Impacts of treatment extent on Per-and Polyfluoroalkyl Substances (PFAS) discharge in wet-weather flows

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent environmental contaminants associated with adverse human health effects. Wastewater treatment plants and stormwater are known sources of PFAS in aquatic environments, but the composition and fate of PFAS in urban sewer systems remains poorly understood, particularly for perfluoroalkyl acid (PFAA) precursors. To address this uncertainty, we studied PFAS occurrence, composition, and PFAA precursor contributions in wastewater treatment plants and stormwater discharges across six Iowa cities. Using targeted analysis, 9 PFAS were quantified in wastewater and 13 PFAS were quantified in stormwater. The TOP assay was used to estimate unidentified precursors. Wastewater influent contained 41.9 - 342.3 ng/L total PFAS, and effluent contained 16.5 - 330.1 ng/L total PFAS. Precursors constituted 50 - 100% of influent PFAS and 4 – 58% of effluent PFAS. Total stormwater PFAS concentrations reached 85.3 ng/L, with up to 79% of the mass as PFAA precursors. Perfluorohexanoic acid (PFHxA) and perfluorooctanoic acid (PFOA) were the most common terminal PFAAs, suggesting that precursors with six and eight perfluorinated carbons (e.g., 6:2 and 8:2 fluorotelomers) are common in wastewater and stormwater. PFAS composition and removal removal varied across wastewater treatment plants and sampling events, as influenced by sources and hydrological conditions. Higher wastewater flows were often associated with more abundant precursor PFAS in wastewater effluent. This study emphasizes the substantial presence of unidentified precursor PFAS in urban water discharges. Recognizing the ubiquity of precursors highlights the importance of quantifying total PFAS beyond just targeted monitoring. Overall, this research underscores the necessity for an improved understanding of PFAA precursor fate and transport to guide regulations and protective strategies for human and environmental health.