Factors Affecting Methylmercury Levels in Surficial Tailings from Historical Nova Scotia Gold Mines

Abstract

Large quantities of Hg remain in tailings dumps from historical Nova Scotian gold mines. Depth profiles of total Hg (HgT) and methylmercury (MeHg) were compared with geochemical and microbiological variables, to identify factors influencing MeHg levels in tailings. HgT and MeHg were highly variable in tailings (0.2–73.5 μ mol kg− 1 and < dl-56.4 nmol kg− 1, respectively), and were influenced by a complex set of in situ factors. Elevated MeHg was linked with > 5 μ mol kg−1 HgT, organic matter, hydrology, abundance and activity of sulfate reducing bacteria, and demethylation processes. Methylmercury levels in tailings from a wet, bog-like site appeared to undergo seasonal fluctuations, with higher concentrations measured in September and October, and lower concentrations in May. Evaluations of amalgamation tailings should examine MeHg and HgT transport out of low-lying, saturated tailings dumps after snowmelt and major rainfall events, and should take into account the possibility of seasonal variation in MeHg levels in northern regions.