Types Of Dissolved Organic Matter Research Articles

Phototransformation and photoreactivity of MPs-DOM in aqueous environment: Key role of MPs structure decoded by optical and molecular signatures

The dissolved organic matter (DOM) derived from microplastics (MPs-DOM) can be one of the photoactive components in DOM. However, information on the properties and photoreactivity of MPs-DOM during phototransformation is limited. Here, we investigated the properties and photoreactivity of MPs-DOM from polyolefins (MPs-DOM-POs), MPs-DOM derived from benzene-containing polymers (MPs-DOM-BCPs), and Suwannee River natural organic matter (SR-NOM), during a 168-hour phototransformation. After phototransformation, all examined types of DOM exhibit a decrease in concentration and molecular weight. Notably, MPs-DOM-POs display increased aromaticity and saturation, while MPs-DOM-BCPs and SR-NOM show reduced aromaticity and saturation. MPs-DOM-POs present higher steady-state concentrations of •OH but much lower steady-state concentrations of 1O2 than those of MPs-DOM-BCPs. In comparison, MPs-DOM produce more •OH but less 1O2 than SR-NOM. This study proposes that the diversification of aliphatic C─H bonds (arylation and carbonylation) by reactive intermediates (especially •OH) is the main pathway for MPs-DOM-POs phototransformation for the first time. On the other hand, the cleavage on the aromatic carboxylic acids by reactive intermediates (especially 1O2) is the main mechanism for MPs-DOM-BCPs and SR-NOM phototransformation. Our findings provide new insights into the phototransformation and photoreactivity of MPs-DOM and help to understand the potential risks of MPs in aqueous environment.

Coral high molecular weight carbohydrates support opportunistic microbes in bacterioplankton from an algae-dominated reef.

Dissolved organic matter (DOM) released by benthic primary producers fuels coral reef food webs. Anthropogenic stressors cause shifts from coral to algae dominance on many reefs, and resulting alterations in the DOM pool can promote opportunistic microbes and potential coral pathogens in reef water. To better understand these DOM-induced effects on bacterioplankton communities, we compared the carbohydrate composition of coral- and macroalgae-DOM and analyzed the response of bacterioplankton from an algae-dominated reef to these DOM types. In line with the proposed microbialization of reefs, coral-DOM was efficiently utilized, promoting energy transfer to higher trophic levels, whereas macroalgae-DOM likely stimulated microbial respiration over biomass production. Contrary to earlier findings, coral- and not algal-DOM selected for opportunistic microbial taxa, indicating that a change in the prevalent DOM composition, and not DOM type, may promote the rise of opportunistic microbes. Presented results may also apply to other coastal marine ecosystems undergoing benthic community shifts.

Unveiling the effects of dissolved organic matter (DOM) extracted from coastal algae and river on the photooxidation of arsenite

The coastal environment is an important ecosystem connecting land and sea, and arsenite (As(III)) in coastal seawater can seriously affect human health through the food chain. However, the effects of dissolved organic matter (DOM) extracted from coastal algae and rivers on As(III) photooxidation remain unclear. Results show that coastal algal DOM (CA-DOM) is significantly more effective than Suwannee River natural organic matter (SRNOM) in photooxidation of As(III), with a rate 8.3 times higher after correcting for light screening effects. CA-DOM accelerates As(III) photooxidation mainly through the 3DOM⁎ pathway, contributing 78.7 % to the process, whereas 3NOM⁎ contributes only 37.2 % for SRNOM. CA-DOM consists primarily of low-excited tyrosine and tryptophan-like protein substances, whereas SRNOM consists of humic and fulvic acid-like substances. Thus, CA-DOM exhibits a higher steady-state concentration of 3DOM⁎, and the 3DOM⁎ reacts much faster with As(III) than the 3NOM⁎. The increase in CA-DOM concentration can significantly accelerate the photooxidation of As(III), whereas the effect of SRNOM concentration is negligible. Increased salinity can accelerate As(III) photooxidation for all types of DOM. Our results provide new insights into the role of DOM from different sources in the photooxidation of As(III) in the natural environment or engineering applications.

