One of the major challenges in evaluating the risk potential of soils and sediments contaminated with mercury is the lack of simple, reliable, environmentally-relevant methods to predict methylmercury formation. Methylmercury is more toxic than inorganic mercury and its accumulation in aquatic organisms, through dietary consumption of fish higher in the food chain, poses a health risk for humans. In anoxic soils and sediments, mercury is transformed to methylmercury via certain types of bacteria carrying mercury-methylating genes. The primary objectives of this study were to compare the bioavailability of different types of inorganic mercury that occur naturally in sediments and understand how carbon amendments might affect mercury methylation potential. The experiments involved sediment-water microcosms amended with four forms of isotopically-labeled inorganic mercury: dissolved Hg2+, Hg sorbed to iron sulfide (Hg-FeS), nanoparticulate HgS and microparticulate HgS.
A glutathione selective leaching test was used to indicate mercury bioavailability, because glutathione is produced by bacteria and has a high affinity for mercury. We hypothesized that glutathione-leached mercury will correlate with methylmercury production, and that the addition of activated carbon will decrease both mercury bioavailability and methylation rate.
This research has broader implications for assessing methylation potential of mercury-contaminated sites, as well as providing evidence for the efficacy of activated carbon as an in situ remediation method.