Pesticide concentrations in multiple physical and biological stream matrices are impacted by a bioenergy production facility receiving pesticide-coated corn seeds.

Insecticide and fungicide seed coatings have become prevalent in conventional agriculture in recent decades. From 2015-2021, the AltEn bioenergy plant (Mead, Nebraska, USA) generated ethanol from almost 100% unused/expired treated corn seeds. This use of these seeds for ethanol production resulted in the accumulation of large amounts of contaminated wastewater and solid residue, a portion of which was applied to surrounding farmland. To better understand the potential long-term environmental effects from the processing of treated seeds at this facility, five nearby stream sites were sampled in 2022 after the closure of the plant; these included two sites directly affected by AltEn, one upstream and two downstream of the affected sites. Water and sediment were collected in March through July, and algae and fish samples were collected in July for chemical analysis. Overall, 60 pesticide compounds (parents and transformation products) were detected in one or more matrices, including 23 fungicides, 20 insecticides, 16 herbicides, and one bacterial growth inhibitor. Pesticide results (maximum detection frequency, maximum concentration) varied substantially by environmental compartment: water (100% multiple pesticides, 4,600 ng L-1 thiamethoxam transformation product [NOA-407475]), algae (100% multiple pesticides, 190 ng g-1 atrazine), sediment (60% dithiopyr, 2.3 ng g-1 acetochlor), and fish (20% pyraclostrobin, 2.2 ng g-1 atrazine). Pesticides associated with treated corn seeds (e.g., insecticides clothianidin and thiamethoxam, fungicides fluoxastrobin and thiabendazole) were detected at significantly higher concentrations (p < 0.05) in stream water from sites affected by the AltEn facility compared with nonaffected sites. Study results indicate that pesticides associated with the AltEn facility continue to be a source of contaminants to aquatic systems after the plant's closure in 2021.