APPLIED ENVIRONMENTAL CHEMISTRY
5MARKS:
1)Environmental chemistry
Environmental chemistry is the scientific study of the chemical and biochemical
phenomena that occur in natural places. It should not be confused with green
chemistry, which seeks to reduce potential pollution at its source. It can be
defined as the study of the sources, reactions, transport, effects, and fates of
chemical species in the air, soil, and water environments; and the effect of human
activity on these. Environmental chemistry is an interdisciplinary science that
includes atmospheric, aquatic and soil chemistry, as well as heavily relying on
analytical chemistry and being related to environmental and other areas of
science.
Environmental chemistry involves first understanding how the uncontaminated
environment works, which chemicals in what concentrations are present
naturally, and with what effects. Without this it would be impossible to accurately
study the effects humans have on the environment through the release of
chemicals.
Environmental chemists draw on a range of concepts from chemistry and various
environmental sciences to assist in their study of what is happening to a chemical
species in the environment. Important general concepts from chemistry include
understanding chemical reactions and equations, solutions, units, sampling, and
analytical techniques.
Contamination
A contaminant is a substance present in nature at a level higher than typical levels
or that would not otherwise be there.[2][3] This may be due to human activity.
The term contaminant is often used interchangeably with pollutant, which is a
substance that has a detrimental impact on the surrounding environment.[4][5]
Whilst a contaminant is sometimes defined as a substance present in the
environment as a result of human activity, but without harmful effects, it is
sometimes the case that toxic or harmful effects from contamination only
become apparent at a later date.
The "medium" (e.g. soil) or organism (e.g. fish) affected by the pollutant or
contaminant is called a receptor, whilst a sink is a chemical medium or species
that retains and interacts with the pollutant.
Environmental indicators
Chemical measures of water quality include dissolved oxygen (DO), chemical
oxygen demand (COD), biochemical oxygen demand (BOD), total dissolved solids
(TDS), pH, nutrients nitrates and phosphorus), heavy metals (including copper,
zinc, cadmium, lead and mercury), and pesticides.
Applications
Environmental chemistry is used by the Environment Agency (in England and
Wales), the Environmental Protection Agency (in the United States) the
Association of Public Analysts, and other environmental agencies and research
bodies around the world to detect and identify the nature and source of
pollutants. These can include:
Heavy metal contamination of land by industry. These can then be transported
into water bodies and be taken up by living organisms.
Nutrients leaching from agricultural land into water courses, which can lead to
algal blooms and eutrophication.[7]
Urban runoff of pollutants washing off impervious surfaces (roads, parking lots,
and rooftops) during rain storms. Typical pollutants include gasoline, motor oil
and other hydrocarbon compounds, metals, nutrients and sediment (soil).[8]
2)Types of Reactions:
Combustion
A combustion reaction is when all substances in a compound are combined with
oxygen, which then produces carbon dioxide and water. Combustion is commonly
called burning. It is an exothermic reaction, which means heat is produced and is
easily distinguished. Combustion occurs predominantly in automobiles, homes,
and in factories. An example of a combustion reaction is as follows:
CxHy + O2 --> CO2 + H2O
Synthesis
A synthesis reaction is when there is a combination of two or more substances
and a compound results. An example of a synthesis reaction is as follows:
A + B --> AB
Decomposition
Decomposition is the opposite of synthesis. It is when a compound is broken
down into simpler substances, usually through electrolysis. An example of
decomposition is as follows:
AB --> A + B
Dissociation
Dissociation is commonly mistaken as decomposition, but there is a difference.
When the compound is broken down, it is broken down into ions rather than
atoms, so there will be a charge on the product side of the equation. An example
of dissociation is as follows:
AB --> A+ + BSingle Replacement Reactions
In a single replacement reaction, there is a rule that is always followed. A metal
replaces a metal, or a nonmetal replaces a nonmetal. An example of a single
replacement reaction is as follows:
A + BC --> AC + B
Double Replacement Reactions
In a double replacement reaction, this rule is always followed. A metal replaces a
metal, and a nonmetal replaces a nonmetal. An example of a double replacement
reaction is as follows:
AB + XY --> AY + XB
3)Definition and measurement
pH
pH is defined as minus the decimal logarithm of the hydrogen ion activity, aH+, in
a solution.
