Qingguo Huang

Per- and poly-fluoroalkyl substances (PFAS) released from contaminated soils can migrate into surface water and groundwater, posing risks to drinking water resources. However, the combined effects of water chemistry and hydrodynamic conditions on PFAS mobilization remain poorly understood. In this study, we investigated the release of six U.S. EPA-regulated PFAS compounds from a PFAS-spiked, landfill-impacted soil under varying water chemistry parameters (pH, ionic strength, calcium, phosphate and humic acid) in both stirring and static water conditions. Under stirring conditions, the PFAS release was rapid, with most PFAS released within 5 min. Variations in water chemistry had minimal influence on PFAS release, indicating that intense mixing dominated mass transfer processes over water chemistry effect. Under static conditions, water chemistry can affect the PFAS release. Departing from conventional understanding, decreasing pH or increasing Ca2+ concentration enhanced PFAS release into the aqueous phase and the corelease of PFAS and metals was observed, indicating that metal precipitation and desorption may play important roles in PFAS release. The presence of phosphate and humic acid facilitated PFAS release, whereas variations in ionic strength exhibited no influence. Overall, these findings highlight rapid PFAS release from soils into surface waters and its potential risks to drinking water supplies.

6:2 Fluorotelomer sulfonic acid (FTS) has been used as an alternative to perfluorooctane sulfonate (PFOS) as chrome mist suppressant in electroplating, emulsion aid in fluoropolymer processing, etc. Its biotic degradation is slow and incomplete, generating short chain perfluoroalkyl acids (PFAAs) and it is frequently detected in the environment. This proof-of-concept study reports possible transformation of 6:2 FTS by enzyme-catalyzed oxidative humification reactions (ECOHRs) in laccase-mediator systems (LMS) using crude or purified laccases, either mediated by a synthetic chemical (1-hydroxybenzotriazole) or a natural organic material (soybean meal extract; SBMe). The LMS with crude laccase, SBMe and 10 mM CuSO ₄ exhibited a 23.8% reduction in concentration (mean of three technical replicates) relative to its control. A 34.8% reduction in adsorbable organic fluorine provided a supporting observation for transformation and potentially degradation. High-resolution mass spectrometry (HRMS) analysis unveiled a suite of tentative transformation products ranging from C8 to C3, including C ₃ F ₇ O ₃ S, a previously unreported candidate formula for 6:2 FTS transformation products and potentially consistent with perfluoropropanesulfonate (PFPrS). Additionally, the calculated bond dissociation energies (BDEs) of the C-C bonds and the C-S bond in the 6:2 FTS were higher than those of PFOS, which could potentially explain the variable degradation observed in different studies. These findings underscore the potential of ECOHRs to transform per-and polyfluoroalkyl substances (PFAS) precursors. Future investigations into the transformation of PFAS mixtures in complex soil systems could provide actionable insights into ECOHRs as a potentially cost-effective remediation technique for vast crop lands, and pastures.

Most previous studies on the degradation of per- and polyfluoroalkyl substances (PFASs) by destruction technologies, such as electrochemical oxidation (EO), focused on the transformation of target PFASs, while a more complete analysis is necessary to verify PFAS mineralization and understand the pathways. This work attempts to analyze the fate of PFASs during EO treatment of still bottoms (SB), a concentrated waste stream resulting from ion exchange resin (IXR) treatment of PFAS-contaminated groundwater. The EO treatment is performed with a Ti ₄ O ₇ anode in a closed reactor in an attempt to analyze all products, including (1) their distribution in solid, liquid, and gas phases, (2) the fate of fluorine by quantifying both fluoride and total organic fluorine (TOF), and (3) semi-quantification of nontarget PFAS by high-resolution mass spectrometry. The results reveal that PFAS accounted for only 33% TOF in the original SB, with target PFAS responsible for merely 34% TOF removal by EO treatment, following which target and nontarget PFAS account for almost all TOF. Data suggest that most unaccounted TOF in the original SB was likely due to undetected PFAS masked by microplastics. Additionally, fluoropolymers may also be responsible. Most fluorine released from PFAS during EO treatment was recovered from the anode and precipitate. The study highlights challenges in tracking the fate of fluorine in destructive treatment of PFAS, especially regarding capturing volatile products in the context of complex environmental samples, while it showcases the capabilities of EO treatment in breaking down target and nontarget PFAS and their precursors.

