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Simplified analytical solutions, developed as source strength functions (SSFs), are capable of describing the temporal dissolution of nonaqueous phase liquids in groundwater, which is useful for predicting source longevity and can serve as a guide for remedial activities. Here, SSF parameters were estimated by fitting enhanced aqueous dissolution data from a flow cell consisting of three injection and four extraction wells to analytical dissolution models (power law model (PLM) and equilibrium streamtube model (EST)) at a trichloroethene (TCE) contaminated site, Alameda Point, California. Both the PLM and the EST model were able to characterize the observed aqueous TCE dissolution during enhanced water flooding. Additional field activities conducted at the site included soil core collection, a recirculated partitioning tracer test, passive flux meter transects, and push–pull tracer tests. The additional site characterization data were used to independently estimate the observed SSF parameters using information such as the TCE mass, distribution and porous media heterogeneity. The exponential decay model (a subset of the PLM) accurately predicted the enhanced dissolution, likely because the site was significantly aged (most of the mass in the plume rather than in the source zone) or middle stage, and the mass in the source zone could be approximately estimated. The EST tracer-based model, when combined with data from the recirculated partitioning tracer test, soil cores, and the push–pull tracer test, was capable of accurately predicting the observed aqueous dissolution. The mass in the source zone and the fraction of contaminated flowpaths were the most important site characteristics, requiring the greatest accuracy to predict aqueous dissolution. Establishing steady state dissolution was essential to provide a more accurate estimate of the fraction contaminated and high resolution data from soil cores in the source zone were needed to estimate the mass present. [ABSTRACT FROM AUTHOR]

Abstract: Energetic residues are scattered around active ranges due to the detonation events and dissolution is usually the first step for the entry of explosive compounds into the environment. The current models for describing the dissolution are subject to limitations in either model applicability or generality. This study attempted to develop a general model that is applicable to various types of energetic residues. Experimental data that were acquired from previous reports were used for testing the developed model. The results showed that the model captured well the dissolution processes of different types of energetic residues: 2,4,6-trinitrotoluene (TNT), Tritonal, Composition B, Octol, and Greener Insensitive Material (GIM). Moreover, it was observed that the mass transfer coefficients of TNT, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and/or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) that were part of the energetic residues increased quantitatively with rising flow rates. In addition, the values of resistance coefficient, a model parameter, were negligible for the drop-impingement experiments, implying that under the conditions of rainfall and/or snowmelt flow, the surface attachment effect on the dissolution of energetic residues that rest on range soils is trivial. The study herein provides a general modeling approach for various types of energetic residues with additional insights in regards to their dissolution processes. [Copyright &y& Elsevier]

The widespread use of aqueous film–forming foam (AFFF) for firefighting and firefighter training has led to extensive per– and polyfluoroalkyl substance (PFAS) contamination in the environment. Challenges remain in the analytical determination of PFASs via liquid chromatography–mass spectrometry (LC–MS), particularly when attempting to include ultrashort–chain perfluoroalkyl acids (PFAAs) and longer–chain anionic and zwitterionic PFASs in a single direct injection. In this study, we assessed the performance of three analytical LC columns (C18, JJ, and Acclaim columns) to separate targeted and suspect PFASs in AFFF–impacted water samples collected from five sites. The C18 column failed to retain ultrashort–chain PFAAs while the JJ and Acclaim columns were not suitable for hydrophobic PFASs. Ultrashort–chain PFAAs were detected at three sites and comprised 1.6–18% of the total perfluoroalkyl carboxylic and sulfonic acids. Semi–quantified concentrations of suspect PFASs comprised 0.70–13% of the total PFASs. When attempting to capture the entirety of the PFAS mass in a water sample, the C18 column captured the broadest suite of suspect PFASs, while the JJ column quantified the most total PFAS mass. Results of this study highlight the importance and tradeoffs of LC column choice to comprehensively determine the composition of PFASs and their concentrations in AFFF–impacted water samples. [Display omitted] • The C18 column failed to retain ultrashort-chain PFAAs and the JJ and Acclaim columns were unsuitable for hydrophobic PFASs. • Ultrashort-chain PFAAs comprised 1.6-18% of total measured PFCAs and PFSAs at three sites. • Semi-quantified concentrations of suspect PFASs comprised 0.70-13% of the total PFASs. • The C18 column captured the broadest suite of suspect PFASs in AFFF-impacted water. • The JJ column quantified the most total PFAS mass in AFFF-impacted water. [ABSTRACT FROM AUTHOR]

