Histopathological evidence of inorganic mercury and methyl mercury toxicity in the arctic charr (Salvelinus alpinus)

In our sustained effort to understand mechanisms of mercury toxicity in fish, the histopathological effects of a 96-h acute exposure to water-borne inorganic mercury (inorganic Hg) (15 μg L−1), as well as those of a single dietary dose of inorganic and methyl mercury (methyl Hg) (0.260.05 μg•Hg g−1 body weight), over 30 days were examined. Samples of gills, olfactory epithelium, kidneys, and liver of arctic charr, Salvelinus alpinus, were studied using light and electron microscopy. The distribution of dietary inorganic and methyl Hg in the intestinal epithelium was determined using 203Hg microautoradiography. Gills of fish exposed to water-borne inorganic Hg presented a severe disorganization of epithelial cells after 12 h and modifications of cilia of ciliated olfactory cells appeared after 24 h. Nevertheless, a partial recovery was seen in both tissues by the end of the 96-h exposure period. Liver was little affected by water-borne and single-trophic-dose contamination of inorganic Hg, but dietary methyl Hg had drastic effects, despite its low dosage, with severe necrosis and alterations of cytoplasmic organization. Microautoradiograms showed that inorganic Hg was distributed evenly in the intestinal epithelium, whereas methyl Hg was found at very specific locations on the epithelial surface.