Reactivity-directed analysis facilitates prioritization of toxic disinfection byproducts (DBPs), yet its data processing remains laborious and inefficient. Herein, we developed an automated approach integrating stable isotopic labeling with reactivity-directed principles. Normal and deuterated glutathione (GSH) probes were used to generate paired isotopic signatures enabling precise localization of reactive DBPs. Customized bioinformatics tools were employed to efficiently extract paired GSH-DBP adducts. The workflow allowed rapid automated processing of large data sets within minutes while maintaining high coverage and accuracy. When applied to chlorinated and chloraminated water samples, 255 adducts were screened from >50 000 raw features, leading to annotation of 202 DBPs, including 193 newly reported. GSH reaction mechanism analysis attributed 65 chlorinated and 132 unsaturated DBPs to nucleophilic substitution and addition, respectively. Notably, 5 sulfur-containing DBPs enabled thiol oxidation, indicating a new GSH reaction pathway. Among annotated DBPs, chlorination favored unsaturated carbonyls, while chloramination generated more nitrile/nitro group DBPs. Toxicity predictions verified that annotated DBPs exhibited toxicities comparable to or greater than those of regulated DBPs. Prevalent toxic DBPs exhibited a high molecular weight or structural characters, such as benzene rings, carbonyls, and Cl/N functionalization. This approach significantly accelerated toxic DBP discovery, and the findings provided new insights into toxicity drivers in disinfected waters.

Organic radicals are key reactive intermediates that govern pollutant transformation and biogeochemical cycling in aquatic environments, yet their direct identification remains challenging because of structural diversity, low concentrations, and transient lifetimes. This study introduces a robust analytical workflow that integrates the spin-trapping agent 5-(diisopropoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DIPPMPO) with ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) for the systematic detection and identification of organic radicals in complex aqueous matrices. Systematic validation confirmed the high stability and linear concentration response of DIPPMPO-radical adducts, while characteristic neutral-loss patterns (42.0470 and 166.0759 Da) provided structural confirmation across multiple organic radical classes, including phenoxyl, semiquinone, acyloxyl, peroxyl, and alkyl radicals. Applied to both engineered and natural aqueous systems, the workflow successfully identified organic radicals generated during UV-irradiated bisphenol A degradation and in sunlight-exposed dissolved organic matter (DOM). The results illustrate its ability to trace pollutant-derived organic radicals and map diverse DOM-generated organic radicals, offering new insights into transformation pathways. By delivering enhanced specificity, structural insight, and semiquantitative capability, this approach advances the mechanistic understanding of radical-mediated processes and provides a versatile platform for studying transient reactive intermediates in water treatment and environmental redox systems.

Biological activated carbon (BAC) filters are extensively employed in drinking water treatment plants (DWTPs) as a post-ozonation step to enhance water quality. However, the efficacy of BAC in removing ozonation transformation products (OTPs) remains inadequately characterized. This study comprehensively evaluated BAC performance by investigating dissolved organic matter (DOM) transformation and disinfection by-product formation potential (DBP FP) in samples collected from a full-scale DWTP utilizing the O3-BAC process. Results showed limited overall DOM removal by O3-BAC: 7.7 % for dissolved organic carbon and 15.0 % for fluorescent fractions. Molecular transformation analysis demonstrated that BAC filtration selectively targeted ozonation-derived saturated and oxidized molecules (characterized by H/Cw = 1.14 and O/Cw = 0.36) while allowing more unsaturated and aromatic OTPs to persist, confirming BAC's crucial role in determining the fate of OTPs and subsequent DBP FP. The BAC filtration achieved significant removal: 25.2 % for trihalomethanes (THMs), 47.4 % for haloaldehydes, 4.6 % for haloacetonitriles (HANs) and 47.0 % for halonitromethanes relative to O3 effluent levels. Spearman analysis revealed the characteristics of molecular formulas strongly associated with DBP FP. Specifically, haloketones and HAN FP-correlated formulas shared more reduced and less oxygenated structural characteristics compared to those associated with other DBP classes. The molecular mechanism underlying O3-BAC efficacy was elucidated: OTPs serve as key DBP precursors; BAC preferentially removes OTP-derived precursors (e.g., 89.1 % for THMs versus 5.8 % for original precursors); this selective removal counteracts ozonation's precursor generation effect. This synergy provides the molecular basis for DBP-FP reduction, clarifying BAC's critical role in controlling ozonation-derived risks.

