Seasonal changes of chemodiversity along with microbial succession in a municipal wastewater treatment plant.

The relationship between chemodiversity and microbial succession in wastewater treatment plants (WWTPs) is highly intricate and bidirectional. The specific contribution of the microbial community to changes in the composition of dissolved organic matter (DOM) within different biological treatment units remains unclear, as does the reciprocal influence of DOM composition on microbial succession. In this study, spectroscopy ((Excitation-emission matrix) EEM-PARAFAC, Ultraviolet (UV)-spectrum, Fourier transform infrared spectrometer (FT-IR)), Liquid chromatograph mass spectrometer (LC‒MS) and Fourier transform ion cyclotron resonance (FT-ICR) MS along with high-throughput sequencing technology were used to explore the relationship between chemodiversity and microbial succession in WWTPs concerning seasonal changes. The results showed that WWTPs with anaerobic/anoxic/oxic (A2O) processes can metabolize and transform most of the wastewater DOM, and the anaerobic unit has the highest removal rate for fluorescence DOM (FDOM, 14.07%-64.43%); the anaerobic unit increased aliphatic/proteins and lignin-like molecules but decreased relative intensity, while the anoxic unit removed unsaturated hydrocarbons, aromatic structures, and lignin-like substances. The impact of seasonal changes on the composition and removal of FDOM and DOM in wastewater treatment is significant, and the variations that occur during different seasons affect microbial activity, as well as the production, degradation, and transformation of organic compounds throughout the wastewater treatment process. Network analysis shows that Parcubacteria_genera_incertae_sedis plays a crucial role in DOM chemodiversity, highlighting the crucial contribution of microbial communities to both the structure and operation of the entire DOM network. The results in this study could provide some theoretical and practical basis for guiding the process optimization of WWTPs.

Humic-like components in dissolved organic matter inhibit cadmium sequestration by sediment.

China's lakes are plagued by cadmium (Cd) pollution. Dissolved organic matter (DOM) significantly regulates Cd(II) transport properties at the sediment-water interface. Understanding the effects of different DOM components on the transportation properties of Cd(II) at the sediment-water interface is essential. In this study, typical DOM from different sources was selected to study Cd(II) mobility at the sediment-water interface. Results showed that terrestrial-derived DOM (fulvic acids, FA) and autochthonous-derived DOM (α-amylase, B1) inhibit Cd(II) sequestration by sediments (42.5% and 5.8%, respectively), while anthropogenic-derived DOM (sodium dodecyl benzene sulfonate, SDBS) increased the Cd(II) adsorption capacity by sediments by 2.8%. Fluorescence quenching coupling with parallel factor analysis (EEM-PARAFAC) was used to characterize different DOM components. The results showed that FA contains three kinds of components (C1, C3: protein-like components, C2: humic-like components); SDBS contains two kinds of components (C1, C2: protein-like components); B1 contains three kinds of components (C1, C2: protein-like components, C3: humic-like components).Three complex reaction models were used to characterize the ability of Cd(II) complex with DOM, and it was found that the humic-like component could hardly be complex with Cd(II). Accordingly, humic-like components compete for Cd(II) adsorption sites on the sediment surface and inhibit Cd(II) adsorption from sediments. Fourier transform infrared spectroscopy (FTIR) of the sediment surface before and after Cd(II) addition was analyzed and proved the competitive adsorption theory. This study provides a better understanding of the Cd(II) mobilization behavior at the sediment-water interface and indicates that the input of humic-like DOM will increase the bioavailability of Cd.

Exploring the diversity of dissolved organic matter (DOM) properties and sources in different functional areas of a typical macrophyte - derived lake combined with optical spectroscopy and FT-ICR MS analysis.

