Unit-I PGDEM-03 WATER POLLUTION Rajesh Kumar STRUCTURE · 1.3.1 Municipal and Domestic Wastes 1.3.1.1 Harmful Effects of Domestic Wastes 1.3.2 Industrial Wastes 1.3.2.1 General Effects
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Unit-I PGDEM-03
WATER POLLUTION
Rajesh Kumar
STRUCTURE
1.0. OBJECTIVES
1.1. INTRODUCTION
1.2. WATER QUALITY STANDARDS
1.2.1 Drinking Water Standards
1.2.2 Stream Standards
1.2.3 Irrigation Standards
1.2.4 Effluent Standards
1.2.5 Minimum National Standards (MINAS)
1.3 SOURCES OF WATER POLLUTION
1.3.1 Municipal and Domestic Wastes
1.3.1.1 Harmful Effects of Domestic Wastes
1.3.2 Industrial Wastes
1.3.2.1 General Effects of Domestic Wastes
1.3.3 Agricultural Wastes
1.3.3.1 General Properties of Pesticides
1.3.3.2 The Effects of Pesticides on Target and Non-
target Organisms.
1.3.4 Heat and Radioactive Wastes
1.4 SUMMARY
1.5 KEYWORDS
1.6 SELF ASSESSMENT QUESTIONS
1.7 SUGGESTED BOOKS
1
1.0 OBJECTIVE:
After shedding this unit, you will be able to:
• Understand what are the main causes of water pollution.
• Understand why there is a need of establishing different
water quality standards.
• Become familiar to different water quality standards
• Become familiar to different sources of water pollution
and their characteristics and harmful effects.
1.1 INTRODUCTION
Water exists in various forms in various places. Water can exist in
vapour, liquid or solid forms and exists in the atmosphere
(atmospheric water), above the ground surface (surface water), and
below the ground surface (sub-surface water). Both surface and
sub-surface water originate from precipitation, which includes all
forms of moisture from clouds, including rain and snow. A portion
of the precipitated liquid water run off over the land (surface
runoff), infiltrates and flows through sub-surface (sub-surface
flow) and eventually finds its way back to the atmosphere through
evaporation from lakes, rivers, and ocean, transpiration from trees
and plants; or evapo-transpiration from vegetation. This chain is
known as Hydrological Cycle.
2
Fresh water accounts for just 1/10000 of the total water available
on the planet, yet this quantity seems immense when the volume
is expressed as 1,25,000 km3 . On global scale, this amount is
quite constant year to year, being constantly replenished by
precipitation of reviously evaporated from the ocean (3,50,000 km3
) and from land (70,000 km3). Unfortunately, most of the
precipitation fall back into the ocean and only area 1,10,000 km3
falls on the land. More than half of the 40,000 km3 of water that
does not evaporate run off to the ocean in flood events and is not
available for use throughout the year.
Lakes contain almost all of the fresh surface water on the planet.
The water in rivers and streams make up less than one percent of
the volume in lakes. This fact alone suggests that lakes require
special protection from contamination.
Another fact to consider is that it takes many years to replenish
lakes owing to the relatively small amount of precipitation that falls
on the lake and the small amount of stream water that runs
directly into lakes. On average, lake replenishment takes 100
years, whereas the replacement time for water in streams and
rivers is 11 days. Thus, if contaminants are distributed throughout
the average lake, the incoming water cannot restore the lake to its
initial quality for a long time.
Water quality characteristics of aquatic environment arise from a
multitude of physical, chemical and biological interaction. The
water bodies (rivers, lakes and estuaries) are continuously subject
to a dynamic state of change with respect to their geological age
and geochemical characteristics. This is demonstrated by
continuous circulation, transformation and accumulation of energy
and matter through the medium of living things and their
activities.
3
The water stored in reservoir and lakes, together with the water
that flows perennially in stream, is subject to heavy stress;
because it is used for water supplies, agriculture, industries and
recreation, it can be easily misused. Most cities and industries
discharge wastewaters to streams and rivers, rather than to lakes
and reservoirs. Even though wastewaters are treated, large
quantities of contaminants flow down steam on the way to the
ocean as the water is used over and over again.
Pollution is a qualitative term. It describes the situation that
occurs when the level of contaminants is such that intended water
use is impaired. It takes just a small amount of contaminant to
pollute a water body intended for a drinking water supply. But the
same water might not be considered polluted if the water were to
be used, for example for agriculture. Pollution is not restricted to
contaminants. Physical factors of the environment can also
contribute to pollution. For example, heated water discharged from
4
a power plant can change the temperature of an aquatic
environment. It might not be a problem in a lake or a river during
the winter, but it can certainly be a problem in the summer time.
The major sources of surface water contamination are
construction, municipalities, agriculture, and industries. However,
the water delivered to earth in the forms of precipitation in not
necessarily pure to begin with. Near the coast, it may contain
particulate and dissolved sea salts; further inland; it may contain
organic compounds and acids scrubbed from contaminants added
to the atmosphere both by natural processes and by anthropogenic
(human) activities. Gases from plant growth and decay and gases
from geological activities are example of naturally derived
atmospheric contaminants that can be returned to earth via
precipitation. The acid rain problem of the New England states is a
classic example of anthropogenically derived atmospheric
contaminants that contribute to surface water pollution.
The Environmental Pollution Panel of the U.S. Presidents Science
Advisory Committee defines environmental pollution as the
unfavorable alteration of our surrounding, wholly or largely as a
by-product of man’s actions, through direct or indirect effects of
changes in energy patterns, radiation levels, chemical and physical
constitution and abundance of organisms. These changes may
affect man directly or indirectly through his supplied of water and
of agricultural and other biological products, his physical objects
or possessions, or his opportunities for recreation and appreciation
of nature.
The substances which cause pollution are known as pollutants.
Pollutants may be defined as any substance that is released
intentionally or unintentionally by man into the environment in
such concentration that may cause adverse affect on environment
health. The Indian Environment (Protection) Act, 1986 defines 5
pollutant as any solid, liquid or gaseous substance present is such
concentration as may be or tend to be injurious to environment.
However, nature by itself treats, recycles and makes good use of
these pollutants. But as the 20th century comes to a close, the
large volume and increasing poisonous nature of man made
pollutants threats the integrity of nature and cultural development
of man.
The term water pollution is referred to the addition to water of an
excess of material (or heat) that is harmful to humans, animals or
desirable aquatic life, or otherwise causes significant departures
from the normal activities of ‘various living communities in or near
bodies of water. The National Water Commission (1973) stated that
‘water gets polluted if it has been not of sufficiently high quality to
be suitable for highest uses; people wish to make of it at present or
in the future.
1.2 WATER QUALITY STANDARDS
All sort of pollutants are added to the water bodies. We have
limited resources of water and the requirements are numerous, so
there lies the demand of conserving and minimizing the pollution
of water.
Polluted water is hardly of any use for most purposes. It cannot be
utilized for drinking due to health risk. Water with high salt
content is unsuitable for agriculture and industrial purposes. The
quality of water interferes with the aesthetic and economic
pursuits of water bodies by affecting the fish and other aquatic
organisms. However, the water which is not suitable for drinking
may be good for irrigation, or water unsuitable for irrigation may
be quite suitable for industrial cooling or fish growth. Thus it can
be seen that each use of water has its own limits on the degree of
pollution it can accept.
6
The achievement for this minimum quality of water for diverse uses
has led to the formation of water quality criteria, water quality
objectives and water quality standards. Water quality criteria can
be considered as specific requirement on which a decision to
support a particular use will be based. The criteria for various uses
are developed based on experimental data, our current knowledge
of health and ecological and economic effects of water quality.
Water quality objectives can be defined as aim or goal with regard
to the water quality which is to be achieved. It is not as rigid and
authoritative as a standard and does not have the enforcement
element of requirement. The term standard applies to any definite
principle or measure established by an authority by limiting
concentration of constituents in water which ensure safe use of
water and safeguard the environment. However, sometime
standards may not be fair due to lack of sound scientific
knowledge. Thus, standard may change with the accumulation of
more scientific knowledge and on other consideration.
To attain desired water quality objectives, the standard can be
applied in two ways. One type called ‘effluent standards’ are
applicable for municipal, agricultural or industrial wastes
discharge into water resources and on land. Second type
concerned with water receiving or affected by the effluents.
1.2.1 Drinking Water Standards
Raw water quality and standards depends upon the end use. The
four main uses are municipal, industrial, agricultural and
recreational (fish and wildlife). As water quality is degraded day by
day, so, it become very important to set the drinking water
standards for the safety of water of our limited resources. Different
agencies have set environment standards for safe drinking water
like Bureau of Indian Standards (BIS), World Health Organization
(WHO), European Economic Community (EEC) etc. 7
Drinking water standards, are regulation that Bureau of Indian
Standards (BIS) set to control the level of contamination in the
drinking water. Bureau of Indian Standard consider the inputs
from many organization i.e. Central, State, Semi Government,
Municipal Corporation, Public Health Organization, etc.
throughout the standard setting process.
Indian Water Standards (ISI)
Property/Consti
tuent
Desirable
Limit
Permissible
Limit
Undesirable effects outside the
desirable limit
Physico-chemical Characteristics
Turbidity (NTU) 2.5 10 Aesthetically undesirable
Colour (Platinum
Cobalt Scale) 5.0 25 Aesthetically undesirable
Taste and Odour Unobjectio
nable
Unobjection
able Aesthetically undesirable
Major Chemical constituents
pH 6.5-8.5 6.5-9.2 Affects taste
Total dissolve
solids (mg/1) 500 1500 Causes gastrointestinal problems.
Hardness (mg/1) 300 600
May cause urinary concretion,
disease of kidney, bladder and
stomach disorder.
Calcium (mg/1) 75 200
Essential for nervous and muscular
system, cardiac function and
coagulation of blood. Deficiency
causes rickets. Excess concentration
causes kidney or bladder stone and
8
irritation in urinary passage.
Magnesium
(mg/1)
<30 if SO4
is 250
mg/1
100
Essential as an activator for may
enzyme system. Excess concentration
may have laxative effects.
Magnesium salts are cathartic and
diuretic.
Chloride (mg/1) 250 1000
Affects taste and potability, causes
indigestion, may be injurious to
people suffering from heart and
kidney diseases.
Sulphate (mg/1) 200 400 Causes laxative effects in presence of
Magnesium.
Nitrate (mg/1) 45 100
Causes infant methemoglobinemia
(blue babies). May cause gastric
cancer and affects central nervous
system and cardiovascular system.
Fluoride (mg/1) 1.0 1.5
Essential for teeth and bones,
reduces dental caries in
concentration range of 0.8-1.0 mg/1.
At high level teeth mottling, skeletal
and crippling fluorosis occurs.
Iron (mg/1) 0.3 1.0 Give bitter sweet astringent taste
Manganese
(mg/1) 0.05 0.5 Unpleasant taste
9
Copper (mg/1) 0.05 1.5
Astringent taste, deficiency results in
nutritional anemia in infants, high
concentration may damage lever and
cause central nervous system,
irritation and depression.
Zinc (mg/1) 5.0 15
Very small amount beneficial Impart
astringent taste at higher
concentration.
Toxic Constituents
Arsenic (mg/1) 0.05 0.05 Skin disease, circulatory system
problem, risk or cancer.
Cadmium (mg/1) 0.01 0.01 Kidney damage
Chromium
(mg/1) 0.05 0.10 Lung tumor, allergic dermatitis.
Cynide (mg/1) 0.05 0.05 Causes nervous damages and
thyroid problem
Lead (mg/1) 0.05 0.05 Serious commutative body position.
Selenium (mg/1) 0.01 0.10 Small amount beneficial, large
amount toxic.
Mercury (mg/1) 0.001 0.001 Large amount causes brain and
kidney damage
PAHs (mg/1) 0.20 0.20 Toxic
Physical and Chemical Quality of Drinking Water (BIS)
Quality Highest Desirable Maximum Permissible
PHYSICAL
10
Turbidity (NTU Units) 5 10
Colour (Hazen Units) 5 25
Taste Agreeable Agreeable
Odour Unobjectionable Unobjectionable
CHEMICAL
PH 6.5 - 8.5 NO relaxation
Total Dissolve Solids
(mg/1)
500 2000
Total hardness as CaCO3
(g/1)
300 600
Alkalinity as CaCO3
(mg/1)
200 600
Calcium (mg/1) 75 200
Magnesium (mg/1) 30 100
Iron (mg/1) 0.3 1.0
Manganese (mg/1) 0.1 0.3
Copper (mg/1) 0.05 1.5
Zinc (mg/1) 5.0 15.0
Aluminum (mg/1) 0.03 0.20
Chloride (mg/1) 250 1000
Sulphate (mg/1) 200 Upto 400 if Mg does not
exceeds 30 (mg/1)
Boron (mg/1) 1.0 5.0
Phenolic Substances
(mg/1)
0.001 0.002
11
Fluorides (mg/1) 0.6-1.2 1.5
Nitrates (mg/1) 45 100
Arsenic (mg/1) 0.05 No relaxation
International Standards for Drinking Water
Parameter Max. Permissible
USPH standards
WHO standards European
standards
PH 6.0-8.5 6.5-9.2 6.5-8.5
Sp. Conductivity
(µmho cm -1)
300 - 400
Arsenic 0.05 0.05 -
Ammonia 0.5 0.5 -
DO 6.0 6.0 -
Boron 1.0 - -
Calcium 100 200 100
Cadmium 0.01 0.01 -
Chromium (vi) 0.05 0.01 -
Copper 1.0 1.0 -
Chloride 250 600 250
Cyanide 0.05 0.05 -
COD 4.0 10 5.0
Iron 0.3 1.0 -
Lead 0.05 0.1 -
Magnesium 30 150 -
12
Manganese 0.05 0.5 -
Mercury 0.001 0.001 -
Nitrate + Nitrite 10 45 -
Polynuclear Aromatic
Hydrocarbons (PAH)
0.002 0.002 0.002
Pesticides (Total) 0.005 - 0.005
E.Coli 100/100ml 10/100ml -
Total Hardness as
CaCO3
- 500 -
Total dissolve solids 500 - -
Phenol 0.001 0.002 0.005
1.2.2 Stream Standards
Fresh water is used for irrigation, drinking, industry, power
generation, recreation and even for discharging waste water into
water bodies. This has lead to the concept of classification and
zoning of water bodies which indicate that their quality has to meet
the requirement of one or more of the above potential uses.
The water resources can be classified or zoned depending upon the
designated best use of the water. The Central Pollution Control
Board (CPCB) along with State Pollution Control Boards (SPCB)
has adopted a scheme of classification and zoning of water bodies.
The water quality criteria for this classification are given for fresh
water as below.
Water Quality Criteria for Freshwater Classification (CPCB,
1979)
13
Classes Criteria
Class A Dissolve oxygen (>6 mg/1), BOD <2 mg/1),
MPN of coliforms (<50 per 100 ml), pH (6.5-8.5)
Class B Dissolve oxygen (>5 mg/1), BOD (<3 mg/1),
MPN of coliforms (<500 per 100 ml), pH (65-8.5)
Class C Dissolved oxygen (>4 mg/1), BOD (<3 mg/1),
MPN of coliforms (5000 per 100 ml), pH (6.0-9.0)
Class D Dissolved oxygen (>4 mg/1), pH (6.5-8.5)
Free ammonia as N (<1.2 mg/1)
Class E PH (6.0 - 8.5), Electric conductivity
(<2,250µ mhos/cm), sodium absorption ratio
(SAR) (<26), Baron (<2 mg/1)
Note: Class A Drinking water source without conventional
treatment but after disinfection.
Class B Outdoor bathing.
Class C Drinking water source with conventional
treatment followed by disinfection.
Class D Propagation of wildlife, fishery.
Class E Irrigation, industrial cooling, and controlled
waste disposal.
1.2.3 Irrigation Standards
14
Major parameters of concern of irrigation water quality are salinity
(dissolved solids and conductivity), potential trace elements and
herbicides.
Class
of
water
TDS
(ppm)
Sulphate
(ppm)
Chloride
(ppm)
Sodium
(%)
Boron
(ppm)
E.C.
(µmho/cm)
Suitability for
Irrigation
I 0-700 0-192 0-142 0-60 0-0.5 0-750 Excellent to good for
irrigation
II >700-
2000
192-480 142-355 60-75 0.5-2.0 >750-2250 Good to injurious,
suitable only with
permeable soil and
moderate leaching,
harmful to sensitive
crops.
III >2000 >480 >355 >75 >2.0 >2250 Unfit for irrigation.
Suitability of Water for Different Constituents for Irrigation
Suitability of Water for Irrigation with Different Values of
Sodium Absorption Ratio (SAR)
SAR Suitability for Irrigation
0-10 Suitability for all crops and all types of soils except for those
crops which are highly sensitive to sodium.
10-18 Suitable for coarse textured or organic soil with good
permeability. Relatively unsuitable in fine textured soil.
18-26 Harmful for almost all types of soil. Required good drainage,
high leaching and gypsum addition.
>26 Unsuitable for irrigation.
15
Trace Elements Limit for Irrigation Water in mg/I, Used
Continuously for Crops
Element Limit
Aluminum 1.0
Arsenic 1.0
Boron 0.75
Cadmium 0.005
Chromium 5.0
Cobalt 0.2
Copper 0.2
Lead 5.0
Manganese 2.0
Molybidenum 0.005
Nickel 0.5
Selenium 0.05
Zinc 5.0
1.2.4 Effluent Standards
The effluent standards pertain to the quality of waste water
originating from community agricultural operations and industry.
In general, these standards control the quality of pollutants in the
effluent through effluent treatment at the desired degree.
16
BIS (ISI) Standards for discharge of sewage and industrial
effluents in surface water sources and public sewers.
Tolerance Limit for
Industrial Effluents
Discharged into
Sr.
No.
Characteristics of
Effluents
Tolerance
Limit for
Sewage
Effluents
Discharged
into Surface
Water
Sources as
per IS 4764-
1973
Inland
Surface
Water, as
per IS
2490-
1974
Public
Sewer as
per IS
3396-
1974
1. BOD5 (mg/1) 20 30 500*
2. COD (mg/1) - 250 -
3. pH - 5.5 to 9.0 5.5 to
9.0
4. Total suspended
solids (TSS) (mg/1)
30 100 600
5. Temperature 0C - 40 45
6. Oil and grease (mg/1) - 10 100
7. Phenolic compounds
(mg/1)
- 1 5
8. Cyanides (mg/1) - 0.2 2
9. Sulphides (mg/1) - 2 -
10. Fluorides (mg/1) - 2 -
11. Total residual
chlorine (mg/1)
- 1 -
17
12. Insecticides (mg/1) - Zero -
13. Arsenic (mg/1) - 0.2 -
14. Cadmium (mg/1) - 2 -
15. Chromium (VI)(mg/1) - 0.1 2
16. Copper (mg/1) - 3 3
17. Lead (mg/1) - 0.1 1
18. Mercury (mg/1) - 0.01 -
19. Nickel (mg/1) - 3 2
20. Selenium (mg/1) - 0.05 -
21. Zinc (mg/1) - 5 15
22. Chloride (mg/1) - - 600
23. % Sodium - - 60
24. Ammonical Nitrogen
(mg/1)
- 50 50
25. Radioactive materials.
i) α-emitters
(micro curie
/ ml)
ii) β-emitters
(micro-
curie/ml)
-
-
10-7
10-6
-
-
*Subject to relaxation or lightening by the local authorities.
1.2.5 Minimum National Standards (MINAS)
The MINAS are industry specific effluent standards which are
being evolved at the National level. Hence, State authorities are not
required to relax them except when the ambient water quality
18
criteria warrants their alteration to suit the location. This suggests
treatment of all wastewater to certain minimum standards
regardless of the type of wastewater and locations. The minimum
treatments is provided to any wastewater aim at the removal of
pathogens, toxic substances, colloidal and dissolve organic solids,
mineral oils and adjustment of pH.
1.3. SOURCES OR WATER POLLUTION
The sources of water pollutants can be classified as :
1. Municipal and domestic oxygen demanding wastes which
contains decomposable organic matter and pathogenic
agents.
2. Industrial wastes which contains toxic agents ranging from
metal salts to complex synthetic organic chemicals.
3. Agriculture wastes which comprises fertilizers, pesticides etc.
and
4. Radioactive wastes and heat.
1.3.1 Municipal and Domestic Wastes
It includes waste water from homes and commercial
establishment, consist of domestic refuge, municipal garbage and
other wastes like animal wastes, crops and yard wastes and
garbage’s are mainly of organic origin. Domestic waste water arises
from many small sources spread over a fairly wide area but is
transmitted by sewer to a municipal waste treatment plant.
Generally, the impurities in domestic wastes get diluted and
seldom total more than 0.1% of the total mass. Some of the main
constituents of sewage are given below in Table.
19
Some of Primary Constituents of Municipal Sewage
Constituents Potential Sources Effects in water
Oxygen-demanding
substances
Mostly organic
materials,
particularly human
faces
Consume dissolve
oxygen.
Refractory Organics Industrial wastes,
household products
Toxic to aquatic life.
Pathogens (Bacteria
viruses etc.)
Human wastes Cause diseases.
Detergents Household
detergents
Esthetics, prevent
grease and oil
removal, toxic to
aquatic life.
Phosphates Detergents Algal nutrients.
Grease and Oil Cooking, food
processing,
industrial wastes
Esthetics, harmful to
some aquatic life.
Salts Human wastes,
water softeners,
industrial wastes
Increase water
salinity
Heavy Metals Industrial wastes,
chemical
laboratories
Toxic
Chelating Agent Detergent and
industrial wastes
Heavy metal ion
stabilization and
transport.
20
Solids All sources Esthetics, harmful to
aquatic life.
The origin of these wastes is clearly connected with human
metabolism and vital activities.
As these wastes are largely of organic nature thus get oxidized by
bacterial decomposition to nitrate, phosphate, carbon dioxide and
water. This type of decomposition consumes the oxygen and places
an oxygen demand on the system which can be monitored by a
common indicator test, known as BOD test. In this analysis the
amount of oxygen for decomposition is measured over a 5 day or 3
day period at 20 0C. If waste contain significant amount of organic
material, the bacterial decomposition will remove large amounts of
dissolve oxygen, which causes oxygen depletion.
Inorganic impurities are sand, clay, particles of ore, chalk, mineral
salt, mineral oils and many other substances which are used by
man for various purposes. Public sewage also contains various
micro-organism like bacteria, yeasts and other moulds, algae, eggs
of helminthes, viruses etc, which spread disease like typhoid and
paratyphoid fever, dysentery, cholera, polio etc. and other human
health problems.
Sewages and run off from agricultural land provide plant nutrients
in natural setting, particularly lakes lead to eutrophication (Greak
:well nourished) which lead to algal blooms and large amount of
other aquatic weeds, causing serious problem of oxygen depletion
in addition to foul smell (due to H2S gas), unaesthetic scene and
even death of the lake. When sewage is discharged into a natural
water body, the receiving water gets polluted due to waste product
present in sewage effluents. But the condition do not remain so
forever, because the natural forces of purification, such as dilution,
21
sedimentation, oxidation, reduction etc., bring back the waste
water into its original state. This natural purification of polluted
water is called as self purification. However, the self purification
can not be achieved when environmental conditions are not
favorable.
1.3.1.1 Harmful Effects of domestic Wastes
1. Increased in incidence of water borne disease, as sewage
contain many type of pathogenic organisms.
2. Water becomes totally unfit for drinking and domestic
purpose.
3. Oxygen depletion leads to death of aquatic organisms and
even death of aquatic ecosystem.
4. Water becomes extremely anesthetic and foul smelling.
1.3.2 Industrial Wastes
Most of the Indian rivers and fresh water streams are seriously
polluted by industrial wastes or effluents which come along waste
water of different industries such as petro-chemical complexes,
fertilizer factories, oil refineries, pulp and paper, textile, sugar and
steel mills, tanneries, distilleries, coal washeries, synthetic
material plants for drugs, fibres, rubber, plastic etc. The industrial
wastes of these industries and mills include metals (copper, zinc,
lead, mercury, cadmium, etc.), detergents, petroleum, acids,
alkalies, phenols, carbonates, alcohols, cyanide, arsenic, chlorine
and many other organic and inorganic toxicants. All these
chemicals of industrial origin have been toxic to animals and many
bring about death or sub-lethal pathology of the liver, kidney,
reproductive system, respiratory system or nervous disorder in
both the vertebrate and invertebrate aquatic animals (Wilpur,
22
1969). Important characteristics of waste water from some of major
industries are given below
Sr. No. Industries Important Characteristics
1. Acid Manufacturing Low pH.
2. Sugar High BOD and COD.
3. Coal Wahery Low pH, high suspended
solids.
4. Coke manufacturing &
phenol & oils
High suspended solids,
ammonia, hydrogen peroxide.
5. Distillery High BOD and COD, brown
colour, disagreeable odour,
high dissolve solids.
6. Electroplating Low pH, high COD, heavy
metals & toxic substances.
7. Paint High BOD, contains synthetic
resins, solvents, pigments and
heavy metals like aluminum,
chromium and lead.
8. Petrochemical High BOD/COD ratio,
hydrocarbon, alcohols, phenols,
oil etc.
9. Plastic Manufacturing Acid, formaldehyde and
phenols.
10. Paper and Pulp High pH, high coloured and
odour, high total solids.
11. Tannery High BOD, COD, total solids, oil
and grease, heavy metals like
23
chromium.
12. Textile High BOD, dyes, acids,
phenolic substances, chlorine
and chromium.
Industrial waste discharge into water body lead to pollution of
water and polluted water results into following:
A. Organic substances deplete the oxygen content of water
body.
B. Inorganic substances make water unfit for drinking and
other purposes.
1.3.2.1 General Effects of Industrial Effluents
A. Industrial water contains coloured material like dyes make
water unaesthetic and objectionable.
B. Effluents having acid and alkalies adversely affects the
growth of fish and other aquatic life.
C. Toxic substances like cyanide, phenol and heavy metals like
Hg, Pb Ar cause damage to flora and fauna.
D. Oil and other greasy floating substances interfere with self
purification mechanism of water bodies and also lead to
suffocation to aquatic life.
E. The polluted water body become unfit for swimming due to
presence of chemical irritants.
F. The presence of dissolve salt contribute to water hardness
and make it unsuitable for industrial use as hard water lead
to scale formation.
G. High pollution in rivers will interfere with navigation by
causing corrosion of ships, boats and form the sludge 24
mounds at the bed i.e. coal washery waste causes extensive
deposits in river and removal of which is very expensive.
H. Thermal pollution will interfere with life cycle of aquatic life.
I. Phosphates and nitrates bring about excessive growth of
vegetation and lead to eutrophication in water bodies.
J. Chemical pollutants can even enter the aquatic human food
chain through bio-accumulation and bio-magnification and
results in serious health problem.
In India, all the 14 major rivers have become polluted. The river
Damodar is perhaps the most heavily polluted river. River Mini-
Mahi in Baroda has been another heavily polluted river which is
having variety of industrial and petrochemical wastes. The river
Ganga from Haridwar to Calcutta is regarded as one unending
sewer which is fit only to carry urban liquid wastes, half burnt
dead bodies, pesticides and insecticides. The 27 cities contribute
about 1000 million liters of waste water to the river each day. The
water of Ganga affects the health of about 250 million people of
Northern Indian. Many or our lakes, Notably the Dal Lake, are
becoming darkened, smelly and choked with excessive growth of
algae.
