Grade 11 Zoology Note

Environmental Pollution

Nature, is a beautiful creation. It is a divine gift to us by god. The earth with its atmosphere of air, land and water which sustain life is known as biosphere. The biotic and abiotic components of this biosphere interact in a delicately controlled and in an orderly manner to sustain life upon the earth. Any adverse effect of the delicate balance of the biosphere caused by man or so can lead to unfavorable conditions for the wall being the survival of mankind. This unfavorable condition may be called pollution of biosphere. 

Pollution is addition of foreign matter to the natural environment to a degree which is insupportable by nature. Air, water, and soil are the major component of biosphere, on which human life dependent but with rapid industrialization and urbanization in the name of progress and development, degradation of air, water and soil is now increasing. So the purity of these components to a degree that human life is not adversely affected is our collective responsibility to know about their pollution problems.


A pollutant is a toxic agent like germs in sewage, chemicals in the effluent, pesticides of agriculture, and gases of the air. A pollutant is a substance which may alter environmental constituents or cause pollution. By definition a pollutant is anything including a chemical, geochemical substance or a biological product that deteriorates our natural environment. Pollutants are residues of the things we make use and through away.

The pollutant categories into two types:

Degradable Pollutant: A degradable pollutant can be decomposed, removed or consumed and this reduced to acceptable levels either by natural processes or by human engineered system such as sewage treatment, as long as the systems are not overloaded.

Non-Degradable pollutant: These are not broken down by natural processes, e.g. lead, aluminum, mercury, DDT etc. they are not cycled in ecosystem naturally.


Air Pollution

Air is the most vital component without which the question of survival dose not arise beyond a few minutes but due to rapid industrialization the air pollution become a cause of public concern. Air pollution can be define as “the presence of one or several substances in the external atmosphere, introduced by man to such an extent as to effect health and welfare of human system and the life in the atmosphere.”

Sources: Air pollution is being done mainly due to gaseous products from industry, thermal power stations, automobiles combustion processes, fire etc. Some source of air pollution is:

a) Industrial units: fluoride, nitric acid, iron-steel, chloro-alkali,cement, mineral acid plant and industries are most common sources of air pollutants. These emits a variety of pollutants in the atmosphere specially oxides of carbon, nitrogen, and sulphur.

b) Thermal power plants: thermal power plants of are main source of dust, carbon oxide, aldehydes, carbon, hydrocarbon, ash etc. are the common emission of power plants.

c) Automobile: Gasoline used in automobiles as fule produces carbon-monooxide, hydrocarbons, lead compounds, carbon particles and some carbonyl compounds in the atmosphere.  They are the major source of air pollution.

d) Mining: The intensive coal minings of world also the main cause of air pollution.

e) Other sources: the other sources of air pollution are solid wastes, radio-active natural sources, viable particles, odour pollutants etc.


Types: Although thousands of air pollutants are present in the atmosphere but some of which are important having an unique position in the air environment. They can be categories into:

1. Primary pollutants: these are directly produced as a result of interaction between two or more primary pollutants e.g. nitrogen peroxide, ozone, sulphur trioxide etc. or those which directly come out from different sources e.g. SO2 from H2SOindustry.

2. Secondary Pollutants: They are photo chemically active and responsible for the formation of smog or which are formed in the atmosphere from primary pollutant e.g. H2SO4 from SO2. They can be categories as,

a) Gaseous: carbon compound, H2S, Halogens etc.

b) Agriculture: Pesticides, Fertilization etc.

c) Complex organic matter: Benzene, ether, aldehyde, ethylene etc.

d) Deposited matter: Soot, smoke, tar, dust etc.

e) Metals: Lead, zinc, iron etc.

f) Others: floride, radioactive rays, toxic substance etc.

Some air pollutants and their effect:

1. Ozone (O3): Ozone is present in the atmosphere mainly in a layer at altitude of 20-30km in ozonosphere. It screens out 99% of solar radiation of harmful wavelength. Over few years it has been clear that the ozone concentration of the earth’s atmosphere is thinning out largely due to increasing use of CFMS or feron by human beings. With the depletion of atmospheric ozone there is danger of the increase in the flux off UV radiation over earth’s surface. And it can cause skin cancer, can damage in cornea and can reduce the crop production.

