Transplacental and Lactational Exposure to Mercury in Hamster Pups after Maternal Administration of Methyl Mercury in Late Gestation

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Abstract
Pregnant Syrian golden hamsters were given a single oral dose of 203Hg‐labelled methyl mercury (MeHg), 1.6 μmol/kg body weight, on day 12 of gestation. The uptake, retention and tissue distribution of 203Hg in the dams and pups was studied by γ‐counting during the following three weeks. The average transplacental transfer of 203Hg was 1.1% of the administered dose per pup, corresponding to 11% of the administered dose to a whole litter. This was considerably more than in our previous studies when the dams were treated on gestational day 2 (1.3%) or 9 (4.6%). The amount of 203Hg transferred to each pup in utero was independent of the litter size. The average additional transfer of 203Hg to a litter via milk was 1.7% of the administered dose. In the pups, the content of 203Hg in the liver and brain decreased, while the content in the kidneys and pelt increased during the second and third week. The highest amount of 203Hg was generally found in the pelt, which indicated that unweaned hamster pups primarily excrete MeHg by binding to hair. The chemical form of mercury in the liver and kidneys of the pups was determined by ion‐exchange separation of inorganic Hg and MeHg followed by γ‐counting. The amount of inorganic Hg in the liver of the pups remained constant throughout the experiment, while it increased in the kidneys after one week due to the demethylation of MeHg. The inorganic Hg in the liver of newborn pups was probably due to maternal demethylation of MeHg and transplacental transfer of inorganic Hg. This hypothesis was supported by the observed transplacental transfer of inorganic Hg in pregnant dams administered 203HgCl2 on day 12 of gestation.