Bth 204 environmental biotechnology

PROF. BALASUBRAMANIAN SATHYAMURTHY 2016 EDITION BTH-204: ENVIRONMENTAL BIOTECHNOLOGY
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FOR MSC BIOTECHNOLOGY STUDENTS
2014 ONWARDS
Biochemistry scanner
THE IMPRINT
BTH-204: ENVIRONMENTAL BIOTECHNOLOGY
As per Bangalore University (CBCS) Syllabus
2016 Edition
BY: Prof. Balasubramanian Sathyamurthy
Supported By:
Ayesha Siddiqui
Kiran K.S.
THE MATERIALS FROM “THE IMPRINT (BIOCHEMISTRY SCANNER)” ARE NOT
FOR COMMERCIAL OR BRAND BUILDING. HENCE ONLY ACADEMIC CONTENT
WILL BE PRESENT INSIDE. WE THANK ALL THE CONTRIBUTORS FOR
ENCOURAGING THIS.
BE GOOD – DO GOOD & HELP OTHERS

DEDICATIONDEDICATIONDEDICATIONDEDICATION
I dediI dediI dediI dedicate this material to my spiritual guru Shri Raghavendra swamigal,cate this material to my spiritual guru Shri Raghavendra swamigal,cate this material to my spiritual guru Shri Raghavendra swamigal,cate this material to my spiritual guru Shri Raghavendra swamigal,
parents, teachers, well wishers and students who always increase my moraleparents, teachers, well wishers and students who always increase my moraleparents, teachers, well wishers and students who always increase my moraleparents, teachers, well wishers and students who always increase my morale
and confidence to share myand confidence to share myand confidence to share myand confidence to share my knowledgeknowledgeknowledgeknowledge totototo reachreachreachreach all beneficiariesall beneficiariesall beneficiariesall beneficiaries....
PREFACEPREFACEPREFACEPREFACE
Biochemistry scanner ‘THE IMPRINT’ consists of last ten years solved question
paper of Bangalore University keeping in mind the syllabus and examination
pattern of the University. The content taken from the reference books has been
presented in a simple language for better understanding.
The Author Prof. Balasubramanian Sathyamurthy has 15 years of teaching
experience and has taught in 5 Indian Universities including Bangalore
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guidance.
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CONTRIBUTORS:
CHETAN ABBUR ANJALI TIWARI
AASHITA SINHA ASHWINI BELLATTI
BHARATH K CHAITHRA
GADIPARTHI VAMSEEKRISHNA KALYAN BANERJEE
KAMALA KISHORE
KIRAN KIRAN H.R
KRUTHI PRABAKAR KRUPA S
LATHA M MAMATA
MADHU PRAKASHHA G D MANJUNATH .B.P
NAYAB RASOOL S NAVYA KUCHARLAPATI
NEHA SHARIFF DIVYA DUBEY
NOOR AYESHA M PAYAL BANERJEE
POONAM PANCHAL PRAVEEN
PRAKASH K J M PRADEEP.R
PURSHOTHAM PUPPALA DEEPTHI
RAGHUNATH REDDY V RAMYA S
RAVI RESHMA
RUBY SHA SALMA H.
SHWETHA B S SHILPI CHOUBEY
SOUMOUNDA DAS SURENDRA N
THUMMALA MANOJ UDAYASHRE. B
DEEPIKA SHARMA
EDITION : 2016
PRINT : Bangalore
CONTACT : theimprintbiochemistry@gmail.com or 9980494461

M. SC. BIOTECHNOLOGY – SECOND SEMESTER
BTH-204: ENVIRONMENTAL BIOTECHNOLOGY
4 units (52 hrs)
UNIT: 1 ENVIRONMENT AND MONITORING 8 hrs
Introduction, renewable and non – renewable sources of energy; Environmental
pollution – Water pollution, soil pollution and air pollution – sources and
measurements. Xenobiotic compounds and their sources. Biomagnification,
Bioindicators.
Biomonitoring: Biosensors and Biochips.
UNIT: 2 WATER MANAGEMENT AND WASTE WATER TREATMENT 12 hrs
Water as a scarce natural resource, water management including rain water harvesting.
Waste water characterisitics, waste water treatment- physical, chemical, biological
processes. Aerobic processes: Activated sludge, oxidation ditches, trickling filter,
oxidation ponds. Anaerobic processes; Anaerobic digestion, anaerobic filters, anaerobic
sludge, membrane bioreactors. Reverse osmosis and ultra filtration. Treatment of
industrial effluents.
UNIT: 3 BIOMINING AND BIODIESEL 4 hrs
Bioleaching of ores to retrieve scarce metals, Bio – mining; Biodiesel production from
Jatropa, Pongamia and Castor.
UNIT: 4 BIOREMEDIATION 8 hrs
Concept and principles, Bioremediation using microbes, In situ and ex situ
bioremediation, biosorption and bioaccumulation of heavy metals; Phytoremediation,
bioremediation of xenobiotics ( heavy metals, pesticides, oil slicks, plastic).
Bioremediation of soil and water contaminated with hydrocarbons and surfactants,
biofilms.
UNIT: 5 BIOWASTE TREATMENT 12 hrs
Microorganisms involved in the degradation of plant fibre, cell wall, lignin, fungal de –
lignifications and pulping of wood. Pitch problems in pulp and paper processes and
solving by enzymes or fungi. Hemicellulases in pulp bleaching. Solving slime problem in
the pulp and paper industry. Reduction of organochlorine compounds in bleach plant
effluents.

Solid wastes: Sources and management, waste as a source of energy. Production of oils
and fuels from solid waste, composting, vermiculture, Biogas production, methanol
production from organic wastes, byproducts of sugar industries.
UNIT: 6 GLOBAL ENVIRONMENTAL PROBLEMS 8 hrs
Global warming, ozone depletion, UV – B, green house effect and acid rain, their impact
and management. Biodiversity and its conservation, status of biodiversity, hotspots,
Red data book.

UNIT: 1 ENVIRONMENT AND MONITORING
Introduction, renewable and non – renewable sources of energy; Environmental
pollution – Water pollution, soil pollution and air pollution – sources and
measurements. Xenobiotic compounds and their sources. Biomagnification,
Bioindicators.
Biomonitoring: Biosensors and Biochips.
INTRODUCTION
Environmental biotechnology deals with far less apparently dramatic topics and, though
their importance, albeit different, may be every bit as great, their direct relevance is far
less readily appreciated by the bulk of the population. Cleaning up contamination and
dealing rationally with wastes is, of course, in everybody’s best interests, but for most
people, this is simply addressing a problem which they would rather have not existed in
the first place.
Even for industry, though the benefits may be noticeable on the balance sheet, the likes
of effluent treatment or pollution control are more of an inevitable obligation than a
primary goal in themselves. In general, such activities are typically funded on a
distinctly limited budget and have traditionally been viewed as a necessary
inconvenience. This is in no way intended to be disparaging to industry; it simply
represents commercial reality.
In many respects, there is a logical fit between this thinking and the aims of
environmental biotechnology. For all the media circus surrounding the grand questions
of our age, it is easy to forget that not all forms of biotechnology involve
xenotransplantation, genetic modification, the use of stem cells or cloning. Some of the
potentially most beneficial uses of biological engineering, and which may touch the lives
of the majority of people, however indirectly, involve much simpler approaches. Less
radical and showy, certainly, but powerful tools, just the same. Environmental
biotechnology is fundamentally rooted in waste, in its various guises, typically being
concerned with the remediation of contamination caused by previous use, the impact
reduction of current activity or the control of pollution. Thus, the principal aims of this
field are the manufacture of products in environmentally harmonious ways, which allow
for the minimisation of harmful solids, liquids or gaseous outputs or the clean-up of the
residual effects of earlier human occupation.

The means by which this may be achieved are essentially two-fold. Environmental
biotechnologists may enhance or optimise conditions for existing biological systems to
make their activities happen faster or more efficiently, or they resort to some form of
alteration to bring about the desired outcome. The variety of organisms which may play
a part in environmental applications of biotechnology is huge, ranging from microbes
through to trees and all are utilised on one of the same three fundamental bases –
accept, acclimatise or alter. For the vast majority of cases, it is the former approach,
accepting and making use of existing species in their natural, unmodified form, which
predominates.
The Scope:
There are three key points for environmental biotechnology interventions, namely in the
manufacturing process, waste management or pollution control, as shown in Fig.
Accordingly, the range of businesses to which environmental biotechnology has
potential relevance is almost limitless. One area where this is most apparent is with
regard to waste. All commercial operations generate waste of one form or another and
for many, a proportion of what is produced is biodegradable. With disposal costs rising
steadily across the world, dealing with refuse constitutes an increasingly high
contribution to overheads. Thus, there is a clear incentive for all businesses to identify
potentially cost-cutting approaches to waste and employ them where possible. Changes
in legislation throughout Europe, the US and elsewhere, have combined to drive these
issues higher up the political agenda and biological methods of waste treatment have
gained far greater acceptance as a result. For those industries with particularly high
biowaste production, the various available treatment biotechnologies can offer
considerable savings.
Manufacturing industries can benefit from the applications of whole organisms or
isolated biocomponents. Compared with conventional chemical processes, microbes and
enzymes typically function at lower temperatures and pressures. The lower energy

