PFAS in stormwater control measures: Removal, distribution, and long-term fate

This study evaluates the performance of various conventional stormwater control measures (SCMs) in mitigating 26 per- and polyfluoroalkyl substances (PFAS), including perfluorooctanesulfonic acid (PFOS), and perfluorooctanoic acid (PFOA). PFAS with carbon chain lengths ≥ 9 exhibited greater particulate affinity, ranging from 35% to 73% of their concentration associated with suspended solids. In contrast, only 17-35% of PFAS with C ≤ 8, which dominated the detected compounds, were associated with particulate phases. As most SCMs studied (biofilters, media filters, hydrocyclones, and a retention pond) heavily rely on particle removal, the treatment of filtered-water PFAS (< 0.7 μm) was poor, with essentially no attenuation. Particulate-phase PFAS removal varied, with some systems, such as the retention pond, effectively reducing concentrations. In contrast, others, including the biofilters and one treatment train (hydrocyclone plus cartridge filters), exhibited unexpected increases, suggesting potential remobilization of particulate-associated PFAS within the system. The retention pond SCM, influenced by evaporation, infiltration, and used for local irrigation, was monitored over a one-year period to assess PFAS persistence, precursor transformation, and the effects of water loss on contaminant concentrations. Analysis of precursor compounds in the pond, including fluorotelomer sulfonates (FTS) and perfluoroalkyl sulfonamides (FASAs), showed decreased concentrations relative to runoff. When coupled with increased concentrations of stable products such as perfluorohexanesulfonic acid (PFHxS), PFOS, and PFOA, these changes suggested in situ transformation due to the extended retention time in the system. Additionally, the concentration of PFAS associated with the filtered water (e.g., PFBA, PFOA) increased over time due to evaporation of water during periods of minimal stormwater inputs or discharges. Perfluoroalkane sulfonic acid (PFSA) concentrations (primarily PFOS) in sediments were higher than those in the incoming particulate phase, suggesting sorption and accumulation of PFOS in sediments. The substantial filtered water fraction of PFAS and the limited removal of PFAS by any of the SCMs underscore the limitations of conventional SCMs in treating PFAS.