Influence of tartaric acid on the electron transfer between oxyanions and lepidocrocite.

Iron oxide minerals control the environmental behavior of trace elements. However, the potential effects of electron transfer directions by iron oxides between organic acids and trace elements remain unclear. This study investigates the redox capacity of tartaric acid (TA) with chromate (Cr(Ⅵ)) or arsenate (As(V)) on lepidocrocite (Lep) from the perspective of electron transfer. The results demonstrated the configurations of TA (bidentate binuclear (BB)), As(V) (BB), and Cr(Ⅵ) (BB and protonated monodentate binuclear (HMB)) on Lep. Frontier molecular orbital calculations and X-ray photoelectron spectroscopy (XPS) binding energy shifts further indicated different electron transfer directions between TA and the oxyanions on Lep. The iron of Lep might act as electron acceptors when TA is adsorbed, whereas the iron and oxygen of Lep act as electron donors when As(V) is adsorbed. The iron of Lep might accept electrons from its oxygen and subsequently transfer these electrons to Cr(Ⅵ). Macroscopic validation experiments showed the reduction of Cr(VI), whereas no reduction of As(V). The XPS analysis showed a peak shift, with the possible formation of As-Fe-TA ternary complexes and electron transfer on Lep. These findings indicate that mineral interfacial electron transfer considerably influences the transport and transformation of oxyanions.

Effect of biochar-derived DOM on contrasting redistribution of chromate during Schwertmannite dissolution and recrystallization.

Biochar-derived dissolved organic matter (BDOM), is extensively involved in the recrystallization of minerals and the speciation alteration of associated toxic metals. This study investigates how BDOM extracted from tobacco petiole (TP) or tobacco stalk (TS) biochar influences the speciation repartitioning of Cr(VI) in environments impacted by acid mine drainage (AMD), focusing on interactions with secondary minerals during Schwertmannite (Sch) dissolution and recrystallization. TP-BDOM, rich in lignin-like substances, slowed down the Cr-Sch dissolution and Cr release under acidic conditions compared to TS-BDOM. TP-BDOM's higher O/C component exerts a delayed impact on Cr-Sch stability and Cr(VI) reduction. In-situ ATR-FTIR and 2D-COS analysis showed that carboxylic and aromatic N-OH groups in BDOM could interact with Cr-Sch surfaces, affecting sulfate and Cr(VI) release. It was also observed that slight recrystallization occurred from Cr-Sch to goethite, along with increased Cr incorporation into secondary minerals within TS-BDOM. This enhances our understanding of BDOM's role in Cr(VI) speciation changes in AMD-contaminated sites.

The effect of heavy precipitation on the leaching of heavy metals from tropical coastal legacy tailings.

The continued growth in demand for mineral resources has led to a large amount of mining wastes, which is a major challenge in the context of carbon neutrality and climate change. In this study, runoff migration, batch leaching, and column experiments were used to investigate the short-, medium-, and long-term leaching of heavy metals from legacy tailings, respectively; the cumulative metal release kinetic equations were established, and the long-term effects of tailings leaching were verified by HYDRUS-1D. In runoff migration experiments, surface dissolution of tailings and the co-migration of adsorbed soil particles by erosion were the main carriers in the early stages of leachate formation (Mn âˆ¼ 65 mg/L and SO42- up to 2697.2 mg/L). Batch leaching tests showed that the concentration of heavy metals in soil leached by acid rain were 0.1 âˆ¼ 22.0 µg/L for Cr, 0.7 âˆ¼ 26.0 µg/L for Cu, 4.8 âˆ¼ 5646.0 µg/L for Mn, 0.3 âˆ¼ 232.4 µg/L for Ni, and 1.3 âˆ¼ 448.0 µg/L for Zn. The results of column experiments indicated that some soluble components and metals with high mobility showed a significant decreasing trend at cumulative L/S ≤ 2. Additionally, the metals have higher leaching rates under TCLP conditions, as shown by Mn > Co > Zn > Cd > Ni > Cu > Pb > Cr. The fitting results of Langmuir equation were closer to the cumulative release of metals in the real case, and the release amounts of Mn, Zn, Co, and Ni were higher with 55, 5.84, 2.66, and 2.51 mg/kg, respectively. The water flow within tailings affects the spatial distribution of metals, which mainly exist in relatively stable chemical fractions (F3 + F4 + F5 > 90 %) after leaching. Numerical simulation verified that Mn in leachate has reached 8 mg/L at a scale of up to 100 years. The research results are expected to provide technical basis for realizing the resource utilization of tailings in the future.