The oxidation of Br⁻ and I⁻ during chlorination leads to the generation of secondary disinfectants, hypobromous acid (HOBr) and hypoiodous acid (HOI), which subsequently results in the formation of highly toxic halogenated disinfection byproducts (DBPs). This study reported the formation of previously overlooked halogenated cyclopentene-diones (halo-CDs) from phenols upon reaction with HOBr and HOI. The known DBPs were found to account for only a minor portion of total organic halogen in reaction of phenols with secondary disinfectants, warranting further investigation of elucidating the unknown fraction. To prioritize and identify the unknown toxic DBPs, the effect-directed analysis (EDA) was applied to the reaction mixtures of model phenols with secondary disinfectants. By integrating cytotoxicity-directed fractionation and high-resolution mass spectrometry, a series of halo-CDs were prioritized and identified. These compounds were then confirmed in simulated and real source waters treated by secondary disinfectants, suggesting their common occurrence in disinfected drinking water. Based on the experimental observation of intermediates, the formation pathways of halo-CDs were theoretically proposed to involve sequential halogenation, hydrolysis, hydroxylation, oxidative ring-cleavage, decarboxylation, and cyclization. Computational toxicity assessments demonstrated that the identified halo-CDs would pose considerable health risks. The findings herein implied that a large number of toxic DBPs might remain covered due to the inadequate focus on secondary disinfectants, which underscored the urgent need to broaden identification of DBPs beyond reaction involving primary disinfectants.

The study of the geochemical behaviors of mercury in methane seepage environments is of great significance for predicting the evolution of extreme ecosystems. However, as there are very few related studies, the source of mercury in methane seepage environments is still controversial. In this study, mercury concentration and isotopic composition, delta C-13(TIC,) delta O-18(TIC,) delta S-34(bluk,) total sulfur content, and the TS/TOC ratio of sediment cores (2 PC and 10 GC) from the Nasha Trough in the South China Sea are reported to elucidate the geochemical behavior of mercury in methane seepage environments. Based on the delta C-13(TIC,) delta S-34(bluk), TS, and TS/TOC data from the study cores, two methane release events were identified at 24 similar to 32 ka and 38 similar to 42 ka. High mercury concentration anomalies were observed during both methane release events. The Hg/TS and Hg/TOC ratios of the study cores exhibit positive excursions during both methane release events. Mercury isotopes display greater variability during methane release events. The scatter plot of Delta Hg-199 and Delta Hg-201 from the study cores shows a slope of 0.7978. The thermal decomposition curves indicate that the primary mercury mineral phase is beta-HgS during methane release events. These clues suggest that the abnormal accumulation of mercury during the methane release events may have been caused by submarine volcanic eruptions that warmed the surrounding seafloor, leading to hydrate decomposition and methane leakage.

The redox activity of dissolved organic matter (DOM) plays a critical role in natural and engineering aquatic systems. Although phenolic moieties are typically recognized as the dominant electron-donating moieties (EDM) in naturally occurring DOM (NOM), the chemical nature and reactivity of EDM in wastewater-derived DOM (EfOM), remain poorly understood. In this study, a kinetic categorizing framework was developed for resolving the composition of EDM within DOM by using the second-order rate constants for the reactions of the radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+) (kapp, ABTS•+) with DOM isolates and a suite of model electron-donating compounds. Our results reveal that NOM contains a larger fraction of rapidly reacting ABTS•+ reducible components with kapp, ABTS•+ > 1 × 103 M-1 s-1, accounting for more than 50% of the total EDM. In contrast, EDM in EfOM mainly consist of antioxidants with relatively low redox activity (kapp, ABTS•+ < 10 M-1 s-1), accounting for 70% of the total EDM. Combining kinetic categorization and Fourier transform ion cyclotron resonance mass spectrometry analysis, the results suggest that EDM in EfOM are associated with nitrogen- and/or sulfur-containing heteroatom compounds. This novel method has important implications for understanding the aquatic redox chemistry of DOM and developing source-adaptive water oxidative treatment strategies in engineering systems.

