Something that pollutes the environment are pollutants. Pollutants are what pollute the environment  while  pollution  is  the  outcome  of that pollutant.  Any substance, as certain chemicals or waste products, that renders the air, soil, water, or other natural resource harmful or unsuitable for a specific purpose. A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource.

CLASSIFICATION OF POLLUTANT

Pollutants can be classified on different basis:

A.Based on degradation

I) Biodegradable  pollutants: Biodegradable  pollutants  get  broken  down  under  natural conditions due to the action of micro-organisms. Therefore they are considerably less harmful.  They  behave  as  pollutants  only  in  very  large  quantities.  Example:  excreta, sewage, etc.

II) 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

I) 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 bypassing on damage that persists well after the benefits received from incurring that damage have been forgotten.

II) 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.