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TitleMethylmercury production and transport from historical gold mine tailings in Nova Scotia
AuthorWinch, S; Fortin, D; Lean, D R S; Parsons, M B
SourceGAC-MAC-CSPG-CSSS Halifax 2005, building bridges - across science, through time, around the world: abstracts/AGC-AMC-SCGP-SCSS Halifax 2005, Jeter des ponts entre les disciplines scientifiques, les époques, et unifier le monde : recueil des résumés; GAC-MAC-CSPG-CSSS Joint Meeting, Abstracts vol. 30, 2005 p. 211
Alt SeriesEarth Sciences Sector, Contribution Series 2004427
MeetingHalifax 2005: GAC-MAC-CSPG-CSSS - AGC-AMC-SCGP-SCSS; Halifax, NS; CA; May 15-18, 2005
Mediapaper; on-line; digital
File formathtm; pdf
ProvinceNova Scotia
NTS10; 11; 20; 21A; 21H
Lat/Long WENS -68.0000 -60.0000 48.0000 43.0000
Subjectsenvironmental geology; geochemistry; mercury; mercury geochemistry; tailings; heavy metals contamination; gold; pore fluids; organic carbon; bacteria; methylmercury; sulphate reduction
ProgramMetals in the Environment (MITE)
AbstractThis study examines the potential for methylmercury (MeHg) produced in Nova Scotia gold mine tailings to be transported to downstream
waters. Between 1861 and the mid-1940s, stamp milling and mercury amalgamation were used to recover gold at most of the 64 gold mining districts in the province. In the present study, six sites were sampled over two periods: in September 2003, samples were collected from two sites at Lake Catcha and two at Lower Seal Harbour (LSH); in May 2004, we resampled the two sites at LSH, and collected samples from Upper Seal Harbour and First Pond (upstream and downstream of LSH, respectively). Depth profiles of MeHg, total Hg (HgT) and related parameters (pH, Eh, sulfate, sulfide, loss on ignition, Fe(II)) were compiled for tailings and porewaters. Since sulfate reducing bacteria (SRB) are known to methylate Hg, geochemical data were compared with sulfate reduction rates (SRR) and SRB abundance, as determined by the most-probable-number method. Nearby surface waters were analyzed for MeHg, HgT, pH, Eh and dissolved organic carbon. Methylmercury concentrations ranged from 17 to 11,300 ppt in tailings. Sulfate and organic carbon were generally low, pH ranged from 4.55 to 7.27, and SRB were present at all sample sites. At locations where HgT was less than ~ 0.5 ppm, MeHg tended to follow HgT profiles at a ratio of ~ 1:1000. When HgT concentrations were much higher (ppm levels), the ratio of MeHg to HgT in the tailings was lower by 1-2 orders of magnitude. These large differences are attributed to demethylation by Hg-resistant bacteria, which are known to dominate microbial communities where HgT concentrations are extremely elevated. A notable exception to this trend is at lower depths and bogtype sites where HgT reached values up to 5 ppm and the ratio of MeHg to HgT was as high as 1:10. In these environments, the tailings are likely saturated year-round, suggesting that demethylation processes are inhibited under reducing conditions. Concentrations of HgT and MeHg in porewaters were generally low in comparison with solid-phase HgT and MeHg concentrations in the same samples, and nearby surface water concentrations were lower still. Organic material clearly influences MeHg concentrations in wet tailings, but is not the sole cause of MeHg and HgT retention in solid phases. These results indicate that gold mine tailings in Nova Scotia can contain high concentrations of HgT and MeHg, but transport to downstream waters is limited.