Environmental Chemistry MANIK

Environmental Chemistry
Arranged By: Md. Imran Nur Manik;B.Pharm.;M.Pharm.;(Thesis) RU Page 1
Environment:
The surroundings, conditions or influences that affect the human life or other organisms
is known as environment.
Environmental chemistry:
Environmental chemistry is a multi-disciplinary subject/science involving chemistry,
physics, life science, agriculture, medical science, public health, sanitary engineering etc.
In simpler terms, it is the science of chemical phenomena in the environment.
Components of the environment: There are two main components.
1) Abiotic: The distribution of all non-living components is known as abiotic components.
Soil, air, climate, pH are examples of abiotic components.
2) Biotic: The distribution of living organisms in a particular environment is known as
biotic components. All living things are biotic component of the environment.
Segments of environment:
1. Atmosphere
2. Hydrosphere
3. Lithosphere
4. Biosphere
a) Ecosystem
b) Different natural cycles
1. Atmosphere:
The atmosphere is the protective blanket of gasses surrounding the earth, which sustains life
on the earth and saves it from hostile environment of outer space.
It absorbs most of the cosmic rays from outer space and a major portion of electromagnetic
radiation from the sun. The atmosphere is about 500 Km deep. Its components can be divided
into three groups-
a) Major components – N2, O2, Water vapour
b) Minor components – Ar, CO2,
c) Trace components – Ne, He, CH4, Kr, N2O, H2, Xe, SO2, O3, NH3, CO, NO2, I2
The atmosphere is polluted by natural activities such as volcanic eruption, vegetation decay
etc. and human activities such as release of industrial waste, automobile gases etc.
2. Hydrosphere:
The hydrosphere includes all types of water resources like oceans, seas, rivers, lakes, streams,
reservoirs, glaciers, polar icecaps and ground water.
Ocean & seas (salt water) → 97% of earth’s water supply
Polar icecaps and glaciers → 2% of earth’s water supply
Surface and ground water (fresh water) → 1% of earth’s water supply

Thus only 1% of earth’s water supply is available for human consumption. Surface water gets
contaminated by various man-made wastes. Industrial waste is most notable.
That is why all industries should have Effluent Treatment Plant (ETP).
3. Lithosphere:
This is the outer mantle of the solid earth consisting of minerals occurring in the earth’s crust
and the soil. The soil is the most important part of the lithosphere.
This segment is polluted by using fertilizers, deforestation etc.
4. Biosphere:
This is the segment of the environment that consists of living organisms (biological world) and
their relationship with other segments.
5. Anthrosphere:
Anthrosphere may be defined as man-made part of the environment i.e. part of the
environment made or modified by human activities.
Few important definitions:
Ecosystem:
Ecosystem may be defined as the smaller unit of the biosphere. An ecosystem consists of plants,
animals and microorganisms which live in a definite zone along with the physical factors such
as soil, water and air.
The biosphere consists of all four segments and exists in the zone 600m above and 10000m
below the sea level. It is very large and complex hence the division into smaller units.
Pollutant:
A pollutant is a substance that is normally found in nature but has detrimental effect on the
environment and human being when it is present in nature in greater amount than its natural
abundance due to human activities and natural causes.
For example, Pb, Hg, Cd, CO2 are normally present in nature but considered pollutant when
they are present in abnormal quantities.
Contaminant:
A contaminant is a material that normally doesn’t occur in nature but introduced to the
environment by human activities and affects the composition of the environment.
A contaminant is a pollutant when it exerts its detrimental effects.
For example Cl2 doesn’t normally occur in nature, thus it is a contaminant. When a contaminant
exerts its detrimental effects it acts as pollutant.
Photochemical oxidant:
When oxides of nitrogen (namely NO and NO2) and hydrocarbons come together in the
presence of sunlight a set of reaction is initiated and a number of pollutants are produced.
These are called photochemical oxidants due their oxidant properties.
O3 is the most abundant photochemical oxidant. It may be noted that photochemical smog is
oxidizing smog whereas smog with SO2 is reducing smog.

Natural cycles:
Natural cycles are continuous processes which help in exchange of a specific component (like
water, oxygen, nitrogen etc.) between the different segments of the environment (the
atmosphere, the land, sea, living plants and animals).
Examples of natural cycles are the hydrological cycle, oxygen cycle, nitrogen cycle etc.
Atmosphere
Different regions of atmosphere:
The atmosphere may be broadly divided into four regions as shown below. It extends
upto 500km with temperature varying from -92⁰C to 1200⁰C.
Troposphere:
The troposphere contains 70% of the mass of the atmosphere. It is spread upto 11km
above the sea level but it may vary depending on factors like temperature, terrestrial surface
etc. The temperature ranges from 15⁰C to -56⁰C. The temperature falls uniformly with
increasing altitude. The coldest portion of troposphere is called tropopause. This marks
transition from negative to positive lapse rates.
Stratosphere:
Stratosphere has a positive lapse rate i.e. the temperature increase with increase in
altitude. The temperature ranges from -56⁰C to -2⁰C at the upper limit of the region.
This positive lapse rate is due to O3 present in the stratosphere which absorbs UV radiation.
Mesosphere:
The mesosphere is located in 50km to 85km above the sea level. This region shows
negative lapse rate i.e. temperature falls with increase of altitude. This effect is due to low

