The symptoms that the victims of this ailment presented were numb hands and feet, sudden difficulty in walking and a definitive impairment in speech. Extreme cases resulted in convulsions and death. Of the 54 cases that presented with this disease in 1956, 31% died. This was a disturbing statistic. This galaxy of symptoms suggested a neurological basis for the disease.
By the year’s end researches at Kumamoto University had identified the etiology of the illness as being heavy metal poisoning from the ingestion of contaminated local fish and shellfish. This diagnosis was consistent with the evidence; heavy metals are known to play havoc with the nervous system as exemplified by lead poisoning. It remained to discover the origin of the contamination and the offending metal.
Investigators focused on the Shin Nippon Chisso Hiryo chemical plant facility that had been known to discharge its untreated waste directed into the local waterways. The plant owners managed to delay a thorough investigation for a number of years. Ultimately the chemical culprit was discovered – methyl mercury, a highly toxic substance.
It was not until May of 1968 that the plant halted production of acetaldehyde that employed a mercury catalyst in its chemical synthesis. This overdue decision finally halted its use of mercury. Furthermore, even though it was shown that there existed a persistent contamination of methylmercury on the seafloor, Minamata Bay was not closed for fishing until 1975.
To this day, the research continues regarding the long term effects of the ingestion of low levels of methyl mercury from contaminated seafood. The controversy has not subsided regarding who has been victimized and who is liable for the costly toll on individual lives.