Pollutants: Definition and Classification of Pollutants

In order to meet the basic needs of increased population, the present society has undertaken a series of steps like rapid indus­trialization, unplanned urbanization, deforestation, over exploi­tation of natural resources etc.

These processes are releasing a variety of extraneous materials and energy into environment in a continuous and uninterrupted manner. Such a disposal which becomes greater than the threshold concentration of a particular substance renders the environment partially or fully unfavor­able for the living world.

This is referred as environmental Pollution. The term pollution is derived from the Latin word Pollution which means to defile or make dirty. The term Pollution has been defined in various ways by various scientists and organizations.

According to U.S. President’s Science Advisory Committee (1966):

“Environmental pollution may be defined as the unfavorable alterations of our surroundings wholly or largely as a byproduct of man’s action through direct or indirect effects of change in energy pattern, radiation levels, chemical and physi­cal constitution and abundance of the organisms”.

According to national Academy of Science, USA (1966), pollution may be de­fined as, “an undesirable change in physical, chemical and bio­logical characteristics of water, air and soil that may harmfully affect human, animal and plant life, industrial progress, living con­ditions and cultural assets.”

According to Odum (1971), “Pollu­tion is an undesirable change in physical, chemical and biologi­cal characteristics of air, water and soil that may harmfully affect the life or create a potential health hazard for living organisms”.

According to Edward (1972) “Pollution is the release of harmful substances or energy into the environment by man in quantities that damage health and resources”. According to tiasmann (1975) “Pollution is the accumulation of substances in the environment or at rates of flow which exceed the capacity of the eco-system to either neutralize or disperse them to harmful levels”.

According to national Environmental Research Council (1976), “Pollution is viewed as the release of substances and energy as waste prod­ucts of human activities which result in harmful changes within the natural environment”.

According to Kudesia, “Pollution is de­fined as the addition of extraneous materials (inorganic, organic, biological or radiological) to water, air or land which adversely affects the natural quality of environment. Pollution is thus, di­rect or indirect change in any component of the environment which is harmful to the living organisms and in particular undesirable for man.

Sometimes, instead of pollution another term “contamina­tion” is used by some scientists. Contamination means the pres­ence of harmful substances or organisms in air, water or soil which may cause diseases or discomfort to the human being. However, the polluted materials need not necessarily be contaminated.

Pollutants:

A pollutant may be defined as, “anything, living or non-living or any physical agent (e.g. heat, sound etc.), that in its excess makes any part of the environment undesirable. The polluted water is undesirable for drinking, recreation, visual enjoyment or as a habitat for the aquatic life normal to it.

The polluted air is undesirable for breathing, for the condition of buildings and monuments exposed to it or for animal and plant life. The pol­luted soil and land undesirable for raising food and fodder for animals or for recreation and aesthetic enjoyments”.

In other words, Pollutant may be defined as “constituent in the wrong amount at the wrong place or at the wrong time.” 

Commonly speaking, the term pollutant is applied to non-living , man-made substances and other nuisances and it refers to their being in excess in a particular location. For exam­ple, nitrogen, phosphorous and potassium are extensively used in agriculture to increase crop yield but sometimes, these in higher concentration cause pollution in lakes and rivers promoting algal growth. This adverse effect of pollution is more severe when the pollutants are man-made rather than natural preparation.

In short, the unserviceable or residues of things which the humanity manufactures, uses and throws away, can also be regarded as pollutants.

Types of Pollutants:

In terms of eco-system, the pollutants can be classified into two basic groups:

(a) 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. radio-active substances, pesticides, smog gases, heavy metals like mercury, lead and their salts.

(b) 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.

Agents Causing Pollution:

Depending upon the nature of the pollutants and their inter­action with environment process, the pollution caused by differ­ent agents can be classified into the following categories:

(a) Pollution caused by solid wastes.

(b) Pollution caused by liquid wastes.

(c) Pollution caused by gaseous wastes.

(d) Pollution caused by wastes without weights.

(a) Pollution caused by Solid wastes:

The solid wastes in­cludes the pollutants like garbage, rubbish, ashes, large wastes formed due to demolition and construction processes, dead ani­mals wastes, agricultural wastes etc. Prom the above examples, it is clear that the solid wastes may be domestic and industrial in nature.

(b) Pollution caused by liquid wastes:

Oxygen cycle is nicely operated in aquatic system maintaining ecological balance. That is, the dissolved oxygen is used by aquatic living organisms for their respiration and in return, these liberate carbon dioxide. Car­bon dioxide molecules are again used by green plants and algae in the process of photosynthesis.

During photosynthesis, oxygen is again liberated to water which remains in dissolved state. How­ever, if some organic matter (food for bacteria) enters the water course, then bacteria oxidise these materials consuming oxygen from water. At such a condition, if the process of re oxygenation is slower than the process of de-oxygenation, then the river will be devoid of life sustaining dissolved oxygen and aquatic living or­ganisms will die.

The most important source of organic pollutants is sewage which contains fecal matter, urine, kitchen washing and oil wash­ings. Sewage also contains a large number of pathogenic and harmless bacteria. The strength of organic waste material of sew­age is measured in terms of biological oxygen demand (B.O.D).

The value is expressed in terms of mg. of oxygen per liter of waste for 5 days at 20C. If the volume of B.O.D. is below 1500 mg per liter, the sewage is termed as weak waste, if it is 4000 mg per liter it is medium and above this value it is termed as strong Waste.

However, if liquid industrial wastes containing acids, alka­lis and poisonous substances enter the river, the aquatic life is affected and self-purification system of water is impaired. Pesticides and herbicides which enter water may Kill some organisms or accumulate in fishes which, when consumed by man, pass on the chemicals giving rise to cumulative poisoning.

