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

MERCURY
2. HEALTH EFFECTS
A 27-year-old female, who worked primarily in a room with a TWA mercury air concentration of
0.709 g/m3 and who had been on the job for 1.5 years, showed a variety of symptoms, including gum pain,
dizziness, poor attention, bad temper, some numbness, hypersalivation, hyperhidrosis, dizziness, and
fatigue. She had initial urine and blood mercury levels of 408 µg/L and 105 µg/L, respectively, but did not
require chelation; the symptoms abated fully approximately 2 months following discontinuation of exposure
(Yang et al. 1994).
Other chronic-duration exposures to metallic mercury vapor have resulted in tremors (which may be mild or
severe depending on the degree of exposure), unsteady walking, irritability, poor concentration, short-term
memory deficits, tremulous speech, blurred vision, performance decrements in psychomotor skills (e.g.,
finger tapping, reduced hand-eye coordination), paresthesias, decreased nerve conduction, and other signs
of neurotoxicity (Albers et al. 1988; Bidstrup et al. 1951; Chaffin et al. 1973; Chang et al. 1995; Chapman
et al. 1990; Fawer et al. 1983; Langolf et al. 1978; Piikivi et al. 1984; Smith et al. 1970; Sunderman 1978;
Uzzell and Oler 1986; Vroom and Greer 1972; Williamson et al. 1982). The majority of studies suggest
that motor system disturbances are reversible upon exposure cessation, while cognitive impairments,
primarily memory deficits, may be permanent (Chaffin et al. 1973; Hanninen 1982; Miller et al. 1975).
Several studies have noted correlations between exposure level or duration and effects (e.g., memory
deficits, psychomotor coordination, motor and sensory nerve conduction velocities, electromyographic
abnormalities, evidence of polyneuropathy, tremor, emotional changes, reflex abnormalities, and
electroencephalographic changes) (Albers et al. 1982; Iyer et al. 1976; Levine et al. 1982; Smith et al. 1983;
Vroom and Greer 1972; Williamson et al. 1982). Early studies suggested that frank neurotoxicity
(pronounced tremors, erethism, restriction of visual fields, difficulty seeing) was generally observed at
>300 µg mercury in a 24-hour urine (Bidstrup et al. 1951) or at >0.1 mg/m 3 (Smith et al. 1970). More
recent studies using sensitive tests for psychomotor skills, tremor, and peripheral nerve function suggest
that adverse effects may be associated with very low exposures (see below). However, conflicting
information exists regarding thresholds for neurotoxic effects.
Several reports have presented essentially negative findings at low exposure levels (0.025–0.076 mg/m3 ).
Chloralkali workers exposed to low air levels of mercury vapors for at least 5 years (group average,
14 years) reported an increase in memory disturbances, sleep disorders, anger, fatigue, confusion, and hand
tremors compared to the controls (Piikivi and Hanninen 1989). However, tests of psychomotor
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