1999 Progress Report: Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment

EPA Grant Number: R825433C051
Subproject: this is subproject number 051 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
Investigators: Rolston, Dennis E.
Institution: University of California - Davis
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


To develop pollutant fate and transport models to be used as tools for assessing exposure in terrestrial ecosystems, investigate the fate of soil-applied chemicals, and estimate potential exposure levels in the atmosphere, soil, and aqueous phases in the shallow vadose zone.

Progress Summary:

We are working on models that will provide investigators in the Sacramento River Watershed project with scenarios of the most significant exposure routes of chemicals in agroecosystems to the birds, small mammals, and aquatic species being studied. We are building upon existing fate and transport models of chemical movement in soil. The modeling will also allow us to evaluate the most important processes requiring further experimental investigation. This includes research in the area of chemical adsorption kinetics, chemical volatilization processes from soil to the atmosphere, and routes of transport to surface water and ground water.

To estimate exposure levels, it is useful to have a conceptual model of the physical system of concern. We are interested in terrestrial ecosystems and the soil processes that govern the movement of chemicals to locations where receptor populations are found. Aboveground terrestrial organisms can be exposed to soil borne chemicals that volatilize from the soil to the adjacent atmosphere or through direct contact with the surface soil. Below ground organisms (e.g., microorganisms, earthworms, plant roots) are exposed directly at all locations in the soil. Aquatic organisms can be exposed to soil borne chemicals that are transferred to waterways through runoff water or on soil particles. Combined with information about the receptor populations related to uptake or ingestion rates, residence time in a particular area, etc., model predictions of chemical concentration profiles can be used to estimate levels to which the organisms are exposed.

Volatilization of pesticides from soil is one of the key processes for transporting chemicals to non-target areas. Our research focused on how water status and water transport in the soil affect volatilization of pesticides. Volatilization of soil-incorporated diazinon [O, O diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate] was measured under various water status and water transport conditions. These conditions were varied by using soil of different initial water content and by passing wet air and dry N2 alternately across the soil surface. When dry sweep N2 was used, diazinon volatilization was accelerated due to the appreciable upward water flow. When upward water flow was insufficient, soil-water content at the soil surface was quickly reduced below a threshold, and diazinon volatilization started to decrease exponentially due to diazinon adsorption on dry soil surfaces. When the sweep gas was switched to humidified air, the soil surface adsorbed water, and diazinon volatilization increased dramatically. Depending on flux of the upward water flow, water content at the soil surface may or may not be increased above the threshold water content. Therefore, diazinon volatilization may or may not be increased as high as the volatilization rate before the soil was dried. Water vapor adsorption alone may be insufficient to raise the soil-water content above the threshold water content. A numerical model was developed to simulate pesticide transport in both wet and dry soils. The calculated and measured results agree well. We have completed this stage of the research and have submitted three manuscripts for publication.

Agricultural soils have been recognized as a significant source of nitric oxide (NO) and nitrous oxide (N2O), which are important trace gases involved in several critical processes in the atmosphere. Nitric oxide is a precursor to nitric acid, and plays a central role in photochemical reactions, which regulate levels of tropospheric ozone. Ozone can have detrimental effects on plants upon extended exposure at fairly low levels. Ozone damage to forests in the Sierra Nevada mountains are considered to be one of the stressors potentially causing premature tree death. Laboratory experiments were conducted with three agricultural soils to examine substrate and process controls over temporal variability of NO and N2O production during nitrification, and to quantify the kinetics of HNO2-mediated chemical reactions. Gross NO production rates were highly correlated with calculated concentrations of HNO2, which were shown to originate from autotrophic microbial oxidation of NH4 to nitrite. Data suggests that even during periods of relatively low nitrite accumulation and rapid overall nitrification, HNO2-mediated reactions may have been the primary source of NO.

It was also shown that elevated NO and N2O emissions following fertilizer application to a moderately acidic agricultural field in the Sacramento Valley were driven by the generation of nitrite from microbial oxidation of NH4 and inhibition of nitrite oxidation due to high levels of ammonia, nitrate, and/or nitrous acid. These measurements indicate that control of soil acidity may be an important strategy for minimizing gaseous N losses from fertilized soils, and possibly for improving air quality in rural areas. The results also demonstrate that both steps of the nitrification sequence, together with abiotic reactions involving nitrite/HNO2 need to be considered in developing improved models of NO and N2O emissions.

