Characteristics of disinfection byproducts from dissolved organic matter during chlor(am)ination of source water in Tibetan Plateau, China.

The Tibetan Plateau, a typical high-altitude area, is less affected by human activities such as industrial development, and the external pollution to water sources is extremely low. Then it is also an important source of water samples for exploring the molecular characteristics of precursors in the dissolved organic matter (DOM) of disinfection byproducts (DBPs) in drinking water. Research data on DBPs in drinking water on the Tibet Plateau remains insufficient, leading to uncertainty about DBP contamination in the area. This study explores the formation potential of 35 typical DBPs, including 6 trihalomethanes (THMs), 9 haloacetic acids (HAAs), 2 halogenated ketones (HKs), 9 nitrosamines (NAs), and 9 aromatic DBPs, during chlorination and chloramination of typical source water samples in the Tibet Plateau of China. Moreover, in order to further investigate the characteristics of the generation of DBPs, the molecular composition of DOM in the collected water samples was characterized by Fourier transform ion cyclotron resonance mass spectrometry. The findings reveal that, for chlorination and chloramination, the average concentration of the five classes of DBPs was ranked as follows (chlorination, chloramination): HAAs (268.1 µg/L, 54.2 µg/L) > THMs (44.0 µg/L, 2.0 µg/L) > HKs (0.7 µg/L, 1.8 µg/L) > NAs (26.5 ng/L, 74.6 ng/L) > Aromatics (20.4 ng/L, 19.5 ng/L). The dominant compounds in THMs, HAAs, and NAs are trichloromethane, dichloroacetic acid, trichloroacetic acid, and nitrosopyrrolidine, respectively. This study highlights a significant positive correlation between DBP generation and UV254, SUV254, and the double bond equivalents of DOM in the source water. It systematically elucidates DOM molecular composition characteristics and DBP formation potential in high-altitude water sources, shedding light on key factors influencing DBP generation at the molecular level in high-altitude areas.

Post Natal Microbial and Metabolite Transmission: The Path from Mother to Infant.

The entero-mammary pathway is a specialized route that selectively translocates bacteria to the newborn's gut, playing a crucial role in neonatal development. Previous studies report shared bacterial and archaeal taxa between human milk and neonatal intestine. However, the functional implications for neonatal development are not fully understood due to limited evidence. This study aimed to identify and characterize the microbiota and metabolome of human milk, mother, and infant stool samples using high-throughput DNA sequencing and FT-ICR MS methodology at delivery and 4 months post-partum. Twenty-one mothers and twenty-five infants were included in this study. Our results on bacterial composition suggest vertical transmission of bacteria through breastfeeding, with major changes occurring during the first 4 months of life. Metabolite chemical characterization sheds light on the growing complexity of the metabolites. Further data integration and network analysis disclosed the interactions between different bacteria and metabolites in the biological system as well as possible unknown pathways. Our findings suggest a shared bacteriome in breastfed mother-neonate pairs, influenced by maternal lifestyle and delivery conditions, serving as probiotic agents in infants for their healthy development. Also, the presence of food biomarkers in infants suggests their origin from breast milk, implying selective vertical transmission of these features.

Metagenomic and FT-ICR MS insights into the mechanism for the arsenic biogeochemical cycling in groundwater.

Arsenic (As) is a groundwater contaminant of global concern. The degradation of dissolved organic matter (DOM) can provide a reducing environment for As release. However, the interaction of DOM with local microbial communities and how different sources and types of DOM influence the biotransformation of As in aquifers is uncertain. This study used optical spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), metagenomics, and structural equation modeling (SEM) to demonstrate the how the biotransformation of As in aquifers is promoted. The results indicated that the DOM in high-As groundwater is dominated by highly unsaturated low-oxygen(O) compounds that are quite humic and stable. Metagenomics analysis indicated Acinetobacter, Pseudoxanthomonas, and Pseudomonas predominate in high-As environments; these genera all contain As detoxification genes and are members of the same phylum (Proteobacteria). SEM analyses indicated the presence of Proteobacteria is positively related to highly unsaturated low-O compounds in the groundwater and conditions that promote arsenite release. The results illustrate how the biogeochemical transformation of As in groundwater systems is affected by DOM from different sources and with different characteristics.

Chemodiversity of dissolved organic matter exports from subtropical humid catchment driven by hydrological connectivity.

