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. 2025 Apr 1;16:3118. doi: 10.1038/s41467-025-58040-w

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© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2025, corrected publication 2025

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Fig. 3 — A ∑PFCAs remain highest at the soil surface more than 15 years after sludge application (B) The surface soils are dominated by chain-lengths C10–C14, but subsurface are dominated by shorter chain-lengths (C4–C8). When PFCAs are grouped according to their inferred intermediate precursor compounds, the FTOHs, surface soils have more long chains (C) and subsurface soils have more short chains (D) than typical sidechain fluorotelomer polymers, but summed over the full soil profile, the homologue distribution compares reasonably with the inferred ultimate precursor (E). F Because of relatively higher mobility of shorter-chain PFCAs and perfluorosulfonates (PFSAs), compared to the surface-soil source, groundwater is burdened with more short chain PFCAs than long, with an absence of detections for PFDA (C10) and longer compounds. G Even 1.5 decades after sludge application, groundwater still contains up to two orders-of-magnitude higher PFCAs than the 2024 EPA MCLs of 10 (PFHxS, PFNA) and 4 (PFOA, PFOS) ng/L.