Location: Agricultural Water Efficiency and Salinity Research Unit
2018 Annual Report
Objectives
The overarching goal of this 5-year research plan is improving the understanding of the soil and environmental factors and agricultural practices that influence the fate, transport and emissions of pesticides in agricultural systems. This will be accomplished by developing new information related to soil mechanisms and their interactions, quantifying environmental factors that significantly affect fate and transport, and in developing a more accurate predictive model. Two objectives have been assigned to this project.
Objective 1: Quantify mechanisms and processes that affect exchange of agricultural contaminants between soil, water, and air.
Objective 1A. Obtain transport, transformation and partitioning coefficients for 1,3-dichloropropene (1,3-D) that can be used in predicting fate and transport.
Objective 1B. Obtain information on initial chloropicrin concentration and soil degradation rate and develop a mathematical relationship to describe this process.
Objective 1C. Test and verify the concentration-dependent soil degradation relationship using a radial-diffusion laboratory experiment.
Objective 2: Develop and test a comprehensive contaminant fate and transport model that focuses on improved prediction of off-site movement (with an emphasis on volatilization).
Approach
Research will be conducted to:
Objective 1A: Obtain basic information on vapor sorption, solubility, degradation, and Henry’s Law appropriate for the soil types and environmental conditions observed during the five 1,3-D field experiments. Develop relationships with soil type, soil water content, temperature and initial concentration that can be used for modeling activities described in Objective 2. Laboratory experiments will be conducted to measure the 1,3-D vapor density, degradation rate and adsorption in soil. These experiments will be conducted at 3 to 4 temperatures in the range 10 to 45 degrees Celsius. The soil vapor density measurements will be obtained at several water contents, including very dry soils. The effect of temperature on these transport parameters will be described using the Arrhenius equation.
Objective 1B: Conduct laboratory column experiments to reveal the effect of initial chloropicrin concentration on emissions and degradation in soil and develop a mathematical relationship describing this process. Soil degradation will be measured in laboratory incubation experiments (see Obj 1A) and in triplicated soil column experiments. The columns will be housed in a controlled temperature room at 25 degrees Celsius. Seven field application rates will be tested (50 to 350 lbs/acre) using native soil. Experiments will also be conducted using sterilized soil at two or three field application rates (e.g., 100, 200, and 300 lbs/acre). A model of the concentration-dependence of the degradation rate will be obtained using a logistic-response model, by fitting the initial concentrations and degradation rates.
Objective 1C: Test and verify the concentration-dependent soil degradation relationship by conducting a radial-diffusion laboratory experiment. Use soil degradation rates obtained in laboratory incubation experiments to parameterize concentration-dependent degradation in a 2-D numerical transport model and determine if the model more accurately predicts the radial diffusion within the 2-D soil monolith. CHAIN-2D, or similar, will be modified to enable simulation of a concentration-dependent degradation process and used to predict the soil concentrations and emissions in the 2-D soil monolith. Numerical predictions using constant degradation rates will be compared to predictions using concentration-dependent rates to determine if the concentration-dependent model performs better.
Objective 2: Develop and test a comprehensive contaminant fate and transport model that focuses on improved prediction of volatilization. Show that soil drying and vapor adsorption controls the timing of the peak fumigant emission rate during daily (i.e., 24 h) periods by comparing measured 1,3-D emission rates to predicted emission rates using a fully coupled heat, water, water vapor and chemical transport model coupled to atmospheric processes. Model accuracy will be determined by comparing field emission measurements and model predictions of soil temperature, soil water content, emissions, and timing of peak emission rates.
Progress Report
Several experiments were completed in support of Objective 1a. Vapor density measurements for 1,3-dichloropropene (1,3-D) were made. This data revealed the relationship describing 1,3-D vapor density at prevailing soil water content and soil temperatures. Experiments have also been completed to obtain Henry’s Law coefficients from 5 to 40 degrees Celsius. These experiments were conducted at two starting concentrations, which gave similar results. The Henry’s Law relationship with temperature was described using the Arrhenius equation, which yielded an activation energy coefficient (34 kilojoules per mole). The 1,3-D solubility and adsorption experiments were also completed.
