Microbial mobilization and immobilization of plutonium

Microorganisms present in transuranic (TRU)- and mixed-wastes and in contaminated soils can bring about the transformation of plutonium (Pu) and affect its stability and mobility. Microbial dissolution of Pu is due to the production of sequestering agents, enzymatic oxidation of Pu(IV) to Pu(V) and Pu(VI) under aerobic conditions, or reduction of Pu(IV) to Pu(III) under anaerobic conditions. Immobilization is due to reduction of Pu(VI) or Pu(V) to Pu(IV), bioaccumulation extracellularly or intracellularly, and bioprecipitation. Disproportionation reactions of Pu(V) can also generate soluble Pu(VI) and insoluble Pu(IV) species. Plutonium is transported predominantly as colloids but microbes under appropriate conditions can affect the formation or destabilization of colloids. In this paper, the abundance of microbes in Pu contaminated soils and radioactive wastes and the mechanisms microbial dissolution and immobilization of Pu are reviewed.