Natural Surface Water Research Articles

Film-immobilized carbon nitride for the degradation of pharmaceuticals: A continuous flow photoreactor performance upheld by excitation-emission matrix fluorescence spectroscopy

The validation of immobilized photocatalysts is a fundamental matter regarding the scaling-up process in the photocatalytic degradation of aqueous pollutants in natural surface waters. This work presents the comprehensive evaluation of graphitic carbon nitride (g-C3N4, CN) immobilized onto a polymeric film (F) placed inside a continuous flow operation planar reactor for the removal of a mixture of pharmaceuticals (i.e., venlafaxine, citalopram, carbamazepine, tramadol, ketoprofen, and diclofenac, 3 μM each) under visible light. The resulting CN/F (8 mg of CN per cm2 of film and with significant preservation of optical and structural properties after more than 350 h of reuse) yielded the complete removal under total recirculation of all pharmaceuticals after 90 min under visible light, except for ketoprofen, probably ascribed to competition for photogenerated holes, as suggested by the proposed mechanism. Under dead-end continuous flow mode, the steady-state conversion averaged 67 % in deionized water, increasing up to 76 %, and 80 % in natural surface waters obtained from the Douro River and the effluent from a wastewater treatment plant (Northwestern Portugal), respectively, related to the promotion effect of carbonates anions and organic matter. The assessment of excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis further demonstrated the removal (ca. 50 %) of the protein- and humic-like substances contained in the collected wastewater, thus evidencing the continuous flow mode performance of the immobilized photocatalyst for real environmental applications.

Nanoplastics Distribution during Ice Formation: Insights into Natural Surface Water Freezing Conditions.

The migration characteristics of nanoplastics (NPs) in the natural freezing process are complex and have attracted increasing attention in simulating natural freezing in recent years. However, simulated freezing conditions often fall short of replicating natural freezing processes, and studies on the vertical distribution of NPs remain inadequate. This study established a more realistic simulation of the natural freezing process in surface water by controlling both the air temperature (T1) and the water temperature (T2). Additionally, we introduced a new parameter, the local distribution coefficient (Kiw1), to compare with the effective distribution coefficient (Kiw2). The values of Kiw1 and Kiw2 for PS-500 nm were 0.18 and 0.21, respectively, at T1 = -20 °C and T2 = 1 °C. The results revealed the NPs concentration differed in ice, near-ice liquid, and far-ice liquid. Both properties of NPs and environmental factors could regulate the vertical distribution of NPs. The findings underscored the importance of freezing temperature regulated by T1 and T2, elucidating the roles of various influencing factors on the vertical distribution characteristics of NPs and unraveling the mechanisms of NPs distribution in the ice-water system. This study can provide valuable insights for understanding the migration of NPs in surface water in cold regions.

Ultraviolet/dielectric barrier discharge enhanced ultrafiltration for treating natural water: Performance, mechanism and iodinated disinfection by-product fate

This study employed ultraviolet (UV)/ dielectric barrier discharge (DBD) pre-treatment to mitigate ultrafiltration membrane fouling and enhance the purification efficiency of natural surface water. Moreover, as an emerging contaminant, the iodinated disinfection by-products’ fate and degradation performance were discussed. The investigation revealed that the generation of numerous active species (⋅OH, ⋅O2−, 1O2, etc) under high input voltage and low pH conditions were advantageous for augmenting membrane flux, with sodium sulfate electrolyte playing a role in promoting the formation of selective sulfate radicals. Fluorescence excitation-emission matrix spectroscopy indicated that the UV/DBD system at 5.5 kV can effectively degrade proteins and humic substances in surface water, leading to an enhancement in water quality. With the assistance of UV radiation, macromolecular organic matter underwent extensive decomposition into smaller molecules, thus creating an ideal environment for controlling membrane fouling in the UV/DBD system. Additionally, it was identified the intermediate products and degradation pathways during iopamidol degradation by UV/DBD. It also affirmed the minimal risk of disinfection by-product generation with this strategy. The study provides a viable and efficient pre-treatment approach for mitigating membrane fouling and purifying water.

