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Suggested Citation:"Needs of the Times." National Research Council. 1972. Effects on Populations of Exposure to Low Levels of Ionizing Radiation. Washington, DC: The National Academies Press. doi: 10.17226/18994.
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Suggested Citation:"Needs of the Times." National Research Council. 1972. Effects on Populations of Exposure to Low Levels of Ionizing Radiation. Washington, DC: The National Academies Press. doi: 10.17226/18994.
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Suggested Citation:"Needs of the Times." National Research Council. 1972. Effects on Populations of Exposure to Low Levels of Ionizing Radiation. Washington, DC: The National Academies Press. doi: 10.17226/18994.
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Suggested Citation:"Needs of the Times." National Research Council. 1972. Effects on Populations of Exposure to Low Levels of Ionizing Radiation. Washington, DC: The National Academies Press. doi: 10.17226/18994.
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Chapter II NEEDS OF THE TIMES A. Quantification of Risk Deleterious effects in individuals and popula- tions of living organisms cannot be attributed to exposure to ionizing radiation at levels near that of average natural background except by inference. Such effects are not directly observ- able. It has been taken for granted by many that exposure to additional radiation near background levels, and especially within varia- tions of natural background, represents a risk so small compared with other hazards of life that any associated non-trivial benefit would far offset any harm caused. The effects of such radiation exposures have been variously re- garded as insignificant, negligible, tolerable, permissable, acceptable. But if in fact any lev- el of radiation will cause some harm (no thresh- old), and if in fact entire populations of nations or of the world are exposed to additional man- made radiation, then, for decisions about radia- tion protection, it becomes necessary to quanti- fy the risks; that is, to estimate the probabili- ties or frequencies of effects. Such estimates, as discussed later, are fraught with uncertainty. However, they are needed as a basis for logical decision-making and may serve to stimulate the gaining of data for assessment of comparative hazards from technological options and development, at the same time promoting better public understand- ing of the issues. B. Cost-Benefit Analysis When the risk from radiation exposure from a given technological development has been estimated, it is then logical for the decision- making process that comparisons be made and consideration given to (a) benefits to be at- tained, (b) costs of reducing the risks, or (c) risks of the alternative options including aban- donment of the development. The concept of always balancing the risk of radiation expo- sure against the expected benefit has been well- recognized and accepted, but no serious at- tempt has been made to evaluate both sides of the equation in any way that could lead to oper- ational guidance. Official recommendations call for radiation exposure to be kept at a level "as low as practicable," a policy that emphasizes and encourages sound practice. However, risk- estimates and cost-benefit analysis are needed for decision-making. An additional important point, often overlooked, is that even if the bene- fit outweighs the biological cost, it is in the public interest that the latter must still be re- duced to the extent possible providing the health gains achieved per unit of expenditure are compatible with the cost-effectiveness of other societal efforts. It appears logical to attempt to express both risks and benefits in comparable terms - dollars. To a limited degree risks can be estimated in such terms. For example, the statement of risk can be expressed in terms of cost to an individu- al or to his family and society since there are specific expenses attributable to an effect. Sim- ilarly, estimates can be made of expenses re- quired to effect given reductions of exposure to harmful agents. In some instances, it may not be necessary to use absolute dollar costs: that is, one can compare the cost of different ways of producing the same desired objective. Given the need for additional electrical power, one might compare nuclear plants and fossil fuel plants directly in terms of total biological and environmental costs per unit of electricity pro- duced. Often however, there will be need for information on absolute costs. This will occur when decisions have to be made on whether the public interest is better served by spending our

