Differentiate between primary and secondary pollutants.

Now-a-days, you might have heard every one talking about pollution. What does pollution mean? Pollution is the addition to the environment (air, water, soil) of substances or energy (heat, sound, radioactivity, etc.) at a rate, and in quantities that are harmful to life. Pollution has a long history. It became noticeable when larger and larger numbers of people began to live in cities. Unplanned growth of the cities,led to difficulties in the disposal of garbage and sanitary wastes. Living .;pace was often shared with animals as is sometimes done in lndia even now. Mud, slush and dusty roads added to the pollution. Air, water and soil, acquired many harmful substances, in the form of wastes, from human activities.

The waste materials (pollutants) that cause pollution are of two types:

i)                   those that remain in an unchanged form for a long time and are known as persistent pollutants,e.g. pesticides, nuclear wastes, and plastlcs etc. Many of these are toxic; those that break down, into simple products, and are known as non-persistent pollutants, e.g., garbage. If this break down process is facilitated by living organisms, then such pollutants are referred to as biodegradable pollutants, e.g., wastes fromanimal sheds.