High-growth industrialization and population growth have the
accumulation of a wide variety of chemicals. Thus, the frequency
and use of “Xenobiotic” chemicals has led to a remarkable effort
to implement new Technologies to reduce or eliminate these
contaminants from the environment. Commonly used Methods of
treatment of pollution had negative effects on the environment; this
can lead to the formation of toxic intermediates. In addition, these
methods are more expensive and sometimes difficult to perform,
like pesticides. A promising Method of treatment is to exploit
the ability of micro-organisms to eliminate contaminated sites,
an effective alternative treatment strategy, minimal, Economical,
versatile and environmentally friendly, is the process known as
bioremediation. Subsequently, it has been found that microbes have
the ability to transform and / or degrade Xenobiotics, scientists
have explored microbial diversity, in particular Contaminated in
search of organisms that can degrade a wide range of pollutants.
Therefore, the biotransformation of organic contaminants in the
natural environment has been Microbial ecology, physiology
and evolution because of their Potential for bioremediation.
The biochemical and genetic basis of Microbial degradation has
received considerable attention. Several genes / enzymes, which
Microorganisms with the ability to degrade organopesticides
have been identified and characterized. Thus, the microorganisms
provide the potential wealth of biodegradation.
The ability of these
organisms to reduce the concentration of xenobiotic is directly
related to their long-term adaptation of areas where there are
these compounds. In addition, genetic engineering can be used
to enhance the efficiency of such micro-organisms having the
appropriate the properties, essential for the biodegradation. About
30% of agricultural produce is lost due to pests. Therefore, the
use of pesticide becomes indispensable in agriculture. Abusive
use of pesticides for pest control is widely used in agriculture.
However, indiscriminate use of pesticides caused serious damage
and problems for people, as well as on biodiversity. Problem environmental pollution by pesticides goes beyond the point where
it is used. Agricultural pesticides, which are generously spread
over the country travel long distances and can move down until it
reaches the water level in detectable concentrations, reaching the
aquatic environment at a much greater distance. So fate Pesticides
are often uncertain; they can infect other areas that are far from the
place where they were originally used.
pesticide contaminated sites is very complex task. Pesticides are
chemicals that kill parasites and herbicides are chemicals that kill
weeds. In the context of soil, parasites are fungi, bacterial insects,
worms and nematodes, etc., which cause damage to field crops.
Thus, in a broad sense, pesticides are insecticides, fungicides,
bactericides, herbicides and nematocides that are used to control
or inhibit plant diseases and insect pests. Although large-scale
application of pesticides and herbicides is an essential element in
increasing crop yields, excessive use of these chemicals leads to
microbial imbalance, environmental pollution and health hazards.
An ideal pesticide should have the ability to destroy the target pest
quickly and should be able to degrade non-toxic substances as
quickly as possible.
The last “pit” of pesticides applied in agriculture and public
health care is soil. The soil, being the storehouse of a multitude
of microbes, in quantity and quality, receives chemicals in various
forms and acts as a trap of harmful substances. The effectiveness and
competence to handle chemicals vary with the soil and its physical,
chemical and biological characteristics. Pesticides reaching soil in
significant quantities have a direct effect on the microbiological
aspects of the soil, which in turn influence plant growth. Some
of the most important effects of pesticides are: alterations in the
ecological balance of the soil micro flora, continued application
of large quantities of pesticides can Soil micro flora, suppression
of nitrifying bacteria, Nitrosomonas and Nitrobacter by soil
fumigants. Inhibition of N2-binding soil microorganisms such as
Rhizobium, Azotobacter, Azospirillum, etc.
How long an insecticide, fungicide or herbicide persists in the soil
is of great importance with regard to pest control and environmental
pollution. The persistence of pesticides in the soil for a long
period of time is undesirable for the following reasons: (a) the
accumulation of chemicals in soil at very toxic levels, (b) can be
assimilated by plants and accumulate in products Edible plants,
(c) Portions of root crops, (d) being eroded with soil particles
and entering watercourses, and eventually leading to pollution of
soil, water, air. The actual persistence of pesticides in soil varies
from one week to several years depending on the structure and
properties of the constituents in the pesticide and the availability of
moisture in the soil. For example, highly toxic phosphates do not
persist for more than three months, while chlorinated hydrocarbon
insecticides persist for at least 4 to 5 Years and sometimes more than
15 years. From the agricultural point of view, a longer persistence
of pesticides leading to the accumulation of residues in the soil
can lead to an increased absorption of these toxic chemicals by
the plants at the level where the consumption of plant products
can prove to be harmful / dangerous for Human beings like cattle.
