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

MERCURY A-5
APPENDIX A
low-dose chronic exposure to metallic mercury can result in adverse health sequelae and the chronic
inhalation MRL that is based upon the Fawer et al. (1983) study of occupationally exposed individuals.
Other occupational studies further support the ability of metallic mercury to induce neurologic deficits.
Several studies have reported significant effects on tremor or cognitive skills among groups exposed
occupationally to comparable or slightly higher (up to 0.076 mg/m 3 ) levels (Ehrenberg et al. 1991; Piikivi et
al. 1984; Roels et al. 1982). Difficulty with heel-to-toe gait was observed in thermometer plant workers
subjected to mean personal breathing zone air concentrations of 0.076 mg/m 3 (range of 0.026–0.27 mg/m 3
(Ehrenberg et al. 1991).
Tremors have also been reported in occupationally exposed workers with urinary mercury concentrations of
50–100 µg/g creatinine, and blood levels of 10–20 µg/L (Roels et al. 1982). By comparison, blood mercury
levels in the Fawer et al. (1983) study averaged 41.3 and 16.6 µmol Hg/L for the exposed and control
groups, respectively. Urinary mercury levels for the exposed workers in the Fawer et al. (1983) study
averaged 11.3 µmol Hg/mol creatinine (about 20 µg/g creatinine), compared with 3.4 µmol/mol creatinine
in the controls. In another study (Piikivi et al. 1984), decreases in performance on tests that measured
intelligence (similarities) and memory (digit span and visual reproduction) were observed in chloralkali
workers exposed for an average of 16.9 years (range, 10–37 years) to low levels of mercury when compared
to an age-matched control group. In this study, significant differences from controls were observed on
these tests among 16 workers with blood levels ranging from 75 to 344 nmol/L and urine levels ranging
from 280 (about 56 µg/L) to 663 nmol/L. Abnormal nerve conduction velocities have also been observed in
chloralkali plant workers at a mean urine concentration of 450 µg/L (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 airborne mercury
concentrations of 20–96 mg/m 3 (Langauer-Lewowicka and Kazibutowska 1989).
Agency Contact (Chemical Manager): John Risher