Environmental Science [HSS05] Unit-3

Unit 3
Environmental pollution:
● Sources of pollution- Natural sources, & Anthropogenic
● Pollutants- Classification & their effects on environment
● Air pollution-Composition of clean air, Sources of air pollution & Air pollutants, Effect
of air pollution on humans, animals and plants & climate
● Water quality–Potable water, Wholesome water, Sources of water pollution Polluted
water & Contaminated water,
● Common impurities in water (physical, chemical and bacteriological), Effects of
impurities on humans & industrial use
● Soil Pollution-Sources, Effects & its control
● Noise pollution- Sources of noise, Effects on human health & its control

Numerical problems on pH, hardness of water, noise pollution

Environmental pollution
The word “pollution” is from Latin word pollutionem (make dirty).”Pollution is an
undesirable change in the physical, chemical or biological characteristics of water, air and
land (soil) which may cause potential health hazard of any living being or species or loss of
cultural and natural assets”.
Pollution of the environment directly leads to the ecological imbalance of the world. Progress
in science and technology is leading to the pollution of environment. In the long run it may
leads to the disaster of mankind and other living organisms. Speedy exploitation of natural
resources by man disturbed the sensitive ecological balance between living and non-living
component of biosphere.
Now a days it is becoming common to find warning boards in public places, stating “Water
unfit for drinking”, Do not eat fish caught here”, “Water is unfit for recreation”, “Air unfit for
breathing”, and so on.
The rapid progress in Industry, Agriculture, Transportation etc, are taken as the general
criterion to measure the development of any nation.. All these activities have created adverse
effect on the biosphere in one or the other way. Rapid industrialization and urbanization leads
to depleted natural resource, contaminated surface (rivers) and ground water, contaminated
soil, contaminated air (atmosphere) and depleted forest resources (animals, plant etc).

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Polluant: Polluant is a substance that causes pollution. Pollution is caused by the addition of
substances by human activity to the environment. When these substances are not removed,
assimilated or decomposed by the nature (physical or biological process), the accumulation of
these pollutants causes pollution. A pollutant may include any activity (sound) chemical,
geochemical (dust), substances, biotic component or product, physical factor (light, heat) etc.
that is released into the environment in such a concentration that may have harmful or
unpleasant effects.
Pollutant is also defined as “any liquid, solid or gaseous substance present in such
concentration as may be or tend to be injurious to the environment”. Pollutants are the
remaining of the things we make use and throw.

Sources of pollution: The sources of pollution is broadly classified into two groups
(a) Natural sources: The pollution originates from the natural calamities and processes
such as volcanic eruptions (releases gases and ash), earthquake, forest fire, dust storm
(deserts), cyst and pollens, spores decay of organic matter etc.
(b) Manmade (artificial) or Anthropogenic sources: The pollution originates due to the
activities of man. Anthropogenic sources cover a wide range of sources. Since man
has aggravated the problem of pollution due to multiple activities for his comfort and
enjoyment. The sources are deforestation, industrialization, automobiles, nuclear
explosions, over population, quarrying and mining, construction activities, wars
agriculture (fertilizers and pesticides) etc.

Classification of pollutants: Pollutants are classified as follows

(a) Based on the form they exist

(i) Primary pollutants: These persist in the form in which they are added to the
environment. Eg.DDT, Plastic.
(ii) Secondary pollutants: These are formed by interaction among the primary
pollutants. For example, peroxy acetyl nitrate (PAN) is formed by the reaction of two
primary pollutants, namely nitrogen oxides and hydrocarbons released from the motor
vehicles in presence of sunlight.

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(b) Based on biological degradability

(i) Biodegradable (Degradable) pollutants: They are actually waste products, which
are slowly degradable by microbial action. They cause pollution when their
production exceeds the capacity of the environment to degrade them. eg. Sewage.
(ii) Non degradable (non-biodegradable) pollutants: They are waste products, which
are not decomposed or are decomposed very slowly. They include wastes (eg.
plastics, glass, plastic bottles, polythene bags, used soft drink cans etc) or poisons (eg.
pesticides like DDT, salts of heavy metals, radioactive substances etc). The non-
biodegradable pollutants are difficult to manage and in most cases there is no
treatment process to handle the anthropogenic input of such materials in the eco
system.

(c) Based on their existence:

(i) Quantitative pollutants: These are the substances, which occur in nature but become
pollutant when their concentration reaches beyond a threshold value in the
environment. eg. Carbon dioxide, nitrogen oxide.
(ii) Qualitative pollutants: These are the substances that do not occur in the environment
but are passed into it through human activity. E.g. Fungicides, herbicides, DDT etc.

(d) Based on their origin:

(i) Natural pollutants: Volcanic eruptions add tons of toxic gases and particulate matter
n the environment.
(ii) Man made or anthropogenic pollutants: It is a man made pollutants such as
industrial pollutants, agricultural pollutants, etc

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Principal polluants: Varions polluants that cause environnemental pollution are

Deposited matter Dust, smoke, soot, grit, tar

Gases Carbon dioxide, carbon monoxide, sulphur dioxide,
Ozone, ammonia, halogens (fluorine, chlorine, bromine, iodine).
Chemical compounds Hydrogen fluoride, aldehydes, detergents, etc.
Acid droplets Nitric acid, sulphuric acid, etc
Metals Iron, zinc, nickel, cadmium, chromium, lead, mercury, etc.
Agrochemicals Pesticides, fungicides, herbicides, insecticides, etc
(poisons)
Organic substances Acetic acid, benzene, ether, toluene, benzopyrenes, etc
Photochemical oxidants Photochemical smog, peroxy acetyl nitrate (PAN),nitrogen oxides,
etc.
Fertilizers Nitrogen, phosphorous, potash, etc
Sewage waste, noise and heat, radioactive waste (iodine-131, cobalt-60, argon-41) etc.

Human Activities & Impact on Environment:

Human activities and technological advancements made to enjoy luxurious life have caused
severe in balances and disturbances in natural environment.
Although there are several individual human activities, which may cause environmental
imbalances, they can be grouped in to the following four major types of actions.

(1) Agriculture: The development of agriculture has been the most important single event in
the evolution of human culture. With the development and increase in human population, the
agriculture on more and more land has been practiced to grow crops. Initially the humans
have grown only food crops to eat but later on they have started growing several kinds of
cash crops. Not only they have brought a large part of the forest land under agriculture, but
also they have started using fertilizers and pesticides to increase the crop production per unit
of agricultural area. The present mode of agriculture is highly mechanized as the modern
technology is constantly inventing new & newer machines for agriculture. This has infact
become virtually imperative as the human population is increasing day by day especially in
developing countries.

