Fluorescent Components Research Articles

UFLIM - Unsupervised analysis of FLIM-FRET microscopy data.

Despite their widespread use in cell biology, fluorescence lifetime imaging microscopy (FLIM) data-sets are challenging to analyse, because each spatial position can contain a superposition of multiple fluorescent components. Here, we present a data analysis method employing all information in the available photon budget, as well as being fast. The method, called uFLIM, determines spatial distributions and temporal dynamics of multiple fluorescent components with no prior knowledge. It goes significantly beyond current approaches which either assume the functional dependence of the dynamics, e.g. an exponential decay, or require dynamics to be known, or calibrated. Its efficient non-negative matrix factorization algorithm allows for real-time data processing. We validate in silico that uFLIM is capable to disentangle the spatial distribution and spectral properties of five fluorescing probes, from only two excitation and detection channels and a photon budget of 100 detected photons per pixel. By adapting the method to data exhibiting Förster resonant energy transfer (FRET), we retrieve the spatial and transfer rate distribution of the bound species, without constrains on donor and acceptor dynamics.

Properties of river organic carbon affected by wastewater treatment plants

Tracking the sources of organic carbon (OC) is critical not only for understanding riverine carbon dynamics but also for providing management options to improve water quality. We collected water samples from upland forest streams to the mainstream Geumho River (GHR) of South Korea, which included a variety of wastewater treatment plants (WWTP) effluents. We analyzed the concentrations, optical properties, and dual carbon isotope ratios of these samples to identify the sources of OC. Dissolved organic carbon (DOC) was the dominant form of OC in the GHR compared to particulate organic carbon (POC), as the former accounted for 87 % of OC. The concentrations of DOC and POC ranged from 1.2 to 11.2 mg L−1 and from 0 and 3.6 mg L−1, respectively, aside from the livestock WWTP effluent. Dominant fluorescence components were terrestrial humic substances in upper reaches whereas protein-like materials in lower reaches of the GHR whose watershed includes a large city with many WWTPs. Significantly lower Δ14C-DOC and Δ14C-POC were observed in industrial WWTP effluents than the other sites due to the contribution of fossil OC. Livestock WWTP effluents had higher δ13C-DOC and δ13C-POC than most of the sites, possibly due to the animal feed derived from C4 plants such as corn. Fossil OC contributed 29–52 % of [DOC] and 36–56 % of [POC] from industrial WWTP effluents, whereas C4-plants derived OC contributed about half of [DOC] and [POC] from a livestock WWTP effluent. The results suggest that anthropogenic sources of organic carbon could alter river carbon dynamics, and that caution is needed when we interpret isotope ratios of riverine organic carbon, particularly when the river passes through highly populated areas wherein WWTP effluents are large.

Changes in Quality of Cold-Pressed Rapeseed Oil with Sinapic Acid Ester-Gelatin Films during Storage.

In recent years, cold-pressed rapeseed oil (CPRO) has become an attractive health-beneficial product and a promising alternative to olive oil. However, a high level of unsaturated fatty acids renders a CPRO more susceptible to oxidative deterioration. Therefore, the effect of new gelatin strips with polyvinyl alcohol (GEL-PVA) and sinapic acid esters (ethyl sinapate-ESA; octyl sinapate-OSA, and cetyl sinapate-CSA) on the oxidative stability, antioxidant activity (AA), and total phenolic content (TPC) in CPRO samples was analyzed during accelerated storage. In addition, the antioxidant properties of the GEL-PVA films loaded with sinapic acid esters were studied. Interestingly, the CPRO stored in an amber glass marasca bottle containing GEL-PVA-ESA strips for 14 days had the highest AA, while the antioxidant potential was the lowest for oil without film strips. Furthermore, oil samples stored in bottles containing GEL-PVA-ESA and GEL-PVA-OSA strips for 14 days had higher antioxidant properties than the AA and TPC in fresh CPRO. Moreover, synchronous fluorescence (SF) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy were applied for the evaluation of changes in the main fluorescent components in CPRO samples during the accelerated storage. Overall, this study revealed that GEL-PVA films incorporated with sinapic acid esters enhanced the antioxidant potential of CPRO and delayed oxidative degradation by releasing amphiphilic antioxidants into the oil.

