Why are you making the measurement? Methods for measuring plant uptake of chemicals: lab and field. General considerations. What are you measuring?

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1 Methods for measuring plant uptake of chemicals: lab and field Modeling plant uptake of chemicals and application in science and engineering Course no August 2015, DTU Why are you making the measurement? Risk assessment (ecological and human) Concentrations in specific plant compartments Biomonitoring Mechanism of uptake (root, foliar?) Relate plant to environmental concentrations Phytoremediation Removal Change in concentration/time, degradation Support model development What are you measuring? Plant concentrations Leaves, fruit, shoot, tree cores Exposure media concentration Groundwater, soil, air (gaseous/particulate) Transformation products Supporting information Transpiration, growth rate, light intensity, etc. ph, organic carbon content, dissolved vs. bound General considerations Chemical properties Volatile/non-volatile, neutral/ionizable, stability Chemical analysis GC, GC/MS, HPLC, LC/MS, LSC ( 14 C-labeled) Exposure type and duration Uptake/fate endpoint(s) being measured BCF, TSCF, distribution in plant Plant species Plant growth environment Field, greenhouse, growth chamber, bench top Controls Plant considerations Species Unique requirements (size, time to harvest, etc.) Exposure concentration-toxicity Growth/exposure media (not always same) Hydroponics, soil, sand, soil/sand etc. Light Photoperiod (often16hr light/8hr dark) Intensity (not often specified or measured) Humidity, temperature Nutrients Variants of Hoagland s solution Oxygen, CO 2 Chemical considerations Exposure Concentration Constant, varies with time Duration Properties of test chemical Hydrophobicity (K OW ) Volatility (vapor pressure, Henry s constant) Charge Chemical and biological stability 1

2 Experimental design Exposure media Hydroponics Water, sand-water, glass beads-water Soil Air Chemical properties Hydrophobicity (K OW )/aqueous solubility Volatility (Henry Law Constant) Biological or abiotic stability Distinguish between root and foliar uptake Goals of laboratory methods Avoid experimental artifacts Use appropriate controls Sufficient replication Consider chemical and biological variability Generate laboratory data that can be accurately extrapolated to field Trade-offs between collecting data in lab or field settings? Advantage: Better control of environmental and confounding variables Disadvantage: Lack of external validity (the extent to which study results can be generalized to other situations) Use Models Case studies Hydroponics Sulfolane & DIPA (high S, low H, low degradability) Benzene (mid S, high H, high degradability TCE (mid S, high H, low degradability) Nonylphenol (low S, low H, mid degradability) Soil Nonylphenol (low S, low H, mid degradability) Air Hydrocarbon and chlorinated solvents (low S, high H, mixed degradability) Sulfolane and Diisopropanolamine Sulfolane S= 1000 g/l, log K ow = H (dimensionless = 7E-8 Slow biodegradability DIPA pk a = 9.1 S= 870 g/l, log K ow = H (dimensionless) = 7E-6 Slow biodegradability Question 1)Are the high concentrations of sulfolane measured in field plant samples reasonable? (note: High uptake not predicted by Briggs model) Initial experimental set up Nutrient solution DO 2-5 ppm Temp. 22±3 C ph = 7 Duration = 50 days (20 mg/l) (40 mg/l) 2

3 Final plant concentrations (mg/kg dry weight) DIPA Sulfolane Roots 46 Exposure: (20 mg/l) /(40 mg/l) Benzene Question 1) Are the concentrations of sulfolane measured in field plant samples reasonable? Answer 1) High field uptake also observed in laboratory. (Suggests Briggs model not universally true) S = 1780 mg/l K OW = 2.13 H (dimensionless) = 0.23 Biodegradable (aerobically) Question What are the main removal mechanisms in a constructed wetlands located in Alberta, CA? Plant uptake? Degradation (DO < 1 mg/l)? Volatilization? (Phragmites (common reed) representative plant) Experimental System Plant uptake studies: DIPA & sulfolane N 2 Gas Root/Foliar Seal Flow = 10 ml/min Water Level [DO] = < 1 mg/l ph = 6 to 8 Flow-through hydroponic/gravel system Flow differential to minimize leaks Sealed above root zone Benzene added manually Dosing/Sampling Needle Flow = ml/min To Vacuum Pump 14 C Organic Traps (EGBE) 14 CO 2 Traps (1M KOH) 3

4 Transpiration Gas Sampling TOTAL RECOVERY Planted: 82% Unplanted: 78% Poisoned: 91% 14 C % Distribution Plants 0.05 leaves 0.6 stems 2.4 roots N 2 Gas Root Zone Solution Organic Traps CO 2 Traps Trichloroethylene Question What are the main removal mechanisms in constructed wetlands? Answer Volatilization and degradation S = 1280 mg/l Log K OW = 2.42 H (dimensionless) = 0.39 Low biodegradability Question Can we accurately measure a TSCF for TCE for predicting plant uptake during phytoremediation? Using TSCF to predict uptake Plant Uptake = (TSCF)(C C )(T) Burken and Schnoor appartus L/min TSCF = transpiration stream concentration factor C C = chemical concentration in GW T = Transpiration ( L/m 2 -yr) Root zone O 2 supplied by headspace Burken, J. G. and J. L. Schnoor (1998). "Predictive relationships for uptake of organic contaminants by hybrid poplar trees." Environmental Science & Technology 32(21):