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Such industrialized agriculture is the root cause of environmental problems. Today’s

agriculture is consuming tremendous amount of energy particularly the fossil fuels like oil,
petrol, diesel etc. These fuels are being used to run machines for agriculture and for the
production of fertilizers & pesticides. These products are seriously polluting our environment
& destabilizing it.
For e.g. the fertilizer residue draining into the streams & rivers add extra energy, which
causes the Algae & Macrophytes (large plants) to bloom in aquatic eco systems. This
modifies the entire eco system in the long run.
Similarly, the pesticides used for killing pests do not kill the pests alone but also kill some
useful organisms like the honey bee, lady bird, beetles etc.
Besides killing useful organisms, they even kill the microorganisms present in the soil and
thus the pesticides poison the whole terrestrial food chain.
The milk given by the cows & buffaloes is now found to contain pesticides since the
vegetations eaten by these animals do contain pesticide sprayed by humans on vegetation.
The pesticide poison has spoiled the drinking water & the entire food leaving all of us to
undergo slow poisoning deaths.
The applications of pesticides have also resulted in the virtual extinction of several predatory
(carnivores) birds like hawks, falcons, eagles etc.
Because of continuous increase in human population, many countries are forced to convert
their forest areas, wetlands & other productive areas into agricultural lands.
This has resulted in changes in climate, hydrological cycle, and mineral resources.
This kind deforestation has lead to the extinction of several plants & animals species all over
the world.

(2) Industrialization: Industrialization means development of industries of various kinds.

These industries cause maximum environmental instability, by polluting water, air and land.
Industrial revolution with rapid growth of human population has increased the demand of raw
materials and other resources by considerable extent. The rapid uncontrolled growth of the
industries are contaminating and spoiling the precious water sources like rivers and lakes by
throwing their wastewaters into water sources. This will ultimately make clean drinking
water totally unavailable. Similarly, the industries are releasing several poisonous gases and
substances in our atmosphere, there by polluting our air. Industries have also placed an extra-
ordinary burden on our petroleum and oil reserves.

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(3) Urbanization: The urbanization is the process of urban development, under which mass
migration of people from rural areas to the industrialized urban areas take place due to the
increased job opportunities. With such a fast urbanization taking place lot of land have been
consumed to build giant urban centers. Precious farming land had been lost to urbanization.
Urbanization changes the green, wet and earthen land to concrete and asphalt paved land.
These increases the rain’s run off thereby increasing floods and reducing ground water
recharge.
Urbanized areas produce enormous quantities of sewage and domestic waste waters, which
on being discharged into the rivers, either in untreated or partly treated condition pollute the
rivers and can totally modify the aquatic ecosystem.
Air pollution and land pollution, prevailing in urban centers, can also modify the ecosystem.
Urbanization modifies the nearby areas. For example, large amount of sand is removed from
the rivers in construction activity which makes the river ecosystem unstable due to abnormal
large pits created in the river bed.
Hills are destroyed to get stones for construction purposes. The removal of hills may change
and modify the climate, not only locally but even regionally over vast areas, as the rainfall in
plains becomes difficult to occur.
Another major requirement of urbanization is wood for furniture, doors. Windows, amirahs,
cupboards etc. This demand is met by destroying the forest, which causes serious
consequences for forest eco system. Any loss of forest will lead to the loss of beneficial
effects of forest.

(4) Mining: Mining is the extraction of minerals & ores from the earth’s crust. Mining
provides coal for the energy, metals for making machines & engines, ores for making
chemicals & fertilizers, clays for making crockery, rocks & stones for buildings, bridges &
dams, the gold, diamond & other precious stones for jewelleries.
The exploitation of mineral resources has increased several times leading to large scale
mining activities.
Mining whether it is at the surface or underground alters the whole landscape & the eco
system existing at the place of mining which cannot be shifted any where.
The removal of minerals from the earth naturally upsets the existing land conditions and
waste tailing produced in this process contain toxic chemicals like mercury & sulphides of
iron. The waters in these areas have become very acidic. No plant grows & no animal

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survives in such areas. Mining activity has given rise to vast areas of waste land that are now
useless from the point of view of agriculture or agro forestry.

Air pollution:
The atmosphere is the thin layer of gases (air) that surrounds the earth surface. Air is defined
as the invisible, tasteless and elastic mixture of gases. Air pollution is assuming global
magnitude and it is not confined to any particular part of earth or country. Under ideal
conditions, the air in the atmosphere has a qualitative and quantitative balance that maintains
the well being of human, plants and materials. When the balance among the air components
are disturbed, then air is said to be polluted.

Definitions:
(1) Air pollution is the presence in the ambient atmosphere of substances, generally resulting
from the activity of humans, in sufficient concentration, present for a sufficient time and
under circumstances which interfere significantly with the comfort, health or welfare of
persons or with the full use or enjoyment of property (Indian standard institution).
(2) The presence in the outdoor atmosphere, of one or more contaminants such as fumes,
dust, gases, mist, grit, odour, smoke or vapors in considerable quantities and of
duration which is injurious to human, animal or plant life or which unreasonably
interferes with the comfortable enjoyment of life and property (Perkins 1974).
(3) Substances introduced into the air by the activity of mankind in such concentrations
sufficient to cause serious effects on his health, plants, property or interfere with the
enjoyment of his property (Sharma and Haur 1997).

Composition of Air: Various gases are present in the atmosphere as shown in the table. The
nitrogen gas is biologically inert but some bacteria and plants utilize it.
The oxygen is essential for all living beings.
Carbon dioxide is utilized in photosynthetic process of plants.
Trace gases (helium, neon, krypton, xenon, etc.) have little or no role with the living
organisms. Atmospheric pollution is the addition of harmful gases by human activities.

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Table: Normal composition of air

Gases Percent (by volume)
Nitrogen 78.084
Oxygen 20.9476
Argon 0.934
Carbon dioxide 0.0314
Methane 0.0002
Hydrogen 0.00005
Other gases Minute

Types of air pollutants: On the basis of physical state, air pollutants are of two types-
gaseous and particulate.
(1) Gaseous pollutants: These pollutants are in gaseous state at normal temperature and
pressure.

(2) Particulate pollutants: These pollutants occur as solid and liquid particles. They are of
two types-settleable and suspended.

