Bioaccumulation of inorganic and methylated mercury by the gills of the shore crab Carcinus maenas: Transepithelial fluxes and histochemical localization

Abstract

In order to better understand the role of the gills in the accumulation of contaminants, branchial uptake and bioaccumulation of inorganic (HgCl2) and monomethylmercury (CH3HgCl) were quantified in the shore crab Carcinus maenas, using living animals and an in vitro perfused gill preparation exposed to 50 μg l-1 of either chemical forms in the external medium. In addition, localization of accumulated mercury was studied using the histochemical autometallographic technique by both light and electron microscopy. Gill tissue strongly accumulated either inorganic or methylated mercury at similar levels in vitro and in vivo. For both chemical forms of the metal, only about 1% of the total mercury input was recovered in the effluent fluid from in vitro perfused gills and could thus be considered available to distribute inside the animal via the circulatory system. Inorganic Hg was histochemically found to be accumulated at 2 markedly different locations in the gills: at the cuticular surface in direct contact with the contaminated medium and at high local levels in the central vacuole of gill nephrocytes. Although also present at these 2 locations, methylmercury was distributed more diffusely and more evenly in all cells. These results suggest that the high affinity of gill tissue for both forms of mercury may confer on this organ the role of an external barrier strongly limiting the invasion of the metal toward other compartments of the body.