levels (or absence) of UV absorbing species, particularly O3. The temperature ranges from -2⁰C
in the lower limit to -92⁰C at the upper limit.
Thermosphere:
In this region the temperature rises once again with the altitude, giving a positive lapse
rate. Here, atmospheric gases particularly O2 and NO undergo ionization after absorbing solar
radiation in the far-UV region.
Major regions of the atmosphere
Region Altitude range (km) Temperature range (⁰C) Important chemical species
Troposphere 0-11 15 to -56 N2, O2, CO2, H2O
Stratosphere 11-50 -56 to -2 O3
Mesosphere 50-85 -2 to -92 O2+, NO+
Thermosphere 85-500 -92 to 1200 O2+, O+, NO+
Significance of ppm, ppb and ppt:
Most toxins aren’t present in their pure form rather suspended in a larger substance
like air, water, food etc. Usually they are present in a very small quantity and may have toxic
effect in a very small dose.
Thus knowing the concentration is very important. Here ppm (Parts Per Million), ppb
(Parts Per Billion), ppt (Parts Per Trillion) can serve as concentration measures.
These can be thought of as analogous to percentage- Just as 1 percent is one part of one
hundred; 1 ppm is one part of one million. Concentrations of toxins are given in this form to
1. Obtain consistent value.
2. Make consistent comparison among many substances that undergo toxicity testing.
For example if a scientist want to evaluate the concentration of a chemical in Lake Okeechobee.
He can take a small sample and the concentration of the chemical in the sample can be
calculated. This conc. can be put in relative term to lake’s total volume by using ppm.
If the conc. is 1ppm then this indicates one ounce of chemical in 1 million ounces (7812.5
gallons) of the lake’s water.
Mathematical significances of ppm are
1. A milligram is 1/1000 of a gram and a gram is 1/1000 of a kilogram. Thus a miligram is
1/1000000 of a kilogram. So we can say that one ppm is equivalent to one mg/kg.
A common toxicological measure LD50 is often measured in mg/kg of body mass.
2. Since 1 litre of water weighs 1kg, therefore 1ppm is also equal to one mg/litre.
3. It is unit less.
Below the ratio of ppm, ppb, and ppt is given with analogical measures.
Unit Measurement Ratio
1 mg/kg 1 ppm (parts per million) 1/1,000,000
1 µg/kg 1 ppb (parts per billion) 1/1,000,000,000
1 ng/kg 1 ppt (parts per trillion) 1/1,000,000,000,000
Air pollution:

Air is hardly found clean rather hazardous substances (natural and man-made
pollutants) are suspended in the air.
These pollutants disturb the dynamic equilibria of the atmosphere and exert detrimental
effects on the environment. This situation is called air pollution.
These pollutants are of two types
1. Natural pollutants which are-
Gases: CO2, SO2, H2S etc.
These are continuously released into the atmosphere through natural activities such as
- Volcanic activities
- Vegetation decay
- Forest fires etc.
Tiny particles of solid/liquid: They are released into air through winds, volcanic explosion etc.
2. Man-made pollutants such as
Gases (CO, NOx, SOx), mists and particulates, aerosols etc. They are results of chemical and
biological processes used by man.
These pollutants hardly exist beyond 2000 ft above ground level (exception CFC).
Classification of the pollutants:
There are two types of pollutants to be considered-
Primary pollutant:
These pollutants are directly emitted into the air from a process such as volcanic
eruption. CO, NOx, SOx, CnH2n+x, Particulate matter etc. are primary pollutants.
Secondary pollutants:
These pollutants aren’t directly emitted into the air rather they are formed in the air
from the reactions of primary pollutants. O3 is an example of secondary pollutant which is
formed from VOC (Volatile Organic Carbon) containing compounds.
Carbon monoxide:
Properties:
It is a colorless, odorless, tasteless gas which is insoluble in water and 96.5% as heavy as air.
Source:
Natural processes → They contribute in a small measure. These are -
- Volcanic action
- Natural gas emission
- Electrical discharge during storms
- Seed germination
- Marsh gas production etc.
Human activities → This makes significant contribution. Such activities are-
i. Transportation (64%)
- Motor vehicles (59.2%)
- Aircrafts (2.4%)
- Railroads (0.1%)

ii. Miscellaneous sources (16.9)
- Forest fires (7.2%)
- Agricultural burning (8.3%)
iii. Industrial processes (9.6%)
- iron and steel industries
- petroleum and paper industries
Formation of CO:The basic chemical reactions yielding CO are-
1. Incomplete combustion of fuel or carbon containing compounds.
22
2
22
22
COOCO
COOC


2. Reaction between CO2 and carbon-containing materials at elevated temperatures in
industrial processes e.g. blast furnaces.
COCCO 22 
3. Dissociation of CO2 at high temperatures.
2CO ⇌ OCO 
Human exposure: Humans are exposed to CO by means of-
1. Surrounding ambient environment
2. Accidental intoxication
3. Environmental problems in the house
4. Occupational exposure (for example, workers of blast furnaces)
5. Cigarette smoking
Traffic policemen on duty in busy street crossings, taxi and bus drivers and workers of heavy
industries are most exposed to CO.
Physiological effects: Normally in our body, hemoglobin picks up O2 in the lungs and forms a
complex called oxyhemoglobin.
22 HbOOHb 
Once hemoglobin reaches the body tissues, HbO2 breaks down to release the O2.
22 OHbHbO 
CO is toxic as it interferes with the normal O2 transport in the blood. CO attacks
hemoglobin and displaces O2 to form carboxyhemoglobin.
HbCOCOHb 
The chemical affinity of CO for hemoglobin is 200 times greater than that of O2. So in the
presence of CO, HbO2 readily releases its O2 to absorb CO.
22 OHbCOCOHbO 
Since the binding sites of each of the polypeptide chains in hemoglobin molecule can’t
be occupied by O2 and CO at the same time, it is apparent that CO can tie up a substantial
quantity of hemoglobin. So, hemoglobin is unable to transport O2.
Carboxyhemoglobin in different concentrations can have following effects-
HbCO (20%) → Mild headache
HbCO (40%) → Mental confusion
HbCO (60%) → Convulsion
HbCO (70%) → Death

Maternal CO poisoning can lead to fetal death.
Effects of continuous exposure to various levels of CO
CO level (ppm) Conversion of
HBO2 to HbCO
Effects on human
10 2 Impairment of judgment and visual perception
100 15 Headache, dizziness, weariness.
250 32 Loss of consciousness
750 60 Death after several hours
1000 66 Rapid death
Control of CO pollution:
The transportation sources are responsible for 74% of all CO emissions. Hence the
efforts for controlling CO pollution are mainly directed towards automobiles. For this purpose
following actions can be taken-
1. Modification of internal combustion engine
2. Development of substitute fuels
3. Development of pollution free power sources.
4. Development of exhaust system.
SOx
Among the sulphur oxides the most concerning oxides are SO2 and SO3. SO2 is present in higher
concentration.
Source of SOx:
Natural processes (67%) → This is distributed evenly all over the globe. e.g.
- Volcanic activities
Man-made sources (33%) → Localized in the urban areas.
- Fuel combustion (coal) (74%)
- Industries (22%)
- Transportation (2%)
Among the man-made sources coal-fired power stations are the major culprit followed by
industrial plants.
SO2:
Properties:
It is a colorless gas with pungent odor. It has a solubility of 11.39gm/100ml water.
Formation of SO2:
2OS  ⇌ 2SO
222 OSO  ⇌ 32SO
Under the humid conditions of the atmosphere, SO3 reacts with water vapour to form droplets
of H2SO4.
4223 SOHOHSO 
Sulphide ores also yields SO2 when burned to extract metals.