Settleable: The particles larger than 10 m in diameter such as water drops, sand etc which
settle down rapidly in still air, are called settleable pollutants.

Suspended: The smaller particles such as dust, smoke, etc. which remain suspended for long
periods in the air are called suspended pollutants. These include soot, asbestos fibers,
pesticides, some metals (including Hg, Pb, Cu and Fe) and also biological agents like tiny
dust, mites and pollen. The larger suspended particles with more than 1m in diameter are
often called dust (solid) and mist (liquid). Aerosols, smokes and fumes are also suspended
particles with a diameter less than 1m.

Sources of air pollution: The sources that contribute pollutants to the air are as follows

(I) Stationary combustion sources: Burning of fuels in industries, residential

establishments, hotels, bakeries, thermal plants and brick kilns contribute most of the gaseous
and particulate pollutants in the air. Coal and wood are largely made of carbon mixed with

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some incombustible minerals, sulphur and nitrogen. Therefore, when fossil fuels are burnt
they produce a mixture of oxides of carbon, nitrogen and sulphur and water vapor. Burning of
coal also produce mineral ash, some of which is discharged as fly ash.

(II) Mobile combustion sources: These include locomotives, automobiles, aircrafts, etc.
With the rapid increase in vehicular traffic, automobiles have become the largest source of air
pollution in cities.

(III) Industrial processing and other sources: The industrial processes involve
metallurgical processing, welding, grinding, synthesis of chemicals, etc. These processes
release several gaseous and particulate pollutants into the air. Gaseous pollutants of different
types are released from the industries that process organic chemicals at high temperatures.

(IV) Secondary air pollutants: These are formed from primary pollutants by photochemical
reaction.

Major air pollutants and their effects:

Air quality surrounding human has a direct impact on health and property. The health effects
of air pollutants are classified as short-term effects and long-term effects. Elderly people and
children often suffer more from the air pollution. The harmful effects of air pollution depend
on the concentration of pollutants and duration of exposure. Following table gives common
air pollutants and their effects.

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Table: Common air pollutants, their sources and effects

Sl.No Pollutants Sources Effects
1 Carbon dioxide, CO2 Coal, petrol, oil, diesel Green house effect
combustion (automobile
exhaust)
2 Carbon monoxide, CO Burning of coal, petrol, Reduce oxygen carrying
diesel, automobile exhaust capacity of blood, causes
headaches and drowsiness,
fatal in high concentration
3 Oxides of sulphur, SO2, Coal and oil combustion Acid rain that damages trees,
SO3 plants, water bodies, materials,
causes headache, aggressive
asthma, vomiting and causes
irritation of eyes, nose and
throat
4 Oxides of nitrogen, High temperature burning in Acid rain formation, effects
NO2, NO automobiles, burning of coal plants, buildings, lakes,
aggressive asthma.
5 Lead compounds Burning of leaded petrol Neural effects in children,
effects on plants
6 Nuclear wastes Nuclear weapon testing, Radioactivity, cancers,
nuclear power plants mutations, etc.
7 Suspended particles Burning of coal, Eye irritation, aggravation of
(ash, fly ash, etc.) manufacturing process asthma, etc.
8 Ozone, O3 Atmosphere chemical Global warming, damage to
reaction of NO2 and plants and materials.
aldehydes
9 Hydrocarbons Burning of petroleum Carcinogenic effect on human,
products, benzene, causes eye irritations,
benzepyrene, etc. respiratory distress, throat
irritation, formation of Pan,
effect on plants
10 Chlorofluorocarbons Refrigerant, aerosole Ozone depletion.
propellants, cosmetics, etc.

Effect of air pollution on human health:

 Eye irritation
 Nose and throat irritation
 Irritation of respiratory tract
 Gases like H2S, NH3 and mercaptans cause odour nuisance even at low
concentrations.
 Increase in mortality rate and morbidity rate.
 A variety of particulates particularly pollens initiates asthmatic attacks.

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 Chronic pulmonary diseases like bronchitis and asthma are aggravated by a high
concentration of SO2, NO2, particulate matter and photochemical smog.
 Carbon monoxide combines with the hemoglobin in the blood and consequently
increases stress on those suffering from cardio vascular and pulmonary diseases.
 Hydrogen fluoride causes dieses of bone (fluorisis) and mottling of teeth.
 Carcinogenic agents cause cancer.
 Dust particles cause respiratory diseases. Diseases like silicosis, asbestosis etc, result
from specific dusts.
 Certain heavy metals like lead may enter the body through the lungs and cause
poisoning.

Effect of air pollution on vegetation:

 Dust, smoke and other particulate matter settle on the leaves of plants and reduce
sunlight, there by retard photosynthesis.
 Sulphur dioxide causes chlorosis, plasmolysis, membrane damage and metabolic
inhibition. The leaves often assume water soaked appearance. Fruit trees and cereal
crops are more sensitive to oxides of sulphur. Therefore, they suffer a great loss in the
areas around smelters and industrial belts.
 Fluorides destroy tissues in leaves causing necrosis of leaf margin and tips.
 Several plant species are also very susceptible to PAN in smog. PAN damages
chloroplasts and thus the photosynthetic efficiency and growth of plants are reduced.
It also inhibits electron transport system and interferes with enzymes that play
important role in cellular metabolism.
 Hydrocarbons such as ethylene cause premature leaf fall, fruit drop, shedding of floral
buds, curling of petals and discoloration of sepals.
 Ozone damage chlorenchyma and thus destructs the foliage in large number of plants.
 Lichens are very sensitive to air pollution. Their growth is inhibited in polluted air.
The death of lichens in an area is an indicator of air pollution.
 Acid rain adversely affects terrestrial and aquatic vegetation. Low PH also damage soil
microbial community.

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Effect air pollution on animals: Air pollution causes large-scale damage to livestock. The
general effects of air pollution on domestic animals in and around industrial area are similar
to those on human beings
 Ingestion of fluorine compounds deposited from the air on fodder causes fluorosis
(excessive calcinations of bones and teeth). It also results in lameness, frequent diarrhea
and loss of weight.
 Several airborne microbes cause diseases.

Effect air pollution on materials: Various material damage due to air pollution is as
follows.
Materials Principle air Effects
pollutants
Metals SO2, acid gases. Corrosion, spoilage of surface, loss of metal
tarnishing.
Building SO2, acid gases and Discoloration and leaching
materials particulates.
Paint SO2, H2S and Discoloration.
particulates.
Textiles and SO2, acid gases and Deterioration, reduced textile strength and
textile dyes NO2 and ozone. fading.
Rubber Oxidants and ozone. Cracking and weakening.
Leather SO2, acid gases. Disintegration and powdered surface.
Paper SO2, acid gases. Embitterment.
Ceramics Acid gases. Change in surface appearance.

