Environmental pollution, in general, may be described as the contamination of the environment with harmful wastes arising mainly from human activities. These activities release certain materials which produce pollution. The various systems of the environment that can be polluted are as follows:
(i) Air. Air comprises a blanket of gaseous layer that extends to a height of about 1600 km above the surface of earth. It consists of gases like N2, O2, H2O(g) as major components, Ar, CO2 as minor components and nobel gases, oxides of nitrogen, Nox, oxides of sulphur (SOx), H2, O3 as trace components. This part of environment is called atomosphere which protects the life on the earth from harmful radiations coming from outer space and sun.
(ii) Water. This comprises about 75% of earth’s surface and includes all the sources of water like oceans, rivers, lakes, glaciers, ground water, etc. This part is commonly called hydrosphere.
(iii) Land. It refers to the earth’s solid crust containing the outer mineral cover like soil, rocks, mountains, etc. Soil is upper most part of earth’s crust which contains weather rocks and organic matter. This part is commonly called lithosphere.
After studying this until the students will be able to:
- explain pollution
- describe natural air pollution
- describe human activities that cause pollution
- describe atmospheric events such as acid-rain, greenhouse effect and ozone depletion
- describe the effects of air pollution
- describe the source of water pollution
- describe the sources of land pollution
Environmental pollution may be defined as direct or indirect changes as a result of human activities, which adversely influence the biological and nonbiological equilibrium of the environment. The environmental pollution may be caused by:
Chemical agents (gases, pesticides, particulates),
Physical agents (heat, noise, radiation) or
Biological agents (micro-organisms).
Pollution produces adverse effect on living as well as non-living materials. For example, it can:
- cause illness or even death in case of humans and animals.
- retard the growth of plants and may cause them severe injury.
- result in corrosion of metals, marble and decolourise paints.
Do You Know?
Some Episodes of Environmental Pollution
(i) About 4000 people died in England in 1952 due to respiratory diseases because of London smog.
(ii) In Japan, thousands of people died during 1953-1960 period by the consumption of fish from polluted Minamta Bay.
(iii) In 1984 about 3500 people died in Bhopal (India) due to leakage of methyl isocyanate vapours. Very large number of people are still suffering from respiratory, lung, eye and throat diseases.
(iv) Radioactive emission from the use of the nuclear weapons in Hiroshima and Nagasaki during second world war resulted heavy loss of human lives.
(v) Consumption of polluted wheat in Iraq resulted loss of about 500 human lives in 1972.
(vi) Acid rains in Greece and Italy caused damage to historical marble statues. Sulphur dioxide emissions are effecting the beauty of Tajmahal in Agra (India).
(vii) Thousands of people lost their lives in Ukrain area of Soviet Union due to world’s worst nuclear disaster.
Any substance or species produced either by a natural source or by human activity, which produces adverse effect on the environment is called pollutant. Some common examples of
pollutants are carbon monoxide, oxides of sulphur (SO2, SO3), oxides of nitrogen, pollens, dust particles, etc .
It may be noted that a name pollutant is given to a substance which is already present in nature but human activity increase its concentration beyond undesirable limit so that it becomes
harmful to natural environment. Quite often pollutants are thought be highly toxic substance only, but even the substances which are normally considered harmless can cause
pollution if they are present in undesirable concentrations or in the wrong places at the wrong time. For example, nitrates are added to soil to increase plant growth but excessive
concentration of nitrates in drinking water can be toxic.
A substance which does not occur in nature but is introduced by human activity into the atmosphere affecting its composition is called contaminant, It may or may not be
harmful to the living organism or non-living component.
The site from which the pollutants or contaminants originate is called source. The source is particularly important because its knowledge helps us to develop the methods to eliminate
The material or medium which consumes or interacts with a long lived pollutant is called sink. For example, a marble wall acts as a sink for atmospheric sulphuric acid because of
CaCO3 + H2S04 → CaSO4 + H2O + CO2
Similarly, the oceans act as sink for atmospheric carbon dioxide and other water soluble gases. Ground water and subsoil water also act as sinks for pesticides used in agriculture.
Anything that is affected by the pollutants is called receptor. For example, human beings are the receptor of photochemical smog which cause irritation in the eyes and also breathing
6. THRESHOLD LIMIT VALUE (TLV)
This indicates the permissible limit of a pollutant in atmosphere to which a healthy worker is exposed during 8 hours a day or 40 hours a week for life time without any adverse effects. TLVs are determined by experimentation on animals, by use of medical know ledge, epidemiology surveys and environmental studies.
For example, TLV of CO is 40 ppm and that of CO2 is 5000 ppm. But TLV for a poisonous gas phosgene is only 0.1 ppm,
The environmental pollution process may be summarized as a follows. A pollutant originates from source and, gets transported by air or water or it is dumped by humans on land. Some of the pollutants may be assimilated (absorbed) or chemically changed by the environment while the rest build up their concentrations slowly and gradually and become harmful to the environment.
This has been shown in the flow sheet in Fig. 52.1.