Air-water interfacial collapse and rate-limited solid desorption control Perfluoroalkyl acid leaching from the vadose zone.

Some Per- and polyfluoroalkyl substances (PFAS) are strongly retained in the vadose zone due to their sorption to both soils and air-water interfaces. While significant research has been dedicated to understanding equilibrium behavior for these multi-phase retention processes, leaching and desorption from aqueous film-forming foam (AFFF) impacted soils under field relevant conditions can exhibit significant deviations from equilibrium. Herein, laboratory column studies using field collected AFFF-impacted soils were employed to examine the leaching of perfluoroalkyl acids (PFAAs) under simulated rainfall conditions. The HYDRUS 1-D model was calibrated to estimate the unsaturated hydraulic properties of the soil in a layered system using multiple boundary condtions. Forward simulations of equilibrium PFAS partitioning using the HYDRUS model and simplified mass balance calculations showed good agreement with the net PFAS mass flux out of the column. However, neither were able to predict the PFAS concentrations in the leached porewater. To better understand the mechanisms controlling the leaching behavior, the HYDRUS 1-D two-site leaching model incorporating solid phase rate limitation and equilibrium air-water interfacial partitioning was employed. Three variations of the novel model incorporating different forms of equilibrium air-water interfacial partitioning were considered using built-in numerical inversion. Results of numerical inversion show that a combination of air-water interfacial collapse and rate-limited desorption from soils can better predict the unique leaching behavior exhibited by PFAAs in AFFF-impacted soils. A sensitivity analysis of the initial conditions and rate-limited desorption terms was conducted to assess the agreement of the model with measured data. The models demonstrated herein show that, under some circumstances, laboratory equilibrium partitioning data can provide a reasonable estimation of total mass leaching, but fail to account for the significant rate-limited, non-Fickian transport which affect PFAA leaching to groundwater in unsaturated soils.

Per- and polyfluoroalkyl substances (PFAS) in grocery store foods: method optimization, occurrence, and exposure assessment.

Dietary exposure to per- and polyfluoroalkyl substances (PFAS) is poorly understood. Evaluating PFAS in food is complicated by the need to evaluate varied matrices and a lack of a standard, matrix-specific sample extraction methods. Prior food studies implemented universal rather than matrix-specific extraction approaches, which may yield false negatives and an underestimation of PFAS dietary exposure if methods are not suitable to all matrices. Here the objectives were to screen and optimize PFAS extraction methods for plants, tissues, and dairy; apply optimized extraction methods to a grocery store food survey; and compare estimated exposure to published reference doses (RfDs). Optimized, matrix-specific extractions generally yielded internal standard recoveries of 50-150% and matrix spike recoveries of 70-130%. The frequency of PFAS detection in grocery store foods (16 of 22 products) was higher than in previous work. PFAS were detected at concentrations of 10 ng kgdw-1 (perfluorobutane sulfonate; washed green beans and perfluorohexanoic acid; unwashed tomato) to 2680 ng kgdw-1 (perfluorohexane sulfonate; radish). Concentrations of perfluorooctanoic acid (PFOA) in carrots, lettuce, radish, and canned green beans yielded median exposure intake (EI) values of 0.016-0.240 ng per kgbw-day, which exceeded the EPA RfD (0.0015 ng per kgbw-day). Washing reduced radish PFOA concentrations below detection, but EIs at the reporting limit still exceeded the RfD. The combination of improved data quality and greater frequency of PFAS detection vs. prior studies plus EI > RfD for some PFAS suggests a need for matrix-specific extractions and analysis of PFAS in additional grocery store foods from broader geographic regions.

Occurrence of quantifiable and semi-quantifiable poly- and perfluoroalkyl substances in united states wastewater treatment plants.

