Impact of microbial activity on arsenic reduction, mobilization and sequestration at the mineral-solution interface

eingeladen durch Prof Matzner.

The interaction of arsenic with mineral surfaces strongly influences its mobility in soil-water systems. Mircobial reduction of arsenate (As(V)) to arsenite (As(III)) may not only increase the mobility but also the toxicity of arsenic in the environment. While previous studies indicated that an uptake by mineral surfaces may slow down microbial As(V) reduction [2], detailed data on this effect is still lacking. Therefore, we investigated the influence of As(V) adsorption to ferrihydrite, goethite and boehmite on the kinetics of As(V) reduction by Shewanella putrefaciens CN-32 and Shewanella ANA-3 in incubation experiments. The As(V) adsorption was changed by varying concentrations of mineral suspension, adding competitive anions (phosphate, sulphate and exopolysaccahride) and the presence of microbial Fe reduction. The presence of minerals apparently decreased the microbial As(V) reduction kinetics. Increasing amounts of ferrihydrite, goethite or boehmite in suspension substantially decreased As(V) reduction rates. This effect increased from goethite to boehmite to ferrihydrite, in parallel with the specific surface area (600, 250, and 18 m2 g−1, respectively) and the As(V) adsorption affinity of the minerals. Both sorption competition with phosphate and bacterial exopolysaccharides isolated from S. putrefaciens enhanced As(V) reduction in the presence of mineral surfaces at low microbe-to-mineral ratios. Both Mössbauer and X-ray absroption spectroscopy indicated the formation of amorphous Fe (hydr)oxides, e.g. ferrihydrite and magnetite, during reductive dissolution of ferrihydrite, leading to sequestration of aqueous As species. In incubations with addition of electron shuttle compounds such as anthraquinone-2,6-disulfonate (AQDS), Fe(III) reduction may at the same time inhibit microbial As(V) reduction. The data presented highlighs the important role of microorganisms in the speciation and mobility of As at the mineral-soultion interface.

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