Introduction:
The fatal brain disease that affected people eating fish caught around Minamata off the Japanese island Kyushu was caused by the metal mercury. This incident, known as the Minamata disease, is one of the most well-known cases of industrial pollution and its devastating effects on human health.

Explanation:
The Minamata disease was caused by the release of methylmercury into the environment by a chemical factory owned by the Chisso Corporation. The factory was producing acetaldehyde, a chemical used in the production of plastics, and was discharging its waste into Minamata Bay. The methylmercury present in the waste bioaccumulated in the fish and shellfish in the bay, which were then consumed by the local population.

Key Points:
- Methylmercury is a highly toxic form of mercury that can accumulate in the tissues of organisms, particularly in the fatty tissues of fish.
- When humans consume fish contaminated with methylmercury, it can be absorbed into their bloodstream and accumulate in their organs, including the brain.
- The symptoms of Minamata disease include neurological disorders such as numbness, muscle weakness, impaired vision and hearing, and in severe cases, paralysis, coma, and death.
- The disease was first recognized in the 1950s when local fishermen and their families began experiencing these symptoms.
- The Minamata disease outbreak led to significant public health and environmental concerns and highlighted the dangers of industrial pollution and the need for stricter regulations to protect both human health and the environment.
- The incident also led to the establishment of the Minamata Convention on Mercury, an international treaty aimed at protecting human health and the environment from the adverse effects of mercury.

Conclusion:
The Minamata disease was caused by the release of methylmercury into the environment by a chemical factory, which contaminated the fish and shellfish in Minamata Bay. The consumption of these contaminated seafood led to the development of a fatal brain disease in the local population. This incident serves as a reminder of the importance of environmental regulations and the need to protect human health from industrial pollution.