Sources, occurrence, and treatment techniques of per- and polyfluoroalkyl substances in aqueous matrices: A comprehensive review

Unseen streams tracing emerging contaminants from stormwater to surface water: A brief review

Emerging contaminants (ECs) have raised global concern due to their adverse effect on ecosystems and human health. However, the occurrence and transport of ECs in stormwater remain unclear. The impact of ECs from stormwater on surface water quality and ecosystem health is also poorly documented. In this review, we examined the variations in EC concentrations in surface water resulting from stormwater. During the wet weather, the concentrations of most investigated ECs, e.g., microplastics, per- and polyfluoroalkyl substances, and vehicle-related compounds, significantly increase in surface water, indicating that stormwater may be a critical source of these contaminants. Furthermore, the potential pathways of ECs from stormwater enter surface water are outlined. Studies demonstrate that surface runoff and combined sewer overflows are important pathways for ECs, with discharges comparable to or exceeding those from wastewater treatment plants. Illicit connection also plays an important part in elevated EC concentrations in surface water. Overall, our findings underscore the importance of stormwater as a source for ECs in surface waters, and urge for increased emphasis on, and reinforcement of, stormwater monitoring and control measures to minimize the transport of ECs into receiving water bodies.

Review on the sources, distribution and treatment of per- and polyfluoroalkyl substances in global groundwater

Per- and polyfluoroalkyl substances (PFAS) have garnered increasing global attention due to their widespread occurrence in groundwater and the potential health risks to humans. This review aimed to clarify the occurrence and treatment of PFAS in groundwater by summarizing literature published in the Web of Science Core Collection from January 2000 to April 2024. Information on 461 reported PFAS-contaminated groundwater sites was compiled, revealing key characteristics of pollution sources and concentrations. The data indicated that firefighting training activities were a major source of PFAS groundwater contamination, accounting for 41 % of cases, followed by other fluorinated industrial activities, landfill leachate, and wastewater leakage. Non-point sources, such as atmospheric deposition, contributed to a lesser extent. The concentrations distribution of 25 PFAS showed a chain-length dependency, with short-chain PFAS generally exhibiting higher concentrations than long-chain PFAS. Additionally, the review systematically examined the application of separation methods and destructive methods at both laboratory and pilot/field-scales for PFAS-contaminated groundwater. Resins were favored for ex-situ treatment, whereas colloidal activated carbon (CAC) was more commonly used for in-situ treatment. In-situ direct injection of CAC was considered a highly promising approach for remediating PFAS source zones and plumes, offering advantages such as minimal surface disruption, high adsorption capacity and long-term effectiveness. Finally, the research focus and development trends in categories and treatment methods for PFAS in groundwater were noted. Overall, this review identified research gaps in the occurrence and treatment of PFAS in groundwater, and suggested further optimization of CAC-based methods to address the challenges of PFAS-contaminated groundwater.

Interference of PFAS sorption on zeolites from natural water characteristics

Per- and polyfluoroalkyl substances (PFAS) are emerging anthropogenic pollutants of concern and are associated with potential human and environmental health concerns. PFAS removal can be achieved using adsorbents such as activated carbon and ion exchange resins. Recently, zeolites have been identified as another potential adsorption technology with increased selectivity and product regenerability that is not currently achieved with other adsorbents. Zeolite CP814E∗ (BEA) was tested in batch reactions for PFAS removal in different water matrix characteristics, including pH, select cations, humic acids (HA), fulvic acids (FA), and natural organic matter (NOM). In synthetic EPA waters, BEA performance increased compared to ultrapure water testing. BEA performance also significantly increased in the presence of Na+, Ca2+, and Mg2+ ions compared to ultrapure waters. PFOA and PFOS sorption did not vary significantly in the 6-9 pH range. HA, FA, and NOM did not significantly impact the sorption of PFOA and PFOS on the BEA at 1 g/L zeolite loading. One organic interferent, Suwannee River humic acids, did reduce PFOA sorption when the ratio of adsorbent to liquid was reduced to 0.1 mg/L. BEA retained sorption capacity over seven thermal regeneration cycles, and a BEA test with a real water demonstrated PFOA, PFOS and PFHxS adsorption at the parts per trillion level.

