Multiple roles of dissolved organic matter released from decomposing rice straw at different times in organic pollutant photodegradation

Spatiotemporal response of the optical characteristics of dissolved organic matter to seasonality and land use in tropical island rivers

Dissolved organic matter (DOM), a pivotal component in the global carbon cycle, plays a crucial role in maintaining the productivity and functionality of aquatic ecosystems. However, the driving factors of variations in the properties of riverine DOM in tropical islands still remain unclear. In this study, the spatiotemporal response of the optical characteristics of riverine DOM to seasonality and land use on Hainan Island in southern China was investigated. Our results revealed that DOM in the rivers of Hainan Island exhibited a relatively high proportion of fulvic acid and demonstrated strong terrestrial sources. The optical properties of DOM exhibited significant variations both seasonally and spatially. Land use exerted a dominant influence on riverine DOM. Specifically, during the wet season, riverine DOM exhibited larger molecular weight, increased chromophoric DOM (CDOM) abundance, and higher Fmax compared to the dry season. Furthermore, riverine DOM influenced by grassland and farmland showed higher CDOM abundance, Fmax, and humification degree in contrast to those impacted by forest and urban. Random forest and correlation analysis results indicated that grassland and farmland enhanced the Fmax of DOM by increasing levels of TP, NO3--N, Chl a, and NH4+-N in the dry season. However, during the wet season, the increased Fmax of DOM induced by grassland and farmland relied on the increments of Chl a and TP concentrations. This study improves our understanding of the spatiotemporal fluctuations of DOM in the rivers of Hainan Island, highlighting the effects of season and land use on DOM. It offers valuable support for improving water quality and contributes to enhancing human comprehension of the global carbon cycle.

Photochemical behavior of dissolved organic matter derived from Alternanthera philoxeroides hydrochar: Insights from molecular transformation and photochemically reactive intermediates

Hydrochar-derived dissolved organic matter (HDOM) enters aquatic ecosystems through soil leaching and surface runoff following the application of hydrochar. However, the photochemical behavior of HDOM remains unclear. The photo-transformation of HDOM was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), multiple spectroscopy methods, high-performance liquid chromatography, and combining synchronous fluorescence and Fourier-transform infrared spectroscopy with two-dimensional correlation spectroscopy. The results showed that with the increase of carbonization temperature, amide II in protein-like substances were observed to be preferentially photolyzed, and the protein-like substances were more sensitive to low irradiation time, while the duration time of the photochemical behavior of amide II and aliphatic C-H were more persistent. FT-ICR MS results showed that N and S-containing molecules, including lignins and lipids were more sensitive to ultraviolet irradiation. Furthermore, the photo-transformation of HDOMs was accompanied by the generation of triple excited state dissolved organic matter and singlet oxygen. Our findings will be beneficial for understanding the mechanisms of photo-transformation of HDOM and for predicting the possible behaviors of hydrochar produced at different temperatures before large-scale application.

Deciphering the bioavailability of dissolved organic matter in thermophilic compost and vermicompost at the molecular level

Studies on compost dissolved organic matter (DOM) previously focus on its composition and humification, without considering DOM bioavailability to understand compost fertility. To decipher the fertility basis of compost, DOM bioavailability in thermophilic compost (TC) and vermicompost (VC) was investigated and linked with its molecular composition. Results showed that DOM bioavailability of VC (36 % BDOC) was generally higher than that of TC (22 % BDOC) due to containing more tannin-like substances. Inversely, only lipid-/carbohydrate-/protein-like substances contributed to DOM bioavailability in TC. Moreover, these differences of bioavailability expanded with C/N decreased in composting materials. Specifically, the %BDOC of VC with N-rich materials (C/N < 25) was 2.1-3.0 times higher than that in TC, while it was only 1.2-1.4 times for C-rich materials (C/N < 25), because N-surplus facilitated the formation of O-/N-containing aromatics (e.g., CHON and tannin) in VC, but inhibited the decomposition of organic materials into small bioactive molecules in TC.