Lake Baiyangdian is one of China's largest macrophyte - derived lakes, facing severe challenges related to water quality maintenance and eutrophication prevention. Dissolved organic matter (DOM) was a huge carbon pool and its abundance, property, and transformation played important roles in the biogeochemical cycle and energy flow in lake ecosystems. In this study, Lake Baiyangdian was divided into four distinct areas: Unartificial Area (UA), Village Area (VA), Tourism Area (TA), and Breeding Area (BA). We examined the diversity of DOM properties and sources across these functional areas. Our findings reveal that DOM in this lake is predominantly composed of protein - like substances, as determined by excitation - emission matrix and parallel factor analysis (EEM - PARAFAC). Notably, the exogenous tyrosine-like component C1 showed a stronger presence in VA and BA compared to UA and TA. Ultrahigh - resolution mass spectrometry (FT - ICR MS) unveiled a similar DOM molecular composition pattern across different functional areas due to the high relative abundances of lignan compounds, suggesting that macrophytes significantly influence the material structure of DOM. DOM properties exhibited specific associations with water quality indicators in various functional areas, as indicated by the Mantel test. The connections between DOM properties and NO3N and NH3N were more pronounced in VA and BA than in UA and TA. Our results underscore the viability of using DOM as an indicator for more precise and scientific water quality management.

Dissolved organic matter characteristics linked to bacterial community succession and nitrogen removal performance in woodchip bioreactors.

Woodchip bioreactors are an eco-friendly technology for removing nitrogen (N) pollution. However, there needs to be more clarity regarding the dissolved organic matter (DOM) characteristics and bacterial community succession mechanisms and their association with the N removal performance of bioreactors. The laboratory woodchip bioreactors were continuously operated for 360 days under three influent N level treatments, and the results showed that the average removal rate of TN was 45.80 g N/(m3·day) when the influent N level was 100 mg N/L, which was better than 10 mg N/L and 50 mg N/L. Dynamic succession of bacterial communities in response to influent N levels and DOM characteristics was an important driver of TN removal rates. Medium to high N levels enriched a copiotroph bacterial module (Module 1) detected by network analysis, including Phenylobacterium, Xanthobacteraceae, Burkholderiaceae, Pseudomonas, and Magnetospirillaceae, carrying N-cycle related genes for denitrification and ammonia assimilation by the rapid consumption of DOM. Such a process can increase carbon limitation to stimulate local organic carbon decomposition to enrich oligotrophs with fewer N-cycle potentials (Module 2). Together, this study reveals that the compositional change of DOM and bacterial community succession are closely related to N removal performance, providing an ecological basis for developing techniques for N-rich effluent treatment.

Characteristics and phytotoxicity of hydrochar-derived dissolved organic matter: Effects of feedstock type and hydrothermal temperature.

The dissolved organic matter (DOM) with high mobility and reactivity plays a crucial role in soil. In this study, the characteristics and phytotoxicity of DOM released from the hydrochars prepared from different feedstocks (cow manure, corn stalk and Myriophyllum aquaticum) under three hydrothermal carbonization (HTC) temperatures (180, 200 and 220°C) were evaluated. The results showed that the hydrochars had high dissolved organic carbon content (20.15 to 37.65 mg/g) and its content showed a gradual reduction as HTC temperature increased. Three fluorescent components including mixed substance of fulvic acid-like and humic acid-like substances (C1, 30.92%-58.32%), UVA humic acid-like substance (C2, 25.27%-29.94%) and protein-like substance (C3, 11.74%-41.92%) were identified in hydrochar DOM by excitation emission matrix spectra coupled with parallel factor analysis. High HTC temperature increased the relative proportion of aromatic substances (C1+C2) and humification degree of hydrochar DOM from cow manure, while it presented adverse effects on the hydrochar DOM from corn stalk and Myriophyllum. aquaticum. The principal component analysis suggested that feedstock type and HTC temperature posed significant effects on the characteristics of hydrochar DOM. Additionally, seed germination test of all hydrochar DOM demonstrated that the root length was reduced by 8.88%-26.43% in contrast with control, and the germination index values were 73.57%-91.12%. These findings provided new insights into the potential environmental effects for hydrochar application in soil.

Spatial and seasonal variability of chlorophyll-a, total suspended matter, and colored dissolved organic matter in the Sundarban mangrove forest using earth observation and field data.

