Fate and Transformation of Quinone Outside Inhibitor (QoI) Fungicides during Simulated Drinking Water Treatment Processes

Abstract

Quinone outside inhibitor fungicides (QoIs) are widely used across the United States, with common QoIs (e.g., azoxystrobin, pyraclostrobin) regularly detected in water resources that could serve as drinking water supplies in agriculturally dominated watersheds. Here, we explored the fate of several QoIs during simulated water treatment via coagulation/flocculation, chemical (lime-soda) softening, chemical disinfection with free chlorine, and granular activated carbon (GAC). Jar tests with Iowa River water found little QoI removal during coagulation/flocculation.Trifloxystrobin and kresoxim methyl underwent base-promoted hydrolysis at pH values and over timescales used in lime-soda softening, with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) data identifying known acid metabolites as major hydrolysis products. Select QoIs, kresoxim-methyl, pyraclostrobin, azoxystrobin, fenamidone, and dimoxystrobin, were reactive toward free chlorine under conditions and over timescales relevant for chemical disinfection, resulting in persistent, often chlorinated, transformation products. Notably, we observed distinct reaction sites during chlorination for each of the five QoIs found to be reactive toward free chlorine, including some cases where the biologically active moiety of the parent molecule was conserved. Successful management of QoIs can likely be achieved with GAC, which quickly removed all QoIs via sorption. Outcomes of this work will help to improve exposure assessments to QoIs and their transformation products through drinking water, while also identifying practical approaches for their removal during drinking water treatment.