This definition was adopted because ion-selective electrodes, which are used to
measure pH, respond to activity. Ideally, electrode potential, E, follows the Nernst
equation, which, for the hydrogen ion can be written as
where E is a measured potential, E0 is the standard electrode potential, R is the
gas constant, T is the temperature in kelvins, F is the Faraday constant. For H+
number of electrons transferred is one. It follows that electrode potential is
proportional to pH when pH is defined in terms of activity. Precise measurement
of pH is presented in International Standard ISO 31-8 as follows:[7] A galvanic cell
is set up to measure the electromotive force (e.m.f.) between a reference
electrode and an electrode sensitive to the hydrogen ion activity when they are
both immersed in the same aqueous solution. The reference electrode may be a
silver chloride electrode or a calomel electrode. The hydrogen-ion selective
electrode is a standard hydrogen electrode.
Reference electrode | concentrated solution of KCl || test solution | H2 | Pt
Firstly, the cell is filled with a solution of known hydrogen ion activity and the
emf, ES, is measured. Then the emf, EX, of the same cell containing the solution of
unknown pH is measured.
The difference between the two measured emf values is proportional to pH. This
method of calibration avoids the need to know the standard electrode potential.
The proportionality constant, 1/z is ideally equal
slope".
to the "Nerstian
The pH scale is logarithmic and therefore pH is a dimensionless quantity.
p[H]
This was the original definition of Sørensen,[4] which was superseded in favor of
pH in 1924. However, it is possible to measure the concentration of hydrogen ions
directly, if the electrode is calibrated in terms of hydrogen ion concentrations.
One way to do this, which has been used extensively, is to titrate a solution of
known concentration of a strong acid with a solution of known concentration of
strong alkali in the presence of a relatively high concentration of background
electrolyte. Since the concentrations of acid and alkali are known, it is easy to
calculate the concentration of hydrogen ions so that the measured potential can
be correlated with concentrations. The calibration is usually carried out using a
Gran plot.[8] The calibration yields a value for the standard electrode potential,
E0, and a slope factor, f, so that the Nernst equation in the form
can be used to derive hydrogen ion concentrations from experimental
measurements of E. The slope factor, f, is usually slightly less than one. A slope
factor of less than 0.95 indicates that the electrode is not functioning correctly.
The presence of background electrolyte ensures that the hydrogen ion activity
coefficient is effectively constant during the titration. As it is constant, its value
can be set to one by defining the standard state as being the solution containing
the background electrolyte. Thus, the effect of using this procedure is to make
activity equal to the numerical value of concentration.
The difference between p[H] and pH is quite small. It has been stated[9] that pH
= p[H] + 0.04. It is common practice to use the term "pH" for both types of
measurement.
pH in nature
pH-dependent plant pigments that can be used as pH indicators occur in many
plants, including hibiscus, red cabbage (anthocyanin) and red wine. The juice of
citrus fruits is acidic because of the presence of citric acid. Other carboxylic acids
occur in many living systems. For example, lactic acid is produced by muscle
activity. The state of protonation of phosphate derivatives, such as ATP is pHdependent. The functioning of the oxygen-transport enzyme hemoglobin is
affected by pH in a process known as the Root effect.
20MARKS:
1)Calculations of Ph
The calculation of the pH of a solution containing acids and/or bases is an
example of a chemical speciation calculation, that is, a mathematical procedure
for calculating the concentrations of all chemical species that are present in the
solution. The complexity of the procedure depends on the nature of the solution.
For strong acids and bases no calculations are necessary except in extreme
situations. The pH of a solution containing a weak acid requires the solution of a
quadratic equation. The pH of a solution containing a weak base may require the
solution of a cubic equation. The general case requires the solution of a set of
non-linear simultaneous equations.
