Degradation of perfluorinated compounds by sulfate radicals - New mechanistic aspects and economical considerations

Environmental Occurrence and Biotic Concentrations of Ultrashort-Chain Perfluoroalkyl Acids: Overlooked Global Organofluorine Contaminants

Per- and polyfluoroalkyl substances (PFASs) are a large group of anthropogenic fluorinated chemicals. Ultrashort-chain perfluoroalkyl acids (PFAAs) have recently gained attention due to their prevalence in the environment and increasing environmental concerns. In this review, we established a literature database from 1990 to 2024, encompassing environmental and biological concentrations (>3,500 concentration records) of five historically overlooked ultrashort-chain PFAAs (perfluoroalkyl carboxylic and sulfonic acids with less than 4 carbons): trifluoroacetic acid (TFA), perfluoropropanoic acid (PFPrA), trifluoromethanesulfonic acid (TFMS), perfluoroethanesulfonate (PFEtS), and perfluoropropanesulfonate (PFPrS). Our data mining and analysis reveal that (1) ultrashort-chain PFAAs are globally distributed in various environments including water bodies, solid matrices, and air, with concentrations usually higher than those of longer-chain compounds; (2) TFA, the most extensively studied ultrashort-chain PFAA, shows a consistent upward trend in concentrations in surface water, rainwater, and air over the past three decades; and (3) ultrashort-chain PFAAs are present in various organisms, including plants, wildlife, and human blood, serum, and urine, with concentrations sometimes similar to those of longer-chain compounds. The current state of knowledge regarding the sources and fate of TFA and other ultrashort-chain PFAAs is also reviewed. Amid the global urgency to regulate PFASs, particularly as countries worldwide have intensified such efforts, this critical review will inform scientific research and regulatory policies.

State of the science and regulatory acceptability for PFAS residual management options: PFAS disposal or destruction options

This systematic review covers the urgent challenges posed by per- and polyfluoroalkyl substances (PFAS) in managing residuals from municipal, industrial, and waste treatment sources. It covers regulatory considerations, treatment technologies, residual management strategies, and critical conclusions and recommendations. A rigorous methodology was employed, utilizing scientific search engines and a wide array of peer-reviewed journal articles, technical reports, and regulatory guidance, to ensure the inclusion of the most relevant and up-to-date information on PFAS management of impacted residuals. The increasing public and regulatory focus underscores the persistence and environmental impact of PFAS. Emerging technologies for removing and sequestrating PFAS from environmental media are evaluated, and innovative destruction methods for addressing the residual media and the concentrated waste streams generated from such treatment processes are reviewed. Additionally, the evolving regulatory landscape in the United States is summarized and insights into the complexities of PFAS in residual management are discussed. Overall, this systematic review serves as a vital resource to inform stakeholders, guide research, and facilitate responsible PFAS management, emphasizing the pressing need for effective residual management solutions amidst evolving regulations and persistent environmental threats.

Electroprecipitating the Sulfate Radical Anion Amplifies Electrochemiluminescence in Space and Time

We have discovered a strategy to synthesize reactive radical salts, effectively bottling up radicals in space and time for future use. We apply this new principle to electrochemiluminescence (ECL) through the simultaneous electro-reduction of peroxydisulfate, S2O82-, and tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+ in a water/acetonitrile mixture. The electrode generates a concentration profile exceeding the solubility of the cation and anion pair, promoting precipitation. After the application of a potential, leads are disconnected, and the crystals electrolessly chemiluminesce during dissolution and can be transported to other solutions for later chemiluminescence uses. Our method extends ECL hundreds of micrometers from the electrode surface and increases the ECL lifetime by orders of magnitude. Control experiments, including electron spin resonance, validate the crystallization of SO4•-, allowing detailed mechanistic insight. We demonstrate platform generalizability by precipitating a radical salt made of calcium and SO4•-, and we demonstrate the salt's ability to drive chemiluminescence. Our results emphasize the elegant chemical tenet that extremely reactive radicals can be bottled up as solids to be used as future reagents if precipitation occurs more quickly than the radical lifetime.

Structural investigation of the complexation between vitamin B12 and per- and polyfluoroalkyl substances: Insights into degradation using density functional theory

Environmental remediation of per- and polyfluoroalkyl substances (PFAS) has become a significant research topic in recent years due to the fact that these materials are omnipresent, resistant to degradation and thus environmentally persistent. Unfortunately, they have also been shown to cause health concerns. PFAS are widely used in industrial applications and consumer products. Vitamin B12 (B12) has been identified as being catalytically active towards a variety of halogenated compounds such as PFAS. It has also been shown to be effective when using sulfide as a reducing agent for B12. This is promising as sulfide is readily available in the environment. However, there are many unknowns with respect to PFAS interactions with B12. These include the reaction mechanism and B12's specificity for PFAS with certain functionalization(s). In order to understand the specificity of B12 towards branched PFAS, we examined the atomistic interactions between B12 and eight different PFAS molecules using Density Functional Theory (B3LYP/cc-pVDZ). The PFAS test set included linear PFAS and their branched analogs, carboxylic acid and sulfonic acid headgroups, and aromatic and non-aromatic cyclic structures. Conformational analyses were carried out to determine the lowest energy configurations. This analysis showed that small chain PFAS such as perfluorobutanoic acid interact with the cobalt center of B12. Bulkier PFAS prefer to interact with the amine and carbonyl groups on the sidechains of the B12 ring system. Furthermore, computed complexation energies determined that, in general, branched PFAS (e.g. perfluoro-5-methylheptane sulfonic acid) interact more strongly than linear molecules (e.g. perfluorooctanesulfonic acid). Our results indicate that it may be possible to alter the interactions between B12 and PFAS by synthetically modifying the sidechains of the ring structure.

Organophotoredox-Catalyzed C-H Functionalizations of Benzophospholes

An organophotoredox-catalyzed oxidative C-H functionalization of benzophospholes has been developed. The C-H alkoxycarbonylation with methyl carbazate occurs in the presence of Rose bengal, whereas Eosin Y enables the dehydrogenative coupling with secondary phosphine oxides and ethers, delivering the C-H phosphinylated and alkylated products. The scope of coupling partners is complementary to that of conventional metal-promoted C-H activation, thus successfully expanding the chemical space of substituted phospholes accessed by C-H functionalization protocols.