Both quantifiable and semi-quantifiable poly- and perfluoroalkyl substances (PFAS) were evaluated in the influent, effluent, and biosolids of 38 wastewater treatment plants. PFAS were detected in all streams at all facilities. For the means of the sums of detected, quantifiable PFAS concentrations were 98 ± 28 ng/L, 80 ± 24 ng/L, and 160,000 ± 46,000 ng/kg (dry weight basis) in the influent, effluent, and biosolids (respectively). In the aqueous influent and effluent streams this quantifiable PFAS mass was typically associated with perfluoroalkyl acids (PFAAs). In contrast, quantifiable PFAS in the biosolids were primarily polyfluoroalkyl substances that potentially serve as precursors to the more recalcitrant PFAAs. Results of the total oxidizable precursor (TOP) assay on select influent and effluent samples showed that semi-quantified (or, unidentified) precursors accounted for a substantial portion (21 to 88%) of the fluorine mass compared to that associated with quantified PFAS, and that this fluorine precursor mass was not appreciably transformed to perfluoroalkyl acids within the WWTPs, as influent and effluent precursor concentrations via the TOP assay were statistically identical. Evaluation of semi-quantified PFAS, consistent with results of the TOP assay, showed the presence of several classes of precursors in the influent, effluent, and biosolids; perfluorophosphonic acids (PFPAs) and fluorotelomer phosphate diesters (di-PAPs) occurred in 100 and 92% of biosolid samples, respectively. Analysis of mass flows showed that, for both quantified (on a fluorine mass basis) and semi-quantified PFAS, the majority of PFAS exited WWTPs through the aqueous effluent compared to the biosolids stream. Overall, these results highlight the importance of semi-quantified PFAS precursors in WWTPs, and the need to further understand the impacts of their ultimate fate in the environment.

Simulated leaching of PFAS from land-applied municipal biosolids at agricultural sites.

Biosolids are an important resource for agricultural practice but have recently received increased focus as a potential source of per- and polyfluoroalkyl substances (PFAS) in the environment. Few studies have investigated the transport of PFAS through the unsaturated zone under conditions relevant to biosolids application sites. Herein, the unsaturated flow and transport model HYDRUS is used to evaluate the leaching of per- and polyfluoroalkyl substances (PFAS) from land-applied biosolids used in agricultural practice to determine the impacts of PFAS leaching on underlying groundwater resources. This numerical case study was based on conditions and operations at two test sites in central Illinois where biosolids were applied at agronomic rates and where PFAS contents and desorption characteristics were previously characterized. Each site possessed different vadose zone soil textural heterogeneity. Simulations were performed under actual present-day meteorological conditions and extended 150 years beyond the initial biosolids application. These long-term simulations demonstrate how soil equilibrium sorption/desorption processes within the biosolids-amended surface soils effectively control the transport rate of individual PFAS to groundwater. Air-water interfacial (AWI) adsorption, which is sometimes considered to be a significant source of PFAS retention in vadose zone soils, was observed to have minimal impacts on PFAS leaching rates within the biosolids-amended surface soils at these sites. Additionally, the impact of AWI adsorption was found to be most significant for PFAS transport within the underlying vadose zone soils when these soils were more texturally homogeneous and considerably less significant within the texturally heterogeneous soils represented herein. The results of multiple long-term simulations were used to develop an empirical equation that relates predicted maximum PFAS pore-water concentrations reaching the saturated zone with changes in PFAS concentrations in the biosolids-amended soil for various biosolids re-application events. This approach is shown to be very useful in developing site-specific PFAS soil screening levels and/or maximum leachate levels for PFAS in support of establishing best management practices (BMPs) for land application of biosolids.

An Integrated Approach for Determination of Total Per- and Polyfluoroalkyl Substances (PFAS).