A complicating factor is that water itself is a weak acid and a weak base. It
dissociates according to the equilibrium
2H2O
H3O+(aq) + OH-(aq)
with a dissociation constant, Kw defined as
Kw = [H+][OH-]
where [H+] stands for the concentration of the aquated hydronium ion and [OH-]
represents the concentration of the hydroxide ion. Kw has a value of about 10-14
at 25°C, so pure water has a pH of about 7. This equilibrium needs to be taken
into account at high pH and when the solute concentration is extremely low.
Strong acids and bases
Strong acids and bases are compounds that, for practical purposes, are
completely dissociated in water. Under normal circumstances this means that the
concentration of hydrogen ions in acidic solution can be taken to be equal to the
concentration of the acid. The pH is then equal to minus the logarithm of the
concentration value. Hydrochloric acid (HCl) is an example of a strong acid. The
pH of a 0.01M solution of HCl, is equal to −log10(0.01), that is, pH = 2. Sodium
hydroxide, NaOH, is an example of a strong base. The p[OH] value of a 0.01M
solution of NaOH, is equal to −log10(0.01), that is, p[OH] = 2. From the definition
of p[OH] above, this means that the pH is equal to about 12. For solutions of
sodium hydroxide at higher concentrations the self-ionization equilibrium must
be taken into account.
Self-ionization must also be considered when concentrations are extremely low.
Consider, for example, a solution of hydrochloric acid at a concentration of
5×10−8M. The simple procedure given above would suggest that it has a pH of
7.3. This is clearly wrong as an acid solution should have a pH of less than 7.
Treating the system as a mixture of hydrochloric acid and the amphoteric
substance water, a pH of 6.89 results.
Weak acids and bases
A weak acid or the conjugate acid of a weak base can be treated using the same
formalism.
Acid: HA
Base: HA+
H+ + AH+ + A
First, and acid dissociation constant is defined as follows. Electrical charges are
omitted from subsequent equations for the sake of generality
and its values is assumed to have been determined by experiment. This being so,
there are three unknown concentrations, [HA], [H+] and [A-]] to determine by
calculation. Two additional equations are needed. One way to provide them is to
apply the law of mass conservation in terms if the two "reagents" H and A.
CA = [A] + [HA]
CH = [H] + [HA]
C stands for analytical concentration. In some texts one mass balance equation is
replaced by an equation of charge balance. This is satisfactory for simple cases
like this one, but is more difficult to apply to more complicated cases as those
below. Together with the equation defining Ka, there are now three equations in
three unknowns. When an acid is dissolved in water CA = CH = Ca, the
concentration of the acid, so [A] = [H]. After some further algebraic manipulation
an equation in the hydrogen ion concentration may be obtained.
[H]2 + Ka[H] - Ka Ca = 0
Solution of this quadratic equation gives the hydrogen ion concentration and
hence p[H] or, more loosely, pH. This procedure is illustrated in an ICE table which
can also be used to calculate the pH when some additional (strong) acid or alkali
has been added to the system, that is, when CA ≠ CH.
For example, what is the pH of a 0.01M solution of benzoic acid, pKa = 4.19?
Step 1: Ka = 10-4.19 = 6.46×10−5
Step 2: Set up the quadratic equation. H]2 + 6.46×10−5[H] - 6.46×10−7 = 0
Step 3: Solve the quadratic equation. [H+] = 7.74×10-4; pH = 3.11
For alkaline solutions an additional term is added to the mass-balance equation
for hydrogen. Since addition of hydroxide reduces the hydrogen ion
concentration, and the hydroxide ion concentration is constrained by the selfionization equilibrium to be equal to Kw/[H+]
CH = [H] + [HA] -Kw / [H]
In this case the resulting equation in [H] is a cubic equation.
