Biogeochemistry of Wetlands Topic: Toxic Organic Compounds (Xenobiotics) Science and Applications

Institute of Food and Agricultural Sciences (IFAS)
Biogeochemistry of Wetlands
Science and Applications
June 23
23--26, 2008
Topic: Toxic Organic Compounds
(Xenobiotics)
Wetland Biogeochemistry Laboratory
Soil and Water Science Department
University of Florida
Instructor:
Todd Z. Osborne
22/06/2008
6/22/2008
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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
™
™
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What is a Xenobiotic?
¾ Xeno means foreign, Bios means life:
¾ Xenobiotic is in essence a compound that is foreign to
life
¾ Synonyms
¾ Toxics, toxic [organic] substances, priority organic
pollutants [POPs], endocrine disruptors
¾ Examples:
¾ Pesticides, fungicides, herbicides, industrial toxins,
petroleum products, landfill leachate
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Are Xenobiotics an issue in
Wetlands?
¾Wetlands are often the receiving bodies of
Agricultural and urban drainage
¾Extent of xenobiotic contamination in
wetlands
¾Approximately 5000 wetlands and aquatic
systems impacted by pesticides
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Are Xenobiotics an issue in
Wetlands?
¾Wetlands may be excellent pollutant
removers (aerobic - anaerobic interfaces)
¾Wetlands are not in the spot light !
¾No wetland superfund site, etc.
¾Upland (aerobic) and aquifier (anaerobic) soil
contamination and remediation is the driving
force in our current know-how
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Ecological Significance
• Lethal
L th l toxicity
t i it to
t biota
bi t
• Non-lethal toxicity to biota
– Endocrine disruptors
– Hormone mimicry
– Reproductive disorders
– Harmful mutation - DNA damage
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Types of Xenobiotics
/ Petroleum products (BTEX, MTBE)
/ Pesticides (DDT, DDE…..)
/ Herbicides (2,4D, Atrazine)
/ Industrial wastes (PCB’s, aromatics)
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Aromatic Compounds
CH3
Napthalene
Benzene
Toluene
OH
Naphthol
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OH
Phenol
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Biphenyl
8
4
Halogenated Compounds
¾Carbon tetrachloride
¾Chloroform
¾Vinyl chloride
¾1,2-Dichloroethane
¾Trichloroethylene
¾T t hl
¾Tetrachloroethylene
th l
¾Benzoates
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Halogenated Aromatic Compounds
¾ Polychlorinated Biphenyls
¾ PCBs
¾ Organochlorine Insecticides
¾ DDT, Toxaphene, …
¾ Chlorinated Herbicides
¾ 2,4-D, 2,4,5-T, Atrazine…..
¾ Chlorinated Phenols
¾ Pentachlorophenol
P t hl
h
l
¾ 2,4-dichlorophenol…2,4-D
¾ 2,4,5-trichlorophenol…. 2,4,5-T
¾ 2,3,and 4-Nitrophenol
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Halogenated Aromatic Compounds
CCl3
Cl
DDT
CH
Cl
Cl
Cl
Chlorobenzene
Cl
CCl2
C
Cl
Cl
Cl
Cl
Cl
Cl
Cl
CCl2
Cl
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Cl
CH
1,3-dichlorobenzene
PCB
DDE
Cl
DDD
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Halogenated Aromatic Compounds
O-CH2COOH
Chlorinated Herbicides
Cl
2,4-Dichlorophenoxyacetic Acid
[2,4-D]
Cl
Chlorinated Phenols
Pentachlorophenol
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OH
Cl
Cl
Cl
Cl
Cl
12
6
Halogenated Aliphatic Compounds
Cl
Cl
C
Cl
C
Br
Cl
Trichloroethylene [TCE]
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H
H
C
C
H
H
Br
Ethylene Dibromide [EDB]
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Sources of Xenobiotics
Wetlands can receive:
- Drainage from agricultural land [pesticides
[pesticides,
herbicides]
- Drainage from urban areas
- Discharge from industrial facilities
- Landfill leachates
- Undetonated military
y explosives
p
[[TNT, HMX,
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 Modeling
– KOW
– KH
– Ka
– Kd
– Kr
– MW
– Sw
Octanol – water partition coefficient
Henry’s Law constant
