Pollutant

• A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource.
• They come in gaseous, solid or liquid form.
• The substances that actually cause pollution are called the pollutants.

Classification of pollutant

A. Based on degradation

a. Biodegradable pollutants:

• Gets broken down under natural conditions due to the action of micro-organisms.
• They behave as pollutants only in very large quantities. Example: excreta, sewage, etc.

b. Non-biodegradable pollutants:

• Cannot be broken down under natural conditions by the action of micro-organisms or they take an extremely long time to be broken down.
• Example: Common plastics, DDT, metal wastes such as lead, mercury, arsenic, etc.

B. Based on absorption capacity of Environment

a. Stock pollutants:

• Pollutants that the environment has little or no absorptive capacity are called stock pollutants (eg. persistent synthetic chemicals, non-biodegradable plastics, and heavy metals). Stock pollutants accumulate in the environment over time.
• The damage they cause increases as more pollutant is emitted, and persists as the pollutant accumulates.
• Stock pollutants can create a burden for future generations by passing on damage that persists well after the benefits received from incurring that damage have been forgotten.

b. Fund pollutants:

• Fund pollutants are those for which the environment has some absorptive capacity.
• Fund pollutants do not accumulate in the environment unless the emission rate exceeds the receiving environment’s absorptive capacity (eg. carbon dioxide, which is absorbed by plants and oceans).
• Fund pollutants are not destroyed, but rather converted into less harmful substances, or diluted/dispersed to non-harmful concentrations.