NCERT Textbook: Environmental Issues (Old NCERT) | NCERT Textbooks (Class 6 to Class 12) - CTET & State TET PDF Download

 Page 1


Human population size has grown enormously over the
last hundred years. This means increase in demand for
food, water, home, electricity, roads, automobiles and
numerous other commodities. These demands are exerting
tremendous pressure on our natural resources, and are
also contributing to pollution of air, water and soil. The
need of the hour is to check the degradation and depletion
of our precious natural resources and pollution without
halting the process of development.
Pollution is any undesirable change in physical,
chemical or biological characteristics of air, land, water or
soil. Agents that bring about such an undesirable change
are called as pollutants. In order to control environmental
pollution, the Government of India has passed the
Environment (Protection) Act, 1986 to protect
and improve the quality of our environment (air, water
and soil).
16.1 AIR POLLUTION AND ITS CONTROL
We are dependent on air for our respiratory needs.  Air
pollutants cause injury to all living organisms. They
reduce growth and yield of crops and cause premature
death of plants. Air pollutants also deleteriously affect the
respiratory system of humans and of animals. Harmful
CHAPTER 16
ENVIRONMENTAL ISSUES
16.1 Air Pollution and Its
Control
16.2 Water Pollution and Its
Control
16.3 Solid W astes
16.4 Agro-chemicals and
their Effects
16.5 Radioactive W astes
16.6 Greenhouse Effect and
Global Warming
16.7 Ozone Depletion in the
Stratosphere
16.8 Degradation by Improper
Resource Utilisation and
Maintenance
16.9 Deforestation
2022-23
Page 2


Human population size has grown enormously over the
last hundred years. This means increase in demand for
food, water, home, electricity, roads, automobiles and
numerous other commodities. These demands are exerting
tremendous pressure on our natural resources, and are
also contributing to pollution of air, water and soil. The
need of the hour is to check the degradation and depletion
of our precious natural resources and pollution without
halting the process of development.
Pollution is any undesirable change in physical,
chemical or biological characteristics of air, land, water or
soil. Agents that bring about such an undesirable change
are called as pollutants. In order to control environmental
pollution, the Government of India has passed the
Environment (Protection) Act, 1986 to protect
and improve the quality of our environment (air, water
and soil).
16.1 AIR POLLUTION AND ITS CONTROL
We are dependent on air for our respiratory needs.  Air
pollutants cause injury to all living organisms. They
reduce growth and yield of crops and cause premature
death of plants. Air pollutants also deleteriously affect the
respiratory system of humans and of animals. Harmful
CHAPTER 16
ENVIRONMENTAL ISSUES
16.1 Air Pollution and Its
Control
16.2 Water Pollution and Its
Control
16.3 Solid W astes
16.4 Agro-chemicals and
their Effects
16.5 Radioactive W astes
16.6 Greenhouse Effect and
Global Warming
16.7 Ozone Depletion in the
Stratosphere
16.8 Degradation by Improper
Resource Utilisation and
Maintenance
16.9 Deforestation
2022-23
271
ENVIRONMENTAL ISSUES
effects depend on the concentration of pollutants, duration of exposure
and the organism.
Smokestacks of thermal power plants, smelters and other industries
release particulate and gaseous air pollutants together with harmless
gases, such as nitrogen, oxygen, etc. These pollutants must be separated/
filtered out before releasing the harmless gases into the atmosphere.
Figure 16.1 Electrostatic precipitator
There are several ways of removing particulate matter; the most widely
used of which is the electrostatic precipitator (Figure 16.1), which 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. These
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. A scrubber (Figure 16.1) can remove gases like sulphur
dioxide. In a scrubber, the exhaust is passed through a spray of water or
lime. Recently we have realised the dangers of particulate matter that are
very very small and are not removed by these precipitators. According to
Central Pollution Control Board (CPCB), particulate size 2.5 micrometers
or less in diameter (PM 2.5) are responsible for causing the greatest harm
to human health. These fine particulates can be inhaled deep into the
lungs and can cause breathing and respiratory symptoms, irritation,
inflammations and damage to the lungs and premature deaths.
