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Plant Uptake Processes in Phytoremediation of Organic Contamination Guangyao Sheng (盛光遥) University of Arkansas Cary T. Chiou ( 邱成財 ) PowerPoint PPT Presentation


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Plant Uptake Processes in Phytoremediation of Organic Contamination Guangyao Sheng (盛光遥) University of Arkansas Cary T. Chiou ( 邱成財 ) National Cheng Kung University. d C d t. = f ( C , t ). Current Plant Uptake Models:. 1. Kinetic Model (Trapp et al .) Mass Balance

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Plant Uptake Processes in Phytoremediation of Organic Contamination Guangyao Sheng (盛光遥) University of Arkansas Cary T. Chiou ( 邱成財 )

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Plant Uptake Processes

in Phytoremediation of Organic Contamination

Guangyao Sheng (盛光遥)

University of Arkansas

Cary T. Chiou (邱成財)

National Cheng Kung University


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dC

dt

= f (C, t)

Current Plant Uptake Models:

1. Kinetic Model (Trapp et al.)

Mass Balance

Differential Equations

2. Equilibrium Model (for roots only)

Briggs et al. (1982, 1983)

Trapp and Matthies (1995)

3. Quasi-equilibrium Model,

Mechanistic Model


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Objectives

1. Develop a partition-limited mechanistic model to describe the passive uptake of organic contaminants by plants from contaminated soils or water.

2. Test the model with experimental data.

3. Establish the relationship between kinetic uptake and equilibrium partition.

4. Offer plant selection guidelines for uptake-based phytoremediation of organic-contaminated soils and water.


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  • References:

  • Chiou, C.T.; Sheng, G.; Manes, M. A partition-limited model for the plant uptake of organic contaminants from soil and water. Environ. Sci. Technol.2001, 35, 1437-1444.

  • Li, H.; Sheng, G.; Chiou, C.T.; Xu, O. Relation of organic contaminant equilibrium sorption and kinetic uptake in plants. Environ. Sci. Technol.2005, 39, 4864-4870.


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Equilibrium Partitioning of Organic Chemicals into SOM or Plants:

• Solubilization Processes

• Q = KpCW

Soil uptake: CS = KpCW = KsomfsomCW

Plant uptake: Cpt = KplCW = KpomfpomCW

= fpw

+ 1Kpom1fpomCW

+ 2Kpom2fpomCW

+ ……


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Model Development

System Parameters:

• Soil properties: effect of soil sorption

• Contaminant physicochemical properties

• Species of plants (or different plant tissues)

• Contaminant levels in soils or water

• Exposure time


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Kinetic Uptake from Soil-Free Water Solution:

Qpt =  CwKpl

=  Cw ( fpw +  fpomiKpomi )

In which fpw + fpomi = 1 i = 1,2,3,…,n.

where:

fpomi = the organic-matter weight fraction for the ith component

Kpomi = the contaminant partition coefficient between ith component plant organic matter and water

fpw = the plant-water weight fraction

 = quasi-equilibrium factor (1)


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Kinetic Uptake from Contaminated Soils:

Qpt =  (Cs / fsomKsom)( fpw +  fpomiKpomi )

withCw = Cs / fsomKsom

Where:

Cs = the contaminant concentration in the whole soil,

fsom = the soil organic-matter (SOM) fraction,

Ksom = the contaminant partition coefficient between SOM and water.


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Important Plant Components and Their Contaminant Partition Coefficients:

Plant Components:

Water; Nutrients; Proteins;lipids; Carbohydrates.

Relevant Partition Coefficients:

Kprt (protein-water);Klip (lipid-water);

Kch (carbohydrate-water);Kow (octanol-water);

Ksom (SOM-water).

