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Understanding Xenobiotics in Wetlands

Explore toxic organic compounds, sources, environmental fate, ecological significance, and abiotic/biotic pathways of xenobiotics. Learn about biogeochemistry applications in wetlands.

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Understanding Xenobiotics in Wetlands

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  1. Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands Science and Applications June 23-26, 2008 Topic: Toxic Organic Compounds (Xenobiotics) Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor: Todd Z. Osborne 10/29/2019 WBL WBL 1

  2. Biogeochemistry of Wetlands Science and Applications Topic: Toxic Organic Compounds (Xenobiotics) • Learning Objectives • Define xenobiotics • Ecological significance of xenobiotics • Sources and common classifications • Environmental fate of xenobiotics • Abiotic pathways • Biotic pathways WBL WBL 2 10/29/2019

  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 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 WBL

  5. Are Xenobiotics an issue in Wetlands? • Wetlands may be excellent pollutant removers (aerobic - anaerobic interfaces) • Wetlands are not in the spot light ! • No wetland superfund site, etc. • Upland (aerobic) and aquifier (anaerobic) soil contamination and remediation is the driving force in our current know-how WBL

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

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

  8. OH Napthalene Naphthol Biphenyl OH CH3 Benzene Toluene Phenol Aromatic Compounds WBL

  9. Halogenated Compounds • Carbon tetrachloride • Chloroform • Vinyl chloride • 1,2-Dichloroethane • Trichloroethylene • Tetrachloroethylene • Benzoates WBL

  10. Halogenated Aromatic Compounds • 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 WBL

  11. Cl CCl3 Cl CH Cl Cl Cl Cl Cl CCl2 C Cl Cl Cl Cl Cl CCl2 CH Cl Cl Cl Halogenated Aromatic Compounds DDT Chlorobenzene DDE 1,3-dichlorobenzene PCB DDD WBL

  12. O-CH2COOH Cl 2,4-Dichlorophenoxyacetic Acid [2,4-D] Cl Halogenated Aromatic Compounds Chlorinated Herbicides OH Chlorinated Phenols Cl Cl Cl Cl Pentachlorophenol Cl WBL

  13. H H C Br C Br H H Ethylene Dibromide [EDB] Cl Cl C C Cl Cl Trichloroethylene [TCE] Halogenated Aliphatic Compounds 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 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 WBL

  16. 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 WBL

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

  19. Abiotic Pathway: Sorption Desorption S Soil Particle Organic Matter Chemical in Solution C Adsorption [mg/L] [mg/kg] Products of Biodegradation Partition coefficient (L/kg) Kd = S (mg/kg)/C (mg/L) WBL

  20. Abiotic Pathway: Sorption • 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 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 WBL

  22. Abiotic Pathway: Sorption • Sorption may protect biota from toxic levels of chemicals • High levels of DOM may increase the mobility of chemicals • Chemicals with high sorption coefficients are generally less mobile WBL

  23. Environmental Fate of Xenobiotics • Biotic pathways • Extracellular enzyme hydrolysis • Microbial degradation • Plant and microbial uptake • Bioaccumulation / magnification 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 WBL

  25. Reaction G (kJ) Benzoate + 7.5O2 2CO2 -3175 Benzoate + 6NO3- 3N2 +7CO2 -2977 Benzoate + 8NO3- 14NH4+ + 7CO2 -1864 Benzoate + 30 Fe3+ 30 Fe2+ + 7 CO2 -303 Benzoate + SO42- 7CO2 + 3.75HS- -185 Benzoate + So 7CO2 + 15HS- -36 Energetics of Xenobiotic Biodegradation • Energetics of aerobic and anaerobic benzoate degradation WBL Thauer et al. 1977

  26. Biodegradation • Hydrolysis [ + H2O ] • Oxidation [ + O2 ] • Reduction [ + e- ] • Synthesis [ + Functional Groups] 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 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 WBL

  29. Biotic Pathway: Oxidation OH OH Benzene H2O H2O OH + O2 + O2 Monooxygenase Monooxygenase + O2 Dioxygenase COOH CO2 + H2O COOH Muconic Acid WBL

  30. 6 H+ + 6 e- 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 WBL

  31. Reductive Dechlorination OH OH OH H++ 2e- H++ 2e- Cl Cl H H Cl H Cl- Cl- Cl Cl Cl Cl Cl Cl Cl Cl Cl • Sequential replacement of Cl- ions with H atoms • Usually results in accumulation of toxic intermediates • Promoted under highly reducing conditions (low redox potential) and high microbial activity WBL

  32. Acetate Oxidation with Different Electron Acceptors Electron acceptor • Go’ ATP • (kJ/ mol Ac) • (mol/mol Ac) -858 28 • O2 / H2O -557 18 • PCP / TeCP -556 18 • NO3 - / NO2- -56 2 • SO4 2- / HS- WBL

  33. Reductive Dechlorination of PCP in Methanogenic Everglades Soils PCP 345 TCP 35 DCP 1 0.8 345 TCP 0.6 PCP µmol/g soil 35 DCP 0.4 0.2 0 0 20 40 60 80 Time, days WBL

  34. 100 2356-CB 80 235-CB 60 26-CB Relative Mole Fraction 40 20 25-CB 0 18 20 22 24 26 28 30 32 34 36 38 Reductive Dechlorination by Anaerobic Microorganisms [Polychlorinated Biphenyls (PCBs)] Van Dort and Bedard, 1991; Appl. Environ. Micro. 57:1576-1578 Incubation time (weeks) WBL

  35. Biotic Pathway: Reduction NH2 NO2 + 6 e- + 6 H+ + H2O OH OH p-nitrophenol p-aminophenol WBL

  36. 120 100 No electron acceptors 80 Sulfate Reducing TNT (ppm) 60 H2 : CO2 40 20 Nitrate Reducing 0 0 10 20 30 40 50 Time (days) Anaerobic Degradation of 2,4,6-trinitrotoluene [TNT] Boopathy et al. 1993 Water Environ. Res. 65:272-275 WBL

  37. Sorption/ Desorption Aerobic Catabolism PCPaq CO2 PCP s Reductive Dechlorination CPaq Aerobic Catabolism Fate Processes of Chlorophenols in Soil • Microbial transformations • Reductive dechlorination • Aerobic catabolism • Sorption WBL

  38. OH Cl Cl Cl Cl Cl OH H H H Cl Cl Coupled Anaerobic-Aerobic PCP Degradation OH H H Anaerobic:Cl- removal H Cl Cl PCP DCP CO2 + H2O + 2Cl- + O2 Aerobic:Cl- removal and ring cleavage WBL

  39. Biotic Pathway: Polymerization • Oxidative coupling under aerobic conditions • Recalcitrant humic-like polymers. Example TNT CH3 toxic, mutagenic NO2 NO2 NO2 NO2 CH3 N N CH3 NO2 NO2 NO2 2,2’,6,6’-tetranitro-4.4’-azoxytoluene 2,4,6-trinitrotoluene Field et al. 1995. Antonie van Leeuwenhoek 67:47-77 WBL

  40. Biotic Pathway: Polymerization OH OH OH Cl Cl O Cl O Cl Cl Cl 2, 4-dichlorophenol 2,3,7,8-dibenzo-p-dioxin Field et al. 1995. Antonie van Leeuwenhoek 67:47-77 WBL

  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. Lake Apopka Marsh WBL

  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

  44. Contaminant Exposures and Potential Effects on Health and Endocrine Status for Alligators in the Greater Everglades Ecosystem Source: Wiebe et al (2003)

  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 WBL

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