The Present Mercury Contents of Scalp Hair and Clinical Symptoms in Inhabitants of the Minamata Area

A total of 191 fishermen and their family (32–82 years) living in some mercury-polluted areas along the Shiranui Sea volunteered for the present study. They made a living by fishery and had formerly eaten the methyl mercury-contaminated fish and shellfish caught there. The questionnaire on subjective symptoms, fish eating habits, and past living history was conducted on the subjects. In addition, they were clinically examined in detail by several neurologists and scalp hair was collected. With six exceptions, all the 185 subjects showed a normal total mercury level in hair (<10 ppm). The ratio of methyl mercury to total mercury was 79–94% on the average for each group examined, suggesting indirect contamination (perhaps through the food chain). Despite their low mercury level in scalp hair, however, the subjects showed various neurological symptoms, particularly, sensory disturbance (such as the glove and stocking type), at a very high rate. Thus, it seems fair to state that, in addition to officially recognized Minamata disease patients, there still exist many people with atypical, slight Minamata disease on the coast of the Shiranui Sea. The current hair mercury level is not necessarily useful as a criterion for diagnosing chronic Minamata disease because of the long lapse of time.