Dissolved Organic Matter Levels Research Articles

Dynamic changes in dissolved organic matter during transport of landfill leachate in porous medium.

The dynamic changes in dissolved organic matter (DOM) during the transport of landfill leachate (LL) in porous medium should be explored, considering the high levels of DOM in the LL of municipal solid waste. Column experiments were carried out at 25°C at a Darcy's flux of 0.29cm/h for 2722h to compare the transport of Cl-, ultraviolet absorbance at 254nm (UV254), chemical oxygen demand (COD), and dissolved organic carbon (DOC) in the simulated porous medium by using the CXTFIT2.1 code. Results showed that the convection-dispersion equation (CDE) could describe Cl- transport well. The high levels of λ and D could be highly correlated with the physicochemical properties of the porous medium. The transport of the studied DOM with evident aromatic character could be described appropriately by the CDE model with the first-order reaction assumption, considering the similar variation trends of UV254, COD, and DOC in the effluent during experiments. Specifically, the values of retardation factor (R) were in the following order: DOC > UV254 > COD, whereas the low values of the first-order decay coefficient (k1) for DOC and COD were still higher than that for UV254. High contents of humic-like substances in the DOM with complex toxic components resulted in the natural low removal efficiencies of COD, DOC, and UV254 (≤ 23%), which could be confirmed by the variations of fluorescence index (FI) and humification index (HIX) in the effluent. The results should be helpful in evaluating the environmental risk induced by the LL leakage in a landfill site.

Seasonal Freezing Drives Spatiotemporal Dynamics of Dissolved Organic Matter (DOM) and Microbial Communities in Reclaimed Water-Recharged River

Although reclaimed water (RW) has become a promising alternative source for alleviating water shortage in arid and semiarid regions, the ecological risks it poses to the receiving water bodies remain largely unknown. Dissolved organic matter (DOM) is crucial for affecting the quality of RW and strongly influences bacterial communities (BCs) in aquatic ecosystems. In this study, we aimed to unravel the role of DOM signatures on the spatiotemporal composition of microbial communities (MCs) in a seasonally ice-sealed urban river that had been chronically replenished by RW. We found that discharging RW resulted in elevated DOM levels in the receiving river. Notably, an increase of 10% in protein-like substances was revealed. The differences between compositional characteristics of DOM and the abundance of riverine BCs between freezing and non-freezing periods were revealed. In the freezing season, humic-like components, aromaticity, and hydrophobicity of DOM were more significant, and bacterial taxa such as Bacteriodetes and Flavobacterium were increased, while Proteobacteria was decreased. Similarly, co-occurrence network analysis revealed an enhanced interplay between DOM and BCs at the same time. However, Klebsiella pneumoniae markedly decreased during the ice-sealed period. These results suggest that variations in DOM characteristics have remarkable impacts on the dynamics of aquatic BCs, which points to the need for a DOM−oriented RW quality monitoring strategy.

Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Understanding microplastic aging driven by photosensitization of algal extracellular polymeric substances

The aging of microplastics (MPs) is extremely influenced by photochemically-produced reactive intermediates (PPRIs), which are mediated by natural photosensitive substances. Algal extracellular polymeric substances (EPS) can produce PPRIs when exposed to sunlight. Nonetheless, the specific role of EPS in the aging process of MPs remains unclear. This work systematically explored the aging process of polystyrene (PS) MPs in the EPS secreted by Chlorella vulgaris under simulated sunlight irradiation. The results revealed that the existence of EPS accelerated the degradation of PS MPs into particles with sizes less than 1 µm, while also facilitating the formation of hydroxy groups on the surface. The release rate of dissolved organic matter (DOM) from PS MPs was elevated from 0.120 mg·L-1·day-1 to 0.577 mg·L-1·day-1. The primary factor contributing to the elevated levels of DOM was humic acid-like compounds generated through the breakdown of PS. EPS accelerated the aging process of PS MPs by primarily mediating the formation of triplet excited states (3EPS*), singlet oxygen (1O2), and superoxide radicals (O2∙-), resulting in indirect degradation. 3EPS* was found to have the most substantial impact. This study makes a significant contribution to advance understanding of the environmental fate of MPs in aquatic environments impacted by algal blooms.

