Pollutants: Any substance produced either by a natural source or by human activity which causes adverse effect on the environment is called pollutant.

Pollutants can be of the following types depending upon the following factors.

Classification on the Basis of Their Degradation

(i) Biodegradable pollutants- Pollutants capable of being degraded by biological or microbial actions are called biodegradable pollutants, e.g., domestic sewage.

(ii) Non-biodegradable pollutants- The substances which are normally not acted upon by microbes are called non-biodegradable pollutants. These undergo biological magnification.

They can further be of two types

(i) Wastes- e.g., glass, plastic, phenols

(ii) Poisons- e.g., radioactive substances, Hg salts, pesticide-heavy metals.

Primary Pollutants  Examples vs Secondary Pollutants Examples

Classification on the Basis of Their Occurrence in Nature
a) Primary pollutants: These are present in same form in which these are added by man e.g., DDT, pesticides, fertilizers etc.

b) Secondary pollutants :These occur in different forms and are formed by the reaction between the primary pollutants in the presence of sunlight e.g., HNO3, H2SO4, PAN, ozone etc.

Classification on the Basis of Their Existence in Nature

a) Quantitative pollutants: These are naturally present in nature and also added by man. These become pollutants when their concentration reaches beyond a threshold value in the environment, e.g., CO2, nitrogen oxide etc.

b) Qualitative pollutants: These are not present in the nature but are added by nature only due to human activities, e.g.pesticides, fungicides, herbicides etc.

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