Behaviour and fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water treatment: a review

Perfluoroalkyl substances and pharmaceuticals removal in full-scale drinking water treatment plants

The concentrations of 14 perfluoroalkyl substances (PFASs) and 46 pharmaceuticals in raw water and drinking water from five drinking water treatment plants were determined to assess removal of the chemicals during treatment. 10 out of 14 PFASs were detected in the raw and drinking water samples. The mean perfluorohexane sulfonate concentrations in raw and drinking water were the highest with levels of 106 and 69.6 ng L^-1, respectively and the other PFAS concentrations were lower. The ∑₁₄PFAS and individual PFAS removal efficiencies for the treatment plants were -36.9% to 70.7% (mean 31.3%) but the granular activated carbon process removed >80% of the total amount of long-chain PFASs that was removed. The removal efficiency increased as the perfluorocarbon chain length increased. The removal efficiencies increased by 14.2% and 11.2% from the shortest to the longest perfluoroalkyl carboxylic acid and perfluoroalkyl sulfonic acid chain lengths, respectively. 20 out of 46 pharmaceuticals were detected in the raw water samples, but most were removed completely during treatment. Only caffeine, carbamazepine, crotamiton, fenbendazole, metformin, and sulfamethoxazole were detected in the drinking water samples. Oxidation processes contributed >90% of the overall treatment plant removal efficiency except for metformin.

Photo enhanced degradation of polyfluoroalkyl and perfluoroalkyl substances

The increase in the presence of highly recalcitrant poly- and per- fluoroalkyl substances (PFAS) in the environment, plant tissues and animals continues to pose serious health concerns. Several treatment methods such as physical, biological and chemical processes have been explored to deal with these compounds. Current trends have shown that the destructive treatment processes, which offer degradation and mineralization of PFASs, are the most desirable process among researchers and policy makers. This article, therefore, reviews the degradation and defluorination processes, their efficiencies and the degradation mechanism of photon-based processes. It shows that high degradation and defluorination efficiency of PFASs could be achieved by photon driven processes such as photolysis, photochemical, photocatalysis and photoreduction. The efficiency of these processes is greatly influenced by the nature of light and the reactive radical generated in the system. The limitation of these processes, however, include the long reaction time required and the use of anoxic reaction conditions, which are not obtainable at ambient conditions.

Electrocatalytic degradation of perfluoroocatane sulfonate (PFOS) on a 3D graphene-lead dioxide (3DG-PbO2) composite anode: Electrode characterization, degradation mechanism and toxicity

In this work, a three-dimension grapnene-PbO₂ (3DG-PbO₂) composite anode was prepared using coelectrodeposition technology for electrocatalytic oxidation of perfluorooctane sulfonate (PFOS). The effect of 3DG on the surface morphology, structure and electrocatalytic activity of PbO₂ electrode was investigated. The results indicated that the 3DG-PbO₂-0.08 anode (3DG concentration in electrodeposition solution was 0.08 g L^-1) possessed the best electrocatalytic activity due to its stronger ·OH radicals generation capacity, more active sites and smaller charge-transfer resistance. The degradation rate constant of PFOS on 3DG-PbO₂-0.08 anode was 2.33 times than that of pure PbO₂ anode. Additionally, the by-products formed in electrocatalytic degradation of PFOS were identified and a PFOS degradation pathway was proposed accordingly, which was dominated by the dissociation of -CF₂- groups via the attack of ·OH radicals. Finally, the toxicity evolution of degradation solution was examined to evaluate the ecological risk of electrocatalytic oxidation of PFOS by acute toxicity assays to zebrafish embryos.

Effect of substrate concentrations on aerobic biotransformation of 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate

Biotransformation of 6:2 fluorotelomer sulfonate (FTS) results in the formation of short-chain (C4 - C6) perfluorocarboxylic acids (PFCAs) in landfill leachate. Although leachate substrate concentrations (i.e., organic carbon, ammonia) vary widely, their effects on 6:2 FTS biotransformation and PFCAs formation are unknown. This study investigated the effect of organic carbon and ammonia concentration in 6:2 FTS aerobic biotransformation and PFCA formation in leachate. Biotransformation experiments were conducted with sediment collected from a landfill leachate ditch, to which deionized (DI) water and various amounts of leachate were added. Microbial community analysis using 16S rRNA indicated that while phylum Proteobacteria dominated the bacterial composition throughout the 60 days, Actinobacteria increased with time. Many genera from Proteobacteria and Actinobacteria can synthesize a wide array of enzymes, indicating that these phyla are likely to play an important role in 6:2 FTS biotransformation. Higher biotransformation of 6:2 FTS was observed in leachate-added microcosms (∼21%), compared to DI water microcosm (∼14%), likely reflecting the substrate dependency of 6:2 FTS biotransformation. Substrate limiting conditions in DI water microcosm resulted in slightly greater formation of ∑(C4 - C6) PFCAs (∼14 mol%), compared with leachate added microcosms (10-13 mol%). The findings suggest that dilution of landfill leachate, (e.g., during wet seasons), likely results in reduced 6:2 FTS biotransformation and increased PFCAs formation compared to dry conditions. Observed formation of C7 - C8 PFCAs in the live microcosms suggested that landfills act as secondary sources of legacy PFCAs (e.g., perfluorooctanoic acid) in the environment.

Effects of different variables on photodestruction of perfluorooctanoic acid in self-assembled micelle system

Perfluoroalkyl substance (PFAS) is a class of anionic surfactants with superior stability in the environment. Due to the harmful health effect, PFASs have been listed as the priority controlled pollutants. Our recent study had developed a cationic surfactant induced ternary self-assembled micelle system to effectively degrade PFASs. In this study, using perfluorooctanoic acid (PFOA) as the model pollutant, we further investigated the effects of different variables on the degradation processes. According to the results of laser flash photolysis and dynamic light scattering, the degradation of PFOA was positively correlated with the chain length of the surfactants. While for double-chain surfactant, the steric effect might hinder the reaction. Our results also indicated that in the presence of high concentration of NaCl, the electrostatic attraction between Cl^- and the positively charged micelle made the micelle structure loose and thus slightly reduced the degradation efficiency. Similarly, the presence of NOM could also affect the degradation process via regulating the micelle structure. Furthermore, the optimal degradation efficiency for PFOA was obtained at neutral pH by the compromise of hydrated electron yield and self-assembled micelle structure. This composite showed good adaptability under ambient conditions and would have great potential for treatment of industrial PFAS containing wastewater, e.g., in the ternary micelle system, 18.95 mg L^-1 PFOA could be completely degraded within 8 h without any pretreatments.

Transcriptomic response of Gordonia sp. strain NB4-1Y when provided with 6:2 fluorotelomer sulfonamidoalkyl betaine or 6:2 fluorotelomer sulfonate as sole sulfur source

Abstract

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are environmental contaminants of concern. We previously described biodegradation of two PFAS that represent components and transformation products of aqueous film-forming foams (AFFF), 6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB) and 6:2 fluorotelomer sulfonate (6:2 FTSA), by Gordonia sp. strain NB4-1Y. To identify genes involved in the breakdown of these compounds, the transcriptomic response of NB4-1Y was examined when grown on 6:2 FTAB, 6:2 FTSA, a non-fluorinated analog of 6:2 FTSA (1-octanesulfonate), or MgSO₄, as sole sulfur source. Differentially expressed genes were identified as those with ± 1.5 log₂-fold-differences (± 1.5 log₂FD) in transcript abundances in pairwise comparisons. Transcriptomes of cells grown on 6:2 FTAB and 6:2 FTSA were most similar (7.9% of genes expressed ± 1.5 log₂FD); however, several genes that were expressed in greater abundance in 6:2 FTAB treated cells compared to 6:2 FTSA treated cells were noted for their potential role in carbon–nitrogen bond cleavage in 6:2 FTAB. Responses to sulfur limitation were observed in 6:2 FTAB, 6:2 FTSA, and 1-octanesulfonate treatments, as 20 genes relating to global sulfate stress response were more highly expressed under these conditions compared to the MgSO₄ treatment. More highly expressed oxygenase genes in 6:2 FTAB, 6:2 FTSA, and 1-octanesulfonate treatments were found to code for proteins with lower percent sulfur-containing amino acids compared to both the total proteome and to oxygenases showing decreased expression. This work identifies genetic targets for further characterization and will inform studies aimed at evaluating the biodegradation potential of environmental samples through applied genomics.

Graphic Abstract

Electronic supplementary material

The online version of this article (10.1007/s10532-020-09917-8) contains supplementary material, which is available to authorized users.