Characterization of microplastic-derived dissolved organic matter in freshwater: Effects of light irradiation and polymer types

This study investigated the impacts of light irradiation and polymer types on the leaching behavior of dissolved organic matter (DOM) from microplastics (MPs) in freshwater. Polypropylene had the highest leaching capacity of DOM after photoaging, followed by polystyrene (PS), polyamide (PA) and polyethylene terephthalate (PET). While similarly low levels of DOM were observed in the remaining 5 MP suspensions under UV irradiation and in almost all MP suspensions (except PA) under darkness. These suggest that the photooxidation of some buoyant plastics may influence the carbon cycling of nature waters. Among 9 MP-derived leachates, PET leachates had the highest chromophoric DOM concentration and aromaticity, probably owing to the special benzene rings and carbonyl groups in PET structures and its fast degradation rate. Protein-like substances were the primary fluorescent DOM in MP suspensions (except PS), especially in darkness no other fluorescent substances were found. Considering the bio-labile properties of proteins together, MPs regardless of floating or suspended in an aquatic environment may have prevalent long-term effects on microbial activities. Besides, from monomers to hexamers with newly formed chemical bonds were identified in UV-irradiated MP suspensions. These results will contribute to a deep insight into the potential ecological effects related to MP degradation.

Self-motivated photoaging of microplastics by biochar-dissolved organic matter under different pyrolysis temperatures

Dissolved organic matter (DOM) released from biochar (BDOM) can interact with microplastics (MPs) in the environment, inevitably affecting their environmental behaviour. Information regarding the influence of BDOM on MPs during photoaging and associated variations in the MP aging mechanism remains unclear. This study evaluated the effect of BDOM on the aging of polystyrene (PS) MPs. The results showed that among three pyrolysis temperatures, low-temperature BDOM significantly enhanced the photoaging process of PS MPs, with the smallest average particle size and highest carbonyl index value after 15 days of aging under light conditions. The DOM level decreased after 5 days, increased after 5–10 days, and stabilised after 15 d. BDOM accelerates PS MPs aging, leading to more DOM released from PS, which can be transformed into 1O2 via triplet-excited state (3DOM⁎ and 3PS⁎) to further enhance PS MPs aging, resulting in the realisation of the self-accelerated aging process of PS MPs. 1O2 plays a crucial role in the self-motivated accelerated aging process of PS MPs. These findings provide new insights into the effects of the DOM structure and composition on reactive oxygen species generation during MPs aging.

Dissolved organic matter and Fe/Mn enhance the combination and transformation of As in Lake Chaohu Basin

The phenomenon of algal blooms resulting from lake eutrophication has the potential to increase the concentration of dissolved organic matter (DOM) and consequently influence the environmental behaviour of arsenic (As). In the subtropical region, the interplay between DOM, Fe/Mn and As becomes complex as Fe/Mn-rich substances from soils and sediments enter eutrophic lakes. The mechanisms by which DOM-Fe/Mn interactions affect the transformation of As species remain uncertain. Therefore, the Chaohu Lake Basin was selected as a representative case study site to investigate the levels of DOM, As, Fe and Mn in the water and to establish their associations. In addition, the interaction mechanism between DOM-Fe/Mn and As was investigated by elucidating the transformation behaviour of DOM-Fe/Mn on As species in a controlled laboratory environment. The results showed that in cases where the coexistence of Fe and Mn concentrations was relatively low (e.g. Fe < ∼0.5 mg/L and Mn < ∼0.6 mg/L), the concentration of As in water would increase proportionally with the simultaneous increase of both Fe and Mn concentrations (As < 5 μg/L). However, when the concentration of either Fe or Mn reached 10 mg/L, the proportion of As complexed by DOM increased significantly, reaching 99.73% and 99.66%, respectively. In the configuration of a metallic bridge, the elements Fe and Mn act as connectors between negatively charged DOM and As, thereby increasing the adsorption capacity of DOM for As. The alcohol and alkene functional groups present on the DOM-Fe/Mn surface show a preference for binding with free species of As in aqueous environments. In addition, the reductive groups on the surface of DOM not only directly convert As(V) to As(III), but also facilitate the reduction of Fe(III) to Fe(II), resulting in the indirect conversion of As(V) to As(III). Thus, this study provides a comprehensive understanding of the transport and transformation processes of arsenic in subtropical eutrophic lakes.

