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.

1. Biodegradation
of Pesticides

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. Classification of Pesticides
1. Organophosphates
2. Organochlorines
3. Carbamates
4. Pyrethrum and pyrethroids
5. Herbicides

5. Organophosphates
Organophosphates (also known as phosphate esters, or OPEs) are a class of
organophosphorus compounds with the general structure O=P(OR)3. They can be
considered as esters of phosphoric acid.
Parathion (LD50= 13mg/Kg of body weight) One of the most poisonous substance used in agriculture.
Parathion
Inhalation Swallowing Skin Contact
Absorbed by Bypass
Blood brain barrier Placenta
Inhibit Acetylcholinesterase
Nerve Coordination

6. Organochlorines
Organochlorine insecticides are chlorinated hydrocarbons to control
insects and insect-borne diseases.
Endrin
LD50= 7 mg/Kg
Dieldrin
LD50= 10 mg/Kg
Endosulfan
LD50= 80 mg/Kg
Chlordane
LD50= 460 mg/Kg
Organochlorine
Breakdown very slowly Accumulate in fatty tissues
Persistence Bio-accumulation

7. Carbamates
Carbamate pesticides are derived from carbamic acid and kill insects in a similar
fashion as organophosphate insecticides. They are widely used in homes, gardens,
and agriculture. Like the organophosphates, their mode of action is inhibition of
cholinesterase enzymes, affecting nerve impulse transmission.
Extremely toxic
Adicarb (LD50 = 0.9 mg/Kg)
Carbofuran (LD50 = 8mg/Kg)
Less toxic
Carbamyl (LD50 = 300 mg/Kg)
Principle mode of absorption
Through Skin
Risk of Poisoning is less, as they are absorbed through skin much more slowly.

8. Pyrethrum and Pyrethroids
Pyrethrum is the natural product derived from plant Chrysanthemum. As
a pure substance, they broke down very rapidly in environment and
living organism.
• Low oral acute toxicity
• High allergic potential
Pyrethroids are synthetic descendent of Pyrethrum.
Products commonly used today:
• Permethrin
• Deltamethrin
• Cyfluthrin
• Cypermethrin
• Fenvalerate

9. Herbicides
Herbicides are used to kill undesirable plants or “weeds”. Some herbicides will kill
all the plants they touch, while others are designed to target one species. They
exhibit lower acute oral toxicity and higher dermal toxicity.
Paraquat (LD50 =150mg/Kg) is the most frequent applied product. Other examples
are Cyperquat and Diquat.
Herbicides 2,4,5-T; 2,4-D; MCPA Derived from phenoxyacetic acid esters contain
contaminant dioxn, the Seveso poison.

10. 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.

11. Strategies for Biodegradation
Passive/ intrinsic
Bioremediation
Biostimulation Bioventing Bioaugmentation
Composting Phytoremediation Bioremediation Mineralization
N P O2 CH4

12. Different Approaches for
Biodegradation
Bacterial degradation
Most bacterial species degrade pesticides.
most of the pesticides undergo partial
degradation leading to the formation and
accumulation of metabolites.
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.
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.

13. Chemical Reactions Leading to
Biodegradation
Detoxification Congugation
Activation Changing the spectrum of toxicity Leaching
Degradation
Pesticide
NH3
COOH
CH4

14. Advantages and Disadvantages
• Advantages • Disadvantages
• Can be done on Site
• Permanently eliminate waste
• Is cheaper
• Minimize the destruction
• Eliminates the long term liability
• Can be coupled with other chemical
techniques
• Treatment time is longer
• Some chemicals can not be degraded
• Unknown by-products can be produced
• Toxicity of contaminants can be a
problem

15. Thank You