Minamata Mercury Pollution Disaster
Minamata and the Chisso Cooperation:
Minamata is a small factory town dominated by the Chisso
Corporation. The town faces the Shiranui Sea, and Minamata Bay is
part of this sea. In Japanese, "Chisso" means nitrogen. The
Chisso Corporation was once a fertilizer and carbicle company, and
gradually advanced to a petrochemical and plastic-maker company.
From 1932 to 1968, Chisso Corporation, a company located in
Kumamoto Japan, dumped an estimated 27 tons of mercury compounds
into Minamata Bay. Kumamoto is a small town about 570 miles
southwest of Tokyo. The town consists of mostly farmers and
fisherman. When Chisso Corporation dumped this massive amount of
mercury into the bay, thousands of people whose normal diet
included fish from the bay, unexpectedly developed symptoms of
methyl mercury poisoning. The illness became known as the
"Minamata Disease". The mercury poisoning resulted from years of
environmental destruction and neglect from Chisso Corporation.
Chisso Corporation started developing plastics, drugs, and perfumes
through the use of a chemical called acetaldehyde in 1932.
Acetaldehyde is produced using mercury as a compound, and was key
component in the production of their products. Not until the mid-1950's did people begin to notice a "strange
disease".
The "Minamata Disease":
Victims were diagnosed as having a degeneration of their
nervous systems. Numbness occurred in their limbs and lips. Their
speech became slurred, and their vision constricted. Some people
had serious brain damage, while others lapsed into unconsciousness
or suffered from involuntary movements. Furthermore, some victims
were thought to be crazy when they began to uncontrollably shout.
People thought the cats were going insane when they witnessed
"suicides" by the cats. Finally, birds were strangely dropping
from the sky. Series of these unexplainable occurrences were
bringing panic to Minamata.
Mercury Concentrations:
Fish & Shellfish Cats Humans
oyster 5.6control 0.9-3.66controlless than 3.0
gray mullet 10.6 kidney 12.2-36.1 kidney 3.1-144.0
short-necked clam 20.0liver 37-145.5liver 0.3-70.5
china fish 24.1brain 8-18brain 0.1-24.8
crab 35.7hair 21-70hair 96-705
Mercury Concentrations in Tissue Samples (ppm)*
Minamata's food chains dramatically illustrate the `concentration of elements'--in this case, of mercury--in successive trophic levels. Assays of tissue from fish and shellfish from the bay, and from cats and humans who died from the poisoning, show high concentrations of mercury. Kidney and liver concentrations indicate how the bodies tried--unsuccessfully--to excrete and detoxify the heavy metal.
Mercury:
The Minamata case is such a vivid example because the town and the bay where the mercury was dumped may be seen as a relatively closed system. The ecological consequences, which are often diffuse and indirect, may be seen as a closed loop: the effects of the effluent led gradually but nevertheless inevitably back to humans. That is, in this exceptional case, one can trace the mercury from its source in Chisso's production process, through the waste water to the organisms inhabiting the bay, and then to the cats or humans consuming the fish and shellfish. As a microcosm, Minamata illustrates the sometimes fuzzy concept that humans and their environment are inextricably interconnected.
(1) Measures against environmental pollution
(Closing down of the pollutant sources)
With regard to the Minamata plant of Chisso Co., Ltd., through the completion of the perfect circulation system in 1966, water effluent containing methylmercury compound had not been discharged outside of the plant in principle, and the pollutant source was eliminated through cessation of the production of acetaldehyde in 1968. In the Agano River basin the process of producing acetaldehyde had already closed before Minamata Disease was discovered.
(Effluent control)
In 1969, drainage of the factory effluent containing methylmercury to Minamata Bay was regutated. In 1970, the Water Pollution Control Law was enacted, which enforced control of discharge of effluent in all water areas in Japan, in relation to toxic substances, for example, mercury and cadmium. Furthermore, conversion of the production method was advised against caustic soda plants that might discharge mercury other than Chisso and Showa Denko plants.
(Restoration of the environment)
Because methylmercury remained a considerable concentration in bottom sediment of the related water areas even after the discharge of the methylmercury compound was stopped, in order to remove this bottom sediment, from 1974 to 1990, Kumamoto Prefecture carried out the project for dealing with about 1,500,000 cubic meters of bottom sediment of Minamata Bay that contained mercury more than the removal standard (25ppm of total mercury) by means of dredging and landfill, and for making 58ha. landfill, at a total cost 48 billion yen (of this total, the responsible company bore 30.5 billion yen). In 1976, Niigata Prefecture carried out dredging river bottom sediment that contained mercury more than the removal standard around the drainage outlets of Showa Denko plant by the burden of the responsible company.
Transition in Pollution Level of fishes
Key Points:
** Early 1950s, strange behavior of "dancing cats" noticed (twitching, stumbling) è brain damage from mercury poisoning
** Mid 1950s, human effects include children born with deformities and mental retardation
** Fish and shellfish from Minamata Bay had high levels of mercury
** Chisso Chemical Plant released mercury into the bay
oo Elemental mercury is not water soluble
oo Assumed would sink to bottom sediments and remain inert
** Bacteria in sediments were able to convert mercury to soluble methylmercury
** 3,500 people affected
** 50 died
** After 20 years of litigation, company admitted guilt and agreed to pay reparations
** Mud containing mercury was dredged and buried elsewhere