title: Competitive reduction of pertechnetate (99TcO4-) by dissimilatory metal reducing bacteria and biogenic Fe(II).
abstract: The fate of pertechnetate ((99)Tc(VII)O(4)(-)) 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 TcO(4)(-) 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)O(2)·nH(2)O 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 TcO(4)(-) 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 TcO(2)·nH(2)O had significantly more Tc-Tc second neighbors and a distinct long-range order consistent with small particle polymers of TcO(2). 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 (99)Tc(IV).
authors.affiliation: Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Plymale
authors.forename: James K
authors.initials: JK
authors.lastname: Fredrickson
authors.forename: John M
authors.initials: JM
authors.lastname: Zachara
authors.forename: Alice C
authors.initials: AC
authors.lastname: Dohnalkova
authors.forename: Steve M
authors.initials: SM
authors.lastname: Heald
authors.forename: Dean A
authors.initials: DA
authors.lastname: Moore
authors.forename: David W
authors.initials: DW
authors.lastname: Kennedy
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Marshall
authors.forename: Chongmin
authors.initials: C
authors.lastname: Wang
authors.forename: Charles T
authors.initials: CT
authors.lastname: Resch
authors.forename: Ponnusamy
authors.initials: P
authors.lastname: Nachimuthu
mesh_terms: D001711:Biotransformation; D020564:Deltaproteobacteria / Q000378:metabolism*; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D045302:Geobacter / Q000378:metabolism; D009231:Myxococcales / Q000378:metabolism; D010084:Oxidation-Reduction; D011848:Radioactive Pollutants / Q000737:chemistry / Q000378:metabolism*; D020592:Shewanella / Q000378:metabolism*; D013670:Sodium Pertechnetate Tc 99m / Q000737:chemistry / Q000378:metabolism*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005290:Ferric Compounds; D011848:Radioactive Pollutants; C092844:ferric oxyhydroxide; D013670:Sodium Pertechnetate Tc 99m