Atmospheric deposition as a diffuse source of PFAS contamination of soils, ground and surface water resources

Atmospheric deposition is an important pathway for PFAS to enter soil, surface water and groundwater, but their persistence and mobility complicate source identification. Understanding these pathways is crucial for safeguarding drinking water production, as PFAS poses risks to human health. This study investigated atmospheric PFAS deposition in two drinking water production locations located 135 km apart, highlighting its potential impact in the contaminating soil, surface water, and groundwater. Aerosol and deposition samples were collected along with meteorological data at both locations. To link the deposition of PFAS fluxes to surface water and groundwater contamination, water samples were collected from hydrologically isolated heathland pools. PFAS concentrations were analysed in all samples, and tracer ions (Na⁺, Mg²⁺) were measured in aerosols to explore associations with sea-spray aerosols (SSA). PFAS concentrations in aerosols were consistent between the two sites, with 12 of 14 PFAS detected at both locations. Trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFMS) were most abundant PFAS compounds, followed by PFBA, PFOA, PFOS, and 6:2 FTS. The PFAS composition of deposition fluxes were similar to aerosol concentrations, suggesting relatively unbiassed atmospheric removal of PFAS by deposition. A unique PFAS fingerprint was identified for future source tracing, while the absence of 6:2 FTS in deposition samples highlighted its distinct atmospheric behaviour. PFAS patterns in heathland pools matched those in aerosol and deposition samples, confirming atmospheric deposition as a the main contamination source. PFPeS, PFHxS, PFHpS, and branched PFOA were present in water samples, but lacking in aerosol and deposition samples. This absence is likely due to historical deposition and accumulation processes, highlighting the potential impact of legacy PFAS inputs. Soils and surface waters may act as both sinks and secondary sources of PFAS, releasing contaminants into groundwater and perpetuating risks. Wind data indicated a potential HFPO-DA source northwest of one location, while PFAS levels were not linked to SSA tracer ions at either location. Consistent results between the two locations indicate that the bulk of PFAS contamination is linked to diffuse, rather than local, sources. The findings of this study highlight the important role of atmospheric deposition as a source of diffuse PFAS contamination to soils, surface waters and groundwater and emphasize that historical PFAS input and accumulation processes should be taken into account when assessing risks and mitigation strategies to protect drinking water supplies and public health.