Quantifying Thiol Abundance and pKa Values in Natural Organic Mixtures Using HERFD-XANES Spectroscopy.

The binding interactions of 1-naphthol with effluent and whole natural dissolved organic matter (DOM) samples were analyzed by using a fluorescence quenching technique. Nonfractionated DOM samples from Lake Biwa (Japan), creek water, treated sewage effluents, and an extracted Lake Biwa fulvic acid (LBFA) standard were used as quenchers and compared at the same 1-naphthol with DOM organic carbon ratios found for low natural dissolved organic carbon (DOC) levels (∼4.5 mg/L). Natural and effluent DOM (eDOM) samples were characterized by the DOC level, relative hydrophobicity (RH%), ultraviolet (UV)-visible absorbance and fluorescence excitation emission spectroscopy. These parameters were compared with those of the reference LBFA standard. Concave-up Stern-Volmer plots accounted for both the partitioning and the adsorptive binding in the eDOM-polycyclic aromatic hydrocarbons (PAH) system as compared with the nonspecific partitioning in the natural DOM-PAH system. Strong linear regressions (r(2) > 0.80) between the log K(DOC) values, the RH%, the UV absorbances, and the Fl(340-435) -UV(340) indices for the structural composition and molecular weights of the DOM samples were obtained. These results suggest that low molecular weight microbial fulvic acid (<800 Da) is dominant in the eDOM-PAH binding interactions, as well as in the distinct molecular structure of the eDOM samples, which resulted in fivefold to sixfold higher binding magnitude for 1-naphthol than for the other samples.

This note describes a novel method to quickly quantify the dissolved organic matter (DOM)-induced catabolic activity from low-volume samples. The concept is based on the catabolic response profiles (CRP) assay and is described as an inverse CRP, where the reactivity of a complex and diverse mixture of organic compounds towards single strains of bacteria is quantified. A strain of Pseudomonas fluorescens was grown and then transferred to an organic carbon-free mineral salt medium. 90 microL of a fluorogenic redox indicator was added to 90 microL of the bacterial suspension in a well on a 96-well microplate. The DOM sample (90 microL) was added to the well and the fluorescence emitted by the reduced indicator was read over the period of incubation. Only 0.8 mL of the DOM sample, including controls and replicates, was required to quantify the activity of each sample. Results are presented for a surface soil DOM sample and they were compared to glucose samples of various concentrations. The detection limit was reached for samples containing as little as 55 microM of glucose (0.3 mg C L(-1)). The assay showed that only 9% of the total carbon of the soil surface DOM sample was readily biodegradable.

BackgroundThe accumulation of dissolved organic matter (DOM) poses an issue in the management of the water quality from recirculating aquaculture systems (RAS), but its characterization is often not detailed enough to understand the DOM transformations in RAS. In this study, we investigated the application of two distinct non-targeted data processing approaches using ultra-performance liquid chromatography (UPLC) with quadrupole time-of-flight mass spectrometry (QTOF-MS) and two software with different algorithmic designs: PetroOrg and Progenesis QI to accurately characterize the molecular composition of DOM in RAS by UPLC-QTOF-MS. ResultsThe UPLC-QTOF-MS resolution in combination with PetroOrg and Progenesis QI software successfully assigned 912 and 106 unique elemental compositions, respectively, including compounds containing carbon, hydrogen, and oxygen (CHO) and nitrogen-containing CHO compounds (CHON), in the DOM samples from RAS. The results of these two distinct data processing approaches were consistent with the list of DOM formulas from RAS identified by higher resolution mass spectrometry techniques confirming their reliability. PetroOrg approach revealed only compositional information in the DOM samples from RAS, while Progenesis QI in addition to identifying new elemental compositions, increased their chemical space by giving information about their polarity and their possible key structures. DOM samples from RAS were found to be rich in unsaturated CHO compounds, with tentatively key structures of terpenoids with medium polarity indicating natural origins in their composition. The analysis also revealed probable structures of sucrose fatty acid esters and polyethylene glycol, indicating anthropogenic sources. Significance and NoveltyThe combination of these two non-targeted data processing approaches significantly improves the characterization of the complex mixture of DOM from RAS by UPLC-QTOF-MS reporting for the first time accurate DOM results in terms of its composition, while proposing its key structures. The presented methods can also be used to analyze different DOM samples with other HRMS techniques and software.

