Mercury methylation in estuaries: Insights from using measuring rates using stable mercury isotopes

Rates of mercury (Hg) methylation and methylmercury (MeHg) demethylation in sediment of the Hudson River, Chesapeake Bay and Bay of Fundy were measured using stable isotopes of mercury (Hg) and methylmercury (MeHg). Methylation of the isotope correlated well with in situ MeHg concentration, and MeHg turnover times were on the order of days. It was concluded that methylation was more important than demethylation in controlling the differences in concentrations of MeHg among ecosystems. Also in situ MeHg concentration appeared to be a good indicator of methylation activity in sediment across ecosystems. Examination of a temporal data set, collected from the vicinity of Hart Miller Island, Chesapeake Bay between 1998 and 2002, and a spatial data set of a longitudinal transect of the main stem of the Chesapeake Bay, is used to further examine the controls on Hg methylation and MeHg concentration. Microbial activity and the formation of sulfide appear to be at least as important as Hg concentration in controlling MeHg concentration in estuarine sediment.