Quantitative tremor assessment in workers with current low exposure to mercury vapor

Measurement of tremor has been used in several occupational studies of workers with long-term exposure to mercury vapor (Hg0). Recent studies indicate an adverse effect even at relatively low exposure levels. In the present study, we used sensitive quantitative methods to assess tremor in chloralkali workers with current low exposure to Hg0. Neurological examinations and recordings of tremor using both an accelerometer and a laser-based system were conducted in 43 mercury-exposed workers and 22 age-matched referents. The median urinary mercury concentration in exposed workers was 5.9 (1.3–25) μg/g creatinine (μg/gC), while it was 0.7 (0.2–4.1) μg/gC in referents. The mean exposure time was 15 years, and the median cumulative mercury index was 161 years × μg/gC in exposed workers. There were no differences between the exposed workers and the referents in the clinical evaluation of tremor. In the quantitative tremor tests, no associations were found with current or cumulative mercury exposure for the majority of tremor measures. There were indications that exposure to Hg0 was associated with a lowering of tremor frequency in the non-dominant hand, and a possible interaction with smoking. The differences were small, however, and overall, this study indicates no significant adverse effects on tremor at these exposure levels.