Identification of novel fluorinated surfactants in aqueous film forming foams and commercial surfactant concentrates

Compositional space: A guide for environmental chemists on the identification of persistent and bioaccumulative organics using mass spectrometry

Since 2001, twenty-eight halogenated groups of persistent organic pollutants (POPs) have been banned or restricted by the Stockholm Convention. Identifying new POPs among the hundreds of thousands of anthropogenic chemicals is a major challenge that is increasingly being met by state-of-the-art mass spectrometry (MS). The first step to identification of a contaminant molecule (M) is the determination of the type and number of its constituent elements, viz. its elemental composition, from mass-to-charge (m/z) measurements and ratios of isotopic peaks (M + 1, M + 2 etc.). Not every combination of elements is possible. Boundaries exist in compositional space that divides feasible and improbable compositions as well as different chemical classes. This study explores the compositional space boundaries of persistent and bioaccumulative organics. A set of ~305,134 compounds (PubChem) was used to visualize the compositional space occupied by F, Cl, and Br compounds, as defined by m/z and isotope ratios. Persistent bioaccumulative organics, identified by in silico screening of 22,049 commercial chemicals, reside in more constrained regions characterized by a higher degree of halogenation. In contrast, boundaries surrounding non-halogenated chemicals could not be defined. Finally, a script tool (R code) was developed to select potential POPs from high resolution MS data. When applied to household dust (SRM 2585), this approach resulted in the discovery of previously unknown chlorofluoro flame retardants.

Sorption and Desorption Mechanisms of Cationic and Zwitterionic Per- and Polyfluoroalkyl Substances in Natural Soils: Thermodynamics and Hysteresis

Sorption linearity and reversibility are implicit in models for the fate and transport of per- and polyfluoroalkyl substances (PFAS). In this study, however, we found that the sorption of cationic and zwitterionic PFAS in natural soils was highly nonlinear. The nonlinearity was so severe that it led to a variation in the coefficient of sorption by several orders of magnitude over the experimental concentration range. This implies a considerable increase in sorption as concentration falls in the natural environment. Sorption of cationic PFAS correlated strongly with the soil organic matter (SOM) content and was reversible in all soils. Sorption of zwitterionic PFAS, on the other hand, displayed concentration-dependent hysteresis in soils with a low SOM content. The irreversibility, which was associated with neither SOM, pore deformation, nor surface complexation, was likely caused by the entrapment of molecules in porous structures within inorganic components of soil aggregates. Furthermore, electrostatic interactions with negatively charged soil constituents and the hydrophobic effect were found to be major sorption driving forces for cationic/zwitterionic PFAS at low and high concentrations, respectively. The maximum electrostatic potential of PFAS ions, computed using density functional theory, was found to be a useful predictor of the sorption of ionic PFAS species.

Column chromatography approach to determine mobility of fluorotelomer sulfonates and polyfluoroalkyl betaines

Betaine-based polyfluoroalkyl surfactants are major perfluoroalkyl and polyfluoroalkyl surfactants (PFASs) found in many aqueous film-forming foams (AFFF) impacted sites, while the transport behavior (i.e., mobility and adsorption) of PFAS-based betaines in groundwater and natural geosorbents interfaces remains unclear. To fill the knowledge gap, partitioning between of 15 AFFF-relevant PFASs, including 3 fluorotelomer sulfonates (FTSAs) and 3 polyfluoroalkyl betaines, and a model soil organic matter (SOM) were systematically assessed using a modified column chromatography approach. Results show that the retention of FTSAs (perfluoroalkyl chain-length of 4, 6, and 8) to SOM are similar to that of corresponding legacy perfluoroalkyl sulfonic acids (PFSAs) with the same chain length; FTSAs also respond to changes in solution chemistry similarly as PFSAs. At a solution pH of 5.9, based on the equilibrium speciation of the betaine-PFASs together with the experimental observations, the predominance of the neutral species over zwitterions gives rise to the relatively higher retention of polyfluoroalkyl betaines than perfluoroalkyl carboxylic acids (PFCAs) of equivalent chain-length. Sorption edges (minimal and maximal logK_oc values over a defined pH range) determined for three polyfluoroalkyl betaines are: 1.90-3.81 for perfluorooctaneamide betaine (PFOAB), 2.03-2.65 for perfluoroctane sulfonamide betaine (PFOSB), and < 3.04 for 6:2 fluorotelomer sulfonamide betaine (6:2 FTAB). Moreover, the increase in pH reduces the sorption of all PFASs to SOM. Increasing calcium ion (concentration ranges from 0.5 to 50 mM) has enhanced the sorption of anionic PFASs to SOM but decreased the sorption of the polyfluoroalkyl betaines. These findings are expected to improve the ability to anticipate and predict the possible subsurface locations (i.e., predominantly in groundwater or sorbed to soil) of both novel and legacy PFASs.

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

Aqueous film-forming foams (AFFFs) are proprietary mixtures containing hydrocarbon surfactants and per- and polyfluoroalkyl substances (PFASs) that are used to extinguish hydrocarbon-based fuel fires. There is limited information on hydrocarbon surfactants in AFFFs and AFFF-contaminated groundwater even though hydrocarbon surfactants are more abundant (5-10% w/w) than PFASs (0.9-1.5% w/w) in AFFFs. Eight commercial AFFFs manufactured between 1988 and 2012 and 10 AFFF-contaminated groundwaters collected from near source zones of fire-fighter training areas were analyzed for suspect hydrocarbon surfactants by liquid chromatography quadrupole time-of-flight mass spectrometry. A suspect list and a homologous series detection computational tool, enviMass, were combined to screen for hydrocarbon surfactants. Nine classes of hydrocarbon surfactants were detected in AFFFs including octylphenol polyethoxylates, linear alcohol ethoxylates, ethoxylated cocoamines, alkyl ether sulfates, alkyl amido dipropionates, linear alkyl benzenesulfonates, alkyl sulfates, and polyethylene glycols. Of those, six were also found in groundwater along with diethanolamines and alkyl amido betaines, which were not found in the eight archived AFFFs. This indicates that although aerobically biodegradable, hydrocarbon surfactants likely persist in groundwater due to anaerobic aquifer conditions. To the best of our knowledge, this is the first screening for hydrocarbon surfactants in AFFFs and in AFFF-contaminated groundwater.

Determination of adsorbable organically bound fluorine (AOF) and adsorbable organically bound halogens as sum parameters in aqueous environmental samples using combustion ion chromatography (CIC)

Because of their toxicity and biomagnification potential individual perfluoroalkyl and polyfluoroalkyl substances (PFAS) are regularly examined in food and environmental matrices by LC-MS/MS. The combustion ion chromatography (CIC) can be used to determine adsorbable organic fluorine (AOF) in aqueous samples. This report describes the optimization and validation of an automated, robust, cost-efficient and rapid CIC method for the determination of AOF. The analysis of 25 fluorinated organic reference substances was performed with recoveries between 16% and 121%. Water from selected surface waters (n = 74), municipal (n = 116) and industrial wastewaters (n = 33) as well as ground water (n = 93) were analyzed by means of CIC. The AOF values of surface water varied between 2.3 and 24.5 μg/L. The concentrations of AOF in 85% of the wastewater discharges were between 2.0 and 8.5 μg/L, while 15% of the samples were below the limit of quantitation (LOQ = 2 μg/L AOF). In 56% of the ground water samples the values were below the LOQ. In 44% of the surface water samples (n = 41) the values were between 2.0 and 6.1 μg/L AOF. CIC analysis was performed in 22 samples from a chemical company wastewater treatment plant, and 14 individual PFAS were determined by LC-MS/MS. AOF values up to 555 μg/L were found in these samples while the total of the individual PFAS, calculated as fluorine, was 8.8 μg/L. This provides evidence, that CIC covers a huge range of fluoroorganic compounds that are presently not detected by LC-MS/MS. Furthermore, the CIC method allowed the determination of four halogens in 26 surface water samples. This demonstrated that the CIC technique can be used as a powerful screening test to support LC-MS/MS methods, and is also useful to detect organic chlorine, bromine and iodine compounds (AOCl, AOBr and AOI).

