Update:April 1, 2010

(4) The Cause of the Disease and Governmental Opinion

1.Establishment of Chisso Co., Ltd. and Outbreak of Minamata Disease

Parallel to the consultation and medical examination on ordinary invalids, the Medical Study Group made clinical observations of patients in the hospital affiliated to the Kumamoto University Medical School. They also made autopsies on deceased bodies and analyzed the drinking water, sea water, soil and marine products sampled in the bay, employing microbiology, hygienics, and public sanitation.
The Medical Study Group has proposed the theory on the causal substance of Minamata Disease known as "organic mercury theory", saying "mercury is suspected as the most likely substance responsible for seafood contamination." Chisso has then announced "the company's opinion against the organic mercury theory" in response to the above, thereby asserting that the theory was a groundless assumption. Meanwhile, various etiological hypotheses such as "explosive theory" and "amine theory" were proposed.
In 1962, the Medical Study Group reported that organic mercury crystals was detected in the sludge discharged from Chisso. Although organic mercury was one of the suspected substances since the early stages, it had been abandoned for a long time until its liability was verified. Damages have been multiplied by such delay in response.
In September 1968, the national government issued "the governmental views on Minamata Disease" based on the latest knowledge and information obtained thereby supporting the explanation that Minamata Disease is a toxic symptom of the central nervous system due to methylmercury compound, which is discharged from the acetaldehyde manufacturing process of Chisso Co., Ltd. and Showa Denko K.K.- the former is located in Minamata City and the latter is at the upper reaches of the Agano River in Niigata Prefecture. They declared that Minamata Disease is caused by a large consumption of seafood in which methylmereury compound has biologically accumulated. Since then, Minamata Disease and Niigata-Minamata Disease have been officially designated as "a pollution-related disease".