ENVIRONMENTAL BIOTECHNOLOGY

ASSIGNMENT

TOPICS-

Biotechnology & organic pollution Biodegradation of halogenated hydrocarbons Polycyclic Aromatic Hydrocarbons (PAHs) Pesticides Detergents

Submitted by-

ANCHAL GARG

MSC EM- 3 SEM

ROLL NO-05

(1)Biotechnology and organic pollution A compound foreign to biological system is known as xenobiotic

compound. Anthropogenic organic pollutants are now dispersed throughout the

environment and can be highly recalcitrant to biodegradation by microorganisms.

Xenobiotics can be- weak, recalcitrant and persistent. Weak xenobiotics can be degraded or easily converted into non toxic one. Recalcitrant- compounds totally resistant to biodegradation (unusual

chlorine substitution,unusual bond sequences (3΄ & 4΄), highly condensed aromatic rings, and excessive molecular size (polyethylene) )

Persistent Organic Pollutants (POPs)- are chemical substances that persist in the environment, bioaccumulate through food web, and pose a risk of causing adverse effects to human health and the environment.

POP Global Historical Use/Source

aldrin and dieldrin

Insecticides used on crops such ascorn and cotton; also used for termite control.

Chlordane

Insecticide used on crops, including vegetables, small grains, potatoes,sugarcane, sugar beets, fruits, nuts,citrus, and cotton. Used on homelawn and garden pests. Also used extensively to control termites.

DDT Insecticide used on agricultural crops, primarily cotton, and insects that carry diseases such as malaria and typhus.

Endrin Insecticide used on crops such ascotton and grains; also used to control rodents.

MirexInsecticide used to combat fire ants, termites, and mealybugs.Also used as a fire retardant in plastics, rubber, and electrical products.

Heptachlor Insecticide used primarily against soil insects and termites. Also used against some crop pests and to combat malaria.

hexachlorobenz Fungicide used for seed treatment.

POP Global Historical Use/Source

ene

Also an industrial chemical used to make fireworks, ammunition, synthetic rubber, and other substances.Also unintentionally produced during combustion and the manufacture ofcertain chemicals.Also an impurity in certain pesticides.

PCBs

Used for a variety of industrial processes and purposes, including in electricaltransformers and capacitors, as heat exchange fluids, as paint additives, incarbonless copy paper, and in plastics.Also unintentionally produced during combustion.

Toxaphene Insecticide used to control pests on crops and livestock, and to kill unwanted fish in lakes.

dioxins and furans

Unintentionally produced during most forms of combustion, including burning of municipal and medical wastes, backyard burning of trash, and industrial processes.Also can be found as trace contaminants in certain herbicides, wood preservatives, and in PCB mixtures.

EPA list of some organic pollutants injected into environment by human activities—

1. Acenaphthlene2. Benzidine3. Carbon tetrachloride4. Chlorinated phenols5. Dichlorobenzene6. Hexachloroethane7. Naphthalene8. Polynucleated aromatic hydrocarbons ( benzopyrine, toluene)9. Polychlorinated biphenyls (PCBs)10.Hexachlorocyclohexane-BHC11. Pesticides- aldrin, DDT, endrin etc

Some of the microbes which can degrade various chemicals-

chemicals microbesHydrocarbons Pseudomonas, Nocardia, Arthrobacter, MycobacteriumPCBs Pseudomonas, Candida, AlcaligenesPhenolics Pseudomonas, Flavobacterium, Trichosporon, Bacillus,

Candida, AspergillusPAHs Arthrobacter, Nocardia, Alcaligenes, PseudomonasNaphthalene Pseudomonas, NocardiaOrganophosphates PseudomonasBenzene Mycobacterium, Alcaligenes

AEROBIC & ANAEROBIC BIODEGRADATION OF ORGANIC COMPOUNDS

Aerobic degradation- extent of degradation is correlated with the rate of oxygen consumption. Mono-oxygenase and dioxygenases and also peroxidases enzymes have the ability to degrade organic compounds by aerobic method.

Anaerobic degradation- though this is slow method, but needs long retention time and produce H2S gas, yet it is more advantageous than aerobic one due to its non dependence of oxygen supply. It thus save the cost of energy for oxygen transfer. Materials like cellulose and fats which remain unaffected by aerobic process, breakdown under this situation.

Biodegradation of petroleum compounds;

Petroleum compounds are categorized into 2 groups

Aliphatic hydrocarbon e.g. alkane, alcohol, aldehyde

Aromatic hydrocarbon e.g. benzene, phenol, toluene, catechol

Degradation of straight chain alliphatic hydrocarbons

BIODEGRADATION OF AROMATIC HYDROCARBONS

(2) Biodegradation of halogenated hydrocarbonsThe recalcitrance of organic pollutants increases with increasing halogenation. Hence our first aim to degrade halogenated hydrocarbons is to dehalogenate the compound.

