Excitation Emission Matrix-parallel Factor Analysis Research Articles

Bacterial community and dissolved organic matter networks in urban river: The role of human influence

Human activities have significantly altered the biogeochemical cycles of carbon, nitrogen, and sulfur in aquatic ecosystems, leading to ecological problems.This study utilized 16S rRNA gene high-throughput sequencing and excitation-emission matrix parallel factor analysis (EEM-PARAFAC) to evaluate the bacterial community composition and dissolved organic matter structure in the upstream (less impacted) and downstream (severely impacted) sections of the river, with a focus on the interactions between bacterial diversity and dissolved organic matter (DOM) characteristics.Results indicated significant spatial diversity in bacterial communities, with a higher α-diversity upstream compared to the more polluted downstream sections. Environmental parameters, particularly total phosphorus (TP) and dissolved oxygen (DO), were found to significantly influence the distribution and composition of bacterial phyla through redundancy analysis. The pattern of bacterial community assembly has shifted from predominantly deterministic to predominantly stochastic as a result of human activities. The analysis of DOM through EEM-PARAFAC identified three main fluorescent components, reflecting varied sources and interactions with bacterial communities. Upstream, microbial activities predominantly contributed to autochthonous DOM, while downstream, increased inputs of allochthonous DOM from human activities were evident. Furthermore, the study revealed that through the introduction of various organic pollutants and nutrient loads that shift microbial metabolic functions towards increased degradation and transformation of complex organic compounds downstream. Structural equation modeling (SEM) revealed that upstream human activities primarily affected bacterial communities indirectly by altering DOM properties. In contrast, downstream activities had both direct and indirect effects due to higher pollutant loads and more complex environmental conditions. These interactions underline the profound effect of anthropogenic factors on riverine ecosystems and emphasize the importance of managing human impacts to preserve microbial biodiversity and water quality.

Effect of rainfall-derived inflow and infiltration on dissolved organic matter in urban sanitary sewers using chemometric and machine learning approaches

This study investigated changes in dissolved organic matter (DOM) properties within urban sanitary sewers influenced by groundwater infiltration and excessive rainfall-derived inflow and infiltration (RDII). It employed optical indices and fluorescence excitation-emission matrix-parallel factor analysis (PARAFAC) coupled with self-organizing map (SOM) to compare DOM characteristics during wet weather flows (WWFs) and dry-weather flows (DWFs). Sampling sites impacted by RDII were identified based on flowrate. Optical indices and PARAFAC components (C1–C4) were used to differentiate DOM properties between DWFs and WWFs. In WWFs, E<sub>2</sub>/E<sub>3</sub> and S<sub>350-400</sub> increased, while spectral ratio (S<sub>R</sub>) decreased, indicating a shift towards smaller organic matters. Reduced fluorescence and humidification indices suggested the input of fresher/terrestrial organic matters. C3 and C4 exhibited significant distinctions, showing increased C3 and decreased C4 levels. The PARAFAC-SOM modeling further illustrated that water samples in the urban sewer system could be categorized based on the dominance of DOM properties. Principal component analysis revealed separation between DWF and WWF samples in principal component 1 (PC1), associated with molecular size. PC2 was linked to microbial activity in WWFs. Notably, DWF samples from the NY-11 site shifted to the positive side of the PC1 axis, while their corresponding WWF samples moved to the negative side.

Spatial distribution of sediment dissolved organic matter in oligotrophic lakes and its binding characteristics with Pb(II) and Cu(II).

