It's raining PFAS in South Florida: Occurrence of per- and polyfluoroalkyl substances (PFAS) in wet atmospheric deposition from Miami-Dade, South Florida

Atmospheric deposition plays a crucial role in the fate and transport of per and polyfluoroalkyl substances (PFAS), especially in areas far from production sites. It could be comparable to or exceed point source inputs. This study assessed the occurrence and composition of legacy and emergent PFAS in wet deposition in the Miami-Dade area, South Florida. Rainwater samples were collected from three locations in Miami-Dade County between 2021 and November 2022 (N = 42), The sample preparation methodology was validated, involving solid phase extraction (SPE) using a weak anion exchange (WAX) cartridge, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using isotopically labeled internal standards. The results indicate that 74 % of the major components were perfluoroalkyl carboxylic acids (PFCAs), while 12 % were perfluoroalkyl sulfonic acids (PFSAs). Specifically, perfluoro-n-butanoic acid (PFBA) was the most frequently detected compound, detected in 95 % of the samples. Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA) levels detected are above EPA-updated health advisory levels for drinking water, averaging 0.24 ng L⁻¹ and 0.32 ng L⁻¹, respectively. PFOS and PFOA fluxes in the Southeast were similar to those reported in the Northeast United States. Compounds such as perfluoro-1-hexanesulfonate (4:2 FTS), perfluoro-1-octanesulfonate (6:2 FTS), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonic acid (PFHxS), PFOA, perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA) showed significant seasonal variation, with higher concentrations during the dry season. The perfluoroheptanoic acid (PFHpA)/PFOA and PFOA/PFNA ratios suggest a mixture of point and non-point sources in rainwater. Air mass simulation indicated that contribution from Northwestern influences the increase in the sum of PFAS.