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

MERCURY 70
2. HEALTH EFFECTS
Hg/kg/day ("high dose"). At postpartum day 3, each litter was reduced to 4 male and 4 female offspring. No
significant differences between the mercury-treated offspring and the controls were observed for surface
righting, negative geotaxis, pinna unfolding, and tooth eruption. Tests of spontaneous motor activity
(locomotion, rearing, rearing time, and total activity) showed that the mercury-treated offspring were
hypoactive at 3 months of age; at 14 months, only total activity differed between exposed and control
groups. In spatial learning tasks, exposed offspring showed retarded acquisition in the radial-arm maze but
no differences in the circular-swim maze. A simple test of learning, habituation to a novel environment
(activity chambers), indicated a reduced ability to adapt. The authors conclude that prenatal exposure to
mercury vapor results in behavior changes in the offspring similar to those reported for methylmercury. On
postpartum days 3–4, the mercury contents in the brain, liver, and kidneys were 0.001, 0.004, and 0.002 mg
Hg/kg, respectively, for control offspring; 0.005, 0.053, and 0.033 mg Hg/kg, respectively, for animals
exposed for 1 hour a day; and 0.012, 0.112, and 0.068 mg Hg/kg, respectively, for animals exposed for
3 hours a day (Danielsson et al. 1993).
Four groups of 12 pregnant Sprague-Dawley rats were exposed to methylmercury or elemental mercury
alone or in combination as follows: (1) administered 2 mg/kg/day methylmercury via gavage during
Gd 6–9; (2) exposed by inhalation to 1.8 mg/m 3 metallic mercury (elemental mercury) vapor for 1.5
hours per day during Gd 14–19; (3) exposed to both methylmercury by gavage (2 mg/kg/day, Gd 6–9) and
elemental Hg vapor by inhalation (1.8 mg/m 3 , Gd 14–19) (methylmercury + elemental mercury); or (4) given
combined vehicle administration for each of the 2 treatments (control). The inhalation regimen
corresponded to an approximate dose of 0.1 mg Hg/kg/day. At postpartum day 3, each litter was reduced
to 4 male offspring. There were no differences between any of the groups in maternal body weight gain
before parturition. No differences in body weight, pinna unfolding, tooth eruption, surface righting reflex,
and negative geotaxis were observed in the offspring. Offspring of dams exposed to elemental Hg
showed hyperactivity in the spontaneous motor activity test chambers over all three parameters:
locomotion, rearing, and total activity; this effect was potentiated in the animals of the methylmercury +
elemental Hg group. In the swim maze test, the methylmercury + elemental mercury and elemental
mercury groups evidenced longer latencies to reach a submerged platform, which they had learned to
mount the day before, compared to either the control group or the methylmercury group. In the modified
enclosed radial-arm maze, both the methylmercury + elemental Hg and elemental Hg groups showed more
ambulations and rearings in the activity test prior to the learning test. During the learning trial, the same groups
(i.e., methylmercury + elemental Hg and elemental Hg) showed longer latencies and made more errors in