Dissolved organic matter (DOM), the most active component in interstitial waters, determines the stability of heavy metals and secondary release in sediments. However, little is known about the composition and metal-binding patterns of DOM in interstitial water from oligotrophic lakes affected by different anthropogenic perturbations. Here, 18 interstitial water samples were prepared from sediments in agricultural, residential, tourist, and forest regions in an oligotrophic lake (Shengzhong Lake in Sichuan Province, China) watershed. Interstitial water quality and DOM composition, properties, and Cu(II)- and Pb(II)-binding characteristics were measured via physicochemical analysis, UV-vis spectroscopic, fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC), and fluorescence titration methods. The DOM, which was produced mainly by microbial activities, had low molecular weights, humification degrees, and aromaticity. Based on EEM-PARAFAC results, the DOM was generally composed of tryptophan- (57.7%), terrestrial humic- (18.7%), microbial humic- (15.6%), and tyrosine-like (8.0%) substances. The DOM in the metal complexes was primarily composed of tryptophan-like substances, which accounted for ~42.6% of the DOM-Cu(II) complexes and ~72.0% of the DOM-Pb(II) complexes; however, microbial humic-like substances primarily contributed to the stability of DOM-Cu(II) (logKCu = 3.7-4.6) and DOM-Pb(II) (logKPb = 4.3-4.8). Water quality parameters did not significantly affect the stability of DOM-metal complexes. We demonstrated that the metal-binding patterns of DOM in interstitial water from oligotrophic lakes are highly dependent on microbial DOM composition and are affected by anthropogenic perturbations to a lesser extent.

Differences in dissolved organic matter (DOM) composition of soils from native eucalypt forests and exotic pine plantations impacted by wildfire in Southwest Australia

In recent decades, plantations of exotic species have transformed large tracts of forested landscapes, where they often form a mosaic with the surrounding native forest. Wildfires have also increased in frequency and intensity globally, impacting both plantation and native forests and affecting soil organic matter (SOM), including dissolved organic matter (DOM). DOM of soils is considered highly labile and likely sensitive to effects of fire and changes in land use. However, it is unclear how wildfire influences key characteristics of DOM in exotic plantations compared to native forest. In this study, we investigated the impacts of wildfire on chemical properties of DOM in exotic Pinus radiata plantations and adjacent native jarrah (Eucalyptus marginata) forest in southwest Australia. We coupled fluorescence excitation-emission matrix parallel factor analysis (EEM-PARAFAC) and 1H‐NMR with soil nutrient analyses to characterise soil DOM (0–5 cm) from burned and unburned plots of each forest type, four months after the fire. Four fluorescent components (humic-, fulvic-, microbial and protein-like substances) were derived from soil DOM using the PARAFAC model. DOM from burnt forest soils was predominantly of lower molecular weight (E2:E3) and contained a greater microbial-derived component and a lower fulvic component than unburnt forest. As expected, soil pH and labile inorganic P increased in both forest types after fire. By contrast, an increase in the amount of DOC after fire was only recorded in native forest, while δ15N signatures were more enriched in pine plantation soils after fire but not in native forest soils. Differences in impacts of fire on DOC and δ15N between forest types suggest a different response to fire according forest type, even though these differences were not evident above ground. The 1H NMR spectra of DOM revealed all samples were largely dominated by aliphatic structures. However, there were no significant differences in the overall spectra between forest types or between burnt and unburnt forests. Overall, our findings suggest that transformations in soil DOM after fire were affected by feedbacks between forest type and fire (where soils from pine plantations appeared to be more affected by fire).

The complex relationships between diatoms, bacterial communities, and dissolved organic matter: Effects of silicon concentration

Complex relationships exist between diatoms, bacterial communities and dissolved organic matter in aquatic ecosystems. Clarifying their relationships is essential to reveal biogeochemical cycles. In this study, the diatom Cyclostephanos invisitatus was cultured in standard silicon (SS), no silicon (NS), and excessive silicon (ES). Integrated 16S rDNA high-throughput sequencing and excitation-emission matrix parallel factor analysis (EEM-PARAFAC) were used to investigate diatom growth, bacterial community and dissolved organic matter (DOM) characteristics. It was found that the abundance of diatoms decreased in no silicon and excessive silicon conditions. Further, the composition and function of the associated bacterial communities were affected. The Proteobacteria and Cyanobacteria were more highly represented in the attached bacteria, whereas the Proteobacteria and Bacteroidetes were more highly represented in the free-living bacteria. Alpha diversity showed different trends with incubation time in all treatments. Moreover, genes (K01995 to K01998) involved in environmental information processing were more abundant in diatoms during the stationary phase in attached bacterial community. Stochastic processes play a key role in the formation of bacterial communities, both for attached and free-living bacteria. In addition, the differences in fluorescence components (protein and humic-like) and spectral indices (fluorescence index, biological index, freshness index, and humification index) revealed intricate relationship between microalgae and bacteria. Overall, this work confirmed the importance of silicon concentration in regulating diatom-associated bacterial communities and DOM characteristics.

