Elimination of recently absorbed methyl mercury depends on age and gender

The toxicokinetics of some toxic metals have been demonstrated to depend on the age of the exposed individuals. Most studies focused solely upon age-dependent differences in degree of absorption. The present study aimed at investigating possible age-dependent differences in elimination of CH3HgCl using 203Hg and repeated whole-body counting of live mice to quantitate the whole-body retention. With increasing age at the time of exposure to a single oral dose of CH3HgCl, the rate of elimination more than doubled in male mice. As intestinal absorption of CH3HgCl is almost complete, the findings must pertain either to an age-related increased excretion capacity or an age-dependent change in the excretion mechanism. To study whether saturation of the excretion mechanism could explain this observation, groups at different age were supplemented with non-labeled CH3HgCl in the drinking water during a two weeks observation period after administration of a single dose of CH3203HgCl. Supplementation did not influence the rate of elimination of CH3HgCl in mature males. Accordingly, the mechanism causing the observed age-dependent change in elimination rate is not a matter of saturation but an age-dependent development of a more efficient mechanism for CH3HgCl elimination. Further, as elimination of mercury absorbed during a prolonged period of exposure through drinking water was not influenced by age, the critical step for the age-dependent mechanism for elimination of CH3HgCl seems to be the initial absorption and distributional phase after exposure and most likely involves the hepatic handling of methyl mercury.