2. Carbon Dioxide (CO2): CO2 is a combustion product. About three billion tonnes of coal and 13 billion barrels of oil burns every year in the world. It also release by animal during the process of respiration. The world’s temperature is becoming warmer due to carbon dioxide.

3. Carbon Monooxide (CO): It comes from gasoline burning, coal combustion and automobiles exhausts. Automobile produce about 80% of total CO emission. Cigarette smoking is one of the major causes of CO poisoning in man. It can cause difficulties in respiration, hearing, and in nervous system when its level increases in air. It also causes leaf curling, leaf dropping and reduction in leaf size in plants.

4. Sulphur Dioxide (SO2): SO2 is one of the most potent pollutant present in the air over and around the industrial areas. Burning of coal, fuel, chemical industries and automobiles are the major sources of SO2 production. In atmosphere SO2 reacts with water to form sulphurous acid. It also reacts with oxygen to form SO3 by photochemical process. The latter react with water in presence of sunlight and produces H2SO4. Matters like papers, textiles, stones, marbels and metals are severely attacked by SO2 in presence of atmospheric moisture. SO2 damages higher plants by causing neurotic lesions on leaves. In human it damage skin, mental disease, respiratory problem etc.

Preventive measures:

1. Public awareness programs should be lunched.

2. The alternative source of energy like solar energy, wind energy, electric energy etc. should be used in place of coal, wood, oil etc.

3. In industries the air filtration technique should be used.

4.  Population growth rate should be controlled.

5. Plantation should be done.

6. The use of cheap fuel with higher sulphur content should be avoided.



Water Pollution

Water is the prime necessity of the life and survival is not possible in the absence of water. No life without water is a common saying. Water may be present in rivers, ponds, lakes etc. Due to population explosion, industrialization and urbanization today, many of these water resources get polluted.  Addition of any substance to the water or any undesirable change in physical chemical or biological characteristics of water, which interferes with its use for legitimate purpose, is called water pollution.

Sources of water pollution

1. Point sources: Point sources of water pollution are of definite identity with almost constant volume and fixed composition of the effluents discharged.

2. Diffused Sources: These are points situated far beyond the sight, having wastes of unknown composition and volume.

3. Potential Sources: The potential source of water pollution in all developing or underdeveloped countries are sewage, industrial effluents and wastes, agriculture and physical pollutants.


1. Sewage and Domestic Wastes: The domestic water borne wastes including human and animal excreta, domestic waters, and industrial water borne wastes, ground and atmospheric waters which enters the sewerage system is collectively known as Sewage. One of the most common sources of water pollution is the discharge of untreated sewage into fresh water bodies. It has been estimated that about 75% water pollution is caused by sewage and domestic waters.

 As the sewage contains organic matter that harbor disease causing microorganism and accelerates dissolved oxygen consumption for decomposition of such huge amount of organic matter by microorganism. This process leads to develop maximum biological water demand.

2. Industrial effluents: Most of the Nepali water streams are seriously polluted by industrial wastes, which come along waste waters of different industries. The industrial effluents contain several toxic substances.

The paper and pulp industries cause mercury pollution. The symptoms of mercury poisoning include visual disturbance, mental disorders, convulsions and genetic diseases and death. The lead causes liver and kidney damage and mental disorder as well as weakness. The oils, hydrocarbon compounds acids, alkalis, cyanides and metals cause several effects in human health.

3.Agricultural wastes: Pesticides is the another major source of water pollution. An important source of pesticides in the aquatic sources is run-off form the fields and industrial effluents. These are responsible for contamination of aquatic ecosystem by which they reach to different tropic levels of food chain of terrestrial ecosystem, causing serious health hazards through the process of biological magnification.

