BIOACCUMULATION AND BIOMAGNIFICATION - Marine Pollution: What Everyone Needs to Know - page 148

mollusks, agencies use the degree of chemical contamination
as part of the classification of harvesting waters; they allow
harvesting from some waters, not from others, or only at cer-
tain times or under certain conditions.
What is Minamata disease?
The first example that made the world aware that the accumu-
lation of contaminants in edible seafood could harm humans
was in Minamata, Japan. This community had a factory that
used Hg in the production of plastics and discharged Hg
into the nearby bay, from which the people ate fish that had
accumulated it in their tissues. From 1932 to 1968, the Chisso
Corporation dumped an estimated 27 tons of Hg compounds
into Minamata Bay. The Hg became methylated in the sedi-
ments of the bay, and then biomagnified up the food web.
Methylmercury, the form that is especially toxic and biomag-
nifies in food webs, is produced by bacteria in the environment
(Figure 5.1). Thousands of residents developed severe neu-
rological and developmental defects, a condition now called
Minamata disease, alerting the world that exposure to Hg can
cause permanent behavioral and neurological effects. Severe
cases led to insanity, deformation, and death. Many children
whose mothers had eaten contaminated fish while pregnant
were born with major disabilities. Congenital Minamata dis-
ease was observed in babies born to affected mothers, but also
to mothers who did not have severe problems. These babies
had symptoms of cerebral palsy. Affected people had numb-
ness in their limbs and lips, slurred speech, and impaired
vision. Some people had serious brain damage. Even before
the symptoms appeared in the people, the cats in the village
showed symptoms of Hg poisoning. The cats, which ate scraps
of fish from fish markets and the table, died with symptoms
similar to those only later seen in humans. People initially
thought the cats were going insane when they witnessed their
odd behavior. This led researchers to believe that the outbreak