(Study Material) Notes on Air and Water Pollution For CBSE Class 8th

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Air and Water Pollution

  • Pollution is an undesirable change in physical, chemical or biological characteristics of our air, land or water caused by excessive accumulation of pollutants.
  • These changes may affect man directly or indirectly through his supplier of water and of agricultural and other biological products.

AIR POLLUTION

  • The air pollution is caused due to dust particles, industrial emission, automobile exhaust, smoke, dispersion of pesticides and radioactive materials.
  • Two major factors responsible for air pollution are population explosion and productivity increase.
  • Air pollutants can be categorised into primary pollutants and secondary pollutants.
  • Primary Air Pollutants and their Effects

Particulate matter comprises of solid and liquid aerosol suspended in the atmosphere. The particulate matter causes corrosion and erosion of surfaces and in human beings, it may cause respiratory problems.

Carbon monoxide (CO) is produced mainly by incomplete combustion of fossil fuels. It is a very poisonous gas. It reduces oxygen carrying capacity of blood and may also lead to death due to anoxia (oxygen starvation).

Hydrocarbons (HCs) or Volatile Organic Carbons (VOCs) are compounds composed of Biodiversity hydrogen and carbon. They may be saturated (methane) or unsaturated (ethylene). They cause irritation on mucous membrane and some may be carcinogenic e.g., formaldehyde.

Sulphur dioxide (SO2) is produced by combustion of coal and petroleum. In human beings, it causes respiratory problems. It also produces acid rain.

Nitrogen oxides (NO, N2O) are produced when nitrogen and oxygen combine together at high temperature in any combustion process. These gases cause the reddish-brown haze (brown-air) which is responsible for respiratory diseases in human beings. They also cause acid rain due to formation of HNO3.

Secondary Air Pollutants and their Effects

Photochemical smog contains pollutants like ozone, oxides of nitrogen, and peroxylacetyl nitrate (PAN). It is often called brown air where solar radiation is intense. The areas where solar radiation is less, smog formation is incomplete and the air is called grey air.

  • Ozone and PAN are commonly referred as oxidants. Ozone breathing affects the respiratory and nervous system in human. PAN damages chloroplast in plant and inhibits electron transport system.

Acid rain includes wet and dry deposition on the earth. Wet deposition refers to acidic water received through rain, fog and snow. Dry deposition refers to the wind blown acidic gases and particles which settle down on the earth. Acid rain damages marble, metal and stonework.

Control of air pollution

  • There are two devices to remove particulate air pollutants, viz. arresters and scrubbers.
  • Electrostatic precipitator (ESP) is most effective method to remove particulate pollutants.
  • Gaseous pollutants are controlled by combustion, absorption and adsorption techniques.
  • Automobile exhaust can be controlled by catalytic converter filters and by using good quality fuels.

WATER POLLUTION

Water pollution may be of following types:

(i) Physical pollution is caused by hot water from industries, oil spills from oil carriers etc.
(ii) Chemical pollution is caused by organic chemicals e.g., biocides, PCBs and inorganic chemicals e.g., phosphates, nitrates, fluoride and heavy metals.
(iii) Biological pollution is caused by pathogens such as viruses, bacteria, algae, protozoa and helminths.

  • Municipal wastewater carries organic wastes which are biodegradable, and this water is directly discharged into rivers.
  • Industrial wastewater is contaminated by a variety of organic and inorganic pollutants. All the rivers of India are heavily polluted by the discharge of industrial wastewater.
  • Surface runoff from land is contaminated with pesticide residues and residues of inorganic fertilisers.
  • Oil spills from oil carriers and oil refineries mainly cause oil pollution to marine ecosystem. Effects of Water Pollution
  • Organic and inorganic wastes decrease the dissolved O2content of water bodies and affect aquatic ecosystem.
  • The demand for oxygen is directly related to increasing input of organic wastes and is expressed as biochemical oxygen demand (BOD) of water.
  • Chemical oxygen demand (COD) is the measure of pollution load in water.
  • Biological magnification is the phenomenon through which certain pollutants e.g., DDT, PCB get deposited in tissues in increasing concentrations along the food chain.
  • Eutrophication is the process of nutrient enrichment of water and consequent loss of species diversity.
  • Contaminated water can any germs of water-borne diseases like jaundice, cholera, typhoid, etc. and thus, may affect human health.
  • Mercury poisoning (Minamata disease) was caused due to consumption of fish captured from Minamata Bay in Japan.
  • Cadmium pollution can cause itai-itai disease and cancer of liver and lung. Ground water Pollution
  • Excess nitrate in groundwater drinking water, reacts with haemoglobin and forms non functional methemoglobin which impairs oxygen transport. This is called methaemogiobinemia or Mtte-baby syndrome.
  • Excessive exposure to arsenic causes black-foot disease. For improving Water Quality
  • Industrial and municipal waste water are treated in Effluent Treatment Plant (ETP) prior to their disposal in rivers or water bodies.

Courtesy: EPA Victoria

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