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

MERCURY
2. HEALTH EFFECTS
were compared with those of a control group consisting of dentists with no detectable mercury levels.
Twenty-three out of 298 dentists with the highest mercury levels were administered neurological tests and
compared to controls. The high mercury group had slowed conduction velocities in motor (median nerve)
and sensory (suralnerve) nerves, mild neuropsychological impairment (increased errors in the Bender-
Gestalt test), mild visuographic dysfunction, and higher distress levels (self-reported) than the control
group. Seven of the high exposure dentists showed manifestations of polyneuropathy. Exposure
concentrations were not specified. No polyneuropathies were detected in the control group (Shapiro et al.
1982). Abnormal nerve conduction velocities have also been observed at a mean urine concentration of
450 µg/L in workers from a chloralkali plant (Levine et al. 1982). These workers also experienced
weakness, paresthesias, and muscle cramps. Prolongation of brainstem auditory-evoked potentials was
observed in workers with urinary mercury levels of 325 µg/g creatinine (Discalzi et al. 1993). Prolonged
somatosensory-evoked potentials were found in 28 subjects exposed to 20–96 mg/m 3 of mercury
(Langauer-Lewowicka and Kazibutowska 1989).
In animals, as in humans, adverse neurological and behavioral effects are prominent following inhalation
exposure to high concentrations of metallic mercury vapor. However, animals appear to be less sensitive
than humans. Marked cellular degeneration and widespread necrosis were observed in the brains of rabbits
following exposures to metallic mercury vapor at 28.8 mg/m 3 for durations ranging from 2 to 30 hours
(Ashe et al. 1953). Exposures of 1 hour produced moderate (unspecified) pathological changes.
Intermediate-duration exposure of rabbits to 6 mg/m3 mercury vapor for periods of 1–11 weeks produced
effects ranging from mild, unspecified, pathological changes to marked cellular degeneration and some
necrosis in the brain (Ashe et al. 1953). The more serious degenerative changes were observed at longer
exposure durations (i.e., 8 and 11 weeks). Mild-to-moderate pathological changes were revealed in the
brains of rabbits exposed to a metallic mercury vapor concentration of 0.86 mg/m 3 for 12 weeks (Ashe et al.
1953). The usefulness of these results is limited because the pathological changes are not specified and no
distinction is made between primary and secondary effects (i.e., pathological changes secondary to induced
shock).
Two of 6 rabbits exposed to 4 mg/m 3 metallic mercury vapor for 13 weeks exhibited slight tremors and
clonus and had mercury concentrations of 0.8–3.7 µg/g wet tissue in the brain (Fukuda 1971). Following
intermittent exposure to 3 mg/m 3 for 12–39 weeks, rats exhibited a decline in conditioned avoidance
response; however, no histopathological changes were evident (Kishi et al. 1978). The change was
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