The Sundarbans, the world's largest mangrove forest, confronts potential threats from various anthropogenic activities leading to degradation of its aquatic ecosystem. To examine the current status of the aquatic ecosystem, this study aimed to evaluate the spatial and seasonal fluctuation of three principal water quality attributes namely Chlorophyll-a (Chl-a), Total Suspended Matter (TSM), and Colored Dissolved Organic Matter (CDOM) in the complex tidal river systems of the Sundarban mangroves forest using earth observation and in-situ data. A set of two bio-optical algorithms, Ocean color-2 (OC-2) and Ocean color-3 (OC-3), were applied to measure Chl-a concentration, Green/NIR and the Red/NIR band ratio algorithms were used for TSM and the Case-2 Regional Coast Color (C2RCC) processor in the SNAP software was applied to obtain CDOM concentration in study area. A total of 50 in-situ samples were collected during post-monsoon and pre-monsoon to validate the results. Our results clearly demonstrated seasonal variability with higher Chl-a concentrations in post-monsoon than pre-monsoon. This was due to the OC-2 algorithm which produced better results with R2 = 0.73, RMSE = 0.27 for post-monsoon and R2 = 0.55, RMSE = 0.32 for pre-monsoon. Whilst, TSM concentration performed the best with R2 = 0.77; RMSE = 15.82 and R2 = 0.65; RMSE = 33.96 in post-monsoon and pre-monsoon according to the Green/NIR band ratio method. The nearshore and narrow waterway regions had the highest concentrations of TSM and Chl-a, whereas the offshore regions had the lowest. Strong association were observed between the in-situ and satellite derive absorption coefficient, aCDOM (m-1). The R2 for a CDOM during pre-monsoon was 0.65 and throughout the post-monsoon, it was 0.74. Pre-monsoon concentrations were found to be higher due to marine sources and higher wind speeds, possibly due to sediment resuspension. This kind of baseline evaluation will help to detect threats, direct preventive measures for the protection of biodiversity, and deepen our knowledge of these distinct ecosystems. The results will help develop flexible management and preservation plans that can adjust to both natural and man-made changes.

Are pools created when restoring extracted peatlands biogeochemically similar to natural peatland pools?

In the last 25 years, several degraded peatlands in eastern Canada have been restored toward their natural structure. Pools are common in natural peatlands and are important habitats for unique flora and fauna. Because of their ecological value, pools have been created in some restored peatland sites. Nevertheless, the biogeochemistry of created pools in a restoration context has seldom been studied. The objective of our study is to characterize the biogeochemistry of created pools from restored peatlands and compare them with natural pools along a chronosequence since their creation. We measured different biogeochemical variables (pH, concentrations of nitrogen (N), phosphorus (P), dissolved organic carbon (DOC), dissolved organic matter (DOM), base cations-calcium (Ca), sodium (Na), magnesium (Mg), and potassium (K)-and dissolved gases-methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O)-) in 61 pools distributed over seven peatlands in eastern Canada. The sites represent a range of conditions, from natural to restored peatlands with pools ranging from 3 to 22 years old. Created and natural pools had distinctive biogeochemistry, with created pools being generally less acidic (pH >5) and 2.5 times more concentrated in nutrients (N and P) than in natural pools. DOC, N, P, dissolved gases, and base cations concentrations were lower in natural pools than in created pools, and varied between created sites. The oldest created pools (age >17 years) tend to approach the biogeochemical characteristics of natural pools, indicating that created pools may, over time, provide habitats with similar conditions to natural pools. A return of created pools to a natural pool-like biogeochemistry could thus inform on the success of peatland restoration.

Molecular fractionation mediates genotoxicity evolution of hydrochar-derived dissolved organic matter at the iron oxyhydroxides-water interface.

