Comprehensive analysis of cyanobacterial secondary metabolites distribution and toxicity in urban water bodies.

This study addresses the increasing concern regarding cyanotoxin contamination of water bodies, highlighting the diversity of these toxins and their potential health implications. Cyanobacteria, which are prevalent in aquatic environments, produce toxic metabolites, raising concerns regarding human exposure and associated health risks, including a potential increase in cancer risk. Although existing research has primarily focused on well-known cyanotoxins, recent technological advancements have revealed numerous unknown cyanotoxins, necessitating a comprehensive assessment of multiple toxin categories. To enhance the cyanotoxin databases, we optimized the CyanoMetDB cyanobacterial secondary metabolites database by incorporating secondary fragmentation patterns using the Mass Frontier fragmentation data prediction software. Water samples from diverse locations in Shanghai were analyzed using high-resolution mass spectrometry. Subsequently, the toxicity of cyanobacterial metabolites in the water samples was examined through acute toxicity assays using the crustacean Thamnocephalus platyurus. After 24 h of exposure, the semi-lethal concentrations (LC50) of the water samples ranged from 0.31 mg L-1 to 1.78 mg L-1 (MC-LR equivalent concentration). Our findings revealed a critical correlation between the overall concentration of cyanobacterial metabolites and toxicity. The robust framework and insights of this study underscore the need for an inclusive approach to water quality management, emphasizing continuous efforts to refine detection methods and comprehend the broader ecological impact of cyanobacterial blooms on aquatic ecosystems.

Phase State Regulates Photochemical HONO Production from NaNO3/Dicarboxylic Acid Mixtures.

Field observations of daytime HONO source strengths have not been well explained by laboratory measurements and model predictions up until now. More efforts are urgently needed to fill the knowledge gaps concerning how environmental factors, especially relative humidity (RH), affect particulate nitrate photolysis. In this work, two critical attributes for atmospheric particles, i.e., phase state and bulk-phase acidity, both influenced by ambient RH, were focused to illuminate the key regulators for reactive nitrogen production from typical internally mixed systems, i.e., NaNO3 and dicarboxylic acid (DCA) mixtures. The dissolution of only few oxalic acid (OA) crystals resulted in a remarkable 50-fold increase in HONO production compared to pure nitrate photolysis at 85% RH. Furthermore, the HONO production rates (PHONO) increased by about 1 order of magnitude as RH rose from <5% to 95%, initially exhibiting an almost linear dependence on the amount of surface absorbed water and subsequently showing a substantial increase in PHONO once nitrate deliquescence occurred at approximately 75% RH. NaNO3/malonic acid (MA) and NaNO3/succinic acid (SA) mixtures exhibited similar phase state effects on the photochemical HONO production. These results offer a new perspective on how aerosol physicochemical properties influence particulate nitrate photolysis in the atmosphere.

Development of a Five-Chemical-Probe Method to Determine Multiple Radicals Simultaneously in Hydroxyl and Sulfate Radical-Mediated Advanced Oxidation Processes.

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO•)- and sulfate radical (SO4•-)-mediated oxidation, are attractive technologies used in water and wastewater treatments. To evaluate the treatment efficiencies of AOPs, monitoring the primary radicals (HO• and SO4•-) as well as the secondary radicals generated from the reaction of HO•/SO4•- with water matrices is necessary. Therefore, we developed a novel chemical probe method to examine five key radicals simultaneously, including HO•, SO4•-, Cl•, Cl2•-, and CO3•-. Five probes, including nitrobenzene, para-chlorobenzoic acid, benzoic acid, 2,4,6-trimethylbenzoic acid, and 2,4,6-trimethylphenol, were selected in this study. Their bimolecular reaction rate constants with diverse radicals were first calibrated under the same conditions to minimize systematic errors. Three typical AOPs (UV/H2O2, UV/S2O82-, and UV/HSO5-) were tested to obtain the radical steady-state concentrations. The effects of dissolved organic matter, Br-, and the probe concentration were inspected. Our results suggest that the five-probe method can accurately measure radicals in the HO•- and SO4•--mediated AOPs when the concentration of Br- and DOM are less than 4.0 µM and 15 mgC L-1, respectively. Overall, the five-probe method is a practical and easily accessible method to determine multiple radicals simultaneously.

