Investigation of the effects of flow velocity on PFAS uptake in POCIS using a small-scale system

• A small-scale system was developed for Rs calibration under laminar flow. • Partition coefficients were quantified for ten PFAS with standard POCIS. • The small system verified strong dependence of Rs on flow velocity. • A benchtop-to-field Rs extrapolation strategy was developed by matching kw,CaSO4. To accurately determine the time-weighted average concentration of water micropollutants using passive sampling, the variability of the sampling rate ( R s ) under different water flow velocities ( v ) needs to be considered. Establishing a robust v – R s relationship requires R s to be evaluated across a wide range of v with replicate treatments, with most previous approaches relying on large-scale systems (>500 L) that are costly and labor-intensive, thus limiting data availability. To address this limitation, we developed a small-scale (500 mL) system for the resource-efficient evaluation of R s . Using this system, we demonstrated that the flow-dependent resistance component accounted for ≥ 86% of the overall mass transfer resistance for per- and polyfluoroalkyl substance (PFAS) uptake in a polar organic chemical integrative sampler (POCIS). The membrane-layer resistance, which is flow-independent, was significant for two of the six PFAS studied and was associated with pronounced transport retardation due to the relatively strong membrane affinity. Based on CaSO 4 dissolution experiments conducted in both the small-scale laminar-flow system and a large-scale (1,040 L) turbulent system, we demonstrated that equivalent R s values occurred when v small = 0.025∙ v large 1.6 (where v is in cm/s). The laboratory-derived v small –R s relationship can thus be extrapolated to the field-applicable v large –R s relationship using this equation. Overall, this study highlights the utility of a novel small-scale system for the analysis of POCIS uptake kinetics and provides an extendible framework for the accurate estimation of R s under field exposure conditions.