Deciphering PFAS in Rainwater: Sources, Distribution, and Environmental Impact

Abstract

ABSTRACT Per‐ and polyfluoroalkyl substances (PFAS) are stable, globally dispersed man‐made compounds used in a wide range of industrial processes and commercial products. Their persistence and mobility in the global environment are attributed to their chemical stability and various atmospheric pathways. PFAS may enter the atmosphere from multiple sources, including stack emissions, fugitive dust, surface water aerosolization, and even entrainment of wind‐born fire suppression foam. Upon entry into the air, they travel through the gas phase as aerosols and particle‐bound processes. Volatile precursor compounds such as fluorotelomer alcohols (FTOHs) and short‐chain PFAS can exist in the gas phase, while longer‐chain, ionized PFAS are typically transported as aerosols, on particulates, or as foam. PFAS are subsequently deposited through wet deposition (e.g., scavenging by raindrops) or dry deposition (e.g., settling of aerosols and particulates), contributing to their presence in soil, surface water, and groundwater at locations distant from the point of generation. Rainwater, in particular, serves as a key pathway for PFAS input to environmental media. This literature review synthesizes the outcomes of studies in 13 US states that examined the occurrence, transport, and deposition of PFAS via precipitation. Legacy compounds (e.g., PFOA, PFOS) and emerging short‐chain PFAS (e.g., trifluoroacetic acid [TFA], hexafluoropropylene oxide dimer acid [HFPO‐DA]) have been detected in rainwater, with evolving profiles reflecting regulation and shifting manufacturing practices. The persistent presence of TFA, especially, emphasizes its atmospheric persistence and worldwide distribution. Concentration patterns of PFAS are regionally variable, with high concentrations typically detected at urban and industrial sites and detectable ambient levels in remote regions, suggesting PFAS in precipitation may be a combination of both local sources and long‐range atmospheric transport. The types of precipitation events could play important roles in PFAS deposition. Stratiform events may collect more extensive regional inputs, whereas convective storms may be more efficient at collecting local emissions and fugitive dust, resulting in higher local PFAS concentrations. Urban surface runoff, which effectively collects precipitation over a large area, has the potential to be an adjunct or even predominant pathway of PFAS transport to receiving waters. In total, this review articulates the complexity of atmospheric PFAS occurrence and highlights the importance of integrated monitoring, source attribution, and varied regulatory approaches in addressing the environmental issues and public health concerns associated with PFAS deposition via precipitation.

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