Calibration of Perfluorinated Alkyl Acid Uptake Rates by a Tube Passive Sampler in Water

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a group of 4000+ man-made compounds of great concern due to their environmental ubiquity and adverse effects. Despite general interest, few reliable detection tools for integrative passive sampling of PFAS in water are available. A microporous polyethylene tube with a hydrophilic–lipophilic balance sorbent could serve as a flow-resistant passive sampler for PFAS. The tube’s sampling rate, R s, was predicted based on either partitioning and diffusion or solely diffusion. At 15 °C, the laboratory-measured R s for perfluorohexanoic acid of 100 ± 81 mL day–1 was better predicted by a partitioning and diffusion model (48 ± 1.8 mL day–1) across 10–60 cm s–1 water flow speeds (15 ± 4.2 mL day–1 diffusion only). For perfluorohexane sulfonate, R s at 15 °C were similarly different (110 ± 60 mL day–1 measured, 120 ± 63 versus 12 ± 3.4 mL day–1 in respective models). R s values from field deployments were in between these estimates (46 ± 40 mL day–1 for perfluorohexanoic acid). PFAS uptake was not different for previously biofouled membranes in the laboratory, suggesting the general applicability of the sampler in environmental conditions. This research demonstrates that the polyethylene tube’s sampling rates are sensitive to the parameterization of the models used here and partitioning-derived values should be used.

Rebuttal to Correspondence on “Calibration of Perfluorinated Alkyl Acid Uptake Rates by a Tube Passive Sampler in Water”

“…However, our previous work showed that sorption is clearly a large factor that requires further experimentation before more complex models can be fully validated. 2 The time-dependent approach outlined in Booij et al seems to be in good agreement with our time-independent approach. 1 The modeling work proposed in Dunn et al…”

“…2 The time-dependent approach outlined in Booij et al seems to be in good agreement with our time-independent approach. 1 The modeling work proposed in Dunn et al…”

“…Booij et al and our published work agree on several key points. , Uptake by the tube sampler is primarily dominated by the high-density polyethylene membrane phase of the model. Sampling rates increase with increasing size of the PFAA, indicating the importance of sorption, rather than solely diffusion, on sampling rates. Biofouling is generally not of concern with respect to reducing sampling rates of various PFAS. …”

“…Their model appears somewhat sensitive to chain length, showing an increase in sampling rate from PFPeA (20 mL day –1 ) to PFHxA but no increase from PFHxA to PFOA, in contrast to ours (Table ). Ultimately, the submodeling proposed by Booij et al seems to suppress the impact of sorption overall, in favor of diffusion, explaining the increase in sampling rate for the low partitioning, fast diffusing PFPeA compound between the two approaches (Table ). However, our previous work showed that sorption is clearly a large factor that requires further experimentation before more complex models can be fully validated …”

“…The time-dependent approach outlined in Booij et al seems to be in good agreement with our time-independent approach . The modeling work proposed in Dunn et al 2023 is a simplified version of the resistance model . Additionally, it is agreed that all models need further evaluation, specifically improved parametrization of sorbent–water partitioning, membrane–water partitioning, and diffusivity of compounds.…”