Degradation Degradation is breakdown of complex organic material into simpler one. Different ways of degradation: 1. Photodegradation by natural day light 2. Oxidation by chemical additives(Catalysts) 3. Thermal degradation by heat 4. Mechanical degradation by mechanical force 5. Biodegradation by Microorganisms.
Degradation Three levels of degradations: 1. Rapid degradation(day- week): HC compounds 2. Slow breakdown(Months- years): HC polymers/ Halogenated compounds 3. No degradation: Recalcitrant/ Xenobiotic: Plastic
Biodegradation “Natural and complex process of decomposition facilitated by biochemical reactions.” It is biological transformation of an complex organic material to simpler by Mos. Reduced organic materials are thermodynamically unstable and oftenly attacked by microbial enzymes. Biodegradibility: Quality, representing the susceptibility of the substrate to biological transformation.
Types of Biodegradation1. Primary biodegradation: Biochemical ways of catalysts where transformation or alteration in chemical structure of a compound occurs by biochemical reactions. Results in loss of specific property- partial biodegradation and leaves molecule mostly intact. Not desirable due to toxicity issues. Ex. Change in toxic halogen gp from Pera to Meta position. Azo dye Amino benzene
Types of Biodegradation2. Acceptable biodegradation: Biological conversion of toxic compounds to non toxic by biological means. Removal of undesirable characteristics occurs. Complete removal of toxic entity occurs.
Types of Biodegradation3. Ultimate biodegradation: The level of degradation where the compound is totally utilized and results in production of CO2 and water and mineral constituents. Molecular cleavage is so extensive that it removes all chemical, biological and toxic properties. The ultimate products are highly stable and can’t be degraded further. Ex.
Factors affecting Biodegradation EnvironmSubstrate Organis ent related m related related
Factors affecting Biodegradation Nature of pollutants Physiochemical properties Substrate Concentration related Biodegradability Toxicity Chemical nature Volatility Polarity
Factors affecting Biodegradation Population density Organism Composition related Intra/ Inter specific interaction Enzyme activity Turn over number Adaptation
Factors affecting Biodegradation Temperature Environment pH related Oxygen availability Nutrient sources- C & e- Salinity
Organisms responsible forbiodegradation Most significant group of living organism involved in biodegradation, responsible for 65% total metabolism due higher growth rate and biomass. Higher organism are also involved but not significantly, inability to degrade complex molecule. Microbes represent most diversified metabolism on earth. Microbes--------Complex material-----simpler form Microbes utilize energy more efficiently in comparison to higher organisms. High rate of reproduction and mutation is the governing factor.
Organisms responsible forbiodegradation Other lower organism- algae and invertebrates too possess some of the criteria- Earthworm, but their biodegradative potential is still unknown. Marine biodegraders: Bacteria and Fungi Soil biodegraders: Bacteria and Fungi Mutations are very often in bacteria and is very useful for progressive adaptation towards the biodegradation pathways. Not all microbe are equipped with all enzyme, so many of them follow….COMETABOLISM
Biodegradation Three categories of biodegradation:I. Usable immediately II. Usable followingacclimatization III. Recalcitrant IV.
Reactions involved inBiodegradation I. Usable immediately Simple sugars, amino acids and fatty acids- direct utilization. The enzymes required for breakdown are either constitutive or inducible. This requires minimum acclimatization period. II. Usable following the acclimatization: A lag phase is required for adaptation where no degradation or very little degradation occurs.
Reactions involved inBiodegradation During lag phase induction of enzyme occurs Duration of acclimatization period varies from few hrs to days or even weeks depending on biodegradability. Example: lag phase of 50 days in pyrazon degradation. III. Recalcitrant/ Xenobiotic: Naturally occurring substances such as lignin as well as antropogenic.
Degradation of petroleum hydrocarbon Aliphatic hydrocarbon belongs to mainly three groups: Aliphatic Hydrocarbon Alkane Alkene Alkyne
Alkane biodegradation Aliphatic hydrocarbons are more saturated compared to aromatic. Saturation α Biodegradation Branching of the aliphatic chain reduces the rate of biodegradation. Alkanes are most commonly metabolized by terminal methyl oxidation. Monooxygenase enzyme plays a key role in that. O2 MonooxygenaseO atom added to 1° or 2 ° alkane and other atom is reduced to H2O
Alkane biodegradation Reduced NADP that is NADPH2 serve as e-donor and oxidizes alkane aldehyde Fatty acid β- oxidation CO2+ H2O Sometimes both terminal methyl groups are oxidized results in formation of dicarboxylic acid.