2022-23
Page 3


Human population size has grown enormously over the
last hundred years. This means increase in demand for
food, water, home, electricity, roads, automobiles and
numerous other commodities. These demands are exerting
tremendous pressure on our natural resources, and are
also contributing to pollution of air, water and soil. The
need of the hour is to check the degradation and depletion
of our precious natural resources and pollution without
halting the process of development.
Pollution is any undesirable change in physical,
chemical or biological characteristics of air, land, water or
soil. Agents that bring about such an undesirable change
are called as pollutants. In order to control environmental
pollution, the Government of India has passed the
Environment (Protection) Act, 1986 to protect
and improve the quality of our environment (air, water
and soil).
16.1 AIR POLLUTION AND ITS CONTROL
We are dependent on air for our respiratory needs.  Air
pollutants cause injury to all living organisms. They
reduce growth and yield of crops and cause premature
death of plants. Air pollutants also deleteriously affect the
respiratory system of humans and of animals. Harmful
CHAPTER 16
ENVIRONMENTAL ISSUES
16.1 Air Pollution and Its
Control
16.2 Water Pollution and Its
Control
16.3 Solid W astes
16.4 Agro-chemicals and
their Effects
16.5 Radioactive W astes
16.6 Greenhouse Effect and
Global Warming
16.7 Ozone Depletion in the
Stratosphere
16.8 Degradation by Improper
Resource Utilisation and
Maintenance
16.9 Deforestation
2022-23
271
ENVIRONMENTAL ISSUES
effects depend on the concentration of pollutants, duration of exposure
and the organism.
Smokestacks of thermal power plants, smelters and other industries
release particulate and gaseous air pollutants together with harmless
gases, such as nitrogen, oxygen, etc. These pollutants must be separated/
filtered out before releasing the harmless gases into the atmosphere.
Figure 16.1 Electrostatic precipitator
There are several ways of removing particulate matter; the most widely
used of which is the electrostatic precipitator (Figure 16.1), which 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. These
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. A scrubber (Figure 16.1) can remove gases like sulphur
dioxide. In a scrubber, the exhaust is passed through a spray of water or
lime. Recently we have realised the dangers of particulate matter that are
very very small and are not removed by these precipitators. According to
Central Pollution Control Board (CPCB), particulate size 2.5 micrometers
or less in diameter (PM 2.5) are responsible for causing the greatest harm
to human health. These fine particulates can be inhaled deep into the
lungs and can cause breathing and respiratory symptoms, irritation,
inflammations and damage to the lungs and premature deaths.
2022-23
272
BIOLOGY
Automobiles are a major cause for atmospheric pollution atleast in
the metro cities.  As the number of vehicles increase on the streets, this
problem is now shifting to the other cities too. Proper maintenance of
automobiles along with use of lead-free petrol or diesel can reduce the
pollutants they emit. Catalytic converters, having expensive metals namely
platinum-palladium and rhodium as the catalysts, are fitted into
automobiles for reducing emission of poisonous gases. As 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. Motor
vehicles equipped with catalytic converter should use unleaded petrol
because lead in the petrol inactivates the catalyst.
In India, the Air (Prevention and Control of Pollution) Act came
into force in 1981, but was amended in 1987 to include noise as an air
pollutant. Noise is undesired high level of sound. We have got used to
associating loud sounds with pleasure and entertainment not realising
that noise causes psychological and physiological disorders in humans.
The bigger the city, the bigger the function, the greater the noise!!  A
brief exposure to extremely high sound level, 150 dB or more generated
by take off of a jet plane or rocket, may damage ear drums thus
permanently impairing hearing ability. Even chronic exposure to a
relatively lower noise level of cities may permanently damage hearing
abilities of humans. Noise also causes sleeplessness, increased heart
beat, altered breathing pattern, thus considerably stressing humans.
Considering the many dangerous effects of noise pollution can you
identify the unnecessary sources of noise pollution around you which
can be reduced immediately without any financial loss to anybody?