Co single-atom-embedded MXene nanosheets as catalytic UF membrane instant water purification with fouling resistant performance

Two-dimensional (2D) catalytic ultrafiltration membranes, tightly assembled with MXene (Ti3C2Tx) lamellae and significantly dispersed Co single atoms (∼ 2.4 wt%), were prepared by a simple solvothermal and low-temperature reduction method. The Co-MXene membrane overcomes the conventional trade-off between selectivity and permeability, and demonstrated an instant water purification (100 % carbamazepine degradation within 240 ms) and a high membrane permeability (∼900 LMH/bar). It has been confirmed that coordinatively unsaturated Co-N1O2 accelerated electron transfer and activated the formation of 1O2 and high-valent Co-oxo species. Nano-confinement channels assembled by the small-sized lamellae facilitated the transport of water molecules. A stable treatment performance with natural surface water was achieved at 3000 L/m2. Good anti-fouling capabilities were also demonstrated with a 96 % alleviation of membrane fouling in the presence of Pseudomonas aeruginosa. These comprehensive mechanistic investigations and stable performances provide a valuable basis for preparing SACs-catalyzed membranes with highly dispersed single atoms and high permeability.

Photochemical Transformation of Ibuprofen and Chlorophene Induced by Dissolved Organic Matter.

Both ibuprofen (IBP) and chlorophene (CP) are frequently detected contaminants in surface aqueous environment. Dissolved organic matter (DOM) is an important component in water with high photo-reactivity, playing an important role in the transformation processes of various organic pollutants. This study systematically studied the influence of DOM on the photochemical transformation of IBP and CP by using humic acid as model DOM. In addition, the effect of inorganic salts on this process is also considered due to the high salt content in the ocean. Further quenching experiments and reactive oxygen species (ROSs) detection were also conducted to explore the reactive species acting on the IBP and CP transformation. Based on the products analysis and theoretical calculation, we proposed the IBP and CP transformation mechanism. Overall, this study provides some new insights into the transformation of organic pollutants in natural surface water, which is significant for assessing the fate of pollutants.

Electro-peroxone process for triclocarban and triclosan removal and reclaimed water disinfection

Water reclamation is a known solution to the water scarcity problem; however, concern over water contamination by emerging contaminants and pathogens is growing. This study investigates the simultaneous removal of emerging contaminants and pathogens by applying the continuous-flow electro-peroxone process. Triclocarban (TCC) and triclosan (TCS) were selected as model contaminants of emerging concern, while Escherichia coli strain DH5α was chosen as a representative pathogen. The effects of the initial concentration, water flow rate, and water matrices (direct reclaimed water (treated wastewater), indirect reclaimed water (groundwater), and natural surface water) on TCC, TCS, and E. coli removal were examined. The removal efficiency of TCC (2 mg/L) was up to 92.54 % in 120 min. TCS (non-ozone-resistant compound) was effectively removed in 15 min, while E. coli was instantly inactivated in 3 min. The increase in flow rate decreased the electrical energy per order (EEO) of TCC removal, with the lowest EEO of 19 kWh/m3 at 45 mL/min. The dissolved organic carbon content in water matrices (consuming O3 and H2O2) markedly inhibited the TCC removal, and the kinetic rate as well as reduced 3,4-dichloroaniline (intermediate product) formation. Overall, these findings show the use of the electro-peroxone process is effective in mitigating ozone- and non-ozone-resistant emerging contaminants (TCC and TCS) and pathogens with consideration of water matrices for reclaimed water application.

Fast and efficient remediation of antimony-contaminated surface water and field soil using alumina supported Fe–Mn binary oxide