Per- and polyfluoroalkyl substances (PFAS) are difficult to analyze in environmental media due challenges such as extraction recovery and lack of analytical standards. The total oxidizable precursor (TOP) assay and suspect screening analysis coupled with semiquantitative (SQ) concentration estimates are two approaches to assess total PFAS in environmental media, but studies are needed to optimize workstreams for total PFAS analysis. This study applied two soil extraction methods, TOP assay, and SQ analysis to three aqueous film-forming foams (AFFFs) and three AFFF-impacted soils. In soils, the total PFAS estimated with results from an extraction method utilizing sequential acidic and basic solvents led to a 35% increase in precursors during TOP assay relative to results from a basic solvent only extraction in one of three soils tested, but concentrations did not increase significantly in remaining soils. Furthermore, sample-specific dilution schemes were required to overcome matrix effects caused by the acidic extraction step that influenced estimates of total PFAS by SQ analysis. The results highlight that there is not an advantage to routine application of an acid extraction step in PFAS-impacted soils. In three AFFFs, suspect screening of post-TOP samples identified eight classes of PFAS present after oxidation. Concentrations of three classes increased, suggesting they are new TOP end points. Concentrations of the remaining five classes either remained constant after TOP or exhibited slight decreases. As a result, combined TOP and SQ workstreams may yield the most representative assessment of total PFAS composition and concentration. The eight classes of PFAS present after TOP did not degrade in harsh conditions. Some are structurally similar to PFCAs and PFSAs and are known to occur in the environment, suggesting a similar degree of persistence and a need for more routine monitoring.

Acute Oral Toxicity of Nonfluorinated Fire-Fighting Foams to Northern Bobwhite Quail (Colinus virginianus).

Long-chain per- and poly-fluoroalkyl substances (PFAS) have been the active ingredients in firefighting foams for more than 50 years. Due to their extreme persistence, regulatory agencies are concerned about their potential adverse environmental and health impacts. Recently, nonfluorinated chemical constituents have been proposed for use in fire-fighting foams in an effort to reduce the potential negative impacts of PFAS on terrestrial and aquatic flora and fauna. However, it is important to also determine the potential ecotoxicity of these nonfluorinated foam products, because we have little toxicological information for many of them. In preparation for a chronic study, we conducted an acute (24-h) oral toxicity test in northern bobwhite quail (Colinus virginianus) using six different fluorine-free foams; five were commercial foams (BioEx ECOPOL A, Fomtec Enviro USP, National Foam Avio Green KHC, National Foam NFD 20-391, and Solberg Re-Healing Foam), and one was an experimental foam (NRL 502W). A short-chain PFAS-based foam (Buckeye Platinum Plus C6) was also evaluated for comparative purposes. Groups of five birds were initially pseudogavaged with a volume of each product corresponding to a "limit" (the highest exposure concentration expected to occur environmentally). Only one bird (1 of 35) died during the limit test, indicating that all seven products have an acute median lethal dose in adult quail at or above the limit (~1500 mg/kg body wt). Environ Toxicol Chem 2022;41:2003-2007. © 2022 SETAC.

Environmental Sources, Chemistry, Fate, and Transport of Per- and Polyfluoroalkyl Substances: State of the Science, Key Knowledge Gaps, and Recommendations Presented at the August 2019 SETAC Focus Topic Meeting.

A Society of Environmental Toxicology and Chemistry (SETAC) Focused Topic Meeting (FTM) on the environmental management of per- and polyfluoroalkyl substances (PFAS) convened during August 2019 in Durham, North Carolina (USA). Experts from around the globe were brought together to critically evaluate new and emerging information on PFAS including chemistry, fate, transport, exposure, and toxicity. After plenary presentations, breakout groups were established and tasked to identify and adjudicate via panel discussions overarching conclusions and relevant data gaps. The present review is one in a series and summarizes outcomes of presentations and breakout discussions related to (1) primary sources and pathways in the environment, (2) sorption and transport in porous media, (3) precursor transformation, (4) practical approaches to the assessment of source zones, (5) standard and novel analytical methods with implications for environmental forensics and site management, and (6) classification and grouping from multiple perspectives. Outcomes illustrate that PFAS classification will continue to be a challenge, and additional pressing needs include increased availability of analytical standards and methods for assessment of PFAS and fate and transport, including precursor transformation. Although the state of the science is sufficient to support a degree of site-specific and flexible risk management, effective source prioritization tools, predictive fate and transport models, and improved and standardized analytical methods are needed to guide broader policies and best management practices. Environ Toxicol Chem 2021;40:3234-3260. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Environmental Source Tracking of Per- and Polyfluoroalkyl Substances within a Forensic Context: Current and Future Techniques.

