Quantitative assessment of neuromotor function in workers with current low exposure to mercury vapor

Evaluation of neuromotor function has been used in several epidemiological studies of workers with long-term exposure to mercury vapor (Hg0). Some recent studies indicate adverse effects at relatively low exposure levels. In the present study, we used sensitive quantitative methods, developed specifically to detect subtle effects of exposure to toxins on motor function. After exclusion of individuals with neurological diseases or other conditions that may affect performance, 43 chloralkali workers with current low exposure to Hg0, and 22 age-matched referents remained for further analysis. The median urinary mercury concentration in exposed workers was 5.9 μg/g (range 1.3–25) creatinine (μg/gC), while that in referents was 0.7 μg/gC (range 0.2–4.1). The mean exposure time was 15 years, and the median cumulative mercury index was 161 years × μg/gC in exposed workers. A eurythmokinesimeter (EKM) was used to quantify eye–hand coordination, and a diadochokinesimeter, to measure rapid alternating rotation of the forearms. In general, the differences in performance between the exposed workers and the referents were small. Age was associated with a decrease in speed, more tremor, and longer contact duration between the stylus and the metal targets in performance of rapid pointing movements. Smokers had significantly more tremor, and more contacts per event in the EKM test, than nonsmokers. Taking age, shift work, and smoking habits into account, no significant associations with current or cumulative mercury exposure were found for the majority of the outcome variables from the quantitative tests. In general, this study indicates no significant adverse effects of Hg0 on neuromotor function at the exposure levels studied.