Pollution (Part - 2) - Notes, Botany, Class 12 Class 12 Notes | EduRev

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Class 12 : Pollution (Part - 2) - Notes, Botany, Class 12 Class 12 Notes | EduRev

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( 1 ) Control of particulate matter – Two d evices are use to remov e particula te air poll utants (a) Arresters (b) Scrubbe rs


These are used to separate particulate matters from contaminated air.

Arresters are of different types :

( i ) Cyclonic separators and Trajectory separators :- The se are commonly used to separate out particulate matters from industrial emissions with minimum moisture content. These separators work on the principle of dust separation by centrifugal force.

( i i ) Electrostatic precipitator :- It is the most efficient device to remove fine particulate pollutants.

Electrostatic precipitation device work on the principle of electrical charging of the dust particles and collecting it on a differently charged platform.


These are used to clean air for both dust and gases. Wet and dry two types of scrubbers are used for dust separation.

( 2 ) Control of Gaseous pollutants – Combus tion, abs orption and adsorption technique are us ed to control gaseous pollutants.

( a ) Combustion – In combustion process, oxidisable gaseous pollutants are complet ly burnt at a high temperature. Petrochemical, fertilizer, paints and varnish industries used combustion control of gaseous pollutants.

( b ) Absorption :- In this technique, gaseous pollutants are absorbed in suitable absorbent materials.

( c ) Adsorption :- This technique is applied to control toxic gases, vapours and inflammable compounds that could not be efficiently removed or transferred by a fore said technique. Such air pollutants are adsorbed on large solid surface.

Some other Method – 

1 . Engine s should not be kept started when vehicle is in rest condition.

2 . Barium compound mixed with petrol reduces the smoke.

3 . It is also very essential to check the quality of gases released from the factories.

4 . Industries should not be established at one plac e.

5 . The smoke should be released into the atmosphere after filtration and purification (by cyclone collector or electrostatic precipitators)

6. To seperate particle s larger than 50 mm, gravity settling tanks or porous filters are being used.



Pollution (Part - 2) - Notes, Botany, Class 12 Class 12 Notes | EduRevPollution (Part - 2) - Notes, Botany, Class 12 Class 12 Notes | EduRev


Euro normsBefore 01-04-2005From 01-04-2005 to 31-03-2010From 01-04-2010
Euro-II (Bharat Stage-II)11 most polluted cities in IndiaRest of India-
Euro-III-11 most polluted citiesRest of India
Euro-IV--11 most polluted cities



  •  Ozone is present in less quantity in atmosphere. But att he heigh t of 16 k m to 25 km on earth, concentration of ozone is maximum in stratosphere.
  •  At normal temperature and pressure thickness of ozone layer is 3 mm. (But at poles thic kness of ozone layer is 4 mm ).
  •  Due to depletion of ozone layer harmful UV radiations are penetrating to the earth which causes skin cancer (Melanoma) and also acts as strong mutagens.
  •  Ozone hole was first discovered in 1985 over Antarctica by Nimbus-7 satelite.

The aerosols like C.F.C. (Chloro flouro carbon) release into the atmosphere from the refrigerators air conditioners and jet planes deplete or reduce the ozone layer. This is called ozone depletion and these substances are called O.

D. S. (ozone depleting substances). This thin layer ozone is also known as ozone holes.

 Pollution (Part - 2) - Notes, Botany, Class 12 Class 12 Notes | EduRev

Number of pollutants like CFCs [14% of total depletion], Nitrogen oxide [3.5%], CH4 and halogens (chlorine) cause depletion of ozone layer. Maximum ODP (ozone depleting potential) is of CFCs due to release of chlorine.

Note :

  1. In this process of one chlorine atom convert one lakh O3 molecules into O2 byphotodissociation.

       2. The life time of CF2Cl2 (CFC-12) is 139 year while that for CFCl3 (CFC = 11) is about 77 years

Chemical process of ozone depletion – chain reaction

CF2Cl2(g) + hv → Cl · (g ) +· CF2 Cl(g )

Cl (g) + O3 (g)→C lO · (g) + O2 (g)

ClO · (g) + O (g) → Cl · (g) + O2 (g)      

active chlorine

Some Other Informations :

  1. Thickness of ozone layer is measured in Dobson unit (1Du = 1ppb)

Year                Ozone thickness of ozone

1979                          225 Du.

