Identification of pesticides and their transformation products in surface water and groundwater surrounding a closed bioethanol production facility using non-targeted analysis

Non-targeted analysis (NTA) was used to identify 36 pesticides and transformation products (TPs) in surface and groundwater surrounding a defunct bioethanol production facility located in Nebraska, USA. The facility had stored and processed pesticide-treated seeds as bioethanol feedstock, which resulted in significant releases of pesticides to the surrounding environment. Targeted chemical methods were previously used to monitor the surrounding surface water for 22 pesticides and select TPs, including neonicotinoid insecticides and strobilurin fungicides, although the full range of pesticides and other chemicals that may have been present was unknown. Targeted sample extracts from 2021 were retrospectively analyzed with NTA using liquid chromatography and time of flight mass spectrometry (LC-Q-ToF) to identify additional chemicals not previously selected for analysis. Sixteen pesticides and 20 TPs were identified in the sample extracts with NTA, 33 of which were confirmed with a reference standard. Of the 20 detected TPs, 17 were not included in the previous targeted analysis. Estimated concentrations were determined for the most abundant TPs using a follow-up semi-quantitative analysis with triple quadrupole tandem mass spectrometry (LC-MS/MS). TP estimated concentrations were typically higher than the parent pesticides, with several TPs reaching the mid-μg/L to low-mg/L range in surface water and exceeding EPA aquatic life benchmarks. Surface water samples were collected in September 2023 and groundwater in June 2024 to provide an update on the chemical profile of the impacted area, which found 16 of the pesticides and TPs detected in 2021 still present, although generally at lower concentrations than observed in 2021.