Approximation:Klip = Kow


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Simplification of the Uptake Model:

Qpt =  CwKpl

=  Cw ( fpw + fpomiKpomi )

=  Cw ( fpw + flipKlip + fchKch )


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Approximate Kch values for contaminants

log KOWKOWKch

 0  1 0.1

0.1-0.91-10 0.2

1.0-1.910-100 0.5

2.0-2.9100-1000 1.0

3.0-3.91000-10000 2.0

 4.0  10000 3.0


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Solution

reservoir

pump

sink

  • Experimental:

  • HCB, Lindane, PCE, TCE

  • Seedlings of wheat and ryegrass: roots and shoots

  • Composition: water, lipids, carbohydrates

  • Plant-water partition: batch equilibration

  • Plant uptake kinetics: constant solution-phase concentrations


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log KOW and Initial Concentrations of Chemicals

Chemical HCBLDN PCE TCE

log Kow 5.503.72 3.38 2.53

Concentration 4.96503.7 1300 3300

(g/L)


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Plant % water % lipids % carbohydrates

Ryegrass

roots87.70.3012.0

shoots88.80.9710.2

Wheat

roots84.40.5115.3

shoots85.21.1013.7

Weight Compositions of Wheat and Ryegrass Parts


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Hexachlorobenzene:

shoots:Qeq = Cw (0.852 + 0.137×3 + 0.0110×316228)

Lipids contribute 99.96%.

roots:Qeq = Cw (0.844 + 0.153×3 + 0.0051×316228)

Lipids contribute 99.92%.

Lipid Contribution

Contributions of Wheat Parts to Equilibrium Sorption

Qeq = Cw ( fpw + fchKch + flipKlip)


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Contributions of Wheat Lipids to Equilibrium Sorption

shoots (%)roots (%)

Hexachlorobenzene 99.96 99.92

Lindane 98.09 95.88

PCE 95.91 91.41

TCE 79.03 63.41


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Plant Uptake Model:

Sorption ModelQeq = CwKpl

Composition Model Qeq = Cw ( fpw + fchKch + flipKlip )

(low log Kow)

Lipid Model Qeq  CwflipKlip

(high log Kow)  CwflipKow


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65000

HCB

shoots:

measured

52000

Kow

roots:

measured

39000

Kow

Concentration in Wheat, Qeq (g/kg)

26000

13000

0

0.0

0.5

1.0

1.5

2.0

Concentration in Water, Cw (g/L)

Sorption of Hexachlorobenzene from Water by Wheat Seedlings


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25000

Lindane

shoots:

measured

20000

Kow

roots:

measured

15000

Kow

Concentration in Wheat, Qeq (g/kg)

10000

5000

0

0

50

100

150

200

250

300

Concentration in Water, Cw (g/L)

Sorption of Lindane from Water by Wheat Seedlings


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shoots roots log Kow

Hexachlorobenzene 5.50

Kpl (L/kg) 3791816900

log Klip 6.54 6.52

Lindane 3.72

Kpl (L/kg) 73.0 45.4

log Klip 3.82 3.95

Comparison of Determined log Klip to log Kow


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Important Issues and Points:

Are plant lipids more effective than octanol in uptake?

Triolein (C57H104O6) > Octanol (C8H18O)

O/C = 0.105 0.125

Do current techniques underestimate plant lipid contents?

Selection of extracting solvents?

Uptake limit (g/kg) can be defined by equilibrium sorption.


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Wheat shoots roots

HCB LDN HCB LDN

limit (g/kg)188073 36770 83824 22868

limit-to-Cw ratio (BCF) 37918 73.0 16900 45.4

Ryegrass shoots roots

PCE TCE PCE TCE

limit (g/kg) 31669 14113 10808 6645

limit-to-Cw ratio (BCF) 24.4 4.28 8.31 2.01

Uptake Limits (g/kg):


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1200

HCB

Roots

1000

800

Plant Concentration, Qt (g/kg)

600

400

Shoots

200

0

0

50

100

150

200

250

300

350

Uptake Time (Hours)

Uptake of Hexachlorobenzene from Water

by Wheat Seedlings (Cw = 4.96 g/L)


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16000

LDN

Roots

12000

Plant Concentration, Qt (g/kg)

8000

Shoots

4000

0

0

50

100

150

200

250

300

Uptake Time (Hours)