Dissolved organic material changes during combined treatment of a mixture of landfill leachate and anaerobic digestate using deammonification and chemical coagulation.

The current study investigates the combined treatment of wastewater of anaerobic digestate and landfill leachate, using deammonification and coagulation/flocculation processes. The deammonification section studies the performance of a full-scale deammonification plant in nitrogen and chemical oxygen demand (COD) removal, monitored over 2 years. For further COD reduction from the deammonification effluent (DE) to meet the environmental regulatory standards, coagulation/flocculation using three different Al-based coagulants was used to treat the DE. Results revealed that the deammonification plant showed 80% average ammonium removal from the mixed feed over the study period. Additionally, 30% of the feed COD was removed in the deammonification plant. COD analysis after treatment using coagulants revealed that the polyaluminum chloride modified with Fe had the best performance in reducing COD to meet the environmental standards. Excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) of the dissolved organic material (DOM) samples indicated that fluorescents were the compounds mostly affected by the coagulant types. DOM analysis using 2D correlation Fourier-transform infrared spectroscopy revealed that the applied coagulants showed minor differences in removing different functional groups, despite having different COD reduction performance. Wastewater elemental analysis indicated elevated metal concentrations in low pH conditions (<6) due to re-stabilization of the flocs using coagulants.

Harnessing the composition of dissolved organic matter in lagoon sediment in association with rare earth elements using fluorescence and UV–visible absorption spectroscopy

Dissolved Organic Matter (DOM) plays a pivotal role in influencing metal binding and mobility within lagoon sediments. However, there exists a gap in understanding the compositional alterations of DOM concerning Rare Earth Elements (REEs) across varying pollution gradients. This study aimed to characterize DOM and examine its relationship with REEs in sediment cores from different pollution levels in Yundang Lagoon, China using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The results raveled four distinct fluorescent components. Among these, two correspond to humic-like substances, while the remaining two are attributed to protein-like substances. Remarkably, the prevalence of protein-like compounds was observed to exceed 58% of the total fluorescence intensity across all the investigated sites. Furthermore, a substantial discrepancy in total fluorescence intensity was detected between the Songbai Lake and the Inner and Outer Lagoon, indicating a variance in DOM content. In terms of REEs, the average concentration of total REEs was notably elevated within the Songbai Lake sediments (318.36 mg/kg) as compared to the Inner and Outer Lagoon sediments (296.36 and 278.05 mg/kg, respectively). Of significance is the enrichment of Light Rare Earth Elements (LREEs), particularly Ce, La, Pr, and Nd, over Heavy REEs (HREEs) across all surveyed locations. Intriguingly, a coherent trend emerged wherein the fluorescence intensity and LREE concentrations exhibited a synchronized increase from Outer to Inner to Songbai Lake core sediments. This observation substantiates a strong correlation between DOM content and pollution levels (p < 0.05). By shedding light on the intricate interplay between DOM and REEs within urban aquatic sediments, this study imparts novel insights which enrich our comprehension of urban environmental dynamics.