Some of major hazards of industrial effects are given below:-
1. The “itai-itai disease in Japan due to cadmium poisoning
was traced due to the discharge of waste water from a mine
processing Cu, Pb, Zn in “Jintsu River”. The river water is
used in paddy crop irrigation. Similarly Minmata was caused
by mercury poisoning (1955).
2. Lake Zurich in Switzerland and lake Erie in Canada are
classic examples of induced eutrophication.
25
3. Hoogly at Calcutta is receiving waste from power station,
paper, jute, textile and chemical mills at an average rate of
52 tones /day. The water quality is worst than 4th grade as
proposed by WHO.
4. The water of ‘Yamuna at Okhala industrial area for about 48
kms stretch is unfit ever for irrigation purposes.
5. Discharge of untreated waste from a group of dye industries
into the Kalu River near Mumbai, resulted in lowering of pH
to 4.0.
1.3.3. Agricultural Wastes
It includes sediments, fertilizers, pesticides and farm animals
wastes, which reach the water bodies through runoff and leaching.
Very broadly, agricultural pollution is caused by refuse of any form
from agricultural operations of any kind. Agricultural refuse
generally includes the following type of wastes:
1. Manure and other wastes from farms and the operation of
feed lots or poultry houses.
2. Slaughter house wastes.
3. Fertilizers runoff from cropland.
4. Harvest wastes
5. Pesticides that escape in the atmosphere or into the water
supply.
6. Salt and silt drained from irrigated land or eroded land.
Until the mid 1950s animal wastes posed little problem, because
they were, for most part reused as fertilizers or other uses. With
advancement of agribusiness, the large numbers of animals are
kept in small areas which lead to excess of animal waste in and
confined to a given area and thus, it become economically
26
impossible to distribute wastes for reuse as fertilizers. This waste
finds its way into water bodies through runoff during the period of
heavy rainfall. As these wastes are organic, they increase the BOD
of the receiving water bodies.
Inorganic fertilizers, being plant nutrients, lead to over fertilization
of water bodies when they inter water bodies through runoff or
during irrigation. Excess plant nutrients lead to excessive plant
growth, the process called eutrophication. When plant dies they
settle to the bottom, since they are organic, increases the BOD of
the water bodies.
Soil erosion is a serious problem. It increases the normal rate of
filling of water bodies and decreases the amount of fertile land for
crop production. Sediments decrease the transparency of water,
which limit the photosynthesis. It addition, sediments into fresh
water bodies tends to clog the gills of adults fish and settles out
over incubating eggs, causing suffocation.
A remarkably large number of pesticides have come into
widespread use in recent time. Many of these compounds have
been not only non-biodegradable but also only slightly soluble in
water. Consequently, when sprayed on crop land they remain in
soil for long period of time. During the period of high rainfall or
irrigation, they tend to be carried into surface, marine or ground
water system. In both fresh and marine water bodies they enter the
food chain, undergo bio-concentration in non-target organisms and
increase in animal tissue to alarming level. Excessive use of the
pesticides like BHC, PCBS, DDT etc., made them an integral part
of chemical and bio-chemical cycles of the earth. Even these
pesticides have been detected in Artic region.
1.3.3.1 General properties of pesticides
27
1. They often strike not only the intended parts but also
several non-target organisms.
2. Many of these chemicals are persistent and cannot be
disposed off.
3. They cause unintended affects like resistance, faunal
displacement and other population changes.
4. They are carried away to place far away from the
points of application.
5. They tend to bioaccumulation and bio-magnification.
1.3.3.2 The effects of pesticides on target and non-target
organisms.
1. Increase disease susceptibility in host.
2. Development of pesticide tolerance.
3. Bio-accumulation and bio-magnification.
4. Disturbance in equilibrium, existing between pests
and their parasites (Pray-Predator relationship)
5. Disturbance in reproductive physiology.
6. Food contamination, and
7. Effects on beneficial living organism.
1.3.4. Heat and Radioactive Wastes
Thermal power plants, nuclear power plants and many chemical
industries use lot of water for cooling purpose and return this
water to stream at higher temperature. Increased temperatures
increase the rate of chemical and biochemical reactions. Biological
systems have the optimum temperature at which enzymes
function.
28
Thus increased temperature affects the enzyme catalysis and even
death of aquatic organisms. Increased temperatures of a water
body also decrease solubility of dissolve gases.
Radio active substances are the most toxic substances, whose
injurious effects are tremendous. Nuclear war material, test
explosions, increased use of power reactor and radioactive
materials in medical, industrial and research purposes are the
principle source of ratio active exposure that threaten the
environment.
1.4 SUMMARY
Water exist in three forms i.e. vapour, liquid or solid. It is present
in atmosphere (atmospheric water), surface (surface water) and
below the ground (sub-surface or ground water). On the earth
water is constantly replenished by precipitation through
hydrological cycle. We have limited resources of water in ice cap,
river, lakes etc and the requirement are numerous, so there lies
the demand of conserving and minimizing the pollution of water.
Polluted water is hardly of any use for most purposes that’s why,
water quality standards are required. The main sources of water
pollution are municipal and domestic wastes, industrial wastes
and agriculture wastes. Impacts of different sources are different
because characteristics of wastes are different for different sources.
Compositions of municipal and agricultural wastes are more less
constant but it vary from one industry to another in case of
industrial wastes.
1.5 KEYWORDS
Water pollution: Water can be regarded its changes its quality or
composition either naturally or as a results of human activities
thus becoming less suitable for drinking, domestic, agricultural,
industrial, recreational, wildlife and other uses.
29
Standards: The term standard applies to any definite principle or
measure established by an authority by limiting concentration of
constituents in water which ensure safe use of water and
safeguard the environment.
Oxygen demanding waste: The wastes which deplete the
dissolved oxygen of a water body are called oxygen demanding
waste.
Municipal wastes: It consist mainly the domestic sewage i.e. water
born waste of community contain of 99% water and 1% solids. Of
the solids 70% are organic 30% are inorganic in nature.
Industrial wastes: The wastes from industry like sugar, dairy,
paper tannery etc. industrial waste have the greatest potential of
the receiving water.
Domestic wastes: The waste generated in household like kitchen,
toilet etc. is called as domestic waste.
1.6 SELF ASSESSMENT QUESTIONS
1. What are Environmental Standards? Give BIS
standards of drinking water and industrial effluent
and sewage discharge in surface water, and public
sewer.
2. Give details of sources of water pollution.
3. How industrial effluents effect the water quality?
4. How the Municipal and domestic wastes effects the
dissolved oxygen of a water body?
5. Give important characteristics of industrial wastes.
6. What is thermal pollution and how it affects the water
quality of receiving water body?
30
7. Water is the water borne diseases and how they
spread?
1.7 SUGGESTED BOOKS
Aggarwal K C (1999). Environmental pollution. Agro Botanica,
Bikaner.
Aggarwal S K (2002). Pollution management-II water pollution.
APH Publishing Corporation, New Delhi.
Coler R A and Rockwood J P (1989). Water pollution biology (A
laboratory /field hand book). Technomic Publishing Co. Inc.,
Pennsylvania (U.S.A.)
Gaur D (2005). Water pollution and its management. Sarup &
Sons, New Delhi.
Goel R P (1997). Water pollution: causes, effects and control. New
Age International (Pvt.) Ltd, New Delhi.
Kumar A (2004). Water pollution – assessment and management.
Daya Publishing House, New Delhi. Manivasakam N (1984).
Environmental pollution. National Book Trust India, New
Delhi.
Mishra P C and Trivedy (1993). Ecology and pollution of Indian
lakes. Ashish Publishing House, New Delhi.
Smith R J (1996). Introduction to water pollution. Asian Books Pvt.
Ltd., New Delhi.
Thakur K (1999). Environmental protection law and policy in India.
Deep and Deep Publication, New Delhi.
Tripathi A K (1995). Water pollution. Ashish Publishing House,
New Delhi.
Tripathi B D and Govil S R (2001). Wate pollution – an
experimental approach. CBS Publisher, New Delhi.
31
32
Unit-I PGDEM-03
WATER POLLUTION
Rajesh Kumar
STRUCTURE 2.0 OBJECTIVES
2.1 INTRODUCTION
2.2 MAJOR POLLUTANTS
2.2.1 Oxygen Demanding Waste
2.2.2 Disease Causing Agents
2.2.3 Plant Nutrients
2.2.4 Synthetic Organic Compounds
2.2.4.1 Soap, Detergents and Detergent
2.2.4.2 Hydrocarbons
2.2.4.3 Pesticides
2.2.5 Oil Pollution
2.2.5.1 Sources of Oil Pollution
2.2.5.2 Fate and Movement of Oil in Marine Environment
2.2.5.3 Effects of Oil on Organisms
2.2.5.4 Control of Oil Pollution
2.2.6 Inorganic Chemical and Minerals
2.2.6.1 Heavy Metals
2.2.6.2 Toxicity of Metals to organisms
2.2.7 Sediments
2.2.7.1 Detrimental Effects of Sediments 2.2.8 Radioactive Materials
1
2.2.8.1Effect of Radiations
2.2.9 Thermal Pollution
2.2.9.1Effects of Thermal Pollution
2.3 SELF PURIFICATION
2.3.1 Oxygen-Sag Cruve
2.4 SUMMARY
2.5 KEYWORDS
2.6 SELF ASSESSMENT QUESTIONS
2.7 SUGGESTED BOOKS
2.0 OBJECTIVE
After studying this unit, you will be able to:-
• Understand the types of pollutants those responsible for water
pollution.
• Become familiar with different sources of different pollutants
and their harmful effects.
2.1 INTRODUCTION
The sign of water pollution are bad taste, massive weed growth in many
water bodies, emission of disgusting odour, decrease in number of fishes,
Oil can be seen floating on the surface of some water bodies or deposited
as scum on beaches etc. The origin of these problems could be attributed
to many sources and types of pollutants. The substance which causes
pollution is defined as pollutants.
2.2 MAJOR POLLUTANTS
The major water pollutants can be classified into 9 categories as given
below:
2
Oxygen demanding wastes.
Disease causing agents.
Plant nutrients.
Synthetic organic compounds.
Oil.
Inorganic chemicals and minerals.
Sediments.
Radioactive materials.
Thermal Pollution (Heat)
2.2.1 Oxygen Demanding Wastes
These are primarily organic materials that are oxidized by bacteria to
carbon dioxide and water and reduce the amount of available oxygen.
Microorganisms
Organic matter + O2 → CO2 + H2O + New cells + Stable product.
Glucose oxygen carbon dioxide water As dissolve oxygen (DO) drops, fish and other aquatic life are threatened
and in extreme case, killed. In addition, as DO levels fall, undesirable
odours, tastes, and colours reduce the acceptability of water as a
domestic supply and reduce its attractiveness for recreational uses.
Oxygen demanding wastes are usually biodegradable organic substance
contained in municipal waste or in effluents from certain industries,
such as food processing and paper production. In addition, the oxidation
of certain inorganic compounds may also contribute to the oxygen
demand. Even naturally occurring organic matter, such as leaves and
animal droppings, that find way into surface water add to the DO
depletion.
A common measurement of this type of pollution is biochemical oxygen
demand (BOD). BOD is amount of oxygen required for oxidation of
3
organic matter over a 5 day period at 200C and expressed in mg oxygen
per liter (mg/1). Fish and other aquatic life required about 5 mg/1 of DO
for their survival (higher in cold water, especially in spawning areas,
which require at least 7 mg/L ). The DO level of water saturated with
oxygen is 9.2 mg /1 at 200C. If sufficient DO is available, micro
organisms are able to oxidize the nitrogen compound and certain
inorganic compounds such as ferrous salts, sulphides and sulphites.
Another important test for this type of pollution is chemical oxygen
demand (COD). COD measurement have been carried out using strong
oxidizing compounds, like potassium dichromate, to oxidize even some
materials that have been biologically degradable and expressed as
milligram per liter (mg/L). COD value will be higher than BOD value.
2.2.2 Disease Causing Agent
It has long been known that contaminated water is responsible for the
spread of much contagious disease. Pasteur in later nineteenth century
established the germ theory of disease, that the role of pathogenic micro-
organisms in epidemic diseases. Pathogens are disease producing
organisms that grow and multiply within the host. Examples of
pathogens associated with water include bacteria responsible for cholera,
bacillary dysentery, typhoid and paratyphoid fever; viruses responsible
for infectious hepatitis and poliomyelitis; protozoa causes dysentery and
giardiasis and helminthes or parasitic worm cause schistosomiasis etc.
The intestical discharges of an infected individual, a carrier, may contain
billions of these pathogens, which, if allowed to enter to water supply,
can cause epidemics of immense proportions.
Contaminated water caused by poor sanitation can lead to both water
borne and water contact diseases. Water borne diseases are those
acquired by ingestion of pathogens not only in drinking water, but also
from water that make its way into the mouth from washing food, utensils
and hands. In developing countries like India, particularly in rural areas,
water is often taken from open wells or streams that are easily polluted.
4
Water contact diseases do not even require that individual ingest the
water Schistosomiasis is most common water contact disease.
Water also plays an indirect role in other diseases, common in
developing countries. Insect that bread in water, or bite near water, are
responsible for the spread of malaria, affecting some 160 million people
and killing 1 million each year. Yellow fever and sleeping sickness are
spread in this same way. Table given below summaries some of these
water related problems.
Type Spread by Example Prevalance
Water
borne
Drinking water
contaminated by
pathogen, or washing
hands, food or
utensils in
contaminated water.
Typhoid,
Cholera,
Dysentery,
Diarrhea,
Hepatitis,
Guinea worm
disease
6 million children
under five die from
diarrhea each year. 10-
20 million children die
each year from all types
of diarrheal disease. 10-
48 million annual
guinea warm cases.
Water
Contact
Invertebrates living
in water which act as
carrier (vectors).
Schistosomiasi
s (bilharzias),
leptospirosis,
tularemia.
Over 200 million people
infected world wide with
schistosomiasis.
Water
hygiene
Inadequate supplies
of water for personal
hygiene
Skin diseases,
scabies,
leprosy, yaws,
eye disease,
trachoma,
conjunctivitis.
500 million infected
with trachoma
(blindness occur in
sever cases; prevalence
of skin diseases
approaches 80% of
population in some
areas.
Source: Adopted from Marrison (1983)
5
The identification of pathogens in water needs very large samples and
many sophisticated techniques and is too time consuming and expensive
for routine pollution test. The standard method involves determination of
most probable number (MPN) of coliform organisms in the water sample.
Coliform bacterial like Escherichia Coli have been normal inhibitants of
human and animal intestine, and the daily per capita excretion in
human faces may number from 125 to 400 billion. Although coliforms
organisms have not been pathogens and are not affected by water
environment in exactly the same manner as pathogens, their existence
and density has proved to be a fairly reliable indicator of the adequacy of
treatment for reducing pathogens and coliform tests are therefore, widely
used.
2.2.3 Plant Nutrients
Nutrients are chemicals, such as nitrogen, phosphorous, carbon,
sulphur, calcium, potassium, iron, manganese, boron, and cobalt that
are essential to the growth of living beings. Aquatic species require a long
list of nutrients for growth and reproduction, but from water quality
perspective, the three most important ones are carbon, nitrogen and
phosphorous. Plant requires relatively large amounts of each of these
three nutrients and unless all three are available, growth will be limited.
The nutrient that is least available relative to plant’s needs is called the
limiting nutrient. This suggests that algal growth can be controlled by
identifying and reducing the supply of that particular nutrient. Carbon is
usually available from a number of natural sources including alkalinity,
dissolved carbon dioxide from atmosphere and decaying organic matter,
so it is not often the limiting nutrient. Rather, it is usually either nitrogen
or phosphorous that control algal growth rates. Major sources of both
nitrogen and phosphorous include municipal discharge, run off from
animal feed lots, chemical fertilizers and detergents.
Plant nutrients like nitrogen and phosphorous are able to estimate
growth of aquatic weed, particularly algae, which got interfere with water
uses and later decay to produce disagreeable odour and add to BOD of
6
water. The enrichment of water with nutrients is a naturally occurring
biological process called eutrophication. The term comes from two Greek
words meaning “Well nourished”. This enrichment leads to other slow
processes collectively referred as-natural aging of lakes. The steps in
eutrophication and aging of a lake have been as follow:
1. Streams from a drainage basin gradually bring soil and
nutrients to a newly formed lake, increasing the fertility of the
lake water.
2. The increased fertility lead to an accumulating growth of
aquatic organism, both plant and animal.
3. As living matter increases and organic deposits pile up on the
bottom of the lake, it become more shallow, warmer, and richer
in nutrients.
4. Plant take root at the bottom and gradually occupy more and
more of the place. Their remains accelerated the filling of the
basin.
5. The lake gradually become a marsh and finally a field or forest
as it has been over-taken by vegetation.
The time needed for this process to be completed could be in
thousands of years, but due to addition of nutrients by man’s activity
in water source increase the speed of this process.
Not only is nitrogen capable of contributing to eutrophication, but
also pose a serious public health problem. Nitrogen in water is
commonly found in the form of nitrate (NO3), which itself is not
harmful. However certain bacteria commonly found in intestinal tract
of infants can convert nitrate to highly toxic nitrite (NO2), which
combine hemoglobin in blood stream. When they replace that needed
oxygen a condition known as methemoglobinemia results ( blue baby
syndrome ). In extreme cases the victim die from suffocation. It occurs
in children of below 6 months age.
7
Essential Plant Nutrients: Sources and functions.
Nutrient Source Function
Macro-nutrient
Carbon (CO2) Atmosphere, decay Biomass constituent
Hydrogen Water Biomass constituent
Oxygen Water, Atmosphere Biomass constituent
Nitrogen (NO3) Decay, atmosphere
(from nitrogen fixing
organisms), pollutants
Protein constituents
Phosphorous (PO4) Decay, minerals
pollutants
DNA/RNA constituent
Potasium (K+) Minerals, pollutants Metabolic function
Sulphur (SO4) Minerals Proteins, enzymes
Magnesium Minerals Metabolic function
Calcium Minerals Metabolic function
Micro-nutrients
B, Cl, Co, Cu, Fe, Mo,
Mn, Na, Si, V, Zn.
Minerals, pollutants Metabolic function and
/ or constituent of
enzymes.
2.2.4 Synthetic Organic Compounds:
Organic chemicals can be considered to be any compound that contain
one or more carbon atoms in its molecular structure. Organic that
commonly enter water ways are pesticides, detergents and hydrocarbons.
The exotic organic chemicals includes surfactants in detergents,
pesticides various industrial products and the decomposition products of
other organic compounds. Analysis of polluted waters reveal the presence
of a wide variety of these compounds and many others have been
8
probably not being detected. Some of these compounds have been found
to be toxic to fish at very low concentration such as I ppm phenol. Many
are not biologically degradable, or are degraded only very slowly. As
many new chemical compounds get introduced each year without much
knowledge of their effects on natural ecosystems.
2.2.4.1 Soap, Detergents, and Detergents
These chemicals are potential sources of organic pollutants. These
pollutants are discussed briefly here.
Soaps: Soaps are salt of higher fatty acids, such as sodium Stearate, C17,
H35, COO-Na+. The cleaning action of soap results largely from its
emulsifying power caused by dual nature of the soap anion. A soap ion
consists of an ionic carboxyl ‘head’ and a long hydrocarbon ‘tail’.
In presence of oils, fats, and other water insoluble organic materials, the
‘tail’ of anion tends to dissolve in the organic matter, whereas the ‘head’
remains in aquatic solution. Thus, the soap emulsifies or suspends,
organic material in water. Soap lowers the surface tension of water, thus
making the water ‘wetter’.
The primary disadvantage of soap as a cleaning agent comes from its
reaction with divalent cations to form insoluble salts of fatty acid:
2 C17H35 COO-Na+ + Ca2 → Ca (C17H35CO2)2(S) + 2Na+
These insoluble products, usually salts of magnesium or calcium, are not
at all effective as cleaning agents and generally precipitate as calcium
and magnesium salts. Therefore, aside from the occasional formation of
unsightly scum, soap does not cause any substantial pollution problems.
9
Detergents
Synthetic detergents have good cleaning properties and do not form
insoluble salt with hardness ions (calcium and magnesium). It includes
as a part of its formulation a petrochemical or other synthetically derived
surfactant (10-30%) (to improve the action of surfactant) and other
ingredients like anti-corrosive sodium silicate, amide, foam stabilizers,
soil-suspending carboxymethyl cellulose sodium sulphate etc.
The surfactant lowers the surface tension of the liquid and it gives a
stable emulsion with soil particles. The builder, added to detergents,
complex with Ca2+ and Mg2+ and react with H2O to form alkaline solution
for functioning of surfactant. Sodium triple-phosphate Na5P3O10 is most
popular builder.
Until the early 1960s, the most surfactant used was alkyl benzene
sulphonate (ABS).
ABS is persistent surfactants and interfered with waste treatment
processes by Stabilizing small particles in colloidal suspension and
decreasing the activity of biological filter beds and activated sludge. The
foam formed by the detergent is visible and unaesthetic for all people.
These problems were solved by modifying the structure of surfactant so
as to make them more readily biodegradable. The linear alkyl sulphonate
(LAS) surface are now used.
10
Most of the environment problems later attributed to detergents arise
from builder rather than surface-active agents. Polyphosphate builder
undergo fast biodegradation by hydrolysis:
P3 O10-5 + 2H2O → 2HPO4-2 + H2PO4-
These hydrolysis products do not pose any threat to aquatic animal life.
However, phosphate act as nutrient for plants and thus cause
eutrophication by excessive growth of plants, particularly algae.
The most promising substitute for poly phosphate builders is the sodium
salt of nitrite-triacetic acid, N(CH2CO2Na)3. It is readily biodegradable
and relatively cheap. But it is hygroscopic
2.2.4.2 Hydrocarbons:
Hydrocarbons in the form of gasoline and motor oil, altogether insoluble
in water, have been carried from motorways and parking areas in rain
water, have been carried from motorways and parking areas in rain
water runoff. These wastes percolate into ground water and /or goes into
steam, rivers and lakes and affect the water quality.
2.2.4.3 Pesticides:
The term pesticides is used to cover a range of chemicals that kill
organisms that consider undesirable and includes the more specific
categories of insecticides, herbicides, rodenticides, and fungicides. There
are three main groups of synthetic organic insecticides: organo chlorines,
organophosphate and carbonates. In addition, number of herbicides,
including the chlorophenoxy compounds 2, 4,5-T and 2,4-D are common
water pollutants. Pesticides are classified as:-
Insecticides – designed to kill insect in crops
Herbicides – meant for killing weeds or undesirable vegetation.
Fungicides – toxic to moulds (fungi) and act to check plant diseases.
Other specific pesticides e.g. rodenticides , nematiocides etc.
11
At present there are more than 10,000 different pesticides. The use of
pesticides has helped in eradication of diseases such as malaria and
typhus and also increased production of food.
Pesticides: nomenclature and uses
Trade Name Uses Fresh
water
permissio
n limit
Chlorinated Hydrocarbon
Aldrin-Dieldrin Soil insecticide for control of
ants, beetles and cotton pests.
0.003
µg/1
Chlordane Effective against termites,
potential carcinogenic.
0.01 µg/1
Lindane Control of cotton insects and
nice stem borer.
0.01 µg/1
Dichloro Diphenyl Trichloro
ethane (DDT)
Broad spectrum-cotton,
soyabean, peanut pests,
mosquito control. Persistant in
environment accumulates in
food chain.
0.001
µg/1
Toxaphene Insect control on crops and
livestock, carcinogenic in nature
5 µg/1
Heptachlor Pest control in soil, carcinogenic. 0.001
µg/1
Eldrin Effective against black current
mud-mit- also used as a zoo-cide
precautions to be taken to avoid
skin contact-during application
0.004
µg/1
Methoxychlor Popular DDT –substitute-
bl bi d d bl l
0.03 µg/1
12
reasonably biodegradable-low
toxicity to mammals
Organophosphate
Malathion Control some pests of fruits and
vegetables little hazard to
mammals
0.1 µg/1
Parathion Larvicide for mosquito control,
also broad, spectrum insecticide
for fruit and vegetable pests.
Methyl parathion Control of plant pests.
Diazinor Control of may fruit and
vegetable pests.
Carbamates
Carbaryl Used on crops-cotton, forage,
fruits and vegetable, lawn and
garden insecticide, lawn toxicity
to mammals.
Baygon Control of flies, mosquitoes, ants
and cockroaches.
Dimetilan Control of house and fruit flies.
Chlorophenoxy acid
2,4-dichlorophenoxy acetic
acid (2,4-D)
Herbicide-control of broad leaved
weeds, aquatic vegetation,
defoliant.
100 µg/1
2,4,5-Trichlorophenoxy acetic
acid (2,4,5-T)
Weed control, defoliant
13
Most of organochlorine are now banned. The well known organochlorinie
pesticide is DDT, widely used to control insect that carry disease like
malaria, typhoid and plague and saved the life of millions of people
worldwide. It is persistent in nature and in term of human toxicity DDT
is considered to be relatively safe. It has its impact on food chain. DDT is
quite soluble in lipids, which means easily accumulated into fatty
tissues. Accumulation of organochlorine pesticides in fatty tissue means
that organisms at successive higher trophic levels in a food chain are
consuming food that has higher concentration of pesticides. At the top of
the food chain are consuming food that has higher concentration of
pesticides. At it is there that organochlorine toxicity has been
recognizable. For example, fish has higher concentration of pesticide
than water body and birds eating on fishes have much higher
concentration than fishes in their body. This phenomenon in which the
concentration of a chemical increase at higher levels in the food chain is
known as “biomagnifications or bio-concentration’.
Some of organochlorine are carcinogenic. Many insects species have
developed biological resistance to these pesticides. Organophosphates
are much more toxic than organochlorine pesticides as they are rapidly
absorbed through skin, lungs and gastro intestinal tract. Human
exposure to excessive amount has shown a range of symptoms including
tremor, confusion, slurred speech, muscle twitching and convulsions.
Acute human exposure to corbamates has lead to a range of symptom,
such as nausea, vomitting, and blurred vision and in extreme case,
convulsions.
Much more work is needed to determine the relationship to environment
of many of synthetic organic compounds. The following facts are known
about them:
1. Some have been resistant to biochemical breakdown by natural
water bacteria or waste treatment processes and therefore,
persist for extended period of time in water.
14
2. Some have been responsible for objectionable and offensive
taste, odors and colours of some fish and shellfish taken from
polluted water.
3. Some have been toxic to fish and other aquatic life when
present in very low concentration.
2.2.5 Oil Pollution
Oil pollution is a special problem due to unique property of oil to form a
thin film over a vast area. Oil pollution has been an almost inevitable
consequence of the dependence of a rapidly growing population on oil-
based technology. The use of natural resources such as oil on grand
scale, without losses, has been almost impossible. At present refined
petroleum products meet more than 62% of global energy requirements.
The extent of losses, intentional or accidental, has been steadily
increasing and has been becoming a great cause of concern. It has been
estimated that total oil influx into the ocean has been between 5-10
million tons annually.
