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

MERCURY 173
2. HEALTH EFFECTS
primates exposed for one year to mercury through amalgams in dental fillings or the maxillary bone
(Danscher et al. 1990).
The kidney is the major organ of mercury deposition after inhalation exposure to metallic mercury vapor.
Mercury concentrations in the kidneys are orders of magnitude higher than in other tissues (Rothstein and
Hayes 1964). Monkeys exposed for one year to metallic mercury vapor from amalgam in dental fillings
accumulated mercury in the spinal ganglia, anterior pituitary, adrenal, medulla, liver, kidneys, lungs, and
intestinal lymph glands (Danscher et al. 1990). The largest deposits of mercury were found in the kidneys
(2.5–5.2 ppm), specifically in the proximal tubule cells.
The kidney contains metallothionein, a metal-binding protein that is also found in fetal and maternal livers
and other organs. In the kidneys, the production of metallothionein is stimulated by exposure to mercury.
The increased levels of metallothionein increase the amount of mercuric ion binding in the kidneys (Cherian
and Clarkson 1976; Piotrowski et al. 1973). Three classes of sulfhydryl groups have been identified in the
kidneys, with metallothionein having the greatest affinity for mercury (Clarkson and Magos 1966). Low
molecular-weight complexes of mercury have been identified in the urine, suggesting that they may exist in
the kidneys and contribute to the kidneys' accumulation of mercury (Piotrowski et al. 1973).
Metallothionein exists in higher concentration in the fetal liver than in the maternal liver of rats. Exposure
to mercury in the pregnant dam results in the binding of mercury to metallothionein in fetal liver initially,
followed by a redistribution to other organs (Yoshida et al. 1990). Metallothionein and mercury levels were
elevated in the kidneys of guinea pig neonates exposed to 6–10 mg/m 3 mercury vapor (Piotrowski et al.
1973).
After exposure to mercury vapor, mercury is distributed throughout the body in different chemical and
physical states. Metallic mercury dissolves in the blood upon inhalation, and some remains unchanged
(Magos 1967). Metallic mercury in the blood is oxidized to its divalent form in the red blood cells
(Halbach and Clarkson 1978). The divalent cation exists as a diffusible or nondiffusible form. The
nondiffusible form is mercuric ions that bind to protein and are held in high-molecular weight complexes,
existing in equilibrium with the diffusible form.
In the plasma, the mercuric ion is predominantly nondiffusible and binds to albumin and globulins (Berlin
and Gibson 1963; Cember et al. 1968; Clarkson et al. 1961). Following mercuric salt administration,