|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1994 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1993 : ¥1,300,000 (Direct Cost : ¥1,300,000)
(1) To find the residual effects of long term exposure to mercury vapor, neurobehavioral tests were given to ex-mercury miners about 18-23 years after the end of mercury exposure. Seventy sixmale ex-mercury miners who had been exposed to high concentrations of mercury vapor (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'symproms 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 poo
rer neurological performance of handeye coordination, tapping, and a color card reading test. Job categories classified by the exposure to mercury also had a significant negative correlation with these performance. The period of years after the end of exposure had a signficant correlation with better performance of reaction time and digit span. On the other hand, the history of intoxication itself had no significant correlation with any of the current neurobehavioral performances. These results suggest that there are slight but persistent effects on neurobehavoral function, especially on motor coordination, among mercury miners even more than 10 years after the end of exposure.
(2) Detailed clinical neurological examination, neurophysiological measurements including the analysis of hand tremor, computerized postural swsy, audio-and visual evoked potential, and neuroimaging techniques such as MRI and CT were also done as a follow-up survey of 28 these ex-miners. Some of the ex-miners who exposed moderately or highly to mercury vapor showed the abnormal value of urine B2-nicroglobulin. Power spectral analyzes (fourier analyzes) revealed a marked reduction in power association with a change in the shape of the spectra. These changes were associated with a reduction in plasma level of mercury. Some of the ex-miners showed significant delay of the latency and decreased level of the amplitudes of the evoked potential, which was probably caused by the results of the hearing loss due to the noisy pet-labor. Preliminary results of neuroradiologic findings using MRI revealed no specific changes in magmetic resonance on T1 or T2 enhancements, only showing lacuna of the vascular infarction among some of ex-miners. However, many ex-miners who exposed to higher concentrations of mercury vapor than others tended to show the atrophy of the cortical brain in X-ray computed tomography. Less