Fluorescence and molecular signatures of dissolved organic matter to monitor and assess its multiple sources from a polluted river in the farming-pastoral ecotone of northern China

Molecular characteristics of dissolved organic phosphorus in watershed runoff: Coupled influences of land use and precipitation

Land use and precipitation are two major factors affecting phosphorus (P) pollution of watershed runoff. However, molecular characterization of dissolved organic phosphorus (DOP) in runoff under the joint influences of land use and precipitation remains limited. This study used Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to study the molecular characteristics of DOP in a typical P-polluted watershed with spatially variable land use and precipitation. The results showed that low precipitation and intense human activity, including phosphate mining and associated industries, resulted in the accumulation of aliphatic DOP compounds in the upper reaches, characterized by low aromaticity and low biological stability. Higher precipitation and widespread agriculture in the middle and lower reaches resulted in highly unsaturated DOP compounds with high biological stability constituting a higher proportion, compared to in the upper reaches. While, under similar precipitation, more aliphatic DOP compounds characterized by lower aromaticity and higher saturation were enriched in the lower reaches due to more influence from urban runoff relative to the middle reaches. Photochemical and/or microbial processes did result in changes in the characteristics of DOP compounds during runoff processes due to the prevalence of low molecular weight and low O/C bioavailable aliphatic DOP molecules in the upper reaches, which were increasingly transformed into refractory compounds from the upper to middle reaches. The results of this study can increase the understanding of the joint impacts of land use and precipitation on DOP compounds in watershed runoff.

Riverine seasonal rainfall event tracing of organic pollution sources using fluorescence fingerprint difference spectrum

Elucidating the dynamics of dissolved organic matter (DOM) transport and transformation under seasonal rainfall events is essential for the conservation of riverine ecosystems, for mitigating the effects of climate change, and for crafting informed water management strategies. Therefore, this study aimed to investigate the evolutionary characteristics of organic pollution sources during consecutive rainfall events in early spring and to quantify their relative contributions to the process of surface water pollution. The results showed seasonal rainfall induces water quality exceedances in rivers due to the combined impacts of terrestrial inputs and endogenous releases. Humic acid (HA) (region V) and fulvic acid (FA) (region III) emerged as the predominant organic matter in the water column, with their fluorescence intensity altering as rainwater flushed the riverbed. Sources of pollution include agricultural and urban domestic sources (AS + DS) (72.29 %), industrial and urban domestic and microbial sources (IS + DS + MS) (37.71 %), and agricultural and industrial sources (AS + IS) (63.32 %), indicating that agricultural surface pollution discharges contribute significantly. The gas-chromatography-mass spectrometry (GC-MS) further confirmed that exogenous inputs were predominantly comprised of particulate pollutants. This study underscores the efficacy of fluorescence difference spectrometry in delineating the migration and transformation of river pollution sources during seasonal rainfall and facilitating the implementation of targeted management strategies for river ecosystems.

Selective molecular characterization of organic aerosols using in situ laser desorption ionization mass spectrometry

RATIONALE

The sources and chemical compositions of organic aerosol (OA) exert a significant influence on both regional and global atmospheric conditions, thereby having far-reaching implications on environmental chemistry. However, existing mass spectrometry (MS) methods have limitations in characterizing the detailed composition of OA due to selective ionization as well as fractionation during cold-water extraction and solid-phase extraction (SPE).

METHODS

A comprehensive MS study was conducted using aerosol samples collected on dusty, clean, and polluted days. To supplement the data obtained from electrospray ionization (ESI), a strategy for analyzing OAs collected using the quartz fiber filter directly utilizing laser desorption ionization (LDI) was employed. Additionally, the ESI method was conducted to explore suitable approaches for determining various OA compositions from samples collected on dusty, clean, and polluted days.

RESULTS

In situ LDI has the advantages of significantly reducing the sample volume, simplifying sample preparation, and overcoming the problem of overestimating sulfur-containing compounds usually encountered in ESI. It is suitable for the characterization of highly unsaturated and hydrophobic aerosols, such as brown carbon-type compounds with low volatility and high stability, which is supplementary to ESI.

CONCLUSIONS

Compared with other ionization methods, in situ LDI helps provide a complementary description of the molecular compositions of OAs, especially for analyzing OAs in polluted day samples. This method may contribute to a more comprehensive MS analysis of the elusive compositions and sources of OA in the atmosphere.

