The correct answer is option 4, mercury. The Minamata episode refers to a tragic incident that occurred in Minamata, Japan in the 1950s and 1960s. The Chisso Corporation, a chemical company, was releasing industrial wastewater containing high levels of methylmercury into Minamata Bay. The mercury bioaccumulated in seafood, primarily fish, which were consumed by the local population. This led to widespread mercury poisoning, causing severe neurological symptoms and even death. The symptoms included numbness, muscle weakness, loss of coordination, and in severe cases, convulsions and coma. The Minamata episode led to the recognition of mercury as a highly toxic metal and raised awareness about the dangers of environmental pollution. It also resulted in stricter regulations and monitoring of industrial wastewater to prevent similar incidents from happening in the future.