Inhibition of Mercury Methylation by Iron Sulfides in an Anoxic Sediment

Abstract

Abstract

It has been reported that methylmercuy (MeHg) production is limited in sulfidic sediments. The inhibition effects of iron sulfides on the methylation of mercury were investigated by amending either laboratory synthesized iron sulfide (Syn-FeS) or a commercial iron sulfide (CIS) into sediment slurries spiked with Hg(II) (from HgCl₂ solution) under anoxic conditions. Analysis of the X-ray powder diffraction (XRPD) spectra of CIS indicated that CIS was a mixture of the oxidation products of FeS, which included but were not limited to mackinawite (FeS), greigite (Fe₃S₄), pyrrhotite (Fe_1-xS), pyrite (FeS₂), and elemental sulfur (S⁰). Laboratory synthesized iron sulfide (Syn-FeS) was predominantly mackinawite. Experimental results showed that both Syn-FeS and CIS were effective at inhibiting Hg(II) methylation. Results indicated that MeHg production was not significantly correlated to THg_D in these experiments. The inhibiting effect of iron sulfides was probably due to the decrease of bioavailable neutral Hg(II)-sulfide complexes (mainly HgS⁰) via formation of charged Hg(II)-polysulfides.