EEG photic driving in workers exposed to mercury vapors

To assess the potential of EEG photic driving (PD) as an indicator of an early neurotoxic effect of long-term, low-level exposure to mercury vapors.

Twenty-four chloralkali workers exposed to mercury vapors; twenty-four age- and gender-matched control subjects. Level of exposure was determined by urinary mercury excreted both spontaneously and after administration of a chelating agent, sodium 2,3-dimercapto-1-propane sulfonate. A computerized method for quantitative evaluation of PD was developed. Five parameters describing PD were compared.

The number of stimulation frequencies eliciting PD was higher in the exposed group, with a median of 17 frequencies, as compared to 10 frequencies in the control group (P < 0.001). The maximum value of PD was higher in the exposed group, with a median of 24.6 z-units as compared to 9.4 in the control group (P < 0.001). The median of the stimulation frequency with maximum PD was shifted from 15 Hz in the control group to 20 Hz in the exposed group (P < 0.01). The median of the sum of PD and the median of the index of PD were significantly higher in the exposed than in the control group (P < 0.001). The increased PD was particularly prominent at high stimulation frequencies in the beta range. There was no significant association between the measures of PD and the measures of exposure.

In comparison with a control group, significantly increased photic driving was observed in a group of workers exposed to mercury vapors. The issue of whether or nor the intergroup differences in PD are mercury related, could not be determined on the basis of our results. Should the enhanced PD be caused by mercury, then this electrophysiological phenomenon might be regarded as a marker of the CNS hyperexcitability due to an early neurotoxic effect of mercury, the clinical expression of which is erethism.