revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 352
2. HEALTH EFFECTS
In general, quantitative data are available to evaluate the rate and extent of distribution, metabolism, and
elimination of mercury in humans and animals following inhalation and oral exposure. Data on
distribution, metabolism, and excretion following dermal exposure are lacking for all forms of mercury.
The distribution data for metallic, inorganic and organic mercury are similar in humans and animals
(Aschner and Aschner 1990; Berlin 1963; Cherian and Clarkson 1976; Cherian et al. 1978; Clarkson 1989;
Clarkson and Magos 1978; Danscher et al. 1990; Grandjean et al. 1992; Nielsen and Andersen 1990,
1991a, 1991b; Nordberg 1976; Schionning et al. 1991; Sin et al. 1983; Suzuki et al. 1992; Warfvinge et al.
1992; Yeoh et al. 1989; Yoshida et al. 1990, 1992). No quantitative distribution data were located for
organic mercury compounds following inhalation exposure. The oxidation and reduction reactions that
control the disposition of elemental mercury were identified in both animals and humans (Clarkson 1989;
Halbach and Clarkson 1978; Nielsen-Kudsk 1973). Quantitative data on the biotransformation of organic
mercury are limited (Norseth and Clarkson 1970). Reliable quantitative evidence on excretion of metallic
and inorganic mercury in humans and animals following inhalation exposure is available (Cherian et al.
1978; Hursh et al. 1976; Joselow et al. 1968b; Lovejoy et al. 1974).
As discussed in the section on data needs for biomarkers, further study is needed on the effects that the
exposure level of methylmercury (as well as other forms of mercury) has on tissue distributions and the
correlation to biomarkers of exposure. Age appears to be a factor in the elimination of mercury in rats
following inorganic and organic mercury exposures (Daston et al. 1986; Thomas et al. 1982). Elimination
of methylmercury in rats may also be sex-related (Ballatori and Clarkson 1982). Nielson et al. (1994)
observed a significant sex-related differences in the toxicokinetics of methylmercury in mice following
administration of a single radiolabeled dose. Drasch et al. (1997) reported that mercury levels in all tissues
assayed in their human cadaver study had higher levels compared to male tissues. Nakagawa (1995) also
report higher mean mercury hair levels in males (2.98 µg/g) compared with females (2.02 µg/g) in a
Japanese population. Further research is, therefore, needed to characterize potential sex related difference
in the toxicokinetics of mercury under different exposure scenarios.
Insufficient data are available to assess whether or not there are any differences in absorption, distribution,
metabolism, and excretion of mercury with respect to time or dose (i.e., if saturation phenomena occur).
The majority of the available toxicokinetic data involve acute exposures to single doses. For all three
routes, studies are needed that compare various dose levels and durations in order to determine if there are
any differences in the toxicokinetics of mercury. Little is known about how mercurials are eliminated
from specific organs. In particular, the mechanism by which mercury is eliminated from the brain is