SummaryMost methods to fractionate natural dissolved organic matter (DOM) rely on sorption of acidified DOM samples onto XAD‐8 or DAX‐8 resin. Procedural differences among methods are large and their interpretation is limited because there is a lack of calibration with DOM model molecules. An automated column‐based DOM fractionation method was set up for 10‐ml DOM samples, dividing DOM into hydrophilic (HPI), hydrophobic acid (HPOA) and hydrophobic neutral (HPON) fractions. Fifteen DOM model components were tested in isolation and in combination. Three reference DOM samples of the International Humic Substances Society were included to facilitate comparison with other methods. Aliphatic low‐molecular‐weight acids (LMWAs) and carbohydrates were classified as HPI DOM, but some LMWAs showed also a partial HPO character. Aromatic LMWAs and polyphenols partitioned in the HPOA fraction, menadione (quinone) and geraniol (terpenoid) in HPON DOM. Molecules with log Kow &gt; 0.5 had negligible HPI fractions. The HPO molecules except geraniol had specific UV absorbance (SUVA, measure for aromaticity) &gt;3 litres g−1 cm−1 while HPI molecules had SUVA values &lt;3 litres g−1 cm−1. Distributions of DOM from eight soils ranged from 31 to 72% HPI, 25 to 46% HPOA and 2 to 28% HPON of total dissolved organic carbon. The SUVA of the HPI DOM was consistently smaller compared with the HPOA DOM. The SUVA of the natural DOM samples was not explained statistically by fractionation and the variation coefficient of SUVA among samples was not reduced by fractionation. Hence, fractionation did not reduce the variability in this DOM property, which casts some doubts on the practical role of DOM fractionation in predicting DOM properties.

Effects of organic sulfur and arsenite/dissolved organic matter ratios on arsenite complexation with dissolved organic matter.

Natural dissolved organic matter mobilizes Cd but does not affect the Cd uptake by the green algae Pseudokirchneriella subcapitata (Korschikov) in resin buffered solutions

The coprecipitation of heavy metals (HMs) with Fe(III) in the presence of dissolved organic matter (DOM) is a crucial process to control the mobility of HMs in the environment, but its underlying immobilization mechanisms are unclear. In this study, Cr(III) immobilization by coprecipitation with Fe(III) in the presence of straw-derived DOMs under different Fe/C molar ratios, pHs, and ionic strengths was investigated using scanning transmission X-ray microscopy (STXM) and ptychography and X-ray absorption near-edge structure (XANES) spectroscopy. The results showed that Cr(III) retention was enhanced in the presence of DOM, a maximum of which was achieved at an Fe/C molar ratio of 0.5. The increase of pH and ionic strength could also promote Cr(III) immobilization. Cr K-edge XANES results indicated that Fe (oxy)hydroxide fractions, instead of organics, provided the predominant binding sites for Cr(III), which was directly confirmed by high spatial resolution STXM-ptychography analysis at the sub-micron- and nanoscales. Moreover, organics could indirectly facilitate Cr immobilization by improving the aggregation and deposition of coprecipitate particles through DOM bridging or electrostatic interactions. Additionally, C K-edge XANES analysis further indicated that the carboxylic groups of DOM were complexed with Fe (oxy)hydroxides, which probably contributed to DOM bridging. This study provides a new insight into Cr(III) immobilization mechanisms in its coprecipitation with Fe(III) and DOM, which could have important implications on the management of Cr(III)-enriched soils, particularly with crop straw returning.

Changes in properties of soil-derived dissolved organic matter induced by biodegradation

As a key geochemical factor in earth system, dissolved organic matter (DOM) plays an important role in controlling environmental quality of watersheds. In this study, a typical agricultural watershed of Three Gorges reservoir areas, Wangjiagou watershed in Fuling district of Chongqing, was selected to characterize DOM in waters through fluorescence and UV-Vis spectroscopy, while the effect of land-use types in this watershed was discussed. The results showed large spatial variances of aquatic DOM in this watershed, with significant differences in compositions and sources. After calculation of <i>a</i>g^*(355) for indicating proportion of chromophoric DOM in bulk DOM, the order of DOM was paddy rice field> ditch> pond> well> outlet point. DOM samples from paddy rice field and ditch showed higher SUVA254 suggesting higher aromaticity. DOM from this watershed showed 2 typical types (4 peaks A, C, B and T) of fluorescent components including humic-like and protein-like components. Dual contributions from autochthonous (e.g., microbial or alga production) and allochthonous both heavily affected the DOM characteristics. Besides active microbial activities due to high organic and nutrients inputs from agricultures, discharge of sewage and water used in agricultural production could contribute proteins possibly inducing ascending proportion of protein-like component as shown in fluorescence analysis. DOM samples from the same sampling points but in different crop plantation seasons were collected to compare, for understanding the differences between two planting seasons. It clearly suggested protein-like component was the key variable to control the DOM dynamics. After land-use changing from rice/corn into mustard plantation, all of DOC, CDOM and <i>r</i>(T/C)showed significant differences, but no such observations were observed in FI, BIX and <i>r</i>(A/C).