The widespread use of per- and polyfluoroalkyl substances (PFAS)-containing products in numerous commercial and industrial applications has resulted in their occurrence in wastewater treatment plants (WWTPs). Herein, proof-of-concept bench-scale experiments were performed to measure the extent to which PFAS could be removed from a WWTP if aerosols generated during aeration were captured. Experiments were designed to mimic the aeration rate:water volume ratio, the water volume:surface area ratio, and aeration bubble size applicable to the full-scale aeration vessel. Results showed that substantial (75%) removal of perfluorooctane sulfonate (PFOS) was observed under these operating conditions in the bench-scale system; up to 97% PFOS removal was observed if the aeration rate was increased 3-fold. PFAS removal generally increased with increasing aerosol capture and with increasing PFAS surface activity. Analysis of semi-quantified PFAS showed that the semi-quantified PFAS accounted for approximately 93% of the identified PFAS in the raw wastewater, dominated largely by the presence of 2:2 fluorotelomer carboxylic acid (2:2 FTCA). This preliminary study suggests that aerosol capture in aeration basins has potential for mitigating PFAS in WWTPs. Further testing is needed to assess the feasibility of this approach at the field scale. [Display omitted] • 75% of PFOS was removed from wastewater when the emitted aerosols were captured. • PFAS removal increased with increasing aerosol capture, aeration rate, and PFAS surface activity. • Non-target PFAS (dominated by 2:2 FTCA) accounted for approximately 93% of the PFAS identified in the raw wastewater. • Existing wastewater aeration processes coupled with aerosol capture may be leveraged for PFAS mitigation. [ABSTRACT FROM AUTHOR]

• Single-use IX resins significantly outperform regenerable resins for PFAS removal. • >180,000 bed volumes treated before breakthrough of perfluoroalkyl sulfonic acids. • Polystyrene resin >> polyacrylic; sorbent hydrophobicity crucial for adsorption. • Analyte-specific adsorption zones show competition among PFAS for exchange sites. • Breakthrough behavior correlates with batch-derived exchange coefficients. This study reports the results of an 8-month pilot study comparing both regenerable and emerging single-use anion exchange resins (AERs) for treatment of per- and polyfluoroalkyl substances (PFASs) at a source zone impacted by historical use of aqueous film-forming foam (AFFF). Two regenerable (Purolite A860 and A520E) and three single-use (Purolite PFA694E, Calgon CalRes 2301, and Dowex PSR2+) AERs were tested in parallel, collecting effluent samples after treatment for 30-sec and 2-min total empty bed contact time (EBCT). Results demonstrate that single-use AERs significantly outperform regenerable resins, particularly for treatment of long-chain perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs). No detectable concentrations of ≥C7 PFCAs or PFSAs were observed within 150,000 bed volumes (BVs) after treatment with the single-use resins (2-min EBCT). Analysis of effluent samples following 30-sec EBCT treatment shows that even the shortest-chain PFSAs do not reach 50% breakthrough within the first 350,000 BVs, though differences in removal of short-chain PFCAs was less dramatic. The regenerable polyacrylic A860 resin performed very poorly compared to all polystyrene resins, with >90% breakthrough of all PFASs occurring within 10,000 BVs. The greater affinity of polystyrene resins is attributed to increased hydrophobic interactions in addition to electrostatic ion exchange. Analysis of breakthrough profiles reveals empirical correlation with ion exchange affinity coefficients (log K ex) measured in batch experiments. Postmortem analysis of PFASs extracted from spent resins revealed chromatographic elution behavior and competition among PFASs for adsorption to the resins. PFSAs and long-chain PFCAs were preferentially adsorbed to earlier sections in the AER columns, whereas short-chain PFCAs were competitively displaced towards the later sections of the columns and into the effluent, consistent with effluent concentrations of the latter structures exceeding influent values. These results provide insights into the mechanisms that govern PFAS adsorption to AERs in real multisolute groundwater matrices and support findings from other diverse sites regarding PFAS affinity, elution behavior, and competition for exchange sites. [Display omitted] [ABSTRACT FROM AUTHOR]

In situ chemical oxidation using permanganate has frequently been used to treat chlorinated solvents in fractured bedrock aquifers. However, in systems where matrix back-diffusion is an important process, the ability of the oxidant to migrate and treat target contaminants within the rock matrix will likely determine the overall effectiveness of this remedial approach. In this study, a series of diffusion experiments were performed to measure the permanganate diffusion and reaction in four different types of sedimentary rocks (dark gray mudstone, light gray mudstone, red sandstone, and tan sandstone). Results showed that, within the experimental time frame (~2months), oxidant migration into the rock was limited to distances less than 500μm. The observed diffusivities for permanganate into the rock matrices ranged from 5.3×10−13 to 1.3×10−11 cm2/s. These values were reasonably predicted by accounting for both the rock oxidant demand and the effective diffusivity of the rock. Various Mn minerals formed as surface coatings from reduction of permanganate coupled with oxidation of total organic carbon (TOC), and the nature of the formed Mn minerals was dependent upon the rock type. Post-treatment tracer testing showed that these Mn mineral coatings had a negligible impact on diffusion through the rock. Overall, our results showed that the extent of permanganate diffusion and reaction depended on rock properties, including porosity, mineralogy, and organic carbon. These results have important implications for our understanding of long-term organic contaminant remediation in sedimentary rocks using permanganate. [ABSTRACT FROM AUTHOR]