Unveiling temporal variation in dissolved organic matter (DOM) with high-frequency spectroscopic measurements in a shallow eutrophic lake

ABSTRACT Dissolved organic matter (DOM) plays an important role in biogeochemistry of lake ecosystems. Studies measuring DOM at short intervals in lakes are rare, and thus its short-term dynamics are largely unknown. We investigated DOM temporal variation in large, shallow, eutrophic Lake Võrtsjärv (Estonia) during one growing season (May–Sep 2016) using a field-deployable in situ spectrometer to measure absorbance spectra (wavelength range 200–708 nm) at a 2 h interval coupled with monthly discrete water sampling. Collected spectra were analyzed together with some in-lake variables, lake metabolic rates, and meteorological and hydrological data using boosted regression tree (BRT) and random forest (RF) models. Different spectral parameters were used to assess total and allochthonous DOM quantity and relative share of autochthonous DOM. All parameters (i.e., DOM quantity and quality) varied on a large scale. For example, dissolved organic carbon (DOC) concentrations ranged from 12.0 to 17.3 mg L−1. High levels of DOM were mainly of allochthonous origin, and a strong relationship with inflow indicated the same. The relative share of autochthonous DOM increased with rising air temperature as primary production rose in warm water; however, we found no direct relationships with gross primary production. RF and BRT models explained up to 38% and 63% of DOM temporal variability, respectively. Our results showed that monthly water samples did not capture large variation in DOM. Therefore, high-frequency measurements using in situ spectrometry improve temporal representativeness of DOM monitoring in lakes compared to traditional sampling methods.

A river of terrestrial dissolved organic matter in the upper waters of the central Arctic Ocean

The Transpolar Drift (TPD) is a mechanism for the rapid transport of shelf-modified Siberian river waters across the Arctic Ocean and out through Fram Strait. We present results from three trans-Arctic research cruises in August–September 2014–2016 to investigate the distribution and dynamics of dissolved organic matter (DOM) in the upper waters across the North Pole, from Svalbard to the Mackenzie River mouth, and in two important outflow gateways of the Arctic Ocean (Fram Strait and Lancaster Sound). Fluorescence measurements of DOM obtained using in situ sensor and laboratory-based spectroscopic analyses, coupled with parallel factor analysis (PARAFAC) were used to map components of DOM at high spatial resolution. The optical properties showed a completely different composition with a much stronger humic-like signal observed in surface waters in the Makarov Basin than in the adjacent Canada Basin, likely due to the substantial amount of Siberian runoff transported by the TPD. The high levels of humic-like in TPD-influenced surface waters were traced from southern Makarov shelves up to the Lomonosov Ridge near the North Pole. Lower DOM levels were observed in the eastern Amundsen basin waters, likely the result of mixing with terrestrial-poor DOM Atlantic waters. The annual flux of humic-like C2 transported to the Atlantic through Fram Strait was estimated at 1816 ±926 r.u. km3. This study reveals the importance of shelf processes and TPD in supplying humic-like material to the central Arctic Ocean to Fram Strait.

Effects of dissolved organic matter derived from chicken manure on the biotransformation of roxarsone in soil

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX), widely used as a livestock feed additive, is excreted untransformed in large concentrations. Accumulation of this manure in the open environment increases dissolved organic matter (DOM) and ROX in soil within the aeration zone. And microbial action plays a dominant role in the transformation of ROX. However, the specific effect of DOM on the biotransformation of ROX is not known. In this paper, we investigated the transformation rate, metabolite content, and microbial community response of ROX in soils with different DOM concentrations (71.61, 100, 200, 500, and 800 mg L−1). The transformation of ROX was consistent with first-order transformation kinetics. DOM promoted the transformation of ROX, and with high DOM (DOM ≥200 mg L−1), ROX was transformed almost completely within two days. In this case, DOM provided nutrients to microorganisms and promoted their growth, accelerating the transformation of ROX. Also, the solubility of ROX was enhanced by DOM to increase its bioavailability. The microbial diversity was negatively correlated with DOM concentration and ROX transformation time; during the transformation of ROX, Bacillus, Arthrobacter, Enterococcus, Acinetobacter, and Pseudomonas became dominant in the soil with anomalously high levels of DOM. This study demonstrates the transformation process of ROX under actual environmental conditions where organic matter coexists with ROX, and this understanding is important for the prevention and control of arsenic pollution in soil within the aeration zone with anomalously high levels of DOM.