The quantity and quality of dissolved organic matter (DOM) exported from source areas are closely related to hydrological linkage between source areas and streams, that is hydrological connectivity. However, understanding of how hydrological connectivity regulates the export of catchment DOM components remains inadequate. In this study, high-frequency monitoring of groundwater and runoff from subtropical humid catchment was conducted for 20 months, and hydrological connectivity was quantitatively characterized by considering both surface and subsurface hydrological processes. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was utilized to investigate the DOM molecular composition. Results showed that over half of the areas in the catchment could not persistently establish hydrological connectivity with the stream during the rainfall. The average proportion of lignin was the highest in DOM components, followed by tannin and proteins. Additionally, both modified aromaticity index and double bond equivalence reached maximums at peak discharge, reflecting terrestrial materials could increase DOM aromaticity and unsaturated degree. Partial least square-structural equation modeling revealed significantly direct effects of rainfall, antecedent conditions, and hydrological connectivity on dissolved organic carbon (DOC) export. Furthermore, nonlinear relationships were observed between hydrological connectivity and DOC, tannin, and condensed aromatics. Specifically, the instantaneous DOC flux increased dramatically when the hydrological connectivity strength exceeded 0.14; tannin and condensed aromatics exhibited a rapid increase with rising connectivity strength, but remained stable at connectivity strength above 0.25. However, hydrological connectivity showed no significant correlation with unstable components (such as lipids, protein, amino sugars, and carbohydrates). These results provide new insights into hydrological controls on the quantity and quality of DOM export and contribute to developing appropriate catchment management strategies for carbon storage.

Qualitative Analysis of Nitrogen and Sulfur Compounds in Vacuum Gas Oils via Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry.

Analysis of the heavy fractions in crude oil has been important in petroleum industries. It is well known that heavy fractions such as vacuum gas oils (VGOs) include heteroatoms, of which sulfur and nitrogen are often characterized in many cases. We conducted research regarding the molecular species analysis of VGOs. Further refine processes using VGOs are becoming important when considering carbon recycling. In this work, we attempted to classify compounds within VGOs provided by Kuwait Institute for Scientific Research. Two VGOs were priorly distillated from Kuwait Export crude and Lower Fars crude. Quantitative analysis was performed mainly using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOFMS). MALDI-TOF-MS has been developed for analyzing high-molecular-weight compounds such as polymer and biopolymers. As matrix selection is one of the most important aspects in MALDI-TOFMS, the careful selection of a matrix was firstly evaluated, followed by analysis using a Kendrick plot with nominal mass series (z*). The objective was to evaluate if this work could provide an effective classification of VGOs compounds. The Kendrick plot is a well-known method for processing mass data. The difference in the Kendrick mass defect (KMD) between CnH2n-14S and CnH2n-20O is only 0.0005 mass units, which makes it difficult in general to distinguish these compounds. However, since the z* value showed effective differences during the classification of these compounds, qualitative analysis could be possible. The analysis using nominal mass series showed the potential to be used as an effective method in analyzing heavy fractions.

Molecular-level insights into dissolved organic matter and its variations of the full-scale processes in a typical petrochemical wastewater treatment plant.

Petrochemical wastewater (PCWW) treatment poses challenges due to its unique and complex dissolved organic matter (DOM) composition, originating from various industrial processes. Despite the addition of advanced treatment units in PCWW treatment plants to meet discharge standards, the mechanisms of molecular-level sights into DOM reactivity of the upgraded full-scale processes including multiple biological treatments and advanced treatment remain unclear. Herein, we employ water quality indexes, spectra, molecular weight (MW) distribution, and Fourier transform ion cyclotron resonance mass spectrometry to systematically characterize DOM in a typical PCWW treatment plant including influent, micro-oxygen hydrolysis acidification (MOHA), anaerobic/oxic (AO), and micro-flocculation sand filtration-catalytic ozonation (MFSF-CO). Influent DOM is dominated by tryptophan-like and soluble microbial products with MW fractions 〈 1 kDa and 〉 100 kDa, and CHO with lignin and aliphatic/protein structures. MOHA effectively degrades macromolecular CHO (10.86 %) and CHON (5.24 %) compounds via deamination and nitrogen reduction, while AO removes CHOS compounds with MW < 10 kDa by desulfurization, revealing distinct DOM conversion mechanisms. MFSF-CO transforms unsaturated components to less aromatic and more saturated DOM through oxygen addition reactions and shows high CHOS and CHONS reactivity via desulfurization and deamination reactions, respectively. Moreover, the correlation among multiple parameters suggests UV254 combined with AImod as a simple monitoring indicator of DOM to access the chemical composition. The study provides molecular-level insights into DOM for the contribution to the improvement and optimization of the upgraded processes in PCWW.

