▉ The rapidly growing industrialization along with an increasing population has resulted in the accumulation of a wide variety of chemicals. Thus, the frequency and widespread use of man-made “xenobiotic” chemicals has led to a remarkable effort to implement new technologies to reduce or eliminate these contaminants from the environment.
▉ Commonlyused pollution treatment methods (e.g. land-filling, recycling, pyrolysis and incineration) for the remediation of contaminated sites have also had adverse effects on the environment which can lead to the formation of toxic intermediates.
In this review we focuss on biodegradation of xenobiotics in environment i-e soil ,humans,in food,cosmetics, plants, water and about the bioremediation of xenobiotics.
▉ INTRODUCTION
Industrialization has become an important factor to the development of a country’s economy, through the establishment of plants and factories. However, the waste or by-products discharged from them are severely disastrous to the environment consists various kind of contaminant which contaminate the surface water, ground water and Some of the contaminants merely cause mild discomfort to human being, while others might be detrimental to human health.
▉ XENOBIOTICS
The word, xenobiotic, is a combination of two different roots, “xeno” and “biotic.” Xeno is from the Greek and means strange, unnatural, or different. Biotic is a word that implies life. Xenobiotic, therefore, refers to an organic compound that mimics natural biochemicals that are essential for life, but which have characteristics about them that are strange and unnatural. Xenobiotics are often toxic to life. Also, they may not be recognized by biochemical processes in plants and microorganisms and are thus resistant to degradation in the environment.
Huge amounts of synthetic chemicals are constantly released into our environment. Man-made chemicals are often referred to as anthropogenic (from Gr. Anthropos – a man, and genos – born of a certain kind) or xenobiotic (from Gr. xen (o) – strange, stranger, and biosis – way of life) since they are foreign to nature. Distributed into different part of the environment chemicals can be transported long or short distances and can also undergo a variety of reactions and transformations.
The synthetic xenobiotic chemicals are often of enormous value to human society, and are usually the majority of the chemicals in such important groups of substances as petrochemicals, pesticides and plastics. Increasingly, humans are subjected to exposureto various xenobiotic.
▉ Structural features of xenobiotic compounds:
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Presence of halogens in place of hydrogen in the molecule and it requires more energy for cleavage.
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Presence of other groups such as nitro, sulphonate, methoxy, amino etc.
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Aromatic compunds, cycloalkanes and heterocyclic compounds are more recalcitrant.
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Branched linear chains are resistant to biodegradation.
▉ Xenobiotic compounds and its chracteristics ,
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They are not recognized as substrate by degradative microorganisms.
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Highly stable in nature.
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Insoluble in water.
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They are highly toxic or release toxic products due to microbial activity.
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They have large molecular weight which prevents entry to microbial cells. of time are called recalcitran.
▉ Types of recalcitrant Xenobiotic compounds
These are categorized into six types-
1. Halocarbons
These compounds consist of different numbers of halogen viz., CI, Br, F (fluorine), or I, atoms in the place of H atoms. They are used in various applications as solvents (chloroform, CHCI3), as propellants in spray cans of cosmetics, paints, etc. Also they are used in condenser units of cooling systems (Freons, CCI3F, CCI2F2, CCIF3, CF4), and as insecticides (DDT, BHC, lindane, etc.) and herbicides (dalapon, 2, 4-D, 2, 4, 5-T, etc). Chloroform, freons are volatile and escape into the atmosphere where they destroy the protective ozone (O3) layer leading to increased UV radiation.
2. Poly chlorinated Biphenyls (PCB’s):
Poly chlorinated Biphenyl compounds have been covalently linked with two benzene rings having halogens in place of hydrogen. These are mainly used as plasticisers, insulator coolants in transformers and as heat exchange fluids.
3. Synthetic Polymers:
Synthetic polymers such as polyethylene, polystyrene, polyvinyl chloride, etc., and nylons, which are used as garments, wrapping materials, etc. They are recalcitrant mainly due to the following reasons such as insoluble in water and molecular size.
4. Alkylhenzyl Sulphonates:
Soil amendments with organic and inorganic fertiliserThese are surface-active detergents which are found to be superior compare to soaps. The sulphonate (-SO3-) group present at one end resists microbial degradation, while the other end becomes recalcitrant if it is branched. In this degree of resistance increases with the increasing branching length. At present, alkylbenzyl sulphonates having non-branched alkyl ends are used; these are biodegraded by beta-oxidation from their alkyl.
5. Oil Mixtures:
Oil is recalcitrant mainly because of its insolubility in water and due to the toxicity of some of its components. It is a natural product contains many components and is biodegradables. Biodegradation process is mainly used to handle small oil seepages. But when large spills occurs the problem of pollution becomes serious. These compounds are mainly recalcitrant in nature.
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