This highly toxic compound was released untreated into the Agano River where it bioaccumulated up the food chain, contaminating fish which when eaten by local people caused symptoms including ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech.
On 31 May, he reported an outbreak of organic mercury poisoning in the Agano River basin to the prefectural government and made his findings public on 12 June.
Unlike their counterparts in Minamata, the victims of Showa Denko's pollution lived a considerable distance from the factory and had no particular link to the company.
The report said, although "the circumstances of the poisoning are extremely complex, and they are difficult to reproduce", the mercury had probably been discharged from the Kanose plant over a long period of time.
[4] A family member of the deceased patient testified in court, "My father was crazed like a wild beast and then died—agonized, in pain... like a dog."
Masazumi Harada has said, "It may sound strange, but if this second Minamata disease had not broken out, the medical and social progress achieved by now in Kumamoto... would have been impossible.