Certain common pollutants of well-developed and developing countries are following: 1. Deposited matter such as soot, smoke, tar, dust and grit. 2. Cases like sulphur dioxide, carbon monoxide, carbon di­oxide, nitrogen oxide, hydrogen sulphide, ammonia, fluorine, chlorine, etc. 3. Chemical compounds such as aldehydes, arsines, hydrogen fluorides, phosgenes, detergents, etc. 4. Metals like lead, iron, zinc, mercury, etc. 5 Economic poisons like herbicides, fungicides, pesti­cides, nematocides, insecticides, rodenticides and other biocides 6. Fertilizers. 7. Sewage. P. Radioactive substances. 9. Noise and heat.

However, from the ecosystem viewpoint, these pollutants can be class lied into two basic types: nondegradable pollutants and biodegradable pollutant; (Odum, 1971). The materials and poisons. Such as aluminium cans, mercurial salts, long-chain phenolic chemi­cals and DDT that either do not degrade or degrade only very slowly in the natural environment, are called nondegradable pollu­tants.

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Such nondegradable pollutants not only accumulate but are often “biologically magnified” as they move in biogeochemical cycles and along food chains. Also they frequently combine with other compounds in the environment to produce additional toxins. The biodegradable pollutants include domestic sewage, heat, etc.

The domestic sewage can be rapidly decomposed by natural pro­cesses or in engineered systems (such as a municipal sewage treat­ment plant) that enhance nature’s great capacity to decompose and recycle. Problems arise with the biodegradable pollutants when their input into the environment exceeds the decomposition or dispersal capacity.