Final Report: Modeling Dissolved Oxygen, Nitrate and Pesticide Contamination in the Subsurface Environment

EPA Grant Number: R825549C008
Subproject: this is subproject number 008 , 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: Modeling Dissolved Oxygen, Nitrate and Pesticide Contamination in the Subsurface Environment
Investigators: Schnoor, J. L.
Institution: University of Iowa
EPA Project Officer: Hahn, Intaek
Project Period: February 1, 1989 through February 1, 1992
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


  • To develop better mathematical model formulations for the fate and transport of pesticides in the unsaturated zone and saturated groundwater
  • To perform field and laboratory experiments on the fate and transport of alachlor and atrazine to test the model formulations
  • To assess the effects of best management practices and reduced pesticide application rates on groundwater contamination and agricultural runoff of pesticides

A purpose of this project was not necessarily to develop a new model but to improve kinetic formulations that can be used in many models. The first objective was necessary because of inherent limitations in state-of-the-art pesticide models. EPA's Pesticide Root Zone Model (PRZM) does not consider the effect of electron acceptor (dissolved oxygen limitation or nitrate respiration) on pesticide transformation rates; it does not include a saturated groundwater compartment; and it has very simple kinetic formulations for pesticide transformation rates (lumped, first order rate constant) and plant uptake rates. Another important purpose of this project was to develop new formulations with results from controlled field studies and laboratory experiments with radio-labeled C-14 pesticides and to test these in existing pesticide fate and transport models. There is a paucity of field and laboratory studies which provide the required measurements for a valid test of models. The model can then be used to evaluate the efficacy of selected BMPs on water quality improvements.

Summary/Accomplishments (Outputs/Outcomes):

A small plot study was initiated near Lily Lake at Main Arnana, Iowa, and planted with corn, poplar trees, and with barren ground. Alachlor and atrazine were applied, singly and in combination in the 1989 field season, and the fate and transport of these pesticides were monitored through the field season of 1989.
Laboratory studies were initiated in spring 1990 to study mineralization and degradation kinetics of the triazine herbicide, atrazine, under different soil environmental conditions, which could be used in the model formulation. Laboratory experiments were performed using 14C ring and isopropyl side chain labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) applied to three Iowa soils incubated in batch reactors under different environmental conditions.

The different soil environmental conditions simulated included two electron acceptor conditions (aerobic and anoxic with nitrate as the electron acceptor), different soil type/organic carbon content, moisture content, addition of surrogate plant exudates in the form of organic acids, and the influence of plant rooting. In addition, the effect of varying soil oxygen content was also studied. Degradation and mineralization kinetics under different temperatures were not performed as there is sufficient information on these in the research literature. The experiments were set-up to simulate conditions in deeper unsaturated soils where air diffusion from the surface will be limited. Comparison of mineralization and primary degradation kinetics under different environmental conditions allowed computations to be made on relative persistence of the primary compound and some of its primary and secondary metabolites which may be toxic too.

EPA's PRZM (Pesticide Root Zone Model, Carsel et al, 1984) model was installed on the ICAEN (Iowa Computer Aided Engineering Network) Hewlett Packard workstations. The model was calibrated with 1989 data from our field site at Lily Lake, Amana, Iowa, and with data from Smith et al. (1988) at Tipton, Georgia. Formulations from the laboratory results were used to predict fate of atrazine at the Amana site with and without BMPs (Nair, 1991).

The field study showed that alachlor was more mobile than atrazine. It showed greater runoff rates and percolation to the groundwater, but it also disappeared at a more rapid rate than atrazine. Atrazine was tightly bound to the soil, especially the small plot planted in poplar trees. Disappearance of atrazine was relatively rapid compared to literature reports. The half-life in the vadose zone moisture (collected by suction lysimeters) was only _ 15 days.

Plant uptake proved to be an important fate process for atrazine applied in a riparian zone buffer strip, densely planted with hybrid poplar trees. It was of equal magnitude to other transformation reactions in the aqueous phase. In addition, we are presently investigating the role of soluble root exudates from densely planted trees. Root exudates may serve as a primary substrate for enhanced biological transformations in the unsaturated zone. To our knowledge, these are totally new research questions that we are addressing with the engineering of riparian zones for nitrate and pesticide removal. We are continuing this research with funding from EPA HSRC at KSU (Project 89-10).

The laboratory experiments for this research (Project 10) showed that mineralization of both the ring and isopropyl side chain carbons were much faster with oxygen as the electron acceptor compared to nitrate as the electron acceptor. Under denitrifying conditions, ring and isopropyl side chain carbon mineralization was 142 times and 35 times lower than under oxygenated conditions, respectively. Oxygen limitation in soils reduced the biotransformation rate of atrazine. This was the most significant finding of this study, and may account for the persistence of atrazine and its metabolites in groundwater.
Under aerobic conditions, atrazine mineralization rates increased with increasing moisture content (provided oxygen was not limiting) and with increasing soil organic carbon content. There were some indications of atrazine or its metabolites inhibiting its own transformation rate at high concentrations (> 4 lbs/acre).
Empirical models were developed to represent the mineralization rate of atrazine ring carbon and isopropyl side chain carbon for different soil organic carbon content, soil water content. temperature and oxygen content.

A modified version of the Pesticide Root Zone Model (Carsel et al, 1984) was calibrated for the pesticides atrazine and alachlor using field data from our small plot at Amana, Iowa. The PRZM (Pesticide Root Zone Model) performed satisfactorily in predicting atrazine concentrations in soil for the two field studies. The existing PRZM model can be used with the kinetic formulations developed in this project for atrazine fate simulations in the unsaturated zone. A new version of the PRZM model called PRZM-2 is now being released by the Center for Exposure Assessment Modeling (CEAM), USEPA, Athens, GA and includes an improved soil moisture movement subroutine, volatization from soil surface, temperature computations, metabolite fate and transport, and the gas phase partition in the soil compartment. This model is similar to the RUSTIC model, first released in 1990, but has now been withdrawn by CEAM due to problems with the groundwater subroutine.

Inclusion of environment dependent atrazine mineralization rates showed that atrazine and its metabolites persist much longer than the parent compound. A hypothetical simulation with deep-planted poplar trees in riparian zone buffer strips showed that significant decrease in pesticide transport to streams and groundwater was possible with this BMP.

The results have been presented at professional meetings and to other interested professionals.

Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other subproject views: All 15 publications 5 publications in selected types All 5 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 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
  • Journal Article Paterson KG, Schnoor JL. Fate of alachlor and atrazine in a riparian zone field site. Water Environment Research 1992;64(3):274-283. R825549C008 (Final)
  • Abstract: JSTOR-Preview
  • Journal Article Paterson KG, Schnoor JL. Vegetative alteration of nitrate fate in unsaturated zone. Journal of Environmental Engineering-ASCE 1993;119(5):986-993. R825549C008 (Final)
  • Abstract: ASCE-Abstract
  • Supplemental Keywords:

    modeling, pesticides, transport, fate, plant uptake, RFA, Scientific Discipline, Waste, Water, 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, pesticides, contaminated soil, bioremediation of soils, groundwater remediation, chemical kinetics, Region 7, Region 8, contaminated groundwater, pesticide runoff, hazardous wate, pesticide residue, nitrate, heavy metal contamination, phytoremediation, dissoloved oxygen, bioremediation, groundwater

    Relevant Websites:

    Center for Hazardous Substance Research at Kansas State University Exit

    Progress and Final Reports:

    Original Abstract
  • 1989
  • 1990

  • 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