Insecticide Fate and Transport in Rivers Adjacent to Agricultural Intensive Regions

Current Use Pesticides such as neonicotinoids, a class of insecticides used in the agricultural industry to control insects, and fungicides, a class of pesticides used to control fungal disease in plants, both exhibit a growing influence on water resources and aquatic ecosystems. Worldwide, over 411,000 kg of pesticides are applied annually, leading to chronic pollution in waterbodies. While substantial work has been completed on the occurrence and distribution of neonicotinoids in both surface and groundwater, little is known on the degradation and transformation of neonicotinoids in natural river environments. Therefore, the overarching goal was to investigate the potential fate and transport mechanisms of several pesticides classes along with quantifying the potential role of two rivers on the photochemical transformation of neonicotinoids and their degradation products in aquatic environments. In Chapter 1, 55 articles reviewed focused on the occurrence and/or fate and transport of neonicotinoids in realistic aquatic environments and 22 articles focused on the toxicity towards insects and invertebrates. The review provided a foundation for improving our understanding of neonicotinoid usage and potential exposure to non-target species and the natural environment at the global scale. In Chapter 2, synoptic field monitoring of pesticides in two distinct watersheds in the United States during a flood season (2019) and non-flood season (2020) was conducted using grab and POCIS sampling techniques, and results indicated prevalence of neonicotinoids in both watersheds at higher concentrations and specifically imidacloprid exceeded chronic toxicity limits. Further comparisons indicated the flood season significantly impacted the movement of pesticides from the field into the monitored watersheds. In chapter 3, neonicotinoid photochemical degradation and potential pathways in natural waters with varying DOM and impact of three potential quenching chemicals in the photolytic process of imidacloprid and thiamethoxam under simulated sunlight was investigated. The photolysis of imidacloprid and thiamethoxam under simulated light in varying DOM, and the addition of quenching agents enhanced our understanding of the role played by each reactive oxygen species in the photolysis of imidacloprid and thiamethoxam