Fate of Hexafluoropropylene Oxide Dimer Acid in Sediments of the Cape Fear River Estuary, North Carolina

Abstract:

Aquatic sediments may act as a substantial reservoir of per- and polyfluoroalkyl substances (PFAS) especially as levels of these contaminants rise in overlying surface waters. Biodegradation is a potentially important removal mechanism for PFAS in sediments because sediments are a natural environment for benthic organisms and microbial communities. As legacy PFAS compounds such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were phased out of production there was a shift to shorter chain PFAS compounds that are branched with ether functionalities such as hexafluoropropylene oxide-dimer acid (HFPO-DA; ammonium salt commonly known as GenX) intended to increase environmental degradability. In this study, we investigated the biogeochemical fate of HFPO-DA over a 12-week time series in HFPO-DA-amended (600 ng spike addition) freshwater and estuarine tidal sediments collected in southeastern North Carolina. A 40% and 59% decrease in HFPO-DA was observed within 14 days for freshwater and estuarine sediments, respectively. This decrease could not be explained by biological and/or chemical degradation because trends were consistent in both bioactive and sterile sediments and no degradation products were detected via high-resolution mass spectrometry. An additional 2-4% of HFPO-DA was recovered when sediments were subjected to a more aggressive extraction (12-hour incubation with 1 M NaOH), suggesting that HFPO-DA may sorb strongly to sediments and remain undetected by less aggressive PFAS sediment extraction methods. The ability to extract more targeted PFAS upon more aggressive extraction has important implications because it suggests that studies employing more commonly utilized methodologies might significantly underestimate PFAS contamination in aquatic sediments. Given that HFPO-DA is resistant to biological and/or chemical 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.