Benthic environments contaminated by mercury pose a health risk due to in-situ microbial production of monomethylmercury (MeHg), a highly bioacccumulative neurotoxin. The overall objectives of our research are to determine the forms of inorganic mercury that are bioavailable to methylating bacteria and to develop a model or framework that can be used to predict biomethylation potential in contaminated settings. We performed experiments with pure bacteria cultures and anaerobic sediment slurry microcosms to determine how mercury methylation rates changed as a function of the type of mercury sulfide added (dissolved, nanoparticulate, or bulk particulate) and microbial growth conditions (i.e. salinity, organic carbon). The results generally indicated that production of MeHg was greatest in cultures receiving dissolved Hg. Cultures receiving nanoparticulate HgS generated less MeHg than the dissolved treatments but much greater than the cultures receiving bulk scale metacinnabar HgS. The differences in MeHg production between dissolved and nanoparticle treatments also varied, depending on whether the productivity of methylating microbes (e.g. sulfate reducers) was a limiting factor. The experimental results have been used in the development of a kinetics-based model that links inorganic mercury speciation (including nanoscale species) and methylation potential. These modeling efforts suggest that the enhanced methylation of nanoparticulate HgS over bulkscale HgS in our experiments was not simply due to faster dissolution rates of nanoparticles. Rather, the nanoparticles may be providing a source of Hg with enhanced bioavailability or a direct route of uptake by methylating bacteria. Overall we anticipiate that this model may provide an example of how to consider the nanoscale geochemistry of trace elements in predicting their reactivity and bioavailability in the environment.

Nanogeochemistry of a neurotoxin: Reactivity and microbial methylation potential of nanoscale mercury sulfides

245th National Meeting (2013)

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