Dissociation constant
Partition [sorption] coefficient
Reaction rate constants
Molecular weight
Solubility in water
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Predicting the Fate of Xenobiotics
• Need to know the biogeochemical /
environmental
i
t l conditions
diti
iin th
the wetland
tl d
soils
– Microbial consortia
– Redox potential
– Salinity
y
– C content
– Other e- acceptors
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- pH
- Temperature
- N,, P availabilityy
- Oxygen status
- Vegetation type
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Environmental Fate of Xenobiotics
¾Abiotic Pathways
¾Sorption
¾Photolysis
¾Volatilization
¾Export
¾Leaching / surface run-off
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Abiotic Pathway: Sorption
S
Soil Particle
Organic Matter
[mg/kg]
Desorption
Adsorption
Chemical
in Solution
C
[mg/L]
Products of
Biodegradation
Partition coefficient (L/kg) Kd = S (mg/kg)/C (mg/L)
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Abiotic Pathway: Sorption
¾ For organic chemicals not adsorbed by soils,
Kd is equal to zero
¾ For a given organic chemical, sorption (Kd) is
greater in soils with larger organic matter
content.. These chemicals move slowly in soils
¾ 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
¾ Bioavailabilityy of xenobiotics to degradation
g
is
strongly influenced by sorption
¾ Chemicals with low sorption coefficients are
generally more soluble, and are more readily
degraded
p
of chemicals increases with amount
¾ Sorption
soil organic matter
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Abiotic Pathway: Sorption
¾Sorption may protect biota from toxic
levels of chemicals
¾High levels of DOM may increase the
mobility of chemicals
¾Chemicals with high sorption coefficients
are generally less mobile
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Environmental Fate of Xenobiotics
¾Biotic pathways
¾Extracellular enzyme hydrolysis
¾Microbial degradation
¾Plant and microbial uptake
¾Bioaccumulation / magnification
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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
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Energetics of Xenobiotic
Biodegradation
¾Energetics of aerobic and anaerobic
benzoate degradation
Reaction
G (kJ)
Benzoate + 7.5O2 Æ 2CO2
-3175
Benzoate + 6NO3 Æ 3N2 +7CO2
-2977
Benzoate + 8NO3- Æ 14NH4+ + 7CO2
-1864
-
3 Æ 30 Fe2+
2 + 7 CO
Benzoate + 30 Fe3+
2
-303
303
Benzoate + SO42- Æ 7CO2 + 3.75HS-
-185
Benzoate + So Æ 7CO2 + 15HS22/06/2008
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Thauer et al. 1977
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Biodegradation
¾ Hydrolysis [ + H2O ]
¾ Oxidation [ + O2 ]
¾ Reduction [ + e- ]
¾ Sy
Synthesis
es s [ + Functional
u c o a G
Groups
oups]
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Biotic Pathway: Hydrolysis
¾ Extracellular, possibly not compound specific
¾ Ether hydrolysis
¾ R-C-O-C-R
R C O C R + H2O
R-C-OH
R C OH + HO
HO-C-R
CR
¾ Ester hydrolysis (Chlorpropham)
R-C-OH + HO-C=O
¾ R-C-O-C=O + H2O
¾ Phosphate ester hydrolysis (Parathion)
¾ R-C-O-P=O + H2O
R-C-OH + HO-P=O
¾ Amide hydrolysis (Propanil)
¾ R-N-C=O + H2O
O=C-OH + H-N-R
¾ Hydrolytic dehalogenation (PCP)
¾ R-C-CL + H2O
-C-OH + HCl
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Biotic Pathway: Oxidation
¾Key to xenobiotic detoxification and
subsequent
b
t mineralization
i
li ti th
through
h
oxidation:
¾Presence of molecular oxygen
¾Presence of selected aerobic or facultative
aerobic microbial groups (fungi or bacteria)
¾Aromatic rings without functional groups
¾Benzene, toluene, naphthalene
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Biotic Pathway: Oxidation
Benzene
H2O
OH
+ O2
H2O
OH
OH
+ O2
Monooxygenase
Monooxygenase
+ O2
Dioxygenase
COOH
COOH
CO2 + H2O
Muconic Acid
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Biotic Pathway: Reduction
¾ Reductive dechlorination
