Health Effects of Exposure to Low Levels of Ionizing Radiation BEIR V (1990) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-8
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In addition, there is concern about radioactivity in the environment around nuclear facilities and a need to set standards for cleanup and disposal of nuclear waste materials. Since the completion of the 1980 BEIR III report, there have been significant developments in our knowledge of the extent of radiation exposures from natural sources and medical uses as well as new data on the late health effects of radiation in humans, primarily the induction of cancer and developmental abnormalities.
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The current BEIR V Committee report includes information and analyses from the BEIR IV report that are appropriate for cancer and genetic risk assessment. In addition, this report addresses the delayed health effects that are induced by low linear energy transfer (LET)
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New analyses of the data on A-bomb survivors exposed in utero, together with the reassessment of the A-bomb dosimetry, have permitted delineation of the time-specific susceptibility to radiation-induced mental retardation, the most prevalent developmental abnormality to appear in humans exposed prenatally, and has allowed the risk of these effects to be estimated. In preparing risk estimates, the committee has relied chiefly on its own evaluations, using recently developed methods for the analysis of population cohort data, rather than relying solely on information in the scientific literature.
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of low dose-rate, low LET radiation is required to double the mutation rape in man. Heritable effects of radiation have yet to be clearly demonstrated in man, but the absence of a statistically significant increase in genetically related disease in the children of atomic bomb survivors, the largest group of irradiated humans followed in a systematic way, is not inconsistent with the animal data, given the low mean dose level, < 0.5 gray (Gy)
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Continued follow-up of the A-bomb survivors also has disclosed that the number of excess cancers per unit dose Induced by radiation is increased with attained age, while the risk of radiogenic cancer relative to the spontaneous incidence remains comparatively constant. As a result, the dose-dependent excess of cancers is now more compatible with previous "relative" risk estimates than with previous `'absolute" risk estimates; the Committee believes that the constant absolute or additive risk model is no longer tenable.
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The Committee examined in some detail the sources of uncertainty in its risk estimates and concluded that uncertainties due to chance sampling variation in the available epidemiological data are large and more important than potential biases such as those due to differences between various exposed ethnic groups. Due to sampling variation alone, the 90~o confidence limits for the Committee's preferred risk models, of increased cancer mortality due to an acute whole body dose of 0.1 Sv to 100,000 males of all ages range from about 500 to 1,200 (mean 760~; for 100,000 females of all ages, from about 600 to 1,200 (mean 810~.
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While experiments with laboratory animals indicate that the carcinogenic effectiveness per Gy of low-LET radiation is generally reduced at low doses and low dose rates, epidemiological data on the carcinogenic effects of low-LET radiation are restricted largely to the effects of exposures at high dose rates. Continued research is needed, therefore, to quantify the extent to which the carcinogenic effectiveness of low-LET radiation may be reduced by fractionation or protraction of exposure.
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As noted previously, the Committee's genetic risk assessment did not attempt to project risk for the category of diseases with complex genetic etiologies. Because genetically related disorders comparable to those in this heterogeneous category of human disorders may have no clearly definable counterparts in laboratory and domestic animals, the required research should be directed towards human diseases whenever feasible.
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