Tracing sulfate sources and transformations of surface water using multiple isotopes in a mining-rural-urban agglomeration area.

Rapid urbanization and mining activities are exacerbating sulfate (SO42-) pollution in surface water, and the information on its sources and transformations is crucial for understanding the sulphur cycle in mining areas. In this study, the SO42- in the surface water of Huaibei mining area were monitored and the main sources of pollution and biogeochemical processes were identified using stable isotopes (δD, δ18O-H2O, δ34S-SO42- and δ18O-SO42-) and water chemistry. The results demonstrated the SO42- content in the Huihe River and Linhuan subsidence water area (SWA) is higher than that in other rivers and SWAs, which exceeded the environmental quality standard of surface water. The SO42- content of different rivers and SWAs showed seasonal differences, and the dry season was higher than the wet season. In addition, the SO42- in Tuohe River and Suihe River is primarily caused by urban sewage and agriculture activities, while in Zhonghu and Shuoxihu SWA is mainly contributed by natural evaporate dissolution. Notably, the input of SO42- in the Huihe River and Linhuan SWA caused by mining activities cannot be disregarded. The aerobic environment and isotopic fractionation of surface water indicate that sulfide oxidation is not the major cause of SO42- formation. This work has revealed the multiple sources and transformation mechanisms of SO42-, and provided a reference for the development of comprehensive management and effective remediation strategies of SO42- contamination in surface water around mining areas.

Freshwater water quality criteria for phthalate esters and recommendations for the revision of the water quality standards.

With increasing urbanization and rapid industrialization, more and more environmental problems have arisen. Phthalates (PAEs) are the foremost and most widespread plasticizers and are readily emitted from these manufactured products into the environment. PAEs act as endocrine-disrupting chemicals (EDCs) and can have serious impacts on aquatic organisms as well as human health. In this study, the water quality criteria (WQC) of five PAEs (dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP)) for freshwater aquatic organisms were developed using a species sensitivity distribution (SSD) and a toxicity percentage ranking (TPR) approach. The results showed that long-term water quality criteria (LWQC) of PAEs using the SSD method could be 13.7, 11.1, 2.8, 7.8, and 0.53 µg/L, respectively. Criteria continuous concentrations (CCC) of PAEs were derived using the TPR method and determined to be 28.4, 13.1, 1.3, 2.5, and 1.6 µg/L, respectively. The five PAEs are commonly measured in China surface waters at concentrations between ng/L and µg/L. DBP, DEHP, and di-n-octyl phthalate (DnOP) were the most frequently detected PAEs, with occurrence rates ranging from 67% to 100%. The ecological risk assessment results of PAEs showed a decreasing order of risk at the national level, DEHP, DBP, DMP, DEP, DnOP. The results of this study will be of great benefit to China and other countries in revising water quality standards for the conservation of aquatic species.

Unique Tubular BiOBr/g-C3 N4 Heterojunction with Efficient Separation of Charge Carriers for Photocatalytic Nitrogen Fixation.

The industrial ammonia synthesis process consumes a lot of energy and causes serious environmental pollution. As a sustainable approach for ammonia synthesis, photocatalytic nitrogen reduction employing water as the reducing agent has a lot of potential. A simple surfactant-assisted solvothermal method is used to synthesize g-C3 N4 nanotubes with flower-like spherical BiOBr grown inside and outside (BiOBr/g-C3 N4 , BC). The hollow tubular structure realizes the full use of visible light by the multi-scattering effect of light. Large surface areas and more active sites for N2 adsorption and activation are present in the distinctive spatially dispersed hierarchical structures. Particularly, the quick separation and transfer of electrons and holes are facilitated by the sandwich tubular heterojunctions and tight contact interface of BiOBr and g-C3 N4 . The maximal NH3 generation rate of the BiOBr/g-C3 N4 composite catalysts can reach 255.04 µmol⋅ g-1 ⋅ h-1 , and it is 13.9 and 5.8 times that of pure BiOBr and g-C3 N4 . This work provides a novel method for designing and constructing unique heterojunctions for efficient photocatalytic nitrogen fixation.

Preparation of NH4Cl-Modified Carbon Materials via High-Temperature Calcination and Their Application in the Negative Electrode of Lead-Carbon Batteries.

