Demethylation and placental transfer of methyl mercury in the pregnant hamster.

The demethylation and placental transfer of methylmercury (MeHg) was studied in Syrian Golden hamsters administered a single oral dose of 203Hg-labeled MeHgCl, 1.6 mumol/kg body weight, on day 2 or 9 of gestation and sacrificed 1 day before expected parturition. In order to evaluate the role of demethylation for transplacental transport of MeHg, four hamsters were administered 203Hg-labeled HgCl2 intravenously on day 9 of gestation. The mean biological halftime of 203Hg in animals administered radiolabeled MeHg was 7.7 days and the fecal route was the main excretory pathway. The fetal content of 203Hg in hamsters administered radiolabeled MeHg on gestational day 2 or 9 corresponded to 1.3% and 4.6% of the administered dose, respectively. The distribution of 203Hg in the fetus was more even than in the dam and the concentration of 203Hg in the fetal brain, liver and kidney was similar to that of the placenta. Inorganic Hg was found in maternal liver (18% of total Hg), kidney (31%) and placenta (21%) and fetal liver (3%). The amount of inorganic 203Hg in fetal liver corresponded to about 0.015% of the dose administered to the dam as MeHg. When hamsters were administered 203HgCl2 by intravenous injection on day 9 of gestation, the concentration of 203Hg in fetal liver corresponded to 0.03% of the administered dose. The inorganic 203Hg detected in fetal liver after maternal exposure to MeHg was probably due to demethylation of MeHg in the dam and transplacental transfer of inorganic Hg.