Pesticide degradation

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

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

2. Content Introduction Type of pesticides Advantage & disadvantages of pesticides Degradation of pesticide M icrobial 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

3. Part-one pesticides

4. 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.

5. 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.

6. Types of Pesticides These are grouped according to the types of pests which they kill: Grouped by Types of Pests They Kill Insecticides – insects Herbicides – plants Rodenticides – rodents (rats & mice) Bactericides – bacteria Fungicides – fungi Larvicides – larvae

7. Based on how biodegradable they are: Pesticides can also be considered as: 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.

8. list of persistent and non-persistent pesticides:

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

10. 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).

11. 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.

12. Chemical classification of pesticides

13. Classification of insecticides

14. 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.

15. 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.

16. 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.

17. Degradation of pesticide Part-two

18. 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: Physical Chemical Biological (microbial degradation)

19. Biological or microbial degradation (biodegradation)

20. 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.

21. 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.

22. Factors affecting Biodegradation Chemical structure of the compound The capability of the individual microorganisms Nutrient and O2 supply Temperature and pH

23. 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

24. 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. Thiocarbonates Nocardia Phenolic Trichoderma viride Malathion Microorganism involved in biodegradation o f pesticides

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

26. 2. NON-ENZYMATIC TYPE Photosynthetic breakdown Contribution via PH change Production of organic and inorganic reactants Production of cofactors

27. 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.

28. 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.

29. 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.

30. 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.

31. 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.

32. 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.

33. Metabolism of DDT DDT was used to control insects during World War 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

34. DDT degradation by MO

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

36. Thank you