TRANSURANICS IN TERRESTRIAL ENVIRONMENT 709 



Historically, assessments of radionuclides in the environment have considered man to 

 be the critical organism. Tlie assumption has often been made that, if adequate protection 

 for man is assured, we need not worry about ecological effects. Auerbach (1971) has 

 addressed this question with the conclusion, "Piesent knowledge based on these and 

 similar studies of the ecological effects of low-level chronic doses, such as could result 

 from routine reactor releases under current standards, guidelines, and operational 

 experience, indicates that any possible biological effects would be undetectable." 

 Althougli this philosophy generally appears defensible, especially for reactor effluents as 

 stated, I hope that we do not blindly adopt it for all situations. For example, 

 nuclear-waste disposal could present unanticipated ecological problems in the future, 

 possibly without causing hazardous doses to humans. 



Present Status and Directions for Future Work 



To add clarity, before discussing research needs and possible directions for future work, I 

 will recapitulate what I think is the status of our knowledge on biological responses to 

 alpha emitters in the environment. Apparently, transuranics have not been experimentally 

 applied to study plots in the field. On the basis of limited observations of terrestrial 

 environments accidentally or inadvertently contaminated with plutonium in the range of 

 10 to 1000 )uCi/m^, no clear-cut ecological effects attributable to plutonium have been 

 found. A few investigations have shown biological differences between areas containing 

 natural alpha radioactivity in the range of 5 to 200 /jCi/m^ in the top 3 cm of soil and 

 nearby control areas. It is not clear, however, that the differences are caused by variations 

 in radiation dose. Simulation models and available data imply that humans should be able 

 to occupy and derive sustenance from land areas containing of the order of 20 to 200 /iCi 

 ^^^Pu/m^ in the top 3 cm of soil without exceeding the nonoccupational maximum 

 permissible dose to critical organs as recognized by the ICRP. Simplified calculations 

 suggest that ^^^Pu applications of roughly 1 Ci/m^ may be required in grassland areas to 

 cause significant mortahty in plant populations. I am not aware of computational models 

 relating ecological effects to the level of apphcation of transuranics other than plutonium. 

 The general lack of confidence in the accuracy of our predictive capability at present 

 appears to justify substanfial research efforts in this area. The shortcomings of the three 

 general approaches have been discussed; yet I see no other approaches to the problem. 

 Therefore it seems that enhanced efforts in each area are called for with continual 

 integration of findings from each. 



For direct measurements of the relationship between levels of transuranic application 

 and ecological effects, such applications would need to be made under controlled 

 experimental designs. The use of shorter Uved transuranics and engineered barriers to 

 prevent unwanted dispersal of the radioactive material would reduce the risks from such 

 an experiment. If such experiments ever become feasible, remote, controlled areas, such 

 as the Hanford Reservation, the Idaho National Engineering Laboratory, and the Nevada 

 Test Site, might be considered. In addition, the application of effect-inducing quanfities 

 of transuranics to terrestrial microcosms might be considered. Although direct-application 

 experiments seem needed from a scientific viewpoint, I do not necessarily advocate them. 



Areas presently contaminated with substantial quantities of transuranics should be 

 investigated for suitabiHty for long-term study. Areas in which higher levels of 

 transuranics occur without a previous history of contamination with other materials, such 

 as fission products, and for which good control areas exist would seem particularly 