Arsenic redistribution associated with Fe(II)-induced jarosite transformation in the presence of polygalacturonic acid.

Jarosite exists widely in acid-sulfate soil and acid mine drainage polluted areas and acts as an important host mineral for As(V). As a metastable Fe(III)-oxyhydoxysulfate mineral, its dissolution and transformation have a significant impact on the biogeochemical cycle of As. Under reducing conditions, the trajectory and degree of abiotic Fe(II)-induced jarosite transformation may be greatly influenced by coexisting dissolved organic matter (DOM), and in turn influencing the fate of As. Here, we explored the impact of polygalacturonic acid (PGA) (0-200 mg·L-1) on As(V)-coprecipitated jarosite transformation in the presence of Fe(II) (1 mM) at pH 5.5, and investigated the repartitioning of As between aqueous and solid phase. The results demonstrated that in the system without both PGA and Fe(II), jarosite gradually dissolved, and lepidocrocite was the main transformation product by 30 d; in Fe(II)-only system, lepidocrocite appeared by 1 d and also was the mainly final product; in PGA-only systems, PGA retarded jarosite dissolution and transformation, jarosite might be directly converted into goethite; in Fe(II)-PGA systems, the presence of PGA retarded Fe(II)-induced jarosite dissolution and transformation but did not alter the pathway of mineral transformation, the final product mainly still was lepidocrocite. The retarding effect on jarosite dissolution enhanced with the increase of PGA content. The impact of PGA on Fe(II)-induced jarosite transformation mainly was related to the complexation of carboxyl groups of PGA with Fe(II). The dissolution and transformation of jarosite drove pre-incorporated As transferred into the phosphate-extractable phase, the presence of PGA retarded jarosite dissolution and maintained pre-incorporated As stable in jarosite. The released As promoted by PGA was retarded again and almost no As was released into the solution by the end of reactions in all systems. In systems with Fe(II), no As(III) was detected and As(V) was still the dominant redox species.

Divergent redistribution behavior of divalent metal cations associated with Fe(II)-mediated jarosite phase transformation.

The Fe(II)/Fe(III) cycle is an important driving force for dissolution and transformation of jarosite. Divalent heavy metals usually coexist with jarosite; however, their effects on Fe(II)-induced jarosite transformation and different repartitioning behavior during mineral dissolution-recrystallization are still unclear. Here, we investigated Fe(II)-induced (1 mM Fe(II)) jarosite conversion in the presence of Cd(II), Mn(II), Co(II), Ni(II) and Pb(II) (denoted as Me(II), 1 mM), respectively, under anaerobic condition at neutral pH. The results showed that all co-existing Me(II) retarded Fe(II)-induced jarosite dissolution. In the Fe(II)-only system, jarosite first rapidly transformed to lepidocrocite (an intermediate product) and then slowly to goethite; lepidocrocite was the main product. In Fe(II)-Cd(II), -Mn(II), and -Pb(II) systems, coexisting Cd(II), Mn(II) and Pb(II) retarded the above process and lepidocrocite was still the dominant conversion product. In Fe(II)-Co(II) system, coexisting Co(II) promoted lepidocrocite transformation into goethite. In Fe(II)-Ni(II) system, jarosite appeared to be directly converted into goethite, although small amounts of lepidocrocite were detected in the final product. In all treatments, the appearance or accumulation of lepidocrocite may be also related to the re-adsorption of released sulfate. By the end of reaction, 6.0 %, 4.0 %, 76.0 % 11.3 % and 19.2 % of total Cd(II), Mn(II), Pb(II) Co(II) and Ni(II) were adsorbed on the surface of solid products. Up to 49.6 %, 44.3 %, and 21.6 % of Co(II), Ni(II), and Pb(II) incorporated into solid product, with the reaction indicating that the dynamic process of Fe(II) interaction with goethite may promote the continuous incorporation of Co(II), Ni(II), and Pb(II).