Adsorption fractionation of dissolved organic matter (DOM) induced by soil minerals is a common geochemical process, which has been widely documented on natural DOM. Hydrochar is a promising functional material in soil remediation but can continuously release abundant endogenic DOM with potential biotoxicity. However, adsorption fractionation at molecular level and its influence on toxicity evolution of hydrochar-derived DOM (HDOM) at genetic level at the soil-water interface remain poorly understood. Herein, we investigated the molecular fractionation of HDOM on three typical soil iron minerals (i.e., ferrihydrite, goethite, and hematite). Results from ultrahigh-resolution mass spectrum showed that HDOM molecules with high molecular weight and high contents of unsaturated oxidized or aromatic structures (e.g., unsaturated phenolic compounds, polyphenols, and organic acids) were preferentially absorbed by iron oxyhydroxides, while aliphatic molecules and poorly oxygenated compounds (e.g., hydrocarbon, phenols, and alcohols) were retained in aqueous phase. Furthermore, we quantitatively evaluated their genotoxicity variation using a toxicogenomics assay using green fluorescence protein-fused whole-cell array, and results showed that oxidative, protein, membrane, and DNA stresses were primary responses upon exposure to original HDOM. Interface fractionation induced by iron oxyhydroxides significantly reduced genotoxicity of HDOM, especially for oxidative, membrane and DNA stresses. Overall, the selective absorption of HDOM molecules by iron oxyhydroxides shifted its biotoxicity, which might change the ecological effects of hydrochar amendment, e.g., microbial community structure, environmental pollutant transformation, and even the ecological function of terrestrial and aquatic ecosystems. These findings would contribute to unraveling the environmental geochemistry process of HDOM in the natural soil-water interface and provide a new insight into the biotoxicity of hydrochar usage to terrestrial and aquatic environments.

Aging of biodegradable microplastics and their effect on soil properties: Control from soil water.

The ecological risks of biodegradable microplastics (BMPs) to soil ecosystems have received increasing attention. This study investigates the impacts of polylactic acid microplastics (PLA-MPs) and polybutylene adipate terephthalate microplastics (PBAT-MPs) on soil properties of black soil (BS) and fluvo-aquic soil (FS) under three water conditions including dry (Dry), flooded (FL), and alternate wetting and drying (AWD). The results show that BMPs exhibited more evident aging under Dry and AWD conditions compared to FL condition. However, BMPs aging under FL condition induced more substantial changes in soil properties, especially dissolved organic carbon (DOC) concentrations, than under Dry and AWD conditions. BMPs also increased the humification degree of soil dissolved organic matter (DOM), particularly in BS. Metagenomic analysis of PBAT-MPs treatments showed different changes in microbial community structure depending on soil moisture. Under Dry conditions, PBAT-MPs enhance the ammonium-producing process of soil microbial communities. Genes related to N nitrification and benzene degradation were enriched under AWD conditions. In contrast, PBAT-MPs do not change the abundance of genes related to the N cycle under FL conditions but significantly reduce genes related to benzene degradation. This reduction in benzene degradation genes under FL condition might potentially slow down the degradation of PBAT-MPs, and could lead to temporary accumulation of benzene-related intermediates. These findings highlight the complex interactions between BMPs, soil properties, and microbial communities, emphasizing the need for comprehensive evaluations of BMPs' environmental impacts under varying soil water conditions.

Direct and indirect photodegradation mechanism of ractopamine in aquatic environment.

As a kind of typical lean meat essences and veterinary drugs, ractopamine (RAC) has been frequently detected in agricultural sewage and livestock, posing potential risk to both aquatic ecosystems and human health. Despite its widespread occurrence, the environmental fate of RAC remains unclear. Here, the mechanisms underlying the direct and indirect photodegradation of RAC was investigated under UV light irradiation at wavelengths of 275 and 365 nm, respectively. The effect of pH, initial concentration, and co-existing ions were examined. For direct photodegradation, the quantum yield of RAC increased with increasing pH values. In solutions containing dissolved organic matter (DOM), indirect photodegradation of RAC intensified with increasing pH values, and the initial concentration of DOM accelerated the process. The presence of Cu2+ was found to inhibit both direct and indirect photodegradation of RAC. Electron spin resonance (ESR) spectrometry and quenching experiments revealed that direct photodegradation was primarily attributed to the decomposition of the triplet state of RAC. Both the triplet state of DOM (3DOM*) and singlet oxygen contributed to the indirect photodegradation of RAC. LC-MS/MS analysis indicated that oxidation of the phenol group and subsequent decarboxylation were the principal photodegradation processes. The energies of each state of RAC and the active sites of RAC molecules were computed using frontier molecular orbitals and Fukui indices based on density functional theory. Combining the analysis of photoproducts with energy calculation, pathways of the direct and indirect photodegradation of RAC were proposed. These findings unveiled the photochemical behaviors of RAC concerning the removal and attenuation in aquatic environment.