Prenatal Exposure to Per- and Polyfluoroalkyl Substances (PFASs) and Association between the Placental Transfer Efficiencies and Dissociation Constant of Serum Proteins-PFAS Complexes

Information on placental transfer and adverse outcomes of short-chain per- and polyfluoroalkyl substance (PFASs) is limited, and factors responsible for PFAS placental transfer are still unclear. In the present study, concentrations of 21 PFASs were analyzed in 132 paired maternal and cord serum samples collected from residents in Beijing, China, and the placental transfer efficiency (PTE) of each PFAS was calculated. PTEs of short-chain perfluoroalkyl acids (PFAAs), including PFBA (146%), PFBS (97%), PFPeA (118%), and PFHxA (110%), were first reported, and a complete U-shaped trend of PTEs from C4 to C13 of perfluoroalkyl carboxylic acids (PFCAs) was obtained. Positive association between maternal weight and PTE of perfluorooctanesulfonate (PFOS) ( p < 0.05) and negative association between maternal PFBA concentration and birth length ( p < 0.01) were observed. Using in vitro experiments, we further determined equilibrium dissociation constants ( K_ds) of human serum albumin (HSA)-PFAS complexes ( K_d-HP), serum proteins-PFAS complexes ( K_d-SP), and liver-fatty acid binding protein (L-FABP)-PFAS complexes ( K_d-LP) and found that they were all significantly correlated with PTEs of PFASs. The correlation coefficient was 0.92, 0.89, and 0.86, respectively ( p < 0.01 in all three tests), suggesting that K_ds of protein (serum)-PFAS complexes can play an important role in trans-placental transfer of PFASs in human and K_d-HP plays a pivotal role.

Efficient removal of perfluorinated compounds from water using a regenerable magnetic activated carbon

Adsorption by powder activated carbon (PAC) is recognized as an efficient method for the removal of perfluorinated compounds (PFCs) in water, while the poor separation of spent PAC makes it difficult for further regeneration, increasing the treatment cost significantly. In this study, an ultrafine magnetic activated carbon (MAC) consisting of Fe₃O₄ and PAC was prepared by ball milling to remove PFCs from water efficiently. Increasing the percentage of Fe₃O₄ and balling milling time decreased its adsorption capacity for perfluoroctane sulfonate (PFOS), whereas increased the magnetic separation property to some degree. The optimized MAC was prepared with a Fe₃O₄ to PAC mass ratio of 1:3 after ball milling for 2 h, and the adsorption equilibriums of all the four PFCs on the optimal MAC were reached within less than 2 h, with the adsorption capacities of 1.63, 0.90, 0.33 and 0.21 mmol/g for PFOS, perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS) and perfluorobutane sulfonate (PFBS), respectively. Increasing the solution pH hindered the adsorption of PFOS significantly when the pH was less than the zero potential point (around 6) of the MAC, due to the decreased electrostatic attraction. The spent MAC could be easily separated with a magnet and regenerated by a small volume of methanol, and the regenerated MAC could be reused for more than 5 time and remain stable adsorption capacity for PFOS after 3 cycles. This study provides useful insights into the removal of PFCs by separable magnetic PAC in wastewater.

Occurrence and Degradation Potential of Fluoroalkylsilane Substances as Precursors of Perfluoroalkyl Carboxylic Acids

Polyfluoroalkylsilanes (PFASis) are a class of artificial chemicals with wide applications in surface coating, which arouse attention due to their hydrophobic/oleophobic properties and potential biological effects. In this study, a robust high-resolution mass spectrometry method through direct injection into a Fourier transform ion cyclotron resonance instrument was established, with the aid of CF₂-scaled Kendrick mass defect analysis and isotope fine structure elucidation. The occurrence of 8:2 polyfluoroalkyl trimethoxysilane (8:2 PTrMeOSi) and 8:2 polyfluoroalkyl triethoxysilane (8:2 PTrEtOSi), as well as their cationic adducts, solvent substitutions, and other compound analogues, were identified in commercial antifingerprint liquid products. In the hydroxyl radical-based total oxidizable precursor assay, differential molar yields of products were observed with regard to varied PFASi carbon-chain lengths and terminal groups. The yields of perfluoroalkyl carboxylic acids (PFCAs) from 8:2 PTrMeOSi conversion were the highest (92 ± 9%, n = 3), with the C ( n - 1) perfluoroheptanoic acid (PFHpA, 49 ± 11%, n = 3) as the dominating product. Distinct conversion of 8:2 PTrMeOSi in the simulated solar exposure experiments found that C ( n) perfluorooctanoic acid (PFOA, 0.6 ± 0.04 ‰, n = 3) was predominant, and 8:2 fluorotelomer carboxylic acid (8:2 FTCA, 0.59 ± 0.08‰, n = 3), 8:2 fluorotelomer unsaturated carboxylic acid (8:2 FTUCA, 0.09 ± 0.00‰, n = 3) intermediates were also observed. To our knowledge, this is the first report regarding the occurrence and degradation potential of several fluoroalkylsilane substances as PFCA precursors.

The role of analytical chemistry in exposure science: Focus on the aquatic environment

Exposure science, in its broadest sense, studies the interactions between stressors (chemical, biological, and physical agents) and receptors (e.g. humans and other living organisms, and non-living items like buildings), together with the associated pathways and processes potentially leading to negative effects on human health and the environment. The aquatic environment may contain thousands of compounds, many of them still unknown, that can pose a risk to ecosystems and human health. Due to the unquestionable importance of the aquatic environment, one of the main challenges in the field of exposure science is the comprehensive characterization and evaluation of complex environmental mixtures beyond the classical/priority contaminants to new emerging contaminants. The role of advanced analytical chemistry to identify and quantify potential chemical risks, that might cause adverse effects to the aquatic environment, is essential. In this paper, we present the strategies and tools that analytical chemistry has nowadays, focused on chromatography hyphenated to (high-resolution) mass spectrometry because of its relevance in this field. Key issues, such as the application of effect direct analysis to reduce the complexity of the sample, the investigation of the huge number of transformation/degradation products that may be present in the aquatic environment, the analysis of urban wastewater as a source of valuable information on our lifestyle and substances we consumed and/or are exposed to, or the monitoring of drinking water, are discussed in this article. The trends and perspectives for the next few years are also highlighted, when it is expected that new developments and tools will allow a better knowledge of chemical composition in the aquatic environment. This will help regulatory authorities to protect water bodies and to advance towards improved regulations that enable practical and efficient abatements for environmental and public health protection.

Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management

This study investigates critical structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While C _nF_{2 n+1}-COO^- with variable fluoroalkyl chain lengths ( n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric C _nF_{2 n+1}-CH₂CH₂-COO^- and C _nF_{2 n+1}-SO₃^- showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF₃COO^-, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C-F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and number of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calculated geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resolution mass spectrometry. Multiple reaction pathways, including H/F exchange, dissociation of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on molecular structures. These findings provide critical information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochemical formulations to avoid releasing recalcitrant PFASs into the environment.