The different environmental conditions (temperature, oxygen and water availabilities), microbial composition, availability of fresh organic inputs and textural and mineralogical properties of soil layers with the depth result differences between the origin, composition, C/N ratio and stability of the dissolved organic matter (DOM) of topsoils and subsoils.This research examines the content and chemical composition of the DOM of topsoil and subsoil layers of a silty Luvisol and a sandy Arenosol. Both soils are derived from oak forests from Hungary. The soils were collected as composite samples (10 random subsamples within a 20 m &amp;#215; 20 m area) from the 0&amp;#8211;20 and 30&amp;#8211;50 cm layers.The DOM was extracted with ultrapure water for 12 h at room temperature with a tumbling shaker. The sample was centrifuged for 35 min (1400 &amp;#215; g) and the supernatant was decanted and passed through a 250 &amp;#181;m-sieve. The fraction that passed through the sieve was filtrated through a 0.45 &amp;#956;m membrane filter to obtain the DOM samples. The filtered samples were acidified to pH 2 with HCl, passed through a solid phase extraction cartridge using a styrene divinyl benzene polymer sorbent (Agilent Mega Bond Elut PPL), eluted with methanol and dried.The dried DOM samples were analyzed with a Bruker Vertex 70 FT-IR spectrometer. For each sample a spectral range of 4000&amp;#8211;400 cm&amp;#8211;1, a resolution of 4 cm&amp;#8211;1, 128 scans, and three replicates were recorded. Relative absorbances were calculated for six peaks (2920, 2850, 1730, 1640, 1515, or 1420 cm&amp;#8211;1) representing characteristic organic matter compounds.The dried DOM samples were dissolved in 0.05 M NaHCO3 solution in order to determine the C and N content and the fluorescence and UV-VIS-NIR spectroscopical properties. The total organic carbon and nitrogen content of the DOM samples were analysed using a TOC/TN analyser (Shimadzu TOC-L). The chemical composition of the DOM samples was determined using fluorescence (Shimadzu RF6000) and UV-VIS-NIR (Shimadzu UV3600) spectrometry. Excitation-emission matrices were obtained by measuring fluorescence intensity excitation wavelengths ranging from 230&amp;#8211;450 nm and emission wavelengths ranging from 260&amp;#8211;600 nm with 2 nm increments. Fluorescence, humification and biological indices were determined from the fluorescence spectra in order to determine the sources, structural complexity and humification degree of the DOM samples. Synchronous fluorescence spectra were recorded with a fixed wavelength difference (&amp;#916;&amp;#955;=18) to separate SOM components with different molecular weights. Specific UV absorption (SUVA254 and SUVA280, L mg-1 m-1) was calculated by dividing the absorption at 254 and 280 nm by the DOC concentration.The study aimed to assess the differences between the sources and the structural and chemical variability of the DOM samples from varying soil depths with different textural properties.This work was supported by the Development and Innovation Fund of Hungary [grant No. NKFIH 142936] and the E&amp;#246;tv&amp;#246;s Lor&amp;#225;nd Research Network [grant No. SA41/2021].

Biodegradation-induced changes in the characteristics of dissolved organic matter (DOM) and the subsequent effects on disinfection byproduct formation potentials (DBPFPs) were investigated using six different sources of DOM (algae, leaf litter, reed, compost, paddy water, and treated municipal sewage effluent). Microbial incubation of the DOM samples increased the specific ultraviolet absorbance and humic-like fluorescence but decreased the protein/tannin-like fluorescence and relative distribution of smaller-sized DOM components. Comparison of the original versus biodegraded DOM samples using resin fractionation and pyrolysis-gas chromatography/mass spectrometry revealed that the biodegradation-induced changes were highly dependent on DOM sources and exhibited no consistent trends among the different sources. Changes in DBPFPs also differed with DOM source. Vascular plant-derived DOM (leaf litter and reed) demonstrated an enhancement in specific DBPFP after biodegradation, whereas little change or even a slight decrease was observed for the other DOM sources. Correlations that were significant between specific DBPFPs and the aromatic content or humic-like fluorescence for the original DOM samples were no longer significant after microbial degradation. The relative abundance of hydrophobic to hydrophilic structures in DOM is suggested to be a general indicator for the formation potential of trihalomethanes irrespective of DOM source and the state of biodegradation.