Unraveling the role of anthropogenic and hydrologic drivers with respect to the optical and molecular properties of dissolved organic matter and organic phosphorus in a P-contaminated river

Anthropogenic and hydrological drivers are key factors influencing the fate of dissolved organic matter (DOM) and dissolved organic phosphorus (DOP) in river runoff. However, how anthropogenic disturbances and hydrological conditions jointly affect the composition and characteristics of DOM and DOP in river runoff remains unclear. This study used fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and the stable water isotopes to interpret the chemical composition and properties of DOM and DOP as well as their linkages to anthropogenic disturbances and hydrological conditions in a typical P-contaminated tributary to the central Yangtze River. The results show in the wet season, the average abundance of humic-like components in DOM exceeded 60 %, while the average abundance of tryptophan-like components in DOM exceeded 50 % in the dry season. During the dry season, hydrological conditions had a greater impact on highly unsaturated DOM compounds compared to anthropogenic disturbances because a decrease in precipitation reduced the transport of terrestrial DOM into aquatic systems and increased water retention time in the river, promoting the production of unsaturated compounds from photochemistry. The effects of the two factors were similar in the wet season because active agricultural activities and intense precipitation jointly facilitated the entry of exogenous humics into the runoff, leading to the similar relative abundance of highly unsaturated DOM compounds associated with both factors. Anthropogenic disturbances had a greater impact on aliphatic DOM and DOP than hydrological conditions, which was associated with intense human activities in the watershed, such as phosphate mining, agricultural cultivation, and domestic sewage discharge. This study provides new knowledge about the composition, properties and underlying mechanisms of DOM and DOP in the P-contaminated watershed runoff.

Insight into spatial variations of DOM fractions and its interactions with microbial communities of shallow groundwater in a mesoscale lowland river watershed

Dissolved organic matter (DOM) plays a crucial role in driving biogeochemical processes and determining water quality in shallow groundwater systems, where DOM could be susceptible to dynamic influences of surface water influx. This study employed fluorescence excitation-emission matrix (EEM) spectroscopy combined with principal component coefficients, parallel factor analysis (PARAFAC), co-occurrence network analysis and structural equation modeling (SEM) to examine changes of DOM fractions from surface water to shallow groundwater in a mesoscale lowland river basin. Combining stable isotope and hydrochemical parameters, except for surface water (SW), two groups of groundwater samples were defined, namely, deeply influenced by surface water (IGW) and groundwater nearly non-influenced by surface water (UGW), which were 50.34 % and 19.39 % recharged by surface water, respectively. According to principal component coefficients, reassembled EEM data of these categories highlighted variations of the tyrosine-like peak in DOM. EEMs coupled with PARAFAC extracted five components (C1-C5), i.e. C1, protein-like substances, C2 and C4, humic-like substances, and C3 and C5, microbial-related substances. The abundance of the protein-like was SW > IGW > UGW, while the order of the humic-like was opposite. The bacterial communities exhibited an obvious cluster across three regions, which hinted their sensitivity to variations in environmental conditions. Based on co-occurrence, SW represented the highest connectivity between bacterial OTUs and DOM fractions, followed by IGW and UGW. SEM revealed that microbial activities increased bioavailability of the humic-like in the SW and IGW, whereas microbial compositions promoted the evolution of humic-like substances in the UGW. Generally, these results could be conducive to discern dissimilarity in DOM fractions across surface water and shallow groundwater, and further trace their interactions in the river watershed.

Molecular composition and characteristics of Sediment-adsorbed Dissolved Organic Matter (SDOM) along the coast of China

Sediment-adsorbed Dissolved Organic Matter (SDOM) in coast plays a crucial role in the terrestrial and marine carbon cycle processes of the global environment. However, understanding the transport dynamics of SDOM along the coast of China, particularly its interactions with sediments, remains elusive. In this study, we analyzed the δ13C and δ15N stable isotopic compositions, as well as the molecular characteristics of SDOM collected from coastal areas spanning the Bohai Sea (BS), Yellow Sea (YS), East China Sea (ECS), and South China Sea (SCS), by using isotope ratio mass spectrometry and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). We identified the predominant sources of carbon and nitrogen in coastal sediments, revealing terrigenous origins for most C and N, while anthropogenic sources dominated in the SCS. Spatial variations in SDOM chemodiversity were observed, with diverse molecular components influenced by distinct environmental factors and sediment sources. Notably, lignins and saturated compounds (such as proteins/amino sugars) were the predominant molecular compounds detected in coastal SDOM. Through Mantel tests and Spearman's correlation analysis, we elucidated the significant influence of spatial environmental factors (temperature, DO, salinity, and depth) and sediment sources on SDOM molecular chemodiversity. These findings contribute to a more comprehensive understanding of the carbon cycle dynamics along the Chinese coast.