Uptake of Lindane from Water by Wheat Seedlings

(Cw = 503.7 g/L)


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5000

PCE

4000

Roots

3000

Plant Concentration, Qt (g/kg)

2000

Shoots

1000

0

0

40

80

120

160

Uptake Time (Hours)

Uptake of Tetrachloroethylene from Water

by Ryegrass Seedlings (Cw = 1300 g/L)


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TCE

6000

Roots

4000

Plant Concentration, Qt (g/kg)

Shoots

2000

0

0

40

80

120

160

Uptake Time (Hours)

Uptake of Trichloroethylene from Water

by Ryegrass Seedlings (Cw = 3300 g/L)


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0.10

HCB

0.08

Roots

0.06

Quasi-Equilibrium Factor, 

0.04

0.02

Shoots

0.00

0

50

100

150

200

250

300

350

Uptake Time (Hours)

Uptake of Hexachlorobenzene from Water

by Wheat Seedlings (Cw = 4.96 g/L)


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0.8

LDN

Roots

0.6

Quasi-Equilibrium Factor, 

0.4

0.2

Shoots

0.0

0

60

120

180

240

300

Uptake Time (Hours)

Uptake of Lindane from Water by Wheat Seedlings

(Cw = 503.7 g/L)


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0.5

PCE

0.4

Roots

0.3

Quasi-Equilibrium Factor, 

0.2

0.1

Shoots

0.0

0

40

80

120

160

Uptake Time (Hours)

Uptake of Tetrachloroethylene from Water

by Ryegrass Seedlings (Cw = 1300 g/L)


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1.0

TCE

0.8

Roots

0.6

Quasi-Equilibrium Factor, 

0.4

Shoots

0.2

0.0

0

40

80

120

160

Uptake Time (Hours)

Uptake of Trichloroethylene from Water

by Ryegrass Seedlings (Cw = 3300 g/L)


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Shoot Uptake and Chemical Lipophilicity:

 PCE and TCE uptake reached steady state within 24 hours

Lindane uptake reached steady state at 90 hours

HCB uptake continued to rise at 300 hours

 An inverse correlation between uptake and lipophilicity or BCF

Transpiration:

chemical HCB LDN PCE TCE

uptake at 24 h (g/kg) 70 1500 990 2380

Cw (g/L) 4.96 503.7 1300 3300

transpiration needed (L/kg/d) 14.1 2.98 0.76 0.72


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Shoot Uptake versus Root Uptake:

 All the  values were <1 (even at steady state)

Shoot uptake was consistently lower than root uptake, in contrast to the measured lipid contents of plants

Possible causes: various dissipation processes, i.e.,

foliar volatilization

plant metabolism

formation of bound residues

plant-growth-induced dilution

variation in plant composition / transpiration with growth


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  • Concluding Remarks:

  • The model appears to give a satisfactory account of the contaminant transport into plants in relation to contaminant levels in water (and soil), the contaminant properties, the plant composition, and the uptake time.

  • Uptake limit can be predicted from equilibrium sorption, which can in turn be directly determined in laboratory or estimated from plant composition and contaminant Kow.

  • There is a need to develop a lipid extraction methodology suitable for plant uptake estimation and to verify the efficiency of Kow as a substitute for Klip.

  • In-plant dissipation processes increase contaminant chemical potential across the plant-water interface, thus maintaining the driving force for continued uptake. A thorough understanding of plant dissipation of contaminants is warranted for accurate implementation of phytoremediation technology and assessment of vegetable contamination.


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  • Concluding Remarks (cont.):

  • Based on our results, the plant uptake capacity may be categorized as:

Low uptake for highly water-soluble compounds, e.g., MTBE, much independent of plant species and not strongly time-dependent. Use of high-transpiration plants.

Moderate uptake for moderately lipophilic compounds, e.g., chlorinated solvents. Results should depend to a good extent on plant composition and uptake time.

High uptake for highly lipophilic compounds, e.g., PAHs and PCBs. Results should depend very sensitively on plant composition and uptake time. Use of high-lipids plants.


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