Evaluation of Groundwater Infiltration in Sewer Networks Using Fluorescence Spectroscopy

Diagnosing water infiltration is imperative to assess the integrity and operation performance of sewer networks, which is challenging and costly due to the complex nature of these networks. This study proposes a simple approach to evaluate the extent of groundwater infiltration via a fluorescence spectroscopy method, i.e., the identification and quantification of the fluorescent signature components of the dissolved organic matter sewage. A newly built sewer network in Shantou, Southern China, was selected for the case study, and a mass balance method based on water quality characteristic factors (total phosphorus and NH4+-N) was applied in parallel for comparison. The results showed that the mass balance method was substantially influenced by fluctuations in sewage and external water concentrations, rendering it unreliable due to the extensive data and calculations required. Conversely, three-dimensional excitation–emission matrix–parallel factor analysis enabled the identification of terrestrial humus compounds as the signatures of underground water sources. The estimation indicates that the groundwater proportion across the four surveyed inspection wells along the pipeline network ranged from 10.8 ± 2.5% to 9.6 ± 3.5%, conforming to the allowable groundwater infiltration limits set for municipal sewage pipelines (10–15%). This study presents a simple method for the in-depth analysis of groundwater infiltration in urban sewage networks, providing valuable insights into maintaining water quality and network integrity.

Air nanobubble water improves plant uptake and tolerance toward cadmium in phytoremediation

Heavy metal contamination continues to be a persistent environmental problem. To address this issue, this study evaluated the impact of air nanobubbles (NBs) in water on the uptake of heavy metals by Alternanthera philoxeroides (A. philoxeroides), a common aquatic plant in China known for its rapid growth, strong vitality, and high capacity for heavy metal remediation. This study found that diluted air NBs (25% concentration) boosted cadmium uptake of A. philoxeroides by 17.39%. They also enhanced plant growth (25–50%) and photosynthetic pigments (10–20%) even at low cadmium levels (0.1 mM). Furthermore, the incorporation of 25% air NBs has been demonstrated to significantly amplify the performance of key antioxidant enzymes, such as superoxide dismutase and catalase, alongside heightened levels of crucial antioxidants such as malondialdehyde. This heightened activity of antioxidant defenses offers a compelling explanation for the potential amelioration of cadmium toxicity and concurrent enhancements in overall plant growth rates. Notably, a comprehensive analysis utilizing the excitation emission matrix–parallel factor analysis (EEM-PARAFAC) technique has revealed alterations in the composition of rhizosphere dissolved organic matter due to the presence of NBs. This ncomposition change of the rhizosphere dissolved organic mattermposition has subsequently exerted an influence on plant complexation processes and the subsequent uptake of cadmium. This study demonstrates that the strategic implementation of air NBs in water systems holds the potential to significantly enhance the plant's ability to detoxify cadmium and improve the uptake of heavy metals during phytoremediation processes.

Sewage-derived substances and dead microbial cells cause gel biofilm formation in membrane bioreactors treating real sewage

Gel fouling is frequently reported as one of the biggest obstacles in membrane bioreactors (MBRs) and is observed under unstable conditions. However, the mechanism and the cause of gel fouling are unknown. In this study, gel fouling was induced and compared with normal fouling (cake fouling) in MBR to identify the source of the substances and microorganisms which form the basis of the gel biofilm. Two anoxic/oxic MBRs were operated under changing and stable sludge loading rate (SLR) to induce gel and cake fouling, respectively. As SLR increased from 0.07 to 0.11 kg-COD/kg-MLSS, transmembrane pressure increased rapidly, and a gel biofilm formed on the membrane surface. By contrast, a cake biofilm was developed under stable SLR of 0.07 kg-COD/kg-MLSS with slow transmembrane pressure increase. Excitation-emission matrix-parallel factor analysis indicated that simple aromatic proteins and soluble microbial byproduct-like substances in the filtered supernatant were efficiently removed in both reactors; however, proteins and polysaccharides accumulated in the supernatant with flocs. Scanning electron microscopy analysis revealed that the gel biofilm had a cloud-like structure, with aggregates of filamentous bacteria and microcolonies. The gel biofilm had a thick dead-cell layer and a small number of dispersed live cells, whereas the cake biofilm had a three-dimensional structure of live and dead cells. In the context of the microbial community in gel biofilms, sewage-derived bacteria, such as Campylobacteria and Clostridia, were highly dominant, and the microbial community resembled more sewage than activated sludge. These results indicate that the accumulation of sewage-derived substances and dead microorganisms might have formed gel biofilm in the MBR.