Source and quality of dissolved organic matter in streams are reflective to land use/land cover, climate seasonality and pCO2

Sources and quality of dissolved organic matter (DOM) in streams may be largely controlled by the landscape and season. In this study, we attempted to answer three critical questions: 1) Do land use/land cover (LULC) types affect DOM characteristics? 2) Is there a seasonal fluctuation in DOM components? 3) How do DOM quality and LULC types influence aqueous carbon dioxide partial pressure (pCO2). To achieve this, we investigated the fluorescence characteristics of DOM and its implication for pCO2 in three streams draining land with different urban intensities under distinctive dry and wet seasons. Four fluorescence components were identified, including two terrestrial humic-like components, one protein-like component and one microbial humic-like component. We found a significant positive relationship of the maximum fluorescence intensity (Fmax) of the four components and fluorescence index (FI370) with urbanization intensity in both the dry and wet seasons. The mean Fmax, biological index (BIX) and FI370 all exhibited an increasing trend from upstream to downstream in the stream with highest proportions of urban and cropland. The fluorescence characteristics were negatively related to proportion of forested land in the both seasons. The terrestrial humic-like DOM was dominating in the studied streams. Moreover, the seasonality altered the DOM composition, with protein-like component emerging only in stream waters during the dry season, while microbial humic-like component exclusively occurred during the wet season. pCO2 values were positively related to terrestrial humic-like and biological protein-like components, and urban land. The dry season had much higher pCO2 than the wet season. Results from the Partial Least Squares Path (PLS-PM) models further indicated that LULC types were important in mediating fluorescence DOM whilst pCO2 was more sensitive to the direct effect from FDOM dynamics. We conclude that DOM source and quality in streams are reflective to LULC and climate seasonality, and are good indicators of pCO2 via source tracer and quality of fluorescence components.

Simultaneous degradation of sulfadiazine and dissolved organic matter based on low‐impact development facilities

Sulfadiazine (SD) is a common antibiotic administered to treat bacterial infections in livestock, and its fate and migration are greatly affected by dissolved organic matter (DOM). The soil infiltration system [a typical low-impact development (LID) facility] can significantly alter DOM properties during runoff pollution, thus affecting the complexation of SD with DOM. Here, the binding characteristics of different DOM components and SD in the soil infiltration system were explored using spectroscopic techniques (excitation–emission matrices, parallel factor analysis, and synchronous fluorescence spectroscopy). Combined with the weakening of DOM fluorescence intensity and 78.63% reduction in mean SD concentration following treatment, synchronous degradation may have occurred. The binding sequence of SD and DOM fluorophores was further explored using two-dimensional correlation spectroscopy. Effluent DOM showed greater sensitivity to SD and more binding sites than influent DOM. Moreover, hydrophobic protein-like substances exhibited higher log KM values than other fluorescent components, indicating that protein-like components play significant roles in SD complexation. The soil percolation system improved the complexation stability and binding sequence of fulvic-like substances. Thus, SD–DOM can be intercepted and degraded using LID facilities to reduce the risk of SD in aquatic environments.

Distribution, spectral characteristics, and seasonal variation of dissolved organic matter in the northern Beibu Gulf, South China Sea

