An Introduction to the Minamata Disease (5) |The Spread of Wastewater, Biomagnification and the Fishermen’s catch

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 24, 2015

Once Methyl Mercury from Chisso’s wastewater enters the Minamata bay in soluble form, pollution would continue to spread throughout the whole bay. Because industrial waste is comprised mainly of freshwater, its spread (direction and extent) is determined by the salinity of the seawater that it is discharged into. In addition, the Methyl Mercury is taken up through the gills of oceanic organisms or through ingestion of contaminated prey. Methyl Mercury persists in the tissue of marine organisms for about 72 days and is biologically magnified up the food-chain. As such, the movement of fish within the Minamata bay further serves to widen the range of Mercury pollution. Minamata bay is situated within the Shiranui Sea, which is bordered by many islands and landforms, making it a considerably closed system with a prominent north to south current. Fish tend to gather and traverse within the Shiranui sea along the main current and thus form the bulk of the fishery catch from fishermen residing in the surrounding islands and lands. Consumption of mercury-contaminated fish was then a major factor that resulted in the spread of pollution to areas bordering the Shiranui sea. Furthermore, the spread of the Minamata Disease could also be attributed to the population’s lack of knowledge of seeking the proper medical treatment. The fishermen who were affected by the Minamata Disease in the islands around the Shiranui sea were also not volunteering themselves for relevant physical examinations in fear that their catch would be banned from the markets due to discrimination against their physical condition. These fishermen usually exhibited non-acute symptoms of mercury poisoning but also had difficulty applying for medical aid due to complications in the certification system. Even up to today, only a fraction of the victims in the islands bordering the Shiranui sea are officially certified as Minamata Disease Patients (Figure 5), leaving the support of “forgotten victims” to several non-governmental organizations.


Figure 5: Fishermen’s catch location in the Shiranui sea, where Minamata bay is situated; and the geographical status of official Minamata Disease patient certification.

Author: Joanne Khew; Figure by Joanne Khew; Contributors: Mahdi Ikhlayel, Heng Yi Teah, Angeli Guadalupe