demands this makes leads to reduced costs, but also has clear benefits in terms of both
the environment and workplace safety. Additionally, biotechnology can be of further
commercial significance by converting low-cost organic feedstocks into high value
products or, since enzymatic reactions are more highly specific than their chemical
counterparts, by deriving final substances of high relative purity. Almost inevitably,
manufacturing companies produce wastewaters or effluents, many of which contain
biodegradable contaminants, in varying degrees. Though traditional permitted
discharges to sewer or watercourses may be adequate for some, other industries,
particularly those with recalcitrant or highly concentrated effluents, have found
significant benefits to be gained from using biological treatment methods themselves on
site. Though careful monitoring and process control are essential, biotechnology stands
as a particularly cost-effective means of reducing the pollution potential of wastewater,
leading to enhanced public relations, compliance with environmental legislation and
quantifiable cost-savings to the business.
Those involved in processing organic matter, for example, or with drying, printing,
painting or coating processes, may give rise to the release of volatile organic compounds
(VOCs) or odours, both of which represent environmental nuisances, though the former
is more damaging than the latter. For many, it is not possible to avoid producing these
emissions altogether, which leaves treating them to remove the offending contaminants
the only practical solution. Especially for relatively low concentrations of readily water-
soluble VOCs or odorous chemicals, biological technologies can offer an economic and
effective alternative to conventional methods.
The use of biological cleaning agents is another area of potential benefit, especially
where there is a need to remove oils and fats from process equipment, work surfaces or
drains. Aside from typically reducing energy costs, this may also obviate the need for
toxic or dangerous chemical agents. The pharmaceutical and brewing industries, for
example, both have a long history of employing enzyme-based cleaners to remove
organic residues from their process equipment. In addition, the development of effective
biosensors, powerful tools which rely on biochemical reactions to detect specific
substances, has brought benefits to a wide range of sectors, including the
manufacturing, engineering, chemical, water, food and beverage industries. With their
ability to detect even small amounts of their particular target chemicals, quickly, easily
and accurately, they have been enthusiastically adopted for a variety of process

monitoring applications, particularly in respect of pollution assessment and control.
Contaminated land is a growing concern for the construction industry, as it seeks to
balance the need for more houses and offices with wider social and environmental
goals. The reuse of former industrial sites, many of which occupy prime locations, may
typically have associated planning conditions attached which demand that the land be
cleaned up as part of the development process.
With urban regeneration and the reclamation of ‘brown-field’ sites increasingly favoured
in many countries over the use of virgin land, remediation has come to play a
significant role and the industry has an ongoing interest in identifying cost-effective
methods of achieving it. Historically, much of this has involved simply digging up the
contaminated soil and removing it to landfill elsewhere.
Bioremediation technologies provide a competitive and sustainable alternative and in
many cases, the lower disturbance allows the overall scheme to make faster progress.
As the previous brief examples show, the range of those which may benefit from the
application of biotechnology is lengthy and includes the chemical, pharmaceutical,
water, waste management and leisure industries, as well as manufacturing, the
military, energy generation, agriculture and horticulture. Clearly, then, this may have
relevance to the viability of these ventures and, as was mentioned at the outset,
biotechnology is an essentially commercial activity.
Environmental biotechnology must compete in a world governed by the best practicable
environmental option (BPEO) and the best available techniques not entailing excessive
cost (BATNEEC). Consequently, the economic aspect will always have a large influence
on the uptake of all initiatives in environmental biotechnology and, most particularly, in
the selection of methods to be used in any given situation.
RENEWABLE SOURCES OF ENERGY
Introduction
Conventional energy sources based on oil, coal, and natural gas have proven to be
highly effective drivers of economic progress, but at the same time damaging to the
environment and to human health. Furthermore, they tend to be cyclical in nature, due
to the effects of oligopoly in production and distribution. These traditional fossil fuel-
based energy sources are facing increasing pressure on a host of environmental fronts,
with perhaps the most serious challenge confronting the future use of coal being the
Kyoto Protocol greenhouse gas (GHG) reduction targets. It is now clear that any effort to

maintain atmospheric levels of CO2 below even 550 ppm cannot be based
fundamentally on an oil and coal-powered global economy, barring radical carbon
sequestration efforts.
The potential of renewable energy sources is enormous as they can in principle meet
many times the world’s energy demand. Renewable energy sources such as biomass,
wind, solar, hydropower, and geothermal can provide sustainable energy services,
based on the use of routinely available, indigenous resources. A transition to
renewables-based energy systems is looking increasingly likely as the costs of solar and
wind power systems have dropped substantially in the past 30 years, and continue to
decline, while the price of oil and gas continue to fluctuate. In fact, fossil fuel and
renewable energy prices, social and environmental costs are heading in opposite
directions. Furthermore, the economic and policy mechanisms needed to support the
widespread dissemination and sustainable markets for renewable energy systems have
also rapidly evolved. It is becoming clear that future growth in the energy sector is
primarily in the new regime of renewable, and to some extent natural gas-based
systems, and not in conventional oil and coal sources. Financial markets are awakening
to the future growth potential of renewable and other new energy technologies, and this
is a likely harbinger of the economic reality of truly competitive renewable energy
systems.
Renewable energy sources currently supply somewhere between 15 percent and 20
percent of world’s total energy demand. The supply is dominated by traditional biomass,
mostly fuel wood used for cooking and heating, especially in developing countries in
Africa, Asia and Latin America. A major contribution is also obtained from the use of
large hydropower; with nearly 20 percent of the global electricity supply being provided
by this source. New renewable energy sources (solar energy, wind energy, modern bio-
energy, geothermal energy, and small hydropower) are currently contributing about two
percent. A number of scenario studies have investigated the potential contribution of
renewables to global energy supplies, indicating that in the second half of the 21st
century their contribution might range from the present figure of nearly 20 percent to
more than 50 percent with the right policies in place.
Biomass Energy
Biomass is the term used for all organic material originating from plants (including
algae), trees and crops and is essentially the collection and storage of the sun’s energy

through photosynthesis. Biomass energy, or bioenergy, is the conversion of biomass
into useful forms of energy such as heat, electricity and liquid fuels.
Biomass for bioenergy comes either directly from the land, as dedicated energy crops, or
from residues generated in the processing of crops for food or other products such as
pulp and paper from the wood industry. Another important contribution is from post
consumer residue streams such as construction and demolition wood, pallets used in
transportation, and the clean fraction of municipal solid waste (MSW). The biomass to
bioenergy system can be considered as the management of flow of solar generated
materials, food, and fiber in our society. These interrelationships are shown in Figure,
which presents the various resource types and applications, showing the flow of their
harvest and residues to bioenergy applications. Not all biomass is directly used to
produce energy but rather it can be converted into intermediate energy carriers called
biofuels. This includes charcoal (higher energy density solid fuel), ethanol (liquid fuel),
or producer-gas (from gasification of biomass).
Biomass and bioenergy flow chart
Wind Energy
Wind has considerable potential as a global clean energy source, being both widely
available, though diffuse, and producing no pollution during power generation. Wind
energy has been one of humanity’s primary energy sources for transporting goods,
milling grain, and pumping water for several millennia. From windmills used in China,
India and Persia over 2000 years ago to the generation of electricity in the early 20th
century in Europe and North America wind energy has played an important part in our
recorded history. As industrialization took place in Europe and then in America, wind
power generation declined, first gradually as the use of petroleum and coal, both

cheaper and more reliable energy sources, became widespread, and then more sharply
as power transmission lines were extended into most rural areas of industrialized
countries. The oil crises of the 70’s, however, triggered renewed interest in wind energy
technology for gridconnected electricity production, water pumping, and power supply
in remote areas, promoting the industry’s rebirth.
Solar Photovoltaic and Solar Thermal Technologies
There are two basic categories of technologies that convert sunlight into useful forms of
energy, aside from biomass-based systems that do this in a broader sense by using
photosynthesis from plants as an intermediate step. First, solar photovoltaic (PV)
modules convert sunlight directly into electricity. Second, solar thermal power systems
use focused solar radiation to produce steam, which is then used to turn a turbine
producing electricity. The following provides a brief overview of these technologies, along
with their current commercial status.
Solar Photovoltaics
Solar PV modules are solid-state semiconductor devices with no moving parts that
convert sunlight into direct-current electricity. The basic principle underlying the
operation of PV modules dates back more than 150 years, but significant development
really began following Bell Labs’ invention of the silicon solar cell in 1954. The first
major application of PV technology was to power satellites in the late 1950s, and this
was an application where simplicity and reliability were paramount and cost was a
secondary concern. Since that time, enormous progress has been made in PV
performance and cost reduction, driven at first by the U.S. space program’s needs and
more recently through private/public sector collaborative efforts in the U.S., Europe,
and Japan.
Hydropower
Hydropower is the largest renewable resource used for electricity. It plays an essential
role in many regions of the world with more than 150 countries generating hydroelectric
power. A survey in 1997 by The International Journal on Hydropower Dams found
that hydro supplies at least 50 percent of national electricity production in 63 countries
and at least 90 percent in 23 countries. About 10 countries obtain essentially all their
commercial electricity from hydro, including Norway, several African nations, Bhutan
and Paraguay. There is about 700 GW of hydro capacity in operation worldwide,
generating 2600 TWh/year (about 19 percent of the world’s electricity production).