Antimony (Sb) pollution in surface water and soil has earned extensive attention. Our previous study synthesized a new class of alumina supported Fe–Mn binary oxide (Fe–Mn@Al2O3) and found that MnO2 in the composite oxidized Sb(III) to Sb(V) and FeOOH and Al2O3 played an indispensable role in adsorption of Sb(III) and Sb(V). This study further explored the removal of Sb in surface water and in situ sequestration of Sb in Sb-contaminated field soil via Fe–Mn@Al2O3. Sb removal from water was pH independent and the removal efficiencies of Sb(III) and total Sb kept constant at 95.4% and 60.5%, respectively, over a pH range of 5.0–10.0. Increasing dissolved organic matter (DOM) from 0 to 22.8 mg/L had negligible effect on Sb(III) removal whereas inhibited the total Sb removal from 60.5% to 51.2%. Dissolved oxygen cannot oxidize aqueous Sb(III), yet, enhanced the Sb(III) removal whereas decreased the total Sb removal. The composite performed well in natural surface water with high DOM and inorganic ligands. In addition, the composite effectively immobilized Sb in field soil. 5% of the composite significantly inhibited the H2SO4 and HNO3 leachable Sb by 93.6% after 30 d. The amendment transformed the Sb speciation from more easily available fractions (i.e., exchangeable, carbonate-bound, and Fe–Mn oxides-bound species) into more stable fractions (i.e., organic material bound and residual species), leading to declined Sb bioaccessibility and reduced environmental risk. The composite facilitated a long-term stability of Sb in soil. The study demonstrated an easy, fast, and effective strategy for efficient immobilization of Sb in water and soil.

Quantification and analysis study for the morphological characteristics of urban waterbodies: Evidences from 42 cases in China

Influenced by the water design principle of Chinese classical garden, the design of urban waterbodies (lakes, ponds and wetlands) in China typically exhibits natural-like morphological characteristics, but what similarities and differences among these characteristics remain unclear. Also, the morphology of urban waterbodies is mostly designed with beauty and lacks quantitative research and methodological support, which is not favourable to the exploration of the correlation between waterbody morphology and ecology. In this study, 11 quantifiable morphological indicators are selected from water surface, shoreline complexity and water-land spatial morphology. A Grasshopper-based model for waterbody morphology quantification and analysis was constructed and applied to 42 cases in China. Combined with frequency, correlation and PCA analysis, the cases and indicators with higher composite scores generally showed more natural water surface morphology, island distribution, and diversified land and water spaces. The thresholds for the more representative indicators are 0.10–0.60 for the circularity ratio (C), 1.01–1.15 for the shoreline fractal dimension (D0), 1.58–29.42 for the island nearest-neighbour index (NN), 1.20–2.50 for the shoreline development index (SDI), 0.20–0.55 for the compactness ratio (Rc) and 0.30–0.85 for the unit water surface morphological difference ratio (ΔB). Focusing on these indicators, along with ΔB and I which describe spatial inclusiveness and island distribution, their regression equations and threshold ranges provide a primary basis for developing waterbody morphology designs and generative algorithms. This methodology has been experimentally applied in the design of a case waterbody in Suqian City Park. Overall, this study constructs and validates the feasibility of a Grasshopper-based algorithm for the quantitative analysis and morphogenetic design of waterbody morphology. It demonstrates the potential of this method for understanding complex waterbody morphology and water-land spaces, and supports a new digital methodology for the optimisation of waterscape design.

Multiple modulating energy-efficient nanofiltration membranes during high-quality drinking water towards high mineral/organic matter selectivity

Solving the low mineral/organic matter selectivity of nanofiltration (NF) membranes and realizing high permeability are effective strategies to satisfy the energy-saving production of high-quality drinking water. Controlling the interfacial polymerization (IP) reaction rate at the molecular level is a feasible approach to customize the functionality of NF membranes and simultaneously modulate multiple membrane properties. Here, we selected 1.4-piperazinediethanesulfonic acid (PIPES) as an aqueous-phase additive, and by taking advantage of the hydrogen-bonding, long-range electrostatic, and steric hindrance effects between PIPES and piperazine (PIP)monomers, as well as the reduction of solution pH, we achieved precise molecular-level regulation of the IP reaction rate. This strategy simultaneously enables the integrated tailoring of various membrane properties such as high hydrophilicity, high surface charge density, uniform pore size distribution and roughness reduction. Molecular dynamics (MD) and computational fluid dynamics (CFD) simulations were used to explore the effects of structural and morphological changes of the polyamide layer on the permeation performance, and the microscopic adsorption mechanism of foulants on the membrane was analyzed by a Quartz Crystal Microbalance (QCM). For pacificating natural surface water, the PIPES-0.75 NF membrane exhibited high permeation performance (23.7 LMH/bar), high mineral/organic selectivity (KCa2+/DOM = 16.5), excellent anti-fouling and anti-scaling properties, and reduced CO2 emissions per ton of water produced up to 90 %. In addition, an attempt was made to correlate the physicochemical properties of the membranes with the permselectivity and membrane fouling, and the economic availability of PIPES-conditioned NF membranes was examined, which provides a novel option for achieving NF in drinking water systems from the perspective of cost reduction and efficiency.