Sonochemical degradation of PFAS in ion exchange regeneration wastes

One of the primary technologies currently being deployed for the removal of per- and polyfluoroalkyl substances (PFAS) from water is ion exchange (IX). For regenerable IX resins, concentrated PFAS in the resulting spent brine and/or still bottoms requires further treatment. This research demonstrated that PFAS in spent brine and still bottoms can be effectively degraded sonochemically at 1000 kHz. Overall, PFAS degradation was negatively impacted by high total organic carbon (TOC) and residual methanol (MeOH) solvent (up to 50 g/kg; 5% w:w), but was enhanced by the high chloride. The addition of caustic (up to 1 N NaOH) partially mitigated the inhibition by TOC and MeOH. Sonochemical degradation of individual PFAS compounds resulted in significant mineralization to form inorganic fluoride, but small quantities of volatile organic fluorine species (VOF) were noted. This is believed to be the first report of sonochemical degradation of PFAS in ion exchange regeneration wastes, and indicates the possibility for the application of this technology as part of a complete PFAS capture and destruction treatment train.

Kinetics and mechanism analysis of advanced oxidation degradation of PFOA/PFOS by UV/Fe3+ and persulfate: A DFT study

UV/Fe3+ and persulfate are two promising advanced oxidative degradation systems for in situ remediation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), yet a lack of comprehensive understanding of the degradation mechanisms. For the first time, we used density functional theory (DFT) to calculate the entire reaction pathways of the degradation of PFOA/PFOS in water by UV/Fe3+ and persulfate. In addition, we have deeply explored the different attack pathways driven by •OH and SO4-•, and found that SO4-• determines PFOA/PFOS to obtain PFOA/PFOS free radicals through single electron transfer to initiate the degradation reaction, while •OH determines the speed of PFOA/PFOS degradation reaction. Both degradation reactions were thermodynamically advantageous and kinetically feasible under calculated conditions. Based on the thermodynamic data, persulfate was found to be more favorable for the advanced oxidative degradation of Perfluorinated compounds (PFCs). Moreover, for SO4-• and •OH co-existing in the persulfate system, pH will affect the presence and concentration of these two types of free radicals, and low pH is not necessary for the degradation of PFOA/PFOS in the persulfate system. These results can considerably advance our understanding of the PFOA/PFOS degradation process in advanced oxidation processes (AOPs), which is driven by •OH and SO4-•. This study provides a DFT calculation process for the mechanism calculation of advanced oxidation degradation of other types of PFCs pollutants, hoping to elucidate the future development of PFCs removal. Further research should focus on determining the advanced oxidation degradation pathways of other types of PFCs, to support the development of computational studies on the advanced oxidation degradation of PFCs.

Efficiency of ozonation and sulfate radical - AOP for removal of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates

This study investigated the elimination of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates during ozonation and UV/persulfate processes. Second-order rate constants for the reactions of candesartan, irbesartan, methyl-benzotriazole, and chloro‑benzotriazole with sulfate radical (SO4·-) were determined for the first time. Experiments were conducted in buffered pure water, in buffered water added with the matrix substituents chloride, carbonate, NOM, and reverse osmosis concentrate with spiked micropollutants (MP). UV/persulfate eliminated all MP to a higher extent than ozonation in RO concentrates due to the higher yield of oxidative species and photolytic degradation. Compounds with electron-rich moieties such as carbamazepine, diclofenac, metoprolol, and sulfamethoxazole were completely eliminated with small ozone doses (< 0.5 mg O3 / mg DOC) and with a small fluence (< 5000 J m-2) in UV/persulfate processes. Photosensitive compounds with high reactivity towards hydroxyl radicals (·OH) and SO4·- like the x-ray contrast media Iopamidol, Iohexol, and Amidotrizoic acid were successfully eliminated with a reasonable fluence in UV/persulfate, whereas these compounds persist in ozonation at common ozone dosages. However, much higher fluences and ozone dosages were required for the least reactive compounds like the class of benzotriazoles. Comparing the application of both oxidative processes to the RO concentrate, ozonation has the disadvantage of forming bromate. The energy input of both processes strongly depends on the target compounds to be eliminated. For the elimination of compounds such as sulfamethoxazole, ozonation is a feasible technique, whereas UV/persulfate is better suited for the elimination of recalcitrant compounds such as x-ray contrast media. In general, oxidative process treatment of RO concentrate could be applied to partly abate micropollutants before discharge.

Occurrence, behaviors, and fate of per- and polyfluoroalkyl substances (PFASs) in typical municipal solid waste disposal sites

Per- and polyfluoroalkyl substances (PFASs) have become a crucial environmental concern owing to their exceptional persistence, ability to bioaccumulate within ecosystems, and potential to adversely affect biota. Products and materials containing PFASs are usually discarded into municipal solid waste (MSW) at the end of their life cycle, and the fate of PFASs may differ when different disposal methods of MSWs are employed. To date, limited research has focus on the occurrence, behaviors, and fate of PFASs emitted from various MSW disposal sites. This knowledge gap may lead to an underestimation of the contribution of MSW disposal sites as a source of PFASs in the environment. In this review, we collated publications concerning PFASs from typical MSW disposal sites (i.e., landfills, incineration plants, and composting facilities) and explored the occurrence patterns and behaviors of PFASs across various media (e.g., landfill leachate/ambient air, incineration plant leachate/ash, and compost products) in these typical MSW disposal sites. In particular, this review highlighted ultrashort-chain perfluoroalkyl acids and "unknown"/emerging PFASs. Additionally, it meticulously elucidated the use of non-specific techniques and non-target analysis for screening and identifying these overlooked PFASs. Furthermore, the composition profiles, mass loads, and ecological risks of PFASs were compared across the three typical disposal methods. To the best of our knowledge, this is the first review regarding the occurrence, behaviors, and fate of PFASs in typical MSW disposal sites on a global scale, which can help shed light on the potential environmental impacts of PFASs harbored in MSWs and guide future waste management practices.

Mechanisms and Opportunities for Rational In Silico Design of Enzymes to Degrade Per- and Polyfluoroalkyl Substances (PFAS)

Per and polyfluoroalkyl substances (PFAS) present a unique challenge to remediation techniques because their strong carbon-fluorine bonds make them difficult to degrade. This review explores the use of in silico enzymatic design as a potential PFAS degradation technique. The scope of the enzymes included is based on currently known PFAS degradation techniques, including chemical redox systems that have been studied for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) defluorination, such as those that incorporate hydrated electrons, sulfate, peroxide, and metal catalysts. Bioremediation techniques are also discussed, namely the laccase and horseradish peroxidase systems. The redox potential of known reactants and enzymatic radicals/metal-complexes are then considered and compared to potential enzymes for degrading PFAS. The molecular structure and reaction cycle of prospective enzymes are explored. Current knowledge and techniques of enzyme design, particularly radical-generating enzymes, and application are also discussed. Finally, potential routes for bioengineering enzymes to enable or enhance PFAS remediation are considered as well as the future outlook for computational exploration of enzymatic in situ bioremediation routes for these highly persistent and globally distributed contaminants.

