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

MERCURY 185
2.3.4 Elimination and Excretion
2. HEALTH EFFECTS
Elimination of metallic mercury occurs through the urine, feces, and expired air, while inorganic mercury is
excreted in the urine and feces in humans. Animal data on excretion are limited but indicate that excretion
is species and dose dependent. The feces are a major elimination route for inorganic mercury compounds,
but high acute doses increase the percentage of excretion via the urine. Excretion of organic mercury is
predominantly thought to occur through the fecal (biliary) route in humans. In animals, phenylmercury is
excreted initially though the bile and then shifts to urine, whereas methylmercury is primarily excreted in
the bile and then the feces. Age is a factor in the elimination of mercury in rats following inorganic and
organic mercury exposure, with younger rats demonstrating significantly higher retention than older rats.
Both inorganic and organic mercury compounds can be excreted in breast milk. There are no data
suggesting that the route of exposure affects the ultimate elimination of inorganic and organic mercury that
is absorbed into the body.
Metallic and Inorganic Mercury. The urine and feces are the main excretory pathways of metallic and
inorganic mercury in humans, with a body burden half-life of approximately 1–2 months (Clarkson 1989).
In a study of former chloralkali workers exposed to metallic mercury vapor for 2–18 years (median,
5 years), Sallsten et al. (1995) found that the elimination of mercury in urine was well characterized by a
one-compartment model, which estimated a half-life of 55 days. There was a tendency toward longer half-
lives with shorter duration exposures than with long-term exposure, when uptake and elimination have
reached a steady state. This might be due to the induction of a higher metabolic rate after a longer exposure
time, but there is no experimental evidence to support such an effect (Sallsten et al. 1995). For high-level
exposure to inorganic divalent mercury, the urine is probably the major elimination route, with a half-life
similar to that of metallic mercury (Clarkson 1989). An elimination half-life from urine was estimated to be
25.9 days following an acute exposure to a high level of mercuric chloride (13.8 mg/kg) (Suzuki et al.
1992). Exhalation in the lungs and secretion in saliva, bile, and sweat may also contribute a small portion
to the excretion process (Joselow et al. 1968b; Lovejoy et al. 1974). After an acute mercury exposure in
humans, urinary excretion accounts for 13% of the total body burden. After long-term exposure, urinary
excretion increases to 58%. Humans inhaling mercury vapor for less than an hour expired approximately
7% of the retained dose of mercury (Cherian et al. 1978; Hursh et al. 1976). The half-life for this
elimination pathway was 14–25 hours; therefore, excretion through expired air is negligible 5–7 days after
exposure (Cherian et al. 1978). Using a two-compartment model, elimination half-lives in the urine of
workers exposed for 20–45 hours to >0.1 mg/m 3 metallic mercury vapor were