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

MERCURY
2. HEALTH EFFECTS
The TWA mercury concentration measured in the work area at the time of the study was 0.026 mg Hg/m 3
(range not reported). It was assumed that the workers were exposed to the same concentration of mercury
for the duration of their employment. However, the group size was small, and the results may have been
influenced by a small number of more severely affected individuals. It is also possible that the tremors may
have resulted from intermittent exposure to concentrations higher than the TWA. Urinary mercury levels in
these workers averaged 11.3 µmol/mol creatinine (.20 µg/g creatinine). Tremors have also been associated
with occupational exposures that produced urinary concentrations of 50–100 µg/g creatinine and blood
levels of 10–20 µg/L (Roels et al. 1982). Difficulty with heel-to-toe gait was observed in thermometerplant
workers subjected to mean personal-breathing-zone air concentrations of 0.076 mg/m 3 (range,
0.026–0.27 mg/m3 ) (Ehrenberg et al. 1991).
Decreases in performance on tests that measured intelligence (a similarities test) and memory (digit span
and visual reproduction tests) were observed in chloralkali workers exposed for an average of 16.9 years to
low levels of mercury when compared to an age-matched control group (Piikivi et al. 1984). Significant
differences from controls were observed among workers with blood levels >75 nmol/L (.15 µg/L) and
urine levels >280 nmol/L (.56 µg/L).
Dentists (n=98, mean age 32, range 24–49) with an average of 5.5 years of exposure to low levels of
mercury showed impaired performance on several neurobehavioral tests (Ngim et al. 1992). Exposure
levels measured at the time of the study ranged from 0.0007 to 0.042 mg/m 3 (average, 0.014 mg/m3 ) and
blood levels ranged from 0.6 to 57 µg/L (average, 9.8 µg/L). Controls were matched for age, fish consumption,
and number of amalgam fillings. Differences in education, sex distribution, and reported use of
Chinese traditional medicines that might contain mercury were adjusted for in the statistical analysis. The
dentists showed significantly poorer performance on finger tapping (measures motor speed), trail making
(measures visual scanning), digit symbol (measures visuomotor coordination and concentration), digit span,
logical memory delayed recall (measures visual memory), and Bender-Gestalt time (measures visuomotor
coordination). The dentists had a higher aggression score than the controls. Correlations were observed for
exposure levels and duration. This study is limited, however, by lack of blinding and failure to report
control mercury levels; the statistical procedures used for confounders (use of traditional Chinese
medicines) were not reported.
In a study of the relation between cumulative exposure to mercury and chronic health impairment,
298 dentists had their mercury levels measured by an X-ray fluorescence technique. Electrodiagnostic and
neuropsychological findings in the dentists with more than 20 µg/g tissue (head and wrist) mercury levels
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