2.2.5.1 Sources of oil pollution
1. Cargo tanker washing at sea.
2. Bilge pumping at sea.
3. In-port oil losses during loading and unloading procedures.
4. Vessel accidents i.e. One of the largest spill “Torrey Canyon
at the off coast of England in March of 1967. The oil spill
amounted to 1, 00,000 tons.
5. Losses during exploration and production of oil.
6. Oil leakage from pipe lines.
2.2.5.2 Fate and movement of oil in Marine Environment
Petroleum pollutants in the ocean may occur at any concentration and
oil in very small quantities, which can remain in the following forms:
1. Floating material
15
2. Emulsions dispersed in sea water
3. Dissolved in sea water
4. Adsorbed on sediments
5. Locked in marine organisms.
The freshly-spilled oil in sea water, after interacting with prevailing
physical chemical conditions and biological factors, undergo
compositional and chemical changes. Lighter fraction of oil evaporated
into the atmosphere by wind-spray and brusting of water bubbles.
Photoxidation form a variety of toxic and non-toxic materials such as free
radicals, carboxylic acids, esters, oxygenated aromatic, and carbonyl
compounds. Due to wave action, some oil droplets form oil in water
emulsion and sink at the bottom by incorporating silt and suspended
particles.
Rest of residual oil form film on the water surface as water-in-oil
emulsion (80% water). Microbial degradation of oil by some bacteria and
fungi results in formation of variety of products.
2.2.5.3 Effect of oil on organisms
Oil effects the organisms in a number of ways depending upon the
characteristics of the oil fraction and their concentration in water and
ranged from mechanical to various toxic effects. Some important effects
are described below:
1. Oil has smoothing effects (suffocation) on most of the aquatic
animals.
2. Effects the buoyancy and thermal insulation of birds and other
animals like seal.
3. Small animals can be caught in oil envelops and die.
4. Oil layer increase the temperature, which may be critical for
several organisms, particularly in Tropics.
16
5. A few aromatics like benezene and its derivatives have a very
high penetration power into the body of organisms and effects
the permeability by modifying the spacing of protein molecules
on each side of lipid layer. Brain and nerve cells are also
effected, which depend upon fatty substances. A few straight
chain and cycloparaffins also cause damage to the nervous
system.
6. Effect of oil on lipids cause maldevelopment of eggs and larvae.
7. Toxic constituents like non-hydrocarbons of oil (naphthanic
acid and those containing nitrogen, sulphur and oxygen with
carbon and hydrogen are more soluble) can affect the enzyme
system and other vital biomolecules in the body.
8. Effect the feeding and mating behavior in several species.
9. Embryo toxicity and disruption of ion regulation in sea birds.
10. Some polyaromatic hydrocarbons (PAHs) are carcinogenic to a
number of animals and PAHs are mutagenic and taratogenic.
11. Oil effect the migration behaviour in salmon.
12. The bioassay tests carried out by different workes reveal that
lighter oil and water soluble fractions (WSF) of fuel oil are
comparatively more toxic than heavy oil.
13. Algal cell division is inhibited at oil concentration as low as 0.01
ppm. At 0.02 ppm photosynthesis is inhibited.
14. Oils promote anaerobic conditions in water by preventing
diffusion of oxygen from air.
2.2.5.4 Control of oil pollution
1. Mechanical Containment
Oil Spill can be controlled from spreading by using containment barrier
(made up of polyethylene, polyurethane, polyvinyl chloride etc.) Another
17
technique is use of bubble and current barrier which generate surface
current in opposite direction of spread.
2. Mechanical Recovery
After containment oil can be removed by a number of means such as use
of weir, suction devices or by lifting surface.
3. Application Agents
Use of application agents help in dispersion, sinking, collection,
hardening, or burning of floating oil slicks.
4. Biodegradation
Several components of oil can be degraded by the microorganisms.
2.2.6 Inorganic Chemicals and Minerals
This category of water pollutants have been including inorganic salts,
mineral acids and finely divided metals or metal compounds. These
substances enter into water body through various activities like smelting,
metallurgical and chemical industries, mine drainage and various
natural processes and bring these general effects: acidity, salinity and
toxicity.
2.2.6.1 Heavy Metals
One of the major problem of inorganic chemical is due to heavy metals.
Sources of heavy metals are
1. Domestic wastewater and urban runoff: Use of detergent add
Fe, Mn Ni, Zn, Co, Cr and As to wastewater. Sewage sludge
contain Cu, Ag, Cd, Zn and Pb. Runoff from urban areas during
rainy season is rich heavy metals like Cu, Cr, Zn and Pb.
2. Industrial wastewater: Industry is important source of heavy
metals. A number of heavy metals are used by various
industries and a proportion of that find their way into effluents.
Industrial wastes contain toxic heavy metals like Zn, Cu, Cr, Ni,
Cd, etc. and generated from industries like Bakery, Brewery,
18
Fish processing, Ice-cream, Laundry, Metal processing,
Chemicals, textile etc.
Occurrence and Significance of Trace Elements in Natural Water
Element Sources Effects and
Singnificance
Arsenic Mining by-product,
pesticides, chemical
wastes.
Toxic possibly
carcinogenic
Beryllium Coal, nuclear power
and space industries
Acute and chronic
toxicity, possibly
carcinogenic
Boron Coal, detergent
formulations,
industrial wastes
Toxic to some plants
Cadmium Industrial discharge,
mining waste, metal
plating, water pipes
Replaces zinc
biochemically, cause
high blood pressure
and kidney damage,
destroys testicular
tissue and red-blood
cells, toxic to aquatic-
biota.
Chromium Metal plating, cooling-
tower water additive
(chromate), normally
found as Cr+6
Essential trace
element (glucose
tolerance factor),
possibly carcinogenic
as polluted water Cr
(VI)
Copper Metal plating,
industrial and
Essential trace
element, not very toxic
19
domestic wastes,
mining, mineral
leaching
to animals, toxic to
plant and algae at
moderate levels
Iron Corroded metal
industrial wastes, in
contact with iron
minerals.
Essential nutrient
(component of
hemoglobin), not very
toxic, damages
materials (bathroom
fixtures and clothing).
Lead
Industrial sources,
mining, plumbing, fuel
(coal)
Toxicity (anemia,
kidney disease,
nervous system),
wildlife destruction
Manganese Mining, industrial
waste, acid mine
drainage, microbial
action on manganese
minerals at low redox
potential (pE)
Relatively nontoxic to
animals, toxic to
plants at higher levels,
stains materials
(bathroom fixtures and
clothing).
Mercury Industrial wastes
mining, coal.
Acute and chroninc
toxicity.
Molybdenum Industrial waste,
natural sources,
cooling tower water
additive.
Toxic to animals,
essential for plants.
Selenium Natural geological
sources, coal.
Essential at low levels,
toxic at higher levels,
possible carcinogenic.
Silver Geological sources,
i i l t l ti
Causes blue-gray
di l ti f ki
20
mining, electroplating,
film-processing wastes
discoloration of skin,
mucous membrane,
eyes.
Zinc Industrial waste,
electroplating
Essential element in
many metallo-
enzymes, aids wound
healing, toxic to plants
at higher levels, major
component of sewage
sludge, limiting land
disposal of sludge.
Agricultural Activities: Use of fertilizer, pesticides, organic manure
cause the problem of heavy metals.
Mining Activities: Most of mineral ores contain varying quantities of
different heavy metals that tend to become free in the environment by
almost all mining and ore processing activities e.g. acid mine drainage is
rich in metal like Fe, Mn, Zn, Cu, Ni, and Co.
2.2.6.2 Toxicity of metals to organisms
Metal ions and their complex exhibit a wide range of toxicity to the
organisms that ranges from sublethal to lethal depending upon the time
of exposure and the prevailing conditions in the ambient water. Toxicity
is also determined by biological factor like the age and size of organisms.
Toxic responses of some of heavy metals are given below;
Metal Toxic Response
Lead (Pb) Anemia and disruption of hemoglobin synthesis,
damage to nervous system and kidneys, brain
damage. Acute lethal dose to man is 300-700 mg/kg.
In mild cases, insomnia, restlessness, loss of
appetite- and gastrointestinal problems.
21
Mercury (Mg) Brain damage.
Cadmium (Cd) Disorder of respiratory system, kidney and lungs,
cadmium salt consumption causes cramps, nausea,
vomiting and diarrhea, general decline in health.
Chromium (Cr) Occupational hazards of chromium (Cr+6) cause skin
and respiratory disorder, ulceratin of skin, inhaled
Cr+6 can cause cancer of respiratory tract.
Arsenic Skin cancer, hyper-pigmentation, black foot disease.
2.2.7 Sediments
Sediments are soil and mineral particles which are washed from land by
storms, and flood water, from cropland, unprotected forest soils,
overgrazed pastures, strip mines, roads and bulldozed urban area. It
represents the most extensive pollutants of surface water. Suspended
solids reaching natural water are about 700 times as large as the solid
loading from sewage discharge.
Bottom sediments are important sources of inorganic and organic matter
in streams, lakes, estuaries and ocean. The bottom sediments are
subjected to anaerobic conditions. The level of organic matter in
sediments are usually higher than in soils. Bottom sediments have the
ability to exchange cations with surrounding aquatic medium. Sediments
and suspended particles are important source of trace metals like Cr,
Cu, Mo, Ni, Co and Mn.
2.2.7.1 Detrimental Effects of Sediments
1. Stream channels, harbors and reservoirs are filled.
2. Destroys aquatic animals like fish and selfish by
blanketing fish nests and food supply.
3. Reduce light penetration into water. Hence reduce
the photosynthesis.
22
4. Increase the cost of water treatment.
2.2.8 Radioactive materials
Four human activities are responsible for radio active pollution.
23
1. Mining and processing of ores to produce unstable radioactive
Isotope Emitted particle Half-life
Americium-241 Alpha 433 yrs
Americium-243 Alpha 7370 yrs
Bismuth-210 Beta 5 days
Carbon-14 Beta 5730 yrs
Curium-245 Alpha 8500 yrs
Cobalt-60 Beta 5.27 yrs
Cesium-135 Beta 3 x 106 yrs
Cesiu yrs m-137 Beta 30.17 yrs
Tritium-3 Beta 12.33 yrs
Iodine-129 Beta 1.6 x 107 yrs
Krypton-85 Beta 10.7 yrs
Neptunium-237 Alpha 2.14x106 yrs
Lead-210 Beta 22.3 yrs
Plutonium-239 Alpha 29000 yrs
Plutonium-240 Alpha 6570 yrs
Radium-226 Alpha 1630 yrs
Radon-222 Alpha 3.82 days
Strontium-90 Beta 28.8 yrs
Thorium-230 Beta 8000 yrs
Uranium-234 Alpha 2.45 x 105 yrs
Uranium-235 Alpha 7.04 x 108 yrs
Uranium-238 Alpha 4.47 x 109 yrs
Xenon-133 Beta 5.25 days.
24
substances.
2. Use of radioactive material in nuclear weapon.
3. Use of radioactive material in nuclear power plants.
4. Use of radioactive isotopes in medical, industrial and research
application.
Massive production of radionucleotide by weapon and nuclear reactors
since World War-II has been accompanied by increasing concern about
effects of radioactivity upon health and the environment. Radionuclides
differ from other nuclei in that they emit ionizing radiation alpha particle
β- particles and gama rays. Some common radio isotopes often
concerned with environmental pollution, with their half life times are
given below in table
Alpha, beta and gamma rays are called ionizing radiation because they
produce ions in materials. Penetration power of gamma ( γ) rays is
highest, and alpha rays (α) have the lowest penetration power out of
these three.
2.2.8.1 Effects of Radiaions
The movement of radioactive material in the environment ultimate effects
the man. The radioactive pollutants reaching the freshwater resources of
ocean are rapidly lost to the sediments and bioaccumulated in plants
and animals directly or through food chain (bio-magnification). e.g.
accumulation of P-32 and Zn-65 is substantial higher in fish than water
source. Which are eaten by the man and these radioactive materials
affects the health of human being.
As α-particles are positive charge, it attracts the electron when pass
through material and bring ionization. β-rays repulsed the electron due
to negative charge and lead to ionization. Whereas, gamma rays directly
colloids the electron and eject the free electron.
These radiations produce the free radicals which interact with double
bonds, hydrogen bonds and sulphahydryl group (SH) present in proteins,
25
DNA, RNA and other bio-molecules. These interaction causes
deactivation of enzymes, mutation, inhibition of cell division, disruption
of cell membrane and overall damage to all cell performance.
Human response to various radiation which are given in short time span
are given below:
Radiation Dose
(Rads)
Human Response
650 or above Death in few fours or in days.
400 30 days LD 50 (death of 50 % humans within 30
days).
100-250 Sub-lethal dose, causes nausea, vomiting and
diarrhea within hours, itching, burning and
ulceration of skin, loss of hair, hemorrhages just
below skin, decline of red and white blood
corpuscles and loss of ability to fight diseases,
genetic mutations.
Less than 100 Delayed effects such as cancer, leukemia, sterility,
cataracts and reduction of life span, genetic
mutation.
26
2.2.9 Thermal Pollution
Thermal pollution can be defined as an accumulation of unstable heat from
human activities that disrupt ecosystem in the natural environment.
The most important anthropogenic sources of thermal pollution are the
industries which discharge vast quantity of heat in the environment. The heat
producing industries includes thermal power plant, nuclear power plant,
petroleum refineries, steel mills, chemical plants, pulp and paper mills etc.
2.2.9.1 Effects of Thermal Pollution
1. Effects the physical property of water, like decrease in solubility of
gases and increase in solubility of liquids and solids, toxicity of
pollutants etc.
2. Increase the evaporation of water and sedimentation.
3. Increase the rate of chemical reactions.
4. As different species favour different temperature. Thermal pollution
decline population of one species and growth of another.
5. Effect the protein and enzymes so effect the behaviors, reproduction
cycle, respiration rates etc. of many aquatic organisms.
6. At higher temperature, dissolve oxygen level decrease which effects the
aquatic life.
2.3 SELF-PURIFICATION
In natural water, self-purification exists in the form of a biological cycle
which is able to adjust itself, within limits, to changes in the environmental
conditions.
27
In a low organic-content stream there is little nutrients material to support
life so that, although, many different organisms may be present, there is
only relatively low number of each type. In streams with high organic
content it is likely that the DO level will be severely depressed producing
conditions unsuitable for animals and higher plant life. In these conditions
bacteria will predominate although given sufficient time the organic matter
will be stabilized, the oxygen demand will fall and full range of life form will
appear again.
Self-purification involves one or more or the following processes:
1. Sedimentation, possibly assisted by biological or mechanical
flocculation. The deposited solids will form benthic deposits which, if
organic, will decay an aerobically and which, if resuspended by flood
flow, can exert sudden high oxygen demands on the system.
2. Chemical oxidation of reducing agents such–as sulphides.
3. Bacterial decay due to the generally inhospitable environment for
enteric and pathogenic bacteria in natural waters.
4. Biochemical oxidation which is normally by far the most important
process. To prevent serious pollution it is important that aerobic
conditions are maintained; this means that the balance oxygen
28
consumed by BOD and that supplied by reaeration from the
atmosphere is not drastically disturbed.
2.3.1 Oxygen-Sag Curve
In streams, the addition of organic wastes results in the formation of a typical
‘oxygen sag curve’. It indicates that the maximum deoxygenation occurs at a
considerable distance away from the outfall because of slow process. According
to Klein (1962), the deoxygenation is influenced by a number of factors such as
the dilution of the organic pollutants after mixing, BOD of the organic wastes
and that receiving waters, the total organic load in the river, the nature of
organic material, temperature, initial dissolve oxygen in the stream extent of
reaeration from the atmosphere, and nature and density of the bacteria. By the
time the oxygen reaches to minimum, most of the organic matter is already
decomposed, and the process of reaeration takes over deoxygenation resulting
in the build-up of oxygen in the stream there after.
2.4 SUMMARY
Polluted water is unfit for different uses become of bad taste and odour,
massive weed growth, harmful effects etc. The substances which cause
pollution of water is defined as pollutants. There are classified as oxygen
29
demanding wastes, disease causing agents, plant-nutrients, synthetic organic
compounds, oil & grease, inorganic chemicals, radioactive substances, heat
etc. Oxygen demanding wastes decrease the D.O level of water bodies which
have harmful effects in aquatic fauna. Oxygen demanding wastes are measured
in the form of BOD. Disease causing agents are different pathogen i.e. viruses,
bacteria, helminthes, protozoa etc. which causes water born diseases. Plant
nutrients are nitrogen and phosphorus which causes eutrophication. Synthetic
organic substances are soap, detergents, pesticides etc responsible for different
human health problems and have harmful effect an aquatic and terrestrial
flora and fauna. Oil & grease causes suffocation because it acts as barrier for
diffusion of oxygen to water. Inorganic substances are mainly heavy metals
which causes toxicity in aquatic and terrestrial flora and fauna in addition to
human being.
Polluted water is self purified by sedimentation, chemical oxidation, bacterial
decay and biochemical oxidation. If pollution level is very high than water
cannot be self-purified or it takes long time. Thus treatment of polluted water is
required.
2.5 KEYWORDS
Water pollutants: A water pollutants can be defined as a physical, chemical or
biological factor causing aesthetic or detrimental affects on aquatic life and on
those who consume water.
Biological Oxygen Demand (BOD): The amount of oxygen used by
microorganisms to oxidize the oxydisable organic matter at 20 0C in 5 days is
known as BOD.
Heavy metals: Heavy metals are the metals which have a density above 5g per cm3.
Plant nutrients: These are the chemicals like nitrate, phosphate etc required
by the plant for their growth and cause eutrophication in a water body.
Eutrophication: It means the enrichment of nutrients in a water body. Which
lead to excessive plant growth in the water body.
30
Water pollution: Water can be regarded its changes its quality or composition
either naturally or as a results of human activities thus becoming less suitable
for drinking, domestic, agricultural, industrial, recreational, wildlife and other
uses.
Standards: The term standard applies to any definite principle or measure
established by an authority by limiting concentration of constituents in water
which ensure safe use of water and safeguard the environment.
Oxygen demanding waste: The wastes which deplete the dissolved oxygen of a
water body are called oxygen demanding waste.
Municipal wastes: It consist mainly the domestic sewage i.e. water born waste
of community contain of 99% water and 1% solids. Of the solids 70% are
organic 30% are inorganic in nature.
Industrial wastes: The wastes from industry like sugar, dairy, paper tannery
etc. industrial waste have the greatest potential of the receiving water.
Domestic wastes: The waste generated in household like kitchen, toilet etc. is
called as domestic waste.
2.6 SELF ASSESSMENT QUESTIONS
1. What are Pollutants? Give different type of water pollutants which
lead to pollution of water.
2. Why the D.O. level of water body falls when high-organic load
discharged into it?
3. What are water borne diseases? Why MPN test is conducted?
4. What is eutrophication and how it lead to aging of a lake?
5. What is biomagnification and bioaccumulation of pesticides? Give the
toxicity effects of different groups of pesticides.
6. What is marine pollution? Describes effects of oil pollution on marine
organisms.
31
7. Give the source of heavy metal pollution and effect of heavy metals on
plants and animals.
2.7 SUGGESTED BOOKS
Aggarwal K C (1999). Environmental pollution. Agro Botanica, Bikaner.
Aggarwal S K (2002). Pollution management-II water pollution. APH Publishing
Corporation, New Delhi.
Coler R A and Rockwood J P (1989). Water pollution biology (A laboratory /field
hand book). Technomic Publishing Co. Inc., Pennsylvania (U.S.A.)
Gaur D (2005). Water pollution and its management. Sarup & Sons, New Delhi.
Goel R P (1997). Water pollution: causes, effects and control. New Age
International (Pvt.) Ltd, New Delhi.
Kumar A (2004). Water pollution – assessment and management. Daya
Publishing House, New Delhi. Manivasakam N (1984). Environmental
pollution. National Book Trust India, New Delhi.
Mishra P C and Trivedy (1993). Ecology and pollution of Indian lakes. Ashish
Publishing House, New Delhi.
Smith R J (1996). Introduction to water pollution. Asian Books Pvt. Ltd., New
Delhi.
Thakur K (1999). Environmental protection law and policy in India. Deep and
Deep Publication, New Delhi.
Tripathi A K (1995). Water pollution. Ashish Publishing House, New Delhi.
Tripathi B D and Govil S R (2001). Wate pollution – an experimental approach.
CBS Publisher, New Delhi.
32
UNIT-II PGDEM-03
AIR POLLUTION: AMBIENT AIR QUALITY STANDARDS & MAJOR ATMOSPHERIC POLLUTANTS
Prof. C.P. Kaushik
STRUCTURE
1.0 OBJECTIVES
1.1 INTRODUCTION
1.2.1 NATIONAL AMBIENT AIR QUALITY STANDARDS
1.2.2 CLASSIFICATION OF AIR POLLUTANTS
1.2.3 SUSPENDED PARTICULATE MATTERS
1.2.4 HYDROCARBONS
1.2.5 INORGANIC GASES
1.2.5.1 Oxides of Carbon
1.2.5.2 Oxides of Nitrogen
1.2.5.3 Photochemical Oxidants
1.2.5.4 Fly Ash
1.3 SUMMARY
1.4 KEY WORDS
1.5 SELF-ASSESSMENT QUESTIONS
1.6 SUGGESTED READINGS
1.0 OBJECTIVES
After going through this unit you would understand the following :
- National ambient air quality standards used for comparison with
observed air quality parameters.
- Primary and secondary air pollutants.
1
- Type, characteristics and health effects of :
* Suspended particulate matter
* Hydrocarbons
* Oxides of carbon
* Oxides of nitrogen
* Photochemical oxidants
* Fly ash
1.1 INTRODUCTION
Pure air is odourless and colourless and has specific composition.
However, many substances, natural or anthropogenic (man-made) in
origin enter the atmosphere and upset the equilibrium which affects man
and his environment. Air pollution can, therefore, be defined as an
atmospheric condition in which some substances are present in such
concentrations which affect human, animal, livestock and plant life or
interfere in enjoyment of property. Air pollution is not a new
phenomenon. In the year 1307 King Edward- I banned the burning of
coal in lime kiln in London. There was a prohibition on use of coal in
London while Parliament was sitting. Queen Elizabeth was allergic to coal
smoke. In more recent times several air pollution episodes have attracted
the attention towards harmful effects of air pollution. London alone has
experienced about 10 air pollution episodes of which the one of Dec.
1952 was the worst and caused 4000 excess deaths. Other important air
pollution episodes occurred in Donora, Belgium, British Columbia,
Pennsylvania, Los Angeles (California) and Bhopal (India).
Most of the air pollution episodes were a result of inversions some of
which-contained high concentrations of SO2, particulate matters, CO,
oxides of nitrogen, various hydrocarbons etc.
2
1.2.1 NATIONAL AMBIENT AIR QUALITY STANDARDS
The concentration of six criteria pollutants i.e. CO, NO2, O3, SO2, PM10
(10 µm dia) and lead are to be maintained at certain permissible level
beyond which these show harmful effects. The concentration of these
criteria pollutants as given in Table - 1 should not exceed more than once
in a calendar year.
Table 1: National Ambient Air Quality Standards (NAAQS)
3
1.2.3 CLASSIFICATION OF AIR POLLUTANTS
The diverse variety of matter emitted into the atmosphere by natural and
anthropogenic sources is usually divided into two categories namely,
primary pollutants and secondary pollutants.
The primary pollutants are those that are emitted directly from the
sources e.g. particulate matter such as ash, smoke, dust, fumes, mist
and spray; inorganic gases such as sulphur dioxide, hydrogen sulphide,
nitric oxide, ammonia, carbon monoxide, carbon dioxide, and hydrogen
fluoride; olefinic and aromatic hydrocarbons; and radioactive
compounds. Of the large number of primary pollutants emitted into the
atmosphere, only a few are present in sufficient concentrations to be of
immediate concern. These are the five major types : particulate matter,
sulphur oxides, oxides of nitrogen, carbon monoxide, and hydrocarbons.
Carbon dioxide is generally not considered an air pollutant but because
of its increased global background concentration, its influence on global
climatic change causing global warming is of great concern. The
radioactive pollutants are of specialized nature and they can cause
mutations and affect plants, animals as well as human beings at genetic
level, if present beyond a threshold concentration.
The secondary pollutants are those that are formed in the atmosphere
by chemical interactions among primary pollutants and normal
atmospheric constituents. Pollutants such as sulphur trioxide nitrogen
dioxide, PAN (peroxyacetyl nitrate), ozone, aldehydes, ketones, and
various sulphate and nitrate salts are included in this category.
Secondary pollutants are formed from chemical and photochemical
reactions in the atmosphere. The reaction mechanisms and various steps
involved in the process are influenced by many factors such as
concentration of reactants, the amount of moisture present in the
atmosphere, degree of photo-activation, meteorological factors and local
4
topography.
1.2.3 SUSPENDED PARTICULATE MATTER (SPM)
In general the term "particulate" refers to all atmospheric substances that
are not gases. They can be suspended droplets, solid particles or
mixtures of the two. Particulates can be composed of inert or extremely
reactive materials ranging in size from 100 µm down to 0.1 µm and even
less. The inert materials do not react readily with the environment
whereas the reactive materials could be further oxidized or may react
chemically with the environment. The particulates may be of the following
types:
• Dust: The particle size ranges from 1 to 200 µm. These are formed by
natural disintegration of rock and soil or by the mechanical processes
of grinding and spraying. They have large settling velocities and are
removed from the air by gravity and other inertial processes. Fine
dust particles- act as centres of catalysis for many of the chemical
reactions taking place in the atmosphere.
• Smoke: It contains fine particles of the size ranging from 0.01 to 1
µm which can be liquid or solid, and are formed by combustion or
other chemical processes. Smoke may have different colours
depending on the nature of material burnt.
• Fumes: These are solid particles of the size ranging from 0.1 to 1 µm
and are normally released from chemical or metallurgical processes.
• Mist: It is made up of liquid droplets generally smaller than 10 µm
which are formed by condensation in the atmosphere or are released
from industrial operations.
• Fog: It is the mist in which the liquid is water and is sufficiently
dense to obscure vision.
5
• Aerosol: Under this category are included all air-borne suspensions
either solid, or liquid; these are generally smaller than 1 µm.
Particles in the size range 1-10 have measurable settling velocities but
are readily stirred by air movements, whereas particles of size: 0.1-1µm
have small settling velocities. Those below 0.1 µm, submicroscopic size
found in urban air, undergo random Brownian motion resulting from
collisions among individual molecules. Most particulates in urban air
have sizes in the range 0.1-10 µm. The finest and the smallest particles
cause most significant damage to health.
The chemical composition of particulate pollutants varies over a wide
range.
Particles from soils and minerals primarily contain calcium, aluminium
and silicon compounds. Smoke from combustion of coal, oil, wood, and
solid waste contains many organic compounds. Insecticide dusts and
certain fumes released from chemical plants also contain organic
compounds; Hydrocarbons themselves can coalesce into aerosol droplets
that constitute one kind of particulate matter. The most harmful
components of incomplete combustion are generally grouped as
particulate polycyclic organic matter (PPOM). These materials are
derivatives of benzopyrene, a potent carcinogen. Some trace metals such
as cadmium, lead, nickel and mercury present in the air may be the
cause of the greatest health hazard.