22
23222
2422
2232
82114
3)(
SOZnOOZnS
SOSFeOFeS
SOFeSOOPyriteFeS



Sulphide ores of Cu, Pb etc. also yield SO2.
SO2 poisoning:
i) SO2 aerosols (smaller than 2µ) → They easily penetrate the innermost passages of
the lungs of humans and cause severe respiratory troubles.
ii) SO2 (0.25-0.50 ppm) → Causes bronchitis and asthma.
iii) SO2 (0.15 ppm) → Causes respiratory problems.
iv) H2SO4 → Lower the pH, so the functions of many enzymes are impaired. Also causes
acid rain.
v) SO2 is deemed to be a serious air pollutant because of the way it affects the aged
population, especially those who suffer from respiratory and cardiovascular
diseases.
vi) The most widespread disaster of SO2 occurs when it is accompanied by smoke. For
example, in 1952, 4000 people died in London due smog conditions which caused
bronchitis, pneumonia etc.
vii)Exposure of high levels of SO2 causes destruction of leaf tissue in plants.
Control of SOx pollution:
1. Use of low-sulphur fuel
2. Substitution of other energy sources for fuel combustion.
3. Removal of SOx from fuel gases.
NOx (oxides of nitrogen):
The oxides of nitrogen are N2O, NO, NO2, N2O3, N2O4 and N2O5. Among them on the basis of
amount exerted NO and NO2 are considered major pollutants in the atmosphere.
Sources:
1. Natural bacterial action produces about 5x108 tonnes (metric tons) of NOx (mainly NO)
per year all over the world. This is uniformly distributed globally.
2. Man-made sources like combustion of fuel, oil, natural gas, power plants, industries,
domestic and commercial heating plants and gasoline produces 5x107 tonnes of NOx
every year. But distribution of NOx varies with urban and rural areas. For example, in
USA and Canada, conc. of NOx in rural areas is respectively 2 ppb and 4 ppb. But in
urban areas conc. can go up to 500 ppb.
Formation:
The basic reactions leading to the formation of NO and NO2 are
The first reaction is favored in high temperature (1210-1763⁰C). The second reaction is
also favored in temperature like 1100⁰C. The second reaction also occurs in photolytic
conditions.

Properties of NO and NO2:
NO is a colorless, odorless gas. NO2 has reddish-brown color and pungent suffocating
odor.
Harmful effects:
1. NO forms bonds with hemoglobin and reduces O2 transport efficiency. But since it is
present in lower amount than CO effect is much less.
2. Exposure to 50-100 ppm of NO2 for 1 hr can lead to inflammation in lung tissue
lasting 6-8 weeks.
3. Exposure of air containing 150-200 ppm of NO2 leads to bronchiolitis fibrosa
obligerans which may be fatal within 3-5 weeks.
4. Exposure of air containing 500 ppm or more of NO2 for 2-10 days leads to death.
5. Various types of NOx specially NO2 can react with hydrocarbons in the presence of
sunlight and produce photochemical smog.
6. NO and NO2 react with water vapour present in the atmosphere and produce nitric
acid causing acid rain.
Control of NOx:
The oxides produced naturally can’t be controlled but man-made sources can be controlled.
Power plants emit about 50-1000 ppm of NOx. Such emission can be reduced by 90% by taking
two procedures for combustion of fuel-
1. The fuel can be fired at relatively high temperature with a sub-optimal amount of air. In
that case yield of NO will be reduced in the absence of excess air.
2. Fuel burnout is completed at a relatively low temperature in excess air. Under this
condition NO isn’t formed.
Photochemical smog:
Photochemical smog is an oxidizing smog having a high concentration of oxidants
formed by the reaction of NO, NO2 and hydrocarbons in the presence of sunlight. This smog is
characterized by brown, hazy fumes which irritates the eyes and lungs and have various
effects.
smogcalPhotochemiSunlightNOnsHydrocarbo x 
Mechanism of photochemical smog formation:
i. Reactive hydrocarbons (containing C=C bond, unsaturated) from auto exhaust interact
with O3 to form a hydrocarbon free radical 2RCH
ii. 2RCH rapidly reacts with O2 to form free radical 22ORCH

iii. 22ORCH reacts with NO to produce NO2 and the free radical ORCH 2
iv. ORCH 2 next interacts with O2 to yield a stable aldehyde, RCHO and hydroperoxyl
radical 2HO
v. 2HO then reacts with another molecule of NO to give NO2 and HO
vi. HO is extremely reactive and rapidly reacts with a stable hydrocarbon RCH3 to yield
H2O and regenerate 2RCH , thereby completing the cycle. This goes on and on as a
chain reaction. One complete cycle yields two molecules of NO2, one molecule of RCHO
and regenerates the free radical 2RCH to start all over again. Very soon there is a
rapid build-up of smog products.
Another incident also occurs during this cycle.
The aldehyde produced in the previous reaction initiate another route by interaction
with the HO radical, leading to the formation of an acyl radical . This radical reacts
with O2 to produce 2RCOO and finally PAN (PeroxyAcyl Nitrate) is produced by reaction
with NO2.
Toxic effects of smog forming products:
1. Eye irritation which is caused by HCHO, PAN, PBzN (Peroxy Benzoil Nitrate) and
acroline present in the smog.
2. Chest constriction
3. Irritation of mucous membrane
4. Cracking of rubber products

