Minamata Timeline


Chisso and Methyl Mercury

Approx. 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.)

Minamata City

Approx. 1949

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

Discovery of Minamata Disease

Approx. May 1, 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

Cat Experimentation

Approx. 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.

Causation found/compensation

Approx. 1959

Kumamoto University research group announces “Minamata disease is caused by consuming fish and
shellfish 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 should
be paid for the deceased.

Methyl Mercury Production Comes to a Halt

Approx. 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.

Lawsuit #1

Approx. 1969

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

Lawsuit #2/ 1st Lawsuit won

Approx. 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 the
deceased, full reimbursement of medical costs, and payment for living expenses.)

Dividing Nets

Approx. 1974

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


Approx. 1977

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