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Suggested Citation:"Summary and Recommendations." 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:"Summary and Recommendations." 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:"Summary and Recommendations." 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:"Summary and Recommendations." 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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SUMMARY AND RECOMMENDATIONS In anticipation of the widespread increased use of nuclear energy, it is time to think anew about radiation protection. We need standards for the major categories of radiation exposure, based insofar as possible on risk estimates and on cost-benefit analyses which compare the ac- tivity involving radiation with the alternative options. Such analyses, crude though they must be at this time, are needed to provide a better public understanding of the issues and a sound basis for decision. These analyses should seek to clarify such matters as: (a) the environ- mental and biological risks of given develop- ments, (b) a comparison of these risks with the benefits to be gained, (c) the feasibility and worth of reducing these environmental and biological risks, (d) the net benefit to society of a given development as compared to the alter- native options. In the foreseeable future, the major contribu- tors to radiation exposure of the population will continue to be natural background with an average whole-body dose of about 100 mrem/ year, and medical applications which now con- tribute comparable exposures to various tis- sues of the body. Medical exposures are not under control or guidance by regulation or law at present. The use of ionizing radiation in medicine is of tremendous value but it is essen- tial to reduce exposures since this can be ac- complished without loss of benefit and at rela- tively low cost. The aim is not only to reduce the radiation exposure to the individual but also to have procedures carried out with maxi- mum efficiency so that there can be a continu- ing increase in medical benefits accompanied by a minimum radiation exposure. Concern about the nuclear power industry arises because of its potential magnitude and widespread distribution. Based on experience to date and present engineering judgment, the contribution to radiation exposure averaged over the U. S. population from the developing nuclear power industry can remain less than about 1 mrem per year (about 1% of natural background) and the exposure of any individu- al kept to a small fraction of background pro- vided that there is: (a) attainment and long- term maintenance of anticipated engineering performance, (b) adequate management of radi- oactive wastes, (c) control of sabotage and di- version of fissionable material, (d) avoidance of catastrophic accidents. The present Radiation Protection Guide for the general population was based on genetic considerations and conforms to the BEAR Committee recommendations that the average individual exposure be less than 10 R (Roent- gens) before the mean age of reproduction (30 years). The FRC did not include medical radia- tion in its limits and set 5 rem as the 30-year limit (0.JJ rem per year). Present estimates of genetic risk are ex- pressed in four ways: (a) Risk Relative to Natu- ral Background Radiation. Exposure to man- made radiation below the level of background radiation will produce additional effects that are less in quantity and no different in kind from those which man has experienced and has been able to tolerate throughout his history, (b) Risk Estimates for Specific Genetic Condi- tions. The expected effect of radiation can be compared with current incidence of genetic effects by use of the concept of doubling dose (the dose required to produce a number of mu- tations equal to those which occur naturally). Based mainly on experimental studies in the mouse and Drosophila and with some support from observations of human populations in Hiroshima and Nagasaki, the doubling dose for chronic radiation in man is estimated to fall in the range of 20-200 rem. It is calculated that the effect of 170 mrem per year (or 5 rem per 30-year reproduction generation) would cause in the first generation between 100 and 1800 cases of serious, dominant or X-linked diseases and defects per year (assuming 3.6 million births annually in the U.S.). This is an inci- dence of 0.05%. At equilibrium (approached af- ter several generations) these numbers would 489-797 O - 72 - 2