Novel insights into antimony mobilization in different high- antimony aquifers from the molecular signatures of dissolved organic matter

The crucial role of the fluorescent components of dissolved organic matter (DOM) in controlling antimony (Sb) mobilization in groundwater has been confirmed. However, the molecular signatures contributing to Sb enrichment in DOM remain unknown. This study aims to investigate the origins and molecular compositions of DOM in different high-Sb aquifers (Sb-mining and no-Sb-mining aquifer), as well as compare different molecular signatures of DOM and mechanisms for Sb migration. The findings showed that Sb concentrations in Sb-mining aquifer exhibited a positive correlation with lignin- and tannin-like molecules characterized by high O/C and low H/C ratios, indicating an increased abundance of aromatic components with higher Humification Index and SUV-absorbance at 254 nm, compared to no-Sb-mining aquifer. Correspondingly, the complexation and competitive adsorption were considered as the predominate formation mechanisms on Sb enrichment in Sb-mining aquifer. In addition, high abundances of bioreactivity DOM may facilitated the migration of Sb via electron transfer and competitive adsorption in native no-Sb-mining aquifer. The outcomes of this investigation offer novel insights into the mechanism on Sb enrichment influenced by DOM at the molecule level.

Seasonal sensitivity of groundwater dissolved organic matter in recognition of chronic kidney disease of unknown etiology: Optical and molecular perspectives

Chronic kidney disease of unknown etiology (CKDu) has aroused a great concern due to its widespread prevalence in many developing countries. Dissolved organic matter (DOM) has been proved to be associated with CKDu in groundwater. However, the responses of their association to abiotic influencing factors like seasonal variation are not carefully disclosed. Herein, we revealed the seasonal variation of DOM in CKDu related groundwater (CKDu groundwater) and control group (non-CKDu groundwater) collected from Sri Lanka during the dry and wet seasons by excitation-emission matrix spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. In both CKDu and non-CKDu groundwaters, the input of exogenous DOM during wet season improved the degree of humification and molecular weight of DOM, while oxidative processes during the dry season increased the ratios of oxygen to carbon (O/C). Furthermore, compared with non-CKDu groundwater, more DOM with high O/C enriched in CKDu groundwater during the dry season, indicating stronger oxidative processes in CKDu groundwater. It may result in the enrichment of carboxyl group and induce the enhanced leaching of CKDu-related Si and F-. The receiver operating characteristic (ROC) analysis showed that the CKDu-recognition ability of most optical and molecular indicators was susceptible to seasonal factors and their recognition abilities were stronger in the wet season. The linkage between DOM and CKDu was affected by seasonal factors through the occurrence, mobility, degradation, and toxicity of typical organic molecules (e.g., C17H18O10S). The study provides a new insight into screening pathogenic factors of other endemic diseases related to organic molecules.

Seasonal variation and dissolved organic matter influence on the distribution, transformation, and environmental risk of pharmaceuticals and personal care products in coastal zone: A case study of Tianjin, China

Pharmaceuticals and personal care products (PPCPs) are emerging contaminants that have raised urgent environmental issues. The dissolved organic matter (DOM) plays a pivotal role on PPCPs' migration and transformation. To obtain a comprehensive understanding of the occurrence and distribution of PPCPs, a seasonal sampling focused on the riverine system in coastal zone, Tianjin, Bohai Rim was conducted. The distribution and transformation of thirty-three PPCPs and their interaction with DOM were investigated, and their sources and ecological risks were further evaluated. The total concentration of PPCPs ranges from 0.01 to 197.20 μg/L, and such value is affected by regional temperature, DOM and land use types. PPCPs migration at soil-water interface is controlled by temperature, sunlight, water flow and DOM. PPCPs have a high affinity to the protein-like DOM, while the humus-like DOM plays a negative influence and facilitates PPCPs' degradation. It is also found that protein-like DOM can represent point source pollution, while humus-like substances indicate non-point source (NPS) emission. Specific PPCPs can be used as markers to trace the source of domestic discharge. Additionally, daily use PPCPs such as ketoprofen, caffeine and iopromide are estimated to be the main risk substances, and their ecological risk varies on space, season and river hydraulic condition.

