About Bio degradation of Xenobiotics.

1. BIODEGRADATION OF
XENOBIOTICS
HYDROCARBONS, PLASTICS &
PESTICIDES

2. XENOBIOTICS
• It is derived from a greek word “XENOS”.
• Xenobiotics are man-made chemicals.
• They are usually synthesized for industrial or agricultural purposes e.g.
pesticides, hydrocarbons, plastics etc.
• They are also called RECALCITRANTS.

3. BIODEGRADATION
• According to the definition by the International Union of Pure and
Applied Chemistry, the term biodegradation is “Breakdown of a
substance catalyzed by enzymes.
• In other words, it is defined as the conversion of toxic chemicals to non-
toxic compounds.
• Biodegradation of xenobiotics can be affected by substrate , nutrition
source, temperature, pH etc.

4. SOURCES OF XENOBIOTICS
1. Petrochemical industry :
-oil/gas industry, refineries.
2. Plastic industry :
- closely related to the petrochemical industry
- uses a number of complex organic compounds
-such as anti-oxidants, plasticizers, cross-linking agents

5. 3. Pesticide industry :
- most commonly found.
- structures are benzene and benzene derivatives,
4. Paint industry :
- major ingredient are solvents,
- xylene, toluene, methyl ethyl ketone, methyl
5. Others :
- Electronic industry, Textile industry, Pulp and Paper industry,
Cosmetics and Pharmaceutical industry, Wood preservation

6. BIODEGRADATION OF PESTICIDES
• Pesticides are substances meant for destroying any pest.
• They are a class of biocide.
• The most common use of pesticides is as plant protection products (also known as crop
protection products).
• It includes: herbicide, insecticide, nematicide, termiticide,molluscicide,
piscicide, avicide, rodenticide, insect repellent, animal repellent,
antimicrobial, fungicide, disinfectant, and sanitizer.

7. DIFFERENT METHODS
a) Detoxification:
 Conversion of the pesticide molecule to a non-toxic compound.
 A single moiety in the side chain of a complex molecule is disturbed(removed),
rendering the chemical non-toxic.
b) Degradation:
 Breakdown or transformation of a complex substrate into simpler products
leading to mineralization.
 E.g. Thirum is degraded by a strain of Pseudomonas and the degradation
products are dimethylamine, proteins, sulpholipids.

8. c) Conjugation (complex formation or addition reaction):
 An organism makes the substrate more complex or combines the pesticide with cell
metabolites.
 Conjugation or the formation of addition product is accomplished by those organisms
catalyzing the reaction of addition of an amino acid, organic acid or methyl crown to the
substrate thereby inactivating the pestcides.
d) Changing the spectrum of toxicity:
 Some pesticides are designed to control one particular group of pests, but are
metabolized to yield products inhibitory to entirely dissimilar groups of organisms, for
e.g. the fungicide PCNB is converted in soil to chlorinated benzoic acids that kill plants.

9. BIODEGRADTION OF PLASTICS
• Plastic refers to different polymers with high molecular weight.
• The biodegradation of plastics is done by microorganisms and enzymes.
• It consist of two steps- fragmentation and mineralization.
• The decomposition of major condensation polymers (e.g. polyesters and polyamides)
takes place through hydrolysis.
• The decomposition of polymers in which the main chain contains only carbon atoms
(e.g. polyvinyl alcohol, lignin) includes oxidation which can be followed by hydrolysis of
the products of oxidation.

10. DIFFERENT METHOD
HYDROLYSIS-
 The process of breaking these chains and dissolving the polymers into smaller fragments is
called hydrolysis. E.g. Pseudomonas.
 Polymeric Chains is broken down into constituent parts for the energy potential
by microorganisms. Monomers are readily available to other bacteria and is used.
ACIDOGENESIS-
 This results in further breakdown of the remaining components by acidogenic (fermentative)
bacteria into ammonia, ethanol, carbon dioxide, and hydrogen sulfide. E.g Streptococcus
acidophilus.

11. ACETOGENESIS-
 Simple molecules created through the acidogenesis phase are further digested by
Acetogens to produce largely acetic acid, as well as carbon dioxide and hydrogen.
METHANOGENESIS-
 Here, methanogens use the intermediate products of the preceding stages and convert
them into methane, carbon dioxide, and water.

12. Some of the microorganism that can degrade plastics are:-
Aliphatic Polyesters
 PolyEthylene Adipate (PEA)- lipases from R. arrizus, R. delemar, Achromobacter sp. and Candida
cylindracea
 Poly (β-Propiolactone) PPL - estereases from Acidovorax sp., Variovorax
paradoxus, Sphingomonas paucimobilis.
Aromatic Polyesters
 Poly-3-Hydroxybutyrate (PHB) – estereases from Pseudomonas
lemoigne, Comamonas sp. Acidovorax faecalis, Aspergillus fumigatus
 Poly Lactic Acid (PLA) - proteinase K from Tritirachium album, Amycolatopsis sp
Strains of Actinimycetes has been reported to degrade polyamide (nylon), polystyrene, polyethylene.

13. BIODEGRADATION OF
HYDROCARBONS
• A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.
• Hydrocarbons are major constituents of crude oil and petroleum.
• It can be biodegraded by naturally occuring microorganisms in fresh water and marine
environments under a variety of aerobic and anaerobic conditions.

14. POLYCYCLIC AROMATIC HYDROCARBONS
(PAH)
• Bacteria, fungi, yeasts, and algae have the ability to metabolize both lower and higher
molecular weight 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 catalyzed mono-oxygenase reaction to
form reactive arene oxides that can isomerize to phenols.
• White-rot fungi oxidize PAHs via ligninases (lignin peroxidases and
laccase) to form highly reactive quinones.

15. AEROBIC DEGRADATION
• Hydrocarbons easily degraded under aerobic condition.
• Alkenes and short-chain alkanes are the most easily degraded followed by branched
alkanes and then aromatics.

16. ANAEROBIC DEGRADATION
• Often slower compared to aerobic.
• Process takes place in the absence of oxygen.
• Degradation process takes from days to months.

17. POLYCHLORINATED BIPHENYLS (PCBs)
• Synthesized chemicals from petro-chemical industry used as lubricants and insulators in
heavy industry.
• First manufactured in 1929 by Monsanto.
• Manufacture and unauthorized use banned in 1978 by USEPA
• Used because-
• Low reactivity
• Non-flammable
• High electrical resistance
• Stable when exposed to heat and pressure
• Used as Hydraulic fluid, Casting wax, Carbonless carbon paper, Compressors, Heat
transfer systems, Plasticizers, Pigments, Adhesives, Liquid cooled electric motors,
Fluorescent light.

18. RISKS-
 Causes reproductive disabilities in animals, human, birds.
 Carcinogenic
 Bioaccumulation
 Soluble in almost all the solvents, fats, oils
 Nervous system damage
 Endocrine gland malfunction

19. METHODS FOR PCB REMOVAL
• Natural Attenuation: Microbes already in the soil are allowed to degrade as they
can naturally and the site is closely monitored.
• Biostimulation: Microbes present in the soil are stimulated with nutrients such as
oxygen, carbon sources like fertilizer to increase degradation.
• Bioaugmentation: Microbes that can naturally degrade PCB’s are transplanted to
the site and fed nutrients if necessary.

20. REFERENCE
www.slideshare.net
www.biotecharticles.com
www.environmentalrestoration.wiki
www.wikipedia.org