Peatland Wildfires Enhance Nitrogen-Containing Organic Compounds in Marine Aerosols over the Western Pacific.

Peatland wildfires contribute significantly to the atmospheric release of light-absorbing organic carbon, often referred to as brown carbon. In this study, we examine the presence of nitrogen-containing organic compounds (NOCs) within marine aerosols across the Western Pacific Ocean, which are influenced by peatland fires from Southeast Asia. Employing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in electrospray ionization (ESI) positive mode, we discovered that NOCs are predominantly composed of reduced nitrogenous bases, including CHN+ and CHON+ groups. Notably, the count of NOC formulas experiences a marked increase within plumes from peatland wildfires compared to those found in typical marine air masses. These NOCs, often identified as N-heterocyclic alkaloids, serve as potential light-absorbing chromophores. Furthermore, many NOCs demonstrate pyrolytic stability, engage in a variety of substitution reactions, and display enhanced hydrophilic properties, attributed to chemical processes such as methoxylation, hydroxylation, methylation, and hydrogenation that occur during emission and subsequent atmospheric aging. During the daytime atmospheric transport, aging of aromatic N-heterocyclic compounds, particularly in aliphatic amines prone to oxidation and reactions with amine, was observed. The findings underscore the critical role of peatland wildfires in augmenting nitrogen-containing organics in marine aerosols, underscoring the need for in-depth research into their effects on marine ecosystems and regional climatic conditions.

The Hunt for Chemical Dark Matter across a River-to-Ocean Continuum.

Thousands of mass peaks emerge during molecular characterization of natural dissolved organic matter (DOM) using ultrahigh-resolution mass spectrometry. While mass peaks assigned to certain molecular formulas have been extensively studied, the uncharacterized mass peaks that represent a significant fraction of organic matter and convey biogenic elements and energy have been previously ignored. In this study, we introduce the term dark DOM (DDOM) for unassigned mass peaks and have explored its characteristics and environmental behaviors using a data set of 38 DOM extracts covering the Yangtze River-to-ocean continuum. We identified a total of 9141 DDOM molecules, which exhibited higher molecular weight and greater diversity than the DOM subset with assigned DOM formulas. Although DDOM contributed a smaller fraction of relative abundance, it significantly impacted the molecular weight and molecular composition of bulk DOM. A portion of DDOM with higher molecular weight was found to increase molecular abundance across the river-to-ocean continuum. These compounds could contain halogenated organic molecules and might have a high potential to contribute to the refractory organic carbon pool. With this study, we underline the contribution of dark matter to the total DOM pool and emphasize that more DDOM research is needed to understand its contribution to global biogeochemical cycles and carbon sequestration.

Revealing Molecular Structures of Nitrogen-Containing Compounds in Dissolved Black Carbon Using Ultrahigh-Resolution Mass Spectrometry Combined with Thermodynamic Calculations.

Landscape wildfires generate a substantial amount of dissolved black carbon (DBC) annually, yet the molecular nitrogen (N) structures in DBC are poorly understood. Here, we systematically compared the chemodiversity of N-containing molecules among three different DBC samples from rice straw biochar pyrolyzed at 300, 400, and 500 °C, one leached dissolved organic carbon (LDOC) sample from composted rice straw, and one fire-affected soil dissolved organic matter (SDOMFire) sample using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). N-Containing molecules contributed 20.0%, 36.1%, and 43.7% of total compounds in Combined DBC (pooling together the three DBC), LDOC, and SDOMFire, respectively, and molecules with fewer N atoms had higher proportions (i.e., N1 > N2 > N3). The N-containing molecules in Combined DBC were dominated by polycyclic aromatic (62.2%) and aromatic (14.4%) components, while those in LDOC were dominated by lignin-like (50.4%) and aromatic (30.1%) components. The composition and structures of N-containing molecules in SDOMFire were more similar to those in DBC than in LDOC. As the temperature rose, the proportion of the nitrogenous polycyclic aromatic component in DBC significantly increased with concurrent enhanced oxidation and unsaturation of N. As indicated by density functional theory (DFT)-based thermodynamic calculations, the proportion of aliphatic amide N decreased from 23.2% to 7.9%, whereas that of nitroaromatic N increased from 10.0% to 39.5% as the temperature increased from 300 to 500 °C; alternatively, the proportion of aromatic N in the 5/6 membered ring remained relatively stable (∼31%) and that of aromatic amide N peaked at 400 °C (32.7%). Our work first provides a comprehensive and thorough description of molecular N structures of DBC, which helps to better understand and predict their fate and biogeochemical behavior.

