Two membrane bioreactors (MBRs) with different operation conditions were employed to investigate the role of dissolved organic matter (DOM) in membrane fouling. DOM characteristics and their ...correlations with membrane fouling in the MBR systems were studied by using three-dimensional excitation-emission matrix (EEM) fluorescence technology, gel filtration chromatography (GFC) analysis, and column chromatographic method for DOM fractionation, etc. The three-dimensional EEM fluorescence spectroscopy analysis indicated that the fluorescence intensity of protein-like peaks in DOM samples collected from the MBR zones showed positive correlations with membrane fouling. The fluorescence spectra of membrane foulants also exhibited two protein-like peaks, confirming that proteins played an important role in membrane fouling. The DOM samples collected from MBR zones were fractionated into four components, i.e., hydrophobic (HPO), transphilic (TPI), charged hydrophilic (HPI-C) and neutral hydrophilic fractions (HPI-N). It was found that HPI-N was the most abundant fraction in all the samples, accounting for 42.0–48.9% of the total DOM. Test results also showed that HPI-N had the highest fouling potential, which could be attributed to the high molecular weight (MW) distribution and the high membrane rejection rate of macromolecules.
•The efficiency of Hg(II) photoreduction mediated by algae-leached DOM was lower than that of humic acid.•The strong complexation between -SH and Hg(II) inhibits the photoreduction of Hg(II) mediated ...by algae-leached DOM.•O2•− played a crucial role in the process of Hg(II) photoreduction.•The algae-leached DOM inhibited the uptake of Hg by aquatic plants through a photoreduction process.
The significant role of aquatic phytoplankton in global primary productivity, accounting for approximately 50 % on an annual basis, has been recognized as a crucial factor in the reduction of Hg(II). In this study, we compared the efficiency of Hg(II) photoreduction mediated by three types of algae leaching dissolved organic matter (DOM) and humic acid (DOM-HA). Especially, we investigated the potential effects of algae-leached DOM on the photoreduction of Hg(II) and its subsequent uptake by lettuce, which serves as an indicator of Hg bioavailability for aquatic plants. The results revealed that under light conditions, the conversion of Hg(II) to Hg(0) mediated by algae-leached DOM and DOM-HA was 6.4–39.9 % higher compared to dark condition. Furthermore, the free radical quenching experiment demonstrated that the reduction of Hg(II) mediated by DOM-HA was higher than algae-leached DOM, mainly due to its ability to generate superoxide anion (O2•−). Moreover, the photoreduction efficiences of Hg(II) mediated by algae-leached DOM were 29–18 % lower compared to DOM-HA. The FT-IR analysis revealed that the production of -SH from algae-leached DOM led to the formation of strong metal-complexes, which restricts the reduction process from Hg(II) to Hg(0). Finally, the hydroponics experiment demonstrated that algae-leached DOM inhibited the bioavailability of Hg(II) to plants more effectively than DOM-HA. Our research emphasizes the significant functional roles and potential mechanisms of algae in reducing Hg levels, thereby influencing the availability of Hg in aquatic ecosystems.
•We examined changes in DBP precursors in forest soils with 22 years of n addition.•N addition decreased the DOM reactivity in forming trihalomethanes.•N addition increased the DOM reactivity in ...forming haloketones.•N addition reduced the microtoxicity of DBPs from chlorination of terrestrial DOM.
Terrestrial dissolved organic matter (DOM) in forested watersheds is a known precursor of disinfection byproducts (DBPs) in drinking water. Although the characteristics of terrestrial DOM may change with increasing nitrogen (N) deposition in forests, how these changes alter formation potential and toxicity of DBPs remains unexplored. We analyzed the speciation and toxicity of DBPs from chlorination of DOM derived from soils (O, A, and B horizons) in an experimental temperate forest with 22 years of N addition. With long-term N addition, the DOM reactivity toward the formation of trihalomethanes (from 27.7–51.8 to 22.8–31.1 µg/mg-dissolved organic carbon (DOC)) and chloral hydrate (from 1.25–1.63 to 1.14–1.36 µg/mg-DOC) decreased, but that toward the formation of haloketones increased (from 0.23–0.26 to 0.26–0.33 µg/mg-DOC). The DOM reactivity toward the formation of haloacetonitriles was increased in the deeper soil but reduced in the surface soil. The DBP formation potential of DOM draining from a certain area of forest soils (in µg-DBP/m2-soil) was estimated to be reduced by 20.3% for trihalomethanes and increased by 37.5% for haloketones and have minor changes for haloacetonitriles and chloral hydrate (both <7%). Furthermore, the DBPs from chlorination of the soil-derived DOM showed lowered microtoxicity with N addition possibly due to reduced brominated DBP formation. Overall, this study highlights that N deposition may not increase drinking water toxicity through altering terrestrial DOM characteristics.
