In Situ Insight into the Availability and Desorption Kinetics of Per- and Polyfluoroalkyl Substances in Soils with Diffusive Gradients in Thin Films

Abstract

The physicochemical exchange dynamics between the solid and solution phases of per-and polyfluoroalkyl substances (PFAS) in soils needs to be better understood. This study employed an in situ tool, diffusive gradients in thin films (DGT), to understand the distribution and exchange kinetics of five typical PFAS in four soils. Results show a nonlinear relationship between the PFAS masses in DGT and time, implying that PFAS were partially supplied by the solid phase in all of the soils. A dynamic model DGT-induced fluxes in soils/sediments (DIFS) was used to interpret the results and derive the distribution coefficients for the labile fraction (K dl ), response time (t c ), and adsorption/desorption rates (k 1 and k −1 ). The larger labile pool size (indicated by K dl ) for the longer chain PFAS implies their higher potential availability. The shorter chain PFAS tend to have a larger t c and relatively smaller k −1 , implying that the release of these PFAS in soils might be kinetically limited but not for more hydrophobic compounds, such as perfluorooctanesulfonic acid (PFOS), although soil properties might play an important role. K dl ultimately controls the PFAS availability in soils, while the PFAS release from soils might be kinetically constrained (which may also hold for biota uptake), particularly for more hydrophilic PFAS.

Levels of per- and polyfluoroalkyl substances (PFAS) in various wastewater-derived fertilizers – analytical investigations from different perspectives

“…Because wastewater-based fertilizers contain various PFAS 42 and different PFAS have different diffusion properties this could be an explanation for the dispersion of the DGT values. Moreover, DGT is sampling the freely available/labile portion of PFAS in the sample and Huang et al 43 showed that pH and texture of a samples are important properties which controls the labile pool size of PFAS. They showed also that the rate of supply of PFAS to DGT devices in soil was controlled by the kinetics of release from the solid phase to the solution phase, which may also apply for wastewater-based fertilizers.…”

“…However, in comparison with the EOF/CIC method the DGT/CIC values were more widely spread because wastewater-based fertilizers contain various PFAS including fluorinated pharmaceutical and pesticides 42 which have different diffusion properties, but also kinetic exchange limitations have been observed for the DGT method previously. 43 Therefore, the DGT approach has the advantage that almost no sample preparation is necessary, but the EOF method is more sensitive to analyse low amounts of “total” PFAS in wastewater-based fertilizers.…”