Novel Fluoroalkylated Surfactants in Soils ... - ACS Publications

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Novel Fluoroalkylated Surfactants in Soils Following Firefighting Foam Deployment During the Lac-Mégantic Railway Accident Sandra Mejia-Avendaño,† Gabriel Munoz,†,‡ Sung Vo Duy,‡ Mélanie Desrosiers,§ Paul Benoıt̂ ,∥ Sébastien Sauvé,‡ and Jinxia Liu*,† †

Department of Civil Engineering, McGill University, Montréal, Québec H3A 0C3, Canada Department of Chemistry, Université de Montréal, Montréal, Québec H3C 3J7, Canada § Centre d’expertise en analyse environnementale du Québec (CEAEQ), Ministère du Développement durable, de l’Environnement, et de la Lutte contre les changements climatiques, Québec City, Québec G1P 3W8, Canada ∥ Direction générale de l’analyse et de l’expertise régionales - Estrie et Montérégie, Ministère du Développement durable, de l’Environnement, et de la Lutte contre les changements climatiques, Longueuil, Québec J4K 2T5, Canada ‡

S Supporting Information *

ABSTRACT: The derailment of an unmanned train carrying crude oil and subsequent fire in the town of Lac-Mégantic, Quebec, led to the use of 33 000 L of aqueous film forming foam (AFFF) concentrate. While it is known that per- and polyfluoroalkyl substances (PFASs) contained in AFFFs pose a potential environmental and health risk, critical knowledge gaps remain as regards to their environmental fate after release. The accident in Lac-Mégantic provided valuable information regarding the identity and concentration of PFASs present in the soil after the AFFF deployment, as well as their possible transformation over time. The current study analyzed four sets of samples from Lac-Mégantic: soil collected days after the accident from a heavily impacted area, soil sampled two years later from the treatment biopiles, soil collected two years after the accident from downtown Lac-Mégantic, and nonimpacted soil from a nearby area. A total of 33 PFASs were quantified in the soils. The highest observed concentrations correspond to those of 6:2 fluorotelomer sulfonamidoalkyl betaine, 6:2 and 8:2 fluorotelomer sulfonates, and short chain perfluorocarboxylic acids. The soils collected in Lac-Mégantic two years after the accident show a total PFAS concentration that is ∼50 times lower than soils collected in 2013, while the proportion of perfluoroalkyl acids in those samples shows an increase. Qualitative analysis revealed the presence in soil of 55 additional PFASs that had been previously identified in AFFF formulations. The present study highlights the need to perform detailed analysis of AFFF impacted sites, instead of focusing solely on perfluoroalkyl acids. date.10−12 Despite the trend toward creation of fluorine-free foams,13,14 most of the newer firefighting formulations are based on shorter chain or fluorotelomer derivatives.2 Because of the large volume of AFFFs used for decades, a high number of AFFFimpacted sites need to be assessed and probably remediated. Information about the composition of AFFF formulations and the chemical structures of PFASs contained in them is rarely available, posing an initial challenge for the assessment of AFFF impacted sites. Recent studies have sought to identify10,11,15,16 and quantify17 PFASs with various polar head groups. Due to environmental transformation potential, mainly via biotransformation, of nonfluorinated moieties in the PFAS structures,15,18−23 it is expected that the PFAS profiles will

1. INTRODUCTION Aqueous film forming foams (AFFFs) are routinely used to extinguish hydrocarbon fuel fires. They rely on a mixture of hydrocarbon and fluoroalkyl surfactants to create a thin film on the surface of the fuel, preventing its contact with oxygen and therefore reignition.1−3 Fluoroalkyl surfactants, also known as polyfluoroalkyl and perfluoroalkyl substances (PFASs), have been in the spotlight for over a decade due to their ubiquitous environmental occurrence, persistence and toxicity. 4−8 Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are the two most well-known and monitored PFASs. The information on their health and environmental effects led to their ban or phase-out in several countries, as well as the addition of PFOS and its salts to Annex B of the Stockholm Convention on Persistent Organic Pollutants in 2009.9 Even though the use of PFASs such as perfluoroalkyl acids (PFAAs) in consumer products and other formulations is believed to be on the decline, PFASs remain key components in AFFF formulations as of this © XXXX American Chemical Society

Received: Revised: Accepted: Published: A

April 19, 2017 June 27, 2017 July 1, 2017 July 1, 2017 DOI: 10.1021/acs.est.7b02028 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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Environmental Science & Technology

contained elevated levels of petroleum hydrocarbon cocontaminants. The second goal was to investigate the changing PFASs profiles over time under field conditions with and without enhanced biodegradation. In the present study, the total and relative concentrations of thirty-six PFASs, for which authentic chemical standards are available (perfluoroalkyl sulfonates and carboxylates, fluorotelomer sulfonates and carboxylates, perfluorooctane sulfonamide derivatives, as well as novel betaine-, amine-, and amine oxide-based fluorosurfactants), were compared across the three types of soils. High-resolution mass spectrometry was performed to reveal the presence of other PFASs, for which chemical standards are not yet available, and a semiquantification approach was used to estimate their concentrations. In total, 88 PFASs have been detected and quantified, including many chemicals that were known to be present in AFFF formulations, but have rarely been reported at AFFF-impacted sites. This study provides much-needed data and an approach for site characterization of AFFF-impacted soils, especially the ones that have similar pollution history with petroleum hydrocarbon cocontamination.

