HR: 0830h
AN: B41D-0920    [PDF]
TI: Biotransformation of pu(VI) by microorganisms
AU: * Ohnuki, T
EM: ohnuki@sparclt.tokai.jaeri.go.jp
AF: Japan Atomic Energy research Institute, Shirakata-2, Tokai, IB 319-1195 Japan
AU: Yoshida, T
EM: yoshida@sparclt.tokai.jaeri.go.jp
AF: Japan Atomic Energy research Institute, Shirakata-2, Tokai, IB 319-1195 Japan
AU: Ozaki, T
EM: tozaki@popsvr.tokai.jaeri.go.jp
AF: Japan Atomic Energy research Institute, Shirakata-2, Tokai, IB 319-1195 Japan
AU: Francis, A J
EM: ajfrancis@bnl.gov
AF: Brookhaven National Laboratory, P.O. Box 5000, Upton, NY 11973 United States
AB: The migration behavior of actinides in the environment due to microbial activity should be elucidated for estimating the potential hazards of geological disposal of high-level radioactive wastes. Actinides exist in the oxidation states, III, IV, V and VI in solution, and their chemical behavior differs each other. Actinides(V) and (VI) are more mobile than actinides(III) and (IV) in groundwater. In this study, we carried out the accumulation experiments of Pu(VI) by {\it Bacillus subtilis} and the mixture of B. subtilis and kaolinite to elucidate the role of microbes for the migration of Pu(VI). Accumulation experiments of Pu by {\it Bacillus subtilis}, kaolinite, and the mixtures were carried out for 4x10$^{-4}$ M Pu(VI) solution containing 0.01 M NaCl with its initial pHs between 3.2 and 6.3. Concentrations and oxidation states of Pu in the solutions were determined at 48 hours after the exposure. Sorbed Pu by {\it Bacillus subtilis}, kaolinite, and the mixtures was extracted with 1:1 H$_{3}$PO$_{4}$ solution for 5 minutes to determine its oxidation states. Oxidation states of Pu were determined by UV/VIS spectrometry. After 48 hours of the contact with Pu(VI) solution, Pu accumulated {\it Bacillus subtilis}, kaolinite and the mixtures were separated from the Pu(VI) solution, then were contacted with a 1 M CH$_{3}$COOK solution to examine reversibility of the sorbed Pu. Approximately 17% of the initial concentrations of Pu(VI) was sorbed by {\it Bacillus subtilis} at pH 3.2 and the amounts of the sorbed Pu increased with increasing pH. Similar trend was observed for the sorption of Pu on kaolinite. The oxidation state of Pu sorbed on {\it Bacillus subtilis} and kaolinite was Pu(IV) and Pu(VI), respectively at 48 hours after the contact. Approximately 30 and 90% of the sorbed Pu was desorbed from {\it Bacillus subtilis} and kaolinite in a 1 M CH$_{3}$COOK solution. The amounts of sorbed Pu increased and the desorbed fractions by a 1 M CH$_{3}$COONa solution decreased with increasing content of {\it Bacillus subtilis} in the mixtures. Oxidation state of the sorbed Pu on the mixture was IV. These results indicate that Pu is accumulated on {\it Bacillus subtilis} through precipitation of insoluble Pu(IV) due to the reduction of Pu(VI), and Pu(VI) is reversibly sorbed on kaolinite. Pu is preferably sorbed on {\it Bacillus subtilis} in the mixture because of the stronger association of Pu(IV) with {\it Bacillus subtilis} than Pu(VI). It is concluded that microorganisms function important roles in the migration of Pu(VI) in the environments.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1045 Low-temperature geochemistry
SC: Biogeosciences [B]
MN: 2003 Fall Meeting