The environmental persistence of extracellular antibiotic resistance genes (eARGs) after wastewater effluent discharge raises significant ecological and public health concerns. Photochemical degradation is considered as a key mechanism for natural attenuation of eARGs, however, its effectiveness is highly variable depending on the composition of dissolved organic matter (DOM) in aquatic systems. This perspective highlights that disinfection applied in wastewater treatment plants could be an important process that fundamentally reprograms the photochemical reactivity of DOM toward eARGs, in particular in wastewater effluent-receiving aquatic environments. Such reprogramming reshapes both the photosensitizing capacity and antioxidant properties of DOM, thereby altering the balance between photochemical damage and repair of eARGs. This perspective outlines a mechanistic framework linking DOM composition, disinfection mechanism, and photochemical fate of eARGs. Also, key knowledge gaps towards photodegradation of eARGs in wastewater-impacted environments are identified for future studies.

As a pivotal unit in water treatment, filters undergo significant media aging during long-term operation, altering their physicochemical properties and heavy metal accumulation behavior. This study investigated long-term operated filter sands from a rapid sand filter (RSF) and a traveling bridge sand filter (TBSF) at a drinking water treatment plant in Guangzhou. Characterization revealed that prolonged operation induced the formation of poorly crystallized Fe-Mn oxide coatings on sand surfaces. The RSF exhibited markedly higher heavy metal enrichment than the TBSF-with substantially more fine particles (+9.5%) and coarse particles (+4.7%)-attributable to its higher proportion of fine particles and greater treated water volume per unit media mass. Distinct vertical distribution patterns were observed; metal concentrations decreased with depth in the RSF, while the TBSF showed minimal variation. Sequential extraction according to the European Community Bureau of Reference indicated that heavy metals (excluding Fe and Ti) were predominantly present in the reducible and acid-soluble fractions, with the RSF showing a higher proportion of the reducible fraction. Although particle size significantly influenced accumulation levels, it did not affect metal speciation within the coatings. Citric acid soaking partially removed Mn, Ni, and Cd; however, the associated Mn loss may compromise the coating's adsorptive capacity. This approach proved insufficient to fully mitigate contamination risk-particularly given that acid-soluble fractions were not reduced, and even increased for Cd in the RSF-thereby substantiating the scientific basis for replacing long-term operated filter sands.

Water treatment efficiency is often limited by complex water matrices that inhibit micropollutant degradation. Organic radicals are emerging as a promising alternative to conventional hydroxyl radical-based oxidation due to their higher selectivity toward electron-rich micropollutants (up to 107-109 M-1·s-1) and lower susceptibility to matrix interference. They can be generated under mild conditions via activation of organic peroxides or natural redox mediators and participate in electron transfer, hydrogen abstraction, addition, and polymerization reactions, enabling both micropollutant transformation and potential valorization. However, concerns about toxic by-products from radical precursors have driven strategies such as precursor immobilization and in situ radical generation. Despite these advances, critical knowledge gaps remain in reaction selectivity and the development of sustainable application frameworks. Future research should emphasize data-driven kinetic modeling, utilization of matrix-derived organic radicals, and the design of stable materials to advance practical implementation of organic radical-based water treatment technologies.