Effect of the molecular weight of DOM on the indirect photodegradation of fluoroquinolone antibiotics

Dissolved organic matter (DOM) is ubiquitous and widespread in natural water and influences the transformation and removal of antibiotics. Nevertheless, the influence of DOM molecular weight (MW) on the indirect photodegradation of antibiotics has rarely been reported. This study attempted to explore the influence of the molecular weight of DOM on the indirect photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and norfloxacin (NOR), by using UV-vis absorption and fluorescence spectroscopy. The results showed that indirect photodegradation was considered the main photodegradation pathway of FQs in DOM fractions. Triplet-state excited organic matter (3DOM*) and singlet oxygen (1O2) were the main reactive intermediates (RIs) that affected the indirect photodegradation of FQs. The indirect photodegradation rate of FQs was significantly promoted in DOM fractions, especially in the low molecular weight DOM fractions (L-MW DOM, MW < 10 kDa). The results of excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) showed that terrestrial humic-like substances had a higher humification degree and fluorophore content in L- MW DOM fractions, which could produce more 3DOM* and 1O2 to promote the indirect photodegradation of FQs. This study provided new insight into the effects of DOM at the molecular weight level on the indirect photodegradation of antibiotics in natural water.

DOM optical parameters as a tool to understand degradation of phenolic contaminants of emerging concern

Composition and source of dissolved organic matter (DOM) in water influence the rate of production of reactive intermediates (RIs), affecting the photodegradation of phenolic contaminants of emerging concern (PhCECs). However, this relationship has not been fully quantified. Here, for the first time, we propose a mechanism for photodegradation of a surrogate of PhCECs, p-cresol, in different DOM standard solutions under simulated sunlight irradiation. More importantly, the correlation of DOM optical parameters and p-cresol photodegradation kinetic parameters was determined by Pearson correlation. Results showed that indirect photodegradation was the only degradation pathway for p-cresol, mainly through reaction with excited triplet state of dissolved organic matter (3DOM*). Singlet oxygen (1O2) and hydroxyl radical (•OH) hindered degradation of p-cresol by decreasing the steady state concentration of 3DOM*. Moreover, less aromatic and smaller molecular size DOM showed higher steady-state concentration and quantum yield of 1O2, and 3DOM*, resulting in faster p-cresol photodegradation. Finally, 7 out of 8 optical parameters showed strong correlation with the p-cresol photodegradation rate constant. The mechanism and correlations found are a potential tool to predict PhCECs photodegradation in water using DOM optical parameters.

Aging rice straw reduces the bioavailability of mercury and methylmercury in paddy soil

Straw amendment is a prevalent agricultural practice worldwide, which can reduce air pollution and improve soil fertility. However, the impact of aging straw amendment on the bioavailability of mercury (Hg) and methylmercury (MeHg) in paddy soil remains unclear. To investigate this, incubation experiments were conducted using the diffusive gradient in thin-film technique. Results showed that amendments of dry-wet aging (DRS), photochemical aging (LRS), and freeze-thaw aging rice straw (FRS) reduced the bioavailable MeHg in paddy soil by 2.2-27.6%, 13.5-69.8%, and 23.5-86.1%, respectively, compared to fresh rice straw (RS) amendment. This result could be due to changes in soil properties such as soil pH and overlying water Fe and Mn as well as microbial abundance (including Clostridiaceae, Firmicutes, and Actinobacteriota). Simultaneously, The LRS and FRS amendments reduced bioavailable Hg in paddy soil by 20.0-40.8% and 17.1-48.6%, respectively, while DRS increased the bioavailable Hg by 15.8-120.0%. This could be attributed to changes in soil oxidation-reduction potential and overlying water SO42- content. Additionally, the results of sand culture experiments showed that the concentrations of Hg uptake by rice seedlings were 97.1-118.2%, 28.1-35.6%, and 198.0-217.1% higher in dissolved organic matter (DOM) derived from DRS, LRS, and FRS than RS, indicating that aging straw leached DOM may promote the Hg bioavailable when straw amendment. This result could be due to lower molecular weight and higher CO functional group content. These results provide new insight into how aging straw amendment affects the bioavailability of Hg and MeHg in paddy soil under different climates.

