We all have been quite familiar with the toxic effects of mercury. The inhalation of mercury vapour can cause severe harm to our nervous, digestive and immune systems, lungs and kidneys, to the extent of being fatal. Dermal exposure to mercury may cause corrosion to skin, eyes and gastrointestinal tract. However, such a situation which required much more research, caused much more panic, was given the name of Minamata Disease. To be explained very briefly, this disease causes neurological degradation, due to organic mercury poisoning.

How did it all start?

Minamata is a small town, across the Yatsushiro Sea, in Southern Japan. In 1956, a five-year-old girl was detected with strange neurological symptoms. She started facing immense difficulties in basic activities like walking and speaking. She is thus known as the first officially documented case of the Minamata disease, on May 1, 1956.

But the question remains, how did this happen? This disease is associated with daily consumption of large quantities of fish and shellfish, heavily contaminated with toxic chemicals.

What are the signs and symptoms of Minamata Disease?

They include ataxia, bodily numbness, loss of peripheral vision, damage to hearing and speech, tremors amongst others.

When more such cases started to be discovered in full swing, this disease was declared as an epidemic by the local public health officials. For the same, a Strange Disease Countermeasures Committee was formed by a group of doctors by May 1956. It was being thought of as a contagious disease and patients were thus being isolated as a precautionary measure. However, later the suspicion of possible contagion was claimed to be false. Still, it became a building cause of discrimination faced by Minamata patients.

This was not enough, it seemed. Cats were being seen having convulsions, and the number of cat deaths was surprisingly soaring. Locals started calling it the ‘Cat dancing disease’. The Strange disease committee then invited researchers from Kumamoto University. They started admitting the patients in their university hospital for their close examination and analysis. It was reported that by October 1956, Minamata disease had an alarming fatality rate of 35%.

What was the causative agent?

The company responsible for this entire episode is Chisso Corporation. Chisso generated methylmercury as a byproduct, for manufacturing acetaldehyde, which used mercury as a catalyst. Methylmercury, after discharging into the sea, was absorbed in the fish and shellfish through gills or digestive tracts.

Interestingly, engineers of Chisso assumed that if the waste contained toxicity, it could be easily eliminated by diluting the waste with excess seawater. Thus, it changed its drainage channel from Minamata Bay to Minamata River. However, it did nothing less than strengthen the suspicions about the close ties between factory waste and the disease, as cases started to be detected near the river as well.

When in late 1959, Kumamoto University researchers pointed out that extremely high concentration mercury was located in Minamata Bay sludge, Chisso argued that:

  • The factory had been using inorganic mercury.
  • There were neighbouring chemical plants using mercury, where the disease was never reported.

However, in its response, the researchers pointed out that it was possible that methylmercury is formed during synthesizing chemical reactions using inorganic mercury. Also, the production of acetaldehyde had increased drastically, alone in Minamata Bay.

In November 1959, the committee presented its official conclusion, that Minamata disease was an organic mercury poisoning, due to the intake of intoxicated fish and shellfish, caught in Minamata Bay.

 Compensation given:

  • The Minamata Fishing Cooperative:

From 1953 to 1957, the fish catch in Minamata had declined by almost 91%.  There came about a widespread fear amongst the local people that the fish of Minamata Bay was unsafe and intoxicated. The fishermen were left with no financial assistance to compensate them for their loss of business and ultimately had to eat the suspected fish they caught to fill their stomach.

With no aid from the government, the Fishing Cooperative had to engage in direct negotiations with the company. The mediation committee between the two parties heavily favoured Chisso and it was concluded that Chisso would pay JPY 20 million directly to the cooperative, and would set up a fund worth JPY 15 million for kickstarting the recovery of fishing.

  • Victim compensation:

The patients had set up an organization named ‘Minamata Disease Patients Families Mutual Aids Society’ in 1957. Even the fishermen were the ones who discriminated against the disease victims because they believed that they were the reason they were going bankrupt and were experiencing a loss in business.

The Mutual Aid society approached Chisso directly and demanded compensation of JPY 234 million, approximately 3 million per person. However, the company replied that the link between its wastewater and disease has not yet been proven, thus the cooperative started to protest at the company’s gates.

The Mediation committee presented a proposal, which set the compensation at JPY 74 million, wherein adult patients of the Minamata disease would receive JPY 100,000 and children JPY 10,000 per annum. In the case of mortality, the family would receive JPY 320,000.

However, later the child payments were increased by the mediation committee to JPY 30,000. However, these payments were of the nature of sympathy money i.e. even if in future the cause of Minamata disease is found out to be Chisso’s wastewater, then also no further compensation can be claimed. This agreement was accepted by both sides by December 1959.

Wastewater treatment:

 In October 1959 Chisso was ordered by the Ministry of International Trade to switch back its drainage system from Minamata river to Hyakken Harbour and to install a wastewater treatment facility at the factory.

Chisso installed a Cyclator purification system in December 1959 and its president also drank a glass of water, treated through Cyclator, to test its purification capability. However, it later was proved that this purification task was just a social gimmick and did nothing to remove organic mercury from the water.

All the parties were duped into believing that the factory’s wastewater was finally made safe, assuming that the issue relating to the disease has been resolved.

However, Chisso ended the manufacture of acetaldehyde in May 1968, 12 years after the first case of the disease. It is believed that the failure to prevent the disease is majorly attributable to the impact that Chisso Minamata plant had on the local economy in respect of employment generated by it and its revenues.


 According to Timothy George, all the protests surrounding the disease assisted in the democratization of Japan. The protests for recognizing the rights of victims, compensating them and ending the constant discrimination against them, were one of the few steps towards building a block of democracy in Japan.

Earlier, victims, fishing families and Chisso’s employees were excluded from decision making. Once the victims were allowed to come to discussion meetings, progress started and it was quoted as a mini-step towards democracy.

The involvement of media, also aided in stressing on the significance of freedom of speech, expression and awareness amongst citizens.


However, the governmental failure to prevent the deterioration of human health due to this fatal disease, due to not taking strict measures against Chisso (powerful company) for a long time, teaches us a lot, even today. It shows how preventive countermeasures should be taken, even in times of scientific uncertainty over the cause or origin of the issue.



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