Reduction of noise in our industries can be affected by use of sound-
absorbent materials or by muffling noise.  Stringent following of laws laid
down in relation to noise like delimitation of horn-free zones around
hospitals and schools,  permissible sound-levels of crackers and of loud-
speakers, timings after which loudspeakers cannot be played, etc., need
to be enforced to protect ourselves from noise pollution.
16.1.1 Controlling Vehicular Air Pollution: A Case
Study of Delhi
With its very large population of vehicular traffic, Delhi leads the coun-
try in its levels of air-pollution – it has more cars than the states of
Gujarat and West Bengal put together.  In the 1990s, Delhi ranked
fourth among the 41 most polluted cities of the world.  Air pollution
problems in Delhi became so serious that a public interest litigation
(PIL) was filed in the Supreme Court of India. After being censured very
strongly by the Supreme Court, under its directives, the government
was asked to take, within a specified time period, appropriate meas-
ures, including switching over the entire fleet of public transport, i.e.,
buses, from diesel to compressed natural gas (CNG).  All the buses of
Delhi were converted to run on CNG by the end of 2002. You may ask
the question as to why CNG is better than diesel. The answer is that
2022-23
Page 4


Human population size has grown enormously over the
last hundred years. This means increase in demand for
food, water, home, electricity, roads, automobiles and
numerous other commodities. These demands are exerting
tremendous pressure on our natural resources, and are
also contributing to pollution of air, water and soil. The
need of the hour is to check the degradation and depletion
of our precious natural resources and pollution without
halting the process of development.
Pollution is any undesirable change in physical,
chemical or biological characteristics of air, land, water or
soil. Agents that bring about such an undesirable change
are called as pollutants. In order to control environmental
pollution, the Government of India has passed the
Environment (Protection) Act, 1986 to protect
and improve the quality of our environment (air, water
and soil).
16.1 AIR POLLUTION AND ITS CONTROL
We are dependent on air for our respiratory needs.  Air
pollutants cause injury to all living organisms. They
reduce growth and yield of crops and cause premature
death of plants. Air pollutants also deleteriously affect the
respiratory system of humans and of animals. Harmful
CHAPTER 16
ENVIRONMENTAL ISSUES
16.1 Air Pollution and Its
Control
16.2 Water Pollution and Its
Control
16.3 Solid W astes
16.4 Agro-chemicals and
their Effects
16.5 Radioactive W astes
16.6 Greenhouse Effect and
Global Warming
16.7 Ozone Depletion in the
Stratosphere
16.8 Degradation by Improper
Resource Utilisation and
Maintenance
16.9 Deforestation
2022-23
271
ENVIRONMENTAL ISSUES
effects depend on the concentration of pollutants, duration of exposure
and the organism.
Smokestacks of thermal power plants, smelters and other industries
release particulate and gaseous air pollutants together with harmless
gases, such as nitrogen, oxygen, etc. These pollutants must be separated/
filtered out before releasing the harmless gases into the atmosphere.
Figure 16.1 Electrostatic precipitator
There are several ways of removing particulate matter; the most widely
used of which is the electrostatic precipitator (Figure 16.1), which 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. These
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. A scrubber (Figure 16.1) can remove gases like sulphur
dioxide. In a scrubber, the exhaust is passed through a spray of water or
lime. Recently we have realised the dangers of particulate matter that are
very very small and are not removed by these precipitators. According to
Central Pollution Control Board (CPCB), particulate size 2.5 micrometers
or less in diameter (PM 2.5) are responsible for causing the greatest harm
to human health. These fine particulates can be inhaled deep into the
lungs and can cause breathing and respiratory symptoms, irritation,
inflammations and damage to the lungs and premature deaths.
2022-23
272
BIOLOGY
Automobiles are a major cause for atmospheric pollution atleast in
the metro cities.  As the number of vehicles increase on the streets, this
problem is now shifting to the other cities too. Proper maintenance of
automobiles along with use of lead-free petrol or diesel can reduce the
pollutants they emit. Catalytic converters, having expensive metals namely
platinum-palladium and rhodium as the catalysts, are fitted into
automobiles for reducing emission of poisonous gases. As 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. Motor
vehicles equipped with catalytic converter should use unleaded petrol
because lead in the petrol inactivates the catalyst.