Microplastic-derived dissolved organic matter (MP-DOM) plays an important role in aquatic environments; however, its influence on the photodegradation of plastic additives remains unclear. In this study, bisphenol A (BPA) was selected as a representative plastic additive to investigate the effects of polystyrene-derived DOM (PS-DOM) on the photodegradation kinetics and mechanisms of BPA at different concentrations. PS-DOM significantly enhanced the photodegradation of BPA, with the promoting effect becoming more pronounced at lower BPA concentrations. Kinetic modeling revealed that as BPA levels decrease from high to low, the dominant contributor to BPA photodegradation shifts from the excited triplet state of PS-DOM (generated via photosensitization) to long-lived organic radicals (LLORs). This finding highlights the indispensable role of LLORs in the photodegradation of trace-level BPA (nM-μM) in surface waters. Probe experiments revealed that the one-electron reduction potentials of LLORs generated by various MP-DOM are around 1.50 V, indicating that LLORs have the potential to degrade plastic additives with oxidation potentials below this range. Furthermore, correlation analysis revealed that variations in unsaturated functional groups and electron-donating moieties (e.g., tannins and lignins) within MP-DOM were key factors controlling the quantum yield coefficients of LLORs across different MP-DOM types. This study provides novel insights into the photochemical reactivity of MP-DOM and its potential role in regulating the environmental transformation of plastic additives.

Remediating antibiotic-contaminated water is a critical challenge due to the persistence of antibiotics and limitations of conventional treatment methods. To address this issue, we fabricated a series of pyrrole-based carbonsupported Fe0 catalysts (CHCP-Py-Fe) through a facile, low-cost and green calcination strategy, avoiding complex precursors and tedious synthetic procedures. The optimized catalyst pyrolyzed at 700 degrees C showed uniform Fe dispersion and low charge-transfer resistance, with a high specific surface area of 336.85 m2/g. Under mild conditions, 20 mg/L tetracycline (TC) was completely degraded within 5 min, with a pseudo-first-order rate constant of 1.1133 min- 1, which is more than 11-folds higher than that of pure Fe0 nanoparticles, outperforming most reported iron-based peroxymonosulfate (PMS) activation catalysts. Superoxide radicals (& sdot;O2- ) were identified as the dominant reactive oxygen species with a contribution of 47.7%, endowing the system with excellent environmental adaptability over a wide pH range of 3.02-11.01, high-salinity conditions and real water matrices, together with a unique Cl- promotion effect. The catalyst maintained 100.0% TC removal efficiency over four cycles. After the fifth cycle, its activity declined slightly, but could be effectively recovered by low-temperature calcination. This work provides a sustainable and efficient catalytic strategy for the remediation of TCcontaminated water.

Far-UVC irradiation at 222 nm (UV222), typically emitted by krypton chloride excimer lamps, has emerged as a promising mercury-free platform for water treatment. This review evaluates recent progress in UV222-based water treatment, with conventional 254 nm UV irradiation (UV254) as the primary benchmark, focusing on disinfection, micropollutant degradation, and UV222-induced dissolved organic matter (DOM) transformation in relation to post-chlorination disinfection byproduct (DBP) formation. UV222 shows strong disinfection performance against representative bacteria and viruses, although its relative advantage over UV254 is more variable for fungal spores. For micropollutants, compiled paired photolysis data indicate that UV222 generally accelerates direct photolysis relative to UV254, with the enhancement arising from stronger absorptivity, higher quantum yield, or both depending on compound structure. UV222-based advanced processes further broaden the treatment scope beyond direct photolysis through reactive-species-mediated transformation. However, UV222 can also reshape DOM composition and DBP precursor pools. Sole UV222 may reshape DOM molecular composition without large DBP increases, whereas nitrate-containing systems can selectively amplify halonitromethane formation. UV222 should not be viewed simply as a more reactive substitute for UV254. Its practical value depends on balancing disinfection and contaminant-removal benefits against matrix-dependent DOM transformation and downstream DBP risks. Future studies should focus on DOM molecular transformation and DBP precursor restructuring, particularly the role of nitrogen incorporation in linking these two processes, as well as realistic treatment-train evaluations.

