1. Biodegradation is the process by which microorganisms like bacteria and fungi break down pesticides into non-toxic substances. 2. Common pesticides that are biodegraded include the soil fumigant methyl bromide, the herbicide dalapon, and the fungicide chloroneb. 3. For effective biodegradation, organisms must be able to degrade the pesticide, the pesticide must be bioavailable, and soil conditions must support microbial growth. Strategies to enhance biodegradation include biostimulation, bioventing, and bioaugmentation.

1. Biodegradation Of
Pesticides
Jain Aachal Dinesh
Class: Msc. Part II
Roll No.: 07
Paper II

2. Introduction
• A pesticide can be defined as any substance or mixture
of substances intended for preventing, destroying,
repelling, or mitigating any pest.
• Pesticides like insecticides, herbicides, fungicides, and various
other substances are used to control or inhibit plant diseases and
insect pests.
• The positive aspect of application of pesticides renders enhanced
crop/food productivity and drastic reduction of vector-borne
diseases.
• However excessive use of these chemicals leads to the microbial
imbalance, environmental pollution and health hazards.
• Due to these problems, development of technologies that
guarantee their elimination in a safe, efficient and economical way
is important.

3. • Degradation of pesticides is very essential for controlling
these problems.
• Biodegradation is a process by which a pesticide is
transformed into a benign substance that is environmentally
compatible with the site to which it was applied.
• The degradation or breakdown of pesticides can occur in
plants, animals, and in the soil and water.
• However the most common type of degradation is carried
out in the soil by microorganisms, especially fungi and
bacteria that use pesticides as food source.
• The soil fumigant methyl bromide, the herbicide dalapon,
and the fungicide chloroneb are examples of pesticides
which are degraded by microorganisms.

4. Criteria for Biodegradation
• For successful biodegradation of pesticide in soil, following
aspects must be taken into consideration.
1. Organisms must have necessary catabolic activity required
for degradation of contaminant at fast rate to bring down the
concentration of contaminant.
2. The target contaminant must be bioavailability.
3. Soil conditions must be congenial for microbial /plant growth
and enzymatic activity.
4. Cost of bioremediation must be less than
other technologies of removal of contaminants.

5. Strategies for Biodegradation
• For the successful biodegradation / bioremediation of a given
contaminant following strategies are needed.
1. Passive/ intrinsic Bioremediation: It is the natural
bioremediation of contaminant by tile indigenous
microorganisms and the rate of degradation is very slow.
2. Biostimulation: Practice of addition of nitrogen and
phosphorus to stimulate indigenous microorganisms in soil.
3. Bioventing: Process of Biostimulation by which gases
stimulants like oxygen and methane are added or forced
into soil to stimulate microbial activity.
4. Bioaugmentation: It is the inoculation/introduction of
microorganisms in the contaminated site/soil to facilitate
biodegradation.

6. 4. Composting: Piles of contaminated soils are constructed
and treated with aerobic thermophilic microorganisms to
degrade contaminants. Periodic physical mixing and
moistening of piles are done to promote microbial activity.
5. Phytoremediation: Can be achieved directly by planting
plants which hyperaccumulate heavy metals or indirectly by
plants stimulating microorganisms in the rhizosphere.
6. Bioremediation: Process of detoxification of
toxic/unwanted chemicals / contaminants in the soil and
other environment by using microorganisms.
7. Mineralization: Complete conversion of an organic
contaminant to its inorganic constituent by a species or
group of microorganisms.

7. Different Approaches for
Biodegradation
• Although a number of techniques are available for
biodegradation, the ones of utmost importance are:
1. Bacterial degradation: Most bacterial species degrade
pesticides. most of the pesticides undergo partial degradation
leading to the formation and accumulation of metabolites.
2. Fungal degradation:. Fungi degrade pesticides by introducing
minor structural changes to the pesticides rendering it non toxic
and are released to soil, where it is susceptible to further
biodegradation by bacteria.
3. Enzymatic degradation: Enzymes have a great potentiality to
effectively transform and detoxify polluting substances because
they have been recognized to be able to transform pollutants at
a detectable rate and are potentially suitable to restore polluted
environments.