Oxidation of Per- and Polyfluoroalkyl Ether Acids and Other Per- and Polyfluoroalkyl Substances by Sulfate and Hydroxyl Radicals: Kinetic Insights from Experiments and Models

Per- and polyfluoroalkyl substances (PFAS) are widely used anthropogenic chemicals. Because of the strength of the carbon-fluorine bond, PFAS are not destroyed in typical water treatment processes. Sulfate (SO4•-) and hydroxyl (•OH) radicals can oxidize some PFAS, but the behavior of per- and polyfluoroalkyl ether acids (PFEAs) in processes involving SO4•- and •OH is poorly understood. In this study, we determined second-order rate constants (k) describing the oxidation of 18 PFAS, including 15 novel PFEAs, by SO4•- and •OH. Among the studied PFAS, 6:2 fluorotelomer sulfonate reacted most readily with •OH [k•OH = (1.1-1.2) × 107 M-1 s-1], while polyfluoroalkyl ether acids containing an -O-CFH- moiety reacted more slowly [k•OH = (0.5-1.0) × 106 M-1 s-1]. In the presence of SO4•-, polyfluoroalkyl ether acids with an -O-CFH- moiety reacted more rapidly [kSO4•- = (0.89-4.6) × 106 M-1 s-1] than perfluoroalkyl ether carboxylic acids (PFECAs) and a chloro-perfluoro-polyether carboxylic acid (ClPFPECA) [kSO4•- = (0.85-9.5) × 104 M-1 s-1]. For homologous series of perfluoroalkyl carboxylic acids, linear and branched monoether PFECAs, and multiether PFECAs, PFAS chain length had little impact on second-order rate constants. SO4•- reacted with the carboxylic acid headgroup of perfluoroalkyl carboxylic acids and PFECAs. In contrast, for polyfluoroalkyl ether carboxylic and sulfonic acids with an -O-CFH- moiety, the site of SO4•- attack was the -O-CFH- moiety. Perfluoroalkyl ether sulfonic acids were not oxidized by SO4•- and •OH under the conditions evaluated in this study.

Electrochemical degradation of per- and poly-fluoroalkyl substances in the presence of natural organic matter

Per- and poly-fluoroalkyl substances (PFAS), a contentious group of highly fluorinated, persistent, and potentially toxic chemicals, have been associated with human health risks. Currently, treatment processes that destroy PFAS are challenged by transforming these contaminants into additional toxic substances that may have unknown impacts on human health and the environment. Electrochemical oxidation (EO) is a promising method for scissoring long-chain PFAS, especially in the presence of natural organic matter (NOM), which interferes with most other treatment approaches used to degrade PFAS. The EO method can break the long-chain PFAS compound into short-chain analogs. The underlying mechanisms that govern the degradation of PFAS by electrochemical processes are presented in this review. The state-of-the-art anode and cathode materials used in electrochemical cells for PFAS degradation are overviewed. Furthermore, the reactor design to achieve high PFAS destruction is discussed. The challenge of treating PFAS in water containing NOM is elucidated, followed by EO implementation to minimize the influence of NOM on PFAS degradation. Finally, perspectives related to maximizing the readiness of EO technology and optimizing process parameters for the degradation of PFAS are briefly discussed.

Occurrence of per- and polyfluoroalkyl substances in aquatic environments and their removal by advanced oxidation processes

Per- and polyfluoroalkyl substances (PFAS), one of the main categories of emerging contaminants, are a family of fluorinated organic compounds of anthropogenic origin. PFAS can endanger the environment and human health because of their wide application in industries, long-term persistence, unique properties, and bioaccumulation potential. This study sought to explain the accumulation of different PFAS in water bodies. In aquatic environments, PFAS concentrations range extensively from <0.03 (groundwater; Melbourne, Australia) to 51,000 ng/L (Groundwater, Sweden). Additionally, bioaccumulation of PFAS in fish and water biota has been stated to range from 0.2 (Burbot, Lake Vättern, Sweden) to 13,900 ng/g (Bluegill samples, U.S.). Recently, studies have focused on PFAS removal from aqueous solutions; one promising technique is advanced oxidation processes (AOPs), including microwaves, ultrasound, ozonation, photocatalysis, UV, electrochemical oxidation, the Fenton process, and hydrogen peroxide-based and sulfate radical-based systems. The removal efficiency of PFAS ranges from 3% (for MW) to 100% for UV/sulfate radical as a hybrid reactor. Therefore, a hybrid reactor can be used to efficiently degrade and remove PFAS. Developing novel, efficient, cost-effective, and sustainable AOPs for PFAS degradation in water treatment systems is a critical area of research.

Photochemical degradation of perfluorooctanoic acid under UV irradiation in the presence of Fe (III)-saturated montmorillonite

Perfluorooctanoic acid (PFOA) has attracted worldwide attention owing to its widespread distribution and potential ecological risks. Developing low-cost, green-chemical and highly efficient treatment approaches is significant for treating PFOA caused environmental issues. Herein, we propose a feasible PFOA degradation strategy under UV irradiation by adding Fe (III)-saturated montmorillonite (Fe-MMT), and the Fe-MMT could be regenerated after reaction. In our system consisting of 1 g L^-1 Fe-MMT and 24 μM PFOA, nearly 90 % initial PFOA could be decomposed within 48 h. The enhanced PFOA decomposition could be explained by the ligand-to-metal charge transfer mechanism based on the generated reactive oxygen species (ROSs) and the transformation of iron species in the MMT layers. Moreover, the special PFOA degradation pathway was revealed according to the intermediate identification and the density functional theory calculation. Further experiments demonstrated that even in the presence of co-existing natural organic natter (NOM) and inorganic ions, efficient PFOA removal could still be obtained in UV/Fe-MMT system. This study offers a green-chemical strategy for PFOA removal from contaminated waters.

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.

Low-temperature persulfate activation by powdered activated carbon for simultaneous destruction of perfluorinated carboxylic acids and 1,4-dioxane

Carbonaceous materials have emerged as a method of persulfate activation for remediation. In this study, persulfate activation using powdered activated carbon (PAC) was demonstrated at temperatures relevant to groundwater (5-25 °C). At room temperature, increasing doses of PAC (1-20 g L^-1) led to increased persulfate activation (3.06 × 10^-6s^-1 to 2.10 × 10^-4 with 1 and 20 g L^-1 PAC). Activation slowed at lower temperatures (5 and 11 °C); however, substantial (>70 %) persulfate activation was achieved. PAC characterization showed that persulfate is activated at the surface of the PAC, as indicated by an increase in the PAC C:O ratio. Similarly, electron paramagnetic resonance (EPR) spectroscopy studies with a spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide (DMPO)) and 2,2,6,6-tetramethylpiperidine (TEMP) revealed that singlet oxygen was not the main oxidizing species in the reaction. DMPO was oxidized to form 5,5-dimethylpyrrolidone-2(2)-oxyl-(1) (DMPOX), which forms in the presence of strong oxidizers, such as sulfate radicals. The persulfate/PAC system is demonstrated to simultaneously degrade both perfluorooctanoic acid (PFOA) and 1,4-dioxane at room temperature and 11 °C. With a 20 g L^-1 PAC and 75 mM persulfate, 80 % and 70 % of the PFOA and 1,4-dioxane, respectively, degraded within 6 h at room temperature. At 11 °C, the same PAC and persulfate doses led to 57% dioxane degradation and 54 % PFOA degradation within 6 h. Coupling PAC with persulfate offers an effective, low-cost treatment for simultaneous destruction of 1,4-dioxane and PFOA.

