The presence of unusually high concentrations of harmful substances in the environment is known as pollution. This means that when there are substances that can be harmful to the health of living organisms in the environment more than the amount they can tolerate, we say that the environment is polluted. The most common pollution causing health hazard today are the air, water and soil pollution.
Any unwanted or harmful substance which pollutes the environment is called a pollutant. Normally harmful substances can be present in the environment. Carbon dioxide, carbon monoxide and nitrogen dioxide are usually present in the air in small quantities and they are not harmful to us. However when present in quantities more than which we can tolerate, they become pollutants.
It is the pollution of air by harmful gases (sulphur diffarmingoxide, carbon monoxide, carbon dioxide etc.), smoke and dust. The major pollutants are Carbon dioxide, nitrogen dioxide, nitrous oxide, sulphur dioxide, suspended particulate matter and carbon monoxide.
Air pollution is usually caused by burning of fossil fuels like petroleum and coal, burning of wood and cow dung cakes in homes, factories, vehicles and power plants. For example New Delhi is one of the most air polluted cities in the world because of excessive use of fossil fuels by cars and factories.
The contamination of water bodies such as lakes, rivers, oceans, underground water and seas by harmful substances is known as water pollution. Polluted water becomes unfit for drinking, bathing, washing and irrigation. The major cause of pollution of water is sewage, industrial wastes, pesticides and fertilizers from farming. Garbage dumping can also leak out pollutants into underground water.
The major pollutants are usually lead, mercury, fertilizer and pesticide compounds. For example the major source of pollution of the Ganga River is sewage and industrial wastes from tanning factories.
Soil pollution is the contamination of soil due by harmful substances. Polluted soil becomes unfit for growing crops and plants and is usually accompanied by water pollution. The major causes of soil pollution are over irrigation, pesticides, sewage and garbage dumping, deforestation and mining. The most common pollutants are heavy metals like lead and mercury, pesticide compounds, salt and mineral ores.
Water and soil pollution usually occur together as polluted water seeps into soil and contaminates it. Pollutants can also leach out from soil into water bodies when it rains.
Thus, this topic has immense significance for the students of Biology. To enhance their knowledge about this topic, students should attempt some practice questions with sample solutions like some illustrations given here- NCERT solutions for pollution air water.
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