Suspect Screening of Hydrocarbon Surfactants in AFFFs and AFFF-Contaminated Groundwater by High-Resolution Mass Spectrometry

Sulfonamide Per- and Polyfluoroalkyl Substances Can Impact Microorganisms Used in Aromatic Hydrocarbon and Trichloroethene Bioremediation

Per- and polyfluoroalkyl substances (PFASs) from aqueous film forming foams (AFFFs) can hinder bioremediation of co-contaminants such as trichloroethene (TCE) and benzene, toluene, ethylbenzene, and xylene (BTEX). Anaerobic dechlorination can require bioaugmentation of Dehalococcoides, and for BTEX, oxygen is often sparged to stimulate in situ aerobic biodegradation. We tested PFAS inhibition to TCE and BTEX bioremediation by exposing an anaerobic TCE-dechlorinating coculture, an aerobic BTEX-degrading enrichment culture, and an anaerobic toluene-degrading enrichment culture to n-dimethyl perfluorohexane sulfonamido amine (AmPr-FHxSA), perfluorohexane sulfonamide (FHxSA), perfluorohexanesulfonic acid (PFHxS), or nonfluorinated surfactant sodium dodecyl sulfate (SDS). The anaerobic TCE-dechlorinating coculture was resistant to individual PFAS exposures but was inhibited by >1000× diluted AFFF. FHxSA and AmPr-FHxSA inhibited the aerobic BTEX-degrading enrichment. The anaerobic toluene-degrading enrichment was not inhibited by AFFF or individual PFASs. Increases in amino acids in the anaerobic TCE-dechlorinating coculture compared to the control indicated stress response, whereas the BTEX culture exhibited lower concentrations of all amino acids upon exposure to most surfactants (both fluorinated and nonfluorinated) compared to the control. These data suggest the main mechanisms of microbial toxicity are related to interactions with cell membrane synthesis as well as protein stress signaling.

Repeated Aqueous Film-Forming Foams Applications: Impacts on Polyfluoroalkyl Substances Retention in Saturated Soil

Historical practices at firefighter-training areas involved repeated aqueous film-forming foams (AFFFs) applications, resulting in source zones characterized by high concentrations of perfluoroalkyl and polyfluoroalkyl substances (PFAS). Repeated applications of AFFF composed of 14 anionic and 23 zwitterionic perfluoroalkyl substances (PFAS) were conducted on a single one-dimensional saturated soil column to quantify PFAS retention. An electrofluorination-based (3M) Milspec AFFF, which was above the mixture's critical micelle concentration (CMC), was at application strength (3%, v/v). Retention and retardation of PFAS mass increased with each successive AFFF addition, although the PFAS concentration profiles for subsequent applications differed from the initial. Greater degree of mass retention and retardation correlated with longer PFAS carbon-fluorine chain length and charged-headgroup type and as a function of AFFF application number. Anionic PFAS were increasingly retained with each subsequent AFFF application, while zwitterionic PFAS exhibited an alternating pattern of sorption and desorption. Surfactant-surfactant adsorption and competition during repeat AFFF applications that are at concentrations above the CMC resulted in adsorbed PFAS from the first application, changing the nature of the soil surface with preferential sorption of anionic PFAS and release of zwitterionic PFAS due to competitive elution. Applying a polyparameter quantitative structure-property relationship developed to describe sorption of AFFF-derived PFAS to uncontaminated, saturated soil was attempted for our experimental conditions. The model had been derived for data where AFFF is below the apparent CMC and our experimental conditions that included the presence of mixed micelles (aggregates consisting of different kinds of surfactants that exhibit characteristics properties different from micelles composed of a single surfactant) resulted in overall PFAS mass retained by an average of 27.3% ± 2.7% (standard error) above the predicted values. The correlation was significantly improved by adding a "micelle parameter" to account for cases where the applied AFFF was above the apparent CMC. Our results highlight the importance of interactions between the AFFF components that can only be investigated by employing complex PFAS mixtures at concentrations present in actual AFFF at application strength, which are above their apparent CMC. In firefighter-training areas (AFFF source zones), competitive desorption of PFAS may result in downgradient PFAS retention when desorbed PFAS become resorbed to uncontaminated soil.

Geophysical signatures of soil AFFF contamination from spectral induced polarization and low field nuclear magnetic resonance methods

Few field methods are available for characterizing source zones impacted with aqueous film forming foam (AFFF). Non-invasive geophysical characterization of AFFF source zone contamination in situ could assist with the delineation and characterization of these sites, allowing for more informed sampling regimes aimed at quantifying subsurface poly- and perfluoroalkyl substances (PFAS) contamination. We present initial results from the investigation of the sensitivity of two existing surface and borehole-deployable geophysical technologies, spectral induced polarization (SIP), and low field nuclear magnetic resonance (NMR), to soils impacted with AFFF. To investigate the sensitivity of these methods to AFFF-impacted soil, bench-scale column experiments were conducted on samples consisting of natural and synthetic soils and groundwater. While our findings do not show strong evidence of NMR sensitivity to soil PFAS contamination, we do find evidence that SIP has sufficient sensitivity to detect sorption of AFFF constituents (including PFAS) to soils. This finding is based on evidence that AFFF constituents associated with the pore surface produce a measurable polarization response in both freshly impacted synthetic soils and in soils historically impacted with AFFF. Our findings encourage further exploration of the SIP method as a technology for characterizing contaminant concentrations across AFFF source zones.

Identification and Coexposure of Neonicotinoid Insecticides and Their Transformation Products in Retail Cowpea (Vigna unguiculata)

There is growing evidence that the transformation products of emerging contaminants in foodstuffs may pose a health risk to humans. However, the exact identities, levels, and estimated dietary intake (EDI) of neonicotinoid transformation products in crops remain poorly understood. We established an extended suspect screening strategy to investigate neonicotinoid insecticides and their transformation products in retail cowpea from 11 cities in Hainan Province, China. Forty-nine transformation products were identified in retail cowpea, of which 22-36 were found in 98.6% of the samples. Notably, 31 new transformation products were derived from new processes or a combination of different transformation processes. The mean concentrations of neonicotinoids and nine of the transformation products (with authentic standards) were in the ranges of 0.0824-5.34 and 0.0636-1.50 ng/g, respectively. The cumulative EDIs of the quantified transformation products were lower than those of parent neonicotinoids with the exception of clothianidin desmethyl, which had a ratio of 1157%. However, the coexistence of the other 40 transformation products (without authentic standards) in cowpea suggested that the exposure risk from all of the transformation products might be higher. This study demonstrated that pesticide transformation products should be considered in food chain risk assessments and included in future regulatory management.

Emerging and legacy perfluoroalkyl and polyfluoroalkyl substances (PFAS) in surface water around three international airports in China

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a large category of crucial environmental contaminants of global concerns. There are limited data on PFAS in surface water around international airports in China. The present study investigated the concentrations, distributions, and sources of emerging and legacy PFAS in surface waters around Beijing Capital International Airport (BC), Shanghai Pudong International Airport (SP), and Guangzhou Baiyun International Airport (GB) in China. Twenty-seven target compounds were quantified. The Σ27PFAS concentrations ranged from 19.0 to 62.8 ng/L (mean 36.1 ng/L) in BC, 25.6-342 ng/L (mean 76.0 ng/L) in SP, 7.35-72.7 ng/L (mean 21.6 ng/L) in GB. The dominant compound was perfluorooctanoic acid (PFOA), which accounted for an average of 27% (5%-65%) of the Σ27PFAS concentrations. The alternatives with -C6F12- group had detection frequencies ranging from 72% to 100%. The partition coefficient results indicate that the longer chain PFAS (C > 8) tend to be more distributed in the particle phase. Fifty suspect and nontarget PFAS were identified. In GB, 44 PFAS were identified, more than SP of 39 and BC of 38. An ultra short-chain (C = 2) precursor, N-methylperfluoroethanesulfonamido acetic acid (MeFEtSAA), was identified and semi-quantified. Domestic wastewater discharges might be the main sources around BC, while industrial and aviation activities might be the main sources around SP and GB.