Dissolved organic matter (DOM) in the land–ocean interface plays a critical role in the global carbon cycle, yet its dynamic is not well understood. Dissolved organic carbon (DOC) in the northern Beibu Gulf was measured seasonally from April 2020 to January 2021. Chromophoric and fluorescent DOM (CDOM and FDOM) were synchronously characterized by absorption and fluorescence spectroscopy. Three fluorescent components were identified from 597 samples using parallel factor analysis, including two humic-like and one protein-like component. DOC displays a significant seasonality with the average level being highest in summer (177 μmol/L) and lowest in winter (107 μmol/L). CDOM and FDOM levels in summer are also higher than those in winter. Although the variation ranges of DOC, CDOM, and FDOM in surface water are generally greater than in bottom water, the difference between the two layers is statistically insignificant. River discharge and anthropogenic input are important external sources of DOM in the low-salinity nearshore waters (i.e., estuaries and coast), whereas DOM in offshore waters is mainly produced by in situ biological activity. The mixing behavior of DOM in the northern Beibu Gulf varies spatially but minimally on a seasonal scale. Two distinct conservative mixing behaviors of DOC, CDOM, and humic-like FDOM occur in the nearshore waters from Tieshangang Bay and excluding Tieshangang Bay, respectively. The removal of protein-like FDOM along the salinity gradient and the negative correlation between protein-like FDOM intensity and apparent oxygen utilization are pronounced in the nearshore waters excluding Tieshangang Bay, jointly indicating that oxygen is consumed by microbial communities. In contrast, a net addition of DOC occurs in the high-salinity offshore waters, whereas the CDOM and humic-like FDOM undergoes quasi-conservative mixing. Overall, this study reveals notable spatial and seasonal variations in the concentration, source, and mixing of DOM at the land–ocean interface and highlights the importance of sources and processes in shaping the amount and composition of DOM exported to the ocean margin.

Molecular Signatures and Sources of Fluorescent Components in Atmospheric Organic Matter in South China

Molecular Signatures and Sources of Fluorescent Components in Atmospheric Organic Matter in South China

Linking fluorescent dissolved organic matters to microbial carbon metabolism in the overlying water during submerged macrophyte Potamogeton crispus L decomposition in the presence/absence of Vallisneria natans

Multi-species submerged plants grow with succession patterns in the same habit and play an important role in the aquatic ecosystems. The decomposition of submerged plants in aquatic environments was a disturbance that affected the water quality and microbial community structures. However, the responses of the microbial community function in surface water to the disturbance remain poorly understood. In this study, the effects of submerged macrophyte Potamogeton crispus L decomposition on the water quality and microbial carbon metabolism functions (MCMF) in the overlying water were investigated in the presence/absence of Vallisneria natans. The result showed that the decomposition rapidly released a large amount of organic matter and nutrients into the overlying water. The presence of Vallisneria natans promoted the removal of dissolved organic carbon and fluorescent component C3, resulting in lower values of the percentage content of C3 (C3%). Under various decomposition processes, the MCMF changed over time and significantly negatively correlated with C3%. The functional diversity of MCMF significantly correlated with the fluorescence organic matters, such as the richness and Simpson index correlated with the amount of C1, C1+C2+C3, and C3%. But UV–visible absorption indexes and nutrients in the overlying water had no relationship with the MCMF, except for the total nitrogen correlated with the richness. These results suggested that under various decomposition conditions, the fluorescent dissolved organic matter could be used as an indicator for quick prediction of MCMF in surface water.

Effect of Colloids in Sediment and Soil on Their Sorption Behavior of Chloramphenicol

Natural colloids (NCs) are ubiquitous in sediments and soils, which could affect the environmental fate of antibiotics. Focusing on chloramphenicol (CAP), different sources of the sediments and soil samples were selected to research the sorption capacity of NCs with different relative molecular weights towards CAP, as well as the impactors, combined with a multi-method approach including cross-flow ultrafiltration, dynamic light scattering, UV-visible absorption spectroscopy, and three-dimensional excitation-emission matrix fluorescence spectroscopy. The results revealed that the low molecular weight (LMW) of NCs was associated with a low autochthonous origin and a higher humification degree. The high molecular weight (HMW) of NCs were mainly terrestrial sources, and the aromatic rings contained more oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups. Four fluorescence components were identified using the parallel factor analysis model, and the humic-like substances were the primary fluorescent components. Moreover, based on batch experiments, the study investigated the sorption behavior of CAP by the different fractions of the solid samples. The results showed that the sorption processes of CAP were well fitted by the linear model and Freundlich model. The average sorption rate of CAP by the original solid samples and the solid samples with removed organic and inorganic carbon were 4.46%, 3.93%, and 6.61%, respectively, indicating that organic carbon played an important role in the sorption behavior of CAP. The results of the sorption experiments indicated that CAP was more easily adsorbed on the LMW NCs that had a high degree of humification and a more aliphatic chain on the aromatic rings. In addition, tryptophan-like protein substances in NCs showed the inhibiting effect on the sorption progress of CAP. Redundancy analysis indicated that the sorption of CAP by NCs in sediment and soil was mainly related to the source, aromatics, oxygen functional groups on aromatic rings, humification degree, and humic-like substances of NCs.