Efficient removal of trifluoroacetic acid from water using surface-modified activated carbon and electro-assisted desorption

Trifluoroacetic acid (TFA) is a very persistent, very mobile substance (vPvM) with potential toxicity, and causes increasing environmental concerns worldwide. Conventional wastewater treatment strategies are inefficient for selective TFA removal in the presence of inorganic anions. Here we show that surface defunctionalized activated carbon felt (DeACF) carrying anion exchange sites exhibits an outstanding adsorption efficiency towards TFA thanks to introduced electrostatic attraction and enhanced interactions between hydrophobic carbon surface and CF₃ moieties (q_max = 30 mg/g, K_d = (840 ± 80) L/kg at c_TFA = 3.4 mg/L in tap water). Flow-cell experiments demonstrated a strongly favored TFA uptake by DeACF from tap water over Cl^- and SO₄^2- but a remarkable co-adsorption of the inorganic water contaminant NO₃^-. Electro-assisted TFA desorption using 10 mM Na₂SO₄ as electrolyte and oxidized ACF as anode showed high recoveries of ≥ 87% at low cell voltages (< 1.1 V). Despite an initial decrease in TFA adsorption capacity (by 33%) caused by partial surface oxidation of DeACF after the 1st ad-/desorption cycle, the system stability was fully maintained over the next 4 cycles. Such electro-assisted 'trap&release' approach for TFA removal can be exploited for on-site regenerable adsorption units and as a pre-concentration step combined with degradation technologies.

Upgradation of sludge deep dewatering conditioners through persulfate activated by ferrous: Compatibility with sludge incineration, dewatering mechanism, ecological risks elimination and carbon emission performance

Serious loss of organic substances and notable release of refractory intracellular organics and cell-free antibiotic resistance genes (ARGs) caused by cell lysis are found when quick lime, FeCl₃, and cationic polyacrylamide (CPAM) were used as sludge conditioners, which is not feasible to sludge separate incineration and increases ecological risks. Therefore, persulfate oxidation through ferrous (Fe²⁺-Na₂S₂O₈) activation was applied for the upgradation of sludge conditioner in China, the specific resistance to filtration (SRF) and capillary suction time (CST) significantly decreased and the removed water increased from 40% to 54%, implying that the persulfate activated by ferrous (PAF) conditioner presents good performance in sludge dewatering. Organic matter content and heating value of sludge merely decreased, and Cl^- content in sludge simultaneously decreased with the use of the PAF conditioner, thereby effectively reducing the corrosion risk to the incinerator and showing good compatibility with sludge separate incineration. In accordance with ferrous activation, sulfate radical plays an important role in sludge dewatering process because remarkable decrease in polysaccharides and protein contents from tightly bound extracellular polymeric substances (TB-EPS) was discovered. Based on flow cytometry analysis, slight cell lysis presented better filtrate quality by the use of PAF conditioner, 49.3% of refractory intracellular organics was removed and the respective ermB, tetW and blaTEM decreased by factors of 37.3%, 54.5% and 63.6% due to the strong oxidizing property of sulfate radical. The intensive decrease in refractory intracellular organics and cell-free ARGs will reduce the ecological risks. The total carbon emission significantly decreases to 1771.1 kgCO₂/tDS when PAF conditioner was employed, which is beneficial to the upgradation of sludge deep dewatering conditioners.

Electrochemical oxidation processes for PFAS removal from contaminated water and wastewater: fundamentals, gaps and opportunities towards practical implementation

Electrochemical oxidation (EO) is emerging as one of the most promising methods for the degradation of recalcitrant per- and poly-fluoroalkyl substances (PFASs) in water and wastewater, as these compounds cannot be effectively treated with conventional bio- or chemical approaches. This review examines the state of the art of EO for PFASs destruction, and comprehensively compares operating parameters and treatment performance indicators for both synthetic and real contaminated water and wastewater media. The evaluation shows the need to use environmentally-relevant media to properly quantify the effectiveness/efficiency of EO for PFASs treatment. Additionally, there is currently a lack of quantification of sorption losses, resulting in a likely over-estimation of process' efficiencies. Furthermore, the majority of experimental results to date indicate that short-chain PFASs are the most challenging and need to be prioritized as environmental regulations become more stringent. Finally, and with a perspective towards practical implementation, several operational strategies are proposed, including processes combining up-concentration followed by EO destruction.

Emerging technologies for PFOS/PFOA degradation and removal: A review

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are highly recalcitrant anthropogenic chemicals that are ubiquitously present in the environment and are harmful to humans. Typical water and wastewater treatment processes (coagulation, flocculation, sedimentation, and filtration) are proven to be largely ineffective, while adsorption with granular activated carbon (GAC) has been the chief option to capture them from aqueous sources followed by incineration. However, this process is time-consuming, and produces additional solid waste and air pollution. Treatment methods for PFOS and PFOA generally follow two routes: (1) removal from source and reduce the risk; (2) degradation. Emerging technologies focusing on degradation are critically reviewed in this contribution. Various processes such as bioremediation, electrocoagulation, foam fractionation, sonolysis, photocatalysis, mechanochemical, electrochemical degradation, beams of electron and plasma have been developed and studied in the past decade to address PFAS crisis. The underlying mechanisms of these PFAS degradation methods have been categorized. Two main challenges have been identified, namely complexity in large scale operation and the release of toxic byproducts. Based on the literature survey, we have provided a strength-weakness-opportunity-threat (SWOT) analysis and quantitative rating on their efficiency, environmental impact and technology readiness.

Ozonation of organic compounds in water and wastewater: A critical review

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, β-diketones) and antibiotic resistance genes.