• Life cycle assessment showed trade-offs in environmental impacts for ion exchange. • Impacts of disposal of waste regeneration solution dominated by incineration. • Impacts were sensitive to amount incinerated and incineration waste type. • Recycling the solvent or brine fraction of regeneration solution decreased impacts. • Alternative salts for regeneration had lower impacts than incineration. Although anion exchange resin (AER) treatment is considered an effective technology for removing per- and polyfluoroalkyl substances (PFASs) from impacted water, the environmental impacts associated with AER regeneration have not been systematically explored. In particular, the trade-offs of altering the composition of the regeneration solution and disposing of or recycling the waste regeneration solution are not known. To fill these important gaps in the literature, this research conducted a comparative life cycle assessment (LCA) of an AER-based PFAS remediation system with different regeneration scenarios including disposing of waste regeneration solution via incineration, reusing the organic cosolvent and brine fractions of the waste regeneration solution, and altering the composition of the regeneration solution to avoid organic cosolvent or NaCl. The results show that disposing of waste regeneration solution via incineration, without recycling organic cosolvent or brine, had the greatest environmental impact, and that incineration accounted for the greatest impact among contributing processes. Recycling of the cosolvent (or cosolvent and brine) fraction of the waste regeneration solution resulted in lower environmental impacts due to reduced mass of waste disposed of via incineration. Replacing NaCl in the brine with an alternative salt resulted in higher environmental impacts, with salts derived from chemical production, such as ammonium chloride and potassium carbonate, showing the largest increases in impacts. The results of this research highlight the importance of understanding the fate of PFASs during incineration, and the need for PFAS destruction technologies that can be coupled to AER regeneration to avoid incineration. [Display omitted] [ABSTRACT FROM AUTHOR]

• Polyacrylic AER and short-chain PFCAs and PFECAs favor electrostatic interactions • Polystyrene AER and long-chain PFAS including neutral FASAs combine interactions • AER selectivity for PFAS: PFBA < PFHxA < GenX < PFBS < PFOA ≈ PFHxS ≈ FOSA < PFOS • Column studies show better removal of short-chain PFAS using polystyrene/gel AER • Weak-base AER best candidate for aqueous-only regeneration and desorption of PFAS [Display omitted] A key gap in the literature on the treatment of per- and polyfluoroalkyl substances (PFAS) in impacted water is the absence of a review article dedicated to anion exchange resin (AER) treatment. This gap is important because previous research has consistently shown adsorption by AER to be one of the most effective treatment processes for PFAS removal from impacted water, and AER is one of the most commonly deployed technologies in the field. Given the scope of the previous review articles on PFAS removal by various adsorbent types, the sections on AER do not explore the full depth of PFAS and AER interactions nor cover the breadth of AER testing conditions. Accordingly, the goal of this paper was to critically review the available peer-reviewed literature on PFAS removal from water by AER. The specific objectives of the review were to synthesize the previous literature results on (1) batch adsorption behavior, (2) impact of water chemistry conditions, (3) continuous-flow adsorption, (4) adsorption modeling, (5) regeneration, and (6) weak-base AER. Following from critical review of the literature, the future research priorities discussed include: (i) improving the underlying science that governs PFAS–resin interactions, (ii) improving methods for resin regeneration and management of PFAS-contaminated concentrate streams, and (iii) comparative life cycle environmental and economic analyses for ion exchange treatment systems relative to competing technologies. [ABSTRACT FROM AUTHOR]

• Indole acetic acid (IAA) and PFOS co-sorb to ALA-intercalated montmorillonite. • Hydrated electrons emitted upon UV irradiation of IAA degrade PFOS at neutral pH. • PFOS degradation pathway is primarily via breakage of the C-F bonds. • Nitrate and bicarbonate have some inhibitory effect on PFOS degradation. Per-and poly-fluoroalkyl substances (PFASs) are a class of persistent compounds that are resistant to degradation. Here we developed an effective method of degrading perfluorooctanesulfonate (PFOS) by hydrated electrons (e aq −) that are generated from 3-indole-acetic-acid (IAA) upon UV irradiation. The method takes advantage of spatial proximity of IAA and PFOS by their co-sorption to an organic polymer, 12-aminolauric acid (ALA), which was pre-intercalated into the interlayer space of an expandable clay mineral, montmorillonite. The interlayer spacing of this clay nanocomposite is greatly expanded relative to unmodified montmorillonite. The maximum adsorption capacity of IAA and PFOS is 168 and 1550 mmol/kg, respectively. This process achieved 40–70% defluorination of a 10 ppm PFOS solution at neutral pH in a 325 mL vessel. The presence of bicarbonate and chloride ions, or natural groundwater showed a minimal impact on PFOS degradation. Based on identification of prominent degradation products, a degradation pathway is proposed, where the primary degradation process is breakage of the C-F bonds (with fluorine replaced by hydrogen), with some cleavage of the C C bond. This approach provides an alternative for treating concentrated PFAS solutions under ambient conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Low permeability source zones sustain long-term trichloroethene (TCE) groundwater contamination. In anaerobic environments, TCE is transformed by both biological reductive dechlorination and abiotic reactions with reactive minerals. Little is known about the relative contribution of these two pathways as TCE diffuses from low permeability zones (LPZs) into high permeability zones (HPZs). This study combines a flow cell experiment, batch experiments, and a diffusion-reaction model to evaluate the contributions of biotic and abiotic TCE transformation in LPZs. Natural clay (LPZ) and sand (HPZ) from a former Air Force base were used in all experiments. In batch, the LPZ material transformed TCE and cis- 1,2-dichloroethene (cis- DCE) to acetylene with pseudo first-order rate constants of 8.57 × 10−6 day−1 and 1.02 × 10−6 day−1, respectively. Biotic and abiotic pathways were then evaluated together in a bench-scale flow cell (16.5 cm × 2 cm × 16.5 cm) that contained a LPZ layer, with a source of TCE at the base, overlain by a HPZ continuously purged with lactate-amended groundwater. Diffusion controlled mass transfer in the LPZ, while advection controlled migration in the HPZ. The mass discharge rate of TCE and its biotic (cis- DCE and vinyl chloride) and abiotic (acetylene) transformation products were measured over 180 days in the flow cell effluent. Depth profiles of these compounds through the LPZ were determined after terminating the experiment. A one-dimensional diffusion-reaction model was used to interpret the effluent and depth profile data and constrain reaction parameters. Abiotic transformation rate constants for TCE to acetylene, normalized to in situ solids loading, were approximately 13 times greater in batch than in the flow cell. Slower transformation rates in the flow cell indicate elevated TCE concentration and/or further degradation of acetylene to other reduced gas compounds in the flow cell LPZ (thereby partially masking TCE abiotic transformation). Biotic and abiotic parameters used to interpret the flow cell data were then used to simulate a field site with a 300 cm thick LPZ. Abiotic processes contributed to a 2% reduction in TCE flux after 730 days. When abiotic rate constants were changed to that observed in batch, or to rate constants previously reported for a pyrite rich mudstone, the TCE flux reduction was 21% and 53%, respectively, after 730 days. Though biotic processes dominated TCE transformation in the flow cell experiment, the simulations indicate that abiotic processes have potential to significantly contribute to TCE attenuation in electron donor limited environments provided suitable reactive minerals are present. • Biotic and abiotic processes can reduce TCE flux from low permeability zones. • A natural clay promoted abiotic TCE and cis -DCE transformation to acetylene. • In a flow cell with lactate, biotic TCE transformation was faster than abiotic. • Simulations showed abiotic TCE flux reductions of 2-53% depending on mineral reactivity. • Increased abiotic TCE flux reduction occurs when more reactive minerals are present. [ABSTRACT FROM AUTHOR]

