In this article we will discuss about the meaning and classification of pollutants.
Meaning of Pollutants:
In general, any substance that causes pollution may be called a pollutant. It can be said that anything in its excess makes any part of the environment undesirable. “The Indian Environment (Protection) Act, 1986” has defined pollutant as any solid, liquid or gaseous substance present in such concentration as may be or tend to be injurious to the environment.
Pollutants are the residues of things we make, use and throw away into the environment. A few examples are: deposited matter (soot, smoke, dust etc.) gases, acid droplets, fluorides, metals, photochemical oxidants, radioactive wastes etc.
Pollutants can be grouped into three types:
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1. Those substances that occur in nature, but due to human activity are found in unusually large concentrations. Examples of such types are carbon dioxide, oxides of nitrogen, smoke, dust, noise etc.
2. Toxic substances produced that are not found in nature and formed due to human activity. An example is the use of pesticides etc.
3. Substances which are themselves not toxic and are released into the environment due to human activity go on to have unfortunate consequences. Such are the effect of certain substances on the ozone hole.
Classification of Pollutants:
I. On the basis of source, pollutants can be classified into two broad groups:
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(a) Point source pollutants. It includes particles such as dust, lead, iron, zinc, chromium, mercury etc. and gases such as carbon monoxide, sulphur dioxide, hydrogen sulphide, fluorine, chlorine etc.
(b) Non-point source pollutants. These are mostly sources that result in run-off, seepage and percolation of pollutants to surface and groundwaters through diffusion and unidentified routes. Important kinds of non-point sources include agriculture, silviculture, mining, ground water arsenic, urban run-off, rural sanitation; land development, heavy construction work etc.
II. From an ecosystem point of view, Odum (1971) has classified pollutants into two types:
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(a) Non-degradable pollutants:
These include materials and poisons (DDT, plastic, aluminium cans, mercurial salts, long-chain phenolic chemicals etc.) that either do not degrade or degrade at a very slow rate in the natural environment. These cannot be recycled in the ecosystem.
These pollutants not only accumulate but are often “biologically magnified” with their subsequent movement in biogeochemical cycles and along food chains. These pollutants also frequently combine with other compounds in the environment to produce additional toxins. Their removal from the system is very expensive. The only sensible solution is to stop their use or production (DDT’s use has been banned).
(b) Bio-degradable pollutants:
These include domestic sewage that can be rapidly decomposed by natural processes or can be engineered in a way so as to enhance their degradation and recycling. Heat or thermal pollution falls under this category as it can easily be dispersed. The problem with this pollutant arises when the input into the environment exceeds the decomposition or dispersal capacity. In other words the system becomes poisoned by “too much of a good thing”.