Ocean Pollution
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,
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are other marine pollutants found worldwide, especially along coastal areas.
Industrial Pollution
In the United States industry is the greatest source of pollution, accounting for more
than half the volume of all water pollution and for the most deadly pollutants. Some
370,000 manufacturing facilities use huge quantities of freshwater to carry away
wastes of many kinds. The waste-bearing water, or effluent, is discharged into
streams, lakes, or oceans, which in turn disperse the polluting substances. In its
National Water Quality Inventory, reported to Congress in 1996, the U.S.
Environmental Protection Agency concluded that approximately 40% of the nation’s
surveyed lakes, rivers, and estuaries were too polluted for such basic uses as
drinking supply, fishing, and swimming. The pollutants include grit, asbestos,
phosphates and nitrates, mercury, lead, caustic soda and other sodium compounds,
sulfur and sulfuric acid, oils, and petrochemicals.
In addition, numerous manufacturing plants pour off undiluted corrosives, poisons,
and other noxious byproducts. The construction industry discharges slurries of
gypsum, cement, abrasives, metals, and poisonous solvents. Another pervasive
group of contaminants entering food chains is the polychlorinated biphenyl (PCB)
compounds, components of lubricants, plastic wrappers, and adhesives. In yet
another instance of pollution, hot water discharged by factories and power plants
causes so-called thermal pollution by increasing water temperatures. Such increases
change the level of oxygen dissolved in a body of water, thereby disrupting the
water’s ecological balance, killing off some plant and animal species while
encouraging the overgrowth of others.