Following dehalogenation processes are carried out for the removal of halogen atom from the ring-

1. Oxidative dehalogenation2. Hydrolytic dehalogenation3. Reductive dehalogenation

Theoretical pathways of TCE oxidation by monooxygenases and dioxygenases

(3) Polycyclic Aromatic Hydrocarbons (PAHs)

PAHs are aromatic compounds made up of 2 or more fused benzene rings. These are recalcitrant and can persist in environment for long periodsbut are conducive to biodegradation by certain enzymes found in bacteria and fungi.

Oxidoreductase such as laccase and cytochrome P450 monoxygenases have been exploited for enzymatic degradation of naphthalene.

Bacteria, fungi, yeasts, and algae have the ability to metabolize both lower and higher M.W. PAHs found in the natural environment most bacteria have been found to oxygenate the PAH initially to form dihydrodiol with a cis-configuration, which can be further oxidized to catechols.

Most fungi oxidize PAHs via a cytochrome P450 catalyzed mono- oxygenase reaction to form reactive arene oxides that can isomerize to phenols.

BIODEGRADATION OF NAPHTHALENE

(4) PesticidesWith the advent of Green revolution, there had been a quantum jump in the use of synthetic pesticides throughout the world to sustain high yielding crop varieties as they get easily attacked by pests.A number of them found to contaminate surface and ground water through run off from agricultural fields. Commonly used ones are- triazine derivatives, carbamates, organophosphates, aldrin, parquet, diuran etc.Although DDT is now banned, forits effect on Cental Nervous System as an organochlorine pesticide, it has however, been reported to be degraded to p-chlorophenyl acetic acid by a number of bacteria, algae and fungi.The filamentous basidiomycetes fungus Phaenerocheate (lignin degrader) is considered as versatile one and can degrade the fungicide PCP(Pentachlorophenol) and DDT as well with the help of mixture of peroxidase enzymes.Pesticide degradation is the process by which a pesticide is transformed into a benign substance that is environmentally compatible with the site to which it was applied. Globally, an estimated 1 to 2.5 million tons of active pesticide ingredients are used each year, mainly in agriculture. Forty percent are herbicides, followed by insecticides and fungicides. Since the discovery ofsynthetic organochlorine compounds in the 1940s, multiple chemical pesticides with different uses and modes of action have been employed. Pesticides are applied over large areas in agriculture and urban settings. Pesticide use therefore represents an important source of diffuse chemical environmental inputs.

Proposed pathways for the microbial degradation of DDT

(5) DETERGENTS A detergent is a surfactant or a mixture of surfactants with cleaning properties

in dilute solutions. These substances are usually alkylbenzenesulfonates, a family of compounds

that are similar to soap but are more soluble in hard water, because the polar sulfonate (of detergents) is less likely than the polar carboxyl (of soap) to bind to calcium and other ions found in hard water.

Increased use of synthetic detergents started in early fifties. They contain some surfactants (surface active agents), some builders eg. tripolyphosphates (to increase the washing efficiency) and some kind of fluorescent whiteners.

The bulk of the materials reaching the environment (soil and natural waters) do so from consumer products via the use of sewage sludge on land, effluents from wastewater treatment plants (WWTP) and industrial discharges into freshwater and marine sites.

Primary degradation can be defined as to have occurred when the structure has changed sufficiently for a molecule to lose its surfactant properties. Ultimate degradation is said to have occurred when a surfactant molecule has been rendered to CO2, CH4, water, mineral salts and biomass.

LAS(linear alkylbenzene sulphonate) are generally regarded as biodegradable surfactants. Very high levels of biodegradation (97–99%) have been found in some WWTP using aerobic processes .In contrast, APE(alkyl phenol ethoxylates) are less biodegradable and values of 0–20% have been quoted based on oxygen uptake and 0–9% based on spectroscopic techniques.

The mechanism of breakdown of LAS involves the degradation of the straight alkyl chain, the sulphonate group and finally the benzene ring .The breakdown of the alkyl chain starts with the oxidation of the terminal methyl group (ω-oxidation) through the alcohol, aldehyde to the carboxylic acid .

The reactions are enzyme catalysed by alkane monooxygenase and two dehydrogenases. The carboxylic acid can then undergo β-oxidation and the two carbon fragment enters the tricarboxylic acid cycle as acetylCo-A.

It is at this stage that problems arise with branched alkyl chains, a side chain methyl group or a gem-dimethyl-branched chain cannot undergo β-oxidation by microorganisms and must be degraded by loss of one carbon atom at a time (α-oxidation).

The second stage in LAS breakdown is the loss of the sulphonate group. Three mechanisms have been proposed for desulphonation according to the

following reactions.

Hydroxyative desulphonation:

equation(1)

Monooxygenase catalysis under acid conditions:

equation(2)

Reductive desulphonation:

equation(3)

Refrences-1. Environmental biotechnology( basic concepts and applications)- by Indu

shekhar Thakur2. Introduction to environmental biotechnology- by Chatterjee3. Wikipedia4. Science direct journals5. Slideshare presentations6. http://www.sciencedirect.com/science/article/pii/S0304415700000137 7. http://www.chem.unep.ch/pops/ 8. http://www2.epa.gov/international-cooperation/persistent-organic-

pollutants-global-issue-global-response

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