Blood mercury concentrations following methyl mercury exposure in adult and infant monkeys

Female monkeys (Macaca fascicularis) were dosed chronically with the equivalent of 10, 25, or 50 micrograms/kg/day methyl mercury until at least 90% of estimated blood equilibrium was reached and were then bred to untreated males. Infants were dosed with the same dose their mothers had received. An additional group of infants was dosed with 50 micrograms/kg/day beginning at birth. Infants exposed in utero were born with higher (1.7x) mercury levels than their mothers, but blood mercury levels of the offspring decreased to less than one-half that of the mothers. The steady-state blood levels of the group exposed postnatally were not different from steady-state levels of the group exposed in utero plus postnatally. When dosing was discontinued, the rate coefficient of elimination from blood did not differ between the adults (mothers) and the in utero plus postnatally exposed group, while that of the group exposed postnatally only was lower. There was no indication of a relationship in the rate of elimination for mother-infant pairs. These results suggest that the kinetics of methyl mercury in blood are complicated and may depend on the age of the individual when exposure begins.