Surface Microstructure Drives Biofilm Formation and Biofouling of Graphene Oxide Membranes in Practical Water Treatment.

Significant progress has been made previously in the research and development of graphene oxide (GO) membranes for water purification, but their biofouling behavior remains poorly understood. In this study, we investigated the biofilm formation and biofouling of GO membranes with different surface microstructures in the context of filtering natural surface water and for an extended operation period (110 days). The results showed that the relatively hydrophilic and smooth Fe(OH)3/GO membrane shaped a thin and spatially heterogeneous biofilm with high stable flux. However, the ability to simultaneously mitigate biofilm formation and reduce biofouling was not observed in the weakly hydrophilic and wrinkled Fe/GO and H-Fe(OH)3/GO membranes. Microbial analyses revealed that the hydrophilicity and roughness distinguished the bacterial communities and metabolic functions. The organic matter-degrading and predatory bacteria were more adapted to hydrophilic and smooth GO surfaces. These functional taxa were involved in the degradation of extracellular polymeric substances (EPS), and improved biofilm heterogeneity. In contrast, the weakly hydrophilic and wrinkled GO surfaces had reduced biodiversity, while unexpectedly boosting the proliferation of EPS-secreting bacteria, resulting in increased biofilm formation and aggravated biofouling. Moreover, all GO membranes achieved sustainable water purification during the entire operating period.

Precipitation and time effects on vegetation change in Southern Arizona abandoned farmland

Farmland abandonment represents a significant issue globally, and in arid environments reclaiming ecosystems is challenging. In the Sonoran Desert, much irrigated farmland has been abandoned since 1950. Our objective was to compare changes in vegetative (canopy) cover and species over a 26-year period on abandoned farmland and unfarmed controls in southcentral Arizona (precipitation <300 mm/year). We evaluated time since abandonment and precipitation effects on these variables between 1976 and 2003 with point frame methods on eight farmland sites using stepwise multiple regression. Results suggest antecedent precipitation (AP) is more important than time since abandonment in explaining cover changes. On 26 abandoned sites, we used non-parametric ANOVA to show that vegetative cover (point frame and line intercept methods) declined by about 43% from 1977 to 2023, which was greater than on non-farmed controls. Few farmlands had cover and species composition like reference communities in 2003. Paired farmland-control sites exhibited similar vegetation in 1977 and 2003 suggesting local factors (e.g., soil chemistry, roadways) may have overwhelmed that of farming. Uninterrupted (natural) surface water flow may predict where revegetation was most successful. Our research indicates that farmland may exist in alternative states, and passive revegetation will not reestablish native Sonoran Desert communities on most abandoned farmland sites.

Study on Mapping and Identifying Risk Areas for Multiple Particulate Matter Pollution at the Block Scale Based on Local Climate Zones

As China’s urbanization process accelerates, the issue of air pollution becomes increasingly prominent and urgently requires improvement, based on the fact that environmental conditions such as meteorology and topography are difficult to change. Therefore, relevant optimization studies from the perspective of architectural patterns are operable to mitigate pollution. This paper takes the Wenhua Road block in Shenyang, China, as the research object; obtains the concentration data of three kinds of particulate matter through fixed and mobile monitoring; and analyzes the spatial distribution characteristics of Local Climate Zones ( LCZ) and particulate matter in the block based on the ArcGIS platform, identifies high-risk areas, and excavates the influence of LCZ on the concentrations of three kinds of particulate matter. The results show that the spatial distribution characteristics of PM1, PM2.5, and PM10 under the same pollution level are relatively similar, while the spatial heterogeneity of the distribution of the same particulate matter under different pollution levels is higher. The time-weighted results show that the PM1 pollution level in the block ranges from 44 to 51 μg/m³, PM2.5 ranges from 75 to 86 μg/m³, and PM10 ranges from 87 to 99 μg/m³. The pollution hot spots throughout the year are located in the central, eastern and western parts of the study area. In terms of the relationship between the LCZ and particulate matter, with the increase in the particulate matter diameter, the correlation between the three kinds of particulate matter and LCZ are all enhanced. The built-up LCZ always has a larger average concentration of particulate matter than that of the natural LCZ, and building height and building density are the main factors causing the difference. In the optimal design of the risk area, the proportion of natural vegetation or water surface should be increased and the building height should be properly controlled and the building density should be reduced in the renewal of the urban building form. This study will largely improve the spatial refinement of the optimization of urban architectural patterns oriented to mitigate particulate matter pollution.