The source tracking of per- and polyfluoroalkyl substances (PFASs) is a new and increasingly necessary subfield within environmental forensics. We define PFAS source tracking as the accurate characterization and differentiation of multiple sources contributing to PFAS contamination in the environment. PFAS source tracking should employ analytical measurements, multivariate analyses, and an understanding of PFAS fate and transport within the framework of a conceptual site model. Converging lines of evidence used to differentiate PFAS sources include: identification of PFASs strongly associated with unique sources; the ratios of PFAS homologues, classes, and isomers at a contaminated site; and a site's hydrogeochemical conditions. As the field of PFAS source tracking progresses, the development of new PFAS analytical standards and the wider availability of high-resolution mass spectral data will enhance currently available analytical capabilities. In addition, multivariate computational tools, including unsupervised (i.e., exploratory) and supervised (i.e., predictive) machine learning techniques, may lead to novel insights that define a targeted list of PFASs that will be useful for environmental PFAS source tracking. In this Perspective, we identify the current tools available and principal developments necessary to enable greater confidence in environmental source tracking to identify and apportion PFAS sources.

Subsurface transport potential of perfluoroalkyl acids (PFAAs): Column experiments and modeling.

Transport of ten perfluoroalkyl acids (PFAAs) was studied with one-dimensional (1-D) saturated column experiments using four soil types with an organic carbon fraction (foc) range of ~0-0.045. Columns were operated under conditions relevant to aqueous film-forming foam (AFFF)-impacted fire protection training areas to determine the ability of equilibrium transport parameters to describe 1-D PFAA transport, if rate-limited sorption influences PFAA transport, and if kinetic parameters can be used to evaluate factors causing rate-limited sorption. Results of initial screening of PFAA breakthrough found that over half of the breakthrough curves deviated from equilibrium transport and merited further investigation. Subsequent analysis showed that, in many cases, these deviations could be accounted for by considering the range of applicable equilibrium Kd values (i.e. based on standard deviation) applicable to the solid phase. Thus, transport of the majority of PFAAs in 3 soils with foc of 0-0.017 was not impacted by rate-limited sorption. Further, low sorption led to transport that was essentially simultaneous for the majority of PFAAs in these porous media. Exceptions were observed for long-chain PFAAs, and also in a fourth soil with foc of 0.045, which indicated the potential for rate-limited sorption to impact transport in some scenarios. Subsequent flow interruption experiments isolating kinetic behavior confirmed rate-limited sorption caused nonequilibrium transport. Linear free energy relationships (LFERs) developed in previous work to predict the inverse relationship between mass transfer coefficients (k) and sorption parameters (i.e., Kd) were used to estimate values of k for PFAAs in this study. Resulting k values were 10-3 to 10-8 h-1, consistent with previously measured kinetic parameters for other polar and anionic compounds. Models incorporating estimated k values resulted in improved predictions of breakthrough observed in nonequilibrium scenarios (R2 0.83-0.98), but k values will require further validation prior to broader application. This work illustrates rate-limited sorption considerations are needed to describe 1-D column saturated transport for some PFAAs and solid phases. At field scales, subsurface heterogeneity and PFAA precursor transformation may be equally or even more important in determining saturated PFAA transport, but kinetic parameters in this study may help to determine relative contributions of rate-limited sorption to overall transport.

Measuring Total PFASs in Water: The Tradeoff between Selectivity and Inclusivity.

Millions of people around the world may be exposed to drinking water impacted by per- and polyfluoroalkyl substances (PFASs) at levels exceeding local or national advisories. Many studies indicate that the full extent of PFAS contamination is significantly underestimated when only targeted analytical methods are used. Here, we review techniques using bulk organofluorine measurement to quantify the (as of yet) unidentified fraction of PFASs. We discuss advantages and disadvantages of specific approaches and their applicability to water analysis with a focus on the tradeoff between selectivity and inclusivity, and provide suggestions for a path forward to better characterize the wide array of PFASs present in environmental samples.