In India, the Air (Prevention and Control of Pollution) Act came
into force in 1981, but was amended in 1987 to include noise as an air
pollutant. Noise is undesired high level of sound. We have got used to
associating loud sounds with pleasure and entertainment not realising
that noise causes psychological and physiological disorders in humans.
The bigger the city, the bigger the function, the greater the noise!!  A
brief exposure to extremely high sound level, 150 dB or more generated
by take off of a jet plane or rocket, may damage ear drums thus
permanently impairing hearing ability. Even chronic exposure to a
relatively lower noise level of cities may permanently damage hearing
abilities of humans. Noise also causes sleeplessness, increased heart
beat, altered breathing pattern, thus considerably stressing humans.
Considering the many dangerous effects of noise pollution can you
identify the unnecessary sources of noise pollution around you which
can be reduced immediately without any financial loss to anybody?
Reduction of noise in our industries can be affected by use of sound-
absorbent materials or by muffling noise.  Stringent following of laws laid
down in relation to noise like delimitation of horn-free zones around
hospitals and schools,  permissible sound-levels of crackers and of loud-
speakers, timings after which loudspeakers cannot be played, etc., need
to be enforced to protect ourselves from noise pollution.
16.1.1 Controlling Vehicular Air Pollution: A Case
Study of Delhi
With its very large population of vehicular traffic, Delhi leads the coun-
try in its levels of air-pollution – it has more cars than the states of
Gujarat and West Bengal put together.  In the 1990s, Delhi ranked
fourth among the 41 most polluted cities of the world.  Air pollution
problems in Delhi became so serious that a public interest litigation
(PIL) was filed in the Supreme Court of India. After being censured very
strongly by the Supreme Court, under its directives, the government
was asked to take, within a specified time period, appropriate meas-
ures, including switching over the entire fleet of public transport, i.e.,
buses, from diesel to compressed natural gas (CNG).  All the buses of
Delhi were converted to run on CNG by the end of 2002. You may ask
the question as to why CNG is better than diesel. The answer is that
2022-23
273
ENVIRONMENTAL ISSUES
CNG burns most efficiently, unlike petrol or diesel, in the automobiles
and very little of it is left unburnt. Moreover, CNG is cheaper than petrol
or diesel, cannot be siphoned off by thieves and adulterated like petrol
or diesel. The main problem with switching over to CNG is the difficulty
of laying down pipelines to deliver CNG through distribution points/
pumps and ensuring uninterrupted supply.  Simultaneously 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.
The Government of India through a new auto fuel policy has laid
out a roadmap to cut down vehicular pollution in Indian cities. More
stringent norms for fuels means steadily reducing the sulphur and
aromatic content in petrol and diesel fuels. Euro III norms, for example,
stipulate that sulphur be controlled at 350 parts-per-million (ppm) in
diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained
at 42 per cent of the concerned fuel. The goal, according to the roadmap,
is to reduce sulphur to 50 ppm in petrol and diesel and bring down the
level to 35 per cent. Corresponding to the fuel, vehicle engines will also
need to be upgraded.
Mass Emission Standards (Bharat Stage II which is equivalent to
Euro-II norms) are no more applicable in any of the cities of India.
Details of the latest Mass Emission Standards in India are provided
below (Table 16.1)
Type of Vehicles Norms Cities of Implementation
4 Wheelers Bharat Stage IV Throughout the country
since April 2017
3 Wheelers Bharat Stage IV Throughout the country
since 1st April 2017
2 Wheelers Bharat Stage IV Throughout the country
since April 2017
Table 16.1: Table Showing the Mass Emission Standards in India
Thanks to the efforts made, the air quality of Delhi has significantly
improved. According to an estimate, a substantial fall in CO
2
 and SO
2
level has been found in Delhi between 1997 and 2005.