¾ (TCE,
(TCE PCB
PCB, PCP)
¾ Reduction of the aromatic ring
¾ (BTEX)
6 H+ + 6 e¾ Reduction of the Nitro group
¾ (Parathion)
¾ R-C-NO2 + 6H+ + 6e22/06/2008
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C-C-NH2
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Reductive Dechlorination
OH
Cl
Cl
Cl
Cl
OH
H++ 2e-
H++ 2e-
OH
Cl
H
H
Cl- Cl
Cl
Cl- Cl
Cl
Cl
H
Cl
Cl
¾ Sequential replacement of Cl- ions with H atoms
¾ Usually results in accumulation of toxic intermediates
¾ Promoted under highly reducing conditions (low redox
potential) and high microbial activity
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Acetate Oxidation with Different
Electron Acceptors
Go’
Electron acceptor
ATP
(kJ/ mol Ac) (mol/mol Ac)
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O2 / H2O
-858
28
PCP / TeCP
-557
18
NO3 - / NO2-
-556
18
SO4 2- / HS-
-56
2
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Reductive Dechlorination of PCP in
Methanogenic Everglades Soils
PCP
345 TCP
35 DCP
1
0.8
345 TCP
0.6
PCP
35 DCP
0.4
0.2
0
0
20
40
60
80
Time, days
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Reductive Dechlorination by
Anaerobic Microorganisms
[Polychlorinated Biphenyls (PCBs)]
Van Dort and Bedard, 1991; Appl. Environ. Micro. 57:1576-1578
Rela
ative Mole Fraction
100
80
235-CB
60
26-CB
40
20
0
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2356-CB
25-CB
18 20 22 24 26 28 30 32 34 36 38
Incubation time (weeks)
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Biotic Pathway: Reduction
NH2
NO2
+ 6 e- + 6 H+
+ H2O
OH
OH
p-nitrophenol
it h l
p-aminophenol
i
h l
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Anaerobic Degradation of
2,4,6-trinitrotoluene [TNT]
Boopathy et al. 1993 Water Environ. Res. 65:272-275
120
No electron acceptors
TNT (ppm)
100
80
Sulfate Reducing
60
H2 : CO2
40
20
Nitrate Reducing
0
0
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10
20
30
Time (days)
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40
50
36
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Fate Processes of
Chlorophenols in Soil
¾Microbial transformations
¾Reductive dechlorination
¾Aerobic catabolism
Sorption/
Desorption
¾Sorption
Aerobic
Catabolism
PCPaq
PCP s
CO2
Reductive
Dechlorination
Aerobic
Catabolism
CPaq
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Coupled Anaerobic
Anaerobic--Aerobic
PCP Degradation
OH
OH
Cl
Cl
Cl
Cl
Anaerobic: Cl- removal
Cl
H
H
H
Cl
Cl
PCP
DCP
OH
H
H
CO2 + H2O + 2Cl-
+ O2
Aerobic: Cl- removal and ring cleavage
H
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Cl
Cl
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Biotic Pathway: Polymerization
¾ Oxidative coupling under aerobic conditions
¾Recalcitrant humic-like
humic like polymers
polymers. Example TNT
CH3
NO2
NO2
toxic, mutagenic
NO2
NO2
N
N
NO2
NO2
2,4,6-trinitrotoluene
NO2
2,2’,6,6’-tetranitro-4.4’-azoxytoluene
Field et al. 1995. Antonie van Leeuwenhoek 67:47-77
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Biotic Pathway: Polymerization
OH
OH
Cl
Cl
OH
O
Cl
O
Cl
2, 4-dichlorophenol
Cl
Cl
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 agricultural
for
i lt l use (19
(19,000
000 acres))
• 1950-1990 extensive eutrophication and
numerous fish / alligator kills
• 1992 alligator / turtle population crash
– Reproduction problems
problems, gender defintion
– 1980 Dicofol spill (90% gator die-off)
Lake Apopka
Marsh
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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)
• 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
¾ Sources and examples
¾ Aerobic-Anaerobic
A bi A
bi iinterfaces
t f
¾ Fate dictated by partitioning
¾ Abiotic pathways
¾Sorption, photolysis, volatilization
¾ Biotic pathways
¾Hydrolosis Oxidation
¾Hydrolosis,
Oxidation, Reduction
Reduction, Synthesis
¾Mediated by microbial consortia
¾Biogeohemical controls
¾Environmental controls
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