Unravelling structure evolution of dissolved organic matter during oxidation by persulfate: Insights from aromaticity and fluorescence analysis

Persulfate advanced oxidation technology is widely utilized for remediating organic-contaminated groundwater. Post-remediation by persulfate oxidation, the aromaticity of dissolved organic matter (DOM) in groundwater is significantly reduced. Nevertheless, the evolution trends of aromaticity and related structural changes in DOM remained unclear. Here, we selected eight types of DOM to analyze the variation in aromaticity, molecular weight, and fluorescence characteristics during oxidation by persulfate using optical spectroscopy and parallel faction analysis combined with two-dimensional correlation spectroscopy analysis (2D PARAFAC COS). The results showed diverse trends in the changes of aromaticity and maximum fluorescence intensity (Fmax) among different types of DOM as the reaction time increases. Four types of DOM (humic acid 1S104H, fulvic acid, and natural organic matters) exhibited an initially noteworthy increase in aromaticity followed by a decrease, while others demonstrated a continuous decreasing trend (14.3%–69.4%). The overall decreasing magnitude of DOM aromaticity follows the order of natural organic matters ≈ commercial humic acid > fulvic acid > extracted humic acid. The Fmax of humic acid increased, exception of commercial humic acid. The Fmax of fulvic acid initially decreased and then increased, while that of natural organic matters exhibited a decreasing trend (86.4%). The fulvic acid-like substance is the main controlling factor for the aromaticity and molecular weight of DOM during persulfate oxidation process. The oxidation sequence of fluorophores in DOM is as follows: fulvic-like substance, microbial-derived humic-like substance, humic-like substance, and aquatic humic-like substance. The fulvic-like and microbial-derived humic-like substances at longer excitation wavelengths were more sensitive to the response of persulfate oxidation than that of shorter excitation wavelengths. This result reveals the structure evolution of DOM during persulfate oxidation process and provides further support for predicting its environmental behavior.

Metagenomic and FT-ICR MS insights into the mechanism for the arsenic biogeochemical cycling in groundwater

Arsenic (As) is a groundwater contaminant of global concern. The degradation of dissolved organic matter (DOM) can provide a reducing environment for As release. However, the interaction of DOM with local microbial communities and how different sources and types of DOM influence the biotransformation of As in aquifers is uncertain. This study used optical spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), metagenomics, and structural equation modeling (SEM) to demonstrate the how the biotransformation of As in aquifers is promoted. The results indicated that the DOM in high-As groundwater is dominated by highly unsaturated low-oxygen(O) compounds that are quite humic and stable. Metagenomics analysis indicated Acinetobacter, Pseudoxanthomonas, and Pseudomonas predominate in high-As environments; these genera all contain As detoxification genes and are members of the same phylum (Proteobacteria). SEM analyses indicated the presence of Proteobacteria is positively related to highly unsaturated low-O compounds in the groundwater and conditions that promote arsenite release. The results illustrate how the biogeochemical transformation of As in groundwater systems is affected by DOM from different sources and with different characteristics.

Photochemical reactivity of dissolved organic carbon in subarctic lakes along a color gradient

ABSTRACT Lake–atmosphere carbon exchanges can be significantly affected by photochemical dissolved organic matter (DOM) mineralization. However, our understanding of how increasing allochthonous organic carbon input affects the photoreactivity of DOM per unit of absorbed incoming light is incomplete. Here, we measured the absorption of ultraviolet (UV) light and subsequent photochemical DOM decay in 148 lakes within the subarctic region of Abisko, Sweden. These lakes range from brown-water lakes with allochthonous input from mires to tundra clear-water lakes with relatively more autochthonous input. We used fluorescence excitation–emission matrix analysis to assess the DOM chemical composition to determine how increasing colored DOM (CDOM) affects photomineralization. We found that the photo decay rates in absolute values were positively correlated to CDOM. However, the photo decay per unit of absorbed light energy did not increase with increasing CDOM; rather, it showed a weak decreasing trend. Fluorescence analyses helped explain these patterns; humic-like fluorescent DOM, presumably of terrestrial origin, was associated with high absolute photo decay rates, but not generally with higher photoreactivity per unit of absorbed light energy than other types of DOM. The results suggest that even though increasing inputs of terrestrial substances lead to a higher abundance of photodegradable materials, CO2 emissions do not necessarily increase in lakes where browning limits the ability of light to penetrate deeper water.

