INFLUENCE OF MICROBIAL ACTIVITIES ON AVAILABILITY AND BIOTRANSPORT OF PLUTONIUM F. H. F. Au and W. F. Beckert Environmental Monitoring and Support Laboratory, Las Vegas U.S. Environmental Protection Agency ABSTRACT In this report, the data and conclusions from previous studies are summarized and discussed in context. Special attention is directed toward the effects of native vegetation and agricultural practices on soil microbial populations and the probable effects of changes in these microbial populations on the bioavailability and transport of plutonium to plants. In addition, the biological movement of transuranics in soil systems is addressed. A special technique developed for these studies to collect small particles is briefly outlined. The use of this technique, which eliminated cross-contamination problems, made possible uptake studies with various plutonium compounds using the soil fungus Aspergtllus niger. ongoing studies. The same technique is applicable to various phases of Experiments currently in progress are designed to elucidate the roles of various common soil microorganisms on the movement of transuranics in soil and on the bioavailability of transuranics to plants and animals. The results of these studies are expected to bring us one step closer toward a broader understanding of the importance of soil microbial interaction with transuranics in the environment. INTRODUCTION Microorganisms in plutonium-contaminated soils may play important roles as solubilizers and translocators of deposited plutonium. Solubilization processes will probably result in an increased transfer of plutonium from soil and plants to livestock, such as cattle, since solubilized plutonium is more readily absorbed by plants and animals. Translocation processes will contribute to plutonium migration within the soil profile. 219