Perchlorate (ClO4⁻) contamination poses serious risks to ecosystems and human health due to its high mobility, persistence, and thyroid-disrupting toxicity. Current technologies struggle with the rapid, selective removal of ClO4⁻, particularly in complex water matrices. In this study, we addressed this challenge by developing a hydrogen-bond interface-engineered adsorbent, Mn/N-coordinated porous carbon modified with formic acid (Mn-NC···HCOOH), to achieve efficient and rapid ClO4⁻ removal. The novelty of this work lies in the engineering of dual active sites (Mn and N-coordinated C), coupled with the polarization of these sites via hydrogen-bonding interactions, which significantly enhances ClO4⁻ binding and suppress competitive hydration from water molecules. This adsorbent exhibited an ultrafast uptake rate of 1.2 × 104 μg/ (g· min) and a Langmuir maximum adsorption capacity of 79.17 mg/g (about 50% higher than the unmodified Mn-NC). The material retained > 80% removal efficiency in the presence of common coexisting ions and natural organic matter over a broad pH range of 3.5-9.0. Importantly, it achieved 98% ClO4⁻ removal within 5 min in real ClO4⁻-contaminated wastewater (62.9 mg/L) and showed stable operation over 10 h continuous-flow packed-bed treatment. This work recommends hydrogen-bonding interface engineering as a promising strategy for designing high-performance adsorbents, which can be extended to the removal of other oxyanions for environmental remediation.

Micropollutants (MPs) are ubiquitously present in aquatic environments at nanomolar (nM) concentrations or lower, yet they pose substantial risks to both ecosystems and human health. However, laboratory studies often examine MP transformation at micromolar (μM) levels due to analytical constraints, potentially overlooking certain MP behaviors under environmentally relevant concentrations. This study investigated the oxidation kinetics (kobs) of model MPs across a wide range of initial concentration (C0), with particular emphasis on the distinct roles of short- and long-lived reactive species (SLRS and LLRS) formed in irradiated dissolved organic matter (DOM) solutions. A generalized kinetic framework was developed and revealed that SLRS, such as triplet-state DOM, dominated MP oxidation at higher C0 (≥μM), while LLRS, primarily DOM radicals, drove MP degradation at sub-μM levels. Laser flash photolysis confirmed that LLRS exhibits much longer lifetimes (∼ms) than SLRS (∼μs), enabling elevated LLRS concentrations under trace MP conditions and significantly enhancing MP oxidation. The observed kobs-C0 relationship features a characteristic "three-platform" behavior governed by RS formation rates, reactivities, and lifetimes. These findings advance our understanding of MP fate under real-world conditions and underscore the critical yet often overlooked role of LLRS in aquatic systems.

Identification of disinfection byproducts (DBPs) precursors remains a longstanding challenge due to the complexity of contaminated source water. Tire wear particles (TWPs) can be an overlooked source of DBPs precursors. To figure out the specific amine additives in tire rubber serving as potential nitrosamine precursors during chlorination, six frequently measured tire-derived amine additives, including N-(1,3-dimethylbutyl)-N '-phenyl-p-phenylenediamine (6PPD), N-isopropyl-N '-phenyl-p-phenylenediamine (IPPD), N-cyclohexyl-N '-phenyl-p-phenylenediamine (CPPD), N,N '-dicyclohexylurea (DCU), diphenylamine (DPhA), and N,N '-dicyclohexylamine (DCHA), were selected to simulate their degradation processes, and their DBPs formation potentials were evaluated under various water matrices. IPPD was found to have a high molar yield of N-nitrosodimethylamine (NDMA, up to 8%), while 6PPD exhibited a lower molar yield (similar to 0.1%) with the molar ratio of chlorine-to-ammonium nitrogen (Cl2:N = 2) and disinfectant-to-precursor (D/P = 10). Suspect and target screening approaches were further applied to identify the transformation products of IPPD, and the formation pathway of NDMA via IPPD was proposed. Furthermore, we assessed NDMA formation from IPPD in simulated TWP leachates through chlorination experiments in the presence of ammonia, which revealed that IPPD contributed up to 24% of the total NDMA formed. This study offers new insights into the previously overlooked source of nitrosamines from tire-derived amine additives.