significantly change over time and differ from original AFFF compositions.24 For instance, Backe et al. were able to confirm the presence in groundwater samples of eight newly identified PFASs with various functionalities.17 However, the newly discovered surfactants despite being major components of AFFF concentrates, presented a minor fraction of total PFASs relative to perfluoroalkyl sulfonic (PFSAs) and carboxylic acids (PFCAs), and fluorotelomer sulfonic acids (FTSAs).17 PFASs have been consistently detected in AFFF-impacted aquatic environments, such as groundwater or surface water, near military facilities or civilian airports that use AFFFs on a regular basis for firefighting training purposes.17,25−32 In the case of soil or sediment, several studies have focused on the presence of legacy PFASs,32−38 whereas fewer have screened newly identified AFFF components in the solid matrices.33,39 Since AFFFs are used to extinguish fires, soil is an environmental compartment of paramount importance, it is commonly the first receptacle for PFASs. Moreover, it plays an important role in the environmental fate of PFASs contained in AFFFs, by influencing processes such as transport from primarily AFFF-impacted site to groundwater and surface water hydrosystems, through processes such as sorption18,40,41 or environmental transformation.15,18−23 There is a major data gap regarding the levels and identities of PFASs in soils directly impacted by AFFF deployment. Hitherto, little information is available on how environmental PFAS profile might change over time, particularly for the samples containing significant levels of newly identified PFASs that are susceptible to undergo environmental transformation processes. The 2013 Lac-Mégantic rail disaster led to the deployment of a large volume of AFFFs, posing a case study to address the knowledge gaps. On July 6, 2013, 63 out of the 72 train cars carrying 8 million liters of crude oil derailed in the town of LacMégantic (southeastern Quebec, Canada) and a major oil fire ignited.42 Firefighting activities deployed seven types of AFFFs43 and approximately 33 000 L of AFFF concentrates.44 As thousands of liters of oil and AFFFs reached the soil and sewer system, extensive environmental cleanup efforts were conducted to treat wastewater and soil.45,46 As part of the remediation efforts, soils with hydrocarbon levels exceeding Quebec soil quality criteria47 were excavated and treated in an off-site biopile facility. A biopile is a petroleum hydrocarbon remediation technique in which the microbial population already present in soil is stimulated by aeration and adjustment of moisture and nutrients. While the hydrocarbon contamination has received particular attention and has been the subject of intense remediation efforts, the environmental fate of PFASs from the use of AFFFs has not been fully characterized. Sediment and fish collected in the Lac-Mégantic area following the accident revealed the presence of certain PFASs such as fluorotelomer sulfonamidoalkyl betaines (FTABs), fluorotelomer betaines (FTBs), fluorotelomer sulfonates (FTSAs), and fluorotelomer thioether amido sulfonate (FTSASs).39 The quantified PFASs in Lac-Mégantic sediments were in the sub- to low ng/g range. The extent of PFASs in soil, however, has not been investigated to date. The Lac-Mégantic derailment accident provided three types of AFFF-impacted soil samples: the soils collected weeks after the accident (July 2013) and two years afterward (July 2015) around the accident site, as well the soil retrieved from the off-site biopile facility (July 2015). These samples served to accomplish two major study goals. One goal was to perform comprehensive characterization of PFASs in AFFF-impacted soils, which also

2. MATERIALS AND METHODS 2.1. Standards and Reagents. Perfluoroalkyl carboxylates (PFCAs), perfluoroalkyl sulfonates (PFSAs), fluorotelomer unsaturated acids (6:2 FTUA and 8:2 FTUA), fluorotelomer sulfonates (8:2, 6:2 and 4:2 FTSA) and perfluorooctane sulfonamido acetic acid (FOSAA) were obtained from Wellington Laboratories, Inc. (Guelph, ON, Canada). EtFOSA and FOSA (98% purity) were purchased from Advanced Technology & Industrial Co (Hong Kong, China). 5:3 FTCA and 7:3 FTCA were obtained from Synquest Laboratories (Alachua, FL). PFOSAm, PFOSAmS, PFOAAmS, PFOSNO, PFOANO, PFOSB, and PFOAB were custom-synthesized at the Beijing Surfactant Institute (Beijing, China). 6:2 FTAB and 6:2 FTNO were obtained from Shanghai Kingpont Industrial Co. Ltd. (Shanghai, China). All isotope-labeled internal standards (MPFBA, MPFHxA, MPFOA, MPFNA, MPFDA, MPFUdA, MPFDoA, MPFHxS, MPFOS, d-EtFOSA-M, M6:2 FTUA, M8:2 FTUA, M6:2 FTSA, M8:2 FTSA) were obtained from Wellington Laboratories (Guelph, ON, Canada). The full chemical names, formula and corresponding acronyms are listed in the Supporting Information (SI). HPLC-grade solvents including acetonitrile (ACN), methanol (MeOH), LC/MSgrade water and acetic acid (HAc), and Optima-grade ammonium hydroxide (NH4OH) were purchased from Fisher Scientific (Ottawa, ON, Canada). 2.2. Soil Sampling. Four sets of surface soil samples were used in the present study: background nonimpacted soil, impacted soil collected in 2013 after the Lac-Mégantic train derailment, soil samples collected in 2015 from Lac-Mégantic downtown area, and soil samples from treatment biopiles in 2015. The background soil was used to estimate the PFAS background levels before the accident. It was sampled in a nearby area, about 5 km from the Lac-Mégantic railway accident site (SI Figure SI-2). The impacted soil samples collected in 2013 come from the western shores of Chaudière River, at the point where the oil and AFFF runoff reached the river, approximately 500 m from the edge of the derailment site (SI Figures SI-3 and SI-4). The location of this sampling survey was selected for its accessibility after the accident, as many areas were closed for accident investigation and were not accessible. The soil collected in July 2015 was sampled in downtown Lac-Mégantic from the fire burn site and adjacent area, where the soil was being B

