Bioreduction of uranium: environmental implications of a pentavalent intermediate

Joanna C. Renshaw, Laura J C Butchins, Francis R. Livens, Iain May, John M. Charnock, Jonathan R. Lloyd

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159 Citations (Scopus)

Abstract

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 {U02}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 {U02}+ 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 {Np02}+, 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.

Original languageEnglish
Pages (from-to)5657-5660
Number of pages4
JournalEnvironmental Science and Technology
Volume39
Issue number15
Early online date28 Jun 2005
DOIs
Publication statusPublished - 1 Aug 2005

Keywords

  • uranium
  • transuranics
  • bioreduction
  • contaminated groundwater

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  • Projects

    Mechanisms for the reduction of actinides and Tc(VII) in Geobacter sulfurreducens

    Lloyd, J. R., Renshaw, J., Livens, F. R. & May, I.

    1/01/0330/11/05

    Project: Projects from Previous Employment

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