Overlooked role of aqueous chromate (VI) as a photosensitizer in enhancing the photochemical reactivity of ferrihydrite and production of hydroxyl radical.

The reactive oxygen species (ROS) photochemically generated from natural iron minerals have gained significant attention. Amidst the previous studies on the impact of heavy metal ions on ROS generation, our study addresses the role of the anion Cr(VI), with its intrinsic photoactivity, in influencing ROS photochemical generation with the co-presence of minerals. We investigated the transformation of inorganic/organic pollutants (Cr(VI) and benzoic acid) at the ferrihydrite interface, considering sunlight-mediated conversion processes (300-1000 nm). Increased photochemical reactivity of ferrihydrite was observed in the presence of aqueous Cr(VI), acting as a photosensitizer. Meanwhile, a positive correlation between hydroxyl radical (•OH) production and concentrations of aqueous Cr(VI) was observed, with a 650% increase of •OH generation at 50 mg L-1 Cr(VI) compared to systems without Cr(VI). Our photochemical batch experiments elucidated three potential pathways for •OH photochemical production under varying wet chemistry conditions: (1) ferrihydrite hole-mediated pathway, (2) chromium intermediate O-I-mediated pathway, and (3) chromium intermediates CrIV/V-mediated pathway. Notably, even in the visible region (> 425 nm), the promotion of aqueous Cr(VI) on •OH accumulation was observed in the presence of ferrihydrite and TiO2 suspensions, attributed to Cr(VI) photosensitization at the mineral interface. This study sheds light on the overlooked role of aqueous Cr(VI) in the photochemical reactivity of minerals, thereby enhancing our understanding of pollutant fate in acid mining-impacted environments.

MXene-Integrated Perylene Anode with Ultra-Stable and Fast Ammonium-Ion Storage for Aqueous Micro Batteries.

The aqueous micro batteries (AMBs) are expected to be one of the most promising micro energy storage devices for its safe operation and cost-effectiveness. However, the performance of the AMBs is not satisfactory, which is attributed to strong interaction between metal ions and the electrode materials. Here, the first AMBs are developed with NH4 + as charge carrier. More importantly, to solve the low conductivity and the dissolution during the NH4 + intercalation/extraction problem of perylene material represented by perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), the Ti3 C2 Tx MXene with high conductivity and polar surface terminals is introduced as a conductive skeleton (PTCDA/Ti3 C2 Tx MXene). Benefitting from this, the PTCDA/Ti3 C2 Tx MXene electrodes exhibit ultra-high cycle life and rate capability (74.31% after 10 000 galvanostatic chargedischarge (GCD) cycles, and 91.67 mAh g-1 at 15.0 A g-1 , i.e., capacity retention of 45.2% for a 30-fold increase in current density). More significantly, the AMBs with NH4 + as charge carrier and PTCDA/Ti3 C2 Tx MXene anode provide excellent energy density and power density, cycle life, and flexibility. This work will provide strategy for the development of NH4 + storage materials and the design of AMBs.

Mechanistic and Kinetic Consideration of the Photochemically Generated Oxidative Organic Radicals in Dissolved Black Carbon Solutions under Simulated Solar Irradiation.