Non-targeted identification and semi-quantitation of emerging per- and polyfluoroalkyl substances (PFAS) in US rainwater

High-resolution mass spectrometry was used to screen for emerging per- and polyfluorinated alkyl substances (PFAS) in precipitation samples collected in summer 2019 at seven sites in the United States. We previously quantified the concentration of ten PFAS in the rainwater samples using the method of isotopic dilution (Pike et al., 2021). Nine of these targeted analytes belonged to the U.S. Environmental Protection Agency Regional Screening Level list, herein referred to as EPA-monitored analytes. In this new work, we identify emerging PFAS compounds by liquid chromatography quadrupole time-of-flight mass spectrometry. Several emerging PFAS were detected across all samples, with the most prevalent compounds being C3-C8 hydrogen-substituted perfluorocarboxylic acids (H-PFCAs) and fluorotelomer carboxylic acids (FTCAs). Concentrations of emerging PFAS were in the 10-1000 ng L-1 range (approximately 1-2 orders of magnitude greater than EPA-monitored PFAS) at all sites except Wooster, OH, where concentrations were even higher, with a maximum estimated ΣPFAS of 16 400 ng L-1. The elevated levels of emerging PFAS in the Wooster samples were predominantly even and odd chain-length H-PFCAs and FTCAs comprised of complex mixtures of branched isomers. This unique composition did not match any known manufactured PFAS formulation reported to date, but it could represent thermally transformed by-products emitted by a local point source. Overall, the results indicate that PFAS outside of the standard analyte lists make up a significant and previously unappreciated fraction of contaminants in rainwater collected within the central U.S.-and potentially world-wide-especially in proximity to localized point sources.

Hydrothermal Alkaline Treatment (HALT) of Foam Fractionation Concentrate Derived from PFAS-Contaminated Groundwater

While foam fractionation (FF) process has emerged as a promising technology for removal of per- and polyfluoroalkyl substances (PFASs) from contaminated groundwater, management of the resulting foam concentrates with elevated concentrations of PFASs (e.g., >1 g/L) remains a challenge. Here, we applied hydrothermal alkaline treatment (HALT) to two foam concentrates derived from FF field demonstration projects that treated aqueous film-forming foam (AFFF)-impacted groundwater. Results showed >90% degradation and defluorination within 90 min of treatment (350 °C, 1 M NaOH) of all 62 PFASs (including cations, anions, and zwitterions) identified in foam concentrates. Observed rate constants for degradation of individual perfluoroalkyl sulfonates (PFSAs, CnF2n+1-SO3-), the most recalcitrant class of PFASs, in both foam concentrates were similar to values measured previously in other aqueous matrices, indicating that elevated initial PFAS concentrations (e.g., PFHxSinit = 0.55 g/L), dissolved organic carbon (DOC; up to 4.5 g/L), and salt levels (e.g., up to 325 mg/L chloride) do not significantly affect PFAS reaction kinetics. DOC was partially mineralized by treatment, but a fraction (∼15%) was recalcitrant. Spectroscopic characterization revealed molecular features of the HALT-recalcitrant DOC fraction, and nontarget high-resolution mass spectrometry tentatively identified 129 nonfluorinated HALT-recalcitrant molecules. Analysis of process energy requirements shows that treating PFAS-contaminated foam concentrates with HALT would add minimally (<5%) to the overall energy requirements of an integrated FF-HALT treatment train.

The wide presence of fluorinated compounds in common chemical products and the environment: a review

The C-F bonds, due to their many unique features, have been incorporated into numerous compounds in countless products and applications. These fluorinated compounds eventually are disposed of and released into the environment through different pathways. In this review, we analyzed the occurrence of these fluorinated compounds in seven types of products (i.e., refrigerants/propellants, aqueous film-forming foam, cosmetics, food packaging, agrochemicals, pharmaceuticals, coating materials) and discussed their fate in the environment. This is followed by describing the quantity of fluorinated compounds from each source based on available data. Total on- and off-site disposal or other releases of 536 fluorinated compounds in 2021 were analyzed using the data sourced from the U.S. EPA Toxics Release Inventory (TRI). Among the chemicals examined, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were the primary contributors in terms of total mass. Upon examining the seven sources of fluorinated compounds, it became evident that additional contributors are also responsible for the presence of organofluorine compounds in the environment. Although various toxic degradation products of fluorinated compounds could form in the environment, trifluoroacetic acid (TFA) was specifically highlighted in this review given the fact that it is a common dead-end degradation product of > 1 million chemicals. This paper ended with a discussion of several questions raised from this study. The path forward was elaborated as well for the purpose of protecting the environment and human health.

Evaluation of sealants to mitigate the release of per- and polyfluoroalkyl substances (PFAS) from AFFF-impacted concrete: Characterization and forecasting

Per- and polyfluoroalkyl substances (PFAS) within concrete pads impacted by historical firefighting training using aqueous film-forming foam (AFFF) may be potential secondary sources of PFAS due to surficial leaching. This study aimed to (i) characterize the effectiveness of two commercially available sealants (Product A and Product B) in mitigating leaching of five PFAS (e.g., PFOS, PFOA, PFHxS, PFHxA, 6:2 FTS) from concrete surfaces at the laboratory-scale, and (ii) develop a model to forecast cumulative leaching of the same five PFAS over 20 years from sealed and unsealed concrete surfaces. Laboratory trials demonstrated that both sealants reduced the surficial leaching of the five PFAS studied, and Product B demonstrated a comparatively greater reduction in surface leaching than Product A as measured against unsealed controls. The cumulative PFOS leaching from an unsealed concrete surface is estimated by the model to be about 400 mg/m2 over 20 years and reached asymptotic conditions after 15 years. In contrast, the model output suggests asymptotic conditions were not achieved within the modeled time of 20 years after sealing with Product A and 85% of PFOS was predicted to have leached (∼340 mg/m2). Negligible leaching of PFOS after sealing with Product B was observed ( < 5 × 10-9 mg/m2). Results from modeled rainfall scenarios suggest PFAS leachability is reduced from sealed versus unsealed AFFF-impacted concrete surfaces.

Discovery of 35 novel classes of per- and polyfluoroalkyl substances in representative commercial fluorinated products in China

Per- and polyfluoroalkyl substances (PFAS) have received increasing scientific and regulatory attention due to their global distribution and health hazards. However, little is known about the PFAS composition of fluorinated products commercially available in China. In this study, a sensitive and robust analytical method was proposed for the comprehensive characterization of PFAS in aqueous film-forming foam and fluorocarbon surfactants in the domestic market based on liquid chromatography-high resolution mass spectrometry in full scan acquisition mode followed by parallel reaction monitoring mode. Consequently, a total of 102 PFAS from 59 classes were elucidated, of which 35 classes are reported for the first time, including 27 classes of anionic, seven classes of zwitterionic, and one class of cationic PFAS. The anionic-type products are mainly C6 fluorotelomerization-based (FT-based) PFAS. Perfluorooctanoic acid and perfluorooctane sulfonate are negligible, while some known electrochemical fluorination-based long-chain precursors in zwitterionic products are worthy of concern because of their high abundance and potential degradation. New precursors detected in zwitterionic products are FT-based PFAS, for example, 6:2 FTSAPr-AHOE and 6:2 FTSAPr-diMeAmPrC. The structural elucidation of PFAS in commercial products facilitates a better assessment of human exposure and environmental release.