A Review of the Applications, Environmental Release, and Remediation Technologies of Per- and Polyfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS) are pollutants that have demonstrated a high level of environmental persistence and are very difficult to remediate. As the body of literature on their environmental effects has increased, so has regulatory and research scrutiny. The widespread usage of PFAS in industrial applications and consumer products, complicated by their environmental release, mobility, fate, and transport, have resulted in multiple exposure routes for humans. Furthermore, low screening levels and stringent regulatory standards that vary by state introduce considerable uncertainty and potential costs in the environmental management of PFAS. The recalcitrant nature of PFAS render their removal difficult, but existing and emerging technologies can be leveraged to destroy or sequester PFAS in a variety of environmental matrices. Additionally, new research on PFAS remediation technologies has emerged to address the efficiency, costs, and other shortcomings of existing remediation methods. Further research on the impact of field parameters such as secondary water quality effects, the presence of co-contaminants and emerging PFAS, reaction mechanisms, defluorination yields, and the decomposition products of treatment technologies is needed to fully evaluate these emerging technologies, and industry attention should focus on treatment train approaches to improve efficiency and reduce the cost of treatment.

Exposure to perfluorobutane sulfonate and perfluorooctanesulfonic acid disrupts the production of angiogenesis factors and stress responses in human placental syncytiotrophoblast

Poly- and per-fluoroalkyl substances (PFAS) have attracted widespread attention in recent years due to their bioaccumulation, toxicity, and ubiquitous nature. We and others have reported that maternal exposure to PFAS is associated with adverse birth outcomes due to altered placental functions. In this study, we investigated the effects of two major PFAS compounds, perfluorobutane sulfonate (PFBS) and perfluorooctanesulfonic acid (PFOS), on the regulation of the production of angiogenic factors and stress response in placental multinucleated syncytial BeWo cells using qRT-PCR and ELISA. Using this in vitro model, we showed that 1) PFOS or PFBS treatment did not seem to interrupt BeWo cell fusion through syncytins; 2) Exposure to PFOS at 10 μM decreased a potent angiogenic factor PlGF gene expression, which is implicated in preeclampsia; 3) Exposure to either PFOS or PFBS significantly decreased the production of CGB7 and hCG except hCG secretion in PFOS (10 nM) and PFBS (100 nM) treatment groups; 4) Exposure to PFOS (10 μM) increased the gene expression of the stress response molecules CRH while neither PFOS nor PFBS treatment affected a stress mitigation factor 11β-HSD2 expression. Our results demonstrate that exposure to PFOS or PFBS impacts several key pathways involved in placental cell functions. PFOS seems more potent than PFBS. These novel findings provide a potential explanation for the adverse reproductive complications associated with prenatal exposure to PFOS or PFBS, including preeclampsia and contribute to our knowledge of the reproductive toxicity of PFAS, specifically PFOS and PFBS.

Demographic and exposure characteristics as predictors of serum per- and polyfluoroalkyl substances (PFASs) levels - A community-level biomonitoring project in Pennsylvania

Per- and polyfluoroalkyl substances (PFASs) are widely used in industrial and consumer products and have been linked to various adverse health effects. Communities near two former military bases in Pennsylvania were exposed to PFAS through contaminated drinking water for several decades. The Pennsylvania Department of Health (DOH) conducted biomonitoring of 235 randomly selected community members living in four public water system (PWS) service areas to evaluate a toolkit developed by the Centers for Disease Control and Prevention (CDC) and the Agency for Toxic Substances and Disease Registry (ATSDR). DOH also collected data on participants' demographics, exposure history and self-reported health conditions. Serum PFAS levels were compared with the national averages for 2013-2014 and their relationships with demographic and exposure characteristics were analyzed. Of the 11 PFASs analyzed for, only perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS) and perfluorononanoic acid (PFNA) were consistently detected in the serum samples. The average levels of PFOA, PFOS, PFHxS and PFNA among the study participants were 3.13, 10.24, 6.64 and 0.74 μg per liter (μg/L), respectively. Overall, 75, 81, 94 and 59 percent of the study participants had levels exceeding the national average for PFOA (1.94 μg/L), PFOS (4.99 μg/L), PFHxS (1.35 μg/L) and PFNA (0.66 μg/L), respectively. Results indicated associations between serum levels of some PFAS compounds and sex, age, employment in the study area, PWS area, quantity of daily tap water consumption, and length of residence in the study area.

A profile analysis with suspect screening of per- and polyfluoroalkyl substances (PFASs) in firefighting foam impacted waters in Okinawa, Japan

Per- and polyfluoroalkyl substances (PFASs) are a group of persistent contaminants detected in firefighting foam impacted waters. Previous studies have performed suspect and non-target screening by high-resolution mass spectrometry (HRMS) to determine the composition of PFAS contamination and to discover unknown PFASs. Here, we performed a profile analysis with suspect screening against two lists in the NORMAN Suspect List Exchange in firefighting foam impacted environmental and drinking water (n = 18) collected in Okinawa, Japan, in April 2019. Samples were analyzed by liquid chromatography (LC) quadrupole time-of-flight (QTOF) MS in electron spray ionization mode. Suspect screening returned 116 candidate PFASs with their molecular weights, functional groups, and perfluoroalkyl chain lengths. Long-chain perfluoroalkyl acids (PFAAs) and some of their precursors were specifically found around the firefighting training area. Short-chain PFAAs were assumed to be formed from precursors by environmental processes. Perfluoroalkyl sulfonamide precursors were found to be transformed to perfluoroalkyl sulfonic acids (PFSAs) in the drinking water treatment process. In contrast, biological activated carbon filtration formed perfluoroalkyl carboxylic acids (PFCAs). The PFAS profile showed that a large number of different substances needs to be considered.

Prevalence of per- and polyfluoroalkyl substances (PFASs) in drinking and source water from two Asian countries

The present study focuses on the determination of the occurrence and levels of per- and polyfluoroalkyl substances (PFASs) in the drinking and source water from the Philippines and Thailand. A total of 46 samples (18 commercial bottled waters, 5 drinking water from vending machine (re-fill stations) and 23 source water) were analyzed using liquid chromatography with tandem high-resolution mass spectrometry. Using the targeted method, 12 different PFASs were detected in the drinking water samples with total quantifiable PFASs (∑PFASs) levels ranging from 7.16 to 59.49 ng/L; 15 PFASs were detected in source water with ∑PFASs ranging from 15.55 to 65.65 ng/L. A 100% detection frequency was observed for perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorosulfonic acid (PFOS) in all water samples. Six other PFASs, not included in the targeted analysis, were detected using the suspect screening approach. For the first time, the presence of 2-(N-methylperfluorooctanesulfonamido) acetic acid (N-MeFOSAA) in drinking water is reported, and 3 novel PFASs (C₅H₅OF_8, C₆H₄O₂F₆, and C₉H₂O₂F₁₆) were detected using suspect screening in source water. Combined results from target and suspect screening analysis showed that PFASs detected were predominantly (52%) short-chain (with fluorinated alkyl chain of ≤6) which could be explained by their high mobility in the environment. The detected PFASs levels in drinking water will not likely pose immediate health risk to consumers according to US EPA health advisory for PFOS and PFOA of 70 ng/L, but inclusion of bottled and drinking water from re-fill stations in monitoring programs is warranted.

Removal of legacy PFAS and other fluorotelomers: Optimized regeneration strategies in DOM-rich waters

We present the first study investigating optimized regeneration strategies for anionic ion exchange (IX) resins during the removal of persistent per- and poly-fluoroalkyl substances (PFAS, including GenX) from surface and treated wastewater effluents. IX regeneration studies are of critical importance from environmental perspectives. Specifically, the knowledge is essential for water utilities who presently operate IX (for PFAS removal) in a single use-and-dispose mode. In this study, legacy PFAS such as PFOA/PFOS were tested along with other harmful short-chained PFAS (PFBA/PFBS) and other toxic perfluorinated substitutes (GenX). Studies were performed on synthetic water (spiked with Suwannee River Natural Organic Matter (SRNOM), Fulvic Acid (SRFA) and Humic Acid (SRHA)), surface water, and wastewater effluents, and the regeneration was performed in batch stirred reactors. The resin service life with and without regeneration was investigated in the presence of background organic matter. In ultra-pure waters, all PFAS (C₀ ∼10 μg/L, concentrations similar to that of natural waters) were effectively removed for >100,000 Bed Volume (BV) of operation. This was reduced to ∼23,500 BV in the presence of SRNOM (C₀ = 5 mg C/L), 20,500 BV in SRFA and 8500 BV in SRHA, after which the saturated resins required regeneration. More importantly, all resin breakthrough (PFAS> 70 ng/L) corresponded to > 90% resin site saturation (in meqs), an essential information for optimizing IX loading. The competitive dissolved organic matter (DOM) fractions were estimated to be approximately 5-9% of the initial DOC, as estimated by the IAST-EBC model. Finally, it was identified that IX regeneration efficiency improved with increasing brine contact time but effectiveness plateaued for brine concentrations above 10% (W/V). Nonetheless, a regeneration with 10% NaCl solution with a contact time of 2 h was found to be optimal for IX operations in synthetic and natural waters. Therefore, this study provides key knowledge essential for the scientific community and the water industry on optimizing IX operational parameters for DOM and PFAS removal and would be highly valuable for systems which presently operate IX in a use-and-dispose mode.

