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Sulfate-Reducing Bacteria Mobilize Adsorbed Antimonate by Thioantimonate Formation

Ye, Li, Chen, Haoze, Jing, Chuanyong
Environmental science & technology letters 2019 v.6 no.7 pp. 418-422
Desulfovibrio vulgaris, antimony, aquatic environment, biogeochemical cycles, density functional theory, goethite, hydrogen sulfide, iron oxides, ligands, mass spectrometry, moieties, pH, sulfate-reducing bacteria, sulfur
The biogeochemical cycling of antimony (Sb) is often coupled with sulfur and sulfate-reducing bacteria (SRB). The biogenic sulfide is usually assumed to facilitate Sb immobilization via Sb₂S₃ precipitation. Here, on the contrary, we discovered that SRB mobilize adsorbed Sb(V). When Sbⱽ(OH)₆–-bearing goethite was incubated anaerobically with Desulfovibrio vulgaris DP4, an elevated level of antimony was released due to the formation of thioantimonate, which is the dominant Sb species in solution. Our Fourier transform ion cyclotron resonance mass spectrometry analysis revealed multiple six- or five-coordinate thioantimonate intermediates, suggesting stepwise ligand exchange of hydroxyl groups on Sbⱽ(OH)₆– by biogenic sulfide. Direct H₂S elimination reactions resulted in four-coordinate thioantimonate species as the stable end product, which was confirmed by our density functional theory calculations. The thiolation of antimonate is pH-dependent and occurs in neutral environments. The thiolation changed Sb(V) from a six-coordinate octahedral coordination to a four-coordinate tetrahedral coordination, weakening its affinity for iron oxides and thus facilitating its release into the aquatic environment. The results of this study highlight the importance of biogenic sulfide produced by SRB for the fate and transport of Sb.