These are defined as the substances which cause pollution. They can be physical or chemical. They involve the smoke, gases and heat etc. They are mostly the waste product or their by products. Sometimes it is necessary to add them for the benefit. For example, the soil needs a phosphate and nitrates for its fertility. They may cause the water pollution too. The pollutants cause an adverse effect on the environment. The increase in concentration of carbon dioxide and the decrease in the concentration of oxygen also cause the pollution. The pollutants are classified into different types and they depend on the form, existence and the natural disposal. On the basis of the form they can be primary or secondary pollutant. The primary pollutants are those which maintain their form in the environment. It includes the DDT. The secondary pollutants are those which are not able to maintain their form in the environment. It includes the peroxyacyl nitrate which is formed due to the reaction between the primary pollutants like the hydrocarbons and nitrogen oxides. On the basis of the existence they can be qualitative or quantitative. The qualitative pollutants are those which do not occur in the environment normally but occur due to the human activities. It includes the DDT, fungicides etc. The quantitative pollutants are those which occur in the environment normally but do occur due to the human activities also. It includes the CO, CO2. On the basis of the natural disposal they can be biodegradable and nondegradable. The biodegradable pollutants are those in which the waste products are degraded slowly by the microbes. When the production is more than the capacity it results in the pollution of environment. The non biodegradable pollutants are those in which the waste products are not degraded slowly by the microbes. It includes the DDT, glass, plastics, phenols, radioactive substances and metal containers.
There are different types of pollution. This includes the air, water, soil, radioactive and noise pollution.