title: High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges.
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 Fe(2+) 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.
authors.affiliation: Institut F.-A. Forel, University of Geneva, Route de Suisse 10, CH-1290 Versoix, Genève, Switzerland. Electronic address: jandriugarcia@gmail.com.
authors.forename: Andrea G
authors.initials: AG
authors.lastname: Bravo
authors.affiliation: LCABIE-IPREM, UMR 5254 CNRS - Université de Pau et des Pays de l'Adour, Hélioparc, 64053 Pau, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Bouchet
authors.affiliation: Institut F.-A. Forel, University of Geneva, Route de Suisse 10, CH-1290 Versoix, Genève, Switzerland; ISTerre, University Grenoble 1, IRD - UMR 5559 (IRD/UJF/CNRS) - BP 53, F-38041 Grenoble, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Guédron
authors.affiliation: LCABIE-IPREM, UMR 5254 CNRS - Université de Pau et des Pays de l'Adour, Hélioparc, 64053 Pau, France.
authors.forename: David
authors.initials: D
authors.lastname: Amouroux
authors.affiliation: Institut F.-A. Forel, University of Geneva, Route de Suisse 10, CH-1290 Versoix, Genève, Switzerland; Istituto di Scienze Marine - Consiglio Nazionale delle Ricercha, Castello 2737/F, I-30122 Venezia, Italy.
authors.forename: Janusz
authors.initials: J
authors.lastname: Dominik
authors.affiliation: Environmental Geosciences, University of Basel, Bernoullistrasse 30, CH-4056 Basel, Switzerland.
authors.forename: Jakob
authors.initials: J
authors.lastname: Zopfi
mesh_terms: D001419:Bacteria / Q000254:growth & development / Q000378:metabolism; D061006:Bays; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D005843:Geography; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology; D007501:Iron / Q000378:metabolism; D060106:Lakes; D008628:Mercury / Q000378:metabolism; D008767:Methylmercury Compounds / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology; D013431:Sulfates / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism; D013557:Switzerland; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D008767:Methylmercury Compounds; D012722:Sewage; D013431:Sulfates; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D013455:Sulfur; D007501:Iron; D008628:Mercury; C004925:methylmercuric chloride
keywords: Iron; Iron-reducing bacteria; Methylmercury; Sediments; Sewage treatment plant; Sulfate-reducing bacteria