ICSE Class 8 Biology Oxford Chapter 06 Pollution

Pollution

Learning Outcomes

Air pollution

Water pollution

Soil pollution

Noise pollution

Setting personal goals and practicing methods of reducing pollution

Figures (a) to (c) show the impact of various human activities on different natural resources. Look at these pictures carefully and try to answer the questions given below.

Questions

1. Can you guess which natural resources are being affected in each of these pictures?

2. Which human activities do you think are affecting these resources?

3. Is the impact of human activities on these resources likely to be beneficial or harmful?

The release of harmful substances, mostly resulting from human activities, into the environment is termed pollution. Pollution adversely affects natural resources such as air, water, and soil. A substance that causes pollution is termed a pollutant.

Note: We can also say that pollutants contaminate the environment. Contamination is the process of making a pure substance impure, infected, or corrupt.

Organisms, including humans, cannot thrive in a polluted environment. The pollutants accumulated in the environment over a period of time can be a serious threat to its inhabitants. In this chapter, we will discuss different kinds of pollution.

Pollution is mainly of four types: air pollution, water pollution, soil pollution, and noise pollution.

Air Pollution

Air pollution is the presence of harmful substances in air, which adversely affect our health or cause other harmful environmental effects.

Sources

Following are the chief sources of air pollution.

1. Automobile exhaust - The exhaust fumes from automobiles contain nitrogen monoxide, carbon monoxide, hydrocarbons, lead, and carbon dioxide, some of which are highly poisonous.

2. Industrial and domestic emissions - The burning of fossil fuels such as coal and oil results in the release of fumes and smoke containing large amounts of sulphur dioxide and solid particles (soot and dust). Hydrocarbons, carbon monoxide, carbon dioxide, and nitrogen oxides are also released.

3. Atomic waste - The radioactive materials produced in an atomic blast also cause air pollution.

Major Air Pollutants

Carbon monoxide (reduces oxygen-carrying capacity of blood)

Sulphur dioxide and nitrogen dioxide (contribute to acid rain)

Fly ash, asbestos, and hydrocarbons (damage lungs)

Radioactive particles (cause cancer/genetic defects)

Effects

Following are the main effects of air pollution.

1. Nitrogen monoxide reacts with oxygen in the atmosphere and produces the highly toxic nitrogen dioxide, which damages the lining of the lungs and may cause bronchitis and cancer.

2. Carbon monoxide combines with haemoglobin in the blood and impairs or prevents the transport of the much needed oxygen to the brain and other parts of the body. This shortage of oxygen, if mild, causes headache and dizziness, but in extreme cases leads to convulsions, unconsciousness, and even death. These effects, arising from the presence of carbon monoxide in the body, are referred to as carbon monoxide poisoning.

Fact File: Carbon monoxide poisoning produces symptoms such as depression, emotional disturbances, and hallucinations. Interestingly, several incidents associated with the so-called 'haunted houses' (such as strange visions and sounds and unexpected death of all inhabitants) can, in fact, be attributed to carbon monoxide poisoning!

3. Hydrocarbons released as a result of burning fossil fuels undergo chemical reactions in the presence of nitrogen monoxide and sunlight, resulting in the formation of peroxyacetylnitrate (PAN) and formaldehyde. These pollutants cause watering of the eyes and damage to the lungs. Vegetation is also affected. Some hydrocarbons can even cause cancer.

4. Lead present in automobile exhaust can gradually accumulate in the body, causing lead poisoning. Lead poisoning affects the nervous system and the kidneys. The use of petrol containing lead compounds aggravates this problem.

5. Sulphur dioxide, a colourless acidic gas, is a major air pollutant in industrial cities where coal and oil are used in large quantities. Besides causing extensive damage to vegetation and reducing crop yields, it can adversely affect the health of humans and of livestock.

6. Acid rain, caused by the accumulation of sulphur dioxide in the atmosphere, damages forests and agricultural crops, besides adversely affecting aquatic life in streams and lakes. It can wear away or corrode stone work and metal fittings in building (particularly marble) (Fig. 6.1) and, thus, pose a threat to historical monuments such as the Taj Mahal. Corrosion is a process of eating into or wearing away gradually, especially by chemical action, by which materials are gradually destroyed over a period of time.

7. The solid particles emitted by factories, in the form of smoke, pose serious health hazards.

8. Smog is produced when smoke is mixed with fog. The smog forms a 'blanket', up to a few hundred feet above the ground, and prevents pollutants from escaping into the upper atmosphere. The pollutants trapped below the blanket of smog may reach abnormally high concentrations. Those who inhale this polluted air risk suffering from chronic diseases and even death. Such disasters have struck many industrial cities all over the world. Smog, at times, also disrupts road, rail, and air traffic by causing poor visibility.

Fact File: The word smog is derived from the words smoke and fog. In December 1952, over 4000 Londoners lost their lives due to smog that lasted for almost a week.

9. The ozone layer, situated 30 km above the Earth's surface, protects us against lethal ultraviolet rays of the sun. Chemicals called chlorofluorocarbons (CFCs) (used as propellants in aerosols, as refrigerants in refrigerators, and as coolants in air conditioners) damage the ozone layer.

10. Strontium 90 is a fission product released during nuclear tests. Absorbed by plants, it enters the food chain and gradually finds its way to human bodies, where it accumulates, particularly in bones and milk. Lactating mothers pass it on to their babies through breast feeding. Strontium 90 damages the blood-forming centres in the bone marrow.

Prevention

A few steps that can be taken to prevent air pollution are listed below.

1. Pollution from automobiles can be prevented by adopting cleaner fuels such as CNG (compressed natural gas).

2. Use of car pools and public transport should be encouraged.

3. Unleaded petrol should be used in vehicles.

4. Use of tall chimneys in factories can help in dispersal of pollutants (Fig. 6.2).

5. Domestic garbage should not be burned in open.

6. Nuclear wastes should be disposed off safely.

Fact File: The Delhi Transport Corporation (DTC) operates the world's largest fleet of CNG buses.

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