The overlooked short- and ultrashort-chain poly- and perfluorinated substances: A review

Poly- and perfluorinated substances (PFAS) comprise more than 3000 individual compounds; nevertheless, most studies to date have focused mainly on the fate, transport and remediation of long-chain PFAS (C > 7). The main objective of this article is to provide the first critical review of the peer-reviewed studies on the analytical methods, occurrence, mobility, and treatment for ultra-short-chain PFAS (C = 2-3) and short-chain PFAS (C = 4-7). Previous studies frequently detected ultra-short-chain and short-chain PFAS in various types of aqueous environments including seas, oceans, rivers, surface/urban runoffs, drinking waters, groundwaters, rain/snow, and deep polar seas. Besides, the recent regulations and restrictions on the use of long-chain PFAS has resulted in a significant shift in the industry towards short-chain alternatives. However, our understanding of the environmental fate and remediation of these ultra-short-chain and short-chain PFAS is still fragmentary. We have also covered the handful studies involving the removal of ultra-short and short-chain PFAS and identified the future research needs.

Removal of per- and polyfluoroalkyl substances using super-fine powder activated carbon and ceramic membrane filtration

Contamination of drinking water sources with per- and polyfluoroalkyl substances (PFASs) is a major challenge for environmental engineers. While granular activated carbon (GAC) is an effective adsorbent-based treatment technology for long-chained PFASs, GAC is less effective for removal of short-chained compounds, necessitating a more complete treatment strategy. Super-fine powder activated carbon (SPAC; particle diameter <1 um) is potentially a superior adsorbent to GAC due to high specific surface area and faster adsorption kinetics. This study served to evaluate SPAC coupled with ceramic microfiltration (CMF) for PFAS removal in a continuous flow system. Comparison of PFAS mass loading rates onto SPAC and GAC to 10% breakthrough of PFASs using contaminated groundwater indicates that SPAC has nearly double the adsorption potential of GAC. Limitations reaching breakthrough for the SPAC system led to additional higher mass loading experiments where PFAS adsorption onto SPAC reached 2990 μg/g (for quantifiable PFASs), 480x greater than GAC and is thought to be a function of adsorbent size, pore content and PFAS chain length. Additional analysis of system performance through the application of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) revealed the presence of additional PFASs in influent samples that were removed by the SPAC/CMF system.

Elucidation of contamination sources for poly- and perfluoroalkyl substances (PFASs) on Svalbard (Norwegian Arctic)

A combination of local (i.e. firefighting training facilities) and remote sources (i.e. long-range transport) is assumed to be responsible for the occurrence of per- and polyfluoroalkyl substances (PFASs) in Svalbard (Norwegian Arctic). However, no systematic elucidation of local PFASs sources has been conducted yet. Therefore, a survey was performed aiming at identifying local PFAS pollution sources on the island of Spitsbergen (Svalbard, Norway). Soil, freshwater (lake, draining rivers), seawater, meltwater run-off, surface snow and coastal sediment samples were collected from Longyearbyen (Norwegian mining town), Ny-Ålesund (research facility) and the Lake Linnévatnet area (background site) during several campaigns (2014-2016) and analysed for 14 individual target PFASs. For background site (Linnévatnet area, sampling during April to June 2015), ΣPFAS levels ranged from 0.4 to 4 ng/L in surface lake water (n = 20). PFAS in meltwater from the contributing glaciers showed similar concentrations (~ 4 ng/L, n = 2). The short-chain perfluorobutanoate (PFBA) was predominant in lake water (60-80% of the ΣPFASs), meltwater (20-30%) and run-off water (40%). Long-range transport is assumed to be the major PFAS source. In Longyearbyen, five water samples (i.e. 2 seawater, 3 run-off) were collected near the local firefighting training site (FFTS) in November 2014 and June 2015, respectively. The highest PFAS levels were found in FFTS meltwater run-off (118 ng/L). Perfluorooctane sulfonic acid (PFOS) was the most abundant compound in the FFTS meltwater run-off (53-58% PFASs). At the research station Ny-Ålesund, seawater (n = 6), soil (n = 9) and freshwater (n = 10) were collected in June 2016. Low ΣPFAS concentrations were determined for seawater (5-6 ng/L), whereas high ΣPFAS concentrations were found in run-off water (113-119 ng/L) and soil (211-800 ng/g dry weight (dw)) collected close to the local FFTS. In addition, high ΣPFAS levels (127 ng/L) were also found in freshwater from lake Solvatnet close to former sewage treatment facility. Overall, at both FFTS-affected sites (soil, water), PFOS was the most abundant compound (60-69% of ΣPFASs). FFTS and landfill locations were identified as major PFAS sources for Svalbard settlements.

Distribution, partitioning behavior and positive matrix factorization-based source analysis of legacy and emerging polyfluorinated alkyl substances in the dissolved phase, surface sediment and suspended particulate matter around coastal areas of Bohai Bay, China

The concentrations and spatial occurrences of 17 legacy per- and polyfluoroalkyl substances (PFAS) and 4 emerging PFAS in the coastal water-dissolved phase, surface sediment phase and suspended particulate matter (SPM) in the coastal areas of Bohai Bay were investigated. In addition, the partition behaviors of PFAS in the water-SPM system and water-sediment system and the potential sources of PFAS in the marine environment were revealed. The total concentrations of PFAS (∑PFAS) in the water-dissolved phase, surface sediment and SPM were 20.5-684 ng/L, 2.69-25.0 ng/g dry weight (dw) and 4.39-527 ng/g dw, respectively. The level of PFAS contamination in the coastal areas of Shandong Province was higher than that in other areas. The average partition coefficients (log K_d) of PFAS in the water-SPM system and water-sediment system were 1.56-3.57 and 0.72-2.95, respectively. Long-chain PFAS and PFECHS (perfluoroethylcyclohexane sulfonate) have a higher log K_d than that of short-chain PFAS. PFAS with short carbon chains were mainly detected in the water-dissolved phase, but long-chain PFAS mainly occurred in the surface sediment and SPM phases. Source analysis based on the positive matrix factorization (PMF) model found that erosion inhibitor factories, aqueous film-forming foam factories, metal plating plants, fluoropolymer chemical manufacture and food contact materials were the main sources of PFAS in Bohai Bay. These results improved our understanding of the partitioning behavior and sources of PFAS in aquatic environments.

Isomer-specific biotransformation of perfluoroalkyl sulfonamide compounds in aerobic soil

As an important reservoir of pollutants, soil may play a critical role in altering isomer ratios of perfluorooctane sulfonate (PFOS) or PFOS precursors (PrePFOS) via microbial processes, but this possibility has not yet been investigated, as well as the feasibility of using PFOS isomer ratio for source tracking in PFOS contaminated sites. In the present study, N‑ethyl perfluorooctane sulfonamide ethanol (EtFOSE) of the technical grade was incubated in soil microcosms for 105 days to examine isomer-specific transformation processes. Experimental data combined with a mathematical model suggest new biotransformation pathways leading to PFOS, including a direct pathway to produce PFOS via hydrolysis of the sulfonamide bond. A similar rate of biotransformation was observed for EtFOSE with an estimated half-life of 8.7 and 9.6 days for the branched and linear isomers, respectively, without statistical difference. Two transformation intermediates, N‑ethyl perfluorooctanoic acid (EtFOSAA) and perfluorooctane sulfonamide (FOSA), also showed preferential biotransformation of branched isomers. On the contrary, one intermediate N‑ethyl perfluorooctane sulfonamide (EtFOSA) showed the preferred transformation of the linear isomer with an estimated half-life of 80.8 and 11.2 days for the branched and linear isomers, respectively. As PFOS is likely to be generated through more than one pathway or one precursor, its final isomer ratio is collectively determined by several upstream reactions, each having specific isomer-specific transformation kinetics. Though the soil showed enrichment of branched PFOS isomers during the 4-month incubation, compared to PFOS standards, some uncertainty arises in concluding preferential generation of branched PFOS from its precursors, due to the lack of standards for branched PreFOS. The complexity of isomer-specific biotransformation only reinforced the challenge of applying the PFOS isomer ratio for source tracking in environmental microbial systems.