Spatial Complexity in Dissolved Organic Matter and Trace Elements Driven by Hydrography and Freshwater Input Across the Arctic Ocean During 2015 Arctic GEOTRACES Expeditions

AbstractThis study traces dissolved organic matter (DOM) in different water masses of the Arctic Ocean and its effect on the distributions of trace elements (TEs; Fe, Cu, Mn, Ni, Zn, Cd) using fluorescent properties of DOM and the terrigenous biomarker lignin. The Nansen, Amundsen, and Makarov Basins were characterized by the influence of Atlantic water and the fluvial discharge of the Siberian Rivers with high concentrations of terrigenous DOM (tDOM). The Canada Basin and the Chukchi Sea were characterized by Pacific water, modified through contact with productive shelf sediments with elevated levels of marine DOM. Within the surface layer of the Beaufort Gyre, meteoric water (river water and precipitation) was characterized by low concentrations of lignin and tDOM fluorescence proxies as DOM is removed during freezing. High‐resolution in situ fluorescence profiles revealed that DOM distribution closely followed isopycnals, indicating the strong influence of sea‐ice formation and melt, which was also reflected in strong correlations between DOM fluorescence and brine contributions. The relationship of DOM and hydrography to TEs showed that terrigenous and marine DOM were likely carriers of dissolved Fe, Ni, Cu from the Eurasian shelves into the central Arctic Ocean. Chukchi shelf sediments were important sources of dCd, dZn, and dNi, as well as marine ligands that bind and carry these TEs offshore within the upper halocline in the Canada Basin. Our data suggest that tDOM components represent stronger ligands relative to marine DOM components, potentially facilitating the long‐range transport of TE to the North Atlantic.

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Groundwater discharge and river runoff are two important ways for allochthonous dissolved organic matter (DOM) to enter the ocean, but they vary spatially. Currently, the source, composition, and efflux of groundwater and riverine dissolved organic matter to the tropical northern South China Sea remain poorly understood, preventing an accurate estimate of coastal carbon budgets. In July 2021, nine groundwater and six river water samples were collected along the coast of western Guangdong and were characterized using dissolved organic carbon (DOC) analysis, UV-visible, and fluorescence spectroscopy techniques. Atypical absorption spectra were strongly observed in groundwaters, which were mainly attributed to the high-level nitrates. An exponential-Gaussian equation showed that the average contribution of nitrate to total groundwater absorbances was up to 36% at ∼ 300 nm. Groundwater showed lower levels of DOC, colored dissolved organic matter (CDOM), and fluorescent dissolved organic matter (FDOM) as compared to river water, whereas the humic-like components dominated both groundwater and river water FDOM pools. Higher values of spectral slope S350–400, fluorescence index, biological index, and the ratio of two humic-like fluorescence jointly reveal that groundwater DOM mainly originated from microbial activities, whereas the river water DOM had considerable contribution from terrestrial soil. High precipitation, natural or agricultural land types, and a lack of seawater intrusion are expected to cause low levels of groundwater DOM in western Guangdong. Among 52 rivers from across the globe, high watershed productivity and precipitation may lead to high–moderate DOM levels in river water in western Guangdong. The DOM fluxes via fresh groundwater discharge in western Guangdong are comparable in magnitude to those by river runoff, accounting for 16%–18% of the Pearl River DOM fluxes. Based on the slopes of linear correlations between CDOM and DOC obtained in groundwater samples and 52 rivers, as well as the data on water fluxes and DOC levels, the global CDOM fluxes via groundwater discharge and river runoff are estimated to be 3.5–12.2 × 1012 m2 yr−1 and 4.3 ± 0.3 × 1014 m2 yr−1, respectively, highlighting the importance of considering groundwater discharge and river runoff in coastal carbon budgets.

