Toxic methylmercury is created in biofilms covering the rocks in streams.
Using enriched stable isotopes of Hg the creation and destruction of the toxic methylmercury (MMHg) in algal biofilms was measured simultaneously.The biofilms produced more MMHg than they destroyed under conditions typical for a local Hg-contaminated creek.Our laboratory results mimicked the seasonal and locational patterns we observed in our creek.
Algal biofilms could create a substantial fraction of the total MMHg in the creek. This source of MMHg in the creek was not recognized before this study.
Mercury (Hg) methylation and methylmercury (MMHg) demethylation activity of periphyton biofilms from the industrially contaminated East Fork Poplar Creek, Tennessee (EFPC) were measured during 2014-2016 using stable Hg isotopic rate assays. 201HgII and MM202Hg were added to intact periphyton samples in ambient streamwater and the formation of MM201Hg and loss of MM202Hg were monitored over time and used to calculate first-order rate potentials for methylation and demethylation. The influences of location, temperature/season, light exposure and biofilm structure on methylation and demethylation potentials were examined. Between-site differences in net methylation for samples collected from an upstream versus downstream location were driven by differences in the demethylation rate potential (kd). In contrast, the within-site temperature-dependent difference in net methylation was driven by changes in the methylation rate potential (km). Samples incubated in the dark had lower net methylation due to lower km values than those incubated in the light. Disrupting the biofilm structure decreased km and resulted in lower net methylation. Overall, the measured rates resulted in a net excess of MMHg generated which could account for 3.71 – 7.88 mg d-1 MMHg flux in EFPC and suggests intact, actively photosynthesizing periphyton biofilms harbor zones of MMHg production.
T. Olsen, C. Brandt, S. Brooks, Periphyton biofilms influence net methylmercury production in an industrially contaminated system. Environ. Sci. Technol. (2016) 10.1021/acs.est.6b01538
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