Investigating the molecular weight distribution of atmospheric water-soluble brown carbon using high-performance size exclusion chromatography coupled with diode array and fluorescence detectors

Atmospheric brown carbon (BrC) contain amounts of organic species, but their molecular weight (MW) distributions is still poorly understood. This study applied high-performance size exclusion chromatography (HPSEC) coupled with a diode array detector (DAD) and fluorescence detector (FLD) to characterize the MW distributions of typical chromophores and fluorophores within water-soluble BrC. The investigation focused on the spring season, encompassing both typical urban and rural aerosols. Our results showed that chromophores (at 254 and 365 nm), and humic-like and protein-like fluorophores identified by excitation-emission matrix parallel factor analysis (EEM-PARAFAC) within BrC were broadly distributed along the MW continuum (∼50–20,000 Da). This suggests that BrC mainly comprises complex chromophores and fluorophores with heterogeneous molecular sizes. High-MW (HMW, >1 kDa) species (66%–74%) dominated the chromophores at 254 and 365 nm. However, the latter chromophores were enriched with more HMW species. This result suggested that the HMW chromophores might contribute more to BrC absorption at longer wavelengths. The PARAFAC-derived fluorescent components also exhibited different MW distributions. Three humic-like substances (HULIS) were all dominated by HMW fractions (51%–74%), but protein-like fluorescent component (PLOM) enriched low-MW (LMW, <1 kDa) species (60%–66%). Furthermore, the molecular size (i.e., weight-averaged and number-averaged MW) and the ratios between HMW and LMW species decreased in the order highly-oxygenated HULIS > less-oxygenated HULIS > PLOM, indicating that the fluorophores with longer Em were generally related to larger MW. To our knowledge, this is the first report on the molecular size of individual fluorescent components within aerosol BrC. The results obtained here enhanced our knowledge of heterogeneous composition, complex physicochemical properties, and potential atmospheric fates of aerosol BrC.

Effects of organic additives on spectroscopic and molecular-level features of photo-induced dissolved organic matter from microplastics

The environmental occurrence and impact of dissolved organic matter leached from microplastics (MP-DOM) has been the subject of increased research interest. Commercial plastics, which typically contain additives, are subject to natural weathering processes and can eventually lose their additives. However, the effects of organic additives in commercial microplastics (MPs) on the release of MP-DOM under UV irradiation remain poorly understood. In this study, four polymer MPs (polyethylene; PE, polypropylene; PP, polystyrene; PS, polyvinylchloride; PVC) and four commercial MPs, including a PE zip bag, a PP facial mask, a PVC sheet, Styrofoam, were subjected to leaching under UV irradiation, and the MP-DOM was characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC). Although UV light promoted the leaching of MP-DOM from both MP groups, the amount released was more pronounced for the polymer MPs than for the commercial MPs. The commercial MP-DOM was characterized by a prominent protein/phenol-like component (C1), while a humic-like component (C2) prevailed in the polymer MPs. FT-ICR-MS identified a higher number of unique molecular formulas for the commercial than for the polymer MP-DOM. The unique molecular formulas of commercial MP-DOM included known organic additives and other breakdown products, while the polymer MP-DOM featured more pronounced unsaturated carbon structures in its identified unique formulas. Several molecular-level parameters showed significant correlations with fluorescence properties, such as CHO formulas (%) with C1 and condensed aromatic structure (CAS-like, %) with C2, suggesting the potential application of fluorescent components as an optical descriptor for the complex molecular-level composition. This study also revealed the possible high environmental reactivity of both polymer MPs and fully weathered plastics due to the unsaturated structures generated in sunlit environments.