Evaluation and Management Strategies for Per- and Polyfluoroalkyl Substances (PFASs) in Drinking Water Aquifers: Perspectives from Impacted U.S. Northeast Communities.

BACKGROUND: Multiple Northeast U.S. communities have discovered per- and polyfluoroalkyl substances (PFASs) in drinking water aquifers in excess of health-based regulatory levels or advisories. Regional stakeholders (consultants, regulators, and others) need technical background and tools to mitigate risks associated with exposure to PFAS-affected groundwater. OBJECTIVES: The aim was to identify challenges faced by stakeholders to extend best practices to other regions experiencing PFAS releases and to establish a framework for research strategies and best management practices. METHODS AND APPROACH: Management challenges were identified during stakeholder engagement events connecting attendees with PFAS experts in focus areas, including fate/transport, toxicology, and regulation. Review of the literature provided perspective on challenges in all focus areas. Publicly available data were used to characterize sources of PFAS impacts in groundwater and conduct a geospatial case study of potential source locations relative to drinking water aquifers in Rhode Island. DISCUSSION: Challenges in managing PFAS impacts in drinking water arise from the large number of relevant PFASs, unconsolidated information regarding sources, and limited studies on some PFASs. In particular, there is still considerable uncertainty regarding human health impacts of PFASs. Frameworks sequentially evaluating exposure, persistence, and treatability can prioritize PFASs for evaluation of potential human health impacts. A regional case study illustrates how risk-based, geospatial methods can help address knowledge gaps regarding potential sources of PFASs in drinking water aquifers and evaluate risk of exposure. CONCLUSION: Lessons learned from stakeholder engagement can assist in developing strategies for management of PFASs in other regions. However, current management practices primarily target a subset of PFASs for which in-depth studies are available. Exposure to less-studied, co-occurring PFASs remains largely unaddressed. Frameworks leveraging the current state of science can be applied toward accelerating this process and reducing exposure to total PFASs in drinking water, even as research regarding health effects continues. https://doi.org/10.1289/EHP2727.

Evaluation of a national data set for insights into sources, composition, and concentrations of per- and polyfluoroalkyl substances (PFASs) in U.S. drinking water.

The United States Environmental Protection Agency (USEPA) completed nationwide screening of six perfluoroalkyl substances in U.S. drinking water from 2013 to 2015 under the Third Unregulated Contaminant Monitoring Rule (UCMR3). UCMR3 efforts yielded a dataset of 36,139 samples containing analytical results from >5000 public water systems (PWSs). This study used UCMR3 data to investigate three aspects of per- and polyfluoroalkyl substances (PFASs) in drinking water: the occurrence of PFAS and co-contaminant mixtures, trends in PFAS detections relative to PWS characteristics and potential release types, and temporal trends in PFAS occurrence. This was achieved through bivariate and multivariate analyses including categorical analysis, concentration ratios, and hierarchical cluster analysis. Approximately 50% of samples with PFAS detections contained ≥2 PFASs, and 72% of detections occurred in groundwater. Large PWSs (>10,000 customers) were 5.6 times more likely than small PWSs (≤10,000 customers) to exhibit PFAS detections; however, when detected, median total PFAS concentrations were higher in small PWSs (0.12 µg/L) than in large (0.053 µg/L). Bivariate and multivariate analyses of PFAS composition suggested PWSs reflect impacts due to firefighting foam use and WWTP effluent as compared to other source types for which data were available. Mann-Kendall analysis of quarterly total PFAS detection rates indicated an increasing trend over time (p = 0.03). UCMR3 data provide a foundation for tiered design of targeted sampling and analysis plans to address remaining knowledge gaps in the sources, composition, and concentrations of PFASs in U.S. drinking water.

