Competitive Reduction of Pertechnetate (99TcO4-) by Dissimilatory Metal Reducing Bacteria and Biogenic Fe(II)

Authors

Andrew Plymale, Pacific Northwest National LaboratoryFollow
James K. Fredrickson, Pacific Northwest National LaboratoryFollow
John M. Zachara, Pacific Northwest National LaboratoryFollow
Alice Dohnalkova, Pacific Northwest National LaboratoryFollow
Steve Heald, Argonne National Laboratory
Dean Moore, Pacific Northwest National LaboratoryFollow
David Kennedy, Pacific Northwest National LaboratoryFollow
Matthew Marshall, Pacific Northwest National Laboratory
Chongmin Wang, Pacific Northwest National Laboratory
Charles Resch, Pacific Northwest National Laboratory
Ponnusamy Nachimuthu, Pacific Northwest National Laboratory

Date of this Version

2011

Citation

Environ. Sci. Technol. 2011, 45, 951–957

Abstract

The fate of pertechnetate (⁹⁹Tc(VII)O₄ ^-) during bioreduction was investigated in the presence of 2-line ferrihydrite (Fh) and various dissimilatory metal reducing bacteria (DMRB) (Geobacter, Anaeromyxobacter, Shewanella) in comparison with TcO₄ ^- bioreduction in the absence of Fh. In the presence of Fh, Tc was present primarily as a fine-grained Tc(IV)/Fe precipitate that was distinct from the Tc(IV)O₂ ·nH₂O solids produced by direct biological Tc(VII) reduction. Aqueous Tc concentrations (<0.2 μm) in the bioreduced Fh suspensions (1.7 to 3.2 × 10^-9 mol L^-1) were over 1 order of magnitude lower than when TcO₄ - was biologically reduced in the absence of Fh (4.0 × 10^-8 to 1.0 × 10^-7 mol L^-1). EXAFS analyses of the bioreduced Fh-Tc products were consistent with variable chain length Tc-O octahedra bonded to Fe-O octahedra associated with the surface of the residual or secondary Fe(III) oxide. In contrast, biogenic TcO₂ ·nH₂O had significantly more Tc-Tc second neighbors and a distinct long-range order consistent with small particle polymers of TcO₂. In Fe-rich subsurface sediments, the reduction of Tc(VII) by Fe(II) may predominate over direct microbial pathways, potentially leading to lower concentrations of aqueous ⁹⁹Tc(IV).