Microbial impacts on the migration of actinides

アクチノイドの移行への微生物影響

尾崎 卓郎; 南川 卓也 ; 香西 直文   ; 坂本 文徳  ; 鈴木 義規; Francis, A. J.

Ozaki, Takuo; Nankawa, Takuya; Kozai, Naofumi; Sakamoto, Fuminori; Suzuki, Yoshinori; Francis, A. J.

アクチノイドの環境中における移行挙動への微生物影響について検討した。有機酸としてDFOを用いた場合、アクチノイドの微生物への吸着の序列はEu(III)(Amの代替)Th(IV)Pu(IV)となった。さらに、酵母細胞表面に吸着したウランが溶液中の化学組成が鉱物生成条件にならない場合でも鉱物化することを見いだした。また、3価希土類元素が微生物による有機酸分解に影響することを明らかにした。

The interaction of actinides with microorganisms has been extensively studied to elucidate migration behavior of actinides in the environments. However, the mechanisms of interaction of microorganisms and actinides are poorly understood. We have been conducting basic on microbial accumulation of actinides in order to elucidate the environmental behavior of actinides under relevant conditions. Effect of desferrioxamine B (DFO) on the sorption of Pu(IV), Th(IV) and Eu(III) (analog for Am(III)) on Pseudomonas fluorescens was studied. In the presence of DFO the sorption of Pu(IV), Th(IV) and Eu(III) on the cells increased with a decrease in pH from 7 to 4. In contrast, without DFO most of Pu(IV), Th(IV) and Eu(III) were precipitated from solution. Adsorption of DFO on the cells was negligible in the solution with and without metals. Adsorption of Pu(IV), Th(IV) and Eu(III) on P. fluorescens cells decreased in the order Eu(III) Th(IV) Pu(IV), which corresponds to increasing stability constant of the DFO complexes. These results indicate that Th(IV), Pu(IV) and Eu(III) dissociate when in contact with cells, after which the metals are adsorbed. Mechanism of uranium(VI) mineralization by the yeast Saccharomyces cerevisia e was examined by batch experiment at pH 3.2. FESEM-EDS, TEM, and visible diffuse reflectance spectrometry revealed the formation of H-autunite, HUOPO 4HO on the yeast cells. Thermodynamic calculations suggest that the chemical compositions of the solutions were undersaturated with respect to H-autunite, but were supersaturated with ten-times more U(VI) and P than were actually observed. Apparently, the sorbed U(VI) on the cell surfaces reacts with Preleased from the yeast to form H-autunite by local saturation. These findings indicate that the yeast's cell surfaces, rather than the bulk solution, offer the specific conditions for this geochemical process. We studied the effect of Eu(III) on the degradation o