5. Damage to vegetation.
Important products of smog with conc.:
i. O3 → 90%
ii. NOx → 9% (about 10%, Ming HO Yu)
iii. PAN → 0.6%
iv. Aldehyde (and Ketones)
v. Alkyl nitrates
Sequence of photochemical smog formation reaction:
1. NO is formed from combustion of fuel and other man-made sources.
NOON 22 2
2. The NO is converted to NO2 by oxidation.
22 NOONO 22 
3. In the presence of sunlight NO2 photolyzes to give atomic oxygen.
ONONO2  h
4. The atomic oxygen forms ozone with the atmospheric O2.
mm  32 OOO
hν represents energy from the sunlight and m represents NO or NO2. The ozone formed
can convert NO to NO2.
223 ONONOO 
Once the reactions reach a steady state, there is no net change in their concentrations
over time.
Atmospheric nitrogen photolytic cycle:
Emission
of NO NO NO2
Atomic
oxygen
(O)
O2
O3
Sun
Fig: N2 photolytic cycle
The above diagram explains the sequence of smog formation in the presence of sunlight
on a typical day.
In the morning, during rush hour the conc. of NO rises due to emission from the traffic.
As the day progresses NO is converted to NO2. With the intensity of the sunlight increasing NO2
forms atomic oxygen which forms O3 with atmospheric O2. O3 is so effective with NO that it
doesn’t allow to raise the NO conc. throughout the rest of the day regardless of new emission of
NO.
Concentration profile of smog ingredients with the time of day:
Photochemical smog shows characteristic variation of smog content concentrations
with the time of day as the figure below.

The hydrocarbon level is maximum during the early morning (traffic rush hour). During
rush hour NO conc. has the peak value and hydrocarbon conc. starts to fall. Then the conc. of
NO falls with the presence of intense sunlight and NO2 conc. increases. Towards the evening the
concentration of NO2 decreases and conc. of O3 and other ingredients increase.
Being one of the largest cities in the world, Los Angeles and Mexico City shows
photochemical smog formation. There is type of concentration profile is observed. The above is
a typical concentration profile in Los Angeles.
Biochemical effects of O3 and PAN:
1. PAN causes irritation of eyes and respiratory tract of human beings.
2. Exposure to 50 ppm of O3 will lead to mortality due to pulmonary edema.
3. Low levels of O3 may cause damage to lung capillaries.
4. O3 and PAN are oxidants which attack sulphur containing amino acids specially cysteine
thus inactivating enzymes like isocitric dehydrogenase, glucose 6-phosphate
dehydrogenase etc.
Particulates
Semi solid particles and liquid droplets which are about 0.0002-500µ in size with
lifetime of few seconds to several months are collectively called particulates. They are present
in the atmosphere in fairly large numbers and sometimes pose serious air pollution.
Particulates can be inorganic, organic or fly-ash etc.
Pollutant source Weight of pollutant (million tones/year) Total weight
produced by
each source
CO NOx HC SO2 Particulates
<20µ
Particulates
>3µ
Transportation 69.7 10.1 10.8 0.8 1.2 1.0 93.6
Fuel combustion 1.2 11.8 1.4 21.9 4.6 1.3 42.2
Industrial processes 7.8 0.7 9.4 4.1 6.3 2.7 31.0
Solid-waste disposal 7.8 0.6 1.6 0.1 1.1 - 11.2
miscellaneous 8.5 0.4 6.3 0.1 1.3 - 16.6
Total weight of each
pollutant produced
95.0 23.6 29.5 27.0 19.5 194.6
Global temperature and greenhouse effect:

From the Stephan-Boltzmann equation planet earth’s temperature was calculated to be
279 K (~ 6⁰C).
But since the earth is not a black body the temperature is even less. The earth has an
albedo of 0.3. Taking this into consideration the earth’s temperature according to Stephan-
Boltzmann equation is 255 K (~ ─18⁰C).
[Albedo: Albedo is the reflecting power of a surface. It is defined as the ratio of reflected
radiation from the surface and incident radiation upon the surface.
It is actually the fraction of radiation emitted by the object. A black body has an albedo of zero
whereas a perfectly white surface has an albedo of 1.]
But the earth is not so cold. It was observed that the value obtained from the above
equation was less because it didn’t consider the greenhouse effect. Due to this effect the long
wave radiation is partially trapped in the atmosphere instead of radiating away because of the
green house gases. Thus the true temperature of the planet is 288 K.
This can be explained better using following graphical representations-
The sun can be represented as a black body with the temperature around 6000 K on the
surface. As seen on the graph above its radiation spectrum gives peak at 0.5µ. This means that

maximum radiation from the sun occurs at the wave length of 0.5µ. On the other hand earth
having surface temperature of approx. 290 K has a peak wavelength of 10.1µ.
From the graph we can see that basically all the radiations emitted by the sun have
wave lengths of less than 4µ (containing UV, IR etc. radiations) while all the radiations emitted
by the earth’s surface have wave lengths of greater than 4µ (thermal radiations). So solar
energy is of shorter wavelength while the energy radiated from the earth’s surface is of longer
wavelength.
Essentially all of the incoming solar radiation is absorbed by O2 and O3 of the
atmosphere in the stratosphere region shielding the earth’s surface from harmful UV radiation.
Most of the energy radiated by the earth is affected by a combination of radiatively active
gases, most important H2O vapor, CO2, N2O and CH4 as well as man-made CFC & O3.
Greenhouse effect
The concept of green house is based on an idea that it is just like a conventional house with a
glass covering where the glass covering is similar to the green house gases. These glasses can
easily transmit short wavelength solar energy into the green house but it is nearly opaque to
the longer wavelength radiation emitted by the green house. Thus radiation is trapped inside
the green house and responsible for the elevated temperature inside the green house.
Similarly the green house gases trap long wavelength energy emitted from the earth’s surface
heating the atmosphere leading to temperature elevation in the planet. This effect has made
this planet livable.
The following graphical representation may give better explanation-