5 10 ml/min 450 ml/min 45 ml/min Schroll, R. and I. Scheunert A laboratory system to determine separately the uptake of organic chemicals from soil by plant roots and by leaves after vaporization. Chemosphere 24(1): Hexachlorobenzene McCardy, McFarlane, Gander The transport of 2,3,7,8-TCDD in soybean and corn. Chemosphere 21(3): TCE uptake-growth chamber Orchard, B. J., W. J. Doucette, J. K. Chard and B. Bugbee (2000). "Uptake of trichloroethylene by hybrid poplar trees grown hydroponically in flow-through plant growth chambers." Environmental Toxicology and Chemistry 19(4): Photo-TCE Question Can we accurately measure a TSCF for TCE for predicting plant uptake during phytoremediation? Answer Maybe 5

6 TSCF Transpiration Stream Concentration Factor TSCF Variability of TSCF for TCE log K ow Davis et al Burken & Schnoor 1998 Dettenmaier et al., 2009 Chard, 1999 Davis et al No standard method, variation in exposure system, duration, analysis Orchard et al Variety of chemicals 25 Chemicals 14 Volatiles (headspace/gc/ms) 2 semi-volatiles (LLE/GC/MS) 9 14 C-labeled (LSC) (1 volatile, 8 semi-volatiles) Ranged in log K ow to 5 Used in previous plant uptake studies Question Can we reproduce the Briggs model using pressure chamber method? Results-pressure chamber Ave TSCF vs log K ow 25 chemicals TSCF vs log Kow predicted (Trapp 2006) log Kow model thick roots only with fine roots Briggs regression Dettenmaier, EM., Doucette, WJ., Bugbee, B Chemical Hydrophobicity and Uptake by Plant Roots. Environ. Sci. Technol. 43 (2): The model predicts that polar, non-volatile compounds will effectively be transported from soil to fruits, while lipophilic compounds will preferably accumulate from air into fruits. 6

7 Reported TSCF Values Method: Intact plants, hydroponics Plant: barley Plant age: 10 days Exposure duration: hrs Water transpired: Average 1 ml/day Root weight: 0.1 g/plant? Method: Pressure chamber Plants: Tomato and Soybean Plant age: days Exposure duration: 5-48 hrs, steady state Water transpired : ml Root weight: g Literature Pressure Chamber TSCF TSCF Pressure chamber vs. intact plants TSCF > Volatilization Metabolism Faster, less costly, more reproducible? Distribution Nonylphenol log K ow = 4.48 This study, log K ow = 3.28 S = 5.4 mg/l H (dimensionless) = 4x10-4 t 1/2 = 28 to 104 days (soil and surface water) Experimental System Design Question: Is there significant translocation of NP move from roots to shoot? Any mineralization? Ethylene glycol monoethyl ether 1 M KOH 7

8 -Foliar tissue -Roots -Nutrient solution Plant Tissue Analysis Parent Compound Foliar tissue- Roots- [NP] = 0.07 mg/l [NPE 4 ] = 0.3 mg/l [NPE 9 ] = 0.4 mg/l A B C D -Organic traps -CO 2 traps 14 C Nonylphenol Steam distillation/hplc SFE/HPLC-fluorescence NPE 4, NPE 9, phenol SFE/HPLC-fluorescence 14 C-labeled NP, NPE 4, NPE 9, phenol Combustion/LSC Distribution of 14 C Foliar region: NP 1.3% NPE 4 4.0% NPE 9 7.8% Phenol 8.6% Trapping solution: VOC CO 2 NP 0.2% 1.2% NPE 4 0.0% 0.9% NPE 9 0.1% 1.1% Phenol 0.1% 18.2% Distribution of 14 C & NP in plant tissue after 99 days. 14 C NP Foliar tissue 2% None detected Roots: NP 73.5% NPE % NPE % Phenol 51.9% Hydroponic solution: NP 17.0% NPE % NPE % Phenol 3.4% 14 C NP Root tissue 98% 4-40 µg/kg NP (dry wt.) Question: Is there significant translocation of NP move from roots to shoot? Any mineralization? Answer: Little translocation of 14 C into foliar tissue and ittle or no mineralization was observed. Nonylphenol log K ow = 4.48 This study, log K ow = 3.28 S = 5.4 mg/l H (dimensionless) = 4x10-4 t 1/2 = 28 to 104 days (soil and surface water) Question: Does NP associated with land applied biosolids persist in the soil environment and contaminate plants? 8