Prediction of Cr(VI) and As(V) adsorption on goethite using hybrid surface complexation-machine learning model.

This study aimed to develop surface complexation modeling-machine learning (SCM-ML) hybrid model for chromate and arsenate adsorption on goethite. The feasibility of two SCM-ML hybrid modeling approaches was investigated. Firstly, we attempted to utilize ML algorithms and establish the parameter model, to link factors influencing the adsorption amount of oxyanions with optimized surface complexation constants. However, the results revealed the optimized chromate or arsenate surface complexation constants might fall into local extrema, making it unable to establish a reasonable mapping relationship between adsorption conditions and surface complexation constants by ML algorithms. In contrast, species-informed models were successfully obtained, by incorporating the surface species information calculated from the unoptimized SCM with the adsorption condition as input features. Compared with the optimized SCM, the species-informed model could make more accurate predictions on pH edges, isotherms, and kinetic data for various input conditions (for chromate: root mean square error (RMSE) on test set = 5.90 %; for arsenate: RMSE on test set = 4.84 %). Furthermore, the utilization of the interpretable formula based on Local Interpretable Model-Agnostic Explanations (LIME) enabled the species-informed model to provide surface species information like SCM. The species-informed SCM-ML hybrid modeling method proposed in this study has great practicality and application potential, and is expected to become a new paradigm in surface adsorption model.

Non-targeted screening and photolysis transformation of tire-related compounds in roadway runoff.

Roadway runoff serves as a crucial pathway for transporting contaminants of emerging concern (CECs) from urban environments to receiving water bodies. Tire-related compounds originating from tire wear particles (TWPs) have been frequently detected, posing a potential ecological threat. Yet, the photolysis of tire-related compounds within roadway runoff remains inadequately acknowledged. Addressing this deficit, our study utilized high-resolution mass spectrometry (HRMS) to characterize the chemical profile of roadway runoff across eight strategically selected sites in Guangzhou, China. 219 chemicals were identified or detected within different confidence levels. Among them, 29 tire-related contaminants were validated with reference standards, including hexa(methoxymethyl)melamine (HMMM), 1,3-diphenylguanidine (DPG), dicyclohexylurea (DCU), and N-cyclohexyl-2-benzothiazol-amine (DCMA). HMMM exhibited with the abundance ranging from 2.30 × 104-3.10 × 106, followed by DPG, 1.69 × 104-8.34 × 106. Runoff sample were exposed to irradiation of 500 W mercury lamp for photodegradation experiment. Photolysis results indicated that tire-related compounds with a low photolysis rate, notably DCU, DCMA, and DPG, are more likely to persist within the runoff. The photolytic rates were significantly correlated with the spatial distribution patterns of these contaminants. Our findings underscore TWPs as a significant source of pollution in water bodies, emphasizing the need for enhanced environmental monitoring and assessment strategies.

Enhancing compound confidence in suspect and non-target screening through machine learning-based retention time prediction.

The retention time (RT) of contaminants of emerging concern (CECs) in liquid chromatography-high-resolution mass spectrometry (LC-HRMS) is crucial for database matching in non-targeted screening (NTS) analysis. In this study, we developed a machine learning (ML) model to predict RTs of CECs in NTS analysis. Using 1051 CEC standards, we evaluated Random Forest (RF), XGBoost, Support Vector Regression (SVR), and Artificial Neural Network (ANN) with molecular fingerprints and chemical descriptors to establish an optimal model. The SVR model utilizing chemical descriptors resulted in good predictive capacity with R2ext = 0.850 and r2 = 0.925. The model was further validated through laboratory NTS compound characterization. When applied to examine CEC occurrence in a large wastewater treatment plant, we identified 40 level S1 CECs (confirmed structure by reference standard) and 234 level S2 compounds (probable structure by library spectrum match). The model predicted RTs for level S2 compounds, leading to the classification of 153 level S2 compounds with high confidence (ΔRT <2 min). The model served as a robust filtering mechanism within the analytical framework. This study emphasizes the importance of predicted RTs in NTS analysis and highlights the potential of prediction models. Our research introduces a workflow that enhances NTS analysis by utilizing RT prediction models to determine compound confidence levels.

