Minamata Disease: Methylmercury Poisoning in Japan Caused by Environmental Pollution

Minamata disease (M. d.) is methylmercury (MeHg) poisoning that occurred in humans who ingested fish and shellfish contaminated by MeHg discharged in waste water from a chemical plant (Chisso Co. Ltd.). It was in May 1956, that M. d. was first officially "discovered" in Minamata City, south-west region of Japan's Kyushu Island. The marine products in Minamata Bay displayed high levels of Hg contamination (5.61 to 35.7 ppm). The Hg content in hair of patients, their family and inhabitants of the Shiranui Sea coastline were also detected at high levels of Hg (max. 705 ppm). Typical symptoms of M. d. are as follows: sensory disturbances (glove and stocking type), ataxia, dysarthria, constriction of the visual field, auditory disturbances and tremor were also seen. Further, the fetus was poisoned by MeHg when their mothers ingested contaminated marine life (named congenital M. d.). The symptom of patients were serious, and extensive lesions of the brain were observed. While the number of grave cases with acute M. d. in the initial stage was decreasing, the numbers of chronic M. d. patients who manifested symptoms gradually over an extended period of time was on the increase. For the past 36 years, of the 2252 patients who have been officially recognized as having M. d., 1043 have died. This paper also discusses the recent remaining problems.