Insight into the binding characteristics of dissolved organic matter(DOM)and Fe(Ⅱ)/Mn(Ⅱ): Based on the spectroscopic and dialysis equilibrium analysis

Dissolved organic matter (DOM) plays an important role in metal migration and transformation within inland surface waters. In our study, spectroscopic and dialysis equilibrium analysis were combined to characterize the binding properties between DOM and Fe(II)/Mn(II). Four different type of DOM including two commercial DOM: humic acid、fulvic acid, and two natural dissolved organic matter collected from macrophyte-dominant region (MDR) and algae-dominated region (ADR) of Taihu Lake. Steady state/time resolved fluorescence spectroscopy indicated that the fluorescence intensity of DOM was quenched by Fe(II)/Mn(II) through a static quenching process. The adsorption isotherm shows that the adsorption capacity of DOM from Taihu Lake for metal ions is significantly higher than that of commercial humic acid. Simultaneously, the combination of MDR and Fe(II) has the highest adsorption capacity at 110.950 mg/g among all combinations. Furthermore, the Pseudo-second-order kinetic model and Elovich model were found to be superior in describing the adsorption process, with chemical adsorption controlling the rate of the adsorption reaction. The results of this study show that potentially toxic elements (PETs) pollution in eutrophic shallow lakes may become more serious due to the excessive expansion of algae dominant regions and the reduction of macrophyte dominant regions. In addition, risk analysis and assessment of PETs should consider the contribution of metal binding capabilities.

Effects of dissolved organic matter on the toxicity of micro- and nanoplastic particles to Daphnia - a meta-analysis

Effects of micro- and nanoplastic particles (MNP) on organisms have been increasingly reported in recent years, with a large number of studies conducted on water fleas of the genus Daphnia. Most of the available studies used pristine particles that have not been exposed to the environment or to organic substances. In natural environments, however, organic substances like dissolved organic matter (DOM) attach to the MNP, forming an ecocorona on the particles’ surface. How the formation of an ecocorona influences MNP toxicity is still uncertain. While some studies suggest that DOM can mitigate the negative effects of MNP on organisms, other studies did not find such associations. In addition, it is unclear whether the DOM attached to the particles’ surface attenuates the effects of MNP directly or whether co-exposure with DOM solved in the medium attenuates MNP toxicity indirectly, for instance by increasing Daphnia‘s resilience to stressors in general. To draw more solid conclusions about the direction and size of the mediating effect of DOM on MNP-associated immobilization in Daphnia spp., we synthesized evidence from the published literature and compiled 305 data points from 13 independent studies. The results of our meta-analysis show that the toxic effects of MNP are likely reduced in the presence of certain types of DOM in the exposure media. We found similar mediating effects when MNP were incubated in media containing DOM before the exposure experiments, although to a lesser extent. Future studies designed to disentangle the effects of DOM attached to the MNP from the general effects of DOM in the exposure medium will contribute to a deeper mechanistic understanding of MNP toxicity in nature and enhance the reliability of MNP risk assessment.Graphical

Distribution characterization of MPs and DOM in ice-covered season in a saline-alkaline Lake in Daihai with an innovative analysis using 2DCOS and structural equation modelling