16.2  WATER POLLUTION AND ITS CONTROL
Human beings have been abusing the water-bodies around the world by
disposing into them all kinds of waste. We tend to believe that water can
wash away everything not taking cognizance of the fact that the water
bodies are our lifeline as well as that of all other living organisms. Can
you list what all we tend to try and wash away through our rivers and
drains? Due to such activities of human kind, the ponds, lakes, stream,
2022-23
Page 5


Human population size has grown enormously over the
last hundred years. This means increase in demand for
food, water, home, electricity, roads, automobiles and
numerous other commodities. These demands are exerting
tremendous pressure on our natural resources, and are
also contributing to pollution of air, water and soil. The
need of the hour is to check the degradation and depletion
of our precious natural resources and pollution without
halting the process of development.
Pollution is any undesirable change in physical,
chemical or biological characteristics of air, land, water or
soil. Agents that bring about such an undesirable change
are called as pollutants. In order to control environmental
pollution, the Government of India has passed the
Environment (Protection) Act, 1986 to protect
and improve the quality of our environment (air, water
and soil).
16.1 AIR POLLUTION AND ITS CONTROL
We are dependent on air for our respiratory needs.  Air
pollutants cause injury to all living organisms. They
reduce growth and yield of crops and cause premature
death of plants. Air pollutants also deleteriously affect the
respiratory system of humans and of animals. Harmful
CHAPTER 16
ENVIRONMENTAL ISSUES
16.1 Air Pollution and Its
Control
16.2 Water Pollution and Its
Control
16.3 Solid W astes
16.4 Agro-chemicals and
their Effects
16.5 Radioactive W astes
16.6 Greenhouse Effect and
Global Warming
16.7 Ozone Depletion in the
Stratosphere
16.8 Degradation by Improper
Resource Utilisation and
Maintenance
16.9 Deforestation
2022-23
271
ENVIRONMENTAL ISSUES
effects depend on the concentration of pollutants, duration of exposure
and the organism.
Smokestacks of thermal power plants, smelters and other industries
release particulate and gaseous air pollutants together with harmless
gases, such as nitrogen, oxygen, etc. These pollutants must be separated/
filtered out before releasing the harmless gases into the atmosphere.
Figure 16.1 Electrostatic precipitator
There are several ways of removing particulate matter; the most widely
used of which is the electrostatic precipitator (Figure 16.1), which 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. These
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. A scrubber (Figure 16.1) can remove gases like sulphur
dioxide. In a scrubber, the exhaust is passed through a spray of water or
lime. Recently we have realised the dangers of particulate matter that are
very very small and are not removed by these precipitators. According to
Central Pollution Control Board (CPCB), particulate size 2.5 micrometers
or less in diameter (PM 2.5) are responsible for causing the greatest harm
to human health. These fine particulates can be inhaled deep into the
lungs and can cause breathing and respiratory symptoms, irritation,
inflammations and damage to the lungs and premature deaths.
2022-23
272
BIOLOGY
Automobiles are a major cause for atmospheric pollution atleast in
the metro cities.  As the number of vehicles increase on the streets, this
problem is now shifting to the other cities too. Proper maintenance of
automobiles along with use of lead-free petrol or diesel can reduce the
pollutants they emit. Catalytic converters, having expensive metals namely
platinum-palladium and rhodium as the catalysts, are fitted into
automobiles for reducing emission of poisonous gases. As 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. Motor
vehicles equipped with catalytic converter should use unleaded petrol
because lead in the petrol inactivates the catalyst.
In India, the Air (Prevention and Control of Pollution) Act came
into force in 1981, but was amended in 1987 to include noise as an air
pollutant. Noise is undesired high level of sound. We have got used to
associating loud sounds with pleasure and entertainment not realising
that noise causes psychological and physiological disorders in humans.
The bigger the city, the bigger the function, the greater the noise!!  A
brief exposure to extremely high sound level, 150 dB or more generated
by take off of a jet plane or rocket, may damage ear drums thus
permanently impairing hearing ability. Even chronic exposure to a
relatively lower noise level of cities may permanently damage hearing
abilities of humans. Noise also causes sleeplessness, increased heart
beat, altered breathing pattern, thus considerably stressing humans.
Considering the many dangerous effects of noise pollution can you
identify the unnecessary sources of noise pollution around you which
can be reduced immediately without any financial loss to anybody?