Some Per- and polyfluoroalkyl substances (PFAS) are strongly retained in the vadose zone due to their sorption to both soils and air-water interfaces. While significant research has been dedicated to understanding equilibrium behavior for these multi-phase retention processes, leaching and desorption from aqueous film-forming foam (AFFF) impacted soils under field relevant conditions can exhibit significant deviations from equilibrium. Herein, laboratory column studies using field collected AFFF-impacted soils were employed to examine the leaching of perfluoroalkyl acids (PFAAs) under simulated rainfall conditions. The HYDRUS 1-D model was calibrated to estimate the unsaturated hydraulic properties of the soil in a layered system using multiple boundary condtions. Forward simulations of equilibrium PFAS partitioning using the HYDRUS model and simplified mass balance calculations showed good agreement with the net PFAS mass flux out of the column. However, neither were able to predict the PFAS concentrations in the leached porewater. To better understand the mechanisms controlling the leaching behavior, the HYDRUS 1-D two-site leaching model incorporating solid phase rate limitation and equilibrium air-water interfacial partitioning was employed. Three variations of the novel model incorporating different forms of equilibrium air-water interfacial partitioning were considered using built-in numerical inversion. Results of numerical inversion show that a combination of air-water interfacial collapse and rate-limited desorption from soils can better predict the unique leaching behavior exhibited by PFAAs in AFFF-impacted soils. A sensitivity analysis of the initial conditions and rate-limited desorption terms was conducted to assess the agreement of the model with measured data. The models demonstrated herein show that, under some circumstances, laboratory equilibrium partitioning data can provide a reasonable estimation of total mass leaching, but fail to account for the significant rate-limited, non-Fickian transport which affect PFAA leaching to groundwater in unsaturated soils., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: John Forrest Stults reports financial support was provided by Strategic Environmental Research and Development Program. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Poly- and perfluoroalkyl substance (PFAS) leaching from unsaturated soils impacted with aqueous film-forming foams (AFFFs) is an environmental challenge that remains difficult to measure and predict. Complicating measurements and predictions of this process is a lack of understanding between the PFAS concentrations measured in a collected environmental unsaturated soil sample, and the PFAS concentrations measured in the corresponding porewater using field-deployed lysimeters. The applicability of bench-scale batch testing to assess this relationship also remains uncertain. In this study, field-deployed porous cup suction lysimeters were used to measure PFAS porewater concentrations in unsaturated soils at 5 AFFF-impacted sites. Field-measured PFAS porewater concentrations were compared to those measured in porewater extracted in the laboratory from collected unsaturated soil cores, and from PFAS concentrations measured in the laboratory using batch soil slurries. Results showed that, despite several years since the last AFFF release at most of the test sites, precursors were abundant in 3 out of the 5 sites. Comparison of field lysimeter results to laboratory testing suggested that the local equilibrium assumption was valid for at least 3 of the sites and conditions of this study. Surprisingly, PFAS accumulation at the air-water interface was orders of magnitude less than expected at two of the test sites, suggesting potential gaps in the understanding of PFAS accumulation at the air-water interface at AFFF-impacted sites. Finally, results herein suggest that bench-scale testing on unsaturated soils can in some cases be used to inform on PFAS in situ porewater concentrations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Both quantifiable and semi-quantifiable poly- and perfluoroalkyl substances (PFAS) were evaluated in the influent, effluent, and biosolids of 38 wastewater treatment plants. PFAS were detected in all streams at all facilities. For the means of the sums of detected, quantifiable PFAS concentrations were 98 ± 28 ng/L, 80 ± 24 ng/L, and 160,000 ± 46,000 ng/kg (dry weight basis) in the influent, effluent, and biosolids (respectively). In the aqueous influent and effluent streams this quantifiable PFAS mass was typically associated with perfluoroalkyl acids (PFAAs). In contrast, quantifiable PFAS in the biosolids were primarily polyfluoroalkyl substances that potentially serve as precursors to the more recalcitrant PFAAs. Results of the total oxidizable precursor (TOP) assay on select influent and effluent samples showed that semi-quantified (or, unidentified) precursors accounted for a substantial portion (21 to 88%) of the fluorine mass compared to that associated with quantified PFAS, and that this fluorine precursor mass was not appreciably transformed to perfluoroalkyl acids within the WWTPs, as influent and effluent precursor concentrations via the TOP assay were statistically identical. Evaluation of semi-quantified PFAS, consistent with results of the TOP assay, showed the presence of several classes of precursors in the influent, effluent, and biosolids; perfluorophosphonic acids (PFPAs) and fluorotelomer phosphate diesters (di-PAPs) occurred in 100 and 92% of biosolid samples, respectively. Analysis of mass flows showed that, for both quantified (on a fluorine mass basis) and semi-quantified PFAS, the majority of PFAS exited WWTPs through the aqueous effluent compared to the biosolids stream. Overall, these results highlight the importance of semi-quantified PFAS precursors in WWTPs, and the need to further understand the impacts of their ultimate fate in the environment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Air-water interfacial retention of poly- and perfluoroalkyl substances (PFASs) is increasingly recognized as an important environmental process. Herein, column transport experiments were used to measure air-water interfacial partitioning values for several perfluoroalkyl ethers and for PFASs derived from aqueous film-forming foam, while batch experiments were used to determine equilibrium K ia data for compounds exhibiting evidence of rate-limited partitioning. Experimental results suggest a Freundlich isotherm best describes PFAS air-water partitioning at environmentally relevant concentrations (10 1 -10 6 ng/L). A multiparameter regression analysis for K ia prediction was performed for the 15 PFASs for which equilibrium K value of 0.65 and validated across a range of relevant concentrations for perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and hexafluoropropylene oxide-dimer acid (i.e., GenX). A mass action model was further modified to account for the changing ionic strength on PFAS air-water interfacial sorption. The final result was two distinct QSPRs for estimating PFAS air-water interfacial partitioning across a range of aqueous concentrations and ionic strengths.ia values were determined, assessing 246 possible combinations of 8 physicochemical and system properties. Quantitative structure-property relationships (QSPRs) based on three to four parameters provided predictions of high accuracy without model overparameterization. Two QSPRs ( R 2 values of 0.92 and 0.83) were developed using an assumed average Freundlich n value of 0.65 and validated across a range of relevant concentrations for perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and hexafluoropropylene oxide-dimer acid (i.e., GenX). A mass action model was further modified to account for the changing ionic strength on PFAS air-water interfacial sorption. The final result was two distinct QSPRs for estimating PFAS air-water interfacial partitioning across a range of aqueous concentrations and ionic strengths.