Aesthetic loss due to air pollution: Air pollution has strong bearing on the aesthetic side of
human life.
 A clear transparent atmosphere is aesthetically pleasing but is necessary for clear vision.
A dust haze or hanging smoke blurs our views
 Foul odour emitted by industries, automobiles, dirty drains and garbage heaps make urban
life unpleasant.
 Coal dust and their materials discharged from the industries settle down on the flour and
other objects of houses and give dirty look.

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Effect of air pollution on climate:

 Heat produced by the industrial plants raises the temperature of the area.
 Carbon dioxide content of the atmosphere is increasing due to destruction of forests and
excessive burning of fossil fuels. It will lead to rise in global temperature by more than
two or three degree due to green house effect. A rise in global temperature may result in
melting of glaciers and polar ice caps, flooding of low-lying coastal plains and
submersion of island. Rainfall pattern may also change, thus affecting agricultural out
puts.
 Aerosols and Chlorofluorocarbons deplete ozone layer in the stratosphere, which permit
most of the harmful ultraviolet radiation to reach the earth.

Water quality:
Water is essential to human life and to health of the environment. As a valuable natural
resource, it comprises marine, estuarine, fresh water (river and lakes) and ground water
environment, across coastal and inland areas. Water quality is commonly defined by its
physical, chemical, biological and aesthetic characteristics. A healthy environment is one in
which the water quality supports a rich and varied community of organisms and protects
public health.
Water quality in a body of water depends upon the way in which communities use the water
for activities such as drinking, swimming or commercial purposes.

Importance of water quality:

Most of the earth’s water is in the oceans or in the form of ice. The largest volumes of fresh
water are stored underground as ground water. Only a tiny fraction is present as fresh water
in lakes, streams and rivers. But, it is this proportion, which is so important for many of our
terrestrial ecosystem, including humans.
The quality of this fresh water is vitally important. We depend on surface and ground water
sources for our drinking water. Our water resources are of major environmental, social and
economic value and if water quality becomes degraded this resources will lose its value.
Water quality is not only important to protect public health but also for the waters used for
farming, fishing, mining, recreation, tourism etc. If water quality is not maintained, it is not
just the environment that will suffer but also the commercial, domestic and recreational value
of water resources will diminish.

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Definitions:
Potable water: Water that is free from apparent turbidity, colour, and odour and free from
any objectionable taste so that it consumed in any desired amount without concern for
adverse effects on health is known as potable water.
Wholesome water: Water that does not contain harmful impurities and does contain other
salts and minerals that are useful to health is known wholesome water.
Polluted water: Water containing any foreign matter (solid, liquid or gaseous) that is
infectious or non-infectious and toxic or non-toxic that affects its beneficial usage is known
as polluted water.
Contaminated water: Water that contains infectious agents or toxic matter that affects the
health of the community and make the water unfit for its beneficial usage is known as
contaminated water.
Common impurities in water and their effect on human health:
The various impurities present in water may be classified into the following three categories.
 Physical impurities: The physical impurities are those impurities that affect the physical
characteristics of water such as colour, odour, taste and turbidity.
 Chemical impurities: The chemical impurities are those impurities that affect the
chemical characteristics of water such as total dissolved solids and suspended solids
present in water, pH value, hardness, chloride content, nitrogen content, etc.
 Bacteriological impurities: The bacteria are minute singe cell organisms that are
universally found in water obtained from any source. They are very small measuring only
1 to 4 micron in length (1 micron = 10-6 m). As such they have to be examined under a
microscope. The bacteria are usually classified according to their shapes, their oxygen
requirements and their effect on mankind.
According to shape the bacteria are classified as cocci (round shaped), bacilli (rod shaped)
and spiralla (spiral shaped).
According to oxygen requirements the bacteria are classified as aerobic bacteria, anaerobic
bacteria and facultative bacteria.
Aerobic bacteria are those which require free oxygen for their survival, thus if present in
water they consume dissolved oxygen from the water and decompose the organic matter
present in water.

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Anaerobic bacteria are those that flourish or thrive in the absence of free oxygen.
Facultative bacteria are those that can survive with or without free oxygen.
According to the temperature they flourish, the bacteria are classified as Psychrophilic,
Mesophilic and Thermophilic.
 Psychrophilic which can persist at low temperatures of 100 C and 200C.
 Mesophilic which can persist at temperature of 200 C and 400C.
 Thermophilic which can persist at temperature of 400 C and 650C.
According to effect on mankind the bacteria may be classified as harmless bacteria and
harmful bacteria. The harmless bacteria are called non-pathogenic bacteria or non-pathogens.
These bacteria besides being harmless, under certain conditions are beneficial to human
beings, animals and crops. The harmful bacteria are called pathogenic bacteria or pathogens.
The pathogenic bacteria are the real foes of mankind, which may cause serious water borne
diseases such as cholera, typhoid, dysentery, infectious hepatitis, etc. Generally non-
pathogenic and pathogenic bacteria occur together, and hence the presence of large amount of
non-pathogenic bacteria in a water sample indicates the possibility of the pathogenic bacteria
being also present in the water sample.

Water pollution:
(1) Water pollution is the contamination of water by foreign matters such as physical matters,
chemicals, microorganisms, sewage, industrial wastes or other wastes. Such matters
deteriorate the quality of the water and renders it unfit for its best uses.
(2) Water pollution is change in physical, chemical and biological characteristics of water
that may cause harmful effects on human, animal and aquatic biota.

Sources of water pollution:

(1) Non point sources: In non point source the point of entry of pollutant is not identifiable.
The pollutants generated from a broad group of human activities and by natural processes.
The pollutant sources are decomposed vegetable and animals, agricultural runoff,
weathering products etc. Addition of these pollutants influence on the chemical
characteristic, colour, odour, biological properties etc.
(2) Point source: The pollutants are added at a known point. The pollutants are collected and
discharged at a single point. The sources are sewage, industrial radioactive mining etc.
The pollutant sources are generated due to the activities of humans.

