Sorption of Hexafluoropropylene Oxide Dimer Acid to Sediments: Biogeochemical Implications and Analytical Considerations

The sedimentary fate of hexafluoropropylene oxide dimer acid (HFPO-DA) was investigated over a 12 week time series in HFPO-DA-amended (600 ng of spike addition) freshwater and estuarine tidal sediments collected in southeastern North Carolina. A 40–59% decrease in the concentration of HFPO-DA was observed within 14 days for freshwater and estuarine sediments. This decrease could not be explained by biological degradation because there were no statistically significant differences in HFPO-DA loss between bioactive and autoclaved sediments and no degradation products were detected via high-resolution mass spectrometry. An additional 2–3% of HFPO-DA was recovered when sediments were subjected to a more aggressive extraction (12 h soak with 80:20 1 M NaOH in methanol/water), suggesting that HFPO-DA sorbs strongly to sediments and remains undetected by less aggressive PFAS sediment extraction methods. Results of this study highlight that (1) PFAS sediment extraction methodologies need to be re-evaluated, particularly as alternative compounds continue to be synthesized and discovered, and (2) studies employing less aggressive extraction methodologies significantly underestimate PFAS contamination in aquatic sediments. Given that HFPO-DA is resistant to biological degradation and has a high sorption affinity, aquatic sediments may be a more significant long-term sink for HFPO-DA and other short-chain alternative PFAS than previously thought.