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.

Transformation of novel polyfluoroalkyl substances (PFASs) as co-contaminants during biopile remediation of petroleum hydrocarbons

Aqueous film forming foams (AFFFs) containing perfluoroalkyl and polyfluoroalkyl substances (PFASs) are commonly deployed to extinguish hydrocarbon fuel fires, resulting in petroleum hydrocarbons coexisting with PFASs in contaminated soil. Nutrient-amended and aerated biopiles used for petroleum hydrocarbon bioremediation could cause unintended transformation of polyfluorinated substances into perfluoroalkyl carboxylates (PFCAs). The study sought to examine environmental behaviors of PFASs in engineered treatment facilities by monitoring AFFF-derived PFASs under three nutrient conditions. The influence of nutrient levels on degradation kinetics and efficiency was found to vary between the two chemical classes and among individual PFASs. A high number of compounds including the zwitterionic polyfluoroalkyl betaines that have aged in the field for two years were continuously biotransforming in lab reactors, demonstrating their slow kinetics and environmental persistence. The low yield to PFCAs implies that the processes such as the formation of bound residues or irreversible sorption might play a major role in reducing detectable levels of zwitterionic PFASs. The high persistence of betaines was further confirmed by the behaviors of a freshly spiked sulfonamide betaine. The study demonstrated complex chemical dynamics in AFFF-impacted soils and the challenges for predicting the fate of PFASs in soil biopiling facilities.

Degradation and defluorination of 6:2 fluorotelomer sulfonamidoalkyl betaine and 6:2 fluorotelomer sulfonate by Gordonia sp. strain NB4-1Y under sulfur-limiting conditions

6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB) is a major component of aqueous film-forming foams (AFFFs) used for firefighting and is frequently detected, along with one of its suspected transformation products, 6:2 fluorotelomer sulfonate (6:2 FTSA), in terrestrial and aquatic ecosystems impacted by AFFF usage. Biochemical processes underlying bacterial biodegradation of these compounds remain poorly understood due to a lack of pure culture studies. Here, we characterized the water-soluble and volatile breakdown products of 6:2 FTSA and 6:2 FTAB produced using Gordonia sp. strain NB4-1Y cultures over seven days under sulfur-limited conditions. After 168 h, 99.9% of 60 μM 6:2 FTSA was degraded into ten major breakdown products, with a mol% recovery of 88.2, while 70.4% of 60 μM 6:2 FTAB was degraded into ten major breakdown products, with a mol% recovery of 84.7. NB4-1Y uses two pathways for 6:2 FTSA metabolism, with 55 mol% of breakdown products assigned to a major pathway and <1.0 mol% assigned to a minor pathway. This work indicates that rapid transformation of 6:2 FTSA and 6:2 FTAB can be achieved under controlled conditions and improves the bacterial metabolism of these compounds.

Deep seepage of per- and polyfluoroalkyl substances through the soil of a firefighter training site and subsequent groundwater contamination

Per- and polyfluoroalkyl substances (PFASs) are utilized in specific firefighting foams. The objectives of this study were i) to map PFAS distribution in the soil and groundwater of a firefighter training site active for more than 3 decades, ii) to locate the main points of entry of PFASs into the aquifer and iii) to identify which PFASs seeped most deeply into the soil. A total of 44 soil cores and 17 groundwater samples were collected. Perfluorooctane sulfonate (PFOS), 6:2 fluorotelomer sulfonic acid (6:2 FTSA) and 6:2 Fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) were the most predominant PFASs in surface soil. The highest total PFAS concentrations (up to 357 μg/g) were measured in two areas. Both areas were considered as potential points of entry of PFASs into the aquifer since PFASs were detected in soil 15 m below the surface, despite the presence of clay layers. The highest total PFAS concentrations were recorded in the monitoring wells located in the perimeter of the firefighter training site and in the spring located downgradient in the direction of groundwater flow. They ranged from 300 to 8300 ng/L. The fluorotelomer 6:2 FTAB was quantified in 6 monitoring wells, suggesting that this FT can reach a water table 20 m below the ground's surface.

Leaching and bioavailability of selected perfluoroalkyl acids (PFAAs) from soil contaminated by firefighting activities

Historical usage of aqueous film-forming foam (AFFF) at firefighting training grounds (FTGs) is a potential source of perfluoroalkyl acids (PFAAs) to the surrounding environment. In this study the leaching of PFAAs from field contaminated soil and their uptake into biota was investigated. Soil was sampled from FTGs at two airports and the total as well as the leachable concentration of 12 PFAAs was determined. A greenhouse study was carried out to investigate the uptake of PFAAs from soils into earthworms (Eisenia fetida) and wheat grass (Elymus scaber). Perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) were the most dominant PFAAs in all soils samples, with concentrations of PFOS reaching 13,400 ng/g. Leachable concentrations of PFOS and PFHxS reached up to 550 μg/L and 22 μg/L, respectively. In earthworms concentrations of PFOS reached 65,100 ng/g after a 28-day exposure period, while in wheat grass the highest concentration was measured for uptake of PFHxS (2,800 ng/g) after a 10-week growth-period. Bioaccumulation factors (BAFs) for earthworms ranged from 0.1 for perfluorohexanoic acid (PFHxA) to 23 for perfluorododecanoic acid (PFDoA) and initially showed a decreasing trend with increasing perfluoroalkyl chain length, followed by an increase with increasing perfluoroalkyl chain length for perfluoroalkyl carboxylic acids (PFCAs). In wheat grass the highest BAF was found for perfluorobutanoic acid (BAF = 70), while the lowest was observed for perfluorononanoic acid (BAF = 0.06). BAFs in wheat grass decreased with increasing perfluoroalkyl chain length for both PFCAs and perfluoroalkyl sulfonic acids (PFSAs). The results show that PFAAs readily leach from impacted soils and are bioaccumulated into earthworms and plants in an analyte dependent way. This shows considerable potential for PFAAs to move away from the original source either by leaching or uptake into ecological receptors, which may be a potential entry route into the terrestrial foodweb.

Identification and Fate of Aqueous Film Forming Foam Derived Per- and Polyfluoroalkyl Substances in a Wastewater Treatment Plant

The fate of per- and polyfluoroalkyl substances (PFASs) derived from aqueous film forming foam (AFFF) was investigated within a wastewater treatment plant (WWTP) receiving large AFFF inputs from a foam refractory testing event. Targeted analysis, the Total Oxidizable Precursor Assay (TOP Assay), and nontargeted analysis with quadrupole time-of-flight (QTOF) were used to characterize the samples. Over the duration of foam testing, approximately 10.8 kg of total PFASs was measured by TOP Assay in the influent, and 6.3 kg of total PFASs was measured in the effluent; 94 g of PFOS was released in the effluent, apparently from remobilization of historical sources. 1.7% of total PFASs measured in the influent were converted to short chain perfluoroalkyl carboxylates in the effluent. Ten PFAS classes previously reported, including 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), and 5 PFAS classes newly reported were identified by QTOF. The trickling filter was the only unit operation that resulted in significant gains and losses of individual PFASs, including near complete loss of 6:2 FtTAoS due to transformation. Similar reaction pathways for 6:2 FtTAoS reported in previously published soil and activated sludge microcosm experiments were observed in this WWTP, although a higher yield of perfluoroheptanoic acid was observed.