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Major water pollutants: The major water pollutants are

(1) Sewage (Domestic wastewater, municipal wastewater): These are wastewater
generated from domestic activities. It adds colour, taste, odour, organic and
inorganic compounds, heavy metals, suspended solids, floating solids etc. To reduce
the pollution treatment of wastewater is necessary.
(2) Agricultural waste: Agriculture is the single largest user of fresh water (surface and
ground water) resources. Most of the agricultural water is recycled back to surface
water and ground water. Modern agricultural practices are the main cause of water
pollution. Agricultural practices such as applying chemical fertilizer, manure
spreading, irrigation methods, pesticides, animal farming, aquaculture etc have wide
impact on surface and ground water quality.
(3) Industrial waste: Most of the rivers, lakes and ground water are polluted by
industrial wastewater. Industrial wastewater contains a variety of organic and
inorganic pollutants such as suspended solids, metallic wastes, oil grease, phenols,
toxic organic and inorganic, plastics, chemicals etc. Many of these pollutants are
susceptible to degradation or slowly degrade to cause serious pollution problems.
(4) Radioactive substances: Radioactive substances are short or long lived products
which are released from nuclear power plants, nuclear fuel processing and nuclear
weapon tests. The long-lived products (uranium, strontium-90, thorium, cesium-137)
will remain in the water for longer duration and contaminate the water for longer
time.
(5) Petroleum products: This consists of hydrocarbons. These are slowly degradable.
Crude oil is the major pollutant of sea, when a large tanker spills the oil when
transporting. The major pollutants are oil, benzene, toluene, chlorinated solvents,
biocides, plastics, pesticides etc. Chlorinated solvents are toxic at very low
concentration.
(6) Thermal pollution: Release of heated water from chemical industries, thermal
power plants, nuclear power plants etc leads to increase of temperature of water
bodies which affects utilization of water for its best uses. It also affects the entire
aquatic environment (increase in bacterial multiplication, consumption of dissolved
oxygen, death of fish etc).

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Types of water pollution: Water pollution can be classified into the following three
categories.
(1) Physical pollution: The physical pollution of water is due to change in colour, turbidity,
odour, taste, foam, thermal properties and conductivity.
(2) Chemical pollution: The chemical pollution of water is due to change in total solids, PH ,
chlorides, nitrogen, phosphorous, fats, sulphates dissolved oxygen, chemical oxygen
demand, biochemical oxygen demand, gases, metals etc. Pollution is caused by organic or
inorganic or by both.
(3) Biological pollution: Biological pollution of water is caused by excretory products of
humans, animals, birds, sewage and industrial waste water (tanneries, slaughter house,
dairy etc). The main biological pollutants are bacteria, viruses, algae, protozoa, parasitic
worm, fecal colifarms, streptococci etc. Contaminated water causes infection of intestinal
system (dysentery, typhoid, cholera etc) infectious hepatitis etc.
Indicator of polluted water: Following are the important indicators of water pollution
 Colour and bad taste of drinking water.
 Increase in turbidity and floating solids (oil and grease).
 Offensive odour from water bodies.
 Growth of aquatic weeds (eutrophication) in water bodies.
 Decrease in aquatic animals (fish).
 Increase in temperature of water.

Effects of water pollution: The effects of water pollution depend on the type of pollutants
present in water. Pollutants brings about physical and chemical changes that make the water
unfit for drinking and harmful to aquatic life. The main effects of pollutants are as mentioned
below.
(1) Effects on aquatic ecosystem: Presence of organic and inorganic wastes in water
decreases the dissolved oxygen (DO) content of the water. Water having DO content
below 8.0 mg/l may be considered as contaminated. Water having DO content below
4.0 mg/l is considered to be highly polluted. DO content of water is important for the
survival of aquatic organisms. A number of factors like surface turbulence,
photosynthetic activity, oxygen consumption by organisms and decomposition of
organic matter determine the amount of DO present in water.

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(2) Biological magnification: The phenomenon through which certain pollutants get
accumulated in the tissue in increasing concentration along the food chain is called
biological magnification. Many of the pesticides are non-degradable and their
residues have long life. The organic chlorine compounds such as DDT, radionuclides
etc are the most persistent pesticides. Once they are absorbed by an organism, they
cannot be metabolized and broken down or excreted out. These pollutants get
accumulated in fat containing tissues of the organisms. A classic example of
biological magnification is the accumulation of DDT in the tissues of organisms of
aquatic food chain.
(3) Eutrophication: The addition of inorganic compounds and decomposition of organic
wastes in water bodies increase the nutrient content of water. It could profuse growth
of algae especially the blue-green-algae, and may totally cover the water surface.
This type of algal growth is called algal boom. The algal boom often releases toxins
in water and inhibits the growth of other algae. Aquatic animals (fish) may also die
due to toxicity or lack of oxygen. The process of nutrient enrichment of water, which
often leads to the loss of species diversity, is called eutrophication.
(4) Effect on human health: A number of health hazards are caused due to various
types of pollutants present in water. The important human health hazards related to
water pollution are as follows:
 The water polluted with sewage usually contains pathogens like virus, bacteria,
parasitic protozoa and worms. The sewage-contaminated water, therefore, is a
source of water borne diseases like jaundice, cholera, typhoid, amoebiasis etc.
 The water contaminated with heavy metals can cause serious health problems.
Mercury compounds wastewater converted by bacterial action into extremely
toxic methyl mercury, which can cause numbness of limbs, lips and tongoue,
deafness, blurring of vision etc.
 Presence of excess nitrate in drinking water is dangerous for human health and
may be fatal for infants. It reacts with hemoglobin to form non-functional
methaemoglobin and impairs oxygen transport. This condition is called
methaemoglobinemia or blue baby diseases.
 Excess fluoride in drinking water causes dental fluorosis and skeletal fluorosis.
 Over exploitation of ground water may lead to leaching of arsenic from soil and
rock sources and contaminate ground water. Chronic exposure to arsenic causes

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black foot disease. It also causes diarrhea, peripheral neuritis, hyperkerotosis and
also lung and skin cancer.
Water borne diseases: Water borne diseases are those that are transmitted by contaminated
water. Water is a good carrier. Lot of disease causing bacteria will contaminate water.
Communicable disease that may be transmitted by water includes bacterial, viral and
protozoal infections.
(i) The disease caused by bacterial infection:
 Typhoid fever
 Paratyphoid
 Bacillary dysentery
 Cholera
 Salmonellosis
 Shigellosis.
(ii) The disease caused by viral infections:
 Infectious hepatitis
 Poliomyelitis
(iii)The disease caused by protozoal infections:
 Amoebic dysentery
 Giardiasis
Typhoid, paratyphoid, dysentery, gastroenteritis and cholera are transmitted by the fecal and
urinary discharges of sick persons and carriers. Through careless disposal of the discharges or
inadequate treatment of city sewage underground water may be contaminated to endanger
well water supplies or streams and lakes may be affected to contaminate surface supplies.
Prevention of water borne outbreaks of these diseases is primarily a matter of treating the
water by different methods.

