Equilibrium Passive Sampling of Per- and Polyfluoroalkyl Substances (PFAS): Design, Validation, Performance Evaluation, and Cross-Environment Application

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants, some of which are mobile in aqueous systems, making quantification of their freely dissolved concentrations important for evaluating transport, partitioning, and exposure potential. Conventional grab sampling provides a snapshot in time and may disturb solid–water equilibria. Equilibrium-based passive sampling offers an alternative approach to estimate the freely dissolved fraction, but its performance for PFAS across different water chemistry conditions requires further evaluation. The overarching goal of this research was to develop and validate equilibrium-based passive sampling for quantifying freely dissolved PFAS in aqueous systems. The work addressed four questions: 1. Can the concentration of freely dissolved PFAS be estimated using an equilibrium sampler with a non-sorptive receiving phase? 2. How do sampler materials and matrix salinity influence PFAS adsorption, diffusion, and equilibration? 3. How do PFAS physicochemical properties affect their diffusion across sampler membranes? 4. Can performance reference compounds (PRCs) be used to estimate PFAS uptake by equilibrium passive samplers? The uptake of PFAS by a peeper sampler was evaluated through laboratory and field experiments to assess its suitability for monitoring anionic PFAS in surface water and sediment porewater (Chapter 3). Results indicated that PFAS uptake was driven by diffusion through a polycarbonate membrane used as the sampling window, and concentrations measured by the sampler were generally comparable (± 30%) to those in grab samples. Material screening experiments further indicated that peepers made of polycarbonate membranes and high-density polyethylene (HDPE) containers are suitable for freshwater deployment, whereas silver membranes and stainless steel containers may be better suited to saline water, where PFAS adsorption to sampler surfaces is more pronounced (Chapters 4 and 5). Performance reference compounds (PRCs), including isotopically labelled PFAS, were also evaluated as tracers of native PFAS uptake and equilibration. Their release kinetics were comparable to those of the native PFAS, supporting their use to confirm equilibrium and quantify non-equilibrium under both freshwater and saline conditions. However, under saline conditions, stronger interactions between PFAS and silver membranes were observed, leading to slower uptake, particularly for longer-chain compounds (C ≥ 9) (Chapters 4 and 5). A regenerated-cellulose dialysis bag (RCDB) sampler (Chapter 5) was also evaluated as an equilibrium sampler for PFAS in both freshwater and synthetic seawater. Equilibrium was reached for C4–C9 compounds within 5–10 days, and the measured concentrations were within ±20% of those in grab samples. Overall, the results indicate that equilibrium passive sampling can be applied to quantify freely dissolved PFAS across a range of aqueous environments. The roles of sampler material, salinity, and PFAS physicochemical properties in controlling uptake and equilibration were clarified, which supports further application of equilibrium sampling for PFAS monitoring.