Suspect and Nontarget Screening of Per- and Polyfluoroalkyl Substances in Wastewater from a Fluorochemical Manufacturing Park

Although per- and polyfluoroalkyl substances (PFASs) have always been a key issue in the global environmental field, there are still a lot of undiscovered PFASs in the environment due to new PFAS alternatives developed by manufacturers. Wastewater treatment plants (WWTPs), as one of the sources for PFASs, are an important part of the process of releasing new PFASs into the environment. In this study, suspect screening and PFAS homologue analysis with quadrupole time-of-flight tandem mass spectrometry were used to discover PFASs in wastewater from a WWTP near Yangtze River. Fifteen classes with 90 PFASs were identified, including 12 legacy PFASs (2 classes), 41 previously reported PFASs (7 classes), and 37 new PFASs (6 classes), and 18 of these PFASs were also detected in the nearby Yangtze River. Only 1 PFAS class was removed through the treatment processes (fold change < 1/6). Conversely, 4 PFAS classes increased through the treatment processes (fold change > 6), which could be the transformation products of PFAS precursors. These results implied that most discovered PFASs were not effectively removed in the WWTP. Chlorine-substituted perfluoroalkyl carboxylates (Cl-PFCAs) as the main component of wastewater were detected only in downstream, meaning that Cl-PFCAs in downstream possibly originated from the WWTP.

In-Vial Extraction Large Volume Gas Chromatography Mass Spectrometry for Analysis of Volatile PFASs on Papers and Textiles

Volatile per- and polyfluorinated alkyl substances (PFASs) are found in consumer goods that contribute to human exposure to PFASs. Volatile PFAS precursors transform to perfluorinated carboxylates (PFCAs) and sulfonates (PFSAs) in both humans and the environment. Established methods for volatile PFASs in consumer goods exist, but higher sample throughput and greener sample preparation methods are needed to minimize analyte loss, while maintaining sensitivity. New analytical methodology was developed where a 1.5 × 1.5 cm piece of paper or textile is placed into an autosampler vial with solvent and mass-labeled internal standards, sonicated for 30 min, and directly injected without removal of material from the autosampler vial. Large volume injection (20 μL) gas chromatography mass spectrometry was applied for the quantification for 21 individual PFASs from five classes: fluorotelomer alcohols (FTOHs), fluorinated sulfonamides (N-MeFASA, N-EtFASA), and fluorinated sulfonamidoethanols (N-MeFASE, N-EtFASE). Nontargeted analysis revealed additional C₂-C₇ homologues of N-MeFASE and N-EtFASE, which accounted for 14-18% of the total volatile PFASs on three textiles. Overlooking short-chain (≤C₇) N-MeFASE, N-EtFASE, and long-chained (10:2-14:2) FTOHs on older textiles from the 1980s leads to an underestimation of human and environmental exposure to volatile PFAS.

Non-Target and Suspect Screening of Per- and Polyfluoroalkyl Substances in Airborne Particulate Matter in China

Airborne particulate matter (APM) has an important role in inhalation exposure, especially in China. The environmental occurrence of conventional and unknown per- and polyfluoroalkyl substances (PFASs) in APM remains unclear. Therefore, in this study, a two-stage experiment was designed to identify potential PFASs and to investigate their distribution in APM. Indoor and outdoor APM samples were collected from five selected cities in China. Through PFAS homologue analysis and suspect screening, 50 peaks were identified with different confidence levels (levels 1-3). Among the identified PFASs, 34 emerging PFASs including p-perfluorous nonenoxybenzenesulfonate, 6:2 polyfluoroalkyl phosphate diester, n:2 fluorotelomer sulfonates, n:2 fluorinated telomer acids, n:2 chlorinated polyfluoroalkyl ether sulfonic acids, 1:n polyfluoroalkyl ether carboxylic acids (1:n PFECAs), perfluoroalkyl dioic acids (PFdiOAs), hydro-substituted perfluoroalkyl dioic acids (H-PFdiOAs), and unsaturated perfluorinated alcohols (UPFAs) were identified in APM. In particular, 1:n PFECAs, PFdiOAs, H-PFdiOAs, and UPFAs were first detected in APM. Although human exposure to perfluorooctanoic acid via inhaled APM was noted to not be a risk (hazard quotient <0.1) in this study, the expansion of the PFASs screened in APM implies that human exposure to PFASs might be much more serious and should be considered in future risk assessments in China.

Predicting Relative Protein Affinity of Novel Per- and Polyfluoroalkyl Substances (PFASs) by An Efficient Molecular Dynamics Approach

With the phasing out of long-chain per- and polyfluoroalkyl substances (PFASs), production of a wide variety of alternative PFASs has increased to meet market demand. However, little is known about the bioaccumulation potential of these replacement compounds. Here, we developed a modeling workflow that combines molecular docking and molecular dynamics simulation techniques to estimate the relative binding affinity of a total of 15 legacy and replacement PFASs for human and rat liver-type fatty acid binding protein (hLFABP and rLFABP). The predicted results were compared with experimental data extracted from three different studies. There was good correlation between predicted free energies of binding and measured binding affinities, with correlation coefficients of 0.97, 0.79, and 0.96, respectively. With respect to replacement PFASs, our results suggest that EEA and ADONA are at least as strongly bound to rLFABP as perfluoroheptanoic acid (PFHpA), and as strongly bound to hLFABP as perfluorooctanoic acid (PFOA). For F-53 and F-53B, both have similar or stronger binding affinities than perfluorooctanesulfonate (PFOS). Given that interactions of PFASs with proteins (e.g., LFABPs) are important determinants of bioaccumulation potential in organisms, these alternatives could be as bioaccumulative as legacy PFASs, and are therefore not necessarily safer alternatives to long-chain PFASs.

Sorption of Perfluoroalkyl Acids to Fresh and Aged Nanoscale Zerovalent Iron Particles

The sorption of perfluoroalkyl acids (PFAAs), particularly perfluorooctanesulfonic acid (PFOS), to freshly synthesized nanoscale zerovalent iron (nZVI) and aged (oxidized) and sulfidated nZVI, was investigated under anaerobic conditions. The sorption of PFAAs to nZVI was 2-4 orders of magnitude higher than what has been reported for sediments, soils, and iron oxides. The hydrophobicity of the perfluorocarbon chain dominated the sorption, although FTIR spectra indicated specific interactions between sulfonate and carboxylate head groups and nZVI. The contributions from electrostatic interactions depended on the surface charge and pH. Humic acids influenced sorption only at concentrations above 50 mg/L. nZVI aged in deoxygenated water up to 95 days showed similar sorption isotherms for PFOS to fresh nZVI, because Fe(OH)₂ was the predominant phase on the nZVI surface independent of aging time. Sulfidation of nZVI reduced sorption of PFOS by 1 log unit owing to the FeS deposited, but the sorption affinity was restored after aging because of formation of Fe(OH)₂. Oxidation of nZVI by water and dissolved oxygen also resulted in similar sorption of PFOS as fresh nZVI at environmentally relevant concentrations. The results suggest that injection of nZVI could reduce PFAA concentrations in groundwater despite changes to its surface chemistry with aging.

