Contamination of the environment with waste products and other impurities is called pollution. And the substances whose presence in air, water or soil is harmful to human beings, animals, plants and soil are termed as pollutants (fig. 20.6)
20.4.1 Types of pollution
Pollution may be classified as
- Air pollution
- Water & soil pollution
- Sea pollution
- Radiation
- Noise
Fig. 20. 6 Air pollution
Air pollution
Air pollution is mainly caused by dust, sulfur dioxide, carbon dioxide, carbon monoxide, nitrogen oxides, hydrocarbons and ozone. Common sources of air pollution are;
- Fuel gases from garbage burning.
- Exhaust gases from fossil fuels burning in industries and auto motives.
Water and soil pollution
This includes untreated sewage, pesticides and fertilizers, inorganic compounds, waste from radioactive metals, heavy metals like mercury, cadmium, arsenic etc. sources of water and soil pollution are;
- Municipal wastes
- Industrial wastes
- Agricultural wastes
Effects of pollution on environment
The environment is being severely damaged by the pollution and is becoming hostile or unfit for the survival of many forms of life including mankind. Following are some of the effects of pollution on environment.
- Sulfur dioxide damages leaves of plants. It corrodes metallic and stone structures.
- Higher concentrations carbon dioxide are harmful to animals.
- Carbon monoxide combines with hemoglobin to reduce oxygen in blood.
- Oxides of nitrogen corrode metals and stones. They produce photo chemical smog that inhibits the plants growth.
- Higher concentrations of ozone reduce air visibility and cause health problems e.g. eyes irritation and headache.
- Untreated sewage is a source of germs causing cholera and typhoid etc.
- Densely populated bacteria in water due to pollution consume the oxygen of water, effecting the water animals and even death of fishes.
Ozone depletion
Oxygen in the upper atmosphere forms ozone that forms a layer over the earth. This ozone shield filters out the ultraviolet rays of the sun and protects the earth from being damaged.
Ozone shield may be in danger of breaking due to air pollutants particularly nitric oxide and chlorine atoms that attack the ozone layer. Nitric oxides come from emission of aircrafts exhaust and chlorine is released by aerosol pollutants (refrigerants) called chlorofluorocarbons (CFC).
Green house effect
Sun rays reach to our earth in the form of visible light and raise the temperature of the earth. This heat energy absorbed by the earth radiates back to space thus temperature of earth remains in balance.
From burning of fossil fuels, much carbon dioxide is produced in atmosphere. About half of this is utilized by plant life or absorbed by the ocean water and the remaining goes on accumulating in the lower areas of atmosphere forming a thick dense layer of carbon dioxide. This thick layer inhibits the re-radiation of atmosphere forming a thick dense layer of carbon dioxide. This thick inhibits the re-radiation of heat energy absorbed by earth back to space and adds more temperature to surface of earth. This warming of earth surface is called green house effect. The thick layer of gas acts like glass of green house that allows the incoming solar radiation but prevents the emission of the outgoing heat waves.
Biological Oxygen Demands (BOD)
It is a measure of water pollution level due to sewage and other organic matter. Biological oxygen demands (BOD) is the amount of oxygen needed by microbes to decompose the organic matters of water in a fixed period of time, normally 5 days. So large amount of sewage waste in water creates a high BOD, which robs the water of dissolved oxygen.
Acid rain
Sulfur dioxide and oxides of nitrogen react with oxygen and rain water readily to form sulfuric acid &nitric acid respectively. Rain containing these acids is known as acid rain.
Large amounts of acid rain may cause death of fish in lakes and rivers. Acid rain dissolves aluminum slats in the soil and washes them into lakes and rivers. High concentrations of these salts are poisonous to fishes.
How to control pollution?
Some of the important measures to be taken for pollution control are;
- Use of lead free and low sulfur fuel oils.
- Appreciated use of environmental friendly products e.g. natural gas and liquefied petroleum gas in place of high speed diesel and furnace oil.
- Use of wet scrubbers in chimneys of power plants to remove sulfur dioxide.
- Adequate maintenance of auto vehicles for proper ignition.
- Installation of heavy process industry far from populated areas.
- Minimum use of non-biodegradable products.
- Use of narrow spectrum biocides.
- Installation of sewage treatment plants.
- Maximum possible arrangements for recycling of wastes.
- Use of incinerators to handle municipal and hospital solid wastes.
- Maximum forestation.
Fig. 20. 7 Acid Rain