All living organisms depend upon a balanced environment for growth, development and reproduction.
All the components required by the organisms are present in the environment. When the balance of the environment gets disturbed for one reason or the other survival of living organisms becomes difficult.
This balance of the environment may be disturbed by the entrance of some harmful and unwanted components in the environment.
These unwanted, harmful components make the environment polluted. This is called pollution. Thus, any undesirable change of the physical, chemical or biological characteristics of the environment, which is harmful to man directly or indirectly through animals, plants, industrial units or raw materials, is called pollution. The substance which contaminates air, water and soil are called pollutants.
The pollutants can be classified into two groups:
1. Biodegradable pollutants
2. Non-biodegradable pollutants.
1. Biodegradable pollutants:
Those pollutants which can be broken down into simpler, harmless, substances in nature in due course of time (by the action of micro-organisms like certain bacteria) are called biodegradable pollutants. Domestic wastes (garbage), urine, faecal matter, sewage, agriculture residues, paper, wood, cloth, cattle dung, animal bones, leather, wool, vegetable stuff or plants are biodegradable pollutants.
2. Non-biodegradable pollutants:
Those pollutants which cannot be broken down into simpler, harmless substances in nature, are called non-biodegradable pollutants. DDT, plastics, polythene, bags, insecticides, pesticides, mercury, lead, arsenic, metal articles like aluminum cans, synthetic fibres, glass objects, iron products and silver foils are non-biodegradable pollutants.