Mesoporous architectural magnetic halloysite-polymer beads for removing toxic streptomycin from water: A sustainable remediation approach

Streptomycin (STR) is a widely used antibiotic to treat various infectious diseases in humans and animals. Increased STR production and distribution result in harmful residue in soil and water. Consequently, STR exists in biotic- and abiotic-counterpart of the environment and poses potential toxicity and risk due to its bioaccumulation and biomagnification properties. Sustainable remediation of STR from wastewater requires selective, minimal, low-cost, regenerable, and reusable materials as adsorbents. In this study, magnetic-halloysite incorporated polymer composite beads (SPHM) were synthesized and used for the efficient clean-up of toxic STR from wastewater. SPHM has a mesoporous structure with an abundance of oxygen-containing functional groups and exhibits a synergistic STR clean up performance (qm = 235.71 ± 13.98 mg/g). Sorption and interfacial studies revealed that diffusion, hydrophobic and ionic interactions, including electrostatic interaction, are involved in STR remediation. Electrostatic interaction plays a vital role alongside the physical sorption mechanism due to the presence of hydroxyl and carboxyl groups induced from poly (vinyl alcohol) and sodium alginate. Moreover, X-ray photoelectron spectroscopy (XPS) and Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses confirm the involvement of opposing charged groups of SPHM and STR in adsorption. SPHM can be magnetically separated in just 20 s and is regenerable and reusable up to 10 times, with outstanding performance and stability. The sorption process requires only a minimal amount of SPHM, i.e., 0.5 g/L for STR clean-up. Even the natural surface water composition did not affect its performance. Hence, natural nanoclay-based, biocompatible and low-cost SPHM has a great potential for the sustainable remediation of streptomycin and other similar antibiotics from wastewater.

The promise of coupling piezo-catalysis and activated persulfate using dual-frequency ultrasound: A novel synergistic method of natural water disinfection

Piezo-coupled catalysis, which is driven by dual-frequency ultrasound (DFUS) at high frequencies (>100 kHz), has emerged as a promising technique for intensifying the oxidation processes in aqueous media. This study aimed at evaluating the performance of high-frequency DFUS (0.12 + 1.7 MHz) coupled with ZnO microparticles (1 µm) and persulfate (S2O82−) for disinfection of filtered natural surface water, spiked with E. coli and E. faecalis, as well as unfiltered natural water with indigenous microflora. Despite the longer treatment times required (as compared to deionized water), this hybrid system provided the fastest inactivation, exhibiting a synergy between DFUS+ZnO and DFUS+S2O82− processes and a high energy-efficiency (231.5 and 91.3 CFU/J for E. coli and E. faecalis, respectively). The obtained results revealed the feasibility of DFUS-driven piezo-coupled catalysis using persulfate for advanced water disinfection.

