الفهرس 
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Abstract
1.1 Defmition of pollution
A widely used definition of pollution is the introduction by man into the
enviromnent of substances or energy liable to cause hazards to humans health,
harm to living resources and ecological systems, damage to structures or amenity,
or interference with legitimate uses of the environment I . Some experts make a
distinction between contamination and pollution, contamination. is used for
situations where a substance is present in the enviromnent, but not causing any
obvious harm, while pollution is reserved for cases where harmful effects are
apparent’.
Pollutants are basically of two types; primary pollutants,. which exert
hannful effects in the form in which they enter the environment and secondary
pollutants, which are synthesized as a result of chemical processes, often from
less harmful precursors, in the environment. Although highly toxic substances are
responsible for many cases of environmental pollution, under some circumstances
materials which are normally considered harmless may cause pollution if they are
present in excessive quantities or in the wrong place at the wrong time and this
makes definitions difficult3.
In all cases of pollution there are; (1) a source of pollutants,
(2) the pollutants themselves, (3) the transport medium (air, water, or direct
dumping onto land) and (4) the target which includes ecosystems, individual
organisms (e.g. humans) and structures.
Pollution can be classified in several ways according to (a) the source
(e.g. agricultural pollution), (b) the media affected (e.g. air pollution or water
pollution), (c) the nature of the pollutant (e.g. metal pollution).