A comparison of the lactational and transplacental deposition of mercury in offspring from methylmercury-exposed mice. Effect of seleno-L-methionine.

Females exposed to methylmercury expose their offspring to mercury across the placenta as well as through milk. The relative importance of these two routes of exposure has hitherto been unresolved. Using a cross-fostering model with female mice, the transplacental and lactational exposures to mercury were evaluated separately. In female mice exposed to low, non-toxic levels of methylmercury in the drinking water the deposition of mercury in offspring before birth was quantitatively more important than later transfer of mercury from milk to offspring. Seleno-L-methionine supplementation of the dams increased the whole-body deposition in offspring. As methylmercury is anticipated to be absorbed completely and the young mice are unable to excrete mercury, these data indicate that seleno-L-methionine affects the kinetics of the inorganic mercury pool, which, due to demethylating processes, is present in both blood and milk of methylmercury-exposed females.