Critical evaluation of the interaction between fluorescent dissolved organic matter and Pb(II) under variable environmental conditions

Dissolved organic matter (DOM) can strongly influence the behavior and risk of metal pollutants in aquatic ecosystems. However, a comprehensive study on the effects of DOM level and environmental factors on the binding of DOM with Pb(II) is lacking. This study examined the DOM-Pb(II) interaction in the river water under variable DOM level, pH, and major ions, using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Four humic-like and one protein-like component were identified, and the abundant humic-like components showed higher Pb(II)-binding fractions (f) than the protein-like component. The f of PARAFAC components decreased while the conditional stability constants (logKM) increased for the diluted DOM, indicating the influence of DOM level on its metal binding. The DOM-Pb(II) interaction was sensitive to changes in pH, with generally higher f and lower logKM at the alkaline condition due to changes in the DOM conformation. The addition of major ions significantly decreased the fluorescence quenching by Pb(II), due to competitive effects and potential DOM conformation changes at elevated ions. Overall, our results show that the DOM-Pb(II) complexation is highly dependent on both the DOM properties and environmental factors, which have implications for optimizing the experimental conditions and for comparing the results in different environments.

Riverine dissolved organic matter (DOM) as affected by urbanization gradient

Rapid urbanization has considerably altered carbon biogeochemical cycle and river hydrology. However, the influences of urban land use and urban-induced nutrient increase on dissolved organic matter (DOM) characteristics are poorly understood. Here we hypothesize that the alterations significantly change sources and levels of DOM in river systems that drain the urban areas. To test the hypothesis, we investigated DOM in headwater rivers with varied urban intensities in the Three Gorges Reservoir Area (TGRA), China, through field sampling conducted in the dry and wet seasons. We found positive relationships of urban land (%Urban) with DOC concentration and chromophoric DOM (CDOM) absorption coefficients a254, a280 and a350, as well as fluorescence index (FI370), indicating the significantly increased levels of DOM and autochthonous sources along an urbanization gradient. A stepwise regression analysis demonstrated that occurrences of DOC and CDOM can be predicted by %Urban, while increasing autochthonous source is predictable by the increase in riverine nitrogen. Moreover, a254, a280 and FI370 values showed distinct seasonal variations, with significantly higher CDOM concentration in the wet season and with much higher autochthonous signal in the dry season with high nitrogen loading. Based on the findings, we conclude that urbanization influences occurrences and sources of DOM, with increasing urbanization making an important and direct contribution to DOM, and an indirect effect of urban induced nutrient enrichment, i.e., enhanced nutrient loadings increase autochthonous DOM production in rivers.

Adaptations of microbial communities and dissolved organics to seasonal pressures in a mesotrophic coastal Mediterranean lake

In lake ecosystems, changes in eukaryotic and prokaryotic microbes and the concentration and availability of dissolved organic matter (DOM) produced within or supplied to the system by allochthonous sources are components that characterize complex processes in the microbial loop. We address seasonal changes of microbial communities and DOM in the largest Croatian lake, Vrana. This shallow lake is connected to the Adriatic Sea and is impacted by agricultural activity. Microbial community and DOM structure were driven by several environmental stressors, including drought, seawater intrusion and heavy precipitation events. Bacterial composition of different lifestyles (free-living and particle-associated) differed and only a part of the particle-associated bacteria correlated with microbial eukaryotes. Oscillations of cyanobacterial relative abundance along with chlorophyll a revealed a high primary production season characterized by increased levels of autochthonous DOM that promoted bacterial processes of organic matter degradation. From our results, we infer that in coastal freshwater lakes dependent on precipitation-evaporation balance, prolonged dry season coupled with heavy irrigation impact microbial communities at different trophic levels even if salinity increases only slightly and allochthonous DOM inputs decrease. These pressures, if applied more frequently or at higher concentrations, could have the potential to overturn the trophic state of the lake.

In Situ Photochemical Transformation of Hg Species and Associated Isotopic Fractionation in the Water Column of High-Altitude Lakes from the Bolivian Altiplano.