DOI: 10.1021/acs.est.7b02028 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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Figure 1. (a) Concentration profile of quantified PFASs in soil collected in 2013, (b) soil collected from biopiles in 2015 (zoomed 10x), and (c) soil collected from downtown Lac-Mégantic in 2015 and background soil (zoomed 100x). (d) Fraction of each quantified analyte (w/w) from total concentration measured in each sample (∑33PFASs).

and cleaned with ENVI-Carb graphite (Sigma-Aldrich). Extracts were stored at −20 °C and spiked with isotope-labeled internal standards just before instrumental analysis. Details on analytical methods are supplied in the SI. All soil concentrations are expressed on a dry weight basis. Quantitative analysis was performed with a Shimadzu UHPLC system coupled to an AB Sciex 5500 Qtrap mass spectrometer working in multiple reaction monitoring (MRM) mode, with positive and negative electrospray ionization (fast polarity switching mode). Separation was achieved using an Agilent Zorbax SB-C8 column (3.5 μm, 100 × 2.1 mm). Qualitative analysis was performed on a Dionex UHPLC system coupled to a Q-Exactive Orbitrap mass spectrometer (both from Thermo Fischer Scientific) operated in full scan MS mode (R: 70 000 at m/z = 200) and with t-MS2 mode, with positive and negative heated electrospray ionization (fast polarity switching

continuously excavated for remediation (SI Figure SI-5). The collection area in 2015 was selected because it was the closest to the actual accident site among the areas open to sampling. The biopile samples were also obtained in July 2015, two years after the accident. Full details on sampling locations can be found in the SI. The soil samples were collected in 1 L or 5 gallon polypropylene containers that were prerinsed with methanol. Soils were sieved with 4 mm sieves and stored at −20 °C in dark before sample preparation. 2.3. Sample Preparation and Instrumental Analysis. A previously developed extraction method was used to analyze soil samples.48 Briefly, methanol plus 0.1% NH4OH was used as the extraction solvent. Two grams of each soil sample was subjected to three sequential cycles of sonication (30 min) and shaking (60 min at 240 rpm) with the extraction solvent. The three extracts were combined, concentrated under a gentle stream of nitrogen C


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7.86 ± 0.78 to 4425 ± 310 ng/g (median 408 ng/g), as illustrated in Figure 1a. In comparison, a nonimpacted background soil collected in Lac-Mégantic showed a total PFAS concentration of 2.73 ng/g (SI Table SI-10). Even though the impacted soils were collected within a small stretch of the sampling area, a high degree of variability in the PFAS concentrations was observed for the AFFF-impacted site. This could be due to the fact that some soil samples could have been directly under the influence of the oil/AFFF runoff stream, while for others the impact was not as acute. For the samples collected two years after the accident, the average total concentrations ranged from 7.28 ± 1.18 to 42.7 ± 2.9 ng/g (median 14.4 ng/g) for those collected from downtown Lac-Mégantic (Figure 1c) and from 8.18 ± 0.76 to 582 ± 128 ng/ g for the samples from the biopiles (median 106 ng/g) (Figure 1b). At the time of sampling, the excavation and remediation efforts were ongoing, the soil was excavated in several batches and piled off-site in remediation biopiles to treat the high petroleum hydrocarbon contamination. Even though a high variability was observed in the concentrations of PFASs among the three sets of samples, the highest concentrations were consistently observed in the samples collected in 2013, whereas the lowest concentrations occurred in the 2015 samples from downtown Lac-Mégantic. These results are not unexpected, due to the fact that the 2013 samples were collected just a few weeks after a major firefighting event, in an area heavily impacted by oil/ AFFF runoff. The soils from the 2015 downtown Lac-Mégantic survey were located in a heavily impacted area, close to the accident and fire burn zone. A likely factor for such a dramatic decrease in concentrations, apart from the fact that the soils might be impacted differently to start with, is the potential of PFASs to leach out of the soil. A similar trend was observed for the hydrocarbon contamination. The highest concentration of total petroleum hydrocarbons (TPH, C10-C50) in samples collected in 2013 was 26 000 mg/kg (3 orders of magnitude higher than the PFASs concentration for the most heavily contaminated soils), while the highest TPH concentrations in 2015 samples from biopiles and from soil in the downtown area amounted to 1400 and 3800 mg/kg, respectively. Half of the soils from the 2013 survey exceeded Québec’s Class C soil quality criteria (3500 mg/kg), while only one sample from downtown Lac-Mégantic in 2015 and none of those collected from the biopiles did (SI Table SI-3). Nevertheless, a direct comparison of the magnitude of each category of the contaminantsbe it PFASs or hydrocarbon among different samples could not provide strict quantitative information on the effect of time (i.e., 2013 versus 2015) or bioremediation on the PFAS contamination, since the area from which each set of samples was collected was impacted in a different way. Therefore, the focus of the discussion is not only on the total concentration but also on the fraction represented by each class of PFASs and the relations between them. As shown in Figure 1d, the highest fractions of quantified PFASs in all soils samples came from PFCAs (especially those of short perfluoroalkyl chain length, from 3 to 5 perfluorinated carbon atoms), n:2 FTSAs and 6:2 FTAB. Together, PFBA, PFPeA, PFHxA, 6:2 FTSA, 8:2 FTSA, and 6:2 FTAB accounted for 64% - 98% of quantified PFASs among all samples (83 ± 12% on average). Note that in Figure 1, all the PFCAs are presented in different shades of yellow, the PFSAs in shades of red, n:2 FTSAs in shades of green, perfluorooctane sulfonamide derivatives in shades of purple, and characteristic fluorotelomer-based degradation products (FTCAs and FTUAs) in shades of violet. Figure 1d (bottom panel) presents the same set of samples with a

