duodenum were 95.1 and 96.6% for plutonium-238; for plutonium-239, they were 44.5 and 90.0%. This study is still in progress, and americium-241 analyses will be included in all future work. The major problem at present involves expediting the sample analyses for transuranium nuclides. FUTURE ACTIVITY PLANS 1. A comparison of the solubilities of biologically incorporated and inorganic plutonium-238 in an artificial rumen and simulated gastrointestinal fluids. The results of the study previously described indicate the possibility that comparatively very small amounts of plutonium may be in an organic form, and that the biological availability may be much greater than that of inorganic forms. The digestion of plutonium-contaminated fungal tissue in an artificial rumen and tn vittro bovine gastrointestinal fluids would provide a convenient means to compare the biological availability of biologically incorporated plutonium with inorganic plutonium. It is proposed that Aspergillus niger be cultured in a medium containing plutonium-238 nitrate. The fungal tissue will be collected and digested in an artificial rumen, | followed by further digestion in simulated abomasal and intestinal fluids. Other digestion flasks will contain plutonium-238 nitrate for comparison. =" The objective of this study is to determine whether organic binding protects plutonium from being removed from solution by competing chemical reactions, such as adsorption, formation of insoluble salts, or polymerization. 38