The photochemically generated oxidative organic radicals (POORs) in dissolved black carbon (DBC) was investigated and compared with that in dissolved organic matter (DOM). POORs generated in DBC solutions exhibited higher one-electron reduction potential values (1.38-1.56 V) than those in DOM solutions (1.22-1.38 V). We found that the photogeneration of POORs from DBC is enhanced with dissolved oxygen (DO) increasing, while the inhibition of POORs is observed in reference to DOM solution. The behavior of the one-electron reducing species (DBC•-/DOM•-) was employed to explain this phenomenon. The experimental results revealed that the DO concentration had a greater effect on DBC•- than on DOM•-. Low DO levels led to a substantial increase in the steady-state concentration of DBC•-, which quenched the POORs via back-electron reactions. Moreover, the contribution of POORs to the degradation of 19 emerging organic contaminants (EOCs) in sunlight-exposed DBC and DOM solutions was estimated. The findings indicate that POORs play an important role in the photodegradation of EOCs previously known to react with triplets, especially in DBC solutions. Compared to DOM solutions, POOR exhibits a lower but considerable contribution to EOC attenuation. This study enhances the understanding of pollutant fate in aquatic environments by highlighting the role of DBC in photochemical pollutant degradation and providing insights into pollutant transformation mechanisms involving POORs.

Study of the growth mechanism of a self-assembled and ordered multi-dimensional heterojunction at atomic resolution.

Multi-dimensional heterojunction materials have attracted much attention due to their intriguing properties, such as high efficiency, wide band gap regulation, low dimensional limitation, versatility and scalability. To further improve the performance of materials, researchers have combined materials with various dimensions using a wide variety of techniques. However, research on growth mechanism of such composite materials is still lacking. In this paper, the growth mechanism of multi-dimensional heterojunction composite material is studied using quasi-two-dimensional (quasi-2D) antimonene and quasi-one-dimensional (quasi-1D) antimony sulfide as examples. These are synthesized by a simple thermal injection method. It is observed that the consequent nanorods are oriented along six-fold symmetric directions on the nanoplate, forming ordered quasi-1D/quasi-2D heterostructures. Comprehensive transmission electron microscopy (TEM) characterizations confirm the chemical information and reveal orientational relationship between Sb2S3 nanorods and the Sb nanoplate as substrate. Further density functional theory calculations indicate that interfacial binding energy is the primary deciding factor for the self-assembly of ordered structures. These details may fill the gaps in the research on multi-dimensional composite materials with ordered structures, and promote their future versatile applications.

Photobleaching-induced changes in the optical and photochemical properties of algal organic matter.

Algal organic matter (AOM), a significant source of endogenous dissolved organic matter (DOM) is released in high concentrations during cyanobacterial blooms, along with cyanotoxins. Subsequent photobleaching of AOM is an important phenomenon to investigate. In this study, intracellular organic matter (IOM) and extracellular organic matter (EOM) were extracted from cultured cyanobacteria taken from Taihu Lake in China. The formation of photochemically produced reactive intermediates in different stages of IOM and EOM photobleaching was compared to Suwannee River DOM (SRDOM, reference standard DOM). Results revealed notable differences influenced by the pigment component among IOM, EOM, and SRDOM. The pigment in IOM contributed to a triplet state pool with strong energy-transfer but limited electron-transfer capabilities. Notably, IOM exhibited the highest triplets state quantum yield value in the visible region, suggesting its potential significance in pollutant degradation in deeper water layers. For EOM, one of the pools exhibits photolability and remarkable electron-transfer capability, indicating it as a high-energy triplet state component. Moreover, three cyanotoxins (MC-LR, ACA, and ATX-a) were detected in the extracted AOM, and their photodegradation was monitored during the AOM photobleaching process. This highlights the potential role of AOM as a photosensitizer in the natural self-cleaning mechanisms of water bodies, facilitating the degradation of organic pollutants through photochemical reactions. The findings of this study contribute to understanding the dynamic nature of AOM and its implications in environmental processes.

Chemodiversity of Cyanobacterial Toxins Driven by Future Scenarios of Climate Warming and Eutrophication.

