Minamata Unit 2015

Game development summary: “Let’s find a solution for compensation issue of Minamata disease”

Minamata Team 015 4- Others, Blog, Minamata Unit 2015, Reports May 1, 2015

Game can be an important component for learning in both informal and formal education. It provides an excellent environment for sharing of ideas and discussion even societal issues. The game development group of Minamata Resilience Exercise 2014 aimed to create an interactive game targeting graduate students in a classroom setting, which of its theme focused on the ongoing compensation issues of Minamata Disease.

Our game, “Let’s find a solution for compensation issue of Minamata disease” requires basic understanding in the historical background and socio-cultural issues of Minamata Disease. We recommend you to watch the video produced by our peer prior to playing our game.

Resources for playing our game are shown below for educational use. We hope you will be able to gain further understanding in the complexity of Minamata Disease, and the issues that remain today.

Game development team, Minamata RE 2015

Introduction to Minamata Unit 2015

Minamata Team 015 Blog, Minamata Unit 2015, Reports April 29, 2015

February 27 to March 4, 2015, the University of Tokyo sent ten students from its Graduate Program on Sustainability Science- Global Leadership Initiative and two students from its Department of Urban Engineering to Minamata City to study the issues behind the Minamata Disease via stakeholder interviews and site visits. This resilience exercise is conducted once in two years. Traditionally, group’s outputs are written review reports. This time, the group aims to produce laypeople-friendly knowledge on the disaster via a blog, a video and a game in order to increase general awareness on the disaster.

The blog consists of three parts-1. Daily Blog Post (Archiving the activities during the trip), 2. The Story in 8 Posts (The concise knowledge to understand Minamata), 3. 八则水俣病的通识课 (The Chinese version for part 2.).

Author: Minamata Unit 2015; This website is created by Mahdi Ikhlayel.

An Introduction to the Minamata Disease (1)|What is the Minamata Disease?

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 28, 2015

The Minamata Disease refers to the symptoms exhibited as a result of Mercury toxicity which was caused in this case, by water-borne Methyl Mercury pollution. As the disease largely affected residents in the vicinity of Minamata Cityw within Kumamoto Prefecture (Figure 1), it was termed as the “Minamata Disease”. Sufferers of the Minamata Disease exhibit symptoms synonymous with the Hunter-Russel syndrome, which was in turn, founded on research on Mercury poisoning resulting in consumption of seed preservatives in England during the 1930s. Hunter-Russel symptoms include: sensory disorder, ataxia, visual field constriction, impaired hearing and speech impairment. Among the victims of the Minamata Disease, initial symptoms exhibited by acute-sufferers include disorientation, which may result in death in a few months; however, thousands of sufferers who have a range of milder symptoms still exist today. Accurate diagnosis of sufferers, regardless of the severity of their symptoms, has proven difficult, resulting in a multitude of legal, social, political and medical disputes over a span of 60 years (and counting).


Figure 1: Map showing location of Minamata city, Kumamoto Prefecture; (inset) map showing the location of Chisso Cooperation’s factory, and its wastewater discharge point, Hyakken Harbour .Inset image credits: Modified from “Map of Minamata Bay and the Chisso Factory”, Wikipedia, CC BY-SA 3.0.

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

An Introduction to the Minamata Disease (2) |Chisso Factory and Mercury Pollution

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 27, 2015

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

An Introduction to the Minamata Disease (3) |Examining the cause of the Minamata Disease (1)

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 26, 2015

Around the 1950s/1960s, even when it was scientifically proven that the Minamata Disease (previously termed by laymen as the strange disease) was caused by water-borne mercury, Chisso was aware that their wastewater contained traces of mercury. This was due in part to an experiment whereby Chisso authorized local researchers to feed cats wastewater contaminated food, resulting in cat #400 developing symptoms typical of the Minamata Disease (movement dis-coordination). Despite this, Chisso refused to acknowledge and amend their faults. Unknowing to them, the buried truth of the experiment would eventually come back to affront them in the future. Today, a tombstone commemorating the death of the cats used in Chisso’s wastewater toxicity experiment stands outside Soushisha’s Minamata Disease Museum as a permanent reminder of Chisso’s fault as perpetrator in the Minamata Disease Incident.