Insights into the mechanisms of natural organic matter on the photodegradation of indomethacin under natural sunlight and simulated light irradiation

Indomethacin (INDO) is an antipyretic and analgesic pharmaceutical that has been widely detected in the aquatic environment. Photodegradation is an essential pathway for removal of INDO in sunlit surface water, however the effect of dissolved organic matter (DOM) on its photodegradation and the ecotoxicity of photodegradation products are largely unknown. In this study, the effect of DOM on the photodegradation of INDO under both natural and simulated light irradiation was studied. The results showed that indirect photolysis is the main photodegradation pathway of INDO in presence of DOM where 3DOM* plays the most important promoting role. Compared to commercial DOM (SRNOM and SRFA), DOM extracted from local-lake water (SLDOM) promoted the photodegradation to the highest extent. Although the steady-state concentrations of 3DOM* of SRNOM and SRFA were higher than SLDOM, their inhibition effect surpassed SLDOM namely higher light screening effect and phenolic antioxidant concentrations. The photodegradation pathway in pure water is different from that in DOM system where the decarboxylation of acetic acid chain and the oxidative fracture of indole ring are the main degradation pathways. Density Functional Theory (DFT) calculation further supports the proposed degradation pathways of INDO. ECOSAR calculation showed that the toxicity of INDO photodegradation products to aquatic organisms may maintain or even exceed its parent compound. Therefore, comprehensive understanding of the impact of DOM on the photodegradation of INDO is of crucial significance for evaluating its ecological risk in the natural environment.

Photodegradation of clindamycin by the dissolved black carbon is simultaneously regulated by ROS generation and the binding effect

As an essential source of the natural dissolved organic matter (DOM), dissolved black carbon (DBC) plays a vital role in the photodegradation of organics; however, there is rare information about the DBC-induced photodegradation mechanism of clindamycin (CLM), one of the widely used antibiotics. Herein, we discovered DBC-generated reactive oxygen species (ROS) stimulated CLM photodegradation. Hydroxy radical (•OH) could directly attack CLM by OH-addition reaction, the singlet oxygen (¹O₂) and superoxide (O₂^•-) contributed to the CLM degradation by transforming to •OH. In addition, the binding between CLM and DBCs inhibited the photodegradation of CLM by decreasing the concentration of freely dissolved CLM. Binding process inhibited CLM photodegradation by 0.25-1.98% at pH 7.0 and 6.1-41.77% at pH 8.5. These findings suggest that the photodegradation of CLM by DBC is simultaneously regulated by the ROS production and binding effect between CLM and DBC, benefiting the exact evaluation of the environmental impact of DBCs.

Sources, distribution and decomposition of soil organic matter based on an effective biomarker in the pastoral areas of Zoige Plateau, China

The degradation of organic matter in soils plays an important role in the carbon cycle. Lignin is the main source of soil organics and it can be used to trace the source, distribution and turnover of organic matter. In this study the distribution and degradation of lignin were investigated to identify the source and degradation of soil organic matter during the succession of China's Zoige Plateau. Lignin monomers were determined by gas chromatography-mass spectrometry with alkaline CuO oxidation and the soils' δ¹³C and δ¹⁵N contents were interpreted to explore the turnover rate of lignin and organic matter. The main source of organics was identified as C3 non-woody angiosperm tissues. Lignin in the topsoil (0-30 cm) was derived from litter and roots, and it then migrated vertically to the deep soil (30-80 cm). Correlations of δ¹³C/δ¹⁵N with the soil's elemental composition showed that the organics degraded more quickly in meadow soil than in bog soil. The soil communities in the meadow and bog soils were generally similar, but there were certain differences in the dominant microbial phyla at different depths. The meadow soil's effectiveness as a carbon sink was gradually weakened, while that of the bog soil strengthened with depth. These results provide a scientific basis for accurately assessing the carbon sink capacity of the soils in Zoige Plateau.