Climate change and eutrophication are two environmental threats that can alter the structure of freshwater ecosystems and their service functions, but we know little about how ecosystem structure and function will evolve in future scenarios of climate warming. Therefore, we created different experimental climate scenarios, including present-day conditions, a 3.0 °C increase in mean temperature, and a "heatwaves" scenario (i.e., an increase in temperature variability) to assess the effects of climate change on phytoplankton communities under simultaneous stress from eutrophication and herbicides. We show that the effects of climate warming, particularly heatwaves, are associated with elevated cyanobacterial abundances and toxin production, driven by a change from mainly nontoxic to toxic Microcystis spp. The reason for higher cyanobacterial toxin concentrations is likely an increase in abundances because under the dual pressures of climate warming and eutrophication individual Microcystis toxin-producing ability decreased. Eutrophication and higher temperatures significantly increased the biomass of Microcystis, leading to an increase in the cyanobacterial toxin concentrations. In contrast, warming alone did not produce higher cyanobacterial abundances or cyanobacterial toxin concentrations likely due to the depletion of the available nutrient pool. Similarly, the herbicide glyphosate alone did not affect abundances of any phytoplankton taxa. In the case of nutrient enrichment, cyanobacterial toxin concentrations were much higher than under warming alone due to a strong boost in biomass of potential cyanobacterial toxin producers. From a broader perspective our study shows that in a future warmer climate, nutrient loading has to be reduced if toxic cyanobacterial dominance is to be controlled.

Pollution characteristics, ecological and health risks of herbicides in a drinking water source and its inflowing rivers in North China.

This study measured the pollution characteristics and ecological and health risks of 19 herbicides found in drinking water sources and their inflowing rivers. The targeted herbicides were prevalent in the study area, but most concentrations were well below 10 ng L-1. Acetochlor and atrazine were the dominant herbicides, although their levels were much lower than previously reported. Total herbicide residual levels were greater in April than in December and increased from upstream to downstream, resulting in the highest pollution levels found in the reservoirs, likely due to herbicides delivered from upstream and dense agricultural planting in the surrounding areas. Only atrazine and ametryn presented moderate ecological risks, while the summed risk quotients (ΣRQs) of each sample were >0.1, indicated that the total herbicide levels represented a moderate risk in all samples. For the human health risks, the risk quotients (RQ) of all target herbicides, the total RQs of each sample, and estimated life-stage RQs were far smaller than the 0.2 threshold, indicating the absence of human health risks when the water was consumed at any stage of life. However, early life stages exhibited 3-6 times higher RQ values than adulthood and should not be overlooked. And crucially, the synergistic or antagonistic effects of mixed herbicides are not well understood, and further research is needed to understand the impact of these herbicides on the ecosystem and human health, particularly possible affects in early life stages, such as infants and children.

Kinetic and Mechanistic Considerations of the Photosensitized Transformation of Chlorine in Chromophoric Dissolved Organic Matter Solutions under Simulated Solar Irradiation.

Chlorination is one of the most common disinfection methods for water treatments. Although the direct photolysis of free available chlorine (FAC) induced by solar irradiation has been extensively investigated, the photosensitized transformation of FAC caused by chromophoric dissolved organic matter (CDOM) has not previously been examined. Our results suggest that the photosensitized transformation of FAC can occur in sunlit CDOM-enriched solutions. Interestingly, the photosensitized decay of FAC can be fitted using a combined zero- and first-order kinetic model. The photogenerated O2•- from CDOM contributes to the zero-order kinetic component. The reductive triplet CDOM (3CDOM*) contributes to the pseudo-first-order decay kinetic component. The bimolecular reaction rate constants of the model triplet (3-methoxyacetophenone) with HOCl and OCl- were (3.6 ± 0.2) × 109 and (2.7 ± 0.3) × 109 M-1 s-1, respectively. Under simulated solar irradiation, the quantum yield coefficient of the reductive 3CDOM* toward FAC attenuation (fFAC = 840 ± 40 M-1) was 13 times greater than that of the oxidative 3CDOM* toward trimethylphenol (TMP) attenuation (fTMP = 64 ± 4 M-1). This study provides new insights into the photochemical transformation of FAC in sunlit surface waters, and the results are applicable when sunlight/FAC system is employed as an advanced oxidation process.

