Final Report: Deep-Rooted Poplar Trees as an Innovative Treatment Technology for Pesticide and Toxic Organics Removal from Soil and Groundwater

EPA Grant Number: R825549C021
Subproject: this is subproject number 021 , established and managed by the Center Director under grant R825549
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (1989) - Great Plains/Rocky Mountain HSRC
Center Director: Erickson, Larry E.
Title: Deep-Rooted Poplar Trees as an Innovative Treatment Technology for Pesticide and Toxic Organics Removal from Soil and Groundwater
Investigators: Schnoor, J. L. , Licht, Louis A.
Institution: University of Iowa
EPA Project Officer: Hahn, Intaek
Project Period: February 22, 1990 through February 1, 1993
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text |  Recipients Lists
Research Category: Organic Chemical Contamination of Soil/Water , Land and Waste Management


The objectives of the research are three-fold:

* To determine if deep-planted poplar trees can be grown in a riparian zone buffer strip to remove pesticides and other toxic organic chemicals (e.g. dioxin, trichloroethylene, tetrachloroethylene, and xylene isomers) as an innovative technology for treatment of groundwaters and contaminated soils

* To construct a mass balance on pesticides (atrazine and alachlor) for a small agricultural plot in the field and on pesticides and toxic organic chemicals in the laboratory greenhouse

* To provide further field data for a mathematical model (Project No. 10 of EPA/KSU HSRC) of pesticide dynamics in the field.

The first objective includes a field demonstration and experiment on the removal of pesticides from groundwater. Treatment of contaminated groundwater will be demonstrated for the pesticides atrazine and alachlor. The second part of the first objective refers to treatment of toxic organic chemicals. This will be performed in the laboratory (greenhouse) in the second and third year of the research. If removal of other toxic organics appears promising, separate funding sources will be sought to demonstrate this technology for toxic organics. The toxic organics will be chosen in consultation with EPA and the KSU Hazardous Substances Research Center, but possibilities include dioxin (because of serious problems remaining in Missouri and other locations), the chlorinated solvents trichloroethylene and tetrachloroethylene (because of their longevity and occurrence at many contaminated sites), and xylene isomers (because they are widely used components of gasoline and jet fuel spills).

Summary/Accomplishments (Outputs/Outcomes):

Research performed by the U.S. Department of Agriculture Forestry Research Stations has demonstrated Populus spp. stem and branch growth of 2 to 10 metric tons per hectare per year and root/stem ratios of 0.3 to 0.9 kg of root mass per kg of branch and stem mass. The genetic potential exists for 0.5 to 9.0 metric tons of root mass to annually be distributed into the soil profile. Root matter contains organic carbon. When placed deeper in the soil profile, the organic carbon serves two purposes: 1) It provides increased organic substrate which stimulates microbial pesticide degradation activity, and 2) It provides a larger quantity of organic material in the surficial aquifer which increases the sorption of hydrophobic chemicals.

Our previous research at the University of Iowa has demonstrated that poplar trees are a fast-growing efficient way of removing nitrate from soil waters, and they can be deep-rooted to intercept groundwater and remove nitrate as a riparian zone buffer strip before stream recharge occurs. Preliminary experiments in the greenhouse indicate that they can also remove pesticides from water, but the mechanism (whether it is metabolism, incorporation, or volatilization) and the rate have not been quantified. It is the purpose of this proposed research to identify and quantify these processes and to demonstrate the technology in a small plot. To summarize, the advantages of poplar trees planted as a buffer strip for toxic chemical removal are the following:

1. Removes nitrate, pesticides, and other volatile compounds
2. Serves as wildlife habitat and cover
3. Provides a biomass energy crop if desired
4. Serves as a wind-break and soil erosion control
5. Helps global CO2 balance by reforestation.

Questions remain as to the efficacy tree strip plantations for removal of pesticides and other toxics. Because the trees are phreatophytes, they will perform well in moist locations such as riparian zones, in the vicinity of agricultural drainage wells, and at the base of slopes from landfill sites which is often where leachate occurs. The only disadvantage of the technology is the extremely large volume of water "pumped" by these trees which will draw down the water table in time of drought, but at contaminated sites, this could be an advantage.

Pesticides alachlor and atrazine and nitrogen fertilizer will be applied at two application rates on three small plots: one grown with corn, one with poplar trees, and one barren plot. Pesticides and nitrates will be sampled at different depths in the vadose zone and groundwater at bi-weekly to monthly intervals after application. Meteorological conditions, soil moisture, temperature, vapor pressure, soil tension, and chemistry will be monitored in the 1990 and 1991 growing seasons. Mass balances on water, nitrogen species, and pesticides will be estimated to determine the efficiency of the treatment technology and for comparison to parallel laboratory studies conducted in a greenhouse. Greenhouse studies will allow better quantification of pesticide and nutrient uptake rates and their stoichiometric ratios. In addition to pesticide uptake studies in the field and greenhouse, toxic organic chemicals (e.g., dioxin, trichloroethylene, tetrachloroethylene, and xylene isomers) will be investigated in an initial feasibility study for poplar tree buffer strip applications at hazardous waste and municipal landfills.

