Transformation of the Neonicotinoid Insecticide Drives Differences in Parent and Product Sorption

Full title: Transformation of the Neonicotinoid Insecticidal Pharmacophore Drives Differences in Parent and Product Sorption: Results from the Field, Lab, and Computational Modeling

Presented on April 28, 2022, by Gregory LeFevre - University of Iowa - at the 2022 Emerging Contaminants in the Environment Conference (ECEC22)

Recently, we reported the initial discovery of neonicotinoid insecticides and their metabolites in finished drinking water. Neonicotinoids are part of a growing class of target-specific pesticides, wherein receptor binding propensity is conferred through a specific structural pharmacophore (e.g., an electronegative nitro-/cyano-group). Although neonicotinoids were not removed via conventional drinking water treatment, GAC was surprisingly effective for these high-solubility (i.e., low Kow) compounds, as demonstrated by analysis of long-term exposed spent GAC from a full scale DWTP. We characterized differences in sorption between neonicotinoid parent compounds and pharmacophore-altered products using functionalized (COOH- and NH2-) and non-functionalized carbon nanotubes and GAC. Results indicate the electronegative pharmacophore drives sorption propensity, and presumed mechanisms likely differ between parents and products. The hypothesized mechanisms of neonicotinoid sorption extend beyond bulk hydrophobic interactions (i.e., electrostatic and hydrogen bonding), rendering currently available prediction models (e.g., pp-LFERs/LSERs) inadequate for neonicotinoids. The lack of commercially-available authentic standards for novel transformation products led us to develop a new QSAR-based model to predict neonicotinoid partitioning using QSAR descriptors that best reflect neonicotinoid interactions that drive partitioning between octanol-water and carbon-water systems. We were able to accurately model (and externally validate) neonicotinoid partitioning, and subsequently predict partitioning of novel neonicotinoid transformation products.