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

MERCURY 233
Inorganic Mercury
C
2. HEALTH EFFECTS
The acute- and intermediate-duration MRLs for oral exposure to inorganic mercury are based on kidney
effects reported in a 1993 NTP study of mercuric chloride (NTP 1993). Most of the supporting studies of
oral exposure to inorganic mercury also use mercuric chloride.
Mercuric sulfide (also known as cinnabar) is the predominant natural form of mercury in the environment
and is a common ore from which metallic mercury is derived. Mercury released to the environment may be
transformed into mercuric sulfide. Several studies suggest that the bioavailability of mercuric sulfide in
animals is less than that of mercuric chloride (Sin et al. 1983, 1990; Yeoh et al. 1986, 1989). For example,
Sin et al. (1983) found an increase in tissue levels of mercury in mice orally exposed to low doses of
mercuric chloride, but elevated levels of mercury were not found in the tissues of mice fed an equivalent
weight of mercuric sulfide. This finding indicates a difference in bioavailability between HgCl2 and HgS in
mice. However, a quantitative determination of the relative bioavailabilities of mercuric sulfide versus
mercuric chloride has not been derived in the available studies, nor has the relative bioavailability of
mercuric sulfide in humans been examined.
An MRL of 0.007 mg Hg/kg/day has been derived for acute-duration oral exposure (14 days or
less) to inorganic mercury.
The MRL was based on a NOAEL of 0.93 mg Hg/kg/day for renal effects in rats administered mercuric
chloride 5 days a week for 2 weeks. The dose used in this study was duration-adjusted for a 5-day/week
exposure and divided by an uncertainty factor of 100 (10 for extrapolation from animals to humans and
10 for human variability). Increased absolute and relative kidney weights were observed in male rats
exposed to 1.9 mg Hg/kg/day as mercuric chloride (NTP 1993). At higher doses, an increased incidence
and severity of tubular necrosis was observed.
Several other studies examining the effects of oral exposure to inorganic mercury salts have also shown
renal toxicity in humans as a result of acute oral exposures. Kidney effects (i.e., heavy albuminuria,
hypoalbuminemia, edema, and hypercholesterolemia) have been reported after therapeutic administration of
inorganic mercury (Kazantzis et al. 1962). Acute renal failure has been observed in a number of case
studies in which mercuric chloride had been ingested (Afonso and deAlvarez 1960; Murphy et al. 1979;
Samuels et al. 1982). The autopsy of a 35-year-old man who ingested a lethal dose of mercuric chloride