Non-target and suspect screening of per- and polyfluoroalkyl substances in Chinese municipal wastewater treatment plants

Wastewater treatment plant (WWTP) is one of the major sources of per- and polyfluoroalkyl substances (PFASs) to the aquatic environment. In this study, wastewater samples were collected from 17 WWTPs in 17 cities of China to investigate emerging PFASs in WWTPs. To comprehensively identify PFASs in the wastewater samples, an integrated suspect screening, homologue-based and fragment-based non-target screening method is proposed. Sixty-three PFASs from 13 classes (25 subclasses) were identified, including 14 legacy and 49 emerging PFASs, and this study is the first to report on 12 of these PFASs. We found that emerging PFASs concentration had a significantly positive correlation with the gross domestic product, indicating more substitution of legacy PFASs in the developed area of China. We also analyzed the removal of the 13 PFAS classes, and found that all discovered PFAS classes were not completely removed after the treatment process, whereas the class of perfluoroalkyl ether alcohols significantly increased. All of these results imply that the release of emerging or unknown PFASs from WWTPs is a universal but not negligible problem in China.

Long-term investigation on the removal of perfluoroalkyl substances in a full-scale drinking water treatment plant in the Veneto Region, Italy

Drinking water contamination by perfluoroalkyl and polyfluoroalkyl substances (PFASs) is an issue of relatively recent concern. The literature indicates that anion exchange resins and granular activated carbon (GAC) are suitable technologies for removing these compounds. While several laboratory-scale and pilot-scale experiments have been conducted to study activated carbon adsorption/desorption mechanisms of a number of PFASs, little data on full-scale plants are available. This work examines a real case of groundwater contamination by PFASs in an area of approximately 200 km². The performance of the main drinking water treatment plant in the area (flowrate = 30,000 m³/d; 100,000 people served), which is equipped with GAC filters, was analysed. Approximately 17,000 analytical data points from a working period of five years were processed. Perfluorobutyric acid (PFBA) was the first compound to attain breakthrough, followed by perfluoropentanoic acid, perfluorohexanoic acid, perfluorobutanesulfonic acid, and perfluorooctanoic acid (PFOA). The adsorption capacity and treated bed volumes at complete breakthrough (saturation) were calculated, and ranged from 1.71 g/t and 7100 (PFBA) to 24.6 g/t and 50,900 (PFOA), with the total organic carbon concentration in the groundwater ranging from <0.1 to 0.5 mg/L. The overall adsorption capacity was approximately 40 g of total PFASs/t. The breakthrough behaviour of PFASs was correlated with the CF chain length, the type of hydrophilic head (either carboxyl or sulfonic), and the n-octanol/water partition coefficients logP and logD. The results corroborate the findings of previously published bench-scale and pilot-scale experiments.

Perfluorobutane sulfonate exposure disrupted human placental cytotrophoblast cell proliferation and invasion involving in dysregulating preeclampsia related genes

We reported that maternal PFBS, an emerging pollutant, exposure is positively associated with preeclampsia which can result from aberrant trophoblasts invasion and subsequent placental ischemia. In this study, we investigated the effects of PFBS on trophoblasts proliferation/invasion and signaling pathways. We exposed a human trophoblast line, HTR8/SVneo, to PFBS. Cell viability, proliferation, and cell cycle were evaluated by the MTS assay, Ki-67 staining, and flow cytometry, respectively. We assessed cell migration and invasion with live-cell imaging-based migration assay and matrigel invasion assay, respectively. Signaling pathways were examined by Western blot, RNA-seq, and qPCR. PFBS exposure interrupted cell proliferation and invasion in a dose-dependent manner. PFBS (100 μM) did not cause cell death but instead significant cell proliferation without cell cycle disruption. PFBS (10 and 100 μM) decreased cell migration and invasion, while PFBS (0.1 μM) significantly increased cell invasion but not migration. Further, RNA-seq analysis identified dysregulated HIF-1α target genes that are relevant to cell proliferation/invasion and preeclampsia, while Western Blot data showed the activation of HIF-1α, but not Notch, ERK1/2, (PI3K)AKT, and P38 pathways. PBFS exposure altered trophoblast cell proliferation/invasion which might be mediated by preeclampsia-related genes, suggesting a possible association between prenatal PFBS exposure and adverse placentation.

Removal of per- and polyfluoroalkyl substances (PFASs) in a full-scale drinking water treatment plant: Long-term performance of granular activated carbon (GAC) and influence of flow-rate

Per- and polyfluoroalkyl substances (PFASs) have been ubiquitously detected in drinking water which poses a risk for human exposure. In this study, the treatment efficiency for the removal of 15 PFASs was examined in a full-scale drinking water treatment plant (DWTP) in the City of Uppsala, Sweden, over a period of two years (2015-2017). Removal of the five frequently detected PFASs was influenced by the total operation time of granular activated carbon (GAC) filters, GAC type and surface loading rate. The average removal efficiency of PFASs ranged from 92 to 100% for "young" GAC filters and decreased to 7.0-100% for "old" GAC filters (up to 357 operation days, 29 300 bed volumes (BV) treated). Flow-rates were adjusted in two full-scale GAC filters of different operational age to examine the removal of PFAS and organic matter depending on GAC operational age and operating flow. The decrease in flow-rate by 10 L s^-1 from 39 to 29 L s^-1 led to an average increase of 14% and 6.5% in total PFAS removal efficiency for an "old" (264 operation days, 21 971 BV treated) and a "young" GAC filter (63 operation days, 5 725 BV treated), respectively. A cost-analysis for various operation scenarios illustrated the dominating effect of treatment goals and costs for GAC regeneration on overall GAC operation costs. The unit costs for GAC filters ranged from 0.08 to 0.10 € m^-3 water treated and 0.020-0.025 € m^-3 water treated for a treatment goal of 10 ng L^-1 and 85 ng L^-1, respectively, for ∑₁₁PFAS. Furthermore, it was concluded that prolonging the GAC service life by lowering the flow-rates after reaching the treatment goal could lead to a 26% cost-deduction. The results and methods presented in this study give drinking water providers valuable tools for the operation of a full-scale treatment train for the removal of PFAS in contaminated raw water.

Exploring the factors that influence the adsorption of anionic PFAS on conventional and emerging adsorbents in aquatic matrices

Per and polyfluoroalkyl substances (PFASs) have raised great concern due to their ubiquity in aquatic environments, and adsorption technologies are among the most promising treatment solutions. This study investigated the key factors that influence the adsorption of anionic PFASs on conventional and emerging adsorbents. Batch adsorption experiments were conducted to evaluate the removal of 20 target PFASs at environmentally relevant concentrations by three different activated carbon (AC) materials and two different β-cyclodextrin polymers (CDPs). Experiments were conducted in Milli-Q water and in groundwater. Major physical properties of the adsorbents were measured, along with general water chemistry parameters for each groundwater sample. Principal component analysis (PCA) was subsequently employed to extract the important associations from the multivariate dataset. The distinct performances of ACs and CDPs were attributed to their different surface chemistry and the distinct nature of their adsorption binding sites. Hydrophobic interactions dominated PFAS adsorption onto ACs while CDPs mostly attracted anionic PFASs via favorable electrostatic interactions. ACs of a smaller average particle size performed better, with our data pointing to an increased external specific surface area as the likely reason. pH and the concentration of cations were the primary contributors to adsorption inhibition in groundwater. Higher pH values limit anionic PFAS adsorption by deprotonating the functional groups on adsorbent surfaces. The elevated levels of cations in some groundwater samples limited the effects of attractive electrostatic interactions. Knowledge of PFAS adsorption mechanisms gained from this study can be used to design more efficient adsorbents and to predict their performance under a range of environmental scenarios.

