Quantificationof Mercury Bioavailability for MethylationUsing Diffusive Gradient in Thin-Film Samplers

摘要

Mercury-contaminated sediment and water contain various Hg species, with a small fraction available for microbial conversion to the bioaccumulative neurotoxin monomethylmercury (MeHg). Quantification of this available Hg pool is needed to prioritize sites for risk management. This study compared the efficacy of diffusive gradient in thin-film (DGT) passive samplers to a thiol-based selective extraction method with glutathione (GSH) and conventional filtration (<0.2 μm) as indicators of Hg bioavailability. Anaerobic sediment slurry microcosms were amended with isotopically labeled inorganic Hg “endmembers” (dissolved Hg²⁺, Hg-humic acid, Hg-sorbed to FeS, HgS nanoparticles) with a known range of bioavailability and methylation potentials. Net MeHg production (expressed as percent of total Hg as MeHg) over 1 week correlated with mass accumulation of Hg endmembers on the DGTs and only sometimes correlated with the 0.2 μm filter passing Hg fraction and the GSH-extractable Hg fraction. These results suggest for the first time that inorganic Hg uptake in DGTs may indicate bioavailabilityfor methylating microbes. Moreover, the methylating microbial communityassessed by hgcA gene abundance was not always consistentwith methylation rates between the experiments, indicating that knowledgeof the methylating community should target the transcript or proteinlevel. Altogether, these results suggest that DGTs could be used toquantify the bioavailable Hg fraction as part of a method to assessnet MeHg production potential in the environment.