ENVIRONMENT AND POLLUTION
Definition: Pollution is an undesirable change in the physical, chemical or biological characteristics of environment (air, water and soil) that may create potential health hazards to any living organisms living in it.
” Any solid, liquid or gaseous substance present in such concentration as may be or tend to be injurious to the environment ” is defined as Pollutants. (As per Environmental Protection Act, 1986)
DIFFERENT TYPES OF POLLUTION
Broadly pollution can be categorized as:
- Air pollution
- Water pollution
- Land pollution
- Noise pollution
All the above mentioned pollutions can be further broadly categorized into :
- Nondegradable Pollution: When pollutants either do not degrade or can be degraded very slowly. Eg : Aluminium, Asbestos, DDT
- Bio-degradable pollution: When the pollutants can be decomposed rapidly under natural conditions. Eg: Domestic waste.
| sl | Types of pollutants | Pollutants | sl | Types of pollutants | Pollutants |
|---|---|---|---|---|---|
| 1 | Deposited materials | Soot, smoke, tar, dust, grit | 6 | Agrochemicals | Pesticides, Weedicides,Fertilizers |
| 2 | Gas | NO, NO2, SO2, CO, Cl2, Br2, I2 | 7 | Organic Substance | Benzene, Benzpyrenes etc. |
| 3 | Fluorides | 8 | Photochemical oxidants | Ozone, Peroxyacetyl nitrate (PAN), etc | |
| 4 | Metals | Hg, Pb, Zn, Ni, Cd, Cr e.t.c. | 9 | Solid and Radioactive waste | |
| 5 | Acid Droplets | H2SO4, HNO3 | 10 | Noise |
Air pollution is caused when the concentration of different gases in the atmosphere exceeds normal concentration value or when there is a new addition of harmful gases into atmosphere.AIR POLLUTION
| MAJOR AIR POLLUTANTS SOURCES | |
|---|---|
| CO2 Burning of fossil fuel from domestic sources and thermal power plants, volcanic eruptions | Greenhouse effect. (See details later in this booklet) |
| Carbon monoxide(CO) Incomplete combustion of fossil fuels, wood, coal, charcoal, oil. | Carbon monoxide gas is harmful over 100 ppm and fatal over 1000 ppm. It combines with blood haemoglobin to form carboxyhaemoglobin about 210 times faster than the combining rate of O2. In plants, CO affects leaf drop, leaf curling, premature aging and sometimes cellular respiration in plants. |
| Sulphur dioxide (SO2)1 Produced by burning of fossil fuel in thermal power plants, smelting industries. | Causes irritation to eyes and respiratory tract. Exposure to 1ppm level of SO2 causes constriction of air passage. Plants are more susceptible to SO2. Leaf Pigments Chlorophyll-a is converted to Phaeophytin-a affecting productivity of plants. It also causes erosion of building materials. |
| Hydrogen Sulphide (H2S) Decaying vegetation and animal matter in aquatic environment, sulphur spring, volcanic eruptions, coal pits and sewers, industrial waste. | At low concentration causes nausea, headache, collapse. At 150 ppm causes conjunctivitis and irritation of mucus membrane. At 550 ppm for 15-30 mins causes bronchial pneumonia and death may occur due to respiratory failure. |
| Nitric oxide (NO) Gasoline production at high temperature and industries that manufacture HNO3 | Produces other pollutants like PAN (Peroxyaclnitrate), O3, carbonyl compounds. Responsible for acid rain (See later) |
| Ozone (O3) Chemical reactions of SO2, NO2 , aldehydes in the presence of UV radiation produce Ozone gas. | O3 concentration near earth’s surface reduces crop yields, it enters plants body through O3. Mostly Tobacco, pine, beans fruits, vegetables crops are affected. |
| Fluorocarbons It comes from industrial processing of phosphate fertilizers, ceramics, aluminium, fluorinated hydrocarbons like refrigerants and aerosol propellants. | Over-concentration of Fluorocarbons causes fluorosis. In plant it causes tip burn of leaves. |
| Hydrocarbons Motor vehicular emission of Benzene, benzpyrene and methane, by evaporation of gasoline through carburetors | Benzene and benzpyrene are causal agents of cancer. Methane in absence of oxygen can act as narcotic on human being. |
| Mercury Fungicides, cosmetics, paints, and papers industries. | Causes damage to nervous system, liver, eyes. Minamata is a common disease caused due to methyl mercury. |
| Lead(Pb) Lead is released in the atmosphere in the form of lead halides (bromides and chlorides ) during the combustion of gasoline. | Inhalation reduces haemoglobin formation, resulting to anaemia. Infection of liver, kidney, mental disorder, infertility, neuromuscular effects are common consequences. |
| Zinc(Zn) Main source of zinc as pollutant mainly comes from zinc smelters, scrap zinc, copper, lead and steel refineries. | White zinc oxide is toxic to human being. |
| Cadmium(Cd) Industries engaged in extraction, refining, electroplating, wielding. | It causes hypertension, emphysema, kidney damage and can be can be carcinogenic. |
| Photochemical smog Oxidising mixture of O3, NOx, H2O2, organic peroxides, PAN. | Causes Emphysema, a disease due to structural breakdown of alveoli of lungs, breathlessness. |