Photochemical reactions are major pathways for the removal of Hg species from aquatic ecosystems, lowering the concentration of monomethylmercury (MMHg) and its bioaccumulation in foodwebs. Here, we investigated the rates and environmental drivers of MMHg photodegradation and inorganic Hg (IHg) photoreduction in waters of two high-altitude lakes from the Bolivian Altiplano representing meso- to eutrophic conditions. We incubated three contrasting waters in situ at two depths after adding Hg-enriched isotopic species to derive rate constants. We found that transformations mostly occurred in subsurface waters exposed to UV radiation and were mainly modulated by the dissolved organic matter (DOM) level. In parallel, we incubated the same waters after the addition of low concentrations of natural MMHg and followed the stable isotope composition of the remaining Hg species by compound-specific isotope analysis allowing the determination of enrichment factors and mass-independent fractionation (MIF) slopes (Δ199Hg/Δ201Hg) during in situ MMHg photodegradation in natural waters. We found that MIF enrichment factors potentially range from -11 to -19‰ and average -14.3 ± 0.6‰ (1 SE). The MIF slope diverged depending on the DOM level, ranging from 1.24 ± 0.03 to 1.34 ± 0.02 for the low and high DOM waters, respectively, and matched the MMHg MIF slope recorded in fish from the same lake. Our in situ results thus reveal (i) a relatively similar extent of Hg isotopic fractionation during MMHg photodegradation among contrasted natural waters and compared to previous laboratory experiments and (ii) that the MMHg MIF recorded in fish is characteristic for the MMHg bonding environment. They will enable a better assessment of the extent and conditions conducive to MMHg photodegradation in aquatic ecosystems.

Effect of light combination on the characteristics of dissolved organic matter and chemical forms of Cd in the rhizosphere of Arabidopsis thaliana involved in phytoremediation

Light, one of the most important natural resources for plant species, significantly influences the biomass yield and nutrient uptake capacity in plants. Light sources with different spectra combinations can impact the bioavailability, toxicity, and solubility of heavy metals in soils by altering the concentrations and fractionations of soil dissolved organic matter (DOM). A series of light irradiation treatments were performed to evaluate the influence of red, yellow, and blue lights on the characteristics of DOM in the rhizosphere soils of Arabidopsis thaliana. The results showed that monochromatic red light significantly raised the levels of DOM and proportions of hydrophilic fractionations in the rhizosphere of A. thaliana relative to the control, while monochromatic blue light had the opposite effect. Moreover, the proportions of hydrophobic acid, which can mobilize Cd effectively, also raised with increasing doses of red light, which stimulated Cd mobilization. The application of yellow light not only increased the levels of hydrophobic acid in monochromatic red light treatment but also decreased the proportion of hydrophobic fractions in monochromatic blue light treatment, partially weakening the negative impacts of pure blue light on soil Cd activation. Moreover, DOM from the combined red, yellow, and blue lights resulted in a significantly stronger Cd extraction efficiency than the other light irradiation treatments, consequently enhancing the Cd phytoextraction efficiency of A. thaliana. The findings of this study demonstrated that a suitable light combination could enhance the phytoremediation effect of A. thaliana by activating soil Cd, and this method can be extrapolated to the real field, where light irradiation can be easily applied and modulated.

UV/Chlorine Process: An Efficient Advanced Oxidation Process with Multiple Radicals and Functions in Water Treatment.

Because of the deterioration of global water quality, the occurrence of chemical and microbial contaminants in water raises serious concerns for the health of the population. Identifying and developing effective and environmentally friendly water treatment technologies are critical to obtain clean water. Among the various technologies for the purification of water, ultraviolet photolysis of chlorine (UV/chlorine), an emerging advanced oxidation process (AOP), has multiple functions for the control of contaminants via the production of hydroxyl radicals (HO·) and reactive chlorine species (RCS), such as Cl·, ClO·, and Cl2·-.This Account centers around the radical chemistry of RCS and HO· in different water matrices and their roles and mechanisms in the abatement of contaminants. The concentrations of Cl·, ClO·, and Cl2·- are comparable to or higher than those of HO· (10-14 to 10-13 M). The reactivities of RCS are more selective than HO· with a broader range of second-order rate constants (k). The k values of Cl· toward most aromatics are higher or similar as compared to those of HO·, while those of Cl2·- and ClO· are less reactive but more selective toward aromatics containing electron-donating functional groups. Their major reaction mechanisms with Cl· are electron transfer and addition, while those with ClO· and Cl2·- primarily involve electron transfer. As for aliphatics, their reactivities with both HO· and RCS are much lower than those of aromatics. The reaction mechanisms for most of them with Cl· and Cl2·- are hydrogen abstraction, except for olefins, which are addition. In addition, RCS greatly contribute to the inactivation of microbial contaminants.Toward future application, the UV/chlorine process has both pros and cons. Compared with the traditional HO·-based AOP of UV/H2O2, UV/chlorine is more efficient and energy-saving for oxidation and disinfection, and its efficiency is less affected by water matrix components. However, the formation of toxic byproducts in UV/chlorine limits its application scenarios. In dissolved organic matter (DOM)-rich water, the formation of halogenated byproducts is enhanced in UV/chlorine. In the presence of ammonia, reactive nitrogen species (RNS) (e.g., ·NO and ·NO2) are involved, and highly toxic nitro(so) products such as nitro(so)-phenolics and N-nitrosodimethylamine are generated. For a niche application, the UV/chlorine process is recommended to be utilized in water with low levels of DOM and ammonia.Strategies should be developed to make full use of highly reactive species (RCS and HO·) for the abatement of target contaminants and to reduce the formation of toxic byproducts. For example, the UV/chlorine process can be used in tandem with other treatments to create multiple barriers for the production of safe water. In addition, halogen radicals are very important in ecosystems as well as other areas such as medical therapy and organic synthesis. UV/chlorine is the most efficient homogeneous system to generate halogen radicals, and thus it provides a perfect system to investigate the fates of halogen radicals for interdisciplinary research.