Purification of dredged water by magnetic coagulation: Response surface optimization and dissolved organic matter removal characteristics

In the present study, magnetic coagulation was used to treat dredged water and the response surface method was used to optimize process parameters. The dissolved organic matter (DOM) removal characteristics were characterized by three-dimensional fluorescence spectrometry and ultra-high resolution mass spectrometry. During the magnetic coagulation process, the suspended solids (SS) removal rate increased initially and then decreased under conditions of increasing magnetic powder dosage and stirring rate. After magnetic coagulation and precipitation for 20 min, the contents of SS, ammonia nitrogen, chemical oxygen demand, and total phosphorus in the treated dredged water met the requirements of the discharge standard (GB8978-1996, China). Three-dimensional fluorescence results showed that magnetic coagulation selectively removed fulvic acids and humic acid substances. After magnetic coagulation with precipitation for 10 min and 20 min, the total relative content of lignins, tannins, proteins, lipids, aminosugars, unsaturated hydrocarbons, condensed aromatic structures, and carbohydrates decreased by 26.3% and 39.4%, respectively. After magnetic coagulation, the distribution range of small molecule DOM shifted to the low H/C and high O/C regions. This study provides a novel perspective for studies on the removal of DOM in dredged water by magnetic coagulation. PRACTITIONER POINTS: SS and DOM removal were significantly enhanced by the use of magnetic coagulation. SS removal efficiency was affected by stirring rate and magnetic powder dosage. Magnetic coagulation selectively removed fulvic acids and humic acid substances. DOM molecule shifted to low H/C and high O/C regions after magnetic coagulation.

Molecular and optical signatures of photochemical transformation of dissolved organic matter: Nonnegligible role of suspended particulate matter in urban river

Natural dissolved organic matter (DOM) is one of the Earth's dynamic carbon pools and a key intermediate in the global carbon cycle. Photochemical processes potentially affect DOM composition and activity in surface water. Suspended particulate matter (SPM) is the integral component of slow-moving rivers, and holds the potential for photochemical reactivity. To further investigate the influence of SPM on DOM photochemical transformation, this study conducted experiments comparing samples with and without SPM irradiated under simulated sunlight. Surface water samples from slow-moving urban rivers were collected. DOM optical characteristics and molecular features obtained by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were investigated. Photolabile DOM was enriched in unsaturated and highly aromatic terrestrial substances. Photoproduced DOM had low aromaticity and was dominated by saturated aliphatics, protein-like substances, and carbohydrates. Study results indicated that the presence of SPM had a nonnegligible impact on the molecular traits of DOM, such as composition, molecular diversity, photolability, and bioavailability during photochemical reactions. In the environment affected by SPM, molecules containing heteroatoms exhibit higher photosensitivity. SPM promotes the photochemical transformation of a wider range of chemical types of photolabile DOM, particularly nitrogen-containing compounds. This study provides an essential insight into the more precise simulation of photochemical reactions of DOM influenced by SPM occurring in natural rivers, contributing to our understanding of the global carbon cycle from new theoretical perspectives.

Exploring the optical properties and molecular characteristics of dissolved organic matter in a large river-connected lake (Poyang Lake, China) using optical spectroscopy and FT-ICR MS analysis