1 Plants like Nerium indicum serves as an indicators of SO2.
SOME EFFECTS OF AIR POLLUTION
Greenhouse Effect: Earth receives sunrays mostly in the form of ultraviolet, visible and infrared light. About 26% of the incident sunrays is reflected back into space and 19% is absorbed by atmosphere and clouds. Rest of the energy is absorbed by the earth’s surface which ultimately is radiated at longer wavelengths. This process helps in maintaining temperature balance in atmosphere under normal conditions ( with CO2 conc.0.0314%, ). The increased level of Greenhouse gases (CO2, H2O vapour, CH4, O3) although allow solar radiation to penetrate through the earth’s atmosphere but they prevent the long wavelength radiation from escaping because of their absorption by the atmospheric CO2 , H2O vapour, and to some extent by O3. This adds to the heat that is already present and acts like a glass panel of a green house that traps the solar energy.
Acid Rain – Acid rain is caused by emissions of SO2 and NO2 which react with the H2O in atmosphere to produce acids.
Sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction:
SO2 + OH· → HOSO2·
HOSO2· + O2 → HO2· + SO3
In the presence of water, sulfur trioxide (SO3) is converted rapidly to Sulfuric acid
SO3 (g) + H2O (l) → H2SO4 (aq)
Nitrogen dioxide reacts with OH to form nitric acid: NO2 + OH· → HNO3
Acid rain increases soil acidity, acidification of lakes and water bodies affecting aquatic life. They also corrodes buildings, monuments, statues, bridges, railings.
Ozone Depletion: Ozone present in stratosphere absorbs UV radiation and heats the Stratosphere causing temperature inversion. This inversion of temperature prevents vertical mixing of pollutant, however, high concentration of ozone depleting agents such as halogens, Chlorofluoro carbons CFCS, Nitrogen oxide, aerosol propellents sometimes react with ozone and are converted to other products, resulting in ozone depletion or reduction of ozone layer near polar regions, a phenomenon called ozone holes.
CFC’s reaching in stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action of ultraviolet light, e.g.
CFCl3 + electromagnetic radiation → Cl· + ·CFCl2
Cl and Br atoms can then destroy ozone molecules through a variety of catalytic cycles. In the simplest example of such a cycle, a chlorine atom reacts with an ozone molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen molecule. The chlorine monoxide (i.e., the ClO) can react with a second molecule of ozone (i.e., O3) to yield another chlorine atom and two molecules of oxygen. The chemical reaction :
- Cl· + O3 → ClO + O2 . Chlorine atom changes an ozone molecule to ordinary oxygen
- ClO + O3 → Cl· + 2 O2 . The ClO from the previous reaction destroys a second ozone molecule and recreates the original chlorine atom, which can repeat the first reaction and continue to destroy ozone.
It is suspected that a variety of biological consequences such as increases in skin cancer, cataracts, damage to plants, and reduction of plankton populations in the ocean’s photic zone may result from the increased UV exposure due to ozone depletion.
The ozone hole is most usually measured by reduction in the total column ozone above a point on the Earth’s surface, which is normally expressed in Dobson units, abbreviated as “DU”.
The first global conference on depletion of Ozone layer was held in Vienna( Austria), 1985, followed by Montreal Protocol in 1987, which called for 50% reduction in use of CFCs ( Ozone depletion gases).
WATER POLLUTION
Water Pollution can be defined as ‘’the addition of any substance to water or changing of water’s physical and chemical characteristics in any way which interferes with its use for legitimate purposes.’’
TYPES:
Surface water pollution
Ground water pollution
Marine pollution
| SURFACE WATER POLLUTION | CAUSES AND EFFECTS |
|---|---|
| Sewage and other waste : Source: Discharge of untreated or partly treated sewage. Pollutants:Water borne waste as human and animal excreta, paper, cloth, detergents. |
|
| Industrial Waste: Source: Inorganic and organic pollutants from breweries, tanneries, dying textiles, paper and pulp mills, steel industries, mining operations. Pollutants: Oils, greases, plastics, plasticizers, metallic wastes, suspended solids, phenols, toxins, acids, dyes, DDT , heavy metals (NA, Cu, Cr, Cd, Hg, Pb) |
|
| Agricultural discharges Source: Chemicals used as fertilizers and pesticides (biocides) Pollutants: Artificial fertilizers (NO3), Pesticides and biocides (bactericides, fungicides, weedicides, DDT-Dichloro-Diphenyl trichloroethane, BHC-Benzene hexachloride, PCBs – polychlorinated biphenyls. |
|
| Industrial wastes from chemical industries, fossil fuel plants and nuclear plants. Source: Thermal and nuclear power plants. Pollutants: Heat and radioactive substances |
|
BIOLOGICAL OXYGEN DEMAND (BOD)
BOD is the amount of oxygen required for biological oxidation by microbes in any unit volume of water. BOD value generally approximates the amount of oxidizable organic matter and is therefore used as a measure of degree of water pollution and waste level. Escherichia coli multiplies tremendously in sewage and waste water. It consumes most of oxygen, causing BOD. It also acts as an indicator of pollution in water.