Suppressing Organic Bromine but Promoting Bromate: Is the Ultraviolet/Ozone Process a Double-Edged Sword for the Toxicity of Wastewater to Mammalian Cells?

Brominated byproducts and toxicity generation are critical issues for ozone application to wastewater containing bromide. This study demonstrated that ultraviolet/ozone (UV/O3, 100 mJ/cm2, 1 mg-O3/mg-DOC) reduced the cytotoxicity of wastewater from 14.2 mg of pentol/L produced by ozonation to 4.3 mg of pentol/L (1 mg/L bromide, pH 7.0). The genotoxicity was also reduced from 1.65 to 0.17 µg-4-NQO/L by UV/O3. Compared with that of O3 alone, adsorbable organic bromine was reduced from 25.8 to 5.3 µg/L by UV/O3, but bromate increased from 32.9 to 71.4 µg/L. The UV/O3 process enhanced the removal of pre-existing precursors (highly unsaturated and phenolic compounds and poly aromatic hydrocarbons), while new precursors were generated, yet the combined effect of UV/O3 on precursors did not result in a significant change in toxicity. Instead, UV radiation inhibited HOBr concentration through both rapid O3 decomposition to reduce HOBr production and decomposition of the formed HOBr, thus suppressing the AOBr formation. However, the hydroxyl radical-dominated pathway in UV/O3 led to a significant increase of bromate. Considering both organic bromine and bromate, the UV/O3 process effectively controlled both cytotoxicity and genotoxicity of wastewater to mammalian cells, even though an emphasis should be also placed on managing elevated bromate. Futhermore, other end points are needed to evaluate the toxicity outcomes of the UV/O3 process.

Size-Resolved Molecular Characterization of Water-Soluble Organic Matter in Atmospheric Particulate Matter from Northern China.

Atmospheric particulate matter (PM) affects visibility, climate, biogeochemical cycles and human health. Water-soluble organic matter (WSOM) is an important component of PM. In this study, PM samples with size-resolved measurements at aerodynamic cut-point diameters (Dp) of 0.01-18µm were collected in the rural area of Baoding and the urban area of Dalian, Northern China. Non-targeted analysis was adopted for the characterization of the molecule constitutes of WSOM in different sized particles using Fourier transform-ion cyclotron resonance mass spectrometry. Regardless of the location, the composition of WSOM in Aitken mode particles (aerodynamic diameter < 0.05 µm) was similar. The WSOM in accumulation mode particles (0.05-2 µm) in Baoding was predominantly composed of CHO compounds (84.9%), which were mainly recognized as lignins and lipids species. However, S-containing compounds (64.2%), especially protein and carbohydrates species, accounted for most of the WSOM in the accumulation mode particles in Dalian. The CHO compounds (67.6%-79.7%) contributed the most to the WSOM in coarse mode particles (> 2 µm) from both sites. Potential sources analysis indicated the WSOM in Baoding were mainly derived from biomass burning and oxidation reactions, while the WSOM in Dalian arose from coal combustion, oxidation reactions, and regional transport.

Effect of Land Use Change on Molecular Composition and Concentration of Organic Matter in an Oxisol.