The performance of lead-acid batteries could be significantly increased by incorporating carbon materials into the negative electrodes. In this study, a modified carbon material developed via a simple high-temperature calcination method was employed as a negative electrode additive, and we have named it as follows: N-doped chitosan-derived carbon (NCC). The performance of this material was compared with a control battery containing activated carbon (AC). X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy were engaged in analyzing the crystal structure and morphology of the material. Afterwards, the electrochemical and battery performance was examined through cyclic voltammetry (CV), linear voltammetry (LSV) and constant current charge-discharge testing. Markedly, the electrode plate containing 1 wt.% NCC indicates the highest specific capacity (106.48 F g-1) as compared to the control battery, which is 1.56 times higher than the AC electrode plate and 4.75 times higher than the blank electrode plate. The linear voltammetry shows that the hydrogen precipitation current density of the 1 wt.% NCC electrode plate is only -0.028 A cm-2, a much higher value than that of the AC electrode plate. In addition, the simulated battery containing 1 wt.% NCC has a cycle life of 4324 cycles, which is 2.36 times longer than that of the same amount of additive AC battery (1834 cycles) and 5.34 times longer than that of the blank battery (809 cycles). In summary, NCC carbon has the advantage of extending the life of lead-acid batteries, rendering it a promising candidate for lead-acid battery additives.

Occurrence and source analysis of heavy metals and dissolved organic matter in Nanyi Lake, Anhui Province.

Nanyi Lake is a tributary in the lower reaches of the Yangtze River and the largest freshwater lake in southern Anhui. Anthropogenic activities have significantly affected the lake with the rapid development of the surrounding economy in recent years. This study collected a total of 39 × 2 water samples of surface water and overlying water, detected the heavy metal concentrations (As, Cr, Cu, Mn, Ni, Pb, Sb, Zn, Fe, Cd), and analyzed the spectral characteristics of the dissolved organic matter (DOM). The results demonstrated that the concentrations of heavy metals (As, Cr, Cu, Mn, Ni, Pb, Sb, Zn, Fe, Cd) in the surface water were 1.00-7.78, 0.40-5.59, 0.20-4.52, 20.00-269.50, 0.40-5.56, 0.20-5.06, 1.00-7.64, 20.00-252.50, 60.00-590.00, and 0.04-0.60, respectively (unit: µg L-1). The risk assessment showed that the carcinogenic risks of heavy metals (As, Cr, Cd) through drinking water were ranged from 10-7 to 10-4a-1 in Nanyi Lake, and Cr was the main carcinogen which should be the focus of environmental health risk management. The average personal non-carcinogenic risks of heavy metals (Cu, Mn, Ni, Pb, Sb, Zn, Fe) were ranged from 10-9 to 10-13a-1, and considered to be acceptable risk level. The contour map of spatial distribution demonstrated different degrees of heavy metals (except Zn) enrichment near the Langchuan River in the East Lake District. Parallel factor analysis showed that the main components of DOM in Nanyi Lake were tryptophan like, fulvic acid like, and tyrosine like, and the dissolved organic matter was primarily derived from autogenous endogenous sources. The heavy metals Cr, Ni, Pb, Fe, Cd, and HIX in the surface water of West Lake were significantly positively correlated, among which Ni, Fe and C2 were significantly negatively correlated (P < 0.05), Mn and BIX demonstrated extremely significant positive correlations (P < 0.01), while no significant correlation was observed between heavy metals and the DOM indexes in the surface water of the East Lake. The principal component and correlation analysis showed that the heavy metals in Nanyi Lake were primarily derived from the production wastewater discharged by the surrounding industrial and mining enterprises through the rivers input, followed by the non-point source runoff input of the surrounding agricultural production and lake aquaculture.

Distribution, Source Apportionment and Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Surface Sediments at the Basin Scale: A Case Study in Taihu Basin, China.