1.2.4 HYDROCARBONS
Hydrocarbons are compounds containing the elements of carbon and
hydrogen. By linking together in various ways, the carbon atoms form a
great variety of chain and ring molecules called Aliphatics and Aromatics
which number more than 1 million. Volatile compounds (VOC's), that
exist in the atmosphere primarily as gases because of their low vapor
6
pressures are the most important polluting hydrocarbons. However, it is
important to note that solid hydrocarbons can also cause an
environmental and health threat. For example, Benzopyrene, a well
known carcinogen, exists in the air as a fine particulate.
More hydrocarbons (HC) are emitted from natural sources than from the
activities of man. The one in greatest abundance is methane which has an
average background concentration of 1.55 ppm. This is produced in the
decomposition of dead material, mostly of plant origin. Methane is joined
by a class of compounds of a more intricate molecular structure known as
terpenes. These substances are emitted by plants, and are most visible as
the tiny aerosol particulates or the “blue haze” found over most forested
areas. Other hydrocarbons found in large concentrations in the ambient
air besides methane (CH4), are Ethane (C2H6), Propane (C3H8) acetylene
(C2H2), butane (C4H10) and isopentane (C5H12). Transportation sources are
by far the largest emitting sources of these hydrocarbons. About 15
percent of all atmospheric hydrocarbon is due to man’s activity. However,
the impact of man made hydrocarbons, by themselves, in air have
relatively low toxicity. They are of concern because of their photochemical
activity in the presence of sunlight and oxides of nitrogen (NOx). They
react to form photochemical oxidants. The primary pollutant is ozone
however, other organic pollutants like peroxyacetyl nitrate (PAN) have been
identified as the next highest component. Background levels of SO2 are
very low, about I ppb (parts per billion). In urban areas maximum
concentrations vary from less than 0.1 to over 0.5 ppm. SO2 itself is a lung
irritant and is known to be harmful to people who suffer from respiratory
disease. However, It is the sulfuric acid aerosol that causes the most
damaging health effects in urban areas. Oxides of Sulfur dioxide (SO2) is a
colorless gas with a concentration range of 0.3 to 0.1 ppm. Above 3 ppm it
has a pungent, irritating odor. Although SO2 emissions may occur from
volcanic eruptions, Most S02 (and sulfur trioxide, SO3) is due to the-
burning of coal and crude oils for electric power and heating.
7
The sulfur content of refined petroleum is usually quite low. At the high
temperatures of combustion, the sulfur in these fuels is converted to SO2
by the reaction:
S+O2 =SO2
1.2.5 INORGANIC GASES
The chemistry of the lower atmosphere is controlled by the reactivity of
oxygen. In the presence of molecular oxygen O2, the stable forms of
almost all of the elements are oxides, with the notable exception of
nitrogen. Thus, many of the major pollutants are oxides (i.e. CO, SO2,
SO3, NO, NO2) and their associated reactive by-products.
1.2.5.1 Oxides of Carbon
Significant amounts of carbon oxides, carbon monoxide (CO) and carbon
dioxide (CO2) are produced by natural and anthropogenic (man made)
sources. CO is considered a major atmospheric pollutant because of its
significant health effects, whereas, CO2 is a relatively non-toxic, present
in troposphere (lower atmosphere) and is, therefore, not usually
described as a major atmospheric pollutants However, anthropogenic
emission of CO2 is of significant concern because of its greenhouse effect
causing global warming.
Carbon monoxide (CO) is a colorless, odorless, tasteless gas formed by
the incomplete combustion of fossil fuels and other organic matter.
During combustion, carbon is oxidized to CO by the following reactions.
2 C + O2 → 2CO
2 CO + O2 → 2CO2
CO, formed as an intermediate in the combustion process, is emitted if
there is insufficient O2 present for reaction to proceed. CO is also
produced naturally by volcanic eruptions, forest fires, lightening and
8
photochemical degradation of various reactive organic compounds.
Biologically, CO is formed by some lower plants during incomplete
decomposition and various microorganisms in the oceans.
Major anthropogenic sources include transportation due to burning of
gasoline, industrial processing, solid waste disposal, agricultural burning
and cigarette smoking. Background concentrations of CO average 0.1
ppm, with peak concentrations in the northern hemisphere during the
autumn months due to the decomposition of fallen leaves. The residence
time for, CO in the atmosphere is estimated to be 0.1 to 0.3 years.
Cigarette smoke contains especially high levels of CO (15,000 to 55,000
ppm) which bind to approximately 3 to 10% of a smoker’s hemoglobin.
The effects of these high levels would be extremely harmful if it were not
for the intermittent nature of the exposure. The inhalation of air between
drags greatly reduces the toxic dose. The major effect of CO in cigarette
smoke appears to be to increase the risk of angina pectoris patients to
myocardial infarction and sudden death. However, cigarette smoke
contains many harmful substances and it is difficult to specifically assess
the harmful effects of CO and its exact role in cardiovascular diseases.
Oxides of sulfur : The sulfuric acid aerosols formed are usually less than
2 microns in diameter can quite effectively penetrate the inner most
passages of the lung as the pulmonary region.
SO2 in atmosphere is converted into sulfuric acid aerosols.
2 S02 + O2 = 2 SO3
SO3 + H2O = H2SO4
1.2.5.2 Oxides of Nitrogen
There are five major gaseous forms of nitrogen in the atmosphere;
nitrogen ammonia (NH3), nitrous oxide (N2O), nitric oxide (NO), and
nitrogen dioxide (NO2). N2 is the major gaseous component in the
9
atmosphere and accounts for 78% of the atmosphere’s mass. NO and
NO2 are important pollutants of the lower atmosphere and because of
their inter-convertibility in photochemical reactions, are usually
collectively grouped as NOx.
Nitric Oxide: It is a colorless, odorless, tasteless, relatively non-toxic gas.
sources include anaerobic biological processes in soil and water,
combustion and photochemical destruction of nitrogen compounds in the
stratosphere worldwide basis, natural emissions of NO are estimated at
approximately 5 x 108 tons per year. Major anthropogenic sources
include automobile exhaust, fossil fuel fired electric generating stations,
industrial boilers, incinerators, and home space heaters. All of these
sources are high temperature combustion processes which follow the
reaction:
N2 + O2= 2NO
This reaction is endothermic, which means that the equilibrium shifts to
the right at high temperatures and to the left at low temperatures.
Therefore, as the combustion temperature of a process increases, so will
be the amount of NO emitted. Background concentrations of NO are
approximately 0.5 ppb. Atmospheric levels of NO are highest during the
peak morning and evening hours. Emissions of NO are also greater in the
winter months since there is an increase in the use of heating fuels. NO
is a relatively non-irritating gas and is considered to pose no health
threat at ambient levels. It is rapidly oxidized to nitrogen dioxide, which
has a much higher toxicity.
Nitrogen dioxide: It is a gas with light yellowish orange colour at low
concentrations and reddish brown colour at high concentrations. It has a
pungent, irritating odor. It is relatively toxic and has a rapid oxidation
rate which makes it highly corrosive as well. The oxidation of NO to N02
follows the reaction:
2NO + O2 → 2N02
10
This reaction is slow at low atmospheric levels and accounts for about
25% of all NO conversion. The major NO conversion processes are
photochemical, involving hydrocarbons, ozone, aldehydes, carbon
monoxide, and other compounds. Background concentrations of NO2 are
approximately 0.5 ppb. Peak morning concentrations of NO are followed
several hours later by peak levels of NO2 produced by the chemical and
photo-chemical oxidation of the NO. Since the conversion of NO to NO2 is
related to solar intensity, more NO2 is produced on warm, sunny days.
1.2.5.3 Photochemical Oxidants
These are secondary pollutants which result from a series of complex
atmospheric reactions involving organic pollutants, NO, O2 and sunlight.
The main photochemical oxidants are ozone, NO2 and to a lesser extent,
peroxyacetyl nitrate.
Ozone (O3) is the most important and widely reported of the photo-
chemical oxidants. It is a bluish gas that is 1.6 times heavier than oxygen
and is normally found at elevated levels in the stratosphere where it
functions to absorb harmful ultraviolet radiation. Ground level ozone is
one of the major constituents of photochemical "smog" which is a
widespread, urban phenomenon. It is formed when nitrogen dioxide
absorbs ultraviolet light energy and dissociates into nitric oxide and an
oxygen atom;
NO2 + hv → O+NO
These oxygen atoms, for the most part, react with oxygen to form ozone:
O + O2 → O3
In addition, the oxygen atoms can react with certain hydrocarbons to
form free radical intermediates and various products such as
peroxyacetyl nitrate (PAN). Since photochemical oxidants are secondary
11
pollutants formed in the atmosphere as result of primary pollutants
reacting, their concentration in the atmosphere will vary proportionally to
the amount of hydrocarbons and NO2 in the air and the intensity of
sunlight. PAN is a very potent eye irritant in addition to being a strong
lung irritant like ozone. O3 is relatively insoluble in respiratory fluids and
can be transported into the pulmonary system where it can damage the
central and terminal pulmonary units such as the respiratory
bronchioles and alveolar ducts. Exposure in excess of ambient levels
affects lung function causing increased respiratory rates and decreased
lung capacity. Prologed low-level exposure may result in decreased lung
elasticity. Studies on micro-organisms, plants and tissue cultures
indicate that O3 is mutagenic, i.e., it can cause permanent, inheritable
changes in genes. Since mutagens and carcinogenes appear to be related,
it is possible that O3 is also carcinogenic.
1.2.5.4 Fly Ash
When any ash-containing fuel is burned fly ash is generated. It is
particularly troublesome in the case of pulverized coal. Everything else
being equal, the quantity of fly ash emitted varies with the ash content of
the coal. For this reason, coal cleaning or washing for ash reduction may
be regarded as a means of air pollution abatement. The problem of fly
ash is not different and the same principles apply that has been able to
govern the control of other types of particulate matter in stack emissions.
Millions of tons or more of fly ash per year is produced.
The disposal has been a problem. Considerable research has been carried
out to find uses for the material. Small quantities are used as a
constituent of Portland cement mixes.
• Removing NOx after combustion by reacting with isocyanic acid
(RCNO). It removes up to 99% NOx but it is yet to be
commercialized.
12
• Removing NOx after combustion in flue gas scrubbers. This would
remove 70-90% NOx but is expensive and has the problem of
sludge disposal.
1.3 SUMMARY
Air pollution is an atmospheric condition in which some substances are
present in such concentrations which affect the living beings and
property. There had been many air pollution episodes which have taken a
heavy toll of life. Bhopal gas tragedy is one of them. There are the
National Ambient Air Quality Standards (NAAQS) with which the
observed air quality parameters are compared. Primary pollutants are the
ones which are emitted from the source and secondary pollutants are
formed in the atmosphere by various combinations.
The suspended particulate matter ranges from 108 to 0.1 µm or smaller
and may of be of various types depending upon their size. Very small
particles are in Brownian movement. Chemical composition of particulate
matter varies depending on their origin. They could be formed from soil,
minerals, combustion smoke, insecticide dust, organic compounds. Some
of the particulate polycyclic organic matter may be carcinogenic. Trace
metals in air are of great health hazard.
Hydrocarbons are emitted naturally and by human activities.
Atmospheric hydrocarbons themselves have low toxicity but they play a
major role in the photochemical reactions leading to formation of
photochemical smog.
Carbon monoxide is formed during combustion, if O2 is insufficient. It
combines with smoker’s haemoglobin and increases the risk of angina
pectoris patients. CO2 is not a pollutant but increasing levels increase the
problem of global warming. SO2 changes to SO3 and to sulfuric acid mist
which may penetrate lungs and cause damage.
13
Oxides of nitrogen are formed from nitrogen at high temperatures. Nitric
oxide (NO) is converted to nitrogen dioxide (NO2) which takes part in
photochemical oxidation. Photochemical oxidants like O3, NO2, and PAN
form photochemical smog. Fly ash is emitted when ash containing fuel is
burnt especially the pulverized coal. Disposal of fly ash is a problem.
1.4 KEY WORDS
Air pollution : Atmospheric condition in which some
substances are present in such
concentration which affect various life
forms and materials.
Primary Pollutants : Pollutants which are emitted from the
source.
Secondary Pollutants : Harmful pollutants formed by the
reaction of two or more primary
pollutants in the air.
NAAQS : Standard limits recommended by the
Central Pollution Control Board for
individual air pollutants, the presence of
such pollutant beyond which amounts
cause of concern.
Hydrocarbons : Organic compounds of hydrogen and
carbon.
Suspended particulate matter: Particulate matter upto 10 µm which
remain suspended in the air.
Fly-ash : Ash formed by burning of the ash
containing fuel. It’s disposal is a
problem.
1.5 SELF ASSESSMENT QUESTIONS
1. Discuss the National Ambient Air Quality Standards.
14
2. What are primary and secondary pollutants? Give examples.
3. Discuss the important inorganic gases in the atmosphere that act
as pollutants.
4. Write a brief note on fly ash.
5. What is suspended particulate matters (SPM)? Name the different
types of SPM.
1.6 SUGGESTED READINGS
Kaushik, A and Kaushik CP (2004) : Perspectives in Environmental
Studies, New Age International Publishers, New Delhi.
Miller & Tyler Jr. 1999. Environmental Science : Working with the Earth,
7th edition. Wedsworth Publishing Company.
Murali Krishna KVSG (1995) : Air Pollution and Control.
Masters, Gilbert M (1994) Introduction to Environmental Engineering and
Science. Prentice-Hall of India- Private Ltd., New Delhi.
15
UNIT-II PGDEM-03
AIR POLLUTION: METEOROLOGY, DISPERSION, AUTOMOBILE POLLUTION AND AIR POLLUTION IMPACTS
Prof. C.P. Kaushik
STRUCTURE
2.0 OBJECTIVES
2.1 INTRODUCTION
2.2.1 METEOROLOGY
2.2.2 PLUME DISPERSION
2.2.3 AUTOMOBILE POLLUTION
2.2.4 EFFECTS OF AIR POLLUTANTS
2.2.4.1 Effects on Human Health
2.2.4.2 Effects on Vegetation
2.2.4.3 Effects on materials
2.2.4.4 Effects on buildings
2.3 SUMMARY
2.4 KEY WORDS
2.5 SELF ASSESSMENT QUESTIONS
2.6 SUGGESTED READINGS
2.0 OBJECTIVES
After reading this unit you would be able to :
1. Role of environmental conditions, environmental lapse rate,
adiabatic lapse rate, plume dispersion.
2. Various types of pollutants emitted by automobiles, their
composition, reasons for poor quality of emission.
3. Effects of air pollution on human health, systems of human body
affected by various pollutants, effects of air pollution on vegetation
and buildings.
1
2.1 INTRODUCTION
Meteorology of the place play a vital role in dispersion of air pollutants.
The plume follows particular path (shape) depending on adiabatic lapse
rate and environmental lapse rate. The extent of pollution near the point
source depends upon dispersion of pollutants.
Automobile pollution is of great concern in the developing countries like
India where the number of vehicles is on an increases. Various types of
vehicle fuels emit a variety of pollutants which affect human health,
vegetation and materials. Increase in number of diseases specially the
pulmonary diseases, in due to increase in air pollution. Plant life is also
affected by air pollution. Various types effects in the leaf leading to
necrosis affects photosynthesis and crop yield. Air pollution damages
materials like metals, buildings paints, dyes, rubber, paper etc. are
affected by air pollution. Various buildings and monuments in various
countries have been affected. In India the quality of the marble of Taj
Mahal is affected by air pollution.
2.2.1 METEOROLOGY
Various environmental factors like wind force, direction in which they are
blowing, temperature profile, availability of sunlight to cause
photochemical reactions, precipitation to clear the air determine the air
quality on day to day basis even if the emission in an area remains
relatively constant. Air quality therefore, depends upon dynamics of
atmosphere, the study of which is called meteorology.
Vertical dispersion of pollutants in the atmosphere is determined the
change of air temperature with altitude. If the physical forces acting on
air help to retain it at that elevation for some temperature profiles, the air
is stable. This discourages dispersion and dilution of pollutants.
The dispersion of a parcel of air depends upon the surrounding
2
environmental temperature. The decrease in temperature with increasing
altitude is called environmental-lapse rate (ELR). If the air parcel does
not exchange heat with the surrounding air, the decrease in temperature
with upward movement of air parcel because of its expansion is at a fixed
rate of 1°C/100 meters. This rate is called as adiabatic lapse rate (ALR).
These two factors determine dispersion of air pollutants, if the
temperature of a parcel of air is same as that of the surrounding air and
it is raised upwards it will cool at adiabatic lapse rate and may remain
denser than the surrounding air. It will try to sink. If the same parcel of
air is lowered, it will compress and will follow adiabatic lapse rate. Its
temperature may be more than the surrounding air. This will result in
upward movement of the parcel. This temperature profile corresponds to
stable atmosphere. The environmental lapse rate is called subadiabatic.
In other conditions the air parcel at the same temperature as that of
surrounding and is moving upwards its temperature is more than the
surrounding, it is buoyant and will try to rise further. If by moving
downwards its temperature remains less than the surrounding, it is
denser and will try to sink. The air is unstable and the environmental
lapse rate is called superadiabatic. Such conditions favour mixing and
dilution of pollutants.
In extreme case of atmospheric stability, upward movement of air is
hindered. It may result if a cold air mass passes under a warm air mass.
Such conditions ate called inversion and result in the build up of
pollution in the inversion layer and may cause severe health problems.
The severity of Bhopal Gas Episode was due to the occurrence of such
conditions in the winter night.
2.2.2 PLUME DISPERSION
'The shape of stack plume is a function of the vertical temperature and
wind profiles. From the plume shape the stability condition and the
3
dispersive capacity of atmosphere can be judged. The behaviour and
dispersion of a plume depend on the environmental lapse rate, (ELR). A
parcel of air released from a stack into the atmosphere follows the dry
adiabatic lapse rate (DALR). If the temperature attained by the parcel is
less than the surrounding environmental temperature, the parcel of air
will be denser and would not rise upwards in the warmer and lighter
atmosphere. Thus, inversion is the most unfavourable condition for the
dispersion of pollutants in atmosphere. Similarly, in superadiabatic
atmospheres the temperature in the environment would decrease at a
faster rate i.e. more than DALR whereas the plume temperature would be
decreasing at the standard rate of 1°C/100 m. Due to this, a plume or
parcel of Air released from a stack is at a higher temperature than its
surrounding environmental temperature. Thus, the parcel of air owing to
its lower density is buoyant and continuously moves upwards. Such
atmosphere is called unstable atmosphere in which the pollutant
dispersion is good and ground level concentrations are less. The plume
behaviour is shown in Figure-1. The plume behaviour in a given
environment may be different for stacks of different heights.
Looping
Coning
Fanning
Lofting
Fumigation
Fig. 1 : Various shapes of plume
4
• Looping: It is associated with turbulent air during warm seasons
with clear skies. It occurs under super-adiabatic conditions and
during day time with clear or partly cloudy skies and intense solar
heating. In this, irregular loops dissipate in patches and relatively
rapidly with distance. It occurs due to light to moderate wind
speeds on a hot summer afternoon when large scale thermal eddies
(small whirls) are present. These eddies carry portions of the plume
to the ground level for short time periods, carrying momentary high
surface concentration of pollutant near stack. Though looping
occurs in unstable atmospheres which are favourable for thorough
mixing higher stacks may be needed to prevent premature contact
with the ground.
• Coning: When the ambient lapse rate is sub-adiabatic the
atmosphere is neutral (or) slightly stable. Under such conditions,
there is limited vertical mixing and the probability of air pollution
problems in the area increases. The typical plume in such situation
is called coning. The visible plume is cone shaped roughly 10
degrees with a horizontal axis. It dissipates further down wind than
a looping plume. In this, small scale mechanical turbulence
dominates since the thermal heating effect is much lower than in
the case of plumes. Coning occurs when skies are overcast during
either the day or night with moderate to strong winds. Unlike in
looping in coning, the major part of the pollutant concentration is
carried fairly far downwind in significant amounts before reaching
the ground level. This is a specially good condition for estimating
pollutant dispersion by the diffusion models. Dispersion is slower
than looping and the pollutant touches at a large distance.
• Fanning: A 'fanning plume' occurs in the presence of large negative
lapse rates (inversion and isothermal lapse rate), so that a strong
surface inversion takes place at a considerable distance above the
5
stack height. The atmosphere is extremely stable, with very little
turbulence and light winds. The typical occurrence of the plume is
at night and in early morning conditions when the earth is cooled
by outgoing radiation. A fanning plume may appear as a narrow
horizontal fan without any vertical spreading for several kilometers
downwind. If the effluent is warm, plume rises slowly and then
drifts horizontally. The dispersion of plume is very slow, and
concentration aloft high - at relatively great distance downwind. A
small probability of ground contact exists, though turbulence can
result in considerable ground contact.
• Lofting: It prevails in the late afternoon and early evening under
clear skies. In the evening (sun sets) radiation from the surface
leads to an inversion layer near ground level. As the inversion layer
deepens, a lofting plume will change to a fanning plume. Due to the
inversion, adiabatic lapse rate forms at stack top which makes the
lower layer stable and the upper layer neutral or unstable. The
plume is in the form of loops or cone with well defined bottom and
diffuses to top. In the upper layer, the winds are of moderate, and
considerable turbulence and they have very little influence in the
layer below. In lofting probability of ground contact is small unless
inversion layer is shallow. It is considered to be the best condition
for dispersion since pollutants are dispersed in upper air with
small probability of ground contact.
• Fumigation: 'Fumigation plumes occur when a stable layer of air
lies a short distance above the release point of the plume and an
unstable air layer lies below the plume. It occurs during changes
from inversion to normal condition and also with sea breeze in late
morning or early afternoon. It stays temporarily for maximum 30
minutes except in case of sea- breeze conditions, in which case it
stays for several hours. The morning sun heats the ground, which
6
in turn leads to the development of a negative temperature gradient
from the ground upward. Once the newly formed unstable layer
reaches the height of the stack, large concentrations of stack gas
will be carried downwind to the surface. The winds are light to
moderate aloft and light below, but thermal turbulence is observed
in lower layer only. The ground level concentrations are high
especially when plume his stagnated aloft. Fumigation is formed
usually under clear skies and light winds, and is more prevalent in
the summer. It usually starts when a fanning plume breaks up into
a looping plume.
• Trapping: It occurs in a stable atmosphere, both above and below
stack with an unstable atmosphere in between the two inversion
layers and can diffuse only in the limited vertical height. It may
occur at any time of the day in any season. If associated with
subsidence inversion it may persist for months as in Los Angeles
and if associated with warm frontal inversions it lasts for less than-
a day. It is probably one of the worst pollution situations.
2.2.3 AUTOMOBILE POLLUTION
Urban growth has resulted in tremendous increase in automobile
pollution. About 60% of the atmospheric pollution in urban areas is
contributed by automobiles. The problem becomes more alarming in view
of the fact that the number of automobiles is increasing day by day. Due
to unprecedented growth of human population as well due to modern life
style, this increase, in vehicular population is occurring. The number of
two, three and four wheelers has increased enormously. The number of 4
wheelers in increasing by 10% each year while the number of 2-wheelers
and 3-wheelers in increasing by 20-25%. The developed, nations have
still more automobile pollution problem where every family has a number
of cars one for each member.
7
Vehicles playing is major metropolitan cities are estimated to account for
a large proportion of air pollution due to various pollutants:
Types of Pollutant Contribution (%)
Carbon monoxide 80%
Hydrocarbons 50%
Oxides of Nitrogen 30-40%
Lead >90%
Vehicular emissions include unburned hydrocarbons, carbon monoxide
(CO), oxides of Nitrogen (NOx), oxides of Sulphur (SOx), particulate
matter, lead and its derivatives etc.
Based on their origin, these pollutants can be grouped into three
categories as discussed below:
A. Exhaust Emissions
Complete oxidation of hydrocarbon fuel, yields only carbon dioxide and
water as the products of chemical combination. When air is used as the
source of the oxygen required for combustion, some of the oxygen and
nitrogen combine to from nitric oxide. Under the conditions of
combustion in an internal combustion engine, other products are also
formed. These include carbon monoxide, hydrogen and partially oxidized
materials primarily in the aldehyde family. Some of the fuel is chemically
rearranged by cracking or synthesizing reactions, both absolute and
relative concentrations of combustion products are influenced by
numerous factors. Some of the prominent factors include air fuel ratio,
ignition timing, absolute charge density combustion chamber geometry
and variable engine parameters such as speed, load and engine
temperature.
Carbonmonoxide: Ideally, gasoline engines could be made to operate
with CO levels near zero. Although the zero limit is not a reasonable
8
target less than 1/2% CO is a reasonable goal. This low level of CO
emission can be achieved only some sacrifice in auto-deriveability or
engine performance. Typically, concentrations of CO in emissions are
high during the engine idle mode and decrease as engine speed is
increased outside of the idle ranges. About 2 ppm of CO being a desirable
value; many cities all-over the world including Bombay, Calcutta and
Delhi are suffering from high CO concentrations of 20-70 ppm. CO is
emitted mostly by vehicles run on petrol like most of the cars, three
wheelers and two-wheelers. In Bombay alone, nearly 300 tonnes of
carbon-monoxide are released from vehicular exhaust everyday.
Unburned Hydrocarbons: Concentrations of unburned hydrocarbons are
influenced by air-fuel ratio in the same manner as; CO is influenced i.e.,
lowest-emission levels are associated with an air-fuel ratio near
stoichiometric. Further as with CO, higher levels of hydrocarbon-
emissions are associated with idle and low-speed operation. Exceptionally
high values of hydrocarbons in the exhaust, usually, are indicative of
misfiring:
Oxides of Nitrogen : This pollutant is generated first as nitric-oxide (NO)
with conversion to nitrogen dioxide (NO2) subsequent to the combustion
event. Other nitrogen oxides are involved in much lesser amounts. The
aggregate of the variable mixture including NO and NO2 is commonly
designated as NOx. Factors that tend to increase combustion
temperature and to increase oxygen availability also tend to increase NOx
emissions. Air-fuel ratio is found to 'be the dominant influence upon NOx
emissions and the highest emissions are associated with air-fuel ratios
slightly on the lean side of stoichiometric. The other factors relevant in
NOx generation engine compression ratio, spark timing and intake air
temperature and humidity.
Particulate Matter: Exhaust emissions produce large numbers of
9
extremely fine particles with approximately 70% by count in the size
range of 0.02-0.06 µm. These particulate materials consist of both
inorganic compounds and organic compounds of high molecular weight.
The most significant fractions of automotive particulate emissions used
to be lead compounds before these were banned, resulting from the use
of tetraethyl lead as a fuel additive to provide the anti-knock
characteristics necessary for high-compression engines.
Lead and other Heavy Metals: Combustion of gasoline containing lead
additives was a primary source of lead in urban atmosphere. Tetraethyl
lead is added to petrol to improve its antiknock quality and after
combustion, lead was released through the exhaust Lead is also emitted
through petrol tanks and while fuelling in the petrol bunks. Lead is
highly toxic even at trace levels. Children should not be exposed to more
than 100-150 µm of Pb per day. Infact many urban children ingest upto
200 µm of Pb everyday. Similarly persons working in petrol bunks are
prone to 'occupational diseases' caused by lead ingestion.