be about five-fold larger. Added to these would be a smaller number caused by chromosomal defects and recessive diseases, (c) Risk Relative to Current Prevalence of Serious Disabilities. In addition to those in (b) caused by single-gene defects and chromosome aberrations are con- genital abnormalities and constitutional dis- eases which are partly genetic. It is estimated that the total incidence from all these including those in (b) above, would be between 1100 and 27,000 per year at equilibrium (again, based on 3.6 million births). This would be about 0.75% at equilibrium, or 0.1% in the first generation, (d) The Risk in Terms of Overall Ill-Health. The most tangible measure of total genetic damage is probably "ill-health" which includes but is not limited to the above categories. It is thought that between 5% and 50% of ill-health is proportional to the mutation rate. Using a value of 20% and a doubling dose of 20 rem, we can calculate that 5 rem per generation would eventually lead to an increase of 5% in the ill- health of the population. Using estimates of the financial costs of ill-health, such effects can be measured in dollars if this is needed for cost- benefit analysis. Until recently, it has been taken for granted that genetic risks from exposure of popula- tions to ionizing radiation near background levels were of much greater import than were somatic risks. However, this assumption can no longer be made if linear non-threshold relation- ships are accepted as a basis for estimating cancer risks. Based on knowledge of mecha- nisms (admittedly incomplete) it must be stated that tumor induction as a result of radiation injury to one or a few cells of the body cannot be excluded. Risk estimates have been made based on this premise and using linear extrapo- lation from the data from the A-bomb survi- vors of Hiroshima and Nagasaki, from certain groups of patients irradiated therapeutically, and from groups occupationally exposed. Such calculations based on these data from irradiat- ed humans lead to the prediction that addition- al exposure of the U. S. population of 5 rem per 30 years could cause from roughly 3,000 to 15,000 cancer deaths annually, depending on the assumptions used in the calculations. The Committee considers the most likely estimate to be approximately 6,000 cancer deaths an- nually, an increase of about 2% in the sponta- neous cancer death rate which is an increase of about 0.3% in the overall death rate from all causes. Given the estimates for genetic and somatic risk, the question arises as to how this infor- mation can be used as a basis for radiation protection guidance. Logically the guidance or standards should be related to risk. Whether we regard a risk as acceptable or not depends on how avoidable it is, and, to the extent not avoidable, how it compares with the risks of alternative options and those normally accept- ed by society. There is reason to expect that over the next few decades, the dose commitments for all man- made sources of radiation except medical should not exceed more than a few millirems average annual dose to the entire U. S. popula- tion. The present guides of 170 mrem/yr grew out of an effort to balance societal needs against genetic risks. It appears that these needs can be met with far lower average expo- sures and lower genetic and somatic risk than permitted by the current Radiation Protection Guide. To this extent, the current Guide is un- necessarily high. The exposures from medical and dental uses should be subject to the same rationale. To the extent that such exposures can be reduced without impairing benefits, they are also un- necessarily high. It is not within the scope of this Committee to propose numerical limits of radiation exposure. It is apparent that sound decisions require technical, economic and sociological considera- tions of a complex nature. However, we can state some general principles, many of which are well-recognized and in use, and some of which may represent a departure from present practice. a) No exposure to ionizing radiation should be permitted without the expectation of a commensurate benefit. b) The public must be protected from radia- tion but not to the extent that the degree of protection provided results in the sub- stitution of a worse hazard for the radia- tion avoided. Additionally there should not be attempted the reduction of small risks even further at the cost of large sums of money that spent otherwise, would clearly produce greater benefit.

c) There should be an upper limit of man- made non-medical exposure for individu- als in the general population such that the risk of serious injury from somatic effects in such individuals is very small relative to risks that are normally accept- ed. Exceptions to this limit in specific cas- es should be allowable only if it can be demonstrated that meeting it would cause individuals to be exposed to other risks greater than those from the radiation avoided. d) There should be an upper limit of man- made non-medical exposure for the gener- al population. The average exposure per- mitted for the population should be consi- derably lower than the upper limit permit- ted for individuals. e) Medical radiation exposure can and should be reduced considerably by limiting its use to clinically indicated procedures utilizing efficient exposure techniques and optimal operation of radiation equipment. Consideration should be given to the fol- lowing: 1) Restriction of the use of radiation for public health survey purposes, unless there is a reasonable probability of significant detection of disease. 2) Inspection and licensing of radiation and ancillary equipment. 3) Appropriate training and certification of involved personnel. Gonad shielding (especially shielding the testis) is strongly recommended as a simple and highly efficient way to reduce the Ge- netically Significant Dose. f) Guidance for the nuclear power industry should be established on the basis of cost- benefit analysis, particularly taking into account the total biological and environ- mental risks of the various options avail- able and the cost-effectiveness of reducing these risks. The quantifying of the "as low as practicable" concept and consideration of the net effect on the welfare of society should be encouraged. g) In addition to normal operating conditions in the nuclear power industry, careful consideration should be given to the prob- abilities and estimated effects of uncon- trolled releases. It has been estimated that a catastrophic accident leading to melting of the core of a large nuclear reactor could result in mortality comparable to that of a severe natural disaster. Hence extraordi- nary efforts to minimize this risk are clearly called for. h) Occupational and emergency exposure limits have not been specifically consi- dered but should be based on those sec- tions of the report relating to somatic risk to the individual. i) In regard to possible effects of radiation on the environment, it is felt that if the guidelines and standards are accepted as adequate for man then it is highly unlike- ly that populations of other living organ- isms would be perceptibly harmed. Never- theless, ecological studies should be im- proved and strengthened and programs put in force to answer the following ques- tions about release of radioactivity to the environment: (1) how much, where, and what type of radioactivity is released; (2) how are these materials moved through the environment; (3) where are they con- centrated in natural systems; (4) how long might it take for them to move through these systems to a position of contact with man; (5) what is their effect on the environment itself; (6) how can this infor- mation be used as an early warning sys- tem to prevent potential problems from developing? j) Every effort should be made to assure ac- curate estimates and predictions of radia- tion equivalent dosages from all existing and planned sources. This requires use of present knowledge on transport in the en- vironment, on metabolism, and on relative biological efficiencies of radiation as well as further research on many aspects.

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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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