If the earth didn’t already have green house effects its temperature would be 255 K (~ ─18⁰C).
From this we can quantify the magnitude of the green house effect.
etemperaturcalculatedetemperatursurfaceActualeffecthouseGreen 
C
CC
TT cs
0
00
33
)18(15



This phenomena heating up of earth’s surface due to trapping of radiation
emitted by the earth by green house gases is called green house effect.
Major Green house gases and their characteristics:
Gases Relative green house
efficiency
Current green house
conc.
Principle source of gas
CO2 1 57 Fossil, fuel burning,
deforestation
CFC 15000 (38000000) 25 Foam, aerosol, refrigerant,
solvents
CH4 25 12 Wetland, rice, livestock, fossil,
fuel
H2O 230 6 Fuel, fertilizer etc.
N2O 3800 4 Industries, transportation
Among these constituents CO2 and H2O are most prevalent as they strongly absorb IR radiation
and effectively block a large fraction of the earth’s emitted radiation.

Result of green houseeffect – global warming:The result of green house effect is global
warming which has following effects-
i. The polar ice caps will melt as the mean temperature rises. This would cause the sea
level to rise in all areas of world.
ii. A slight increase in the temperature can adversely affect the world food production as
the agricultural zones may be shifted. Some areas of the world may become better
suited to agriculture (50 years from now Midwest of Sahara is predicted to be cooler
and wetter) while other areas will be adversely affected.
iii. Extreme whether conditions may become prevalent. Some areas may become extremely
hot and some areas may become extremely cold. Also proper season may not appear at
proper time.
Causes of green house effect:It is concerned with the emission of green house gases.
i. CO2 emission: In carbon cycle CO2 is removed by two sinks (the medium or mechanism
associated with the removal of a long-lived pollutant)
a) Ocean
b) Vegetation
Thus deforestation has a great effect on the net increase in CO2 content. It is
occurring as a result of-
- Cutting down vegetation
- Reduction in soil organic matter (fertility) due to fuel extraction
In 1910 India had 40% forests. Now it has been reduced to 20%. Deforestation is
currently taking place in India at a rate of 50000 Km2/year. 40 hectors of forests are
destroyed per minute.
This phenomenon is also visible elsewhere. In china the deforestation rate has
increased from 5% to 13% from 1950 to 1980.
ii. Energy production: 50% of the green house gases are by products of energy production.
This includes fuel burning, coal fired power stations etc.

iii. Water logging rice fields releases CH4 (due to a swamp-like environment ideal for
methanogenesis).
iv. One mole of CFC is 1000(?) times more powerful than one mole of CO2 with respect to
GWP (global Warming Potential). The reason behind such efficiency is their long life
span and high absorbing power for IR radiation.
Control of green house effect:
i. Social foresting i.e. start of community based forests
ii. Adaptation to alternate energy sources like tidal power stations, wind power plants,
solar power systems etc.
iii. To avoid water logging rice fields for higher crop yield.
iv. Control of use of CFCs as refrigerants and propellants.
Acid rain
Deposition of dilute solutions of acids (mainly HNO3 and H2SO4 combined with HCl from HCl
emission) with rainfall in the earth termed as acid rain.
To meet the demand of the society industrialization has evolved. This is responsible for
burning of fossil fuel and release of chemical by products. Result of such activities is the release
of pollutants like CO2, N2O, NO, SO2 etc. when these compounds come in contact with
atmospheric water they are converted to H2CO3, HNO3 and H2SO4 and cause acid rain.
Most important of above mentioned pollutants are NOx as well as SO2 (which travels 100-200
km per hour in air).
Formation of acid rain:
- Large number of industries &
- Burning of fossil fuel

- Motor vehicles
- Natural phenomena etc. causes release of pollutants responsible for acid
rain and following reaction occurs-
Air contaminated with these chemicals is 200 times more acidic than normal. Infact the pH of
clear rain water is 5.6 whereas the pH of acidic rain water is 4.5 or lower.
Effects of acid rain:
i. Causes damage to buildings & sculptural materials of marbles, limestone, slate etc. as
the carbonates of these materials are replaced by sulphates via reaction similar to
following-
(gypsum)(limstone)
OHCOCaSOSOHCaCO 224423 
As a result these materials become weakened as soluble sulphates are formed.
For example in the above reaction CaSO4 is formed which is water soluble and easily
washes away leaving behind a pitted surface.
ii. Acid rain damages leaves of trees by inhibiting photosynthesis. Such incident occurred
in Sweden which retarded the growth of Swedish forests. Acidity also affects
germination of seeds and growth of trees leading varnishing of greenery and
destruction of forests.
iii. Green algae and many forms of bacteria which are essential for aquatic life are killed
due to acidity induced by acid rain. High acidity is also responsible for reproduction
failure, reduced growth and killing of fish.
iv. At low pH decomposition of organic material is lowered. This causes accumulation of
organic matter in lakes and increases the degree of water pollution.
v. Acidity increases the concentration of heavy metals (Pb, Cu, Zn, Mg) in water. These
chemicals are highly toxic and badly affect the quality of water.
Control of acid rain:
i. Since oxides of nitrogen and sulphur are responsible for acid rain their emission must
be controlled. For this purpose proper control equipments and stringent legislation
must be applied to industries and power plants.
ii. Periodic application of lime (CaO-base) to neutralize acidity is a solution it is expensive
and can’t be applied on a large scale.
Ozone layer depletion
In nature O3 is continuously formed and destroyed through photochemical interaction thus an
equilibrium in ozone concentration is present. This equilibrium is upset due to the discharge of
anthropogenic air pollution such as emission of CFC in the atmosphere.
Sources of CFC:
CFCs are a group of synthetic chemicals developed in 1930s. They are also known as
Freons. Example of CFCs are given below-
# Freon-11 → CCl3F
# Freon-12 → CCl2F2
# Freon-22 → CCl2HF
# Freon-114 → ClF2C-CClF2
# Freon-115 → ClF2C-CF3

