Chronic toxicity of methylmercury in the rat

Groups of 50 male and 50 female Wistar rats were fed diets containing methylmercuric chloride to provide daily doses of 0, 0.002, 0.010, 0.050 and 0.250 mg Hg/kg/day for up to 26 months. Food consumption, and body weight measurements were monitored weekly on all rats. Hematological examinations were done at 0, 6, 12, 15 and 17 months of treatment. Histopathologic examination and analysis for total mercury levels were performed terminally. Male rats receiving 0.25 mg Hg/kg/day had decreased body weights, decreased hematocrit and hemoglobin values, overt clinical signs of neurotoxicity and increased mortality compared to controls. Female rats receiving 0.25 mg Hg/kg/day had decreased body weights and minimal clinical signs of neurtoxicity. Histopathological examination revealed demyelination of the dorsal nerve roots and peripheral nerves, severe kidney damage and decreased basophilia of hepatocytes in male rats receiving 0.25 mg Hg/kg/day. Male rats receiving 0.05 mg Hg/kg/day had minimal renal damage. Female rats receiving 0.25 mg Hg/kg/day had demyelination of the dorsal nerve roots and peripheral nerves and minimal renal damage. No histopathological lesions were observed in the female rats receiving 0.05 mg Hg/kg/day and in male and female rats in the other dose groups.