Semester of Graduation

Spring 2020

Degree

Master of Science (MS)

Department

Environmental Sciences

Document Type

Thesis

Abstract

Pesticide resistance in rice fields is an ongoing issue that has resulted in the development and use of pesticides with new modes of action. Benzobicyclon is the first registered hydroxyphenylpyruvate(HPPD)-inhibiting pesticide in the United States and has gained attention as a resistance management strategy to control weed pests in rice fields. Understanding the environmental fate and dissipation mechanisms of benzobicyclon is important due to the unique rotation of rice and crayfish in Louisiana on the same fields. Benzobicyclon persistence into the crayfish growing seasons may lead to unintended consequences for crayfish growth and production, assuming there is toxicity to crawfish. Multiple studies have investigated the dissipation of benzobicyclon in lab settings, but no published works have reported the dissipation of the pesticide in a field setting throughout a rice growing season. The environmental fate of benzobicyclon was tested in field studies spanning two rice growing seasons. Benzobicyclon and the principal degradation product, benzobicyclon hydrolysate, behaved as expected based upon their physical and chemical properties. Benzobicyclon partitioning favored sediment while the metabolite favored water with a slow partitioning of the metabolite into the water column as the parent degraded in sediment. Published literature on the dissipation mechanisms of benzobicyclon rarely mentions the dissipation of the pesticide by hydroxyl radicals. Hydroxyl radicals are an important mechanism in pollutant degradation but are rarely considered with other dissipation mechanisms. The hydroxyl radical rate constant of benzobicyclon hydrolysate was calculated and its influence modeled in an EXAMS2 simulation. A significant difference between benzobicyclon hydrolysate dissipation with and without the hydroxyl radical rate constant was observed in these simulations, with simulations including degradation by hydroxyl radicals more closely matching observed field behavior.

Committee Chair

Kevin Armbrust

Available for download on Friday, March 12, 2021

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