Predicting Interfacial Tension and Adsorption at Fluid-Fluid Interfaces for Mixtures of PFAS and/or Hydrocarbon Surfactants

Many per- and polyfluoroalkyl substances (PFAS) are surface-active and adsorb at fluid-fluid interfaces. The interfacial adsorption controls PFAS transport in multiple environmental systems, including leaching through soils, accumulation in aerosols, and treatment methods such as foam fractionation. Most PFAS contamination sites comprise mixtures of PFAS as well as hydrocarbon surfactants, which complicates their adsorption behaviors. We present a mathematical model for predicting interfacial tension and adsorption at fluid-fluid interfaces for multicomponent PFAS and hydrocarbon surfactants. The model is derived from simplifying a prior advanced thermodynamic-based model and applies to nonionic and ionic mixtures of the same charge sign with swamping electrolytes. The only required model inputs are the single-component Szyszkowski parameters obtained for the individual components. We validate the model using literature interfacial tension data of air-water and NAPL (non-aqueous phase liquid)-water interfaces covering a wide range of multicomponent PFAS and hydrocarbon surfactants. Application of the model to representative porewater PFAS concentrations in the vadose zone suggests competitive adsorption can significantly reduce PFAS retention (up to 7 times) at some highly contaminated sites. The multicomponent model can be readily incorporated into transport models to simulate the migration of mixtures of PFAS and/or hydrocarbon surfactants in the environment.

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.

A meta-analysis of the occurrence of alkylphenols and alkylphenol ethoxylates in surface waters and sediments in the United States between 2010 and 2020

Nonylphenol (NP), Octylphenol (OP), and their ethoxylates (NPEO and OPEO) have been the subject of considerable scientific and regulatory attention, primarily due to concerns about their aquatic toxicity and endocrine activity. Environmental monitoring has been conducted and reported for these substances in the United States (U.S.) for several decades. This paper develops an updated statistically based meta-analysis of the occurrence and ecological relevance of these substances in fresh and marine surface waters and sediments in the U.S. between 2010 and 2020. The overall objectives of this study were: (1) to evaluate the impact of analytical detection limits (DLs) and treatment of censored or non-detected (ND) samples on reported results, (2) to summarize and evaluate recent (2010-2020) occurrence and concentrations of these substances in surface waters and sediments, (3) to conduct an ecological screening assessment of the potential risks of these substances to aquatic organisms in surface waters and sediments for this same period, and (4) to examine temporal trends of these substances in surface waters and sediments relative to previous investigations. Given that a large proportion of all NP, NPEO, OP and OPEO samples in recent (2010-2019) U.S. monitoring studies were below their respective method Limit of Detection/Limit of Quantification (LOD/LOQ) detection frequency ranging from 0 to 24%), proxy values were imputed using robust regression of order statistics (ROS). Nationally, NP and OP concentrations in fresh surface waters and sediments have decreased from 2010 to 2019. In contrast, changes in NP and OP concentrations in marine waters and sediments were more variable with some increases noted. A screening environmental risk assessment indicated that less than 1% of all samples exceeded U.S. or Canadian environmental quality guidelines. No exceedances were noted after 2016 which indicates a low potential for risk to aquatic organisms.

Insight into chemical features of migrated additives from plastics and associated risks to estuarine ecosystem

Distinct hydrodynamic conditions created a hotspot of plastic and associated additive pollution within estuaries, which is of considerable scientific interest. However, the effects of specific estuarine weathering (severe mechanical wear, constant turbulence, and strong ultraviolet radiation) on migration of additives remain unclear. Therefore, we investigated the release of migrated plastic additives (MPAs) from three representative plastics, namely floating foam, fishing nets, and packaging bags, under simulated estuarine conditions. Sixty-seven MPAs leached out under the wave scenario, greater than those under the ultraviolet radiation (62) and shoal (40) scenarios. We detected forty MPAs in the plastic bag leachates, whereas fewer MPAs were released from the foam and nets. Several MPAs were peculiar to specific plastics, e.g., antistatic and curing agents in the bag and foam leachates, respectively. Particularly, a suite of nonionic surfactants, octylphenol polyethoxylates (OPEO_n), exhibited outstanding responses in the packaging bag leachates and had elevated toxic potential. OPEO_n significantly inhibited the hatching of zebrafish and caused cardiovascular system disorder and morphological distortions even at environmentally relevant concentrations as in estuaries. Collectively, the leaching of MPAs was significantly enhanced by wave actions, and the plastic leachates, particularly those of plastic bags, can cause detrimental risks to the estuarine ecosystem.

Role of Mineral-Organic Interactions in PFAS Retention by AFFF-Impacted Soil

A comprehensive, generalized approach to predict the retention of per- and polyfluoroalkyl substances (PFAS) from aqueous film-forming foam (AFFF) by a soil matrix as a function of PFAS molecular and soil physiochemical properties was developed. An AFFF with 34 major PFAS (12 anions and 22 zwitterions) was added to uncontaminated soil in one-dimensional saturated column experiments and PFAS mass retained was measured. PFAS mass retention was described using an exhaustive statistical approach to generate a poly-parameter quantitative structure-property relationship (ppQSPR). The relevant predictive properties were PFAS molar mass, mass fluorine, number of nitrogens in the PFAS molecule, poorly crystalline Fe oxides, organic carbon, and specific (BET-N2) surface area. The retention of anionic PFAS was nearly independent of soil properties and largely a function of molecular hydrophobicity, with the size of the fluorinated side chain as the main predictor. Retention of nitrogen-containing zwitterionic PFAS was related to poorly crystalline metal oxides and organic carbon content. Knowledge of the extent to which a suite of PFAS may respond to variations in soil matrix properties, as developed here, paves the way for the development of reactive transport algorithms with the ability to capture PFAS dynamics in source zones over extended time frames.

Distribution of legacy and novel per- and polyfluoroalkyl substances in surface and groundwater affected by irrigation in an arid region

Frequent exchange of surface water and groundwater occurs in arid/semi-arid areas due to high evaporation and intensive irrigation activities, affecting the migration and transformation of per- and polyfluoroalkyl substances (PFASs) and threatening drinking water safety. This study analyzed legacy PFASs and potential precursors in surface water, groundwater, soil, and aquifer solid samples collected from a typical arid area, the Hetao Irrigation District of Northern China, to explore PFASs distribution and transformation between surface and ground. Total PFASs (ΣPFASs) in surface water was 29-232 ng/L, higher than 2-77 ng/L in groundwater. ΣPFASs in soil were 0.29-0.59 ng/g, higher than 0.09-0.27 in the aquifer solids. Regarding horizontal distribution, the concentration of PFASs in groundwater increased in downtowns and the areas recharged with lake water. In terms of vertical distribution, ΣPFASs decreased with the increase of depth, and more PFASs adsorbed on clay particles in the aquifer. The total oxidable precursor analysis showed that 8:2 FT and 4:2 FT were the dominant precursors of PFASs, resulting in an increment of 0.1-4 ng/L PFASs. Hydrogen and oxygen stable isotope compositions suggest similar sources between surface water and groundwater in the study area, while principal component analysis and Bayesian inference also indicate that surface water is an important source of groundwater PFASs. The annual infiltration PFASs to groundwater from Ulansuhai was estimated by the water balance approach to be 9.39 kg. Results highlight the influence of agricultural irrigation activities and lake infiltration on groundwater PFASs in the arid region.

