2. Outbreak of Minamata Disease
Report of the first patient
In 1956, in Minamata City located on the Yatsushiro Sea coast in Kumamoto Prefecture, the first Minamata Disease patient was reported as a patient suffering from neurological symptoms of unknown cause.
Investigation of causes
After the report of the first patient, Minamata City established the Committee on Unknown Disease immediately for taking measures against the patients and investigating to find out the cause. The investigation was carried out energetically mainly by Kumamoto University, and in November 1956, the university reported that the disease is a certain type of heavy metal poisoning transmitted via fish and shellfish. However, because knowledge and experience about environmental pollution were not enough at that time and technology for analysis of very small amounts of chemical substances was insufficient, a great deal of time was required until the cause was made clear.
Fig.1: Map of the Areas with Outbreak of Minamata Disease
Outbreak of Niigata Minamata Disease
In 1965, Minamata Disease patients were also reported in the Agano River basin in Niigata Prefecture.
The government's announcement
In 1968, the government sorted out the knowledge related to Minamata Disease that had been collected by that time, and announced its opinion. According to this, Minamata Disease is a poisoning disease of central nervous system caused by methylmercury compound, which was produced as by-product in the process of manufacturing acetaldehyde at Chisso Co., Ltd. in Minamata City and Showa Denko Co., Ltd. located upstream of Agano River, and was discharged with the factory effluent and polluted the environment, and then, through the food chain, it was accumulated in fish and shellfish. Consequently Minamata Disease occurred when the inhabitants ate high amount of these seafoods.
The conditions of the occurrence
As for Minamata Disease patients, by the end of March 2001, 2,265 persons have been certified on the Yatsushiro Sea coast and 690 persons in the Agano River basin based on the relief system described later. Even now, a small number of patients are certified, but all of them became the disease in the past, and according to the various investigations, it is thought that no conditions exists for a new occurrence of Minamata Disease at least since the early 1970s.