Per- and polyfluoroalkyl substances (PFASs) are frequently found at high concentrations in the subsurface of aqueous film forming foam (AFFF)-impacted sites. Geochemical parameters affect the release of PFASs from source area soils into groundwater but have not been extensively studied for soils that have been historically impacted with AFFF. This study investigated the effects of pH and salt concentrations on release of anionic and zwitterionic PFASs from AFFF-impacted soils in flow-through saturated columns. High pH (10) columns with elevated sodium concentrations had higher cumulative masses eluted of several PFASs compared to pH 3 and pH 7 columns with lower sodium concentrations, likely caused by changes to soil organic matter surface charge. Four PFASs ( e.g. 4:2 fluorotelomer sulfonate, perfluorobutane sulfonamido acetic acid) eluted significantly earlier in both pH 3 and pH 10/high NaCl columns compared to pH 7 columns. The results of this study suggest that shifts in pH for soils located at AFFF-impacted sites - particularly raising the pH - may mobilize sorbed PFASs, specifically longer-chain and zwitterionic compounds that are typically strongly sorbed to soil.

While several studies have focused on perfluoroalkyl acid (PFAA) leaching from soils, field studies evaluating the relationship between PFAA mass removal and porewater concentrations as the PFAA source becomes depleted are lacking. Herein, in situ water flushing was performed at a site historically impacted with AFFF to accelerate the leaching of PFAAs from unsaturated soils in a highly characterized field test cell. Porous cup suction lysimeters were used to assess the changes in PFAA porewater concentrations as a function of PFAA mass removal from the unsaturated soils, where flushing was intermittently paused to determine ambient PFAA porewater concentrations. Results showed that the fractional decreases in PFAA porewater concentrations during flushing exceeded the fractional decrease in PFAA mass removal from the soil. PFOS porewater concentrations decrease by 76% (with negligible rebound) compared to only a 7.4% decrease in overall PFOS mass removed from the unsaturated zone. Overall, the results observed herein suggest that, when considering soil impacts to groundwater, less stringent soil cleanup criteria than those that consider an equivalent relationship between mass removal and mass discharge may be appropriate. In addition, remedial approaches that remove only a modest fraction of the PFAA soil mass may be protective of underlying groundwater, particularly for perfluorinated sulfonates with at least six carbons.

