Minamata disease describes methylmercury poisoning, which results in irreversible damage to the nervous system. The disease first occurred when toxic pollutants affected the fish that comprised the food supply of the coastal community in Minamata, Japan.
There is evidence that mercury has been affecting people since the 19th century. Still, the impact did not gain recognition until the late 1950s, after industrial mercury pollution caused tragic health damage to the people of Minamata Bay and the surrounding communities.
This article explores Minamata disease, its symptoms, causes, treatments, aftereffects, and frequently asked questions.
Minamata disease is a large-scale mercury poisoning that results from methylmercury contamination, usually in seafood.
The original case to gain recognition began when a factory in Minamata City released discharge that included methylmercury, a by-product of acetaldehyde production, into Minamata Bay.
The factory started producing acetaldehyde in 1932, with increased production after World War 2 between 1939 and 1945. By around 1950, residents were noticing the effects on local wildlife. The situation gained official recognition in May 1956 when two children developed neurological symptoms.
By August 1956, there were numerous reports of neurological conditions, and 13 people had died.
Researchers established the cause to be mercury contamination in fish and shellfish, with the factory highlighted as the primary cause. However, at this time, Japan’s Ministry of Health and Welfare suggested insufficient evidence to implement the Food Sanitation Act.
In 1965, health experts reported another epidemic of Minamata disease in the Agano River basin in Niigata Prefecture.
During the following years, researchers collated more evidence and determined that the factory was responsible for the outbreak in 1962. Research suggests the government officially acknowledged the correlation in 1968. By this point, the mercury poisoning had spread along the entire coastline of the inland sea.
Minamata disease causes neurological signs and symptoms, including:
- sensory disturbance
- ataxia, a lack of muscle coordination that may affect a person’s voluntary movements.
- dysarthria, a collective term for a group of speech disorders that occur due to muscle weakness
- tunnel vision
Findings from Minamata showed that the onset of symptoms was often sudden. People who developed difficulty hearing, seeing, and swallowing deteriorated particularly quickly, experiencing convulsions and then coma and death.
The degree of symptoms varied, depending on how much exposure people had to mercury. In more severe cases, the symptoms were irreversible, but lower levels of methylmercury resulted in milder symptoms.
It is difficult to know the death rate from Minamata disease. As of 2019, there were 2,282 cases that had official recognition. However, many more cases are likely to have gone without recognition.
There have been several epidemics of Minamata disease, but each time, pollution has been the underlying cause of symptoms.
The cases in Minamata and Niigata both resulted from consuming contaminated fish. The largest methylmercury poisoning outbreak was in Iraq during the winter of 1971–1972, when bread became contaminated, as the seed wheat contained methylmercury fungicide.
Research has highlighted the importance of rapid recognition, suggesting that the original Minamata disease outbreak would have been much smaller if there had been measures to reduce contamination from the start.
There is little guidance in place for treating methylmercury poisoning. The main treatment measures include:
- supportive therapy
- removal from the source
However, the neurological effects of Minamata disease are often irreversible, making them impossible to cure.
In solving the overarching issue of Minamata disease and in line with the Sustainable Development Goals, the United Nations established the Minamata Convention on Mercury in 2013.
The Minamata Convention on Mercury is an international treaty to protect people from exposure to mercury and mercury compounds. The treaty established a set of measures to meet this goal, including:
- controlling the supply and trade of mercury
- limiting mercury sources
- controlling processes that use mercury or mercury compounds, such as gold mining
- controlling mercury-added products
Despite decades of restoration efforts by the United Nations Environment Programme (UNEP), the methylmercury poisoning event continues to affect people in Minamata Bay.
Research varies, but as well as Minamata disease affecting people who ate the fish directly, findings suggest that fetuses started developing the condition while still in the uterus. At the time, people thought the placenta would protect them.
Still, as babies were born with conditions resembling cerebral palsy, researchers have now firmly established the idea that methylmercury poisoning can transmit through the placenta.
According to UNEP, human activities over the past few decades have caused mercury levels to rise by approximately 450% over their natural levels.
Given the knowledge available today, it is increasingly important to take action to reduce mercury poisoning and minimize pollution going into water bodies and the rest of the environment.
Below are answers to frequently asked questions on Minamata disease.
Is Minamata disease still around?
Mercury and mercury-component poisoning still exist. However, monitoring has improved since the start of the Minamata Convention on Mercury.
In and around Minamata Bay, people continue to experience the aftereffects of the original epidemic.
Is it curable?
Some symptoms of Minamata disease are curable, but it depends on how much exposure the person has had to mercury. Symptoms that result from neurological implications are not reversible.
Is it painful?
Symptoms start as a sensory disturbance but can be extremely physically and mentally painful.
When did health officials recognize the issue?
The original case in Minamata Bay received official recognition in 1968, four months after the factory stopped producing mercury compounds. This was 12 years after the start of the epidemic.
Minamata disease refers to a tragic event where people in the coastal community of Minamata Bay, Japan, developed severe neurological disorders following exposure to methylmercury. The event resulted from the industrial release of mercury compounds into the local water. The fish and shellfish consumed these compounds, thereby compromising the local food supply.
Since the original outbreak, other communities have experienced forms of Minamata disease, where pollutants have caused mercury contamination, resulting in neurological signs and, in severe cases, death.
Despite events such as the Minamata outbreak, environmental pollution continues, with contaminants entering the water and atmosphere and, ultimately, people. A more sustainable future will reduce these toxins and improve human health.