Environmental Issues Class 12 | Term 2 | Ecology |


Environmental Issues Class 12, Term 2, Ecology


  • Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water or soil.
  • Human population explosion increases the demand for food, water , home , electricity , roads , automobiles etc.
  • It leads to pollution of air, water and soil.
  • Agents that cause pollution are called pollutants.
  • The government of India has passed the Environment Act , 1986 to control environmental pollution and protect and improve the quality of our environment.

Types of Pollution

There are four types of pollution namely;

  • Air pollution
  • Water pollution
  • Noise pollution
  • Soil pollution

Air Pollution

The air pollution is caused due to undesirable change in the physical , chemical and biological characteristics of air.

Factors Involved in Air pollution

  1. Concentration of pollutants
  2. duration of exposure to the pollutants
  3. Type of organism it affects

Causes of Air pollution

  • Particulate and gaseous air pollutants from smokestacks of thermal power plants , smelters etc.
  • Pollutants from automobiles .
  • Uses of leaded petrol.
  • Garbage decomposition.

Effects of Air pollution

a. Human and Animals

  • According to Central Pollution Control Board (CPCB), particulate size of less than 2.5 micrometer in diameter (PM 2.5) causes greatest harm such as respiratory problems , irritation , inflammations and damage to lungs and premature deaths.
  • It also causes cancer and genetic mutations.

b. Plants

  • It causes fruit damage and various leaf diseases like necrosis , chlorosis etc.
  • It decreases the crop yield resulting in premature death of plants.
  • It increases infestation by pests.

Control of Air Pollution

Air pollution can be controlled by

  1. Catalytic converters
  2. Electrostatic precipitator
  3. Scrubber
  • Catalytic converters- having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing emission of poisonous gases and when the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
  • Electrostatic precipitator
  • Electrostatic precipitator can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant.
  • It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.
  • The electrons attach to dust particles giving them a net negative charge.
  • The collecting plates are grounded and attract the charged dust particles.
  • The velocity of air between the plates must be low enough to allow the dust to fall.

Environmental Issues Class 12

Fig. Electrostatic Precipitator

  • Scrubber
  • A scrubber can remove gases like sulphur dioxide.
  • In a scrubber, the exhaust is passed through a spray of water or lime.

Environmental Issues Class 12

Fig. a scrubber

  • In Delhi, Entire fleet of public transport switched over to Compressed Natural Gas (CNG)because
  • CNG burns most efficiently
  • Very little of it is left unburnt
  • CNG is cheaper than petrol or diesel
  • Cannot be siphoned
  • Cannot be adulterated like petrol or diesel.
  • The problem of using CNG is the difficulty of laying down pipelines to deliver CNG through distribution points/pumps and ensuring uninterrupted supply.
  • Parallel steps taken in Delhi for reducing vehicular pollution include
  • Phasing out of old vehicles
  • Use of unleaded petrol
  • Use of Low-Sulphur petrol and diesel
  • Use of catalytic converters in vehicles
  • Application of stringent pollution level norms for vehicles, etc.

Environmental Issues Class 12

Fig. catalytic converters

Noise Pollution

  • Noise pollution is undesired high level of sound.

Effects of Noise Pollution

  • Psychological and physiological disorders in humans.
  • High sound level, 150 dB or more damage ear drums thus permanently impairing hearing ability..
  • Chronic exposure to a relatively lower noise level permanently damage hearing abilities of humans.
  • Causes sleeplessness, increased heart beating, altered breathing pattern.

Causes of Noise Pollution

  • Burning of crackers.
  • Transportation system.
  • Air craft and rail traffic.

Control of Air Pollution

  • Use of sound absorbent materials or by muffling noise.
  • Making horn-free zones around hospitals and schools
  • Using permissible sound-levels of crackers and of loudspeakers
  • Laying down timings after which loudspeakers cannot be played.


Fig. Noise pollution

Water Pollution 

  • Water bodies are lifeline of all living organisms.
  • Water pollution refers to the concentration of water bodies due to changes in physical , chemical and biological properties of water that affect the living beings .
  • Due to human activities , the ponds , lakes , streams , rivers , estuaries and oceans are become polluted.
  • The government of India has passed the Water Act , 1974 to safeguard our water resources.
  • The amount of organic matter in sewage water by measuring Biochemical Oxygen Demand (BOD).
  • Biochemical oxygen demand is the amount of oxygen required by aerobic microorganisms to break down all organic matter.

Harmful Effects of Water Pollution

  • Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge which causes mortality of fish and other aquatic creatures.
  • Sewage from our homes as well from hospitals contains many undesirable pathogenic microorganisms which can cause diseases like dysentery, typhoid, jaundice, cholera.

