Pollution is the effects by different agents which results in the damage of environment. Pollutants can be classified according to their nature and decomposition levels. On the Basis of Nature

Depending upon the nature of the pollutants and their interaction with environment process, the pollution caused by different agents can be classified into the following categories:

1) Pollution Caused by Solid Wastes:The solid wastes includes the pollutants like garbage, rubbish, ashes, large wastes formed due to demolition and construction processes, dead animals wastes, agricultural wastes, etc.

2) Pollution Caused by Liquid Wastes:Oxygen cycle is nicely operated in aquatic system maintaining ecological balance. That is, the dissolved oxygen is used by aquatic living organisms for their respiration and in return, these liberate carbon dioxide. Carbon dioxide molecules are again used by green plants and algae in the process of photosynthesis. During photosynthesis, oxygen is again liberated to water which remains in dissolved state.On the Basis of Decomposition

1) Non-Degradable Pollutants:These are not broken down by the natural processes like action of microbes. Most of these pollutants get accumulated in the environment and also get biologically magnified as these moves along the food chains in an under-composed state. These may also react with other compounds in the environment to produce toxins. These can be further sub-divided into two more classes:

i) Waste: e.g., glass, plastic, phenolics, aluminium cans, etc.

ii) Poisons: e.g., radio-active substances, pesticides, smog gases, heavy metals like mercury, lead and their salts.

2) Degradable Pollutants or Bio-degradable Pollutants:These are natural organic substances which can be decomposed, removed or consumed and thus, reduced to acceptable levels either by natural processes like biological or microbial action or by some engineered systems, like sewage treatment plants