The Research (1/1)

By October 1956, 40 patients had been discovered, 14 of whom had died: an alarming mortality rate of 36.7%Finding the causeResearchers from Kumamoto University also began to focus on the cause of the strange disease. They found that the victims, often members of the same family, were clustered in fishing hamlets along the shore of Minamata Bay. The staple food of victims was invariably fish and shellfish from Minamata Bay. The cats in the local area, who tended to eat scraps from the family table, had died with symptoms similar to those now discovered in humans. This led the researchers to believe that the outbreak was caused by some kind of food poisoning, with contaminated fish and shellfish the prime suspects.On November 4 the research group announced its initial findings: "Minamata disease is rather considered to be poisoning by a heavy metal... presumably it enters the human body mainly through fish and shellfish."Identification of mercuryAs soon as the investigation identified a heavy metal as the causal substance, the wastewater from the Chisso plant was immediately suspected as the origin. The company's own tests revealed that its wastewater contained many heavy metals in concentrations sufficiently high to bring about serious environmental degradation including lead, mercury, manganese, arsenic, selenium, thallium and copper. Identifying which particular poison was responsible for the disease proved to be extremely difficult and time consuming. During the years 1957 and 1958, many different theories were proposed by different researchers. Initially manganese was thought to be the causal substance due to the high concentrations found in fish and the organs of the deceased. Thallium, selenium and a multiple contaminant theory were also proposed but it was not until March 1958, when visiting British neurologist Douglas McAlpine suggested that Minamata symptoms resembled those of organic mercury poisoning, that the focus of the investigation centered on mercury.In February 1959, the mercury distribution in Minamata Bay was investigated. The results shocked the researchers involved. Large quantities of mercury were detected in fish, shellfish and sludge from the bay. The highest concentrations centered around the Chisso factory wastewater canal in Hyakken Harbor and decreased going out to sea, clearly identifying the plant as the source of contamination. At the mouth of the wastewater canal, a figure of 2 kg of mercury per ton of sediment was measured: a level which would be economically viable to mine. Ironically, Chisso did later set up a subsidiary to reclaim and sell the mercury recovered from the sludge.Hair samples were taken from the victims of the disease and also from the Minamata population in general. In patients the maximum mercury level recorded was 705 ppm (parts per million), indicating very heavy exposure and in non-symptomatic Minamata residents the level was 191 ppm. This compared to an average level of 4 ppm for people living outside the Minamata area.On November 12, 1959 the Ministry of Health and Welfare's Minamata Food Poisoning Subcommittee published its results:"Minamata disease is a poisoning disease that affects mainly the central nervous system and is caused by the consumption of large quantities of fish and shellfish living in Minamata Bay and its surroundings, the major causative agent being some sort of organic mercury compound."