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Dissolved organic matter (DOM) contains complex molecular compounds that dominate its heterogeneous dynamics and behaviors in aquatic environments. Fourier transform ion cyclotron resonance mass ...spectrometry (FTICR-MS) with ultra-high resolution has proven to be effective in characterizing aquatic DOM. However, a systematic summary of molecular-level compositions and behaviors of DOM in natural and engineered water systems remains insufficient. This study provides a critical review of DOM characterization by FTICR-MS, with emphasis on composition diversity, chemical properties, transformation, and dynamics in the natural and engineered water systems. First, FTICR-MS strategies for DOM characterization are introduced on data interpretation and collaborative analysis of complementary datasets (e.g. spectroscopic data). Second, DOM characteristics, including spatiotemporal distribution, photochemical activity, microbial modification, and interface adsorption in natural water environments were comprehensively summarized based on current FTICR-MS findings. Third, DOM molecular changes caused by different engineered treatment methods were reviewed to highlight the molecular variation, reaction, and transformation by focusing on the FTICR-MS results. Finally, we summarized current limitations, biases, and future directions of FTICR-MS, and future extended studies of natural/engineered-derived DOM behavior. This FTICR-MS application review provides favorable strategies for understanding the molecular chemistry and behaviors of aquatic DOM.
To identify possible dominating processes involved in soil microbial community assembly, dissolved organic matter (DOM) and multi-nutrient cycling (MNC) interactions and contribute to understanding ...of climate change effects on these important cycles, we investigated the interaction of soil chemistry, DOM components and microbial communities in five vegetation zones - ranging from evergreen broad-leaved forest to alpine meadow - along an elevation gradient of 290–1960 m in the Wuyi Mountains, Fujian Province, China. Soil DOM composition and microbial community assembly were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and Illumina MiSeq high-throughput sequencing, respectively. Sloan's neutral model and the modified stochasticity ratio were used to infer community assembly processes. Key microbial drivers of the soil MNC index were identified from partial least squares path models. Our results showed that soil DOM composition is closely related to the vegetation types along an elevation gradient, the structure and composition of the microbial community, and soil nutrient status. Overall, values of the double bond equivalent (DBE), modified aromaticity index (AImod) increased, and H/C ratio and molecular lability boundary (MLBL) percentage decreased with elevation. Lignins/CRAM-like structures compounds dominated soil DOM in each vegetation type and its relative abundance decreased with elevation. Aliphatic/protein and lipids components also decreased, but the relative abundance of aromatic structures and tannin increased with elevation. The alpha diversity index of soil bacteria gradually decreased with elevation, with deterministic processes dominating the microbial community assembly in the highest elevation zone. Bacterial communities were conducive to the decomposition of labile degradable DOM compounds (H/C ≥ 1.5) at low elevation. In the cooler and wetter conditions at higher-elevation sites the relative abundance of potentially resistant soil DOM components (H/C < 1.5) gradually increased. Microbial community diversity and composition were important predictors of potential soil nutrient cycling. Although higher elevation sites have higher nutrient cycling potential, soil DOM was assessed to be a more stable carbon store, with apparent lower lability and bioavailability than at lower elevation sites. Overall, this study increases understanding of the potential linkage between soil microbial community, multiple nutrient cycling and DOM fate in subtropical mountain ecosystems that can help predict the effect of climate change on soil carbon sequestration and thus inform ecosystem management.
