US Department of Defense-Funded Fate and Transport Research on Per- and Polyfluoroalkyl Substances at Aqueous Film-Forming Foam-Impacted Sites

Chronic Toxicity of Per- and Polyfluoroalkyl Substance-Free Firefighting Foams to Aquatic Organisms

Amid global concern regarding the health and environmental impacts of per- and polyfluoroalkyl substances (PFAS), there is an urgent need to develop and implement alternative products without PFAS. Consequently, PFAS-free firefighting foams used for fire suppression have been developed for use in military and residential settings. To facilitate the selection of lower-risk PFAS-free foams, the present study focused on the chronic toxicity of seven PFAS-free and one PFAS-containing foam to six aquatic species. Target species included two cladocerans, Daphnia magna and Ceriodaphnia dubia; the chironomid Chironomus dilutus; the mysid Americamysis bahia; and two fish species, Pimephales promelas and Cyprinodon variegatus, with endpoints including growth, development, reproduction, and survival. To facilitate comparison and product toxicity rankings, effective concentrations (20%, 50%) and no- and lowest-observed-effect concentrations (NOECs and LOECs, respectively) were calculated. Effective concentrations, NOECs, and LOECs varied by over an order of magnitude among foams and species, with several of the PFAS-free formulations ranked as highly toxic based on US Environmental Protection Agency alternatives assessment hazard criteria. Overall, the PFAS-free foams were found to exhibit either similar or greater toxicity compared to the PFAS-containing reference foam across several species and endpoints. Nonmonotonic and hormetic dose responses were observed in D. magna for several of the tested foams, with increased reproduction and growth at intermediate exposures. Generally, tested foam toxicity rankings were consistent with a related acute toxicity study using the same species and formulations, and other research using soil invertebrates. Combined with related efforts for other taxa including mammals, birds, and plants, the present research will facilitate the selection of appropriate PFAS-free firefighting foams that minimize harm to the environment. Environ Toxicol Chem 2024;00:1-19. © 2024 SETAC.

Spatial and temporal distribution of perfluoroalkyl substances (PFAS) detected after an aqueous film forming foam (AFFF) spill

In 2015, > 460,000 L of aqueous film-forming foam (AFFF) and fire suppressors containing per- and polyfluoroalkyl substances (PFAS) were used to combat a fire at a petrochemical fuel storage terminal in the Port of Santos (Brazil). Sediments from seven sites were sampled repeatedly from 2 weeks to 1 year after the fire (n = 30). Ʃ15PFAS concentrations ranged from 115 to 15,931 pg g-1 dry weight (dw). Perfluorooctane sulfonic acid (PFOS) was the most frequently detected compound with concentrations ranging from 363 to 4517 (average = 1603) pg g-1dw to <47.1 to 642 (average = 401) pg g-1 dw, followed by perfluorohexanoic acid (PFHxA) (from 38.8 to 219 (average = 162) pg g-1 dw after 15 days and from <20.8 to 161 (average = 101) pg g-1 dw one year later). Together, the hydrodynamics and fire events documented in the region were important features explaining the spread of PFAS.

Comparative Toxicity of Seven Aqueous Film-Forming Foam to In Vitro Systems and Mus

The comparative toxicity of six per- and polyfluoroalkyl substance (PFAS)-free and one PFAS-containing aqueous film-forming foam (AFFF) was evaluated in an outbred mouse species as well as several in vitro assays. The in vivo toxicological profile of PFAS-free AFFFs in short-term, high-concentration exposures is different than that of a PFAS-containing AFFF. The PFAS-containing reference product induced increased liver weights, while the PFAS-free AFFFs were linked to either decreased or unaffected relative liver weights. The in vitro toxicological profile across PFAS-free AFFFs was uniform except in the Microtox® assay, where thresholds were variable and spanned several orders of magnitude. This direct comparison of products through short-term toxicity tests and in vitro screenings represents early data to support evaluation of potential regrettable substitutions when selecting alternative PFAS-free AFFFs. Further work in diverse taxa (e.g., aquatic organisms, terrestrial invertebrates, birds) and mammalian studies capturing sensitive life stages will refine and expand this data set across a range of risk-relevant toxicological endpoints. Environ Toxicol Chem 2023;42:2364-2374. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Molecular detection of per- and polyfluoroalkyl substances in water using time-of-flight secondary ion mass spectrometry