About half of this capacity and generation is in Europe and North America with Europe
the largest at 32 percent of total hydro use and North America at 23 percent of the total.
However, this proportion is declining as Asia and Latin America commission large
amounts of new hydro capacity. Small, mini and micro hydro plants (usually defined as
plants less than 10 MW, 2 MW and 100kW, respectively) also play a key role in many
countries for rural electrification. An estimated 300 million people in China, for
example, depend on small hydro.
Small Hydro
Small-scale hydro is mainly ‘run of river,’ so does not involve the construction of large
dams and reservoirs. It also has the capacity to make a more immediate impact on the
replacement of fossil fuels since, unlike other sources of renewable energy, it can
generally produce some electricity on demand (at least at times of the year when an
adequate flow of water is available) with no need for storage or backup systems. It is
also in many cases cost competitive with fossil-fuel power stations, or for remote rural
areas, diesel generated power. Small hydro has a large, and as yet untapped, potential
in many parts of the world. It depends largely on already proven and developed
technology with scope for further development and optimization. Least-cost hydro is
generally high-head hydro since the higher the head, the less the flow of water required
for a given power level, and so smaller and less costly equipment is needed. While this
makes mountainous regions very attractive sites they also tend to be in areas of low
population density and thus low electricity demand and long transmission distances
often nullify the low cost advantage. Low-head hydro on the other hand is relatively
common, and also tends to be found in or near concentrations of population where
there is a demand for electricity. Unfortunately, the economics also tend to be less
attractive unless there are policy incentives in place to encourage their development.
Geothermal Energy
Geothermal energy, the natural heat within the earth, arises from the ancient heat
remaining in the Earth's core, from friction where continental plates slide beneath each
other, and from the decay of radioactive elements that occur naturally in small amounts
in all rocks. For thousands of years, people have benefited from hot springs and steam
vents, using them for bathing, cooking, and heating. During this century, technological
advances have made it possible and economic to locate and drill into hydrothermal
reservoirs, pipe the steam or hot water to the surface, and use the heat directly (for

space heating, aquaculture, and industrial processes) or to convert the heat into
electricity.
The amount of geothermal energy is enormous. Scientists estimate that just 1 percent
of the heat contained in just the uppermost 10 kilometers of the earth’s crust is
equivalent to 500 times the energy contained in all of the earth's oil and gas resources.
Yet, despite the fact that this heat is present in practically inexhaustible quantities, it is
unevenly distributed, seldom concentrated and often at depths too great to be exploited
industrially and economically. Geothermal energy has been produced commercially for
70 years for both electricity generation and direct use. Its use has increased rapidly
during the last three decades and from 1975 – 1995 the growth rate for electricity
generation worldwide has been about 9 percent per year and for direct use of
geothermal energy it has been about 6 percent per year. In 1997 geothermal resources
had been identified in over 80 countries and there were quantified records of
geothermal utilization in at least 46 countries.
NON – RENEWABLE SOURCES OF ENERGY
Introduction
Sufficient, reliable sources of energy are a necessity for industrialized nations. Energy is
used for heating, cooking, transportation and manufacturing. Energy can be generally
classified as non-renewable and renewable. Over 85% of the energy used in the world is
from non-renewable supplies. Most developed nations are dependent on non-renewable
energy sources such as fossil fuels (coal and oil) and nuclear power. These sources are
called non-renewable because they cannot be renewed or regenerated quickly enough to
keep pace with their use. Some sources of energy are renewable or potentially
renewable. Examples of renewable energy sources are: solar, geothermal, hydroelectric,
biomass, and wind. Renewable energy sources are more commonly by used in
developing nations.
Industrialized societies depend on non-renewable energy sources. Fossil fuels are the
most commonly used types of non-renewable energy. They were formed when
incompletely decomposed plant and animal matter was buried in the earth's crust and
converted into carbon-rich material that is useable as fuel. This process occurred over
millions of years. The three main types of fossil fuels are coal, oil, and natural gas. Two
other less-used sources of fossil fuels are oil shales and tar sands.
Coal

Coal is the most abundant fossil fuel in the world with an estimated reserve of one
trillion metric tons. Most of the world's coal reserves exist in Eastern Europe and Asia,
but the United States also has considerable reserves. Coal formed slowly over millions
of years from the buried remains of ancient swamp plants.
During the formation of coal, carbonaceous matter was first compressed into a spongy
material called "peat," which is about 90% water. As the peat became more deeply
buried, the increased pressure and temperature turned it into coal.
Different types of coal resulted from differences in the pressure and temperature that
prevailed during formation. The softest coal (about 50% carbon), which also has the
lowest energy output, is called lignite. Lignite has the highest water content (about
50%) and relatively low amounts of smog-causing sulfur. With increasing temperature
and pressure, lignite is transformed into bituminous coal (about 85% carbon and 3%
water). Anthracite (almost 100% carbon) is the hardest coal and also produces the
greatest energy when burned. Less than 1% of the coal found in the United States is
anthracite. Most of the coal found in the United States is bituminous. Unfortunately,
bituminous coal has the highest sulfur content of all the coal types. When the coal is
burned, the pollutant sulfur dioxide is released into the atmosphere.
Coal mining creates several environmental problems. Coal is most cheaply mined from
near-surface deposits using strip mining techniques. Strip-mining causes considerable
environmental damage in the forms of erosion and habitat destruction. Sub-surface
mining of coal is less damaging to the surface environment, but is much more
hazardous for the miners due to tunnel collapses and gas explosions. Currently, the
world is consuming coal at a rate of about 5 billion metric tons per year. The main use
of coal is for power generation, because it is a relatively inexpensive way to produce
power.
Coal is used to produce over 50% of the electricity in the United States. In addition to
electricity production, coal is sometimes used for heating and cooking in less developed
countries and in rural areas of developed countries. If consumption continues at the
same rate, the current reserves will last for more than 200 years. The burning of coal
results in significant atmospheric pollution.
The sulfur contained in coal forms sulfur dioxide when burned. Harmful nitrogen
oxides, heavy metals, and carbon dioxide are also released into the air during coal
burning. The harmful emissions can be reduced by installing scrubbers and

electrostatic precipitators in the smokestacks of power plants. The toxic ash remaining
after coal burning is also an environmental concern and is usually disposed into
landfills.
Oil
Crude oil or liquid petroleum is a fossil fuel that is refined into many different energy
products (e.g., gasoline, diesel fuel, jet fuel, heating oil). Oil forms underground in rock
such as shale, which is rich in organic materials. After the oil forms, it migrates upward
into porous reservoir rock such as sandstone or limestone, where it can become trapped
by an overlying impermeable cap rock.
Wells are drilled into these oil reservoirs to remove the gas and oil. Over 70 percent of
oil fields are found near tectonic plate boundaries, because the conditions there are
conducive to oil formation.
Oil recovery can involve more than one stage. The primary stage involves pumping oil
from reservoirs under the normal reservoir pressure. About 25 percent of the oil in a
reservoir can be removed during this stage. The secondary recovery stage involves
injecting hot water into the reservoir around the well. This water forces the remaining
oil toward the area of the well from which it can be recovered. Sometimes a tertiary
method of recovery is used in order to remove as much oil as possible. This involves
pumping steam, carbon dioxide gas or nitrogen gas into the reservoir to force the
remaining oil toward the well.
Tertiary recovery is very expensive and can cost up to half of the value of oil removed.
Carbon dioxide used in this method remains sequestered in the deep reservoir, thus
mitigating its potential greenhouse effect on the atmosphere. The refining process
required to convert crude oil into useable hydrocarbon compounds involves boiling the
crude and separating the gases in a process known as fractional distillation. Besides its
use as a source of energy, oil also industrial chemicals.
Over 50 percent of the world's oil is found in the Middle East; sizeable additional
reserves occur in North America. Most known oil reserves are already being exploited,
and oil is being used at a rate that exceeds the rate of discovery of new sources. If the
consumption rate continues to increase and no significant new sources are found, oil
supplies may be exhausted in another 30 years or so.

Despite its limited supply, oil is a relatively inexpensive fuel source. It is a preferred fuel
source over coal. An equivalent amount of oil produces more kilowatts of energy than
coal. It also burns cleaner, producing about 50 percent less sulfur dioxide.
Oil, however, does cause environmental problems. The burning of oil releases
atmospheric pollutants such as sulfur dioxide, nitrogen oxides, carbon dioxide and
carbon monoxide. These gases are smog-precursors that pollute the air and greenhouse
gases that contribute to global warming. Another environmental issue associated with
the use of oil is the impact of oil drilling. Substantial oil reserves lie under the ocean.
Oil spill accidents involving drilling platforms kill marine organisms and birds. Some
reserves such as those in northern Alaska occur in wilderness areas. The building of
roads, structures and pipelines to support oil recovery operations can severely impact
the wildlife in those natural areas.
Natural gas
Natural gas production is often a by-product of oil recovery, as the two commonly share
underground reservoirs. Natural gas is a mixture of gases, the most common being
methane (CH4). It also contains some ethane (C2H5), propane (C3H8), and butane
(C4H10). Natural gas is usually not contaminated with sulfur and is therefore the
cleanest burning fossil fuel. After recovery, propane and butane are removed from the
natural gas and made into liquefied petroleum gas (LPG). LPG is shipped in special
pressurized tanks as a fuel source for areas not directly served by natural gas pipelines
(e.g., rural communities). The remaining natural gas is further refined to remove
impurities and water vapor, and then transported in pressurized pipelines. The United
States has over 300,000 miles of natural gas pipelines. Natural gas is highly flammable
and is odorless. The characteristic smell associated with natural gas is actually that of
minute quantities of a smelly sulfur compound (ethyl mercaptan) which is added during
refining to warn consumers of gas leaks.
The use of natural gas is growing rapidly. Besides being a clean burning fuel source,
natural gas is easy and inexpensive to transport once pipelines are in place. In
developed countries, natural gas is used primarily for heating, cooking, and powering
vehicles. It is also used in a process for making ammonia fertilizer. Current usage
levels, this supply will last an estimated 100 years. Most of the world's natural gas
reserves are found in Eastern Europe and the Middle East.
Oil shale and tar sands