Optical properties of straw-derived dissolved organic matter and growth inhibition of Microcystis aeruginosa by straw-derived dissolved organic matter via photo-generated hydrogen peroxide

The chemical composition and carbon isotope signature of aquatic dissolved organic matter (DOM) in five boreal forest catchments in Scandinavia were investigated. The DOM was isolated during spring and fall seasons using a reverse osmosis technique. The DOM samples were analyzed by elemental analysis, FT-IR, solid-state CP-MAS 13C-NMR, and C-1s NEXAFS spectroscopy. In addition, the relative abundance of carbon isotopes (12C, 13C, 14C) in the samples was measured. There were no significant differences in the chemical composition or carbon isotope signature of the DOM sampled in spring and fall seasons. Also, differences in DOM composition between the five catchments were minor. Compared to reference peat fulvic and humic acids, all DOM samples were richer in O-alkyl carbon and contained less aromatic and phenolic carbon, as shown by FT-IR, 13C-NMR, and C-1s NEXAFS spectroscopy. The DOM was clearly enriched in 14C relative to the NBS oxalic acid standard of 1950, indicating that the aquatic DOM contained considerable amounts of organic carbon younger than about 50 years. The weight-based C:N ratios of 31 ± 6 and the $$\delta^{13}\hbox{C}$$ values of $$-29\pm2\permille$$ indicate that the isolated DOM is of terrestrial rather than aquatic origin. We conclude that young, hydrophilic carbon compounds of terrestrial origin are predominant in the samples investigated, and that the composition of the aquatic DOM in the studied boreal forest catchments is rather stable during low to intermediate flow conditions.

The objectives of the present study were to elucidate the chemical and structural properties of dissolved organic matter (DOM) derived from aerobic decay of rice straw and to quantify the effect of the DOM on the sorption of pyrene on soil. The DOM samples were obtained from microcosms incubated at 0, 21, 63, and 180 d. The bulk DOM samples were fractionated to four fractions: hydrophilic matter (HIM), acid-insoluble matter (AIM), hydrophobic acid (HOA), and hydrophobic neutral (HON) fractions. The bulk DOM and the four DOM fractions were characterized for their elemental compositions and functionalities. The results showed that HIM had the highest H/C atomic ratios, whereas HOA and AIM had the lowest H/C atomic ratios. These DOM samples were used as the background DOMs in the initial aqueous solutions for measuring sorption of pyrene on a paddy soil. The results indicated that, among the four DOM fractions, HOA, HON, and AIM significantly lowered the pyrene sorption coefficients, but HIM had little or no effect on the pyrene sorption by the soil. It appears that less polar AIM and HON had stronger binding affinities for pyrene in water, reducing the sorption coefficient for the soil, whereas more polar and less aromatic HIM had much weaker binding affinity for pyrene in water, causing little or no effect on the pyrene sorption by the soil. The present study showed that rice straw-derived DOM may enhance desorption and transport of organic pollutants in soil-water systems.

Dissolved organic matter (DOM) has been widely studied in streams, lakes, and oceans due to its role in biogeochemical processes, allowing it to act as a sunscreen, food source, trace metal chelator, and photosensitizer. Few studies have examined DOM in oilfield-produced water. In this study, three major types of solid-phase extraction (SPE) sorbents, a silica-based sorbent (ENVI-18), an active carbon (ENVI-Carb), and polymer-based sorbents (PPL, XAD resins, and HLB), were used to isolate DOM from oilfield-produced brine. Isolated SPE DOM samples were analyzed using dissolved organic carbon (DOC), Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Results showed that the oilfield-produced brine DOM sample was dominated by aliphatic hydrocarbons and aromatic compounds. Nitrogen-containing compounds and carbohydrates were also observed; however, polycyclic aromatic hydrocarbons, fatty acids, and sulfur-containing compounds were relatively absent. Under acidic conditions, extraction efficiencies of DOM from oilfield-produced brine were enhanced for different SPE sorbents as follows from high to low: XAD-8/4 tandem, HLB, PPL, ENVI-18, and ENVI-Carb. DOM samples isolated by different sorbents exhibited different properties. ENVI-18 and XAD-4 DOM isolates were enriched in aliphatic hydrocarbons but devoid of aromatic compounds, XAD-8, HLB, and PPL samples contained relatively higher levels of aromatics, and HLB and PPL samples showed a high retention capacity for carbohydrates, while ENVI-Carb and HLB DOM isolates contained more nitrogen compounds than those obtained using other sorbents. In addition, XAD-8 and PPL extracts were characterized by higher concentrations of sulfur-containing compounds. This is the first study of its type to study oilfield-produced brine DOM, and the results will help us better understand their structures and properties.