Making waves: Defining advanced reduction technologies from the perspective of water treatment

Studies related to advanced reduction technologies (ARTs) have grown exponentially since the term was first coined in 2013. Despite recent interests in ARTs, the conditions and requirements for these processes have yet to be defined and clarifed. In comparision to well defined advanced oxidation technologies/processes (AOTs/AOPs) which involve the generation of hydroxyl radical as the common characteristic, ARTs function by electron donation from a variety of reducing agents and activators. Based on an extensive literature review, we propose that ARTs be defined as processes employing strong chemical reductants with E° ≤ -2.3 V vs. normal hydrogen electrode at 25 ºC. While extensive studies have revealed critical fundamental details of AOTs/AOPs mediated processes, there are still significant gaps in elucidation of the mechanistic details of reductive degradation/transformation of highly toxic compounds by ARTs. A significant number of pollutants and toxins resistant to AOTs/AOPs treatment are effectively degraded by ARTs. A great leap is needed on understanding ARTs to fully utilize their potential to efficiently remediate recalcitrant compounds of different sources and structures.

Mechanistic Understanding of Superoxide Radical-Mediated Degradation of Perfluorocarboxylic Acids

Perfluorocarboxylic acids (PFCAs) exhibit strong persistence in sunlit surface waters and in radical-based treatment processes, where superoxide radical (O₂^•-) is an important and abundant reactive oxygen species. Given that the role of O₂^•- during the transformation of PFCAs remains largely unknown, we investigated the kinetics and mechanisms of O₂^•--mediated PFCAs attenuation through complementary experimental and theoretical approaches. The aqueous-phase rate constants between O₂^•- and C3-C8 PFCAs were measured using a newly designed in situ spectroscopic system. Mechanistically, bimolecular nucleophilic substitution (S_N2) is most likely to be thermodynamically feasible, as indicated by density functional theory calculations at the CBS-QB3 level of theory. This pathway was then investigated by ab initio molecular dynamics simulation with free-energy samplings. As O₂^•- approaches PFCA, the C-F bond at the alpha carbon is spontaneously stretched, leading to the bond cleavage. The solvation mechanism for O₂^•--mediated PFCA degradation was also elucidated. Our results indicated that although the less polar solvent enhanced the nucleophilicity of O₂^•-, it also decreased the desolvation process of PFCAs, resulting in reduced kinetics. With these quantitative and mechanistic results, we achieved a defined picture of the O₂^•--initiated abatement of PFCAs in natural and engineered waters.

Ferrous oxalate covered ZVI through ball-milling for enhanced catalytic oxidation of organic contaminants with persulfate

Zero-valent iron (ZVI), with high reduction capacity and cost effectiveness, has been widely used as an activator for persulfate in remediation of organic pollutants. However, the existence of inherent iron oxide shell blocked the transfer of proton and further reduced its reactivity. In present study, a novel persulfate (PS) activator BZVI@OA was synthesized via ball milling ZVI with oxalic acid dihydrate. Scanning electron microscope, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry and Time-of-flight secondary ion mass spectroscopy confirmed the original low proton conductive oxidation shell was replaced by a high proton conductive FeC₂O₄ shell. The generated shell significantly improved persulfate activated capacity, through which degradation rates of various contaminants were enhanced for 1.64 to 2.33 times. Dissolved oxalate was proved to form complexes with iron ions, dramatically reduced the potential difference and relieved the blocked cyclic conversion. Electron paramagnetic resonance and quenching experiments confirmed an inner sphere adsorption of PS on FeC₂O₄·2H₂O shell which facilitated the peroxide bonds cleavage, leading high efficiency of ROS generation. The accelerated proton transition was confirmed with AC impedance method, resulting in fast and elevated surface bound Fe²⁺ for persulfate decomposition into active species. Furthermore, BZVI@OA/PS system demonstrated high tolerance over wide initial pH range and promising reusability within 6 cycles. This work clarifies an effective strategy for developing efficient modified ZVI as a PS activator for organic pollutant degradation in water.

Unravelling the impacts of perfluorooctanoic acid on anaerobic sludge digestion process

Perfluorooctanoic acid (PFOA) is a type of persistent organic pollutant that has been detected in wastewater treatment systems, subsequently entering the waste activated sludge (WAS) anaerobic digesters. Nevertheless, how PFOA affects the anaerobic digestion of WAS has never been reported till now. In this study, a series of batch digesters were set up to assess the performance of the anaerobic sludge digestion processes with exposures to different levels of PFOA. Experimental results revealed that the increased PFOA concentration (3-60 μg/g-TS) caused the 11.1-19.2% decrease in methane production than the control. Correspondingly, the relative abundances of several key microbes related to acidification (e.g., Longilinea sp.) and methanation (e.g., Methanosaeta sp.) decreased when exposed to PFOA, as demonstrated by microbial community analysis. Further investigations based on modelling and intermediate metabolites analysis confirmed the inhibition of acidification and methanation caused by PFOA, thus decreasing the methane production potential of WAS in anaerobic digestion.

Role of pH in the Transformation of Perfluoroalkyl Carboxylic Acids by Activated Persulfate: Implications from the Determination of Absolute Electron-Transfer Rates and Chemical Computations

Perfluoroalkyl carboxylic acids (PFCAs) are ubiquitous contaminants known for their bioaccumulation, toxicological harm, and resistance to degradation. Remediating PFCAs in water is an ongoing challenge with existing technologies being insufficient or requiring additional disposal. An emergent approach is using activated persulfate, which degrades PFCAs through sequential scission of CF₂ equivalents yielding shorter-chain homologues, CO₂ and F^-. This transformation is thought to be initiated by single electron transfer (SET) from the PFCA to the activate oxidant, SO₄^•-. A pronounced pH effect has been observed for thermally activated persulfate PFCA transformation. To evaluate the role of pH during SET, we directly determined absolute rate constants for perfluorobutanoic acid and trifluoroacetic acid oxidation by SO₄^•- in the pH range of 0.5-4.0 using laser flash photolysis. The average of the rate constants for both substrates across all pH values was 9 ± 2 × 10³ M^-1 s^-1 (±2σ), implying that acid catalysis of thermal persulfate activation may be the primary culprit of the observed pH effect, instead of pH influencing the SET step. In addition, density functional theory was used to investigate if SO₄^•-protonation might enhance PFCA transformation kinetics. We found that when calculations include explicit water molecules, direct SO₄^•- protonation does not occur.

Near-Quantitative Defluorination of Perfluorinated and Fluorotelomer Carboxylates and Sulfonates with Integrated Oxidation and Reduction

The UV-sulfite reductive treatment using hydrated electrons (e_aq^-) is a promising technology for destroying perfluorocarboxylates (PFCAs, C_nF_2n+1COO^-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, C_nF_2n+1-CH₂CH₂-COO^-) and sulfonates (FTSAs, C_nF_2n+1-CH₂CH₂-SO₃^-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidation (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixture of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent reduction (Red) with UV-sulfite achieved deep defluorination of the PFCA mixture for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examined the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, C_nF_2n+1-SO₃^-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quantitative overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technology design and water sample analysis.