9 NP experimental design 9

10 [ Trichloroethylene Question: Does NP associated with land applied biosolids persist in the soil environment and contaminate plants? Answer 10 % mineralization, minimal plant uptake S = 1280 mg/l Log K OW = 2.42 H (dimensionless) = 0.39 Low biodegradability Question Will fruit from trees growing over TCE contaminated groundwater contain TCE? Risk Assessment Sampling and analysis Leaves, Branches, Fruit Combustion/LSC- 14 C Headspace GC/MS-TCE Trunk Irrigation Water Soil Roots [ 14 C]TCE/H 2O Reservoir Elevated Stand D1 Greenhouse fruit uptake photo C3 A3 D3 B2 F1 C1 A1 Apple & peach photo B3 C2 E1 D2 A2 B2 A: 5 mg/l apple B: 500 mg/l apple C: 5 mg/l peach D: 500 mg/l peach E: Control apple F: Control peach G: Control apple (2) H: Control peach (2) 10

11 Comparing Peaches to Peaches Average [ 14 C] data 2 nd yr high/low (µg/kg fresh wt) Fruit flesh 44 / 0.6 Leaves 260 / 3.2 Branches 560 / 8.4 Elevated Stand Irrigation water (µg/l) 690/ 5.3 Comparing Apples to Peaches average [ 14 C] 2 nd yr (µg/kg fresh wt) 171 days 14 C [TCE] exposure Elevated Stand 67 Fruit peel Fruit flesh TCE <0.1 TCE <0.1 Branches TCE < Leaves* 259 TCE <0.1 Irrigation water TCE 690 *No statistical difference Elevated Stand 220 days 14 C [TCE] exposure Sulfolane in apple trees Apple: 16 mg/kg Treatment apple trees (100 ppm sulfolane added) Control apple trees (no sulfolane added) Leaves: 3700 mg/kg 30-day exposure: 55 mg/l Tentative Hypothesis TCE (glycoside metabolite, Volatilization trichloroethanol) Phloem (TCE) sulfolane Xylem (TCE, sulfolane) Volatile organic compounds (VOC) Aromatic hydrocarbons Benzene, toluene, xylene Chlorinated solvents Trichloroethylene, tetrachloroethylene Static Headspace Study Question: Could house plants be used to monitor indoor air concentrations of VOCs? 11

12 Concentration Ratio Concentration Ratio Air Sampling Plant Sampling Flow Through Chamber Diagram Constant flow Sampling Pumps Tenax Sorbent tubes Thermal desorption GC/MS Leaves collected by gloved hand Headspace GC/MS Flow Through Chamber (Ficus) 1.2 PCE Time (min) m-xylene Time (min) Blank Chamber Soil and Pot Ficus Blank Chamber Soil and Pot Ficus Question: Could house plants be used to monitor indoor air concentrations of VOCs? Answer: Probably for initial screening and monitoring trends over time. OCSPP : Plant Uptake and Translocation Test US EPA Office of Chemical Safety and Pollution Prevention Primary endpoints: Concentrations of free parent compound, metabolites, soluble residues, and bound residues in pooled plant organs and whole plants Laboratory Hydroponic, soil Field Table 2. Summary of Test Conditions for Plant Uptake and Translocation Test Test duration To provide sufficient biomass (or to allow gas exchange measurements), or until fruit or seeds are mature. Substrate Quartz sand or glass beads. Hydroponic system may also be used. (For pesticides, natural or synthetic soil may also be used.) Nutrients Temperature Relative humidity Carbon dioxide Light quality Light intensity Photoperiod Watering Watered with nutrient solution (half-strength modified Hoagland s medium) 25/20 C (daytime/nighttime) ± 3 C (applicable to growth chambers) 70/90% (daytime/nighttime) ± 5% (applicable to growth chambers) 350 ± 50 μmol/m2/sec (applicable to growth chambers) Fluorescent or representative of natural sunlight 350 ± 50 μmol/m2/sec 16 hours light: 8 hours dark for all species except soybean with 11 hours light: 13 hours dark prior to flowering Bottom watering as needed, using nutrient solution Test chamber (pot) size Varies with plant species selected. Number of organisms per test chamber Number of replicate chambers per test treatment Number of organisms per test treatment Test treatment levels Typically, 1-4 seedlings of one species per pot 6 (minimum) 6-24 (minimum) Minimum of 3 treatment levels plus appropriate controls 12

13 Minimum acceptable criteria? Chemical (name, CAS #); plant species identified; Units explicitly defined; Appropriate chemical analysis: exposure medium & plant; Chemical conc. in exposure media (beginning, during, end); No apparent toxicity to the plant; Amount of water transpired; plant mass, growth rate; Reasonable growth conditions (i.e. light and nutrients); Exposure medium properties (e.g. organic carbon content in the soil, ph for ionogenic organics); Composition of plant compartments (i.e. lipid & water %); Appropriate controls; USE PROBE OR STANDARD COMPOUNDS? Summary Easier to control exposure and other variables in laboratory Difficult to simulate field conditions in lab Light, humidity, duration of experiment, changes over time Anticipate impact of key variables Maximize information collected Information not considered study focus may be critical in modeling/understanding mechanism 13