In situ air–water and particle–water partitioning of perfluorocarboxylic acids, perfluorosulfonic acids and perfluorooctyl sulfonamide at a wastewater treatment plant

In situ measurements of air and water phases at a wastewater treatment plant (WWTP) were used to investigate the partitioning behavior of perfluorocarboxylic acids (PFCAs), perfluorosulfonic acids (PFSAs) and perfluorooctyl sulfonamide (HFOSA) and their conjugate bases (PFC−s, PFS−s, and FOSA−, respectively). Particle-dissolved (Rd) and air–water (QAW) concentration ratios were determined at different tanks of a WWTP. Sum of concentrations of C4–12,14 PFC(A)s, C4,6,8,10 PFS(A)s and (H)FOSA were as high as 50 pg m−3 (atmospheric gas phase), 2300 ng L−1 (aqueous dissolved phase) and 2500 ng L−1 (aqueous particle phase). Particle-dissolved concentration ratios of total species, log Rd, ranged from −2.9 to 1.3 for PFS(A)s, from −1.9 to 1.1 for PFC(A)s and was 0.71 for (H)FOSA. These field-based values agree well with equilibrium partitioning data reported in the literature, suggesting that any in situ generation from precursors, if they are present in this system, occurs at a slower rate than the rate of approach to equilibrium. Acid QAW were also estimated. Good agreement between the QAW and the air–water equilibrium partition coefficient for C8PFCA suggests that the air above the WWTP tanks is at or near equilibrium with the water. Uncertainties in these QAW values are attributed mainly to variability in pKa values reported in the literature. The WWTP provides a unique environment for investigating environmental fate processes of the PFCAs and PFSAs under ‘real’ conditions in order to better understand and predict their fate in the environment.