What is Minamata Disease?

Minamata disease is a condition that people in most parts of the world are not familiar with, but it is painfully real to those living in the city of Minamata, Japan. The city lends its name to the condition that was first identified here. Minamata disease is not really a disease in the strict sense of the word; it is a neurological syndrome that results from industrial pollution and environmental contamination. It means that poisoning with the pollutant has an effect on the central nervous system. The specific pollutant responsible for this condition is methyl-mercury.(1)

The disease was first identified in the city of Minamata in 1956. The condition began affecting residents and local wildlife, or cats to be more precise, and the problem continued to afflict more people through the following decade as nothing was done to control the contamination.

Causes of Minamata Disease

Minamata disease is caused through the absorption of methyl mercury into the body through various environmental sources, primarily through seafood. The level of mercury in the body is tested with hair samples and it is widely agreed that when these levels are higher than 50ppm (parts per million), there is likely to be nerve damage. While people living outside of the Minamata area had an average level of 4ppm, people living in Minamata had levels even as high as 700ppm!

While the underlying cause is mercury poisoning through environmental pollution and contamination, there are other causes too:

Cause of Mercury Poisoning - Environmental Pollution
  • The most common source is through contaminated seafood, as was the case for people residing in Minamata. A company by the name of Chisso, which was one of the biggest Japanese companies at the time, released its waste into the Minamata Bay. Methyl mercury was just one of the pollutants in the waste that was dumped and this particular pollutant accumulated in the food chain. It was absorbed and ingested by plankton, which is the primary food source for shellfish and fish in the water. Larger fish that ate such contaminated fish also absorbed the mercury and the poisoning continued to spread further in the food chain. Birds that fed on fish were also contaminated and so were other predators that preyed on these birds. In Minamata Bay, the pollutants were not dispersed over a wide area, but remained concentrated within the bay and this made the risk even greater as residents got their protein intake from seafood.
  • There were many cases of mercury poisoning found in New Mexico, USA, which resulted from the consumption of livestock that was fed mercury-tainted grain.
  • Similarly, in Iraq, over 6,000 people were affected by exposure because they ate flour that was processed from grains treated with methyl mercury.
  • Mercury poisoning is also a huge health risk for pregnant women, as Minamata disease is known to affect the unborn child as well. Methyl-mercury can enter the fetus via the placenta and it has an adverse effect on brain development.

In the case of residents in Minamata Bay area, it was observed that methyl-mercury deposits are concentrated in neural tissues. This pattern also serves as an explanation for the effect of neurotoxicity, especially in new-born babies as fetal transfer of the toxin cannot be prevented.(2)

Symptoms and Signs of Minamata Disease

  • Severe uncontrollable tremors
  • Loss of motor control
  • Sensory loss affecting both auditory and visual senses
  • Partial paralysis
  • Loss of muscle control during voluntary movements, known as ataxia
  • Numbness in the extremities like the hands and feet
  • Speech impairment may also be observed

While these are typical symptoms of mercury poisoning, the symptoms and combinations of symptoms can differ in severity. In children and infants who have inherited the condition, the symptoms can include the following:

  • Infants will display symptoms that are similar to those afflicted with cerebral palsy, which is not surprising as it results in impaired neurological development and causes seizures.
  • Growth and developmental problems with both physical and mental health
  • Microcephaly, a neurodevelopmental disorder, in children
  • Mental retardation
Symptoms and Signs of Minamata Disease

Diagnosis of Minamata Disease

Mercury poisoning is most often diagnosed with a laboratory measuring mercury levels in a hair sample. This is obviously non-invasive and is a very straightforward procedure. If you live in an area where there have been cases of mercury poisoning or if there is a sudden rise in similar cases with symptoms resembling those of mercury poisoning, health care providers would most likely request testing.

Whether a person in Japan has Minamata disease is not just decided by your doctor but by the national government and local governors because of the legal requirements with regard to compensation and pollution-related health incidents. If the symptoms are hard to identify, especially in newer cases with mild symptoms, and health care providers suspect Minamata Disease, they can request electro-ophthalmography (EOG) and optokinetic nystagmus pattern (OKP) to obtain referential data.(3)

Treatment for Minamata Disease

Treatment may vary depending on severity of the condition and the symptoms present. However, there are certain standard approaches that are followed:

  • Identifying and isolating the source of exposure so as to prevent any further exposure. This is obviously the first step and is in many ways a prerequisite to treatment.
  • The most important aspect of treatment is the removal of mercury from the body using chelating agents. Chelating agents prevent heavy metals like mercury from binding with body tissue, by reacting with and binding with it themselves. This obviously comes with its own set of side-effects, which is why experts recommend agents with the lowest levels of toxicity. One risk from the use of chelating agents is that mercury may be redistributed and can even get to the brain.
  • Loss of muscle function and paralysis are extremely common in patients and although severity may vary, physical rehabilitation is almost always necessary or useful as it helps patients regain some amount of control over mobility.
  • In some cases, patients may suffer from convulsions in which case doctors will prescribe anticonvulsant drugs.
Anticonvulsant Drug Helps Treat Minamata Disease


  1. Minamata Disease - (https://www.bu.edu/sustainability/minamata-disease/)
  2. Minamata Disease: Methylmercury Poisoning in Japan Caused by Environmental Pollution - (https://www.ncbi.nlm.nih.gov/pubmed/7734058)
  3. Evaluation of Mercury Exposure Level, Clinical Diagnosis and Treatment for Mercury Intoxication - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4724159/)
  4. Investigation of the Cause of Minamata Disease - (http://nimd.env.go.jp/archives/english/tenji/b_corner/b03.html)

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