9:00 am - 10:00 am
Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Jackie Maxwell. This seminar is open to the general public to attend via Zoom:
Thesis Topic: Development of an Extraction Method for Estimating Phytoaccessible Fractions of Soil Sterilants Bromacil and Tebuthiuron
Seminar Abstract: Bromacil and tebuthiuron are soil sterilants used from the 1960s to 1990s on industrial sites to control vegetation. Approximately 61,750 sites are considered contaminated when comparing total sterilant concentrations (estimated by 99 percent methanol extraction) against Alberta’s remediation guidelines. Remediation of these sites requires treatment or removal of soil to bring sterilant concentrations below applicable guidelines. As time passes from initial application, a portion of bromacil and tebuthiuron is thought to adsorb to the soil solid phase. The total sterilant concentration in soil is then comprised of the adsorbed (solid phase) and the phytoaccessible (plant accessible) concentrations. Measuring phytoaccessible or soluble sterilant concentrations in soil would avoid unnecessary ex-situ treatment or landfilling. It is likely that adsorption to soil organic matter or mineral particles reduces phytoaccessibility and immobilization technologies could be used to increase the natural soil adsorptive capacity to manage in-situ sites with sterilant contamination.
Calcium chloride solution (0.01 M) is often used to assess soluble (phytoaccessible) concentrations of nutrients and to conduct adsorption/desorption studies of metals and organics. In this work, it was used as an extractant to estimate the phytoaccessible concentrations of bromacil and tebuthiuron in soil. A t-test for non-parametric data with homogeneous variances was used to compare calcium chloride-extractable sterilant concentrations to total concentrations (estimated by 99 percent methanol extraction of aged soil samples, or by spiking soils using a known sterilant concentration). Estimated total concentrations were higher than calcium chloride-extractable concentrations, indicating that a significant portion of the sterilants adsorbed to soils was not recovered by the calcium chloride solution.
In reviewed literature, organic matter and clay contribute most to bromacil or tebuthiuron adsorption. A two-by-two Analysis of Variance (ANOVA) assessed if increasing percentage of clay and organic matter increased the apparently adsorbed fraction, which was estimated by subtracting the calcium chloride-extracted concentration from the total estimated concentration. For both bromacil and tebuthiuron, mean apparently adsorbed fractions were higher for high organic matter compared to low organic matter soils. Clay did not significantly increase apparent adsorption. Where there are large areas of marginal contamination, approaches are needed to reduce risk, meet regulatory requirements, and protect soil health. Soils with low phytoaccessible concentrations could remain in place and retain nutrients, organic matter, and structure, providing resiliency against current and future challenges to soil ecosystems.