IV. The discovery of Minamata disease and the difficulty in determining its cause

In May 1956, four patients suffering from a yet unheard-of disease were brought to the city hospital. They all had common symptoms such as severe convulsions, intermittent loss of consciousness, repeated lapses into crazed mental states, and then finally permanent coma. Then, after the onset of a very high fever, they would die. Dr. Hosokawa, the director of the hospital, began an epidemiological survey of the immediate area in co-operation with local medical associations and health centres. The same type of patients had indeed been discovered in the fishing villages surrounding Minamata City and it was determined that 17 people in all had so far died after showing the same symptoms. This initial stage was characterized by a profound sense of shock at the high death-rate.

The initial survey indicated that the disease had not occurred suddenly but had been noticed by doctors before, except that it had not been recognized as a new disease. The one factor that was common to all patients was that they ate large amounts of fish from Minamata Bay. At first there were suspicions that the disease was contagious but this fear was laid to rest after more intensive surveys had been taken. Then there were thoughts that the cause might be related to toxic substances. At this point efforts at determining the cause of the disease were handed over to a medical research group at Kumamoto University in Kyushu. The group continued investigations for about two years but was not able to discover any definitive cause for the disease. It was, however, deduced that the fish and the shellfish in Minamata Bay were poisonous: toxic symptoms did in fact develop in laboratory animals which had been fed these same poisonous fishery products, but their symptoms seemed to be completely different from those seen in human patients.

The initial survey indicated that the common conditions surrounding all the patients made it almost certain that the problem was related to the Chisso Minamata chemical complex, but it was completely taboo to speak of this possibility in the community, with its complete economic dependence on the facility. The fish from Minamata Bay were poisoned to a much greater extent than fish taken from other locations, and all of the wastes from the chemical complex had been discharged into the bay for a very long period of time. Waste sludge taken from the bay contained so many different kinds and such huge amounts of poisons that there was no telling which of them was the cause. The sludge contained great amounts of manganese, selenium, and thallium, substances which could conceivably be related to the disease, although animal experiments resulted in very different symptoms. The research group asked the chemical company to indicate what substances were being used for production synthesis apart from the materials contained in the waste discharge, but the company was unwilling to co-operate in this regard. Furthermore, the engineering department of Kumamoto University, which had more precise information on the inner workings of the Minamata chemical complex, was predisposed not to co-operate with the medical research group. Finally, when the medical research team indicated that the probable cause of the Minamata disease was heavy metal poisoning, the chemical company provided their own report to dispute this theory.

Then, after two years of survey work, the medical research group was able to eliminate every pollutant one by one, until they came upon mercury as the last heavy metal in the list. At that time they did not know that mercury was employed in massive amounts in the chemical complex, and they also presumed that the company would probably not waste mercury, for it was a very expensive material. The company kept the use of mercury a production secret, although industrial circles and engineers were aware of it. There were massive amounts of mercury in the sludge taken from the bay, as well as in the poisonous fish and in the patients who had died of the disease. The epidemiological distribution of the disease among the human population was the same as the distribution of poisonous fish in Minamata Bay. The characteristics of the disease were the same as those encountered in alkyl mercury poisoning. The medical research group, which was severely criticized by the Chisso chemical company, continued its survey efforts for another year and in July 1959 came to the interim conclusion that mercury was the most probable cause of the Minamata disease.