Pesticide concentrations in silicone bands and bee tissue near agricultural fields, Brookings County, South Dakota, 2022–2023

To better understand the pesticide exposure of bees (Bombus, Melissodes) while foraging in an agriculturally influenced landscape in Brookings County, South Dakota, bee tissue samples were collected from April/May through October in 2022 and 2023. Bees, included wild Bombus and Melissodes, were collected biweekly using blue vane traps and B. impatiens were collected from commercially-available colonies after a 1-month deployment. Bees were separated by species and Bombus queens were separated from workers. Additionally in 2023, silicone bands were used as passive samplers to assess pesticide levels in the surrounding environment. The United States Department of Agriculture (USDA) Agricultural Research Service (ARS) collected the bee samples and also deployed and collected the silicone bands. The USGS Organic Chemistry Research Lab (OCRL) quantified the pesticide concentrations in both the bee tissue and the silicone bands to determine pesticide exposure and accumulation. Bee tissues were freeze dried, homogenized, and then extracted in acetonitrile using an Energized Dispersive Guided Extraction (EDGE) system. Sample clean-up was performed using Captiva EMR-Lipid solid-phase extraction cartridges. Silicone bands were extracted by shaking twice for two hours in approximately 20 milliliters (mL) of ethyl acetate. Samples were analyzed for 169-221 pesticides and their transformation products using gas chromatography-tandem mass spectrometry and liquid chromatography-tandem mass spectrometry. Pesticides known to be applied in the area were added to the method for the analysis of the 2023 samples. Of the 169 compounds analyzed in bee tissue from 2022, 12 different pesticides were detected; 24 of 203 compounds analyzed were detected in bee tissue from 2023, and 61 of 221 compounds analyzed were detected in the 2023 bands. In 2022, bifenthrin and cyhalothrin were the most frequently detected pesticides in bee tissue, appearing in 29% of environmental samples. In 2023, metolachlor was the most commonly found in bee tissue, detected in 21% of samples. Acetochlor and metolachlor were the most detected pesticides in the 2023 silicone bands, present in 100% of environmental samples.