The Chisso Corporation’s chemical plant dominated the fishing town of Minamata on Japan’s Kyushu coast — employer, taxpayer, landlord. From 1932 its acetaldehyde process used a mercury catalyst, and a by-product, methylmercury, went out with the wastewater into Minamata Bay, where it concentrated up the food chain into the fish and shellfish that fed the town.
The first officially recorded sign came in the early 1950s: cats convulsing, spinning, and throwing themselves into the sea — locals called it the “cat dancing disease.” Birds fell from the sky. Then the fishing families began to sicken.
The strange disease
On 1 May 1956, the director of Chisso’s own factory hospital reported an “epidemic of an unknown disease of the central nervous system.” Patients stumbled, slurred, lost vision at the edges, lost feeling in their hands; the worst convulsed, screamed, and died — over a third of early identified patients within months. Children were born with devastating congenital damage to mothers who showed few symptoms themselves: the poison had crossed the placenta.
Kumamoto University researchers traced the cause to heavy-metal poisoning through seafood within two years, and to organic mercury by 1959. Chisso denied everything, commissioned rebuttals, and pointed at wartime munitions dumps. That same year the company’s own physician, Dr Hajime Hosokawa, fed factory wastewater to a cat — designated cat 400 — and reproduced the disease exactly. Chisso suppressed the experiment, barred him from continuing, and paid victims token “sympathy money” under contracts waiving future claims.
The dumping continued until 1968 — twelve years after identification, during which the acetaldehyde line ran at record output and the poisoned continued to eat from the bay. Only when the process became obsolete did it stop; weeks later, the Japanese government officially declared Chisso’s mercury the cause.
The reckoning
Hosokawa, dying of cancer, testified from his hospital bed in the victims’ 1970-71 lawsuit; the court’s 1973 verdict found Chisso negligent from the beginning, and later rulings put the national and prefectural governments at fault too. The struggle over victim certification ground on for decades: some 2,283 people were officially certified, tens of thousands more compensated under broader settlements, against estimates that hundreds of thousands ate contaminated fish.
The American photographer W. Eugene Smith lived in Minamata from 1971 documenting the victims; his photograph Tomoko in Her Bath — a mother cradling her congenitally poisoned daughter — carried the disease’s name around the world. In 1972 Chisso-linked men attacked Smith at a protest, injuring him severely.
“Minamata disease” is now the textbook name for methylmercury poisoning, and the 2013 UN treaty controlling mercury worldwide is called the Minamata Convention — the town’s name permanently attached to the lesson its company refused to learn.