Degradable pollutants or Bio-degradable Pollutants Paper 1

Degradable pollutants or Bio-degradable Pollutants (Odum 1971):

These are natural organic substances which can be decomposed, removed or consumed and thus, reduced to acceptable levels either by natural processes like biological or microbial action or by some engineered systems, like sewage treat­ment plants.

The degradable pollutants can be further sub–divided into two categories:

(i) Rapidly degradable or non-persistent pollutant:

The degradation of these pollutants is very faster process. For example, the decomposition of sewage and wastes of animals and plants is a faster process. The domestic sewage can be rapidly decomposed by natural processes. However, the problems become complicated when the input into environment get exceeded of the decomposi­tion or dispersal capacity.

(ii) Slowly degradable or persistent pollutant:

The degra­dation of these pollutants is a very slower process. It seems as if the amount of pollutant remains unchanged with time. For example, degradation of synthetic com­pounds and radio–active elements like Iodine 137, Stron­tium 90 or Plutonium 239 takes a longer period of time.

(b) Non-degradable Pollutants:

These are not broken down the natural processes like action of microbes. Most of these Mutants get accumulated in the environment and also get bio­logically magnified as these move along the food chains in an under composed state. These may also react with other com­pounds in the environment to produce toxins.

These can be fur­ther subdivided into two more classes:

(i) Waste:

e.g. glass, plastic, phenolic, aluminum cans etc.

(ii) Poisons:

e.g. radioactive substances, pesticides, smog gases, heavy metals like mercury, lead and their salts.

These are the substances that either do not degrade or degrade very slowly in the natural environment. These include mercury salts, long chain phenolic chemicals, DDT and Aluminum cans etc.

Such non–degradable pollutants accumulate and are biologically magnified as they move in the biogeochemical cycle and along food chains in the ecosystem. For example, DDT, when washed from the ground goes to the streams where it is absorbed by the phytoplankton’s which are eaten by the fishes.

So, the initial dose of DDT which was harmless in the phytoplankton becomes very harmful as it accumulates in the fish day by day, with the result that large populations offish die or become sterile and same is the case with the birds feeding on such fishes. This phenomenon is known as bio-magnification or biological magnification.