mode).21,33 Chromatographic separation was achieved with a Thermo C18 Hypersil Gold column (1.9 μm, 100 × 2.1 mm). Extracts were first analyzed in full scan MS mode, and when the exact mass of PFASs that have been previously reported in AFFFs10,11,17,33 was detected within a 5 ppm window, the analysis was performed in high resolution t-MS2 mode for structural confirmation. Full details on chromatographic methods, mobile phases, monitored transitions, and internal standards used are provided in the SI. The determination of total petroleum hydrocarbons was performed with a hexane extraction and analysis by gas chromatography-flame ionization detection (GC-FID) according to the reference method from the Centre d’expertise en analyse environnementale du Québec.49 2.4. Quality Assurance and Quality Control. The limit of detection (LOD) was defined as the lowest concentration to yield a signal-to-noise ratio of 3, and generally fell between 0.005 and 2 ng/mL. Quantification was performed based on internal standardization solvent-based calibration curves fitted with an inverse-weighted linear model and comprising at least 6 points (compound specific LODs and linearity ranges provided in the SI). Procedural blanks were included within each batch of samples; no reported PFASs levels were reported in such blanks. Soil samples were thoroughly homogenized before extraction, and all extractions were performed in triplicates; the resulting relative standard deviation was generally less than 15%. Details on method performance (recovery, precision, accuracy) can be found in Mejia-Avendano et al.48 The concentrated soil extracts were diluted (dilution factor of 50-times or higher) prior to IS addition in order to fall within the linear working range. 2.5. Quantification Confidence Levels. The quantification of PFASs was classified into three different levels: (i) Quantitative analytes (Qn): those for which true standards were available (detailed in SI Table SI-1); (ii) Semiquantitative analytes (sQ): those for which a true standard was not available, but an analogue with a different chain length could be used; (iii) Indicative analytes (Ql): those for which no true standard was available. The concentration of Ql analytes was tentatively estimated by comparison with the solvent-based calibration curve of a structurally similar compound assuming equimolar response;33 the most important factor considered when selecting such a reference compound was a similar terminal functional group. Details on the quantification strategy for Ql and sQ analytes can be found in the SI. 2.6. Statistical Analysis. Statistical analyses were performed with the R statistical software.50 Due to the large variability in the concentrations of PFASs detected across different types of samples, only nonparametric tests were performed. Statistical dependence between variables was tested using Kendall’s tau test, while the correlation between them is expressed by the Akritas-Theil-Sen nonparametric line. Each correlation was performed on a consistent set of samples, that is, separately for soil samples collected in 2013, 2015, or from biopiles.

3. RESULTS AND DISCUSSION 3.1. Quantitative analysis of PFASs in Soil. Thirty-six compounds, for which chemical standards are available, were quantitatively investigated in the soil samples. All of them were detected in at least one sample at levels higher than their corresponding detection limits, except for PFHxDA, PFOAB, and PFOAAmS. The measured concentrations for all the quantitative PFAS analytes in all the samples are provided in the SI (Table SI-11). For the soil samples collected days after the accident in 2013, the sum of all quantified PFASs ranged from D


