Samuel Adam Miller Lee Blaney Paul M. Bradley Kaycee E. Faunce Jacob Fleck Malinda Frick Ke He Ryan D. Hollins Conor J. Lewellyn Emily H. Majcher Mitchell A. McAdoo Kelly Smalling Larry B. Barber 2025 <p><span>Managing per- and polyfluoroalkyl substances (PFAS) in water resources requires a basin-scale approach. Predicted environmental concentrations (PEC) and stream-vulnerability scores for PFAS were determined for the Potomac River watershed in the eastern United States. Approximately 15% of stream reaches contained municipal and/or industrial wastewater treatment plant (WWTP) discharges that are presumptive PFAS sources, comprising from &lt;1 to &gt;90% of streamflow. Mean annual PEC, based on the summed concentrations of eight PFAS detected in WWTP effluents (ΣPFAS</span>_PEC<span>), for all stream reaches in the watershed was 3.8 ng L</span>^–1<span>, and stream reaches impacted by WWTP had perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) PEC of 0.39 and 0.14 ng L</span>^–1<span>. For locations where measured-environmental concentrations (MEC) were determined, municipal and industrial WWTP contributed 7.8% (0 to 65%) of the total annual streamflow and MEC were greater than PEC in 99% of the samples, indicating additional potential PFAS sources. The mean ΣPFAS</span>_PEC<span>&nbsp;was 9.1 ng L</span>^–1<span>&nbsp;compared to a mean sum of PFAS MEC of 34 ng L</span>^–1<span>. Under mean-August low-flow, 17% and 9.4% of the water-supply intakes had maximum PFOA and PFOS PEC exceeding drinking water maximum contaminant levels.</span></p> application/pdf 10.1021/acs.est.4c12167 en American Chemical Society Municipal and industrial wastewater treatment plant effluent contributions to per- and polyfluoroalkyl substances in the Potomac River: A basin-scale measuring and modeling approach article