Effects of mercury vapor exposure on neuromotor function in Chinese miners and smelters

Objectives Current risk assessment of elemental mercury vapor is based on the tremor toxicity. To clarify the neuromotor effects of occupational exposure to mercury vapor, hand tremor and postural sway were measured in 27 miners and smelters (i.e., exposed workers) and 52 unexposed subjects. Methods Urine samples were collected and total mercury and creatinine concentrations were determined. Data of the tremor and postural sway were analyzed using the fast Fourier transformation. Results The geometric means of the urinary mercury level (UHg) were 228 (range 22.6–4,577) μg/g creatinine for the exposed workers and 2.6 (1.0–17.4) μg/g creatinine for the unexposed subjects. Total tremor intensity and frequency-specific tremor intensities at 1–6 and 10–14 Hz were significantly larger in the exposed workers than in the unexposed subjects (P < 0.05), but they were not significantly related to the UHg among the exposed workers (P > 0.05). In contrast, there were no significant differences in any postural sway parameters between the above two groups (P > 0.05), but the transversal sway with eyes open was positively related to the UHg among the exposed workers in using multiple regression analysis (P < 0.05). Conclusions These findings suggest that postural sway, as well as hand tremor, may be affected by elemental mercury vapor exposure, but the former test seems to be less sensitive to mercury than the latter one.