Major Types of
Pollutants
The
major water pollutants are chemical, biological, or physical materials
that degrade water quality. Pollutants can be classed into eight
categories, each of which presents its own set of hazards.
Petroleum Products
Oil and chemicals derived from oil are used for fuel, lubrication,
plastics manufacturing, and many other purposes. These petroleum
products get into water mainly by means of accidental spills from
ships, tanker trucks, pipelines, and leaky underground storage tanks.
Many petroleum products are poisonous if ingested by animals, and
spilled oil damages the feathers of birds or the fur of animals,
often causing death. In addition, spilled oil may be contaminated
with other harmful substances, such as polychlorinated biphenyls
(PCBs).
Pesticides and
Herbicides
Chemicals
used to kill unwanted animals and plants, for instance on farms
or in suburban yards, may be collected by rainwater runoff and carried
into streams, especially if these substances are applied too lavishly.
Some of these chemicals are biodegradable and quickly decay into
harmless or less harmful forms, while others are nonbiodegradable
and remain dangerous for a long time. When animals consume plants
that have been treated with certain nonbiodegradable chemicals,
such as chlordane and dichlorodiphenyltrichloroethane (DDT), these
chemicals are absorbed into the tissues or organs of the animals.
When other animals feed on these contaminated animals, the chemicals
are passed up the food chain. With each step up the food chain,
the concentration of the pollutant increases. In one study, DDT
levels in ospreys (a family of fish-eating birds) were found to
be 10 to 50 times higher than in the fish that they ate, 600 times
the level in the plankton that the fish ate, and 10 million times
higher than in the water. Animals at the top of food chains may,
as a result of these chemical concentrations, suffer cancers, reproductive
problems, and death. Many drinking water supplies are contaminated
with pesticides from widespread agricultural use. More than 14 million
Americans drink water contaminated with pesticides, and the Environmental
Protection Agency (EPA) estimates that 10 percent of wells contain
pesticides. Nitrates, a pollutant often derived from fertilizer
runoff, can cause methemoglobinemia in infants, a potentially lethal
form of anemia that is also called blue baby syndrome.
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