696 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 2 Comparison of Transuranic Health Risk Estimates 



*National Academy of Sciences- National Research Council, 1972. 



t Relative-risk model with lifetime plateau (U. S. Atomic Energy Commission, 1974). 



JAbsolute-risk model with 30-year plateau (U. S. Atomic Energy Commission, 1974). 



§ United Nations, New York, 1977. 



H Medical Research Council, 1975. 



**Mays, 1976. 



ft Data from Bair and Thomas, 1976. 



1 1 Expressed by UNSCEAR as risk per 10* rads of low-LET radiation to endosteal cells, 

 which should be roughly equivalent to risk per 10* rem of plutonium alpha radiation averaged 

 throughout bone. 



§§Data from Mays, 1976. 



m Specific genetic defects. 



***Defects with complex etiology. 



long-term low-level exposure to transuranics are lung, bone, and possibly liver cancers. 

 Most of these data are from experiments with plutonium, but they can probably be 

 applied to other transuranics with less error than is involved in many other unavoidable 

 assumptions. Although quantitative extrapolation from animal to man involves consider- 

 able uncertainty, the animal data suggest cancer risks per 10^ organ-rem of 60 to 200 for 

 lung (Bair and Thomas, 1976) and 10 to 100 for bone (Bair, 1974; Mays et al., 1976). 

 These estimates are compared with others in Table 2. 



Experience with Transuranics in Man 



It is clearly impossible to relate specific observed biological effects in man to the 

 exposure of man at present levels of environmental plutonium. Some conclusions have 

 been drawn from the absence of observed effects in the substantial numbers of persons 

 occupationally exposed to very much higlier levels of plutonium. Cave and Freedman 

 (1976), investigating the adequacy of present plutonium exposure limits, conclude that, 

 "total exposure represented by the available human data is not yet large enough to 

 substantiate fully, on a statistical basis, the value of 0.016 fJiCi for the maximum 

 permissible lung burden. However, regarded as a 'best estimate' this value should not be 

 too higli by a factor of more than 15 or by a factor of more than 40 at the 95% upper 

 confidence level." On the basis of the long-term survival without bone tumors of eiglit 

 "terminal" patients injected with plutonium, Rowland and Durbin (1976) conclude that, 



