DO; equivalent, 4,61 Dose reduction, 15,22,27,33,40,49,57 recommendations,57 Effective doae equivalent, 4, 8, 12, 15,19, 20,25,31,37,42,45-63,56,61

annual (See annual effective dose equivalent) average (See annual effective dose equivalent) from all sources, 52,53,56 Enhanced natural sources, 1

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INDEX

External-beam therapy, 42, a,51 External radiation, 10 Fallout from nuclear weapons testing, 39, 40 dose equivalent commitment, 39, 40 Genetically significant dose (GSD), 5, 14, 22,42, 46-49, 52, 56, 62 1 GWe reactor, dose associated with, 27, 62 conversion, 27 enrichment, 27 fabrication, 27 low-level waste storage, 27 milling, 27 mining, 27 nuclear power plant, 27 transportation, 27 Industrial radiographers, 17 Inhaled radionuclides, 12 Inhaled radon, 12, 15 Magnetic resonance imaging, 49 Medical diagnosis, 41 Medical examinations, 47 diagnostic x rays, 47 dose equivalent to bone marrow, 47 dose equivalent to gonads, 47 effective dose equivalents, 47 nuclear medicine, 47 number of dental x rays, 47 number of medical x rays, 47 Medical exposures, 41-51,53,54,59 Medical workers, 17 Military nuclear fuel cycle, 23 Miners, 18 uranium, 18 other, 18 Miscellaneous environmental sources, 3540, 53, 54, 59 air emissions, 35-38 transportation of radioactive materials, 35,36, 38 transport index, 36, 38 Natural 1)ackground.8-16.53, 54, 58 Ni~tu ri~llvoccurring radionuclides, 9 I Iioriu111-2:W.9 ~ ) 0 l i l h i l l l l l ~ - 4 09 ,

Naturally occurring radionuclides (Continued) rubidium-87,9 uranium-235,9 uranium-238, 9 Natural sources, 1,8, 53 Nuclear fuel cycle, 23-28,53, 59 fuel reprocessing, 23 milling, 23, 25-27 mining, 23,25-27 power production, 23, 25-27 radioactive waste management, 23, 2527 transportation of radioactive materials, 23, 25, 27 uranium-235 enrichment, 23,25-27 uranium hexafluoride production, 23, 25-27 uranium oxide fuel fabrication, 23, 2527 Nuclear medicine, 4 2 - 4 4 , 6 4 9 , 53,54 examinations. 4 4 4 6 Nuclear power, 23-28,53-55 Occupational exposures, 17-22, 53, 54, 58 radiation workers, 17 Personnel in aircraft, 18 Radiation therapy, 42, 50 Radiation workers, 17, 19, 20 high-LET, 20 DOE contractors, 20 navy, 20 nuclear power, 20 underground mining, 20 low-LET, 19 government, 19 industry, 19 medicine, 19 miscellaneous, 19 nuclear fuel cycle. 19 other workers, 19 other, 19 additional, 19 Radioluminous products, 29,31 Radionuclides naturally present in the body, 1, 10, 11, 13, 15 carbon-14,ll potassium-40, 11 rubidium-87, 11 Radon, 12, 15,33,53-55,57,59,60

INDEX Radon (Continued) WLM, 15,63 Radon mitigation, 34 natural gas heaters and cooking ranges, 34 Recommendations, 15, 16, 22, 27, 28, 33, 34.40.49, 58,59 consumer products, 33,34,59 for improved data, 58, 59 medical sources, 49, 59 miscellaneous environmental sources, 40.59 natural background, 15, 16,58 nuclear fuel cycle, 27, 28, 59 occupational, 22, 58 the future, 58

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Sources of population exposure, 1 consumer products, 29 medical, 41 miscellaneous environmental, 35 natural background, 8 nuclear power. 23 occupational, 17 Static eliminators, 29 Terrestrial gamma radiation, 1,10,11, 15, 54 Three Mile Island Nuclear Plant, 28 Uncertainties in estimates, 15, 21, 24-27, 30,32, 36, 48, 55,56 Weighting factors 14, 15, 32, 63 gonadal dose equivalent, 14