Causes of Water Pollution

  • Presence of large amounts of nutrients in waters also causes excessive growth of planktonic (free-floating) algae, called an algal bloom.

Environmental Issues Class 12

Fig. Algal bloom

  • Algal blooms cause deterioration of the water quality and fish mortality and some bloom-forming algae are toxic to human beings and animals.
  • Water hyacinth (Eichhorniacrassipes) called as ‘terror of Bengal’ is the most problematic water weed which grow abundantly in eutrophic water bodies, and lead to an imbalance in the water ecosystem.


Fig. water hyacinth


  • It is the increase in concentration of the toxicant at successive trophic levels.
  • Biomagnification happens because a toxic substance accumulated by an organism cannot be metabolized or excreted, and is thus passed on to the next higher trophic level.
  • Example of toxic substances- mercury, DDT.


  • Eutrophication is the natural aging of a lake by biological enrichment of its water.

Natural eutrophication-

  1. Streams draining into the lake introduce nutrients such as nitrogen and phosphorus due to which aquatic organisms grow.
  2. As silt and organic debris pile up, the lake grows shallower and warmer, with warm-water organisms supplanting those that thrive in a cold environment.
  • Marsh plants take root in the shallows and begin to fill in the original lake basin.
  1. Lake gives way to large masses of floating plants (bog), finally converting into land.

Cultural or Accelerated Eutrophication

  1. Pollutants from man’s activities like effluents from the industries and homes can radically accelerate the aging process and the process is called as Cultural or Accelerated Eutrophication.
  2. It causes by
  • Sewage, agricultural and industrial wastes.
  1. Nitrates and phosphates, which act as plant nutrients.
  • Sewage and plant nutrients overstimulate the growth of algae, causing unsightly scum and unpleasant odors, and robbing the dissolved oxygen from water, and other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the water’s dissolved oxygen content and thus a lake can choke to death.
  • Thermal wastewaters flowing out of electricity-generating units are another cause of pollution.
  • Thermal wastewater can eliminate the number of organisms sensitive to high temperature and also can enhance the growth of plants and fish in extremely cold areas but only after causing damage to the indigenous flora and fauna.

Control of Water Pollution

  • The cleaning of waste water occurs in two stages –
  1. The conventional sedimentation, filtering and chlorine treatments are given.
  2. The biologists developed a series of six connected marshes over 60 hectares of marshland.
  • Plants, algae, fungi and bacteria were seeded into this area, which neutralize, absorb and assimilate the pollutants.
  • The water flows through the marshes, it gets purified naturally.
  • A citizens group called Friends of the Arcata Marsh (FOAM) is responsible for the upkeep and safeguarding of this wonderful project.
  • Ecological sanitation is a sustainable system for handling human excreta, using dry composting toilets.
  • With the help of ecological sanitation human excreta can be recycled into a resource (as natural fertilizer).

Solid Wastes

  • Solid wastes refer to everything that goes out in trash.
  • Municipal solid wastes are wastes from homes, offices, stores, schools, hospitals.


Fig. solid wastes

Types of Solid Wastes

  1. Bio-degradable- the wastes which can be degraded by microorganisms. Example- food materials.
  2. Recyclable- the wastes which can be converted into new materials. Example- glass, paper.
  • Non-biodegradable-the wastes which cannot be degraded or takes long time to get degraded. Example – plastic.

Prevention of Solid Wastes

  1. Reduction in use of plastics and use of eco-friendly packaging.
  2. Carrying cloth or other natural fiber carry-bags.
  3. Refusing polythene bags.
  • Burning and open dumps are used to reduce the volume of the wastes.
  • Open dumps serve as the breeding ground for rats and flies.
  • Sanitary landfills were adopted as the substitute for open-burning dumps.


Fig. Landfill

  • Polyblend is a fine powder of recycled modified plastic which is mixed with bitumen to lay roads.
  • Hospitals wastes contain disinfectants, harmful chemicals and pathogenic micro-organisms.
  • Incinerators are used to dispose hospital waste.
  • Irreparable computers and other electronic goods are known as electronic wastes (e-wastes).
  • E-wastes are buried in landfills or incinerated.


Fig. electronic wastes

Agro-chemicals and their Effects

  • The chemicals which are used in agriculture are called agro-chemicals. Example- herbicides, fungicides, pesticides.
  • Increasing amounts of artificial fertilizers can cause eutrophication.
  • Integrated organic farming is a cyclical zero-waste procedure where waste products from one process are cycled in as nutrients for other processes.


  1. Cattle excreta (dung) are used as manure.
  2. Crop waste is used to create compost, which can be used as a natural fertilizer or can be used to generate natural gas.