Perfluoroalkyl substances: a risk for the aquatifc environment? A 1-year case study in river waters of central Italy

Perfluoroalkyl substances (PFASs) are a large class of persistent emerging pollutants, ubiquitous in different environmental compartments. In this study, twenty-one PFASs were determined in seventy-eight water samples collected from six different rivers in the Umbria region (central Italy) during a 13-month monitoring campaign. The sum of the twenty-one target analytes (Σ21PFASs) ranged from 2.0 to 68.5 ng L-1, with a mean value of 22.0 ng L-1. The highest concentrations of Σ21PFASs were recorded in the warmest months (from June to September) due to reduced river streamflow caused by low rainfall and high temperatures. PFASs with a number of carbon atoms between four and nine prevail over C10-C18 congeners due to their higher water solubility and to their increased use in industry. PFBA, followed by PFPeA, PFHxA, and PFOA, was the most abundant congeners detected in the analyzed river water samples. Finally, the calculation of risk quotients (∑RQs) has allowed to assess the risk for three aquatic organisms (fish, algae, and daphnid) deriving from the exposure to PFASs. The survey showed that the risk for the three aquatic organisms during the four seasons and throughout the year was always negligible. The only exception was a low risk for fish and daphnid in GEN river considering the annual exposure.

Out of sight, into the spotlight: Beyond the current state of science on per- and poly-fluoroalkyl substances in groundwater

Per- and poly-fluoroalkyl substances (PFAS) have emerged as a silent menace, infiltrating groundwater systems worldwide. Many countries, preoccupied with tackling legacy pollutants, have inadvertently neglected the emerging threat of PFAS. This review provides an exhaustive analysis beyond the current state of knowledge and sustainable pathways vis-a-vis addressing PFAS in groundwater systems globally. Despite the positive progression in PFAS research, significant knowledge gaps and paucity of data persist globally. Sampling trains, smart contaminant detectors, filters, and sensors offer promising pathways for the complete extraction and detection of novel and transformed PFAS species. Major hotspots are firefighting locations, landfills, and superfund sites. While studies have documented the global occurrence of PFAS in groundwater, with concentrations increasing over time and varying across regions, the factors influencing these trends, transport, fate, toxicity, and interactions with co-contaminants, remain largely unexplored. Advanced models accounting for environmental complexities and interactions are crucial for understanding PFAS migration in groundwater, however, their development is hindered by a scarcity of studies on the complexities and PFAS interactions. Emerging technologies, including nanotechnology, enzyme, genetic engineering, flexible treatment train, and machine learning algorithms present exciting opportunities for PFAS treatment, however, their cost-effectiveness, scalability, and long-term stability must be thoroughly investigated. Sustainable management requires addressing nomenclature inconsistencies and developing region-specific mitigative measures. These serve as a clarion call for the scientific community, policymakers, and stakeholders to unite in confronting the formidable challenges posed by PFAS contamination, as the fate of our groundwater resources and the well-being of countless lives hang in the balance.

Neurotoxic Effects of Mixtures of Perfluoroalkyl Substances (PFAS) at Environmental and Human Blood Concentrations

Per- and polyfluoroalkyl substances (PFAS) may cause various deleterious health effects. Epidemiological studies have demonstrated associations between PFAS exposure and adverse neurodevelopmental outcomes. The cytotoxicity, neurotoxicity, and mitochondrial toxicity of up to 12 PFAS including perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, 6:2 fluorotelomer sulfonic acid (6:2 FTSA), and hexafluoropropylene oxide-dimer acid (HPFO-DA) were tested at concentrations typically observed in the environment (e.g., wastewater, biosolids) and in human blood using high-throughput in vitro assays. The cytotoxicity of all individual PFAS was classified as baseline toxicity, for which prediction models based on partition constants of PFAS between biomembrane lipids and water exist. No inhibition of the mitochondrial membrane potential and activation of oxidative stress response were observed below the cytotoxic concentrations of any PFAS tested. All mixture components and the designed mixtures inhibited the neurite outgrowth in differentiated neuronal cells derived from the SH-SY5Y cell line at concentrations around or below cytotoxicity. All designed mixtures acted according to concentration addition at low effect and concentration levels for cytotoxicity and neurotoxicity. The mixture effects were predictable from the experimental single compounds' concentration-response curves. These findings have important implications for the mixture risk assessment of PFAS.