Spatio-temporal variation of Dissolved Organic Matter (DOM) in the Bohai Sea and the Yellow Sea

The seasonal and spatial variations of dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM), and fluorescent dissolved organic matter (FDOM) were evaluated in the Bohai Sea (BS) and the Yellow Sea (YS) during three cruises. Two fluorescence components, such as marine humic-like (C1) and visible humic-like (C2), were identified using excitation-emission matrix fluorescence spectroscopy (EEMs) and parallel factor analysis (PARAFAC). The average values of DOC concentration, CDOM absorption coefficient (aCDOM(355)) and fluorescence component intensities (C1 and C2) were significantly higher in the BS (2.14 mg C L−1, 0.77 m−1, 0.035 RU, 0.026 RU, respectively) than those in the YS (1.55 mg C L−1, 0.50 m−1, 0.025 RU, 0.019 RU, respectively). The average DOC value was highest in winter (2.16 mg C L−1) and lowest in spring (1.62 mg C L−1), while aCDOM(355) was the opposite (winter: 0.45 m−1; spring: 0.62 m−1; summer: 0.58 m−1). The average C1 (0.042 RU) and C2 (0.028 RU) values were highest during the winter and summer respectively, and lowest during spring (C1: 0.024 RU; C2: 0.016 RU). DOC and CDOM were mainly derived from terrestrial input, during the winter and spring, while they were primarily derived from phytoplankton production during the summer. C1 and C2 were not correlated with salinity or chlorophyll a during the three seasons. The SUVA355 values generally decreased with increasing salinity during the spring and summer, indicating that sources and sinks of CDOM and DOC were uncoupled. DOC, CDOM, and FDOM were dominated by terrestrial input and phytoplankton production activities and their spatial distributions and seasonal variations were also affected by currents, microbial activities, and photobleaching.

Changes in soil dissolved organic matter optical properties during peatland succession

• Topsoil and subsoil DOM respond differently to aboveground vegetation succession. • Succession increases the content of humic-like substances in topsoil DOM. • The content of protein-like material of the subsoil is stable under succession. • pH is a key factor affecting changes in fluorescence properties of topsoil DOM. Dissolved organic matter (DOM) is the most active component in the soil environment. Understanding the chemical diversity of DOM and the interaction of the physicochemical properties of the soil are key to managing peatland under succession. In this study, we aimed to understand the effects of peatland succession on soil DOM. We collected soil samples (topsoil: 0–10 cm, subsoil: 10–20 cm) from peatland during different stages of peatland succession in mid–high latitude northern regions, determined the changes in quantity and quality of DOM using fluorescence spectroscopy and parallel factor analysis. We found that peatland succession altered the effectiveness of soil nutrients and water content. During the succession, the content of humus-like substances in the DOM of the topsoil increased and the content of protein-like material decreased, whereas the content of substances in the subsoil remained stable. pH was the key factor affecting the change in the composition of the DOM in the topsoil during peatland succession. The variation of DOM in the subsoil may be related to the vegetation composition. The results suggest that fluorescent DOM components respond significantly to changes in peatland succession, and DOM properties are driven by soil pH and vegetation composition during peatland succession. In conclusion, our results reveal the optical changes and factors that influence DOM in peatlands under succession. This suggests that DOM can be modified by simultaneous changes of the physicochemical properties in the soil and the vegetation cover.

