Dose- and sex-dependent alterations in mercury distribution in fetal mice following methylmercury exposure.

Methylmercuric chloride was orally given to inbred C57BL/6N mice on d 13 of pregnancy at doses of 2.5, 5, 10, and 20 mg/kg. Animals were sacrificed on each of d 14-18 of pregnancy, and mercury levels in the brain, liver, and kidney of both the fetus and dam were determined. The dose effect on the time course of mercury accumulation in the brain was observed both in the fetus and dam; after the higher doses administered, the brain mercury reached the highest concentration later than it did after the lower doses. In addition, the mercury concentration in the fetal brain was disproportionately higher after a dose of 20 mg/kg, which was toxic in the fetus since the weight of the brain was reduced. The concentration in the fetal brain was 1.6-4.9 times higher than in the maternal brain. The sex difference of fetuses in mercury levels was observed in the brain after a dose of 2.5 mg/kg, in which mercury concentration was higher in females than in males. This corresponded to the previously reported difference in adult mice and rats. However, the sex difference was not seen after doses of 5, 10, or 20 mg/kg.