Progress in the study of mercury methylation and demethylation in aquatic environments

Mercury (Hg) and its compounds are a class of highly toxic and pervasive pollutants. During the biogeochemical cycling of Hg, methylmercury (MeHg), a potent neurotoxin, can be produced and subsequently bioaccumulated along the food chain in aquatic ecosystems. MeHg is among the most widespread contaminants that pose severe health risks to humans and wildlife. Methylation of inorganic mercury to MeHg and demethylation of MeHg are the two most important processes in the cycling of MeHg, determining the levels of MeHg in aquatic ecosystems. This paper reviews recent progress on the study of Hg methylation and demethylation in aquatic environments, focusing on the following three areas: (1) sites and pathways of Hg methylation and demethylation, (2) bioavailability of Hg species for methylation and demethylation, and (3) application of isotope addition techniques in quantitatively estimating the net production of MeHg.