Maximizing Electron Channels Enabled by MXene Aerogel for High-Performance Self-Healable Flexible Electronic Skin.

Among the increasingly popular miniature and flexible smart electronics, two-dimensional materials show great potential in the development of flexible electronics owing to their layered structures and outstanding electrical properties. MXenes have attracted much attention in flexible electronics owing to their excellent hydrophilicity and metallic conductivity. However, their limited interlayer spacing and tendency for self-stacking lead to limited changes in electron channels under external pressure, making it difficult to exploit their excellent surface metal conductivity. We propose a strategy for rapid gas foaming to construct interlayer tunable MXene aerogels. MXene aerogels with rich interlayer network structures generate maximized electron channels under pressure, facilitating the effective utilization of the surface metal properties of MXene; this forms a self-healable flexible pressure sensor with excellent sensing properties such as high sensitivity (1,799.5 kPa-1), fast response time (11 ms), and good cycling stability (>25,000 cycles). This pressure sensor has applications in human body detection, human-computer interaction, self-healing, remote monitoring, and pressure distribution identification. The maximized electron channel design provides a simple, efficient, and scalable method to effectively exploit the excellent surface metal conduction of 2D materials.

Maximizing the ion accessibility and high mechanical strength in nanoscale ion channel MXene electrodes for high-capacity zinc-ion energy storage.

Two-dimensional transition-metal carbides (MXenes) have superhydrophilic surfaces and superior metal conductivity, making them competitive in the field of electrochemical energy storage. However, MXenes with layered structures are easily stackable, which reduces the ion accessibility and transport paths, thus limiting their electrochemical performance. To fully exploit the advantages of MXenes in electrochemical energy storage, this study reports the etching of large-sized MXene into nanosheets with nanoscale ion channels via a chemical oxidation method. While the resulting ion-channel MXene electrodes retain the excellent mechanical strength and electrical conductivity of large-sized MXene nanosheets, they can effectively shorten the ion transport distance and improve the overall electrochemical activity. The fabricated self-healing MXene-based zinc-ion microcapacitor exhibits a high areal specific capacitance (532.8 mF cm-2) at the current density of 2 mA cm-2, a low self-discharge rate (4.4 mV h-1), and high energy density of 145.1 µWh cm-2 at the power density of 2800 µW cm-2. The proposed nanoscale ion channel structure provides an alternative strategy for constructing high-performance electrochemical energy storage electrodes, and has great application prospects in the fields of electrochemical energy storage and flexible electronics.

Sunlight-Induced Interfacial Electron Transfer of Ferrihydrite under Oxic Conditions: Mineral Transformation and Redox Active Species Production.

Fe(II)-catalyzed ferrihydrite transformation under anoxic conditions has been intensively studied, while such mechanisms are insufficient to be applied in oxic environments with depleted Fe(II). Here, we investigated expanded pathways of sunlight-driven ferrihydrite transformation in the presence of dissolved oxygen, without initial addition of dissolved Fe(II). We found that sunlight significantly facilitated the transformation of ferrihydrite to goethite compared to that under dark conditions. Redox active species (hole-electron pairs, reactive radicals, and Fe(II)) were produced from the ferrihydrite interface via the photoinduced electron transfer processes. Experiments with systematically varied wet chemistry conditions probed the relative contributions of three pathways for the production of hydroxyl radicals: (1) oxidation of water (5.0%); (2) reduction of dissolved oxygen (40.9%); and (3) photolysis of Fe(III)-hydroxyl complexes (54.1%). Results also showed superoxide radicals as the main oxidant for Fe(II) reoxidation under acidic conditions, thus promoting the ferrihydrite transformation. The presence of inorganic ions (chloride, sulfate, and nitrate) did not only affect the hydrolysis and precipitation of Fe(III) but also the generation of radicals via photoinduced charge transfer reactions. The involvement of redox active species and the accompanying mineral transformations would exert a profound effect on the fate of multivalent elements and organic contaminants in aquatic environments.