Iron-enhanced microscale laboratory aerated filters in the treatment of artificial mariculture wastewater: A study on nitrogen removal performance and the impact on microbial community structure.

This study investigates the nitrogen removal efficacy and microbial community dynamics in seawater aquaculture effluent treatment using three different substrate combinations of microscale laboratory aerated filters (MFs) - MF1 (LECA), MF2 (LECA/Fe-C), and MF3 (LECA/Pyrite). The findings indicated that the COD removal exceeded 95% across all MFs, with higher removal efficiencies in MF2 and MF3. In terms of nitrogen removal performance, MF2 exhibited the highest average nitrogen removal of 93.17%, achieving a 12.35% and 3.56% increase compared to MF1 (80.82%) and MF3 (89.61%), respectively. High-throughput sequencing analysis revealed that the Fe-C substrate significantly enhanced the diversity of the microbial community. Notably, in MF2, the salinophilic denitrifying bacterium Halomonas was significantly enriched, accounting for 42.6% of the total microbial community, which was beneficial for nitrogen removal. Moreover, an in-depth analysis of nitrogen metabolic pathways and microbial enzymes indicated that MF2 and MF3 possessed a high abundance of nitrification and denitrification enzymes, related to the high removal rates of NH4+-N and NO3--N. Therefore, the combination of LECA with iron-based materials significantly enhances the nitrogen removal efficiency from mariculture wastewater.

Efficient removal of heavy metals in water utilizing facile cross-link conjugated linoleic acid micelles.

Micellar-enhanced ultrafiltration (MEUF) technology is an effective method to treat low-concentration heavy metal wastewater. However, the leakage of surfactants in the ultrafiltration (UF) process will inevitably cause secondary pollution. In this study, a biosurfactant of conjugated linoleic acid (CLA) with conjugated double bonds was selected to bind its micelles by simple thermal crosslinking to obtain morphologically stable stearic acid (SA) nanoparticles. The pure SA nanoparticles were obtained by repeated dialysis. The stability of the SA nanoparticles was verified by comparing the particle size distribution and solubility of the materials before and after crosslinking at different pH levels. The effectiveness of SA nanoparticle-enhanced UF in removing heavy metals was verified by exploring the adsorption performance of SA nanoparticles. The dialysis device was used to simplify the UF device, wherein SA nanoparticles were assessed as adsorbents for the elimination of Cu2+, Pb2+, and Cd2+ ions from aqueous solutions under diverse process parameters, including pH, contact time, metal ion concentration, and coexisting ions. The findings indicate that the SA nanoparticles have no evidence of secondary contamination in UF and exhibit compatibility with a broad pH range and coexisting ions. The maximum adsorption capacities for Cu2+, Pb2+, and Cd2+ were determined to be 152.77, 403.56, and 271.46 mg/g, respectively.

Optimization and verification of selective removal of organophosphate esters from wastewater by molecularly imprinted adsorbent.

Tributyl phosphate (TNBP), a new type of flame retardant, is an emerging pollutant and has been frequently detected in various matrices such as wastewater. Efficient removal of TNBP is critical for wastewater treatment. In this study, molecularly imprinted polymer (MIP) was prepared using precipitation polymerization for selective adsorption of TNBP. The results showed that MIP had a porous structure and formed effective imprinting cavities, which was primarily responsible for its superior adsorption ability. The adsorption of TNBP by MIP was carried out following both the pseudo-secondary kinetic model and the Langmuir isothermal adsorption model. MIP adsorbed TNBP rapidly and reached adsorption equilibrium within 30 min with 923 µmol g-1 at 298 K. The adsorption capacity and adsorption rate of MIP were respectively 2 and 5.49 times those of non-molecularly imprinted polymers. In addition, MIP could effectively counter disturbances from external parameters like temperature and pH, exhibiting strong environmental flexibility. MIP can specifically adsorb organophosphate esters, and can selectively adsorb TNBP under the interference of coexisting contaminants such as1,3-diphenylguanidine and isazofos. In actual bodies of water, MIP's highly selective adsorption of TNBP retains its advantage. The selective adsorption of MIP was mainly due to the common phosphate skeleton, and the specific substituent of organophosphate esters played an important role in the imprinting process. Hydrogen bonding might be involved in the polymerization process of TNBP with acrylamide and the adsorption process of TNBP by MIP.MIP exhibited good reuse efficiency, the total adsorption capacity decreased by no more than 25% after 7 reuse cycles. This study provides a simple and efficient method for selective removal of organophosphate from wastewater.

