Mercury (Hg) in contaminated sediments comprise a variety of chemical forms that are associated with organic matter and sulfide particles, yet only a small fraction of the total Hg is generally bioavailable to microorganisms that produce monomethylmercury (MeHg), a bioaccumulative neurotoxin. The reactivity of inorganic Hg at microbial interfaces is likely crucial to determining the uptake and bioavailability of this metal. The development of effective remediation strategies at contaminated sites is greatly limited by the lack of reliable methods to quantify this reactive Hg pool for biomethylation. The objective of this study was to compare the efficacy of diffusive gradient in thin-film (DGT) passive samplers, a thiol-based selective extraction with glutathione, and conventional filtration (&lt;0.2 um) as indicators of Hg bioavailability to methylating microbial communities. These methods were tested on a series of anaerobic sediment slurry microcosms that were amended with multiple, isotopically labelled endmembers of inorganic Hg (204Hg2+, 196Hg-humic acid, 199Hg-sorbed to FeS, 200HgS nanoparticles) with a known range of bioavailability and methylation potentials. Net production of MeHg (as a % of the total) over a one week time frame was generally greater for the dissolved endmembers than the particulate endmembers, as expected. The accumulation of each isotopic Hg(II) endmember on DGTs correlated with %MeHg at each time point in the experiment. In contrast, net methylation poorly correlated with the filter passing fraction of Hg and only sometimes correlated with the thiol extractable fraction of Hg in the slurries. These results suggest that inorganic Hg uptake in DGTs might be useful indicators of bioavilability for methylating sediment microbes. While field testing of this hypothesis is needed, the use of DGTs might be a valuable tool, in conjunction with measures of the methylating microbial community and MeHg degradation, in assessing net Hg methylation potential in contaminated sediment sites.

Quantification of mercury biomethylation potential in sediments

255th National Meeting (2018)

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