Oil shale and tar sands are the least utilized fossil fuel sources. Oil shale is
sedimentary rock with very fine pores that contain kerogen, a carbon-based, waxy
substance. If shale is heated to 490º C, the kerogen vaporizes and can then be
condensed as shale oil, a thick viscous liquid. This shale oil is generally further refined
into usable oil products. Production of shale oil requires large amounts of energy for
mining and processing the shale. Indeed about a half barrel of oil is required to extract
every barrel of shale oil. Oil shale is plentiful, with estimated reserves totaling 3 trillion
barrels of recoverable shale oil. These reserves alone could satisfy the world's oil needs
for about 100 years. Environmental problems associated with oil shale recovery include:
large amounts of water needed for processing, disposal of toxic waste water, and
disruption of large areas of surface lands.
Tar sand is a type of sedimentary rock that is impregnated with a very thick crude oil.
This thick crude does not flow easily and thus normal oil recovery methods cannot be
used to mine it. If tar sands are near the surface, they can be mined directly. In order to
extract the oil from deep-seated tar sands, however, steam must be injected into the
reservoir to make the oil flow better and push it toward the recovery well. The energy
cost for producing a barrel of tar sand is similar to that for oil shale. The largest tar-
sand deposit in the world is in Canada and contains enough material (about 500 billion
barrels) to supply the world with oil for about 15 years. However, because of
environmental concerns and high production costs these tar sand fields are not being
fully utilized.
Nuclear power
In most electric power plants, water is heated and converted into steam, which drives a
turbine-generator to produce electricity. Fossil-fueled power plants produce heat by
burning coal, oil, or natural gas. In a nuclear power plant, the fission of uranium
atoms in the reactor provides the heat to produce steam for generating electricity.
Several commercial reactor designs are currently in use in the United States. The most
widely used design consists of a heavy steel pressure vessel surrounding a reactor core.
The reactor core contains the uranium fuel, which is formed into cylindrical ceramic
pellets and sealed in long metal tubes called fuel rods. Thousands of fuel rods form the
reactor core. Heat is produced in a nuclear reactor when neutrons strike uranium
atoms, causing them to split in a continuous chain reaction. Control rods, which are

made of a material such as boron that absorbs neutrons, are placed among the fuel
assemblies.
When the neutron-absorbing control rods are pulled out of the core, more neutrons
become available for fission and the chain reaction speeds up, producing more heat.
When they are inserted into the core, fewer neutrons are available for fission, and the
chain reaction slows or stops, reducing the heat generated. Heat is removed from the
reactor core area by water flowing through it in a closed pressurized loop. The heat is
transferred to a second water loop through a heat exchanger. The water also serves to
slow down, or "moderate" the neutrons which is necessary for sustaining the fission
reactions. The second loop is kept at a lower pressure, allowing the water to boil and
create steam, which is used to power the turbine-generator and produce electricity.
Originally, nuclear energy was expected to be a clean and cheap source of energy.
Nuclear fission does not produce atmospheric pollution or greenhouse gases and it
proponents expected that nuclear energy would be cheaper and last longer than fossil
fuels. Unfortunately, because of construction cost overruns, poor management, and
numerous regulations, nuclear power ended up being much more expensive than
predicted. The nuclear accidents at Three Mile Island in Pennsylvania and the
Chernobyl Nuclear Plant in the Ukraine raised concerns about the safety of nuclear
power. Furthermore, the problem of safely disposing spent nuclear fuel remains
unresolved. The United States has not built a new nuclear facility in over twenty years,
but with continued energy crises across the country that situation may change.
ENVIRONMENTAL POLLUTION
Pollution has become one of the most frequently talked about of all environmental
problems by the world at large and yet, in many respects, it can often remain one of the
least understood. The word itself has a familiar ring to it and inevitably the concept of
pollution has entered the wider consciousness as a significant part of the burgeoning
‘greening’ of society in general.
The UK Environmental Protection Act (EPA) 1990 statutorily offers the following:
‘Pollution of the environment’ means pollution of the environment due to the release
(into any environmental medium) from any process of substances which are capable of
causing harm to man or any other living organisms supported by the environment.
In essence, then, pollution is the introduction of substances into the environment
which, by virtue of their characteristics, persistence or the quantities involved, are likely

to be damaging to the health of humans, other animals and plants, or otherwise
compromise that environment’s ability to sustain life. It should be obvious that this is
an expressly inclusive definition, encompassing not simply the obviously toxic or
noxious substances, but also other materials which can have a polluting effect under
certain circumstances.
Classifying Pollution
While, as we said earlier, this diverse nature of potential pollutants makes their
systematisation difficult in absolute terms, it is possible to produce functional
classifications on the basis of various characteristics. However, it must be clearly borne
in mind that all such classification is essentially artificial and subjective, and that the
system to be adopted will typically depend on the purpose for which it is ultimately
intended. Despite these limitations, there is considerable value in having some method,
if only as a predictive environmental management tool, for considerations of likely
pollutant effect.
Classification may, for example, be made on the basis of the chemical or physical
nature of the substance, its source, the environmental pathway used, the target
organism affected or simply its gross effect. Fig.shows one possible example of such a
categorisation system and clearly many others are possible. The consideration of a
pollutant’s properties is a particularly valuable approach when examining real-life
pollution effects, since such an assessment requires both the evaluation of its general
properties and the local environment. This may include factors such as:
Toxicity;
Persistence;
Mobility;
Ease of control;
Bioaccumulation;
Chemistry.
Toxicity
Toxicity represents the potential damage to life and can be both short and long term. It
is related to the concentration of pollutant and the time of exposure to it, though this
relationship is not an easy one. Intrinsically highly toxic substances can kill in a short
time, while less toxic ones require a longer period of exposure to do damage. This much
is fairly straightforward. However, some pollutants which may kill swiftly in high

concentrations may also have an effect on an organism’s behaviour or its susceptibility
to environmental stress over its lifetime, in the case of low concentration exposure.
Availability also features as an important influence, both in a gross, physical sense and
also in terms of its biological availability to the individual organism, together with
issues of its age and general state of health. Other considerations also play a significant
part in the overall picture of toxicity and we shall return to look at some of them in
greater depth shortly.
Persistence
This is the duration of effect. Environmental persistence is a particularly important
factor in pollution and is often linked to mobility and bioaccumulation.
Highly toxic chemicals which are environmentally unstable and break down rapidly are
less harmful than persistent substances, even though these may be intrinsically less
toxic.
Mobility
The tendency of a pollutant to disperse or dilute is a very important factor in its overall
effect, since this affects concentration. Some pollutants are not readily mobile and tend
to remain in ‘hot-spots’ near to their point of origin. Others spread readily and can
cause widespread contamination, though often the distribution is not uniform. Whether
the pollution is continuous or a single event, and if it arose from a single point or
multiple sources, form important considerations.
Ease of control
Many factors contribute to the overall ease with which any given example of pollution
can be controlled, including the mobility of the pollutant, the nature, extent or duration
of the pollution event and local site-specific considerations. Clearly, control at source is
the most effective method, since it removes the problem at its origin. However, this is
not always possible and in such cases, containment may be the solution, though this
can itself lead to the formation of highly concentrated hot-spots. For some substances,

the dilute and disperse approach, which is discussed more fully later in this chapter,
may be more appropriate, though the persistence of the polluting substances must
obviously be taken into account when making this decision.
Bioaccumulation
As is widely appreciated, some pollutants, even when present in very small amounts
within the environment, can be taken up by living organisms and become concentrated
in their tissues over time. This tendency of some chemicals to be taken up and then
concentrated by living organisms is a major consideration, since even relatively low
background levels of contamination may accumulate up the food chain.
WATER POLLUTION – SOURCES AND MEASUREMENTS
Introduction:
Any physical, biological, or chemical change in water quality that adversely affects living
organisms or makes water unsuitable for desired uses can be considered pollution.
There are natural sources of water contamination (e.g. poison springs and oil
seeps).Pollution control standards and regulations usually distinguish between point
and nonpoint pollution sources. Point sources: discharge pollution from specific
locations (e.g. drain pipes, ditches, or sewer outfalls).Nonpoint sources: pollution is
scattered or diffuse, having no specific location where they discharge into a particular
body of water (e.g. runoff from farm fields and feedlots, golf courses, lawns, and
gardens). The ultimate in diffuse, nonpoint pollution is atmospheric deposition of
contaminants carried by air currents and precipitated into watersheds or directly onto
surface waters as rain, snow, or dry particles.
Types and Effects of Water Pollution
Infectious Agents
The most serious water pollutants in terms of human health worldwide are pathogenic
organisms. The main source of these pathogens is from untreated or improperly treated
human wastes. In developed countries, sewage treatment plants and other pollution-
control techniques have reduced or eliminated most of the worst sources of pathogens
in inland surface waters. The situation is quite different in less-developed countries.
The United Nations estimates that at least 2.5 billion people in these countries lack
adequate sanitation, and that about half these people also lack access to clean drinking
water. Water quality control personnel usually analyze water for the presence of

coliform bacteria, any of the types that live in the colon or the intestines of humans and
other animals (e.g. E. coli)
Oxygen-Demanding Wastes
The amount of oxygen dissolved in water is a good indicator of water quality and of the
kinds of life it will support. The addition of certain organic materials, such as sewage,
paper pulp, or food-processing wastes, to water stimulates oxygen consumption by
decomposers. Biochemical oxygen demand (BOD): a standard test of the amount of
dissolved oxygen consumed by aquatic microorganisms over a five-day period. Dissolved
oxygen content (DO): measure dissolved oxygen content directly using an oxygen
electrode. The oxygen decline downstream from point source is called the oxygen sag.
Immediately below the source of pollution, oxygen levels begin to fall as decomposers
metabolize waste materials.
Plant Nutrients and Cultural Eutrophication
Water clarity is affected by sediments, chemicals, and the abundance of plankton
organisms, and is a useful measure of water quality and water pollution.
Oligotrophic: describes rivers and lakes that have clear water and low biological
productivity.
Eutrophic: describes waters that are rich in organisms and organic materials. Human
activities can greatly accelerate eutrophication (cultural eutrophication).
High biological productivity of eutrophic systems is often seen in "blooms" of algae or
thick growth of aquatic plants stimulated by elevated phosphorous or nitrogen levels.
Eutrophication also occurs in marine ecosystems, especially in near-shore waters and
partially enclosed bays or estuaries.
Toxic Tides
Red tide: bloom of deadly aquatic microorganisms called dinoflagellates.
Red tides - and other colors, depending on the species involved-have become
increasingly common in slow-moving rivers, brackish lagoons, estuaries, and bays.
One of the most feared of these organisms is Pfiesteria piscicida, an extraordinarily
poisonous dinoflagellate that has recently wiped out hundreds of thousands to millions
of fish every year in polluted rivers and estuaries such as North Carolina's Palmico
Sound.
Under the right conditions, a population explosion can produce a dense bloom of these
cells.

