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Unformatted text preview: ermethrin 3.3.4 Minamata and environmental
toxicity of mercury
The environmental toxicity of mercury is a
good example of the interaction of three
important properties of a substance. These
are: toxicity, volume of use (as an
industrial substance, the release of which
was poorly regulated and controlled) and
mobility. In the case of mobility, an important principle is illustrated, that of biological transformation in the environment. The effect
of this problem was relevant to humans, however, similar biomagnification also occurs in
organisms at the top of the food chain such as predatory fish, dolphins, and whales.
The city of Minamata is situated on a bay in the Yatsushiro Sea on the south island of Japan. The
bay is sheltered and the tidal range makes it a good habitat for the production of seafood such as
molluscs and seaweed. In the 1950s, Minamata City was the location of the Shin Nihon Chisso
Co., a manufacturer of PVC for which mercury was used as a catalyst.
The symptoms of the disease that developed in Mina mata were probably first noticed in cats and
in humans. Human symptoms were those of degeneration of the nervous system with loss of
vision, hearing, speech and motor control predominating. Fatalities were as great as 40% of
those affected with the sympt oms. The disease was also observed in newborns as being similar
to cerebral palsy. The mother was often unaffected although the fetus was more sensitive, either
through a greater accumulation of mercury or through greater sensitivity of the developing
nervous system. Similar symptoms were noted in cats which showed tremors and unusual
behavior. Crows and other scavenging birds were affected and were reported to have dropped
dead or dying from the sky. Other animals were probably affected but this was n ot noticed at the
time. Of the 40 affected families, all had cats and, of these 82%, died of mercury poisoning.
The disease was not immediately recognized as such, in fact, in the early 1950s, tonnes of
mercury were still being released into the bay while doctors were searching for the elusive cause
of the disease. The sequence was as follows: Date
Factory wastes directed to Minamata Bay. 1951 First cases appeared but not recognized. 1952 A few cases each year but mercury use
Sick children reported to the hospital, 40 cases
identified, University Medical Team becomes
Fishing banned but cases continue and spread to
greater distances from the bay. 1956 1957
1959 Assessment Pathogens eliminated
Most likely trace
eliminated as cause but toxins Mercury suspected as cause, but not inorganic
1963 111 cases confirmed, 41 dead. 1966 Chronic subclinical cases identified. 1973 704 cases confirmed, 83 deaths. 1975 Investigation
mercury compounds begins.
Methyl mercury identified as
Sediment recognized as a
potential risk. 899 cases confirmed, 143 deaths. With the recognition of the problem and mercury dumping as a cause, the factory was re...
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This document was uploaded on 04/07/2014.
- Fall '14
- The Land