Role of hydrogenated moiety in redox treatability of 6:2 fluorotelomer sulfonic acid in chrome mist suppressant solution

6:2 Fluorotelomer sulfonic acid (6:2 FTS) is used as alternative to perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) for different purposes such as chrome mist suppressant (CMS) and active ingredient in fire-fighting foams. In this study, degradability of 6:2 FTS under ultraviolet/persulfate (UV/PS) and ultraviolet/sulfite (UV/SF), which are typical technologies for advanced oxidation and reduction, were investigated respectively. Due to the hydrogenated moiety, 6:2 FTS was decomposed completely by UV/PS within 10 min, forming a mixture of short-chain perfluoroalkyl carboxylic acids with variable chain length (2-7 carbon atoms). Such oxidation products account for > 50% organofluorine of 6:2 FTS unmineralized portion. 6:2 FTS degradability under reductive UV/SF system was dramatically slowed down by the hydrogenated moiety, which lowered electron affinity and, consequently, reactivity with aqueous electron (e_aq‾) produced by UV/SF. Fluorine mass balance showed that degradation intermediates were almost negligible: most of decomposed 6:2 FTS fluorine was converted to fluoride. A real 6:2 FTS-based CMS solution prepared from a commercial product was also tested. Both types of treatment were effective and in good agreement with the trends observed for tests with sole 6:2 FTS. Moreover, experimental results highlighted a remarkable amount of identifiable (like 4:2 FTS, 8:2 FTS and other per-/polyfluoroalkyl substances) and unidentifiable components in the CMS mixture. Indeed, fluoride concentration under UV/SF (73.8 mg/L) and UV/PS (44.9 mg/L) treatment were both higher than the estimated total concentration (<23 mg/L, according to 6:2 FTS concentration). Results strongly suggest that an oxidation pretreatment followed by reduction might be a better way to degrade and defluorinate 6:2 FTS and other precursors with non-fluorinated moieties, rather than employing single reduction or oxidation technology.

Photodegradation of Perfluorooctanesulfonic Acid on Fe-Zeolites in Water

Perfluorooctanesulfonic acid (PFOS) decomposition in an aqueous environment remains a huge challenge because of its extreme chemical and biological inertness even when compared with other per- and polyfluoroalkyl substances (PFAS). In this work, we demonstrate for the first time a successful photochemical PFOS degradation by irradiation with 254 nm ultraviolet (UV) light after adsorption on μm-sized Fe(III)-loaded zeolites under ambient conditions with oxygen (O₂) as the terminal oxidant. Twenty μM PFOS loaded on 0.5 g L^-1 Fe-zeolites in aqueous suspension was degraded up to 99% within 96 h under acidic conditions (pH ≤ 5.5) in the presence of oxygen. Besides fluoride and sulfate, short-chain perfluorinated carboxylic acids (PFCAs) were identified and quantified as products. In addition, the effects of initial pH, catalyst dosages, and operation temperature on the degradation of PFOS were investigated. We also successfully applied the system to real groundwater samples where trace PFOS was present. Our results indicate that PFOS degradation is initiated by electron transfer from sulfonate to iron. The presented experimental study offers an option for a novel water remediation technology, comprising first a zeolite-based adsorption step followed by a step for photochemical regeneration of the adsorbent.

Facing the Challenge of Poly- and Perfluoroalkyl Substances in Water: Is Electrochemical Oxidation the Answer?

Electrochemical treatment systems have the unique ability to completely mineralize poly- and perfluoroalkyl substances (PFASs) through potential-driven electron transfer reactions. In this review, we discuss the state-of-the-art on electrooxidation of PFASs in water, aiming at elucidating the impact of different operational and design parameters, as well as reported mechanisms of PFAS degradation at the anode surface. We have identified several shortcomings of the existing studies that are largely limited to small-scale laboratory batch systems and unrealistic synthetic solutions, which makes extrapolation of the obtained data to real-world applications difficult. PFASs are surfactant molecules, which display significant concentration-dependence on adsorption, electrosorption, and dissociation. Electrooxidation experiments conducted with high initial PFAS concentration and/or in high conductivity supporting electrolytes likely overestimate process performance. In addition, the formation of organohalogen byproducts, chlorate and perchlorate, was seldom considered. Nevertheless, the first step toward advancing from laboratory-scale to industrial-scale applications is recognizing both the strengths and limitations of electrochemical water treatment systems. More comprehensive and rigorous evaluation of novel electrode materials, application of scalable proof-of-concept studies, and acknowledgment of all treatment outputs (not just the positive ones) are imperative. The presence of PFASs in drinking water and in the environment is an urgent global public health issue. Developments made in material science and application of novel three-dimensional, porous electrode materials and nanostructured coatings are forging a path toward more sustainable water treatment technologies and potential chemical-free treatment of PFAS-contaminated water.

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.

First Direct and Unequivocal Electron Spin Resonance Spin-Trapping Evidence for pH-Dependent Production of Hydroxyl Radicals from Sulfate Radicals

Recently, the sulfate radical (SO₄^•-) has been found to exhibit broad application prospects in various research fields such as chemical, biomedical, and environmental sciences. It has been suggested that SO₄^•- could be transformed into a more reactive hydroxyl radical (^•OH); however, no direct and unequivocal experimental evidence has been reported yet. In this study, using an electron spin resonance (ESR) secondary radical spin-trapping method coupled with the classic spin-trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and the typical ^•OH-scavenging agent dimethyl sulfoxide (DMSO), we found that ^•OH can be produced from three SO₄^•--generating systems from weakly acidic (pH = 5.5) to alkaline conditions (optimal at pH = 13.0), while SO₄^•- is the predominant radical species at pH < 5.5. A comparative study with three typical ^•OH-generating systems strongly supports the above conclusion. This is the first direct and unequivocal ESR spin-trapping evidence for ^•OH formation from SO₄^•- over a wide pH range, which is of great significance to understand and study the mechanism of many SO₄^•--related reactions and processes. This study also provides an effective and direct method for unequivocally distinguishing ^•OH from SO₄^•-.