Molecular properties of dissolved organic matter leached from microplastics during photoaging process.

The occurrence of dissolved organic matter (DOM) derived from microplastics (MPs) and its effect on aquatic systems has attracted great interest recently. However, the photoaging effect on the molecular structure of MP-derived DOM (MP-DOM) remains unclear. This paper presents the characteristics of DOM leached from three commercial MPs, i.e., polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) under UV irradiation. With prolonged aging periods, the surface roughness and oxygen-containing groups on the surface of MPs increase as more DOM leachate is generated. Moreover, the dissolved organic carbon (DOC) content of the leached DOM from PET MPs varies from 0.52 mg/L to 2.25 mg/L, which is higher than PE and PP MPs, due to the larger increased surface reaction area and the cleavage of the benzene ring. According to the excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), the plastic-derived protein/phenolic-like components (C1 and C3) in MP-DOM were changed into photo-induced humic-like components (C2), which were closely related to the intermediates during photo-oxidation. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis further identified that the highest proportion of antioxidants (24.8 %∼34.6 %) was contained in MP-DOM. Plasticizers, intermediate additives, and antimicrobial agents were also detected in DOM leachate. Correlation analysis identified that the composition of leached DOM was positively correlated with the surface roughness, the carbonyl index (CI), and the chemical groups of MPs. Moreover, a partial least square structural equation model (PLS-SEM) analysis further verified that the change of morphology and the chemical structure of MPs could affect the DOM structures and fractions directly. This study provides an in-depth understanding of the composition of MP-derived DOM during the aging process, as well as a comprehensive environmental impact assessment of MPs.

Influence of spectral and molecular composition of dissolved organic matter on labile Cd mobility in riparian soils in the Three Gorges Reservoir, China.

The periodic anti-seasonal inundation of the Three Gorges Reservoir (TGR) leads to changes in the molecular composition of dissolved organic matter (DOM) in riparian soils, further impacting the geochemical processes and ecological risk of heavy metals. However, the intrinsic driving mechanisms of DOM influencing the cadmium (Cd), a major pollutant in riparian soils in TGR, at the molecular level remain unclear. In this study, the DOM molecular composition, labile Cd in riparian soils and the key driving mechanism before and after flooding were explored using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), the diffusive gradients in thin films (DGT) and partial least squares path modeling (PLS-PM). A spectral analysis revealed that after flooding, the relative abundance of terrestrial humic-like substances decreased whereas that of microbial humic-like substances increased. Furthermore, FT-ICR MS analysis revealed that the relative abundance of lignin, the main molecular components of DOM in riparian soils, increased after flooding. The linkage of DOM with the concentration and kinetic processes of labile Cd indicated that the higher aromaticity and unsaturation, larger molecular weight, and higher humification level of DOM promoted the mobility of labile Cd from the soil solid phase to the liquid phase. In particular, our findings indicated that at the molecular level, the most significant factor influencing the mobility of labile Cd was lignin, which was primarily governed by the complexation of lignin with labile Cd. The complexation mechanism between lignin and labile Cd resulted in increased ecotoxicological risk of labile Cd after flooding, while the overall ecotoxicological risk was low in riparian soils in TGR. This study provides better insight into the geochemical cycling and fate of toxic elements in reservoir ecosystems under the change of hydrological regime.

Response of phytoplankton community to dissolved organic matter composition and lake trophic state.