8. Chemical Reactions Leading to
Biodegradation
• The biodegradation of pesticides, is often complex and involves
a series of biochemical reactions:
1. Detoxification: Conversion of the pesticide molecule to a non-
toxic compound. A single chance in the side chain of a complex
molecule may render the chemical non-toxic.
2. Degradation: The breaking down / transformation of a complex
substrate into simpler products leading finally to mineralization.
e.g. Thirum (fungicide) is degraded by a strain of Pseudomonas
and the degradation products are dimethlamine, proteins,
sulpholipaids, etc.
3. Congugation: In which an organism make the substrate more
complex or combines the pesticide with cell metabolites.
Conjugation is accomplished by those organisms catalyzing the
reaction of addition of an amino acid, organic acid or methyl
crown to the substrate, for e.g., in the microbial metabolism of
sodium dimethly dithiocarbamate, the organism combines the
fungicide with an amino acid molecule normally present in the
cell and thereby inactivate the pesticides/chemical.

9. 4. Activation: It is the conversion of non-toxic substrate into
a toxic molecule, for eg. Herbicide, 4-butyric acid (2, 4-D
B) and the insecticide Phorate are transformed and
activated microbiologically in soil to give metabolites that
are toxic to weeds and insects.
5. Changing the spectrum of toxicity: Some
fungicides/pesticides are designed to control one particular
group of organisms / pests, but they are metabolized to
yield products inhibitory to entirely dissimilar groups of
organisms, for e.g. the fungicide PCNB fungicide is
converted in soil to chlorinated benzoic acids that kill
pests.
6. Leaching: Since many of the pesticides can be solublized,
they are removed by leaching.

10. Example of Biodegradation of
Pesticides
 Dichloro Diphenyl Tricholroethene (DDT):
• Probably the best known example of a chlorinated pesticide.
• This compound has been used in vast quantities as insecticide to
control numerous insect pests.
• However, its use has been banned or restricted in many countries
because of its deleterious effects.
• DDT present in the soil can be degraded in two years, while others
have found that the process can take from fifteen to twenty years or
more.
• The degradation products of DDT are mainly the dechlorination
products DDE and DDD.
• The pathway can be DDT DDE DDD, or from DDT to DDD
directly.
• Anaerobically, DDE is readily dechlorinated to DDNU and then to
further products.
• Among microorganisms, bacteria comprise the major group
• involved in DDT degradation,especially soil habitants belonging to
genera Bacillus, Pseudomonas, Arthrobacter and Micrococcus.

12.  Carbamates :
• Carbamates were introduced as pesticides in the early
1950s and are still used extensively in pest control due to
their effectiveness and broad spectrum of biological activity.
• They are used as alternatives to the highly stable
organochlorines such as DDT.
• Degradation of pesticide occurs mainly through the
hydrolysis of methylcarbamate linkage by an enzyme called
carbofuran hydrolyase.
• Microbial strains capable of degrading carbamate belong to
the genera Psuedomonas, Flavobacterium,
Achromobacterium, Sphingomonas, Arthrobacter.

14. Advantages and Disadvantages
Advantages
• often less expensive and
site disruption is minimal.
• it eliminates waste
permanently.
• eliminates long-term
liability.
• it can be coupled with
other physical or chemical
treatment methods.
Disadvantages
• Treatment time is typically
longer.
• Range of contaminants that
can be effectively treated is
limited to compounds that
are biodegradable.
• The process is sensitive to
the level of toxicity and
environmental conditions in
the ground.
• If the process is not
controlled it is possible the
organic contaminants may
not be broken down fully
resulting in toxic by-products
that could be more mobile
than the initial contamination.

15. Thank You