CHEMISTRY - Environmental Pollution

The addition of any undesirable material to air, water and soil by natural source or due to human activity to sucha level of concentration which adversely affect the quality of environment is called an "Environmental Pollution". The undesirable material thus added to the environment is called a "Pollutant".
There was a time when our ancestor used to talk to purity in everything that we needed for our growth. However, with the advancement in technology and industrilisation, such undesirable material are being added into the environment that have disturbed this ecological balance . Today everything is polluted. The air we breathe in is polluted by the exhaust gases due to increase in vehicles, the fruit and vegetables are polluted due to use of pesticides added into the soil and water is polluted due to toxic effluent being thrown into seas, rivers and lakes by the industries.
Environmental pollution affects human beings, animals, plants as well as materials. It does not only slow down growth of plants or bring illness to human being but can cause havoc. A few episodes that have occured in the recent past due to environmental pollution are given below :-

* In 1952, about 4000 people died in london due to respiratory diseases ( London smog ).
* During 1953-1960, hundereds of Japanese died due to eating of fish from polluted Minamata Bay.
* The use of nuclear weapons in Hiroshima and Nagasaki killed thousands of people and the subsequent emition of radiations affected hundereds of thousands of people.
* In 1972, about 500 Iraqis died after consuming polluted wheat.
* In Greece and Italy, the historic marble statues have been damaged by acid rain.
* Sulphur dioxides fumes are affecting the whiteness of the marble of Taj Mahal and making it pale.
* In the Ukaraine area of Soviet Union, thousand people had lost their lives due to the world's worst nuclear disaster.

The main cause of pollutuion are :-
1. Fast population growth.
2. Rapid urbanisation.
3. Excessive Industrilisation.
4. Use of pesticides in Agricultures.

It is important to mention here that in a number of cases, the effect of the pollutant does not remain localized. Some of these pollutants are carried by air or by other means so rapidly that their effect can be felt within days or weeks in almost all parts of the world. Foe example, if a nuclear test is carried out in any part of the world, its fall out can be detected in any other part of the world within a very short period. Similarly, pesticides such as DDT have been found to have the adverse effect on animals living thousands of kilometer away from the place of their actual use.
The gradual increase in population has now reached alarming pproportions. Developed countries started taking steps to check population since early sixities. In 1970, they celebrated, ' Earth Day ' which was organised by United Nations. In 1972, United Nations held a conference on human environment at Stockholm. Since than the developing countries including india have also become concious to protect their environment. The first step taken by Govt. of India was to set up Central Ganga Authority to take necessary steps to purify the water of Ganga aand to make it pollution free. The latest step taken is the use of CNG (Condesed Natural Gas) in place of petrol and diesel in metropolitan cities.

Difference between a pollutant and a contaminant :- A contanimant is a substance which does not occur in nature but is introduced into the environment by human activity. It may or may not be harmful to the living organism or non-living components. On the other hand, a pollutant is a substance produced either by natural sources or by human activity or by the combined effect of both such that the concentration of that substance becomes so high in the environment that it has harmful effect on the living organismor non-living components. Example of pollutant include oxides of nitrogen, dust particle etc. One well known example of contaminant is that of pyrosulphuric acid that had leaked from a defective tank in Delhi killing many persons and causing skin and breathing problems to many others. As pyrosulphuric acid does not occur in the atmosphere, therefore, it is a contaminant. Further, as it had dangeroous effect, so it is also pollutant. Generally, highly toxic substances are considered as pollutants.
Threshold Limit Value (TLV) :- The permissible limit of a pollutant in the atmosphere to which if a healthy worker is exposed for 8 hours a day or a 40 hours in a week throughout of his life, there is no adverse effect on him is called threshold limit value. These studies are made by experimentation on animals.