Evidence of remediation-induced alteration of subsurface poly- and perfluoroalkyl substance distribution at a former firefighter training area.

Poly- and perfluoroalkyl substances (PFASs) are a class of fluorinated chemicals that are utilized in firefighting and have been reported in groundwater and soil at several firefighter training areas. In this study, soil and groundwater samples were collected from across a former firefighter training area to examine the extent to which remedial activities have altered the composition and spatial distribution of PFASs in the subsurface. Log Koc values for perfluoroalkyl acids (PFAAs), estimated from analysis of paired samples of groundwater and aquifer solids, indicated that solid/water partitioning was not entirely consistent with predictions based on laboratory studies. Differential PFAA transport was not strongly evident in the subsurface, likely due to remediation-induced conditions. When compared to the surface soil spatial distributions, the relative concentrations of perfluorooctanesulfonate (PFOS) and PFAA precursors in groundwater strongly suggest that remedial activities altered the subsurface PFAS distribution, presumably through significant pumping of groundwater and transformation of precursors to PFAAs. Additional evidence for transformation of PFAA precursors during remediation included elevated ratios of perfluorohexanesulfonate (PFHxS) to PFOS in groundwater near oxygen sparging wells.

Subsurface transport potential of perfluoroalkyl acids at aqueous film-forming foam (AFFF)-impacted sites.

Subsurface transport potential of a suite of perfluoroalkyl acids (PFAAs) was studied in batch sorption experiments with various soils and in the presence of co-contaminants relevant to aqueous film-forming foam (AFFF)-impacted sites. Specifically, PFAA sorption to multiple soils in the presence of nonaqueous phase liquid (NAPL) and nonfluorinated AFFF surfactants was examined. This study is the first to report on sorption of perfluorobutanoate (PFBA) and perfluoropentanoate (PFPeA) (log Koc = 1.88 and 1.37, respectively) and found that sorption of these compounds does not follow the chain-length dependent trend observed for longer chain-length PFAAs. Sorption of PFBA was similar to that of perfluorooctanoate (PFOA, log Koc = 1.89). NAPL and nonfluorinated AFFF surfactants all had varying impacts on sorption of longer chain (>6 CF2 groups) PFAAs. The primary impact of NAPL was observed in low foc soil (soil A) where Freundlich n-values increased when NAPL was present. Impacts of nonfluorinated AFFF surfactants varied with surfactant and soil. The anionic surfactant sodium decyl sulfate (SDS) illicited PFAA chain-length dependent impacts in two negatively charged soils with varying foc. In soil A, Kd values for perfluoroheptanoate (PFHpA) increased 91% with SDS, whereas values for perfluorodecanoate (PFDA) increased only 28%. An amphoteric surfactant, n,n-dimethyldodecylamine n-oxide (AO), had the most notable impact on PFAA sorption to a positively charged soil (soil C). In this soil, AO oxide significantly increased sorption for the longer chain PFAAs (i.e., 528% increase in Kd for PFDA). Changes in sorption caused by SDS and AO may be due to mixed hemimicelle formation, competitive sorption, or changes to PFAA solubility. Short-chain PFAA behavior in the presence of NAPL, SDS, and AO was again notable. Co-contaminants generally increased the sorption of these compounds to all soils. Log Kd values of PFBA in soil A increased 85%, 372%, and 32% in the presence of NAPL, SDS, and AO, respectively. Use of Kd values to calculate retardation factors (Rf) of PFAAs demonstrates the variability of co-contaminant impacts on PFAA transport. Whereas NAPL and nonfluorinated surfactants decreased the sorption of perfluorooctanesulfonate (PFOS) at lower PFOS concentrations (1 µg/L), they led to increases in sorption at higher PFOS concentrations (500 µg/L). These results demonstrate that PFAA groundwater transport will depend on the solid phase characteristics as well as PFAA concentration and chain length. Detailed site-specific information will likely be needed to accurately predict PFAA transport at AFFF-impacted sites.