Due to the characteristics of low density, light weight, and strong hydrophobicity, microplastics (MPs) can adsorb dissolved organic matter (DOM) in lake water to jointly accomplish migration and transformation in the ice/water medium, which causes serious pollution to the lake during the ice period through accumulation. In this study, the distribution of Daihai Lake MPs and DOM was studied by fluorescence excited emission matrix (EEM) and micro-infrared spectroscopy, and the relationship between them was examined by two-dimensional correlation spectroscopy (2DCOS) and structural equation modelling (SEM) to obtain the influencing factors of pollution. The results indicate that the concentration of MPs in the surface ice layer is 1.35 times more than in the water and in the surface and bottom ice layers 1–2 times more than the middle layer. DOM in the ice cover is mainly protein-like (73.33%), and humus-like DOM (44.8%) is dominant in the water under the ice that is consistent with the distribution of MPs in the ice and water layer. As a result, MPs are more prospective to adsorb humus-like substances into the ice during migration. Through SEM analysis, it was concluded that human activities and the degree of economic development seriously affect the pollution level and the type of MPs and DOM in lakes. One of the most important factors in winter is the ice cover, and there is a strong correlation between the MPs and DOM in different ice layers. Combined with experimental data, it was concluded that the ice layer influences the distribution characteristics of the pollutants in lakes as well as the direction of migration. However, the adsorption mechanism of the ice is not clear, which will be a key direction for future research on microplastics in ice-covered lakes.

Mechanisms of cadmium release from manganese-rich sediments driven by exogenous DOM and the role of microorganisms

Dissolved organic matter (DOM) is a crucial component of natural sediments that alters Cd sequestration. Nevertheless, how different types of DOM fuel Cd mobilization in Mn-rich sediments has not been elucidated. In the present study, four typical DOM, fluvic acid (FA), bovine serum albumin (BSA), sodium alginate (SA), and sodium dodecyl benzene sulfonate (SDBS), were used to amend Cd-contaminated sediment to study their effects on Cd/Mn biotransformation and microbial community response. The results demonstrated that different DOM drive microbial community shifts and enhance microbially mediated Mn oxide (MnO) reduction and Cd release. The amendment of terrestrial- and anthropogenic-derived DOM (FA and SDBS) mainly contributed to enriching Mn-reducing bacteria phylum Proteobacteria, and its abundance increased by 38.16–74.47 % and 56.41–73.98 %, respectively. Meanwhile, microbial-derived DOM (BSA and SA) mainly stimulated the abundances of metal(loid)-resistant bacteria phylum Firmicutes. Accompanied by microbial community structure, diversity, and co-occurrence network shifts, the DOM concentration and oxidation-reduction potential changed, resulting in enhanced Cd mobilization. Importantly, FA stimulated Cd release most remarkably, probably because of the decreased cooperative interactions between bacterial populations, stronger reduction of MnOs, and higher aromaticity and hydrophobicity of the sediment DOM after amendment. This study linked DOM types to functional microbial communities, and explored the potential roles of different DOM types in Cd biotransformation in lake sediments.

Effect of UV-LED Wavelength on Reactive Species Photogeneration from Dissolved Organic Matter

The photogeneration of reactive species from dissolved organic matter (DOM) plays a crucial role in the photochemical and photobiochemical processes in natural aquatic systems. However, the impact of the ultraviolet (UV) wavelength on the photogeneration of reactive species by different sources of DOM remains unclear. In this study, UV light at four wavelengths (365 nm, 310 nm, 280 nm, and 260 nm) provided by UV-LEDs were irradiated onto three types of DOM: humic acid (HA), fulvic acid (FA), and effluent organic matter (EfOM). Three reactive species produced by DOM, including excited triplet-state DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radicals (•OH), were determined. UV365 proved to be the most efficient wavelength for generating 1O2 and •OH, with formation rates of 3.47 × 10−6 M s−1 and 1.67 × 10−8 M s−1, respectively, with the addition of FA and EfOM. The highest steady-state concentrations of all three reactive species were also generated under UV365, reaching 3.00 × 10−13 M (3DOM*) and 1.64 × 10−11 M (1O2) with the FA addition, and 1.44 × 10−10 M (•OH) with the EfOM. Across the different DOM sources, UV365 obtained the maximum quantum yields of reactive species, indicating the stronger effect of UV365 on inducing the photosensitization of DOM compared to the other shorter wavelengths. This study expands our understanding of the photochemistry of DOM in aquatic environments.

