REFERENCE THE RELATIONSHIP OF MICROBIAL PROCESSES TO THE FATE OF TRANSURANIC ELEMENTS IN SOIL Fried, 5., A. M. Friedman, J. J. . Hines, » R. R. W. W , Atcher, » L. A L. A. Qu Quarterman, and A. Volesky, 1976. "The Migration of Plutonium and Americium in the Lithosphere." In: Actinidee in the Environment. ACS Symposium Series #35, April 9, 1976. A. M. Friedman, Ed pp. 19-46. , R. E. Wildung, H. Drucker and F. H. F. Au*® Battelle Pacific Northwest Laboratories Richland, Washington ABSTRACT This review considers the influence of soil physiochemical and microbial processes on the long-term solubility, form, and plant availability of plutonium and other transuranic elements important in the nuclear fuel cycle. Emphasis is placed on delineation of the relationships between soil chemical and microbial processes and the role of soil microorganisms in effecting solubilization and transformation of elements considered largely insoluble in soils strictly on the basis of their inorganic chemical characteristics. Soluble, diffusible Pu in soile (usually less than 0.1% of total) appears to be largely present as particulates of hydrated oxide, but several lines of evidence suggest that microorganisms may influence the solubility of Pu and that the nonparticulate plant-available fraction is stabilized in solution by inorganic or organic ligands of limited concentration in soil. The role of soil microorganisma in influencing the solubility, form and plant-availability of the transuranics is discussed on the basis of the (1) known chemistry of organic ligands in soils, (2) effects on the soil microflora, and (3) principal microbial transformation mechanisms, including direct alteration (valence state, alkylation), indirect alteration (metabolite interactions, influence on the physiochemical environment), and cycling processes (biological uptake and release on decomposition of tissues). The toxicity of Pu to microorganisma depends on Pu solubility in soil. However, soil microorganisms are generally resistant to Pu, with toxicity apparently due to radiation rather than chemical effects. Highly resistant bacteria, fungi, and actinomycetes have been isolated from soil, and these organisms have been shown to be capable of transporting Pu into the cell and altering its form in thé ce]li and in solution. The resulting soluble Pu complexes tend to be of higher molecular weight than simple complexes (Pu-DTPA) and negatively charged, The form of Pu, although not welldefined, is dependent upon organism type, carbon source, and time of Pu exposure during growth. These factors, in turn, are a function of Pu source, soil properties, and soil environmental conditions. Knowledge of the relative influence of these factors serves as a valuable basis for predicting the long-term behavior of Pu and other transuranic elements in the terrestrial environment. * Environmental Monitoring and Support Laboratory U.S. Environmental Protection Agency Las Vegas, Nevada 126 127