Land use change from native vegetation to cropping can significantly affect the quantity and quality of soil organic matter (SOM). However, it remains unclear how the chemical composition of SOM is affected by such changes. This study employed a sequential chemical extraction to partition SOM from an Oxisol into several distinct fractions: water-soluble fractions (ultrapure water (W)), organometal complexes (sodium pyrophosphate (PP)), short-range ordered (SRO) oxides (hydroxylamine-HCl (HH)), and well-crystalline oxides (dithionite-HCl (DH)). Coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the impact of land use change on the molecular composition of different OM fractions was investigated. Greater amounts of OM were observed in the PP and HH fractions compared to other fractions, highlighting their importance in SOM stabilization. The composition of different OM fractions varied based on extracted phases, with lignin-like and tannin-like compounds being prevalent in the PP and HH fractions, while aliphatic-like compounds dominated in the DH fraction. Despite changes in the concentration of each OM fraction from native vegetation to cropping, there was little influence of land use change on the molecular composition of OM associated with different mineral phases. No significant selective loss or preservation of organic carbon compounds was observed, indicating the composition of SOM remained unchanged.

High throughput identification of carbonyl compounds in natural organic matter by directional derivatization combined with ultra-high resolution mass spectrometry.

Carbonyl compounds are important components of natural organic matter (NOM) with high reactivity, so that play a pivotal role in the dynamic transformation of NOM. However, due to the lack of effective analytical methods, our understanding on the molecular composition of these carbonyl compounds is still limited. Here, we developed a high-throughput screening method to detect carbonyl molecules in complex NOM samples by combining chemical derivatization with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). In six different types of dissolved organic matter (DOM) samples tested in this study, 20-30 % of detected molecules contained at least one carbonyl group, with relative abundance accounted for 45-70 %. These carbonyl molecules displayed lower unsaturation level, lower molecular weight, and higher oxidation degree compared to non-carbonyl molecules. More importantly, the measured abundances of carbonyl molecules were consistent with the results of 13C nuclear magnetic resonance (NMR) analysis. Based on this method, we found that carbonyl molecules can be produced at DOM-ferrihydrite interface, thus playing a role in shaping the molecular diversity of DOM. This method has broad application prospects in screening carbonyl compounds from complex mixtures, and the same strategy can be used to directional identification of molecules with other functional groups as well.

Spectral and molecular insights into the characteristics of dissolved organic matter in nitrate-contaminated groundwater.

The characteristics of dissolved organic matter (DOM) serve as indicators of nitrate pollution in groundwater. However, the specific DOM components associated with nitrate in groundwater systems remain unclear. In this study, dual isotopes of nitrate, three-dimensional Excitation emission matrices (EEMs) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were utilized to uncover the sources of nitrate and their associations with DOM characteristics. The predominant nitrate in the targeted aquifer was derived from soil organic nitrogen (mean 46.0%) and manure &sewage (mean 34.3%). The DOM in nitrate-contaminated groundwater (nitrate-nitrogen >20 mg/L) exhibited evident exogenous characteristics, with a bioavailable content 2.58 times greater than that of uncontaminated groundwater. Regarding the molecular characteristics, DOM molecules characterized by CHO + 3N, featuring lower molecular weights and H/C ratios, indicated potential for mineralization, while CHONS formulas indicated the exogenous features, providing the potential for accurate traceability. These findings provided insights at the molecular level into the characterization of DOM in nitrate-contaminated groundwater and offer scientific guidance for decision-making regarding the remediation of groundwater nitrate pollution.

High-Resolution Mass Spectrometry Combined with Reactive Oxygen Species Reveals Differences in Photoreactivity of Dissolved Organic Matter from Microplastic Sources in Aqueous Environments.

Microplastics (MPs)-derived dissolved organic matter (MPs-DOM) is becoming a non-negligible source of DOM pools in aquatic systems, but there is limited understanding about the photoreactivity of different MPs-DOM. Herein, MPs-DOM from polystyrene (PS), polyethylene terephthalate (PET), poly(butylene adipate-co-terephthalate) (PBAT), PE, and polypropylene (PP), representing aromatic, biodegradable, and aliphatic plastics, were prepared to examine their photoreactivity. Spectral and high-resolution mass spectrometry analyses revealed that PS/PET/PBAT-DOM contained more unsaturated aromatic components, whereas PE/PP-DOM was richer in saturated aliphatic components. Photodegradation experiments observed that unsaturated aromatic molecules were prone to be degraded compared to saturated aliphatic molecules, leading to a higher degradation of PS/PET/PBAT-DOM than PE/PP-DOM. PS/PET/PBAT-DOM was mainly degraded by hydroxyl (•OH) via attacking unsaturated aromatic structures, whereas PE/PP-DOM by singlet oxygen (1O2) through oxidizing aliphatic side chains. The [•OH]ss was 1.21-1.60 × 10-4 M in PS/PET/PBAT-DOM and 0.97-1.14 × 10-4 M in PE/PP-DOM, while the [1O2]ss was 0.90-1.35 × 10-12 and 0.33-0.44 × 10-12 M, respectively. This contributes to the stronger photoreactivity of PS/PET/PBAT-DOM with a higher unsaturated aromatic degree than PE/PP-DOM. The photodegradation of MPs-DOM reflected a decreasing tendency from aromatic-unsaturated molecules to aliphatic-saturated molecules. Special attention should be paid to the photoreactivity and environmental impacts associated with MPs-DOM containing highly unsaturated aromatic compounds.