As a systematic research at basin scale, this study investigated the spatial distribution, source apportionment and ecological risks of eighteen polycyclic aromatic hydrocarbons (PAHs) in surface sediments at different functional regions (rivers, lakes and reservoirs) from Taihu basin. Results showed that the mean values of 18 PAHs (defined as ∑18PAHs) in river sediments (1277 ng/g) was much higher than those observed in lake sediments (243 ng/g) and reservoir sediments (134 ng/g). The accumulation of PAHs in river sediments was largely impacted by the local social-economic development and energy consumption. The positive matrix factorization (PMF) and isomer ratios analysis of PAHs suggest that relative contributions to PAHs in sediments were 15% for gasoline and heavy oil combustion, 9% for oil spills, 30% for coal combustion, 23% for traffic source, and 23% for diagenetic source. Ecological risk assessment based upon risk quotient (RQ) method indicated that sediments at Taihu basin have suffered moderate risk of PAHs.

A novel sensitive ACNTs-MoO2 SERS substrate boosted by synergistic enhancement effect.

Integrating chemical enhancement (CM) and electromagnetic enhancement (EM) into one substrate is of great significance, but as far as we know, little research has been done on this project. In this paper, the novel bead chain like acidified carbon nanotubes-MoO2 (ACNTs-M) were designed by a simple two-step hydrothermal synthesis method. Benefitting from a good adsorption capacity, chemical enhancement and surface electromagnetic field enhancement effect, ACNTs-M exhibits a stunning SERS performance. The maximum enhancement factor (EF) of 5.13 × 107 is obtained with R6G molecules on ACNTs-M. The limit of detection (LOD) of R6G is 10-10 M. In addition, ACNTs-M also exhibits SERS sensitivity of other organic dyes (CV, RhB and MB). The results of Raman signal enhancement mechanism research verified that the synergy of CM and EM is the reason for the high SERS sensitivity of ACNTs-M. We believe that our work may bring cutting edge of development of stable and highly sensitive nonmetal SERS substrates.

Derivation of water quality criteria of zinc to protect aquatic life in Taihu Lake and the associated risk assessment.

Zinc is a widely distributed environmental pollutants and has been listed as priority heavy metal pollutant in China. Similar as other heavy metals, toxicity of zinc to aquatic organisms affects by environmental factors such as water hardness. It is necessary to develop regional water quality criteria (WQC) to protect native aquatic life against zinc due to the diversity of aquatic organisms' variability across different water systems, as a concretization and supplement for national zinc WQC. This study derived WQC for zinc by species sensitivity distribution (SSD) curve method. The zinc toxicity data of the aquatic organisms in Taihu Lake used in SSD curve was collected based on published toxicity data for zinc with hardness values and supplemented with acute toxicity tests conducted in this study. Six aquatic organism natives to Taihu Lake were selected to conduct zinc acute toxicity test in a range of hardness conditions. The relationship between water hardness and zinc toxicity was constructed. The criterion maximum concentration (CMC) and criterion continuous concentration (CCC) for zinc in Taihu Lake were then derived, which considered the water quality and taxonomic groups in Taihu Lake. The CMC and CCC were 100.69 µg/L and 30.79 µg/L, respectively. The environmental risk of zinc to Taihu Lake are acceptable, at moderate to low levels. This study has provided a basis for regional water quality criterion derivation and risk assessment in China.

Controlled manipulation of TiO2 nanoclusters inside mesochannels of core-shell silica particles as stationary phase for HPLC separation.

Based on a detailed study of the hydrolysis process of tetrabutyl orthotitanate (TBOT), TiO2 nanoclusters were modified inside the pores of SiO2 core-shell particles instead of the outside. The pore size distribution of SiO2 core-shell spheres modified with TiO2 (SiO2@dSiO2@TiO2) was analyzed by Barrett-Joyner-Halenda (BJH) method and density functional theory (DFT) method, respectively. The results of the DFT calculations demonstrate that the TiO2 nanoclusters are always first formed in bulk solution and then enter the pores. By regulating the rate of hydrolysis of TBOT, almost all of the TiO2 nanoclusters are modified into the pores and the structure of the original SiO2 core-shell sphere is hardly affected. The morphology of the particles was characterized by scanning electron microscopy and transmission electron microscopy. The crystal phase of TiO2 was measured by XRD. SiO2@dSiO2@TiO2 spheres functionalized with C18 were packed into a stainless steel column. The chemical stability of SiO2@dSiO2@TiO2 spheres under alkaline was tested by flushing of a mobile phase at pH 13 for 7 days. The efficiency of the column after the alkali solution treatment still reaches 98,430 plates m-1, which is only about 1.6% lower than that before the alkali solution treatment. A series of basic and acidic analytes were also separated on the column. Graphical abstract TiO2 nanocrystals were coated into the pore of core-shell silica spheres. The prepared particles were packed into the column and separation performance up to 98,430 plates per meter was achieved.

