Atmospheric Flux of Legacy and Emerging Per- and Polyfluoroalkyl Substances (PFAS) Through Wet and Dry Deposition at Wilmington, North Carolina

Abstract:

Per- and polyfluoroalkyl substances (PFAS) from direct and indirect sources are ubiquitous in the environment due to atmospheric transport. Wet and dry deposition of PFAS contaminate surface waters, soils, and groundwaters, and pose threats to human and environmental health. Although legacy PFAS have been studied in wet deposition previously, there remains a paucity of information on the short-chain and functionalized replacement PFAS in wet and dry deposition. Wet and dry deposition measurements were made in Wilmington, NC, using wet/dry samplers to collect event-based wet deposition and continuous 2-week dry deposition samples. Following extraction via weak anion exchange, the legacy and replacement PFAS including perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluoro-2-methoxy- acetic acid (PFMOAA), perfluoro-2-propoxypropanoic acid (PFMOPrA)/perfluoro-2-methoxypropanoic acid (PMPA), perfluoro-4-methoxybutanoic acid (PFMOBA), and hexafluoropropylene oxide dimer acid (HFPO-DA) were quantified by liquid chromatography coupled to electrospray ionization with triple quadrupole mass spectrometry. PFOS, HFPO-DA, and PFMOAA were more frequently detected (>58%) than the other compounds. Total concentrations ranged from below the limit of quantification to 110 ng/L in wet deposition, and 0.4 to 22 ng m^-2 day^-1 in dry deposition. Event-based flux through wet deposition was one to three orders of magnitude larger than daily flux through dry deposition, indicating these PFAS are more effectively removed from the atmosphere by wet deposition than dry deposition. The air mass origin had no apparent impact to the concentration or flux of PFAS in wet deposition, and the washout effect was observed in our data. These observations suggest that the particle-bound and gas-phase PFAS compounds that underwent atmospheric transport can be incorporated into raindrops and rapidly removed locally. The estimated annual flux of all six PFAS was 30 µg m^-2 through wet deposition and 1.3 µg m^-2 through dry deposition. Our results provide a first direct comparison of wet and dry PFAS deposition and annual flux.