Detection of per- and polyfluoroalkyl substances (PFASs) is crucial in environmental mitigation and remediation of these persistent pollutants. We demonstrate that time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a viable technique to analyze and identify these substances at parts per trillion (ppt) level in real field samples without complicated sample preparation due to its superior surface sensitivity. Several representative PFAS compounds, such as perfluorooctanesulfonic acid (PFOS), perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluoheptanoic acid (PFHpA), and perfluorononanoic acid (PFNA), and real-world groundwater samples collected from monitoring wells installed around at a municipal wastewater treatment plant located in Southern California were analyzed in this work. ToF-SIMS spectral comparison depicts sensitive identification of pseudo-molecular ions, characteristic of reference PFASs. Additionally, principal component analysis (PCA) shows clear discrimination among real samples and reference compounds. Our results show that characteristic molecular ion and fragments peaks can be used to identify PFASs. Furthermore, SIMS two-dimensional (2D) images directly exhibit the distribution of perfluorocarboxylic acid (PFCA) and PFOS in simulated mixtures and real wastewater samples. Such findings indicate that ToF-SIMS is useable to determine PFAS compounds in complex environmental water samples. In conclusion, ToF-SIMS provides simple sample preparation and high sensitivity in mass spectral imaging, offering an alternative solution for environmental forensic analysis of PFASs in wastewater in the future.

Ecotoxicity and Accumulation of Perfluorononanoic Acid in the Fathead Minnow (Pimephales promelas) and an Approach to Developing Protective Thresholds in the Aquatic Environment Through Species Sensitivity Distribution

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment. Locations where PFAS-containing aqueous film-forming foam (AFFF) has been used or accidentally released have resulted in persistently high concentrations of PFAS, including in surface water that may be adjacent to release sites. Perfluorooctane sulfonic acid (PFOS) is most frequently measured near AFFF release sites; however, other PFAS are being quantified more frequently and, of those, perfluorononanoic acid (PFNA) is common. The goal of our study was to fill data gaps on PFNA toxicity to freshwater fish using the fathead minnow (Pimephales promelas). We aimed to understand how PFNA may impact apical endpoints following a 42-day exposure to mature fish and a 21-day exposure to second-generation larval fish. Exposure concentrations were 0, 124, 250, 500, and 1000 µg/L for both adult (F0) and larval (F1) generations. The most sensitive endpoint measured was development in the F1 generation at concentrations of ≥250 µg/L. The 10% and 20% effective concentration of the tested population for the F1 biomass endpoint was 100.3 and 129.5 µg/L, respectively. These data were collated with toxicity values from the primary literature on aquatic organisms exposed to PFNA for subchronic or chronic durations. A species sensitivity distribution was developed to estimate a screening-level threshold for PFNA. The resulting hazard concentration protective of 95% of the freshwater aquatic species was 55 µg PFNA/L. Although this value is likely protective of aquatic organisms exposed to PFNA, it is prudent to consider that organisms experience multiple stressors (including many PFAS) simultaneously; an approach to understand screening-level thresholds for PFAS mixtures remains an uncertainty within the field of ecological risk assessment. Environ Toxicol Chem 2023;42:2229-2236. © 2023 SETAC.

Sunrise of PFAS Replacements: A Perspective on Fluorine-Free Foams

One type of firefighting foam, referred to as aqueous filmforming foams (AFFF), is known to contain per- and polyfluoroalkyl substances (PFAS). The concerns raised with PFAS, and their potential environmental and health impacts, have led to a surge in research on fluorine-free alternatives both in the United States and globally. Particularly, in January 2023, a new military specification (MIL-PRF-32725) for fluorine-free foam was released in accordance with Congressional requirements for the U.S. Department of Defense. This paper provides a critical analysis of the present state of the various fluorine-free options that have been developed to date. A nuanced perspective of the challenges and opportunities of more sustainable replacements is explored by examining the performance, cost, and regulatory considerations associated with these fluorine-free alternatives. Ultimately, this evaluation shows that the transition to fluorine-free replacements is likely to be complex and multifaceted, requiring careful consideration of the trade-offs involved. Yet, the ongoing work will provide valuable insights for future research on alternatives to AFFF and enhancing the safety and sustainability of fire suppression systems.