River-connected lakes are complicated and dynamic ecosystems due to their distinctive hydrological pattern, which could significantly impact the generation, degradation, and transformation processes of dissolved organic matter (DOM) and further regulate DOM chemistry in lakes. However, the molecular compositions and characteristics of DOM in river-connected lakes are still poorly understood. Thus, here the spatial variations of optical properties and molecular characteristics of DOM in a large river-connected lake (Poyang Lake) were explored via spectroscopic techniques and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed high degree of spatial heterogeneity of DOM chemistry (variations in DOC concentrations, optical parameters, and molecular compounds) in Poyang Lake, and the diversity at the molecular level was primarily caused by the heteroatom compounds (N- and S- containing). Compared with classic lakes and rivers, DOM compositions of the river-connected lake had distinctive characteristics (differences in the AI_mod and DBE values, and CHOS proportions). And the composition characteristics of DOM between the southern and northern parts of Poyang Lake were different (such as the lability and molecular compounds), suggesting the changes of hydrologic conditions may affect the DOM chemistry. In addition, various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) were identified agreeably based on optical properties and molecular compounds. Overall, this study first characterizes the DOM chemistry and reveals its spatial variations in Poyang Lake at the molecular level, which could improve our understanding of DOM in large river-connected lake systems. Further studies are encouraged to investigate the seasonal variations of DOM chemistry under different hydrologic conditions in Poyang Lake to enrich the knowledge of carbon cycling in river-connected lake systems.

Molecular composition and possible transformations of labile soil organic matter fractions in Mediterranean arable soils: Relevance and implications

With the increased global interest in sequestering carbon in soil, it is necessary to understand the composition of different pools of soil organic matter (SOM) that cycle over suitably short timeframes. To explore in detail the chemical composition of agroecologically relevant yet distinct fractions of SOM, the light fraction of SOM (LFOM), the 53-μm particulate organic matter (POM), and the mobile humic acid (MHA) fractions were sequentially extracted from agricultural soils and characterized using both ¹³C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy and also Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The NMR results showed a decrease in the O-alkyl C region assigned to carbohydrates (51-110 ppm) and an increase in the aromatic region (111-161 ppm) proceeding from the LFOM to the POM and then to the MHA fraction. Similarly, based on the thousands of molecular formulae assigned to the peaks detected by FT-ICR-MS, condensed hydrocarbons were dominant only in the MHA, while aliphatic formulae were abundant in the POM and LFOM fractions. The molecular formulae of the LFOM and POM were mainly grouped in the high H/C lipid-like and aliphatic space, whereas a portion of the MHA compounds showed an extremely high (17-33, average of 25) double bond equivalent (DBE) values, corresponding to low H/C values of 0.3-0.6, representative of condensed hydrocarbons. The labile components appeared most pronounced in the POM (93% of formulae have H/C ≥ 1.5) similar to the LFOM (89% of formulae have H/C ≥ 1.5) but in contrast to the MHA (74% of formulae have H/C ≥ 1.5). The presence of both labile and recalcitrant components in the MHA fraction suggests that the stability and persistence of soil organic matter is influenced by a complex interaction of physical, chemical, and biological factors in soil. Understanding the composition and distribution of different SOM fractions can provide valuable insights into the processes that govern carbon cycling in soils, which can help inform strategies for sustainable land management and climate change mitigation.

Isolation of dissolved organic matter from aqueous solution by precipitation with FeCl3: mechanisms and significance in environmental perspectives

Ferric ions can bind strongly with dissolved organic matter (DOM), including humic acids (HA), fulvic acids (FA), and protein-like substances, whereas isolation of Fe-DOM precipitates (Fe-DOM_P) and their biochemical characteristics remain unclear. In this work FeCl₃ was used to isolate DOM components from various sources, including river, lake, soil, cow dung, and standard tryptophan and tyrosine, through precipitation at pH 7.5-8.5. The Fe-DOM_P contribute to total DOM by approximately 38.6-93.8% of FA, 76.2% of HA and 25.0-30.4% of tryptophan and tyrosine, whilst fluorescence spectra allowed to monitor/discriminate the various DOM fractions in the samples. The relative intensity of the main infrared peaks such as 3406‒3383 cm^-1 (aromatic OH), 1689‒1635 cm^-1 (‒COOH), 1523-1504 cm^-1 (amide) and 1176-1033 cm^-1 (‒S=O) show either to decline or disappear in Fe‒DOM_P. These results suggest the occurrence of Fe bonds with various functional groups of DOM, indicating the formation of π-d electron bonding systems of different strengths in Fe‒DOM_P. The novel method used for isolation of Fe-DOM_P shows promising in opening a new frontier both at laboratory and industrial purposes. Furthermore, results obtained may provide a better understanding of metal-organic complexes involved in the regulation of the long-term stabilization/sequestration of DOM in soils and waters.

