Discovery Guides Areas


Methylmercury Contamination in Fish and Shellfish
(Released February 2007)

  by Laura Griesbauer  


Key Citations



The Minamata Bay Incident


In the 1950's, one of the most severe incidents of industrial pollution and mercury poisoning occurred in the small seaside town of Minamata, Japan. A local petrochemical and plastics company, Chisso Corporation, dumped an estimated 27 tons of methylmercury into the Minamata Bay over a period of 37 years. Mercury was used as a catalyst in the production of acetaldehyde, a chemical employed in the production of plastics. Methylmercury-contaminated wastewater, a byproduct of the process, was pumped into the bay, creating a highly toxic environment that contaminated local fish. Residents of Minamata, who relied heavily on fish for food, were at risk of exposure to methylmercury with every bite of fish they ate. The high contamination levels in the people of Minamata led to severe neurological damage and killed more than 900 people. An estimated 2 million people from the area suffered health problems or were left permanently disabled from the contamination (McCurry, 2006). This form of toxicity in humans is now called Minamata disease. Symptoms include sensory disorders of the four extremities, loss of feeling or numbness, cerebellar ataxia, tunnel vision or blindness, smell and hearing impairments, and disequilibrium syndrome. More serious cases lead to convulsions, seizures, paralysis, and possibly death. In addition to the outbreak among the townspeople, congenital Minamata disease was observed in babies born to affected mothers. These babies demonstrated symptoms of cerebral palsy (Honda et al., 2006).

map of Japan
Map of Minamata

Doctors struggled to diagnose the mysterious disease when it first was noticed in the early 1950's. Local cats were seen acting strangely before falling over and birds would fall from the sky. In 1959, doctors at Kumamota University determined that organic mercury poisoning was the cause of the symptoms exhibited by so many of the townspeople. However, it was not until 1968 that the Tokyo government acknowledged that the mercury dumping by Chisso was the ultimate cause. Five years later, Chisso admitted legal responsibility for the dumping. Yet the environmental impact on the bay had already occurred. In 1977, the Japanese government took on the huge task of cleaning the sediments in the bay by vacuuming up 1.5 million cubic meters of mercury-contaminated sludge. After $359 million dollars and 14 years, the project was completed in 1997 (McCurry, 2006).

scenic picture

Go To Fish Consumption Advisories
and Mercury Levels

© Copyright 2007, All Rights Reserved, CSA

List of Visuals