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

Bench-scale experiments were performed to interrogate poly- and perfluoroalkyl substance (PFAS) enrichment in the water surface microlayer (SML). In initial experiments using electrolyte-only solutions, the perfluorooctane sulfonate (PFOS) and perfluorooctane carboxylate (PFOA) enrichment in the SML were reasonably (with a factor of 2) described by the Gibbs adsorption equation coupled with a Freundlich-based interfacial adsorption model. Enrichment in the SML among perfluorinated sulfonates and perfluorinated carboxylates of varying chain lengths was proportional to their surface activity. The PFOS enrichment factor (EF), defined as the PFAS concentration in the SML divided by the concentration in the bulk water, was 18 in a 200 mg/l NaCl solution. The presence of elevated organic carbon levels in synthetic surface waters inhibited PFAS accumulation in the SML, with resulting EF values of approximately 1 for all PFAS. However, in the presence of elevated organic levels coupled with foam, PFAS enrichment in the foam was observed, with a foam EF of 25 measured for PFOS in synthetic surface waters. PFAS EF values measured in several natural surface waters without foam showed little variation among the waters tested, with PFOS EF values ranging between 6 and 10. Together, these results suggest that PFAS accumulation in the SML is largely controlled by PFAS sorption at the air-water interface for the conditions examined in this study, and the presence of foam with natural organics enhances PFAS uptake at the water surface., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Jennifer Field reports financial support was provided by Strategic Environmental Research and Development Program., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Finished biosolids were collected and characterized from seven municipal water resource recovery facilities. Poly- and perfluoroalkyl substances (PFAS) for the 54 quantified in the biosolids ranged from 323 ± 14.1 to 1100 ± 43.8 µg/kg (dry weight basis). For all biosolids, greater than 75% of the PFAS fluorine mass was associated with precursors. Di-substituted polyfluorinated phosphate esters (diPAPs) were the most abundant PFAS identified in the biosolids. The total oxidizable precursor assay on biosolids extracts generally failed to quantify the amount of precursors present, in large part due to the fact that diPAPS were not fully transformed during the TOP assay. Outdoor biosolids column leaching experiments intended to simulate biosolids land application showed sustained PFAS leaching over the 6-month study duration. Perfluoroalkyl acid (PFAA) concentrations in leachate, when detected, typically ranged in the 10 s to 100 s of ng/L; no diPAPs were detected in the leachate. The PFAA leaching from the biosolids exceeded the PFAA mass initially present in the biosolids (typically by greater than an order of magnitude), but the cumulative PFAA mass leached did not exceed the molar equivalents that could be explained by transformation of quantified precursors. These results highlight the importance of PFAA precursors initially present in biosolids and their contribution to long term leaching of PFAAs from land-applied biosolids., (Copyright © 2022. Published by Elsevier Ltd.)

Field-deployed lysimeters were used to measure the concentrations of poly- and perfluoroalkyl substances (PFASs) in soil porewater at a site historically impacted with aqueous film forming foam (AFFF). Samples collected over a 49-day period showed that perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) were the PFASs with the highest concentrations in porewater, with concentrations of approximately 10,000 and 25,000 ng L -1 , respectively. The corresponding average mass flux to underlying groundwater observed for PFOS and PFHxS was 28,000 ± 11,000 and 92,000 ± 32,000 ng m -2 d -1 , respectively. Employing the use of batch desorption isotherms (soil:water slurries) to determine desorption K d values resulted in an overestimation of PFAS porewater concentrations by a factor for 1.4 to 4. However, using the desorption K d values from the batch desorption isotherms in combination with a PFAS mass balance that incorporated PFAS sorption at the air-water interface resulted in improved predictions of the PFAS porewater concentrations. This improvement was most notable for PFOS, where inclusion of air-water interfacial sorption resulted in a 58% reduction in the predicted PFOS porewater concentration and predicted PFOS porewater concentrations that were identical (within the 95% confidence interval) to the lysimeter measured PFOS porewater concentration. Overall these results highlight the potentially important role of air-water interfacial sorption on PFAS migration in AFFF-impacted unsaturated soils in an in situ field setting., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Ultraviolet photochemical reaction of sulfite (SO 3 ) photosensitizer generates strongly reducing hydrated electrons (e 2- ; NHE = -2.9 V) that have been shown to effectively degrade individual per- and polyfluoroalkyl substances (PFASs), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). However, treatment of complex PFAS mixtures in aqueous film-forming foam (AFFF) remains largely unknown. Here, UV-sulfite was applied to a diluted AFFF to characterize e aq reactions with 15 PFASs identified by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) targeted analysis. Results show that reactivity varies widely among PFASs, but reaction rates observed for individual PFASs in AFFF are similar to rates observed in single-solute experiments. While some structures, including long-chain perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) were readily degraded, other structures, most notably short-chain PFSAs and fluorotelomer sulfonic acids (FTSs), were more recalcitrant. This finding is consistent with results showing incomplete fluoride ion release (up to 53% of the F content in AFFF) during reactions. Furthermore, results show that selected PFSAs, PFCAs, and FTSs can form as transient intermediates or unreactive end-products via e - ; NHE = -2.9 V) that have been shown to effectively degrade individual per- and polyfluoroalkyl substances (PFASs), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). However, treatment of complex PFAS mixtures in aqueous film-forming foam (AFFF) remains largely unknown. Here, UV-sulfite was applied to a diluted AFFF to characterize e aq - reactions with 15 PFASs identified by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) targeted analysis. Results show that reactivity varies widely among PFASs, but reaction rates observed for individual PFASs in AFFF are similar to rates observed in single-solute experiments. While some structures, including long-chain perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) were readily degraded, other structures, most notably short-chain PFSAs and fluorotelomer sulfonic acids (FTSs), were more recalcitrant. This finding is consistent with results showing incomplete fluoride ion release (up to 53% of the F content in AFFF) during reactions. Furthermore, results show that selected PFSAs, PFCAs, and FTSs can form as transient intermediates or unreactive end-products via e aq - reactions with precursor structures in AFFF. These results indicate that while UV-sulfite treatment can be effective for treating PFOS and PFOA to meet health advisory levels, remediation of the wider range of PFASs in AFFF will prove more challenging.