Direct contact membrane distillation for effective concentration of perfluoroalkyl substances - Impact of surface fouling and material stability

Polyfluoroalkyl and perfluoroalkyl substances (PFAS) are ecotoxic amphiphilic compounds containing alkyl-fluorinated chains terminated with weak acid moieties, and hence difficult to be degraded or removed from water sources. Direct contact membrane distillation (DCMD) was used for concentrating and removing of perfluoropentanoic acid (PFPeA) compounds from model contaminated water using commercially available poly (tetrafluoroethylene) (PTFE) membranes. The membranes were characterised for surface morphology, roughness, contact angle and pore size distribution before and after the DCMD test to investigate and evaluate membrane fouling. During the DCMD test performed for 6 h using 10 ppm PFPeA solution, the membrane exhibited progressive increased flux (from 17 to 43 kg m^-2 h^-1) and decreased PFPeA rejection (from 85 to 58%), as the feed temperature was increased from 50 to 70 °C. Further, the feed/retentate side showed a 1.8, 2.1 and 2.8-fold increase in PFPeA concentration tested at feed temperatures 50, 60, and 70 °C, respectively. The permeate side contained less than 1 ppm of PFPeA revealing that the PFPeA moved across the PTFE membrane during DCMD, which is attributed to progressive surface diffusion over time. This study opens a new route to concentrate and remove amphiphilic molecules, such as PFAS, from source points, relevant to landfill leachates or surface waters. The study also points at gaps in materials science and surface engineering to be tackled to deal with PFAS compounds efficiently.

Uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid and perfluorooctane sulfonic acid by wetland plant Alisma orientale

Perfluoroalkyl substances (PFASs) are of particular environmental concern due to their environmental persistence and potential toxicity. Phytoremediation may be used to remove PFASs from wastewater. Here we investigated the uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS) in the wetland plant Alisma orientale by using a series of hydroponic experiments. Active uptake facilitated by water transporters and anion channels was involved in the uptake of PFASs by plant roots. PFOA and PFOS were mainly distributed in the water-soluble fraction (46.2-70.8%) and in cell walls (45.6-58.4%), respectively. The uptake process was proposed as follows: PFOS and PFOA were first distributed in the soluble fraction; a proportion of PFOS and PFOA were adsorbed gradually by the cell wall, and a proportion of PFOS and PFOA in the cell wall passed through the cell wall and plasmalemma and bind with organelles. PFOS and PFOA were transported from the external solution to the vascular bundle of the plant root through both symplastic and apoplastic routes.

Scientific Basis for Managing PFAS as a Chemical Class

This commentary presents a scientific basis for managing as one chemical class the thousands of chemicals known as PFAS (per- and polyfluoroalkyl substances). The class includes perfluoroalkyl acids, perfluoroalkylether acids, and their precursors; fluoropolymers and perfluoropolyethers; and other PFAS. The basis for the class approach is presented in relation to their physicochemical, environmental, and toxicological properties. Specifically, the high persistence, accumulation potential, and/or hazards (known and potential) of PFAS studied to date warrant treating all PFAS as a single class. Examples are provided of how some PFAS are being regulated and how some businesses are avoiding all PFAS in their products and purchasing decisions. We conclude with options for how governments and industry can apply the class-based approach, emphasizing the importance of eliminating non-essential uses of PFAS, and further developing safer alternatives and methods to remove existing PFAS from the environment.

Recent Developments of PFAS-Detecting Sensors and Future Direction: A Review

Per- and poly-fluoroalkyl substances (PFASs) have recently been labeled as toxic constituents that exist in many aqueous environments. However, traditional methods used to determine the level of PFASs are often not appropriate for continuous environmental monitoring and management. Based on the current state of research, PFAS-detecting sensors have surfaced as a promising method of determination. These sensors are an innovative solution with characteristics that allow for in situ, low-cost, and easy-to-use capabilities. This paper presents a comprehensive review of the recent developments in PFAS-detecting sensors, and why the literature on determination methods has shifted in this direction compared to the traditional methods used. PFAS-detecting sensors discussed herein are primarily categorized in terms of the detection mechanism used. The topics covered also include the current limitations, as well as insight on the future direction of PFAS analyses. This paper is expected to be useful for the smart sensing technology development of PFAS detection methods and the associated environmental management best practices in smart cities of the future.

Cytotoxicity of perfluorodecanoic acid on mouse primary nephrocytes through oxidative stress: Combined analysis at cellular and molecular levels

Long-chain perfluoroalkyl acids (PFAAs) such as perfluorodecanoic acid (PFDA) are toxic, persistent organic pollutants. This study investigated the harmful effect of PFDA on mouse primary nephrocytes and its mechanism at cellular and molecular levels. Cellular results showed that PFDA exhibited nephrotoxicity with decreased cell viability and increased apoptosis. The increase of intracellular reactive oxygen species (ROS) content and the decrease of intracellular superoxide dismutase (SOD) activity were significant (p < 0.01) when PFDA concentration exceeded 10 μM. Additionally, the molecular results indicated that PFDA bind with Val-A98 in the surface of Cu/Zn-SOD by a 3.11 Å hydrogen bond driven by Van der Waals' force and hydrogen bonding force, which triggered the structural changes and decreased activity of Cu/Zn-SOD. Altogether, the intracellular oxidative stress is the main driver of nephrocyte apoptosis; and the interaction of PFDA and Cu/Zn-SOD exacerbated the oxidative stress in nephrocytes, which is also a nonnegligible reason of cytotoxicity induced by PDFA. This study represented a meaningful method to explore the toxic effect and mechanism of xenobiotics at cellular and molecular levels. The findings have implications for revealing the clearance of long-chain PFAAs in vivo.

Measurement of Novel, Drinking Water-Associated PFAS in Blood from Adults and Children in Wilmington, North Carolina

BACKGROUND

From 1980 to 2017, a fluorochemical manufacturing facility discharged wastewater containing poorly understood per- and polyfluoroalkyl substances (PFAS) to the Cape Fear River, the primary drinking water source for Wilmington, North Carolina, residents. Those PFAS included several fluoroethers including HFPO-DA also known as GenX. Little is known about the bioaccumulation potential of these fluoroethers.

OBJECTIVE

We determined levels of fluoroethers and legacy PFAS in serum samples from Wilmington residents.

METHODS

In November 2017 and May 2018, we enrolled 344 Wilmington residents ≥ 6  years of age into the GenX Exposure Study and collected blood samples. Repeated blood samples were collected from 44 participants 6 months after enrollment. We analyzed serum for 10 fluoroethers and 10 legacy PFAS using liquid chromatography-high-resolution mass spectrometry.

RESULTS

Participants' ages ranged from 6 to 86 y, and they lived in the lower Cape Fear Region for 20 y on average (standard deviation: 16 y). Six fluoroethers were detected in serum; Nafion by-product 2, PFO4DA, and PFO5DoA were detected in > 85 % of participants. PFO3OA and NVHOS were infrequently detected. Hydro-EVE was present in a subset of samples, but we could not quantify it. GenX was not detected above our analytical method reporting limit (2  ng / mL ). In participants with repeated samples, the median decrease in fluoroether levels ranged from 28% for PFO5DoA to 65% for PFO4DA in 6 months due to wastewater discharge control. Four legacy PFAS (PFHxS, PFOA, PFOS, PFNA) were detected in most (≥ 97 % ) participants; these levels were higher than U.S. national levels for the 2015-2016 National Health and Nutrition Examination Survey. The sum concentration of fluoroethers contributed 24% to participants' total serum PFAS (median: 25.3  ng / mL ).

CONCLUSION

Poorly understood fluoroethers released into the Cape Fear River by a fluorochemical manufacturing facility were detected in blood samples from Wilmington, North Carolina, residents. Health implications of exposure to these novel PFAS have not been well characterized. https://doi.org/10.1289/EHP6837.

Enhanced adsorption of perfluorooctanoic acid (PFOA) from water by granular activated carbon supported magnetite nanoparticles

A new composite material (Fe₃O₄@GAC, Fe₃O₄ nanoparticles loaded on a commercial granular activated carbon (GAC)) was prepared through a facile hydrothermal process at controlled Fe²⁺:Fe³⁺ molar ratios in air. Fe₃O₄@GAC was thoroughly characterized and tested for adsorption of perfluorooctanoic acid (PFOA) in water. Fe₃O₄@GAC(2:1), prepared at an Fe²⁺:Fe³⁺ molar ratio of 2:1, showed the best PFOA removal and offered 28.8% higher adsorption capacity than the parent GAC at final pH 4.0. The enhanced adsorption of PFOA was attributed to concurrent hydrophobic, electrostatic and complexation interactions between PFOA, GAC and Fe₃O₄. GAC in the composite played an important role for PFOA adsorption. The presence of Ca²⁺ ions (10 mM) at final pH 5.0-10.0 more than doubled the PFOA equilibrium uptake of PFOA by Fe₃O₄@GAC(2:1) due to the calcium bridging effect between PFOA and the Si-OH or Fe-OH groups in Fe₃O₄@GAC(2:1), and because of the Ca²⁺-modification induced formation of PFOA hemi-micelles on the surface or in the relatively large pores (2.27 nm) of Fe₃O₄@GAC(2:1). Fe₃O₄@GAC(2:1) was amenable to efficient regeneration using a mixture of NaOH solution and methanol. Fe₃O₄@GAC holds the potential to be used as a simple and low-cost adsorbent for enhanced adsorption of PFOA, especially in waters of high hardness and alkalinity.

