A Neurobehavioral Study of Chloralkali Workers after the Cessation of Exposure to Mercury Vapor

Neurobehavioral functions were examined in 49 male workers who had been previously exposed to mercury vapor. They were compared with 49 age-matched male referents in a cross-sectional study. The average duration of exposure in the index group was 13.1 years at a calculated mean urinary mercury (U-Hg) concentration of 9.3 nmol Hg/mmol creatinine (Cr.)/year. The exposure had ceased on average 4.8 (range 4.2-10.0) years prior to the examinations. Forty-one exposed participants and 40 referents had also been examined approximately 5 years previously, while they were still under ongoing exposure. The neurobehavioral test scores and the number of subjective symptoms were similar in the previously exposed subjects and the referents. No significant differences in the development of the neurobehavioral test scores were observed between those 41 previously exposed subjects who had also been examined while they were still being exposed when compared to the 40 referents. However, the difference in the Digit Symbol Test scores between the two occasions was associated with the concentration of inorganic mercury in whole blood while they were still under exposure. The results suggest that no long-term effects of mercury vapor exposure are found at the exposure level experienced by these workers. The study may indicate that the test performance on the Digit Symbol Test improves after exposure cessation in the subjects with the highest B-Hg concentrations, and that this test may be quite sensitive to the effects of mercury vapor exposure.