Pyrolysis temperature dependent effects of biochar on shifting fluorescence spectrum characteristics of soil dissolved organic matter under warming

Biochar generally shift the content and molecular composition of soil dissolved organic matter (DOM) which represent the reactive components and have essential roles in coupling elemental cycling in soil. However, it is not clear how the effects of biochar on soil DOM composition is shifted under warming. This causes a knowledge gap to fully understand the fate of SOM affected by biochar application in a warming climate. To fill this gap, we conducted a simulated climate warming incubation of soil to study the influence of biochar with different pyrolysis temperatures and feedstock types on soil DOM components composition. Three-dimensional fluorescence spectrum analysis combining excitation emission matrix-parallel factor analysis (EEM-PARAFAC), fluorescence region integral (FRI), UV–vis spectrometry, principal component analysis (PCA), clustering analysis, Pearson correlation and multi-factor analysis of variance on fluorescence parameters (including FRI on Region I-V, FI, HIX, BIX, H/P) and soil DOC and DON content were analyzed for this purpose. Results showed that biochar shifted soil DOM composition and enhanced soil humification, which was dominantly pyrolysis-temperature dependent. Biochar shifted the soil DOM components composition probably through mediating soil microbial processing rather than direct input of their pristine DOM, and the influence of biochar on soil microbial processing was pyrolysis-temperature dependent and highly affected by warming. Medium-temperature biochar was more efficient for enhancing soil humification, by accelerating the transformation of protein-like components into humic-like components. Soil DOM composition presented a rapid response to warming, and long-term incubation may eliminate the effects of warming on shifting soil DOM composition. By revealing the heterogeneous effects of biochar with different pyrolysis temperatures on fluorescence characteristics of soil DOM components, our study provides a hint for the essential role of biochar on enhancing soil humification, and also suggests a vulnerability of biochar for soil carbon sequestration under warming.

Release of adsorbed copper and carbon during Fe(Ⅱ) catalytic conversion of ferrihydrite-humic acid coprecipitation under acidic condition: Mechanism and properties

The mobility of copper (Cu) may be significantly impacted during the conversion of ferrihydrite-humic acid (Fh-HA) coprecipitates. However, the environmental behavior of the adsorbed Cu in Fh-HA coprecipitation and the kinetic process of organic carbon (C) during the Fe(Ⅱ)-catalyzed Fh-HA coprecipitates conversion remains unclear. In this study, a series of Fh-HA coprecipitates with various C/Fe molar ratios were synthesized. Furthermore, the effects of the Fe(Ⅱ) mediated Fh and Fh-HA conversion processes on Cu mobility and carbon release characteristics under acidic condition were investigated. The results show that the specific surface area of Fh-HA is reduced as compared to pure Fh, which impedes the conversion of Fe minerals and increases the release of Cu to the solution. The rate of conversion can be accelerated by increasing the Fe(II) concentration, resulting in the retention of Cu in the mineral structure. As compared to artificial HA, Elliott soil humic acid (ESHA) coprecipitated with Fh resulted in a reduced Cu release. According to results of the fluorescence excitation emission matrix-parallel factor analysis, the "release-resorption" process of carbon occurred during conversion and low molecular weight HA related to the biological activity was the main source of the released organic carbon. The major functional groups were C-O functional groups and phenolic hydroxyl groups, and Cu was involved in the formation of Fe-O-Cu after conversion. The findings of this study provide crucial information for comprehending the biogeochemical process of Cu associated with Fh and Fh-HA coprecipitates.

Spectral change of dissolved organic matter after extracted by solid-phase extraction and its feasibility in predicting the acute toxicity of polar organic pollutants in textile wastewater.

Spectroscopic parameters can be used as proxies to effectively trace the occurrence of organic trace contaminants, but their suitability for predicting the toxicity of discharged industrial wastewater with similar spectra is still unknown. In this study, the organic contaminants in treated textile wastewater were subdivided and extracted by four commonly-used solid-phase extraction (SPE) cartridges, and the resulting spectral change and toxicity of textile effluent were analyzed and compared. After SPE, the spectra of the percolates from the four cartridges showed obvious differences with respect to the substances causing the spectral changes and being more readily adsorbed by the WAX cartridges. Non-target screening results showed source differences in organic micropollutants, which were one of the main contributors leading to their spectral properties and spectral variations after SPE in the effluents. Two fluorescence parameters (C1 and humic-like) identified by the excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were closely correlated to the toxicity endpoints for Scenedesmus obliquus (inhibition ratios of cell growth and Chlorophyll-a synthesis), which can be applied to quantitatively predict the change of toxicity effect caused by polar organic pollutants. The results would provide novel insights into the spectral feature analysis and toxicity prediction of the residual DOM in industrial wastewater.

