Effect of iron redox transformations on arsenic solid-phase associations in an arsenic-rich, ferruginous hydrothermal sediment

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dc.contributor.author Handley, Kim en
dc.contributor.author McBeth, JM en
dc.contributor.author Charnock, JM en
dc.contributor.author Vaughan, DJ en
dc.contributor.author Wincott, PL en
dc.contributor.author Polya, DA en
dc.contributor.author Lloyd, JR en
dc.date.accessioned 2015-11-17T22:06:20Z en
dc.date.available 2012-10-15 en
dc.date.issued 2013-02-01 en
dc.identifier.citation Geochimica et Cosmochimica Acta, 2013, 102 pp. 124 - 142 en
dc.identifier.issn 0016-7037 en
dc.identifier.uri http://hdl.handle.net/2292/27493 en
dc.description.abstract Well-constrained laboratory incubations of a ferruginous marine hydrothermal sediment from Santorini, Greece, were used to elucidate the effect of microbially induced redox transformations on arsenic speciation and mobility. Despite naturally high arsenic concentrations (∼400 mg/kg), the sediment has a low As:Fe ratio (1:1000 wt/wt). Acetate-amendment of sediment, extracted from the naturally-occurring suboxic–anoxic (Eh −60 to −138 mV) transition zone, promoted Fe(III) reduction, and increased the concentration of Fe(II) from ∼40% to ∼60% in the bulk sediment. Sulfate, which was present at lower concentrations, was also reduced. Phylogenetic 16S rRNA and dsr gene analysis suggested that Fe(III) and sulfate were reduced by bacteria related to Malonomonas rubra and Desulfosarcina variabilis, respectively. Arsenic remained predominantly as arsenic trioxide (As2O3) throughout the amendment experiment. However, the percentage of total arsenic present within poorly-crystalline iron oxides decreased from ∼69% to ∼32%, while the percentage incorporated within crystalline iron-containing minerals or sorbed to surfaces via inner-sphere complexes increased significantly (to 22% and 30%, respectively). Re-oxidation of the system with nitrate resulted in incomplete reduction of the nitrate pool, and partial re-association of arsenic with the poorly-crystalline iron fraction. Exposure to air led to virtually complete reversal of the arsenic partitioning, and oxidation of 71% As(III) to As(V). During aeration, oxidation of sediment-bound sulfur/sulfide occurred, alongside an observed ∼63% decrease in arsenic bound to this minor component. Analogous trends in arsenic-sediment associations were observed in the natural, unamended sediment depth-profile, whereby a greater proportion of arsenic (34% As(III), 66% As(V)) was bound within poorly-crystalline iron oxides at the sediment–water interface. Arsenic (96% As(III)) was increasingly incorporated within well-crystallized forms of iron with depth and decreasing Eh values. At the greatest depth sampled (35 cm) arsenic increased substantially within the sulfide/organic fraction. Results here contribute to existing evidence that arsenic is not necessarily released from iron-rich sediment systems under conditions of anoxia, but that Fe(II)-bearing minerals forming concomitantly can immobilize arsenic in the solid-phase. Such results may have implications for other systems with high Fe:As ratios. en
dc.language English en
dc.publisher Elsevier en
dc.relation.ispartofseries Geochimica et Cosmochimica Acta en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. Details obtained from http://www.sherpa.ac.uk/romeo/issn/0016-7037/ https://www.elsevier.com/about/company-information/policies/sharing en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.title Effect of iron redox transformations on arsenic solid-phase associations in an arsenic-rich, ferruginous hydrothermal sediment en
dc.type Journal Article en
dc.identifier.doi 10.1016/j.gca.2012.10.024 en
pubs.begin-page 124 en
pubs.volume 102 en
dc.rights.holder Copyright: Elsevier en
pubs.author-url http://www.sciencedirect.com/science/article/pii/S0016703712006060 en
pubs.end-page 142 en
pubs.publication-status Published en
dc.rights.accessrights http://purl.org/eprint/accessRights/RestrictedAccess en
pubs.subtype Article en
pubs.elements-id 488380 en
pubs.org-id Science en
pubs.org-id Biological Sciences en
pubs.record-created-at-source-date 2015-11-18 en

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