There is a chronic problem of agricultural chemicals, which has
entered the food chain at very inadmissible levels in India, Pakistan,
Bangladesh and several other developing countries around the
world. For example, intensive use of DDT to control insect pests
and mercury fungicides to control diseases in agriculture was
known to persist longer and thus accumulate in the food chain,
leading to food contamination and health hazards. Therefore,
DDT and mercury fungicides have been banned in agriculture and
public health. Pesticides reaching the soil are subject to several
physical, chemical and biological forces.
and chemical forces act on / degrade pesticides to some extent;
microorganisms play a major role in the degradation of pesticides.
Many soil microorganisms have the ability to act on pesticides and
convert them into simpler, non-toxic compounds. This process
of pesticide degradation and conversion to non-toxic compounds
by micro-organisms is known as “biodegradation”. All pesticides
that reach the soil are not biodegradable and chemicals that have
complete resistance to biodegradation are called “recalcitrants”.
The chemical reactions leading to the biodegradation of pesticides
fall into several broad categories which are discussed.
Conversion of the pesticide molecule into a non-toxic compound
is known as detoxification. Detoxification is not synonymous with
degradation. Since a single chance in the side chain of a complex
molecule can make the chemical non-toxic. The decomposition
/ transformation of a complex substrate into simpler products
ultimately leading to mineralization. Degradation is often considered
synonymous with mineralization, fungicide is degraded by a strain
of Pseudomonas and degradation products are dimethlamine, proteins, sulfolipids, etc. In which a body makes the substrate more
complex or combines the pesticide with the cellular metabolites.
The conjugation or formation of an adduct is accomplished by the
organisms catalyzing the addition reaction of an amino acid, an
organic acid or a methyl crown to the substrate, for example in
the microbial metabolism Of sodium dimethyldithiocarbamate, the
organism combines the fungicide with an Amino acid normally
present in the cell and thus inactivate the pesticides / chemical. It is
the conversion of the non-toxic substrate into a toxic molecule, for
example. The herbicide, 4-butyric acid and the phorate insecticide
are transformed and activated microbiologically in soil to yield
metabolites that are toxic to weeds and insects.
/ pesticides are designed to control a particular group of pests /
organisms but are metabolized to give inhibitory products to
completely different groups of organisms, the fungicide PCNB
is converted into the soil into chlorinated benzoic acids that kill
the plants. Biodegradation of pesticides / herbicides is strongly
influenced by soil factors such as moisture, temperature, PH
and organic matter, in addition to the solubility of the microbial
population and pesticides. Optimum temperature, humidity and
organic matter in the soil provide a suitable environment for the
decomposition or retention of any pesticide added to the soil. Most
organic pesticides degrade in a short period in tropical conditions.
The metabolic activities of bacteria, fungi and actinomycetes play
an important role in the degradation of pesticides. Bioremediation
strategies: For the successful biodegradation / bioremediation of a
given contaminant, the following strategies are required.
1) Biostimulation: Practice the addition of nitrogen and phosphorus
to stimulate indigenous microorganisms in the soil.
2) Passive /
Intrinsic Bioremediation: This is the natural bioremediation of
the contaminant by indigenous microorganisms and the rate of
degradation is very slow.
3) Bioaccumulation: A bio-stimulation
process by which stimulant gases such as oxygen and methane
are added or forced into the soil to stimulate microbial activity.
Composting: Piles of contaminated soils are constructed and treated
with aerobic thermophilic microorganisms to degrade contaminants.
Periodic physical mixing and moistening of the piles are carried
out to promote microbial activity.
5) Bioaugmentation: It is the
inoculation / introduction of microorganisms on the contaminated
site / soil to facilitate biodegradation.
6) Phytoremediation: Can
be obtained directly by planting plants those hyper accumulate
heavy metals or indirectly by plants stimulating microorganisms
in the rhizosphere.
7) Bioremediation: The process of detoxifying
chemicals / toxic / undesirable contaminants in soil and other media
8) Mineralization: Complete conversion of
an organic contaminant into its inorganic constituent by a species
or group of microorganisms.