Human activities, intensified urbanization and climate changes altered source and quantity of dissolved organic matter (DOM), complicating its interaction with phytoplankton in aquatic ecosystems. However, relationship between DOM and phytoplankton in urban lakes strongly disturbed by human activities was still unclear. Thus, a whole-year sampling campaign was conducted in the Tangxun Lake, China's largest urban lake, to reveal the interaction between DOM and phytoplankton. Results indicated that trophic state in the Tangxun Lake varied from mesotrophic to moderately eutrophic. Parallel factor analysis method combined with excitation-emission matrix fluorescence spectroscopy revealed that DOM in the Tangxun Lake consisted of three components, two protein-like components (C1, C3), and one humic-like component (C2). Protein-like components occupied 80% ± 11% of total CDOM pool, mainly due to urbanization driving DOM to be more protein-like, less humic-like. Besides, DOM in the Tangxun Lake was mainly autochthonous input and more recently formed. Furthermore, a total of 129 phytoplankton species were identified, belonging to 78 genera and 7 phyla. Tangxun Lake's phytoplankton community structure was dominated by the Chlorophyta-Bacillariophyta-Cyanophyta type. The temporal succession of phytoplankton varied significantly. It was found that the abundance of Cryptophyta and Cyanophyta were predominant in the mesotrophic state, while Cyanophyta and Bacillariophyta were prevailing in the eutrophic and middle-eutrophic states. As for the interaction between DOM and phytoplankton, results demonstrated that phytoplankton biomass was significantly positively correlated with a (254), a proxy of DOM abundance. Moreover, phytoplankton abundance and biomass significantly positively correlated with autochthonous and freshly released DOM, indicating that the more autochthonous and freshly released DOM, the higher phytoplankton abundance and biomass. Overall, this study provides profound environmental implications for aquatic ecosystem management, especially those strongly affected by human activities.

The concentration of dissolved organic matter impacts the neurobehavior in zebrafish larvae exposed to cyclophosphamide.

Dissolved organic matter (DOM) occurs ubiquitously in various water matrices and affects the chemical speciation and toxicity of emerging contaminants, such as cyclophosphamide (CP). However, the effects of CP in aquatic organisms with the presence of DOM have been relatively less addressed. In this study, zebrafish eggs < 4 h post fertilization (hpf) were exposed to CP (0 and 50 µg/L) and humic acid (HA, a main component of DOM, 0, 3, 10, and 30 mg-C/L) until 7 days post fertilization, and its toxicity was evaluated by behavioral approaches and transcription of nervous-related genes. An increase in swimming velocity and anxiety was noticed in zebrafish larvae exposed to CP. The related genes of neurotransmitter (drd1, mao, thp1b, and gad2), neurodevelopment (gli2b, nrd, and gfap), and neuroinflammation (thfα, casp3, and il-6) were upregulated by CP. In the presence of HA (3 mg-C/L), the behaviors and gene transcripts of zebrafish larvae were enhanced, while at 10 mg-C/L, they were mitigated. This study has demonstrated that DOM at low concentration increases the toxicity of CP and at high concentration alleviates its toxicity. This study highlights the importance of emerging contaminant exposure with the presence of DOM on their toxicities in aquatic organisms.

Two-Dimensional Liquid Chromatography Tandem Mass Spectrometry Untangles the Deep Metabolome of Marine Dissolved Organic Matter.

Dissolved organic matter (DOM) is an ultracomplex mixture that plays a central role in global biogeochemical cycles. Despite its importance, DOM remains poorly understood at the molecular level. Over the last decades, significant efforts have been made to decipher the chemical composition of DOM by high-resolution mass spectrometry (HR-MS) and liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS). Yet, the complexity and high degree of nonresolved isomers still hamper the full structural analysis of DOM. To address this challenge, we developed an offline two-dimensional (2D) LC approach using two reversed-phase dimensions with orthogonal pH levels, followed by MS/MS data acquisition and molecular networking. 2D-LC-MS/MS reduced the complexity of DOM, enhancing the quality of MS/MS spectra and increasing spectral annotation rates. Applying our approach to analyze coastal-surface DOM from Southern California (USA) and open-ocean DOM from the central North Pacific (Hawaii), we annotated in total more than 600 structures via MS/MS spectrum matching, which was up to 90% more than that in iterative 1D LC-MS/MS analysis with the same total run time. Our data offer unprecedented insights into the molecular composition of marine DOM and highlight the potential of 2D-LC-MS/MS approaches to decipher the chemical composition of ultracomplex samples.