B. Evaporative Emissions
10 to 30% of the hydrocarbons in vehicular emissions belong to this
category. The estimate is uncertain because techniques for measuring
evaporative emissions involve large uncertainities. However, even at the
lower limit of the estimate, these losses are significant. Fuel tank losses
consist primarily, of the more volatile fractions of gasoline displaced from
the vapor space above the liquid fuel in the gas tank. Depending upon
the direction of temperature changes, tank fill and tank agitation, the
vapors may be discharged at any time, with vehicle either operating or
stationary.
C. Crank Case blow-by
Crankcase blow-by accounts for about one-fifth of the hydrocarbons in
10
all vehicle emissions. Vehicles with badly worn engines may discharge
blow-by in much larger quantity to account for upto one-third or more of
the total. Experimental evidence fully establishes that the blow-by gases
are primarily (i.e. about 85%) carburetted fuel air mixture that flows past
the piston during the compression stroke and prior to the passage of
flame through the mass.
2.2.4 EFFECTS OF AIR POLLUTANTS
The effects-of the main air pollutants namely CO, SOx, NOx, oxidants,
Hydrocarbons and particulates on man, material and vegetation are
described in detail of follows:
2.2.4.1 Impact on Human Health
Carbon Monoxide (CO) : The sources of CO are both natural and
anthropogenic. Oxidation of methane gas from decaying vegetation,
human metabolism and gasoline powered internal combustion engines
lead to CO emission. Carbon-monoxide, present at ambient levels, has
little effects on property, vegetation or materials. ‘CO’, when inhaled,
passes through the lungs and diffuses directly into the blood stream
where it combines with the red blood pigment called hemoglobin forming
carboxyhemoglobin, COHb.
The affinity of carbon monoxide for hemoglobin is 210 times greater than
that of oxygen and as a result amount of hemoglobin available for
carrying oxygen to body tissue is considerably reduced. The body tissues
are thus deprived of their oxygen supply. Heart patients may lack
sufficient cardiac reserve to compensate. Patients with angina pectoris
require less exertion to induce chest pain. Carbon-monoxide
concentrations are especially high in congested urban areas where traffic
is heavy and slow moving. A person trapped in traffic at such a location
for an hour would show a COHb blood level close to 2-3 percent. This
11
exposure would affect the central nervous system, impairing a person's
time interval discrimination, brightless discrimination and other psycho-
motor function. The absorption of CO by the human system increases
with its concentration, exposure time and the activity being performed.
The chronic effects of CO are not full known but they may induce heart
and respiratory disorders. While CO itself has not been found to be
carcinogenic, there is concern that it may increase the carcinogenic effect
of other air pollutants by inhibiting the mucociliary clearance mechanism
in the lungs. 1-2% of COHb levels have an evident effect on the
behavioral performance of the humans. If COHb levels exceed 5%,
cardiac and pulmonary functional changes are observed. 10% and more
COHb levels may cause headaches, fatigue, drowsiness, coma,
respiratory failure and death.
Oxides of Sulfur: The burning of fossil fuels contributes more than 80
percent of anthropogenic S02 missions. Fuel combustions in stationary
sources and industrial processes are the principal contributors of SOx.
Combination of these oxides with water (H2S03 and H2S04 and the salts
derived from these acids) when combined with other elements are well-
known at atmospheric pollutants. Intense irritation and reduction of
visibility have also been recorded from epidemiological studies pertaining
to sulfur oxides. Sulfur dioxide (S02) and sulfate salts tend to irritate the
mucous membrane of the respiratory tract and expedites the
development of chronic respiratory diseases, particularly bronchitis and
pulmonary emphysema.
Oxides of Nitrogen : Some oxides of nitrogen are produced naturally.
Small concentrations of NOx produced in the upper atmosphere by solar
radiation reach the lower atmosphere through downward diffusion. Small
amounts of NOx are produced by lightning and forest fires. Bacterial
decomposition of organic matter also releases NOx into the atmosphere.
The implementation of more stringent controls for carbon monoxide and
12
hydrocarbons resulted in the increased emissions of NOx. The greatest
significance of NO is related to its tendency to undergo oxidation to NO2.
Affinity of hemoglobin for absorbing, NO2 is 3,00,000 times that for O2.
This affinity drastically reduces the O2 carrying capacity of the blood. NO
is a relatively inert gas and only moderately toxic. NO2 irritates the alveoli
of the lungs. The response of the human respiratory system to long-term
exposure to nitrogen dioxide depends upon the concentration of NO2. The
olfactory threshold value of NO2 is about 225 µg/m3 (0.12 ppm).
Exposure, to 9.4 mg/m3 for 10 minutes has produced transient increase
in air way resistance and occupational exposure to 162 mg/m3 for 30
minutes has produced pulmonary oedema. NO2 is the basic pulmonary
irritant. Long term exposure, to NO2 at concentrations between 100 and
200 µm3 and mean suspended nitrate level at 3.8 µg/m3 results in acute
respiratory disease. It has been stated that 95 percent of nitrogen oxides
inhaled remain in the body where they can also produce mutations in
cells. Nitrogen oxides cause lung tissues to become leathery and brittle
and may cause lung cancer.
Oxidants: Ozone contributes about 90% of the total oxidants.
Concentrations of ozone exceeding 200µg/m3 will cause eye irritation.
The threshold for both nasal and throat irritation is set higher at 0.3 ppm
over an 8-hour period. Some states permit 0.15 ppm for 1-hour periods.
When the level of ozone in the ambient air is more than 0.7 ppm over a
20 to 90 minutes period, coughing, checking and severe fatigue will
result. Exposure to oxidants causes severe chest pains, headache,
damage to red blood cells, loss of coordination and difficulty in
articulation. Other important oxidants are nascent oxygen, '0'; excited
molecular oxygen, O2; peroxy acetyl nitrate, PAN; peroxy propionyl
nitrate, PPN; peroxy butyl nitrate, PBN nitrogen dioxide, NO2 and
hydrogen peroxide (H2O2). The desirable ambient air levels of
photochemical oxidants are 240 µg/m3 for 1 hour duration.
13
Hydrocarbons: Hydrocarbons are evolved into the atmosphere from
crankcase of automobile, various refrigerants, decay of several organic
matters and from trees. Methane is the major naturally occurring
hydrocarbon emitted into the atmosphere. Human activities contribute
nearly 20% of the hydrocarbons emitted to the atmosphere every year.
Animals contribute about 80-85 million tonnes of methane in the
atmosphere every year. The hydrocarbons on reacting with nitric oxide
and sunlight form photochemical smog which causes irritation to eye end
decrease in visibility. Formaldehyde and peroxy acetyl nitrate (even at 1
ppm) are eye irritants. PAN also causes plant damage. The oxidation
reactions accompanied by formation of aerosols or haze also result in eye
irritation and plant damage. Hydrocarbons at high concentrations have
carcinogenic effects on lungs. They cause swelling when they enter the
lungs. Aromatic hydrocarbons are more dangerous than a cyclic and
alicyclic hydrocarbons. The inhalation of their vapours cause acute
irritation to the mucous membrane. Excess of hydrocarbon increases
mucous secretion as a result of which respiratory tracks are blocked and
man coughs regularly. Because of continuous cough much pressure is
caused on the trachea of lungs due to which the lining membrane of
alveoli bursts and very small area is left for exchange of oxygen and
carbon dioxide, Benzopyrene, which is present as trace amounts in
tobacco, charcoal, boiler stacks and gasoline exhausts etc. is a
dangerous cancer inducing hydrocarbon pollutant. Methane also is a
severe gas pollutant and occurs in air by volume of 0.0002 percent: Its
higher levels in absence of oxygen create narcotic effects on human
beings. A group of hydrocarbons, especially the carcinogenic
hydrocarbons, cause cancer in man and animal affecting DNA and cell
growth.
14
TABLE-I: HAZARDS OF CARCINOGENIC HYDROCARBONS
Sr. No. Compound Health Hazards
1. Benzene Bladder cancer
2. Naphthylamine Cancer in urinary bladder
3. Bichloromethyl ether Lung cancer
4. Ethylene dichloride Stomach, spleen and lung cancer,
5. Vinyl chloride Liver cancer
6. Ethyleneamine Cancer
7 . Propiolacetone Potential carcinogen
8. Naphthylamine Bladder cancer
9. Nitrophenol Bladder cancer
10. 3-3' dichlorobenzidine Cancer
Particulates : The effect of particulates on human beings depends
mainly on their size and characteristics. Size is one of the most important
physical parameters of particulates. Particle sizes are measured in
micrometers. Particle sizes larger than 50 µm can be seen with unaided
eye. Particulates smaller than 1 µm do not tend to settle out rapidly.
Settling is the major natural self-cleansing process for the removal of
particulates from atmosphere. Particulates can generally be classified as
suspended or settleable. Suspended particulates vary in size from less
than 1 µm to nearly 20 µm. Settleable particles or dust, are larger and
heavier and settle out close to their sources. They are generally greater
than 10 µm in size. Particulates greater in size (over 10 µm) are easily
removed by hairs at the front of nose.
Generally, coarse dusts, fly ash etc. are greater in size and seldom enter
the human system. Particulates with size range in between 2 to 10 µm
like fumes, dusts and smoke particles, are removed as movement of cilia
sweeps mucous upward, carrying particles from wind pipe to mouth
where they are swallowed. If the size of the particulates is less than 2 µm
(like aerosols and fumes) they will enter the lungs easily. Lymphocytes
15
and phagocytes in the lung attack some submicron particles, but all of
them cannot be removed effectively. Similarly, there is a great variation in
the chemical composition of the particulates found in the atmosphere.
Atmospheric particulates contain both organic components like phenols,
organic acids and alcohols and inorganic components like dusts. The
biological particles include protozoa, bacteria, viruses, fungi, spores,
pollens and algae. Their life time is very small due to lack of nutrients
and presence of UV rays from sun. However certain bacteria and fungi
can survive for longer periods.
Effects of Particulates : The success or failure of respiratory defense
system depends, in part upon the size of the particulates inhaled and the
depth of their penetration into the respiratory tract. About 40 percent of
the particles 1-2 µm in size are retained in bronchioles and alveoli
Particles ranging in size from 0.25 to 1 µm show a decrease in retention.
2.2.4.2 Air Pollution Effects on Vegetation
The most obvious damage caused by air pollutants to vegetation occurs
in leaf structure. The surface of leaf is covered by a waxy layer known as
cuticle. Between the waxy layers, epidermis is present, which is a single
layer of cells forming the surface skin of the leaf. The epidermis protects
the inner tissues from excessive moisture loss and prevents the
admission of CO2 and oxygen to these internal tissues. The leaf surface
has a large number of openings called the stomata. Guard cells protect
the stomata and also control the opening and closing of stomata. A
typical plant cell has three components-the cell wall, the protoplasm and
the non-living inclusions within the cell. Because the cell wall is
extremely thin during the formative stage, new growth is very much
susceptible to air pollution damage. The protoplasm is composed of
several chemical compounds, water and the central nucleus which
contains the hereditary and reproductive mechanism. The leaf also
16
contains the chloroplasts, which are the key structures in the
photosynthesis process of food manufacture in the green plant. These
plant inclusions are the store house for food and waste material. A cross
section of a leaf shows four principal layers, the upper epidermal cells,
the palisade parenchyma, the spongy parenchyma and the lower
epidermal cells. The excess oxygen generated in this process escapes
from the plant into the atmosphere and helps to purify the air. Many of
the atmospheric pollutants act as phytotoxicants (plant damaging
substances) and result in various injuries to the plants:
• Bifacial Necrosis: Tissues are killed on both upper and lower
surfaces of the leaf.
• Pigmented Lesions : Dark brown, black, purple or red spots
appear on the leaf surface.
• Epinasty : The rapid growth of the upper side of the leaves,
causing the leaf blade to curl under.
• Acute injury: Results from short term exposure to high
concentrations of pollutants. A severe visible damage to leaf tissues
is often associated with plasmolysis and tissue collapse.
• Chronic Injury: Resulting from long-term exposure, to low levels of
pollutants and often, shows up as a colour change or chlorosis
because of destruction of chlorophyll with no apparent cell damage.
• Chlorosis: The loss of the green plant pigment chlorophyll is called
chlorosis. The loss of chlorophyll results in yellow pattern.
Chlorosis indicates a deficiency in some nutrient required by the
plant.
• Abscission : Leaf abscission is the dropping of leaves. This will
decrease the life of the plant.
17
• Necrosis: It is the killing or collapse of the plant tissue. Tissue
injured by phytotoxicants often has a characteristic colour. For
example, bleaching is associated with SO2, yellowing with
ammonia, browning with fluoride and silvering or bronzing of
under surfaces of some leaves with PAN.
2.2.4.3 Air Pollution Effects on Materials
Air pollution damage to property is a very important economic aspect of
pollution. Air pollution damage to property covers a wide range of
corrosion of metals, soiling and eroding of building surfaces, fading of
dyed materials, rubber cracking etc. The processes responsible for the
effects of air pollution on materials are:
• Abrasion: Solid particles of considerable size travelling at higher
speeds cause abrasive action, Large sharp edged particles
embedded in fabrics can accelerate wear.
• Chemical Action : Some air pollutants react directly and
irreversibly with materials to cause deterioration. SO2 bleaches
marble, hydrogen sulfide tarnishes silver and acidic mists cause
etching of metallic surfaces.
• Absorption: Certain materials absorb some pollutants and get
damaged when the pollutants undergo chemical changes. SO2
absorbed by leather will be converted to sulfuric acid, which
deteriorates leather.
• Corrosion : Action of air pollutants facilitated by the presence of
moisture causes corrosion. The atmospheric deterioration of
ferrous metal is due to corrosion by an electrochemical process.
• Deposition and Removal : Solid and liquid particles deposited on
surface may damage the material by spoiling its appearance.
18
2.2.4.4 Effects of Air Pollution on Buildings
Polluted air containing oxides of sulfur and nitrogen and particulates,
deteriorate building materials and may ultimately result in a loss in
structural integrity. When buildings dating from antiquity and structures
of great artistic and historic values are disfigured the loss is irreparable.
Less than 100 years of exposure to air pollutants in London has done
more damage to the Cleopatra's Needle than what was caused by nature
during 3500 years in the dry atmosphere of Egypt. The miraculous and
historical monuments built by long years of hard labour are losing their
faces. This shows how materialistic man has become, in years where he
is giving importance to industrial production even at the cost of the art
treasures brought up by his ancestors. Disintegration of stone caused
largely by the expansion of iron by corrosion had badly damaged the
houses of parliament in London in 1920. The Parthenon of Athens, the
Coliseum and Arch of Titus in Rome and the San Marco Basilica in
Venice are fast deteriorating. The situation in Florence, Italy has been
described as disastrous. The massive twin aspired cologne cathedral, the
most magnificent church building of German High Gothic era is facing
the threat of corrosion. Similar is the case in Japan wherein most of the
industrial areas, the century-old shrines and temples are facing the
threat. Taj Mahal at Agra, in India, a miracle in marble is facing the grave
danger from pollution caused by existing foundries, power houses,
railway yards and other industrial units. The problem now seems to be
more aggravated because of the commissioning of the Mathura refinery,
within 30 km. range of the priceless monument which is emitting SO2 in
the air and the wind direction is such that Taj at Agra is under direct
corrosion by the acidic fumes. Some alternative solutions must be
considered. One of the methods that may prove successful is to transport
the corrosive gases form the refinery through a set of anticorrosive
pipelines bye passing Agra, purify the gases and release the emission into
atmosphere at a safest place on the down-wind side of Taj Mahal.
19
Plantation of trees around Taj will give a cover which may absorb atleast
a part of the pollution. The renowned temple of Sri Channakeshava at
Belur (Hasan district, Karnataka State) India is threatened with a similar
hazard. A plywood factory located close to the temple emits soot-laden
fumes which get deposited on the sculptures in the temple and discolour
the surface, inside and outside. Jagannath temple, at Puri and the
Konark Sun temple situated on the East Coast of India are badly hit by
particulates present in air. The abrasive action of the sea sprays is
threatening the longevity of these temples. The Statue of Liberty is also
badly affected by air pollution. Sensitive art objects displayed inside
buildings can be placed in hermetically sealed containers. Air
conditioning can also be used as a protective measure. The sides of books
kept in closely packed rows with restricted air circulation remain in good
conditions for a much longer period, than their exposed backs.
Bacteriocides may be used to protect stones as some bacteria convert
atmospheric SO2 to sulfuric acid which they use as a digestive fluid in
attacking the carbonate stone. Thus air pollution can result in serious
health impacts to humans, plants as well as affect and degrade various
types of materials and buildings.
2.3 SUMMARY
Study of dynamics of atmosphere is called meteorology. Atmospheric
conditions prevailing at a time determine air quality. Decrease in
temperature with increasing altitude is called environmental lapse rate
(ELR). Air parcel, if it despoil exchange heat with the surrounding will
experience decrease of 1°C/100 m due to expansion. This is called
adiabatic lapse rate (ALR). ELR and ALR will determine the dispersion of
air pollutants. In relation to prevailing environmental conditions the
plume will experience. Various shaped like looping, coning, fanning,
lofting, fumigation and trapping.
20
Automobiles contribute to urban air pollution to a great extent.
Hydrocarbons, Co, NOx, SOx and particulate matter are the major
pollutants in the vehicular exhaust of these various pollutants CO forms
about 80% of the total exhaust. Petrol driven vehicles contribute more
CO. The concentration of unburned hydrocarbons are influenced by air-
fuel ratio and is lowest near the stiochiometric ratio.
NO is generated first due to oxidation of nitrogen which changes into
NO2. Mixture of oxides of nitrogen is represented as NOx. Higher
emission of NOx results from the air-fuel ratio on the lean side of the
stiochiometric ratio, enquire compression ratio, spark timing and intake
air temperature and humidity. 70% of particulate matter is in the range
of 0.02 – 0.06 µm. It consists of both organic and inorganic compounds
with high molecular weight. Lead used to form a significant part in the
leaded petrol.
Hydrocarbons that are emitted due to evaporation form 10 to 30% of the
hydrocarbons of the vehicular emission, and 1/5 by the crank case blow
by. Air pollutants have adverse effects on the living beings and materials.
CO combines with haemoglobin (210 times more than oxygen) and
causes problem for people suffering from angina pectoris. Chronic effect
of CO may result in heart and respiratory problems. It may increase the
carcinogenic effects of other pollutants. Symptoms associated with CO
exposure are headache, fatigue, drowsiness, coma and respiratory failure
and death.
Oxides of sulfur may cause intense irritation and reduction of visibility.
Exposure irritates mucous membrane of the respiratory tract and chronic
respiratory diseases like bronchitis and emphysema may develop. Oxides of
nitrogen adversely affect health. NO2 is absorbed by haemoglobin much
more than O2. NO2 irritates the alveoli and lungs. High concentration and
occupational exposure may produce pulmonary oedema.
21
Oxidants like O3 may cause coughing, and severe fatigue, severe chest
pain, headache, damage to RBC, loss of co-ordination and difficulty in
articulation. Hydrocarbons result in eye irritation, lung swelling and
plant damage. May have carcinogenic effects at high concentrations. May
result in excess mucous secretion. Particular matter may carry other
pollutants absorbed on them and enter the respiratory system.
Various pollutants affect the plants by causing injuries. Necrosis may of
the tissue may be on both the sides of the leaf, lesions on the leaf
surface, plasmolysis and tissue collapse. Pollutants may destroy
chlorophyll, result in dropping of leaves. Materials are also affected by
pollutants by causing corrosion of metals, erosion of the building
materials, fading of dyed materials, cracking of rubber.
Various buildings like in Egypt, Athens, Rome, Venice, Italy, India etc.
have been affected.
2.4 KEY WORDS
Meteorology : Study of dynamics of atmosphere
ELR : Decrease in temperature with increase in
altitude is called Environmental Lapse Rate
(ELR).
ALR : Decrease in temperature in the air parcel in
upward movement became of expansion. It is
1°C/100 meters.
Plume Dispersion : Movement of stack plume depending upon
vertical temperature and wind profile.
Chronic Bronchitis : Persistent inflammation and damage to the
cell lining the bronchi and bronchides
causing building up of mucus, painful,
coughing and shortness of breath.
Emphysema : Irreversible damage to air sacs alveoli leading
22
to abnormal dilation of air spaces, loss of
lung elasticity and acute shortness of breath.
Epinasty : The rapid growth of the upper side of the
leaves, causing the leaf blade to curl under.
2.5 SELF ASSESSMENT QUESTIONS
1. Define adiabatic and environmental lapse rate.
2. Discuss Sub adiabatic and Superadiabatic conditions.
3. Discuss various types of plumes in relation to environmental
conditions.
4. Write a short note on automobile pollution.
5. Discuss the major effects of atmospheric pollutants on human
health.
6. Discuss the impact of air pollutants on plants.
2.6 SUGGESTED READINGS
Kaushik, A and Kaushik CP (2004) : Perspectives in Environmental
Studies, New Age International Publishers, New Delhi.
Miller & Tyler Jr. 1999. Environmental Science : Working with the Earth,
7th edition. Wedsworth Publishing Company.
Murali Krishna KVSG (1995) : Air Pollution and Control.
Masters, Gilbert M (1994) Introduction to Environmental Engineering and
Science. Prentice-Hall of India- Private Ltd., New Delhi.
23
Unit-III PGDEM-03
Noise Pollution
Dr. Krishan Kumar
STRUCTURE
1.0 Objectives
1.1 Wave Motion
1.2 Sound Waves
1.3 Audible, Infrasonic and Ultrasonic sound
1.4 Definition of Noise
1.5 Sound Pressure Level – The Decibel Scale
1.6 Sources of Noise
1.7 Measurement of Noise
1.8 Indices of Noise Pollution
1.9 Standards of Noise Pollution
1.10 Summary
1.11 Key words
1.12 Review Questions
1.13 Suggested Readings
1.0 Objectives
After studying this unit, you will be able to understand:
• What is the nature of sound waves?
• The concept of noise and the sound pressure level
• How do we measure noise?
• What are various parameters/indices of noise pollution in which standards
of noise pollution are often expressed?
1.1 Wave Motion
We are everyday exposed to sounds of different kinds. Our ears are able to characterize a
sound on the basis of its properties. This ability allows us to discriminate between
different kinds of sounds. What makes these sounds so different from each other? To
know this, we first must understand wave motion. In the following section, we shall
introduce our readers to the fundamentals of wave motion.
What is a wave?
Well a wave is a perturbation/disturbance that travels onwards through a medium due to
the periodic motion of its particles from their mean position. A medium must possess
three important properties for the propagation of wave motion through it : (i) elasticity so
that it tries to return to its original position after being disturbed; (ii) inertia so as to be
able to store up energy and (iii) small frictional resistance so that there is very little
damping of the oscillating particles of the medium.
Based upon the manner in which particles oscillate about their mean position, waves can
be classified into two distinct categories – (i) transverse waves and (ii) longitudinal
waves.
Transverse Waves are the one in which particles of the medium oscillate simple
harmonically up and down about their mean position at right angles to the direction of
propagation of wave. This type of wave motion travels in the form of crests and troughs,
e.g. waves generated in a pond of water when a stone/pebble is thrown into it.
Longitudinal Waves are the one in which the particles oscillate simple harmonically to
an fro about their mean position along or parallel to the direction of propagation of wave.
This type of wave travels in the form of compressions (or condensations) and
rarefactions, e.g. waves produced in air by a source of sound.
To further develop our concepts about wave motion, it is relevant here to define certain
terms related to it.
Wavelength (λλλλ) – It is defined as the distance between two nearest particles of the
medium in the same phase, i.e. the distance between centers of two nearest crests or
troughs in case of transverse waves (fig. ) or that between two nearest condensations and
rarefactions in case of longitudinal waves. Alternatively, it may be defined as the distance
traveled by the wave during the time particles of the medium complete one full
oscillation.
Time Period – The time taken by the wave to complete one full oscillation/cycle is
called its time period. It is reciprocal of frequency (νννν) which means the number of
oscillations/cycles occurring per second.
Wave Velocity (v) – This is the distance traveled by the wave in one second. If λ is the
wavelength of the wave and ν its frequency, then the distance traveled by the wave in one
second is equal to νλ. Thus, the wave velocity may be related to the wavelength and
frequency of the wave by the following expression:
v = νλ
Finally, certain clarifications need to be given regarding wave motion to remove any
doubts from reader’s minds.
• A wave is only a disturbance or a condition that travels through the medium. It
does not involve transfer of any part of the medium from one place to the other.
• Each particle of the medium receives the disturbance a little later than its
predecessor, repeats its movements and passes the disturbance on to the next
succeeding particle. This means that there is a definite phase lag between one
particle and the next i.e. two adjacent particles do not reach their mean and
extreme positions at the same time.
• The velocity with which particles of the medium oscillate is entirely different
from the velocity of the wave.
1.2 Sound Waves
Sound waves are longitudinal in nature and thus travel in the form of condensations
(compressions) and rarefactions in the medium. To understand how a sound wave travels
in a medium, let us consider a vibrating tuning fork (fig. 1.1) whose two prongs move to
and fro about their mean position. As the prongs move to the right of their mean position,
they compress the air in their immediate neighborhood, which in turn, compress the
layers next to them due to the tendency of the medium to regain its original volume
because of its volume elasticity. Therefore, a pulse of compression travels onwards. As
the prongs move backwards to the left of their mean position, the air to the right gets
more space and expands thus producing a rarefaction. Again due to the property of
volume elasticity possessed by the medium, the rarefaction produced also travels towards
the right. Thus, as the tuning fork vibrates, it generates an alternating pattern of
compressions and rarefactions, which travels through the medium. This constitutes what
we call as a sound wave.
Fig. 1.1 Sound wave emission from a tuning fork
So, a sound wave is basically a pressure perturbation that travels through a medium
whose particles oscillate in a to and fro motion along the direction in which the
perturbation travels. During compressions, particles of the medium experience a push in
the positive direction (i.e. the direction in which wave travels) and are closer to each
other. For this reason, compressions are regions of higher pressure. On the contrary,
particles of the medium experience a pull in the negative direction (i.e. opposite to the
direction of wave travel) during a rarefaction and hence are farther apart from each other.
As a result, rarefactions are regions of lower pressure. Mathematically, the sound
pressure at any point (or at any instant of time) may be expressed by the following
equation:
Pt = P0 sin(wt-φ) [N/m2
or Pa] ……………….(1.1)
Where,
P0 = amplitude of sound pressure (N/m2)
t = time (s)
w = 2πf, angular frequency (rad/s)
f = frequency of oscillation (Hz)
φ = phase difference (dependent on initial conditions) (rad)
From the above equation, it may be inferred that two sound waves may be different in
terms of their frequency (or wavelength), amplitude and phase angle. In real life
situations, the sound field at a given point is a combination of sound waves which are
different from each other in all the above aspects.
1.3 Audible, Infrasonic and Ultrasonic Sound
Are we able to hear all the sounds that are incident upon a point. Well, not necessarily.
