Pesticide degradation

Degradation of Pesticides
Abdulhaq Mehran
Roll No 1938
M.Sc. second year
Department of environmental science MDU

Content
• Introduction
• Type of pesticides
• Advantage & disadvantages of pesticides
• Degradation of pesticide
• Microbial degradation of pesticides
• Mode of microbial metabolism of pesticides
• Strategies for biodegradation
• Approaches for biodegradation of pesticide
• Chemical reaction leading biodegradation of pesticide
• Metabolism of pesticides by MO
• Metabolism of DDT

Introduction
• A pesticide is defined as a chemical agent used to destroy
or control pests. The root word is the Latin word “cida”
which means to kill.
• pesticide use is not just a modern practice (Hayes, 1991).
Perhaps the first recorded use of pesticide was around
1550 B.C., when Egyptians used unspecified chemicals to
drive fleas from homes.
• modern times, however, pesticide use has been much
more prevalent, and by 1990, about 300 insecticides were
in use.

Definition of Pesticides
The Food and Agriculture Organization (FAO) has defined
pesticide as:
• A pesticide is any substance or mixture of substances
intended for preventing, destroying, repelling, or
mitigating any pest (insects, mites, nematodes, weeds,
rats, etc.), including insecticide, herbicide, fungicide, and
various other substances used to control pests. The
definition of pesticide varies with times and countries.
However, the essence of pesticide remains basically
constant: it is a (mixed) substance that is poisonous and
efficient to target organisms and is safe to non-target
organisms and environments.

Types of Pesticides
These are grouped according to the types of pests which
they kill:
Grouped byTypes of PestsThey Kill
1. Insecticides – insects
2. Herbicides – plants
3. Rodenticides – rodents (rats & mice)
4. Bactericides – bacteria
5. Fungicides – fungi
6. Larvicides – larvae

 Based on how biodegradable they are:
Pesticides can also be considered as:
1. Biodegradable:
The biodegradable kind is those which can be broken down
by microbes and other living beings into harmless
compounds.
2. Persistent:
While the persistent ones are those which may take
months or years to break down.
Another way to classify these is to consider those that are
chemical forms or are derived from a common source or
production method.

list of persistent and non-persistent
pesticides:

Persistence of some pesticides in the
environment
Pesticides
Aldrin >15YEARS
Chlordane >15YEARS
DDT >15YEARS
Dieldrin >15YEARS
Endrin >14YEARS
Malathion 3YEARS
Parathion >16YEARS
PCP >5YEARS
Simazine 2YEARS
2,4,5T 190 DAYS

 Based on Chemical Composition
 Organophosphate:
Most organophosphates are insecticides, they affect the
nervous system by disrupting the enzyme that regulates a
neurotransmitter.
 Carbamate:
Similar to the organophosphorus pesticides, the carbamate
pesticides also affect the nervous system by disrupting an
enzyme that regulates the neurotransmitter. However, the
enzyme effects are usually reversible.
 Organochlorine insecticides:
They were commonly used earlier, but now many countries
have been removed Organochlorine insecticides from their
market due to their health and environmental effects and
their persistence (e.g., DDT, chlordane, and toxaphene).

 Pyrethroid:
These are a synthetic version of pyrethrin, a naturally
occurring pesticide, found in chrysanthemums(Flower).
They were developed in such a way as to maximize their
stability in the environment.
 Biopesticides:
The biopesticides are certain types of pesticides derived
from such natural materials as animals, plants, bacteria,
and certain minerals.

Chemical classification of pesticides

Classification of insecticides

Advantages of Pesticides
The major advantage of pesticides is that they can
save farmers. By protecting crops from insects and
other pests. However, below are some other primary
benefits of it.
• Controlling pests and plant disease.
• Controlling human/livestock disease vectors and
nuisance organisms.
• Controlling organisms that harm other human
activities and structures.

Disadvantage of pesticides
• The toxic chemicals in these are designed to deliberately
released into the environment. Though each pesticide is
meant to kill a certain pest, a very large percentage of
pesticides reach a destination other than their target.
Instead, they enter the air, water, sediments, and even
end up in our food.
• Pesticides have been linked with human health hazards,
from short-term impacts such as headaches and nausea
to chronic impacts like cancer, reproductive harm.
• The use of these also decreases the general biodiversity
in the soil. If there are no chemicals in the soil there is
higher soil quality, and this allows for higher water
retention, which is necessary for plants to grow.

Impacts on Environment
Impacts on non-target organism
• Most insecticides once applied to kill pests; it may also
adversely nontarget organisms such as earthworm, natural
predators and pollinator.
Loss of biodiversity
• Biodiversity is often considered as a measure of the healthy
biological systems.
Impacts on soil micro-flora
• A major portion of the non-target pesticides from
agriculture application and other sources may accumulates
in soil.

Degradation of pesticide
Part-two

Degradation of pesticide
Pesticide degradation is the breaking down of toxic
pesticides into a nontoxic compounds and, in some cases,
down to the original elements from which they were
derived.
In general there are three ways to degrade pesticides:
1. Physical
2. Chemical
3. Biological (microbial degradation)

Biological or microbial degradation
(biodegradation)

Biodegradation of pesticides
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 biodegradation 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.

