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Biogeochemistry of WetlandsInstitute of Food and Agricultural Sciences (IFAS)

Science and ApplicationsScience and ApplicationsJune 23June 23--26, 200826, 2008

Topic: Toxic Organic Compounds (Xenobiotics)

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Instructor:Todd Z. Osborne

Wetland Biogeochemistry LaboratorySoil and Water Science Department

University of Florida

Biogeochemistry of WetlandsScience and ApplicationsScience and Applications

Topic: Toxic Organic Compounds (Xenobiotics)

Learning Objectives

Define xenobioticsEcological significance of xenobioticsSources and common classificationsEnvironmental fate of xenobiotics

WBL 26/22/2008

WBL 2

Abiotic pathwaysBiotic pathways

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What is a Xenobiotic?What is a Xenobiotic?

Xeno means foreign, Bios means life:Xenobiotic is in essence a compound that is foreign toXenobiotic is in essence a compound that is foreign to life

SynonymsToxics, toxic [organic] substances, priority organic pollutants [POPs], endocrine disruptors

Examples:

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Examples: Pesticides, fungicides, herbicides, industrial toxins, petroleum products, landfill leachate

Are Xenobiotics an issue in Are Xenobiotics an issue in Wetlands?Wetlands?

Wetlands are often the receiving bodies of Agricultural and urban drainage Extent of xenobiotic contamination in wetlands

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Approximately 5000 wetlands and aquatic systems impacted by pesticides

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Are Xenobiotics an issue in Are Xenobiotics an issue in Wetlands?Wetlands?

Wetlands may be excellent pollutantWetlands 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

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Upland (aerobic) and aquifier (anaerobic) soil contamination and remediation is the driving force in our current know-how

Ecological Significance

L th l t i it t bi t• Lethal toxicity to biota• Non-lethal toxicity to biota

– Endocrine disruptors– Hormone mimicry

Reproductive disorders

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– Reproductive disorders– Harmful mutation - DNA damage

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Types of Xenobiotics

Petroleum products (BTEX, MTBE)Petroleum products (BTEX, MTBE)

Pesticides (DDT, DDE…..)

Herbicides (2,4D, Atrazine)

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Industrial wastes (PCB’s, aromatics)

CH3

Aromatic Compounds

Napthalene

OH

BenzeneToluene

OH

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BiphenylNaphthol Phenol

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Carbon tetrachlorideChloroform

Halogenated Compounds

ChloroformVinyl chloride1,2-DichloroethaneTrichloroethyleneT t hl th l

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TetrachloroethyleneBenzoates

Polychlorinated BiphenylsPCBs

Halogenated Aromatic Compounds

Organochlorine InsecticidesDDT, Toxaphene, …

Chlorinated Herbicides2,4-D, 2,4,5-T, Atrazine…..

Chlorinated PhenolsP t hl h l

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Pentachlorophenol2,4-dichlorophenol…2,4-D2,4,5-trichlorophenol…. 2,4,5-T2,3,and 4-Nitrophenol

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ClCH

CCl3 DDT

Halogenated Aromatic Compounds

ClCl

ClCl

CCCl2

ClCl

CH

ClCl

CCl

Cl DDE

Chlorobenzene

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ClCl CH

CCl2

ClCl

Cl

DDDPCB1,3-dichlorobenzene

O-CH2COOH

Cl

Chlorinated Herbicides

Halogenated Aromatic Compounds

Cl

Cl

2,4-Dichlorophenoxyacetic Acid[2,4-D]

Chlorinated PhenolsCl

OH

Cl

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Cl Cl

ClCl

ClPentachlorophenol

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Halogenated Aliphatic Compounds

CCCl Cl

ClCl

Trichloroethylene [TCE]

CC

HH

HH

BrBr

Ethylene Dibromide [EDB]

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Sources of Xenobiotics

Wetlands can receive:Drainage from agricultural land [pesticides- Drainage from agricultural land [pesticides, herbicides]

- Drainage from urban areas- Discharge from industrial facilities- Landfill leachates- Undetonated military explosives [TNT, HMX,

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y p [RDX, etc.] in war zones and training bases- Spills [fuels, etc.] due to transportation accidents- Atmospheric deposition

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Environmental Fate of Xenobiotics

• Need to know constants• Fugacity ModelingFugacity Modeling

– KOW Octanol – water partition coefficient– KH Henry’s Law constant– Ka Dissociation constant– Kd Partition [sorption] coefficient