Tracking the impact of perfluoroalkyl acid emissions on antibiotic resistance gene profiles in receiving water by metagenomic analysis

The ecological risks posed by perfluoroalkyl acids (PFAAs) to the aquatic environment have recently been of great concern. However, little information was available on the impact of PFAAs on antibiotic resistance genes (ARGs) profiles. In this study, the receiving river of the largest fluoropolymer production facility in China was selected to investigate the effects of PFAAs on ARGs profiles. The highest PFAAs concentration for water samples near the industrial effluent discharge point was 310.9 μg/L, which was thousands times of higher than the average concentration collected at upstream sites. Perfluorooctanoic acid accounted for more than 67.2 % of ∑PFAAs concentration in water samples collected at the downstream sites, followed by perfluorohexanoic acid (3.6 %-15.9 %). 145 ARG subtypes including high-risk ARGs were detected by metagenomic technology. The results indicated that the discharge of PFAA-containing effluents had a significant impact on the abundance and diversity of ARGs in receiving waters, and PFAAs and water quality parameters (e.g., pH, NH3N, CODMn, TP) could largely affect ARG profiles. Specifically, short-chain PFAAs had similar impacts on ARG profiles compared to the restricted long-chain PFAAs. This study confirmed the potential effects of PFAAs on ARGs in aquatic environment and provided more insights into the ecological risk raised by PFAAs.

Adsorptive removal of perfluorooctanoic acid from aqueous matrices using peanut husk-derived magnetic biochar: Statistical and artificial intelligence approaches, kinetics, isotherm, and thermodynamics

Removal of perfluorooctanoic acid (PFOA) from water matrices is crucial owing to its pervasiveness and adverse ecological and human health effects. This study investigates the adsorptive removal of PFOA using magnetic biochar (MBC) derived from FeCl3-treated peanut husk at different temperatures (300, 600, and 900 °C). Preliminary experiments demonstrated that MBC600 exhibited superior performance, with its characterization confirming the presence of γ-Fe2O3. However, efficient PFOA removal from water matrices depends on determining the optimum combination of inputs in the treatment approaches. Therefore, optimization and predictive modeling of the PFOA adsorption were investigated using the response surface methodology (RSM) and the artificial intelligence (AI) models, respectively. The central composite design (CCD) of RSM was employed as the design matrix. Further, three AI models, viz. artificial neural network (ANN), support vector machine (SVM), and adaptive neuro-fuzzy inference system (ANFIS) were selected to predict PFOA adsorption. The RSM-CCD model applied to optimize three input process parameters, namely, adsorbent dose (100-400 mg/L), pH (3-10), and contact time (20-60 min), showed a statistically significant (p < 0.05) effect on PFOA removal. Maximum PFOA removal of about 98.3% was attained at the optimized conditions: adsorbent dose: 400 mg/L, pH: 3.4, and contact time: 60 min. Non-linear analysis showed PFOA adsorption was best fitted by pseudo-second-order kinetics (R2 = 0.9997). PFOA adsorption followed Freundlich isotherm (R2 = 0.9951) with a maximum adsorption capacity of ∼307 mg/g. Thermodynamics and spectroscopic analyses revealed that PFOA adsorption is a spontaneous, exothermic, and physical phenomenon, with electrostatic interaction, hydrophobic interaction, and hydrogen bonding governing the process. A comparative analysis of the statistical and AI models for PFOA adsorption demonstrated high R2 (>0.99) for RSM-CCD, ANN, and ANFIS. This research demonstrates the applicability of the statistical and AI models for efficient prediction of PFOA adsorption from water matrices using MBC (MBC600).

Analysis of perfluorinated compounds in sewage sludge and hydrochar by UHPLC LTQ/Orbitrap MS and removal assessment during hydrothermal carbonization treatment