limited resources on health gains from reduc- ing contamination or by spending for other so- cietal needs. It must be emphasized that there are many inherent problems in cost-benefit analysis that will prevent rigorous application in the very complex systems of present concern to society. These include the implication of assigning a monetary value to human life, suffering or productivity; the difficulty in assessment of factors related to the quality of life such as recreational water and land resources; the fact that the costs and benefits may not accrue to the same members of the population, or even to the same generation; and the virtual impossi- bility of establishing a single cost system that would be socially acceptable and still take into account differences in individual willingness to accept various types of risks. An illustration of the latter points is the observation that health and environmental effects from power plants would be reduced by their location in relatively unpopulated areas. Yet the people in such areas generally are not the ones who need the additional electrical energy. Despite these uncertainties, there are impor- tant advantages in attempting cost-benefit analyses. There is a focus on the biological and environmental cost from technological develop- ments and the need for specific information becomes apparent. Thus, for example, we find relatively little data available on the health risks of effluents from the combustion of fossil fuels. Furthermore, it is becoming increasingly important that society not expend enormously large resources to reduce very small risks still further, at the expense of greater risks that go unattended; such imbalances may pass unno- ticed unless a cost-benefit analysis is attempt- ed. If these matters are not explored, the deci- sions will still be made and the complex issues resolved either arbitrarily or by default since the setting and implementation of standards represent such a resolution. C. Standards The present radiation standards used by the Federal Government are based on the recom- mendations of the Federal Radiation Council (FRC). The FRC developed the Radiation Pro- tection Guide that is defined as "the radiation dose which should not be exceeded without care- ful consideration of the reasons for doing so; every effort should be made to encourage the maintenance of radiation doses as far below this guide as practicable." The FRC also indi- cated that "there should not be any man-made radiation exposure without the expectation of benefit resulting from such exposure." The present status of Radiation Protection Guides for the general population is presented as direct quotation from FRC Report No. 1 (italics added). 5.2 We believe that the current population exposure resulting from background radia- tion is a most important starting point in the establishment of Radiation Protection Guides for the general population. This expo- sure has been present throughout the histo- ry of mankind, and the human race has dem- onstrated an ability to survive in spite of any deleterious effects that may result. Ra- diation exposures received by different indi- viduals as a result of natural background are subject to appreciable variation. Yet, any differences in effects that may result have not been sufficiently great to lead to attempts to control background radiation or to select our environment with background radiation in mind. 5.3 On this basis, and after giving due consid- eration to the other bases for the establish- ment of Radiation Protection Guides, it is our basic recommendation that the yearly radiation exposure to the whole body of indi- viduals in the general population (exclusive of natural background and the deliberate exposure of patients by practitioners of the healing arts) should not exceed 0.5 rem. We note the essential agreement between this value and current recommendations of the ICRP and NCRP. It is not reasonable to es- tablish Radiation Protection Guides for the population which take into account all possi- ble combinations of circumstances. Every reasonable effort should be made to keep exposures as far below this level as practica- ble. Similarly, it is obviously appropriate to exceed this level if a careful study indicates that the probable benefits will outweigh the potential risk. Thus, the degree of control effort does not depend solely on whether or not this Guide is being exceeded. Rather, any

exposure of the population may call for some control effort, the magnitude of which in- creases with the dose. 5.4 Under certain conditions, such as wide- spread radioactive contamination of the en- vironment, the only data available may be related to average contamination or expo- sure levels. Under these circumstances, it is necessary to make assumptions concerning the relationship between average and maxi- mum doses. The Federal Radiation Council suggests the use of the arbitrary assumption that the majority of individuals do not vary from the average by a factor greater than three. Thus, we recommend the use of 0.17 rem for yearly whole-body exposure of aver- age population groups. (It is noted that this guide is also in essential agreement with cur- rent recommendations of the NCRP and the ICRP.) It is critical that this guide be applied with reason and judgment. Especially, it is noted that the use of the average figure, as a substitute for evidence concerning the dose to individuals, is permissible only when there is a probability of appreciable homogeneity concerning the distribution of the dose with- in the population included in the average. Particular care should be taken to assure that a disproportionate fraction of the aver- age dose is not received by the most sensitive population elements. Specifically, it would be inappropriate to average the dose between children and adults, especially if it is be- lieved that there are selective factors mak- ing the dose to children generally higher than that for adults. 5.5 When the size of the population group under consideration is sufficiently large, con- sideration must be given to the contribution to the genetically significant population dose. The Federal Radiation Council endors- es in principle the recommendations of such groups as the NAS-NRC, the NCRP, and the ICRP concerning population genetic dose, and recommends the use of the Radiation Protection Guide of 5 rem in 30 years (exclu- sive of natural background and the purpose- ful exposure of patients by practitioners of the healing arts) for limiting the average genetically significant exposure of the total U. S. population. The use of 0.17 rem per cap- ita per year, as described in paragraph 5.4 as a technique for assuring that the basic Guide for individual whole body dose is not exceed- ed, is likely in the immediate future to assure that the gonadal exposure Guide is not ex- ceeded. The data in Section III indicates that allocation of this population dose among various soure-es is not needed now or in the immediate future. A major difficulty has been the misinterpre- tation of these standards, particularly in the public mind. The intent as stated is that no in- dividual in the general population should re- ceive whole-body exposure of more than 0.5 rem/year and that the average exposure of population groups should not exceed 0.17 rem/ year. What is often not realized is that one or the other of these limits may be governing de- pending on the nature of exposure. For exam- ple, if the exposure were to arise from specific locations such as nuclear power plants or re- processing plants and it were assured that no individual at the boundaries of the installa- tions could be exposed to more than 0.5 rem/ year, it would be physically impossible for the U. S. population averages to approach any- where near the level of 0.17 rem/year from such sources. Accordingly, we feel (disregarding numerical values) that both individual and average population guidelines should be main- tained but that clarification should be included as an integral part of the regulatory state- ment. In addition to individual and average popula- tion guidelines, we recommend that an addition- al limitation be formulated (not as a basic standard but for generating guidance) that takes into account the product of the radiation exposure and the number of persons exposed; this might be expressed in terms of person- rems. This need arises from acceptance of the non-threshold approach in risk estimates which implies that absolute harm in the popu- lation will be related to such a product. Opera- tionally, for example, there would be advan- tage in assessment of trade-offs in connection with the siting of nuclear installations as re- lated to the population densities of areas under consideration. The above recommendations could be imple- mented with present knowledge. We now come to an important area that requires newer ap- 9

