Chisso Cooperation is a major Japanese company. In its early years (1908), Chisso was inaugurated at Minamata city where it utilized the neighbouring high mountains with its natural streams as a resource for hydroelectricity generation for the production of fertilizers. Mercury was only used in Chisso’s industrial processes in 1932 when Mercury Oxide was utilized as a catalyst in the synthesis of acetaldehyde. However, the Mercury Oxide catalyst is reduced in the process of acetaldehyde production. For continued acetaldehyde production, oxidation of the reduced catalyst was carried out using Permanganate (MnO4–) in a method specially devised by Chisso. This method was later changed in 1951 to the prevailing, commercial method of using Ferric Iron (Fe3+) and nitric acid as replacements for Permanganate. Although this change was suspected to be the cause of the onset of the Minamata Disease in 1952 and 1953, scholars were unable to pinpoint with certainty that the source of mercury pollution originated from the wastewater released into the Minamata Bay from Chisso’s acetaldehyde production process. Chisso also did not help investigations and attempted to deflect responsibility up till 1966 where they were forced by legal decree to stop acetaldehyde production (Figure 2: Timeline of important events). Furthermore, Chisso raised two main objections in the process of their trail: If they were truly the culprits, 1) why did victims of the Minamata disease only appear in the 1950s, although they started the acetaldehyde synthesis process in the 1930s; and 2) why were victims only found in the vicinity of Minamata city, although acetaldehyde synthesis was carried out in factories around the world?
Figure 2: Timeline of important events concerning Chisso factory and Mercury pollution.
Author: Joanne Khew; Figure by Joanne Khew; Contributors: Mahdi Ikhlayel, Heng Yi Teah, Angeli Guadalupe