All three of the sub-plots in Figure 2 have been instrumented. The plots will be referred to as poplar, corn, and barren plots. The poplar plot is the main subject of the research; the corn plot was chosen as a reference to compare uptake by corn to the fast-growing poplar trees; the barren plot gives a control for the importance of vegetative uptake. A nested set of suction lysimeters, tensiometers, and thermistors were installed at three depths. All three plots will have pesticides, fertilizer, and a tracer (KBr) applied at the beginning of June, using a backpack sprayer. The exact day and time of application will be chosen to minimize volatilization by heat and dispersion by wind. The pesticides atrazine and alachlor will be applied at 6 lb/acre on the corn and barren plots and 2 lb/acre on the trees. Only atrazine will be applied to the stand of poplar trees because they are sensitive to alachlor. Concurrently, an ammonia fertilizer will be applied at 200 lb/acre to fertilize the crop and to study nitrification and uptake. KBr will be applied as a conservative tracer to check our hydrologic budget. The actual rate delivered to each sub-plot will be determined by analysis of grid-spaced petri dishes throughout the plots during chemical application.

Soil waters will be sampled with vacuum lysimeters and measured for pH, bromide, pesticide concentrations, dissolved oxygen, and nitrate. Frequent sampling will take place following application, and bi-weekly to monthly samples will be collected thereafter. Atrazine is rather slow to biodegrade and sorbs strongly. It is expected to carry-over to the next field season. Alachlor is less sorptive and undergoes biotransformations (hydroloysis and dealkylation) more rapidly. It should disappear within a few months. Precipitation, runoff, and groundwater exchange with the lake will be monitored continuously at the site. Soil samples for sorbed and bound pesticide analyses will be taken at three depths during each sampling period at each depth. They will be measured in the laboratory for atrazine and alachlor and moisture content (a check on the tensiometer measurements and to develop a characteristic curve for moisture content as a function of suction head). Aqueous pesticide concentrations will be measured using a methylene chloride extraction followed by electron capture gas chromatography. Soils will be extracted using a Soxhlet extraction technique. Methods of analyses are documented in references 4-15.

Greenhouse studies will consist of trees grown in Plexiglas containers containing clean vermiculite, approximately 2 m deep x 15 cm thick x 1 m wide. Each container holds three trees, planted from 6 foot cuttings. Tree cuttings will be obtained from Mike Brandrup, Energy Division, Iowa Department of Natural Resources. A total of 24 trees will be planted in the greenhouse for various treatments. They will be cut off at the soil level at the end of the first year to allow regrowth of these coppicing trees. Input solutions of nutrients, pesticides and organics will be fed to the trees on a flow-through system. Concentrations of organic chemicals and volume of water lost due to evap-concentration will be monitored on a weekly basis. Chemical analyses will be the same except C-14 labeled organics will be used for ease of chemical determinations by scintillation counting. Use of C-14 labeled pesticides and organics allows some knowledge of fate processes occurring and metabolites formed, depending on whether the ring or the side-chain is labeled.

Concentrated landfill leachate samples taken directly from the Iowa City landfill leachate collection system were acutely toxic to hybrid poplar trees. However. when diluted by fifty percent, no toxic effects were apparent.

Application of benzene, carbon tetrachloride, m-dichlorobenzene, m-xylene, toluene and trichloethylene were not lethal to hybrid poplar trees at individual concentrations of up to 120 mg/L each, nor in a combination of 120 mg/L of each chemical for a total volatile organic concentration of 720 mg/L. These doses of volatile organics appeared to weaken the trees in making them more sensitive to low moisture conditions

The deep rooted poplar trees decreased the migration of volatile organic chemicals through the unsaturated zone. It took the chemicals somewhat longer to move through the poplar's root zone and the concentration of chemicals found at depth was less than that found in the fallow ground. Laboratory experiments with the same soil showed that over 20% of the applied atrazine was accumulated in the poplar trees over 22 days and over 90 % from silica sand over 22 days.
Addition of surrogate organics (oxalate, acetate, and formate) as model compounds for plant-root exudates failed to stimulate the microbial transformation of uniformly ring-labeled 14C atrazine in Iowa Nodaway-Ely soil. Only high concentrations of oxalate showed mild stimulation in related experiments.