Wastewater treatment plants have been recognized as important sinks for per- and polyfluoroalkyl substances (PFAS) because of their ineffectiveness in removing them reflecting both water and sewage sludge discharge routes. Hydrothermal treatment represents an alternative technology for treating sludge to recover energy and other valuable products. In this study, 15 PFAS were determined in sludge and hydrochar substrates using sonication-solid phase extraction procedure and analyzed using LC-Orbitrap-High Resolution-MS/MS. The method was fully validated, exhibiting very good linearity, recoveries in the range of 48 to 126 %, low detection and quantification limits with expanded uncertainty and precision below 32 % and 21.9 %, respectively. The method was applied to sludge samples from the WWTP of Ioannina city (Greece), as well as to hydrothermally treated samples under various conditions. The most abundant PFAS were PFHxA (0.5-38.3 ng g-1) and PFOS (4.4-22.1 ng g-1). Finally, the hydrothermally treated sludge samples spiked with PFAS presented removal efficiencies for total PFAS of 86.9 %, 91.8 % and 95.7 % at three spiking levels namely 10, 50 and 200 ng g-1, respectively. Results indicated that PFCAs were almost completely removed, except for PFOA, while the concentrations of PFSAs increased in the produced hydrochar with the formation of several intermediates, as detected by HR-LC-MS/MS. The results of this study demonstrate the effect of hydrothermal treatment to the fate of PFAS in sewage sludge and contribute for further studies on design and scale up of hydrothermal carbonization technology as a management option for safer disposal of municipal wastewater sludge.

Accumulation features and temporal trends (2002-2015) for legacy and emerging per- and polyfluoroalkyl substances (PFASs) in finless porpoises bycaught off Korean coasts

Legacy and emerging per- and polyfluoroalkyl substances (PFASs) were measured in livers of finless porpoises (Neophocaena asiaeorientalis; n = 167) collected in Korean waters from 2002 to 2015 to investigate their occurrence, bioaccumulation feature, temporal trends, and ecotoxicological implications. Perfulorooctane sulfonate (PFOS), perfluoroundecanoate (PFUnDA), and perfluorotridecanoate (PFTrDA) were the predominant PFASs found in the porpoises. The concentration of 6:2 chlorinated polyfluoroalkyl ether sulfonate (F-53B), an alternative to PFOS, was comparable to that of PFTrDA. Perfluorooctane sulfonamide (FOSA), a precursor of PFOS, was also detected in all the porpoises examined. All PFASs, including F-53B, accumulated to higher concentrations in immature porpoises compared with mature specimens, implying substantial maternal transfer and limited metabolizing capacity for PFASs. A significant correlation was observed between PFOS and F-53B concentrations, indicating similar bioaccumulation processes. Based on prenatal exposure and toxicity, F-53B is an emerging contaminant in marine ecosystems. Significantly increasing trends were observed in the concentrations of sulfonates, carboxylates, and F-53B between 2002/2003 and 2010, whereas the FOSA concentration significantly decreased. During 2010-2015, decreasing trends were observed in the concentrations of FOSA and sulfonates, whereas concentrations of carboxylate and F-53B increased without statistical significance, likely due to a gap for the implementation of regulatory actions between sulfonates and carboxylates. Although PFOS and PFOA were found to pose little health risk to porpoises, the combined toxicological effects of other contaminants should be considered to protect populations and to mitigate PFAS contamination in marine ecosystems.

A review on superior advanced oxidation and photocatalytic degradation techniques for perfluorooctanoic acid (PFOA) elimination from wastewater

Perfluorooctanoic acid (PFOA) has been identified as the most toxic specie of the family of perfluorinated carboxylic acids (PFCAs). It has been widely distributed and frequently detected in environmental wastewater. The compound's unique features such as inherent stability, rigidity, and resistance to harsh chemical and thermal conditions, due to its multiple and strong C-F bonds have resulted in its resistance to conventional wastewater remediations. Photolysis and bioremediation methods have been proven to be inefficient in their elimination, hence this article presents intensive literature studies and summarized findings reported on the application of advanced oxidation processes (AOPs) and photocatalytic degradation techniques as the best alternatives for the PFOA elimination from wastewater. Techniques of persulfate, photo-Fenton, electrochemical, photoelectrochemical and photocatalytic degradation have been explored and their mechanisms for the degradation and defluorination of the PFOA have been demonstrated. The major advantage of AOPs techniques has been centralized on the generation of active radicals such as sulfate (SO₄^•-) hydroxyl (•OH). While for the photocatalytic process, photogenerated species (electron (e) and holes (h ⁺ _vb)) initiated the process. These active radicals and photogenerated species possessed potentiality to attack the PFOA molecule and caused the cleavage of the C-C and C-F bonds, resulting in its efficient degradation. Shorter-chain PFCAs have been identified as the major intermediates detected and the final stage entails its complete mineralization to carbon dioxide (CO₂) and fluoride ion (F^-). The prospects and challenges associated with the outlined techniques have been highlighted for better understanding of the subject matter for the PFOA elimination from real wastewaters.