Movement of the Neonicotinoid Seed Treatment Clothianidin into Groundwater, Aquatic Plants, and Insect Herbivores

Agricultural use of the neonicotinoid clothianidin (CLO) as a seed treatment of corn and soybeans has been linked to contamination of waterways and irrigation water. By analyzing samples collected from field lysimeters with liquid chromatography tandem mass spectrometry (LC-MS), this study reports the highest CLO concentrations within leachate following planting, with maximum concentrations occurring 4 weeks post-planting (3370 ng L-1). This concentration is approximately 10x greater than previously reported CLO concentrations in streams/rivers and prairie wetlands, likely the result of reduced dilution and photolysis impacts. To document nontarget vegetation translocation dynamics, the macrophyte Lemna gibba was exposed to varying CLO concentrations for 12 h within a laboratory setting. Quantification of CLO uptake occurred every 4 h. Finally, trophic level impacts were investigated by exposing the water lily aphid Rhopalosiphum nymphaeae to L. gibba grown in CLO-contaminated water. Aphids lived and fed on contaminated duckweed for 48 h, after which an LC50 of 8.71 ng g of the plant tissue(-1) was calculated. While uptake of CLO by duckweed was rapid, aphids are unlikely to suffer acute mortality at previously reported environmental CLO concentrations. Future research should expand on this work with other macrophytes/herbivores and longer-term experiments to more realistically mimic chronic field exposures.