Besides the aforementioned experiment, other evidence exist to trace Chisso’s responsibility in causing the Minamata Disease outbreak in 1953. According to research by Professor Nishimura (The University of Tokyo), Chisso initially (1931) utilized their own process for oxidizing the Mercury Oxide catalyst reduced during the process of acetaldehyde synthesis in order to avoid paying the high patent cost attached with the prevalent commercial method. Chisso’s process involved using Permanganate (MnO4) as an oxidizing agent while the prevalent commercial method has Ferric iron (Fe3+) . However, the reason behind the effectiveness of Chisso’s method was ironically due to the presence of Ferric iron impurities in the Permaganate oxidizing agent. Chisso’s method also coincidentally lowered the production of Methyl Mercury to about a tenth of what would have been produced if the commercial method had been used. During the post-war years, when rebuilding and hence, material production (e.g. PVC) was important, Chisso switched their method of acetaldehyde synthesis to the commercial method, which utilized Ferric iron, in order to increase their production output. This method required the use of another oxidizing agent (Nitric Acid), to oxidixe the reduced Ferric Iron (Fe2+) back to Fe3+ (Figure 3), producing even more Methyl Mercury in the process. However, why did this commercial and widely used method result in a serious case of mercury poisoning only in the vicinity of Minamata city?

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Figure 3: Chisso’s acetaldehyde synthesis process and two alternate routes to oxidize Mercury Oxide catalyst, and the corresponding amounts of Methyl Mercury (the organic compound which causes Mercury toxicity in the Minamata Disease).

Source: Adapted from the Science of Minamata (水俣病の科学)

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

An Introduction to the Minamata Disease (4) |Examining the cause of the Minamata Disease (2)

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 25, 2015

In reality, the Minamata Disease did not just occur in Minamata City (and its vicinity). In 1965, Methyl Mercury was also released by a factory into a river in Niigata, resulting in people around the vicinity exhibiting a range of Mercury toxicity symptoms. However, what was different in the case of Methyl Mercury discharge in the case of Showa Denko (Niigata) and Chisso (Minamata City) was that the latter was situated nearer to the sea and hence wastewater was discharged directly into the ocean waters. According to Professor Nishimura’s research (The Science of the Minamata Disease -水俣病の科学), the concentration of Chlorine ion present in solution would affect the solubility of the Methyl Mercury compound. When wastewater containing Methyl Mercury is discharged directly into seawater (as in Chisso’s case), the high concentration of chlorine ions present readily combine with it to form the soluble Methyl Mercury Chloride compound. This compound is highly mobile in water and can be easily taken into body tissue of sea-creatures and humans that directly or indirectly ingest the polluted water.

In the case of mercury pollution in Niigata, mercury-containing wastewater was discharged into a river where concentration of chlorine ion is comparatively lower than seawater. The Methyl Mercury ion then conjugates with abundant organic debris present in the river water (e.g. protein colloids, algae) and sinks into the riverbed. As Methyl Mercury in this form is insoluble and therefore, not mobile, it is not as readily transferred to the human body. However, mobility of this form of Methyl Mercury can occur when it is consumed by benthic organisms as sediment; and biologically magnified up the food chain; or when it is transported to the sea along with riverbed sediment through erosion (Figure 4). Once at the sea, the Methyl Mercury ion trapped in the insoluble compound can recombined with the abundant supply of chlorine ions in the seawater, forming soluble Methyl Mercury Chloride. In Chisso’s case, seawater was also used for the cooling of factory reactors, resulting in the formation of more Methyl Mercury Chloride when seepage occurred. As such, this post, combined with the previous one [Examining the cause of the Minamata disease (1)], thus answers the two questions posed by Chisso on the post: An Introduction to the Minamata Disease (2) |Chisso Factory and Mercury Pollution.


Figure 4: The different forms of Methyl Mercury: i. The case of Minamata City where Methyl mercury is released directly into the sea; ii. The case of Niigata where Methyl Mercury is released into the river and conjugated with sediment

Source: Adapted from the Science of Minamata (水俣病の科学)

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

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

An Introduction to the Minamata Disease (6)|The Status of Compensation and Political Settlements

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 23, 2015

Since the outset of the Minamata Disease, there has been about 50 years of multiple lawsuits which generated a host of governmental compensation and relief schemes. In 1959, researchers from the Kumamoto university first published proof that wastewater from Chisso’s factory was the causative agent in the Minamata Disease, compounding the findings with proof from a prior experiment where a cat (#400) was found to exhibit Minamata Disease symptoms after consuming Chisso factory wastewater. Chisso however, refused to acknowledge their fault and insisting on the payment of “sympathy money” instead of full compensation to victims. The criteria for victims to receive sympathy money from Chisso under the Mimaikin Agreements was extremely stringent, and accessed entirely by representatives approved by Chisso. However, official lawsuits started in 1968 when Chisso was found responsible for pollution by the national government. As the number of affected patients increased, the amount of money spent on compensation schemes also increased proportionally, resulting in Chisso and the local government trying to tighten criteria to reduce the amount of patients under compensation.