The loss of dissolved organic matter from biological soil crust at various successional stages under rainfall of different intensities: Insights into the changes of molecular components at different rainfall stages.

Biological soil crusts (BSCs) are typical covers in arid and semiarid regions. The dissolved organic matter (DOM) of BSCs can be transported to various aquatic ecosystems by rainfall-runoff processes. However, the spatiotemporal variation in quality and quantity of DOM in runoff remains unclear. Herein, four kinds of runoff plots covered by four successional stages of BSCs were set up on slopes, including bare runoff plot (BR), cyanobacteria crust covered runoff plot (CR), mixed crust covered runoff plot (MIR), and moss crust covered runoff plot (MOR). The quantity and quality of DOM in runoff during rainfall was investigated based on the stimulated rainfall experiments combined with optical spectroscopy and ultra-high resolution mass spectrometry analyses. The results showed that the DOM concentrations (i.e., 0.30 to 45.25 mg L-1) in runoff followed the pattern of MOR>MIR>CR>BR, and they were exponentially decreased with rainfall duration. The DOM loss rate of BR (8.26 to 11.64 %) was significantly greater than those of CR, MIR, and MOR (0.84 to 3.22 %). Highly unsaturated compounds (HUCs), unsaturated aliphatic compounds (UACs), saturated compounds (SCs), and peptide-like compounds (PLCs) were the dominated compounds of the water extractable DOM from the original soils. Thereinto, PLCs and UACs were more easily leached into runoff during rainfall. The relatively intensity of HUCs in runoff generally decreased with rainfall duration, while the relatively intensities of UACs, PLCs, and SCs slightly increased with rainfall duration. These findings suggested that the DOM loss rate was effectively decreased with the successional of BSCs during rainfall; meanwhile, some labile compounds (e.g., PLCs and UACs) were transported into various aquatic ecosystems by rainfall-runoff processes.

Composition regulates dissolved organic matter adsorption onto iron (oxy)hydroxides and its competition with phosphate: Implications for organic carbon and phosphorus immobilization in lakes.

Dissolved organic matter (DOM) is a heterogeneous pool of compounds and exhibits diverse adsorption characteristics with or without phosphorous (P) competition. The impacts of these factors on the burial and mobilization of organic carbon and P in aquatic ecosystems remain uncertain. In this study, an algae-derived DOM (ADOM) and a commercially available humic acid (HA) with distinct compositions were assessed for their adsorption behaviors onto iron (oxy)hydroxides (FeOx), both in the absence and presence of phosphate. ADOM contained less aromatics but more protein-like and highly unsaturated structures with oxygen compounds (HUSO) than HA. The adsorption capacity of FeOx was significantly greater for ADOM than for HA. Protein-like and HUSO compounds in ADOM and humic-like compounds and macromolecular aromatics in HA were preferentially adsorbed by FeOx. Moreover, ADOM demonstrated a stronger inhibitory effect on phosphate adsorption than HA. This observation suggests that the substantial release of autochthonous ADOM by algae could elevate internal P loading and pose challenges for the restoration of restore eutrophic lakes. The presence of phosphate suppressed the adsorption of protein-like compounds in ADOM onto FeOx, resulting in an increase in the relative abundance of protein-like compounds and a decrease in the relative abundance of humic-like compounds in post-adsorption ADOM. In contrast, phosphate exhibited no discernible impact on the compositional fractionation of HA. Collectively, our results show the source-composition characters of DOM influence the immobilization of both DOM and P in aquatic ecosystems through adsorption processes. The preferential adsorption of proteinaceous compounds within ADOM and aromatics within HA highlights the potential for the attachment with FeOx to diminish the original source-specific signatures of DOM, thereby contributing to the shared DOM characteristics observed across diverse aquatic environments.

