Residual neurobehavioural effects associated with chronic exposure to mercury vapour.

Abstract

To find the residual effects of long term exposure to mercury vapour, neurobehavioural tests were given to ex-mercury miners about 18 years after the end of mercury exposure. Seventy six male exmercury miners who had been exposed to high concentrations of mercury vapour (over 1.0 mg/m3) and with a history of mercury intoxication were compared with controls matched for age (within 3 years), sex, and education. Although the extent of the workers' symptoms caused by mercury poisoning, termed erethismus merculialis, decreased considerably after the end of exposure, matched paired comparison showed that performances of motor coordination, simple reaction time, and short term memory had deteriorated significantly in the exposed group. Multiple linear regression analysis of exposure variables with neurological examination measures showed positive correlations between poorer neurological performance and variables related to mercury exposure. Thus the duration of exposure correlated with poorer performance of hand-eye coordination, tapping, and a colour card reading test. Job categories classified by exposure to mercury also had a significant negative correlation with these performances. The period of years after the end of exposure hada significant correlation with better performance of reaction time and digit span. On the other hand, the history of intoxication itself had no significant correla- (1) disturbances of the motor system, such as fine tremor of the extremities and poor psychomotor performance,2" (2) deterioration of intellectual capacity, such as memory disturbances and poor verbal intelligence,5-'0 (3) alterations of the emotional state such as depressive mood, irritability, and listlessness,' and (4) peripheral neurotoxicity, such as polyneuropathy with prolonged motor and sensory nerve conduction. '1-4 There are, however, only a limited number of reports on neurobehavioural effects after the end of exposure. Albers et al recently examined 247 ex-workers who had been exposed to mercury vapour for 20 to 35 years previously to identify potential exposure related neurological abnormalities."5 They found that subjects with a history of peak urinary mercury concentrations above 0-6 mg/l showed significantly decreased strength, decreased coordination, increased tremor, decreased sensation, and increased prevalence of Babinski and snout reflexes when compared with the subjects with lower exposure. In our study we have surveyed symptoms and neurobehavioural performances of ex-mercury miners about 18 years after the end of exposure to mercury to find if there were any adverse residual effects of long term exposure to mercury vapour. Methods STUDY POPULATIONSThe subjects were ex-miners of a mercury mine in Hokkaido, Japan, which started mining in 1939

Neuropsychological effects associated with exposure to mercury vapor among former chloralkali workers

“…The poorer performance on this test among the exposed workers is in accordance with the observation of impaired coordination in the clinical neurological examination of the same workers (24,25). Impaired manual dexterity or coordination has been suggested as an effect of past exposure to mercury vapors in other neuropsychological studies of previously exposed workers (26,27). Workers exposed to mercury vapors at the time of examination have been shown to have poorer results in similar tests (lo), whereas other studies on populations with lower exposure have shown no difference between exposed subjects and ref- erents (1 1, 17, 18).…”

“…This test did not discriminate between previously mercury-exposed lithium production workers and referents (27), and the test was not administered to previously exposed Japanese mercury miners (26). Soleo et a1 (12) did not observe poorer performance on this test in a small study on currently exposed workers who were compared with referents.…”

“…year)], and 25 workers with high exposure intensity (cum U-Hg/ exposed to mercury vapors are available to our knowledge (26,27). Fine et a1 (27) found poorer performance on a hand-eye coordination test for 247 workers formerly exposed to mercury vapors when they were compared with unexposed referents.…”

“…The history of prior mercury intoxication showed no significant correlation with current neurobehavioral performance overall, but the age-related deterioration in performance in several tests was reported to be more pronounced among the older ex-miners with a prior history of intoxication. Exposure had ceased approximately 20 years prior to the study (26).…”

“…There is, however, evidence of persisting neurological abnormalities in subjects with past exposure (22)(23)(24)(25). In addition, evidence of persisting neurobehavioral impairment in former Japanese mercury miners, especially motor coordination, has been presented (26). The workers included in the study also had a history of clinically overt mercury poisoning, and the reported air mercury concentrations at the time of exposure were usually above 1.0 mg/m3.…”