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•Relative abundance of DOM tannin and aromatic structures increased with elevation•Deterministic processes dominated microbial community assembly at high elevation•Bacteria promote decomposition of potentially labile DOM compounds at low elevation•Fungal community Shannon index and multi-nutrient cycling index negatively related
The impact of thermal remediation on soil function has drawn increasing attention. So far, as the most active fraction of soil organic matter, the evolution of dissolved organic matter (DOM) during ...the thermal remediation lacks in-depth investigation, especially for the temperatures value below 100 °C. In this study, a series of soil thermal treatment experiments was conducted at 30, 60, and 90 °C during a 90-d period, where soil DOM concentration increased with heating temperature and duration. The molecular weight, functional groups content and aromaticity of DOM all decreased during the thermal treatment. The excitation-emission matrices (EEM) results suggested that humic acid-like substances transformed into fulvic acid-like substances (F
III
/F
V
increased from 0.27 to 0.44) during the heating process, and five DOM components were further identified by EEM-PARAFAC. The change of DOM structures and components indicated the decline of DOM stability and hydrophilicity, and can potentially change the bioavailability and mobility. Elevated temperature also resulted in the decline of DOM complexation ability, which may be caused by the loss of binding sites due to the decrease of polar function groups, aromatic structures and hydrophilic components. This study provides valuable information about the evolution of DOM during thermal remediation, which would potentially change the fate of metal ions and the effectiveness of the post-treatment technologies in the treated region.
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•DOM decreased bioaccumulation of ERY in aquatic organisms.•SRHA and SRFA inhibited ERY bioavailability greater than the other DOM.•ERY KDOC values increased with the content of humic ...and fulvic acid-like compounds.•DOM interacted with ERY via reactions of −COO− with ERY+ and H-bonding.•Inhibitory effects of DOM were related with its sources and properties.
Macrolides are widely used antibiotics with ubiquitous occurrence in aquatic environments. Unlike many emerging contaminants, macrolides are positively charged on their amine groups and are likely to interact with negative charge groups of dissolved organic matters (DOMs), which may alter macrolide bioaccumulation but yet to be explored. Here we evaluated the effects of different DOM (LeHA, PPHA, SRHA and SRFA) on erythromycin (an important macrolide) bioaccumulation into aquatic biota with 14C tracing. Results showed that ERY uptake in organisms was significantly inhibited by DOM (P < 0.05). In the presence of DOM at 20 mg L−1, the averaged equilibrium concentration (Ce) decreased by 28.1–40.6% for zebrafish and 10.9–25.8% for duckweed, corresponding to reductions in the bioconcentration factor (BCF) by 15.9–32.8% and 10.9–18.5%, respectively. Likely due to their higher carboxyl group content, SRHA and SRFA exhibited stronger inhibitory effects than LeHA or PPHA. The possible interactions between ERY and DOM were explored and results suggested that DOM inhibited ERY bioavailability by forming DOM-ERY complexes via ionic bonding of −COO− and ERY+, hydrogen bonding and hydrophobic partitioning. This study was the first to report on inhibitory effects of DOM on erythromycin bioavailability and has important implications for better understanding risks of macrolides.
The concentration of dissolved organic matter (DOM) in aquatic ecosystems has manifold direct and indirect consequences for primary and secondary production. Theoretical approaches suggest a negative ...effect of DOM on phytoplankton and a positive effect on bacteria, both of which alter the development of metazooplankton, the main consumer of bacteria and phytoplankton. However, experimental observations give heterogeneous results on the effect sizes of plankton in relation to DOM addition. Here, the synthesis of 411 effect sizes of plankton in response to DOM is presented from 59 studies. The referenced studies display effect sizes in relation to various DOM sources and different experimental designs. Thus, the hypothesis that neither DOM quality nor the type of experiment bias the effect size response of plankton was tested; the hypothesis was tested separately for bacterioplankton, phytoplankton and metazooplankton with the use of a meta-analytical approach. DOM quality was represented by the five different sources of DOM that are used most often in these experiments, i.e., natural water, bog leachate, glucose/sucrose, terrestrial plant leachate, and soil leachate. The experiment types comprised in situ experiments, i.e., experiments taking place under manipulated conditions in a natural ecosystem, and ex situ experiments, i.e., those taking place outside of a natural ecosystem. The meta-analyses showed that, although total DOM had a positive influence on the effect size of bacterioplankton and an insignificant influence on metazooplankton, the effect sizes differed significantly in relation to DOM source and the type of experiment. The effect size of phytoplankton, although not significantly related with total DOM, differed in response to DOM source but not experiment type. The results suggest that experimental conditions may produce artifacts in the strength of responses of aquatic biota to DOM concentrations.
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•The results of 59 experiments on plankton responses to DOM were synthesised.•The synthesis was made in regard to DOM source and type of experiment.•DOM source and type of experiments biased effect sizes of plankton.•Ambient conditions of experiments are critical to plankton responses to DOM.
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