Inorganic Pollutants
Some toxic inorganic chemicals are released from rocks by weathering, are carried by
runoff into lakes or rivers, or percolate into groundwater aquifers.
Humans can accelerate the rate of release of these inorganic chemicals through the
mining, processing, using, and discarding of minerals.
Metals
Many metals such as mercury, lead, cadmium, and nickel are highly toxic.
A famous case of mercury poisoning occurred in Japan in the 1950s. Heavy metals
released as a result of human activities also are concentrated by hydrological and
biological processes so that they become hazardous to both natural ecosystems and
human health. Mine drainage and leaching of mining wastes are serious sources of
metal pollution in water.
Nonmetallic salts
Desert soils often contain high concentrations of soluble salts, including toxic selenium
and arsenic. Salts such as sodium chloride that are nontoxic at low concentrations also
can be mobilized by irrigation and concentrated by evaporation, reaching levels that are
toxic for plants and animals. Acids and bases
Acids are released as by-products of industrial processes (e.g. leather tanning, metal
smelting and planting) Coal and oil combustion also leads to formation of atmospheric
sulfuric and nitric acids, which are disseminated by long-range transport processes.
Organic Chemicals
Many chemicals used in the chemical industry to make pesticides, plastics,
pharmaceuticals, pigments, and other products we use in everyday life are highly toxic.
The two most important sources of toxic organic chemicals in water are improper
disposal of industrial and household wastes and runoff of pesticides.
Many of the toxic organic chemicals (e.g. DDT, Dioxins, and other chlorinated
hydrocarbons) in water are passed through ecosystems and accumulated at high levels
in certain nontarget organisms. Hundreds of millions of toxic hazardous organic wastes
are thought to be stored in dumps, landfills, lagoons, and underground tanks in the
United States.
Sediment
Rivers have always carried sediment to the oceans, but erosion rates in many areas
have been greatly accelerated by human activities. Sources of erosion include forests,

grazing lands, and urban construction sites. Sediment fills lakes and reservoirs,
obstructs shipping channels, clogs hydroelectric turbines, and makes purification of
drinking water more costly. Excess sediment deposits can fill estuaries and smother
aquatic life on coral reefs and shoals near shore.
Sediment can also be beneficial. Mud carried by rivers nourishes floodplain farm fields.
Thermal Pollution and Thermal Shocks
Raising or lowering water temperatures from normal levels can adversely affect water
quality and aquatic life. Humans cause thermal pollution by altering vegetation cover
and runoff patterns, as well as by discharging heated water directly into rivers and
lakes. The cheapest way to remove heat from an industrial facility is to draw cool water
from an ocean, river, lake, or aquifer, run it through a heat-exchanger to extract excess
heat, and dump the heated water back into the original source. In some circumstances,
introducing heated water into a water body is beneficial.
Warming catfish-rearing ponds
Attract fish, birds, and marine mammals that find food and refuge there, especially
during cold weather.
Water Pollution Control
Source Reduction
The cheapest and most effective way to reduce pollution is to avoid producing it or
releasing it to the environment in the first place.
Industry can modify manufacturing processes so fewer wastes are created.
Recycling or reclaiming materials that otherwise might be discarded in the waste stream
also reduces pollution.
Nonpoint Sources and Land Management
Among the greatest remaining challenges in water pollution control are diffuse,
nonpoint pollution sources.
Nonpoint sources have many origins and numerous routes by which contaminants
enter ground and surface waters; therefore, it is difficult to identify, monitor, and
control all these sources and routes.
Some main causes of nonpoint pollution include agriculture, urban runoff, construction
sites, and land disposal.
Generally soil conservation methods also help protect water quality.
In urban areas, reducing materials carried away by storm runoff is helpful.

A good example of watershed management is seen in the Chesapeake Bay, America's
largest estuary.
Principal objectives of this plan include reducing nutrient loading, pollution prevention
measures, replanting thousands of hectares of seagrasses, and restoring wetlands that
filter out pollutants.
Although progress has been made, the goals of reducing both nitrogen and phosphate
levels by 40 percent and restoring viable fish and shellfish populations are still decades
away
Human Waste Disposal
Human and animal wastes usually create the most serious health-related water
pollution problems.
Natural Processes
In poorer countries of the world, most rural people simply go out into the fields and
forests to relieve themselves as they have always done. When population densities are
low, natural processes eliminate wastes quickly. Where intensive agriculture is
practiced, it has long been customary to collect human and animal waste to be spread
on the fields as fertilizer and become a source of disease-causing pathogens in the food
supply.
Until about fifty years ago, most rural American families and quite a few residents of
towns and small cities depended on a pit toilet or "outhouse" for waste disposal from
which the untreated wastes would seep into the ground.
The development of septic tanks and properly constructed drain fields represented a
considerable improvement in public health.
Municipal Sewage Treatment
Over the past 100 years, sanitary engineers have developed effective municipal
wastewater treatment systems to protect human health, ecosystem stability, and water
quality.
Primary treatment is the first step in municipal waste treatment that physically
separates large solids from the waste stream.
Secondary treatment consists of biological degradation of the dissolved organic
compounds.
Tertiary treatment removes plant nutrients, especially nitrates and phosphates, from
the secondary effluent.

In many American cities, sanitary sewers are connected to storm sewers, which carry
runoff from streets and parking lots which generally contain a variety of refuse,
fertilizers, pesticides, oils, rubber, tars, lead, and other undesirable chemicals.
Low-Cost Waste Treatment
The municipal sewage systems used in developed countries are often too expensive to
build and operate in the developing world where low-cost, low-tech alternatives for
treating wastes are needed.
One option is effluent sewerage, a hybrid between a traditional septic tank and a full
sewer system.
Another alternative is to use natural or artificial wetlands to dispose of wastes.
Wetland waste treatment systems are now operating in many developing countries.
Effluent from these operations can be used to irrigate crops or raise fish for human
consumption if care is taken to first destroy pathogens.
SOIL POLLUTION – SOURCES AND MEASUREMENTS
Addition of substances which adversely affect the quality of soil or its fertility is known
as soil pollution. Generally polluted water also pollute soil. Solid waste is a mixture of
plastics, cloth, glass, metal and organic matter, sewage, sewage sludge, building debris,
generated from households, commercial and industries establishments add to soil
pollution. Fly ash, iron and steel slag, medical and industrial wastes disposed on land
are important sources of soil pollution. In addition, fertilizers and pesticides from
agricultural use which reach soil
as run-off and land filling by municipal waste are growing cause of soil pollution. Acid
rain and dry deposition of pollutants on land surface also contribute to soil pollution.
Sources of soil pollution
Plastic bags – Plastic bags made from low density polyethylene (LDPE), is virtually
indestructible, create colossal environmental hazard. The discarded bags block drains
and sewage systems. Leftover food, vegetable waste etc. on which cows and dogs feed
may die due to the choking by plastic bags. Plastic is non biodegradable and burning of
plastic in garbage dumps release highly toxic and poisonous gases like carbon
monoxide, carbon dioxide, phosgene, dioxine and other poisonous chlorinated
compounds.

Industrial sources – It includes fly ash, chemical residues, metallic and nuclear
wastes. Large number of industrial chemicals, dyes, acids, etc. find their way into the
soil and are known to create many health hazards including cancer.
Agricultural sources – Agricultural chemicals especially fertilizers and pesticides
pollute the soil. Fertilizers in the run off water from these fields can cause
eutrophication in water bodies. Pesticides are highly toxic chemicals which affect
humans and other animals adversely causing respiratory problems, cancer and death.
Control of soil pollution
Indiscriminate disposal of solid waste should be avoided.
To control soil pollution, it is essential to stop the use of plastic bags and instead use
bags of degradable materials like paper and cloth. Sewage should be treated properly
before using as fertilizer and as landfills. The organic matter from domestic, agricultural
and other waste should be segregated and subjected to vermicomposting which
generates useful manure as a by product. The industrial wastes prior to disposal should
be properly treated for removing hazardous materials. Biomedical waste should be
separately collected and incinerated in proper incinerators.
AIR POLLUTION – SOURCES AND MEASUREMENTS
Natural Sources of Air Pollution
There are many natural sources of air quality degradation.
Natural fires release smoke.
Volcanoes spew out ash, acid mists, hydrogen sulfide, and other toxic gases.
Sea spray and decaying vegetation are major sources of reactive sulfur compounds in
the air.
Trees and bushes emit millions of tons of volatile organic compounds.
Pollen, spores, viruses, bacteria, and other small bits of organic material are present in
the air.
Bacterial metabolism of decaying vegetation in swamps and of cellulose in the guts of
termites and ruminant animals is responsible for large methane releases.
Human-Caused Air Pollution
Primary and Secondary Pollutants
Primary pollutants: those released directly from the source into the air in a harmful
form.

