ELIMINATION OF RECENTLY ABSORBED METHYL MERCURY DEPENDS ON AGE AND GENDER

The toxicokinetics of some toxic metals have been demonstrated to depe nd on the age of the exposed individuals. Most studies focused solely upon age-dependent differences in degree of absorption. The present st udy aimed at investigating possible age-dependent differences in elimi nation of CH3HgCl using Hg-203 and repeated whole-body counting of liv e 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 eli mination more than doubled in male mice. As intestinal absorption of C H3HgCl 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 mec hanism could explain this observation, groups at different age were su pplemented with non-labeled CH3HgCl in the drinking water during a two weeks observation period after administration of a single dose of (CH 3HgCl)-Hg-203. Supplementation did not influence the rate of eliminati on of CH3HgCl in mature males. Accordingly the mechanism causing the o bserved age-dependent change in elimination rate is not a matter of sa turation but an age-dependent development of a more efficient mechanis m 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 f or elimination of CH3HgCl seems to be the initial absorption and distr ibutional phase after exposure and most likely involves the hepatic ha ndling of methyl mercury.