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 δC, δN, and specific Hg (including MMHg and inorganic Hg (IHg)) isotopes. The results showed that δC and δN values exhibit different patterns in coastal and freshwater species. ΔHg/δHg values suggested that coastal and freshwater seafood undergo similar aqueous MMHg photodegradation processes. The ΔHg values could distinguish that, coastal fish absorb MMHg from water column whereas coastal shellfish absorb MMHg mainly from sediment. The positive values of ΔHg in seafood could reflect in vivo MMHg demethylation and IHg reabsorption. Positive correlation between δN and ΔHg 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.