Chronic toxicity of PFAS-free AFFF alternatives in terrestrial plant Brassica rapa

Fluorine (F)-free firefighting foams will be replacing per- and polyfluoroalkyl substances (PFAS)-containing aqueous film-forming foams (AFFFs) at U.S. military installations imminently, yet the environmental impacts of F-free foams are largely unknown. Ecotoxicity assessment of F-free foams is urgently needed to avoid replacement regret. In this study, we comparatively assessed phytotoxicity of six F-free formulations and one current short-chain fluorinated AFFF in terrestrial plant Brassica rapa. Five of six F-free formulations exerted higher toxicity than the short-chain AFFF to the growth and reproduction of B. rapa, with 8-51 times and > 10 times lower EC₅₀ values, respectively. Nontargeted analysis indicated the occurrence of transformation products of the test formulations in the above-ground plant tissues. In agreement with their phytotoxicity, the five highly toxic F-free formulations generated more transformation products with higher peak intensities in plant tissues than the two weakly toxic formulations. The most abundant transformation products detected in plant extracts were suspect transformation products derived from diethylene glycol monobutyl ether, a common ingredient of the five toxic formulations. This study provides ecotoxicological data that, combined with data from all related ongoing research, should be used in decision making regarding recommendations for manufacturing and use of candidate F-free foams.

Suspect screening and nontargeted analysis of per- and polyfluoroalkyl substances in representative fluorocarbon surfactants, aqueous film-forming foams, and impacted water in China

Massive usage of aqueous film-forming foams (AFFF) containing fluorocarbon surfactants (FS) is one of the major sources of per- and polyfluoroalkyl substances (PFAS) contamination, which poses negative environmental and health effects. However, there is a critical knowledge gap regarding PFAS chemical compositions in high consumption FS products which were used in AFFFs on the Chinese market and in water impacted by such products. This study firstly applied a comprehensive suspect screening and nontargeted analysis (NTA) workflow to investigate the main ionic and neutral PFAS in FS products from the largest Chinese vendor and compared with two international brands to unveil the PFAS used in AFFF. Overall, 24 classes of PFAS, including 69 compounds, were tentatively identified in FS products, and high concentrations of neutral PFAS were found in polymer-based products, indicating potential environmental risk. In addition, we applied a simplified data mining process to capture 36 PFAS from the impacted water, and the relationship among FS, AFFF concentrates and impacted water was explored. This study parsed the PFAS characteristics in AFFF-related industrial products and impacted water in China, which is instrumental for managing and controlling prioritized PFAS in this field.

The first quantitative investigation of compounds generated from PFAS, PFAS-containing aqueous film-forming foams and commercial fluorosurfactants in pyrolytic processes

Pyrolysis as a thermochemical technology is commonly used in waste management and remediation of organic-contaminated soil. This study, for the first time, investigated fluorinated and non-fluorinated compounds emitted from per- and polyfluoroalkyl substances (PFAS) and relevant products upon pyrolysis (200-890 °C) and their formation mechanisms. Approximately 30 non-fluorinated compounds were detected from PFAS-containing aqueous film-forming foams (AFFFs) and commercial surfactant concentrates (SCs) after heating, including glycols and glycol ethers that were predominant at 200 °C. Oxygen (e.g., 1,4-dioxane) and nitrogen heterocycles and benzene were unexpectedly observed at higher temperatures (300-890 °C), which were likely formed as a consequence of the thermal dehydration, dehydrogenation, and intermolecular cyclization of glycols and glycol ethers. Fluorinated volatiles in six major classes were detected at low and moderate temperatures (200-500 °C), including perfluoroalkenes, perfluoroalkyl aldehydes, fluorotelomer alcohols, and polyfluorinated alkanes/alkenes. Several features of the pyrolyses of PFAS suggest that the underlying decomposition mechanism is radical-mediated. Perfluoroheptene thermally decomposed at 200 °C to shorter-chain homologues following a radical chain-scission mechanism. Most of these volatiles observed at low/moderate temperatures were not detected at 890 °C. Ultra-short-chain fluorinated greenhouse gases (e.g., perfluoromethane) were not found.

Neutral Per- and Polyfluoroalkyl Substances, Butyl Carbitol, and Organic Corrosion Inhibitors in Aqueous Film-Forming Foams: Implications for Vapor Intrusion and the Environment

Per- and polyfluoroalkyl substances (PFAS), butyl carbitol, and corrosion inhibitors are components of aqueous film-forming foams (AFFFs). Volatile (neutral) fluorotelomerization (FT)- and electrochemical fluorination (ECF)-based PFAS, butyl carbitol, and organic corrosion inhibitors were quantified in 39 military specification (MilSpec), non-MilSpec, and alcohol resistant-AFFF concentrates (undiluted) from 1974 to 2010. Fluorotelomer alcohols were found only in FT-based AFFFs and N-methyl- and N-ethyl-perfluoroalkyl sulfonamides, and sulfonamido ethanols were found only in ECF-based AFFFs. Neutral PFAS and benzotriazole, 4-methylbenzotriazole, and 5-methybenzotriazole occurred at mg/L levels in the AFFFs, while butyl carbitol occurred at g/L levels. Neutral PFAS concentrations in indoor air due to vapor intrusion of a nearby undiluted AFFF release are estimated to be anywhere from 2 to >10 orders of magnitude higher than documented background indoor air concentrations. Estimated butyl carbitol and organic corrosion inhibitor concentrations were lower than and comparable to indoor concentrations recently measured, respectively. The wide range of neutral PFAS concentrations and Henry's law constants indicate that field, soil-gas measurements are needed to validate the estimations. Co-discharged butyl carbitol likely contributes to oxygen depletion in AFFF-impacted aquifers and may hinder the natural PFAS aerobic biotransformation. Organic corrosion inhibitors in AFFFs indicate that these are another source of corrosion inhibitors in the environment.

Suspect Screening and Chemical Profile Analysis of Storm-Water Runoff Following 2017 Wildfires in Northern California

The combustion of structures and household materials as well as firefighting during wildfires lead to releases of potentially hazardous chemicals directly into the landscape. Subsequent storm-water runoff events can transport wildfire-related contaminants to downstream receiving waters, where they may pose water quality concerns. To evaluate the environmental hazards of northern California fires on the types of contaminants in storm water discharging to San Francisco Bay and the coastal marine environment, we analyzed storm water collected after the northern California wildfires (October 2017) using a nontargeted analytical (NTA) approach. Liquid chromatography quadrupole time-of-flight mass spectrometric analysis was completed on storm-water samples (n = 20) collected from Napa County (impacted by the Atlas and Nuns fires), the city of Santa Rosa, and Sonoma County (Nuns and Tubbs fires) during storm events that occurred in November 2017 and January 2018. The NTA approach enabled us to establish profiles of contaminants based on peak intensities and chemical categories found in the storm-water samples and to prioritize significant chemicals within these profiles possibly attributed to the wildfire. The results demonstrated the presence of a wide range of contaminants in the storm water, including surfactants, per- and polyfluoroalkyl substances, and chemicals from consumer and personal care products. Homologs of polyethylene glycol were found to be the major contributor to the contaminants, followed by other widely used surfactants. Nonylphenol ethoxylates, typically used as surfactants, were detected and were much higher in samples collected after Storm Event 1 relative to Storm Event 2. The present study provides a comprehensive approach for examining wildfire-impacted storm-water contamination of related contaminants, of which we found many with potential ecological risk. Environ Toxicol Chem 2022;41:1824-1837. © 2022 SETAC.