These are used-
i. Mainly as refrigerants. Such use is due their low toxicity, non-inflammability and
least chemical reactivity.
ii. As propellants for dispersing aerosols
iii. As cleaning solvents
iv. For sterilizing surgical instruments
They can exist in the atmosphere for a century before finally breaking down.
Photochemistry of ozone layer depletion:
The chlorine, fluorine and sometimes bromine atoms of CFC are converted into their
reactive free radical form.
The chlorine and fluorine free radicals thus formed reacts freely with O3 disintegrating it into
O2 and nascent oxygen. Each atom of chlorine can destroy more than 100,000 molecules
converting to O2.
Although the natural concentration of ozone is maintained by balancing of ozone
forming and ozone destroying reactions, but due to man-made materials the abundance of
chlorine monoxide (ClO) rich air continue to rise. Thus ClO reacts with nascent oxygen & free
chlorine is formed and cycle continues.
The whole process can be illustrated as below

The advantages of ozone layer:
i. Ozone layer absorbs dangerous UV radiation having wavelength from 200-280 nm from
the sun and convert it into heat and energy.
ii. For this activity it causes rise in the temperature making the planet livable.
Effects of ozone hole:
i. 1% loss of ozone is responsible for 2% increase in diseases.
ii. The most significant effect on human being would be an increase in various skin cancers
like melanoma, basal and squamus cell carcinomas etc. The UV radiation also causes
leukemia and breast cancer.
iii. It may also increase the incidence of cataracts and photokeratitis as UV rays are easily
absorbed by the lens and the camera of eye.
iv. UV radiations may damage cell DNA and thus genetic structure of human, animal and
other organisms as well as vegetation may be altered.
v. UV radiations causes dilation of blood vessels making them carry more blood. Thus skin
becomes hot, swollen and red. This is called sun-burn.
vi. Melanin which plays a key role in the human immune system is destroyed by the UV
rays. So complexioned people are easily affected by skin diseases.
Control of O3 depletion:
80% of ozone depletion is due to the action of CFCs. Thus control of ozone layer
depletion is directed towards control of CFCs. For this purpose following may be considered-
i. Use of substitute chemicals → Nitshubishi electric and Tayo & Sayo have claimed to
develop an alternative to CFCs. These alternatives may be a solution. e.g. Freon-7 is
more suitable than Freon-12.
ii. Recently the US scientists have discovered bacteria which eat the main chemical
threatening the ozone layer. This may be a very important solution to control the
depletion.
iii. The Satellite Research Institute of Frankfurt, Germany has developed a method to use
hydrogen as a propellant in aerosol sprays. It is environmentally friendly and safe
alternative to CFCs.
Introduction:
Pollution caused by heavy metals is now a worldwide phenomenon. Among these Hg,
Pb, Cd, As, Cu, Zn and Fe are of most concern. A few of these are essential for human nutrition
as well. Other than that, all of these metals find irreplaceable need in human civilization.
Heavy metals
Definition:

Heavy metals are a group of metallic elements having high density and atomic mass that
exhibit certain chemical and electrical properties and have toxic effect on the environment.
It may be IUPAC consider the term “heavy metal” as a misinterpretation. They are
grouped usually based on the fact that they have detrimental effects on the environment.
A heavy metal should have density greater than 5g/cm3 and atomic mass greater than
calcium.
Sources of heavy metals: Heavy metals enter the environments through
 Mining
 Soil erosion
 Pesticides
 Disease control agents applied to plants
 Batteries and electronics
 Paints, inks, dyes, pottery glazes etc.
Industries particularly metal planting, oil production etc. are great sources for metals to enter
the environment in the forms that are toxic.
Heavy metals are toxic:
Heavy metals are toxic to the living organisms because they are soluble in water as ions
and as compounds. Thus they can be readily absorbed into animal or plant tissue. After
absorption these metals tend to bind to vital cellular components such as structural proteins,
enzymes and nucleic acids. Thus heavy metals interfere with their functioning. Thus they can
cause severe physiological and health problems.
Among the heavy metals mercury, lead, cadmium, arsenic are most toxic in our
environment. These are discussed in details below.
Lead
Characteristics:
Lead (Pb) is one of the metals well known by human from ancient times. It possesses
great importance in our civilization and it ubiquitous in our environment.
It is a malleable metal of low melting point and thus it can be given different shapes. It
also forms alloys with many other metals.
Use:
i. Products containing Pb are used in solders, glass, pottery glazes, rubber, plastics,
insecticides,
ii. Lead was formerly used in pipes intended to supply water. They still find this use.
iii. Until recently alkyl lead compounds were used as anti-knocking agents.
iv. Lead is used in lead acid batteries used in auto mobiles.
v. Several construction materials like roofing materials, gutter joints contain Pb.
vi. Leads form colored compounds which are used in paints.
Exposure to lead:
Airborne lead:
i. Industrial sources like power plants, incinerators, recycling units, refinery of scraps,
lead smelting etc.
ii. By lead storage batteries and cells used in automobiles.

iii. Dust release from house paints containing Pb compounds like PbCO3 (white paint) and
PbO (red paint).
iv. Smoke released from incomplete burning of lead compounds.
v. Until very recently the largest source for airborne lead was alkyl lead from gasoline.
Waterborne lead:
i. Piped water may contain lead.
ii. Water contamination with lead is possible if the reservoir is near lead emission areas
like busy highway.
Lead in soil:
i. Lead may be deposited on soil from polluted air.
ii. Previously areas near busy roadways were shown to be highly contaminated with lead
but that has been significantly decreased.
iii. Paints, insecticides are another source.
Lead in food:
i. Vegetation may be contaminated by lead when exposed to lead emission. Thus
vegetation growing near highways has been shown to accumulate lead. This vegetation
when ingested by animals or humans may cause lead toxicity.
ii. Pb may be ingested through use of Pb contaminated containers or Pb pottery glazes.
Lead toxicity:
Lead is a systemic poison and once it is absorbed into the circulation it is distributed
throughout the body and causes serious health problems. It is shown that adults absorb 10% of
ingested Pb whereas children absorb 50% of ingested Pb. Thus lead is a greater risk factor for
children. Inhaled lead is absorbed in even greater number.
It has a half life of 25 days in blood, 40 days in tissue and 25 years in bones. Thus the
bones act as reservoir of Pb and influence the exposure of the metal throughout the body. It
causes following effects-
i. It causes anemia by inhibiting hematopoiesis.
ii. Affect the kidney by inducing renal tubular dysfunction.
iii. Causes nausea, anorexia, severe abdominal cramps and constipation.
iv. It damages the lung and causes difficulty in breathing as bronchitis and pneumonia
is developed.
v. It also affects the CNS and may cause retardation and behavioral change. In some
cases convulsion, delirium etc. occurs. In severe cases this may end in death.
vi. Pb-acetate and Pb-phosphate are anticipated to be carcinogenic to human. Several
inorganic and organic lead compounds have been proven to be carcinogenic in
animals.
vii. Lead can cross placental barrier and may reach the fetus resulting in miscarriages,
abortions and stillbirths.
Biochemical effects of lead:
Inhibition of hematopoiesis:

