Persistence of florpyrauxifen-benzyl in sediments following application to a large oligotrophic lake to control Eurasian watermilfoil

Florpyrauxifen-benzyl (FPB) is a recently registered arylpicolinate herbicide used to control dicots including Eurasian watermilfoil (EWM). Laboratory studies indicate rapid degradation of FPB in water, but sediment persistence in aquatic systems remains poorly understood, creating uncertainty in ecological risk assessments. We evaluated the environmental fate and transport of FPB and its degradants in water, plants, and sediment following application of the herbicide to two bays of Lake George, NY. FPB was rapidly lost from the water column within 72 hours, consistent with prior studies, but persisted in sediments for at least one year. Sediment cores revealed vertical migration of FPB, which may contribute to frequent non-detects in surface sediments and potentially explain why US EPA was unable to establish sediment half-lives in aquatic systems. Measured concentrations exceeded the 28-day no observable adverse effect concentration (NOAEC) for chironomids for at least a year, highlighting the potential for long-term chronic exposure to benthic organisms. Modeled sorption and dilution scenarios aligned with field observations and indicated that circulation dynamics expanded the affected area beyond the direct treatment zones. These results demonstrate that FPB and its degradants persist longer in sediments than suggested by laboratory studies, raising important questions about long-term ecological risks, effects of repeated applications, and underestimation of sediment persistence. Long-term studies such as this are essential for understanding the fate of these compounds and for guiding informed decisions about future herbicide applications.