Determination of total reducible organofluorine in PFAS-impacted aqueous samples based on hydrated electron defluorination

Per- and polyfluoroalkyl substances (PFASs) is a large group of thousands of anthropogenic chemicals. Recently, measurement of total organic fluorine (TOF) to reflect the total PFASs has been recommended in limits and advisories. In this study, a total reducible organofluorine (TROF) assay is developed based on hydrated electron (e_aq^-) conversion of PFASs into inorganic fluorine combined with ion chromatograph, which is a common and widespread instrument. The e_aq^- is generated in UV/sulfite system with alkaline condition, and the concentration of TROF (C_{F_TROF}) is the difference of fluoride concentration before and after assay. Method validation uses perfluorooctanesulfonic acid, perfluorooctanoic acid and their main alternatives, and F^- recoveries are 76.6%-101%, except for perfluorobutanesulfonic acid (48.5%). Method application of TROF assay uses industrial surfactant products and fluorochemical industry-contaminated water, meanwhile, target PFAS analysis and total oxidizable precursors (TOP) assay are concurrently conducted. Concentrations of PFASs detected in target analysis and TOP assay were converted to fluorine equivalents concentrations (C_{F_Target} and C_{F_TOP}). ∑C_{F_Target} and ∑C_{F_TOP} account for 0.80%-36% of C_{F_TROF} in industrial samples, 0.12%-54% in environmental water and 9.7%-14% in wastewater. The TROF assay can be used to initially judge whether PFASs contamination occurred near a hotspot with known sources. The C_{F_TROF} could infer the extent of PFAS contamination in PFAS-impacted samples and estimate the fraction of uncharacterized PFAS.

Widening the Lens on PFASs: Direct Human Exposure to Perfluoroalkyl Acid Precursors (pre-PFAAs)

Determining health risks associated with per-/polyfluoroalkyl substances (PFASs) is a highly complex problem requiring massive efforts for scientists, risk assessors, and regulators. Among the most poorly understood pressing questions is the relative importance of pre-PFAAs, which are PFASs that degrade to highly persistent perfluoroalkyl acids. How many of the vast number of existing pre-PFAAs are relevant for direct human exposure, and what are the predominant exposure pathways? What evidence of direct exposure to pre-PFAAs is provided by human biomonitoring studies? How important are pre-PFAAs and their biotransformation products for human health risk assessment? This article outlines recent progress and recommendations toward widening the lens on human PFAS exposure to include the pre-PFAA subclass.

Analysis of per- and polyfluoroalkyl substances in Houston Ship Channel and Galveston Bay following a large-scale industrial fire using ion-mobility-spectrometry-mass spectrometry

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants of concern because of their ubiquitous presence in surface and ground water; analytical methods that can be used for rapid comprehensive exposure assessment and fingerprinting of PFAS are needed. Following the fires at the Intercontinental Terminals Company (ITC) in Deer Park, TX in 2019, large quantities of PFAS-containing firefighting foams were deployed. The release of these substances into the Houston Ship Channel/Galveston Bay (HSC/GB) prompted concerns over the extent and level of PFAS contamination. A targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based study of temporal and spatial patterns of PFAS associated with this incident revealed presence of 7 species; their levels gradually decreased over a 6-month period. Because the targeted LC-MS/MS analysis was focused on about 30 PFAS molecules, it may have missed other PFAS compounds present in firefighting foams. Therefore, we utilized untargeted LC-ion mobility spectrometry-mass spectrometry (LC-IMS-MS)-based analytical approach for a more comprehensive characterization of PFAS in these water samples. We analyzed 31 samples from 9 sites in the HSC/GB that were collected over 5 months after the incident. Our data showed that additional 19 PFAS were detected in surface water of HSC/GB, most of them decreased gradually after the incident. PFAS features detected by LC-MS/MS correlated well in abundance with LC-IMS-MS data; however, LC-IMS-MS identified a number of additional PFAS, many known to be components of firefighting foams. These findings therefore illustrate that untargeted LC-IMS-MS improved our understanding of PFAS presence in complex environmental samples.

Effects of anionic hydrocarbon surfactant on the transport of perfluorooctanoic acid (PFOA) in natural soils

The widespread usage of per- and polyfluoroalkyl substances (PFASs) has led to their ubiquitous co-existence with hydrocarbon surfactants in the subsurface environment. In this study, column experiments were conducted to investigate the effect of an anionic hydrocarbon surfactant (sodium dodecylbenzene sulfonate, SDBS, 1 and 10 mg/L) on the transport of perfluorooctanoic acid (PFOA) in two saturated natural soils under different cation type (Na⁺ and Ca²⁺) conditions. Results showed that SDBS (10 mg/L) significantly enhanced the transport of PFOA in two soils. This was likely because SDBS had a stronger adsorption affinity to the soils than PFOA, and can outcompete PFOA for the finite adsorption sites on the soil surface. The effect of SDBS on PFOA transport varied greatly in the two soils. More negatively charged soil surface and greater soil particle size likely contributed to the more noticeable transport-enhancement of PFOA resulting from the presence of SDBS. Also, the enhancement effect of SDBS (10 mg/L) with Ca²⁺ on PFOA transport was more significantly than that with Na⁺. This was possibly due to the blocking effect of SDBS to the more positively charged soil surface induced by Ca²⁺. Findings of this study point out the importance of anionic hydrocarbon surfactants on PFOA transport when assessing its environmental risks and implementing remediation efforts.

Occurrence of PFASs and its effect on soil bacteria at a fire-training area using PFOS-restricted aqueous film-forming foams

Fire-training areas (FTAs) are an important source of perfluoroalkyl and polyfluoroalkyl substances (PFASs) pollution. However, the effect of PFASs on soil bacterial communities remains limited. Here, we detected the PFASs in soils ranging from 3.4 to 531.7 μg kg⁻¹ dry weight in seven plots at an FTA where PFOS-restricted aqueous film-forming foams (AFFFs) have been used for 6 years. PFOS was still the dominant homologue despite the restriction by Stockholm Convention, but it was almost three orders of magnitude lower than that in previous studies. PFASs played an important role in shaping the bacterial community, and high levels of PFASs (>100 μg kg⁻¹ dw) reduced the biodiversity and connectivity of soil bacteria. The extreme condition-tolerant bacteria were identified as biomarkers at the FTA. Our study provides valuable insights into the effect of PFOS-restricted AFFFs on soil bacterial communities at the FTA.

•

PFOS was still the dominant PFAS despite the restriction by Stockholm Convention

•

PFASs played an important role in shaping bacterial community

•

High level of PFASs reduced the biodiversity and connectivity of soil bacteria

•

The extreme condition-tolerant bacteria were identified as biomarkers at the FTA

PFAS Analysis with Ultrahigh Resolution 21T FT-ICR MS: Suspect and Nontargeted Screening with Unrivaled Mass Resolving Power and Accuracy

Per- and polyfluoroalkyl substances (PFASs) are a large family of thousands of chemicals, many of which have been identified using nontargeted time-of-flight and Orbitrap mass spectrometry methods. Comprehensive characterization of complex PFAS mixtures is critical to assess their environmental transport, transformation, exposure, and uptake. Because 21 tesla (T) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers the highest available mass resolving power and sub-ppm mass errors across a wide molecular weight range, we developed a nontargeted 21 T FT-ICR MS method to screen for PFASs in an aqueous film-forming foam (AFFF) using suspect screening, a targeted formula database (C, H, Cl, F, N, O, P, S; ≤865 Da), isotopologues, and Kendrick-analogous mass difference networks (KAMDNs). False-positive PFAS identifications in a natural organic matter (NOM) sample, which served as the negative control, suggested that a minimum length of 3 should be imposed when annotating CF₂-homologous series with positive mass defects. We putatively identified 163 known PFASs during suspect screening, as well as 134 novel PFASs during nontargeted screening, including a suspected polyethoxylated perfluoroalkane sulfonamide series. This study shows that 21 T FT-ICR MS analysis can provide unique insights into complex PFAS composition and expand our understanding of PFAS chemistries in impacted matrices.

