Markland, K.M., Kolpin, D.W., Hubbard, L.E., Cwiertny, D.M., Meppelink, S.M., Thompson, D.A., and Gray, J.L.

Due to their chemical and physical properties (e.g., persistence, mobility, and bioaccumulation), per- and polyfluoroalkyl substances (PFAS) remain of high public concern, with only limited research currently available on environmental exposures in agricultural regions of the United States. Building upon an initial statewide assessment of PFAS in Iowa streams, samples from 54 wadable streams, 4 wastewater treatment plant (WWTP) outfalls, 4 industrial outfalls, 2 tile drains, 6 foam (accumulated foam was sampled wherever it was observed), and 8 field blanks (no PFAS were detected in the field blanks) were collected from April 2022 to March 2023. All samples were sent to the U.S. Geological Survey’s National Water Quality Laboratory for the analysis of 34 PFAS, with reporting limits ranging from 1.9 to 52.4 nanograms per liter (ng/L). The sampling network locations were selected based on the potential effects from: agriculture (crops and/or livestock), industrial outfalls, WWTP outfalls, and airports. Except for samples collected in 2023, samples were collected during a prolonged dry period. PFAS exposures varied substantially by sample type, with the greatest number of PFAS and largest cumulative concentrations being found in streams downgradient of airports (11 PFAS, 752 ng/L) and WWTP outfalls (6 PFAS, 324 ng/L). One PFAS, perfluorooctanoic acid (PFOA), was detected in five samples with a maximum concentration of 192 ng/L, and another, perfluorooctanesulfonic acid (PFOS), was detected in 4 samples with a maximum concentration of 261 ng/L. These concentrations are greater than the U.S. Environmental Protection Agency’s (EPA) newly proposed maximum contaminant level of 4 ng/L. The proposed EPA hazard index of 1 for the combined concentrations of perfluorohexanesulfonic acid (PFHxS), perfluorononanoic acid (PFNA), perfluorobutanesulfonic acid (PFBS), and hexafluoropropylene oxide dimer acid and its ammonium salt (HFPO-DA [GenX chemicals]) was exceeded in 4 samples, all of which were collected from streams downgradient of airports. No PFAS were detected in samples from agricultural streams during this study, which likely was due to prolonged dry conditions during sampling resulting in minimal runoff and transport of PFAS from potential nonpoint agricultural sources (e.g., biosolids and livestock manure). Results of this study provide an increased understanding of potential PFAS sources and exposures in small Iowa streams in Iowa, especially during drought conditions.