Repurposing of spent lithium-ion battery separator as a green reductant for efficiently refining the cathode metals

Developing green and high-efficient pyrometallurgy processes to recycle precious metals from spent lithium-ion batteries (LIBs) is of great importance for resource sustainability and environmental protection. Herein, a novel reduction roasting approach relying on spent LIB separator to refine the spent cathode is proposed. The efficiency of repurposing separator as a reductant for roasting the spent LiCoO₂ cathode and the underlying mechanisms were investigated. After the separator-mediated roasting at 500 °C for 2 h, Li⁺ leaching efficiency of the cathode reached 93.2 %, >2.6 times higher than those after roasting without reductant (25.2 %) or with benchmark reductant graphite (26.1 %). Under the separator-added roasting condition, the cathode was converted to the desired products, CoO and Li₂CO₃. Based on the analysis of in-situ reaction using thermogravimetric/differential scanning calorimetry and pyrolysis gas species identification, the separator-mediated reduction roasting of cathode was composed of two stages, i.e., reducing gas generation due to separator pyrolysis, followed by the reducing gas mediated LiCoO₂ reduction. During the process, the generated C₂H₄ and CO dominated the reduction. The use of co-existing separator to recover precious metals from spent LIBs is an effective and sustainable strategy to maximize the utilization of spent LIBs.

Molecular mechanisms of Chromium(III) sorption by organo-ferrihydrite coprecipitates induced by crop straws

Agricultural organo-ferrihydrite (Fh) coprecipitates (OFCs), resulting from the coprecipitation of Fe(III) and dissolved organic carbon (DOC) from returned straws, significantly affect the bioavailability of heavy metals in farmland. However, the molecular sorption mechanisms of Cr(III) by the OFCs remain unclear. Here, we explored the sorption behaviors of Cr(III) by the OFCs formed with wheat or maize straws derived-DOC (wheat-DOC or maize-DOC) under various environmental conditions, and further underlying molecular sorption mechanisms using Cr K-edge X-ray absorption near edge structure (XANES) spectroscopy. Results showed that high C loadings reduced the specific surface areas (SSAs) and Cr(III) sorption capacities of the OFCs, implying the blockage of binding sites by C loading. Additionally, although the wheat-DOC induced OFC had a smaller SSA than the maize-DOC induced OFC, their Cr(III) sorption were comparable, which was likely to be compensated by the more carboxyl in the wheat-DOC. Moreover, at a higher ionic strength, the increased or slightly decreased Cr(III) sorption indicated that the inner-sphere sorption was dominant regardless of high or low C loadings, which was also supported by the extremely low Cr(III) extraction percentage. The Cr K-edge XANES spectroscopy suggested that Cr(III) could be immobilized by both the Fh and organic fractions, with the Fh fractions playing a significant role. These findings contribute to a molecular-level mechanistic understanding of Cr(III) sorption by the OFC, which will aid in the prevention and control of Cr-contaminated agricultural soils.

Roles of microplastic-derived dissolved organic matter on the photodegradation of organic micropollutants

Microplastic-derived dissolved organic matter (MP-DOM) is ubiquitous in water environment and exhibits photosensitivity. However, little is known about the effects of MP-DOM on the photodegradation of organic micropollutants in natural water. In this study, we investigated the effect of MP-DOM derived from two typical plastics, i.e., polystyrene (PS), and polyethylene (PE), on the photodegradation of a typical organic micropollutants sulfamethoxazole (SMX) in a simulative natural water system. MP-DOM exerted a significant inhibition on the SMX photodegradation, mainly attributed to the direct photolysis inhibition of SMX caused by the inner filter effect and the complexation effect. Despite the enhanced reactive oxygen species (ROS) generation with the increase of their steady-state concentration by 41.1 - 160.7 %, PS-DOM exhibited high oxidation resistance, causing an inhibition on the photodegradation of SMX probably through transferring electrons to the SMX intermediates. This study helps to deepen the understanding of microplastic photochemical behavior in natural water.

