Effect of FeS on mercury behavior in mercury-contaminated stream sediment: A case study of Pohang Gumu Creek in South Korea

[Display omitted] •Hg contamination was investigated in anoxic sediment containing FeS.•Beta-HgS and Hg-S bonds were identified as the main Hg speciation in the contaminated sediment.•Hg(II) reduction to Hg(0) may help suppress the formation of methyl mercury. This study investigated mercury contamination with respect to the sediment characteristics in Gumu Creek near the Pohang Industrial Complex, South Korea. The contaminated sediment had high levels of Hg, exceeding 250 mg Hg/kg sediment at the sampling position, and high concentrations of iron, sulfur, and organic carbon under extreme anaerobic conditions. The anoxic condition of the sediment produced large amounts of FeS. Hg L3-edge EXAFS analysis revealed that FeS controlled the Hg species in the sediment mainly as β-HgS like precipitation or Hg-S complexation. We also speculated that the presence of FeS induced the abiotic reduction of Hg(II) to Hg(0) and consequently suppressed the formation of highly toxic methylated mercury species. The results obtained in this study are mostly consistent with those reported in previous studies of geochemical reactions of FeS in controlling Hg(II) under pure FeS mineral systems under laboratory scenarios. This study demonstrates that the laboratory controlled reaction scenarios can explain the field behavior of Hg in the contaminated anoxic sediment of the Gumu Creek site.