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Environmental Science & Technology transformed y-axis, in which the fraction of each analyte, relative to the total concentration of quantified PFASs, is shown rather than the individual concentration. The levels of PFAAs are noteworthy, since previous soil surveys have found levels of PFAAs ranging from sub-ng/g to low ng/g in soils or sediments,51−54 whereas soils amended with municipal biosolids showed slightly higher concentrations, particularly for PFOS, at 2−483 ng/g.55 In comparison, the soils in the present study showed a total amount of PFASs shortly after the AFFF deployment that surpasses 4400 ng/g in some samples. Equally noteworthy is the dominance of short-chain PFCAs, while previous soil surveys have found a preponderance of longer-chain congeners, particularly PFOA.34,51,53,55 Furthermore, as opposed to the previous reports in which PFOS (or other PFSAs) represented an important fraction of the total PFAA concentrations in soils,34,52,53,55 the present study showed that PFSAs were on average 45 times less concentrated than PFCAs. The most plausible explanation is that the firefighting foams used in the Lac-Mégantic emergency response were formulated from fluorotelomer-based PFASs, rather than PFOSbased ones, the latter having been largely phased out of production in North America.2 The highest level of PFOS and PFOA detected was 9.34 ± 0.40 ng/g and 29.0 ± 1.9 ng/g respectively, for sample RC2013−7 (SI Table SI-11), which falls well below the soil screening levels values for perfluoroalkylated substances proposed by Health Canada, 2100 and 850 ng/g for residential/parkland use for PFOS and PFOA, respectively.56 The other significant analytes besides PFAAs detected in soil were 6:2 FTAB (dark blue in Figure 1) and n:2 FTSAs (green shades in Figure 1). 6:2 FTAB was detected in every sample, and happened to be the most significant one in more than half of the 2013 samples. 6:2 FTAB has been recently reported to be a key component in several brands of AFFF formulations.10,11,15,17 The magnitude of its concentration and frequency of detection in these sets of samples raise the question of its inadvertent presence in other impacted sites elsewhere. 6:2 FTAB can exist in either zwitterionic or cationic form; its environmental behaviors, which are yet to be investigated, are probably very different from anionic PFASs. As for the high concentrations of n:2 FTSAs, this is not unexpected given that newer AFFF formulations are commonly fluorotelomer-based. 6:2 FTSA has frequently been reported in AFFF-impacted groundwater and surface water samples at significant levels.17,25,32,39 Backe et al. previously reported the presence of n:2 FTSAs in two AFFF brands-only one of which, National Foam, was reportedly used in the firefighting efforts in Lac-Mégantic-albeit at low concentrations as compared to other PFASs. They did, nonetheless, find 6:2 FTSAs at significant concentrations in impacted water.17 The biotransformation of 6:2 FTAB and 6:2 FTA in activated sludge has been shown to produce short-chain PFCAs as degradation products, as well as FTCAs, FTUAs, and FTOHs. 22 Biotransformation studies of n:2 FTSAS, on the other hand, have found n:2 FTSAs are generated as major degradation products.19,20 Even though n:2 FTSASs do not appear to be major PFASs in Lac-Mégantic soils (see Section 3.3), other fluorotelomer derivatives present have the potential to behave in a similar manner. Both reasons−original presence in the AFFF formulation and result of biotransformation process−are possible explanations for the presence of n:2 FTSAs in soil. 3.2. Trends in PFAS Concentration Profiles. The three sets of samples exhibited distinct PFAS concentration profiles as illustrated in Figure 1d. Changing profiles over time could be a result of combined environmental processes (e.g., sorption or

leaching off-site, photolysis, biotransformation) and human interventions (e.g., dilution by mixing with soils of low PFAS levels), apart from the influence of the AFFF deployment. For further assessment, the relation between different PFAS classes was analyzed using nonparametric correlation, as described in the Statistical Analysis section. The statistically significant correlations are summarized in SI Table SI-12, which presents the values of Kendall’s Tau coefficients and slopes for Akritas-Theil-Sen nonparametric regression lines. Noteworthy, there is a significant monotonic correlation between TPH and PFASs, which should come as no surprise as it is expected that areas more heavily impacted by fuel should also present a higher content of AFFFs. Figure 2 illustrates the regression lines for the nonparametric correlation of ∑PFASs versus ∑FTSAs and ∑PFCAs. The sum

Figure 2. Total PFCAs and FTSAs versus total PFASs concentration and Theil-Sen lines for the regression in each set of samples. Solid lines represent the Theil-Sen lines over the magnitude of the data, while dotted lines are an extension over a larger range with the sole objective of comparing the slopes.

of all perfluoroalkyl carboxylates (∑PFCAs) was found to be significantly correlated to the total PFAS concentration, as demonstrated by the value of Kendall’s Tau coefficient reflecting the existence of a monotonic positive relation. In other words, samples which displayed high ∑PFASs also tended to display elevated ∑PFCAs, and vice versa. The comparative data of Theil-Sen slopes provided further information to distinguish between sample types. The slopes of the regression (∑PFCAs = f(∑PFASs)) were 0.0468, 0.408, and 0.569 for samples from 2013, downtown 2015 and biopiles 2015, respectively. Even though there is always a positive relation between ∑PFCAs and ∑PFASs in all sets of samples, the greater magnitude of the slope in the samples from the biopiles also imply that PFCAs were more prevalent (in terms of relative abundance) in biopiletreatment samples, which may reflect significant biotransformation of PFAA-precursors into short-chain PFCAs. The generation of short chain (3−5 perfluorinated carbons) PFCAs E


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Figure 3. High resolution MS/MS spectrum of 8:2 FTSHA-sulfoxide using ultrahigh performance liquid chromatography coupled to a Q-Exactive orbital ion trap, showing the molecular ion (M+) and elucidated major fragment ions.