Sub-objective 1B: Experiments were conducted to determine the effect of application rate on soil degradation for chloropicrin (CP). Using laboratory soil columns, we aimed to investigate the relationship between chloropicrin (CP) application rate and its emissions from soil across a wide range of CP applications (equivalent to 56–392 kilogram per hectare (kg ha-1)). In contrast to the known behavior of other fumigants, total emission percentages were strongly and positively related to application rate (i.e., initial mass), ranging from 4 to 34 percent across the application rate range. When combined, data from a previous study and the present study showed good overall comparability in terms of CP application rate versus emission percentage, yielding a second-order polynomial relationship with a fraction of variance or R2 value of 0.93 (n=12). The study revealed that mass losses of CP were strongly disproportional to application rate, also showing a polynomial relationship. Based on degradation studies, we consider that a shorter half-life (faster degradation) at lower application rates limited the amount of CP available for emission. The non-linear relationship between CP application rate and CP emissions (both as percent of that applied and as total mass) suggests that low application rates likely lead to disproportionally low emission losses compared with higher application rates; such a relationship could be considered when assessing/mitigating risk, e.g., in the setting of buffer zone distances.
Sub-objective 1C and Objective 2: Progress has been made to incorporate a concentration-dependent fumigant degradation process into numerical models. The concentration-dependent degradation sub-model was developed that accurately describes soil degradation in laboratory experiments with varying initial fumigant concentration. Computer coding was completed and incorporated into both One-Dimensional and Two-Dimensional Simulation programs. Substantial progress was made in preparing SOLUTE-1D for the addition of fully-coupled water-heat-vapor transport equations. The basic code for the non-coupled model has been verified by comparison to analytical solutions for appropriate soil and environmental conditions. Furthermore, SOLUTE-1D has been compared to a popular commercial simulation software program (i.e., HYDRUS) and shown to give equivalent results over a wide range of soil and environmental conditions and for various fumigant-application and emission-reduction scenarios.
Numerical simulations of earlier field experiments were conducted in predictive mode (i.e., no calibration) to determine if simulation could be used as a substitute for field experimentation to obtain information needed by regulators. The results show that the magnitude of the volatilization rate and the total emissions could be adequately predicted for these experiments, except for a scenario where the field was periodically irrigated after fumigation. In addition, the timing of the daily peak 1,3-D emissions was not accurately predicted for these experiments due to the peak emission rates occurring during the night or early-morning hours. This study revealed that more comprehensive mathematical models (or adjustments to existing models) are needed to fully describe emissions of soil fumigants from field soils under typical agronomic conditions.
The sole scientist attached to this project retired this year. Discussions have commenced with National Program Staff and Deputy Administrator(s) to determine how to best proceed.
Accomplishments
Review Publications
Yates, S.R., Ashworth, D.J. 2017. Simulating emissions of 1,3-dichloropropene after soil fumigation under field conditions. Science of the Total Environment. 621:444-452. https://doi.org/10.1016/j.scitotenv.2017.11.278.
Ma, L., Ashworth, D., Yates, S.R. 2016. Simultaneous determination of estrogens and progestogens in honey using high performance liquid chromatography-tandem mass spectrometry. Journal of Pharmaceutical and Biomedical Analysis. 131:303-308. https://doi.org/10.1016/j.jpba.2016.09.001.
Yates, M.D., Ma, L., Sack, J., Golden, J.P., Strycharz-Glaven, S.M., Yates, S.R., Tender, L.M. 2017. Microbial electrochemical energy storage and recovery in a combined electrotrophic and electrogenic biofilm. Environmental Science and Technology Letters. 4:374-379. https://pubs.acs.org/doi/ipdf/10.1021/acs.estlett.7b00335.
Ashworth, D., Yates, S.R., Stanghellini, M., Van Wesenbeeck, I.J. 2017. Application rate affects the degradation rate and hence emissions of chloropicrin in soil. Science of the Total Environment. 622:764-769. https://doi.org/10.1016/j.scitotenv.2017.12.060.
Ashworth, D.J., Yates, S.R., Anderson, R.G., Van Wesenbeeck, I.J., Sangster, J.L., Ma, L. 2018. Replicated flux measurements of 1,3-dichloropropene from a bare soil under field conditions. Atmospheric Environment. 191:19-26. https://doi.org/10.1016/j.atmosenv.2018.07.049.