Simultaneous removal of organic and nitrogenous compounds in mature landfill leachate by a hybrid electro-oxidation-dialysis (EOD) system

ABSTRACT Electrochemical process has been widely applied to eliminate recalcitrant contaminants (i.e., organic and nitrogenous compounds) in landfill leachate. This study aimed to evaluate the performance of a hybrid electro-oxidation-dialysis (EOD) system to minimize organic and nitrogenous compounds through a synergistic process of electrochemical oxidation (EO) and electrodialysis (ED) as well as the dissolved organic matter was characterized in terms of fluorescent component and molecular weight distribution. The EOD was carried out using boron-doped diamond (BDD) and Pt alternately. The results have shown that pH adjustment to acidic conditions is beneficial to EO. At optimal pH (pH 4), BDD-based EO is superior to removing COD and NH 4 + up to around 56% and 64%, respectively. During EOD process, the lower current density at 20.83 mA cm−2 is preferred for the recovery of nitrogenous ions (i.e. NH 4 + and NO 3 – ), especially for BDD-EOD. In addition, the dominant humic acid-like (HAL) and soluble microbial products-like (SMPL) substances in the mature leachate are mostly degraded to smaller molecules from 105 Da to 103 Da in both EOD processes. Overall, BDD-EOD favours indirect oxidation and has a higher energy consumption efficiency than Pt-EOD induced by direct oxidation for simultaneous removal of organic and nitrogenous compounds. BDD-EOD requires a lower total operation cost of around $2.33/m3 compared to Pt-EOD. It is concluded that the hybrid BDD-EOD process is technically feasible as a powerful pre-treatment approach to mature landfill leachate for refractory organics degradation and nitrogenous nutrients recovery.

Blue, green and yellow carbon dots derived from pyrogenic carbon: Structure and fluorescence behaviour

Fluorescence lifetimes and quantum yields featuring polycyclic aromatic hydrocarbons (PAHs) and other organics constituting pyrogenic carbon particulate matter (PM) are seldom measured. In this work, PM sampled in a fuel-rich ethylene flame was firstly separated in organic carbon (OC), soluble in dichloromethane, and refractory organic carbon (ROC), soluble in N-methyl pyrrolidinone, and then analyzed by size exclusion chromatography (SEC) coupled with online UV and fluorescence detection, and by offline fluorescence spectroscopy and mass spectrometry. It was found that three classes of differently light emitting carbon dots (CDs) could be bottom-up synthesized in the same flame system by selecting appropriately the residence time. Actually, OC presented blue fluorescence regardless the residence time, whereas ROC sampled at low and high residence time emitted fluorescence in the green (green CDs) and in the yellow (yellow CDs) region, respectively. The SEC molecular weight of all CDs presented similar trimodal distributions, centered around 300, 1000 and 10,000 u. For the first time fluorescence lifetimes and quantum yields of pyrogenic CD fractions were measured as additional parameters useful for discriminating the fluorescent components and inferring their structural properties, with the support of mass spectrometry. The different spectroscopic features of CDs could be associated to different compositional characteristics as the polydispersity of molecular components featuring blue CDs, opposed to the oligomer-like nature of green and yellow CDs. Pyrogenic CDs showed different fluorescence emission ranges, quantum yield and lifetimes, appealing for their possible applications in the fields of imaging, electronics and sensors.

Emission Mechanism of Self-Trapped Excitons in Sb3+-Doped All-Inorganic Metal-Halide Perovskites.

Sb3+ doping confers highly efficient and color-diverse broadband light emission to all-inorganic metal-halide perovskites. However, the emission mechanism is still under debate. Herein, a trace amount of Sb3+ ions (<0.1% atomic percentage) doping in the typical all-inorganic perovskites Cs2NaInCl6, Rb3InCl6, and Cs2InCl5·H2O allows universal observation of the fine structure in the photoluminescence excitation spectrum of the ns2 electron. A lifetime mapping method was utilized to reveal the origin of broadband emission triggered by Sb3+ doping, by which various fluorescence components can be differentiated. In particular, free-exciton emission was identified at the high-energy end of the broadband emission for all three doped systems. The excitation-energy- and temperature-dependent fluorescence decay further indicates the existence and origin of self-trapped states. The observed structural and vibrational symmetry-dependent emission behaviors suggest dipole interactions can dramatically alter Stokes-shift energy and modulate the light-emitting wavelength.