Water Treatment: Are Membranes the Panacea?

Alongside the rising global water demand, continued stress on current water supplies has sparked interest in using nontraditional source waters for energy, agriculture, industry, and domestic needs. Membrane technologies have emerged as one of the most promising approaches to achieve water security, but implementation of membrane processes for increasingly complex waters remains a challenge. The technical feasibility of membrane processes replacing conventional treatment of alternative water supplies (e.g., wastewater, seawater, and produced water) is considered in the context of typical and emerging water quality goals. This review considers the effectiveness of current technologies (both conventional and membrane based), as well as the potential for recent advancements in membrane research to achieve these water quality goals. We envision the future of water treatment to integrate advanced membranes (e.g., mixed-matrix membranes, block copolymers) into smart treatment trains that achieve several goals, including fit-for-purpose water generation, resource recovery, and energy conservation.

Application of zero-valent iron coupled with biochar for removal of perfluoroalkyl carboxylic and sulfonic acids from water under ambient environmental conditions

Advanced oxidation and reduction processes have been intensively investigated as potential methods to promote the decomposition of perfluoroalkyl substances (PFASs). However, extreme operational conditions such as highly acidic pH, high temperature, and high pressure are required to promote degradation reactions, which makes these technologies costly and less feasible for full-scale applications. The objective of this study was to evaluate the effectiveness of zero-valent iron (ZVI) alone and a mixture of ZVI and biochar (ZVI + BC) for removal of seven target PFASs from water under ambient environmental conditions. Target PFASs included three perfluoroalkyl carboxylic acids (PFCAs) [perfluorooctanoic acid (PFOA, C8-PFCA), perfluoroheptanoic acid (C7-PFCA), and perfluorohexanoic acid (C6-PFCA)] and four perfluoroalkyl sulfonic acids (PFSAs) [perfluorooctane sulfonic acid (PFOS, C8-PFSA), perfluoroheptane sulfonic acid (C7-PFSA), perfluorohexane sulfonic acid (C6-PFSA), and perfluorobutane sulfonic acid (C4-PFSA)]. Batch test results show that PFSAs (up to 94% removal) were more effectively removed than PFCAs (up to 60% removal) when utilizing either ZVI or (ZVI + BC). About 20-60% of input PFOA (~18,550 μg L^-1) and 90-94% of input PFOS (~18,580 μg L^-1) were removed by ZVI alone or the mixture of (ZVI + BC). The removal efficiencies of PFCAs and PFSAs by reactive media increased with increasing chain length, from 0 to 17% for short-chain PFCAs (C6-C7) and 20 to 70% for short-chain PFSAs (C4-C7). About 5-10% of input PFOA and PFOS was partially defluorinated by ZVI alone as indicated by F^- release; however, the defluorination efficiency may be underestimated due to the sorption of F^- by the reactive media. Overall, the reactive mixture (ZVI + BC) may be an effective and environmentally sustainable material for removing PFASs from water under ambient environmental conditions.

Removal of persistent organic pollutants (POPs) from waters and wastewaters by the use of ionizing radiation

The most important advantages of the use of ionizing radiation over other AOPs are exceptionally efficient in situ generation of very reactive oxidizing free radicals ^•OH from water radiolysis and very unique simultaneous generation of strongly reducing hydrated electrons. They allow to carry out Advanced Oxidation and Reduction Processes (AO/RPs) simultaneously. Carrying out only oxidative or reductive processes is also possible by the use of appropriate scavengers of free radicals in irradiated solutions. For the application of these processes for environmental protection purposes gamma-rays from radioisotope sources or beams of accelerated electrons are most commonly used. In the case of particularly resistant POPs some chemical additives to the irradiated solutions may enhance the yield of decomposition. This review based on 125 references reported so far presents the applications of the discussed technology in removing POPs from waters and wastewaters, including pesticides listed among POPs, dioxins, polychlorinated biphenyls, polycyclic aromatic hydrocarbons and selected perfluorinated surfactants.

Uptake and Translocation of Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) by Wetland Plants: Tissue- and Cell-Level Distribution Visualization with Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) and Transmission Electron Microscopy Equipped with Energy-Dispersive Spectroscopy (TEM-EDS)

Perfluoroalkyl substances (PFASs) are persistent chemicals in the environment. So far, little is known about their uptake potential in wetland plants. Here, we investigated the uptake and translocation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in eight common wetland plants, namely, Canna indica (Ci), Thalia dealbata (Td), Cyperus alternifolius (Ca), Phragmites australis (Pa), Arundo donax (Ad), Pontederia cordata (Pc), Cyperus papyrus (Cp), and Alisma orientale (Ao) by hydroponic experiments and visualized their tissue- and cell-level distribution with desorption electrospray ionization mass spectrometry (DESI-MS) and transmission electron microscopy equipped with energy-dispersive spectroscopy (TEM-EDS). The results showed that the PFASs accumulated in plants accounted for 1.67-16.7% of the total mass spiked into the hydroponic systems, and PFOS accumulated largely in roots (48.8-95.8%), while PFOA was stored mostly in the aboveground part (29.3-77.4%). DESI-MS and TEM-EDS analysis showed that PFASs in Ci, Td, Pa, and Ca were transported from the hydroponic solution to the root cortex via both apoplastic (e.g., across cell walls and/or intercellular spaces) and symplastic routes (e.g., across plasma membranes or via plasmodesmata) and further to the vascular bundle via symplastic route in Td and Pa and via both routes in Ci and Ca. These two chemicals were transported from roots to stems mainly through the cortex in Td and through both the cortex and vascular bundles in Ci and Ca.

Liquid Chromatographic Tandem Mass Spectrometric (LC-MS/MS) Determination of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) in the Yolk of Poultry Eggs in Malaysia

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are widely used in products, and are known for their water and grease repellent properties. The persistence nature and potential toxicity of these substances have raised substantial concerns about health effects. Regarding humans, food consumption has reportedly been a significant source of exposure for both compounds. Hence, this study was performed to develop and validate an analytical method for PFOS and PFOA in egg yolks using liquid chromatographic tandem mass spectrometry (LC-MS/MS) followed by the determination of concentration of both compounds in the yolk of poultry eggs in Malaysia. A total of 47 poultry egg yolk samples were extracted by a simple protein precipitation technique using acetonitrile. The analytical method was developed using LC-MS/MS and validated based on the Food and Drug Administration (FDA)’s Bioanalytical Method Validation guidelines. The results revealed that PFOS was quantitatively detected in six samples, with the concentration range between 0.5 and 1.01 ng g⁻¹. Among these, five samples were from home-produced chicken eggs, and one sample was from a quail egg. The levels of PFOA in all samples were below the quantifiable limit (<0.1 ng g⁻¹). This indicated that the contamination of PFCs in poultry eggs were mostly attributed to the nature of free foraging animals, which had direct contact with the contaminants in soil and feed. In conclusion, a fast and robust analytical method for analyzing PFOS and PFOA in egg yolk samples using LC-MS/MS was successfully developed and validated. The presence of these emerging contaminants in this study signified widespread pollution in the environment.

On the Behavior of Perfluorinated Persistent Organic Pollutants (POPs) at Environmentally Relevant Aqueous Interfaces: An Interplay of Hydrophobicity and Hydrogen Bonding

The behavior of perfluorinated persistent organic pollutants (POPs), especially perfluoroalkyl carboxylic and sulfonic acids, at aqueous interfaces is crucial for their transport and speciation in the environment and subsequent immunotoxicity. Here, we investigate the surface prevalence and interfacial interaction of a prototype perfluorinated-POP, perfluoroheptanoic acid (PFHA), with environmentally relevant amphiphiles of varying hydrophobicity and head groups (C_nH_2n+1-X; n: 8 vs 16; -X: -OH vs -COOH) using interface-selective vibrational sum frequency generation (VSFG) spectroscopy. SFG intensity spectra in the CH- and OH-stretch regions reveal that PFHA prevails at aqueous interfaces that contain amphiphiles of intermediate chain length such as 1-octanol (n = 8) and heptanoic acid (n = 6). PFHA partially expels as well as increases the alkyl chain order of octanol on the water surface. Whereas heptanoic acid, though less hydrophobic than octanol, is retained at the water surface through hydrogen-bonding with the PFHA head group (^(PFHA)COO^-···HOOC^{(heptanoic-acid)}). Long chain amphiphiles (n = 16) such as hexadecanol and palmitic acid expel PFHA from the water surface regardless of the difference in their head groups. Interestingly, the dangling OH (3710 cm^-1) which is diminished at the hydrogenated-amphiphile-water interface is preserved at the perfluorinated-POP-water interface.