Plasmonic MoO2 nanospheres assembled on graphene oxide for highly sensitive SERS detection of organic pollutants.

The molybdenum oxide and graphene oxide (MoO2/GO) nanocomposite has been fabricated via simple hydrothermal assisted synthesis using Mo and MoO3 as precursors. The MoO2 nanospheres with porous hollow structure are assembled onto GO nanosheets. Profiting from the plasmonic effects of MoO2 and synergistic effect of MoO2 and GO, this hybrid nanomaterial exhibits significantly enhanced surface enhanced Raman scattering (SERS) activity for organic pollutants. The detection limit for rhodamine 6G (R6G) is 1.0 × 10-9 M, and the maximum enhancement factor (EF) reaches up to 1.05 × 107, which is the best among the semiconductor-based SERS materials. For practical application, the MoO2/GO SERS substrates are also applied to detect Methylene blue (MB) in river water, and the detection limit (1.0 × 10-8 M) can be acquired. Pyrene is also chosen as probe molecule, and quantitative determination is achieved with detection limit of 1.0 × 10-7 M. These demonstrate the well feasibility for multi-molecule detection. Furthermore, the nanocomposite displays high stability, reproducible stability, and acid and alkali resistance. Graphical abstract.

Occurrence of phosphorus, iron, aluminum, silica, and calcium in a eutrophic lake during algae bloom sedimentation.

Phosphorus (P) in a water body is mainly controlled by the interaction between surface sediment and the overlying water column after the complete control of external pollution. Significant enhancement of P in a water body would cause eutrophication of lakes. Thus, a better understanding is needed of the occurrences of P between the sediment and water column in eutrophic lakes. Here, we measured total phosphorus (TP) and major elements (Fe, Al, Ca, Mn, Si) in the water column, and total nitrogen, organic matter, TP and major oxides (Fe2O3, Al2O3, CaO, SiO2) in surface sediment of Chaohu Lake, a continuously eutrophic lake. The results showed that the rank of TP levels was western lake > eastern lake > southern lake. There were significantly positive correlations between TP (including water TP and sedimentary TP) and Fe, Al, Mn, while the correlation coefficients between water TP and sedimentary TP were -0.43, -0.41 and 0.18 for the western, eastern and southern lake respectively. The negative and significant correlations of water TP and sedimentary TP may indicate that the risk of sedimentary P release was great in the western and eastern lake during algae bloom sedimentation, while the southern lake showed weak P exchange between the sediment and water column.

Removal of phosphate from eutrophic lakes through adsorption by in situ formation of magnesium hydroxide from diatomite.

Since in situ formation of Mg(OH)2 can efficiently sorb phosphate (PO4) from low concentrations in the environment, a novel dispersed magnesium oxide nanoflake-modified diatomite adsorbent (MOD) was developed for use in restoration of eutrophic lakes by removal of excess PO4. Various adsorption conditions, such as pH, temperature and contact time were investigated. Overall, sorption capacities increased with increasing temperature and contact time, and decreased with increasing pH. Adsorption of PO4 was well described by both the Langmuir isotherm and pseudo second-order models. Theoretical maximum sorption capacity of MOD for PO4 was 44.44-52.08 mg/g at experimental conditions. Characterization of PO4 adsorbed to MOD by use of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and solid state (31)P nuclear magnetic resonance revealed that electrostatic attraction, surface complexation and chemical conversion in situ were the major forces in adsorption of PO4. Mg(OH)2 formed in situ had a net positive charge on the surface of the MOD that could adsorb PO4(3-) and HPO4(2-) anion to form surface complex and gradually convert to Mg3(PO4)2 and MgHPO4. Efficiency of removal of PO4 was 90% when 300 mg MOD/L was added to eutrophic lake water. Results presented here demonstrated the potential use of the MOD for restoration of eutrophic lakes by removal of excess PO4.