Discrimination based on commercial/craft origin and on lager/ale fermentation of undiluted Spanish beer samples: front-face excitation-emission matrices and chemometrics

Spanish beer samples of different origin (craft and commercial) and with different type of fermentation (ale and lager) were analyzed employing molecular fluorescence. Excitation-emission matrices were obtained of the bulk samples, employing front-face mode. PARAFAC was performed on the data, obtaining a 6-components model that could be related to the fluorescent components of the beer. A statistical analysis of the scores was carried out, from which it was deduced that the commercial samples are more similar to each other than the craft ones. In addition, ale-fermented samples tend to differ more between them than lager-fermented samples. Finally, an attempt was made to relate the iso-α-acid component to the bitterness values of the samples. This study describes the fluorophores of Spanish beers, and has allowed its qualitative characterization on the basis of their origin, type of fermentation and degree of bitterness.

Effect of UV/ClO2 pretreatment on controlling ultrafiltration membrane fouling of different natural organic matter (NOM) fractions

The ultrafiltration membrane fouling caused by natural organic matter (NOM) is a prevalent problem. In this research, UV/ClO2 pretreatment was employed to control ultrafiltration (UF) membrane fouling induced by various components of NOM. Three typical organic model foulants, including humic acid (HA), sodium alginate (NaAlg) and bovine serum albumin (BSA) were used as representative organic components in natural waters, and their mixture was employed as simulated NOM water. The results showed that UV/ClO2 pretreatment was effective in alleviating membrane fouling induced by HA, NaAlg, BSA, and NOM, which was demonstrated by the enhanced hydrophilicity and interfacial free energy after UV/ClO2 pretreatment. Besides, it showed remarkable removal performance of UV254 and fluorescent components, but caused a deterioration of dissolved organic carbon (DOC) in the permeate, which was attributed to the oxidation of unsaturated organic compounds and reductive organic molecular weight (MW). Moreover, the significantly degradation of disinfection byproduct precursors (DBPs) and micro-polluted organic matter of sulfamethoxazole (SMX) were confirmed. With UV/ClO2 pretreatment, the dominant fouling mechanism in the initial stage of HA and NaAlg showed a tendency that pore blocking played a dominated role, which was opposite with BSA and NOM.

Temporal and spatial distribution characteristics and source analysis of dissolved organic nitrogen in the surface sediment of the Caohai Lake, southwest China.

Caohai Lake is a typical natural lake-type karst plateau wetland, which is sensitive to environmental changes, and the release of dissolved organic nitrogen (DON) in sediment is a potential factor of nitrogen pollution in this lake. Therefore, we aimed to reveal the temporal and spatial distribution characteristics and source analysis of DON in karst lake sediment. Surface sediment samples were collected from Caohai Lake in southwest China, and the sample locations were distributed across almost the entire wetland area, during both the wet and dry seasons. The DON content and fluorescence spectroscopy were determined and analysed using a three-dimensional fluorescence-parallel factor analysis (3DEEM-PARAFAC) model. The mean DON content in the sediment during the dry season (67.79 ± 42.96 mg/kg) was higher than that in the wet season (28.57 ± 20.97 mg/kg). There were four fluorescent components of DON in the sediment: C1 (tyrosine-like protein), C2 (terrestrial humus), C3 (tryptophan-like protein) and C4 (terrestrial humus). The DON in the surface sediment of Caohai Lake was influenced by terrestrial sources and biological activities. These findings help reveal the circulation mechanism of endogenous nitrogen in the lake and provide theoretical support for the prevention and control of nitrogen pollution in Caohai Lake.

