of the humic acids and some other microorganisms are known to produce acids agents then xing comple These type which also have complexing properties. which can forms into tuents attack minerals, transforming the mineral consti e that assum can We . plants and more easily be taken up by microorganisms altered is ) ranics transu other deposited, relatively insoluble plutonium (or nces. substa c organi xing comple by similar processes, namely by the action of from soil NTS s of studie This view is supported by the results of extraction excess of Area 13 which demonstrated that citric acid solutions can remove in s showing r result Simila 5% of the deposited plutonium (Beckert and Au, 1975). the efficiency of certain naturally occurring chelating agents for solubilizing plutonium were reported by others (Bondietti et al., 1975; Tamura, 1975). Obviously, the production of complexing agents is not limited to soil microorganisms; compounds with complexing properties are also contained in and exuded by plant roots and other organisms. Once the soil-deposited, relatively insoluble plutonium has been transformed into a more soluble form, a larger fraction will probably be taken up by microorganisms and by plant roots. Also, more soluble forms of plutonium may more easily be translocated vertically and horizontally by rain, or transferred to soil-ingesting animals ranging from earthworms to cattle, or become airborne with dust particles. Microbial cells can be transported or dispersed laterally or vertically in the soil by water or by predatory actions (Griffin, 1972; This adds another dimension to the translocation and Ireland, 1975a, 1975b). bioavailability of plutonium with time because predators, such as protozoa, nematodes, and arthropods, have a broader range of movement than soil fungi or bacteria. It has been emphasized that the importance attached to the incorporated and soluble over the nonincorporated, insoluble forms of plutonium.in soils lies in the probable differences in bioavailability and in biotransport to other trophic levels (Dunaway, 1976). We do not know in what complexed form or forms plutonium is stored in microbial cells; but whatever form it may be, it is very probable that the complexed plutonium is more soluble upon release from cells than the relatively insoluble plutonium as deposited in soil. However, definite proof is lacking as to whether successive microbial generations enhance the bioavailability of plutonium, and thus, with time, increase its availability to other trophic levels and its biotransport in the soil system. Experiments have therefore been initiated to determine if under laboratory conditions the availability and transfer of plutonium are increased during successive generations of microbial growth. Several fungal genera including AspergtiZus will be cultured and incubated on malt agar plates which contain plutonium-238. Following incubation, part of the fungal materials will be collected and analyzed for plutonium; the remaining fungal growth will be terminated by ethylene oxide in part of the experiment and by heat treatment in another part. The plates will then be inoculated with spores of Aspergillus niger. After two or three weeks of incubation, aerial spores of A. ntger will be collected with the collection system described earlier (Au and Beckert, 1975b) and analyzed for plutonium. As many collections as feasible will be made to measure the transport of plutonium to successive generations. 223