Fig. Cattle dung used as manure


Biomagnification is the increase in concentration of a toxic substance with the increase in trophic levels. Biomagnification also called as Biological magnification.

Toxic substances are accumulated in the body of an organism and are neither metabolised nor excreted. Hence, it is passed on as such in the food chain but concentration is increased at each successive trophic level.

Let us take an example. (see the picture below) DDT is an insecticide. When it is sprayed on the crops, it also enter the water bodies. The concentration of DDT in water is 0.003 ppm. It keeps on increasing at each successive trophic levels. It reaches to 0.04 ppm in zooplanktons and reaches to 25 ppm in fish eating birds.

Radioactive Wastes

  • Radioactive wastes are those which contain radioactive materials.
  • Radiation given off by nuclear waste causes mutations to occur at a very high rate.
  • At high doses nuclear radiation is lethal but at lower doses it creates various genetic disorders such as cancer.
  • Storage of nuclear waste after pre-treatment done in shielded containers buried within the rocks, about 500 m deep below the earth’s surface.


Fig. shielded containers to store nuclear waste

Greenhouse Effect and Global Warming

  • The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth’s surface and atmosphere.
  • Carbon dioxide and methane are commonly known as greenhouse gases.
  • Greenhouse effect is important to increase the temperature which is essential for the organisms to live.
  • Due to the increase in the level of greenhouse gases the Earth gets heated which is known as Global warming.


Fig. Greenhouse effect

Effects of global warming

  1. Deleterious changes in the environment and resulting in odd climatic changes.
  2. Increased melting of polar ice caps as well as of other places like the Himalayan snow caps.
  • Rise in sea level that can submerge many coastal areas.
  1. Cutting down use of fossil fuel
  2. Improving efficiency of energy usage
  3. Reducing deforestation,
  • Planting trees and slowing down the growth of human population.

Ozone Depletion in the Stratosphere

  • Upper part of the atmosphere is called the stratosphere.
  • Ozone is a layer in the earth’s stratosphere which acts as a shield absorbing ultraviolet radiation from the sun.


Fig. Ozone layer

  • UV rays are highly injurious toliving organisms as the chemical bonds within DNA and proteins of living organisms break by its high energy.
  • The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
  • Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere so there should be a balance between production and degradation of ozone in the stratosphere.
  • The balance has been disrupted due to enhancement of ozone degradation by chlorofluorocarbons (CFCs).
  • CFCs discharged in the lower part of atmosphere move upward and reach stratosphere.
  • In stratosphere, UV rays act on them releasing Cl atoms.
  • Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts.
  • Ozone depletion resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole.
  • UV-B damages DNA and mutation may occur which causes aging of skin, damage to skin cells and various types of skin cancers.
  • In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow-blindness cataract.
  • An international treaty Montreal Protocol, was signed at Montreal (Canada) to control the emission of ozone depleting substances.

Degradation by Improper Resource Utilization and Maintenance

  • The degradation of natural resources can occur by improper resource utilization practices such as
  1. Soil erosion and desertification
  2. Soil erosion is the removal of the top layer of the soil.
  3. Human activities such as over-cultivation, unrestricted grazing, deforestation and poor irrigation practices, results in arid patches of land which when extend and meet over time, a desert is created.


Fig. soil erosion

  1. Waterlogging and soil salinity
  • Irrigation without proper drainage of water leads to waterlogging in the soil.
  1. Waterlogging draws salt to the surface of the soil which is then deposited as a thin crust on the land surface or starts collecting at the roots of the plants and damages the crop production.


Fig. water logging in the soil


  • Deforestation is the conversion of forested areas to non-forested ones..
  • Causes of deforestation
  1. Slash and burn jhum cultivation.
  2. Famers cut down the trees of the forest and burn the plant remains.
  • Ash is used as fertilizer.
  1. Land is used for farming or cattle grazing,
  2. If land is left uncultivated for several years replenishment of minerals occur.

Effects of Deforestation

  1. Enhanced carbon dioxide concentration in the atmosphere.
  • Loss of biodiversity.
  • Disturbs hydrologic cycle
  1. Soil erosion
  2. Desertification in extreme cases.
  • Reforestation is the process of restoring a forest that once existed but was removed at some point of time.
  • The Government of India has recently instituted the Amrita Devi Bishnoi Wildlife Protection Award.
  • Government of India has introduced the concept of Joint Forest Management (JFM) so as to work closely with the local communities for protecting and managing forests.
  • Chipko movement was started by local women of Garhwal Himalayas to protect trees.


Fig. Deforestation and Fig. Reforestation


# Environmental Issues Class 12

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