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– Kr Reaction rate constants– MW Molecular weight– Sw Solubility in water

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Predicting the Fate of Xenobiotics

• Need to know the biogeochemical / i t l diti i th tl denvironmental conditions in the wetland

soils– Microbial consortia - pH– Redox potential - Temperature– Salinity - N, P availability

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y , y– C content - Oxygen status– Other e- acceptors - Vegetation type

Environmental Fate of Xenobiotics

Abiotic PathwaysSorptionPhotolysisVolatilizationExport

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ExportLeaching / surface run-off

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Abiotic Pathway: Sorption

Soil ParticleOrganic Matter

Chemicalin Solution

Products of

Desorption

AdsorptionS C

[mg/kg] [mg/L]

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Products of Biodegradation

Partition coefficient (L/kg) Kd = S (mg/kg)/C (mg/L)

Abiotic Pathway: SorptionFor organic chemicals not adsorbed by soils, Kd is equal to zeroKd 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

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For a given soil, organic chemicals with smaller Kd values are sorbed to lesser extent… and highly mobile

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Abiotic Pathway: Sorption

Bioavailability of xenobiotics to degradation is y gstrongly influenced by sorptionChemicals with low sorption coefficients are generally more soluble, and are more readily degradedSorption of chemicals increases with amount

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psoil organic matter

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

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Chemicals with high sorption coefficients are generally less mobile

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Environmental Fate of Xenobiotics

Biotic pathwaysExtracellular enzyme hydrolysis

Microbial degradation

Plant and microbial uptake

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Plant and microbial uptake

Bioaccumulation / magnification

Biotic Pathways:Microbial ecology: why do microbes degrade

Xenobiotics?1) Derive energy

i) Electron acceptorii) Electron donor

2) A source of Carbon3) Substitution for a similar “natural” compound:

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Cometabolism.Cometabolism: organisms mediating the mineralization of a

certain compound obtain no apparent benefit from the process

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Energetics of Xenobiotic Biodegradation

Energetics of aerobic and anaerobic benzoate degradationbenzoate degradationReaction G (kJ)

Benzoate + 7.5O2 2CO2 -3175

Benzoate + 6NO3- 3N2 +7CO2 -2977

Benzoate + 8NO3- 14NH4

+ + 7CO2 -1864

30 3 30 2 CO 303

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Benzoate + 30 Fe3+ 30 Fe2+ + 7 CO2 -303

Benzoate + SO42- 7CO2 + 3.75HS- -185

Benzoate + So 7CO2 + 15HS- -36

Thauer et al. 1977

Biodegradation

Hydrolysis [ + H2O ]Hydrolysis [ + H2O ]Oxidation [ + O2 ]Reduction [ + e- ]Synthesis [ + Functional Groups]

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Sy es s [ u c o a G oups]

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Biotic Pathway: HydrolysisBiotic Pathway: HydrolysisExtracellular, possibly not compound specific

Ether hydrolysis R C O C R H O R C OH HO C RR-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)

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Amide hydrolysis (Propanil)R-N-C=O + H2O O=C-OH + H-N-R

Hydrolytic dehalogenation (PCP)R-C-CL + H2O -C-OH + HCl

Biotic Pathway: Oxidation Biotic Pathway: Oxidation

Key to xenobiotic detoxification and b t i li ti th hsubsequent mineralization through

oxidation:Presence of molecular oxygen Presence of selected aerobic or facultative aerobic microbial groups (fungi or bacteria)

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Aromatic rings without functional groups Benzene, toluene, naphthalene

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Biotic Pathway: OxidationBiotic Pathway: Oxidation

OHH O

OHH O OH

Benzene

+ O2

H2O+ O2

H2O OH

+ O2

COOHCOOHCO2 + H2O

Monooxygenase Monooxygenase

Dioxygenase

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COOH2 2

Muconic Acid

Biotic Pathway: Reduction Biotic Pathway: Reduction Reductive dechlorination

(TCE PCB PCP)(TCE, PCB, PCP) Reduction of the aromatic ring

(BTEX)

6 H+ + 6 e-

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Reduction of the Nitro group (Parathion) R-C-NO2 + 6H+ + 6e- C-C-NH2

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Reductive DechlorinationReductive Dechlorination