has indeed been observed as a result of the biotransformation of fluorotelomer derivatives present in AFFFs.19,20,22,23 FTSAs and 6:2 FTAB also showed a positive correlation with PFASs, but the opposite trend when compared to PFCAs, that is, the highest slope was observed in samples from the 2013 survey, followed by samples from downtown Lac-Mégantic in 2015 and finally samples collected from the biopiles, m = 0.442, 0.139, and 0.100 respectively for FTSAs, and m = 0.512, 0.294, and 0.225 respectively for 6:2 FTAB. This observation is consistent with the trend in Figure 1, where the proportion of PFCAs increased in both sets of samples from 2015, while FTSAs and 6:2 FTAB dominated the profiles in samples from 2013. The samples collected in 2013 are the closest representation of the situation shortly after the accident, in which the observed PFAS concentration profile was the closest to the AFFFs used during the emergency response. 6:2 FTAB has been observed as a major component of AFFFs,11,15,17 which explains its presence at high concentrations. On the other hand, n:2 FTSAs have been observed only as minor components of AFFFs themselves,17 but in higher concentrations at impacted sites.17,25,39 The high initial concentration of n:2 FTSAs could be due to rapid initial biotransformation of some AFFF components that are precursors to n:2 FTSAs. However, after two years have passed, there has been enough time for FTSAs and other fluorotelomer derivatives to transform as a result of microbial activity in soil. Biotransformation of certain fluorotelomer derivatives present in AFFF formulations has been reported to generate PFCAs as terminal products.19,20,22,23 Therefore, a possible explanation for the high concentrations of short-chain PFCAs is the biotic transformation of the components 6:2 FTAB and FTSAs which are observed at high concentrations, particularly at earlier times. Moreover, the samples collected from biopiles presented a higher proportion of PFCAs and lower proportion of polyfluoroalkyl substances, when compared to samples collected at the same time from nonexcavated downtown soil. This situation most likely arises from the fact that the biopiles are by design optimized to enhance microbial activity, which could be

degrading not only petroleum hydrocarbons but also PFAA precursors originating from the AFFF formulations used at the Lac-Mégantic accident site. Even when considering a rather consistent set of samples, such as those from the 2013 survey, heterogeneity at very small spatial scale is apparent in the wide variations of the ∑PFAS between samples. Some uncertainties in data interpretation remain due to the complexity of the site and sampling design. It should be borne in mind that the downtown soils from the 2013 and 2015 surveys could not be collected from the exact same area and it cannot be ruled that that other causes, such as differences in how the distinct soils were exposed to different AFFF formulations or differences in inherent soil characteristics affecting their sorption and leaching, could be confounding factors for the observed changes. Adding to the complexity is the fact that at least seven AFFF formulations were deployed on site, and possible sitespecific differences in exposure to such foams could render the comparisons delicate. The decrease of several orders of magnitude in the median PFAS concentrations in soil is most likely related to the leaching out of the surfactants, particularly considering their high solubility in water. However, betaine-type precursorswhich make up a large portion of quantified PFASs in this studyhave shown slightly stronger sorption to soil organic matter as compared to PFCAs with the same perfluoroalkyl chain length.57 If leaching out was the sole explanation for the differences in PFASs, it was expected that a higher proportion of betaines would be found over time. Therefore, biotransformation seems a likely explanation for the changing PFAS profiles between different sets of samples. 3.3. Qualitative and Semiquantitative Analysis. The potential presence of other PFASs in soil was addressed by extensive qualitative analysis. Compounds that have been previously detected in AFFF formulations or AFFF-impacted sites10,11,17,33 were scouted by high-resolution mass spectrometry as described in section 2.3. According to these criteria, 55 compounds were qualitatively identified, across seven different F


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Figure 4. Structures of PFASs qualitatively detected in Lac-Mégantic soil samples.

Figure 5. Estimated concentration of qualitatively detected PFASs in (a) soils collected in July 2013, (b) soils collected from biopiles in 2015 and (c) soils collected from downtown Lac-Mégantic in 2015.

is noteworthy that polyfluoroalkyl compounds (i.e., fluorotelomer derivatives) were most prevalent among the qualitatively scouted analytes. For each class of PFASs, congeners of different chain lengths were observed, consistent with the telomerisation

classes, including longer-chain congeners of some quantified compounds (namely, FTSA, FTAB, and FTNO). SI Table SI-13 shows details on calculated and observed exact mass of each analyte, as well as their retention time and exact mass accuracy. It G


