Bioaccumulation and Biomagnification
: Minamata Disease
History of Minamata Disease.
In 1908 the Chisso Corporation, a major chemical manufacturer in Japan, opened a nitrogenous fertilizer factory in the small fishing town of Minamata (figure 1). Over time the corporation chose to branch out and began producing other chemicals such as acetylene, acetic acid, vinyl chloride and octanol. The waste product from these chemicals was released into Minamata Bay via the factories wastewater system, causing major damage to the fisheries; reducing their catch sizes by up to 91%.
In 1932 the Chisso Corporation began manufacturing a chemical known as acetaldehyde (C2H4O), also known as ethanal. By 1951 production of C2H4O had jumped from 210 pounds produced in the first year of manufacturing to 6,000 tons per year. Although the large quantities of production were good for the Chisso Corporation, the effects of chemical production were beginning to effect the ecosystem and the organisms within.
The reaction used to make C2H4O requires mercury sulfate (HgSO4) as a catalyst and in 1951 Chisso changed the co-catalyst from manganese dioxide (MnO2) to ferric sulfide (FeS2). When mercury sulfate and ferric sulfide react, small amounts of a highly toxic, organic mercury compound known as methylmercury (CH3Hg+ or MeHg+) is produced as a by-product (figure 2)
As previously mentioned, Chisso was releasing their waste through the wastewater and into Minamata Bay; among this waste was the methylmercury produced in the manufacturing of C2H4O.
On the 21st April, 1956, a five-year-old girl was admitted to the Shin Nippon Chisso Fertilizer Co. factory hospital with severe complaints including the inability to talk, walk or eat. Soon after, three more, one of which was the girl’s younger sister, were admitted with similar symptoms. On the 1st May, Dr Hajime Hosokawa reported these four cases to the Minamata public health centre, stating that it was an "epidemic of an unknown disease of the central nervous system" (Dr. Hosokawa). This was the official discovery of Minamata disease.
Locals began to call this unidentified disease the “strange disease” and on the 28th May the Minamata Strange Disease Action Committee was formed by the Minamata public health centre, Minamata City, the City Medical Association, the Municipal Hospital, and the Chisso Hospital. On 24th August, the Kumamoto University research group was formed and began to conduct medical examinations on patients and autopsies on the bodies of those who had died as a result of the disease.
On the 12th November, 1959, the Minamata Food Poisoning Special Committee of the Ministry of Health and Welfare Food Sanitation Investigation Council submitted a report stating that "the organic mercury compound in the fish and shellfish around Minamata Bay [was] the main causative factor of Minamata disease".
On 20th February, 1963, the Kumamoto University research group found that “Minamata disease [was] a disease of the...