Secondary pollutants: modified to a hazardous form after they enter the air or are
formed by chemical reactions as components of the air mix and interact.
Solar radiation often provides the energy for these reactions.
Fugitive emissions: those that do not go through a smokestack (e.g. dust from soil
erosion, strip mining, rock crushing, and building construction).
Unconventional Pollutants
EPA has authority under the Clean Air Act to set emission standards (regulating the
amount released) for certain unconventional or noncriteria pollutants that are
considered especially hazardous or toxic.
Examples of these unconventional pollutants include asbestos, benzene, beryllium,
mercury, polychlorinated biphenyls, and vinyl chloride.
Aesthetic degradation: includes any undesireable changes in the physical
characteristics or chemistry of the atmosphere (e.g. noise, ordors and light pollution).
Conventional or Criteria Pollutants
Sulfur compounds
Natural sources: evaporation of sea spray, erosion of sulfate-containing dust from arid
soils, fumes from volcanoes and fumaroles, and biogenic emissions of hydrogen sulfide
and organic sulfur-containing compounds.
The predominant form of anthropogenic sulfur is sulfur dioxide from combustion of
sulfur-containing fuel.
Sulfur dioxide is a colorless corrosive gas that is directly damaging to both plants and
animals.
Can be oxidized to sulfur trioxide, which reacts with water vapor or dissolves in water
droplets to form sulfuric acid (major component of acid rain).
Nitrogen compounds
Nitrogen oxides: highly reactive gases formed when nitrogen in fuel or combustion air is
heated to temperatures above 650deg.C in the presence of oxygen, or when bacteria in
soil or water oxidize nitrogen-containing compounds.
Nitrogen oxides combine with water to make nitric acid, which is a major component of
atmospheric acidification.
Excess nitrogen also causes fertilization and eutrophication of inland waters and
coastal seas.
Carbon Oxides

Carbon dioxide (CO2) is the predominant form of carbon in the air.
Usually considered nontoxic and innocuous, increasing levels of carbon dioxide appears
to be causing a global climate warming.
Burning of fossil fuels is estimated to add between 5 and 5.5 billion tons of carbon to
the atmosphere each year.
Uncertainty exists about where the extra carbons goes.
Carbon monoxide: colorless, odorless, nonirritating but highly toxic gas.
About 90 percent of the carbon monoxide in the air is consumed in photochemical
reactions that produce ozone.
Metals and Halogens
Many toxic metals are mined and used in manufacturing processes or occur as trace
elements in fuels, especially coal.
Lead
Worldwide lead emissions amount to about 2 million metric tons per year, or two-thirds
of all metallic pollution.
Most lead is from leaded gasoline.
An estimated 20 percent of all inner-city children suffer some degree of mental
retardation from high environmental lead levels.
Mercury
Two largest sources of atmospheric mercury appear to be coal-burning power plants
and waste incinerators.Other toxic metals of concern are nickel, beryllium, cadmium,
thallium, uranium, cesium, and plutonium.Halogens (fluorine, chlorine, bromine, and
iodine) are highly reactive and generally toxic in their elemental form. About 600 million
tons of highly persistent chlorofluorocarbons (CFCs) are used annually worldwide in
spray propellants, refrigeration compressors, and for foam blowing. CFCs diffuse into
the stratosphere where they release chlorine and fluorine atoms that destroy the ozone
shield that protects the earth from U.V. radiation.
Particulate material
Particulate material: all atmospheric aerosols, whether solid or liquid.
Includes dust, ash, soot, lint, smoke, pollen, spores, algal cells, and many other
suspended materials. Particulates often are the most apparent form of air pollution
since they reduce visibility and leave dirty deposits on windows, painted surfaces, and

textiles. Respirable particles smaller than 2.5 micrometers are among the most
dangerous of this group because they can be drawn into the lungs.
Volatile organic compounds
Volatile organic compounds (VOCs): organic chemicals that exist as gases in the air.
Plants are the largest source of VOCs. A large number of other synthetic organic
chemicals, such as benzene, toluene, formaldehyde, vinyl chloride, phenols, chloroform,
and trichloroethylene, are released into the air by human activities.
These chemicals play an important role in the formation of photochemical oxidants.
Of the 188 air toxics listed in the Clean Air Act, about two-thirds are VOCs and most of
the rest are metal compounds. EPA has identified 33 chemical compounds considered
to be the greatest threat to public health in urban areas.
Photochemical oxidants
Photochemical oxidants: products of secondary atmospheric reactions driven by solar
energy. One of the most important reactions involves formation of singlet (atomic)
oxygen by splitting nitrogen dioxide (NO2). Then the atmoic oxygen reacts with another
molecule of O2 to make ozone (O3).
Ozone formed in the stratosphere provides a valuable shield for the biosphere by
absorbing incoming ultraviolet radiation. In ambient air, however, O3 is a strong
oxidizing reagent and damages vegetation, building materials, and sensitive tissues.
Effects of Air Pollution
Human Health
Heart attacks, respiratory diseases, and lung cancer all are significantly higher in
people who breathe dirty air, compared to matching groups in cleaner

environments.Conditions are often much worse in other countries than Canada or the
United States. The United Nations estimates that at least 1.3 billion people around the
world live in areas where air is dangerously polluted.
The most common route of exposure to air pollutants is by inhalation, but direct
absorption through the skin or contamination of food and water are also important
pathways. Because they are strong oxidizing agents, sulfates, SO2, NOx, and O3 act as
irritants that damage delicate tissues in the eyes and respiratory passages.
Carbon monoxide binds to hemoglobin and decreases the ability of red blood cells to
carry oxygen.
Some important chronic health effects of air pollutants include bronchitis and
emphysema.
Bronchitis: persistent inflammation of bronchi and bronchioles (large and small
airways in the lung) that cause a painful cough and involuntary muscle spasms that
constrict airways.
Emphysema: an irreversible obstructive lung disease in which airways become
permanently constricted and alveoli are damaged or even destroyed.
Half of all lungs examined at autopsy in the United States have some degree of alveolar
deterioration.
Smoking is undoubtedly the largest cause of obstructive lung disease and preventable
death in the world.
Plant Pathology
In the early days of industrialization, fumes from furnaces, smelters, refineries, and
chemical plants often destroyed vegetation and created desolate, barren landscapes
around mining and manufacturing centers.
Copper-nickel smelter at Sudbury, Ontario, is a notorious example of air pollution
effects on vegetation and ecosystems.
There are two probable ways that air pollutants damage plants.
They can be directly toxic, damaging sensitive cell membranes much as irritants do in
human lungs.
They can act as metabolic regulators or plant hormones and disrupt normal patterns of
growth and development.
Synergistic effects: effects caused following exposure to two factors which together is
more than the sum of exposure to each factor individually.

Pollutant levels too low to produce visible symptoms of damage may still have important
effects.
Acid Deposition
Acid precipitation: the deposition of wet acidic solutions or dry acidic particles from the
air. By the 1940's, it was known that pollutants, including atmospheric acids, could be
transported long distances by wind currents.
pH and atmospheric acidity
Acidity is described in terms of pH (the negative logarithm of the hydrogen ion
concentration in a solution). pH scale ranges from 0 to 14 with 7, the midpoint, being
neutral. Values less than 7 indicate progressively greater acidity, while above 7 are
progressively more alkaline. Normal, unpolluted rain generally has a pH of about 5.6
due to carbonic acid created by CO2 in the air.
Aquatic effects
Generally, reproduction is the most sensitive stage in fish life cycles.
Eggs and fry of many species are killed when the pH drops to about 5.0.
This level of acidification (pH 5.0) can also disrupt the food chain by killing aquatic
plants, insects, and invertebrates on which fish depend for food.
There are several ways acids kill fish.
Alters body chemistry
Destroys kills and prevents oxygen uptake
Causes bone decalcification
Disrupts muscle contraction.
Acid water leaches toxic metals, such as mercury and aluminum, out of soil and rocks.
Studies in the Adirondack Mountains of New York revealed that about half of the high
altitude lakes are acidified and have no fish.
Much of the western United States has relatively alkaline bedrock and carbonate-rich
soil, which counterbalance acids from the atmosphere.
Sulfates account for about two-thirds of the acid deposition in eastern North America
and most of Europe, while nitrates contribute most of the remaining one-third.
Forest damage
In the early 1980s, disturbing reports appeared of rapid forest declines in both Europe
and North America.