The dependence in microcystin removal with powdered activated carbon on variant properties, carbon properties, and dissolved organic matter

Powdered activated carbon (PAC) is commonly used by water treatment plants to remove harmful cyanotoxins such as microcystins (MCs) produced during seasonal harmful algal blooms. MC removal by PAC depends upon the properties of the PAC, the properties of the MC variant, and the presence and properties of dissolved organic matter (DOM). To identify which of these factors has the greatest impact on the removal of MC by PAC, we evaluated the removal of four different MC variants (MC-LR, MC-LA, MC-RR and desmethylated MC-RR) by three different PAC types (wood-based, coal-blend and coal-based). The role of DOM properties was evaluated using DOM isolated from two different sources, a terrestrial source (Suwannee River Fulvic Acid, SRFA) and a microbial source (Grand Lake St Marys DOM, GLSM). The results of adsorption experiments conducted over a period of 72 h demonstrated the wood-based PAC, which had the highest surface area and mesopore volume of the PAC tested, had the highest adsorption rate and capacity for all four MC variants. Of the variants studied, neutrally charged MC-RR was adsorbed more rapidly and to a greater extent on all of the PAC types than were the other variants. Although MC-LA and MC-LR had the greatest hydrophobicity, their negative charges resulted in their being adsorbed the least. As expected, DOM inhibited microcystin adsorption to PAC. The degree of inhibition, however, did not significantly vary for the two DOM types evaluated, indicating the properties of the DOM on MC adsorption to PAC was less important than the PAC properties or MC variant properties. Overall, PAC properties were a more important factor in MC removal than were the MC properties or DOM conditions.

Interactions of manganese oxides with natural dissolved organic matter: Implications for soil organic carbon cycling

Metal (oxyhydr)oxides are key factors for the transformation and stabilization of organic carbon (OC) in soil. While sorptive interactions between Al and Fe (oxyhydr)oxides and dissolved organic matter (DOM) are well studied, the role of Mn(IV) oxides (manganates) in DOM sorption, fractionation, and oxidation has not been extensively investigated. Therefore, we examined sorptive interactions between manganates (δ-MnO2, birnessite, cryptomelane; 5 g L−1) and different DOM types (beech litter and Oa/Oe material under pine; ∼100 mg L−1 dissolved organic carbon, DOC) at pH 4 and 7 in different background electrolytes (BGE; no salt, 0.01 M NaCl or CaCl2) for up to 32 h. Changes of DOM solutions and mineral phases were assessed by solid, liquid, and gas analyses, and statistically evaluated for the effects of manganate, DOM type, pH, and BGE on DOC sorption, fractionation, and oxidative transformation. Manganates sorbed 0.2–8.7 mg OC g−1. Per unit mass, δ-MnO2 was least effective in DOC retention due to its high DOC oxidation capacity. Manganates sorbed more DOC at acidic pH and more aromatic pine than more aliphatic beech DOC, with Ca2+ generally facilitating DOC sorption. Up to 56 % of added DOC (average: 25 %) was oxidized to CO2, which is comparable to the extent of DOC respiration by soil microorganisms. DOC oxidation by δ-MnO2 and cryptomelane exceeded that of birnessite, which had the lowest specific surface area of all manganates. However, we found no difference in the efficiency of manganates to oxidize DOC, implying a similar redox activity of phyllo- and tectomanganates. More beech than pine DOM was oxidized to CO2 and an acidic pH facilitated DOC decomposition. While the presence of Na-BGE increased DOC oxidation to CO2 relative to no-salt treatments, Ca-BGE had the opposite effect, as Ca2+ apparently impeded the electron transfer from sorbed OC to structural Mn(III/IV). Contact of DOM with manganates also produced high concentrations of dissolved low-molecular-weight organic acids (mainly formate, acetate, and oxalate), accounting for up to 19 % of the initial DOC concentration. In addition, reduced specific ultraviolet absorbance of DOM solutions at 280 nm indicated preferential sorption of aromatic moieties, especially in Ca-BGE. However, in the absence of Ca2+ and at neutral pH, manganates increased the aromaticity of beech DOM, most likely due to polymerization reactions. No mineral transformations occurred after reaction of manganates with DOM, despite reductive manganate dissolution. Our results imply that soil manganates accumulate more OC in acidic soils and in presence of more aromatic DOM. However, manganates oxidatively destabilize DOC by generating CO2 and low-molecular-weight organic compounds, which is presumably more relevant in acidic soils with low concentrations of polyvalent cations and for more aliphatic DOM. The produced low-molecular-weight organic compounds may promote microbial activity and foster mineral weathering. Our results suggest a pivotal role of manganates in soil OC cycling, including the fate and bioavailability of nutrient elements associated with DOM, and in supporting ligand-promoted mineral weathering and soil formation.