(c) Pollution caused by Gaseous Wastes:

The gaseous wastes include Carbon monoxide (CO), Sulphur dioxide (SO2), nitrogen dioxide (NO2), Ozone (O3) and smog gases (composed of a com­plex mixture of photochemical oxidation products of hydrocar­bons). These gases are more abundant in the atmosphere of in­dustrial cities.

(d) Pollution from Waste without weight:

This type of pollu­tion is also known as pollution by energy waste; Wastes without weight may be of the following types:

(i) Radio-active

(ii) Heat

(iii) Noise

(i) Radio-active Substance:

Despite of all possible precau­tions in the functioning and maintenance of nuclear reac­tors, it is seen that minute quantity of radio-active waste escapes out into the environment. From the mining opera­tion of the uranium to the use and final disposal of wastes from the reactor, radio-active materials continuously escape out into the environment. Besides, a lot of radio-active wastes enter into environment during the nuclear tests.

(ii) Heat:

A large quantity of waste heat energy is dissipated into environment by the way of hot liquid streams or hot gases released by industries and automobiles.

(iii) Noise:

The unwanted sound is known as noise. These sources of noise for the general public are the machines in the in­dustry, traffic noise, indiscriminate use of transistor, radios, public address systems, etc.

Classification of Pollution:

Pollution can be classified according to the environment (air, water, and soil) in which it occurs or according to the type of pol­lutant (lead, mercury, carbon dioxide, solid waste, noise, biocide, heat, etc.) by which pollution is caused.

Sometimes, pollution is made to classify into two broad cat­egories:

1. Natural Pollution:

It originates from the natural process.

2. Artificial Pollution:

It originates artificially by the interac­tion in between humanity and environment.

Different types of pollutions are as follows:

1. Air pollution

2. Water pollution

3. Terrestrial pollution

4. Noise pollution

5. Radiation pollution

6. Thermal pollution

7. Industrial pollution

General Effects of Pollution:

Each and every component of environment is influenced by pollution in a number of ways.

The impact of pollution on some biotic and abiotic components may be discussed as below:

(i) Effect on Plants:

Photo-chemical smog’s, sulphur-dioxide (obtained from copper and lead smelter) and hydrogen fluo­ride (obtained from fertilizer manufacturing and aluminum reduction) cause injury to the plants and thereby reduce their growth and vegetation.

In some cases, even when pol­lution levels have been not high enough to produce notice­able injury, the retardation in growth rate may occur. On the whole, the pollutants (air or water pollutant or radiation) bring about complex changes in the plant eco-system, hav­ing effects on one species leading to effects on the other.

(ii) Effect on Animals:

Air pollutants cause eye and respiratory irritation in animals as well as in human beings. Water pol­lutants can endanger aquatic life killing millions of fishes and other animals every year. Sewage, toxic chemicals and diseased animals can make water unfit for use by farm ani­mals.

There are some types of pollutions known to have adverse effects on animals at levels that do not appear to affect human health. Thermal pollution in rivers and lakes can kill fishes. Pesticide levels can reduce reproduction rates through mechanisms like interference in calcium metabo­lism.

(iii) Effect on Human Beings:

Human beings are probably the most concerned about the direct and indirect effects of pol­lution. Sufficiently high levels of pollutants are toxic or even lethal to every human being, although there is a wide range of sensitivities among the human population.

For example, tartar emetic (antimony potassium tartrate) can be lethal at doses as low as 130 mg but some persons have survived doses as high as 15 gm. On the other hand, sufficiently low doses appear to have no toxicological effects.

It is seen that many diseases are water borne and can be checked through the purification of municipal and individual water supplies. Still, the drinking water of most of the world’s population is considerably less safe than that of the devel­oped nations due to inadequacies in public health programs.

 

Definition:

Any substance present in the environment in harmful concentration, which ad­versely alters the environment by damaging the growth rate of a species and by interfering with the food chains, is toxic and affects the health, comfort and property etc. is considered as a pollutant.

Smoke from industries and automobiles, domestic and commercial sewage, ra­dioactive substances from nuclear plants and discarded household articles (tins, bottles, broken crockery etc.) come under the category of pollutants.

Classification of Pollutants:

The classification of pollutants is done from different points of view:

1. Depending upon their existence in nature pollutants are of two types, namely quantitative and qualitative pollutants.

(a) Quantitative Pollutants:

These are those substances normally occurring in the environment, who acquire the status of a pollutant when their con­centration gets increased due to the unmindful activities of man. For exam­ple, carbon dioxide, if present in the atmosphere in concentration greater than normal due to automobiles and industries, causes measurable effects on humans, animals, plants or property, then it is classified as a quantita­tive pollutant.

(b) Qualitative Pollutant:

These are those substances which do not normally occur in nature but are added by man, for example, insecticides.

1. Depending upon the form in which they persist after being released into the environment, the pollutants are categorized into two types, namely pri­mary and secondary pollutants.

1. Primary Pollutants:

These are those which are emitted directly from the source and persist in the form in which they were added to the environ­ment. Typical examples of pollutants included under this category are ash, smoke, fumes, dust, nitric oxide, sulphur dioxide, hydrocarbons etc.

(b) Secondary Pollutants:

These are those which are formed from the pri­mary pollutants by chemical interaction with some constituent present in the atmosphere. Examples are: Sulphur trioxide, nitrogen dioxide, alde­hydes, ketones, ozone etc.

Nitrogen oxides and hydrocarbons are two primary pollutants released from automobiles but in the presence of sunlight, they react to form peroxyacyl ni­trate (PAN) and ozone, two secondary pollutants which are far more toxic than the primary pollutants from which they are derived. This phenomenon of in­creased toxicity by chemical interaction among the pollutants is known as Synergism.