Mercury methylation and methylmercury demethylation in boreal lake sediment with legacy sulphate pollution

• Published in: Environmental science--processes & impacts Vol. 24; no. 6; pp. 932 - 944
• Main Authors: Huang, Haiyong, Mangal, Vaughn, Rennie, Michael D, Tong, Huan, Simpson, Myrna J, Mitchell, Carl P. J
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 22.06.2022
• Subjects: Aquatic ecosystems; Aquatic environment; Bioaccumulation; Demethylation; Dimethylmercury; Dissolved organic matter; Inhibitors; Lake sediments; Lakes; Mercury; Mercury (metal); Methylation; Methylmercury; Neurotoxins; Pollution; Sediment pollution; Sediments; Sulfate reduction; Sulfate-reducing bacteria; Sulfates; Sulfur; Toxins
• ISSN: 2050-7887; 2050-7895
• DOI: 10.1039/d2em00064d

Sulphate and dissolved organic matter (DOM) in freshwater systems may regulate the formation of methylmercury (MeHg), a potent neurotoxin that biomagnifies in aquatic ecosystems. While many boreal lakes continue to recover from decades of elevated atmospheric sulphate deposition, little research has examined whether historically high sulphate concentrations can result in persistently elevated MeHg production and accumulation in aquatic systems. This study used sediment from a historically sulphate-impacted lake and an adjacent reference lake in northwestern Ontario, Canada to investigate the legacy effects of sulphate pollution, as well as the effects of newly added sulphate, natural organic matter (NOM) of varying sulphur content and a sulphate reducing bacteria (SRB) inhibitor on enhancing or inhibiting the Hg methylation and demethylation activity ( K meth and K demeth ) in the sediment. We found that K meth and MeHg concentrations in sulphate-impacted lake sediment were significantly greater than in reference lake sediment. Further adding sulphate or NOM with different sulphur content to sediment of both lakes did not significantly change K meth . The addition of a SRB inhibitor resulted in lower K meth only in sulphate-impacted sediment, but methylation was not entirely depressed. Methylmercury demethylation potentials in sediment were consistent across lakes and experimental treatments, except for some impacts related to SRB inhibitor additions in the reference lake sediment. Overall, a broader community of microbes beyond SRB may be methylating Hg and demethylating MeHg in this system. This study reveals that legacies of sulphate pollution in boreal lakes may persist for decades in stimulating elevated Hg methylation in sediment. Effects of sulphate pollution on enhancing elevated MeHg production in lake sediment persist even if sulphate levels in lake water have recovered for decades.