Effect of some impurities on human health:

Colour: Colour may be imparted to water by the presence of natural metallic ions (iron and
manganese), peat (decayed vegetable matter), weeds, humus, plankton and industrial wastes.
An undesirable appearance is produced by colour in water and people may not like to drink
coloured water. Further coloured water may spoil the clothes washed in it and it may affect
various industrial processes. As such colour should be removed from water to make it
suitable for general and industrial purposes.

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Taste and odour: The taste of water may be bitter, salty, sour and sweet. Similarly water
may possess odour such as unpleasant, earthy, fishy, grassy, muddy, peaty and sweetish.
Taste and odour are closely related and these may be imparted to water by the presence of
dissolved gases such as H2S, CH4, CO2, O2 etc, combined with organic matter, mineral
substances like NaCl, iron compounds, carbonates and sulphates of other elements, and
phenol and other tarry or oily matter. It is evident that water to be supplied from a public
water supply scheme should not have any undesirable taste and odour.

Turbidity: Turbidity in water is caused by suspended matter, such as clay, silt, finely divided
organic and inorganic matter, soluble coloured organic compounds and plankton and other
microscopic organism. Turbidity is an important consideration in public water supplies for
three major reasons, such as aesthetic, filterability and disinfection. A turbid water has muddy
or cloudy appearance and it is aesthetically unattractive. Filtration of water is rendered more
difficult and costly with the increase in turbidity. In cases where turbidity is caused by
sewage solids the disinfection of public water supplies may not be effective because many of
the pathogenic organisms may be encased in the particles and protected from the disinfectant.
As such the water supplied to the consumers from a public water supply scheme should be
free from turbidity.

Total solids: The total solids present in water comprise total dissolved solids (TDS) and
suspended solids. Out of the two the dissolved solids usually predominate and these mainly
consist of inorganic salts and small amounts of organic matter. The suspended solids are
usually present in small amounts.
For drinking water the amount of total dissolved solids should not exceed 500 mg/l.
However, the amount total dissolved solids present in water in excess of 500 mg/l may be
tolerated but it should not exceed 1500 mg/l, which is the maximum permissible limit for the
total dissolved solids in water to be considered suitable for human consumption.

pH: pH is defined as the logarithm of the reciprocal of hydrogen ion (H+ ions) concentration.
The pH value of water is a measure of acidity and alkalinity of water.
The acidity in water is caused by the presence of mineral acids, free carbon dioxide, sulphates
of iron, aluminium etc. The alkalinity in water is caused by the presence of bicarbonates of
calcium and magnesium or by the presence of carbonates or hydroxides of sodium,
potassium, calcium and magnesium.

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Figure shows the pH scale. The pH scale varies from 0 to 14 with 0 to 7 as acidic range, 7 as
neutral and 7 to 14 as alkaline range. It may be observed from the pH scale that when the
value of pH is equal to zero there is maximum acidity in water and when the value of pH is
equal to14 there is maximum alkalinity in water.

For drinking water the value pH should be between 7.0 and 8.5.However, water having pH
value less than 7.0 or more than 8.5 may also be accepted but the one having pH <6.5 or >9.2
is not suitable for human consumption and it should be rejected. Further from general
considerations the waters having lower values of pH (i.e., acidic waters) may cause
tuberculation and corrosion, while those waters having higher values of pH (i.e., alkaline
waters) may cause incrustation, sediment deposits, difficulties in chlorination, certain
physiological effects in human system, etc.

Hardness: Hardness is that characteristic of water that prevents the formation of sufficient
lather or foam with soap. The presence of bicarbonates, sulphates, chlorides and nitrates of
calcium and magnesium cause the hardness of water. The hardness caused by the presence of
carbonates and bicarbonates of calcium and magnesium is known as carbonate hardness. The
carbonate hardness is also known as temporary hardness because it can be removed by
boiling the water or by adding lime to the water.

On the other hand the hardness caused by the presence of sulphates, chlorides and nitrates of
calcium and magnesium is known as non-carbonate hardness. The non-carbonate hardness is
also known as permanent hardness because it cannot be removed by simply boiling. It
requires special treatment of water softening. The hardness of water is usually expressed in
mg/l. A scale of hardness showing different levels of hardness of water is as follows.

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Range (mg/l) Hardness level

0-50 Soft
50-100 Moderately soft
100-150 Slightly hard
150-250 Moderately hard
Over 250 Hard

The excess hardness of water is undesirable because it causes more consumption of soap,
modifies colour if used in dyeing work, carbonate hardness produces scale in boilers, causes
corrosion and incrustation of pipes and makes food tasteless.

Chloride content: Chlorides are usually present in water in the form of sodium chloride
(common salt). These impart a salty taste to water. The chlorides may be added to water due
to solvent power of water dissolving salts from topsoils as well as from underground
formations, intrusion of seawater into fresh water in the coastal regions, disposal of industrial
and domestic wastes and human excreta into streams or rivers, etc. The presence of large
quantity of chlorides in water indicates its pollution due to sewage, minerals, etc. The
chloride concentrations of raw waters being used for public water supplies should therefore
be tested regularly, so as to detect any sudden increase in their chloride contents and
possibility of the organic pollution of the source of water.

Nitrates: The amount of nitrates in drinking water should not exceed 45 mg/l. The presence
of excess amount of nitrates in drinking water may adversely affect the health of infants,
causing a disease called ‘methemoglobinemia’ (commonly known as ‘blue baby disease’)
which may result in the death of the child in extreme cases.

Fluorides: Fluoride is a mineral cation that is beneficial and as well as harmful to human.
Desired concentration of fluorides in drinking water is 1 to 1.5 mg/l. A fluoride concentration
of less than 1 mg/l may be harmful and may cause ‘dental carries’ (tooth decay) due to
formation of excessive cavities in the teeth of young children during calcinations of
permanent teeth. Therefore a minimum amount of fluoride is beneficial to fight against
‘dental carries’ (tooth decay). On the other hand excessive concentration of fluorides (greater
than 1.5 mg/l) may be harmful, causing spotting and discolorations of teeth leading to a

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disease called ‘dental fluorisis’. Consumption of excessive fluorides for long periods causes
crippling of bones, a disease called ‘skeletal fluorisis’. Hence fluoride is called as doubled
edged weapon.