Hydrologic changes induced by groundwater abstraction lead to arsenic mobilization in shallow aquifers.

Intensive groundwater abstraction leads to hydrologic changes of groundwater. Nevertheless, the effects of hydrologic change on groundwater arsenic (As) mobilization remain controversial. Here, we investigated fluctuations in water levels and their effects on As mobilization in the shallow aquifer of the Hetao Basin. Results showed that large groundwater level fluctuations and high horizontal hydraulic gradients occurred in irrigation seasons. In the groundwater near the wetland with higher surface water levels than groundwater levels, biological index values of dissolved organic matter (DOM) ranged from 0.54 to 0.72, and a positive correlation between δ18O values and dissolved organic carbon (DOC) was observed, indicating that groundwater DOM was mainly sourced from surface water. The degradation of allochthone labile DOM drove the reductive dissolution of As-bearing Fe(III) oxides to Fe(II). Both DOC and humification indices of DOM exhibited positive correlations with horizontal hydraulic gradients downstream of the study area, implying that the humified organic matter flushed from aquifer sediments contributed to groundwater DOM. The humified DOM controlled by hydraulic conditions participated in the redox reactions mainly by shuttling electrons to As-bearing Fe(III) oxides. These findings highlight distinct roles of hydrologic changes induced by groundwater abstraction in As mobilization.

Pollution of organophosphorus pesticides in the Dongting Lake, China and its relationship with dissolved organic matter: Occurrence, source identification and risk assessment.

The escalating global demand for food and industrialization has placed significant pressure on the integrity and management of inland lake ecosystems. Herein, the organophosphorus pesticides (OPPs) pollution status and their relationship with dissolved organic matter (DOM) in Dongting Lake were investigated to identify the ecological risks and potential sources of OPPs. The total concentrations of 18 detected OPPs were in the range of 13.49-375.24 ng/L, with higher concentration observed in east and west lake regions. Among these, fenthion was the dominant contributor, accounting for 64% of total OPPs, posing significant ecological risk to aquatic organisms. Nearly all of sites showed high combined risk of total OPPs. Parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) technique showed that DOM was mainly composed of terrestrial humic-like and tryptophan-like substances. Moreover, correlation analysis revealed a close association between DOM optical parameters and OPP concentrations. Specifically, OPPs exhibited a significantly positive correlation with tyrosine-like substances, while displaying a negative correlation with fulvic acid-like substances. These results indicated that OPP concentrations may decrease with increasing humification levels and declining tyrosine-like substance contents. This study underscores the critical role of DOM in assessing the occurrence and sources of OPPs in aquatic environments, providing valuable insights for effective environmental management strategies.

Scallop farming impacts on dissolved organic matter cycling in coastal waters: Regulation of the low molecular weight fraction.

