Invisible inputs, lasting outputs: Implications of PFAS conversion in California wastewater

This study investigates the sources and transformation processes affecting per- and polyfluoroalkyl substances (PFAS) in wastewater treatment plants (WWTPs). Paired influent and effluent samples from 27 WWTPs across California were obtained from the California GeoTracker database and analyzed using positive matrix factorization (PMF). The data were compiled in two ways: first, as individual influent and effluent samples entered independently (data set A), yielding 16 analytes in 154 samples, and second, as paired influent-effluent samples (data set B), yielding 30 analytes in 52 samples. Sixteen PFAS compounds were detected frequently enough to be included in the analysis. All but two compounds (perfluoropentanesulfonic acid [PFPeS] and n-methyl perfluorooctane sulfonamidoethanol [NMeFOSE]) displayed higher concentrations in the effluent than influent, suggesting minimal biosolid partitioning and the generation of PFAS from precursors during treatment. PMF analysis of data set A generated five factors that represent PFAS sources, including precursor conversion to perfluorocarboxylic acids (PFCAs). PMF analysis of data set B identified three source factors: (1) stable PFAS in influent and effluent; (2) PFAS precursors in influent converted to PFCAs in effluent; and (3) unmeasured precursors in influent converting to PFCAs. Overall, an estimated 40-80% of PFCA mass in WWTP effluents was attributable to precursor transformation. These findings demonstrate that WWTPs can act as net sources of PFAS by generating PFCAs, highlighting the need for regulatory and treatment strategies that address PFAS precursors in wastewater.