Assessing Reliability of Non-targeted High-Resolution Mass Spectrometry Fingerprints for Quantitative Source Apportionment in Complex Matrices

Effective management of contaminated sites requires differentiating and deconvoluting contaminant source impacts in complex environmental systems. The existing source apportionment approaches that use targeted analyses of preselected indicator chemicals are limited whenever target analytes are below the detection limits or derived from multiple sources. However, non-targeted analyses that leverage high-resolution mass spectrometry (HRMS) yield rich datasets that deeply characterize sample-specific chemical compositions, providing additional potential end-members for source differentiation and apportionment. Previous work demonstrated that HRMS fingerprints can define sample uniqueness and support accurate, quantitative source concentration estimates. Here, using two aqueous film-forming foams as representative complex sources, we assessed the qualitative fidelity and quantitative accuracy of HRMS source fingerprints in increasingly complex background matrices. Across all matrices, HRMS-derived source concentration estimates were 0.81 ± 0.11-fold and 0.64 ± 0.24-fold of actual in samples impacted solely by analytical matrix effects (MEs) or by sample processing recovery and analytical MEs, respectively. Isotopic internal standards were not easily paired to individual unidentified non-target features, but bulk internal standard-based abundance corrections improved apportionment accuracy in higher matrix samples (to 0.90 ± 0.12-fold of actual) and/or informed concentration estimate relative errors. HRMS fingerprint mining could identify, based on the dilution behavior, effective individual chemical end-members across 16 homologous series. Although method development is needed, the results further demonstrate the potential applications of non-targeted HRMS data for source apportionment and other quantitative outcomes.

Field-Scale Demonstration of PFAS Leachability Following In Situ Soil Stabilization

A field-scale validation is summarized comparing the efficacy of commercially available stabilization amendments with the objective of mitigating per- and polyfluoroalkyl substance (PFAS) leaching from aqueous film-forming foam (AFFF)-impacted source zones. The scope of this work included bench-scale testing to evaluate multiple amendments and application concentrations to mitigate PFAS leachability and the execution of field-scale soil mixing in an AFFF-impacted fire-training area with nearly 2.5 years of post-soil mixing monitoring to validate reductions in PFAS leachability. At the bench scale, several amendments were evaluated and the selection of two amendments for field-scale evaluation was informed: FLUORO-SORB Adsorbent (FS) and RemBind (RB). Five ∼28 m³ test pits (approximately 3 m wide by 3 m long by 3 m deep) were mixed at a site using conventional construction equipment. One control test pit (Test Pit 1) included Portland cement (PC) only (5% dry weight basis). The other four test pits (Test Pits 2 through 5) compared 5 and 10% ratios (dry weight basis) of FS and RB (also with PC). Five separate monitoring events included two to three sample cores collected from each test pit for United States Environmental Protection Agency (USEPA) Method 1315 leaching assessment. After 1 year, a mass balance for each test pit was attempted comparing the total PFAS soil mass before, during, and after leach testing. Bench-scale and field-scale data were in good agreement and demonstrated >99% decrease in total PFAS leachability (mass basis; >98% mole basis) as confirmed by the total oxidizable precursor assay, strongly supporting the chemical stabilization of PFAS.

Analysis of surfactants by mass spectrometry: Coming to grips with their diversity

Surfactants are surface-active agents widely used in numerous applications in our daily lives as personal care products, domestic, and industrial detergents. To determine complex mixtures of surfactants and their degradation products, unselective and rather insensitive methods, based on colorimetric and complexometric analyses are no longer employable. Analytical methodologies able to determine low concentration levels of surfactants and closely related compounds in complex matrices are required. The recent introduction of robust, sensitive, and selective mass spectrometry (MS) techniques has led to the rapid expansion of the surfactant research field including complex mixtures of isomers, oligomers, and homologues of surfactants as well as their chemically and biodegradation products at trace levels. In this review, emphasis is given to the state-of-the-art MS-based analysis of surfactants and their degradation products with an overview of the current research landscape from traditional methods involving hyphenate techniques (gas chromatography-MS and liquid chromatography-MS) to the most innovative approaches, based on high-resolution MS. Finally, we outline a detailed explanation on the utilization of MS for mechanistic purposes, such as the study of micelle formation in different solvents.

Immunotoxicity of an Electrochemically Fluorinated Aqueous Film-Forming Foam

Aqueous film-forming foams (AFFFs) are complex per- and polyfluoroalkyl substance (PFAS)-containing mixtures used extensively as fire suppressants. AFFF-impacted groundwater and surface water have contaminated drinking water with PFASs in many communities, raising concerns about health effects from drinking water exposures. As individual PFASs have been identified as immune hazards, the immunotoxicity of complex PFAS mixtures is also a concern. Adult female and male C57BL/6 mice were given a commercial AFFF formulation for 10 days via gavage; administered dose was based on combined content of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) measured in the formulation (0, 1.88, 3.75, 7.5, or 10 mg PFOS+PFOA/kg body weight). A PFOA positive control of 7.5 mg/kg body weight was also given. Compared with the 0 mg/kg group, the following changes were noted: Body weights of males exposed to 7.5 and 10 mg PFOS+PFOA/kg were reduced by 15%, on average; female body weights did not differ. Average relative liver weights were increased 50%-200% in males and 37.5%-193% in females and liver peroxisome proliferation was increased 2- to 12-fold in all doses of both sexes. Antigen-specific antibody production was suppressed, on average, by 13% in males and by 12.4% in females across all doses. Spleen cellularity and lymphocyte subpopulations did not differ by dose for either sex. Our data indicate that though this complex PFAS mixture contained fairly low PFOA content, it induced changes in C57BL/6 mice similar to changes induced by PFOA alone, likely due to the presence of PFOS and many other PFASs.

Impact of a Hydrocarbon Surfactant on the Retention and Transport of Perfluorooctanoic Acid in Saturated and Unsaturated Porous Media

The transport and retention behavior of perfluorooctanoic acid (PFOA) in the presence of a hydrocarbon surfactant under saturated and unsaturated conditions was investigated. Miscible-displacement transport experiments were conducted at different PFOA and sodium dodecyl sulfate (SDS) input ratios to determine the impact of SDS on PFOA adsorption at solid-water and air-water interfaces. A numerical flow and transport model was employed to simulate the experiments. The PFOA breakthrough curves for unsaturated conditions exhibited greater retardation compared to those for saturated conditions in all cases, owing to air-water interfacial adsorption. The retardation factor for PFOA with a low concentration of SDS (PFOA-SDS ratio of 10:1) was similar to that for PFOA without SDS under unsaturated conditions. Conversely, retardation was greater in the presence of higher levels of SDS (1:1 and 1:10) with retardation factors increasing from 2.4 to 2.9 and 3.6 under unsaturated conditions due to enhanced adsorption at the solid-water and air-water interfaces. The low concentration of SDS had no measurable impact on PFOA air-water interfacial adsorption coefficients (K_ia) determined from the transport experiments. The presence of SDS at the higher PFOA-SDS concentration ratios increased the surface activity of PFOA, with transport-determined K_ia values increased by 27 and 139%, respectively. The model provided very good independently predicted simulations of the measured breakthrough curves and showed that PFOA and SDS experienced various degrees of differential transport during the experiments. These results have implications for the characterization and modeling of poly-fluoroalkyl substances (PFAS) migration potential at sites wherein PFAS and hydrocarbon surfactants co-occur.