ClOH

Cl

OH OHCl H H H

H++ 2e- H++ 2e-

Sequential replacement of Cl- ions with H atoms

ClCl

Cl ClCl

Cl ClCl

ClCl- Cl-

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Usually results in accumulation of toxic intermediates Promoted under highly reducing conditions (low redoxpotential) and high microbial activity

Acetate Oxidation with Different Electron Acceptors

Electron acceptor Go’ ATP

(kJ/ mol Ac) (mol/mol Ac)

O2 / H2O

PCP / TeCP

-858

-557

28

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NO3 - / NO2

-

SO4 2- / HS-

-556

-56

18

2

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Reductive Dechlorination of PCP in Reductive Dechlorination of PCP in Methanogenic Everglades SoilsMethanogenic Everglades Soils

PCP 345 TCP 35 DCP

0.40.60.8

1

35 DCP

345 TCPPCP

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00.2

0 20 40 60 80Time, days

100n

Reductive Dechlorination byAnaerobic Microorganisms

[Polychlorinated Biphenyls (PCBs)]Van Dort and Bedard, 1991; Appl. Environ. Micro. 57:1576-1578

80

60

40

ativ

e M

ole

Frac

tio

2356-CB235-CB

26-CB

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20

018 20 22 24 26 28 30 32 34 36 38

Rel

a

25-CB

18

NH

Biotic Pathway: Reduction Biotic Pathway: Reduction

NO2

OH

+ 6 e- + 6 H+

NH2

OH

+ H2O

it h l i h l

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p-nitrophenol p-aminophenol

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Anaerobic Degradation of2,4,6-trinitrotoluene [TNT]

Boopathy et al. 1993 Water Environ. Res. 65:272-275

120

10080

6040TN

T (p

pm)

Sulfate Reducing

H2 : CO2

No electron acceptors

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200

0 10 20 30 40 50Time (days)

Nitrate Reducing

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Fate Processes of Fate Processes of Chlorophenols in SoilChlorophenols in Soil

Microbial transformationsReductive dechlorinationAerobic catabolism

Sorption CO2CO2PCPaqPCPaqPCP sPCP s

Sorption/Desorption

AerobicCatabolism

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CPaqCPaq

ReductiveDechlorination

AerobicCatabolism

Coupled AnaerobicCoupled Anaerobic--Aerobic Aerobic PCP DegradationPCP Degradation

ClOH

Cl

OHH HCl Cl

ClCl

Cl ClCl

H

H H

PCP DCPOH

Anaerobic: Cl- removal

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Aerobic: Cl- removal and ring cleavageCl

ClH

H H+ O2 CO2 + H2O + 2Cl-

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Biotic Pathway: PolymerizationBiotic Pathway: PolymerizationOxidative coupling under aerobic conditions

Recalcitrant humic-like polymers Example TNT

NO2

NO

CH3

NO2

N N

NO2

NO2

NO2

NO

Recalcitrant humic like polymers. Example TNT

toxic, mutagenic

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NO2NO2 NO2

2,4,6-trinitrotoluene 2,2’,6,6’-tetranitro-4.4’-azoxytoluene

Field et al. 1995. Antonie van Leeuwenhoek 67:47-77

Biotic Pathway: PolymerizationBiotic Pathway: Polymerization

Cl

OHCl

Cl

OH

Cl

OHClCl O

O

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2, 4-dichlorophenol 2,3,7,8-dibenzo-p-dioxin

Field et al. 1995. Antonie van Leeuwenhoek 67:47-77

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Case Study: Lake Apopka

• 1940’s marshes of lake Apopka drained f i lt l (19 000 )for agricultural use (19,000 acres)

• 1950-1990 extensive eutrophication and numerous fish / alligator kills

• 1992 alligator / turtle population crashReproduction problems gender defintion– Reproduction problems, gender defintion

– 1980 Dicofol spill (90% gator die-off)

Lake ApopkaMarsh

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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)birds)

• Necropsy found DDT, Diedrin, Toxaphene

Contaminant Exposures and Potential Effects on Health and Endocrine Status for Alligators in the

Greater Everglades Ecosystem

Source: Wiebe et al (2003)

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Xenobiotics in Wetlands

Sources and examplesA bi A bi i t fAerobic-Anaerobic interfacesFate dictated by partitioningAbiotic pathways

Sorption, photolysis, volatilizationBiotic pathways

Hydrolosis Oxidation Reduction Synthesis

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Hydrolosis, Oxidation, Reduction, SynthesisMediated by microbial consortiaBiogeohemical controls Environmental controls