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

MERCURY 107
2. HEALTH EFFECTS
different results were obtained following 350-day exposure of a different strain of rats to 7 mg Hg/kg/day as
mercuric chloride in drinking water (Boscolo et al. 1989; Carmignani et al. 1989). In the chronic study,
positive inotropic response, increased blood pressure and cardiac contractility, and decreased baroreceptor
reflex sensitivity were observed. The investigators suggested that the mechanism for the cardiac effects in
the chronic study involved the release of norepinephrine from presynaptic nerve terminals. Evidence of this
release was provided by the fact that mercury administration reduced the cardiovascular response to
bretylium (which blocks presynaptic release of the neurotransmitter norepinephrine) but not tyramine
(which releases neurotransmitter from nerve terminals).
Organic Mercury. Electrocardiography in four family members who ate meat from a hog that had
consumed seed treated with ethylmercuric chloride had abnormal heart rhythms (ST segment depression
and T wave inversion) (Cinca et al. 1979). Death of the two children in the family was attributed to cardiac
arrest, and autopsy of these boys showed myocarditis. Cardiovascular abnormalities were also observed in
severe cases of poisoning in the Iraqi epidemic of 1956, when widespread poisoning resulted from eating
flour made from seed grains treated with ethylmercury p-toluene sulfonanilide (Jalili and Abbasi 1961).
These abnormalities included irregular pulse, occasionally with bradycardia, and electrocardiograms
showing ventricular ectopic beats, prolongation of the Q-T interval, depression of the S-T segment, and
T inversion.
A decrease in heart rate was observed in male rats given 2 gavage doses of 12 mg Hg/kg as methylmercuric
chloride (Arito and Takahashi 1991). An increase in systolic blood pressure was observed in male rats after
daily oral gavage doses of 0.4 mg Hg/kg/day as methylmercuric chloride for 3–4 weeks (Wakita 1987).
This effect began approximately 60 days after initiation of exposure and persisted for at least 9 months. No
treatment-related histopathological changes were observed in the hearts of rats exposed to 0.1 mg
Hg/kg/day as methylmercuric chloride in the diet for up to 2 years (Verschuuren et al. 1976).
Gastrointestinal Effects
Inorganic Mercury. Ingestion of metallic mercury results in negligible absorption and little effect on the
gastrointestinal tract. The two case histories identified are unusual in that the dose levels could be
reasonably well quantified. The first case history reported ingestion of 15 mL (204 g) of metallic mercury
by a 17-year-old male storekeeper who swallowed mercury from the pendulum of a clock (apparently out of
curiosity rather than as a suicide attempt). On admission, and 24 hours later, he was symptom free, and