As we can see that it inhibits heme synthesis. Thus it prevents hemoglobin synthesis
and ultimately RBC synthesis. [It inactivates ALA-dehydrogenase by interacting with cofactor
Zn2+]
Inactivation of enzymes:
As an electropositive metal Pb has a high affinity towards the sulfhydryl (SH) group.
Thus it binds with SH group of the enzyme protein and breaks the disulfide bridge as follows-

 2HRSPbSRPb2RSH 2
So enzymes depended upon SH group are inactivated. Again it may interact with
cofactors related to several enzymes and replace them.
Enzymes inhibited by lead include
i. Acetylcholine esterase
ii. Alkaline phosphatase
iii. ATPase
iv. Carbonic anhydrase
v. Cytochrome oxidase
vi. Some key enzymes involved in heme synthesis
vii. Adenyl cyclase

viii. Aminotransferase
ix. Adenyl cyclase
Effect on nuclei acid:
Pb can interact with nucleic acids to decrease or increase protein synthesis. It also may
reduce the ability of t-RNA to bind with ribosomal membrane.
Other functions:
It can compete with Ca2+ in several cases. Since Ca2+ is an important messenger this can
have disastrous effects. For example it can cause increased level of acetylcholine release across
synapses.
Arsenic
Characteristics:
Arsenic is a ubiquitous element present in various compounds throughout earth’s crust.
It has the oxidation state of -3, +3 & +5. The trivalent compounds are more soluble in water
compare to the pentavalent form and thus more hazardous.
Occurrence:
1. In the earth’s crust as
a. Arsenate (H3AsO4 and salts)
b. Arsenite (H3AsO3 and salts)
2. As methylation products by fungi, yeasts like
a. Monomethyl arsenate
b. Dimethyl arsinate
c. Gaseous derivatives of arsine
3. As methylation products by vertebrates and invertebrates e.g. organoarsenicals.
Use:
i. Arsenic compounds were preferred for the control of agricultural pests before the
use of organochlorine and organophosphates. Such compounds are lead arsenate
(PbHAsO4), white arsenic (As2O3), methyl arsenic sulfide (CH3AsS).
ii. In pigments, dyes, glaze manufacturing; wood preservation, and also in veterinary
medicine (organic arsenicals)
Sources o exposure:
i. Natural sources: Volcanic ashes, weathering (wear away) of arsenic containing mineral
and ores, forest fire etc.
ii. Anthropogenic: Mining and mining related activity, burning of fossil fuel.
Human exposure:
There are two main ways of arsenic exposure – 1) Water supply & 2) Ingestion through food.
The standard for arsenic in U.S. water supplies has been set at 50µg/L by the EPA
(United States Environmental Protection Agency). In our country contamination by water is of
greater risk.
For general population the main point of exposure is through food. Both organic and
inorganic arsenic is present in various foods, e.g. Fish contain relatively high concentration of
organic arsenic.

Inhalation of arsenic contaminated air is also a cause. When arsenic ores are treated
with acid AsH3 (arsine) is liberated. Thus workers of smelters, ore refineries and metal
processing units are at risk.
Distribution in the body:
Acute arsenic poisoning is related to high conc. of arsenic in liver, kidney, intestinal
mucosa and spleen. High conc. of arsenic is seen in skin, hair and nails. Once inorganic arsenic
is ingested it is transported by blood and methylated.
Toxicity: Toxicity is related to the rate and extent of absorption of different chemical forms of
arsenic.
Thus
Inorganic
arsenites
Organic trivalent
compounds (arsenoxides)
Inorganic
arsenates
Arsonium
compounds
Elemental
arsenic
> >>>
This toxicity is related to the solubility of the arsenicals in water. Since elemental arsenic is
least soluble in water its toxicity is low. Trivalent arsenic is more toxic than pentavalent
arsenic.
Biochemical effects:
a) As (III) exerts its toxic action by attacking SH groups of an enzyme, thereby inhibiting
enzyme action.
SH
SH
Enzymes
O
As
O
O Enzymes
S
S
As O 2OH
+
+
b) The enzymes of the TCA cycle are adversely affected as well. It forms complex and
inactivates pyruvate dehydrogenase (it actually converts pyruvate to acetyl coA, not part of
TCA cycle).

O
As
O
O
SH CH2
CH2
CHSH
CH2
CH2
CH2
CH2
CO
Protein
S CH2
CH2
CHS
CH2
CH2
CH2
CH2
CO
Protein
AsO
Dihydrolipoic acid
protein
Inactivated protein complex
with arsenic (III)
+
c) It is similar to P and interferes with some biological process involving P.
CH2OPO3
2-
C
C
H
H OH
O
CH2OPO3
2-
C
C
OPO3
2-
H OH
O
Phosphate
Additional process
leading to
ATP
Glyceraldehyde-3-PO4 1,3 bisphospho
glycerate
CH2OPO3
2-
C
C
O
H OH
O
As
O
O
O
1-arseno-3-phospho
glycerate
3-phospho
glycerate
Nonenzymatic spontaneous
hydrolysis preventing ATP
formation
As2O3Arsenite