The majority of disinfection byproducts (DBPs) remain unknown and may pose toxic risks. By mimicking the molecular interactions of toxicants with biomolecules, we developed a solid-phase microextraction (SPME) reactivity-directed analysis method for identifying unknown toxic DBPs. The probe 4-mercaptophenylboronic acid (MPA) was covalently immobilized onto the SPME fiber coating through cis-diol bonding. After the capture of potentially toxic DBPs through thiol reactions, the pH-responsive cleavage of boronate ester allowed for release of the MPA-DBP adducts. The boron isotope pattern (1:4) and characteristic fragments derived from the MPA moiety allowed for efficient prioritization of the adducts. Compared to the current homogeneous approach using liquid extracts, this heterogeneous method exhibited the advantages of biomimetic toxicity focus, effective pretreatment, and enhanced detection performance. The application in chlorinated simulated source water discovered 30 DBP-MPA adducts, in which the molecular structures of seven adducts, i.e., seven DBPs, were identified, including a known DBP chloroacetic acid and six newly found DBPs. Two of them were confirmed as 1-penten-3-one and methacrolein by using authentic standards. The toxicity and health risks of newly found DBPs were predicted using computational tools, indicating their toxicity contributions in disinfected waters. This study represents an important advance in the qualitative methodology for identifying unknown toxic DBPs.

Advanced oxidation processes based on peroxymonosulfate (PMS) have attracted increasing attention for the removal of refractory organic contaminants. Yet, the structure-activity relationship governing PMS activation over carbon-based catalysts remains poorly understood. Here, we demonstrate an orders-of-magnitude enhancement in PMS activation driven by curvature-dependent reactivity of carbonyl (C=O) active sites on carbon nanotubes (CNTs). Six CNT catalysts with diameters ranging from 1 to 60 nm and comparable surface oxygen functionalization were systematically investigated to decouple curvature effects. Using 2,4-dichlorophenol as a target contaminant, 1 nm single-walled CNTs achieve pseudo-first-order reaction rate constants up to 0.67 min−1, which are 1–2 orders of magnitude higher than those of large-diameter multi-walled CNTs. Turnover-frequency analysis, normalized to the abundance and surface density of C=O groups, reveals that this enhancement originated from the substantially higher intrinsic reactivity of individual C=O sites rather than from differences in active-site density or edge localization. Mechanistic investigations show that highly curved CNTs preferentially activate PMS via non-radical pathways dominated by singlet oxygen (1O2) generation and electron-transfer processes, which account for 90.1–94.6% of contaminant removal. Density functional theory calculations further demonstrated that increased curvature strengthens interfacial charge transfer and PMS adsorption, stabilizes key reaction intermediates, and lowers the energy barriers for 1O2 formation. Furthermore, integration of CNTs into a membrane filtration device enables contaminant removal efficiencies exceeding 90% during continuous operation for over 45 h in real water matrices. This work identifies curvature as a key design parameter for engineering high-performance metal-free CNT catalysts and provides new insights into the development of efficient PMS-based oxidation technologies.

Nanofiltration (NF) has significant potential for water reclamation, but it encounters several critical challenges, including unsatisfactory removals of dissolved small-molecular contaminants such as antibiotics, an inherent permeability-selectivity trade-off, and severe membrane fouling. Herein, we present a groundbreaking advancement in addressing these issues through an electric field-assisted filtration with a conductive NF membrane fabricated by interfacial polymerization of polyamide on a carbon nanotube substrate (pCNT-PA). The effects of electric field strength, solution pH, ionic strength, and combined organic-inorganic foulants on the removal efficiencies of various antibiotics of the conductive NF membrane under electric field-assisted filtration were investigated. The results show that, when the conductive membrane was used as a cathode under an applied voltage of 1.5 V, the rejection rates of sulfamethoxazole and ibuprofen substantially increased from 79.3 % and 59.3 % to 99.5 % and 90.8 %, respectively. This improvement is primarily attributed to the electric field induced increase in membrane charge density, rather than the alteration of membrane pore size. The elevated charge density enhances the electrostatic repulsion between anionic antibiotics and negatively polarized membrane. Based on this mechanism, the pCNT-PA membrane presented voltage-gated separation towards binary and ternary antibiotics with distinct charge characteristics. Furthermore, the electric field-assisted NF process exhibited remarkable antifouling performance, maintaining over 95 % sulfamethoxazole removal efficiency in the presence of combined organic-inorganic foulants. This work advances the understanding of electric fieldregulated antibiotic removal mechanisms in NF systems, providing new theoretical insights for the development of intelligent responsive membrane separation technologies.