High biodegradability of microbially-derived dissolved organic matter facilitates arsenic enrichment in groundwater: Evidence from molecular compositions and structures.

Although biodegradation of organic matter is well-known to trigger enrichment of arsenic (As) in groundwater, the effects of DOM sources and biodegradability on As enrichment remain elusive. In this study, groundwater samples were collected from the Hetao basin to identify DOM source and evaluate biodegradability by using spectral and molecular techniques. Results showed that in the alluvial fan, DOM was mainly sourced from terrestrially derived OM, while DOM in the flat plain was more originated from microbially derived OM. Compared to terrestrially derived DOMs, microbially derived DOMs in groundwater, which had relatively higher H/Cwa ratios, NOSC values and more biodegradable molecules, exhibited higher biodegradability. In the flat plain, microbially derived DOMs with higher biodegradability encountered stronger biodegradation, facilitating the reductive dissolution of Fe(III)/Mn oxides and As enrichment in groundwater. Moreover, the enrichment of As depended on the biodegradable molecules that was preferentially utilized for primary biodegradation. Our study highlights that the enrichment of dissolved As in the aquifers was closely associated with microbially derived DOM with high biodegradability and high ability for primary biodegradation.

Simulated nitrogen load promoted mineralization of N2P1 compounds and accumulation of N4S2 compounds in soil dissolved organic matter in a typical subtropical estuarine marsh.

Soil dissolved organic matter (DOM) is the most reactive pool in estuarine marshes, playing an important role in the biogeochemical processes of biogenetic elements. To investigate the impacts of enhanced nitrogen (N) load on DOM molecular composition and its interactions with microbes in typical Cyperus malaccensis mashes of the Min River estuary, a field N load experiment with four N levels (0, 37.50, 50 and 100 g exogenous N m-2 yr-1, respectively; applied monthly for a total of seven months) was performed. DOM molecular composition was characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the microbial community compositions (MCC, including fungi and bacteria) were determined by high-throughput sequencing technique, and their relationships were presented by co-occurrence network analysis. The results indicated that enhanced N load had significant impacts on soil DOM molecular composition, with N/C and P/C of DOM decreasing but S/C increasing markedly. Meanwhile, enhanced N load decreased the percentages of N2P1 compounds (primarily lipids) but increased those of N4S2 compounds (mainly lignins and lipids). The relative abundances of lignins significantly increased with increasing N load levels, whereas the proportions of lipids decreased. The abundance of N2P1 and N4S2 compounds was primarily positively correlated with eutrophic and oligotrophic microorganisms, respectively. Therefore, mineralization of N2P1 compounds might act as a source to replenish inorganic P, while enrichment of N4S2 compounds may make great contribution to organic S accumulation. Overall, enhanced N load promoted P depletion and S enrichment via altering plant growth, litter decomposition and MCC.

Characteristics of DOM and Their Relationships with Potentially Toxic Elements in the Inner Mongolia Section of the Yellow River, China.

The characterization of dissolved organic matter (DOM) is important for better understanding of the migration and transformation mechanisms of DOM in water bodies and its interaction with other contaminants. In this work, fluorescence characteristics and molecular compositions of the DOM samples collected from the mainstream, tributary, and sewage outfall of the Inner Mongolia section of the Yellow River (IMYR) were determined by using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In addition, concentrations of potentially toxic elements (PTEs) in the relevant surface water and their potential relationships with DOM were investigated. The results showed that the abundance of tyrosine-like components increased significantly in downstream waters impacted by outfall effluents and was negatively correlated with the humification index (HIX). Compared to the mainstream, outfall and tributaries have a high number of molecular formulas and a higher proportion of CHOS molecular formulas. In particular, the O5S class has a relative intensity of 41.6% and the O5-7S class has more than 70%. Thirty-eight PTEs were measured in the surface water samples, and 12 found above their detective levels at all sampling sites. Protein-like components are positively correlated with Cu, which is likely indicating the source of Cu in the aquatic environment of the IMYR. Our results demonstrated that urban wastewater discharges significantly alter characteristics and compositions of DOM in the mainstream of IMYR with strongly anthropogenic features. These results and conclusions are important for understanding the role and sources of DOM in the Yellow River aquatic environment.