Brief Chronology of Minamata Disease Incident
Year

Event

1889

Official designation of Minamata Village (population: 12,040 )1908

Nippon Nitrogen Fertilizer Co., Ltd. (at present Chisso Co., Ltd.) builds a factory in Minamata.

1932

Chisso starts discharging methyl mercury, which was the causative substance of Minamata
disease, to Minamata Bay. (Mercury was used to make acetaldehyde, which is used for vinyl,
and mercury was drained with industrial wastewater.)

1949

Minamata Village becomes Minamata City (population: 42,270 )1956

A disease of unknown cause (Minamata disease) is discovered.
(The official recognition date of Minamata disease : May 1st, 1956)
The administration suspects the disease is infectious, so they disinfect the patients’ houses.
The population reaches a peak at 50,461 people.

1957

Minamata Public Health Center and Kumamoto University undertake experiments on cats. A cat
develops Minamata disease after being fed fish from Minamata Bay.
Kumamoto Prefecture calls on the people not to eat fish and shellfish in Minamata Bay.

1959

Kumamoto University research group announces “Minamata disease is caused by consuming fish andshellfish from Minamata Bay. It is strongly suspected that mercury is the causative agent.”
Chisso begins experiments with cats by feeding factory wastewater, and a cat shows symptoms,
although it is not revealed.
Patients’ families conclude “sympathy money contract” with Chisso, which states 300,000 yen shouldbe paid for the deceased.

1968

Chisso stops producing acetaldehyde and discharging methyl mercury.
(Chisso had polluted Minamata Bay and the Shiranui Sea since 1932 for 36 years.)
The Japanese government affirms that Minamata disease is a pollution-triggered disease caused by
Chisso Minamata Factory’s wastewater.

1969

The first Minamata disease lawsuit starts.
(The suit was filed to clarify Chisso’s responsibility.)

1973

The second Minamata disease lawsuit starts.
(The suit was filed for compensation for uncertified patients.)
The first lawsuit rules in favor of the patients.
Compensation agreement between Minamata disease patients and Chisso is reached.
(At last, the certified Minamata disease patients received compensation, such as 1.8 million yen for thedeceased, full reimbursement of medical costs, and payment for living expenses.)

1974

Kumamoto Prefecture sets up the dividing nets.
(The nets were extended to prevent the contaminated fish from spreading.)

1977

Minamata Bay Pollution Prevention Project begins.
(The work was to dredge mercury-containing sludge.)

Year
1980

EventThe third Minamata disease lawsuit starts.
(The suit was filed to clarify the national and prefectural governments’ responsibility.)

1990

Minamata Bay reclaimed land “Eco-Park Minamata” is completed.
(The site was built by reclaiming mercury-containing sludge.)

1992

Minamata City declares its creation of a model environmental city.
(In response to the lessons of Minamata disease, Minamata City decided to create anenvironment-friendly city.)

1993

Garbage starts to be collected by type by citizens.

1995

The final plan for the settlement by the national government is decided.
(The national government proposed a solution for aiding uncertified patients, who had not received any
compensation. Apart from the plaintiffs in the Kansai lawsuit, those who had instituted the suits
accepted the solution. Most of the lawsuits and negotiations for Minamata disease had finished by thenext year.)

1997

Kumamoto Prefecture Governor announces the Minamata Bay Safety Declaration.
(The dividing nets were removed and the safety of fish in Minamata Bay was declared.)1999

Minamata City acquires ISO14001 certification and starts to create an environment-friendly city basedon ISO14401.

2004

Both the national and prefectural governments’ responsibility is affirmed by the Supreme Court.
(In the Kansai Lawsuit, which was the only pending lawsuit associated with Minamata disease, theSupreme Court affirmed both the national and prefectural governments’ responsibility for not regulating
Chisso’s industrial wastewater.)
Population of Minamata City: 30,159