Organic matter biofiltration performance modeling: Influence of influent water quality, operating conditions, and biomass

The impact of source water dissolved organic matter (DOM) origin, empty bed contact time (EBCT), temperature, and pretreatment methods on biofiltration performance was evaluated and predictive models based on experimental data were developed. Three DOM source water types, terrestrial, microbial, and treated wastewater (WW) effluent, were utilized. A model was developed to predict biofilter performance for dissolved organic carbon (DOC) removal based on the influent biodegradable DOC (BDOC) fraction, a single active biomass measurement from the top of the filter and the filter EBCT. A biomass distribution model was developed to predict total active biomass throughout the filter based on a single biomass measurement from the top of the filter. The measured BDOC fractions were 21 % for the nonWW impacted source waters, 36 % for the WW effluents and 62 % for the ozonated WW effluents. At an EBCT of 15 min, biofilters removed between 7 and 21 % of the DOC (19 to 50 % for BDOC) depending on the DOM type and use of ozonation. When the EBCT decreased to 5 min DOC removal decreased by 40 % and when increased to 30 min removal increased by 42 %. When the temperature decreased from 22 °C to 6 °C DOC removal was 33 % lower and when increased to 28 °C removal was 42 % higher. ATP values were found to be a function of temperature and DOM origin, as the average ATP values from the WW effluent biofilters were almost double that of the non-WW impacted sources and pre-ozonation of the WW effluent yielded values three times higher. The model was applied to the results of 27 different biofilter runs at three EBCTs yielding one distinct rate constant for the non-WW impacted source waters and one rate constant for the WW effluents. The model was successfully applied to the results of 19 filter runs from the literature and to those from a pilot plant over 6 months of operation.

Copper Safeguards Dissolved Organic Matter from Sunlight-Driven Photooxidation.

Sunlight plays a crucial role in the transformation of dissolved organic matter (DOM) and the associated carbon cycle in aquatic environments. This study demonstrates that the presence of nanomolar concentrations of copper (Cu) significantly decreases the rate of photobleaching and the rate of loss of electron-donating moieties of three selected types of DOM (including both terrestrial and microbially derived DOM) under simulated sunlight irradiation. Employing Fourier transform ion cyclotron resonance mass spectrometry, we further confirm that Cu selectively inhibits the photooxidation of lignin- and tannin-like phenolic moieties present within the DOM, in agreement with the reported inhibitory impact of Cu on the photooxidation of phenolic compounds. On the basis of the inhibitory impact of Cu on the DOM photobleaching rate, we calculate the contribution of phenolic moieties to DOM photobleaching to be at least 29-55% in the wavelength range of 220-460 nm. The inhibition of loss of electrons from DOM during irradiation in the presence of Cu is also explained quantitatively by developing a mathematical model describing hydrogen peroxide (a proxy measure of loss of electrons from DOM) formation on DOM irradiation in the absence and presence of Cu. Overall, this study advances our understanding of DOM transformation in natural sunlit waters.

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 the 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 the 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 the PPCPs ecological risk varies on space, season and river hydraulic condition.

Arsenic-dissolved organic matter complexation in water soluble extracts from lignite