Ecological water replenishment to the Yongding River, China: effects of different water sources on inorganic ions and organic matter characteristics

Ecological water replenishment is considered to be an important project to adjust river ecosystems with water shortages and degradation, and its impact on the water quality of the target river section deserves attention. By investigating the characteristics of inorganic ions and organic components of the Beijing section of the Yongding River (YDR) from upstream to downstream, the sources of inorganic ions and dissolved organic matter (DOM) during an ecological water replenishment event were analysed and discussed. This study illustrated the hydrochemical response to different supplemental water sources in three sections of the YDR (mountain gorge section (MGS), urban plain section (UPS), and suburb plain section (SPS)). The results showed that the total dissolved solids (TDS) and ion concentrations were significantly different (p < 0.001) in the three river sections due to different supplemental water sources. The highest concentration of TDS was found in the UPS (870.92 mg/L) replenished by reclaimed water, while the lowest concentration of TDS was found in the SPS (306.95 mg/L) replenished by the water of the South-to-North Water Diversion Project (SNWD). Despite the differences in the water sources of replenishment, the optical parameters of DOM and fluorescent components showed similar protein-like dominated endogenous source characteristics in the three river sections of the YDR, which was due to the influence of reservoir water (MGS and SPS) and reclaimed water (UPS). Our study emphasizes the importance of understanding the impact of different water sources on the water replenishment process, which provides a scientific reference for the management of ecological water replenishment.

Identification of Trace Components in Sauce-Flavor Baijiu by High-Resolution Mass Spectrometry

Sauce-flavor Baijiu is one of the most complex and typical types of traditional Chinese liquor, whose trace components have an important impact on its taste and quality. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is one of the most favorable analytical tools to reveal trace molecular components in complex samples. This study analyzed the chemical diversity of several representative sauce-flavor Baijiu using the combination of electrospray ionization (ESI) and FT-ICR MS. The results showed that ESI+ and ESI- exhibited different chemical features characteristic of trace components. Overall, sauce-flavor Baijiu was dominated by CHO class compounds, and the main specific compound types were aliphatic, highly unsaturated with low oxygen, and peptide-like compounds. The mass spectral parameters resolved by FT-ICR MS of several well-known brands were relatively similar, whereas the greatest variability was observed from an internally supplied brand. This study provides a new perspective on the mass spectrometry characteristics of trace components of sauce-flavor Baijiu and offers a theoretical foundation for further optimization of the gradients in Baijiu.

An advanced LC-MS/MS protocol for simultaneous detection of pharmaceuticals and personal care products in the environment

RATIONALE

The development of appropriate analytical screening techniques for pharmaceuticals and personal care products (PPCPs) is the basis for studying the distribution and environmental impact of emerging contaminants (ECs). Mass spectrometry-based screening methods vary with the complexity of the target compounds. It is challenging to balance both positive and negative ion quantification with a low detection limit. To establish a set of experimental methods including extraction, chromatography-separation and mass spectrometry screening is one of the most important topics in PPCP research. This paper describes a universal and efficient qualification and quantification protocol for the simultaneous detection of 34 PPCPs in different environmental samples in a single analytical data acquisition run.

METHODS

Thirty-four representative PPCPs, which are widely distributed in the environment with high ecological toxicity and complex chemical structures, were selected as representative target ECs. The extraction of the target PPCPs was achieved using only one solid-phase extraction cartridge without the need to adjust the pH of samples. The enriched samples were detected by LC-MS/MS in both positive and negative ion modes simultaneously. The protocol was evaluated based on the accuracy, precision, detection limits and matrix effects.

RESULTS

This method achieved simultaneous detection of PPCPs in both positive and negative ion modes, with a single analytical cycle of 12 min. The observed SPE recoveries were between 40% and 115%. The instrumental detection limits (IDL) varied from 0.01 to 1 pg, and the method detection limits (MDL) were between 0.002 and 3.323 ng/l in different matrices. Most of the PPCPs were subjected to matrix suppression below 30%. The method was successfully applied for quantitative analysis of the PPCPs in different environmental samples, including river samples, wastewater treatment plant (WWTP) samples and soil samples.