Among the various practice to decrease the load of pesticides
in soil and water, the degradation by micro-organisms has
given sufficient encouragement . Bollag (1974)
Suggested four major possibilities for transformation of
inactivation pesticides by microorganisms they are:
 The pesticides is used as substrate and energy.
 The pesticides undergo co-metabolism i.e. organism
transform it but cannot derive energy for growth from it.
 The entire pesticide molecules or its intermediate can be
conjugated with naturally occurring compounds.
 The pesticides is incorporated and accumulated with in the
organisms.

Factors affecting Biodegradation
1. Chemical structure of the compound
2. The capability of the individual microorganisms
3. Nutrient and O2 supply
4. Temperature and pH

Microorganism
Many micro organisms belonging to diverse groups i.e.
bacteria, actinomycetes, fungi are found to degrade
different pesticides they metabolic diversity of the micro
organisms enable them to degrade this chemical different
pesticides .
It is interesting to note that two taxonomically
microorganism may degrade the same pesticide in similar
pathway .
Examples: Achromobacter , agrobacterium, Enterobacter,
aspergillus, candida….etc

BACTERIA PESTICIDE FUNGI PESTICIDE
Achromobacter DDT,2,4, -D
Carbaryl
Pyricularia oryzae Pyrazophos,
Hinson
A. Aerogenes Dieldrin, Endrin Aspergills sp. Atrazine,
simagine
Agrobacterium Chlorophan Penicillium
chrysogenum
Parathion,
dieldrin
Enterobacter DDT Candida tropical Phenols
Micrococcus Aldrin, Dieldrin Phanerochaeta DDT
Pseudomonas
sp.
Endrin, 2,3-D
Aldrin
Saccharomyces sp. Thiocarbonate
s
Nocardia Phenolic Trichoderma viride Malathion
Microorganism involved in
biodegradation o f pesticides

Mode of microbial metabolism of pesticides
There are two modes :
1. ENZAYMATIC TYPE
2. NON-ENZYMATIC TYPE
1. ENZYMATIC TYPE
This divided into three phases
a) Incidental metabolism of pesticides which cannot serve as
energy source.
b) Catabolism insecticides serve as energy source.
c) Detoxification serving as resistance mechanism.

2. NON-ENZYMATIC TYPE
a) Photosynthetic breakdown
b) Contribution via PH change
c) Production of organic and inorganic reactants
d) Production of cofactors

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

• 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.
• Phytoremediation: Can be achieved directly by planting
plants which hyperaccumulate heavy metals or indirectly
by plants stimulating microorganisms in the rhizosphere.
• Bioremediation: Process of detoxification of
toxic/unwanted chemicals / contaminants in the soil and
other environment by using microorganisms.
• Mineralization: Complete conversion of an organic
contaminant to its inorganic constituent by a species or
group of microorganisms.

Chemical Reactions Leading to
Biodegradation
The biodegradation of pesticides, is often complex and involves a
series of biochemical reactions:
• 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.
• 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 dimethylamine, proteins,
sulpholipaids, etc.
• Conjugation: 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 dimethyl dithiocarbonate, the organism combines the
fungicide with an amino acid molecule normally present in the cell
and thereby inactivate the pesticides/chemical.

• Activation: It is the conversion of non-toxic substrate
into a toxic molecule, for e.g. Herbicide, 4-butyric acid (2,
4-D B) and the insecticide Pharate are transformed and
activated microbiologically in soil to give metabolites
that are toxic to weeds and insects.
• 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.
• Leaching: Since many of the pesticides can be
solubilized, they are removed by leaching.

Metabolism of pesticides by MO
Metabolism of pesticides may involve a three-phase
process:
• Phase I
• Phase II
• Phase III
Phase I- In Phase I metabolism, the initial properties of a
parent compound are transformed through oxidation,
reduction, or hydrolysis to generally produce a more water-
soluble and usually a less toxic product than the parent.

Phase II- The second phase involves conjugation of a
pesticide or pesticide metabolite to a sugar or amino acid,
which increases the water solubility and reduces toxicity
compared with the parent pesticide.
Phase III- The third phase involves conversion of Phase II
metabolites into secondary conjugates, which are also
non-toxic. In these processes fungi and bacteria are
involved producing intracellular or extra cellular enzymes
including hydrolytic enzymes, peroxidases, oxygenases,
etc.

Metabolism of DDT
DDT was used to control insects duringWorldWar II, and
then as an agricultural insecticide. Almost all uses of DDT
were banned in most developed countries in the 1970s–
1980s. In some countries, DDT was applied to the inside
walls of homes to kill or repel mosquitoes.
Dichlorodiphenyltrichloroethane (DDT) is an
organochlorine.
Its degradation by Phanerochaeta chysosporium is well
established chlorine substituents make DDT more resistant
for degradation how ever the production of two alginolytic
oxidase along with mono and dioxygenases convert the
DDT into co2

No chemist In the world that degrade
pesticides like microorganisms can!

Pesticide degradation

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