Underestimated burden of per-and polyfluoroalkyl substances in global surface waters and groundwaters

PFAS comprise more than 14,000 chemicals valued for oil- and water-repellency and thermal stability, and are persistent in the environment. Regulatory limits for PFAS in drinking water vary widely across jurisdictions (e.g., Health Canada’s 30 ng/L sum of all PFAS, EU’s 100 ng/L for 20 PFAS or 500 ng/L for total PFAS, proposed US EPA limits for PFOS and PFOA at 4 ng/L and a hazard index for PFNA, PFBS, PFHxS and GenX). Toxicity generally increases with fluorinated chain length. Despite numerous regional and compartment-specific studies, the global extent of PFAS in surface waters (SW) and groundwaters (GW) and the frequency of exceedance of drinking water guidelines remain unclear. This study aims to quantify the global extent and distribution of PFAS in SW and GW, evaluate exceedances against current and proposed drinking water regulations/advisories, and investigate likely sources—including PFAS embodied in consumer and industrial products—to inform assessments of environmental burden and mitigation needs.

Prior research has estimated global PFAS production and emissions, documented PFAS occurrence in environmental compartments, and identified that concentrations of select PFAS may exceed proposed planetary boundaries. Toxicological literature links higher fluorinated chain length with longer biological half-lives and increased concern. Numerous regional studies have measured PFAS in waters, but coverage is uneven and often targets a limited suite of legacy compounds. Analytical methods used in monitoring (e.g., US EPA methods 533, 537.1, 8327, draft 1633) typically quantify a subset of PFAS classes, often missing important precursor groups like fluorotelomer alcohols (FTOH). Assays such as the total oxidizable precursor (TOP) test indicate that a substantial fraction of PFAS precursors convert to perfluoroalkyl acids upon oxidation, revealing hidden PFAS mass not captured by routine targeted methods. However, TOP assay approaches vary and may not oxidize certain ether PFAS, complicating interpretation of environmental burden.

The authors compiled a global dataset of PFAS measurements by reviewing and collating 48,985 samples from 367 published papers and government websites (Supplementary Table 4). A core analysis subset summarized 273 environmental studies since 2004, including over 12,000 surface water and 33,900 groundwater samples, covering 57 distinct PFAS in groundwater on average (mean of 16 PFAS per study; up to 38) and a comparable scope in surface waters. Data processing included: conversion of reported concentrations to consistent units (ng/L for water; ppb for product matrices via appropriate conversions); extraction and geolocation of sampling coordinates (assigning a random major city when only country was reported for mapping purposes); handling of censored data by substituting values below detection limits with a random number between zero and the study-specific detection limit to reduce clustering bias (a sensitivity analysis also set BDL to zero); and classification of sites by source type (known AFFF, known non-AFFF such as production facilities/landfills, unknown). Analyses and statistical validation were conducted using Python scripts and Microsoft Excel. The study benchmarked measured PFAS suites against regulatory/analytical panels (US EPA methods 533, 537.1, 8327, draft 1633; EU 20-PFAS list; Health Canada total PFAS; US EPA PFOS/PFOA MCLs and Hazard Index) to evaluate exceedance frequencies. For source attribution and product composition, PFAS in 943 non-AFFF consumer products across 15 categories and 148 AFFF formulations were compiled from 38 and 11 literature studies respectively. PFAS were grouped into terminal classes (PFCAs, PFSAs) and precursor classes (fluorotelomers—FTOH, FTS, FTCA/FTUCA, etc.—sulfonamides, PAPs), plus novel/ether PFAS. Comparisons assessed how much of the total PFAS mass would be captured by draft EPA method 1633 and regulated subsets, and how TOP assay results implied unmeasured precursor burdens.