Next-generation PFAS 6:2 fluorotelomer sulfonate reduces plaque formation in exposed white-footed mice

6:2 fluorotelomer sulfonate (6:2 FTS) has been used as a replacement for legacy per- and polyfluoroalkyl substances (PFAS). We assessed reproductive and developmental effects in a human-wildlife hybrid animal model based on the association of adverse effects linked to legacy PFAS with these sensitive life stages. In this study, white-footed mice were exposed orally to 0, 0.2, 1, 5, or 25 mg/kg-day 6:2 FTS for 112 days (4 weeks premating exposure plus at least 4 weeks mating exposure). Pregnancy and fertility indices were calculated, and litter production, total litter size, live litter size, stillbirths, litter loss, average pup weight, and pinna unfolding were assessed. Sex steroid and thyroid hormone serum levels were assessed. Body weight, histopathology, and immune function were also assessed in this study. Reproductive endpoints were not significantly altered in response to 6:2 FTS. Spleen weight increased in male mice dosed with 6:2 FTS. Immune function determined via a plaque-forming cell (PFC) assay was decreased in both male and female mice in the 2 highest doses. A low benchmark dose was calculated based on PFCs as the critical effect and was found to be 2.63 and 2.26 mg/kg-day 6:2 FTS in male and female mice, respectively. This study characterizes 6:2 FTS as being potentially immunotoxic with little evidence of effect on reproduction and development; furthermore, it models acceptable levels of exposure. These 2 pieces of information together will aid regulators in setting environmental exposure limits for this PFAS currently thought to be less toxic than other PFAS.

Application of High-Resolution Mass Spectrometry to Evaluate UV-Sulfite-Induced Transformations of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF)

UV-sulfite has been shown to effectively degrade per- and polyfluoroalkyl substances (PFASs) in single-solute experiments. We recently reported treatment of 15 PFASs, including perfluoroalkyl sulfonic acids (PFSAs), perfluoroalkyl carboxylic acids (PFCAs), and fluorotelomer sulfonic acids (FTSs), detected in aqueous film-forming foam (AFFF) using high-resolution liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) targeted analysis. Here, we extend the analysis within those original reaction solutions to include the wider set of PFASs in AFFF for which reactivity is largely unknown by applying recently established LC-QTOF-MS suspect screening and semiquantitative analysis protocols. Sixty-eight additional PFASs were detected (15 targeted + 68 suspect screening = 83 PFASs) with semiquantitative analysis, and their behavior was binned on the basis of (1) detection in untreated AFFF, (2) PFAS photogeneration, and (3) reactivity. These 68 structures account for an additional 20% of the total fluorine content in the AFFF (targeted + suspect screening = 57% of total fluorine content). Structure-reactivity trends were also revealed. During treatment, transformations of highly reactive structures containing sulfonamide (-SO₂N-) and reduced sulfur groups (e.g., -S- and -SO-) adjacent to the perfluoroalkyl [F(CF₂)_n-] or fluorotelomer [F(CF₂)_n(CH₂)₂-] chain are likely sources of PFCA, PFSA, and FTS generation previously reported during the early stages of reactions. The results also show the character of headgroup moieties adjacent to the F(CF₂)_n-/F(CF₂)_n(CH₂)₂- chain (e.g., sulfur oxidation state, sulfonamide type, and carboxylic acids) and substitution along the F(CF₂)_n- chain (e.g., H-, ketone, and ether) together may determine chain length-dependent reactivity trends. The results highlight the importance of monitoring PFASs outside conventional targeted analytical methodologies.

