Photoreduction of Hg(ii) and photodemethylation of methylmercury: the key role of thiol sites on dissolved organic matter.

This study examined the kinetics of photoreduction of Hg(ii) and photodemethylation of methylmercury (MeHg(+)) attached to, or in the presence of, dissolved organic matter (DOM). Both Hg(ii) and MeHg(+) are principally bound to reduced sulfur groups associated with DOM in many freshwater systems. We propose that a direct photolysis mechanism is plausible for reduction of Hg(ii) bound to reduced sulfur groups on DOM while an indirect mechanism is supported for photodemethylation of MeHg(+) bound to DOM.