4 BIOLOGICAL EFFECTS OF ATOMIC RADIATION 



the earlier estimates of genetic damage from fallout were based on data from acute rather than 

 chronic irradiation means that the effect of a given amount of fallout, or other radiation de- 

 livered at a low rate, may be less than was previously estimated. It should be emphasized that 

 estimates of human hazards continue to be based largely on data from mice. 



Because of the finding that genetic effects per unit of radiation dose received at a low dose 

 rate might be less than previously estimated, the Committee has reconsidered its earlier recom- 

 mendation. It is presumably safe to conclude that the estimates of the genetic effects of fallout 

 radiation and of other radiation at similar low intensities should now be based on mutation 

 rates at least as low as those found with chronic irradiation of mice. However, most of the 

 man-made radiation to which the population of the United States is exposed involves dose 

 rates not yet adequately investigated experimentally. For example, we do not know whether 

 the effects of low doses given at high dose rates, as in medical exposures, will be more like 

 the response from acute irradiation or more like that from chronic irradiation. In the future 

 it may be desirable to relate maximum permissible exposures to dose rate at well as to total 

 dose. But before this can be done, more information is needed at additional radiation in- 

 tensities and for fractionated exposures. In the absence of such information, the Committee 

 continues to recommend that for the general population the average gonadal dose accu- 

 mulated during the first thirty years of life should not exceed 10 r of man-made radiation, and 

 should be kept as far below this as is practicable. This is in essential agreement with the most 

 recent suggestion of the International Commission on Radiological Protection. 



The medical and dental professions are commended for their continuing efforts to reduce 

 diagnostic and therapeutic radiation exposures to the lowest levels consistent with sound 

 medical and dental practice. At the same time it is urged that further steps be taken to im- 

 prove medical records, including those of radiation exposures, in ways that will make them 

 more useful than they now are for investigations of the genetic and other effects of radiation, 

 as well as for studies of human genetics in general. 



The new findings have not changed the evaluations presented in 1956. These new de- 

 velopments do, however, emphasize the unique responsibility of geneticists to so stimulate and 

 guide research that the urgently needed technical information is obtained as effectively and as 

 promptly as possible. 



II. Responsibilities Of Geneticists 



The dramatic exploitation of nuclear energy for military and peacetime purposes has 

 made informed persons acutely aware that man-made ionizing radiation, whatever its source, 

 is now an important addition to a constantly changing list of hazards to human existence and 

 well-being. Exposures from medical uses in technologically advanced nations are now about 

 equal to background and need to be taken into account to a corresponding degree. 



Insofar as the uses of nuclear energy add radioactive contaminants to the general en- 

 vironment of man, and especially to the atmosphere, important moral issues arise even though 

 the magnitude of the radiation to the germ line is now small relative to natural background 

 levels. These new uses make possible, for the first time in human history, the inescapable 

 exposure of world populations, in some instances without consent, to additional radiation un- 

 detectable by the unaided human senses and capable of producing deleterious changes in the 

 hereditary material. 



