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

MERCURY
2. HEALTH EFFECTS
coordination and memory showed no significant deficits in the exposed group. The exposed and control
groups were matched for age, sex, vocational status, education, and mean number of amalgam fillings. A
group-average exposure concentration of 0.025 mg/m 3 mercury vapors was estimated from repeated
analyses of blood mercury concentration (mean, 51.3 nmol/L .10 µg/L) (see the discussion regarding these
estimated exposure levels in Section 2.5). Also, no effects on tremors, bimanual coordination, color
determination, or reaction time were observed in chloralkali workers with more than 7 years of exposure to
low levels of mercury; ambient air levels measured for 2 years prior to testing averaged 0.076 mg/m 3 and
the average blood level in the workers was 19.9 µg/L (Schuckmann 1979). Negative findings were also
noted when the results of tremor frequency spectra and psychometric tests of a group of chloralkali workers
exposed for an average of 13.5 years were compared to unexposed controls (Langworth et al. 1992a). The
TWA exposure level was estimated to be 0.025 mg/m 3 , based on measurements taken at the time of the
study, and blood levels in the workers averaged 55 nmol/L (.11 µg/L). Despite the negative objective
findings, subjective reports of fatigue, memory disturbances, and confusion were significantly higher in the
exposed workers.
Boogaard et al. (1996) evaluated the effects of exposure to elemental mercury on the nervous system and
the kidneys of workers producing natural gas in the Netherlands. Early signs of alterations in renal and
neurological functions were studied in three groups of workers who were exposed to different levels of
mercury that were below the current ACGIH biological exposure index of 35 µg/g creatinine. Air
concentrations ranged from 10 to 1,500 µg/m 3 (median, 67) at locations where mercury exposure was
anticipated; the potential 8-hour TWA exposure ranged from 33 to 781 µg/m 3 (median, 88). Air
concentrations ranged from 0 to 6 µg/m 3 at locations where little mercury exposure was expected. Current
mercury concentrations in urine were 23.7, 4.1, and 2.4 µg/g in high, low, and control exposure groups,
respectively; mercury concentrations in blood were 3.5, 1.5, and 2.2 µg/L, respectively. There were no
differences among the three study groups with respect to either motor nerve conduction velocity or tremor
frequency spectra of physiological tremors. Also, no significant correlations were found between the
results of the neurological tests and any of the present or historical biological monitoring data.
In contrast to the negative findings above, several studies have shown significant effects on tremor or on
cognitive skills at comparable or lower group-average exposure levels (0.014–0.076 mg/m 3 ). Using the
same paradigm as Langworth et al. (1992a), a significant difference was seen in the tremor frequency
spectra in mercury-exposed workers from three industries who were exposed to low levels of mercury for
an average of 15.3 years (range, 1–41 years) when compared to unexposed controls (Fawer et al. 1983).
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