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the fate of xenobiotics in wetlands

Lucy
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the fate of xenobiotics in wetlands

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    1. 03/09/2011 WBL 1

    2. WBL 2

    3. 03/09/2011 WBL 3 What is a Xenobiotic? Xeno means foreign, Bios means life: Xenobiotic is in essence a compound that is foreign to life Synonyms Toxics, toxic [organic] substances, priority organic pollutants [POPs], endocrine disruptors Examples: Pesticides, fungicides, herbicides, industrial toxins, petroleum products, landfill leachate

    4. 03/09/2011 WBL 4 Are Xenobiotics an issue in Wetlands? Wetlands are often the receiving bodies of Agricultural and urban drainage Extent of xenobiotic contamination in wetlands Approximately 5000 wetlands and aquatic systems impacted by pesticides

    5. 03/09/2011 WBL 5

    6. 03/09/2011 WBL 6 Ecological Significance Lethal toxicity to biota Non-lethal toxicity to biota Endocrine disruptors Hormone mimicry Reproductive disorders Harmful mutation - DNA damage

    7. 03/09/2011 WBL 7 Types of Xenobiotics Petroleum products (BTEX, MTBE) Pesticides (DDT, DDE…..) Herbicides (2,4D, Atrazine) Industrial wastes (PCB’s, aromatics)

    8. 03/09/2011 WBL 8

    9. 03/09/2011 WBL 9 Carbon tetrachloride Chloroform Vinyl chloride 1,2-Dichloroethane Trichloroethylene Tetrachloroethylene Benzoates

    10. 03/09/2011 WBL 10 Polychlorinated Biphenyls PCBs Organochlorine Insecticides DDT, Toxaphene, … Chlorinated Herbicides 2,4-D, 2,4,5-T, Atrazine….. Chlorinated Phenols Pentachlorophenol 2,4-dichlorophenol…2,4-D 2,4,5-trichlorophenol…. 2,4,5-T 2,3,and 4-Nitrophenol

    11. 03/09/2011 WBL 11

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    14. 03/09/2011 WBL 14 Sources of Xenobiotics Wetlands can receive: - Drainage from agricultural land [pesticides, herbicides] - Drainage from urban areas - Discharge from industrial facilities - Landfill leachates - Undetonated military explosives [TNT, HMX, RDX, etc.] in war zones and training bases - Spills [fuels, etc.] due to transportation accidents - Atmospheric deposition

    15. 03/09/2011 WBL 15 Environmental Fate of Xenobiotics Need to know constants Fugacity Modeling KOW Octanol – water partition coefficient KH Henry’s Law constant Ka Dissociation constant Kd Partition [sorption] coefficient Kr Reaction rate constants MW Molecular weight Sw Solubility in water

    16. 03/09/2011 WBL 16

    17. 03/09/2011 WBL 17 Predicting the Fate of Xenobiotics Need to know the biogeochemical / environmental conditions in the wetland soils Microbial consortia - pH Redox potential - Temperature Salinity - N, P availability C content - Oxygen status Other e- acceptors - Vegetation type

    18. 03/09/2011 WBL 18 Environmental Fate of Xenobiotics Abiotic Pathways Sorption Photolysis Volatilization Export Leaching / surface run-off

    19. 03/09/2011 WBL 19 Abiotic Pathway: Sorption

    20. 03/09/2011 WBL 20 For organic chemicals not adsorbed by soils, Kd is equal to zero For a given organic chemical, sorption (Kd) is greater in soils with larger organic matter content.. These chemicals move slowly in soils For a given soil, organic chemicals with smaller Kd values are sorbed to lesser extent… and highly mobile

    21. 03/09/2011 WBL 21 Abiotic Pathway: Sorption Bioavailability of xenobiotics to degradation is strongly influenced by sorption Chemicals with low sorption coefficients are generally more soluble, and are more readily degraded Sorption of chemicals increases with amount soil organic matter

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    24. 03/09/2011 WBL 24 Biotic Pathways: Microbial ecology: why do microbes degrade Xenobiotics? 1) Derive energy i) Electron acceptor ii) Electron donor 2) A source of Carbon 3) Substitution for a similar “natural” compound: Cometabolism. Cometabolism: organisms mediating the mineralization of a certain compound obtain no apparent benefit from the process

    25. 03/09/2011 WBL 25 Energetics of Xenobiotic Biodegradation Energetics of aerobic and anaerobic benzoate degradation

    26. 03/09/2011 WBL 26 Biodegradation Hydrolysis [ + H2O ] Oxidation [ + O2 ] Reduction [ + e- ] Synthesis [ + Functional Groups]

