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

MERCURY 321
2. HEALTH EFFECTS
EEGs) (Davis et al. 1974; Jaffe et al. 1983; McFarland and Reigel 1978). Some studies have examined the
relationship between nerve function and mercury levels in blood, urine, and tissue. Tissue levels of
mercury have also been found to correlate with impaired nerve function. Among 23 dentists with mercury
levels greater than 20 µg/g (measured in wrist tissue), 30% exhibited reduced nerve conduction velocity
when compared with dentists with tissue levels of mercury below 20 µg/g (Shapiro et al. 1982). The
decrease in nerve conduction velocity was observed in both sensory and motor nerves.
A dose-response relationship has also been reported for the association between paresthesia and blood
mercury concentrations in an Iraqi population exposed to methylmercury. At a blood mercury level of
24 µg/100 mL 65 days after cessation of exposure, the incidence of paresthesia caused by methylmercury
rose significantly (Clarkson et al. 1976). Below this concentration, any incidence of paresthesia was
assumed to be related to other causes, according to the investigators. As a result of the reported blood
mercury half-life of 65 days in this population, the maximum blood mercury concentration was likely to
have been 48 µg/100 mL at the end of the exposure. Some evidence of paresthesia, sensory impairment,
general ataxia, and visual field effects in exposed Swedes was reported; however, no significant increases
in occurrence were found in Swedes with high levels of mercury in blood cells (82–1,100 ng/g) as
compared to Swedes with lower blood cell mercury levels (12–75 ng/g) (Skerfving 1974). The study did
not include a matched control group.
Many possible biomarkers of effect for mercury exposure have been correlated with urinary mercury
levels. Workers exposed to elemental mercury vapor with urinary mercury excretion levels ranging from
7 to 1,101 µg/day exhibited significantly reduced tibial nerve velocity and increased median nerve latency
in both motor and sensory nerves as compared with controls (Vroom and Greer 1972). Prolonged motor
and sensory nerve latency was also associated with urine mercury levels ranging from 20 to 450 µg/L in
18 male workers exposed to elemental mercury vapor at a mercury cell chlorine plant (Levine et al. 1982).
Urine mercury levels exceeding 200 µg/L have been reported to be associated with tremors and poor eye-
hand coordination (Williamson et al. 1982). Twelve workers chronically exposed to elemental mercury
vapor had urinary mercury levels ranging from