RELATIONSHIP OF MICROBIAL PROCESSES 331 



(litter incorporation and root decomposition); (4) processes of solubilization and/or 

 transformation of refractory materials entering soil and the factors influencing the form 

 and equilibria between relatively insoluble forms and soluble chemical species (soil type, 

 soil solution composition, pH, temperature, redox conditions, diffusion, and microbial 

 action); (5) the capacity of representative plant species to assimilate soluble chemical 

 species, plant alteration of chemical form, and translocation to edible plant components 

 as a function of plant growth stage, form, and concentration in soil and the presence of 

 competitive ions in the soil solution; and (6) the nature and extent of the above processes 

 on a regional basis, as influenced by soil, plant, and climatic factors and land-use 

 practices. This information is currently being accumulated in laboratory studies, and 

 initial investigations are under way in several geographic regions to selectively validate the 

 findings in the tleld. 



The role of the soil microflora must be viewed as only one contributory factor among 

 a number of highly important physicochemical and biological phenomena influencing the 

 overall behavior of the transuranic elements in terrestrial environments. However, 

 evidence is increasing that organic ligands resulting from microbial activity will play an 

 important part in influencing the behavior and plant availability of hydrolyzable species, 

 such as plutonium, in soils. Future studies in this area should involve a systematic 

 investigation of the major classes of soil organisms exhibiting highest transuranic-element 

 resistance and representing different metabolic types, determination of their ability to 

 alter transuranic-element form in soil, and evaluation of the soil and environmental 

 factors influencing the rate and extent of alteration. In view of the relatively high 

 concentrations of transuranic elements associated with roots and other organic 

 components in soil, particular emphasis should be placed on determining the role of the 

 microflora in recycling and redistribution processes. It is possible that microbial processes 

 responsible for alteration of metal form may function in a like manner for metals 

 exhibiting similar chemical properties, particularly for organisms exhibiting cross 

 resistance to these metals. Thus model systems may be available for those organisms 

 likely to be most responsible for alteration of metal form in soil over the long term, i.e., 

 those organisms capable of growth and reproduction at higher metal concentrations in the 

 immediate vicinity of refractory oxides or soil colloids with surface deposits of the 

 transuranic elements. 



A key integrating factor, in all studies of the transuranic elements and in 

 interpretation of environmental phenomena, is a knowledge of the chemical form of the 

 element. With this information studies conducted under broadly different conditions in 

 various substrates and biological media can be compared, and toxicological interpreta- 

 tions can be made on a common basis. 



Investigations that are currently under way in several institutions across the country 

 should ultimately provide a realistic evaluation of the role of microbial processes in 

 influencing the long-term behavior of the transuranic elements in soil. Furthermore, the 

 studies should provide a basis for evaluation of the availabihty of transuranic metabohtes 

 to plants and insight into the potential for entrance of these elements into foodstuffs for 

 a broad geographical region over the long term. 



Acknowledgments 



Appreciation is extended to H. Drucker for his technical contributions and advice during 

 the conduct of the PNL microbiological studies and to F.H.F. Au for review of portions 