Molecular compositions and optical properties of water-soluble brown carbon during the autumn and winter in Guangzhou, China

Brown carbon (BrC) has attracted increasing attention due to its significant effects on the atmospheric environment and climate. In this study, we investigated the seasonal variations of the optical and molecular properties of water-soluble BrC in Guangzhou and the key factors affecting its light absorption and fluorescence properties. The mass absorption efficiency at 365 nm (MAE365) indicated that water-soluble BrC had a stronger light absorption capacity in winter than in autumn. An excitation emission matrix-parallel factor analysis (EEM-PARAFAC) identified four fluorescent components (C1–C4) in the water-soluble organic compound (WSOC) fraction, of which the humic-like components (C1, C2, and C4) were the dominant fluorophores. More C1 and C4 components were detected in autumn WSOC, whereas more C3 component in winter WSOC, which was mainly due to the differences in the sources and oxidation processes of WSOC in different seasons. The molecular composition of WSOC also indicated significant seasonal variations as revealed by an electrospray ionization ultrahigh-resolution mass spectrometry (ESI-UHRMS) analysis. The autumn WSOC had a higher degree of oxidation, whereas the winter WSOC had a higher aromaticity. Furthermore, a principal component analysis (PCA) and the Pearson correlation coefficients indicated that the light absorption of water-soluble BrC over Guangzhou was mainly affected by their aromaticity and N-containing species, with aromatic CHO and CHON compounds being the most important chromophores. The fluorescent components C1 and C4 were characterized by a relatively high oxidation level, which may be more relevant to aged organic aerosols with a high aromaticity and oxidation. The fluorescent component C3 may be more relevant to the primary emission of organic aerosols or fresh organic aerosols with low oxidation, and some non-nitrogen-containing species also had associations with previously assigned protein-like components (C3).

Variations in the concentration, composition, and sources of WEOM in erosion and deposition landscapes over an erosion intensity gradient on the Loess Plateau of China

Water-extractable organic matter (WEOM) is the most active and mobile fraction of soil organic matter and responds sensitively to soil erosion. However, previous studies on the chemical nature of WEOM in the erosion and deposition landscapes were controversial at site-level studies and mainly focused on surface soils, limiting our assessment of WEOM’s environmental fate at larger and deeper scales. Here, we collected eroded soils and deposited sediments from a depth of 0–200 cm in five eroding catchments with an erosion intensity gradient across the Loess Plateau. We examined the concentration, composition, and potential sources of WEOM using UV–visible absorption and fluorescence excitation-emission matrix-parallel factor analysis. Soil WEOM quantity and quality varied significantly in the erosion and deposition landscapes, with greater variations in soils below 20 cm, where WEOM in the deposition zone was characterized by higher concentration, aromaticity, hydrophobicity, and UVA and UVC humic-like components derived from terrestrial and soil organic matter. WEOM variations in deep soils increased with increasing erosion modulus among sites, and were mainly driven by changes in soil organic carbon concentration, aggregate stability, and carbon to nitrogen ratio. However, the pattern of WEOM parameters between erosion and deposition zones at 0–20 cm was opposite to that in soils below 20 cm. Vegetation inputs compensated the loss of organic matter in sites with suitable climatic status and weak erosion, and led to higher concentrations and exogenous features of WEOM in the surface erosion area. Concludingly, the WEOM concentration, components, and sources differed significantly between erosion and deposition zones, and these differences, as well as their response to erosion intensity, revealed an opposing pattern in surface and deep soils.

