Reduction of Pu by Dissimulatory Metal-Reducing Microorganisms

Plutonium is a radionuclide contaminant of interest to the DOE that occurs at a number of DOE legacy waste sites, including Hanford, Washington. In many cases, it was co-disposed with EDTA (ethylendiaminetetraacetate), a strong chelating agent that may enhance Pu solubility and thus its mobility. Little is known about the microbial effects on Pu speciation and fate, and the role co-contaminants may play in these reactions. However, in contrast to most other metal ions that reduce to insoluble precipitates, the microbial reduction of Pu(IV) is expected to present products with potentially greater solubility and thus, mobility. Therefore, a comprehensive understanding of the microbial effects on Pu geochemistry is needed particularly to discriminate between Pu solubilization and reduction reactions. We hypothesized that dissimilatory metal-reducing bacteria could reduce Pu(IV) and ultimately increase its solubility. In the experiment presented here, Shewanella oneidensis MR-1 was able to reduce PuO2(am), but not solubilize it; S. oneidensis MR-1 and EDTA together were observed to enhance Pu reduction and solubilize it. Ongoing research seeks to identify the speciation of Pu during these reactions, the stability of the equilibrium products, and also strives to identify the location of these reactions (cellular, extracellular).