Combining of C, N and specific Hg stable isotopes to track bioaccumulation of monomethylmercury in coastal and freshwater seafood.

Human exposure to monomethylmercury (MMHg) through seafood consumption is a global concern. This study investigates the potential sources and processes of MMHg in seafood of coastal and freshwater areas through combing of δ13C, δ15N, and specific Hg (including MMHg and inorganic Hg (IHg)) isotopes. The results showed that δ13C and δ15N values exhibit different patterns in coastal and freshwater species. Δ199HgMMHg/δ202HgMMHg values suggested that coastal and freshwater seafood undergo similar aqueous MMHg photodegradation processes. The Δ199HgMMHg values could distinguish that, coastal fish absorb MMHg from water column whereas coastal shellfish absorb MMHg mainly from sediment. The positive values of Δ199HgIHg in seafood could reflect in vivo MMHg demethylation and IHg reabsorption. Positive correlation between δ15N and Δ199HgIHg indicated that aquatic organisms in various trophic levels may have different MMHg demethylation efficiency. We proposed that combining of multiple isotopes can provide overall profiles on aquatic MMHg biogeochemical cycle and bioaccumulation.