A 1980 survey on Camel's Hump Mountain in Vermont showed that seedling
production, tree density, and viability of spruce-fir forests at high elevations had
declined about 50 percent in 15 years.
By 1990, almost all the red spruce, once the dominant species on the upper part of the
mountain, were dead or dying.
European forests also are dying at an alarming rate.
In 1982, German foresters estimated only 8 percent of their forests showed pollution
damage.
By 1983, some 34 percent of the forest was affected.
By 1985, more than 4 million hectares (about half the total) were reported to be in a
state of decline.
Similar damage is reported in Czechoslovakia, Poland, Austria, and Switzerland.
Researchers at the Hubbard Brook Experimental Forest in New Hampshire have shown
that forest soils have become depleted of natural buffering reserves of basic cations
such as calcium and magnesium through years of exposure to acid rain.
Plant pathogens and insect pests may damage trees or attack trees debilitated by air
pollution.
Buildings and monuments
In cities throughout the world, some of the oldest and most glorious buildings and
works of art are being destroyed by air pollution.
Air pollution also damages ordinary buildings and structures by corroding steel in
reinforced concrete in the buildings as well as roads and bridges.
Visibility reduction
Foul air obscuring the skies above industrialized cities has long been recognized as a
problem.
Pollution affects rural areas as well (e.g. Grand Canyon National Park and Shenandoah
National Park).
Air Pollution Control
Moving Pollution to Remote Areas
Among the earliest techniques for improving local air quality was moving pollution
sources to remote locations and/or dispersing emissions with smokestacks.
Particulate Removal

Filters remove particle physically by trapping them in a porous mesh of cotton cloth,
spun glass fibers, or asbestos-cellulose, which allows air to pass through but holds
back solids. Electrostatic precipitators are the most common particulate controls in
power plants. Fly ash particles pick up an electrostatic surface charge as they pass
between large electrodes in the effluent stream.
Performance depends on particle size and chemistry, strength of the electric field, and
flue gas velocity.
Sulfur Removal
Sulfur removal can be done a variety of ways either by using low-sulfur fuel or by
removing sulfur from effluents.
Fuel switching and fuel cleaning
Switching from soft coal with a high sulfur content to low-sulfur coal can greatly reduce
sulfur emission.
Changing to another fuel, such as natural gas or nuclear energy, can eliminate all
sulfur emissions as well as those of particulates and heavy metals.
Alternative energy sources, such as wind and solar power, are preferable to either fossil
fuel or nuclear power, and are becoming economically competitive.
Coal can be crushed, washed, and gassified to remove sulfur and metals before
combustion.
Limestone injection and fluidized bed combustion
Sulfur emissions can be reduced as much as 90 percent by mixing crushed limestone
with coal before it is fed into a boiler.
A relatively new technique for burning, called fluidized bed combustion, offers several
advantages in pollution control.
Flue gas desulfurization
Crushed limestone, lime slurry, or alkali can be injected into a stack gas stream to
remove sulfur after combustion.
Sulfur recovery processes
Sulfur can be removed from effluent gases by processes that yield a usable product,
such as elemental sulfur, sulfuric acid, or ammonium sulfate.
Nitrogen Oxide Control
Staged burners, in which the flow of air and fuel are carefully controlled, can reduce
nitrogen oxide formation by as much as 50 percent.

The approach adopted by U.S. automakers for NOx reductions has been to use selective
catalysts to change pollutants to harmless substances.
Raprenox (rapid removal of nitrogen oxides) is a new technique for removing nitrogen
oxides that was developed by the U.S. Department of Energy Sandia Laboratory in
Livermore, California.
Hydrocarbon Controls
Closed systems that prevent escape of fugitive gases can reduce many hydrocarbon
emissions (e.g. positive crankcase ventilation (PCV) systems in automobiles).
Controls on fugitive losses from valves, pipes, and storage tanks in industry can have a
significant impact on air quality.
Afterburners are often the best method for destroying volatile organic chemicals in
industrial exhaust stacks.
XENOBIOTIC COMPOUNDS AND THEIR SOURCES
The word is derived from the Greek ‘xenos’ meaning foreign. Xenobiotics are compounds
which are not produced by a biological procedure and for which no equivalent exists in
nature. They present a particular hazard if they are subject to bioaccumulation
especially so if they are fat soluble since that enables them to be stored in the body fat
of organisms providing an obvious route into the food chain. Despite the fact that these
chemicals are man made, they may still be degraded by micro-organisms if they fit into
one of the following regimes; gratuitous degradation, a process whereby the xenobiot
resembles a natural compound sufficiently closely that it is recognised by the
organism’s enzymes and may be used as a food source, or cometabolism where the
xenobiot is degraded again by virtue of being recognized by the organism’s enzymes but
in this case its catabolism does not provide energy and so cannot be the sole carbon
source.
Consequently, cometabolism may be sustained only if a carbon source is supplied to
the organism. The ability of a single compound to be degraded can be affected by the
presence of other contaminants. For example, heavy metals can affect the ability of
organisms to grow, the most susceptible being Gram positive bacteria, then Gram
negative.
Fungi are the most resistant and actinomycetes are somewhere in the middle.
This being the case, model studies predicting the rate of contaminant degradation may
be skewed in the field where the composition of the contamination may invalidate the

study in that application. Soil micro-organisms in particular are very versatile and may
quickly adapt to a new food source by virtue of the transmission of catabolic plasmids.
Of all soil bacteria, Pseudomonads seem to have the most highly developed ability to
adapt quickly to new carbon sources.
In bacteria, the genes coding for degradative enzymes are often arranged in clusters,
or operons, which usually are carried on a plasmid. This leads to very fast transfer from
one bacterium to another especially in the case of Pseudomonas where many of the
plasmids are self-transmissible. The speed of adaptation is due in part to the exchange
of plasmids but in the case of the archaeans particularly, the pathways they carry,
which may have been latent over thousands of bacterial generations, owe their
existence to previous exposure over millions of years to an accumulated vast range of
organic molecules. It is suggested that, unless there has been evolutionary pressure to
the contrary, these latent pathways are retained to a large extent requiring little
modification if any to utilise new xenobiotics.
Briefly, the pathways may be expanded by adaptation to the new molecule, or very
much less commonly, wholescale insertion of ‘foreign’ genes may occur by genetic
manipulation. There have been several cases reported where catabolic pathways have
been expanded in the laboratory. Hedlund and Staley (2001) isolated a strain of Vibrio
cyclotrophicus from marine sediments contaminated with creosote. By supplying the
bacteria with only phenanthrene as a carbon and energy source, the bacteria were
trained to degrade several PAHs although some of these only by cometabolism with a
supplied carbon source.
Endocrine disrupters
To date, there are chemicals, including xenobiotics, which still resist degradation in the
environment. This may be due to a dearth, at the site of contamination, of organisms
able to degrade them fully or worse, microbial activity which changes them in such a
way that they pose a bigger problem than they did previously. One such example is
taken from synthetic oestrogens such as 17α-ethinyloestradiol commonly forming the
active ingredient of the birth control pills, and the natural oestrogens which, of course,
are not xenobiotics. Natural oestrogens are deactivated in humans by glucuronidation,
as shown in Fig., which is a conjugation of the hormone with UDP-glucuronate making
the compound more polar and easily cleared from the blood by the kidneys. It is in this
modified and inactive form that it is excreted into the sewage.

However, bacteria present in the aerobic secondary treatment in sewage treatment
plants, have the enzyme, β-glucuronidase, which removes this modification thus
reactivating the hormone. As an aside, glucuronidation is not confined to hormones but
is a process used to detoxify a number of drugs, toxins and carcinogens in the liver. The
enzyme catalysing this process is induced in response to prolonged exposure to the
toxin thus imparting increased tolerance or even resistance to the chemical.
Returning to the problem of elevated levels of active hormones in the waterways,
another aspect is that steroids do not occur in bacteria, although they are present in
fungi, and so bacteria lack the necessary pathways to allow complete degradation of
these hormones at a rate compatible with the dwell time in sewage treatment plants.
The consequence has been raised levels of reactivated oestrogen and 17α-
ethinyloestradiol in the waterways leading to disturbances of the endocrine, or
hormonal, system in fauna downstream from sewage treatment plants. Such
disturbances have been monitored by measuring the presence of the protein vitellogenin
(Sole et al. 2001) which is a precursor to egg yolk protein, the results of which have
indicated feminisation of male fish in many species including minnows, trout and
flounders. The source of environmental oestrogens is not confined to outfall from
sewage treatment plants; however, the fate of endocrine disrupters, examples of which
are given in Fig., in sewage treatment plants is the subject of much research (Byrns
2001).

Many other chemicals, including polyaromatic hydrocarbons (PAHs), dichloro
diphenyltrichloroethane (DDT), alkyl phenols and some detergents may also mimic the
activity of oestrogen. There is general concern as to the ability of some organisms to
accumulate these endocrine disrupters in addition to the alarm being raised as to the
accumulative effects on humans of oestrogen-like activity from a number of xenobiotic
sources.
To date there is no absolute evidence of risk to human health but the Environmental
Agency and Water UK are recommending the monitoring of environmental oestrogens in
sewage treatment outfall. Assays are being developed further to make these
assessments (Gutendorf and Westendorf 2001) and to predict potential endocrine
disrupter activity of suspected compounds (Takeyoshi et al 2002).
Oestrogen and progesterone are both heat labile. In addition, oestrogen appears to be
susceptible to treatment with ultra-violet light, the effects of which are augmented by
titanium dioxide (Eggins 1999). The oestrogen is degraded completely to carbon dioxide
and water thus presenting a plausible method for water polishing prior to consumption.
Another method for the removal of oestrogens from water, in this case involving
Aspergillus, has also been proposed (Ridgeway and Wiseman 1998). Sulphation of the
molecule by isolated mammalian enzymes, as a means of hormone inactivation is also
being investigated (Suiko 2000). Taken overall, it seems unlikely that elevated levels of
oestrogen in the waterways will pose a problem to human health in drinking water
although, this does not address the problem affecting hormone-susceptible organisms
living in contaminated water and thus exposed to this potential hazard.
New discoveries