Enzyme-Catalyzed Oxidative Humification Reactions (ECOHRs) are primarily recognized for their involvement in the degradation of lignin. Lignolytic fungi produce extracellular enzymes under nutrient-deficient conditions, which can act directly or indirectly through small-molecule mediators to modify a range of compounds in the environment. The enzymes mediating ECOHRs mainly include laccases, lignin peroxidases (LiP), and manganese peroxidases (MnP), whose properties and catalysis mechanisms are summarized and compared in this review. As an example showcasing the possible environmental application of ECOHRs, the effects of ECOHRs in mediating the transformation of two key per- and polyfluoroalkyl substances (PFAS), perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), were discussed. Reports have shown their significant concentration reduction (40%–59%) in systems with ECOHRs induced by amendments with laccases and mediators. Nontarget products identification using high-resolution mass spectrometry suggests that PFOA and PFOS degraded in ECOHR systems primarily through free-radical chain reactions. Reports on the use of laccase to reduce and manage the thatch layer on turf grass are also discussed in this review as another example of ECOHRs application. Laccase application at a rate of 2 U/cm ² once per month was found to be as effective as traditional thatch management methods, with the ECOHR effects leading to a reduction in the thatch thickness by 18%–22% in bermudagrass and 21%–30% in zoysiagrass. Overall, this review addresses the concept of ECOHRs, with the major enzymes and systems introduced, and highlights their possible environmental applications exemplified by PFAS remediation and thatch management.

Understanding the environmental impacts and economic costs of treatment technologies is essential for developing sustainable strategies for managing per- and polyfluoroalkyl substances (PFASs). This study focuses on the treatment of PFAS-contaminated landfill leachate using foam fractionation (FF) technology. A parametrized life cycle assessment and life cycle costing analysis were conducted to evaluate the performance of one-stage and three-stage FF systems. Full-scale operational data and EPA design models were used to assess environmental and economic impacts based on a functional unit of treating 1000 m³ of PFAS-contaminated landfill leachate. The global warming potential was estimated at 818 kg CO₂ eq for the one-stage system with 20% foam fraction, 357 kg CO₂ eq for the one-stage system with 1% foam fraction, and 402 kg CO₂ eq for the three-stage system with 1% foam fraction. Life cycle costs were estimated at $77.4 and $110.6 per functional unit for the one-stage and three-stage systems, respectively, using the net present value method. Sensitivity and scale-up analyses were also performed to evaluate the influence of operational parameters and system configurations on both environmental and economic outcomes.

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants that may pose health risks due to strong protein interactions. While AlphaFold 3 (AF3) was recently introduced for protein-ligand modeling with high claimed accuracy, its reliability for docking PFAS remains unclear. This study evaluates AF3's performance in predicting protein-PFAS interactions using a curated data set from the Protein Data Bank, divided into a "Before Set" (seen during AF3 training) and an "After Set" (unseen). AF3 accurately predicts protein structures and pockets but shows reduced performance in pocket-aligned ligand predictions, achieving ∼74.5% success in "Before Set" but only ∼55.8% in "After Set", indicative of possible overfitting. We further assess the effects of PFAS type on docking outcomes. Although AF3 accurately predicts binding pockets, it favors poses where the headgroup of environment-relevant PFAS interacts with polar or positively charged residues. This is different from another native binding mode in several cases, where the hydrophobic tail is inserted in the protein, but the headgroup is exposed to the solvent. Notably, a hybrid approach combining AF3 and Vina, especially considering multiple top-ranked poses, can improve prediction accuracy. These findings support the complementary use of AF3 and Vina for accurately modeling protein-PFAS interactions.

