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1. When does water pollution occur?
2. Why do plants and animals require pure water?
3. What are the major water pollutants?
4. How can pollutants be separated?
5. How do petroleum products affect the animals?
6. Why can pesticides and herbicides be dangerous if they penetrate into streams, rivers and
lakes?
7. What do heavy metals result in?
8. How do fertilizers penetrate to water?
9. What damage can thermal pollution cause?
текст
Water pollution occurs mostly, when people overload the water environment such as streams,
lakes, underground water, bays or seas with wastes or substances harmful to living beings.
Water is necessary for life. All organisms contain it, some drink it and some live in it. Plants and
animals require water that is moderately pure, and they cannot survive, if water contains toxic chemicals
or harmful microorganisms. Water pollution kills large quantity of fish, birds, and other animals, in some
cases killing everything in an affected area.
Pollution makes streams, lakes, and coastal waters unpleasant to swim in or to have a rest. Fish
and shellfish harvested from polluted waters may be unsafe to eat. People who use polluted water can
become ill, if they drink polluted water for a long time, it may develop cancer or hurt their future children.
The major water pollutants are chemical, biological, and physical materials that lessen the water
quality. Pollutants can be separated into several different classes:
The first class is petroleum products: oil, fuel, lubrication, plastics. The petroleum products get
into water by accidental spills from ships, tanker trucks and when there are leaks from underground
storage tanks. Many petroleum products are poisonous for animals. Spilled oil damages the feathers of
birds and the fur of animals, often it causes death.
The second class is pesticides and herbicides. There are chemicals used to kill harmful animals
and plants. If they penetrate into streams, rivers, lakes, these chemicals can be very dangerous. The
chemicals can remain dangerous for a long time. When an animal eats a plant that's been treated with it,
the poisons are absorbed into the tissues and organs of the animals.
When other animals feed on a contaminated animal, the chemicals are passed up to them. As it
goes up through the food chain, the chemical becomes more harmful, so animals at the top of the food
chains may suffer cancers, reproductive problems, and death. Nitrates can cause a lethal form of
anaemia in infants.
The third class is heavy metals. They get into the water from industries, automobile exhausts,
mines, and natural soil. Heavy metals also become more harmful as they follow the food chain. They
accumulate in living being's cells and when they reach high levels of concentration in the organism, they
can be extremely poisonous, or can result in long-term health problems. They can sometimes cause liver
and kidney damage.
The fourth class is fertilizers and other nutrients used to promote plant growth on farms and in
gardens.
The fifth class is infectious organisms and pathogens. They enter water through sewage, storm
drains, runoff from farms, etc.
The last one is thermal pollution. Water is often taken from rivers, lakes or seas to be used in
factories and power plants. The water is usually returned to the source warmer than when it was taken.
Even a small temperature change in a body of water can drive away the fish and other species that were
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originally there, and attract other species in place of them. It breaks a balance and can cause serious
circumstances in future.