Minamata disease is methylmercury poisoning that leads to neurological symptoms. It occurs after daily consumption of heavily contaminated seafood. The first record of Minamata disease happened in Japan in the 1950s, when people ate fish contaminated by large quantities of mercury compounds that were discharged into Minamata Bay by a chemical factory.

The Minamata Disaster

There were several small fishing villages on the edge of Minamata, Japan, on the coast of the Shiranui Sea. Naturally, the people of these villages ate a lot of seafood.

In the mid-1950s, the villagers began to notice their cats were behaving strangely and falling into the sea. Some people thought the cats were committing suicide.

Soon after, a strange illness appeared to be going around. The villagers reported numbness in their limbs and lips. Some had difficulty hearing or seeing. Others developed tremors in their arms and legs, difficulty walking, and even brain damage. And, like the cats, some people were behaving strangely, shouting uncontrollably. Something was affecting their nervous system.

The fish-based diets of the villagers and cats seemed to be the common thread between those showing symptoms, leading scientists to suspect the fish in Minamata Bay were being poisoned.​

Finally, in July 1959, researchers from Kumamoto University discovered the source of the illness—high levels of mercury poisoning—which they then named Minamata disease. A large petrochemical plant in Minamata, run by Chisso Corporation, was suspected immediately.

Chisso denied the allegations and continued its manufacturing without changing its method of production. Chisso continued to deny its involvement or that its mercury waste was causing any illness. It was later estimated that Chisso Corporation had dumped 82 tons of mercury compounds into Minamata Bay.

As the mercury dumping continued, poisoned women gave birth to poisoned babies. These children were born with severe deformities including gnarled limbs, mental retardation, deafness, and blindness.

The fishermen of Minamata began protesting Chisso Corporation in 1959. They demanded Chisso quit dumping toxic waste and compensate them for their illnesses.

Chisso, in turn, tried to make deals with people affected by mercury poisoning using legal documents that stated it would compensate individuals for their illnesses but would accept no present or future liability. Many people felt this was their only chance of receiving any compensation, and signed the papers.

Recovering From Minimata Disease

Chisso finally quit poisoning Minamata’s waters in 1968. According to the Japanese Ministry of the Environment, as of 2013, almost 3,000 people had been certified as Minamata patients and more than 2,300 had since died.

Researchers believe, however, that the criteria the government uses to diagnose Minamata disease are too strict, and that anyone showing any level of sensory impairment should be considered a victim.

In October 1982, 40 plaintiffs filed suit against the Japanese government, saying it had failed to stop Chisso from polluting the environment and had actually looked the other way while Chisso violated pollution laws.

In April 2001, the Osaka High Court determined that the government’s Health and Welfare Ministry should have begun taking regulatory action to stop the poisoning at the end of 1959 after researchers concluded that Minamata disease was caused by mercury poisoning. The court also ordered Chisso to pay $2.18 million in damages to the plaintiffs.

On October 16, 2004, the Supreme Court of Japan ordered the government to pay 71.5 million yen ($703,000) in damages to the Minamata disease victims. The Environment Minister bowed in apology to the plaintiffs. After 22 years, the plaintiffs achieved their goal of making those responsible for Japan’s worst case of industrial pollution pay for their negligence.

In 2010, Chisso was ordered to pay 2.1 million yen and monthly medical allowances to those not originally certified by the government as having the condition. More than 65,000 people applied for this compensation, showing how, over five decades later, the effects of this disaster are still felt.

Frequently Asked Questions

  • What metal causes Minamata?
  • The organic form of the metal mercury, known as methylmercury, causes Minamata disease.
  • What are the symptoms of mercury poisoning?
  • Notable symptoms of mercury poisoning include headache, tremors, insomnia, loss of memory, weakened muscles, cognitive dysfunction, and motor dysfunction.The severity of symptoms depends on the type of mercury, the amount and duration of exposure, a person’s age, and whether mercury was ingested, inhaled, or absorbed through the skin.
  • Learn More:
  • Mercury Poisoning: What You Should Know
  • How do I avoid mercury poisoning?
  • Most people in the US can avoid mercury poisoning by limiting their intake of seafoods containing high amounts of methylmercury. For example, fish such as salmon and flounder contain less mercury than swordfish and king mackerel.Additionally, be careful when using products that contain metallic mercury. Certain thermostats, fever thermometers, and even novelty jewelry can pose the risk of mercury exposure if their contents are released.

The organic form of the metal mercury, known as methylmercury, causes Minamata disease.

Notable symptoms of mercury poisoning include headache, tremors, insomnia, loss of memory, weakened muscles, cognitive dysfunction, and motor dysfunction.

Most people in the US can avoid mercury poisoning by limiting their intake of seafoods containing high amounts of methylmercury. For example, fish such as salmon and flounder contain less mercury than swordfish and king mackerel.