Roles of humic substances redox activity on environmental remediation

Humic substances (HS) as representative natural organic matters and the most common organic compounds existing in the environment, has been applied to the treatment and remediation of environmental pollution. This review systematically introduces and summarizes the redox activity of HS for the remediation of environmental pollutants. For inorganic pollutants (such as silver, chromium, mercury, and arsenic), the redox reaction of HS can reduce their toxicity and mobilization, thereby reducing the harm of these pollutants to the environment. The concentration and chemical composition of HS, environmental pH, ionic strength, and competing components affect the degree and rate of redox reactions between inorganic pollutants and HS significantly. With regards to organic pollutants, HS has photocatalytic activity and produces a large number of reactive oxygen species (ROS) under the light which reacts with organic pollutants to accelerate the degradation of organic pollutants. Under the affection of HS, the redox of Fe(III) and Fe(II) can enhance the efficiency of Fenton-like reaction to degrade organic pollutants. Finally, the research direction of HS redox remediation of environmental pollution is prospected.

Fate and transport of pharmaceuticals in water systems: A processes review

Pharmaceuticals are globally consumed by humans and animals to support daily health and to treat disease. Following consumption, they may reach the aquatic environment either directly through the discharge of untreated wastewater to water bodies, or indirectly via treated wastewater as a result of their incomplete removal from wastewater treatment plants. This paper reviews the processes that control the occurrence and fate of pharmaceuticals in water systems, including sorption, photodegradation, hydrolysis and biodegradation. The degree to which these four processes occur is influenced by pharmaceutical types and their chemical structure as well as environmental factors such as sunlight, water depth, organic matter content, water chemistry, sediment properties, and type and abundance of microorganisms. Depending on the complex interactions of these factors, pharmaceutical compounds may be mineralized, partially degraded, or remain intact because they are resistant to degradation. Kinetic rate parameters and the half-life of a variety of pharmaceutical products are provided herein for the above processes under different environmental conditions. Usually, photodegradation and biodegradation represent dominant reaction processes, while hydrolysis only affects some pharmaceuticals, particularly antibiotics. The identified sorption and reaction rate parameters can be incorporated into a concise modeling framework to assess and predict longitudinal concentration profiles of pharmaceutical products in the manmade and natural systems, particularly when large amounts of pharmaceuticals are discharged during abnormal events such as a virus outbreak. Finally, future research is suggested, including the fate of transformed products (intermediates) in water systems.

Straw return in paddy field alters photodegradation of organic contaminants by changing the quantity rather than the quality of water-soluble soil organic matter

Straw return, an important agricultural management practice, is worldwide adopted to enhance soil carbon sequestration and soil fertility. Although water-soluble soil organic matter (WSOM) in paddy field is known to affect the photodegradation of organic contaminants, how straw return regulates the photosensitization of WSOM by changing its properties remain unclear. Here, we determined the temporal variations in the content, chemical characteristics, and photosensitizing ability of WSOM after wheat straw return in a wheat-rice rotation system using optical spectroscopy and steady-state photodegradation tests. After straw return, the WSOM content first increased to a maximum and then gradually decreased to pre-return level at day 90. Nevertheless, the relative abundance of humic-like components in WSOM was not shifted by straw return, and protein-like component in WSOM just showed a slight decrease at day 45. All the WSOM samples inhibited sulfamethoxazole (SMX) photodegradation by light filtering, reactive species quenching and other mechanisms, while promoted diuron (DIU) degradation via reacting with •OH, ¹O₂ and excited triplet WSOM. The photodegradation of SMX and DIU was little affected by straw return changing WSOM composition and photochemical activity. However, straw return could decelerate SMX and DIU photodegradation by elevating WSOM content in a relatively short-term. This study emphasizes that straw return may reduce the photodegradation of organic contaminants by increasing WSOM concentration instead of altering WSOM chemical characteristics.

