Lactational exposure and neonatal kinetics of methylmercury and inorganic mercury in mice

The concentration of mercury in milk and the distribution pattern in the su cking pup was followed over time after administration of a single iv inject ion of 0.5 mg/kg body wt of Hg-203-labeled methylmercuric chloride or mercu ric chloride to lactating mice on Day 10 of lactation. Mercury concentratio ns in milk of the dams and in whole body, blood, plasma, GI-tract, liver, k idneys, and brain of the offspring were followed up to 11 days after dosing (until lactational Day 21), Following the inorganic mercury dose to the da ms, most of the mercury in milk was delivered to the pups during the first 24 h, but the maximum mercury concentration in plasma and tissues of pups w as not reached until 7 days after dosing, indicating a prolonged absorption of inorganic mercury in the sucking pup. Pups of dams given methylmercury were exposed to a much lower and constant mercury concentration in milk. Th e estimated accumulated mercury dose via milk per pup of dams given methylm ercury was less than half of that estimated after the inorganic mercury dos e. When the accumulated dose via milk from methylmercury-exposed dams was c ompared to the amount of mercury in pup's carcass (whole body minus GI-trac t including content), it was revealed that almost all mercury delivered via milk was absorbed, and that the suckling pups had a very low elimination o f mercury until lactational Day 17, Lactational exposure following a matern al methylmercury or inorganic mercury dose resulted in almost similar mercu ry concentrations in liver, kidneys, and plasma of the suckling, but higher concentrations in brain (as most 14 times) and also twice as high mercury body burden in the methylmercury group. Thus, differences in kinetics indic ate that lactational exposure of methylmercury is a greater hazard for the breast-fed infant than inorganic mercury. (C) 1999 Academic Press.