TY - CONF A1 - Kappler, A. A1 - Paul, Andrea A1 - Amstaetter, K. A1 - Borch, T. A1 - Larese-Casanova, P. A1 - Jiang, J. A1 - Bauer, I. T1 - Arsenic redox transformation by humanic substances and Fe minerals T2 - Ninth International Symposium on the Geochemistry of the Earth's Sureface (GES-9) CY - Boulder, CO, USA DA - 2011-06-01 PY - 2011 AN - OPUS4-25154 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Roden, E. A1 - Kappler, A. A1 - Bauer, I. A1 - Jiang, J. A1 - Paul, Andrea A1 - Stoesser, R. A1 - Konishi, H. A1 - Xu, H. T1 - Extracellular electron transfer through microbial reduction of solid-phase humic substances KW - Natural organic-matter KW - Electron-acceptors KW - Reducing bacteria KW - Ferric iron KW - Reduction KW - Acid KW - Groundwater KW - Release KW - Kinetics KW - PH PY - 2010 DO - https://doi.org/10.1038/NGEO870 SN - 1752-0894 SN - 1752-0908 VL - 3 SP - 417 EP - 421 PB - Nature Publishing Group CY - London AN - OPUS4-22345 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jiang, J. A1 - Bauer, I. A1 - Paul, Andrea A1 - Kappler, A. T1 - Arsenic redox changes by microbially and chemically formed semiquinone radicals and hydroquinones in a humic substance model quinone N2 - Arsenic is a redox-active metalloid whose toxicity and mobility strongly depends on its oxidation state, with arsenite (As(III)) being more toxic and mobile than arsenate (As(V)). Humic substances (HS) are also redox-active and can potentially react with arsenic and change its redox state. In this study we show that semiquinone radicals produced during microbial or chemical reduction of a HS model quinone (AQDS, 9,10-anthraquinone-2,6-disulfonic acid) are strong oxidants. They oxidize arsenite to arsenate, thus decreasing As toxicity and mobility. This reaction depends strongly on pH with more arsenite (up to 67.3%) being oxidized at pH 11 compared to pH 7 (12.6% oxidation) and pH 3 (0.5% oxidation). In addition to As(III) oxidation by semiquinone radicals, hydroquinones that were also produced during quinone reduction reduced As(V) to As(III) at neutral and acidic pH values (less than 12%) but not at alkaline pH. In order to understand redox reactions between arsenite/arsenate and reduced/oxidized HS, we quantified the radical content in reduced quinone solutions and constructed Eh-pH diagrams that explain the observed redox reactions. The results from this study can be used to better predict the fate of arsenic in the environment and potentially explain the occurrence of oxidized As(V) in anoxic environments. KW - Natural organic-matter KW - Electron-acceptors KW - Reducing bacteria KW - Ferric iron KW - Reduction KW - Acid KW - Groundwater KW - Release KW - Kinetics KW - pH PY - 2009 DO - https://doi.org/10.1021/es803112a SN - 0013-936X SN - 1520-5851 VL - 43 IS - 10 SP - 3639 EP - 3645 PB - ACS Publ. CY - Washington, DC AN - OPUS4-19982 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -