Mercury: Minamata Bay
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Methylmercury poisoning in Minamata Bay, Japan

(More extensive notes on Minamata are available here )

During the 1960/70’s, the Minamata Bay mercury pollution problem received world-wide media attention, opening the world’s eyes to the negative health effects of methylmercury and contributing to raising public awareness of the importance of environmental protection. More than forty years ago, Minamata Bay in Japan was seriously polluted by wastewater containing methylmercury, formed as a by-product in the acetaldehyde synthesizing process of the local acetaldehyde chemical plant; 70-150 metric tons or more of mercury, mixed in the effluents from the factory, were discharged over a number of years into the Bay. The pollution affected the people of Minamata in the form of methylmercury poisoning, referred to as "Minamata disease", causing damage to the central nervous system in people eating large quantities of contaminated fish and shellfish from Minamata Bay. In addition, Congenital Minamata disease occurred, in which victims were born with a condition resembling cerebral palsy, caused by methylmercury poisoning of the fetus via the placenta when the mother consumed contaminated seafood during pregnancy. The numbers of people affected vary in reports over the world for reasons that are possible to explain (see ) but it is officially accepted that the number of people affected is in the region of 3,000.

The disease, which was officially recognized on 1 May 1956 (although legal action over responsibility continues to the present day), severely affected the local community and was a great burden to the city. Many people lost their lives or suffered from physical deformities and have had to live with the physical and emotional pain of "Minamata Disease" since. After the cause of the disease was finally confirmed, a number of measures were gradually implemented to deal with the problems arising from the mercury pollution, ranging from regulation of the factory effluent, voluntary restrictions on harvesting of fish and shellfish from the Bay, installation of dividing nets in order to enclose the mouth of the Bay and prevent the spread of contaminated fish, to dredging of mercury-containing sediments in the Bay and appropriate deposit to contain the mercury-contaminated sludge. Finally, in October 1997, the dividing nets that had closed off the bay for 23 years were removed. After several studies confirming that mercury levels in fish were below regulatory levels and had remained so for three years, Minamata Bay was reopened as a general fishing zone and the Minamata Fisheries Co-op recommenced harvesting for the fish market

(Minamata City, 2000).

The National Institute for Minamata Disease was formed to investigate the impacts of mercury contamination, and has contributed substantially to the knowledge of mercury toxicology and exposure both nationally and in other regions of the world since then. The Ministry of Environment of Japan, in its report "Our Intensive Efforts to Overcome the Tragic History of Minamata Disease (JME, 1997)" concludes:

"From the incidence of Minamata Disease, Japan has learned a very important lesson on how activities that place priority on the economy, but lack consideration for the environment can cause grave damage to health and environment, and how it is difficult to recover from this damage later on. From the purely economic standpoint, too, a large amount of cost and a great deal of time are required to deal with such damages, and, when we compare these costs incurred vs. the cost of the measures that could have prevented the pollution, allowing such pollution is certainly not an economically advisable option. In our country, with the experience of suffering from disastrous damage by pollution including the Minamata Disease as a turning point, measures to protect the environment have made dramatic progress. But the sacrifices incurred on the way were truly huge, indeed.

We sincerely hope that Japan's experience can be utilized as a vital lesson by other countries, that consideration is paid to the importance of the environment, and that pollution will be prevented without ever undergoing this kind of tragic pollution-related damage."