Risk assessment of PFASs in drinking water using a probabilistic risk quotient methodology

We evaluated health risks associated with perfluorinated and polyfluorinated alkyl substances (PFASs) found in drinking water applying human risk assessment (HRA) methodology. Using data on worldwide occurrence of PFASs in drinking water and recent guidelines for PFASs in drinking water, we applied four scenarios based on different toxicological threshold values to calculate age-dependent risk quotients (RQ) for different PFASs. The mean concentrations of the most frequently detected compounds (PFOS and PFOA) were highest in North America (99.2 and 30.7 ng L^-1, respectively), and lowest in Asia (PFOS: 3.0 ng L^-1) and Europe (PFOA: 4.87 ng L^-1). Using HRA methodology and maximum reported concentrations, only PFOS and PFOA, examined individually, showed any threat to human health. Specifically, calculations with the average and maximum concentrations of PFOS showed RQ values higher than 0.2 or 1, respectively, for some age groups under specific scenarios. Similarly, using maximum PFOA concentrations, a RQ equal to 0.2 for infants up to 3 months was calculated under scenario 4. Regional differences on RQ values were observed when PFOS concentrations from Europe, North America and Asia were used. Estimation of the human health risk due to mixtures of PFASs using average concentrations showed that the RQ_mix was higher than 0.2 for infants up to 3 months (scenario 3) and infants and children up to 6 years old (scenario 4). More importantly, evaluation of the guideline values set by the EU and the Health Advisory Levels issued by the USEPA resulted (under some scenarios) in RQ values higher than 0.2 for PFOS and PFOA for specific age groups, indicating that further discussion is needed for the monitoring and prioritization of these compounds.

Formation of perfluorocarboxylic acids from 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate: Role of microbial communities

Fluorotelomer compounds in landfill leachate can undergo biotransformation under aerobic conditions and act as a secondary source of perfluorocarboxylic acids (PFCAs) to the environment. Very little is known about the role of various microbial communities towards fluorotelomer compounds biotransformation. Using an inoculum prepared from the sediment of a leachate collection ditch, 6:2 fluorotelomer sulfonate (6:2 FTS) biotransformation experiments were carried out. Specific substrates (i.e., glucose, ammonia) and ammonia-oxidizing inhibitor (allylthiourea) were used to produce two experimental runs with heterotrophic (HET) growth only and heterotrophic with ammonia-oxidizing and nitrite- oxidizing bacteria (HET + AOB + NOB). After 10 days, ∼20% of the spiked 6:2 FTS removal was observed in HET + AOB + NOB, compared to ∼7% under HET condition. Higher 6:2 FTS removal in HET + AOB + NOB likely resulted from ammonia monooxygenase enzyme that catalyzes the first step of ammonia oxidation. The HET + AOB + NOB condition also showed higher PFCA (C4-C6) formation (∼2% of initially spiked 6:2 FTS), possibly due to higher overall bioactivity. Microbial community analysis through 16s rRNA sequencing confirmed that Proteobacteria and Bacteroidetes were the most abundant phyla (>75% relative abundance) under all experimental conditions. High abundance of Actinobacteria (>17%) was observed under the HET + AOB + NOB condition on day 7. Since Actinobacteria can synthesize a wide range of enzymes including monooxygenases, they likely play an important role in 6:2 FTS biotransformation and PFCA production.

Are (fluorinated) ionic liquids relevant environmental contaminants? High-resolution mass spectrometric screening for per- and polyfluoroalkyl substances in environmental water samples led to the detection of a fluorinated ionic liquid

Fragmentation flagging (FF), a high-resolution mass spectrometric screening variant that utilizes intentionally produced indicative in-source fragments, was used to screen for per- and polyfluoroalkyl substances (PFASs) in surface waters. Besides expected legacy PFAS, FF enabled the detection of some rarely investigated representatives, such as trifluoromethanesulfonic acid (TFMSA). Additionally, a novel PFAS was detected and identified as tris(pentafluoroethyl)trifluorophosphate (FAP) via MS/MS experiments and confirmed with a reference standard. The first monitoring of FAP in 20 different surface waters revealed a localized contamination affecting three connected rivers with peak concentrations of up to 3.4 μg/L. To the best of our knowledge, this is the first time FAP has been detected in environmental water samples. The detection of FAP, which is exclusively used as a constituent of ionic liquids (ILs), raises questions about the environmental relevance of ILs in general and particularly fluorinated ILs. A following comprehensive literature search revealed that ILs have already been intensely discussed as potential environmental contaminants, but findings reporting ILs in environmental (water) samples are almost non-existent. Furthermore, we address the relevance of ILs in the context of persistent, mobile, and toxic chemicals, which are at present gaining increasing scientific and regulatory interest, and as part of the PFAS "dark matter" that represents the gap between the amount of fluorine originating from known PFAS and the total adsorbable organically bound fluorine. Graphical abstract.

Removal of poly- and perfluoroalkyl substances (PFAS) from water by adsorption: Role of PFAS chain length, effect of organic matter and challenges in adsorbent regeneration

Poly- and perfluoroalkyl substances (PFAS) are a wide group of environmentally persistent organic compounds of industrial origin, which are of great concern due to their harmful impact on human health and ecosystems. Amongst long-chain PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are the most detected in the aquatic environment, even though their use has been limited by recent regulations. Recently, more attention has been posed on the short-chain compounds, due to their use as an alternative to long-chain ones, and to their high mobility in the water bodies. Therefore, short-chain PFAS have been increasingly detected in the environmental compartments. The main process investigated and implemented for PFAS removal is adsorption. However, to date, most adsorption studies have focused on synthetic water. The main objective of this article is to provide a critical review of the recent peer-reviewed studies on the removal of long- and short-chain PFAS by adsorption. Specific objectives are to review 1) the performance of different adsorbents for both long- and short-chain PFAS, 2) the effect of organic matter, and 3) the adsorbent regeneration techniques. Strong anion-exchange resins seem to better remove both long- and short-chain PFAS. However, the adsorption capacity of short-chain PFAS is lower than that observed for long-chain PFAS. Therefore, short-chain PFAS removal is more challenging. Furthermore, the effect of organic matter on PFAS adsorption in water or wastewater under real environmental conditions is overlooked. In most studies high PFAS levels have been often investigated without organic matter presence. The rapid breakthrough of PFAS is also a limiting factor and the regeneration of PFAS exhausted adsorbents is very challenging and needs more research.

Treatment train approaches for the remediation of per- and polyfluoroalkyl substances (PFAS): A critical review

Per- and polyfluoroalkyl substances (PFAS) have recently drawn great attention due to their ubiquitous presence in aquatic environments and potential toxicity to human health and the environment. A number of recent studies have demonstrated that "passive" removal approaches, such as adsorption, filtration, and reverse osmosis or "active" degradation technologies, such as enhanced photolysis, electrochemical oxidation, and sonochemical destruction, are all able to individually conduct remedial measures for PFAS contamination at some level. However, drawbacks, specifically high energy consumption, low cost-efficiency, and extreme operating conditions, are commonly observed from these studies which significantly suppress the future for commercialization of these innovative technologies. Since 2015, a new trend of PFAS remediation has emerged that uses multiple synergetic technologies simultaneously (known as treatment train processes) to effectively achieve in-situ remediation of PFAS. This paper provides new insight of the recently reported treatment train studies selected from approximately 150 different publications with regards to the remediation of PFAS and discusses their innovative designs, remediation performances, present limits, and possible improvements. Based on a comprehensive review of the current treatment train studies, this review work proposes a new design that consists of three individual technologies, namely, nanofiltration, electrochemical anodic oxidation, and electro-Fenton degradation, to maximize economic and environmental benefits of PFAS remedial measures.

