Combined effects of water pH and salinity on the bioaccumulation of inorganic mercury and methylmercury in the shore crab Carcinus maenas

Tissue mercury concentrations were analysed in the whole organism and various organs of the euryhaline shore crab Carcinus maenas after 3 and 15 days of exposure to inorganic mercury (Hg(II)) and methylmercury (MeHg) at a nominal concentration of 1 μgHg l−1. Chemical speciation of the metals was varied by using four pH/salinity conditions (combinations between pH 7.0 and 8.5/salinity 560 and 140 mM NaCl). In all conditions, the results showed a particularly important Hg accumulation in gill tissue, smaller levels in the carapace and internal organs, and very low concentrations in circulating haemolymph. For Hg(II), accumulation was generally favoured at low salinity, but the data revealed complex pH/salinity interactions. Positive correlations were found between tissue metal levels and the abundance of some inorganic Hg species: HgCl2, HgCl−3, Hg2+, HgCl+, indicating that chemical speciation may be an important factor governing metal uptake. The balance of evidence favours HgCl2 and CH3HgCl as the most bioavailable species for uptake of Hg(II) and MeHg, respectively.