A Outline of Minamata Disease
1. Cause and Damage of Minamata Disease

Minamata disease is an encephalopathy and peripheral neuropathy caused by daily intake of fish and shellfish highly contaminated by methylmercury. Through gills and gastrointestinal tracts, fishery products such as fish, shrimp, crabs, and shellfish, take in methylmercury discharged from chemical plants into rivers and seas. Flesh-eating fish that eat those contaminated fish also accumulate the toxicsubstance (food web). Thus accumulated methylmercury in sea food intoxicates people who have eaten a lot of such sea food daily.

Minamata disease broke out in the Yatsushiro Sea coastal area, particularly around Minamata Bay in Kumamoto Prefecture. At first the disease was regarded as a kind of disease of nervous system of unidentified causes. Later it occurred in the Agano river basin in Niigata Prefecture.

In the Minamata bay area, an outbreak of Minamata disease was first reported in May 1956. At the end of that year the number of identified patients reached 52, of which 17 had already died. In 1957, this unknown disease was named Minamata disease. In the Agano river basin, the first report on Minamata disease patients was filed in May1965; by July 1965, a total of 26 patients were recognized, of which 5 had already died.

Today, whether or not a patient is afflicted by Minamata disease is certified by either governors of prefectures concerned or the national government in accordance with the Law Concerning Compensation and Prevention of Pollution-related Health Damage.