Results from plant chamber experiments indicate mineralization of ring-labeled 14C atrazine to carbon dioxide occurs in the soil as does plant uptake and metabolism. However, the dominant mechanism seems to be the direct uptake of atrazine by the plant in growth chamber experiments and bioflasks. Uptake correlated to plant transpiration and can be explained with a simple uptake model. Evolution of 14CO2 from the plant to the atmosphere was negligible. Stimulation of atrazine mineralization was not fully quantified in the plant bioreactors. This was attributed to poplar uptake of the big-available organic and enhanced reducing conditions in the plant big-reactors.

Exudation of organics was observed in a new set of experiments still being conducted. TOC concentrations up to 200 mg/l were observed for some of the plant reactors. Work was done to relate TOC exudates to plant leaf area, transpiration and growth, but this was inconclusive. Studies are being continued on the relation of exuded organics to atrazine mineralization.

The results have been communicated at professional meetings workshops, and through tours at field sites.

Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other subproject views: All 15 publications 5 publications in selected types All 4 journal articles
Other center views: All 904 publications 230 publications in selected types All 182 journal articles
Type Citation Sub Project Document Sources
Journal Article Madison MF, Licht LA. Agricultural ecosystems-the world is watching. Agricultural Engineering 1990;71(1):12-15. R825549C021 (Final)
  • Other: Kansas State University (verified citation)
  • Journal Article Nair DR, Schnoor JL. Effect of two electron acceptors on atrazine mineralization rates in soil. Environmental Science & Technology 1992;26(11):2298-2300. R825549C008 (Final)
    R825549C021 (Final)
  • Abstract: ACS-Abstract
  • Journal Article Nair DR, Burken JG, Licht LA, Schnoor JL. Mineralization and uptake of triazine pesticide in soil-plant systems. Journal of Environmental Engineering-ASCE 1993;119(5):842-854. R825549C008 (Final)
    R825549C021 (Final)
  • Abstract: ASCE-Abstract
  • Journal Article Nair DR, Schnoor JL. Effect of soil conditions on model parameters and atrazine mineralization rates. Water Research 1994;28(5):1199-1205. R825549C008 (Final)
    R825549C021 (Final)
  • Full-text: ScienceDirect-Full Text PDF
  • Abstract: ScienceDirect-Abstract
  • Supplemental Keywords:

    vegetation, poplar trees, pesticides, organics, RFA, Scientific Discipline, Water, Waste, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Contaminated Sediments, Remediation, Environmental Chemistry, Geochemistry, Chemistry, Fate & Transport, Analytical Chemistry, Hazardous Waste, Ecology and Ecosystems, Hazardous, EPA Region, sediment treatment, fate and transport, contaminant transport, soil and groundwater remediation, fate and transport , mathmatical modeling, contaminated sediment, Poplar trees, pesticides, contaminated soil, bioremediation of soils, groundwater remediation, chemical kinetics, Region 7, Region 8, contaminated groundwater, pesticide runoff, hazardous wate, pesticide residue, phytoremediation, bioremediation

    Relevant Websites: Exit

    Progress and Final Reports:

    Original Abstract
  • 1990
  • 1991

  • Main Center Abstract and Reports:

