Sorption of per- and polyfluoroalkyl substances to suspended solids in the Dutch national waters: in situ distribution coefficients and mass discharges

Abstract

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals found in all environmental compartments. In surface waters, PFAS can bind to suspended solids (SSs), which can affect their fate. In this study, sorption of 22 PFAS to SSs from 16 locations in the Netherlands was quantified, using monitoring data from the Dutch Ministry of Infrastructure and Water Management. A total of 2,280 to 3,105 (number depending on the data inclusion criterion) SS-water distribution coefficients (Kss-w) were calculated, assuming equilibrium conditions, although these may not have applied to all locations, due to for example, local discharges. Significant differences were observed between location-specific Kss-w values. These could not be explained from SS or water characteristics, including the SS organic carbon content, which has previously been assumed to control PFAS sorption to SSs. However, for about half the PFAS studied, an inverse relationship between logKss-w and the PFAS concentration in water was observed. This may suggest that sorption of (these) PFAS to SSs is a nonlinear process, whereas in previous reports, it has been considered concentration-independent. Location-averaged Kss-w values varied between approximately 100 and 10,000 and increased with the number of PFAS carbon atoms, although the values for perfluorocarboxylic acids with < 8 carbon atoms were statistically indistinguishable. These values and patterns are consistent with several previous reports from Asia and France. Using the Kss-w values derived here, PFAS concentrations in SSs could be estimated from measured PFAS concentrations in water within an average factor of 2. Therefore, the added value of analytical PFAS concentration determinations in SSs in the Netherlands seems limited, also because PFAS masses associated with SSs carried by the major rivers generally appeared to be negligible compared with the masses dissolved in water. Consequently, including SSs as a partitioning phase in PFAS fate models does not seem essential for north-European rivers.