1985                          136 Du.

1994                          94 Du.

  1. The Ozone hole over Antarctica develops each year between late august and early october and in general Ozone hole occurs mainly during spring time (Feb. - Apr.) and lowest during (July - October)
  2. Shewood Rowland, Mario Molina with Paul Crutzen got nobel prize in (1995) for chemistry on environmental science.


The water pollution is caused by the addition of organic and inorganic chemicals as well as the biological materials which change the physical and chemical properties of water. This harmful process is called water pollution.

The water pollution is caused by many sources such as sewage matter, industrial wastage, agricultural wastage, domestic wastage, hot water of thermal plant and nuclear reactors etc.

  • Water having D. O. content below 8.0 mgL-1 may be considered as contaminated and below 4.0 mgL-1 heavily polluted.
  • D. O. is measured by oximeter.

1 . Bioc hemica l Oxy gen Demand  (B. O. D.) :

The water pollution by organic wastes is measured in terms of Biochemical oxygen demand. It is the amount of dissol v ed o xyge n (D.O . = Di ssolved Oxygen) needed by bacteria in decomposing the organic wastes present in water.

B. O. D.  increased = water pollutedB. O. D. µ input of organic wastes


If B. O. D. is increased dissolved oxygen is decreased in water. Higher amount of organic waste increase the rates of decomposition in water. O2 is rapidly consumed by microbes, thereby causing drop in D. OD. O. content in water.

Note :

  • Daphnia is the indicator of B. O. D. w Biochemical oxygen demand [BOD] is the amount of oxygen taken up by the micro organisms present in water BOD is measured by keeping a sample of water containing known amount of oxygen for 5-days at 200C in the dark. At end of this period the oxygen content is again measured. A high BOD indicates intense level of microbial pollution.

Pollution (Part - 2) - Notes, Botany, Class 12 Class 12 Notes | EduRev

2. Chemical Oxygen Demand (C. O. D.) : It is the oxygen requirement by chemical for oxidation of total organic matter (biodegradable + non biodegradable) in water.

Note : C. O. D. value is always higher than B. O. D. value. 3. Biological magnification :-The non biodegradable pollutant like Al, Hg, Fe, D. D. T., pesticides, phenolic compound ABS(Alkyl benzene sulphonate) are not decomposed by  micro-organisms.
Theyget accumulated in tissue in increasing concentration along the food chain is called biological magnification. The highest concentration occur's in top consumer.

Note : High concentration of DDT distrub calcium metabolism in birds, which causes thinning of egg shell and their permature breaking, eventually causing decline in bird populations.

4. Eutrophication :-The process of nutrient enrichment of water and consequent loss of species diversity (or death of aquatic animals) is referred to as eutrophication and lake is known as eutrophic lake. In this process presence of nutrients in lake stimulates growth of algae (algal bloom) increase organic loading and bring about reduction in the oxygen content of water causing death of aquatic animals.
Note :

  • Eutrophication is the natural aging of a lake by biological enrichment of its water. Natural aging of a lake may span thousands of years and lake finally converted into land due to deposition of silt. Pollutants from man's activities like effluents from the industries and homes can radically accelerate the aging process, this phenomenon is called accelerated eutrophication.
  • B.O.D. of Eutrophic lake is very high.

Water Pollution can be caused by the following man made sources 

I. Household Detergents: - The household detergents include the compounds of phosphate, nitrate, ammonium and alkyl-benzene sulphonate etc. harmful substances which are gathered in water. Alkyl benzene sulphonate is non degradable (ABS), so its concentration increases which is harmful for aquatic life.  

Inorganic phosphorus and Nitrogen :- The growth of algae is very fast due to presence of higherconcentration of these substances,After the death of algae their carbonic material decomposed and deprived of oxygen, which causes death of aquatic organisms. The presence of large amount of organic material leads to eutrophication because of this, amount of oxygen in water decreases. Some of the algae also secrete toxic materials. The drinking of such polluted (toxic) water causes death of the cattles.