Almost daily, there are novel bacteria being reported in the literature which have been
shown to have the capacity to degrade certain xenobiots. Presumably the mutation
which occurred during the evolution of the organism conferred an advantage, and
selective pressure maintained that mutation in the DNA, thus producing a novel strain
with an altered phenotype.
Some example of such isolates is described here. Reference has already been made to
some PAHs mimicking oestrogen which earns those chemicals the title of ‘endocrine
disrupters’. This is in addition to some being toxic for other reasons and some being
carcinogenic or teratogenic. The PAHs are derived primarily from the petrochemicals
industry and are polycyclic hydrocarbons of three or more rings which include as
members, naphthalene and phenanthrene and historically have been associated with
offshore drilling, along with alkylphenols. Several genera of bacteria are now known to
be able to degrade PAHs and recently, a novel strain of Vibrio cyclotrophicus able to
digest naphthalene and phenanthrene, was isolated from creosote-contaminated marine
sediments from Eagle Harbour, Washington, USA.
It would appear that bacteria isolated from the same marine or estuarine environments
may vary quite considerably in their abilities to degrade certain PAHs.
This observation is viewed as indicative of diverse catabolic pathways demonstrated by
these organisms and awaiting our full understanding (Hedlund and Staley 2001).
Polycyclic hydrocarbons (PCBs) are xenobiotics which, due to their high level of
halogenation, are substrates for very few pathways normally occurring in nature.
However, a strain of Pseudomonas putida able to degrade PCBs, was isolated recently
from wastewater outflow from a refinery. This was achieved by the bacterium employing
two pathways encoded by two separate operons; the tod pathway employed in toluene
degradation, and the cmt pathway which normally is responsible for the catabolism of
p-cumate which is a substituted toluene. The mutation which allowed this strain to
utilise the cmt pathway was found to be a single base change to the promoter-operator
sequence. This allowed all the enzymes in this pathway to be expressed under
conditions where their synthesis would normally be repressed. Thus, the two pathways
could work in conjunction with each other to metabolise PCBs, a relationship described
as mosaic (Ohta et al 2001).

The pthalates are substituted single-ring phenols and include terephthalic acid and its
isomers, the major chemicals used in manufacture of polyester fibres, films, adhesives,
coatings and plastic bottles.
In a recent analysis of anaerobic sewage sludge, a methanogenic consortium of over 100
bacterial clones was found to have the capability to digest terephthalate.
Characterisation of these by analysis of their ribosomal DNA sequences revealed that
almost 70% were archaeans most of which had not been previously identified, and that
nearly 90% of the total bacteria comprised two of the novel Archaean species. These two
species are believed to be responsible for the degradation of terephthalic acid (Wu et al
2001). During wastewater treatment, terepthalic acid is usually treated by aerobic
processes. However, this consortium, or others like it provide an anaerobic alternative
which, being methanogenic, may be structured to offset processing costs by the
utilisation of the methane.
BIOMAGNIFICATION
Pollutants that exist in small amounts in the environment (such as certain heavy
metals and organic agents found in pesticides) become concentrated in organisms near
the top of the food chain. In an estuary, for example, microorganisms called plankton
may absorb small amounts of pollutants such as PCBs (polychlorinated biphenyls); fish
that eat lots of plankton might retain the pollutants in their tissues; birds or people that
eat the fish might concentrate the pollutants still more. This process, called
biomagnification, can produce health issues. Some substances that are capable of
bioaccumulating include PCBs, fluoride, dioxins, boron, DDT, and mercury.
BIOINDICATORS
Bioindicators are organisms, such as lichens,birds and bacteria, that are used to
monitor the health of the environment. The organisms and organism associations are
monitored for changes that may indicate a problem within their ecosystem. The changes
can be chemical, physiological or behavioural. Bioindicators are relevant for Ecological
health. Ecological health can be viewed in terms of ecosystems, whereby structural and
functional characteristics are maintained. Ecological health can be expanded to include
many aspects of human health and well-being. Each organism within an ecosystem has
the ability to report on the health of its environment.
Bioindicators are used to: detect changes in the natural environment, monitor for the
presence of pollution and its effect on the ecosystem in which the organism lives,

monitor the progress of environmental cleanup and test substances, like drinking
water, for the presence of contaminants.
Specific physiological and behavioral changes in bioindicators are used to detect
changes in environmental health. The specific changes differ from organism to
organism. The use of organisms as bioindicators encompasses many areas of science.
Wildlife conservation genetics is an example of how traditional approaches can be
combined with emerging biotechnologies to improve accuracy, and to collect information
not available through conventional methods. Wildlife conservation genetics combines
traditional monitoring of wildlife populations, like raccoons, with the scientific discipline
of genetics, to gain information about the health of ecosystems.
Several biotechology – based methods use microorganisms to test environmental health.
Unlike traditional methods,biotechnology - based methods do not rely on observation
alone but set out to create specific reactions that indicate the presence of a specific
pollutant or an unwanted microorganism. In this way they are similar to traditional
chemical analysis of environmental samples.
In traditional bioassays,a bioindicator organism or organisms association are
introduced to environmental samples, such as soil or water,and researchers observe
any changes that occur as a result of exposure. These methods are based primarily on
observation to detect changes. Bioindicators can be a measure, an index of measures,
or a model that characterizes an ecosystem or one of its critical components. They are
also a method of monitoring or detecting the negative impacts that industrial activity
has on the environment. This information helps develop strategies that will prevent or
lower such effects and make industry more sustainable. The role of bioindicators in
sustainable development will help ensure that industry leaves the smallest footprint
possible on the environment.
BIOMONITORING: BIOSENSORS AND BIOCHIPS.
A biosensor is a two-component analytical device comprised of a biological recognition
element that outputs a measurable signal to an interfaced transducer (Fig.).

Biorecognition typically relies on enzymes, whole cells, antibodies, or nucleic acids,
whereas signal transduction exploits electrochemical (amperometric,
chronoamperometric, potentiometric, field-effect transistors, conductometric,
capacitative), optical (absorbance, reflectance, luminescence, chemiluminescence,
bioluminescence, fluorescence, refractive index, light scattering), piezoelectric (mass
sensitive quartz crystal microbalance), magnetic, or thermal (thermistor, pyroelectric)
interfaces. This wide selection of interchangeable components has resulted in a
similarly wide selection of biosensors focused here toward those related to
environmental monitoring.
The detection of specific analytes of importance to environmental monitoring can be
achieved with great precision using analytical techniques that center around mass
spectrometry (MS), such as gas chromatography (GC)-MS, liquid chromatography (LC)-
MS, liquid chromatography coupled to tandem MS (LC-MS2), ion trap (IT)-MS, and
quadrupole linear ion trap (QqLIT)-MS. With great precision, however, comes significant
time, effort, and expense. Samples must be collected and transported to the obligatory
confinements of the laboratory, and requisite preconcentration and cleanup steps must
be performed prior to the sample being analyzed on an expensive, high-technology
instrument by accompanying trained technical personnel.
Considering that some percentage of the samples collected will be negative, either not
being contaminated or containing the target analyte at concentrations too low to be
detected, the adjusted cost on a per positive sample basis can be extensive. Although
biosensors cannot unequivocally replace the replicate accuracy and reproducibility of
conventional analytical instrumentation, they can complement and supplement their
operation through ease of sample preprocessing, which is often minimal to none, on-site
field portability, simplicity and rapidity of operation, versatility, real-time to near-real-
time monitoring capabilities, and miniaturization that has evolved down to a “lab-on-a-
chip” format. Biosensors can therefore often find their niche as continuous monitors of

environmental contamination or as bioremediation process monitoring and control tools
to provide informational data on what contaminants are present, where they are
located, and a very sensitive and accurate evaluation of their concentrations in terms of
bioavailability. Bioavailability measurements are central to environmental monitoring as
well as risk assessment because they indicate the biological effect of the chemical,
whether toxic, cytotoxic, genotoxic, mutagenic, carcinogenic, or endocrine disrupting,
rather than mere chemical presence as is achieved with analytical instruments.
Despite their benefits, biosensors remain relatively unused in the environmental
monitoring/bioremediation fields, due primarily to a lack of real-world, real-sample
testing and standardization against conventional analytical techniques. Thus, although
biosensors show significant promise, it is clear that more field validation studies need to
be performed before regulatory agencies and other end users will gain sufficient
confidence to adopt their routine use.
Enzyme-based biosensors
The historical foundation of the biosensor rests with the enzyme glucose oxidase and its
immobilization on an oxygen electrode by Leland Clark in the 1960s for blood glucose
sensing. Although the research emphasis of enzyme-based biosensors continues to be
driven by more lucrative medical diagnostics, there has been a predictable application
overlap toward environmental monitoring as well. Enzymes act as organic catalysts,
mediating the reactions that convert substrate into product. Since enzymes are highly
specific for their particular substrate, the simplest and most selective enzyme-based
biosensors merely monitor enzyme activity directly in the presence of the substrate.
Perhaps the most relevant examples are the sulfur/sulfate-reducing bacterial
cytochrome c3 reductases that reduce heavy metals. Michel et al. (2003) immobilized
cytochrome c3 on a glassy carbon electrode and monitored its redox activity
amperometrically in the presence of chromate [Cr(VI)] with fair sensitivity (lower
detection limit of 0.2 mg/L) and rapid response (several minutes) (Figure 9.2). When
tested under simulated groundwater conditions, the biosensor did cross-react with
several other metal species, albeit at lower sensitivities, and was affected by
environmental variables such as pH, temperature, and dissolved oxygen, thus
exemplifying certain disadvantages common to enzyme-based biosensors. Similarly
operated biosensors for the groundwater contaminant perchlorate using perchlorate
reductase as the recognition enzyme (detection limit of 10 µg/L) (Okeke et al., 2007),

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