The colloidal stability of molybdenum disulfide nanosheets in different natural surface waters: Combined effects of water chemistry and light irradiation

With the increasing production and application, more molybdenum disulfide (MoS2) nanosheets could be released into environment. The aggregation and dispersion of MoS2 nanosheets profoundly impact their transport and transformation in the aquatic environment. However, the colloidal stability of MoS2 remains largely unknown in natural surface waters. This study investigated the colloidal stability of MoS2 nanosheets in six natural surface waters affected by both light irradiation and water chemistry. Compared to that of the pristine MoS2 nanosheets, the colloidal stability of MoS2 photoaged in ultrapure water declined. Light irradiation induced the formation of Mo-O bonds, the release of SO42− species, and the decrease in 1T/2H ratio, which reduced negative charge and enhanced hydrophobicity. However, the colloidal stability of MoS2 photoaged in natural surface waters was increased relative to that in ultrapure water not only for the smaller extent of photochemical transformation but more importantly the surface modification by water chemistry. Furthermore, the colloidal stability of MoS2 photoaged in natural surface waters followed the order of sea water > lake water > river water. The abundant cations (e.g., Ca2+ and Mg2+) in sea water facilitated the covalent grafting (S-C bonds) of more dissolved organic matter (DOM) on MoS2 via charge screening and cation bridging, thus inducing stronger electrostatic repulsion and steric effect to stabilize nanosheets. The crucial role of the covalent grafting of DOM was further confirmed by the positive correlation between the critical coagulation concentration values and S-C ratios (R2 = 0.82, p < 0.05). Our results highlighted the dominant role of water chemistry than light irradiation in dictating the colloidal stability of MoS2 photoaged in natural surface waters, which provided new insight into the environmental behavior of MoS2 in aquatic environment.

Microplastics removal from natural surface water by coagulation process

The present study aimed to compare the efficiency of microplastic removal from natural surface water by coagulation with ferrous and aluminum sulfate in the presence and without the selected coagulant aids. Coagulation with Fe(II) and Al(III) sulfates at doses conventionally used for drinking water treatment (10 – 80 mg.L−1) was effective in polystyrene and polyvinyl chloride removal. Fe(II) salts showed up to 5 % efficiency higher in microplastic removal under the conditions of the experiment. The addition of the flocculating agent to support the aggregation of flocs allowed for the improvement of microplastic removal efficiency at the same dose of up to 10 %. Based on the results, flocculating agents are recommended for microplastic removal. Coagulation without flocculating agent amendment is enough to remove most microplastics if filtration is applicable.

Enhanced mitigation of membrane fouling and degradation of perfluorooctanoic acid in the treatment of natural surface water through the application of dielectric barrier discharge/sulfite

The present study employed a dielectric barrier discharge (DBD)/sulfite system to mitigate membrane fouling and enhance the degradation of perfluorooctanoic acid (PFOA) in surface water. Results showed that the membrane flux was remarkably enhanced by 93.6%, and the degradation of PFOA showed an impressive increase of 87.9%. The synergistic redox effect of free radicals, including hydroxyl radical (•OH), sulfate radical (SO4∙-), electron (e-/eaq-), su-peroxide anion radicals (∙O2-), and other radical, played a crucial role in mitigating membrane fouling, accounting for 36.26%, 30.10%, 18.69%, 6.75%, and 8.20%, respectively. The correlation analysis revealed that effective removal of UV254 and TOC emerged as the most crucial factors positively contributing to mitigating membrane fouling. Additionally, SO4∙-, •OH, and eaq- were identified as the primary active substances responsible for attacking PFOA, accounting for 41.30%, 25.20%, and 23.70%, respectively. The degradation pathway of PFOA was proposed through analysis using density functional theory and mass spectrometry, reducing the biotoxicity of its degradation products. This study presents a suitable strategy for simultaneous mitigation of membrane fouling and enhancement of PFOA degradation, which holds great potential for advancing the field of water treatment towards practical applications.

The effects of interaction with audiovisual elements on perceived restoration in urban parks in freezing weather

