SYNTHESIS OF THE RESEARCH LITERATURE 33 



The transfer to humans seems Umited because the transuranic elements are not 

 significantly enriched in fresh edible fish (Edgington, Wahlgren, and Marshall, 1976; 

 Dahlman, Bondietti, and Eyman, 1976; Eyman and Trabalka, 1977; Pentreath and 

 Lovett, 1976; 1978; Pentreath et al., 1979). 



Prediction of Long-Term Behavior 



The long half-lives of several isotopes of the transuranic elements necessitate tlie 

 estimation of their behavior and effects over thousands of years. The behavior of 

 transuranic elements over a 30-yr interval may not properly represent behavior over more 

 extended periods. Uncertainties arise principally from effects of physical and biogeo- 

 chemical processes on the redistribution and form of transuranic elements in the 

 environment and from effects of these changes on biological availability. 



Several research approaches have been taken to estimate the long-term behavior of 

 transuranic elements. These include (1) basic studies of environmental influences and 

 mechanisms that may alter distribution and biological availability over time; (2) investiga- 

 tions of the behavior of naturally occurring elements that have been in the environment 

 over geologic time and may exhibit analogous behavior; and (3) investigations of the 

 distribution and behavior of transuranic elements presently in the environment as a result 

 of defense activities. These approaches have developed information highly useful for 

 predictive purposes, but considerable research remains to be done before a reliable model 

 can be developed. It is essential to understand factors influencing the chemical speciation 

 of plutonium in the vicinity of biological membranes prior to uptake and how these 

 chemical changes influence the transfer within organisms and between trophic levels. This 

 will require more refined mechanistic studies (approach 1) using studies of analog 

 elements and plutonium distribution from fallout (approaches 2 and 3) to verify 

 predictions. For example, the behavior of plutonium is largely governed by the chemistry 

 of its lower oxidation states, Pu(III) and Pu(IV). However, Pu(V and VI) may be present 

 in highly oligotrophic lakes. Thus, under conditions in wliich the valence state controls 

 plutonium chemistry, the behavior of naturally occurring Th(IV) and U(VI) may serve as 

 analogs of Pudll + JV) and PufVI) in tests of predictions with respect to matrix and 

 environmental factors (e.g., pH, Eh, and ionic composition). The results of investigations 

 to define the distribution of plutonium from defense activities (approach 3) can be used 

 in a similar manner. 



The complexity of the environmental chemistry of plutonium has required a major 

 basic research effort. Unless the mechanisms responsible for the behavior of plutonium 

 are known, it is not possible to develop or validate predictive models. For example, to 

 determine the validity of certain analog elements of plutonium, one must first determine 

 the predominant plutonium valence states and the conditions under which these valences 

 exist. Only then can comparisons be made with naturally occurring elements with similar 

 valences. Americium and neptunium, which have more than one oxidation state, must be 

 studied in this manner. The chemistry of these elements is less complex than that of 

 plutonium, and more rapid progress can be expected. Curium has only one oxidation 

 state, Cu(III), and analog chemistry should be straightforward. 



Perhaps the most important factor Umiting our ability to predict the transport of 

 transuranic elements in ecosystems is our knowledge of ecosystem structure and function. 

 Prediction of the behavior of transuranic elements in the environment requires 

 infoirnation as to the concentrations of these elements in important ecosystem 