Identification of nitrate accumulation mechanism of surface water in a mining-rural-urban agglomeration area based on multiple isotopic evidence.

The accumulation of nitrate (NO3-) in surface waters resulting from mining activities and rapid urbanization has raised widespread concerns. Therefore, it is crucial to develop a nitrate transformation information system to elucidate the nitrogen cycle and ensure sustainable water quality management. In this study, we focused on the main river and subsidence area of the Huaibei mining region to monitor the temporal and spatial variations in the NO3- content. Multiple isotopes (δD, δ18O-H2O, δ15N-NO3-, δ18O-NO3-, and δ15N-NH4+) along with water chemistry indicators were employed to identify the key mechanisms responsible for nitrate accumulation (e.g., nitrification and denitrification). The NO3- concentrations in surface water ranged from 0.28 to 7.50 mg/L, with NO3- being the predominant form of nitrogen pollution. Moreover, the average NO3- levels were higher during the dry season than during the wet season. Nitrification was identified as the primary process driving NO3- accumulation in rivers and subsidence areas, which was further supported by the linear relationship between δ15N-NO3- and δ15N-NH4+. The redox conditions and the relationship between δ15N-NO3- and δ18O-NO3-, and lower isotope enrichment factor of denitrification indicated that denitrification was weakened. Phytoplankton preferentially utilized available NH4+ sources while inhibiting NO3- assimilation because of their abundance. These findings provide direct evidence regarding the mechanism underlying nitrate accumulation in mining areas, while aiding in formulating improved measures for effectively managing water environments to prevent further deterioration.

Source-specific probabilistic health risk assessment of heavy metals in surface water of the Yangtze River Basin.

The detrimental effects of heavy metal accumulation on both ecosystems and public health have raised widespread concern. Source-specific risk assessment is crucial for developing effective strategies to prevent and control heavy metal contamination in surface water. This study aims to investigate the contamination characteristics of heavy metals in the Yangtze River Basin, identifying the pollution sources, assessing the risk levels, and further evaluating the health risks to humans. The results indicated that the average concentrations of heavy metals were ranked as follows: zinc (Zn) > arsenic (As) > copper (Cu) > chromium (Cr) > cadmium (Cd) > nickel (Ni) > lead (Pb), with average concentrations of 38.02 µg/L, 4.34 µg/L, 2.53 µg/L, 2.10 µg/L, 1.17 µg/L, 0.84 µg/L, and 0.32 µg/L, respectively, all below the WHO 2017 standards for safe drinking water. The distribution trend indicates higher concentrations in the upper and lower reaches and lower concentrations in the mid-reaches of the river. By integrating the Absolute Principal Component Scores-Multiple Linear Regression (APCS-MLR) receptor model and Positive Matrix Factorization (PMF) model, the main sources of heavy metals were identified as industrial activities (APCS-MLR: 41.3 %; PMF: 42.1 %), agricultural activities (APCS-MLR: 30.1 %; PMF: 27.4 %), and unknown mix sources (APCS-MLR: 29.1 %; PMF: 30.4 %). The calculation of the hazard index (HI) for both children and adults was <1, indicating no non-carcinogenic or carcinogenic risks. Based on the source-specific risk assessment, agricultural activities contribute the most to non-carcinogenic risks, while industrial activities pose the greatest contribution to carcinogenic risks. This study offers a reference for monitoring heavy metals and controlling health risks to residents, and provides crucial evidence for the utilization and protection of surface water in the Yangtze River Basin.

Combined toxicity and adverse outcome pathways of common pesticides on Chlorella pyrenoidosa.