Urban green spaces, crucial for urban residents’ wellbeing, offer restorative benefits mainly through natural elements, as established in existing literature which were generally conducted in warm weather. Yet, cold weather modifies how both natural and anthropogenic elements appear and function, and hence their impacts on restorativeness may deviate. In cold weather, whether an urban green space would be overall restorative, and which type of elements would be more beneficial remains poorly understood. Here we present the results of a walk experience experiment with 20 participants on three typical landscape routes in a waterside park in a winter city. Participants' restorative experiences and their visual and auditory exposures were evaluated using the Restorative Experience Scale, eye tracker, and binaural acoustic measurement system. By comparing participants’ restorative experience and their visual and auditory exposure, we found that in the cold weather, natural elements vegetation and water surfaces, the appearances of which were subjective to major seasonal changes, ceased to promote restorativeness. Aesthetically pleasing landscape decorations instead promoted the restorativeness of the environment strongly (β = 0.286, p = 0.004). Additionally, soundscape appropriateness (β = 0.320, p = 0.002) and lower environmental loudness (for N5, β = −0.430, p = 0.000) were also strong positive influencers. These collectively explained 49.7 % of the overall restorative experience in a multiple linear regression model (adjusted R2 = 0.497). Our findings should guide the rational wellbeing-directed landscape design of restorative environments in cold regions to allow sustained restorativeness throughout the year.

Role of low-molecular-weight organic compounds on photochemical formation of Mn(III)-ligands in aqueous systems: Implications for BPA removal

Aqueous trivalent manganese [Mn(III)], an important reactive intermediate, is ubiquitous in natural surface water containing humic acid (HA). However, the effect of low-molecular-weight organic acids (LMWOAs) on the formation, stability and reactivity of Mn(III) intermediate is still unknown. In this study, six LMWOAs, including oxalic acid (Oxa), salicylic acid (Sal), catechol (Cat), caffeic acid (Caf), gallic acid (Gal) and ethylene diamine tetraacetic acid (EDTA), were selected to investigate the effects of LMWOAs on the degradation of BPA induced by in situ formed Mn(III)-L in the HA/Mn(II) system under light irradiation. The chromophoric constituents of HA could absorb light radiation and generate superoxide radical to promote the oxidation of Mn(II) to form Mn(III), which was further involved in transformation of BPA. Our results implied that different LMWOAs did significantly impact on Mn(III) production and its degradation of BPA due to their different functional group. EDTA, Oxa and Sal extensively increased the Mn(III) concentration from 50 to 100 μM compared to the system without LMWOAs, following the order of EDTA > Oxa > Sal, and also enhanced the degradation of BPA with the similar patterns. In contrast, Cat, Caf and Gal had an inhibitory effect on the formation of Mn(III), which is likely because they consumed the superoxide radicals generated from irradiated HA, resulting in the inhibition of Mn(II) oxidation and further BPA removal. The product identification and theoretical calculation indicated that a single electron transfer process occurred between Mn(III)-L and BPA, forming BPA radicals and subsequent self-coupling products. Our results demonstrated that the LMWOAs with different structures could alter the cycling process of Mn via complexation and redox reactions, which would provide new implications for the removal of organic pollutants in surface water.

The high cost of movement in an arid working landscape for an endangered amphibian.

Connectivity is essential for the maintenance of genetic diversity and stability of wildlife populations. Drought and changing precipitation regimes have caused natural aquatic amphibian breeding habitats to disappear or become isolated and have led to the replacement of natural surface water with artificial livestock water tanks. Terrestrial movement is the only means of responding to aquatic threats in arid landscapes and to allow population connectivity. Aridity may present an impenetrable barrier in hydrologically fragmented environments. We used a facultatively paedomorphic and federally endangered salamander to assess the challenges of movement across arid working lands. Sonoran tiger salamanders (Ambystoma mavortium stebbinsi) are endemic to the San Rafael Valley of southeastern Arizona, United States of America, where they depend on livestock water tanks as breeding habitat. The ecology of this species' metamorphs outside of stock tanks is virtually unknown. To assess survival on the landscape during terrestrial movement we used radio-transmitters to track 78 adult metamorphosed salamanders over 2 years. Sonoran tiger salamanders moved up to 1 km from the tank edge, and average distances moved of over 400 m were higher than most Ambystoma species. However, during the study period, none reached neighboring stock tanks. We found high mortality due to predation and desiccation. Individuals that dispersed to terrestrial habitat in summer survived longer than individuals that dispersed in spring. High mortality suggests terrestrial movement is exceptionally risky and may contribute to isolated subpopulations and elevated levels of inbreeding. Conservation actions that improve and maintain artificial aquatic habitats as well as increase connectivity may improve long-term management for pond-breeding amphibians in arid regions.