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Microbial Reduction of Cobalt III EDTA - in the Presence and Absence of Manganese(IV) Oxide

1998; American Chemical Society; Volume: 32; Issue: 2 Linguagem: Inglês

10.1021/es970516r

1520-5851

Yuri A. Gorby, Frank Caccavo, H. Bolton,

Chemical Synthesis and Characterization

Codisposal of 60Co2+ and EDTA has promoted the transport of radioactive 60Co in the environment as 60CoEDTA complexes. Chemical oxidation of CoIIEDTA2- to highly stable and mobile CoIIIEDTA- by manganese(VI) oxide minerals can occur under aerobic and anaerobic conditions. Reduction of Co(III) to Co(II) decreases the stability of the radionuclide−chelate complex and can limit the transport of the 60Co in subsurface environments. This study investigated the microbial reduction of CoIIIEDTA- in the presence and absence of reactive manganese(IV) oxides. The metal-reducing bacterium Shewanella alga strain BrY enzymatically reduced CoIIIEDTA- to CoIIEDTA2- with a 1:1 stoichiometry. Reduction of CoIIIEDTA- was not affected by radioactive 60CoIIIEDTA- at concentrations exceeding those recorded in contaminated environments. Bacterial reduction of CoIIIEDTA- could be coupled to the chemical oxidation of CoIIEDTA2- by the manganese(IV) oxide mineral pyrolusite, resulting in biotic-abiotic cycling between CoIIEDTA2- and CoIIIEDTA-. CoIIIEDTA- significantly increased the rate and extent of manganese(IV) oxide reduc tion in the presence of metal reducing bacteria, and the CoIIEDTA2- complex did not dissociate in these anoxic studies. Direct reduction of CoIIIEDTA- by microorganisms and geochemical oxidation of CoIIEDTA2- by manganese(IV) oxides are important components of a complex set of coupled microbial and geochemical reactions that may influence the fate and transport of 60CoIIIEDTA2- in the environment.