Journal
APPLIED GEOCHEMISTRY
Volume 24, Issue 12, Pages 2332-2341Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.apgeochem.2009.09.006
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Funding
- Natural Sciences and Engineering Research Council of Canada
- US Department of Energy [W-31-109-Eng-38, DE-FG03-97ER45628]
- NSERC
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In reduced aqueous environments, the presence of As in solution is a function of both biotic and abiotic mechanisms. Recent studies have demonstrated a significant release of As(Ill) through the microbial reduction of dissolved and mineral-bound As(V), which raises health concerns when the greater comparative mobility and toxicity of As(III) is considered. These release mechanisms do not operate in isolation but occur in concert with a number of removal processes, including secondary mineralization and sorption to other natural substrates. Thermodynamic and applied experimental studies have shown that ferrous arsenates, such as symplesite [Fe(II)(3)(AS(V)O-4)(2)center dot 8H(2)O], may provide a significant sink for Fe(II) and As(V). In this study, the stability of a representative ferrous arsenate phase in the presence of the arsenate-reducing bacterium Shewanella sp. strain ANA-3 is examined. The reduction of ferrous arsenate by ANA-3 results in the release of aqueous As(III) and, subsequently, the progressive nucleation of a biogenic ferrous arsenite phase proximal to the microbial cells. The valence states of secondary solid-phase products were verified using X-ray absorption spectroscopy (XAS). Electron microscopy reveals that nucleation occurs on cellular exudates which may imply a role of extracellular reduction through c-type cytochromes as investigated in recent literature. These observations provide new insights into the reduction mechanisms of ANA-3 and the biogeochemical cycling of As(III) in natural systems. (C) 2009 Elsevier Ltd. All rights reserved.
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