‘Minamata disaster’ in Japan was caused by pollution due to

Concept

Heavy metals discharged into a water body do not simply dilute away. Microbes convert some of them into fat-soluble organic compounds that living tissue cannot excrete, so the concentration rises at each step of the aquatic food chain — a process called biomagnification. A community that eats fish from such water therefore receives a dose far larger than the metal concentration in the water itself, and the poisoning appears as a disease of the population rather than of individual workers.

Application to this question

From 1932 the Chisso Corporation's acetaldehyde plant at Minamata, in Kumamoto Prefecture on the island of Kyushu, discharged effluent containing methylmercury into Minamata Bay. The methylmercury biomagnified in the bay's fish and shellfish, which were the staple food of the local fishing community. Residents began to show numbness of the limbs, slurred speech, an unsteady gait and constricted vision, and infants were born with congenital damage. The outbreak was officially recognised in 1956 and named Minamata disease; the pollutant responsible was mercury.

Contrast with the other metals

Hence the Minamata disaster was caused by pollution due to mercury. The Minamata Convention on Mercury, adopted in 2013 and named after this event, is the global treaty that now regulates mercury emissions and releases.