ABSTRACT
Wastewater treatment plant (WWTP) discharges can be a source of organic contaminants, including pesticides, to rivers. An integrated model was developed for the Potomac River watershed (PRW) to determine the amount of accumulated wastewater (ACCWW) and calculate predicted environmental concentrations (PECs) for 14 pesticides in non-tidal National Hydrography Dataset Plus Version 2.1 stream segments. PECs were compared to measured environmental concentrations (MECs) from 32 stream sites that represented a range of ACCWW and land use to evaluate model performance and to assess possible non-WWTP loading sources. Agreement between PECs and MECs was strongest for insecticides, followed by fungicides and herbicides. Principal component analysis utilizing optical fluorescence and ancillary water quality data further separated wastewater from urban runoff sources. Pesticides that indicated relatively larger sources from WWTPs included dinotefuran, fipronil, carbendazim, thiabendazole, and prometon while imidacloprid, azoxystrobin, propiconazole, tebuconazole, and diuron were more strongly related to urban runoff. However, PECs generally comprised a low proportion of MECs, which suggests dominant loading sources beyond WWTP discharges. Cumulative potential toxicity was higher for sites with greater ACCWW and/or located in developed areas. Imidacloprid, fipronil, and carbendazim accounted for the largest portion of predicted potential toxicity across sites. The chronic aquatic life toxicity benchmarks for freshwater invertebrates were exceeded for 82â¯% of the imidacloprid detections (nâ¯=â¯28) and 47â¯% of the fipronil detections (nâ¯=â¯19). These results not only highlight the significant ecological implications of pesticide contamination from WWTP discharges but also underscores the potential legacy effects from accumulated soil and groundwater sources, emphasizing the need for management strategies to mitigate both current and historical impacts on aquatic ecosystems.