CONCLUSIONS

This protocol developed a rapid and efficient detection method to simultaneous qualitative and quantitative 34 representative PPCPs in the environment. The IDL ranged from 0.01 to 1 pg and the MDL ranged from 0.002 to 3.323 ng/l in different matrices. The detection limit was one order of magnitude lower compared to previous studies. The protocol also provided a wide application range for different environmental matrices, which permitted the migration and transformation of PPCPs to be explored.

Characterizing the spatiotemporal distribution of dissolved organic matter (DOM) in the Yongding River Basin: Insights from flow regulation

Artificial flow regulation is an important measure to alleviate water shortages and improve the ecological quality of river basins. Dissolved organic matter (DOM) plays a crucial role in the carbon cycle and regulates biogeochemical and ecological processes in aquatic systems. Among the numerous studies on the effects of anthropogenic activities on the quality and quantity of river DOM, few studies have focused on the influence of different artificially regulated flow on the composition, source, and fate of fluvial DOM. This study aims to elucidate the impact of different artificial regulation modes of river flows on the source, migration, and transformation of DOM. The optical properties of DOM were used to explore the temporal and spatial distribution characteristics of DOM in the Yongding River Basin, where artificial regulation of river flows by cross-basin and inner-basin water transfers were implemented. Excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis revealed four fluorescent substances of DOM in the water: one microbial humic-like (C1), one terrestrial humic-like (C2), one non-point source pollution humic-like (C4), and one tryptophan-like (C3) substance. Due to cross-basin water transfer from the Yellow River, the flow is the highest (21.79 m³/s) during spring, which was the reason that the signal of C2 was stronger during spring (71.45 QSU) compared to summer (57.12 QSU) and autumn (51.78 QSU). Due to inner-basin water transfer from upstream reservoirs, C3 derived from autochthonous sources were higher during autumn (130.81 QSU) than during spring (77.17 QSU) and summer (93.16 QSU). With no water transfer, more C1 were present at higher temperatures during summer (141.51 QSU) than during spring (126.73 QSU) and autumn (128.8 QSU). Moreover, C4 originating from urban and/or agricultural non-point source runoff increased during summer (57.07 QSU) than during spring (33.29 QSU) and autumn (52.27 QSU) because of increased rainfall. The different modes of artificial regulation of river flows changed the hydrological characteristics of the basin, which in turn altered the temporal and spatial distribution characteristics of the quantity and quality of DOM. The finding of this study can help promote the development of appropriate management strategies for artificial regulation of river flows in the basin. Furthermore, this study provides a basis for investigating the effects of different artificial flow regulations on the carbon cycles and ecological risks of rivers in the basin.

Fractionation and characterization of dissolved organic matter using solid-phase extraction followed by Fourier transform ion cyclotron resonance mass spectrometry with electrospray, atmospheric pressure photoionization, and laser desorption ionization

RATIONALE

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) combined with different ionization techniques provides a powerful means to characterize dissolved organic matter (DOM) at the molecular level. Solid-phase extraction (SPE) is currently the most widely utilized method for extracting the DOM, but one-step elution using methanol does not provide a comprehensive picture of DOM. The development of efficient extraction and enrichment methods as well as characterization techniques from water samples remains a priority for DOM research, which is investigated in this study.

METHODS

The DOM was extracted from lake water by SPE using one-step elution (methanol or dichloromethane) and multistep elution (water, methanol, acetone, and dichloromethane). A combination of electrospray ionization (ESI), atmospheric pressure photoionization (APPI), and matrix-free laser desorption ionization (LDI) was utilized for FT-ICR MS analysis in both positive (+) and negative (-) ion modes.

RESULTS

The total recovery of the multistep elution was 23.5% higher as compared to the investigated one-step elution procedure (85% vs. 61.6%); however, a comparison of the observed molecular species and the range of diversity under different ionization techniques along with the statistical analyses showed that proper selection of solvent and ionization method was required to explore specific compounds from the sample.

CONCLUSIONS

For DOM species containing different heteroatoms, a combination of ESI, APPI, and LDI can offer a comprehensive profile of DOM in aquatic ecosystems. The specific molecular formulae of each ionization technique are characterized as follows: ESI- mode exhibited strong selectivity for lignin-like and tannins-like species with high oxygen content, as well as organosulfates. ESI+ favored lipid species and peptide/protein compounds. Unsaturated and condensed aromatic hydrocarbons with low oxygen were preferably ionized by both APPI and LDI.