Pesticides due to their extensive use have entered the soil and water environment through various pathways, causing great harm to the environment. Herbicides and insecticides are common pesticides with long-term biological toxicity and bioaccumulation, which can harm the human body. The concept of the adverse outcome pathway (AOP) involves systematically analyzing the response levels of chemical mixtures to health-related indicators at the molecular and cellular levels. The AOP correlates the structures of chemical pollutants, toxic molecular initiation events and adverse outcomes of biological toxicity, providing a new model for toxicity testing, prediction, and evaluation of pollutants. Therefore, typical pesticides including diquat (DIQ), cyanazine (CYA), dipterex (DIP), propoxur (PRO), and oxamyl (OXA) were selected as research objects to explore the combined toxicity of typical pesticides on Chlorella pyrenoidosa (C. pyrenoidosa) and their adverse outcome pathways (AOPs). The mixture systems of pesticides were designed by the direct equipartition ray (EquRay) method and uniform design ray (UD-Ray) method. The toxic effects of single pesticides and their mixtures were systematically investigated by the time-dependent microplate toxicity analysis (t-MTA) method. The interactions of their mixtures were analyzed by the concentration addition model (CA) and the deviation from the CA model (dCA). The toxicity data showed a good concentration-effect relationship; the toxicities of five pesticides were different and the order was CYA > DIQ > OXA > PRO > DIP. Binary, ternary and quaternary mixture systems exhibited antagonism, while quinary mixture systems exhibited an additive effect. The AOP of pesticides showed that an excessive accumulation of peroxide in green algae cells led to a decline in stress resistance, inhibition of the synthesis of chlorophyll and protein in algal cells, destruction of the cellular structure, and eventually led to algal cell death.

Effect of sucrose-based carbon foams as negative electrode additive on the performance of lead-acid batteries under high-rate partial-state-of-charge condition.

Lead-acid batteries are noted for simple maintenance, long lifespan, stable quality, and high reliability, widely used in the field of energy storage. However, during the use of lead-acid batteries, the negative electrode is prone to irreversible sulfation, failing to meet the requirements of new applications such as maintenance-free hybrid vehicles and solar energy storage. In this study, in order to overcome the sulfation problem and improve the cycle life of lead-acid batteries, active carbon (AC) was selected as a foaming agent and foam fixing agent, and carbon foams (CF) with layered porous structure was prepared by mixing with molten sucrose. Sucrose as raw material is green and cheap, and the material preparation process is simple. The prepared CF material was then added as an additive to the negative electrode plate, and the electrochemical performance of the electrode plate and the battery was studied. The results proved that the addition of CF could effectively inhibit the sulfate formation of the negative electrode plate, with the 1.0 % CF negative electrode plate showing the best electrochemical performance. Specifically, according to the result of battery cycle testing, the simulated battery with CF had a cycle life of 3642 times, which was 2.87 times that of the blank group and 2.39 times of the AC group. Meanwhile, rate testing showed that the simulated battery with CF could maintain a high capacity even under high-rate discharge conditions.

Algal toxicity and food chain transport characteristics of three common bisphenols and their mixtures.

Various bisphenols (BPs) have been frequently detected in the aquatic environment and coexist in the form of mixtures with potential huge risks. As we all know, food chain is a media by which BPs mixtures and their mixtures probably enter the organisms at different trophic levels due to their environmental persistence. As a result, the concentrations of BPs and their mixtures may continuously magnify to varying degrees, which can produce higher risks to different levels of organisms, and even human health. However, the related researches about mixtures are few due to the complexity of mixtures. So, the ternary BP mixtures were designed by the uniform design ray method using bisphenol A (BPA), bisphenol S (BPS) and bisphenol F (BPF) to investigate their food chain effects including bioconcentration and biomagnification. Here, Chlorella pyrenoidosa (C. pyrenoidosa) and Daphnia magna (D. magna) were selected to construct a food chain. The toxic effects of single BPs and their mixtures were also systematically investigated by the time-dependent microplate toxicity analysis (t-MTA) method. Toxicity interaction within the ternary mixture was analyzed by the concentration addition model (CA) and the deviation from the CA model (dCA). The results show that the C. pyrenoidosa and D. magna had obvious bioconcentration and biomagnification effects on BPs and their mixture. The mixture had the potential to enrich at higher nutrient levels. And BPF had the largest bioconcentration effect (BCF1 = 481.86, BCF2 = 772.02) and biomagnification effect (BMF = 1.6). Three BPs were toxic to C. pyrenoidosa by destroying algal cells and decreasing protein and chlorophyll contents, and their toxicity order was BPF > BPA > BPS. Moreover, their ternary mixture exhibits synergism with time/concentration-dependency. The obtained results are of significant reference value for objectively and accurately assessing the ecological and environmental risks of bisphenol pollutants.