Characterization of advanced wastewater treatment with ozone and activated carbon using LC-HRMS based non-target screening with automated trend assignment

Advanced treatment is increasingly being applied to improve abatement of micropollutants in wastewater effluent and reduce their load to surface waters. In this study, non-target screening of high-resolution mass spectrometry (HRMS) data, collected at three Swiss wastewater treatment plants (WWTPs), was used to evaluate different advanced wastewater treatment setups, including (1) granular activated carbon (GAC) filtration alone, (2) pre-ozonation followed by GAC filtration, and (3) pre-ozonation followed by powdered activated carbon (PAC) dosed onto a sand filter. Samples were collected at each treatment step of the WWTP and analyzed with reverse-phase liquid chromatography coupled to HRMS. Each WWTP received a portion of industrial wastewater and a prioritization method was applied to select non-target features potentially resulting from industrial activities. Approximately 37,000 non-target features were found in the influents of the WWTPs. A number of non-target features (1207) were prioritized as likely of industrial origin and 54 were identified through database spectral matching. The fates of all detected non-target features were assessed through a novel automated trend assignment method. A trend was assigned to each non-target feature based on the normalized intensity profile for each sampling date. Results showed that 73±4% of influent non-target features and the majority of industrial features (89%) were well-removed (i.e., >80% intensity reduction) during biological treatment in all three WWTPs. Advanced treatment removed, on average, an additional 11% of influent non-target features, with no significant differences observed among the different advanced treatment settings. In contrast, when considering a subset of 66 known micropollutants, advanced treatment was necessary to adequately abate these compounds and higher abatement was observed in fresh GAC (7,000-8,000 bed volumes (BVs)) compared to older GAC (18,000-48,000 BVs) (80% vs 56% of micropollutants were well-removed, respectively). Approximately half of the features detected in the WWTP effluents were features newly formed during the various treatment steps. In ozonation, between 1108-3579 features were classified as potential non-target ozonation transformation products (OTPs). No difference could be observed for their removal in GAC filters at the BVs investigated (70% of OTPs were well-removed on average). Similar amounts (67%) was observed with PAC (7.7-13.6 mg/L) dosed onto a sand filter, demonstrating that a post-treatment with activated carbon is efficient for the removal of OTPs.

Rapid, low-cost, and in-situ analysis of per- and polyfluoroalkyl substances in soils and sediments by ambient 3D-printed cone spray ionization mass spectrometry

A rapid method to empirically determine the presence of trace per- and polyfluoroalkyl substances (PFAS) in solid media, such as soils, sands, and sediments, without any sample preparation, through ambient ionization mass spectrometry (MS), is described. 3D-printed cone spray ionization (3D-PCSI) is an ambient ionization technique that employs a 3D-printed conductive plastic cone to perform both sampling and ionization. The 3D-PCSI sources are fabricated in the shape of a hollowed square pyramid to hold bulk matrices, and consist of rigid walls to aid in the uniformity and consistency of sampling and ionization. Solid samples are placed within the hollowed pyramid and a solvent is added to perform an in-situ extraction, followed by spray-based ionization when a voltage is applied. The low cost of 3D-printing, its reproducibility at scale, and lack of sample preparation, enables 3D-PCSI-MS to rapidly and efficiently screen for trace PFAS, in-situ, in bulk samples. Demonstrated here is the detection of trace PFAS that were doped into six different soil and sediment matrices, by 3D-PCSI-MS, to validate the universality of the method, irrespective of matrix composition. All PFAS were identified by their indicative MS³ spectra and ranged in detection limits from 100 ppt to 10 ppb depending on the compound and soil classification. Legacy aqueous film forming foams (AFFF) were analyzed in soil by 3D-PCSI-MS, as were soil samples collected around an AFFF testing facility. The sampling rate for 3D-PCSI-MS was less than 2 min per sample, demonstrating the applicability to high-throughput mapping of a contaminated area.

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.

Utilization of a NIST SRM: a case study for per- and polyfluoroalkyl substances in NIST SRM 1957 organic contaminants in non-fortified human serum

The National Institute of Standards and Technology (NIST) generates and maintains thousands of Standard Reference Materials (SRMs) to serve commerce worldwide. Many SRMs contain metrologically traceable mass fractions of known organic chemicals and are commercially available to aid the analytical chemistry community. One such material, NIST SRM 1957 Organic Contaminants in Non-Fortified Human Serum, was one of the first materials issued by NIST with measurements for per- and polyfluoroalkyl substances (PFAS) listed on the Certificate of Analysis and was commercially available in 2009. Since the release of SRM 1957, nearly 400 units have been sold to date, and over 50 publications related to PFAS measurements have included this material for multiple analytical purposes, such as a quality control material, for interlaboratory comparison, as an in-house comparison tool, for inter- and intra-day measurement accuracy, as an indicator of isomeric patterns of PFAS, and for other uses. This perspective details the ways SRM 1957 is utilized by the analytical community and how data have been reported in the literature. A discussion on accurately comparing SRM data to generated data is included. Furthermore, we conducted an in-depth investigation around additional applications for NIST SRMs, such as a matrix-matched reference material, and for the identification of targeted compounds during high-resolution mass spectrometry data collection. Ultimately, this manuscript illustratively describes the ways to utilize a NIST SRMs for chemicals of emerging concern.

Assessment of emerging polar organic pollutants linked to contaminant pathways within an urban estuary using non-targeted analysis

A comprehensive, non-targeted analysis of polar organic pollutants using high resolution/accurate mass (HR/AM) mass spectrometry approaches has been applied to water samples from San Francisco (SF) Bay, a major urban estuary on the western coast of the United States, to assess occurrence of emerging contaminants and inform future monitoring and management activities. Polar Organic Chemical Integrative Samplers (POCIS) were deployed selectively to evaluate the influence of three contaminant pathways: urban stormwater runoff (San Leandro Bay), wastewater effluent (Coyote Creek, Lower South Bay), and agricultural runoff (Napa River). Grab samples were collected before and after deployment of the passive samplers to provide a quantitative snapshot of contaminants for comparison. Composite samples of wastewater effluent (24 hours) were also collected from several wastewater dischargers. Samples were analyzed using liquid-chromatography coupled to high resolution mass spectrometry. Resulting data were analyzed using a customized workflow designed for high-fidelity detection, prioritization, identification, and semi-quantitation of detected molecular features. Approximately 6350 compounds were detected in the combined data set, with 424 of those compounds tentatively identified through high quality spectral library match scores. Compounds identified included ethoxylated surfactants, pesticide and pharmaceutical transformation products, polymer additives, and rubber vulcanization agents. Compounds identified in samples were reflective of the apparent sources and pathways of organic pollutant inputs, with stormwater-influenced samples dominated by additive chemicals likely derived from plastics and vehicle tires, as well as ethoxylated surfactants.

Characterization of water-soluble synthetic polymeric substances in wastewater using LC-HRMS/MS

Synthetic water-soluble polymeric materials are widely employed in e.g. cleaning detergents, personal care products, paints or textiles. Accordingly, these compounds reach sewage treatment plants and may enter receiving waters and the aquatic environment. Characteristically, these molecules show a polydisperse molecular weight distribution, comprising multiple repeating units, i.e. a homologous series (HS). Their analysis in environmentally relevant samples has received some attention over the last two decades, however, the majority of previous studies focused on surfactants and a molecular weight range <1000 Da. To capture a wider range on the mass versus polarity plane and extend towards less polar contaminants, a workflow was established using three different ionization strategies, namely conventional electrospray ionization, atmospheric pressure photoionization and atmospheric pressure chemical ionization. The data evaluation consisted of suspect screening of ca. 1200 suspect entries and a non-target screening of HS with pre-defined accurate mass differences using ca. 400 molecular formulas of repeating units of HS as input and repeating retention time shifts as HS indicator. To study the fate of these water-soluble polymeric substances in the wastewater treatment process, the different stages, i.e. after primary and secondary clarifier, and after ozonation followed by sand filtration, were sampled at a Swiss wastewater treatment plant. Remaining with two different ionization interfaces, ESI and APPI, in both polarities, a non-targeted screening approach led to a total number of 146 HS (each with a minimum number of 4 members), with a molecular mass of up to 1200 detected in the final effluent. Of the 146 HS, ca 15% could be associated with suspect hits and approximately 25% with transformation products of suspects. Tentative characterization or probable chemical structure could be assigned to almost half of the findings. In positive ionization mode various sugar derivatives with differing side chains, for negative mode structures with sulfonic acids, could be characterized. The number of detected HS decreased significantly over the three treatment stages. For HS detectable also in the biological and oxidative treatment stages, a change in HS distribution towards to lower mass range was often observed.

