326 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 7 Stability of DTPA Complexes with the Transuranic Elements* 



*From Hafez (1969). 



fCurium can be expected to form complexes of stabilities similar to 

 americium. 



:(: Unstable in oxygenated solutions. 



However, considering the known products of microbial metabolism of organic substances, 

 including a number of strong complexing agents and the susceptibility of a number of the 

 transuranic elements to complexation, it can be concluded that the transuranic elements, 

 initially immobilized through biological uptake, may be at least as soluble and perhaps 

 more soluble on decomposition. 



In preliminary studies (R. E. Wildung and T. R. Garland, unpublished) plutonium- 

 amended soil containing largely undecomposed roots from a previous barley crop was 

 leached with water, and plutonium solubility was compared with a fallow soil containing 

 plutonium at similar levels. The results indicated that soluble plutonium was initially 

 immobilized by incorporation into roots, decreasing by a factor of 10 after root growth. 

 Root decomposition studies are in progress. Previously observed (Romney, Mock, and 

 Larson, 1970) increases in plutonium uptake from soils by plants with increased time, 

 generally attributed to increased root development, may have been due to increased 

 availability through a recycling process on the decomposition of plant roots. The 

 importance of the process will be dependent on transuranic-element availability to 

 different plants and microorganisms, the turnover rate of this tissue in soils under 

 different conditions, and the stability, chemistry, and biological availability of trans- 

 uranic-element metabolites. Studies are presently under way to provide this information 

 as a basis for establishing the long-term effects of recycling processes. 



Microbial Influence on the Availability and Form of 

 Transuranic Elements in Plants and Animals 



Plants 



The results of investigations to physicochemically characterize the mobile forms of 

 plutonium in soils (<0.1% of total plutonium) suggested that mobile plutonium was 

 largely particulate (Garland and Wildung, 1977; previous section). The nonparticulate, or 

 soluble, fraction was present in insufficient quantities, at any single point in time, to 

 separate from soil and chemically characterize with the present methods. However, for 



