HR: 1340h
AN: B23B-1044    [Abstracts]
TI: Arsenic Redox Transformation as a Consequence of Microbial Reduction of Ferric Iron Oxides and Humic Substances
AU: * Amstaetter, K
EM: Katja.Amstaetter@uni-tuebingen.de
AF: Geomicrobiology Group, Center for Applied Geosciences, University of Tuebingen, Wilhelmstr. 56, Tuebingen, 72074 Germany
AU: Jiang, J
B23B-1044 AF: Geomicrobiology Group, Center for Applied Geosciences, University of Tuebingen, Wilhelmstr. 56, Tuebingen, 72074 Germany
AU: Navarro, L
B23B-1044 AF: Geomicrobiology Group, Center for Applied Geosciences, University of Tuebingen, Wilhelmstr. 56, Tuebingen, 72074 Germany
AU: Kappler, A
EM: Andreas.Kappler@uni-tuebingen.de
AF: Geomicrobiology Group, Center for Applied Geosciences, University of Tuebingen, Wilhelmstr. 56, Tuebingen, 72074 Germany
AB: The toxic metalloid arsenic represents a significant drinking water contamination in particular in countries such as Bangladesh or Vietnam. In these countries millions of people are directly affected by toxic concentrations of arsenic in drinking water. At neutral pH, arsenate (As(V)), present in anionic form as (H2AsO4)- and (HAsO4)2- (pK1 = 2.2, pK2 = 7.0) is mostly adsorbed to iron(III) and aluminum oxide surfaces. In contrast, arsenite (As(III)), present at neutral pH as uncharged species (H3AsO3, pK1 = 9.2), adsorbs less strongly to aluminum oxides and is assumed to be the more mobile form of arsenic. Natural organic matter (humic substances) was shown to complex As(V) and As(III); in some cases even redox reactions of humic substances with arsenic species were described. Increased As-concentrations in drinking water were suggested to result either from reduction of As(V) to As(III) or from dissolution of iron(III) oxides which leads to the release of adsorbed arsenic. However, the mechanisms leading to mobilization of arsenic are still under debate and the role of humic substances for the mobilization of arsenic is unclear. Fe(III) oxides as well as redox-active natural organic matter (humic substances) can be reduced enzymatically by a variety of microorganisms. Microbial Fe(III) reduction produces Fe(II) that can adsorb to the Fe(III) mineral surface and thus becomes a better reductant. Microbial reduction of humic substances produces reduced humic substances. Both surface-adsorbed Fe(II) and reduced humic substances represent reactive intermediates that potentially can undergo further redox reactions. Here we present recent data on redox transformation of arsenic by both reactive intermediates. Arsenic redox transformation by reactive iron species and reactive humic substances is of particular interest because i) As(III) is more mobile and more toxic than As(V) and ii) in arsenic contaminated areas the presence of arsenic often correlates with the presence of iron minerals and natural organic matter.
UR: http://www.uni-tuebingen.de/zag/geomicrobiology
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0448 Geomicrobiology
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0496 Water quality
SC: Biogeosciences [B]
MN: Fall Meeting 2005