Reproductive and developmental toxicity of perfluorooctane sulfonate (PFOS) in the white-footed mouse (Peromyscus leucopus)

Concerns about per- and polyfluoroalkyl substances (PFAS) stem from their ubiquitous presence in the environment, bioaccumulation, resistance to degradation, and toxicity. Previously, toxicity data relevant to ecological risk assessment has largely been aquatic, terrestrial invertebrates, or avian in origin. In this study, repeated oral exposures of perfluorooctane sulfonate (PFOS) were administered to white-footed mice (Peromyscus leucopus) to evaluate effects on reproduction and development. Prenatal exposure to high doses of PFOS caused neonatal mortality, though growth and development were unaffected by low doses. Additionally, parental (P) generation animals exhibited increased liver:body weight, increased hepatocyte cytoplasmic vacuolization, and decreased serum thyroxine (T4) levels. Total litter loss was selected as the protective critical effect in this study resulting in a benchmark dose low (BMDL) of 0.12 mg/kg-d PFOS. Importantly, PFOS exposure has been linked to reduced adult recruitment in myriad species and at similar thresholds to this study. Similarities in critical/toxicologic effects across taxa may add confidence in risk assessments at sites with multiple taxa or environments.

Biotransformation of 6:2 Fluorotelomer Thioether Amido Sulfonate in Aqueous Film-Forming Foams under Nitrate-Reducing Conditions

Despite the prevalence of nitrate reduction in groundwater, the biotransformation of per- and polyfluoroalkyl substances (PFAS) under nitrate-reducing conditions remains mostly unknown compared with aerobic or strong reducing conditions. We constructed microcosms under nitrate-reducing conditions to simulate the biotransformation occurring at groundwater sites impacted by aqueous film-forming foams (AFFFs). We investigated the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a principal PFAS constituent of several AFFF formulations using both quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) and qualitative high-resolution mass spectrometry analyses. Our results reveal that the biotransformation rates of 6:2 FtTAoS under nitrate-reducing conditions were about 10 times slower than under aerobic conditions, but about 2.7 times faster than under sulfate-reducing conditions. Although minimal production of 6:2 fluorotelomer sulfonate and the terminal perfluoroalkyl carboxylate, perfluorohexanoate was observed, fluorotelomer thioether and sulfinyl compounds were identified in the aqueous samples. Evidence for the formation of volatile PFAS was obtained by mass balance analysis using the total oxidizable precursor assay and detection of 6:2 fluorotelomer thiol by gas chromatography-mass spectrometry. Our results underscore the complexity of PFAS biotransformation and the interactions between redox conditions and microbial biotransformation activities, contributing to the better elucidation of PFAS environmental fate and impact.

Anaerobic Microbial Dechlorination of 6:2 Chlorinated Polyfluorooctane Ether Sulfonate and the Underlying Mechanisms

The microbial transformation potential of 6:2 chlorinated polyfluorooctane ether sulfonate (6:2 Cl-PFESA) was explored in anaerobic microbial systems. Microbial communities from anaerobic wastewater sludge, an anaerobic digester, and anaerobic dechlorinating cultures enriched from aquifer materials reductively dechlorinated 6:2 Cl-PFESA to 6:2 hydrogen-substituted polyfluorooctane ether sulfonate (6:2 H-PFESA), which was identified as the sole metabolite by non-target analysis. Rapid and complete reductive dechlorination of 6:2 Cl-PFESA was achieved by the anaerobic dechlorinating cultures. The microbial community of the anaerobic dechlorinating cultures was impacted by 6:2 Cl-PFESA exposure. Organohalide-respiring bacteria originally present in the anaerobic dechlorinating cultures, including Geobacter, Dehalobacter, and Dehalococcoides, decreased in relative abundance over time. As the relative abundance of organohalide-respiring bacteria decreased, the rates of 6:2 Cl-PFESA dechlorination decreased, suggesting that the most likely mechanism for reductive dechlorination of 6:2 Cl-PFESA was co-metabolism rather than organohalide respiration. Reductive defluorination of 6:2 Cl-PFESA was not observed. Furthermore, 6:2 H-PFESA exhibited 5.5 times lower sorption affinity to the suspended biosolids than 6:2 Cl-PFESA, with the prospect of increased mobility in the environment. These results show the susceptibility of 6:2 Cl-PFESA to microbially mediated reductive dechlorination and the likely persistence of the product, 6:2 H-PFESA, in anaerobic environments.