Arsenic in groundwater is a global threat to public health. Recently, As mobility has been tied to the concentration and chemical characteristics of dissolved organic matter (DOM) through formation of As-DOM complexes. To date, there has been a wide range of DOM types studied to understand As-DOM interactions, but most of these have focused on surface water derived materials and not groundwater DOM. We address this gap in knowledge by simulating groundwater DOM using water extractable organic matter (WEOM) from two lignite deposits and treating the extracts with increasing concentrations of As. As-DOM complexes were measured using size-exclusion chromatography coupled to multiple detectors including an inductively coupled plasma mass spectrometer (ICPMS) for As detection as well as fluorescence and variable wave detectors for organic matter detection. First, we found two different size fractions of As-DOM, one of ∼1 kDa and another of ∼15 kDa, depending on the DOM types. The smaller As-DOM complex (∼1 kDa) was approximately 10 times more abundant than the larger complex (∼15 kDa). Second, we found that the lignite derived DOMs showed higher conditional distribution coefficients than did the surface water reference material (Suwanee River Natural Organic Matter, SRNOM). Finally, the data showed good fit (R2 > 0.92) to one-site ligand binding models, and the lignite derived DOMs showed higher maximum sorbate concentrations (Bmax) compared to SRNOM. Together, this study shows that As-DOM complexation is an important control on As speciation, even in groundwater systems.

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.

Atomic-Level Structural Differences between Fe(III) Coprecipitates Generated by the Addition of Fe(III) Coagulants and by the Oxidation of Fe(II) Coagulants Determine Their Coagulation Behavior in Phosphate and DOM Removal.

In situ Fe(III) coprecipitation from Fe2+ oxidation is a widespread phenomenon in natural environments and water treatment processes. Studies have shown the superiority of in situ Fe(III) (formed by in situ oxidation of a Fe(II) coagulant) over ex situ Fe(III) (using a Fe(III) coagulant directly) in coagulation, but the reasons remain unclear due to the uncertain nature of amorphous structures. Here, we utilized an in situ Fe(III) coagulation process, oxidizing the Fe(II) coagulant by potassium permanganate (KMnO4), to treat phosphate-containing surface water and analyzed differences between in situ and ex situ Fe(III) coagulation in phosphate removal, dissolved organic matter (DOM) removal, and floc growth. Compared to ex situ Fe(III), flocs formed by the natural oxidizing Fe2+ coagulant exhibited more effective phosphate removal. Furthermore, in situ Fe(III) formed through accelerated oxidation by KMnO4 demonstrated improved flocculation behavior and enhanced removal of specific types of DOM by forming a more stable structure while still maintaining effective phosphate removal. Fe K-edge extended X-ray absorption fine structure spectra (EXAFS) of the flocs explained their differences. A short-range ordered strengite-like structure (corner-linked PO4 tetrahedra to FeO6 octahedra) was the key to more effective phosphorus removal of in situ Fe(III) than ex situ Fe(III) and was well preserved when KMnO4 accelerated in situ Fe(III) formation. Conversely, KMnO4 significantly inhibited the edge and corner coordination between FeO6 octahedra and altered the floc-chain-forming behavior by accelerating hydrolysis, resulting in a more dispersed monomeric structure than ex situ Fe(III). This research provides an explanation for the superiority of in situ Fe(III) in phosphorus removal and highlights the importance of atomic-level structural differences between ex situ and in situ Fe(III) coprecipitates in water treatment.

Effect of dissolved organic matter on copper bioavailability to a coastal dinoflagellate at environmentally relevant concentrations

The speciation and bioavailability of copper (Cu) in the marine environment are affected by the presence of dissolved organic matter (DOM). Previous studies conducted at dissolved Cu concentrations >100 nM confirmed that Cu bioavailability depends on the concentration of labile Cu, as measured by anodic stripping voltammetry (ASV), which aligns with the expectations of the biotic ligand model (BLM). However, ambient Cu concentrations in coastal waters are generally lower, ranging between 1 and 80 nM, and the effect of DOM on the bioavailability of Cu to marine organisms has not been tested within that range of Cu concentrations. The present study aims to assess the impact of two types of DOM, a commercially available fulvic acid, and marine DOM extracted by ultrafiltration, on Cu bioavailability to phytoplankton using short-term 65Cu internalisation by the marine dinoflagellate Prorocentrum micans. Results showed that Cu internalisation decreases with DOM additions as expected according to the BLM and in agreement with ASV measurements of labile Cu, at the highest tested Cu concentration (100 nM). On the contrary, at a lower Cu concentration (20 nM), organic complexes appear to be partially bioavailable, thereby challenging the general applicability of the BLM model at environmentally relevant concentrations in coastal areas.