Abdullahi Adeola, David Green, William Crumpton, Joseph A. Charbonnet

The persistence, bioaccumulation, and toxicity of per- and polyfluoroalkyl substances (PFAS) make them pollutants of global concern. Understanding the spatial and seasonal dynamics of PFAS in rivers is critical for identifying pollution sources and protecting water resources. We sought to determine the hydrological and anthropogenic influences on PFAS pollution patterns in the Ames watershed in central Iowa. Between April and November 2023, water samples were collected weekly at three locations along the South Skunk River and one on Ioway Creek. Samples underwent solid-phase extraction and analysis with liquid chromatography-tandem mass spectrometry. We evaluated relationships between flow rate, PFAS yield, and PFAS concentrations at each location. Of the 40 PFAS targeted, 15 were detected, and PFBS, PFHxA, PFOA, and 6:2 FTS were present in over 50% of samples from the South Skunk River. The mean total target PFAS concentrations ranged from 4 ng/L upstream of Ioway Creek to 27 ng/L downstream of the South Skunk River at the Ames wastewater treatment plant (WWTP). PFAS yields ranged from 162 ng/s/km² to 1,241 ng/s/km² for different watershed portions. PFAS concentrations were inversely correlated with flow rates; concentrations were highest during low-flow conditions in the fall. The correlation between flow rate and PFAS yield ranged from moderate upstream to strong downstream. Particularly along the main stem of the South Skunk River, the concentrations of C4-C8 PFCAs were closely correlated. These findings suggest a common source of PFCAs or their precursors (e.g., the WWTPs) whose contributions are diluted by stream flows. PFOS and PFOA concentrations were below the EPA's maximum contaminant levels for drinking water (4 ng/L). This study provides the first comprehensive assessment of PFAS loads and yields in Iowa surface waters, identifying WWTP discharges as a primary contamination source in this watershed and highlighting the need for targeted mitigation strategies to manage PFAS contamination and safeguard water quality.