FluoroMatch 2.0-making automated and comprehensive non-targeted PFAS annotation a reality

Because of the pervasiveness, persistence, and toxicity of per- and polyfluoroalkyl substances (PFAS), there is growing concern over PFAS contamination, exposures, and health effects. The diversity of potential PFAS is astounding, with nearly 10,000 PFAS catalogued in databases to date (and growing). The ability to detect the thousands of known PFAS, and discover previously uncatalogued PFAS, is necessary to understand the scope of PFAS contamination and to identify appropriate remediation and regulatory solutions. Current non-targeted methods for PFAS analysis require manual curation and are time-consuming, prone to error, and not comprehensive. FluoroMatch Flow 2.0 is the first software to cover all steps of data processing for PFAS discovery in liquid chromatography-high-resolution tandem mass spectrometry samples. These steps include feature detection, feature blank filtering, exact mass matching to catalogued PFAS, mass defect filtering, homologous series detection, retention time pattern analysis, class-based MS/MS screening, fragment screening, and predicted MS/MS from SMILES structures. In addition, a comprehensive confidence level criterion is implemented to help users understand annotation certainty and integrate various layers of evidence to reduce overreporting. Applying the software to aqueous film forming foam analysis, we discovered over one thousand likely PFAS including previously unreported species. Furthermore, we were able to filter out 96% of features which were likely not PFAS. FluoroMatch Flow 2 increased coverage of likely PFAS by over tenfold compared to the previous release. This software will enable researchers to better characterize PFAS in the environment and in biological systems.

The Case for Direct Measures of Soil-to-Groundwater Contaminant Mass Discharge at AFFF-Impacted Sites

Many entities around the world are initiating massive field campaigns to characterize the environmental distribution of per- and polyfluoroalkyl substances (PFAS), particularly at aqueous film-forming foam (AFFF) impacted sites where historic point-source discharges occurred at the ground surface. Concurrently, many regulatory agencies are publishing criteria used in practice to define the "nature and extent" of PFAS-impacted environmental media. Specific to the soil-to-groundwater transport pathway protective of the groundwater ingestion end point, these soil criteria (or screening values) are to date exclusively based on the traditional approach used for hydrophobic organics with a number of simplifying assumptions. Research has clearly contradicted these assumptions, yet alternative methodologies have yet to emerge from the literature. This Perspective provides a rationale for why alternative approaches are critically necessary and proposes the application of lysimetry as a practical solution to accurately assess PFAS transport within unsaturated vadose zone soils. Ultimately, there is an urgent need to justify soil remediation on the basis of groundwater protection and to prioritize remedial efforts in order to optimize limited fiscal resources.

Identifying and Managing Aqueous Film-Forming Foam-Derived Per- and Polyfluoroalkyl Substances in the Environment

The use of aqueous film-forming foam (AFFF) has resulted in the widespread occurrence of per- and polyfluoroalkyl substances (PFAS) in groundwater, drinking water, soils, sediments, and receiving waters throughout the United States and other countries. We present the research and development efforts to date by the Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP) to measure PFAS in the environment, characterize AFFF-associated sources of PFAS, understand PFAS fate and behavior in the environment, assess the risk to ecological receptors, develop in situ and ex situ treatment technologies for groundwater, treat soils and investigation-derived wastes, and examine the ecotoxicity of PFAS-free fire suppression formulations. Environ Toxicol Chem 2021;40:24-36. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Mass-Based, Field-Scale Demonstration of PFAS Retention within AFFF-Associated Source Areas