- Global extent and exceedances: - PFAS are pervasive in surface waters and groundwaters worldwide. Geographic hotspots (e.g., Australia, China, Europe, North America) reflect higher sampling intensity; comparable contamination likely exists elsewhere near high-use sites (e.g., airports/AFFF). - Groundwater exceedance rates depend on source classification and jurisdictional criteria. For known AFFF-source GW samples: 71% exceeded proposed US EPA Hazard Index (n=6,312), 72% exceeded proposed PFOS MCL (n=6,442), and 63% exceeded proposed PFOA MCL (n=6,447). For GW with no known source: 31% (HI; n=14,905), 50% (PFOS; n=15,351), 40% (PFOA; n=15,499). - For GW with no known source, exceedance of Health Canada’s total PFAS criterion (30 ng/L) occurred in 69% of samples (n=16,151), versus 6% for the EU 500 ng/L total PFAS criterion, and 16% for the EU 100 ng/L sum of 20 PFAS (n=16,143). Overall, a large fraction of GW would be unacceptable for drinking under many criteria. Surface waters show similar exceedance patterns for known AFFF sources, with lower exceedance for unknown or non-AFFF sources, consistent with shorter residence times. - Handling of BDL values (random 0–DL vs zero substitution) modestly affected exceedance rates; both approaches indicated substantial exceedances, with better resolution expected as detection limits decline. - Underestimation due to analyte coverage: - Monitoring typically quantifies a limited PFAS suite (LC-MS/MS methods), often omitting important precursors like FTOH (requiring GC-MS/MS; no current US EPA aqueous GC-MS/MS method). Consequently, environmental PFAS burdens are likely underestimated. - Limited application of TOP assays in waters, WWTP effluents, and landfill leachates reveals substantial hidden precursor mass converting to PFCAs, though TOP has limitations (incomplete oxidation of ether PFAS, lack of standardization). - Consumer product PFAS composition (non-AFFF): - Across 943 products, when multiple classes were measured, fluorotelomers are the dominant subclass by mass (median 72%), followed by PFCAs (25%), PAPs (14%), sulfonamides (7%), and PFSAs (4%). Many studies under-quantify fluorotelomers and PAPs relative to PFCAs/PFSAs. - If only PFAS in draft EPA method 1633 are counted, total PFAS mass in products is substantially underestimated. Method 1633 yields a median distribution across products of 73% PFCAs, 11% PFSAs, 16% fluorotelomers, 10% sulfonamides, 0.1% novel PFAS, with phosphate-based PFAS not quantified—overestimating PFCAs/PFSAs/sulfonamides by ~2.8–4.2x and underestimating fluorotelomers by ~25x relative to full quantitation. - Long-chain PFAS are prevalent: on average 66% of quantified PFAS mass in products are long-chain, and only about 4% are currently under the Stockholm Convention, rising to 18% when candidate long-chain PFCAs are included. - AFFF formulations: - In historic 3M AFFF (n=14), PFOS accounted for a median 51% of PFAS mass; other PFSAs and sulfonamides were also important. In Angus AFFF (n=28), fluorotelomers and PFCAs dominated (median 64% and 36%). In other AFFF samples without supplier identified (n=83), fluorotelomers were dominant (median 93%), particularly FTS (median 73% of total PFAS; n=69) and FTOH (median 10%; n=38). - Counting only draft EPA method 1633 analytes underrepresents total PFAS in AFFF by a median factor of 2.8. A substantial fraction of PFAS in historic 3M AFFF is subject to Stockholm Convention (~60%), while Angus AFFF contains none; for non-3M AFFF, inclusion of candidates/long-chain slightly increases regulatory coverage (~0.6–1%). - Evidence for under-measured FTOH: - Few water studies measured FTOH; two surface water datasets reported that FTOH constituted a median 53% (46–62%) of total PFAS in 16 urban river samples in South China and 2% (0.9–34%) in eight Bangladesh river samples. One WWTP study reported FTOH at ~8% of influent PFAS mass. These findings, combined with product data, indicate FTOH are an important, often unquantified contributor to environmental PFAS.

The study demonstrates that PFAS contamination in global surface and groundwaters frequently exceeds drinking water regulations or advisories, particularly near known sources such as AFFF sites and PFAS-using industries. Even in areas without identified sources, exceedance rates remain substantial across several regulatory frameworks. These results address the core question by quantifying the global extent and regulatory relevance of PFAS in waters, revealing that many supplies would be unsuitable for drinking under stringent criteria. The analysis highlights that current monitoring likely underestimates actual PFAS burdens because targeted methods focus on a narrow set of analytes, often excluding key precursors such as FTOH and phosphate-based PFAS, and because TOP assay limitations may still miss certain transformation products (e.g., ether PFAS). Differences in exceedance by jurisdiction reflect both varying thresholds and analyte lists. Observed lower exceedances in surface waters compared to groundwater for unknown or non-AFFF sources are consistent with shorter residence times and dilution/attenuation in surface systems. The documented PFAS compositions in consumer products and AFFF formulations explain the widespread detection of terminal PFCAs/PFSAs and indicate that large unmeasured precursor pools will continue to degrade to regulated PFAS, compounding long-term environmental burdens. The study underscores the need for expanded analytical capabilities (including GC-MS/MS for FTOH), harmonized methods, broader monitoring campaigns beyond suspected hotspots, and product-focused interventions to reduce future inputs.

A comprehensive global compilation of PFAS measurements shows that a large fraction of surface and groundwaters exceed existing or proposed drinking water advisories and regulations. Current monitoring practices and analytical panels substantially underestimate total PFAS burdens, particularly due to under-quantification of precursor classes such as fluorotelomers and FTOH. Product and AFFF composition data indicate that long-chain and precursor PFAS dominate, implying continued transformation to regulated terminal PFAS and sustained environmental and human exposure risks. To mitigate future burden, the study calls for broader and standardized analytical methods (including GC-MS/MS for FTOH), systematic global sampling beyond known hotspots, improved understanding of PFAS use in products, and development of regulatory and mitigation strategies that address PFAS as a class and capture precursor contributions. Future research should refine precursor-to-terminal transformation models, standardize TOP assay protocols, and evaluate health/ecological impacts across the broader PFAS universe.

The dataset relies on previously published studies and government data, constraining analyte coverage, analytical methods, and geographic representativeness; sampling is biased toward suspected contaminated sites. Censored data were handled by substitution (random between zero and detection limit), which, although tested in sensitivity analyses, can influence exceedance estimates. Geolocation approximations were used when only country-level data were available. Analytical methods primarily targeted PFCAs/PFSAs and select precursors, with limited or no direct measurement of key species such as FTOH in aqueous matrices, leading to likely underestimation of total PFAS. The TOP assay, while informative about precursors, lacks standardization and may not oxidize all PFAS (e.g., ether PFAS), potentially underrepresenting future burdens. Differences in jurisdictional thresholds and analyte lists complicate direct comparisons of exceedance rates.