51. High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges
- Author
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Sylvain Bouchet, Stéphane Guédron, Janusz Dominik, Jakob Zopfi, Andrea G. Bravo, and David Amouroux
- Subjects
Geologic Sediments ,Environmental Engineering ,Sulfide ,Iron ,chemistry.chemical_element ,Ferric Compounds ,Waste Disposal, Fluid ,Gas Chromatography-Mass Spectrometry ,Iron-reducing bacteria ,Sediments ,chemistry.chemical_compound ,Iron bacteria ,Dissimilatory sulfate reduction ,medicine ,Organic matter ,Sulfate-reducing bacteria ,Waste Management and Disposal ,Methylmercury ,Water Science and Technology ,Civil and Structural Engineering ,chemistry.chemical_classification ,Bacteria ,Geography ,Sewage ,Sulfates ,Ecological Modeling ,Mercury ,Methylmercury Compounds ,Pollution ,Mercury (element) ,Sewage treatment plant ,Lakes ,Bays ,chemistry ,Environmental chemistry ,Ferric ,Oxidation-Reduction ,Sulfur ,Switzerland ,Water Pollutants, Chemical ,medicine.drug - Abstract
Sewage treatment plants (STPs) are important point sources of mercury (Hg) to the environment. STPs are also significant sources of iron when hydrated ferric oxide (HFO) is used as a dephosphatation agent during water purification. In this study, we combined geochemical and microbiological characterization with Hg speciation and sediment amendments to evaluate the impact of STP's effluents on monomethylmercury (MMHg) production. The highest in-situ Hg methylation was found close to the discharge pipe in subsurface sediments enriched with Hg, organic matter, and iron. There, ferruginous conditions were prevailing with high concentrations of dissolved Fe2+ and virtually no free sulfide in the porewater. Sediment incubations demonstrated that the high MMHg production close to the discharge was controlled by low demethylation yields. Inhibition of dissimilatory sulfate reduction with molybdate led to increased iron reduction rates and Hg-methylation, suggesting that sulfate-reducing bacteria (SRB) may not have been the main Hg methylators under these conditions. However, Hg methylation in sediments amended with amorphous Fe(III)-oxides was only slightly higher than control conditions. Thus, in addition to iron-reducing bacteria, other non-SRB most likely contributed to Hg methylation. Overall, this study highlights that sediments impacted by STP discharges can become local hot-spots for Hg methylation due to the combined inputs of i) Hg, ii) organic matter, which fuels bacterial activities and iii) iron, which keeps porewater sulfide concentration low and hence Hg bioavailable.
- Published
- 2015