Our ears are able to hear sounds only within a certain frequency interval. This interval
starts from 20Hz and ends at 20,000Hz for a normal healthy human ear. This frequency
interval is called the audible range of sound frequencies. Even within this range, our ear
is not equally sensitive to all the frequencies. It is less sensitive at the extremes and more
sensitive in the middle of the audible range. Sounds having frequencies less than 20Hz
are called the infrasonic sounds while those having frequencies greater than 20,000Hz are
called the ultrasonic sounds. Our ear is not able to detect sounds outside the audible
range. However, many animals are able to hear sounds belonging to a much wider
frequency interval. For instance, bats can hear sounds even up to 100000Hz. In fact, they
locate their prey in the night with the help of their highly developed capability of hearing.
What makes us sense a sound? To understand this, it is necessary for us to understand the
structure and function of the human ear. The human ear basically consists of three parts-
the outer ear, the middle ear and the inner ear (fig.1.2). The outer ear is comprised of the
pinna and the ear canal leading to the ear drum. The pinna is basically a sound collecting
and focusing device for the incident sound energy. Though most animals can move the
pinna in the direction of the sound source, humans have lost this ability and hence they
have to move their head to identify the direction of a sound source. The ear canal is about
¼ inch in diameter and 1 inch in length. This length supports resonance for sound waves
of the order of 1000Hz frequencies and this is the reason why human ear is more
sensitive at middle frequencies of the audible spectrum. The ear canal terminates at the
ear drum which oscillates when the sound energy is incident upon it. The ear drum
consists of a very sensitive and delicate membrane. After this starts the middle ear which
contains a number of bones connected to each other in a manner that they transmit the
vibrations of ear drum to the inner ear. The inner ear is a complex bony cavity called the
cochlea which is filled with a colorless fluid. The cochlea is divided in the middle by
membranes that are partly gelatinous and partly bony. These membranes have fine hair
like cells which move when the cochlear fluid vibrates. This motion is sensed by nerve
cells and processed by the brain to give us a sensation we call as sound. These hair-cells
become stiff in people who are exposed to high noise levels for a long period and are the
major cause of hearing loss in such people.
Fig. 1.2 Structure of human ear
1.4 Definition of Noise
Noise means any irritating sound which affects the physiological and psychological well
being of a person in an adverse manner. It is now established that repeated exposure to
noise may either result in temporary or permanent hearing loss which in extreme cases
may lead to total deafness. Further, noise may interfere with speech communication,
disturb sleep and affect work performance, thus, causing anxiety in a person.
Human responses to a sound may be different for different persons. Also, a person may
respond to same sound differently at different times. Thus, the identification of a sound as
noise becomes a subjective problem, even though there are some sounds that may be
universally regarded as noise. The degree of annoyance and discomfort experienced by a
person depends on the frequency spectrum and intensity of sound, the aural sensitivity of
the listener and upon the time and surrounding environment when the individual is
exposed to noise.
1.5 Sound Pressure Level – The Decibel Scale
Since the range of sound pressures commonly encountered by the human ear is very
wide, it has been condensed into a more manageable logarithmic scale by the acoustical
scientists by devising the concept of sound pressure level ( Lp ), given by
L p pp re= 10 10
2 2log ( / ) [dB] or
L p pp re= 20 10log ( / ) [dB] ..........(1.2)
where
pre = international reference pressure of 2 10 5× − Pa which represents the
average threshold of hearing for the normal healthy human ear.
p = root mean square (rms ) sound pressure (N/m2)
In terms of equation (1.1), the root mean square pressure can be given by
pT
t dtrmsT
T
= −→∞ ∫lim
1
0
p sin ( ) 0
2 2 ω φ ...............(1.3)
Fig. 1.3 The decibel scale
An average normal human ear can respond to sound waves in a frequency range of 20Hz
to 20,000Hz and to pressures ranging from 20µPa (~ 0 dB) which represents the
threshold of hearing to more than 100Pa which corresponds to the threshold of pain. A
scale showing the sound pressure levels (in decibels) of certain common noise
phenomena in relation to sound pressures (in micropascals) is depicted in fig. 1.3.
1.6 Sources of Noise
Noise sources may be classified differently.
(i) Point Source
If the dimensions of a source are small compared with the distance to the
listener, it is called a point source, for example, fans and chimney stacks. The
sound energy spreads out spherically, so that the sound pressure level is the
same for all the points equidistant from the source and decreases by 6dB per
doubling of distance. This holds true until ground and air attenuation
noticeably affect level.
(ii) Line Source
If a noise source is narrow in one direction and long in the other compared to
the distance to the listener, it is called a line source. It can be a single source
such as a pipe carrying a turbulent fluid, or it can be composed of many point
sources operating simultaneously, such as a stream of vehicles on a busy road.
Here, the sound energy spreads out cylindrically, so that the sound pressure
level is the same at all points at the same distance from the line and decreases
by 3 dB per doubling of the distance. This holds true until ground and air
attenuation noticeably affect the level.
Another way to categorize noise is on the basis of type of activity producing the noise.
Thus noise can be classified as traffic noise, industrial noise, commercial noise,
community noise etc.
Noise assessment is generally about evaluating the impact of one specific source, for
example, the noise from a specific production plant. This is not always an easy task. In
reality, a large number of different sources contribute to the ambient noise at a particular
point. Ambient noise is the noise from all sources combined – e.g. factory noise, traffic
noise, birdsong, running water etc. Specific noise is the noise from the source under
investigation. The specific noise is a component of the ambient noise and can be
associated with a specific source. Noise levels emitted by different types of sources are
shown in fig.
1.7 Measurement of Noise
The job of measuring the sound field at a given point is accomplished with the help of a
sound level meter. The principal components of a typical sound level meter are shown in
the schematic diagram of fig. 1.4. The microphone senses a sound pressure signal and
converts it to an analog electrical signal. The preamplifier is used for impedance
matching. Different frequency weighting networks (fig. 1.5) namely, A, B, C are used to
modify the frequency response characteristics of the measuring instrument. This is done
to improve the correlation between sound sensation and instrument reading in accordance
with the sensitivity of human ear in the audible range. The selection of the appropriate
frequency weighting network is dependent upon the type of measurements being made.
For most common steady noises A- weighting network is considered to be most
appropriate. The root mean square detector is the most common detector used in sound
level meters. It provides the running time average of the square of the sound pressure
signal. Finally, display is the component where the results of the measurements are
displayed. The display may be digital or analog in nature.
Fig. 1.4: Schematic Diagram showing the major component of a Sound Level Meter
Fig. 1.5 Different weighting networks used for measuring noise pollution
1.8 Indices of Noise Pollution
Since noise levels in actual field conditions may fluctuate quite wildly, certain
statistically derived indices have been used by acoustical scientists. Few of the most
commonly employed indices in the studies of noise pollution are discussed below:
1. Statistical Percentiles:
The percentile index, Ln , is defined as that level of noise which is exceeded n%
of the time in the total data points obtained for a certain interval of time. L1 is
used as a measure of peak noise levels , L10 , as a representative of levels during
periods of intense noise, L50 , as an indication of the average noise level and
L90 gives an idea of the background noise levels.
2. Traffic Noise Index TNI
In studies related `to traffic noise , another index TNI is also used . This is usually
expressed in terms of L10 and L90 (Magrab 1975 ) as follows :
TNI L L L= − + −4 3010 90 90( )
Where the term L L10 90− indicates the range of "noise climate" and describes the
variability of noise, L90 as mentioned above represents the background noise
level and the third term 30 is introduced to give convenient numbers. It
emphasizes that a significant degree of annoyance arises from the variable
character of noise.
3. Equivalent Continuous Sound Level Leq
One of the most important and widely used index to characterized noise is the
Equivalent Continuous Sound level Leq .This is the level of a theoretical constant
noise equivalent in energy content to the actual fluctuating noise over a given
period of time. Mathematically
LT
p
pdt
Tdteq
T
L
T
=
=
∫ ∫10
110
11010
0
2
0
10
10
0
log log ( / )
where L = sound pressure level
T = time interval of observation.
If the sound levels are measured over discrete time intervals ∆Ti s, then Leq can be
given by
LT
Teq i
L
i
n
i=
=
∑101
1010
10
1
log ( / )∆
1.9 Standards of Noise Pollution in India
Following are the ambient noise pollution standards prescribed by CPCB in India.
Area Code Category of Areas Day Time Leq
Levels
Night Time Leq
Levels
A Industrial Area 75 70
B Commercial Area 65 55
C Residential Area 55 45
D Silence Zone 50 40
Here, day time refers to 6.00a.m. to 9.00p.m. while the night time means 9.00p.m. to
6.00a.m. Silence zone includes the areas upto 100meters around certain premises like
hospitals, educational institutions and courts. Honking of vehicle horns, use of
loudspeakers, bursting of crackers etc. are banned in these zones.
1.10 Summary
A wave is a perturbation/disturbance that travels onwards through a medium. A
wave is characterized by its frequency, wavelength and amplitude. Sound waves
are longitudinal waves that travel in the form of condensations (compressions)
and rarefactions in the medium. A normal healthy human ear can hear sounds in
the frequency interval 20 Hz to 20,000 Hz. Noise means any irritating sound
which affects the physiological and psychological well being of a person in an
adverse manner. Since the range of sound pressures commonly encountered by
the human ear is very wide, it has been condensed into a more manageable
logarithmic scale by the acoustical scientists by devising the concept of sound
pressure level, which is expressed in decibels. Sources from which sound is
emitted may be typically classified as the point source and the line source. The
sound pressure level in a sound field is measured with the help of a sound level
meter. The data collected by a sound level meter is then used to compute various
indices of noise pollution, some of which are utilized to formulate standards of
noise pollution at a given place.
1.11 Key Words
Sound Waves: Longitudinal waves that travel in the form of condensations
(compressions) and rarefactions in the medium.
Noise: Any irritating sound which affects the physiological and psychological
well being of a person in an adverse manner.
The percentile index, Ln : The level of noise which is exceeded n% of the time
in the total data points obtained for a certain interval of time
Equivalent Continuous Sound Level Leq : The level of a theoretical constant
noise equivalent in energy content to the actual fluctuating noise over a given
period of time
1.12 Review Questions
1. Define the following:
(i) Transverse waves
(ii) Longitudinal waves
(iii) Wavelength
(iv) Frequency
(v) Time period
2. What is sound? Explain audible, infra-sonic and ultra-sonic sounds?
3. What is noise? Explain the decibel scale with the concept of sound
pressure level.
4. Differentiate between point source and line source.
5. What are different indices of noise pollution?
6. How is noise pollution measured? What are the standards of noise
pollution in India?
1.13 Suggested readings
1. Bell, L. H. and Bell, D. H. (1994), "Industrial Noise Control", Marcel
Dekker, Inc.
2. Kryter, K. D. (1985), “The Effect of Noise on Man”, New York, Academic
Press.
3. Stephens, R. W. B. (1986),"Noise Pollution Effects and Control", SCOPE
John Wiley and Sons.
4. Singal, S. P. (2005), “ Noise Pollution and Control Strategy”, Narosa
Publishing House.
5. Aggarwal, S. K. (2005), “ Noise Pollution” APH Publishing Corporation.
Unit-IV PGDEM-04 Noise and Air Pollution Control-I
Dr. Krishan Kumar
STRUCTURE
1.0 Objectives
1.1 Introduction
1.2 Particulate Control Devices
1.2.1 Electrostatic Precipitators
1.2.2 Fabric Filters
1.3 Strategies for Noise Pollution Control
1.3.1 Silencers
1.4 Summary
1.5 Key words
1.6 Review Questions
1.7 Suggested readings
1.0 Objectives
To sensitize the students about the following major devices for the control of air
and noise pollution
• Electrostatic precipitators
• Fabric Filters
• Silencers
1.1 Introduction
Air pollutants are of two types: gaseous and particulates. Gaseous pollutants are
the pollutants in gas phase. They have the property of filling any available space
until their concentrations reach equilibrium by diffusion. If the space is too large,
the resulting concentration may be negligible. On the other hand, if space is small,
the resulting concentration may reach significant levels e.g. concentrations of
carbon dioxide due to continuous running of a motor vehicle in a closed garage.
Particulates are finely divided solids and liquids, such as dusts, fumes, smoke, fly
ash, mist and spray.
• Dusts are small particles (1.0 to 1000µm) of solids created from the break up
of larger particles by operations such as crushing, grinding and blasting.
• Fumes are fine solid particles (0.03 to 0.3µm) that condense from vapors of
solid materials.
• Smoke is unburned carbon (0.5 to 1.0 µm) that results from the incomplete
combustion of carbon containing substances.
• Fly ash (1.0 to 1000µm) is the noncombustible particle admixed with
combustion gases in the burning of coal.
• Mists are the particles (0.07 to 10µm) formed from the condensation of liquid
vapors.
• Sprays are particles (10 to 1000µm) formed from the atomization of liquids
through nozzles.
Air pollution control may be defined as the various measures taken to meet certain
emission standards. These measures may include changes in processes/raw
materials or modification of equipment. Another method is the installation of
devices at the end of process equipment to treat the exhaust gas stream. These
devices are called air pollution control equipment. In the coming section, we shall
focus on the equipments that are used for the control of particulate matter.
1.2 Particulate Control Devices
There are three general types of particulate control equipment: force-field settlers,
fabric filters, and scrubbers. Force-field settlers are equipments that use a field of
force for the collection of particulate. There are three types of force fields:
gravitational, centrifugal, and electrical. Equipments that make use of gravitational
field for settling particulates are called gravitational settling chambers. Settlers
that utilize centrifugal force for the collection of particulates are called centrifugal
collectors. Devices, which utilize an electric field of force to collect particulates,
are called electrostatic precipitators (ESPs). Fabric filters are devices that use the
principle of filtration for the removal of particulates. Scrubbers remove
particulates from the exhaust gas stream by using water droplets for capturing
them. Of all the devices mentioned above, electrostatic precipitators (ESPs) and
the fabric filters possess the highest collection efficiencies. Particularly, they are
very effective for the collection of small particulates that can be respired by
human beings. Other devices mentioned above are often used for pretreatment of
the effluent gas before directing it ESPs or fabric filters.
1.2.1 Electrostatic Precipitators
Electrostatic precipitators make use of electric field force for the collection of
particulate matter. This is done by applying a high voltage pulsating direct current
to an electrode system consisting of a small diameter discharge electrode which is
usually negatively charged, and a collection plate electrode which is grounded.
This produces a unidirectional, nonuniform electric field whose magnitude is
highest near the discharge electrode. A corona (a kind of glow) is generated near
the discharge electrode, a condition that is essential for the process of charging.
The electric field near the wire (discharge electrode) accelerates electrons present
in the gas to velocities sufficient to cause ionization of the gas in the region near
the wire. The ions produced as a result of the corona migrate toward the collection
electrode and in the process collide with and become attached to particles
suspended in the gas stream. The attachment of ions results in a build up of
electric charge, the magnitude of which is determined by the number of ions
attached.
The charge on the particles in the presence of an electric field results in a new
force in the direction of the collection electrode. The magnitude of the force is
dependent upon the charge and the field. This force causes particles to be
deposited on the collection electrode where they are held by a combination of
mechanical, electrical and molecular forces.
Once the particles are collected, they can be removed by coalescing and draining,
in case of the liquid aerosols, or by periodic impact or rapping, in case of solid
material. In case of rapping, a sufficiently thick layer of dust must be collected so
that it falls into the hopper in coherent masses to prevent excessive re-entrainment
of the particles in the gas stream.
Fig.1.1 A typical ESP installed in an industrial set up
Fig 1.2 Schematic diagram of an Electrostatic Precipitator
1.2.1.1 Components of Electrostatic Precipitator
An electrostatic precipitator is composed of the following components:
(i) Discharge Electrodes
The discharge electrodes are thin round wires varying from 0.05 to 0.15
inch (0.13 to 0.38 cm.) in diameter. Most common designs use wires
approximately 0.1 inch (0.25 cm) in diameter. The discharge electrodes
consist of vertically hung wires supported at the top and held taut and
plumb by the weight at the bottom. The wires are usually made from
high-carbon steel, or of stainless steel, copper, titanium alloy and
aluminum. The weights are made of cast iron and are generally 11.4 Kg
or more. The weights at the bottom are attached to guide frames to help
maintain wire alignments.
(ii) Collecting Electrodes
Most precipitators use plate collection electrodes. The plates are
generally made of carbon steel, stainless steel, or some kind of alloy,
depending upon the gas stream conditions. The plates range from 0.02
to 0.08 inch (0.05 to 0.2cm) in thickness. Plates are spaced from 4 inch
(10 cm) to 12 inch (30 cm) apart. Normal spacing for high efficiency
units is 20-23 cm. Plates are usually 20 to 50 ft (6 to 15 m ) high.
(iii) Shells
The shell structure encloses the electrodes and supports the precipitator
component in a rigid frame. This is done to maintain proper electrode
alignment and configuration. Providing supporting structures to the
precipitator component is a very important aspect of design. Collecting
plates and discharge electrodes are supported at the top so that elements
hang vertically under the force of gravity. This allows the elements to
expand or contract with temperature changes without binding or
distorting.
(iv) Rappers
Removal of accumulated dust deposit on collection electrode is
accomplished by rapping. Dust deposits are dislodged by mechanical
impulses or vibrations imparted to the electrodes. A rapping system is
designed so that rapping intensity and frequency can be adjusted for
varying operational conditions. Rapping of collection plates can be done
by a number of methods. One of the popular methods of mechanical
rapping uses hammers mounted on a rotating shaft. As the shaft rotates,
hammers drop by gravity and strike anvils attached to the collection
plates. Rapping intensity is governed by the weight of hammers and
length of the hammer mounting arm. The frequency of rapping can be
changed by altering the speed of the rotating shafts.
(v) Transformer-Rectifier Sets
The T-R sets are required to control the strength of electric field
generated between the discharge and collection electrodes. They step up
the normal service voltages from 400 to 480V to approximately
50,000V and convert alternating to direct current.
1.2.1.2 Efficiency Of Electrostatic Precipitator
The efficiency of an electrostatic precipitator is given by the Deutsch-Anderson
equation given below:
)/( 1 QwAeE
−−=
Where E is the collection efficiency of the precipitator, A is the effective
collecting plate area of the precipitator, Q is the gas flow rate of the precipitator
and w is the drift velocity i.e. the velocity with which particles migrate towards the
collecting electrode.
The efficiency of an electrostatic precipitator is greatly affected by the particle
resistivity. Therefore, discussion about the performance of electrostatic
precipitator would remain incomplete if no mention is made about it. Rsistivity
refers to the resistance offered by the collected dust layer to the flow of electric
current. By definition, resistivity is the electrical resistance of a dust sample 1.0
cm2 in cross-sectional area, 1.0 cm thick, and recorded in units of ohm.cm. Dust
resistivity values can be classified roughly into three groups:
1. Between 104 and 10
7 ohm.cm – low resistivity
2. Between 107 and 10
10 ohm.cm – normal resistivity
3. Above 1010
ohm.cm – high resistivity
Particles that have low resistivity are difficult to collect since they are easily
charged and lose their charge upon arrival at collection electrode. This happens
very fast and the particles can take on the charge of collection electrode. Particles
thus bounce off plates and are re-entrained in the gas stream.
Particles that have normal resistivity do not rapidly lose their charge upon arrival
at collection electrode. These particles leak their charge to ground and are retained
on the collection plates by intermolecular adhesive and cohesive forces. This
allows a particulate layer to build up, which is then dislodged into hopper through
rapping. At this range of resistivity (i.e. 107 to 10
10 ohm.cm ), therefore, particles
are collected most efficiently.
Particles that exhibit high resistivity are difficult to charge. Once they are finally
charged, they do not readily give up the acquired negative charge upon arrival at
the collection electrode. As the dust layer builds up on the collection electrode, the
layer and the electrode form a high potential electric field.. This produces a
condition called as back corona which produces small holes or craters in the dust
layer, from which back corona discharges occur. Positive ions are generated
within the dust layer and are accelerated toward the negative (discharge) electrode.
This counteracts the process of ion generation at the discharge electrode and thus
results in the reduction of collection efficiency.
1.2.2 Fabric Filters
Fabric filters remove dust from a stream of gas by means of a porous fabric and a
cake of dust as the filter media. These systems are commonly called as baghouses
since the fabric is usually configured in cylindrical bags installed within a housing.
The basic principle of baghouse operation involves the removal of dust from the
dust laden gas by passing the dirty gas through a filtration medium. The cleaned
gas emerges from one side of the medium while the dust is collected on the other
side. Periodically, the collected gas is removed from the fabric.
The type of filter fabric used depends on the temperature and acidity of the gas
stream, the characteristics of the dust, the gas-to-cloth filtration ratio, and the type
of bag cleaning used.
Because all baghouses impose extra pressure drop on any operating process, a fan,
blower, or compresser of some kind must be used to draw the process gases
through the system. Usually, such devices are installed on the baghouse outlet,
which is the clean side of the filtration process. This location has the advantage
that it does not subject the fan to the dust so that the possibility of dust leakage
into the clean gas coming out of the baghouse is reduced. This becomes
particularly important when the dust is toxic.
There are a number of mechanisms through which the fabric filter traps the dust.
Interception takes place when a particle traveling along a stream line in a gas
stream approaches a fiber in the filter. The path of the particle is such that it strikes
the fiber and gets stuck on it. In case of inertial impaction, a gas stream bends its
direction if it comes across a fiber in its path. However, the dust particle being
heavy, can not change its path (due to the property of inertia) and bangs the fiber
where it gets stuck. This collection mechanism is effective for particles about
10µm or larger. For particles below 10µm, this is not a very effective mechanism.
For smaller particles, there is another mechanism that is effective. This is the
process of diffusion. When the particles are too small, their motion can be affected
by collisions with gas molecules. Frequent collisions with gas molecules make the
path of a small particle erratic or random. The random motion of these small
particles continues until they bump into the fiber and collected. Electrical
entrapment can be another mechanism through which particles are collected in a
fabric filter. Often, fibers and particles, both are charged. If these charges are of
opposite sign, the particles are attracted to the fiber and collected on it. Another
mechanism is sieving in which the particles larger than the pore size of the fabric
cannot pass through the fabric. Sieving is a very important mechanism particularly
after the building of dust cake on the surface of fabric. Without the dust cake, the
efficiency of a fabric filter would be just 60 to 70%. It is the dust cake on the
surface of the fabric, which reduces the pore size and thereby, increases the
efficiency of a fabric filter to 99 percent.
Fig. 1.3 A typical baghouse assembly
1.2.2.1 -Types of Fabric Filters
Fabric filters can be classified into different groups in a number of ways. One such
is to group the fabric filter designs by their cleaning methods. There are three
major cleaning methods: shakers, reverse-air, and pulse jets. Another approach is
to group fabric filters as per their capacity to deal different volumes of exhaust
gases. There are three groupings: low volume, medium volume and high volume
fabric filters. Yet another way is to classify the fabric filters according to the type
of filter media they use i.e. woven or felted. Still another way is to categorize on
the basis of temperature applications i.e. high temperature (>400°F), medium
temperature (200 to 400°F) and low temperature (<200°F) applications group.
1.2.2.2 -Cleaning Methods of Fabric Filters
(i) Shakers
Shakers remove the collected dust from the surface of bag by
mechanically shaking it. This is done manually in small dust collectors.
In large size collectors, this process is motorized. The bag is generally
open at the bottom and close at the top where it is attached to the
shaking mechanism. In this configuration, the dust is collected on the
inner sides of the bags. Shaking is done at a frequency of several cycles
per second with the amplitude of a fraction of an inch to a few inches.
The duration of shaking may be 30s to a few minutes. Common bag
diameters are 5, 8 and 12 inches. The operation of shaking is performed
in the off-stream mode.
(ii) Reverse_Flow Cleaning
Reverse-air cleaning involves the removal of dust from the bags by
backflushing them with a low-pressure reverse flow. In the case of high
temperature applications, the just cleaned hot gas is employed to
backflush rather than the ambient air. Woven filter media are generally
employed in conjunction with reverse-air cleaning. Dust is collected on
the inners side of the bags, which are closed at the bottom and open at
the top. Most often, reverse flow systems are comprised of isolatable
compartments. Normally, cleaning is done one compartment at a time.
Duration of cleaning may vary from 1-2minutes. Cleaning is performed
in the off-stream mode. Common bag diameters are 8, 12 inch.
(iii) Pulse Jet Cleaning
Pulse-jet cleaning employs high pressure compressed air, with or
without a venturi, to backflush the bags vigorously. This method creates
a shock wave that travels down the bag, knocking the dust away from
filter medium. This method is generally employed in conjunction with
felted filter media. The duration of cleaning is lower than that of other
two methods. The pulse/shock wave lasts only for a fraction of a
second. The baghouse is often not subdivided into compartments when
pulse-jet cleaning is employed. The bag is closed at the bottom and open
at the top. Dust is collected on the outside of the bag. Usually, a row of
bags is cleaned simultaneously by introducing compressed air briefly at
the top of each bag.
1.2.2.3 -Baghouse Selection
A baghouse is selected on the basis of certain basic information about the
process, the gas stream, and the dust to be collected. Following are the
factors that go behind the selection of a baghouse for a particular
application:
(i) Description of Application – What is the application? It is
important to know fully the application for which the fabric filter
is required.
(ii) The gas volume - An important aspect is the gas flow rate to be
filtered. Normal gas flow, as well as surges and maximum flows,
must be established in order for a properly sized baghouse.
(iii) The gas temperature – Maximum and minimum temperatures
determine to a large degree the selection of bag fabric and other
materials of construction.
(iv) Chemical properties of the gases – It is important to identify the
corrosive gases, combustible gases, and condensable vapors at
inlet conditions. These inputs can greatly influence the selection
of fabric and materials of construction.
(v) Description of dust – Knowledge of dust concentration (grains
per cubic feet of gas), properties of dust such as particle size
distribution, shape, chemical composition, tendencies to
agglomerate or develop electrostatic charges, abrasive
characteristics, and bulk density are all very important factors in
the selection of baghouse and auxiliary equipment.
(vi) Available space – Availability of space is another important
criterion that determines the size of a baghouse to be installed for
a particular application.
(vii) Other equipment in the dust collection system – The dust
collection system may include other equipment, which may
influence the selection of baghouse.
Selection of filter media is another very important aspect of baghouse selection.
The filter media should be able to withstand temporary heat surges. Depending
upon the specific applications, a particular filter media may be selected. The fiber
must also be able to resist degradation from exposure to acids, alkalies, solvents or
oxidizing agents found in the dust laden gas stream. Dimensional stability of the
filter medium is another important factor. The fiber may shrink or stretch within
the application environment. However, these effects must be controlled to
maintain the dimensional stability of the fiber. Finally, cost of the fiber is a very
important factor in the selection of filter medium. Generally, the least costly
selection that satisfies the above mentioned requirements, is preferred. Table 1.1
presents the characteristics of some of the widely used filtration media.
Table 1.1- Characteristics of some common fabric filter media.
Fabric Max.
Temp.
