Minamata Disease


Minamata Disease, which is a typical example of the pollution-related health damage in Japan, was first discovered in 1956, around Minamata Bay in Kumamoto Prefecture, and in 1965, in the Agano River basin in Niigata Prefecture. Since the discovery of the disease, investigation of the cause has been made, and finally in 1968, the government announced its opinion that Minamata Disease was caused by the consumption of fish and shellfish contaminated by methylmercury compound discharged from a chemical plant.
It is known that Minamata Disease is a disorder of the central nervous system and shows various signs and symptoms including sensory disturbance in the distal portions of four extremities, ataxia, concentric contraction of the visual field, etc. At the end of March 2001, 2,955 Minamata Disease patients have been certified, of which 2,265 patients have been located on Yatsushiro Sea coast.
Due to the clinical and protective measures taken after the discovery of the disease, Minamata Disease no longer seems to occur in Japan.

With regard to relief of the victims, a large-scale survey of health damage was carried out in order to grasp the extent of health damage. The structure is set up, that the government certifies persons as Minamata Disease based on Pollution-related Health Damage Compensation Law, and those who are recognized as Minamata Disease from the point of view of medical science can receive compensation from the company which is responsible for the pollution. (A lump-sum payment of about 22,000,000 yen had been paid to each of 2,955 certified patients on average, and the total payment amounts to approximately 144 billion yen by March 2001).


As of March 2001, 2,265 victims have been officially certified (1,784 of whom have died) and over 10,000 people have received financial compensation from Chisso, although they are not recognised as official victims. The issue of quantifying the impact of Minamata disease is complicated, as a full epidemiological study has never been conducted and patients were only ever recognised if they voluntarily applied to a Certification Council in order to seek financial compensation. Many victims of Minamata disease faced discrimination and ostracism from the local community if they came out into the open about their symptoms. Some people feared the disease to be contagious and many local people were fiercely loyal to Chisso, depending on the company for their livelihoods. In this atmosphere sufferers were understandably reluctant to come forward and seek certification. Despite these factors, over 17,000 people have applied to the Council for certification. Also, in recognising an applicant as a Minamata disease sufferer, the Certification Council qualified that patient to receive financial compensation from Chisso. As such, the Council has always been under immense pressure to reject claimants and minimise the financial burden placed on Chisso. Rather than being a Council of medical recognition, the decisions of the Council were always affected by the economic and political factors surrounding Minamata and the Chisso corporation. Furthermore, compensation of the victims led to continued strife in the community, including unfounded accusations that some of the people who sought compensation did not actually suffer from the disease.


According to Timothy S. George, the environmental protests that surrounded the disease appeared to aid in the democratization of Japan. When the first cases were reported and subsequently suppressed, the rights of the victims were not recognised, and they were given no compensation. Instead, the afflicted were ostracised from their community due to ignorance about the disease, as people were afraid that it was contagious.

The people directly impacted by the pollution of Minamata Bay were not originally allowed to participate in actions that would affect their future. Disease victims, fishing families, and company employees were excluded from the debate. Progress occurred when Minamata victims were finally allowed to come to a meeting to discuss the issue. As a result, postwar Japan took a small step towards democracy.

Through the evolution of public sentiments, the victims and environmental protesters were able to acquire standing and proceed more effectively in their cause. The involvement of the press also aided the process of democratization because it caused more people to become aware of the facts of Minamata disease and the pollution that caused it.

Although the environmental protests did result in Japan being more democratized, it did not completely rid Japan of the system that first suppressed the fishermen and victims of Minamata disease.


Closing down of the pollutant sources

With regard to the Minamata plant of Chisso Co., Ltd., through the completion of the perfect circulation system in 1966, water effluent containing methylmercury compound had not been discharged outside of the plant in principle, and the pollutant source was eliminated through cessation of the production of acetaldehyde in 1968. In the Agano River basin the process of producing acetaldehyde had already closed before Minamata Disease was discovered.

Effluent Control

In 1969, drainage of the factory effluent containing methylmercury to Minamata Bay was regutated. In 1970, the Water Pollution Control Law was enacted, which enforced control of discharge of effluent in all water areas in Japan, in relation to toxic substances, for example, mercury and cadmium. Furthermore, conversion of the production method was advised against caustic soda plants that might discharge mercury other than Chisso and Showa Denko plants.