Biotransformation of AFFF Component 6:2 Fluorotelomer Thioether Amido Sulfonate Generates 6:2 Fluorotelomer Thioether Carboxylate under Sulfate-Reducing Conditions

The fate of per and polyfluoroalkyl substances (PFASs) in aqueous filmforming foams (AFFFs) under anaerobic conditions has not been well characterized, leaving major gaps in our understanding of PFAS fate and transformation at contaminated sites. In this study, the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a component of several AFFF formulations, was investigated under sulfate-reducing conditions in microcosms inoculated with either pristine or AFFF-impacted solids. To identify the transformation products, we used high-resolution mass spectrometry and employed suspect-screening and nontargeted compound identification methods. These analyses demonstrated that 6:2 FtTAoS was transformed primarily to a stable polyfluoroalkyl compound, 6:2 fluorotelomer thioether propionate (6:2 FtTP). It did not undergo further reactions to produce the perfluoroalkyl carboxylates and fluorotelomer sulfonates and carboxylates that were observed during aerobic transformations. Here, the 6:2 FtTP was recalcitrant to biotransformation, indicating the stability of the thioether group under sulfate reducing conditions. The total oxidizable precursor (TOP) assay was used to assess the presence of other PFASs. Although nearly all of the PFAS mass initially present was recovered from the pristine microcosms, only 67% of the initial PFAS mass was recovered from the contaminated microcosms, suggesting the formation of volatile biotransformation products or those that could not be detected by the TOP assay.

Per- and Polyfluoroalkyl Substances in Swedish Groundwater and Surface Water: Implications for Environmental Quality Standards and Drinking Water Guidelines

The aim of this study was to assess per- and polyfluoroalkyl substances (PFASs) in the Swedish aquatic environment, identify emission sources, and compare measured concentrations with environmental quality standards (EQS) and (drinking) water guideline values. In total, 493 samples were analyzed in 2015 for 26 PFASs (∑₂₆PFASs) in surface water, groundwater, landfill leachate, sewage treatment plant effluents and reference lakes, focusing on hot spots and drinking water sources. Highest ∑₂₆PFAS concentrations were detected in surface water (13 000 ng L^-1) and groundwater (6400 ng L^-1). The dominating fraction of PFASs in surface water were perfluoroalkyl carboxylates (PFCAs; 64% of ∑₂₆PFASs), with high contributions from C₄-C₈ PFCAs (94% of ∑PFCAs), indicating high mobility of shorter chain PFCAs. In inland surface water, the annual average (AA)-EQS of the EU Water Framework Directive of 0.65 ng L^-1 for ∑PFOS (linear and branched isomers) was exceeded in 46% of the samples. The drinking water guideline value of 90 ng L^-1 for ∑₁₁PFASs recommended by the Swedish EPA was exceeded in 3% of the water samples from drinking water sources ( n = 169). The branched isomers had a noticeable fraction in surface- and groundwater for perfluorooctanesulfonamide, perfluorohexanesulfonate, and perfluorooctanesulfonate, highlighting the need to include branched isomers in future guidelines.

Worldwide drinking water occurrence and levels of newly-identified perfluoroalkyl and polyfluoroalkyl substances

In the last decade or so, concerns have arisen with respect to the widespread occurrence of perfluoroalkyl acids (PFAAs) in the environment, food, drinking water, and humans. In this study, the occurrence and levels of a large range of perfluoroalkyl and polyfluoroalkyl substances (PFASs) were investigated in drinking water (bottled and tap water samples) from various locations around the world. Automated off-line solid phase extraction followed by ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry was used to analyze PFASs of various chain lengths and functional groups. In total, 29 target and 104 suspect-target PFASs were screened in drinking water samples (n=97) from Canada and other countries (Burkina Faso, Chile, Ivory Coast, France, Japan, Mexico, Norway, and the USA) in 2015-2016. Out of the 29 PFASs quantitatively analyzed, perfluorocarboxylates (PFCAs: C_4/14), perfluoroalkane sulfonates (PFSAs: C₄, C₆, C₈), and perfluoroalkyl acid precursors (e.g., 5:3 fluorotelomer carboxylate (5:3 FTCA)) were recurrently detected in drinking water samples (concentration range: <LOD to 39ngL^-1). Tap water samples from Canada showed noteworthy differences depending on their source; for instance, ∑₂₉PFASwas significantly greater in those produced from the Great Lakes/St. Lawrence River ecosystem than those produced from other types of sources (14 versus 5.3ngL^-1, respectively). A suspect-target screening approach indicated that other perfluoroalkane sulfonamides (FBSA, FHxSA), perfluoroethyl cyclohexane sulfonate (PFECHS), ultrashort chain (C₂-C₃) PFSAs (PFEtS, PFPrS), and two additional PFSAs (PFPeS (C₅) and PFHpS (C₇)) were repeatedly present in tap water samples (concentration ranges: <LOD to 4.0ngL^-1). To the authors' best knowledge, this constitutes the first observation of a cyclic perfluoroalkane sulfonate (PFECHS) and C₄-C₆ perfluoroalkane sulfonamides (FBSA, FHxSA) in drinking water. According to the newly updated US EPA health advisory for PFOS and PFOA (70ngL^-1), the drinking water samples collected in the present monitoring would not pose a health risk to consumers as regards PFAA levels.

6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), a novel perfluorooctane sulfonate alternative, induced developmental toxicity in zebrafish embryos

6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) is a major component of Forafac^®1157, a novel perfluorooctane sulfonate (PFOS) alternative used globally in aqueous film forming foams (AFFFs). Although 6:2 FTAB has been recently detected in the aquatic environment, its toxic effects on aquatic organisms remain unclear. Here, zebrafish embryos were exposed to various concentrations of 6:2 FTAB (0, 5, 10, 20, 40, 60, 80, and 100 mg/L) from 6 to 120 h post-fertilization (hpf) to investigate its developmental toxicity and possible mechanism of action. Results showed that exposure to 40 mg/L or higher concentrations of 6:2 FTAB significantly decreased the survival percentage and increased the malformation percentage. The median lethal concentration (LC₅₀) at 120 hpf was 43.73 ± 3.24 mg/L, and the corresponding benchmark dose lower limit (BMDL) of lethal effect was 33.79 mg/L. These values were both higher than those for PFOS, supporting the notion that 6:2 FTAB is less toxic than PFOS to zebrafish embryos. The most common developmental defect in 6:2 FTAB-treated embryos was rough-edged skin/fins. TUNEL assay showed that 6:2 FTAB exposure induced cell apoptosis in the tail region compared with that of the control, which might explain the rough-edged skin/fins. The increased transcriptional levels of p53, bax, and apaf1 and the increased activities of caspase-3, -8, and -9 provided further evidence of 6:2 FTAB-induced apoptosis. We also analyzed the effects of 6:2 FTAB on oxidative stress and the immune system. Results showed that reactive oxygen species and malondialdehyde accumulated in concentration-dependent manners after exposure to 6:2 FTAB, and antioxidant enzyme activities (catalase and glutathione peroxidase) also changed. Exposure to 6:2 FTAB also altered the transcriptional levels of ccl1, il-1β, il-8, tnfα, ifn, and cxcl-c1c, which play important roles in the innate immune system. Collectively, our data suggest that 6:2 FTAB exposure can induce cell apoptosis, oxidative stress, and immunotoxicity, thus highlighting the developmental toxicity of 6:2 FTAB in zebrafish embryos.