Organophosphate pesticides sequestered in tissues of a seagrass species - Zostera capensis from a polluted watershed

Organophosphate pesticides (OPPs) are persistent in the environment, but little information is available on their bioaccumulation in seagrass. In this study, the seagrass - Zostera capensis was collected from Swartkops Estuary in South Africa to investigate the bioaccumulation of OPPs from contaminated sediments and the water column. This plant was chosen because it grows abundantly in the estuary's intertidal zone, making it a viable phytoremediator in the urban environment. Extraction was performed by the QuEChERS method followed by GC-MS analysis. The mean concentration of ∑OPPs ranged from 0.01 to 0.03 μg/L for surface water; 6.20-13.35 μg/kg dw for deep-rooted sediments; 18.79-37.75 μg/kg dw for leaf tissues and 12.14-39.80 μg/kg dw for root tissues of Z. capensis. The biota-sediment accumulation factors (BSAFs) were greater than one, indicating the potential for Z. capensis to bioaccumulate and intercept the targeted pesticides. A weak insignificant correlation observed between log BSAFs and log Kow indicates that the bioaccumulation of OPPs in tissues of Z. capensis were not dependent on the Kow. Eight of the selected pesticides had root-leaf translocation factors (TFr-l) greater than 1, indicating that Z. capensis can transport these chemicals from roots to leaves. The results from this study implies that this plant species can clean up OPP contamination in the environment.

Assessing the potential to use CDOM as an indicator of water quality for the sediment-laden Yellow river, China

Chromophoric dissolved organic matter (CDOM) in rivers is mainly affected by natural conditions and human activities and can reflect the watershed pollution status to a certain extent. The Yellow River is one of the largest contributors to the global riverine sediment flux from the land to ocean, and there is a paucity of information on how the optical properties of CDOM have the potential to serve as an indicator of water quality for the sediment-laden Yellow River. In this study, a three-dimensional fluorescence parallel factor (PARAFAC) analysis method was applied to investigate the seasonal and spatial variations in CDOM fluorescence components and spectral characteristics from the source region to the estuary in the mainstream of Yellow River. The relationships of CDOM with water quality indicators and trophic state were also analyzed. Six PARAFAC components (C1-C6) were identified and grouped into two categories: humic-like components (C1-C4), which accounted for 85.8 %, and protein-like components (C5 and C6), which accounted for only 14.2 %. The CDOM components, spectral parameters, and their clear correlations with the main ions (Na⁺ and Cl^-) all indicated that the humic-like components may be primarily derived from nonpoint source erosion, and the protein-like components were mainly derived from point source discharges in the watershed. The combination of the CDOM absorption coefficient at 254 nm (a(254)), spectral slope ratio (S_R), specific UV absorbance SUVA_254, and fluorescence index (FI) had a good predictive ability for the key water quality indicators (total nitrogen (TN), dissolved total nitrogen (DTN), total phosphorus (TP), dissolved total phosphorus (DTP), and chlorophyll a (Chl a)) and trophic state index (TSI). Therefore, some fluorophores and UV spectral parameters of CDOM in the Yellow River can be used for rapid water quality monitoring and pollution source indication, especially pollutants related to nitrogen and phosphorus nutrients in the basin.

Effects of natural colloidal particles derived from a shallow lake on the photodegradation of ofloxacin and ciprofloxacin

Natural colloidal particles (NCPs), which are ubiquitous and abundant in surface waters, may play a crucial role in the sunlight-driven transformation of organic contaminants. This research focused on the effects of NCPs on the photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and ciprofloxacin (CIP), and assessed the photosensitivity of colloidal organic matter (COM). Results showed that the photodegradation rate constants (k_obs) of OFL and CIP in NCP solutions ranged from 9.28 × 10^-2 h^-1 to 15.98 × 10^-2 h^-1 and 63.88 × 10^-2 h^-1 to 196.59 × 10^-2 h^-1, respectively, and NCPs can significantly accelerate the photodegradation rate of OFL and CIP. Indirect photodegradation (IP) accounted for >50% of the overall observed degradation in most treatments and was the dominant degradation pathway for the two FQs, especially for CIP, for which IP reached 82%-94%. In the IP process, the contributions of triplet states of colloidal organic matter (³COM^⁎) to the photolysis of OFL and CIP were close to 42% and 46%, respectively. The compositions of COM played an important role in the IP of the FQs, among which terrestrial sources of COM tended to have higher photoreactivity than biological sources. This study is essential in predicting the photochemical effect of FQs and also allows for a better understanding of the real environmental fate of antibiotic contaminants.