To elucidate the impacts of scallop farming on the biogeochemical characteristics of low molecular weight (LMW, <1 kDa) dissolved organic matter (DOM), samples collected from a bay scallop mariculture area (MA) and its surrounding areas were determined for absorption and fluorescence spectroscopy after microfiltration and centrifugal ultrafiltration. The values of absorption coefficient a350 showed a spatial variation trend of inshore area (IA) > MA > non-mariculture area (NMA) for both bulk (<0.7 µm) and LMW fractions. Four fluorescent components, namely two protein-like components (tryptophan-like C1 and tyrosine-like C2) and two humic-like components (microbial humic-like C3 and terrestrial humic-like C4), were identified. Scallop farming influenced DOM transformation by altering phytoplankton abundance and promoting microbial degradation. In July, the net contributions of phytoplankton to the spectroscopy parameters of LMW-DOM in the surface seawater were 11.0% for a350, 4.3% for C1, 0.8% for C2, 0.6% for C3 and 3.0% for C4, respectively; the corresponding values of bulk DOM in the surface seawater were 24.3% for a350, 20.1% for C1, 5.9% for C2, 2.0% for C3, 2.9% for C4, respectively. Compared with NMA, the contributions of microbial degradation to a350 in MA's surface seawater increased by 9.0% for LMW-DOM and 6.9% for bulk DOM in July; however, the effects on different fluorescent components varied. In August, compared with NMA, the contributions of microbial degradation to spectroscopy parameters in the bottom water of MA decreased by 35.7% for a350, 6.3% for C2, 1.3% for C3, and 4.4% for C4 for LMW-DOM fraction; for bulk DOM, the corresponding contribution decreased by 10.8% for C1. These variations indicate that protein-like substances from scallop aquaculture are easily degraded into LMW substances, while humic-like substances degradation diminishes over time.

Interactions between dissolved organic matter with different molecular weights and nonylphenol in surface water bodies.

Dissolved organic matter (DOM) has a complex composition, which can interact with various pollutants and affect the removal of pollutants. Therefore, a thorough understanding of the interaction between the encccvironmental hormone nonylphenol (NP) and DOM is crucial for environmental impact and development. In this study, the interaction was investigated by means of excitation emission matrix (EEM) fluorescence spectroscopy, UV-Vis spectroscopy, FT-IR spectroscopy, nuclear magnetic resonance (NMR) and complex model analysis. The interaction between different MW DOM and NP was verified by the spectral characterization data. According to the characterization analysis, the main components of DOM in water samples were proteinoid (C1, C2, C4) with MW < 1 k Da, and their binding capacity (log Ka value) and binding site number (n) showed the maximum values (3.37, 3.24, 3.26; 0.81, 1.22, 0.52). For the humus like substance (C3) with larger molecular weight, the log Ka value and the number of binding points n increased with increasing molecular weight, and the maximum values were 3.13 and 0.31, respectively. It can be seen that low molecular weight proteins have strong binding ability and binding sites with NP, and high molecular weight humus also have strong binding ability. Overall, the interaction between DOM and NP has molecular weight dependence and heterogeneity. The purpose of this study is to deeply understand the interaction characteristics of different MW DOM with NP, and to provide theoretical support and reference for the study of the removal effects of NP pollutants.

Transformation of dissolved organic matter leached from biodegradable and conventional microplastics under UV/chlorine treatment and the subsequent effect on contaminant removal.

The ultraviolet (UV)/chlorine process has been widely applied for water treatment. However, the transformation of microplastic-leached dissolved organic matter (MP-DOM) in advanced treatment of real wastewater remains unclear. Here, we investigated alterations in the photoproperties of MP-DOM leached from biodegradable and conventional microplastics (MPs) and their subsequent effects on the degradation of sulfamethazine (SMT) by the UV/chlorine process. Spectroscopy was used to assess photophysical properties, focusing on changes in light absorption capacity, functional groups, and fluorescence components, while photochemical properties were determined by calculating the apparent quantum yields of reactive intermediates (ΦRIs). For photophysical properties, our findings revealed that the degree of molecular structure modification, functional group changes, and fluorescence characteristics during UV/chlorine treatment are closely linked to the type of MPs. For photochemical properties, the ΦRIs increased with higher chlorine dosages due to the formation of new functionalities. Both singlet oxygen (1O2) and hydroxyl radicals (•OH) formation were strongly correlated with excited triplet state of DOM (3DOM*) in the UV/chlorine treatment. Additionally, we found that the four types of MP-DOM inhibit the degradation of SMT and elucidated the mechanisms behind this inhibition. We also proposed degradation pathways for SMT and assessed the ecotoxicity of the resulting intermediates. This study provides important insights into how the characteristics and transformation of MP-DOM affect contaminant degradation, which is critical for evaluating the practical application of UV-based advanced oxidation processes (UV-AOPs).