Concentrations of Per- and Polyfluoroalkyl Substances in the Rainwater of South-Eastern Australia

Abstract Atmospheric deposition contributes to the long-range transport of per- and polyfluoroalkyl substances (PFAS). It is thus a potentially important source of these compounds to seas, lakes and other water bodies. However, measurements of PFAS in southern hemisphere rain are limited. Here we present data on PFAS in Australian rainwater. Eight of the 30 compounds tested for were detected, with substantial variation in amounts and composition. The concentration of ∑30 PFAS in rain was 18.05 ng/L in 2024 and 4.95 ng/L in 2025. Longer-chain (>C7) compounds were the predominant class during the wet autumn period, whereas shorter-chain (C4–C7) PFAS were more prevalent during the drier summer. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) modelling indicated that air originating over the ocean had the lowest concentrations of PFAS, whereas air that passed over land had the highest concentrations. The concentrations of Perfluorooctanoic acid and Perfluorooctanesulfonic acid (PFOS) in rainwater did not exceed current Australian drinking water guidelines. Concentrations of PFOA exceeded the U.S. Environmental Protection Agency Lifetime Drinking Water Health Advisory limits in 2024 and 2025; PFOS concentrations exceeded the guidelines in 2025. Preliminary calculations based on Melbourne rainfall and the surface area of Port Philip Bay indicated that rainwater could contribute ∼10.6 kg of PFAS to the bay each year.