Restoration of the Environment

Because methylmercury remained a considerable concentration in bottom sediment of the related water areas even after the discharge of the methylmercury compound was stopped, in order to remove this bottom sediment, from 1974 to 1990, Kumamoto Prefecture carried out the project for dealing with about 1,500,000 cubic meters of bottom sediment of Minamata Bay that contained mercury more than the removal standard (25ppm of total mercury) by means of dredging and landfill, and for making 58ha. landfill, at a total cost 48 billion yen (of this total, the responsible company bore 30.5 billion yen). In 1976, Niigata Prefecture carried out dredging river bottom sediment that contained mercury more than the removal standard around the drainage outlets of Showa Denko plant by the burden of the responsible company.

Restraint on intake of fish and shellfish and compensation to the industry

In the area around Minamata Bay, in 1956, when it became clear that intake of fish and shellfish might be the cause of the disease, the control of intake of fish and shellfish taken from Minamata Bay and self-restraint of work by the fishing cooperative are started by guidance of Kumamoto Prefecture et al. This guidance had lasted with some interruptions until early in October 1997, when the dividing nets in Minamata Bay were completely removed. During this period, Chisso Co. Ltd. paid to the fishing industry as compensation, 140 million yen in 1959 fiscal year (FY), 3,930 million yen in 1973-74 FYs, and 950 million yen in 1992-98 FYs.
In the Agano River basin, after June 1965, when Minamata Disease was just discovered there, Niigata Prefecture took measures that are guidance for the concerned fishing cooperative to self-restrain catching fish and shellfish, and for the concerned people to control intake

Transition in conditions of Pollution

In the area around Minamata Bay and the Agano River basin, until now various types of investigations about water quality, bottom sediment, fish and shellfish, hair sample, etc., have been carried out with respect to environmental pollution As a result, it is thought that continuous methylmercury exposure at the level which could cause Minamata Disease existed until no later than 1968 in the area around Minamata Bay, and until no later than 1965 in the Agano River basin, and that, from that time, there has not been such exposure that could lead to the occurrence of Minamata Disease.
Monitoring of methylmercury concentration of fish and shellfish continues even today in the area around Minamata Bay and in the Agano River basin.


Clinical features of Minamata Disease

Minamata Disease is a poisoning disease that nervous system, mainly central nervous system, is damaged by methylmercury. It is established that the disease differs from inorganic mercury poisoning which damages kidneys, etc., and also, it isn't confirmed that it damages organs other than nervous system.
Clinically diverse signs and symptoms are manifested; the main signs and symptoms are sensory disturbance in the distal portions of four extremities, cerebellar ataxia, bilateral concentric contraction of the visual field, disturbed ocular movement caused by central nervous system (CNS), impairment of hearing caused by CNS, and equilibrium disturbance caused by CNS, etc. Also, fetal Minamata Disease is reported, that shows impairments similar to cerebral infantile paralysis because mother is exposed to methylmercury during pregnancy.
In the initial stage of the outbreak of Minamata Disease, there were patients who had all major signs and symptoms, and some cases resulted in death. However, many patients do not shave all major signs and symptoms together.

The process of onset of Minamata Disease

There is the possibility of occurrence of Minamata Disease, like the poisoning by other substances, when the quantity of methylmercury (the causal substance) accumulated within the body reaches the threshold value for the onset. Because methylmercury taken into the body is discharged outside of the body at the same time, on the condition to continue that a certain amount of the substance is taken into the body methylmercury will not be accumulated in the body in excess of the limit accumulative amount correspond to the amount of continuous intake.
And these knowledge is supported by "IPCS Environmental Health Criteria 101 Methylmercury" issued by WHO in 1990.

Diagnosis of Minamata Disease

Because each neurological sign and symptom of Minamata Disease can be caused by other diseases as well, diagnosis of Minamata Disease is carried out for people who have been exposed to methylmercury on the basis of the diagnostic criteria which is composed of combinations of signs and symptoms in order to raise probability of decision. While diagnosis is easy for typical patients who have all major signs and symptoms, in the case of incomplete type or mild type of the disease, it may be difficult to distinguish it from other diseases.


(1) Relief based on the law : At the beginning of outbreak of Minamata Disease, the concerned local government had provided Minamata Disease patients particular financial assistance for medical expense.
However, because matters of health damage caused by pollution had become obvious all over Japan since 1960s, the Law Concerning Relief of Pollution-related Health Damage was enforced in 1970, under which benefits for medical expense, cost for hospital visits, etc., were provided for sufferers of pollution-related health damage, and Minamata Disease of Kumamoto and Niigata became subject of the law. Then in 1974, based on liability for damages of a civil suit, the Pollution-related Health Damage Compensation Law [now the Law Concerning Compensation for Pollution-Related Health Damage and Other Measures (hereinafter referred to as the Compensation Law)] was enacted, under which income compensation was provided in addition to medical expense for sufferers of pollution-related health damage, so the content of relief provided to sufferers of pollution-related health damage has been improved.

