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Pollution : |
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Pollution
Pollution may be defined as an undesirable change in the physical,
chemical or biological characteristics of our air, water and
land that may or will harmfully affect human life, the lives
of the desirable species, our industrial processes, living conditions
and cultured assets, or that may or will waste or deteriorate
our raw material resources.
Pollution is different from contamination which is the presence
of harmful organisms or their products causing disease or discomfort.
Pollution can be natural or man made. Natural pollution comes
from volcanic eruptions, emission of natural gas, soil erosion,
ultraviolet rays, cosmic rays, etc. Most of the pollution is
man-made.
Pollutants. They are substances (e.g., smoke), chemicals (e.g.,
sulphur dioxide) or factors (e.g., heat) which cause a potential
or actual adverse effect on the natural quality of any constituent
of the environment. Pollutants are generally waste products
or by-products. Sometimes, pollutant is a constituent in a wrong
proportion. For example, addition of nitrate and phosphate is
a must for soil fertility. They, however, cause water pollution.
Similarly, excess of carbon dioxide or low concentration of
oxygen in the atmosphere are also pollutants. Pollutants are
classified into different ways:
- According to the form in which the pollutants persist
after
release into the environment, they may be primary or
secondaiy.
- Primary Pollutants. Pollutants persisting in the
environment in the form they are passed into it, e.g.,
DDT.
- Secondary Pollutants. Pollutants which are formed
by reaction amongst the primary pollutants. For example,
peroxyacyl nitrates (PAN), are formed through reaction
between nitrogen oxides and hydrocarbons in the presence
of sunlight.
- According to their existence in nature, the pollutants
may be
quantitative or qualitative.
- Qualitative Pollutants. They are pollutants which
do not normally occur in the environment but are passed
into it through human activity, e.g., DDT and other
pesticides, fungicides, herbicides, etc.
- Quantitative Pollutants. They become pollutants only
when their concentration reaches beyond a threshold
value in the environment, e.g., CO, C02, nitrogen oxides.
- According to their natural disposal, the pollutants may
be
biodegradable or non-degradable.
- Biodegradable (Degradable) Pollutants. They are actually
waste products which are slowly degraded by microbial
action. Pollution results when their production exceeds
the capacity of the environment to degrade them.
- Non-Degradable (Non-Diodegradable) Pollutants. They
are pollutants which do not get easily decomposed. They
include wastes (e.g., phenolics, plastics, glass or
metallic containers) or poisons (e.g., pesticides like
DDT, salts of heavy metals, radioactive substance).
Types of Pollution. Pollution is of five types : air pollution,
water pollution, soil pollution, radioactive pollution and noise
pollution. |
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