4. Hot Water: when hot water is mixed with water bodies from industries affects aquatic animals.

5.Surface run-off: Minerals, slits and organic wastes are carried to the lakes , rivers and the seas from construction sites, agriculture fields and other land parts are also responsible for water pollution.

Prevention of water pollution:

Different types of waste should be recycled or treated before transfer into the rivers.

Use of the pesticides should be reduces.

Public awareness programs should be lunched.

Dissolved substances from the water should be removed by physical or chemical method.

Proper drainage for sewage and efficient sewage collection should be managed properly.

Industrial effluents should be treated before discharging into the water bodies

Bad habits of people like open disposal of wastes, and washing clothes near the water sources must be changed.

Soil Pollution

Soil is the surface layer of earth on which human civilization depends for its existence. It provides us place to live, as reservoir for the mineral wealth and sustains plant life on earth.Any undesirable change in physical, chemical and biological characteristics of soil, which reduces soil fertility and affects plants and animals life, is called soil pollution.

Sources of soil pollution

There are numerous sources of soil pollution, but the important among them are,


1. Indiscriminate discharges of industrial effluents on land and in water.

2. Unscientific disposal of solid water on land.

3. Increasing intensive fertilizers and pesticides.

4. Open defection of animal and human beings especially in rural areas.

5. Radioactive out fall is putting additional poisonous ingredients into the land.



1. Pesticides: In the recent years, there has been tremendous use of pesticides in agriculture. When pesticides are used in agricultural land, they accumulate in plant. Through food chain, they reach to animal body. So large amount of pesticides used in crops can affect human being directly.

2.  Chemical Fertilizer: In excess concentration chemical fertilizers pollute soil and cause damage of soil flora and fauna. These are capable to alter the nature of soil too. Nitrogenous chemical fertilizers have been found responsible for reduced plant growth, if they are present in more concentration.

3. Radioactive Substance: Radioactive substances produced during fission and fusion process enter into the life supporting soil through leaching and percolation.

4. Acids:Acids like HNO3 and H2SO4 coming from acid rain makes the soil acidic. Which cause death of number of micro flora and plants. They also degrade the quality and fertility of soil.

5.Metals: Soil pollution also occurs due to surface run-off of water containing considerable amount of metals from various sources. Metal in soil is basically due to industrial and domestic discharges in or on land surface.

Control measures:

The waste product should be recycled.

Sewage or dumping sites should be properly managed.

The use of fertilizer and pesticides should be reduced and replaced by bio fertilizers.

The use of pesticides should be reduced and the biological method should be used to control pests and diseases

Education awareness and plantation should be increased.

Water logging in the field should be prevented.

Pesticides: A pesticide is any substance used to kill, repel, or control certain forms of plant or animal life that are considered to be pests. Pesticides include herbicides for destroying weeds and other unwanted vegetation, insecticides for controlling a wide variety of insects, fungicides used to prevent the growth of molds and mildew, disinfectants for preventing the spread of bacteria, and compounds used to control mice and rats. Because of the widespread use of agricultural chemicals in food production, people are exposed to low levels of pesticide residues through their diets. Scientists do not yet have a clear understanding of the health effects of these pesticide residues. People may also be exposed to pesticides used in a variety of settings including homes, schools, hospitals, and workplaces.

DDT:DDT ("dichlorodiphenyltrichloroethane") is a colorless, crystalline, tasteless and almost odorless organochloride known for its insecticidal properties. DDT has been formulated in almost every conceivable form, including solutions in xylene or petroleum distillates, emulsifiable concentrates, water-wettablepowders, granules, aerosols, smoke candles and charges for vaporizers and lotions.

First synthesized in 1874, DDT's insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939. It was then used in the second half ofWorld War II to control malaria and typhus among civilians and troops. After the war, DDT was made available for use as an agricultural insecticide and its production and use duly increased.


Effects of Pesticides:

1.They are toxic in nature

2. The small doses of DDT in human are reported to have lethal effects.

3. They excess use of pesticides decrease the soil fertility.

4. Some pesticides can also effect on human DNA.


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