General method
Some systems, such as with polyprotic acids, are amenable to spreadsheet
calculations.[22] With three or more reagents or when many complexes are
formed with general formulae such as ApBqHr the following general method can
be used to calculate the pH of a solution. For example, with three reagents, each
equilibrium is characterized by and equilibrium constant, β.
[ApBqHr] =βpqr[A]p[B]q[H]R
Next, write down the mass-balance equations for each reagent
CA = [A] + Σp βpqr[A]p[B]q[H]r
CB = [B] + Σq βpqr[A]p[B]q[H]r
CH = [H] + Σr βpqr[A]p[B]q[H]r - Kw[H]-1
Note that there are no approximations involved in these equations, except that
each stability constant is defined as a quotient of concentrations, not activities.
Much more complicated expressions are required if activities are to be used.
There are 3 non-linear simultaneous equations in the three unknowns, [A], [B]
and [H]. Because the equations are non-linear, and because concentrations may
range over many powers of 10, the solution of these equations is not
straightforward. However, many computer programs are available which can be
used to perform these calculations; for details see chemical
equilibrium#computer programs. There may be more than three reagents. The
calculation of hydrogen ion concentrations, using this formalism, is a key element
in the determination of equilibrium constants by potentiometric titration.
2)Branches:
The branches of microbiology can be classified into pure and applied sciences.[16]
Microbiology can be also classified based on taxonomy, in the cases of
bacteriology, mycology, protozoology, and phycology. There is considerable
overlap between the specific branches of microbiology with each other and with
other disciplines.
Pure microbiology
Taxonomic arrangement






Bacteriology: The study of bacteria.
Mycology: The study of fungi.
Protozoology: The study of protozoa.
Phycology (or algology): The study of algae.
Parasitology: The study of parasites.
Immunology: The study of the immune system.
 Virology: The study of the viruses.
 Nematology:The study of the nematodes
Integrative arrangement
 Microbial cytology: The study of microscopic and submicroscopic details of
microorganisms.
 Microbial physiology: The study of how the microbial cell functions
biochemically. Includes the study of microbial growth, microbial
metabolism and microbial cell structure.
 Microbial ecology: The relationship between microorganisms and their
environment.
 Microbial genetics: The study of how genes are organized and regulated in
microbes in relation to their cellular functions. Closely related to the field of
molecular biology.
 Cellular microbiology: A discipline bridging microbiology and cell biology.
 Evolutionary microbiology: The study of the evolution of microbes. This
field can be subdivided into:
 Microbial taxonomy: The naming and classification of microorganisms.
 Microbial systematics: The study of the diversity and genetic relationship of
microorganisms.
 Generation microbiology: The study of those microorganisms that have the
same characters as their parents.
 Systems microbiology: A discipline bridging systems biology and
microbiology.
 Molecular microbiology: The study of the molecular principles of the
physiological processes in microorganisms.
Other
 Nano microbiology: The study of those microorganisms on nano level.
 Exo microbiology (or Astro microbiology): The study of microorganisms in
outer space.
 Weapon microbiology: The study of those microorganisms which are using
in weapon industries.
Applied microbiology
 Medical microbiology: The study of the pathogenic microbes and the role of
microbes in human illness. Includes the study of microbial pathogenesis
and epidemiology and is related to the study of disease pathology and
immunology.
 Pharmaceutical microbiology: The study of microorganisms that are related
to the production of antibiotics, enzymes, vitamins,vaccines, and other
pharmaceutical products and that cause pharmaceutical contamination and
spoil.
 Industrial microbiology: The exploitation of microbes for use in industrial
processes. Examples include industrial fermentation and wastewater
treatment. Closely linked to the biotechnology industry. This field also
includes brewing, an important application of microbiology.
 Microbial biotechnology: The manipulation of microorganisms at the
genetic and molecular level to generate useful products.
 Food microbiology and Dairy microbiology: The study of microorganisms
causing food spoilage and foodborne illness. Using microorganisms to
produce foods, for example by fermentation.
 Agricultural microbiology: The study of agriculturally relevant
microorganisms. This field can be further classified into the following:
 Plant microbiology and Plant pathology: The study of the interactions
between microorganisms and plants and plant pathogens.