Bench-scale experiments were performed to assess uptake of poly- and perfluoroalkyl substances (PFAS), both single compounds and mixtures, at the air-water interface. The focus was on evaluating uptake at field-relevant PFAS concentrations (<2 × 10 -4 mol m -3 or 0.1 mg L -1 ), assessing the impacts of various PFAS mixtures, and quantifying the impacts of background NaCl concentrations. Both interfacial tension measurements and direct quantification of PFAS mass sorbed at the air-water interface in water films were used to evaluate PFAS interfacial partitioning. Results showed that a Freundlich-based model, rather than a Langmuir-based model, described perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) interfacial uptake. At lower and field-relevant PFOS and PFOA concentrations, the Langmuir-based model underpredicted interfacial uptake by up to several orders of magnitude. The interfacial partition coefficient, k aw , increased as PFAS concentrations decreased. Results also showed that the interfacial tension and interfacial uptake of PFAS mixtures were (within a factor of 2) predicted based on the single solute systems assuming ideal dilute behavior. Furthermore, the addition of NaCl at concentrations of up to 0.01 M increased PFOS uptake by less than a factor of 2 at field-relevant PFOS concentrations. The results presented herein have important implications for PFAS migration in unsaturated soils as well as for remedial technologies that rely on PFAS interfacial sorption, particularly at field-relevant PFAS concentrations.

An in situ field demonstration was performed in fractured rock impacted with trichloroethene (TCE) and cis-1,2-dichloroethene (DCE) to assess the impacts of contaminant rebound after removing dissolved contaminants within hydraulically conductive fractures. Using a bedrock well pair spaced 2.4m apart, TCE and DCE were first flushed with water to create a decrease in dissolved contaminant concentrations. While hydraulically isolating the well pair from upgradient contaminant impacts, contaminant rebound then was observed between the well pair over 151days. The magnitude, but not trend, of TCE rebound was reasonably described by a matrix back-diffusion screening model that employed an effective diffusion coefficient and first-order abiotic TCE dechlorination rate constant that was based on bench-scale testing. Furthermore, a shift in the TCE:DCE ratio and carbon isotopic enrichment was observed during the rebound, suggesting that both biotic and abiotic dechlorination were occurring within the rock matrix. The isotopic data and back-diffusion model together served as a convincing argument that matrix back-diffusion was the mechanism responsible for the observed contaminant rebound. Results of this field demonstration highlight the importance and applicability of rock matrix parameters determined at the bench-scale, and suggest that carbon isotopic enrichment can be used as a line of evidence for abiotic dechlorination within rock matrices., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The objective of this research was to evaluate the potential for two gases, methane and ethane, to stimulate the biological degradation of 1,4-dioxane (1,4-D) in groundwater aquifers via aerobic cometabolism. Experiments with aquifer microcosms, enrichment cultures from aquifers, mesophilic pure cultures, and purified enzyme (soluble methane monooxygenase; sMMO) were conducted. During an aquifer microcosm study, ethane was observed to stimulate the aerobic biodegradation of 1,4-D. An ethane-oxidizing enrichment culture from these samples, and a pure culture capable of growing on ethane (Mycobacterium sphagni ENV482) that was isolated from a different aquifer also biodegraded 1,4-D. Unlike ethane, methane was not observed to appreciably stimulate the biodegradation of 1,4-D in aquifer microcosms or in methane-oxidizing mixed cultures enriched from two different aquifers. Three different pure cultures of mesophilic methanotrophs also did not degrade 1,4-D, although each rapidly oxidized 1,1,2-trichloroethene (TCE). Subsequent studies showed that 1,4-D is not a substrate for purified sMMO enzyme from Methylosinus trichosporium OB3b, at least not at the concentrations evaluated, which significantly exceeded those typically observed at contaminated sites. Thus, our data indicate that ethane, which is a common daughter product of the biotic or abiotic reductive dechlorination of chlorinated ethanes and ethenes, may serve as a substrate to enhance 1,4-D degradation in aquifers, particularly in zones where these products mix with aerobic groundwater. It may also be possible to stimulate 1,4-D biodegradation in an aerobic aquifer through addition of ethane gas. Conversely, our results suggest that methane may have limited importance in natural attenuation or for enhancing biodegradation of 1,4-D in groundwater environments.