Soil pollution:
Soil: Soil is one of the most significant ecological factors. It is an aggregation of
unconsolidated mineral and organic particles produced by physical and biological process. It
is a medium that supports the growth of plants, water, mineral supply and anchorage. Soil is
also defined, as a highly generalized structure of the shallow upper layers of land surface of
the earth, which by weathering of underlying rocks, intimate association with organic matter
and with living organisms, has become a suitable habitat for the living beings.
Sources of soil pollution:
 Solid wastes
 Industrial wastes
 Agricultural practices
 Radioactive wastes
 Biological pollutants
Effects of soil pollution:
 Industrial wastes consist of chemicals that are extremely toxic and hazardous to living
beings. Industries such as steel, fertilizers, pesticides, pulp and paper, refineries etc,
discharge suspended solids, oil and greases, solvents, heavy metal, organic and
inorganic pollutants, hazardous wastes and nondegradable compounds into soil. The
toxicants are transferred to organisms present in soil and enter food chain, which leads
to undesirable effects.
 Discharge of metallic compounds (Hg, Zn, Cd, Cr, Na, K, Cu, As etc) effects the
beneficial microorganisms, worms and bacteria in the soil. Accumulation of these in
the soil for long period may kill the living organisms and contaminate water.
 Utilization of sewage, septic tank effluent, sludge of municipal wastewater treatment
for irrigation and manure for longer period will decrease the agricultural production
and effects soil fertility.
 Radiation from radionuclides affects the soil fertility. This intense radiation affects the
plant growth, production etc.

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 Excessive use of nitrogenous fertilizers for agriculture leads to accumulation of nitrate

in the soil and later percolates into the ground water and becomes toxic (>45 mg/l).
This nitrates leads to blue baby diseases in newborn babies.
 Excess use of pesticides and insecticides leads to accumulation in soil, which
concentrates in vegetables, fruits, crops etc and make them unfit for use.

Control of soil pollution:

 Use of pesticides should be minimized.
 Use of fertilizers should be judicious.
 Cropping techniques should be improved to prevent growth of weeds.
 Special pits should be selected for dumping wastes.
 Controlled grazing and forest management.
 Wind breaks and wind shield in areas exposed to wind eosin.
 Planning of soil binding grasses along banks and slopes prone to rapid eosin.
 Forestation and reforestation.

Noise pollution: The term noise may be defined as

 The unwanted unpleasant sound and is also characterized by its undesirability and
loudness.
 Noise is the wrong sound at the wrong time in the wrong place.
 Noise in physics, is an acoustic, electrical or electronics signal consisting of a random
mixture of wavelength.

A particular sound may be a pleasure to one but may be a noise to another. Whether a given
sound is as pleasant as music or a noise depends on its loudness, duration, rhythm and the
mood of the person. Loudness is the most significant criterion, which makes sound into noise.
Noise is a physical form of pollution and its effects are more on the receiver (human). The
noise may be classified by its occurrence in time as, steady state noise (continuous), impact
noise (single impulse of short duration at regular or irregular intervals) and intermediate
noise.

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Sources of noise pollution: The sources noise may be classified into

(a) Natural sources:
 Earthquake.
 Volcano.
 Thunder.
 Fast wind blows.
(b) Artificial sources:
 Industrial noise.
 Transportation noise.
 Construction noise.
 House hold and residential noise.
 Urban or community noise.

Effects of noise pollution:

(a) Effect on hearing ability: The most immediate and acute effect of noise pollution is
impairment of hearing:
 Eardrum may be damaged by sudden loud noise or prolonged exposure to noise
 The sensory cells meant for hearing in our ears may be permanently damaged, if they
are subjected to repeated sounds of high intensity before their recovery.
 The noise in cities is often enough to deafen people gradually as they grow old.
(b) Effect on general health: Following adverse effects on general health are caused by
noise pollution
 Noise cause anxiety and stress and in extreme cases may lead to fright.
 Constant exposure to noise causes hormonal imbalance leading to several disorders
such as increased rate of heartbeat, constriction of blood vessels and increase in
cholesterol level producing high blood pressure, hypertension and decreased heart
output.
 Noise causes digestive spasms and dilation of eye pupil, impairment of night vision
and decrease in the rate of colour perception.
 A sudden high intensity noise produces a startle reaction which may affect
psychomotor performance of a person and even heart failure in heart patients.
 Noise also detracts attention and causes emotional disturbance.

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 Damage to heart, brain and liver has been reported in animals due to prolonged noise
pollution.
(c) Other effects: Noise interferes with our conversation, disturb concentration and
upsets mood.

Control of noise pollution: Noise pollution can be minimized by the following measures.
 Reduction at source: The best method of controlling noise pollution is to reduce the
noise at the source itself. Measures should be planned such that it can generate less
noise. The measures are installing noisy machines in sound proof chambers, covering
the noise producing machines with sound absorbing materials, use of silencer to
control noise from ducts, automobiles etc. Providing vibrating machine by vibration
damping ( rubber, neoprene cock etc), use quieter machines(designing & fabricating)
to replace noisy ones, better lubrication methods and maintenance of machines.
 Reduction at receivers end: The workers working in the area of noisy machines
should be provided with ear protection aids such as ear-muffs, head phones, ear plugs
etc. By using these aids noise can be controlled effectively.
 Acoustic zoning: A rational town planning can help to reduce outdoor noise
pollution. A city or town can be divided into residential area, industrial area, bus
terminals area, aerodromes area, railway station area, hospital area etc so that
sufficient distance can be maintained between the noisy area and residential areas. A
silence zone can be maintained near residential areas, hospital area and educational
institution.

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Problems on water pollution

Problem 1: If Hydrogen ion concentration in a sample of water is 0.000001. Calculate its pH

value.
Solution:

Problem 2: If the concentration of OH- in a water solution is 0.008, find the value of pH.
Solution:
We know that

Problem 3: In a water treatment plant, the pH value of entering and leaving water is 6.5 and
8.5 respectively. Assuming linear variation of pH with time, calculate the average pH value
of water.

Solution:

For entering water, pH = 6.5 For leaving water, pH = 8.5

Average value of H + ion concentration =

= 1.596 x 10-7

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Environmental Science [HSS05] Unit-3

(Note: Only divalent cat-ion causes hardness).

