330 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 8 Gastrointestinal Transfer of Plutonium in Rats as a 

 Function of Plutonium Source 



*Analyzed 4 days after a single administration. 



a factor of 2. Thus the differences in the gastrointestinal absorption between leaves and 

 stems appeared to reflect differences in relative solubility. The results of preliminary 

 studies indicated that more than 90% of the soluble plutonium in either stems or leaves 

 was complexed Pu(IV). These studies are continuing in an effort to evaluate the 

 importance of the ingestion pathway for transuranic-element uptake by man and to 

 determine the factors that influence the rate and extent of biological uptake. 



Recommendations for Future Research 



A broad range of soil— plant concentration ratios (10~^ to 10~^) has been reported for 

 the transuranic elements (Energy Research and Development Administration, 1976). If 

 this variability is attributed to the usual unexplained experimental and environmental 

 parameters, the information would be of little use in predicting the long-term behavior of 

 these elements. However, a closer examination shows that, although the ratios ranged 

 over many orders of magnitude, they encompassed, and were often dependent on, 

 different source terms, soil types, plant species, plant components, climatic conditions, 

 extent of foUar contamination, and kinetic factors. Consideration of these variables and 

 use of rapidly accumulating information on transuranic-element behavior at the chemical, 

 microbiological, and physiological levels should allow reduction of the level of 

 unexplained variabihty by many orders of magnitude and provide a valuable basis for the 

 prediction of transuranic-element behavior over a broad range of conditions. 



There is a need to continue to develop a basic understanding of the processes 

 influencing the fate of transuranic elements in soils and plants over a range of soil types 

 and experimental conditions representing those likely to be encountered in the 

 environment. Research should emphasize those elements which are (1) expected to be 

 present in soil in the highest concentration, (2) most soluble in soil, (3) mobile in the 

 plant, and (4) transported to edible tissues. Source terms receiving future emphasis should 

 be those likely to result from the nuclear fuel cycle as opposed to fallout. From previous 

 discussions of the soil chemistry of the transuranic elements, which illustrate the marked 

 differences in soil behavior and plant availability resulting from different source terms, 

 sources due to fallout and local nuclear testing, useful for initial approximations, cannot 

 be taken as fully representative for validation purposes. 



Research should emphasize determination of (1 ) source-term physicochemical 

 characteristics (composition, mineralogy, particle size, and valence) as a function of 

 source (fallout, reactor operation, reprocessing, and burial leachates); (2) physical 

 redistribution processes (erosion and resuspension); (3) biological redistribution processes 