Subsequently, patients who could not meet the strict selection criteria and their supporters mounted the first Minamata Disease Lawsuit in 1973. The lawsuit was successful and resulted in the establishment of a modified, less stringent criteria for compensation in 1977. This in turn, resulted in an increased number of applicants and the issuing of compensation became more and more delayed. In order to ease the mounting tensions in 1995, the government further modified the compensation criteria through a political settlement. This modified criteria was again relaxed in comparison to previous qualifying criteria and was targeted to provide lifetime medical compensation depending on the severity of the sufferer’s symptoms. There was however, still a string of parallel lawsuits filed by victims who were rejected by the certification board and their supporters. Notably, these lawsuits ended in the 2009 political settlement (result of the Kansai Lawsuit), which further relaxed the selection criteria. Spanning several decades, these cumulative legal fights (which are still continuing today), have weathered many victims off the compensation applications due to either old age or due to the victims succumbing to their illnesses. Despite the first and second Minamata disease lawsuits and their corresponding compensation and relief schemes, there are still a large amount of patients who remain unaccounted for. This is due to the difficulty in ascertaining their symptoms as Minamata disease symptoms and the difficulty of assigning the category of their compensation.

Figure 6: A summary of about 50 years of lawsuits, negotiations and their corresponding compensation and relief schemes related to the Minamata Disease from 1959 to 2009.

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

An Introduction to the Minamata Disease (7)|Societal Conflicts

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 22, 2015

Societal conflicts between various citizen groups have emerged as a result of the Minamata Disease Saga. Even as early as 1908, before Chisso established their factory in Minamata city, societal rifts were present between the fisherfolk in the south and the other citizens who were living closer to the city center. Due to their status as migrants (from other parts of the country or abroad), and their low income, people from the fishing communities were unfortunately seen as lower-class citizens. Chisso’s inauguration in Minamata City in 1930 brought further economic growth to Minamata city through providing the resources for the city to expand, providing jobs and increasing living standards. When the Minamata Disease started to spread due to the discharge of factory wastewater into the Minamata Bay, the people who were most affected by Mercury poisoning were the fishermen – the group of people who benefited least from Chisso’s economic contributions to Minamata city. When Chisso was found guilty of causing the Minamata Disease in the 1970s, many Minamata City citizens were still employees of the factory. As such, they felt no incentive to be sympathetic towards the victims of the Minamata disease, partially in fear that the company would be in an economically bad situation if they had to pay too much compensation. Patients of the Minamata Disease were further ostracized by the other citizens due to the misconception that the disease was contagious. In fear of being discriminated against, sufferers of the Minamata Disease became hesitant to apply for compensation. There was also conflicts even between the patients who receive compensation because of differences in perceived fairness of demand due to varying compensation amounts and their symptoms. Perhaps the most ironic of all developments is that Chisso still remains the main economic provider of Minamata city, and despite causing the Minamata Disease, it is still highly esteemed by the populace as the employer-of-choice.


Figure 7: Chisso’s involvement in altering the social conflict scene in Minamata City

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

An Introduction to the Minamata Disease (8)|Environmental Pollution or Societal Problems

Minamata Team 015 2-The Story in 8 Posts, Blog, Minamata Unit 2015, Reports April 21, 2015

The social problems plaguing the Islands surrounding the Shiranui sea 70 years after the onset of the Minamata Disease still remain. One of the takeaway lessons from the Minamata Disease saga is that pollution is not merely just an environmental issue. Stopping the discharge of pollutants into the Minamata Bay could have been done swiftly by the industry. However, the choice to favor economic benefit over health issues resulted not only in huge environmental problems but social conflicts and issues of discrimination. Idealistically, in order to work towards sustainable development, industrial pollution should be avoided in its entirety. This is however, not possible especially in the case of developing countries. As a commemoration of the adverse impact of the Minamata Disease, the Minamata city government marks every 1st of May as a commemoration day. In the recent years, the government has actively rewarded environmental activists (local and abroad) and promoted environmental clean-up programs. Minamata city now has Japan’s most comprehensive recycling program with 22 different ways of classifying garbage. The city has also been selected as Japan’s greenest city in the recent years. These steps help to classify the city in a positive light which could not only throw off the past shadow of the Minamata Disease saga but help the populace look towards better tomorrows.


  1. MinamataDisease – Its History and Lessons, 2007, Minamata City.
  2. 水俣病の科学,2006,西村肇,日本评论社。

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