Pollution is usually brought about by the addition of waste product of human activity to the environment are called pollutants.
Pollutants are the physical or biotic component which adversely alters the environment by altering growth rate of species, interfere with the food chain, health, comfort or properties, value of man.
Classification of Pollutants :
Pollutants are classified as follows:
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(1) Primary Pollutants:
These substances emitted directly from an identifiable source. These pollutants exist as such after being added or related into the environment e.g., sulphurdioxide, nitrogen oxide etc.
(2) Secondary Pollutants:
These are substances, derived from primary pollutants by chemical reactions e.g., primary pollutants such as hydrocarbons and nitrogen oxide, react in presence of sunlight to form a group of nitrous compounds like peroxyacetyl nitrate (PAN) as the secondary pollutants.
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From the view point of ecosystem, the pollutants are further classified as under:
These include domestic sewage, heat etc. The domestic sewage can be readily decomposed by natural processes which enhance capacity of the nature to decompose and recycle. These are called biodegradable pollutants.
Non-biodegradable Pollutants :
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These are many pollutants such as Aluminium, Iron, Mercury salts, phenolic compounds and DDT etc. which either do not degrade or degrade only very slowly or partially, and therefore pollute the environment. Such pollutants are termed as non-biodegradable pollutants.