Spectroscopic fingerprinting of dissolved organic matter in a constructed wetland-reservoir ecosystem for source water improvement-a case study in Yanlong project, eastern China

The coupling between constructed wetlands and reservoir (CWs-R) afforded a novel ecosystem to improve the water quality and increase the emergency storage capacity of micro-polluted river drinking water source. In this study, spectroscopic characteristics of DOM in YL CWs-R ecosystem were first systematic studied based on a three-year field monitoring to investigate the chemical composition, sources and track the involved biogeochemical processes in the ecosystem. Three humic-like components (C1, C2, and C4, em >380 nm) and one protein-like component (C3, em < 380 nm) were identified by PARAFAC model. Significant spatiotemporal variations in concentration and composition of FDOM were observed in YL CWs-R ecosystem. The improved water transparency (SD) and, the increased hydraulic retention time (HRT) along YL CWs-R ecosystem enhance photochemical processes, leading to significant decreases in the intensities of humic-like components in effluent (P < 0.05) with lower degrees of aromaticity, molecular weights, and humification (decrease in HIX and increases in S_R and BIX). In contrast, no significant spatial difference was observed for protein-like component (P > 0.05), which implies that the biodegradation and production of protein-like component may balance each other in the CWs-R ecosystem. The ecological pond unit plays a major role in the removal and transformation of DOM, especially in summer, while wetland purification unit contributes little to DOM reduction. In addition, the decay of aquatic macrophytes in wetland purification unit and the risk of algal bloom in the ecological pond unit might become important autochthonous sources of DOM, especially in summer and autumn. These findings are critical for further understanding the transformation processes of DOM in large-scale CWs-R ecosystems, and could provide important implications to improve sustainable safety of drinking water sources.

Release Mechanism, Secondary Pollutants and Denitrification Performance Comparison of Six Kinds of Agricultural Wastes as Solid Carbon Sources for Nitrate Removal

Agricultural wastes used as denitrification carbon sources have some drawbacks such as excessive organic carbon release and unclear release characteristics of nitrogen, phosphorus, and chromatic substances, which can cause adverse effects on the effluent quality during the denitrification process. The composition and surface characteristics, carbon release mechanisms, and secondary pollutant release properties of six kinds of agricultural wastes, i.e., rice straw (RS), wheat straw (WS), corn stalk (CS), corncob (CC), soybean stalk (SS), and soybean hull (SH) were studied and analyzed in this research. The denitrification performance of these agricultural wastes was also investigated extensively by batch experiments. The results showed that the carbon release basically followed the second-order reaction kinetic equation and Ritger-Peppas equation in the 120 h reaction, and it was mainly controlled by the diffusion process. The kinetic equation fitting results and bioavailability test suggested that the potential risk of excessive effluent COD of CC was the lowest due to the appropriate amount and degradability of its released carbon. The NH₄⁺-N, TN, and TP in the leachate of RS were higher than those of the other five agriculture wastes, and the chroma in the leachate of WS and CS was heavier than that of the others. CC released the lowest pollutants, which resulted in slight fluctuations of effluent quality in the start-up period (1-11 d), and it had the best nitrogen removal capacity in the denitrification experiment. The average NO₃^--N removal of CC was 5.12 mg for each batch in the stable period (11-27 d), which was higher than that of others, and less NO₂^--N, NH₄⁺-N, and COD were accumulated in the CC effluent during the whole denitrification process.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

This assessment by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) provides the latest scientific update since our most recent comprehensive assessment (Photochemical and Photobiological Sciences, 2019, 18, 595-828). The interactive effects between the stratospheric ozone layer, solar ultraviolet (UV) radiation, and climate change are presented within the framework of the Montreal Protocol and the United Nations Sustainable Development Goals. We address how these global environmental changes affect the atmosphere and air quality; human health; terrestrial and aquatic ecosystems; biogeochemical cycles; and materials used in outdoor construction, solar energy technologies, and fabrics. In many cases, there is a growing influence from changes in seasonality and extreme events due to climate change. Additionally, we assess the transmission and environmental effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the COVID-19 pandemic, in the context of linkages with solar UV radiation and the Montreal Protocol.