HUMAN EFFECTS AND RISK ESTIMATES 697 



"the bone-tumor risk from plutonium is no greater than that from radium, and might be 

 less." Certainly it would seem clear by now that occupational exposure to plutonium has 

 not resulted in the kind of tragedy visited on the radium dial painters or the uranium 

 miners. 



Experience with Natural Radiation in Man 



Alpha-emitting elements are a natural part of man's environment. He has lived with these 

 internally deposited radioelements and with radiation from other natural sources 

 throughout the history of the species. It is of some relevance to note that inhaled 

 naturally occurring alpha-emitting radionuchdes contribute an average annual dose of 

 about lOOmrem to the lung and that naturally occurring alpha emitters in bone 

 contribute an average annual dose at bone surfaces of about 40 mrem (National Council 

 on Radiation Protection and Measurements, 1975). Although these doses cannot be 

 related to any measure of specific effects, they have been at least tolerable on the 

 evolutionary scale, and therefore sUght increases would not be expected to have 

 catastrophic effects. 



Experience with Other Types of Radiation in Man 



Inferences concerning the effects of transuranic elements in man may be drawn from 

 information available on the effects of other forms of ionizing radiation in man; e.g., data 

 derived from medical, occupational, accidental, or wartime exposure of humans to 

 different radiation sources, including external X radiation, atomic bomb gamma and 

 neutron radiation, and radium, radon, and radon daughters. Such information was 

 summarized by the BEIR Committee (National Academy of Sciences-National Research 

 Council, 1972) and, most recently, by the United Nations Scientific Committee on the 

 Effects of Atomic Radiation (UNSCEAR) (1977). Both groups arrived at comparable risk 

 estimates. England's Medical Research Council (MRC) (1975), considering much the same 

 information covered in the BEIR and UNSCEAR reports, derived risk estimates 

 specifically applicable to plutonium. 



Of particular relevance are recently accumulated data on the carcinogenicity of 

 ^^"^Ra in human bone (Spiess and Mays, 1970; 1973); ^^"^Ra has a very short half-Ufe 

 (3.62 days) and, because of this, irradiates only the surface layer of bone in much the 

 same manner as transuranics. From these ^^"^Ra data. Mays et al. (1976) have estimated 

 human bone cancer risks from plutonium; Mays (1976) has also estimated liver cancer 

 risks, which are based largely on experience with Thorotrast, and lung cancer risks, which 

 are based largely on data from the Japanese atomic bomb survivors. 



Concluding Comments 



Table 2 compares estimates of cancer risk from several sources previously discussed. Also 

 included in Table 2 are estimates of genetic risk as derived in the BEIR and UNSCEAR 

 reports. 



Although of dubious quantitative applicabiUty to the problems of environmental 

 exposure because of the extrapolation uncertainties discussed previously, the kind of data 

 presented in Table 2 will inevitably be used to estimate health effects from such 

 exposure. As an example of such an exercise, in Table 3 we have derived an estimate of 

 the human health consequences of the environmental dispersal of bomb-test plutonium in 