Structural control of the non-ionic surfactant alcohol ethoxylates (AEOs) on transport in natural soils

Surfactants, after use, enter the environment through diffuse and point sources such as irrigation with treated and non-treated waste water and urban and industrial wastewater discharges. For the group of non-ionic synthetic surfactant alcohol ethoxylates (AEOs), most of the available information is restricted to the levels and fate in aquatic systems, whereas current knowledge of their behavior in soils is very limited. Here we characterize the behavior of different homologs (C12-C18) and ethoxymers (EO3, EO6, and EO8) of the AEOs through batch experiments and under unsaturated flow conditions during infiltration experiments. Experiments used two different agricultural soils from a region irrigated with reclaimed water (Guadalete River basin, SW Spain). In parallel, water flow and chemical transport were modelled using the HYDRUS-1D software package, calibrated using the infiltration experimental data. Estimates of water flow and reactive transport of all surfactants were in good agreement between infiltration experiments and simulations. The sorption process followed a Freundlich isotherm for most of the target compounds. A systematic comparison between sorption data obtained from batch and infiltration experiments revealed that the sorption coefficient (K_d) was generally lower in infiltration experiments, performed under environmental flow conditions, than in batch experiments in the absence of flow, whereas the exponent (β) did not show significant differences. For the low clay and organic carbon content of the soils used, no clear dependence of K_d on them was observed. Our work thus highlights the need to use reactive transport parameterization inferred under realistic conditions to assess the risk associated with alcohol ethoxylates in subsurface environments.

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.

Different submicellar solubilization mechanisms revealed by 1H NMR and 2D diffusion ordered spectroscopy (DOSY)

Different submicellar solubilization mechanisms of two systems, Triton X-100 (TX-100)/tetradecane and sodium dodecyl sulfate (SDS)/butyl methacrylate, are revealed on the molecular scale by ¹H NMR spectroscopy and 2D diffusion ordered spectroscopy (DOSY). It is evident that the apparent solubilities of both tetradecane and butyl methacrylate are enhanced, even at much lower surfactant concentrations than the CMCs. Solubilized solutes also contribute to the early formation of surfactant micelles. In general, the molar solubilization ratios (MSRs) of both solutes linearly increase as the surfactant concentrations increase. However, variations in MSRs of the two systems are different below and above the CMC, which is probably related to the different solubilization mechanisms. For TX-100/tetradecane, as the TX-100 concentration increases, the tetradecane resonance in the independent state transforms into that of the aggregated state and the corresponding evolution of diffusions is shown in the 2D DOSY spectra. These results demonstrate that below the CMC, tetradecane is first solubilized in TX-100 solutions, and then solubilized in TX-100 micelles above the CMC. For SDS/butyl methacrylate, the appearance of oligomeric SDS resonances below the CMC indicates that butyl methacrylate is partially solubilized in SDS oligomers. Then, when the CMC is reached, the dominant, monomeric SDS molecules aggregate into oligomers, and the similar diffusivity trend of butyl methacrylate with that of SDS indicates that a proportion of butyl methacrylate molecules are solubilized in it. Finally, the fusion of SDS resonances in the two states and the tendency of co-diffusion of SDS and butyl methacrylate indicate that all the SDS molecules gradually aggregate into micelles, and almost all the butyl methacrylate molecules are solubilized in them. In conclusion, above the CMCs, the solubilization manners of these two systems are similar. However, they are different below CMCs. The solubilization of tetradecane by TX-100 is driven by the intermolecular hydrophobic interaction, i.e., molecular-pair formation. However, the polar interaction between functional groups of butyl methacrylate and the polar head of SDS contributes to the solubilization of butyl methacrylate. The different submicellar solubilization mechanisms are mainly caused by the different properties of solutes and surfactants, which also results in different MSRs and solubilization sites in the micelles.

Nontarget Screening of Per- and Polyfluoroalkyl Substances Binding to Human Liver Fatty Acid Binding Protein

More than 1000 per- and polyfluoroalkyl substances (PFASs) have been discovered by nontarget analysis (NTA), but their prioritization for health concerns is challenging. We developed a method by incorporating size-exclusion column co-elution (SECC) and NTA, to screen PFASs binding to human liver fatty acid binding protein (hL-FABP). Of 74 PFASs assessed, 20 were identified as hL-FABP ligands in which eight of them have high binding affinities. Increased PFAS binding affinities correlate with stronger responses in electrospray ionization (ESI^-) and longer retention times on a C18 column. This is well explained by a mechanistic model, which revealed that both polar and hydrophobic interactions are crucial for binding affinities. Encouraged by this, we then developed an SECC method to identify hL-FABP ligands, and all eight high-affinity ligands were selectively captured from 74 PFASs. The method was further applied to an aqueous film-forming foam (AFFF) product in which 31 new hL-FABP ligands were identified. Suspect and nontargeted screening revealed these ligands as analogues of perfluorosulfonic acids and homologues of alkyl ether sulfates (C₈- and C₁₀/EO_n, C₈H₁₇(C₂H₄O)_nSO₄^-, and C₁₀H₂₁(C₂H₄O)_nSO₄^-). The SECC method was then applied to AFFF-contaminated surface waters. In addition to perfluorooctanesulfonic acid and perfluorohexanesulfonic acid, eight other AFFF chemicals were discovered as novel ligands, including four C₁₄- and C₁₅/EO_n. This study implemented a high-throughput method to prioritize PFASs and revealed the existence of many previously unknown hL-FABP ligands.

Characterization of the Chemical Contents of Fluorinated and Fluorine-Free Firefighting Foams Using a Novel Workflow Combining Nontarget Screening and Total Fluorine Analysis

Aqueous film-forming foams (AFFFs) are widely used to extinguish liquid fires due to their film-forming properties. AFFF formulation historically contains per- and polyfluoroalkyl substances (PFASs) that can be very persistent and pose a health risk to biota and humans. Detailed analysis of the chemical composition of AFFFs can provide a better understanding on the potential environmental impact of the ingredients. In this study, a novel workflow combining target analysis, nontarget screening analysis (NTA), total fluorine (TF) analysis, and inorganic fluoride (IF) analysis was applied to disclose the chemical composition of 24 foams intended for liquid fires. Foams marketed as containing PFASs as well as fluorine-free foams were included. By comparing the sum of targeted PFASs and total organofluorine concentrations, a mass balance of known and unknown organofluorine could be calculated. Known organofluorine accounted for <1% in most fluorine-containing AFFFs, and it was confirmed that the foams marketed as fluorine-free did not contain measurable amounts of organofluorine substances. Five fluorinated substances were tentatively identified, and non-fluorinated zwitterionic betaine compounds, which are considered to be replacement substances for PFASs, were tentatively identified in the organofluorine-free foams.