Laboratory batch experiments were performed to assess the impacts of temperature and mineralogy on the abiotic dechlorination of tetrachloroethene (PCE) or trichloroethene (TCE) due to the presence of ferrous minerals in natural aquifer clayey soils under anaerobic conditions. A combination of x-ray diffraction (XRD), magnetic susceptibility, and ferrous mineral content were used to characterize each of the 3 natural soils tested in this study, and dechlorination at temperatures ranging from 20 to 55°C were examined. Results showed that abiotic dechlorination occurred in all 3 soils examined, yielding reduced gas abiotic dechlorination products acetylene, butane, ethene, and/or propane. Bulk first-order dechlorination rate constants (k bulk ), scaled to the soil:water ratio expected for in situ conditions, ranged from 2.0×10 -5 day -1 at 20°C, to 32×10 -5 day -1 at 55°C in the soil with the greatest ferrous mineral content. For the generation of acetylene and ethene from PCE, the reaction was well described by Arrhenius kinetics, with an activation energy of 91kJ/mol. For the generation of coupling products butane and propane, the Arrhenius equation did not provide a satisfactory description of the data, likely owing to the complex reaction mechanisms associated with these products and/or diffusional mass transfer processes associated with the ferrous minerals likely responsible for these coupling reactions. Although the data set was too limited to determine a definitive correlation, the two soils with elevated ferrous mineral contents had elevated abiotic dechlorination rate constants, while the one soil with a low ferrous mineral content had a relatively low abiotic dechlorination rate constant. Overall, results suggest intrinsic abiotic dechlorination rates may be an important long-term natural attenuation component in site conceptual models for clays that have the appropriate iron mineralogy., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Laboratory experiments were performed to evaluate the use of electrochemical treatment for the decomposition of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), as well as other perfluoroalkyl acids (PFAAs), in aqueous film forming foam (AFFF)-impacted groundwater collected from a former firefighter training area and PFAA-spiked synthetic groundwater. Using a commercially-produced Ti/RuO2 anode in a divided electrochemical cell, PFOA and PFOS decomposition was evaluated as a function of current density (0-20 mA/cm(2)). Decomposition of both PFOA and PFOS increased with increasing current density, although the decomposition of PFOS did not increase as the current density was increased above 2.5 mA/cm(2). At a current density of 10 mA/cm(2), the first-order rate constants, normalized for current density and treatment volume, for electrochemical treatment of both PFOA and PFOS were 46 × 10(-5) and 70 × 10(-5) [(min(-1)) (mA/cm(2))(-1) (L)], respectively. Defluorination was confirmed for both PFOA and PFOS, with 58% and 98% recovery as fluoride, respectively (based upon the mass of PFOA and PFOS degraded). Treatment of other PFAAs present in the groundwater also was observed, with shorter chain PFAAs generally being more recalcitrant. Results highlight the potential for electrochemical treatment of PFAAs, particularly PFOA and PFOS, in AFFF-impacted groundwater., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Explosives and energetics continue to be prominent contaminants on many military installations. This research was undertaken to understand the extent to which microscale (10's of μm) particles are produced when macroscale residues are weathered by artificial precipitation. Initial experiments, in which artificial rainwater was applied drip-wise to single chunks of Composition B detonation residues from multiple heights, confirmed that microscale particles were produced during precipitation-driven aging, with 30% of the explosive mass collected detected as particulate Composition B (e.g., particles >0.45 μm in diameter). Follow-on experiments, during which multiple cm-sized residue chunks were subjected to realistic simulated precipitation, demonstrated an initial large pulse of particulate Composition B, followed by sustained production of microscale particles that represented 15-20% of recovered explosives. These findings indicate that the effective footprint of detonation residues likely increases as particulates are produced by the production and spreading of microscale particles across the soil surface. Combined with results published elsewhere that microscale particles can move into porous media to become a distributed source term, these findings point to the need for inclusion of these processes in explosive contaminant fate and transport modeling., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Laboratory batch experiments were performed to evaluate the effectiveness of nickel catalysts, nanoscale zerovalent iron (nZVI) doped with palladium, and microscale ZVI for treatment of tetrachloroethene, trichloroethene, and n-nitrosodimethylamine (NDMA) in soil-groundwater slurries. Results indicated that the presence of NDMA inhibited degradation of chlorinated solvents. Although both the nickel catalyst and nZVI were able to degrade NDMA in deionized water, neither of these metals was effective at degrading NDMA in the soil-groundwater system evaluated in this study. The effectiveness of the nickel catalyst and nZVI, with respect to treatment of the chlorinated solvents, also appeared to be highly dependent on the groundwater geochemical conditions. Overall results of this study suggest that the degradation mechanisms involving nickel catalysts and nZVI in natural soil/groundwater systems are not well-understood, and addition of metal catalysts to ZVI may not necessarily enhance observed degradation rates in natural systems.