Future Activities:

Our future work will include two components. One will be to develop modeling approaches for use in ecotoxicological exposure assessments in terrestrial ecosystems. The second component will be to conduct basic research on areas of fate and transport needing further work. This includes research in the areas of physical processes associated with chemical sorption mechanisms, transport processes in the vapor and liquid phases, and volatilization into the atmosphere, with emphasis on the shallow vadose zone. Many of these processes are fundamental information for conducting exposure assessments in any ecosystem; therefore the results will be useful for all projects in the EPA Center. Development of tools for exposure assessment, as well as new information on processes determining the movement and persistence of toxicants in the environment, are directly relevant to EPA's strategic plan. We propose to continue interactions with the investigators of the Sacramento River Watershed project and to evaluate data sets that may be appropriate for testing and validating the combined transport and fate model. Close interaction with researchers involved in the Sacramento River Watershed project will ensure that the model will provide results that can be used directly in exposure estimates. We have initiated discussions with other investigators on campus that have been working with watershed-scale water and pesticide transport models. Our goal is to see if these models may be useful in predicting the spatial and temporal quantities of pesticides entering the Sacramento River. To test a volatilization model developed in Israel, we plan to conduct field experiments on volatilization of a chemical relevant to the research in the Sacramento River Watershed. The postdoctoral scholar that developed the model will be working with us on collecting the necessary data to test the model.

We also plan to continue basic research on production and emission of nitric oxide (NO) from soils. In this regard, this research will support ongoing research in the Sierra Nevada Watershed Project on the sources of ozone and its subsequent transport into the forests of the Sierra Nevada Mountains. We plan to conduct laboratory and field research on the basic mechanisms for the production and consumption of NO in forest soils of the Sierra Nevada. We will use these data to test a simulation model of the formation and transport of NO in soil and emission from soils into the atmosphere.

Supplemental Keywords:

RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Restoration, Aquatic Ecosystem, Fate & Transport, Monitoring/Modeling, Environmental Microbiology, Biochemistry, Terrestrial Ecosystems, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Watersheds, aquatic, fate and transport, ambient particle properties, ecosystem assessment, watershed management, Sacramento River, water circulation, pesticides, sediment transport, modeling, restoration strategies, Clear Lake, hydrology, watershed influences, chemical kinetics, integrated watershed model, wetland restoration, aquatic ecosystems, environmental stress, groundwater contamination, watershed sustainablility, source load modeling, material transport, ecology assessment models, ecological impact, agrochemicals, ecosystem stress, ecological research, watershed restoration

Progress and Final Reports:

Original Abstract
  • 1997
  • 1998
  • Final Report

  • Main Center Abstract and Reports:

    R825433    EERC - Center for Ecological Health Research (Cal Davis)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
    R825433C002 Sacramento River Watershed
    R825433C003 Endocrine Disruption in Fish and Birds
    R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
    R825433C005 Fish Developmental Toxicity/Recruitment
    R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
    R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
    R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
    R825433C009 Modeling Ecosystems Under Combined Stress
    R825433C010 Mercury Uptake by Fish
    R825433C011 Clear Lake Watershed
    R825433C012 The Role of Fishes as Transporters of Mercury
    R825433C013 Wetlands Restoration
    R825433C014 Wildlife Bioaccumulation and Effects
    R825433C015 Microbiology of Mercury Methylation in Sediments
    R825433C016 Hg and Fe Biogeochemistry
    R825433C017 Water Motions and Material Transport
    R825433C018 Economic Impacts of Multiple Stresses
    R825433C019 The History of Anthropogenic Effects
    R825433C020 Wetland Restoration
    R825433C021 Sierra Nevada Watershed Project
    R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
    R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
    R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
    R825433C025 Regional Movement of Toxics
    R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
    R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
    R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
    R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
    R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
    R825433C031 Pre-contact Forest Structure
    R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
    R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
    R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
    R825433C035 Border Rivers Watershed
    R825433C036 Toxicity Studies
    R825433C037 Watershed Assessment
    R825433C038 Microbiological Processes in Sediments
    R825433C039 Analytical and Biomarkers Core
    R825433C040 Organic Analysis
    R825433C041 Inorganic Analysis
    R825433C042 Immunoassay and Serum Markers
    R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
    R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
    R825433C045 Microbial Community Assays
    R825433C046 Cumulative and Integrative Biochemical Indicators
    R825433C047 Mercury and Iron Biogeochemistry
    R825433C048 Transport and Fate Core
    R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
    R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
    R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
    R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
    R825433C053 Currents in Clear Lake
    R825433C054 Data Integration and Decision Support Core
    R825433C055 Spatial Patterns and Biodiversity
    R825433C056 Modeling Transport in Aquatic Systems
    R825433C057 Spatial and Temporal Trends in Water Quality
    R825433C058 Time Series Analysis and Modeling Ecological Risk
    R825433C059 WWW/Outreach
    R825433C060 Economic Effects of Multiple Stresses
    R825433C061 Effects of Nutrients on Algal Growth
    R825433C062 Nutrient Loading
    R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
    R825433C064 Chlorinated Hydrocarbons
    R825433C065 Sierra Ozone Studies
    R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
    R825433C067 Terrestrial - Agriculture
    R825433C069 Molecular Epidemiology Core
    R825433C070 Serum Markers of Environmental Stress
    R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
    R825433C072 Molecular Monitoring of Microbial Populations
    R825433C073 Aquatic - Rivers and Estuaries
    R825433C074 Border Rivers - Toxicity Studies