Perfluorooctane sulfonate (PFOS) removal with Pd0/nFe0 nanoparticles: Adsorption or aqueous Fe-complexation, not transformation?

PFOS removal at 6 and 21days (d) when reacted with palladium coated zero valent iron nanoparticles (Pd⁰/nFe⁰ NPs) was quantified as a function of pH (3.6, 5.5, and 8.7) and temperature (22, 45 and 70°C). PFOS concentrations were measured in aqueous phases and NP extracts. The greatest PFOS removal occurred at 6 d with the lowest pH and highest temperature; however, recovered PFOS increased at 21 d. Furthermore, neither F^- nor SO₄^2- (from SO₃^2- cleavage) generation was observed indicating the absence of PFOS transformation. X-ray diffraction analysis of PFOS-reacted NPs at 45°C revealed generation of FeO(OH) on the NPs at 21 d, which was concomitant with subsequent increases in PFOS recovery. Under anaerobic conditions, strongly adsorbing Fe(OH)₃ is formed which can then transform to less sorptive FeO(OH) via Fe²⁺ catalyzed transformation. In the process of exploring causes for apparent PFOS removal with Pd⁰/nFe⁰ NPs, PFOS as well as other perfluoroalkyl acids (PFAAs) were found to form aqueous-phase complexes with Fe(II/III) which can reduce their quantifiable levels. PFOS-Fe complexation was greater with Fe(III) and increased with Fe concentration and decreasing pH. Complexation was also greater for longer chain perfluoroalkyl acids and complexation of PFNA was greater than for PFOS.

Discovery of a Novel Polyfluoroalkyl Benzenesulfonic Acid around Oilfields in Northern China

The existence of more than 3000 per- and polyfluoroalkyl substances (PFASs) on the global market has prompted the identification and hazard characterization of hitherto unknown PFASs. In the present study, a novel PFAS, sodium p-perfluorous nonenoxybenzenesulfonate (OBS), was identified using Orbitrap MS/MS in water samples around a suspected application area, Daqing Oilfield, China. The peak OBS concentration was 3.2 × 10³ ng/L in a sample taken near the oil well with the longest production history in Daqing. The concentrations of OBS and contribution to the sum of PFASs in surface waters displayed considerable variation among the three sampling areas (mean levels at 6.9, 50, and 5.6 × 10² ng/L with mean percentages at 9.8%, 45%, and 69% in the background, new and old oilfield areas respectively) confirming that the density of oil wells and the oil production history are important factors influencing OBS contamination in the studied areas. A preliminary assessment of acute toxicity and environmental fate indicates that OBS exhibits similar toxicity and environmental persistence to perfluorooctanesulfonic acid (PFOS). The widespread occurrence of OBS, in conjunction with its potential hazard properties, underscores the need to further study on the bioaccumulation and potential for human exposure.

Alternate Reductants with VB12 to Transform C8 and C6 Perfluoroalkyl Sulfonates: Limitations and Insights into Isomer-Specific Transformation Rates, Products and Pathways

Previous studies evaluating Vitamin B12 (VB12) with Ti(III)-citrate for potential use in in situ remediation of perfluorooctanesulfonate (PFOS) found that linear (L)-PFOS was unaltered. We explored if alternate reductants could overcome this limitation with a primary focus on nanoscale zerovalent zinc (nZn⁰). Transformation over time with VB12-nZn⁰ was quantified at 22, 70, and 90 °C for PFOS, at 70 °C for perfluorohexanesulfonate (PFHxS), and VB12-nFe⁰ and VB12-Pd⁰/nFe⁰ at 70 °C for PFOS. Only branched (br-) isomers were transformed generating F^- (no SO₄^2-) and polyfluoroalkyl intermediates/products. The absence of L-PFOS transformation by VB12 appears to be due to the inability of L-perfluoroalkyl sulfonates to complex with VB12 and not an activation energy issue that can be overcome by stronger reductants/catalysts. At 90 °C, 95% of br-PFOS isomers were transformed within 5 days. Isomer-specific removal rates were positively correlated to the br-CF₃'s proximity to the terminal CF₃. Br-PFHxS transformation was approximately two times slower with less defluorination than br-PFOS. C8/C7 and C6/C5 polyfluorinated sulfonates from br-PFOS and br-PFHxS, respectively, were identified as both intermediates and apparent dead-end products. Pathways included 4 F replaced by 2 H and a C═C bond, and serial F replacement by H with up to 12 F atoms removed from br-PFOS.

Certain Perfluoroalkyl and Polyfluoroalkyl Substances Associated with Aqueous Film Forming Foam Are Widespread in Canadian Surface Waters

The presence of perfluoroalkyl and polyfluoroalkyl substances (PFASs) commonly associated with aqueous film forming foams (AFFFs) at sites without known AFFF contamination is a largely unexplored area, which may reveal widespread environmental contaminants requiring further investigation. Sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) screening for 23 classes of PFASs, followed by quantitative analysis was used to investigate surface waters from rural, urban, and AFFF-impacted sites in Canada. The PFASs detected included perfluorohexane sulfonamide (FHxSA), 6:2 fluorotelomer sulfonamide (FTSAm), fluorotelomer sulfonamide alkylbetaines (FTABs), fluorotelomer betaines (FTBs), 6:2 fluorotelomer mercaptoalkylamido sulfonate sulfone (FTSAS-SO₂), 6:2 fluorotelomerthiohydroxyl ammonium sulfoxide (FTSHA-SO), 6:2 fluorotelomer sulfonamide alkylamine (FTAA) and C3 to C6 perfluoroalkane sulfonamido amphoterics. Detection of FHxSA in all urban and AFFF-impacted sites (0.04-19 ng/L) indicates the widespread presence of rarely considered perfluorohexanesulfonate (PFHxS) precursors in Canadian waters. FTABs and FTBs were especially abundant with up to 16-33 ng/L of 6:2 FTAB in urban and AFFF-impacted water suggesting it may have additional applications, while FTBs were only in AFFF-impacted sites (qualitative; ∑FTBs 80 ng/L). The distributions of PFASs moving downstream along the AFFF-impacted Welland River and between water and sediment suggested differences in the persistence of various AFFF components and enhanced sorption of long-chain fluorotelomer betaines. Total organofluorine combustion-ion chromatography (TOF-CIC) revealed that fluorotelomer betaines were a substantial portion of the organofluorine in some waters and 36-99.7% of the total organofluorine was not measured in the targeted analysis.

Influence of Environmental Factors on the Fate of Legacy and Emerging Per- and Polyfluoroalkyl Substances along the Salinity/Turbidity Gradient of a Macrotidal Estuary

This study aimed at bridging knowledge gaps regarding the land-sea transport of per- and polyfluoroalkyl substances (PFASs) through riverine discharge into coastal waters. The present survey was conducted in the Gironde estuary (southwestern France) where PFASs were ubiquitously detected albeit at low levels. Emerging PFASs such as fluorotelomer sulfonates or polyfluoroalkyl phosphate diesters accounted for a relatively minor proportion of ∑PFASs, while perfluorooctanesulfonate, perfluorohexanesulfonate, and perfluorohexanoate were the predominant congeners. Multiple linear regressions provided insights into the relative influence of factors controlling PFAS sediment levels. In that respect, the organic carbon fraction (strongly correlated to sediment grain size) appeared as a more important controlling factor than black carbon or distance from upstream sources for long-chain perfluoroalkyl acids. In the maximum turbidity zone (suspended solids up to 2600 mg L^-1), the particle-associated fraction was almost consistently >50% for long-chain perfluoroalkyl carboxylates and sulfonates (≥C8 and ≥ C6, respectively). Empirical models of K_D partitioning coefficients were derived by integrating, for the first time, both particle-concentration and salting-out effects. These results represent significant progress toward the development of numerical transport models integrating both PFAS partitioning and 3D-hydrosedimentary dynamics, with a view to estimate PFAS mass budgets at the land-sea interface.

