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Large and small craft significantly pollute both inland and coastal waters
by dumping their untreated sewage. Oil spilled accidentally or flushed
from tankers and offshore rigs (900,000 metric tons annually) sullies
beaches and smothers bird, fish, and plant life. In 1989 in one of the
world's worst single instances of water pollution, the Exxon Valdez
spilled 11 million gallons of oil in Prince William Sound, Alaska, causing
great environmental destruction. In 1997, the 22 oil spills reported
worldwide involved a total of 15 million gallons (57 million liters) of
oil. In addition to its direct damage to wildlife, oil takes up
fat-soluble poisons like DDT, allowing them to be concentrated in
organisms that ingest the oil-contaminated water; thus such poisons enter
the food chains leading to sea mammals and people.
Both DDT, which has been
banned in the United States since 1972, and PCBs are manufactured in many
parts of the world and are now widespread in the Atlantic and Pacific
oceans. In addition, tarry oil residues are encountered throughout the
Atlantic, as are styrofoam and other plastic rubbish. Plastic bits litter
sections of the Pacific as far north as Amchitka Island near Alaska.
Garbage, solid industrial wastes, and sludge formed in sewage treatment,
all commonly dumped into oceans, are other marine pollutants found
worldwide, especially along coastal areas. |