 Soil microbiology: The study of those microorganisms that are found in soil.
 Veterinary microbiology: The study of the role in microbes in veterinary
medicine or animal taxonomy.
 Environmental microbiology: The study of the function and diversity of
microbes in their natural environments. This involves the characterization
of key bacterial habitats such as the rhizosphere and phyllosphere, soil and
groundwater ecosystems, open oceans or extreme environments
(extremophiles). This field includes other branches of microbiology such as:
o Microbial ecology
o Microbially-mediated nutrient cycling
o Geomicrobiology
o Microbial diversity
o Bioremediation
 Water microbiology (or Aquatic microbiology): The study of those
microorganisms that are found in water.
 Aeromicrobiology (or Air microbiology): The study of airborne
microorganisms.
 Epidemiology: The study of the incidence, spread, and control of disease.
3) Environmental microbiology:
Environmental microbiology is the study of the composition and physiology of
microbial communities in the environment.[1][2][3] The environment in this case
means the soil, water, air and sediments covering the planet and can also include
the animals and plants that inhabit these areas. Environmental microbiology also
includes the study of microorganisms that exist in artificial environments such as
bioreactors. This field of microbiology was started as a result of experiments led
by Martinus Beijerinck and Sergi Winogradsky.
Microbial life is amazingly diverse and microorganisms literally cover the planet.
Biodegradation of pollutants
Microbial biodegradation of pollutants plays a pivotal role in the bioremediation
of contaminated soil and groundwater sites. Such pollutants include
chloroethenes, steroids, organophosphorus compounds, alkanes, PAHs and PCBs.
Oil biodegradation
Petroleum oil is toxic, and pollution of the environment by oil causes major
ecological concern. Oil spills of coastal regions and the open sea are poorly
containable and mitigation is difficult; much of the oil can, however, be
eliminated by the hydrocarbon-degrading activities of microbial communities, in
particular the hydrocarbonoclastic bacteria (HCB). These organisms can help
remedy the ecological damage caused by oil pollution of marine habitats. HCB
also have potential biotechnological applications in the areas of bioplastics and
biocatalysis.
Environmental genomics of cyanobacteria
The application of molecular biology and genomics to environmental microbiology
has led to the discovery of a huge complexity in natural communities of microbes.
Diversity surveying, community fingerprinting and functional interrogation of
natural populations have become common, enabled by a range of molecular and
bioinformatics techniques. Recent studies on the ecology of cyanobacteria have
covered many habitats and have demonstrated that cyanobacterial communities
tend to be habitat-specific and that much genetic diversity is concealed among
morphologically simple types. Molecular, bioinformatics, physiological and
geochemical techniques have combined in the study of natural communities of
these bacteria.
Corynebacteria
Corynebacteria are a diverse group Gram-positive bacteria found in a range of
different ecological niches such as soil, vegetables, sewage, skin, and cheese
smear. Some, such as Corynebacterium diphtheriae, are important pathogens
while others, such as Corynebacterium glutamicum, are of immense industrial
importance. C. glutamicum is one of the biotechnologically most important
bacterial species with an annual production of more than two million tons of
amino acids, mainly L-glutamate and L-lysine.
Legionella
Legionella is common in many environments, with at least 50 species and 70
serogroups identified. Legionella is commonly found in aquatic habitats where its
ability to survive and to multiply within different protozoa equips the bacterium
to be transmissible and pathogenic to humans.
Archaea
Originally, Archaea were once thought of as extremophiles existing only in hostile
environments but have since been found in all habitats and may contribute up to
20% of total biomass. Archaea are particularly common in the oceans, and the
archaea in plankton may be one of the most abundant groups of organisms on the
planet. Archaea are subdivided into four phyla of which two, the Crenarchaeota
and the Euryarchaeota, are most intensively studied.
