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

MERCURY 180
2. HEALTH EFFECTS
in the brain in relation to the blood mercury concentration was found after exposure in utero compared to
exposure in milk. Mercury was present as methylmercury in the blood of the offspring exposed only
during gestation, indicating little or no demethylation during the first 15 days after birth. However,
inorganic mercury was present in the blood of offspring exposed only through milk, probably resulting
from demethylation of methylmercury in the dam and transport of inorganic mercury to the sucklings
through milk.
In animal studies, mercury transfer to and distribution in offspring depends on the form administered to the
dam. Yoshida et al. (1994) administered either mercury chloride or methylmercury at 1 mg Hg/kg body
weight to maternal guinea pigs (Hartley strain) via intraperitoneal injection 12 hours after parturition.
Exposure of the offspring was studied on days 3, 5, and 10 postpartum. Concentrations of mercury were
lower in the milk than in maternal plasma regardless of the form of administered mercury, but total milk
mercury was higher in the dams given mercury chloride. While the ratio of methylmercury to total
mercury decreased in plasma from dams, it did not decrease in the milk. Regardless of the form of
mercury given to the dams, the highest concentration of mercury in the offspring was found in the kidney,
followed by the liver and the brain. Brain mercury, however, was significantly higher in the offspring of
methylmercury-treated dams. Mercury levels in major organs of the offspring peaked at 5 days from
mercury-chloride-treated dams and at 10 days from methylmercury-treated dams.
Tissue distribution of phenylmercury is initially similar to methylmercury. One week after administration,
the distribution pattern resembles that seen after administration of inorganic compounds (Nordberg 1976).
Once in the blood, phenylmercury distributes to a greater extent into the red blood cells than the plasma.
Phenylmercury also predominantly distributes to the liver (Berlin 1963). It is less permeable to the
placental and blood-brain barriers than methylmercury (Yamaguchi and Nunotani 1974). Phenylmercury
also accumulates in the fur of rats but to a lesser extent than detected with methylmercury exposure (Gage
1964).
2.3.2.3 Dermal Exposure
No information was identified for distribution of metallic, inorganic, or methylmercury via dermal
absorption. A case history for a dermal absorption of dimethylmercury (see Section 2.3.1.3) does provide
some information on distribution (Blayney et al. 1997; Nierenberg et al. 1998). A 48-year-old female
absorbed approximately 0.4–0.5 mL of dimethylmercury (about 1,500 mg) through the skin on the dorsal