Photosensitized Transformation of Hydrogen Peroxide in Dissolved Organic Matter Solutions under Simulated Solar Irradiation.

Hydrogen peroxide plays an important role in photochemical processes in aquatic environments. However, whether it can be transformed by photoexcited chromophoric dissolved organic matter (CDOM) remains unclear. Therefore, this study examined the photosensitized degradation of H2O2 in CDOM-enriched solutions under simulated solar irradiation. Our results suggest that the presence of CDOM enhances the photodegradation rate of H2O2 via the photosensitization process and ·OH is generated stoichiometrically with H2O2 attenuation. Experimental results with model photosensitizers indicate that one-electron reducing species of CDOM (CDOM·-), not triplet CDOM, is the primary reactive species that reduces H2O2 to yield ·OH. By monitoring the variation of CDOM·-, the reaction rate constant of CDOM·- with H2O2 was estimated to be 1.5-fold greater than that with O2. Furthermore, a wastewater effluent was exposed to simulated solar irradiation with the addition of H2O2, and the results demonstrated that the photodegradation of trace organic contaminants (TrOCs) was significantly enhanced by the increased ·OH level. Overall, the current study provided new insights into the photochemical formation of ·OH via the one-electron reduction of H2O2 by CDOM·-. The solar irradiation of wastewater with H2O2 enhancement could be a useful and economically beneficial advanced oxidation process for TrOC abatement.

The binding effect and photooxidation on oxytetracycline with algal extracellular polymeric substances and natural organic matter.

Surface water contains a large amount of dissolved organic matter (DOM). Interactions between DOM and micropollutants have a significant impact on micropollutant degradation. In this study, algal extracellular polymeric substances (EPS) and natural organic matter (NOM) were selected as two DOM sources and oxytetracycline (OTC) as a representative micropollutant. EPS was mainly composed of tryptophan and protein-like organics, while NOM was mainly composed of fulvic acid-like, humic acid-like, and hydrophobic acid components. In addition, OTC degradation significantly decreased when bound with EPS and the C=O and C-H bonds of CH2 or CH3 groups may be involved in binding EPS and OTC, respectively, while -COOH may be involved in the binding of NOM and OTC. Furthermore, triplet intermediates were found to play a major role in OTC photodegradation in both EPS and NOM, with the contribution calculated as 49.96% and 44.61%, respectively. Steady-state concentrations of 3EPS* in EPS and 3NOM* in NOM were 3.59 × 10-14 mol L-1 and 5.54 × 10-15 mol L-1, respectively. These results provide new insights into the degradation of antibiotic-containing wastewater in the natural environment or engineering applications.

Determination of trace organic contaminants by a novel mixed-mode online solid-phase extraction coupled to liquid chromatography-tandem mass spectrometry.

In this study, a novel mixed-mode online solid-phase extraction (SPE) method was developed to recover miscellaneous trace organic contaminants (TrOCs) from environmental water samples. Six kinds of sorbents, including C18 substances, hypercross-linked polymers (2), cation-exchange resins, anion-exchange resins, and graphitized nonporous carbons, were packed into a single online SPE cartridge. Furthermore, a fully automated analytic method was established by coupling this mixed-mode online SPE with liquid chromatography tandem mass spectrometry (online SPE-LC-MS/MS). Sixty-nine TrOCs with diverse properties were selected to examine the performance of this mixed-mode SPE cartridge in comparison with solo-mode online SPE cartridges. The method quantification limit (MQL) and the relative recovery coefficient of TrOCs in diverse water matrices, including groundwater, surface water and sewage effluent were evaluated. The MQL of most TrOCs was lower than 10 ng L-1. The relative recovery coefficients for most TrOCs in the groundwater (50/69) and surface water (38/69) matrix fit in the satisfactory range. Moreover, mixed-mode online SPE coupled with LC-high-resolution MS was applied for a suspect screening of TrOCs in sewage effluents. A series of highly polar TrOCs that had scarcely been reported by previous studies were identified by this practical and easily accessible method. Finally, this novel mixed-mode online SPE with LC-MS/MS method was applied to quantify the TrOCs in the environmental water samples.