Reduction of noise in our industries can be affected by use of sound-
absorbent materials or by muffling noise.  Stringent following of laws laid
down in relation to noise like delimitation of horn-free zones around
hospitals and schools,  permissible sound-levels of crackers and of loud-
speakers, timings after which loudspeakers cannot be played, etc., need
to be enforced to protect ourselves from noise pollution.
16.1.1 Controlling Vehicular Air Pollution: A Case
Study of Delhi
With its very large population of vehicular traffic, Delhi leads the coun-
try in its levels of air-pollution – it has more cars than the states of
Gujarat and West Bengal put together.  In the 1990s, Delhi ranked
fourth among the 41 most polluted cities of the world.  Air pollution
problems in Delhi became so serious that a public interest litigation
(PIL) was filed in the Supreme Court of India. After being censured very
strongly by the Supreme Court, under its directives, the government
was asked to take, within a specified time period, appropriate meas-
ures, including switching over the entire fleet of public transport, i.e.,
buses, from diesel to compressed natural gas (CNG).  All the buses of
Delhi were converted to run on CNG by the end of 2002. You may ask
the question as to why CNG is better than diesel. The answer is that
2022-23
273
ENVIRONMENTAL ISSUES
CNG burns most efficiently, unlike petrol or diesel, in the automobiles
and very little of it is left unburnt. Moreover, CNG is cheaper than petrol
or diesel, cannot be siphoned off by thieves and adulterated like petrol
or diesel. The main problem with switching over to CNG is the difficulty
of laying down pipelines to deliver CNG through distribution points/
pumps and ensuring uninterrupted supply.  Simultaneously 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.
The Government of India through a new auto fuel policy has laid
out a roadmap to cut down vehicular pollution in Indian cities. More
stringent norms for fuels means steadily reducing the sulphur and
aromatic content in petrol and diesel fuels. Euro III norms, for example,
stipulate that sulphur be controlled at 350 parts-per-million (ppm) in
diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained
at 42 per cent of the concerned fuel. The goal, according to the roadmap,
is to reduce sulphur to 50 ppm in petrol and diesel and bring down the
level to 35 per cent. Corresponding to the fuel, vehicle engines will also
need to be upgraded.
Mass Emission Standards (Bharat Stage II which is equivalent to
Euro-II norms) are no more applicable in any of the cities of India.
Details of the latest Mass Emission Standards in India are provided
below (Table 16.1)
Type of Vehicles Norms Cities of Implementation
4 Wheelers Bharat Stage IV Throughout the country
since April 2017
3 Wheelers Bharat Stage IV Throughout the country
since 1st April 2017
2 Wheelers Bharat Stage IV Throughout the country
since April 2017
Table 16.1: Table Showing the Mass Emission Standards in India
Thanks to the efforts made, the air quality of Delhi has significantly
improved. According to an estimate, a substantial fall in CO
2
 and SO
2
level has been found in Delhi between 1997 and 2005.
16.2  WATER POLLUTION AND ITS CONTROL
Human beings have been abusing the water-bodies around the world by
disposing into them all kinds of waste. We tend to believe that water can
wash away everything not taking cognizance of the fact that the water
bodies are our lifeline as well as that of all other living organisms. Can
you list what all we tend to try and wash away through our rivers and
drains? Due to such activities of human kind, the ponds, lakes, stream,
2022-23
274
BIOLOGY
rivers, estuaries and oceans are becoming polluted in several parts of the
world. Realising the importance of maintaining the cleanliness of the water
bodies, the Government of India has passed the Water (Prevention and
Control of Pollution) Act, 1974 to safeguard our water resources.
16.2.1 Domestic Sewage and Industrial Effluents
As we work with water in our homes in the cities and towns, we wash
everything into drains.  Have you
ever wondered where the sewage
that comes out of our houses go?
What happens in villages? Is the
sewage treated before being
transported to the nearest river
and mixed with it?  A mere 0.1
per cent impurities make
domestic sewage unfit for human
use (Figure 16.2). You have read
about sewage treatment
plants in Chapter 10. Solids are
relatively easy to remove, what
is most difficult to remove are
Figure 16.2 Composition of waste water
Figure 16.3  Effect of sewage discharge on some important characteristics of a river
2022-23