Daramend® in the Remediation of Bromacil in Surface Soil

Until the early 1990s, bromacil was frequently applied on industrial sites within Alberta as part of total vegetation control practices. Bromacil is a brominated organic compound that is used as a non-selective, persistent herbicide. Due to its persistence after frequent applications, bromacil concentrations in soil on these industrial sites remain above Alberta Tier 1 Soil and Remediation Guideline limits. As these sites reach the end-of-life, industry owners and government regulators are addressing the challenge of remediating bromacil in soil. Since bromacil is highly soluble and has low sorption to soil, it often migrates with surface and groundwater flow, impacting soil off-site, and risking freshwater aquatic life receptors. Anaerobic biodegradation is the primary mechanism that degrades bromacil through reductive debromination. The reductive debromination process removes the bromine atom from bromacil, producing the byproducts bromine ions and 3-sec-butyl-6-methyluracil that are less toxic than bromacil. Reductive debromination is a similar reductive dehalogenation process that is used in the remediation of chlorinated organic compounds. The dehalogenation of chlorinated organic compounds can be done by anaerobic biodegradation or through reductive chemical processes. Common remediation technologies include the use of zero valent iron (ZVI) to abiotically remediate chlorinated organics through reductive dehalogenation. In 2019, the Soil Sterilants Program (SSP) was established to address the challenges associated with bromacil, including identifying and testing bromacil remediation technologies. The research in this thesis is a subset of the remediation experiments conducted by the SSP. The SSP identified Daramend®, a remediation soil amendment composed of organic matter and ZVI, as a potential technology to remediate bromacil in soil. Currently, it is used in the remediation of chlorinated organic compounds in soil, including chlorinated herbicides. Daramend® remediates chlorinated organic compounds through a combination of anaerobic biotic and abiotic reductive dehalogenation. Bench- and meso-scale testing conducted by the SSP showed that Daramend® can degrade in bromacil in soil. For this thesis, a series of experiments were conducted to evaluate how Daramend® degrades bromacil in soil under anaerobic conditions and to assess its performance in meso-scale settings. The hypothesis was that Daramend® would degrade bromacil at lab and meso-scales through a combination of abiotic and biotic mechanisms. The research objectives were to: (1) identify whether degradation of bromacil in soil amended with Daramend® was one or a combination of abiotic and biotic mechanisms; (2) identify the Daramend® optimal dosage and water application frequency for the remediation of bromacil in surface soil; and (3) determine if Daramend® can effectively remediate bromacil in surface soil in a meso-scale study. Results from these experiments found that: (1) Daramend® can enhance bromacil degradation and can degrade limited amounts of bromacil abiotically, but (2) maintaining sufficiently anaerobic conditions can degrade bromacil without additional amendments, and (3) maintaining sufficiently anaerobic conditions in surface soil at field scales is not feasible in surface soil. Below ground bromacil impacts pose a greater challenge in Alberta. Despite being under anaerobic conditions, bromacil in the groundwater zone often does not degrade. Injecting Daramend® or similar organic amendments into the contaminated zone or installing as a permeable reactive barrier may initiate biodegradation of bromacil in the below ground, saturated zone.

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