Rapid Characterization of Per- and Polyfluoroalkyl Substances (PFAS) by Ion Mobility Spectrometry-Mass Spectrometry (IMS-MS)

Per- and polyfluoroalkyl substances (PFAS) are an ensemble of persistent organic pollutants of global interest because of their associations with adverse health outcomes. Currently, environmental PFAS pollution is prolific as a result of the widespread manufacturing of these compounds and their chemical persistence. In this work, we demonstrate the advantages of adding ion mobility spectrometry (IMS) separation to existing LC-MS workflows for PFAS analysis. Using a commercially available drift tube IMS-MS, we characterized PFAS species and isomeric content in both analytical standards and environmental water samples. Molecular trendlines based on intrinsic mass and structural relationships were also explored for individual PFAS subclasses (e.g. PFSA, PFCA, etc.). Results from rapid IMS-MS analyses provided a link between mass and collision cross sections (CCS) for specific PFAS families and are linked to compositional differences in molecular structure. In addition, CCS values provide additional confidence of annotating prioritized features in untargeted screening studies for potential environmental pollutants. Results from this study show that the IMS separation provides novel information to support traditional LC-MS PFAS analyses and will greatly benefit the evaluation of unknown pollutants in future environmental studies.

Critical review of magnetic biosorbents: Their preparation, application, and regeneration for wastewater treatment

The utilisation of magnetic biosorbents (metal or metal nanoparticles impregnated onto biosorbents) has attracted increasing research attention due to their manipulable active sites, specific surface area, pore volume, pore size distribution, easy separation, and reusability that are suitable for remediation of heavy metal(loid)s and organic contaminants. The properties of magnetic biosorbents (MB) depend on the raw biomass, properties of metal nanoparticles, modification/synthesis methods, and process parameters which influence the performance of removal efficiency of organic and inorganic contaminants. There is a lack of information regarding the development of tailored materials for particular contaminants and the influence of specific characteristics. This review focuses on the synthesis/modification methods, application, and recycling of magnetic biosorbents. In particular, the mechanisms and the effect of sorbents properties on the adsorption capacity. Ion exchanges, electrostatic interaction, precipitation, and complexation are the dominant sorption mechanisms for ionic contaminants whereas hydrophobic interaction, interparticle diffusion, partition, and hydrogen bonding are the dominant adsorption mechanisms for removal of organic contaminants by magnetic biosorbents. In generally, low pyrolysis temperatures are suitable for ionic contaminants separation, whereas high pyrolysis temperatures are suitable for organic contaminants removal. Additionally, magnetic properties of the biosorbents are positively correlated with the pyrolysis temperatures. Metal-based functional groups of MB can contribute to an ion exchange reaction which influences the adsorption capacity of ionic contaminants and catalytic degradation of non-persistent organic contaminants. Metal modified biosorbents can enhance adsorption capacity of anionic contaminants significantly as metal nanoparticles are not occupying positively charged active sites of the biosorbents. Magnetic biosorbents are promising adsorbents in comparison with other adsorbents including commercially available activated carbon, and thermally and chemically modified biochar in terms of their removal capacity, rapid and easy magnetic separation which allow multiple reuse to minimize remediation cost of organic and inorganic contaminants from wastewater.

Examining the degradation of environmentally-daunting per- and poly-fluoroalkyl substances from a fundamental chemical perspective

In this work, ground and excited-state properties were used as descriptors for probing mechanisms as well as to assess potential alternatives for tackling the elimination of per- and poly-fluoroalkyl substances (PFAS).

TiO2 quantum dots loaded sulfonated graphene aerogel for effective adsorption-photocatalysis of PFOA

With the pollution of perfluoroalkyl substances (PFASs) became increasingly serious, the researches focused on removal of PFASs by adsorption-photocatalysis method has attracted considerable attention. To make the catalyst TiO₂ disperse uniformly as quantum dots onto hydrophobic surface which was liable to attract perfluorooctanoic acid (PFOA), the surfactant sodium dodecyl sulfate (SDS) were used in this work, which not only connected the hydrophilic TiCl₃ to the hydrophobic sulfonated graphene (SG) nanosheets, but also behaved as the molecular template for controlled nucleation and growth of the nanostructured TiO₂. After 3D SG-TiO₂ QD nanosheets were fabricated, a series of 3D SG-TiO₂ QD aerogels were self-assembled by ice-template. TiO₂ uniformly distributed on the surface of SG aerogel at QD size level (2-3 nm) and the size of TiO₂ could be effectively regulated by concentration of SDS. Compared with aggregated TiO₂ material, 3D SG-TiO₂ QD aerogels owned higher adsorption and photocatalytic performance. Benefiting from the hydrophobic surface of 3D SG as well as dispersed TiO₂ QDs, 3D SG-TiO₂ QD could enrich PFOA instantaneously (0.0381/s) and photocatalytic decomposed them effectively (1.898 E^-4/s). PFOA degradation by hole and hydroxyl radicals proceeded via a stepwise mechanism. The column made of 3D SG-TiO₂ QD could remove PFOA persistently in cycles of permeation. 3D SG-TiO₂ QD possessed powerful adsorption-photocatalytic decomposition capability of PFOA and steady reusability performance. The present work highlights the individual roles and synergistic effect of TiO₂ QD and 3D SG for effectively removing PFOA.

Perfluorooctane sulfonate disrupts the blood brain barrier through the crosstalk between endothelial cells and astrocytes in mice

Perfluorooctane sulfonate (PFOS), a classic environmental pollutant, is reported to accumulate in brain and induce neurotoxicity. However, little is known the route and mechanism of its entrance in brain. In the present study, ICR mice were treated with PFOS for 28 days, the cerebral PFOS were measured and the morphological and ultrastructural changes of blood-brain barrier (BBB) were observed. Also, the expression and localization of the proteins related to the cerebral damages, tight junctions (TJs) and p38 activation were detected. Additionally, U87 cells were used to explore the role of p38 in PFOS-induced damages of astrocytes. PFOS significantly decreased the expression of TJ-related proteins (ZO-1, Claudin-5, Claudin-11, Occludin) in endothelial cells and disrupted BBB, which subsequently led PFOS to astrocytes and increased the expression of the proteins related to astrocytic damages (Aquaporin 4 and S100β). These results aggravated BBB disruption and further increased the cerebral PFOS levels. Besides, phosphorylated p38 activation was involved into PFOS-induced astrocytic damages in vivo and in vitro. In conclusion, the crosstalk between endothelial cells and astrocytes facilitated the BBB disruption and increased the accumulation of PFOS in brain. Our findings provided a new insight into the toxicological and physiological profiles of PFOS-induced neurotoxicity.

Occurrence and transport behaviors of perfluoroalkyl acids in drinking water distribution systems

Although human exposure to perfluoroalkyl acids (PFAAs) through tap water is an ongoing concern, knowledge of the PFAAs occurrence in the tap water and the associated transport behaviors of PFAAs in drinking water distribution systems (DWDSs) are scarce. This investigation profiled the occurrence of 17 kinds of PFAAs in tap water of some Chinese cities, and the transport behaviors of PFAAs in DWDS were observed in eastern China. Tap water samples both along trunk pipelines and at the distal ends were collected to display the PFAAs occurrence scenarios. Loose deposit solids were also obtained to reveal their possible accumulation effect on PFAAs. The results showed that perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA) widely existed in tap water samples, and were the predominant PFAAs in eastern China areas. The mean concentration of the 17 PFAAs was 77.49 ng/L (ranging from 9.29 ng/L to 266.68 ng/L). Short-chain PFAAs (mainly PFBA) concentrations were relatively stable from water treatment plant to consumer taps, while long-chain PFAAs (mainly PFOA) exhibited a significant decrease in concentration, which could be attributed to their accumulation by the loose deposits in the DWDSs. It was calculated that PFOA has a higher partition coefficient than PFBA; this means that the former has a stronger potential to be adsorbed by loose deposits. In addition, the accumulation ability of loose deposits might be associated with the composition of Al, Fe and Si in the loose deposits. The positive correlation between the short-chain PFAAs and dissolved organic carbon (DOC) indicated the possible interactions between PFAA and natural organic matter could favor short-chain PFAAs to retain in bulk water. When water quality conditions change or hydraulic disturbance occur, loose deposits may enter tap water bringing accumulated PFAAs with it, which may result in potential health risks.

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide

This study investigated the degradation of perfluorooctanesulfonate (PFOS) in a reactive electrochemical membrane (REM) system in which a porous Magnéli phase titanium suboxide ceramic membrane served simultaneously as the anode and the membrane. Near complete removal (98.30 ± 0.51%) of PFOS was achieved under a cross-flow filtration mode at the anodic potential of 3.15 V vs standard hydrogen electrode (SHE). PFOS removal efficiency during the REM operation is much greater than that of the batch operation mode under the same anodic potential. A systematic reaction rate analysis in combination with electrochemical characterizations quantitatively elucidated the enhancement of PFOS removal in REM operation in relation to the increased electroactive surface area and improved interphase mass transfer. PFOS appeared to undergo rapid mineralization to CO₂ and F^-, with only trace levels of short-chain perfluorocarboxylic acids (PFCAs, C₄-C₈) identified as intermediate products. Density functional theory (DFT) simulations and experiments involving free radical scavengers indicated that PFOS degradation was initiated by direct electron transfer (DET) on anode to yield PFOS free radicals (PFOS^•), which further react with hydroxyl radicals that were generated by water oxidation and adsorbed on the anode surface (^•OH_ads). The attack of ^•OH_ads is essential to PFOS degradation, because, otherwise, PFOS^• may react with water and revert to PFOS.