(2) Survey of health damage : In the area around Minamata Bay, the research to investigate the cause and the nature of Minamata Disease was carried out mainly at the beginning of outbreak of Minamata Disease, and the first full-scale survey to grasp the extent of the health damage was the one on about 110,000 habitants of the area around Minamata Bay in 1971 after the cause of the Minamata Disease was made clear. In the Agano River basin, immediately after the discovery of patients, a series of health surveys on the inhabitants were carried out by the prefectural government, and the scale of the survey has been approximately 80,000 for cumulative total of objects.

(3) Environment health measures for inhabitants : At the present time, there is no possibility of exposing to methylmercury that could lead to the occurrence of Minamata Disease and no evidence that intake of such a level of methylmercury results in any effect on health. However, in the area where there had been an outbreak of Minamata Disease, because fish and shellfish polluted with methylmercury were widely distributed and eaten in the past, even there is a possibility that those who did not fall Minamata Disease may have been exposed to various levels of methylmercury, and the anxiety about health effect of methylmercury exits among inhabitants of the concerning area.
In order to reduce and get rid of the matter of health in these area, the Government takes the Task of the Comprehensive Measures against Minamata Disease from fiscal year of 1992, which consists of the Task of Health Care that is to do periodic health examination for inhabitants, etc., and the Task of Medicine that is to provide medical expense and medical allowance as a cost related medical treatment to those who suffer from neurological signs and symptoms similar to those of Minamata Disease.

(4) Financial assistance to the responsible company : Compensation for patients of Minamata Disease in the Yatsushiro Sea area is being carried out by Chisso Co., Ltd. Because of limitation on its solvency of the compensation and the burden charge of the dredging project, necessary financial assistance is designed to ensure that there will be no interruption in the payment of compensation, maintaining the basic principle of the responsible company bearing the burden.

(5) Promotion of research and investigation : With regard to Minamata Disease, a large number of researches and investigations have been carried out since before, and many facts have been clarified; the clinical feature of Minamata Disease, the mechanism of damage to the living body caused by methylmercury, etc.
The Government has provided broad range of support to these researches and investigations, and has actively carried out its own researches and investigations including establishment of the National Institute of Minamata Disease (NIMD) for comprehensive research program. The Institute was designated as a cooperating institution of WHO in 1986. In 1996, NIMD was reorganized, it is aiming to provide accumulations of Japanese experiences related to the mercury poisoning with the request from other countries, and to make contribution in terms of international cooperation in the field of environmental health.


The case of Minamata is surely engaging because the relationship between the causal agent and the effect is so unambiguous (at least today). Yet a full account also includes the more "human" dimension--those elements which contributed to the figurative poisoning of the city, and that make the case both more striking and more valuable for reflection.

For example, because the disease was related to the unexplainable behavior of wildly-acting cats, the disease became stigmatized, often in the victim's own eyes. In the Japanese view of medicine, the condition of the body reflects how the individual has maintained his or her balance with the external world--and sickness can be viewed as something "deserved." The victims were thus often implicitly "blamed" for their own condition. Also, wary of contagion, residents ostracized disease patients. Neighbor turned against neighbor. One tatami mat-maker, Yahei Ikeda, for instance, disparaged those who had the disease--until one day he, too, ironically, showed the symptoms. Neighbors with whom he had earlier shared his isolationist sentiments regarding the victims now turned those same feelings against him.

Fishermen and their families were the earliest and most severely afflicted, having consumed the most contaminated fish. But it was also the fishermen, perhaps, who most embodied the traditional Japanese appreciation of nature, so evident in classical haiku poetry and watercolor painting. For the fishermen, the sea, viewed romantically perhaps, was life-giving. It was hard for the villagers to comprehend that the sea could also take life away. One fisherman expressed his love of the sea:

The most disturbing social overtones in Minamata may have involved the employees of Chisso. In the 1950s and 60s, Chisso employed about 60% of the town's workforce. Having essentially inherited the role of patriarchal lord from feudal Japan, Chisso was both provider and protector. The employees depended on Chisso for their livelihood and, in turn, honored this with their loyalty. So deep was this loyalty that Dr. Hosokawa, who had uncovered his company's role in causing Minamata disease, felt he could not divulge the results of his research publicly (though he did so later on his deathbed). Even today, Chisso enjoys a favorable image among many residents. When fishermen began to demonstrate against Chisso for damages, therefore, there were counter-demonstrations by company employees. To have admitted Chisso's "guilt" would have been to acknowledge that the corporation had abandoned its filial responsibility and that the relationship, now violated, could no longer be trusted. Though members of Chisso's Workers' Union could sympathize with those in Minamata's Fishermen's Union, in this case there was no question where loyalty would lie. The whole town of Minamata was thus splintered. The mercury not only poisoned individuals' bodies, but also the community's social relations.