Biomimetic degradability of linear perfluorooctanesulfonate (L-PFOS): Degradation products and pathways

The reductive degradability and decomposition pathways of linear perfluorooctanesulfonate (L-PFOS) were investigated in a biomimetic system consisting of Ti(III)-citrate and Vitamin B₁₂. Biomimetic degradation of L-PFOS could well be described by a first-order exponential decay model. Accompanied by the release of fluoride ion, technical PFOS could not only be transformed to perfluorocarboxylates (PFCAs) and perfluoroalkylsulfonates (PFSAs) with perfluoroalkyl carbon chain length < C8 (thereafter referred as carbon-chain-shortened degradation products), but also be transformed to PFCAs with perfluoroalkyl carbon chain length ≥ C8 (thereafter referred as carbon-chain-lengthened degradation products). Perfluorohexanesulfonate and perfluorotetradecanoate were the most abundant carbon-chain-shortened and -lengthened degradation products of technical PFOS, respectively. Based on the various degradation products detected during biomimetic reduction of linear [1,2,3,4-¹³C₄]-PFOS, the degradation pathways of L-PFOS were proposed as follows: L-PFOS was first reduced to C₈F₁₇• radical by cleavage of C-S bond, and then transformed to PFOA through hydrolysis. However, the carbon-chain-shortened products were not generated through the sequential chain-shortening via C₈F₁₇• radicals and/or L-PFOS, while the carbon-chain-lengthened products were not formed via C₈F₁₇• radicals by stepwise addition of CF₂ moiety. In fact, C₈F₁₇• radical and/or L-PFOS were further reduced to form C_nF_2n+1• (n = 1, 2, 3, 4) radicals, and these radicals were chain-lengthened by stepwise addition of C₄F₈ moiety and eventually transformed to various degradation products via hydrolysis (PFCAs) or combination reaction with sulfonyl hydroxide (PFSAs). All carbon-chain-lengthened chemicals were first reported as the degradation products during the decomposition of L-PFOS, while carbon-chain-shortened compounds were first identified as the biomimetic reduction products of L-PFOS.

Efficient decomposition of perfluorooctanic acid by persulfate with iron-modified activated carbon

Using persulfate (PS) oxidation to remove the persistent perfluorooctanoic acid (PFOA) in water typically requires an elevated temperature or an extended reaction time. Under relatively ambient temperatures (15-45 °C), feasibility of employing PS with iron-modified activated carbon (AC) for PFOA oxidation was evaluated. With presence of Fe/AC in PS oxidation, 61.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 41.9% defluorination efficiency at 25 °C after 10 h. Adsorption of PFOA onto Fe/AC can be regarded as a pre-concentration step prior to subsequent oxidation of PFOA. Fe/AC not only removes PFOA through adsorption, but also activates PS to form sulfate radicals that accelerate the decomposition and mineralization of PFOA. With Fe/AC in the PS system, activation energies (E_a) of PFOA removal and defluorination were significantly reduced from 66.8 to 13.2 and 97.3 to 14.5 kJ/mol, respectively. It implies that PFOA degradation and defluorination could proceed at a lower reaction temperature within a shorter reaction time. Besides, the surface characteristics of AC and Fe/AC before and after PS oxidation were evaluated by XPS and SEM. A quenching test used MeOH as an inhibitor and EPR spectra of free radicals were conducted to develop the proposed reaction mechanisms for PFOA oxidation.

Persulfate-Based Advanced Oxidation: Critical Assessment of Opportunities and Roadblocks

Reports that promote persulfate-based advanced oxidation process (AOP) as a viable alternative to hydrogen peroxide-based processes have been rapidly accumulating in recent water treatment literature. Various strategies to activate peroxide bonds in persulfate precursors have been proposed and the capacity to degrade a wide range of organic pollutants has been demonstrated. Compared to traditional AOPs in which hydroxyl radical serves as the main oxidant, persulfate-based AOPs have been claimed to involve different in situ generated oxidants such as sulfate radical and singlet oxygen as well as nonradical oxidation pathways. However, there exist controversial observations and interpretations around some of these claims, challenging robust scientific progress of this technology toward practical use. This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfate and the formation pathways of oxidizing species. Properties of the main oxidizing species are scrutinized and the role of singlet oxygen is debated. In addition, the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry are discussed. The opportunity for niche applications is also presented, emphasizing the need for parallel efforts to remove currently prevalent knowledge roadblocks.

Binding specificities of estrogen receptor with perfluorinated compounds: A cross species comparison

BACKGROUND

Perfluorinated compounds (PFCs) were reported to result in the endocrine disruption by activating the estrogen receptor (ER) and inducing ER-mediated transcriptions.

OBJECTIVE

The aim of the present work was to perform cross-species comparisons on the characteristics of eight PFCs binding to humans ERα and to rats ERα.

METHODS

In the present work, in vivo tests, including serum estradiol level assay and immunohistochemical staining, fluorescence assay and molecular models were applied.

RESULTS

Based on the in vivo experiments, the exposure of PFOA and PFOS to female rats was proved to increase the ERα expression in the terus, suggesting that PFCs may act as estrogenic compounds to activate ERα in vivo. The further fluorescence assay presented that these eight PFCs have stronger binding abilities to human ERα than to rat ERα. In addition, the differences in binding specificities between human ERα and rat ERα were identified in the process of molecular dynamics modeling with the term of helix position and the ability of coregulator recruitment. It can be found that more and stronger charge clamps could form between PFCs with human ERα than with rat ERα. Also, the eight PFCs presented lower binding energies in human ERα systems, which proved that eight PFCs presented much stronger binding abilities with human ERα.

DISCUSSION

In all, it can be concluded that PFCs might be more sensitive to human ERα than to that of rats, which also suggested the greater susceptibility to adverse effects on humans. The present work was a beginning assessment of a cross-species comparison, providing important information on health impacts of PFCs in humans.

Novel chitosan-ethylene glycol hydrogel for the removal of aqueous perfluorooctanoic acid

It is urgent to explore an effective removal method for perfluorooctanoic acid (PFOA) due to its recalcitrant nature. In this study, a novel chitosan-based hydrogel (CEGH) was prepared with a simple method using chitosan and ethylene glycol through a repeated freezing-thawing procedure. The adsorption of PFOA anions to CEGH agreed well to the Freundlich-Langmuir model with a maximum adsorption capacity as high as 1275.9 mg/g, which is higher than reported values of most adsorbents for PFOA. The adsorption was influenced by experimental conditions. Experimental results showed that the main removal mechanism was the ionic hydrogen bond interaction between carbonyl groups (COO^-) of PFOA and protonated amine (NH⁺) of the CEGH adsorbent. Therefore, CEGH is a very attractive adsorbent that can be used to remove PFOA from water in the future.

