Genetic risks to man from exposure to long-lived radionuclides

Ionizing radiation, irrespective of whether it is received from external sources or from internally-deposited radionuclides, is capable of causing genetic damage that will be transmitted from one generation to the next. Since strictly relevant human data is limited at present, there is no alternative to the use of data collected in experimental mammals for estimating genetic risks associated with the exposure of human populations to ionizing radiation.Animal studies reveal that plutonium reaching the testes and concentrates in the interstitial tissue but is later aggregated by macrophages, apparently leading to a reduction in effectiveness. For protracted alpha irradiation from testicular plutonium in the mouse, the RBE (relative biological effectiveness) for genetic effects of concern may be in a range of between 10 and 20, relative to chronic gamma irradiation. In female mice, plutonium appears to be much less effective although the data is very limited.Studies with beta emitters provide reasonable grounds for believing that in the case of chronic exposures to tritium, the RBE value may be about 2, whereas for others such as carbon-14, it may not be significantly different from unity.These and other results support the view that for plutonium alpha rays, the genetic risks following exposure of human males may be 10–20 times that estimated for chronic, low level, low LET irradiation, per unit absorbed testicular dose; for tritium exposures, the risks may be higher by a factor of 2, (again, relative to chronic gamma ray exposures) while for carbon-14, the risks are the same as that for chronic gamma irradiation. For estimating genetic risks following exposure of human females to radionuclides, in the absence of adequate data, it would be prudent to assume that the risks will be similar to those for irradiation of males.