d) Arsenic compounds at high concentration coagulate protein by attacking the sulphur bonds
which maintain the secondary and tertiary structure of protein.
Lewisite and BAL:
Lewisite is an arsenic containing poisonous gas used in the 1st world war to disable &
kill people. It is a vesicant (causes formation of sac containing fluid) and acts on lungs.
British scientists tried to understand how arsenic compounds act as poisons. Their
research led them to understand that lewisite poisoned people because of the inactivation and
coagulation protein by attacking the sulfhydryl (thiol) group of protein.
SH
SH
Enzymes Enzymes
S
S
As+ As
This led them to invent a agent to counteract the poison which contained a highly
reactive sulfhydryl group that could compete with the protein sulfhydryl group for arsenic. So
the agent would render the arsenic compound ineffective against body proteins. This
compound is called British Anti Lewisite (BAL).
So BAL is defined as the chelating agent that can react with some metal ions to render
them useless to inactivate/coagulate protein.
H2C
HC
H2C
SH
SH
OH
BAL
M2+
H2C
HC
H2C
S
S
OH
M
+ 2H+
2,3-Dimercaptopropanol
+
Mercury (Hg)
Characteristics:
Mercury is one of the metals which is liquid at room temperature (other being Cs). It
has a high specific gravity of 13.6. It has a low b.p. of 357⁰C and also the highest volatility of any
metal. Many metals dissolve in Hg to form amalgams.
Extraction & uses:
The principle ore from which Hg is obtained is cinnabar (red sulphide, HgS). Hg is
extracted as follows-
HgS + O2 Hg + SO2
4HgS + 4CaO 4Hg + 3CaS + CaSO4
Uses are
1. In the manufacture of Hg batteries & other electrical apparatus.
2. In laboratory equipments and widely in barometers.
3. High-pressure Hg-vapor lamps are now widely used for lighting streets and highways.
4. In paints, jewelry making, pesticides and other manufacturing processes.

Sources:
1. Natural sources → Volcanic action, erosion of Hg-containing sediments and gaseous
emissions from the earth’s crust.
2. Anthropogenic sources → Mining, combustion of fossil fuels in municipalities and
hospitals, transporting Hg ores, processing pulp & paper, incineration, use of Hg
compounds as seed dressings in agriculture, exhaust from metal smelters.
Chemical species of mercury:
Species Chemical & Biochemical importance
Hg (elemental
mercury)
Relatively inert and nontoxic. Highly toxic when inhaled. It damages Brain
nervous system.
Hg+
(Mercurous
ion)
Insoluble as chloride. Low toxicity.
Hg+
+ Cl-
HgCl
As our stomach contains high conc. of Cl-, Hg+ is not toxic.
Hg++
(mercuric
ions)
Toxic but not easily transported across biological membrane. It is toxic
because
a) It has high affinity for sulphur atom i.e. sulphur containing amino acids
of protein.
b) Hg++ can form bonds with hemoglobin & serum albumin (which contain
sulfhydryl group).
RHg+ (organic
mercurials)
Highly toxic because it is easily transported across the biological membrane.
Particularly methyl-Hg causes irreversible brain & nerve damage. It is stored
in fatty & adipose tissue.
Covalent Hg-C bond is not disrupted easily and thus alkyl Hg is retained in
cells for long time. When mercury attaches itself to cell membrane active
transport of sugar is inhibited. Energy deficiency in brain cells causes damage.
Also it allows passage of K to the membrane causing disorder of nerve impulse
transmission.
R2Hg Low toxicity but when converted to RHg+ in acidic medium.
HgS Highly insoluble and non-toxic. It is trapped in soil in this form.
Biological methylation:
Soluble inorganic mercury salts can be converted to Me-Hg in the presence of alkyl
cobalamines (as alkylating agents) while methyl-B12 acts as coenzyme.
Remedial measures:
1. All alkyl mercury pesticides must be banned.
2. Chlor-alkali plants must stop using Hg electrodes and move on to new technology.
3. Other mercurial pesticides must be limited.
Cadmium (Cd)
Cadmium toxicity came into consideration during outbreak of “itai-itai-byo” or “ouch-ouch-
disease” in Japan. In 1945 Japanese farmers living downstream to a cadmium mine began
suffering from pain in back & legs with fractures and decalcification.
It was understood that the high concentration of Cd in the water used to irrigate rice paddies
and drink was responsible.

This forced researchers to consider Cd to be one of the most toxic elements.
Characteristics & uses:
It is a non-essential trace element and not found in a pure state in nature. It has a
similar electronic configuration as Zn and has greater affinity towards the thiol groups than
does Zn. It is similar to Ca++ ion in size and charge density.
It is used for plating of steel, Fe, Cu, brass and other alloys to protect them from
corrosion. It is also used in aircraft manufacture and semiconductors. It is also used as control
rod in nuclear reactors.
Exposure:
Tobacco smoke is the single largest source of Cd exposure in humans. This is because
the absorption from the lungs is greater than from the GIT.
Metabolism:
Cd in food/water
(40-90 g/day
Cd in air
(0.02-0.05 g/day
Blood circulation
GIT Lungs
Tissues
(liver, kidney)
Cd2+
Cd-MT
MT
Cd-Albumin, Cd-MT
Feces
Urine
90-95%
25-40%5-10%
Cd2+
MT = Metallothionein

Biochemical effects:
1. Lung cancer, lung damage & high blood pressure.
2. Inhibition of protein synthesis, enzyme activity and competition with other metals (to
be used as cofactors) are the main deleterious effects of Cd.
Two mechanisms are at works for inhibition of enzymes.
1. Binding with the sulfhydryl groups of enzyme protein.
2. By competing with Zn and displacing it from metalloenzymes.

Cadmium and nutrition:
1. Cadmium has been shown to decrease serum Zn level. It adversely affects serum insulin
levels and glucose tolerance.
2. A harmful synergism exists between Fe deficiency and Cd toxicity. Studies on mice have
shown that Fe absorption was significantly inhibited when the conc. of Cd in their
drinking water reached 1mg/mL.
3. Cadmium utilizes same transport system as Ca and thus it inhibits the functioning of Ca.
This affects the young the greatest as they require Ca for proper growth.

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