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thiohydroxyl ammonium (n:2 FTSHA and n:2 FTSHAsulfoxide), fluorotelomer thioether amido sulfonate (n:2 FTSAS and n:2 FTSAS-sulfoxide), fluorotelomer thioalkylamido betaine (n:2 FTSAB), fluorotelomer thioalkylamido amine (n:2 FTSAA) and fluorotelomer sulfinyl alkylamido ammonium (n:2 FTSoAAmS). The sum of the estimated concentrations of the 55 detected PFASs detected in samples from 2013 ranged from 22.6 to 55 450 ng/g, with a median of 1155 ng/g. The ratio of total PFASs (Quantitative and Qualitative analytes combined) to PFAAs ranges from 10 to 324 for samples collected in 2013, and from 1.6 to 8.0 in samples collected in 2015. The lower fraction of qualitatively detected polyfluoroalkyl substances in soils from 2015 compared to soils from 2013 is consistent with the previous discussion of increasing PFCAs over time due to likely ongoing environmental transformation.22,23 The presence of n:2 FTSASs and n:2 FTSHAs and their corresponding sulfoxides also suggests that the sulfoxides are formed as a result of FTSAS or FTSHAS microbial degradation, as has been discussed elsewhere.19,20 Even though the concentrations shown in Figure 5 are only indicative and do not represent true concentrations of detected PFASs, they highlight the potential underestimation of the extent of PFAS contamination when only a handful of compounds are targeted, most commonly PFCAs and PFSAs. The level of total PFASs could well be underestimated by several orders of magnitude. 3.4. Short-Chain versus Long-Chain PFAS. The levels of PFOS and other PFSAs were low and comparable to background soil collected from nonimpacted area, which suggested the likely effectiveness of banning PFOS-containing AFFFs in the region59,60 In the meantime, short-chain PFASs are expected to be dominant, as the known trend in fluorochemical industry is to shift toward short-chain formulations for lower bioaccumulation potential and toxicity than the long-chain ones.2,12 In the present study, for each class quantitatively or qualitatively detected, several congeners of different chain lengths were observed, consistent with the synthesis process, which usually yields a mixture of chain lengths. The criteria used to differentiate long versus short chain are outlined by Buck et al. where PFCAs (C n F 2n+1 COOH) with n ≥ 7, PFSAs (CnF2n+1SO3H) with n ≥ 6, and all FOSA derivatives are considered long-chain PFASs.4 As “long chain” was not defined with respect to fluorotelomer derivatives, n ≥ 7 was chosen as the threshold because it is the shortest fluorinated chain that has the potential to biotransform to a long-chain PFCA. Figure 6 illustrates the percentages of long-chain PFASs relative to the total PFASs that were quantified against authentic standards. The percentage ranged from 3.0 to 37% across all the soil samples, and there is no detectable trend with regards to sampling year. It has been observed in the past that microbial transformation of fluorotelomer derivatives into PFCAs generally experiences faster kinetics for short-chain congeners than the long-chain ones, and the transformation can lead to shortening of perfluoroalkyl chains.18 However, for the PFASs without authentic standards and semiquantitatively estimated, the percentage of long-chain PFASs ranged from 60 to 97% of the total (see SI Figure SI-6). Different instrumental response of Ql/sQ PFASs with respect to the reference analyte, as well as different sensitivity of Ql/sQ PFASs with varying chain lengths, could entail possible overestimation or underestimation of the levels of long-chain PFASs. New AFFFs are said to be formulated with short chain PFASs, on the basis of short-chain PFAAs being less

synthesis process, in which a fraction of subproducts/coproducts of different chain lengths than the one desired can be formed. Retention time patterns among congeners of a common class are also consistent with previously observed results; a median increment of 0.45 min in retention time was typically observed for each extra CF2 unit in the perfluoroalkyl chain, the magnitude of the increase being smaller with increasing molecular weight. Further structural confirmation was achieved in high-resolution t-MS2 mode. An example is shown in Figure 3 for 8:2 fluorotelomer thiohydroxyl ammonium sulfoxide (8:2 FTSHAsulfoxide). The fragmentation of PFASs within the same class was analogous for different chain lengths, with certain peaks consistently detected among classes (such as the 104 m/z fragment for betaines or the 206 m/z fragment for FTSASs and FTSAS-sulfoxides), and the molecular masses increasing by 100 Da for each additional CF2CF2 unit. For each detected class, MS/ MS spectra of one representative compound have been provided in the SI (see Figure SI-7). The qualitatively identified compounds presented fit the criteria for identification at Level 2b according to the description of small molecule identification by high-resolution mass spectrometry proposed by Schymanski et al.58 Level 2b is equivalent to a probable structure, when there is no true standard to compare the experimental data, but the MS/MS data, the exact formula and the experimental context fit no other structure. Figure 4 shows the structure of all the compounds that were qualitatively detected in the soil extracts. All the qualitatively identified PFASs are consistent with the structural features of fluorotelomers with mostly n:2 fluoroalkyl chains, although fluorotelomer betaines with n:3 and n:1:2 patterns were also detected. In order to estimate the total concentration of PFASs including qualitatively identified analytes, the response of each compound detected in full scan MS mode was compared to the calibration curve of a related compound, assuming equimolar response. For each qualitatively detected PFASs, the related native compound that was used for a tentative estimate of the concentration is specified in the SI (Table SI-9). Even though this approach is not strictly quantitative, it can still serve as an indication of the potential extent of the PFAS contamination. Estimated concentrations for quantified PFASs and qualitatively identified PFASs are shown in Figure 5. Qualitatively identified analytes from a common class were grouped and colorcoded correspondingly; within each class, each subsection of the stacked bars represents analytes of different chain length. Panel (b) shows a 35x amplification with respect to (a) for soil samples collected from biopiles, while panel (c) shows a 350x amplification with respect to (a) for soil samples collected in 2015. The n:1:2 fluorotelomer betaines (FTB) stand out as being the class of compounds with the highest estimated concentrations− up to 33 627 ng/g for all congeners combined (n = 5−15). It is, however, unclear if the high calculated concentration of FTBs is due to a truly high concentration in soils, or simply to a very sensitive instrumental response compared to 6:2 FTAB (the model native analyte that was used for semiquantification purposes of FTB). Other classes that appear to be present at significant concentrations are n:3 FTBs (up to 5559 ng/g for n = 5−15) and n:2 FTABs (up to 433 ng/g for n = 8−12). As expected, the samples with the highest estimated concentrations were those collected days after the release of AFFFs. Other PFASs detected at apparent lower concentrations include fluorotelomer sulfonamide amines (n:2 FTAs), fluorotelomer H