Alkene biodegradation CH3- (CH2)n- CH= CH2 HOOC- (CH2)n-CH= CH2 CH3- (CH2)n- CH2O= CH2O Sat. end oxidation Formation of diol Further oxidation to Carboxylic acid β- oxidation
Degradation of alicyclichydrocarbon Waxes, Plant Oils, microbial lipids, Cyclohexane. Hydroxylation of alicyclic alcohol by Monooxigenase enzyme catalyzed reaction and dehydrogenation by dehydrogenase enzyme leads to formation of ketone. Further oxidation inserts oxygen into ring and lectone is formed. Ring cleavageLinearizedAldehydeCarboxylic acid
Biodegradation of aromatichydrocarbonsMost notorious environmental pollutants due to stability.Example: Polychlorinated Biphenyls (PCBs) Polyaromatic hydrocarbons(PAHs) The principle reason behind increased resistance to biodegradation is….. Introductionof electronegative groups such as Chloride, Sulfate, Nitrate. Lowered reactivity of aromatic HC due to halogen conjugate which decreases interaction with O2
Biodegradation of aromatichydrocarbons They are oxidized by dioxygenase enzyme which incorporates 2 oxygen atoms leading to formation of CATECHOL. Dihydroxylated aromatic HC- CATECHOL is cleaved by two ways…1. Orthocleavage Ring cleavage between twoadjacent hydroxyl group by 1,2- Dioxygenase2. Metacleavage Ring cleavage between thecarbon atom containing hydroxyl group and adjacentcarbon without hydroxyl group by 2,3- Dioxygenase
Example: Benzene biodegradation Conversion of benzene to Catechol:
Crude Oil biodegradation Crude oil= aliphatic HC+ alicyclic HC+ aromatic HC Auto- oxidation in absence of light plays minor role because low temperature of marine environment provide no opportunity for activation. However, photo- oxidation contribute significantly for self purification of marine environment. Lab. experiments suggests that, 8 Hrs of effective photoemission may destroy 0.2 metric tons of oil per square Km.
Crude Oil biodegradation More than 100 spp of bacteria, yeast and fungi are capable of oxidizing crude oil. For ex. Pseudomonas spp, Methanomonas spp, Nocardia spp Since oil is deficient in some microbial nutrients(especially N, P), so nitrate & phosphate are added to accelerate mineralization. Optimum temperature: 20- 35ºC Free/ Dissolved oxygen Turbulent condition
Biodegradation of halogenated HC Carbon halogen bond- highly stable and cleavage of this bond requires substantial energy input. It is an endothermic reaction. In aliphatic halogenated compound, complete degradation occurs in two stages-1. Removal of halogen2. Degradation of organic entity Removal of halogen occurs by two possible mechanisms….
Biodegradation of Halogenated HC 1. Elimination of hydrogen halide: Direct removal of hydrogen halide between two adjacent carbon atom yields double bond and such reaction occurs rarely.
Biodegradation of Halogenated HC 2. Substitution of halogen group by…(a) –H group (Reductive reaction)(a) -OH group
Biodegradation of Halogenated HC S (thio) group: Most common type of reaction is –OH, which incorporate reactive oxygen group into it.
Biodegradation of Halogenated HC Elimination of halide occurs by two possible routes:(a) Elimination of halide after ring cleavage(b) Elimination of halide before ring cleavage(A) Elimination of halide after ring cleavage:Aerobic degradation of chlorinated aromatic compoundusually achieved by a sequence of reaction.HydroxylationCleavage- aromatic ringElimination of cl- from aliphatic intermediate.
Biodegradation of Halogenated HC The pathway 1. Formation of cl- catechol: The key intermediate in degradation of many chlorinated compounds.
Biodegradation of Halogenated HC The pathway 2. Oxidation by Orthocleavage & Metacleavage: Orthocleavage leads to ring cleavage by 1,2 dioxygenase enzyme followed by elimination of halogen entity. The remaining non halogenated product can be metabolized further. Metacleavage produces highly toxic intermediate and can’t be taken further by organism involved in biodegradation.