Sorption of Fluorotelomer Sulfonates, Fluorotelomer Sulfonamido Betaines, and a Fluorotelomer Sulfonamido Amine in National Foam Aqueous Film-Forming Foam to Soil

During fire-fighter training, equipment testing, and emergency responses with aqueous film-forming foams (AFFFs), milligrams per liter concentrations of anionic, zwitterionic, and cationic per- and polyfluoroalkyl substances (PFASs) enter the environment. Because the behavior of zwitterionic and cationic PFASs in the subsurface is unknown, batch sorption experiments were conducted using National Foam AFFF, which contains anionic fluorotelomer sulfonates (FtSs), zwitterionic fluorotelomer sulfonamido betaines (FtSaBs), and cationic 6:2 fluorotelomer sulfonamido amine (FtSaAm). Sorption of the FtSs, FtSaBs, and 6:2 FtSaAm to six soils with varying organic carbon, effective cation-exchange capacity, and anion-exchange capacity was evaluated to determine sorption mechanisms. Due to the poor recovery of the FtSaBs and 6:2 FtSaAm with published PFAS soil extraction methods, a new soil extraction method was developed to achieve good (90-100%) recoveries. The 6:2 FtSaAm was depleted from the aqueous phase in all but one soil, which is attributed to electrostatic and hydrophobic interactions. Sorption of the FtSs was driven by hydrophobic interactions, while the FtSaBs behave more like cations that strongly associate with the solid phase relative to groundwater. Thus, the sorption mechanisms of the FtSs, FtSaBs, and 6:2 FtSaAm are more complex than expected and cannot be predicted by bulk soil properties.

Contribution of precursor compounds to the release of per- and polyfluoroalkyl substances (PFASs) from waste water treatment plants (WWTPs)

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous in sludge and water from waste water treatment plants, as a result of their incorporation in everyday products and industrial processes. In this study, we measured several classes of persistent PFASs, precursors, transformation intermediates, and newly identified PFASs in influent and effluent sewage water and sludge from three municipal waste water treatment plants in Sweden, sampled in 2015. For sludge, samples from 2012 and 2014 were analyzed as well. Levels of precursors in sludge exceeded those of perfluoroalkyl acids and sulfonic acids (PFCAs and PFSAs), in 2015 the sum of polyfluoroalkyl phosphoric acid esters (PAPs) were 15-20ng/g dry weight, the sum of fluorotelomer sulfonic acids (FTSAs) was 0.8-1.3ng/g, and the sum of perfluorooctane sulfonamides and ethanols ranged from non-detected to 3.2ng/g. Persistent PFSAs and PFCAs were detected at 1.9-3.9ng/g and 2.4-7.3ng/g dry weight, respectively. The influence of precursor compounds was further demonstrated by an observed substantial increase for a majority of the persistent PFCAs and PFSAs in water after waste water treatment. Perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), and perfluorooctane sulfonic acid (PFOS) had a net mass increase in all WWTPs, with mean values of 83%, 28%, 37% and 58%, respectively. The load of precursors and intermediates in influent water and sludge combined with net mass increase support the hypothesis that degradation of precursor compounds is a significant contributor to PFAS contamination in the environment.

Emerging poly- and perfluoroalkyl substances in the aquatic environment: A review of current literature

Poly- and perfluoroalkyl substances (PFASs) comprise a group of synthetic organic surfactants with a wide range of industrial and commercial applications. A few PFASs such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are now known to be ubiquitously present in the aquatic environment. They have become a global concern because of the toxicity and bioaccumulative properties. With the increasing availability of high-resolution mass spectrometers, many novel PFASs have been identified. Studies published between 2009 and 2017 have discovered 455 new PFASs (including nine fully and 446 partially fluorinated compounds), 45%, 29%, 17%, and 8% of which are anions, zwitterions, cations, and neutrals, respectively. They have been identified in natural waters, fish, sediments, wastewater, activated sludge, soils, aqueous film-forming foams, and commercial fluoropolymer surfactants. This article integrates and critically evaluates what is known about these newly identified PFASs. It discusses the different aspects of detection methodologies. It also surveys the removal of these compounds during conventional and advanced drinking-water and wastewater treatment, predicts the relevant physicochemical properties by means of four software programs, and identifies major knowledge gaps. Notably, a number of these newly identified PFASs are potential precursor compounds of PFOS and PFOA. Studies are critically needed to understand the removal and transformation of these compounds in natural and engineered environmental systems and their contribution, if any, to the secondary formation of PFOS and PFOA in these systems.

Discovery of novel per- and polyfluoroalkyl substances (PFASs) at a fire fighting training ground and preliminary investigation of their fate and mobility

Aqueous film forming foams (AFFFs) have been released at fire training facilities for several decades resulting in the contamination of soil and groundwater by per- and polyfluoroalkyl substances (PFASs). AFFF compositions are proprietary and may contain a broad range of PFASs for which the chemical structures and degradation products are not known. In this study, high resolution quadrupole-time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS) in combination with data processing using filtering strategies was applied to characterize and elucidate the PFASs present in concrete extracts collected at a fire training ground after the historical use of various AFFF formulations. Twelve different fluorochemical classes, representing more than 60 chemicals, were detected and identified in the concrete extracts. Novel PFASs homologues, unmonitored before in environmental samples such as chlorinated PFSAs, ketone PFSAs, dichlorinated PFSAs and perfluoroalkane sulphonamides (FASAs) were detected in soil samples collected in the vicinity of the fire training ground. Their detection in the soil cores (from 0 to 2 m) give an insight on the potential mobility of these newly identified PFASs.

Per- and polyfluoroalkyl substances in firefighting foam concentrates and water samples collected near sites impacted by the use of these foams

To extinguish large-scale fuel fires, fluorosurfactant based foams (FSBFs) were developed in the 1960s and have been used ever since. In this study, 154 per- and polyfluoroalkyl substances (PFASs) including 122 emerging PFASs used as surfactants in FSBFs were sought in nine different foam concentrates. Field investigations were also carried out in the vicinity of four sites where FSBFs are or were intensively used (two airports, a training center for firefighters and an oil storage depot after a large explosion). In the foam concentrates, only three PFASs were quantified with concentrations ranging from 22,500 to 3,188,000 μg/L. Thirteen emerging PFASs were also identified in these samples based on their mass transitions and intensities. Overall, each foam was a mixture of at least two classes of PFASs. In three concentrates, none of the 122 emerging PFASs were identified as the main ingredient. A perfluoroalkyl acid precursor oxidation assay was therefore performed, and revealed the presence of high amounts of unidentified PFASs. In the vicinity of the four investigated sites, several PFASs were systematically quantified in all of the samples collected downstream of the sites. PFAS profiles were heavily influenced by parameters such as route of PFAS transport after use (runoff, seepage, direct discharge), time elapsed since the cessation of firefighting activities, and firefighting foam composition. The PFAS concentrations found around the investigated sites are the highest recorded in France and resulted in the closure of certain drinking water resources.