Most unpolluted water bodies will have a 5 day carbonaceous BOD below 1 mg/L. Moderately polluted (2 to 8 mg/L) and Municipality waste sewage have a value of 20mg/L or less.
EUTROPHICATION
Due to addition of domestic waste, industrial waste, phosphates, nitrates and other decomposed matter in water, the water body becomes highly productive. An explosive growth of aquatic plants and algal blooms occur in this condition called as eutrophication. When these algae and plants die they consume the oxygen in the body of water creating a state of hypoxia (low oxygen condition). So in oxygen poor water, fish and other animals start to die and turns it into a stinking drain.
With the addition of nutrients there is stimulated luxuriant growth of algae in water. There is also generally a shift in algal flora; blue green algae begin to predominate. These start forming algal bloom floating scum or blankets of algae making the water unfit for usage.
Following are harmful effects of eutrophication:
i) Pathogens (bacteria, protozoa, virus) begin to grow in the water bodies under anaerobic condition
ii) Spread of fatal water borne disease like cholera, polio, typhoid, dysentery, diarrhea, amoebiasis.
Following are few methods to check eutrophication
i) Treatment of waste water before its discharge into lakes.
ii) Stimulation of bacterial growth after decomposition of algae.
iii) Removal of dissolved nutrients (phosphorus by precipitation, nitrogen by biological nitrification and denitrification or by air stripping of NH3 from an alkalized waste water).
GROUND WATER POLLUTION
Ground water pollution is a major problem in areas outskirts of larger cities and villages. This results in inadequate supply of water for drinking and other household purposes. The main causes for ground water pollution are:-
- seepage pits, leaking septic tanks, refuse dumps.
- dumping of raw sewage in shallow soak pits.
- deposition of industrial waste containing high metals such as Mercury, Arsenic, Cadmium, Lead and other metals like Ni, Fe, Cu, Cr, Cyanides to ground water.
Ground water pollution affects human as well as animal health. It give rise to water borne diseases like cholera, polio, hepatitis, dysentery etc.
Marine Pollution:
Marine pollution is caused when huge amounts of sewage, garbage, agricultural discharge, biocides, heavy metals, oils, plastics are added to sea. Besides these discharges of petroleum products and dumping of radio nuclides waste into sea are also responsible for marine pollution. Huge quantity of plastic is also another cause.
The pollutants in sea may become dispersed or precipitate down at the bottom by processes like adsorption, precipitation and accumulation.
The effects of marine pollution are as follows:
i) Ingestion of plastic causes gastro-intestinal disorders in marine birds.
ii)Ingestion of PCBs causes thinning of eggshell and tissue damage.
iii) It brings changes to species diversity.
iv)Oil soaked in feathers, displaces the air and interferes with buoyancy and disrupts the maintenance of body temperature – this kills a large number of aquatic birds.
v)Hydrocarbons and benzpyrene accumulate in food chain of fish (bioaccumulation) and consumption of these fishes by man increases the concentration of heavy metals in human as well – a process called biomagnification.
Some important facts:
Bioaccumulation: Bioaccumulation refers to how pollutants such as toxic chemicals enter a food chain and accumulate in the tissue of a particular organism. This occurs on consuming toxic contaminated food in high concentration such as food containing lead, mercury, DDT.
Biomagnification: It is the increase in concentration of toxic substances such as DDT, Mercury, Polychlorinated biphenyles (PCBs) in the tissues of organisms at successively higher levels in a food chain.
Bioaccumulation occur within an organism, and biomagnification occurs across trophic (food chain) level.
Example: Mercury in sea water is present in very small amount. It is absorbed by algae as methylmercury and is excreted very slowly, process called bioaccumulation. These algae are consumed by zooplankton and nektons which in turn are eaten by small fishes and then by big fishes. In this way the toxic substance gradually enters the food chain of higher trophic level and gets accumulated in higher concentration, a process called biomagnification.
RADIOACTIVE POLLUTION:
It is the deposition or presence of radioactive substances on surfaces or within solids, liquids or gases (including the human body) where their presence is unintended or undesirable. Eg: Alpha, beta and gamma rays or neutrons.
Fukushima Daiichi nuclear disaster (11th March 2011 triggered by Tsunami and earthquake) and Chernobyl disaster (26th April, 1986) are notable radioactive tragedy .
IMPORTANT ACTS :
- Environment Protection Act, 1986
- The Air (Prevention and Control of Pollution) Act,1981
- The Water (Prevention and Control of Pollution) Act, 1974
- The Motor Vehicles Act, 1988