Dissolved organic matter derived from biodegradable microplastic promotes photo-aging of coexisting microplastics and alters microbial metabolism

Dissolved organic matter (DOM) leaching from biodegradable microplastics (BMPs) and its characteristics and corresponding environmental implication are rarely investigated. In this study, the main component of DOM leachate from the two BMPs (polyadipate/butylene terephthalate (PBAT)/polycaprolactone (PCL)) was verified by using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The PBAT-DOM (PBOM) was aromatized and terrestrial. Comparatively, PCL-DOM (PLOM) had low molecular weight. PBOM contained protein-like components while PLOM contained tryptophan and tyrosine components. Interestingly, both PBOM and PLOM could accelerate the decomposition and oxidation of coexisting polystyrene (PS) under light irradiation. Further, the difference in composition and the properties of BMPs-DOM significantly affected its photochemical activity. The high territoriality and protein-like component of PBOM significantly promoted the generation of 1O2 and O2•-, which caused faster disruptions to the backbone of PS. Simultaneously, the microbial community's richness, diversity, and metabolism were obviously improved under the combined pressure of aged PS and BMPs-DOM. This study threw light on the overlooked contribution of DOM derived from BMPs in the aging process of NMPs and their impact on the microbial community and provided a promising strategy for better understanding of combined MPs' fate and environmental risk.

Effects of bisphenols and perfluoroalkylated substances on fluorescence properties of humic and amino acids substances of dissolved organic matter: EEM-PARAFAC and ATR-FTIR analysis

Abiotic, biotic, and sparingly the xenobiotic factors are considered to influence the compositional variation of dissolved organic matter (DOM) in aquatic environments. Increasing discharge of xenobiotics into water bodies necessitates the need to investigate their effects on the key components of DOM. The effects of bisphenols (BP) and perfluoroalkylated substances (PFAS) on the fluorescence characteristics of pure humic substances (HS) and amino acids (AA) of DOM were examined by using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) and the attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy in this work. The results showed that interactions of fulvic acid (FA), humic acid (HA), and tryptophan (Trp) with the xenobiotic compounds could generate some fluorescence components like both HS and AA components, whereas the interactions with tyrosine (Tyr) could only generate AA fluorescence components. In addition, it was revealed that the fluorescence intensity of HS decreases by 50–70% and 18–25% in the treatments of HA and FA, respectively, at low concentration (2.5 × 10−3 mg/L) of BP, while this increases by 350–425% and 18–25% at the same concentration of PFAS. However, both BP and PFAS increase the fluorescence intensity of AA. The findings suggest that the xenobiotic compounds are important factors affecting the compositional variation of DOM, especially in the anthropogenically-impacted water bodies.

Hydrothermal pretreatment improves humification in co-composting of oil palm fronds and paper mill sludge

The co-composting of oil palm fronds and paper mill sludge may be economical and eco-friendly, yet the complex indigenous configuration of lignocellulose reduces the bioavailability of waste, resulting in the hindrance to the humification process. In this work, oil palm fronds after hydrothermal pretreatment were mixed with paper mill sludge for co-composting, and the effect of hydrothermal pretreatment on the humification process was explored using excitation-emission matrix-parallel factor analysis and 16S rDNA sequencing. The results showed that the duration of thermophilic phase was extended from 13 days to 17 days after hydrothermal pretreatment. During hydrothermal-pretreated composting, the consumption of protein-like substances and the production of humus-like substances increased by 24.7% and 33.9%, respectively, compared with those of control. The degradation of polysaccharide (decreased from 76.5 to 20.0 g/kg) was accelerated and the content of reducing sugar (ranged from 11.5 to 13.5 g/kg) was increased. The key microbial communities (including Bacillaceae, Sphingobacteriaceae, Streptosporangiaceae and Thermonosporaceae) showed obviously stronger activity. Correlation analysis showed that the production of reducing sugar and the activity of key microbial communities were reinforced, and both were favorable for the rapid synthesis of humus. Collectively, this work provides an overview of a regulatory mechanism underlying humus formation during the composting of lignocellulosic wastes.