Environmental pollutants are substances, chemicals or any other thing which change the natural balance of the environment and thus cause pollution. Pollutants stimulate, initiate or terminate the vital reactions of an organism. These may also bring about changes in the organisms modifying the entire ecosystem.
Pollutants accumulate in the environment in large quantities due to human activities.The types, number and amount of pollutants increases with increase in the human population and his developmental activities.
Types of environmental pollutants
Following are the different types of pollutants:
1.Depending upon unchanged or changed nature, pollutants can be primary or secondary.
Primary pollutants are pollutants persisting in the environment in the form they are passed into it, for example DDT. They are released directly from their source, e.g. oxides of carbon and sulphur from burning of fossil fuels, unburt hydrocarbons from automobiles, smoke, ash from factories, dust from various factories such as cement factories, mills,etc. Their toxicity is comparatively less.
Secondary pollutants are pollutants which are formed by reaction amongst the primary pollutants. For example, peroxyacetyl nitrates (PAN) are formed through reaction between nitrogen oxides and hydrocarbons in the presence of sunlight. Secondary pollutants are often more harmful than primary pollutants. The enhanced effect is termed as synergism. They are not only toxic but also carcinogenic.
Differences between primary and secondary pollutants
Primary air pollutants
Secondary air pollutants
|1. Primary air pollutants are air pollutants which enter air directly from the source.||1. Secondary air pollutants are air pollutants which develop from interaction of primary pollutants and atmospheric constituents.|
|2. Photochemical reactions do not occur in their formation.
|2. Secondary pollutants are formed through photochemical reactions that release nascent oxygen.|
|3. They are of different categories (i.e., some are reduced, some oxidized and others particulate).
|3. They are commonly oxidants.
|4. There is no enhancement of effect of primary air pollutants.||4. Secondary pollutants are more important than the primary pollutants due to synergism.|
2. According to the nature or quantity the pollutants may also be quantitative or qualitative.
They are pollutants which do not normally occur in the environment but are passed into it through human activity. For example, DDT and other pesticides, herbicides etc.
They become pollutants only when their concentration reaches beyond a threshold value in the environment. For example, carbon monoxide, carbon dioxide, nitrogen oxides.
3. According to their degradability pollutants may be bio-degradable or non degradable.
Pollutants such as domestic sewage, cloth, paper, wood etc., come under the category of biodegradable pollutants as they can be decomposed by microorganisms. However, the decomposition becomes difficult when such materials accumulate in large quantities.
Non degradable pollutants
Non-degradable pollutants are neither decomposed by micro organisms nor do these materials break down by physical and chemical agents present in the environment. There is no treatment in nature for their recycling. Therefore these continue to accumulate and occupy large useful space on the earth. Pollutants such as aluminium cans, articles made of plastic, compounds of mercury, DDT, glass etc., are examples of non-degradeable pollutants.
Differences between biodegradable and non-biodegradable pollutants
|Biodegradable Pollutants||Non-biodegradable Pollutants|
|1. Biodegradable pollutants are those pollutants which are decomposed and degraded by microbes such as cloth, paper, wood etc.||1.The pollutants are not decomposed by microbes such as glass, plastics etc.|
|2. The pollutants are degraded quite rapidly.||2. They are degraded very slowly
|3. Biodegradable pollutants do not pile-up.||3. Non Biodegradable pollutants often accumulate.|
|4. They can be used in a benificial way (i.e., can be used to produce energy, manure, compost and biogas).||4. Some of the pollutants, if properly separated can be recycled others are not manageable.
|5. They become part of rapid turnover in biogeochemical cycles.
|5. Many of them do not enter biogeochemical cycles, others are very slow and often intoxic.
|6. Pollutants such as garbage, sewage, livestock, wastes are examples of biodegradable pollutants.||6. Pollutants such as DDT, BHC, plastics, polythene, cans broken glass, etc are examples of non-biodegradable pollutants.
Major Environmental Pollutants
Following are some of the major environmental pollutants:
1. Gases such as carbon monoxide, sulphur dioxide, hydrogen sulphide, oxides nitrogen and halogens (i.e., chlorine bromine Iodine) etc.
2. Particulate matter,e.g., dust, soot, grit,etc.
3. Droplets of acid such as sulphuric and nitric acid.
4. Metals such as chromium, lead, zinc, mercury, nickel, cadmium,etc.
5. Agro chemicals such as insecticides, herbicides, weedicides, pesticides,etc.
6. Organic substances such as benzene, benzpyrene, alkyl benzene sulphonates (ABS), etc.
8. Photochemical oxidants,e.g., ozone, peroxyacetyl nitrate (PAN), ethylene,etc.
9. Radioactive substances such as uranium, plutonium, strontium iodine etc.
10. Noise also is a major environmental pollutant.
Importance of pollutants
Biodegradable pollutants provide energy in the form of organic substances and also nutrients such as carbonate, phosphate, etc. The productivity of ecosystem continues to increase till the amount of such substances is moderate. When the amount reaches a certain critical limit the activities in the ecosystem show severe fluctuations. If these pollutants are added to the ecosystem even beyond this critical limit, the balance is completely lost and it becomes disturbed.
Non degradable pollutant, not only accumulates in the ecosystem but also pass from one organism of the food chain to another till it reaches the last trophic level. During this transport the amount of the pollutant continues to increase with each trophic level. This is termed as biomagnification. The pollutants form toxic substances in combination with other substances when it passes through different trophic levels. Such substances are harmful and even kill the biotic components.
Effect of Environmental pollutants
Following are some of the major harmful effects.
1. Loss of raw materials such as grains, vegetables, etc.
2.Unnecessary expenditure on pollution control.
3. Health hazards due to pollution related diseases such as asthma, cancer etc.
4. Environmental pollutants also causes an increase in the death rate.
5. It also decreases the working efficiency of man.
6. The acidic pollutants such as acid rain damage the crops. This results in the economic loss.
7. Pollutants also cause damage to the buildings, metals, paints, varnishes, cloth etc.
8. Environment of the earth becomes progressively unfit for living due to environmental pollutants.