    27. 03/09/2011 WBL 27 Biotic Pathway: Hydrolysis Extracellular, possibly not compound specific Ether hydrolysis R-C-O-C-R + H2O R-C-OH + HO-C-R Ester hydrolysis (Chlorpropham) R-C-O-C=O + H2O R-C-OH + HO-C=O Phosphate ester hydrolysis (Parathion) R-C-O-P=O + H2O R-C-OH + HO-P=O Amide hydrolysis (Propanil) R-N-C=O + H2O O=C-OH + H-N-R Hydrolytic dehalogenation (PCP) R-C-CL + H2O -C-OH + HCl

    28. 03/09/2011 WBL 28 Biotic Pathway: Oxidation Key to xenobiotic detoxification and subsequent mineralization through oxidation: Presence of molecular oxygen Presence of selected aerobic or facultative aerobic microbial groups (fungi or bacteria) Aromatic rings without functional groups Benzene, toluene, naphthalene

    29. 03/09/2011 WBL 29 Biotic Pathway: Oxidation

    30. 03/09/2011 WBL 30 Biotic Pathway: Reduction Reductive dechlorination (TCE, PCB, PCP) Reduction of the aromatic ring (BTEX) Reduction of the Nitro group (Parathion) R-C-NO2 + 6H+ + 6e- C-C-NH2

    31. 03/09/2011 WBL 31

    32. 03/09/2011 WBL 32 Acetate Oxidation with Different Electron Acceptors 1. The thermodynamics of acetate oxidation varies depending on the type of electron acceptors utilized by microbial groups in wetland soils. 2. The high redox potential associated with O2 indicates that aerobes may gain more energy (ATP) from oxidation of acetate compared to anaerobic groups that use alternate electron acceptors. Organisms that gain the most energy (ATP), outcompete other groups for electron donors, vitamins, nutrients. Because of this, the activity of one group typically excludes the activity of another, allowing the development of distinct zones of microbial activity in the soil. 3. PCP was included in this table to show that certain types of toxic organics can potentially be used as electron acceptors. Having a redox potential slightly higher than NO3, PCP is potentially a better electron acceptor than commonly occurring electron acceptors. Recently, Tiedjes research group at MSU isolated a bacterium capable of using PCP as electron acceptor coupled to ATP production and growth. The PCP was not used as C source, but was critical for energy generation for the organism. 4. One question I plan to address is how PCP degradation is affected by microbial consortia associated with different electron acceptor reducing conditions. 1. The thermodynamics of acetate oxidation varies depending on the type of electron acceptors utilized by microbial groups in wetland soils. 2. The high redox potential associated with O2 indicates that aerobes may gain more energy (ATP) from oxidation of acetate compared to anaerobic groups that use alternate electron acceptors. Organisms that gain the most energy (ATP), outcompete other groups for electron donors, vitamins, nutrients. Because of this, the activity of one group typically excludes the activity of another, allowing the development of distinct zones of microbial activity in the soil. 3. PCP was included in this table to show that certain types of toxic organics can potentially be used as electron acceptors. Having a redox potential slightly higher than NO3, PCP is potentially a better electron acceptor than commonly occurring electron acceptors. Recently, Tiedjes research group at MSU isolated a bacterium capable of using PCP as electron acceptor coupled to ATP production and growth. The PCP was not used as C source, but was critical for energy generation for the organism. 4. One question I plan to address is how PCP degradation is affected by microbial consortia associated with different electron acceptor reducing conditions.

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    39. 03/09/2011 WBL 39 Biotic Pathway: Polymerization

    40. 03/09/2011 WBL 40

    41. Case Study: Lake Apopka 1940’s marshes of lake Apopka drained for agricultural use (19,000 acres) 1950-1990 extensive eutrophication and numerous fish / alligator kills 1992 alligator / turtle population crash Reproduction problems, gender defintion 1980 Dicofol spill (90% gator die-off)

    42. 03/09/2011 WBL 42

    43. Case Study: Lake Apopka 1997 muck farm buy out by state ($100m) 1998 marsh restoration and reflooding begins (July) November 1998 massive wading bird kill on Apopka with dispersion (est. 1000+ birds) Necropsy found DDT, Diedrin, Toxaphene

    45. 03/09/2011 WBL 45 Xenobiotics in Wetlands Sources and examples Aerobic-Anaerobic interfaces Fate dictated by partitioning Abiotic pathways Sorption, photolysis, volatilization Biotic pathways Hydrolosis, Oxidation, Reduction, Synthesis Mediated by microbial consortia Biogeohemical controls Environmental controls

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