Methyl mercury exposure at Niigata, Japan: results of neurological examinations of 103 adults.
BACKGROUND
Large-scale poisonings caused by methyl mercury (MeHg) have occurred in Japan (Minamata in the 1950s and Niigata in the 1960s) and Iraq (in the 1970s). The current WHO neurological risk standard for adult exposure (hair level: 50 μg/g) was based partly on evidence from Niigata which did not consider any cases who were diagnosed later and/or exposed to low level of MeHg (hair mercury level less than 50 μg/g).


METHODS
Early in the Niigata epidemic in June 1965 there were two extensive surveys. From these two surveys, we examined 103 adults with hair mercury measurement who consulted two medical institutions. We compared the prevalence and the distribution of neurological signs related to MeHg poisoning between exposure categories.


RESULTS
We found 48 subjects with neurological signs related to MeHg poisoning who had hair mercury concentration less than 50 μg/g. Among the neurological signs, sensory disturbance of the bilateral distal extremities was observed more frequently, followed by disequilibrium, hearing impairment, and ataxia, in groups with hair MeHg concentration both below 50 μg/g and over 50 μg/g.


CONCLUSIONS
The present study suggests the possibility that exposure to MeHg at levels below the current WHO limits could cause neurologic signs, in particular, sensory disturbance.
Department of Social Welfare and Psychology, Faculty of Nursing, Social Welfare and Psychology, Niigata Seiryo University, 1-5939 Suido-cho, Niigata 951-8121, Japan. k-maruyama@n-seiryo.ac.jp
Kimio
K
Maruyama
Takashi
T
Yorifuji
Toshihide
T
Tsuda
Tomoko
T
Sekikawa
Hiroto
H
Nakadaira
Hisashi
H
Saito
D000328:Adult; D004781:Environmental Exposure / Q000032:analysis*; D005260:Female; D006197:Hair / Q000378:metabolism; D006801:Humans; D007564:Japan; D008297:Male; D008767:Methylmercury Compounds / Q000506:poisoning*; D009420:Nervous System / Q000473:pathology*; D009460:Neurologic Examination; D016017:Odds Ratio
D008767:Methylmercury Compounds