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

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.

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  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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 + ……

  6. 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

  7. 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)

  8. Kinetic Uptake from Contaminated Soils: Qpt =  (Cs / fsomKsom)( fpw +  fpomiKpomi ) with Cw = 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.

  9. 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

  10. Simplification of the Uptake Model: Qpt =  CwKpl =  Cw ( fpw + fpomiKpomi ) =  Cw ( fpw + flipKlip + fchKch )

  11. Approximate Kch values for contaminants log KOWKOWKch  0  1 0.1 0.1-0.9 1-10 0.2 1.0-1.9 10-100 0.5 2.0-2.9 100-1000 1.0 3.0-3.9 1000-10000 2.0  4.0  10000 3.0

  12. 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

  13. log KOW and Initial Concentrations of Chemicals Chemical HCB LDN PCE TCE log Kow 5.50 3.72 3.38 2.53 Concentration 4.96 503.7 1300 3300 (g/L)

  14. Plant % water % lipids % carbohydrates Ryegrass roots 87.7 0.30 12.0 shoots 88.8 0.97 10.2 Wheat roots 84.4 0.51 15.3 shoots 85.2 1.10 13.7 Weight Compositions of Wheat and Ryegrass Parts

  15. 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)

  16. 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

  17. Plant Uptake Model: Sorption ModelQeq = CwKpl Composition Model Qeq = Cw ( fpw + fchKch + flipKlip ) (low log Kow) Lipid Model Qeq  CwflipKlip (high log Kow)  CwflipKow

  18. 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

  19. 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

  20. shoots roots log Kow Hexachlorobenzene 5.50 Kpl (L/kg) 37918 16900 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

  21. 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.

  22. 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):

  23. 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)

  24. 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)

  25. 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)

  26. 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)

  27. 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)

  28. 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)

  29. 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)

  30. 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)

  31. 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

  32. 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

  33. 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.

  34. 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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