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Concentrations were particularly high in samples collected weeks after the accident. The concentration of PFASs in soil collected two years later is 1or 2 orders of magnitude lower. The large decrease in concentration overtime is likely caused by leaching of PFASs into water. Meanwhile, the different PFAS profile could be caused by a series of reasons such as different initial impact, different mobility of distinct PFAS components, or by biotic transformation of original PFASs present in AFFFs. Biotransformation arises as a probable cause for the observation of an increased ratio of short chain PFCAs in samples collected two years after the accident, since short chain PFCAs have been proven to be transformation products of fluorotelomer compounds. The variation in the PFAS profile should be considered during the assessment of an impacted site, since degradation products can potentially have distinct toxicity and mobility as compared to their parent compounds. The low concentration of PFOS confirms that the phase-out of PFOSbased formulations has indeed resulted in an increased use of fluorotelomer-based AFFFs, which, however, were found to contain a significant portion of long-chain PFASs that can still lead to PFOA or longer chained congeners through environmental transformation processes. The present study also highlights the need for specific studies related to the effect that hydrocarbon contamination remediation efforts could have on PFASs originating from AFFFs and reiterates the need for more authentic standards for a more comprehensive assessment of contaminated sites.

Figure 6. Fraction of the long-chain PFASs relative to the total quantified PFASs.

bioaccumulative as compared to their long chain congeners.61 However, this observation suggests the possibility that longerchain fluorotelomer derivatives are used in newer formulations, despite the trend of shifting toward short chain products.

4. ENVIRONMENTAL IMPLICATIONS The analysis of four sets of soil samples collected after the LacMégantic train derailment yielded several noticeable findings. The quantification of a suite of available PFASs with true standards revealed that the total amount of PFASs was considerably higher than the concentrations of PFOS and PFOA. Therefore, quantifying only these two compounds, as routinely performed in commercial R&D institutes and laboratories, would likely result in vastly underestimating the total PFASs content. Moreover, six compounds (PFBA, PFPeA, PFHxA, 6:2 FTSA, 8:2 FTSA, and 6:2 FTAB) represented most of the quantified PFAS. All of the analyzed samples were well below the PFOS and PFOA soil screening values proposed by Health Canada (2100 and 850 ng/g for residential/parkland use for PFOS and PFOA respectively).56 The quantification revealed distinctive patterns of PFASs across different types of samples, with a much higher relative abundance of perfluoroalkyl carboxylic acids in samples collected two years after the accident. This trend suggests the influence of soil microbial degradation of PFAA-precursors, either with or without treatment intended for remediation of petroleum hydrocarbons. A qualitative analysis further revealed the presence of 55 additional compounds that were identified through highresolution mass spectrometry, but for which strict quantification was not possible due to the lack of true standards. This implies that less than half (33 out of 88) of the total number of PFASs identified could be quantified. The major classes detected were n:1:2 FTBs, n:3 FTBs, n:2 FTABs, and to a lesser extent FTSAS, FTSAS-sulfoxide, FTSHA, FTSHA-sulfoxide, FTSAB, FTSAA, and FTSoAAmS. Even though these substances have been detected in formulations or impacted water, this is the first time that their presence is reported in impacted soil. The fact that less than half (33/88) of the detected compounds could be quantified should bring attention to the immense lack of true standards for the quantification of PFASs, or for the creation of alternative methods for total PFASs estimation in soil, such as the total oxidizable precursors assay for water,62 or total fluorine estimation using proton induced gamma-ray emission (PIGE).63

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.7b02028. Compounds with authentic standards; soil sampling details; AFFFs used during firefighting at Lac-Mégantic; hydrocarbon concentrations in soils; sample preparation and analytical methods; details on calibration curves; investigated families of PFASs and their semiquantification; PFASs concentration in soils; trends of PFASs concentration profiles; details on qualitatively detected PFASs (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phonel: +1 514 398 7938; fax: +1 514 398 7361; e-mail: jinxia. [email protected]. ORCID

Sandra Mejia-Avendaño: 0000-0003-4302-5518 Sébastien Sauvé: 0000-0001-8584-1690 Jinxia Liu: 0000-0003-2505-9642 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the funding support by Canada Foundation for Innovation (CFI), the Fonds de recherche du Québec − Nature et technologies (FQRNT) Team Grant, NSERC Strategic Project Grant, and McGill MEDA Scholarship and J.W McConnell Memorial Fellowship awarded to S. MejiaAvendaño. The authors also acknowledge the support from the Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques (MDDELCC) and LVM I


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Inc. who provided access to the impacted site and biopiles for soil sampling.

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