Emmy Noether Nachwuchsgruppe Hydrogeochemical speciation of arsenic, gold, and copper in ferrous sulfidic environments considering abiotic and microbially catalyzed interactions

DFG PL 302/3-1

The focus of the present project is on arsenic-sulfur compounds, so-called thioarsenates (As^VO_4-xS_x^3-) and thioarsenites (As^IIIO_3-xS_x^3-). Even though the affinity between arsenic and sulfur has been known for a long time, the relevance of thioarsenic species in environmental chemistry is only slowly emerging.

Key achievements within the present project were:

- To reconcile contradictory spectroscopic and chromatographic evidence that has existed on As-S-chemistry for about 10 years, showing that thioarsenates and thioarsenites can co-exist in solution (which has previously only been postulated by modeling) and that the sole detection of thioarsenates in HPLC-ICP-MS is an artifact due to the rapid oxidation of thioarsenites to thioarsenates or their transformation to arsenite due to competitive ligand exchange at high pH; to provide unambiguous XAS spectra of thioarsenates and thioarsenites (Planer-Friedrich et al., 2010; Planer-Friedrich and Wallschläger, 2009; Suess et al., 2009).

- To transfer experiences gained from arsenic-sulfur chemistry to enable the correct determination and structural characterization of antimony-sulfur compounds, prove their natural occurrence (Planer-Friedrich and Scheinost, 2011) and determine stability and competing interactions in an As-Sb-S-system (Wilson and Planer-Friedrich, submitted).

- To show by development of new preservation methods that thioarsenates can predominate As speciation in Fe-rich solutions which has been regarded unlikely because of limited availability of excess S for As-S-complexation due to precipitation of FeS phases; to further demonstrate that the presence of sulfide increases arsenite desorption from iron hydroxides by formation of thioarsenates in-situ, and that the re-sorption potential for monothioarsenate on iron hydroxides is significantly lower than that of arsenite and arsenate; to provide XAS spectra for thioarsenates on iron hydroxides (Suess and Planer-Friedrich, submitted; Suess et al., 2011).

- To unravel a substantial impact of thermophile microorganisms on “unusual” arsenic redox chemistry, e.g. Thermocrinis ruber transforming thioarsenates in a purely oxidizing environment via arsenite to arsenate (Härtig and Planer-Friedrich, submitted) or a culture isolated from Mono Lake using sulfide to enhance microbial arsenite oxidation to arsenate by formation of thioarsenates (Fisher et al., 2008) as well as to show accelerated growth of known sulfide-oxidizers (Thermocrinis ruber and MLMS-1) on thioarsenates indicating new degradation pathways.

- To enhance interpretations on the toxicity of arsenic-sulfur species from simple bioluminescent tests by improved speciation analysis and providing individual dose-response curves for thioarsenate standards (Planer-Friedrich et al., 2008); to show the effect of free sulfide in reducing arsenite cytotoxicity by formation of thioarsenates and to provide individual dose-response curves for thioarsenates in human liver, bladder, and skin cells.

For a list of publications please click here...