For the controlof this pollution, lime ferric chloride, etc. are used to precipitate the phosphate.Zirconium is considered best for this purpose.

II. Industrial waste:- The wastes of industries are discharged into the running water of rivers and canals.
Industrial waste mainly contains inert suspended particles such as dust, coal, toxins like acid, base phenols, cyanides, mercury, zinc etc., inorganic reduced material like-ferrous salts sulphide, oils and other residues of organic material and hot water. The water polluted by mercury, lead etc metals when used which causes disorganisation of nervous system. It means it produces insanity. The minamata disease was caused in Japan by eating of polluted fishes from the water polluted by mercury. So, many humans died because of this disease.
For the control of the industrial wastes and toxic components should be purified before draining into rivers, lakes and ponds or sea.So the water pollution by industrial effluents can be controlled by suitably treating the pollutants.

III. Sewage - Sewage contains highest amount of carbonic materials and biological material, as pollutants.
These carbonic materials increase the number of decomposers like bacteria and fungus. The rate of reoxygenation is reduced as compared to deoxygenation in a water reservoirs. The acceleration of microbial activity increases BOD of water. This indicates the essential amount of oxygen for decomposition in bacteria.

BOD is very less in pure water. The higher BOD is the indication of water pollution and the water of polluted reservoir can not be utilized and very bad smell spreads around the locality. The infections or  infectious diseases also takes place.
Method of water purification : The industrial and municipal waste water are treated in "Effluent Treatment Plant" (ETP).
Generally following treatments are given in ETP.

1. Primary treatment :- This physical process involves the separation of large debris (particles), followed by sedimentation intanks.

2. Secondary treatment :- This is a biological process and is carried out by microorganism. In this process, the waste water is pumped in shallow stabilisation or oxidation ponds or activated sludge chamber, where the microbes oxidise its organic matter. The process results in release COand this CO2 is used by algae in photosynthesis. In photosynthesis process algae  release O2.

3. Tertiary treatment :- This physiochemical process removes turbidity in waste water caused by the presence of nutrients (nitrogen, phophorus etc.), dissolved organic matter, metals or pathogens.
This step involves chemical oxidation of waste water by strong oxidising agents, such as chlorine gas, perchlorate salts, ozone gas and UV radiations.
After tertiary treatment, the waste-water can be discharged into natural water sources or used irrigation.

Daphnia, trout fishes and larva of stone fly are sensitive to water pollution and show the intensity of water pollution.
Some animals are very specific to their habitat, other have wider choice or tolerance levels. For example Tubifex (an annelid) and many insect larva such as chironomous larva lives in polluted water. They can survive in water with very low oxygen quantity and high organic content. Certain fishes liketrout can live only in fresh water, whereas others likeHilsa can live in both fresh water and saline water.

Soil is also polluted through polluted water and air. These pollutants are mixed into the soil through the rain water.
Such as H2SO4 acid is formed by mixing of SO2 with rainy water in the air. The fertilizers, pesticides and weedicides are being sprayed over the crops. All these are mixed with soil to produce harmful effects. The growth of plants is inhibited or reduced due to this type of pollution and sometime their death also take place.
Excluding these, soil pollution also caused by the disposal of house hold detergents, sewage, flowing oils, radio active substances and hot water etc. The main pollutants of soil are D.D.T. and weedicides [2, 4D ( 2, 4 di chlorophenoxy acetic acid),2, 4, 5-T ( 2, 4, 5, tri chloropheinoxy acetic acid)].
Control : Soil pollution can be controlled through biological degradation of waste materials.The various carbonic materials of agriculture waste, cattle dung etc can be minimised by the use of bio-gas plants which can produce energy also. Inspite of all the measures pesticides and weedicides should be used in limited quantity only when it is required.

Plant indicators :- "Such type of plants which give additional information about the environment or habitat are called plant indicators". e.g. growing ofViola plants indicates the presence of Zinc in soil.
Occimum shows presence of copper in soil.Silene (a plant) indicate presence of cobalt. The presence of Lichens shows that atmosphere is free from the pollutants like CO and SO2.


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