Minamata disease symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death follow within weeks of the onset of symptoms. A congenital form of the disease can also affect foetuses in the womb. The Minamata disease was first discovered in Minamata city in 1956. It was caused by the release of methylmercury in the industrial wastewater from the Chisso Corporation's petro-chemical and plastics factory, which continued from 1932 to 1968. The company dumped an estimated 27 tons of methylmercury into the Minamata Bay over a period of 37 years. Mercury was used as a catalyst in the production of acetaldehyde, a chemical employed in the production of plastics.This highly toxic chemical bioaccumulated in Minamata Bay and the Shiranui Sea, which was then eaten by the local populace resulting in mercury poisoning.

At first doctors were unable to diagnose the cause of the disease, then in 1959, doctors at Kumamoto University determined that organic mercury poisoning was the cause of the symptoms exhibited by so many of the townspeople. Only in 1968 however did the Tokyo government acknowledge that the mercury dumping by Chisso was the ultimate cause. Five years later, Chisso admitted legal responsibility. It was proven that Chisso withheld critical information in 1959 and continued to dump waste. The government also supported the company and they were not held legally liable for their negligence until 1972. Chisso stopped production of acetaledyde in 1968--when an alternative technology for producing plastics was developed.

As of March 2001, 2,265 victims had been officially recognised (1,784 of whom had died) and over 10,000 had received financial compensation from Chisso. Over $611 million has been paid to victims in compensation [2]. In 1977, the Japanese government cleaned up the bay by vacuuming up 1.5 million cubic meters of mercury-contaminated sludge. After $359 million dollars and 14 years, the project was completed in 1997. [1] Chisso still operates in Minamata and now produces chemicals, fertilizer.

The local population has declined by 70% since its peak.

On May 1, 1956, the hospital director reported to the local public health office the discovery of an 'epidemic of an unknown disease of the central nervous system', marking the official discovery of Minamata disease.

By October 1956, 40 patients had been discovered, 14 of whom had died: an alarming mortality rate of 36.7%.

Minamata disease remains an important issue in contemporary Japanese society. Lawsuits against Chisso and the prefectural and national governments are still continuing and many regard the government responses to date as inadequate.

The highest result recorded was that of a woman from Goshonoura island who had 920 ppm in her blood sample.

In 2001, 2,265 victims had been officially recognized as having Minamata disease (1,784 of whom had died).