Exploring toxicity of perfluorinated compounds through complex network and pathway modeling

Perfluorinated compounds (PFCs) have serious impacts on human health, which could interfere with the body's signal pathways and affect the normal hormone balance of humans. PFCs were reported to bind to many proteins causing a series of biological effects. It was quite possible that the in vivo action of PFCs was not a single target or a single pathway, suggesting the toxic effect was due to the disturbance of protein or gene network, not limited to the modification of a single target protein or gene. Thus, a PFCs-targets interaction network was constructed and the significant differences in the characteristics of complex networks between the branched PFCs and linear PFCs were observed. A molecular dynamics simulation proved that binding ability of the branched PFCs to the target protein was much weaker than that of the linear PFCs, explaining why the branched PFCs presented significantly difference from the linear PFCs in terms of complex network characteristics. In addition, four target genes were identified as the central node genes of the network. The four target genes were proved to present certain influences on some diseases, which suggested a high correlation between PFCs to these diseases, including obesity, hepatocellular carcinoma and diabetes. The present work was helpful to develop new approaches to identify the key toxic targets of compounds and to explore the toxicity effects on pathways. AbbreviationsARandrogen receptorBPAbisphenol AESR1estrogen receptor 1ESR2estrogen receptor 2GLTPglycolipid transfer proteinHbFthe fetal hemoglobinHBG1hemoglobin subunit γ-1hERαhuman ERαHSD17B1hydroxysteroid 17-β dehydrogenase 1KEGGKenya encyclopedia of genes and genomesMDmolecular dynamics simulationPFCsperfluorinated compoundsPFOAperfluorooctanoic acidPFOSperfluorooctane sulfonatePOPspersistent organic pollutantsRMSDroot-mean-square deviationSHBGsex hormone binding globulinSPC/Eextended simple point charge modelTRthyroid hormone receptorCommunicated by Ramaswamy H. Sarma.

Rate constants of sulfate radical anion reactions with organic molecules: A review

The rate constants of sulfate radical anion reaction (k_SO4-) with about 230 organic molecules of environmental interest are tabulated and discussed, together with both the methods of rate constant determinations and the reaction mechanisms. k_SO4-'s were collected from the original publications. The highest values in the ∼10⁹ M^-1 s^-1 range are published for aromatic molecules. There is a tendency that electron donating substituents increase and electron withdrawing substituents decrease these values. There are just a few compounds with rate constants established using different techniques in different laboratories. k_SO4-'s determined in different laboratories by the direct techniques, pulse radiolysis or laser flash photolysis, in most cases agree reasonably. The values determined by competitive experimental techniques, by complex kinetics calculations, or by modelling show a large scatter. Some of these techniques seem to be questionable for k_SO4- determination. The sulfate radical anion reacts with ketone and amine moieties of molecules by electron transfer. The same mechanism is also suggested for the reaction with aromatic rings. However, in a few cases addition to the double bond and sulfate anion elimination reactions were distinguished. A typical reaction with the aliphatic parts of the molecule is H-abstraction.

Interactive effects of changing stratospheric ozone and climate on tropospheric composition and air quality, and the consequences for human and ecosystem health

The composition of the air we breathe is determined by emissions, weather, and photochemical transformations induced by solar UV radiation. Photochemical reactions of many emitted chemical compounds can generate important (secondary) pollutants including ground-level ozone (O₃) and some particulate matter, known to be detrimental to human health and ecosystems. Poor air quality is the major environmental cause of premature deaths globally, and even a small decrease in air quality can translate into a large increase in the number of deaths. In many regions of the globe, changes in emissions of pollutants have caused significant changes in air quality. Short-term variability in the weather as well as long-term climatic trends can affect ground-level pollution through several mechanisms. These include large-scale changes in the transport of O₃ from the stratosphere to the troposphere, winds, clouds, and patterns of precipitation. Long-term trends in UV radiation, particularly related to the depletion and recovery of stratospheric ozone, are also expected to result in changes in air quality as well as the self-cleaning capacity of the global atmosphere. The increased use of substitutes for ozone-depleting substances, in response to the Montreal Protocol, does not currently pose a significant risk to the environment. This includes both the direct emissions of substitutes during use and their atmospheric degradation products (e.g. trifluoroacetic acid, TFA).

Micropollutants removal by full-scale UV-C/sulfate radical based Advanced Oxidation Processes

The high chemical stability and the low biodegradability of a vast number of micropollutants (MPs) impede their correct treatment in urban wastewater treatment plants. In most cases, the chemical oxidation is the only way to abate them. Advanced Oxidation Processes (AOPs) have been experimentally proved as efficient in the removal of different micropollutants at lab-scale. However, there is not enough information about their application at full-scale. This manuscript reports the application of three different AOPs based on the addition of homogeneous oxidants [hydrogen peroxide, peroxymonosulfate (PMS) and persulfate anions (PS)], in the UV-C tertiary treatment of Estiviel wastewater treatment plant (Toledo, Spain) previously designed and installed in the facility for disinfection. AOPs based on the photolytic decomposition of oxidants have been demonstrated as more efficient than UV-C radiation alone on the removal of 25 different MPs using low dosages (0.05-0.5 mM) and very low UV-C contact time (4-18 s). Photolysis of PMS and H₂O₂ reached similar average MPs removal in all the range of oxidant dosages, obtaining the highest efficiency with 0.5 mM and 18 s of contact time (48 and 55% respectively). Nevertheless, PMS/UV-C reached slightly higher removal than H₂O₂/UV-C at low dosages. So, these treatments are selective to degrade the target compounds, obtaining different removal efficiencies for each compound regarding the oxidizing agent, dosages and UV-C contact time. In all the cases, H₂O₂/UV-C is more efficient than PMS/UV-C, comparing the ratio cost:efficiency (€/m³·order). Even H₂O₂/UV-C treatments are more efficient than UV-C alone. Thus, the addition of 0.5 mM of H₂O₂ compensates the increased of UV-C contact time and therefore the increase of electrical consumption, that it should be need to increase the removal of MPs by UV-C treatments alone.

Oxidation Processes in Water Treatment: Are We on Track?

Chemical oxidants have been applied in water treatment for more than a century, first as disinfectants and later to abate inorganic and organic contaminants. The challenge of oxidative abatement of organic micropollutants is the formation of transformation products with unknown (eco)toxicological consequences. Four aspects need to be considered for oxidative micropollutant abatement: (i) Reaction kinetics, controlling the efficiency of the process, (ii) mechanisms of transformation product formation, (iii) extent of formation of disinfection byproducts from the matrix, (iv) oxidation induced biological effects, resulting from transformation products and/or disinfection byproducts. It is impossible to test all the thousands of organic micropollutants in the urban water cycle experimentally to assess potential adverse outcomes of an oxidation. Rather, we need multidisciplinary and automated knowledge-based systems, which couple predictions of kinetics, transformation and disinfection byproducts and their toxicological consequences to assess the overall benefits of oxidation processes. A wide range of oxidation processes has been developed in the last decades with a recent focus on novel electricity-driven oxidation processes. To evaluate these processes, they have to be compared to established benchmark ozone- and UV-based oxidation processes by considering the energy demands, economics, the feasibilty, and the integration into future water treatment systems.