    R825549    HSRC (1989) - Great Plains/Rocky Mountain HSRC

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825549C006 Fate of Trichloroethylene (TCE) in Plant/Soil Systems
    R825549C007 Experimental Study of Stabilization/Solidification of Hazardous Wastes
    R825549C008 Modeling Dissolved Oxygen, Nitrate and Pesticide Contamination in the Subsurface Environment
    R825549C009 Vadose Zone Decontamination by Air Venting
    R825549C010 Thermochemical Treatment of Hazardous Wastes
    R825549C011 Development, Characterization and Evaluation of Adsorbent Regeneration Processes for Treament of Hazardous Waste
    R825549C012 Computer Method to Estimate Safe Level Water Quality Concentrations for Organic Chemicals
    R825549C013 Removal of Nitrogenous Pesticides from Rural Well-Water Supplies by Enzymatic Ozonation Process
    R825549C014 The Characterization and Treatment of Hazardous Materials from Metal/Mineral Processing Wastes
    R825549C015 Adsorption of Hazardous Substances onto Soil Constituents
    R825549C016 Reclamation of Metal and Mining Contaminated Superfund Sites using Sewage Sludge/Fly Ash Amendment
    R825549C017 Metal Recovery and Reuse Using an Integrated Vermiculite Ion Exchange - Acid Recovery System
    R825549C018 Removal of Heavy Metals from Hazardous Wastes by Protein Complexation for their Ultimate Recovery and Reuse
    R825549C019 Development of In-situ Biodegradation Technology
    R825549C020 Migration and Biodegradation of Pentachlorophenol in Soil Environment
    R825549C021 Deep-Rooted Poplar Trees as an Innovative Treatment Technology for Pesticide and Toxic Organics Removal from Soil and Groundwater
    R825549C022 In-situ Soil and Aquifer Decontaminaiton using Hydrogen Peroxide and Fenton's Reagent
    R825549C023 Simulation of Three-Dimensional Transport of Hazardous Chemicals in Heterogeneous Soil Cores Using X-ray Computed Tomography
    R825549C024 The Response of Natural Groundwater Bacteria to Groundwater Contamination by Gasoline in a Karst Region
    R825549C025 An Electrochemical Method for Acid Mine Drainage Remediation and Metals Recovery
    R825549C026 Sulfide Size and Morphology Identificaiton for Remediation of Acid Producing Mine Wastes
    R825549C027 Heavy Metals Removal from Dilute Aqueous Solutions using Biopolymers
    R825549C028 Neutron Activation Analysis for Heavy Metal Contaminants in the Environment
    R825549C029 Reducing Heavy Metal Availability to Perennial Grasses and Row-Crops Grown on Contaminated Soils and Mine Spoils
    R825549C030 Alachlor and Atrazine Losses from Runoff and Erosion in the Blue River Basin
    R825549C031 Biodetoxification of Mixed Solid and Hazardous Wastes by Staged Anaerobic Fermentation Conducted at Separate Redox and pH Environments
    R825549C032 Time Dependent Movement of Dioxin and Related Compounds in Soil
    R825549C033 Impact of Soil Microflora on Revegetation Efforts in Southeast Kansas
    R825549C034 Modeling the use of Plants in Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances
    R825549C035 Development of Electrochemical Processes for Improved Treatment of Lead Wastes
    R825549C036 Innovative Treatment and Bank Stabilization of Metals-Contaminated Soils and Tailings along Whitewood Creek, South Dakota
    R825549C037 Formation and Transformation of Pesticide Degradation Products Under Various Electron Acceptor Conditions
    R825549C038 The Effect of Redox Conditions on Transformations of Carbon Tetrachloride
    R825549C039 Remediation of Soil Contaminated with an Organic Phase
    R825549C040 Intelligent Process Design and Control for the Minimization of Waste Production and Treatment of Hazardous Waste
    R825549C041 Heavy Metals Removal from Contaminated Water Solutions
    R825549C042 Metals Soil Pollution and Vegetative Remediation
    R825549C043 Fate and Transport of Munitions Residues in Contaminated Soil
    R825549C044 The Role of Metallic Iron in the Biotransformation of Chlorinated Xenobiotics
    R825549C045 Use of Vegetation to Enhance Bioremediation of Surface Soils Contaminated with Pesticide Wastes
    R825549C046 Fate and Transport of Heavy Metals and Radionuclides in Soil: The Impacts of Vegetation
    R825549C047 Vegetative Interceptor Zones for Containment of Heavy Metal Pollutants
    R825549C048 Acid-Producing Metalliferous Waste Reclamation by Material Reprocessing and Vegetative Stabilization
    R825549C049 Laboratory and Field Evaluation of Upward Mobilization and Photodegradation of Polychlorinated Dibenzo-P-Dioxins and Furans in Soil
    R825549C050 Evaluation of Biosparging Performance and Process Fundamentals for Site Remediation
    R825549C051 Field Scale Bioremediation: Relationship of Parent Compound Disappearance to Humification, Mineralization, Leaching, Volatilization of Transformaiton Intermediates
    R825549C052 Chelating Extraction of Heavy Metals from Contaminated Soils
    R825549C053 Application of Anaerobic and Multiple-Electron-Acceptor Bioremediation to Chlorinated Aliphatic Subsurface Contamination
    R825549C054 Application of PGNAA Remote Sensing Methods to Real-Time, Non-Intrusive Determination of Contaminant Profiles in Soils
    R825549C055 Design and Development of an Innovative Industrial Scale Process to Economically Treat Waste Zinc Residues
    R825549C056 Remediation of Soils Contaminated with Wood-Treatment Chemicals (PCP and Creosote)
    R825549C057 Effects of Surfactants on the Bioavailability and Biodegradation of Contaminants in Soils
    R825549C058 Contaminant Binding to the Humin Fraction of Soil Organic Matter
    R825549C059 Identifying Ground-Water Threats from Improperly Abandoned Boreholes
    R825549C060 Uptake of BTEX Compounds by Hybrid Poplar Trees in Hazardous Waste Remediation
    R825549C061 Biofilm Barriers for Waste Containment
    R825549C062 Plant Assisted Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances: Experimental and Modeling Studies
    R825549C063 Extension of Laboratory Validated Treatment and Remediation Technologies to Field Problems in Aquifer Soil and Water Contamination by Organic Waste Chemicals