CBSE – 8th Standard Science

CBSE - 8th Standard Science

Pollution Of Air And Water

  • The substances which contaminate the air are called air pollutants
  • When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution.
  • The sources of air pollutants are factories, power plants, automobile exhausts and burning of firewood and dung cakes.
  • Many respiratory problems are caused by air pollution.


  • Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides
  • .Carbon monoxide is a poisonous gas, reduces the oxygen-carrying capacity of the blood.
  • Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays. CFCs damage the ozone layer of the atmosphere
  • The trapping of radiations by the atmosphere it is called the greenhouse effect.
  •  Methane, Nitrous oxide and CO2, are also called greenhouse gases



  • Gases like CO2 methane, nitrous oxide and water vapour traps heat and does not allow it to escape into space.
  •  As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.
  • Use Cleaner fuels like CNG and LPG. alternative  fuels for our energy requirements. solar energy, hydropower and wind energy.
  • The substances that pollute water are called water pollutants. sewage, toxic chemicals, silt, get mixed with water, the water becomes polluted.



  • The soil is also affected by impure water, causing changes in acidity, growth of worms, pesticides and weedicides chemicals dissolve in water and seep into the ground to pollute ground water.
  • Water contaminated with sewage may contain bacteria , viruses, fungi and parasites which cause diseases like cholera, typhoid and jaundice.
  • Water which is suitable for drinking is called potable water
  • Boiling and Chlorination is used for purifying water.
  • Water treatment plants should be installed in all industrial areas
  • Air pollution is the contamination of air by impurities which may have a harmful impact on the living organisms and the non-living components.
  • Pollutants are the substances which contaminate air and water.
  • Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants of air.
  • Increasing levels of greenhouse gases like CO2 are leading to global warming.
  • Water pollution is the contamination of water by substances harmful to life.
  • Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.
  • Water which is purified and fit for drinking is known as potable water.
  • If the vehicles registered in Delhi are lined up one after the other, the total length would be nearly equal to the combined lengths of the two longest rivers in the world, Nile and Amazon.
  • Global warming can cause sea levels to rise dramatically. In many places, coastal areas have already been flooded.



  •  Global warming could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals.
  •  Majority of people living in regions which are threatened by global warming are in Asia.
  • A recent climate change report gives us only a limited time to keep the greenhouse gases at the present level.
  • Otherwise, the temperature may rise by more than 2 degrees Celsius by the end of the century, a level considered dangerous.
  • 25% of the world is population is without safe drinking water.
  • While brushing your teeth, leaving the tap running may waste several liters of water.
  • A tap that drips once every second wastes a few thousand liters of water every year. Think about it.
  • Over the past 2 decades, Indiaís most famous tourist attraction, Taj Mahal located in Agra has become a matter of concern.
  •  Experts have warned that pollutants in air are discolouring its white marble.
  •  So, it is not only living organisms that get affected by polluted air but non-living things like buildings, monuments and statues also get affected.
  • The industries located in and around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide.
  • These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid.
  • The acids drop down with rain, making the rain acidic. This is called acid rain.
  •  Acid rain corrodes the marble of the monument. The phenomenon is also called ìMarble cancerî.



  • Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble.
  • The Supreme Court has taken several steps to save the Taj.
  • We are all aware that our environment is not what it used to be.
  • Our elders talk about the blue sky, clean water and fresh air that was available in their times.
  • Now the media regularly reports on the falling quality of the environment. We ourselves feel the impact of the falling quality of air and water in our lives.
  • The number of people suffering from diseases of the respiratory system, for example, is steadily rising.
  • We shudder to imagine a time when clean air and water may no longer be available
  •  You have learnt about the importance of air and water, we will study about the harmful changes taking place in our surroundings and their effects on our lives.
  • The chemicals released include arsenic, lead and fluorides which lead to toxicity in plants and animals.
  • There are regulations to prevent this.
  • Industries are supposed to treat the waste produced before discharging it into waters, but quite often the rules are not followed.
  •  The soil is also affected by impure water, causing changes in acidity, growth of worms, etc.
  • The importance of pesticides and weedicides for the protection of crops.
  • However, all these chemicals dissolve in water and are washed into water bodies from the fields.
  • They also seep into the ground to pollute ground water.
  • Have you seen ponds which look green from a distance because they have a lot of algae growing in them?
  • This is caused by excessive quantities of chemicals which get washed from the fields.
  • These act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria.
  •  A lot of oxygen in the water body gets used up.
  •  This results in a decrease in the oxygen level which may kill aquatic organisms.