Aquatic occurrence, fate and potential ecotoxicity of insecticide and fungicide residues originating from a biofuels production facility using pesticide-treated seeds

Little is known about the potential impact of point source contamination from seed treatment pesticide residues and degradation products in waste products in treated seed. The presence of these pesticides and their degradation products in the environment has been associated with toxic effects on non-target organisms including bees, aquatic organisms and humans. In this study, we investigated the occurrence of twenty-two pesticide residues and their degradation products in two streams receiving runoff from land-applied wet cake, applied and spilled wastewater originating at a biofuels production facility using pesticide-treated seed as a feedstock. Monthly grab and passive samples were taken between April 2021 to November 2023 and analyzed using liquid chromatography/tandem mass spectrometry (LC-MS/MS). Eighteen out of twenty-two target pesticide residues were detected at concentrations ranging up to 344 µg/L. Results revealed varying detection frequencies and concentrations of pesticides, with clothianidin (98.6 %), thiamethoxam (97.2 %), and the degradation product imidacloprid desnitro (95.3 %) among the most frequently detected compounds. Spatial distributions indicate higher levels pesticide concentrations occurred in an intermittent waterway downstream from a wastewater spill occurring at the facility prior to monitoring. The risk quotient analysis shows that except for the most upstream (nonpoint source) location, at least one sample from each site posed elevated exposure risk for three different trophic levels (Algae, Daphnia magna and Fathead Minnow). Acute and chronic aquatic toxicity benchmarks set by US EPA for aquatic invertebrates were exceeded due to elevated concentrations of imidacloprid, clothianidin and thiamethoxam in both waterways. Few, if any studies have documented the occurrence of neonicotinoid degradation products at these concentrations in aquatic environments, and concentrations of desnitro imidacloprid at up to 85 µg/L are particularly concerning, given its reported toxicity. Findings from the study highlight the risks of using pesticide-treated seed as a feedstock for ethanol production.