(Note: Only divalent cat-ion causes hardness).
Problem 4: A River water was proposed as the raw water source for a city. Chemical
analysis of the water indicates the constituents given below. Calculate the hardness of water.
Assume Eq wt. of CaCO3 as 50, Mg2+ as 12.2 and Ca2+ as 20
Ions Zn- Na+ Mg2+ Cl- SO42- Ca2+
Concentration 4 18 16 68 20 50
(mg/l)

Solution:
Only divalent cat-ion causes hardness.
Sl.No. Divalent Cat-ion Concentration (mg/l) Eq.wt of Hardness
Cat-ion (mg/l)
1 Ca2+ 50 20 (50x 50)/20 = 125.00
2 Mg2+ 16 12.2 (16 x 50)/12.2 =65.57
Total hardness in mg/l 190.57 Ans

Problem 5:- An analysis of a sample of water with pH 7.5 has produced the following
concentrations(mg/L). Calculate the total hardness of water. Assume Equivalent weight. of
CaCO3 as 50, Mg2+ as 12.2 and Ca2+ as 20
Ions Ca2+ Mg2+ Na+ k+
Concentration 80 30 72 6
(mg/l)

Solution:
Only divalent cat-ion causes hardness.
Sl.No. Divalent Cat-ion Concentration Eq.wt of Hardness
(mg/l) Cat-ion (mg/l)
1 Ca2+ 80 20 (80x 50)/20 = 200
2 Mg2+ 30 12.2 (30 x 50)/12.2 =122.95
Total hardness in mg/l 322.95 Ans

Problem 6:-A River water was proposed as the raw water suitable for a city. Chemical
analysis of the water indicated the constituents given below. Calculate the hardness of water.
Assume Eq wt. of CaCO3 as 50, Mg2+ as 12.2 and Ca2+ as 20
Ions Zn- Na+ Mg2+ Ca2+ Cl-
Concentration (mg/l) 4 18 16 50 68

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Solution:
Only divalent cat-ion causes hardness.
Sl.No. Divalent Cat-ion Concentration (mg/l) Eq.wt of Hardness
Cat-ion (mg/l)
1 Ca2+ 50 20 (50x 50)/20 = 125.00
2 Mg2+ 16 12.2 (16 x 50)/12.2 =65.57
Total hardness in mg/l 190.57Ans

Problem 7: Calculate the hardness of the water sample with the following analysis.
Assume Eq wt. of CaCO3 as 50, Mg++ as 12.2, Ca++ as 20 and Sr++ as 43.80.
Ions Sr++ Na+ Mg++ Cl- SO4- - Ca++
Concentration 03 20 12 54 15 15
(mg/l)

Solution:
Only divalent cat-ion causes hardness.
Sl.No. Divalent Cat-ion Concentration (mg/l) Eq.wt of Hardness
Cat-ion (mg/l)
1 Ca++ 15 20 (15 x 50)/20 = 37.5
2 Mg++ 12 12.2 (12 x 50)/12.2 = 49.2
3 Sr++ 03 43.8 (3 x 50)/43.8 = 3.4
Total hardness in mg/l 90.1 Ans

Problem 8:-A lake water has been proposed as a raw water source for a town. Chemical
analysis of the water indicates the constituents given below. Calculate the total hardness of
water. Assume Eq wt. of CaCO3 as 50.
Ions Na+ Cl- Sr2+ Mg2+ Ca2+ K+
Eq. Wt. 23 35.5 43.8 12.2 20.0 40.0
Concentration 10 52 14 40 72 40
(mg/l)

Solution:
Only divalent cat-ion causes hardness.
Sl.No. Divalent Cat-ion Concentration Eq.wt of Hardness(mg/l)
(mg/l) Cat-ion
1 Ca2+ 72 20 (72x 50)/20 = 180
2 Mg2+ 40 12.2 (40 x 50)/12.2 =163.9
3 Sr2 14 43.8 (14 x 50)/43.8 =15.98
Total hardness in mg/l 359.88 Ans

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Problem on noise pollution : Unit of noise is deci-Bell (dB)

Equivalent noise level (Leq):- Equivalent noise level also called the equivalent continuous
equal energy level is the statistical value of sound pressure level that can be equated to any
fluctuating noise level.

Eg. A sound of 100 dB lasting for 10 minutes, followed by a sound of 110 dB for the next 80
minutes and then followed by a sound of 120 dB for the next 5 minutes, will compose a
fluctuating noise level, which can be represented by a certain dB value which is indicative of
producing the same effect over the entire time period of 10+80+5 = 95 minutes, as the
original fluctuating noise.

Leq is thus defined as the constant noise level, which over a given time, expands the same
amount of energy, as is expanded by the fluctuating levels over the same time. This value is
expressed by the equation:

Where n = Total number of sound samples

Li = The noise level of any ith sample
ti = Time duration of ith sample,
tt = Total time duration of samples.

Problem 9:- A sound of 80 dB lasted for 10 minutes, followed by a sound of 60 dB lasted for
next 80 minute and then followed by a sound of 100 dB lasting for the next 5 minutes will
compose a fluctuating noise level. Calculate the equivalent noise level which is indicative of
producing the same effect over the entire time period of 95 minutes.

Solution:
We know that Equivalent noise level (Leq) is given by equation

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Problem 10:- A sound of 90 dB lasted for 10 minutes, followed by a sound of 65 dB lasted

for next 70 minute and then followed by a sound of 110 dB lasting for the next 6 minutes will
compose a fluctuating noise level. Calculate the equivalent noise level which is indicative of
producing the same effect over the entire time period of 86 minutes.
Solution:
We know that Equivalent noise level (Leq) is given by equation

Problem 11:- A sound of 90 dB lasted for 15 minutes, followed by a sound of 65 dB lasted

for next 80 minute and then followed by a sound of 110 dB lasting for the next 12 minutes
will compose a fluctuating noise level. Calculate the equivalent noise level which is
indicative of producing the same effect over the entire period of time.
Solution:
We know that Equivalent noise level (Leq) is given by equation

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Environmental Science [HSS05] Unit-3

Problem 12:- A sound of 90 dB lasted for 15 minutes, followed by a sound of 70 dB lasted

for next 45 minute and then followed by a sound of 110 dB lasting for the next 16 minutes
will compose a fluctuating noise level. Calculate the equivalent noise level which is
indicative of producing the same effect over the entire period of time.
Solution:
We know that Equivalent noise level (Leq) is given by equation

Siddaganga Institute of Technology, Tumakuru 3.32