preaches. It is suggested that numerical radia- tion standards be considered for each major type of radiation exposure based upon the re- sults of cost-benefit analysis. As a start, con- sideration should be given to exposures from medical practice because of present relatively high levels of exposure and from nuclear power development because of future problems of energy production and the need for public un- derstanding. With the development of modern health care programs in the Western world, there has been a marked increase in the use of radiation in the healing arts—medical diagnostic radiology, clinical nuclear medicine, and radiotherapy. This has resulted in the recognition that medi- cal radiation now contributes the largest frac- tion, by one or two orders of magnitude, of the dose from man-made radiation to the United States public. In 1970, it is estimated that 129 million persons, or 63% of the population in the United States, received 210 million diagnostic radiological examinations, i.e., a rate of 68.5 examinations per 100 persons, and an increase of about 2% per year since 1964. The exposure rate is further increased by the estimated 8 mil- lion pregnant females at risk during the year 1970. At present, the estimated dose which is genetically significant to the population is of the order of 30 to 60 mrem per person per year, i.e. about 50% the level of natural radiation exposure in the United States. The significance of this lies in the absolute reduction of expo- sure that could be brought about at relatively low cost with no reduction in medical benefit and in addressing four important issues which center on the continued growth of health care delivery in this country, (a) At present, it does not appear feasible that the large number of variables involved in the use of radiation in health care to the public permit valid effica- cious guidelines for medical practice. However, there is convincing evidence that certain non- selective mass screening radiographic proce- dures do not provide sufficient diagnostic health rewards for costs incurred, e.g., mass chest radiography for carcinoma of the bron- chus and possibly for pulmonary tuberculosis, mass gastric radiography, routine pre-employ- ment radiography for insurance purposes of some foodhandlers, and possibly screening mammography. (b) Attention must be directed toward the reduction of medical radiation dose to the pregnant or potentially pregnant fe- male, in view of the evidence for significantly greater radiation sensitivity of the developing ovum and fetus, (c) Significant reduction of mean genetically significant dose can be brought about through programs of education, improvement of equipment, and certification of all persons in the healing arts who use radia- tion for diagnosis and therapy. Special atten- tion should be given to testis shielding. On the basis of mouse data, we would expect the hu- man male to be much more susceptible to radia- tion-induced mutation than the female. Also, the genetically significant dose of medical ra- diation is about twice as great in males as in females. For these two reasons, testis shield- ing, which is relatively simple, could reduce the number of radiation-induced mutations to a small fraction of the present number, (d) Con- trol and regulation of present and future tech- nological equipment responsible for medical exposure may be among the most feasible ave- nues to effect a continued reduction of dose due to medical radiation exposure. The difficulties in attaining a useful cost- benefit.analysis for nuclear power are formida- ble and will require interdisciplinary ap- proaches well beyond those that have yet been attempted. Areas that require evaluation in- clude: (a) projection of energy demands, (b) availability of fuel resources, (c) technological developments (clean combustion techniques, coal gasification, breeder reactors, fusion proc- esses, magnetohydrodynamics, etc.), (d) public health and environmental costs of electrical energy production from both nuclear and fossil fuel including aspects of fuel extraction, con- version to electrical energy, and transmission and distribution. 10

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In the summer of 1970, the Federal Radiation Council (whose activities have since been transferred to the Radiation Office of the EPA) asked the National Academy of Science for information relevant to an evaluation of present radiation protection guidelines. This report is a response to that request.

It presents a summary and analysis, by members of the Advisory Committee on the Biological Effects of Ionizing Radiations and its subcommittees, of current knowledge relating to risks from exposure to ionizing radiation. In many respects, the report is a sequel to the reports of the Committee on the Biological Effects of Atomic Radiation, published by the NRC-NAS from 1956-1961.

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