Laboratory validation of an integrative passive sampler for per- and polyfluoroalkyl substances in water

Abstract

A passive sampler for per- and polyfluoroalkyl substances (PFAS) in water has been developed which uses a porous organosilica adsorbent. Some performance characteristics, which remained incompletely answered after prior lab- and field-based testing, were assessed. The integrated response mode of the sampler was verified in bench-scale experiments where the aqueous phase concentration was varied 50-fold in the flow across passive samplers. It was found that the passive samplers were able to accumulate analytes and provide an accurate time-averaged concentration in situations where the PFAS concentration changed significantly over time. The integrated response is facilitated by an average 40-fold slower back diffusion rate compared to PFAS adsorption rates, attributed to in-particle diffusion. The maximum deployment time was assessed using a multi-month laboratory-based sampling event. It was found that the integrated response was maintained over 90 days except for perfluorobutanoic acid (PFBA) and perfluorodecanoic acid (PFDA) where adsorption reached equilibrium after 45 and 60 days of total sampling time, respectively. The mechanism of PFAS adsorption was explored using a column breakthrough curve in combination with previously reported adsorption isotherm data. The use of isotopic dilution for PFAS measurement was studied by measuring the adsorption, recovery, and stability of mass labeled surrogates in laboratory analysis. Surrogates were quantitatively bound and determined to be stable for at least 4 weeks in the adsorbed state. Sampling rates for EPA Method 1633 compounds N-methyl perfluorooctanesulfonamidoacetic acid and N-methyl perfluorooctanesulfonamide were also measured, expanding the existing sampling rate database to a total of 21 PFAS species.