Predicting the occurrence of antagonism within ternary guanidine mixture pollutants based on the concentration ratio of components.

The widespread prevalence and coexistence of diverse guanidine compounds pose substantial risks of potential toxicity interactions, synergism or antagonism, to environmental organisms. This complexity presents a formidable challenge in assessing the risks associated with various pollutants. Hence, a method that is both accurate and universally applicable for predicting toxicity interactions within mixtures is crucial, given the unimaginable diversity of potential combinations. A toxicity interaction prediction method (TIPM) developed in our past research was employed to predict the toxicity interaction, within guanidine compound mixtures. Here, antagonism were found in the mixtures of three guanidine compounds including chlorhexidine (CHL), metformin (MET), and chlorhexidine digluconate (CDE) by selecting Escherichia coli (E. coli) as the test organism. The antagonism in the mixture was probably due to the competitive binding of all three guanidine compounds to the anionic phosphates of E. coli cell membranes, which eventually lead to cell membrane rupture. Then, a good correlation between toxicity interactions (antagonisms) and components' concentration ratios (pis) within binary mixtures (CHL-MET, CHL-CDE, MET-CDE) was established. Based on the correlation, the TIPM was constructed and accurately predicted the antagonism in the CHL-MET-CDE ternary mixture, which once again proved the accuracy and applicability of the TIPM method. Therefore, TIPM can be suggested to identify or screen rapidly the toxicity interaction within ternary mixtures exerting potentially adverse effects on the environment.

Basin-wide tracking of nitrate cycling in Yangtze River through dual isotope and machine learning.

The nitrate (NO3-) input has adversely affected the water quality and ecological function in the whole basin of the Yangtze River. The protection of water sources and implementation of "great protection of Yangtze River" policy require large-scale information on water contamination. In this study, dual isotope and Bayesian mixing model were used to research the transformation and sources of nitrate. Chemical fertilizers contribute 76 % of the nitrate sources in the upstream, while chemical fertilizers were also dominant in the midstream (39 %) and downstream (39 %) of Yangtze River. In addition, nitrification process occurred in the whole basin. Four machine learning models were used to relate nitrate concentrations to explanatory variables describing influence factors to predict nitrate concentrations in the whole basin of Yangtze River. The anthropogenic and natural factors, such as rainfall, GDP and population were chosen to take as predictor variables. The eXtreme Gradient Boosting (XGBoost) model for nitrate has a better predictive performance with an R2 of 0.74. The predictive models of nitrate concentrations will help identify the nitrate distribution and transport in the whole Yangtze River basin. Overall, this study represents the first basin-wide data-driven assessment of the nitrate cycling in the Yangtze River basin.

Characterization of organic phosphorus in lake sediments by sequential fractionation and enzymatic hydrolysis.

The role of sediment-bound organic phosphorus (Po) on lake eutrophication was studied using sequential extraction and enzymatic hydrolysis by collecting sediments from Dianchi Lake, China. Bioavailable Po species including labile monoester P, diester P, and phytate-like P were identified in the sequential extractions by H2O, NaHCO3, and NaOH. For the H2O-Po, 36.7% (average) was labile monoester P, 14.8% was diester P, and 69.9% was phytate-like P. In NaHCO3-Po, 19.9% was labile monoester P, 17.5% was diester P, and 58.8% was phytate-like P. For NaOH-Po, 25.6% was labile monoester P, 7.9% was diester P, and 35.9% was phytate-like P. Labile monoester P was active to support growth of algae to form blooms. Diester P mainly distributed in labile H2O and NaHCO3 fractions was readily available to cyanobacteria. Phytate-like P represents a major portion of the Po in the NaOH fractions, also in the more labile H2O and NaHCO3 fractions. Based on results of sequential extraction of Po and enzymatic hydrolysis, lability and bioavailability was in decreasing order as follows: H2O-Po > NaHCO3-Po > NaOH-Po, and bioavailable Po accounted for only 12.1-27.2% of total Po in sediments. These results suggest that the biogeochemical cycle of bioavailable Po might play an important role in maintaining the eutrophic status of lakes.