Plasma-mediated aging process of different microplastics: Release of dissolved organic matter and formation of disinfection by-products

The release of dissolved organic matter (DOM) from microplastics (MPs) in the water environment under physical, chemical, and biological transformation has been widely concerned. However, the impacts of released DOM on the subsequent generation of chlorinated disinfection by-products (DBPs) are still unknown. In this study, the leaching behaviors of organic matter from four types of MPs by plasma treatment were investigated, with polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) as the model MPs. The plasma treatment led to cracks, pits, and loose porous surfaces of MPs, and the C/O ratios of these four MPs significantly decreased. Simultaneously, the long-chain alkyl groups of the four MPs were weakened, and O-containing functional groups were introduced after the plasma treatment. As a result, the dissolved organic carbon (DOC) released from PP, PVC, PS, and PE after 120 min of plasma treatment were 4.35, 4.33, 5.09, and 14.0 mg L−1, respectively. The released conjugated organic compounds contained aromatic hydrocarbons and double bonds or hydroxyl groups, which were soluble microbial byproduct-like and humic acid-like substances. Trichloromethane (TCM) and dichloroacetic acid (DCAA) were the main DBPs in trihalomethanes (THMs) and haloacetic acids (HAAs). The DBPs in the four MPs filtrates were mainly HAAs, which reached 811.2, 780.2, 1234.7, and 420.7 μg L−1 in the PVC, PP, PE, and PS filtrates after 120 min of plasma treatment, respectively. Correlations among DBPs, UV–visible and fluorescence components of these four MPs were established. Overall, the released byproducts of MPs had the potential to be the precursors of DBPs, and thus their risks deserve more attention.

Reduction capacity of humic acid and its association with the evolution of redox structures during composting

The reducing capacity (RC) of compost-derived humic acid (HA) is related to the type and number of redox-active functional moieties in its structure and has a considerable environmental influence on its geochemical redox cycle. Composting treatment can affect the redox-active fractions of organic substances through microbial transformation and degradation. However, the relationship between the RC of compost-derived HA and its fluorescence component and infrared spectra remains unclear. In this study, we assessed the response of the organic reducing capacity (ORC) and inorganic reducing capacity (IRC) of compost-derived HA to the stabilization of organic solid waste materials by analyzing the redox-active functional groups of HA extracted at different composting times. The results demonstrated that the RC of compost-derived HA continuously increased during composting because of the formation of fulvic- and humic-like fluorescent components, which consist of amide, phenolic hydroxyl, quinone, and aromatic groups. Adsorption occurred between HA and FeCit by aliphatic and out-of-plane aromatic CH, which released free hydrogen and increased the Fe-binding site; consequently, ORC was obviously higher than IRC. The results of this study could provide an understanding of the transformation of the fluorescent substances and functional groups that affect redox properties during composting; therefore, this study has considerable significance for exploring the application of compost products.

Large-scale study on groundwater dissolved organic matter reveals a strong heterogeneity and a complex microbial footprint

Dissolved organic matter (DOM) in terrestrial groundwater is generally low in concentration compared to inland surface waters. However, the overall amount of groundwater DOM is huge, as there is 100 times more fresh groundwater than fresh surface water. To date, research on groundwater DOM has merely focused on specific threats to humans such as e.g. DOM and heavy metal complexations and DOM from hydrocarbon contamination. A comprehensive, large-scale study of groundwater is still missing. Here, we examine DOM properties in a large-scale approach with regards to surface characteristics such as land use and altitude, aquifer characteristics as well as microbial features. We analyzed 1600 water samples from 100 groundwater bodies all over Austria with regards to their DOM quantity, quality and bacterial abundance (BA). DOM quality was evaluated with self-organizing maps on fluorescence excitation-emission-matrices (EEMs) combined with Ward clustering and subsequent parallel factor analysis to describe DOM properties of each cluster. We evaluated how these clusters differed among each other, based on DOC and nitrate concentrations, BA and selected environmental characteristics. Our results show that fluorescence components in groundwater resemble components found in other groundwater studies, in studies from forest streams, the dark ocean, agricultural catchments and wastewater treatment plants. The latter fluorescence components were associated with a cluster that is characterized by agricultural and urban land use, as well as by high nitrate concentrations. Clusters with an increased abundance of high-molecular weight and humic components, commonly associated with vascular plant and soil origin, correlated with a higher bacterial abundance. This observation provides evidence that elevated numbers of suspended bacteria mainly originate from the surface. Our study shows that DOM fluorescence can be a fast monitoring tool to identify aquifers under anthropogenic stress and delineate sensitive recharge areas with high surface-groundwater interaction.