DOM Characteristics Analysis of Surface Sediment-overlying Water in Suzhou Landscape River Course

In order to understand the characteristics and interrelationship of dissolved organic matter (DOM) in interstitial water and overlying water of a landscape river in Suzhou, the characteristics of DOM in interstitial water and overlying water of landscape river sediments in the urban area of Suzhou from July to September after the 2020 flood season were analyzed using the UV-Vis absorption spectrum, high-performance liquid chromatography(HPLC), and fluorescence spectrum combined with the fluorescence region integration method. The results showed that the relative molecular weight of DOM in both the interstitial water and the overlying water was about 1000, and the relative molecular weight tended to increase in the same way over time. Both interstitial water and overlying water had the highest DOM of protein-like content, with a mass fraction that reached 68%-79%. By contrast, the content of humus-like substances was lower, with a mass fraction accounting for approximately 21%-32%, and both were dominated by low-excitation tryptophan. From July to September, a large increase in DOM levels appeared in the interstitial water, followed by a gradual increase in DOM levels in overlying water. These increases might have come from the deposition of algae on the river bottom after summer outbreaks, likely followed by cleavage and release into the interstitial and overlying water. The fluorescence indices (FI) of the interstitial water and overlying water differed more in July and then increased and decreased following the same trend; however, both were greater than 1.2. The authigenic indicator BIX indicator values were all greater than 0.8 and tended toward 1. The humification index (HIX) values were all less than 4; moreover, the interstitial water and overlying water became smaller in the same trend. The same positive correlation was present between the six fluorescent components of DOM (P<0.05), with a significant correlation between low-excitation tyrosine, α254, and HIX. The relationship between interstitial water and DOM in the overlying water in the Suzhou landscape river was closely related, and the interstitial water may be a potential source of DOM in overlying water.

Interference of dissolved organic matter and its constituents on the accurate determination of hydrogen peroxide in water

Hydrogen peroxide (H2O2) is ubiquitous in natural waters, and plays an important role in both biological and chemical processes. This study investigated the influence of dissolved organic matter (DOM) and its substituents on the accurate measurement of H2O2 by peroxidase-mediated depletion of scopoletin fluorescence method which is one of the most widely used methods for the determination of low concentration H2O2 in water. Six DOM and its 24 substituents interfered the determination of H2O2 at environmentally relevant concentration of 200 nM with different levels except 2,6-dimethoxy-1,4-benzoquinone and benzoic acid, which may be associated with origin and types of DOM, and numbers and position of active functional groups in DOM constituents. Each substance concentration and the corresponding decreasing ratio to the measured H2O2 concentration was fitted well to the linear model (R2 > 0.9), and the obtained interfering ratios (k, (mgC L−1)−1), expressing the degree of DOM or its substituents per unit concentration to the measurement of H2O2, were approximate for DOM, but the order of magnitude of k values of DOM constituents took on a large span from 10–3 to 10–7. When DOM levels exceed 0.1 mgC L−1 or its substituent concentration is at nM level (low to 20 nM), the H2O2 content will be underestimated substantially. A quantitative structure–activity relationship model with remarkable stability and strong predictability for the k of DOM substituents to H2O2 measurement was established, and the k was related to the electron transfer capacity, hydrophobicity and stability of these compounds.