Bioreduction of Uranium:  Environmental Implications of a Pentavalent Intermediate

• Published in: Environmental science & technology Vol. 39; no. 15; pp. 5657 - 5660
• Main Authors: Renshaw, Joanna C, Butchins, Laura J. C, Livens, Francis R, May, Iain, Charnock, John M, Lloyd, Jonathan R
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.08.2005
• Subjects: Applied sciences; Bacteria; Biodegradation of pollutants; Biodegradation, Environmental; Biological and medical sciences; Bioremediation; Biotechnology; Earth sciences; Earth, ocean, space; Electron Transport; Engineering and environment geology. Geothermics; Environment and pollution; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geobacter - growth & development; Geobacter sulfurreducens; Groundwater pollution; Groundwaters; Industrial applications and implications. Economical aspects; Natural water pollution; Oxidation-Reduction; Pollution; Pollution, environment geology; Radioactive wastes; Solubility; Spectrometry, X-Ray Emission; Uranium; Uranium Compounds - analysis; Uranium Compounds - chemistry; Wastes; Water Pollutants, Radioactive - analysis; Water treatment and pollution; Microbial activity; Radioactive pollution; Uranium V; Radioisotope; EXAFS spectrometry; Chemical reduction; Intermediate-level radioactive wastes; Decontamination; Biotransformation; Environment impact; Uranium VI; Bacteria; Water pollution; Bioremediation; Low level radioactive waste; Uranyl; Ground water
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es048232b

The release of uranium and other transuranics into the environment, and their subsequent mobility, are subjects of intense public concern. Uranium dominates the inventory of most medium- and low-level radioactive waste sites and under oxic conditions is highly mobile as U(VI), the soluble uranyl dioxocation {UO2}2+. Specialist anaerobic bacteria are, however, able to reduce U(VI) to insoluble U(IV), offering a strategy for the bioremediation of uranium-contaminated groundwater and a potential mechanism for the biodeposition of uranium ores. Despite the environmental importance of U(VI) bioreduction, there is little information on the mechanism of this transformation. In the course of this study we used X-ray absorption spectroscopy (XAS) to show that the subsurface metal-reducing bacterium Geobacter sulfurreducens reduces U(VI) by a one-electron reduction, forming an unstable {UO2}+ species. The final, insoluble U(IV) product could be formed either through further reduction of U(V) or through its disproportionation. When G. sulfurreducens was challenged with the chemically analogous {NpO2}+, which is stable with respect to disproportionation, it was not reduced, suggesting that it is disproportionation of U(V) which leads to the U(IV) product. This surprising discrimination between U and Np illustrates the need for mechanistic understanding and care in devising in situ bioremediation strategies for complex wastes containing other redox-active actinides, including plutonium.