Neonicotinoids in the aquatic environment

Neonicotinoids are an important class of systemic insecticides in agricultural and household use. Neonicotinoids, such as imidaclorprid (IMI), clothianidin (CLO), thiamethoxam (TMX), and acetamiprid (ACE), are used to control sap feeding insects and underground grubs. Nicotinic acetylcholine receptor (nAChR) agonism is the primary mode of action. Surface water contamination by neonicotinoids is common and photodegradation proceeds quickly in water. The impact of water constituents on the analysis and photodegradation of neonicotinoids is relatively unknown. Studies have shown neurobehavioral impacts of IMI and TMX on larval zebrafish, but it is uncertain how photoproducts or clothianidin exposure may alter neurodevelopment. This dissertation research includes analytical method optimization for the extraction of neonicotinoids from soil, sediment, and water; the direct and indirect photolysis of imidacloprid; and the neurotoxicological effects of neonicotinoids and associated photoproducts in zebrafish. Several potential causes of neonicotinoid underestimation in surface water were assessed including analyte stability, SPE extraction materials, and the influence of dissolved organic carbon (DOC) and pH on extraction efficiency. The best extraction results were obtained when samples were extracted using 30 µm particle size HLB and analyte retention by C18 sorbent was particularly affected by DOC content. Analyte stability was determined to not be of concern if samples are stored at or below 20 °C. The use of matrix-matched standards to reduce matrix induced ionization issues without the addition of further cleanup steps in the LC-MS/MS determination of neonicotinoid pesticides was assessed for sediment and soil. Recovery of analytes was within limits set by the EU commission guidance document on pesticide residues or all analytes; the highest recovery was from sediment followed by laboratory sand and agricultural soil. The impact of several aquatic constituents on the degradation rate of imidacloprid (IMI) were independently determined under natural sunlight. Dissolved iron and DOC decreased the rate of IMI degradation and nitrate had no effect. There was no change in degradation rate of imidacloprid in natural water compared to the light control. The neurobehavioral changes from exposure of embryo-larval zebrafish to IMI and desnitro-imidacloprid (DNIMI) photoproduct were observed. The DNIMI photoproduct and clothianidin (CLO) had the most significant impacts on gene expression of the acetylcholine receptor α7 subunit and dopaminergic pathway genes. This research will aid in the accurate environmental monitoring of neonicotinoids in surface water and ecological risk assessment of neonicotinoids.