Lactobacillus
Lactobacillus species are found in the environment mainly associated with plant
material. They are also found in the gastrointestinal tract of humans, where they
are symbiotic and make up a portion of the gut flora.
Aspergillus
Aspergillus spores are common components of aerosols where they drift on air
currents, dispersing themselves both short and long distances depending on
environmental conditions. When the spores come in contact with a solid or liquid
surface, they are deposited and if conditions of moisture are right, they
germinate. The ability to disperse globally in air currents and to grow almost
anywhere when appropriate food and water are available means that ubiquitous
is among the most common adjectives used to describe these moulds.[15]
Microbial nitrogen cycling
Microorganisms that convert gaseous nitrogen (N2) to a form suitable for use by
living organisms are pivotal for life on earth. This process is called nitrogen
fixation. Another set of microbial reactions utilise the bioavailable nitrogen
creating N2 and completing the cycle in a process called denitrification. This
crucial nutrient cycle has long been the subject of extensive research.
Rhizobia
Symbiotic nitrogen fixation is a mutualistic process in which bacteria reside inside
plants and reduce atmospheric nitrogen to ammonia. This ammonia can then be
used by the plant for the synthesis of proteins and other nitrogen-containing
compounds such as nucleic acids. The Gram-negative soil bacteria that carry out
this process are collectively referred to as rhizobia (from the Greek words Riza =
Root and Bios = Life).
4)Colorimetry:
Colorimetry is "the science and technology used to quantify and describe
physically the human color perception."[1] It is similar to spectrophotometry, but
is distinguished by its interest in reducing spectra to the physical correlates of
color perception, most often the CIE 1931 XYZ color space tristimulus values and
related quantities.
Instruments
Colorimetric equipment is similar to that used in spectrophotometry. Some
related equipment is also mentioned for completeness.
 A tristimulus colorimeter measures the tristimulus values of a color.[3]
 A spectroradiometer measures the absolute spectral radiance (intensity) or
irradiance of a light source.[4]
 A spectrophotometer measures the spectral reflectance, transmittance, or
relative irradiance of a color sample.[4][5]
 A spectrocolorimeter is a spectrophotometer that can calculate tristimulus
values.
 A densitometer measures the degree of light passing through or reflected
by a subject.[3]
 A color temperature meter measures the color temperature of an incident
illuminant.
Tristimulus colorimeter
In digital imaging, colorimeters are tristimulus devices used for color calibration.
Accurate color profiles ensure consistency throughout the imaging workflow,
from acquisition to output.
Spectroradiometer, Spectrophotometer, Spectrocolorimeter
The absolute spectral power distribution of a light source can be measured with a
spectroradiometer, which works by optically collecting the light, then passing it
through a monochromator before reading it in narrow bands of wavelength.
Reflected color can be measured using a spectrophotometer (also called
spectroreflectometer or reflectometer), which takes measurements in the visible
region (and a little beyond) of a given color sample. If the custom of taking
readings at 10 nanometer increments is followed, the visible light range of 400700 nm will yield 31 readings. These readings are typically used to draw the
sample's spectral reflectance curve (how much it reflects, as a function of
wavelength)—the most accurate data that can be provided regarding its
characteristics.
CRT phosphors
The readings by themselves are typically not as useful as their tristimulus values,
which can be converted into chromaticity co-ordinates and manipulated through
color space transformations. For this purpose, a spectrocolorimeter may be used.
A spectrocolorimeter is simply a spectrophotometer that can estimate tristimulus
values by numerical integration (of the color matching functions' inner product
with the illuminant's spectral power distribution).[5] One benefit of
spectrocolorimeters over tristimulus colorimeters is that they do not have optical
filters, which are subject to manufacturing variance, and have a fixed spectral
transmittance curve—until they age.[6] On the other hand, tristimulus
colorimeters are purpose-built, cheaper, and easier to use.
The CIE recommends using measurement intervals under 5 nm, even for smooth
spectra.[4] Sparser measurements fail to accurately characterize spiky emission
spectra, such as that of the red phosphor of a CRT display, depicted aside.