Minamata Disease - 1959

1959

During the investigation by researchers at Kumamoto University, the causal substance had been identified as a heavy metal and it was widely presumed that the Chisso plant was the source of the contamination. Chisso was coming under closer scrutiny and in order to deflect criticism the wastewater output route was changed. Chisso knew of the environmental damage caused by its wastewater and was well aware that it was the prime suspect in the Minamata disease investigation. Despite this, from September 1958, instead of discharging its waste into Hyakken Harbour (the focus of investigation and source of original contamination), it discharged wastewater directly into Minamata River. The immediate effect was the death of fish at the mouth of the river, and from that point on new Minamata disease victims began to appear in other fishing villages up and down the coast of the Shiranui Sea, as the pollution spread over an even greater area.

Chisso failed to co-operate with the investigation team from Kumamoto University. It withheld information on its industrial processes, leaving researchers to speculate what products the factory was producing and by what methods. The Chisso factory's hospital director, Hajime Hosokawa, established a laboratory in the research division of the plant to carry out his own experiments into Minamata disease in July 1959. Food to which factory wastewater had been added was fed to healthy cats. Seventy-eight days into the experiment cat 400 exhibited symptoms of Minamata disease and pathological examinations confirmed a diagnosis of organic mercury poisoning. The company did not reveal these significant results to the investigators and ordered Hosokawa to stop his research.

In an attempt to undermine Kumamoto University researchers' organic mercury theory, Chisso and other parties with a vested interest that the factory remain open (including the Ministry of International Trade and Industry and the Japan Chemical Industry Association) funded research into alternative causes of the disease, other than its own waste.