Transport of poly- and perfluoroalkyl substances (PFAS) at aqueous film-forming foam (AFFF)-impacted sites is limited by various processes that can retain PFAS mass within the source area. This study used concentration data obtained via a high-resolution sampling and analytical protocol to estimate the PFAS mass distribution in source and downgradient areas of a former firefighter training area. The total PFAS mass present at the site was approximately 222 kg, with 106 kg as perfluoroalkyl acids (PFAAs) and 116 kg as polyfluorinated precursors. Zwitterionic and cationic PFAS represented 83% of the total precursor mass and were found primarily in the source and up/side-gradient areas (75%), likely due to preferential hydrophobic partitioning, electrostatic interactions, and diffusion into lower-permeability soils. Based on the release history and the high percentage of total PFAS mass represented by precursors (primarily electrochemical fluorination-derived compounds), the estimated conversion rate of precursors to PFAAs was less than 2% annually. Eighty-two percent of the total PFAS mass was encountered in lower-permeability soils, which limited the potential for advection and transformation. This contributed to a 99% decrease in the mass discharge rate at the far-downgradient plume (0.048 kg/yr compared to the near-source area (3.6 kg/yr)). The results provide field-scale evidence of the importance of these PFAS retention processes at sites where AFFF has been released.

Rapid Characterization of Emerging Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foams Using Ion Mobility Spectrometry-Mass Spectrometry

Aqueous film-forming foams (AFFF) are mixtures formulated with numerous hydrocarbon- and fluoro-containing surfactants. AFFF use leads to environmental releases of unknown per- and polyfluoroalkyl substances (PFAS). AFFF composition is seldom disclosed, and their use elicits concerns from both regulatory agencies and the public because PFAS are persistent in the environment and potentially associated with adverse health effects. In this study, we demonstrate the use of coupled liquid chromatography, ion mobility spectrometry, and mass spectrometry (LC-IMS-MS) to rapidly characterize both known and unknown PFAS in AFFF. Ten AFFF formulations from seven brands were analyzed using LC-IMS-MS in both negative and positive ion modes. Untargeted analysis of the formulations was followed by feature identification of PFAS-like features utilizing database matching, mass defect and homologous series evaluation, and MS/MS fragmentation experiments. Across the tested AFFF formulations, we identified 33 homologous series; only ten of these homologous series have been previously reported. Among tested AFFF, the FireStopper (n = 85) contained the greatest number of PFAS-like features and Phos-Check contained zero. This work demonstrates that LC-IMS-MS-enabled untargeted analysis of complex formulations, followed by feature identification using data-processing algorithms, can be used for rapid exposure characterization of known and putative PFAS during fire suppression-related contamination events.

Bioaccumulation of Novel Per- and Polyfluoroalkyl Substances in Mice Dosed with an Aqueous Film-Forming Foam

Per- and polyfluoroalkyl substances (PFASs) are widespread in the blood of the general human population, and their bioaccumulation is of considerable scientific and regulatory interest. PFAS exposure resulting from aqueous film-forming foam (AFFF) ingestion is poorly understood due to the complexity of AFFF mixtures and the presence of polyfluorinated substances that may undergo metabolic transformation. C57BL/6 mice were dosed with an AFFF primarily containing electrochemically fluorinated PFASs for 10 days, followed by a 6 day depuration. Urine was collected throughout the study and serum was collected post-depuration. Samples were analyzed via high-resolution mass spectrometry. Relative to the dosing solution, C6 and C7 perfluoroalkyl sulfonates (PFSAs) were enriched in dosed mouse serum, suggesting in vivo transformation of sulfonamide precursors. Some substituted C8 PFSAs [keto-perfluorooctane sulfonate (PFOS), hydrogen-PFOS, and unsaturated PFOS] appeared to be more bioaccumulative than linear PFOS, or were formed in vivo from unidentified precursors. A series of seven peaks in dosed mouse serum was tentatively identified as sulfonimide dimers that were either a minor component of the AFFF or were formed via metabolism of other AFFF components. This work highlights the importance of sulfonamide precursors in contributing to bioaccumulation of AFFF-associated PFSAs and identifies several classes of potentially bioaccumulative novel PFASs that warrant further investigation.