Acid
Resistance
Fluoride
Resistance
Alkali
Resistance
Abrasion
Resistance
Cotton 180°F Poor Poor Good Very Good
Polypropylene 200°F Excellent Poor Excellent Very Good
Polyester 275°F Good Poor to
Fair
Good Very Good
Nomex 400°F Poor to
Fair
Good Excellent Excellent
Teflon 450°F Excellent Poor to
Fair
Excellent Fair
Fiberglass 500°F Fair to
Good
Poor Fair to
Good
Fair
1.2.2.4 Performance of a Baghouse
Despite several sophisticated formulae that have been developed, there is no
satisfactory set of published equations that allows a designer to calculate the
efficiency of a prospective baghouse. One parameter that helps the baghouse
designers is the Gas-to –Cloth (G/C) ratio. This is a measure of the amount of gas
driven through each square foot of fabric in the baghouse. It is given in terms of
the number of cubic feet of gas per minute passing through one square foot of
cloth. Factors influencing the appropriate G/C ratio for a baghouse include the
cleaning method, filter media, dust size, dust density, dust loading, and other
factors that are unique to each situation. Because of their variability, however, it
has not been possible to satisfactorily quantify each of these factors for
application. One approach to overcome this problem is to collect all empirical data
available for the source in question. If there are no data for the industry at hand,
then go to a similar industry, which is using a baghouse and determine the G/C
range successfully employed in that industry and conservatively apply it to your
case.
1.3 Strategies for Noise Pollution Control
There are four general methods of controlling noise: enclosing the noise source,
enclosing the noise receiver, putting a barrier between the noise source and the
receiver, and controlling the noise generator.
Noise is transmitted by vibration. Hence the property of the enclosure must be
such that it should not vibrate when a sound wave hits its surface; otherwise, the
enclosure itself becomes the source of noise. Since vibration is inversely related to
the mass of the material, in the use of enclosures, the effectiveness of control is,
therefore, a function of the mass of the enclosure. Thus, by the mass law, the ideal
enclosure is the heavy enclosure (materials of high density). Table 1.2 shows
surface densities of some common materials of construction.
Table 1.2 – Densities of some common materials of construction.
Material Surface Density in kg/m2/cm of thickness
Brick 19-23
Concrete Blocks 15
Dense Concrete 23
Wood 4-8
Common glass 29
Lead sheets 125
Gypsum board 10
Steel 108-112
Putting a barrier between the source and the receiver is generally used for
controlling highway noise. The effectiveness of a barrier is dependent on the
geometry of the source, barrier and receiver, and on the ground cover. Studies on
different kind of noise barriers reveal that noise attenuation up to 8-14 dBA may
be achieved using barriers 8ft high and 4 inches thick.
1.3.1 Silencers
Control of noise at points of generation may be done with the help of mufflers or
silencers and isolation of noise source by vibration control. There are three basic
types of silencers:
(i) Absorptive Silencers
In these silencers, a lining of some acoustic material is provided directly
on the interior of the duct. The duct may be straight or may have bends,
or the duct may be expanded into plenum lined with the acoustic
material. The acoustic material absorbs the noise, thus attenuating it.
The absorptive silencer is a type of dissipative muffler since it dissipates
the noise by absorbing it.
(ii) Reactive Silencers
These have no lining of absorptive acoustic materials. In them,
attenuation of noise is achieved by reflecting the sound waves so as to
cancel the waves of incoming noise. This process is called destructive
interference. Reactive silencers are found in trucks and automobiles.
(iii) Diffusers
High velocity mass of air impinging on stationary air or solid objects
produces noise due to the turbulence created. Diffusers attenuate noise
by reducing this velocity. The source flow is diffused out into a
multitude of tiny flows having lower velocities using some appropriate
mechanism. The diffuser is an exhaust muffler, since it attenuates noise
by installing it at the end of a duct or pipe.
1.4 Summary
Due to their obvious adverse effects on the physiological as well as
psychological health of human beings, air and noise pollution control are two of
the major components of any pollution management program. Control of
particulate matter, emitting from an industrial process, is one of the important
objectives of any air pollution control initiative. Two of the most efficient devices
used for this purpose are the Electrostatic Precipitators (ESP’s) and Fabric Filters
or the Baghouses. Whereas, electrostatic precipitators work on the principle of
electrostatic charging and subsequent collection of particles by employing a strong
non-uniform electric field, fabric filters use the simple mechanisms of inertial
impaction, diffusion, and sieving for trapping particulate matter. As far as control
of noise pollution is concerned, two of the main strategies in this regard are (i)
controlling noise at the source itself and (ii) isolating the source from the receiver
using a barrier. Silencers and mufflers are important devices used for controlling
the noise at the source itself. Different types of silencers use different principles
for controlling noise.
1.5 Key Words
Particulates: Finely divided solids and liquids, such as dusts, fumes,
smoke, fly ash, mist and spray.
Electrostatic Precipitator: A device that makes use of a strong non-
uniform electric field for the removal of particulate matter from the effluent
gas.
Baghouse: Systems consisting of assemblies of bags which remove dust by
means of a porous fabric and a cake of dust as the filter media.
Silencers: Devices consisting of ducts designed to reduce the level of sound.
1.6 Review Questions
1. What is the principle on which electrostatic precipitator works?
2. What are different components of an electrostatic precipitator?
Explain their significance.
3. How do you calculate the efficiency of an electrostatic
precipitator?
4. What is resistivity? How does it affect the efficiency of a
precipitator?
5. What are different mechanisms through which a baghouse traps
dust?
6. What are different types of cleaning methods used for the
removal of dust from the fabric in the baghouse filters?
7. What are the factors that must be considered before selecting a
baghouse for a particular application?
8. What are different ways of achieving noise control?
9. What are different types of silencers used for noise control?
1.7 Suggested readings
1. Masters, G. M. (1998), “Introduction to Environmental Engineering and
Science” – Prentice Hall of India
2. Boubel, R.W., Fox, D.L., Turner, B. and Stern, A.C. (2005), “
Fundamentals of Air Pollution” – Academic Press.
3. Bell, L. H. and Bell, D. H. (1994), "Industrial Noise Control", Marcel
Dekker, Inc.
4. Stephens, R. W. B. (1986),"Noise Pollution Effects and Control", SCOPE
John Wiley and Sons.
5. Singal, S. P. (2005), “ Noise Pollution and Control Strategy”, Narosa
Publishing House.
UNIT-IV PGDEM-03
RADIOACTIVITY IN ENVIRONMENT
Written by Dr. Hardeep Rai Sharma, SIM conversion by Prof. Anubha Kaushik
STRUCTURE
1.0 OBJECTIVES
1.1 INTRODUCTION
1.2 RADIO ACTIVITY
1.2.1 Radio nuclides
1.2.1.1 Kinds of Radiations
a) Electromagnetic radiation b) Particulate radiation c) Ionizing radiation d) Non-ionizing radiation
1.2.1.2 Sources of Radioactivity in Environment
a) Natural sources b) Man made sources
1.2.1.3 Fate and Movement of Radioactivity in Environment
- Physical and biological half-lives of radio nuclides
1.2.1.4 Biological Effects of Radiations
1.3 SUMMARY
1.4 KEY WORDS
1.5 SELF ASSESSMENT QUESTIONS
1.6 SUGGESTED READINGS
1.0 OBJECTIVES
After studying this unit you should be able to know :
* About radionuclides
* About various kinds of radiations
* Natural and man made sources and fate and movement of
radioactivity in environment.
* Biological effects of radiations.
1.1 INTRODUCTION
1
The smallest unit of an element (as hydrogen carbon, oxygen) that can
exist while retaining the characteristics of that element is called atom.
Each atom has proton (+), neutron (uncharged) and electron (-). Atom of
each element has characteristic numbers of protons, neutrons and
electrons. Most elements, however, in nature contain atoms that are not
exactly like the predominant form. These atoms have different number of
neutrons. These different forms of the same element are called isotopes.
Some isotopes of common elements are stable under ordinary conditions
while others have various degrees of instability, and some of them
disintegrate with the emission of radiations of one kind or the other.
1.2 RADIOACTIVITY
1.2.1 RADIO NUCLIDES
Radioactive isotopes are isotopes that emit ionizing radiation. Since the
radiations are highly energetic (as x-rays) and these tend to split
substances, including living matter, into ions, they are called ionizing
radiation. The term isotope has been used loosely and the appropriate
general term for a particular kind of atom is nuclide. Natural radioactivity
occurs only in elements whose atoms hold a nuclear charge more than
83. The nuclei of such atom are quite, unstable due to large positive
charges on it and emit α (alpha) and β (beta particles). The atomic
nucleus attains an excited state in this manner and emits X-rays or
γ (gamma) rays in order to relieve this energy state .
When the α rays are given off, a new element is formed whose nuclear
charge is reduced by 2 units and whose nuclear mass is reduced by 4
units. For example, the element radium (Ra) is transformed into the rare
gas radon (Rn). 226 4 226
Ra -- He → Rn + energy 88 2 86
If a nucleus loses beta particles of electrons the element receives an
2
additional positive charge on its nucleus without changing the mass of
the nucleus. For example, the lead (isotope) 214Pb is transformed into the
element bismuth (Bi): 214 214
Pb – e– → Bi + energy 88 83
The ions that form in α and β decay proceed quickly into a neutral state
by giving or receiving electrons. The unstable elements which forms from
α and β decay in turn form new elements by further decay, until a-stable
element is found.
Nuclear rays are high energy rays while α rays have 4-9 million electron
volts (MeV) of energy, β rays have usually 0.5-2 Me.V and γ-rays about
0.1-2 MeV of energy. The unusually high energy of the nuclear rays
decreases progressively as they pass through air, water or other media,
because collisions with other materials occur during such passage and
with every collision the atom is excited or ionized. The electron moves
temporally to a higher energy level as it takes an additional energy, and
then again releases that energy and return to its original level. The
energy released can be harnessed for chemical reactions or one can
harness the light it emits, e.g. in a scintillation counter.
The larger the particles of the nuclear rays are, the more frequently they
will collide with molecules and the more quickly they will lose their
energy. The distance that the ray travels is affected by this. (The photons
of γ-rays travel a greater distance than helium nuclei, though their
ionization strength is less than helium nuclei. β-rays lie between α-rays
and γ-rays both in distance they travel and their ionization strength. In
the air γ-rays travel a distance of several to many metres depending on
their energy content. They penetrate entirely the soft tissues of
organisms, as do free neutrons. β rays can travel about 150-850 cm in
the air; they penetrate at most a few centimeters into the soft tissues of
3
organisms. Helium nuclei travel 2.5-9 cm in the air and penetrate only
fractions of millimeters into soft tissues, α-rays and β rays therefore
release their entire energy during their short passage through the tissue.
That implies that the cells suffer severe damage at the point at which
these rays penetrate them.
As radioactive elements decay more frequently, they become more
hazardous to body tissue; for that reason the number of instances of
decay in a ,given quality of food is a matter of importance. The Becquerel
is the unit of measurement; I Becquerel (Bq) = 1 decay per second. The
number of rays, or the dose, is determined by reference to the ion pairs
generated. Rontgen (R) is the unit of measurement; I R = number of rays
that produces 2.082 billion ion pairs in 1 cm3 of air. The number of rays
that is absorbed by body tissue and that is responsible for the biological
effect is measured in “radiation absorbed dose” (rad) i.e. as the number of
rays that is absorbed by a given mass of material, 1 rad =0.01 J/kg. The
rad is usually replaced by the Gray (Gy) in present day measurements.
The relationship between the two is 1 Gy. 1 J/Kg = 100 rad.
Metabolism of radio nuclides
If a radio nuclide absorbed into the body is an isotope of element
normally present (e.g. Na, K or Cl), it will behave like the stable element.
Also, if it has chemical properties similar to an element normally present,
it will tend to follow the metabolic pathway of the natural metabolite (e.g. 137Cs and K or 90Sr and Ca). For other radio Nuclides, their metabolism
will depend on their affinity for biological ligands and for membrane
transport systems.
Calcium has an important function as a major component of bone,
although bone also act as a reservoir of calcium in the body : in man
about 17% of calcium in the skeleton is recycled each year. About 30% of 45Ca is absorbed from the gut and about 65% of that is deposited in the
4
skeleton. 90Sr follows a similar route, although urinary excretion is
greater.
Plutonium mainly enters the body by inhalation. Its compounds can may
be soluble in water (e.g. plutonium nitrate or chloride), or chemically
inert and insoluble (plutonium dioxide). The soluble component is rapidly
absorbed from the lungs and transported in the blood to be either
excreted through the kidneys or deposited in tissues (bones and liver).
Out of plutonium entering the blood, about 45% is deposited in the liver,
45% in the skeleton, and the remainder either excreted or deposited in
other tissues. Biological half-life of Plutonium in the bone and liver are
about 100 years and 40 years, respectively. From animal studies, it is
apparent that the lungs, the cells of inner surface of bone, the bone
marrow and the liver are at the most at risk from accidental intake of
plutonium.
1.2.1.1 Kinds of Radiation
There are different types of radiation discussed below:
a. Electromagnetic Radiations
This form is similar to light in its physical properties. These include a
broad spectrum of energy. These are : a) Ultraviolet rays ; b) X-rays c)
Gamma rays; d) Infra Red rays; e) Radio waves; f) Visible light rays. All
the different kinds of electromagnetic radiations are nothing more than
light rays of different wave length and frequency.
• Ultraviolet Rays
The wavelength of UV rays extends from 0.1 µm (100 nm) to 0.4 µm (400
nm). Ultraviolet radiation is divided into UV-C (wavelength of 200-280
nanometers), UV-B (280-320 nm), and UV-A (320-400 nm). The most
biologically damaging is UV-C and the least damaging is UV-A, with UV-B
5
having intermediate efficiency of biological action. The solar spectrum at
the earth's surface contains only the UV-B and UV-A radiations.
Stratospheric ozone strongly absorbs UV-C radiation and the shorter
wavelength portion of UV-B radiation, thus providing some biological
protection.
• X-rays
X-rays are also a form of electromagnetic radiation, but differ from
gamma radiation in that they result from extra-nuclear loss of energy of
charged particles, for example electrons, but having shorter wavelengths
than ultraviolet radiation. They may be emitted when an electron of an
atom jumps from one orbit to another orbit of lower energy. This
difference in energy is radiated as electromagnetic radiation. If the energy
is high enough to cause ionization the emission is called X-rays.
• γ-Rays
Gamma radiation is emitted only in conjunction with other types of decay
and belongs to the class known as electromagnetic radiation (like radio
waves and visible light, but of very much shorter wavelength and higher
energy). It is emitted when the nucleus produced following radioactive
decay is in an excited state, and then returns to the ground state by
emitting this radiation to carry away excess energy.
• Radiowaves/Microwaves
These are the waves in or near the extremely high frequency or shorter
wavelength range (3 mm to 200 cm). Microwave energy is too low to
disrupt living tissues by ionization. Instead, the energy gets absorbed as
oscillation energy and is converted to heat. This makes it possible to use
microwaves for cooking.
b) Particulate Radiations
6
They consist of the particles ejected from atoms at high speed and often
with tremendous energy. These have electrons, proton or neutron.
Whether the radiation emitted from nuclear disintegration is
electromagnetic or particulate, the emanations are so energetic and
forceful that they can do great damage to living tissues. The radiation
include β-particles, α-particles, proton, neutron and cosmic rays.
• α-radiation
α radiation has been shown to be composed of helium nuclei, consisting
of two protons and two neutrons bound together very tightly to give a
very stable unit. Consequently each particle possesses a positive charge
of 2 units, and a mass of 4 units. One electron volt (eV) is defined as the
energy gained by an electron passing through an electric potential of 1
volt. One gram of radium emits 3.7 x 1010 α-particles and 2 x 109 cal,
which is 2 X 105 times the calorific value of coal.
• β-Radiation
Normally the term beta particle or radiation refers to the high speed
negative electrons of kinetic energy up to more than 3 MeV originating in
the nucleus. One further type of beta particle, is also known, having
same mass as an electron, but is, positively charged and known as
positron radiation Indicated by β+.
• Neutron
Neutron is very common particle, being a basic constituent of the
nucleus and having a mass almost identical to the proton but carrying no
charge. There are no significant naturally occurring neutrons emitters,
but radio nuclides that emit neutrons can be produced artificially. The
neutrons are of great importance both in nuclear fission reactors and in
the production of radio nuclides not available naturally.
• Proton
7
Protons are 1,835 times heavier than electrons. Beta-particle drives into
a tissue like a tiny particle of sand, while the proton lumbers along like a
rock, knocking off pieces of atoms and molecules as it goes. The proton
does not penetrate as far as an electron of the same energy, but it causes
more disruption in a small area.
• Cosmic Rays
The extremely penetrating radiation falling upon the earth's surface
beyond the atmosphere are called cosmic rays. The cosmic rays which
are just entering on earth's atmosphere from outer space are called
primary cosmic rays. They are almost composed of positively charged
atomic nuclei, mostly proton about 89% and about 9% are α-particles
and rest are heavy nuclei such as carbon, nitrogen, oxygen, iron etc.
They have energies ranging from 109 to 1018 eV.
As the primary cosmic rays enter the earth's atmosphere from outer
space, its constituent charged particles collide with the nuclei of
atmospheric gases and splits into smaller nuclear fragments. These
fragments move with high speed and collide with other nuclei and
produce high speed particles and some elementary particles. When these
short lived elementary particles decay, electrons and highly penetrating
γ-rays are emitted. These protons and other high speed particles that are
produced are called as secondary cosmic rays.
Types of radiation on the basis of ionization
Radiation is energy being propagated from one place to another through
space. There are mainly two types of radiation on the basis of ionization:
• Ionising Radiation.
lonising radiation is sufficiently energetic to cause ionizations. An atom
gets ionized when it gains sufficient energy for one or more of its
electrons to get separated from the atom. Ionisation of a molecule might
8
yield two charged fragments, such as H2O → H+ + OH–. If the fragments
are uncharged, then they are referred to as ‘free radicals' as H20 → H +
OH.
• Non-Ionising Radiation
Radiations of shorter wavelength but having greater energy may be able
to harm the microorganisms but are able to injure only the surface
tissues of higher plants and animals. These radiations includes
ultraviolet radiation, microwaves and extra low frequency (ELF)
electromagnetic radiation.
1.2.1.2 Sources of Radioactivity in Environment
Man is exposed to different sources of radiation. These are :
a) Natural sources
These include: a) cosmic rays; b) environment (rocks, water, air); c) living
organisms (internal).
Radio nuclides of radium, thorium, uranium and isotopes of potassium
(40K) and carbon (14C) are very common in soil, rocks, air and water.
Marine sediments generally have higher concentrations of radio nuclides.
On an average, man receives about 50 m rads/yr from terrestrial
radiations and it may be as high as 2000 m rads/yr in areas where
uranium containing rocks exist as in Kerala.
Radiations from atmosphere are also common. For instance, radioactive
gases like radon are present in air through with low values of roughly 2
m rad/yr.
Man is also exposed to internal radiations from radioactive substances in
the body tissues. For instance, uranium, thorium and isotopes of
potassium, strontium and carbon exist in small amounts in the body.
Internal radiation values vary from 25 to 75 m rads/yr.
9
b) Man made sources
These include :
(i) Use of X-ray machines and laser beam (diagnostic and radio
therapeutic) is one such source.
(ii) Radioactive fall out (nuclear test) : Explosion of nuclear weapons
would generate small particles that would drift in the atmosphere
as an aerosol, and in the course of months and years would settle
on the earth's surface as fallout and is the cause of fairly uniforml
release of radioactivity.
(iii) Nuclear reactor wastes: The use of radioactive substances like 233U, 235U or 239Pu in nuclear power plants is another source of
radioactivity in the environment. The risk of melting down of a
reactor is a major risk in case of atomic power plants. Two very
serious instances have already occurred : one in Harrisburg in
1979 and another in the super reactor in Chernobyl in 1986. An
area of at least 100,000 km2 of the soil has been so intensively
polluted with radioactive material that in future no agriculture will
be possible on it. A nuclear power plant must be stopped after
about 30 years because of the constant contamination it sustains.
The process of dismantling a retired plant and of removing the
contaminated parts is hazardous and is a cause of radioactivity in
environment. The disposal of the tritium contaminated Water in
the reactor is also a problem. If the release of water is uncontrolled
the tritium enters the air and drinking water and eventually
reaches humans through the food chain.
(iv) Industrial and research uses of radioactive materials : Radio active
material are used in R & D activities and from there enter into
environment.
10
(v) Miscellaneous, (fulminous watch dials) : Several radioactive
materials find use in daily life and emit the radiations.
1.2.1.3 Fate and Movement of Radioactivity in Environment:
The radioactive pollutants reaching the freshwater resources or oceans
are rapidly lost to the sediments and may bio-accumulate in the body of
plants and animals directly or through food chains (bio-magnification). In
the body of the organisms, they behave chemically as their stable
counterparts, but are more dangerous because of the radiation which
they emit internally. Algae, macrophytes and fish concentrate the radio
nuclides in greater amounts from ambient water.
Man is the ultimate sufferer who consumes the contaminated food and
water. However dose radioactive waste extremely low. The irrigation by
contaminated water will pollute the soil from where the radio nuclides are
transferred to the crops. Soils also get polluted by a direct release of low
activity waste waters and by radioactive fall out. The radioactivity from
the soil moves through the food chains and reaches man after
consumption of crops, meat, milk, eggs etc. The underground water may,
also receive radio nuclides after leaching from the soil.
The radioactivity released into the atmosphere is rapidly diluted by
atmospheric processes, but it may be of concern to man in certain highly
contaminated areas, for example, in the vicinity of atomic explosions or
in atomic power plants. The atmospheric fall out depositing directly onto
the leaves is efficiently passed into the grazing animals, such as cattle,
and reach to us. Cesium-I37 and Strontium-90 are two most important
radio nuclides found to reach humans in this manner.
Physical and Biological half-lives of Radio nuclides
The amount of a radioactive element that decays in a unit of time is
always proportional to the remaining amount. Every element has a
11
constant decay time, so different elements have different decay times. For
practical purposes time in which· the number of radioactive atom of a
nuclide is reduced by half called half-life is used.
To assess the time during which a radioactive element contaminates the
body after its incorporation, the biological half-life is relevant. The term
biological half-life is the time span during which half of the received
material is eliminated from the body, since radio nuclides do not
decompose in the body. From the biological half-life Tb. and the physical
half-life Tp, the effective half-life (Teff) for the entire organism or for a
specific organ can be calculated; this figure indicates how long the
organism or a specific tissue has been exposed to radiation.
Teff = Tb Tp Tb+Tp
The physical, biological and effective half lives of a few radioactive
elements are given in Table 1.
Table-1: Physical, biological and effective half-life of some radionuclides. For plutonium and half-life refer to bones. In the lung (as a non-water-soluble compound) the value is one year.
Element Half-life Type of ray
Physical Biological Effective
H-3 12.26 Years 19 Days 19 Days β-
C-14 5730 Years 35 Days 35 Days β-
P-32 14.3 Days 10 Years 14.1 Days β-
K-40 1.25 x 109 Years 37 Days 37 Days β-, β+
Ca-45 165 Days 50 Years 163.5 Days β-, γ
Sr-90 28.1 Days 11 Years 7.9 Days β-
1-131 8.07 Days 138 Days 7.6 Days β-, γ
Cs-137 30.23 Years 70 Days 69.6 Days β-, γ
Ba-140 12.8 Days 200 Days 1.2 Days β-, γ
12
Rn-222 3.824 Days α
Ra-226 1600 Years 55 Days 53.2 Years α, γ
U-233 1.62 x 105 Years 300 Days 300 Days α, γ
Pu-239 2.44 x 104 Years 120 Years 120 Years α, γ
Source : The Chemistry of Pollution, Gunter Fellenberg, pp. 164
1.2.1.4 Biological Effects of Radiations
Radioactive substances are among the most toxic substances known.
Radium is 25,000 times more lethal than arsenic. The most tragic early
evidence of the potency of radiation toxicity was the death of Marie Curie,
while working with her husband; Pierre Curie. She died of leukemia due
to radiation exposure.
Ionizing radiations bring about more dangerous effects than other
toxicants. Their effect may continue in subsequent generations. They
bring about following two types of undesirable effects in organisms.
i) Somatic Effects
These are the direct results of action of radiation on the body cells and
tissues. Radiologists, uranium mine workers and painters of radium dials
suffer the most. More evidence of degree and kind of damage from
radiation comes from studies of the Nagasaki and Hiroshima survivors.
The somatic effects may be immediate or delayed.
High radiation exposures have much acute toxicity and can kill animals
quickly. A dose of 400 to 500 roentgen on whole body is fatal in about
50% cases of man, and 600-700 roentgen in practically every case. The
victim declines in vitality and dies from anemia, infection and
hemorrhage. Parts of body differ in sensitivity. The most sensitive tissues
are intestine, lymph nodes, spleen and bone marrow.
The radiations destroy the body's immune response. The effects of low
13
penetrating radiations are less severe than the penetrating ones.
In delayed effects the patient may survive for months or years. Delayed
effects of radiations include eye cataracts, leukemia, malignant tumors,
cardiovascular disorders, premature ageing and reduced life span.
Diagnostic X-rays exposure of pregnant women may increase the risk of
cancer in child.
ii) Genetic Effects
Both, natural and man-made radiations bring about genetic effects.
Studies on Drosophila (fruit fly) have shown that mutation rates go very
high due to radiation exposures. Most genetic effects are brought about
by man-made radiations mostly from medicare and exposure from
nuclear power plants. People in industry, research and medicine using
radio nuclides are exposed more than others. The greatest damage is in
dividing cells, chiefly the gonads. The effects include mutation or lethal
effects on egg or embryo. The intensity of radiation affects the rate of
mutation. Generally higher animals are more susceptible to genetic
damage than lower animals as insects. Genetic effects also occur in
plants.
1.3 SUMMARY
Radioactive isotopes are the ones that emit ionizing radiations, which are
highly energetic and tend to split substances including living matter.
There is emission of alpha (α), beta (β) and gamma (γ) particles, each
having characteristic charge, penetrating power and energy. Radioactive
elements are more hazardous to body tissue as they decay more
frequently and Bequerel (Bq) is the unit of measurement of 1 decay per
second. Radionuclides, when absorbed into the body, behave like a stable
element and follow the metabolic pathway of a natural metabolite e.g. 90Sr behaves like calcium. Radiations can be of various types. The
14
electromagnetic radiations include ultra-violet rays (UV), X-rays, gamma
rays, radio waves and infrared rays. UV-B and UV-C rays are very
hazardous for biological systems. We are exposed to radiations from
natural sources like cosmic rays, rock, air, water etc. or from man-made
sources like X-rays, nuclear reactor wastes or nuclear fall-outs. The
radioactivity also moves through the food chain and reaches man’s body.
Half life of the radionucleides is very important to know how long the
radioactive substance will remain in the tissue or in the environment.
Radiations have adverse effects on living organisms causing damage to
body cells and tissues, destruction of immune response, genetic effects,
cancer and even death.
1.4 KEY WORDS
Isotopes : An element having atoms with different
number of neutrons.
Radioactive isotopes : Isotopes that emit radiations
Becquerel : Unit of measurement of decay (1 Bq = 1 decay
per second).
Rontgen (R) : Unit of measurement of X-ray
Rad : Radiation absorbed dose i.e. the number of
rays absorbed by a given mass of material.
UV rays : Ultraviolet rays with wavelength 0.1 µm to 0.4
µm. UV-C and UV-B are very harmful.
Alpha rays : Positively charged particles consisting two
protons and two neutrons
Beta rays : High speed negatively charged electrons.