Increasing perfluoroalkyl substances and ecological process from the Yongding Watershed to the Guanting Reservoir in the Olympic host cities, China

Perfluoroalkyl substances (PFASs) have raised great attention, particularly in regions of rapid urbanization. Zhangjiakou and Beijing will jointly host the Winter Olympic Games in 2022, which will likely increase local PFASs pollution and their associated risks over the coming period. In this study, we identified ecological process of PFASs, including sources, environmental fate, and risks, from the Yongding Watershed to the Guanting Reservoir. The concentrations of total 12 PFASs in water of the Guanting Reservoir were higher than that from the Yongding Watershed, with mean of 48.9 and 33.7 ng/L, respectively. The concentrations of PFASs in sediment of the Yongding Watershed and the Guanting Reservoir were similar, with mean of 1.01 and 0.827 ng/g dry weight, respectively. Detected levels of PFASs in the Guanting Reservoir significantly increased during the past eight years, possibly due to an improving economy and a rapidly developed service industry. Moderate PFASs levels in fish of the Guanting Reservoir were detected relative to other lakes and reservoirs. The daily intake of PFASs via fish and water ranged from 4.96 to 15.0 ng/kg bw/day, with higher levels found in children relative to adults. In total, approximately 9.06 kg of PFASs from riverine flow and atmospheric deposition annually entered the Guanting Reservoir. PFASs from the Yongding River significantly contributed to the pollution of Guanting Reservoir, with predominance of perfluorobutanoic acid (PFBA) in water, and long-chain perfluorinated carboxylic acids (PFCAs) and perfluorooctane sulfonate (PFOS) in sediment in both the Yongding Watershed and the Guanting Reservoir. Most of the PFASs (23.5 kg) were stored in water of the Guanting Reservoir, while the annual storage of PFASs in sediment and fish was only 4.68 × 10^-2 kg and 4.36 × 10^-2 kg via deposition and accumulation, respectively. The results suggest that water quality management of the Yongding Watershed is necessary for effective control on PFASs pollution in the Guanting Reservoir.

Adsorption of perfluoroalkyl and polyfluoroalkyl substances (PFASs) from aqueous solution - A review

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have gained increasingly global attention in recent years. Due to their unique amphiphilic properties and stability, PFASs are recognized as highly persistent, toxic, and environmentally bioaccumulative. Among several physicochemical technologies, adsorption has been extensively used and proved to be an effective method for removing PFASs from aqueous environment. In this review article, the technical feasibility of the use of different adsorbents, such as activated carbon, ion exchange resins, minerals, molecularly imprinted polymer (MIP), carbon nanotubes (CNTs), and a wide range of potentially low-cost biosorbents, for PFASs removal from water or wastewater is critically reviewed. The evaluation and comparison of their PFASs sorption behavior in terms of kinetics and isotherms is presented. The mechanisms involved in PFASs adsorption processes, such as diffusion, electrostatic interaction, hydrophobic interaction, ion exchange and hydrogen bond, are discussed. The effects of the parameters variability on sorption process are highlighted. Based on the literature reviewed, a few recommendations for future research on PFASs adsorption are also elaborated. Capsule: The adsorption behavior and mechanisms of perfluoroalkyl and polyfluoroalkyl substances (PFASs) on various adsorbents are reviewed.

Removal of pharmaceutical compounds, artificial sweeteners, and perfluoroalkyl substances from water using a passive treatment system containing zero-valent iron and biochar

Emerging contaminants are widely detected and persistent in environmental waters. Advanced oxidation processes are among the most effective methods for removing emerging contaminants from water; however, high energy consumption greatly increases the operating costs and limits large-scale applications. In this study, a passive treatment system consisting of four columns packed with mixtures of silica sand, zero-valent iron (ZVI), biochar (BC), and a mixture of (ZVI + BC) were evaluated for simultaneous removal of eight pharmaceuticals, four artificial sweeteners, and two perfluoroalkyl substances (PFASs) from water. Overall, the passive treatment system was more effective for removing target pharmaceuticals (almost complete removal) than artificial sweeteners and PFASs (partial removal). Columns ZVI, BC, and (ZVI + BC) exhibited similarly effective removal (>97%) of target pharmaceuticals, including carbamazepine, caffeine, sulfamethoxazole, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine, ibuprofen, gemfibrozil, and naproxen, from ~9 to <0.25 μg L^-1; pharmaceuticals were more rapidly removed by Columns ZVI and (ZVI + BC) than Column BC, except for ibuprofen. Column ZVI was more effective for removing artificial sweeteners acesulfame-K and sucralose than Columns BC and (ZVI + BC); however, BC exhibited relatively greater removal of saccharin than ZVI and (ZVI + BC). Acesulfame-K and saccharin (~110 μg L^-1) were partially removed in the treatment columns. Cyclamate was not removed in any of the columns. However, >76% of input sucralose (~110 μg L^-1) was removed in the three treatment columns. Reactive medium BC alone was more effective for removing target PFASs than ZVI and (ZVI + BC). Input perfluorooctanoic acid (PFOA) (~45 μg L^-1) was partially removed in the columns containing BC but not ZVI alone. Between 10 and 80% of input perfluorooctane sulfonic acid (PFOS) (24 ̶ 90 μg L^-1) was removed in Column ZVI; greater removals (57 ̶ 99%) were observed in Columns BC and (ZVI + BC).

Spatial and temporal variability of perfluoroalkyl substances in the Laurentian Great Lakes

Per- and polyfluoroalkyl substances (PFAS) are a diverse group of fluorinated organic chemicals that have been used in industrial and consumer applications since the 1950s. PFAS are resistant to chemical and biological degradation and are ubiquitous in the environment, including in water, sediment, and biota in the Laurentian Great Lakes. This critical review evaluates the spatial and temporal variability of commonly studied perfluoroalkyl sulfonates (PFSAs) and perfluoroalkyl carboxylates (PFCAs) in the Great Lakes by synthesizing data collected in water, surface sediment, sediment cores, lake trout (Salvelinus namaycush), and herring gull (Larus argentatus) eggs. The lowest PFAS concentrations in all matrices are detected in Lake Superior, which is located in the most pristine region of the Great Lakes Basin. In contrast, higher concentrations are observed in Lakes Erie and Ontario, which are more impacted by industrial activity and wastewater discharge. The distribution of individual PFAS compounds also varies across the lakes in response to changes in PFAS sources, with higher proportions of PFSAs in the eastern lakes. Sediment and biota are enriched in long chain PFSAs and PFCAs relative to concentrations in the water column, as expected based on predicted partitioning behavior. Sediment cores and bioarchives consistently demonstrate that PFAS concentrations increased in the Great Lakes from the initial time points until the early 2000s. The available data indicate that PFOS and PFOA concentrations decline after this period in the upper Great Lakes, but are stable in Lake Ontario. However, these trends depend on the lake, the individual compound, and the organism considered.

Application of surfactant modified montmorillonite with different conformation for photo-treatment of perfluorooctanoic acid by hydrated electrons

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a class of highly persistent contaminants with high bioaccumulation and toxicity. Our previous studies showed that perfluorooctanoic acid (PFOA) can be completely defluorinated under UV irradiation in organo-montmorillonite/indole acetic acid (IAA) system. However, there is still lack of information for the degradation mechanism and the test for wastewater treatment. Here, we systematically investigated the defluorination reaction in the presence of different organo-montmorillonites and found that the degradation process was apparently controlled by the configuration of surfactants. In hexadecyltrimethyl ammonium (HDTMA)-modified montmorillonite, HDTMA exists as a tilt conformation and isolated clay interlayer from the aqueous solution, protecting hydrated electrons generated by photo-irradiation of IAA from quenching by oxygen. Defluorination hydrogenation process was the dominant degradation pathway. While in poly-4-vinylpyridine-co-styrene (PVPcoS)-modified montmorillonite, due to the multiple charges of PVPcoS, a flat conformation parallel to clay surface was expected. Hydroxyl radicals, which were generated by the reaction of hydrated electrons with oxygen molecules diffused into clay interlayer, are also involved in the degradation process. Our results further demonstrate that mixture modified montmorillonite could combine the advantages of both modifications, thus showing superior reactivity even for actual industrial wastewater without any pretreatment. This technique would have great potential for treatment of actual wastewater.