Rational interfacial engineering design of an electrocatalyst, such as a heterojunction structure, can effectively enhance its catalytic activity. This study aims to address a critical challenge associated with the use of carbon material@Ti₄O₇ heterojunction composite electrodes for wastewater treatment─electrode stability over long-term operation. Herein, we report a highly stabilized interfacial engineering strategy, i.e., the use of conductive inorganic CeO₂ as a "cement" to firmly encapsulate N-doped graphene oxide nanosheets (N-GS) on the Ti₄O₇ surface. The defect-rich N-GS encapsulated on the Ti₄O₇ surface significantly enhances interfacial charge transfer. This enhancement results in the N-GS/CeO₂@Ti₄O₇ heterojunction composite electrode exhibiting excellent efficiency in the electro-oxidation of hexafluoropropylene oxide dimer acid (HFPO-DA or GenX). Furthermore, a flow-through N-GS/CeO₂@Ti₄O₇ reactive electrochemical membrane system effectively mineralizes other 35 PFASs in a real fluorochemical wastewater sample, achieving a high defluorination rate of 70-90% and exhibiting better performance in PFAS destruction and energy efficiency compared to the UV/KI-SO₃^2- process. Results of this study enhance our understanding of the electrochemical oxidation of PFAS and offer valuable insight into the design of stabilized Ti₄O₇ heterojunction composites. These findings are instrumental in advancing the development of effective treatments for PFAS-contaminated environments.

Hundreds of per- and polyfluoroalkyl substances (PFAS) are present in fluorochemical production effluents, and existing adsorption devices are inadequate to address this PFAS challenge given their extreme structural diversity. Here, we achieve the broad-spectrum capture of 107 PFAS from fluorochemical effluents using a treatment-train strategy that combines Zn-based electrocoagulation (EC) with anion-exchange resin (AER) beds. The “zero-carbon” adsorbent, zinc hydroxide flocs generated insitu by Zn-based EC, bulk removes PFAS with log K _ow > 4 through a semi-micellar adsorption mechanism similar to mineral flotation and achieves adsorption capacities at the optimal level of all reported adsorbents. Technical-economic analysis and life-cycle environmental impact show that coupling Zn-based EC reduces the cost by an order-of-magnitude and the carbon-footprint by 70% compared to AER beds alone. It is also observed that iodinated PFAS, with some fluorine atoms are replaced by iodine atoms, exhibit significantly improved adsorption selectivity, which may shed light on designing environmentally-friendly fluorochemicals.

Per‐ and polyfluoroalkyl substances (PFAS) are being studied in all environmental matrices because of their ubiquitous presence and adverse human health impacts. This study conducted a surveillance of 27 water resource recovery facilities throughout the United States and Canada to screen the range of PFAS concentrations in pre‐stabilized sludge and post‐stabilized product. Among the 27 water resource recovery facilities, 82% use anaerobic digestion and the rest use chemical stabilization and/or incineration for sludge stabilization. Forty PFAS compounds were evaluated by US Environmental Protection Agency Method SW846/537.1, and four and nine compounds were reported in the pre‐stabilized sludge and post‐stabilized product, respectively. Concentrations of reported compounds in pre‐stabilized sludge and post‐stabilized product varied from 5 to 33 ng/g dry basis and 2 to 220 ng/g dry basis, respectively. 3‐Perfluoropentylpropanoic acid (5:3 FTCA) and perfluorooctanesulfonic acid (PFOS) were the most frequently observed compounds, and PFAS concentrations in the post‐stabilized products were generally higher than the corresponding pre‐stabilized sludge. Practitioner Points: Among the 40 target PFAS, four were above reporting limit in the pre‐stabilized sludge and nine in the post‐stabilized product. Incineration ash (post‐stabilized product) samples did not have any reportable PFAS. 5:3 FTCA and PFOS were the two frequently observed compounds; concentrations were higher in the post‐stabilized product compared to the pre‐stabilized sludge. PFPeA and PFHxA were the only two short chain perfluoroalkyl carboxylic acids reported. PFOA was reported in only one of the 54 samples evaluated.