1.5 SELF ASSESSMENT QUESTIONS
1. What are the different sources of radioactivity in environment?
15
2. Explain the somatic effects and genetic effects caused by
radiations.
3. Describe various types of electromagnetic and particulate radiation.
4. Differentiate between ionizing and non-ionizing radiations.
5. Write a brief note on :
i) α-rays ii) β-rays iii) χ-rays iv) γ-rays v) Radionuclides vi) Cosmic rays
1.6 SUGGESTED READINGS
1. Environmental Science, the natural environment and human
impact by Andrew R. W. Jackson and Julle M. Jackson. Addison
Wesley Longman Limited, England, Page No.295-296.
2. Water pollution : causes, effects and control by P.K.Goel, New Age
International (P) Publishers, Delhi. Page No. 143-150.
3. Radioactivity. In "The Chemistry of Pollution" Gunter Fellenberg,
John Wiley & Sons Ltd., pp 161-172 (2000).
4. Radiation biology "McGraw Hill Encyclopedia of Environment
Science & Energy" 3rd Edition (Eds.) Sybil. P. Parker and Robert
A.Corbitt. Mc Graw Hill, Inc., (I 993), pp 424-429.
5. Non-ionizing Radiations In “Encyclopedia of Environment Science
& Engineering" 3rd Edition (Eds.) James R. Pfafflin and Edward
N.Ziegler, VoL-II (J-Z) Gordan & Breach Science Publishers, S.A.
16
UNIT-IV PGDEM-04
NUCLEAR, THERMAL, INDOOR & ELECTROMAGNETIC POLLUTION
Written by Dr. Hardeep Rai Sharma, SIM conversion by Prof. Narsi Ram Bishnoi
STRUCTURE
2.0 OBJECTIVES 2.1 INTRODUCTION 2.2 SOURCES OF NUCLEAR WASTE 2.2.1 Mining of ores 2.2.2 Milling of ores 2.2.3 Feed material preparation and fuel fabrication 2.3 NUCLEAR POWER 2.3.1 Some major nuclear disasters 2.3.1.1 Hiroshima 2.3.1.2 The Fire of Windscale 2.3.1.3 Chernobyl 2.4 THERMAL POLLUTION 2.4.1 Impact of thermal pollution 2.4.2 Standards for thermal pollution 2.5 INDOOR POLLUTION 2.5.1 Indoor pollutants sources 2.5.2 Precaution/preventive measures of indoor pollution. 2.6 ELECTROMAGNETIC POLLUTION 2.7 SUMMARY 2.8 KEYWORDS 2.9 SELF ASSESSMENT QUESTION 2.10 SUGGESTED READINGS 2.0 OBJECTIVES
While studying this unit, you will be able to understand:
Major nuclear disaster and impact of thermal pollution and
electromagnetic pollution.
Sources of indoor pollution, precaution and measures for indoor pollution.
2.1 INTRODUCTION
Nuclear waste management is the field where most stringent possible
degree of quality control is required to be achieved. Unlike other waste
management problems in industry, no compromise is made against safety
standard due to its high cost incurring figure. In most countries regulations lay
down the maximum permissible exposure to radiation for workers in nuclear
industry and also for the general population. The thermal power industry in India
has an important role in development of industry as well as development of rural
India. But in the wake of its coming it also brings the dangers of pollution which
unless controlled can have short-term and long-term effects.
2.2 SOURCES OF NUCLEAR WASTE
Nuclear waste is generated in the multifarious fields of nuclear energy
systems and also in different stages of operations.
2.2.1 Mining of Ores. Mining of uranium and thorium ores generate scant liquid
radioactive waste. Dry mining is generally employed. Where drainage is required,
the activity has generally been sufficiently low for permitting direct discharge into
the environment.
However, the underground mining of uranium causes gaseous release
and insufficient ventilation results in lung cancer among the miners due to radon
products.
2.2.2 Milling of Ores. The first potentially serious waste generation starts with
milling operation. The specific process of milling operation for extraction of the
desired mineral is dependent on the composition and nature of the ore itself.
In the uranium mills, both acid and alkaline leaching processes are utilised
for separating the uranium from the extraneous matrix. As the ores are milled
and leached, only about fourteen percent of the total radioactivity in the ore fed to
the mill is recovered in the uranium concentrate. The process waste water
containing trace quantities of radium and thorium ends up in a tailing pond.
Leaching and seepage from the tailing ponds have caused concentrations of
Ra226 and Th230 greater than permissible below some of the tailing piles. The
radium 226 is in an undissolved form when it is discharged from the plant.
The milling operations also produce hazardous radioactive silica dust as
gaseous waste.
2.2.3 Feed Material Preparation and Fuel Fabrication. Feed material
preparation and fuel fabrication also entail radioactivity though of very low level.
The principal product is metallic uranium which is processed from high grade
uranium concentrates. Uranium trioxide is reduced to uranium hexafluoride for
the purpose of enrichment. The fluoride of uranium is finally converted to metallic
uranium.
The filters used in the intermediate steps are contaminated with uranium dust
and both solid and organic contaminated wastes and produced in the various
other steps in the processing operations.
2.3 NUCLEAR POWER Conventional steam electric power plants use fossil fuel such as coal, oil
or natural gas. The fuel is burnt in a boiler that produces steam which, in turn,
drives a steam turbine generator, called a turbo generator. Heat in commercial
quantities can also be produced indirectly involving atomic nuclei, this energy
sources is called nuclear energy. There are two processes by which energy is
obtained from atomic nuclei, fission and fusion. In fission, the collision of a
certain type of heavy nuclei is (having many neutrons and protons) with a
neutron results in the splitting of the nucleus into two smaller sized fragments.
Since together the fragments are more stable energetically than was the original
heavy nucleus, energy is released by the process.
The combination of two very light nuclei to form one combined nucleus is
called fusion and also results in the release of huge amounts of energy (E=mc2)
again since the combined nucleus is more stable than the lighter ones. Since
nuclear forces are much stronger than chemical forces, the energy released in
nuclear reactions is immense as compared to those obtained in combustion
process.
In a nuclear power plant, the heat is produced in a device called a nuclear
reactor instead of a boiler. Nuclear power is a modern means of generating
electricity. The fuel of a nuclear electric generator is atomic pellets of uranium
metal. Uranium contains 3 million times as much potential energy as coal. One
gram of fissionable material releases 23,000 K watt hours of heat. One ton of
uranium would provide as much energy as 3 million tons of coal or 12 million
barrels of oil.
Both, natural and man-made atomic fuels are used for reactors. These
fuels have the ability of fission. Uranium-235 (235U) is a natural fuel, containing
0.71% of the uranium found in nature, the rest being. 238U which does not
undergo fission spontaneously. It can be changed to fissionable material by
bombarding with neutrons called conversion. Thus atoms of U-238 are changed
through decay to plutonium-239 a man-made substance.
2.3.1 Some Major Nuclear Disasters of Historic Importance 2.3.1.1 Hiroshima The group of people from whom the most reliable data have been
gathered concerning radiation hazards are the survivors of the atom bomb
dropped at Hiroshima at 8:15 am on Aug. 6, 1945. Exhaustive studies have
shown that the heavily exposed people, called the hibakusha had a 29% greater
chance of dying from cancer than normal. Excess numbers of leukemia cases
began appearing in the late 1940’s and peaked in the early 1950’s, but by the
early 1970’s they had dropped to levels near those of unexposed Japanese. One
of the most feared hazards of radiation is that of congenitally deformed in infants
because of radiation induced genetic defects in the mothers.
Dozens of mentally retarded infants were born in the areas around
Hiroshima and Nagasaki in the months following the blasts. Abortions were also
numerous.
2.3.1.2 The fire at Windscale (Oct. 8, 1957)
This occurred in the plutonium production reactor and was the result of
human error coupled with inadequate operating instructions. A major fire had
taken hold and was consuming the uranium metal fuel and the graphite
moderator. The operators attempted to maintain secrecy for 24 hours after the
fire was discovered. It was estimated that the most hazardous release was that
of 20,000 curies of I131 and the Govt. ordered the disposal of all milk from dairy
herds within radius of about 25 miles. The full report of the subsequent enquiry
was never published.
2.3.1.3 Chernobyl The most recent and highly publicized nuclear disaster was Chernobyl,
Ukrane in April of 1986. Explosions from runaway nuclear reactor burst through a
4000 tonne steel concrete cover. The reactor core temperature was shown to be
more than 2000°C. Fuel and radioactive debris spread into air and hit the
surrounding areas. Radioactive particles spread out but in a volcanic cloud along
with streams of gases from molten mass in the core. In less than a week, deadly
debris and gases had drifted over most of Europe. The neighbouring countries
such as Poland had banned sale of cow milk as there were chances of
contamination of grass with long lived isotopes, due to radioactive fall-out.
Twenty per cent of the reactor radioactive iodine escaped along with 10-20% of
its radioactive cesium and other isotopes. 1,35,000 people lived in a 30 km
radius, of the power plant. There were 30 deaths and 237 cases of severe
radiation injury. Russian scientists estimated an increase in the cancer rate of
0.04% over the next 20 years. Thousands of reindeer had to be destroyed in
Northern Scandinavia because they had grazed on contaminated pasture. Stress
and fear created an understandable desire in these people to be moved out of
the area causing psychological damage.
2.4 THERMAL POLLUTION Water is able to absorb large quantities of heat without changing from its
liquid state. The high heat capacity means, that it is extensively used as a
coolant in many industries. Thermal pollution can be defined as an accumulation
of unusable heat from human activities that disrupts ecosystems in the natural
environment. Much of the heat produced by industries is in the form of condenser
cooling water. The principal user of water as a coolant include the electricity
generating industry, thermal power plants, nuclear power plants, petroleum
refineries, steel mills, chemical plants, paper and pulp mills etc.
The coolant water required by industry is drawn directly from water bodies,
frequently rivers. After use of water, the warmed water is often directly
discharged back into the original water body. This results in thermal water
pollution. The increase in heat contributes to the physical, chemical and
biological changes in the receiving water bodies.
Soil erosion and shoreline deforestation also contribute to thermal water
pollution but upto less extent. The soil erosion makes the water muddy, which in
turn increases the light absorbed and thus the water temperature is raised.
Deforestation of shorelines further contributes to the problem in two ways. First, it
increases soil erosion and secondly, it increases the amount of light that strikes
the water, both of which increase the temperature of water.
2.4.1 Impacts of thermal pollution (Physical, chemical and biological)
1. Temperature influences the viscosity, density, vapour pressure, surface
tension, gas solubility and gas diffusion rates.
2. Heated water has low density and spreads on the surface of water bodies
causing them to stratify thermally. The stratification is barrier to the oxygen
penetration into the deeper layers.
3. At elevated temperature, the sedimentation of suspended materials
increased due to reduction in density and viscosity of water.
4. Evaporation rate of water increased at high temperature.
5. Rate of chemical reactions normally increased with rise in temperature
which is about two-fold with every rise of 10ºC. BOD is also increased with
temperature.
6. The species composition changes as species tolerant of warmer water
replace those that are unable to adapt. This transition is often
accompanied by on overall decrease in species richness. For example,
attached algae in heated effluents were reported to show an increase in
biomass but a decrease in the number of species represented.
7. The rates of photosynthesis and plant growth are increased. An increase
in plant growth may seem to be a good thing at first glance but more live
plant means more dead plants. The pile up of dead plants leads to an
increase of bacterial population which consume oxygen along with dead
plants. There is now less oxygen and a greater demand for it.
8. The warmer water also increased the metabolic rate of fish, which leads
to, a sharp decrease in the life expectancy of aquatic insects. The
enhanced metabolism required more oxygen. However, the amount of
dissolved oxygen present in water is inversely related to its temperature.
On the other hand with the lack of aquatic insects, fish faces shortage of
food.
9. The disease resistance in fishes decreased and pollutants become more
toxic at elevated temperature. The species become more vulnerable to
parasites.
10. Thermal pollution can also interfere with the natural reproductive cycles of
fish. For example, premature hatching of eggs by artificially raised
temperatures may lead to mass mortality of the young fish through
starvation. Mass killing of fish and other aquatic organisms can occur
when there is a very rapid changes in water temperature. This is known as
thermal shock.
11. A continuous exposure to heat leads to the development of a new
ecosystem comprising of thermally adapted species. Sudden stoppage of
the industrial plants will again disrupt the system. Thousands of warm
water fishes and other animals were found dead when a thermal power
plant in New Jersey, U.S.A. was stopped for repairing for one day in
February 1972.
12. Natural migration of fish is also affected due to the formation of thermally
polluted zones which act as barrier to the migration.
2.4.2 Standards for thermal pollution
The Central Pollution Control Board (CPCB) in India has specified the
standards for thermal discharges from thermal power plants. The condenser
cooling water should not have temperature more than 5ºC higher than the intake
water temperature. Thermal water pollution can be avoided by pre-cooling the
warm water prior to its discharge. The major principles involved in heat loss are
conduction, convection, radiation and evaporation. For example, cooling ponds
and cooling towers are often used for cooling water in the electricity generating
industry. In cooling ponds the water from condensers is stored in earthen ponds
where natural evaporation brings down the temperatures. The water after cooling
is recirculated or discharged to the nearby water body. Alternatively, the warm
waste water can be effectively used by other industries. The potential uses of
waste heat may be in green houses, agriculture, aquaculture and space heating
beside others.
2.5 INDOOR POLLUTION
In the last several years, a scientific evidences has clearly indicated that
the air within homes and other buildings can be more seriously polluted than the
outdoor air. People spend approximately 90% of their time indoors. Thus, for
those people the risks to health may be greater due to exposure to air pollution
indoor than outdoors. Peoples like the young, the elderly and the chronically ill
people especially those suffering from respiratory or cardiovascular disease who
may be exposed to indoor air pollutants for the longest periods of time are often,
the most susceptible to the effects of indoor air pollution.
Indoor pollution sources that release gases or particles into the air are the
primary cause to indoor air quality problem in homes. Inadequate ventilation can
increase indoor pollutant levels by not bringing in enough outdoor air to dilute
emissions from indoor sources and by not carrying indoor air pollutants out of the
home.
2.5.1 Pollutant Sources
There are many sources of indoor air pollution in any home. These include
combustion sources, such as oil, gas, kerosene, coal, wood and tobacco
products building materials and furnishings, asbestos-containing insulation, wet
or damp carpet, furniture made of pressed wood products, products for
household cleaning and maintenance, personal care or hobbies central heating,
cooling in humidification devices, radon, pesticides and outdoor air pollution.
Some sources such as building materials, furnishings and household
products like fresheners, release pollutants more or less continuously. Other
sources related to activities carried out in the home, release pollutants
intermittently. These include smoking the use of unvented or malfunctioning
stoves, furnaces, space heaters, the use of solvent in cleaning and hobby
activities and the use of cleaning products and pesticides in housekeeping.
a) Radon
The most common source of indoor radon is uranium in the soil or rock
from which homes are built. As uranium naturally breaks down, it releases radon
gas which is colorless, odorless, radioactive gas. This gas enters homes through
dirt on floors, Cracks in concrete walls and floors, flow drains and sumps. Any
home may have a radon problem. This means new and old homes, well-sealed
and drafty homes and homes with or without basements will have radon problem.
Sometimes radon enters the home through well water. In a small number of
homes, the building materials can give off radon. The predominant health effect
associated with exposure to elevated levels of radon is lung cancer. Smoking
increase the risk of lung cancer in homes already having high radon levels.
Environment Protection Agency (EPA) estimates that radon causes about 14,000
death per years in U.S.A. only.
b) Environmental Tobacco Smoke (ETS)
It is the mixture of smoke that comes from the burning end of a cigarette,
pipe or cigar and smoke exhaled by the smoker. It is a complex mixture of over
4000 compounds, more than 40 of which are known to cause cancer in humans
or animals. According to EPA, ETS is responsible for approximately 3,000 lung
cancer deaths each year in non-smoking adults and impairs the respiratory
health of hundreds of thousands of children. Infants and young children whose
parents smoke in their presence are at increased risk of lower respiratory tract
infections (pneumonic and bronchitis) and are more likely to have symptoms of
respiratory irritation like cough, excess phlegm and wheeze.
c) Biological Environments
Biological environments include bacteria, molds, mildew viruses, house
dust mites, cockroaches and pollen grains. Pollens originate from plants, viruses
are transmitted by people and animals and bacteria are carried by people,
animals, soil and plant debris. Household pets are sources of saliva and animal
dander. The protein in urine from rats and mice is a potent allergen.
Contaminated central air conditioning systems can become breeding grounds for
mold, mildew and sources of other biological contaminants.
By controlling the relative humidity level in a home, the growth of some
sources of biological environment can be minimized. A relative humidity of 30-
50% is generally recommended for homes. Standing water, water damaged
materials or wet surfaces also serve as a breeding ground for mold, mildews,
bacteria and insects. House dust mites the source of one of the most powerful
biological allergens grow in damp, warm environments.
Some biological contaminants trigger allergic reactions, including
hypersensitivity pneumonitis, allergies and some types of asthma. Infectious
illnesses, such as influenza, measles and chickenpox are transmitted through the
air. Molds and mildews release disease causing toxins. Biological pollutants
include sneezing, watery eyes, coughing, shortness of breath, dizziness,
lethargy, fever and digestive problems.
d) Stove heaters, fireplaces and chimneys
In addition to environmental tobacco smoke, other sources of combustion
products are unvented kerosene and gas space heaters, woodstoves, fireplaces
and gas stoves. The major pollutants released are carbon monoxide (CO),
nitrogen dioxide (NO2) particles and acid aerosols. CO is a colorless, odorless
gas that interferes with the delivery of O2 throughout the body. At high
concentration, it can cause unconsciousness and death. Lower concentration
can cause a range of symptoms from headaches, dizziness, weakness, nausea,
confusion, and disorientation, fatigue in healthy people and episodes of
increased chest pain in people with chronic heart disease. Fetuses, infants,
elderly people, and people with anemia or with a history of heart or respiratory
disease can be especially sensitive to co-exposures.
NO2 is a colorless, odorless gas that irritates the mucous membranes in
the eye, nose and throat and causes shortness of breath after exposure to high
concentration.
Particles are released when fuels are incompletely burnt which can lodge
in the lungs and irritate or damage lung tissue. A number of pollutants including
radon and benzo-α-pyrene, both of which can cause cancer, attach to small
particle that are inhaled and then carried deep into the lung.
e) House-hold Products
Organic chemicals are widely used as ingredients in household products.
Paints, varnishes and wax contain organic solvents, as many cleaning,
disinfecting cosmetic, degreasing and tubby products. Eye and respiratory tract
irritation, headache, dizziness, visual disorders and memory impairment are
among the immediate symptoms that some people have experienced soon after
exposure to some organics.
Paint strippers, adhesive remarks and aerosol spray paints contain
methylene chloride which is carcinogenic in animals. Laboratory studies showed
that perchloroethylene, the chemical widely used in dry cleaning is causing
cancer in animals. Benzene, a known human carcinogen has its source in
tobacco smoke, stoved fuels and paint supplies and automobile emissions in
attached garages.
Formaldehyde is an important chemical used widely by industries to
manufacture building materials and numerous household products. It is also a
by-product of combustion and certain other natural processes. It is used to add
permanent press qualities to clothing and draperies, as a component of gases
and adhesives and as a preservative in some paints and coating products. In
houses, the most significant source of formaldehyde are adhesives containing
urea formaldehyde (UF) resins and phenol formaldehyde (PF) resins used in
pressed wood products. Besides this, the other sources are building materials,
smoking, household products and use of unvented, fuel burning appliance like
gas stoves or kerosene space heaters. Formaldehyde, a colorless pungent smell
of gas, can cause watery eyes, burning sensations in the eyes and throat,
nausea and difficulty in breathing in some humans and carcinogenic in animals.
In homes, insecticides and disinfectants are often used to control insects,
termites, rodents, microbes, fungi and contaminated soil or dust that floats or its
trapped in from outside. They are sold as spray, liquids, sticks, powders, crystals,
balls and foggers. Exposure to high levels of pesticides produced symptoms like
headaches, dizziness, muscle weakness, nausea, damage to liver and central
nervous system as well as an increased risk of cancer.
f) Lead
Lead has long been recognized as a harmful environmental pollutant.
Humans are exposed to lead through air, drinking water, lead contaminated soil,
deteriorating paint and dust. Airborne lead enters the body through inhalation
swallowing of lead particles or dust.
High concentration of airborne lead particles in houses can also result
from outdoor sources, including contaminated soil trapped inside and use of lead
in certain indoor activities such as soldering and stained glass making.
Lead affects practically all systems within the body. At high levels it can
cause convulsions, coma and even death. Lower levels of lead can adversely
affect the brain, central nervous system, blood cells and kidneys. The effects of
lead exposure on fetuses and young children can also be severed and may lead
to delay physical and mental development, lower IQ level, shortened attention
spans and increased behavioral problems. Fetuses, infants and children are
more vulnerable to lead exposure than adults since lead is more easily absorbed
into growing bodies and the tissues of small children are more sensitive to the
damaging effects of lead.
g) Asbestos
Asbestos is mineral fiber commonly used in a variety of insulating and
building construction materials. Today, asbestos is most commonly found in older
houses, in pipes and furnace insulation materials, millboard, textured paints and
floor tiles.
The most dangerous asbestos fibers are too small to be visible. After
inhalation they can remain and accumulate in the lungs. Asbestos can cause
lung cancer, mesothelioma (a cancer of the chest and abdominal linings) and
asbestosis (irreversible lung scarring that can be fatal).
2.5.2 Precautions/Preventive measures for Indoor Pollution
i) Scientific evidence indicates that smoking combined with radon is especial
source causing health risk. Stop smoking and lower radon level to reduce
lung cancer risk.
ii) Open windows or use exhausts fans, Ventilation, a common method of
reducing exposure to indoor. Air pollutants will also reduce but not
eliminate exposure to environmental tobacco smoke.
iii) Do not smoke if children are present, particularly infants.
iv) Use thoroughly clean carpets.
v) Keeping the house clean. House dust mites, pollens and other allergy
causing agents can be reduced, although not eliminated through regular
cleaning.
vi) Install and use exhaust fans or chimney over gas cooking stoves and keep
the burners properly adjusted.
vii) Follow label instruction carefully in case of household chemicals.
viii) Throw away partially full containers of old or unneeded chemicals safely.
ix) Ventilate the area well after pesticide use. Use non-chemical methods of
pest control when possible.
x) Limit exposure to repellents to a minimum.
xi) Keep areas where children play as dust free and clean as possible.
2.6 ELECTROMAGNETIC POLLUTION
Electromagnetic radiation consists of electric fields produced by voltages
and magnetic fields produced by electrical currents. Although electrical field can
be shielded by conducting materials, magnetic fields can penetrate almost
anything that stands in their way, including the human body. Power lines give off
extra low frequency (ELF) electric and magnetic fields whose waves vibrate back
and forth 60 times per second. The magnetic fields can be particularly strong in
houses that are close to high voltage transmission lines and to the ordinary high
current distribution lines. We are inundated with radiation from television, radio,
microwaves, cellular phones, heaters, dryers, clocks, electric appliances and the
wiring in the walls. In some locations additional frequencies are generated by
video display terminals (VDT, computer monitors, televisions, etc) on the top of
electrically heated water beds and under electric blankets and heating pots.
Because the magnetic fields from these sources vibrate back and forth at 60
times per second, the same to and fro movement will occur in brain and body
molecules of exposed human beings.
Recent research indicates that regular chronic exposure to
electromagnetic fields (EMF) can have adverse impacts on our health and well-
being and on biological systems in the environment. Electromagnetic radiation
can affect physiology and create chronic conditions producing symptoms like
fatigue, headache and vision problem, short term memory loss, sleep
disturbances, confusion, ringing in the ears and irritability. Electromagnetic
radiation have been found to cause an increase incidence of leukemia,
lymphoma, brain cancer and breast cancer (in women). Many of workers suspect
that extra low frequency radiation impairs the ability of the T-lymphocyte cells,
the infection fighting “soldiers” of the immune system to combat cancer. The
central nerves system, cellular process, the immune system and the human
psychic infrastructure all are the most vulnerable to electromagnetic radiation.
To protect ourselves
1. Avoid use of electric blankets, heating pads, heated waterbeds.
2. Keep the dial face electric clocks at least three feet away from bed, desk
or chair.
3. Pressure must be brought on local, state and federal officials to measure
electromagnetic radiation near power lines and substations. In areas
where the radiation is unacceptably high, wires will have to be re-routed,
buried and shifting of substations.
2.7 SUMMARY
Nuclear reactors are also major source of radioactive pollution, whereas
Hiroshima and Chernobyl are major nuclear disasters that effected huge
population. Unusable heat from human activity disrupts ecosystems in the natural
environment. Thermal pollution is another type of pollution caused by the heat
released in coolant waters, which affects physical, chemical and biological
properties of water. The central pollution control Board in India has specified the
standards for thermal discharge from thermal power plants. In the last several
years, a scientific evidences has clearly indicated that air within house and other
building can be more seriously polluted than the outside air, people spend
approx. 90% of their times indoors. Our indoor environment is also polluted by
several sources like, radon, microorganisms, tobacco smoke, smoke from
kitchen or fire-place, paints, varnish, wax etc. Household products release
formaldehyde, benzene etc. which also affect the health. These days we are
using several electronic gadgets like, TV, clocks, microwave, cellular phones,
vide etc. which release are electromagnetic pollution. This type of pollution can
affect our physiology, nervous system and immune system.
2.8 KEYWORDS
Thermal Pollution: It can be defined as an accumulation of unusable heat from
human activities that disrupts natural ecosystems in the natural environment.
Nuclear Fission: It is a collision of a certain type of heavy nucleus with a
neutron results in the splitting of the nucleus into two smaller sized fragments
and three neutrons. A huge amount of energy is released in this process
(E=mc2).
Nuclear fusion: The combination of two very light nuclei to form one combined
nucleus.
Electromagnetic radiation: It consists of electric fields produced by voltages
and magnetic fields produced by electrical currents.
2.9 SELF ASSESSMENT QUESTIONS
1. What are different types of indoor air pollutants?
2. What short of pollution is associated with electric and magnetic fields
described along with health effect caused by it.
3. Write in brief causes and effects of thermal pollution.
4. Write down the preventive measures to be taken for indoor pollution.
5. Enumerate major nuclear disasters of historic importance.
6. What are the sources of nuclear waste?
2.10 SUGGESTED READINGS:
Jackson, A.R.W. and Jackson, J.M. (2004). Environment Science, the
natural environment and human impact by Addison Wesley Longman
Limited, England.
Goyel, P.K. (2001). Water pollution causes, effects and control, New Age
International (P) Publishers, Delhi.
Fellengerg, G. (2000). Radioactivity in “The Chemistry of Pollution”, John
Wiley & Sons Ltd., New York.
Parker, S.P. and Cobitt, R.A. (1993). Radiation biology “Mc Graw Hill
Encyclopedia of Environment Science & Energy” 3rd Edition (Eds.). Mc
Graw Hill, Inc. New York.
Spiro, T.G. and Stigliani, W.M. (2006). Chemistry of Environment 2nd
Edition. Prentice Hall of India Pvt. Ltd., New Delhi.
Miller, G.T. (2004). Environment Science, Thomson Press, U.K.
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