Photosensitized Transformation of Peroxymonosulfate in Dissolved Organic Matter Solutions under Simulated Solar Irradiation.

Sulfate radical (SO4•-)-mediated advanced oxidation processes via peroxymonosulfate (PMS) activation have been extensively investigated. However, the phototransformation of PMS in sunlit dissolved organic matter (DOM) solution has not been previously examined. For the first time, the photosensitized transformation of PMS in DOM-enriched solutions under simulated solar irradiation was observed. The generation of reactive species, including 1O2, SO4•-, and •OH, was confirmed by electron paramagnetic resonance and quantified by chemical probes. SO4•- was the primary reactive species generated via the reaction of excited triplet DOM (3DOM*) with PMS. 3DOM* acted as a reactive reductant and was quickly oxidized by PMS, with an estimated reaction rate constant of (4.09 ± 0.21) × 108 M-1 s-1. Compared to 3DOM*, one-electron-reducing DOM (DOM•-) was a minor contributor to the photosensitized transformation of PMS, and the contribution of DOM•- relied on the phenolic constituents. In addition, a series of different types of DOM, including terrestrial DOM, autochthonous DOM, and effluent organic matter and its fractions, were employed to examine the photosensitized transformation kinetics of PMS. Overall, the photosensitized transformation of PMS by irradiated DOM could be a useful and economical approach to generate SO4•- under environmentally relevant conditions.

Fluorescent whitening agents in Baiyangdian Lake in North China: Analysis, occurrence, distribution and ecological risk assessment.

Fluorescent whitening agents (FWAs) are very important chemical additives that are widely applied in the industrial production field. The history of global FWA production and use spans more than 60 years, but the environmental fate of FWAs has been less reported in the public literature and most studies predate 2000; in addition, the studied FWAs were still limited to FWA71 and FWA351. In this study, the occurrence and distribution of 9 commonly used FWAs in a lake in North China were reported for the first time. We found that 6 target FWAs were prevalent in the lake, and the concentration levels were usually at the ng L-1 level. Decreasing FWA levels with increasing distance from the estuary area were observed in summer. FWA135, FWA185, and FWA367, the most detected 3 FWAs, with the ecological risk at high levels, and ΣRQ >10 were obtained from all the investigated samples, suggesting that all the sampling sites could be considered with certain ecological risk for aquatic life. As a category of heavily and widely used dyes, FWAs in environmental media have been ignored for a long time. Substantial additional research needs to be conducted to determine the environmental behavior and ecological toxicology of FWAs.

Microheterogeneous Distribution of Hydroxyl Radicals in Illuminated Dissolved Organic Matter Solutions.

Hydroxyl radicals (•OH) are important reactive species that are photochemically generated through solar irradiation of chromophoric dissolved organic matter (CDOM) in surface waters. However, the spatial distribution within the complex three-dimensional structure of CDOM has not been examined. In this study, we used a series of hydrophobic chlorinated paraffins as chemical probes to elucidate the microheterogeneous distribution of •OH in illuminated CDOM solutions. The steady-state concentration of •OH inside the CDOM microphase is 210 ± 31-fold higher than the concentration in the aqueous phase. Our results suggest that the most photochemically generated •OH are confined into the CDOM microphase. Thus, illuminated CDOM behaves as a natural microreactor for •OH-based oxidations. By including intra-CDOM •OH, the quantum yield of •OH for CDOM solutions was estimated to be 2.2 ± 0.5 × 10-3, which is 2 orders of magnitude greater than previously thought. The elevated concentrations of photogenerated •OH within the CDOM microphase may improve the understanding of hydrophobic pollutant degradation in aqueous environments. Moreover, our results also suggest that •OH oxidation may play more important roles in the phototransformation of CDOM than previously expected.