Minamata disease remains an important issue in contemporary Japanese society. Lawsuits against Chisso and the prefectural and national governments are still continuing and many regard the government responses to date as inadequate.

A memorial service was held at the Minamata Disease Municipal Museum on 1 May 2006 to mark 50 years since the official discovery of the disease. Despite bad weather the service was attended by over 600 people, including Chisso chairman Shunkichi Goto and Environment Minister Yuriko Koike.

Most congenital patients are now in their forties and fifties and their health is deteriorating. Their parents, who are often their only source of care, are into their seventies or eighties or already deceased. Often these patients find themselves tied to their own homes and the care of their family, in effective isolation from the local community. Some welfare facilities for patients do exist. One notable example is Hot House, a vocational training centre for congenital patients as well as other disabled people in the Minamata area. Hot House members are also involved in raising awareness of Minamata disease, often attending conferences and seminars as well as making regular visits to elementary schools throughout Kumamoto Prefecture.


Finally, Minamata can teach us about politics, particularly as they might apply to environmentalism. The patients of Minamata disease suffered not only from a physical handicap alone. Due to their economic status and the social dimensions of the disease, the victims were also politically handicapped. They--and the fishermen whose livelihoods (if not whose lives) had been destroyed--did not initially command the power or the resources to obtain proper compensation from Chisso. The story of their struggle, therefore, is equally informative.

In the late 1950s, the disease patients organized a "Mutual Help Society." Through continued petitioning, recruiting of grass-roots support across Japan, months of sit-ins at Chisso headquarters, and an unsightly tent settlement on their front sidewalk in Tokyo, they focused unfavorable public attention on Chisso. Eventually Chisso management agreed to negotiate directly with the patients, rather than appeal to the government's authority (which supported Chisso). Other patients brought suit, wherein Dr. Hosokawa's testimony was made public and became instrumental in demonstrating Chisso's particular negligence. The court ruled in favored of the patients and the demands of the negotiations group were met soon thereafter. The political campaign succeeded, but only through an investment of considerable effort and time. Here, bearing witness, patience and persistence proved effective.

Political lessons may seem inappropriate in a biology classroom. However, students today are increasingly exposed to acts of violence intended to "resolve" conflicts. An example where bearing witness, patience and persistence have proven their effectiveness can provide a significant alternative model for action. Even in environmentalism, we are easily reminded of the ethical issues involved in spiking trees and other forms of "monkey-wrenching" or ecological sabotage.


Minamata disease came into being as a result of one chemical complex that was, at a certain point in time, positioned at the heart of a new and rapidly growing industry. Because of the company's pride in its own technological prowess, it was blinded to the dangers of the waste effluents that it allowed to enter the human environment. The industry and various governmental organizations understood pollution problems only in terms of economic viability, and these same sectors of society tried to evade and cover up these problems through an initially successful series of oppressive measures. However, the problem reared its ugly head again, and this time the company was forced into a situation in which it could no longer continue operations. The way in which these problems were dealt with is beyond the comprehension of the present age. Where there are no people's movements, no progress is made toward meaningful solutions and the complexities are finally forgotten. Through active citizens' movements, new methods are discovered and new ways opened up. Most Minamata-disease-related citizens' movements employed non-violent direct action. In this way, the disease victims, even though they were socially weak, did not lose the battle, but were able to turn their deeply shared mutual experiences into powerful weapons for the fight. When such movements aim at returning basic human rights to the people, and when the appeal is directed at the full humanity of all persons, success is assured and progress can be made on a firm basis of human support.

One issue that has not yet been fully dealt with is that of the potential contribution of the disease victims to a full assessment of the damage done to the human environment by methyl mercury poisoning. The magnitude of the problem is such that, on the basis of present knowledge, it cannot be left to experts in the environmental sciences alone. Thus the adequacy of the work ahead depends upon how positively the socially weak disease victims are allowed, and able, to participate in the much needed overview of the problem, and in the process of finding solutions. These experiences are ones that we should all learn from, as we look ahead to other potential environmental disasters brought about by human greed.

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