Insight into the interaction of tetrabromobisphenol A with sediment-derived dissolved organic carbon in a multiphase system by direct immersion solid phase microextraction.

Tetrabromobisphenol A (TBBPA), a ubiquitously used commercial brominated flame retardant (BFR), has been widely detected in aquatic environments, and has aroused much attention due to its potential adverse effects on aquatic organisms. However, current research on the environmental fate and transport of TBBPA in the sediment-dissolved organic carbon (DOC)-water polyphase system is lacking. In this study, the sorption behavior of TBBPA in a water-DOC-sediment system was investigated using the direct-immersion solid-phase microextraction (DI-SPME) method, and the free dissolved concentration (Cw-SPME) and DOC adsorption concentration (CDOC) of TBBPA in water were measured by applying this DI-SPME approach. In addition, the effects of pH, ionic strength, and soluble organic concentration on the adsorption of TBBPA in the multiphase system were evaluated. The adsorption kinetics experimental results show that the adsorption behavior of TBBPA on sediments conforms to a linear model, suggesting that it could be mainly absorbed by sediments. The solid-water partition coefficient (Kd) of TBBPA was artificially reduced 1.54 times using the traditional liquid-liquid extraction method because the sorption behavior of the DOC was ignored, which could be accurately corrected using the DI-SPME method. The logKd and logKOC of TBBPA in the multiphase system were 4.12 ± 0.25 and 6.48 ± 0.25, respectively. Finally, the interference experiment revealed that the sorption behavior of TBBPA was affected by the pH, ionic strength (calcium ion), and humic acid concentration, apart from the lead ion concentration itself.

Application of Nontarget High-Resolution Mass Spectrometry Fingerprints for Qualitative and Quantitative Source Apportionment: A Real Case Study.

High-resolution mass spectrometry (HRMS) provides extensive chemical data, facilitating the differentiation and quantification of contaminants of emerging concerns (CECs) in aquatic environments. This study utilizes liquid chromatography-HRMS for source apportionment in Chebei Stream, an urban water stream in Guangzhou, South China. Initially, 254 features were identified as potential CECs by the nontarget screening (NTS) method. We then established 1689, 1317, and 15,759 source-specific HRMS fingerprints for three distinct sources, the mainstream (C3), the tributary (T2), and the rain runoff (R1), qualitatively assessing the contribution from each source downstream. Subsequently, 32, 55, and 3142 quantitative fingerprints were isolated for sites C3, T2, and R1, respectively, employing dilution curve screening for source attribution. The final contribution estimates downstream from sites C3, T2, and R1 span 32-96, 12-23, and 8-23%, respectively. Cumulative contributions from these sources accurately mirrored actual conditions, fluctuating between 103 and 114% across C6 to C8 sites. Yet, with further tributary integration, the overall source contribution dipped to 52%. The findings from this research present a pioneering instance of applying HRMS fingerprints for qualitative and quantitative source tracking in real-world scenarios, which empowers the development of more effective strategies for environmental protection.

Using machine learning to explore oxyanion adsorption ability of goethite with different specific surface area.

In this study, we developed prediction models for the adsorption of divalent and trivalent oxyanions on goethite based on machine learning algorithms. After verifying the reliability of the models, the importance of goethite specific surface area (SSA) and the average oxyanion adsorption capacities of goethite with different SSAs were calculated by shapley additive explanations (SHAP) importance analysis and partial dependence (PD) analysis. Despite there were differences in the feature importance of divalent and trivalent oxyanions, the contribution of goethite's SSA to the adsorption amount ranked the fourth based on SHAP importance, indicating SSA played the important role in oxyanion adsorption. Meanwhile, the PD values of SSA and the optimized complexation constants from surface complexation modeling (SCM) both indicated a non-monotonic relationship between the goethite with different SSA and its oxyanions binding capacity. When the total site concentration and crystal face composition were used as the machine learning model input features, the SHAP importance values of crystal faces and the PD decomposition results indicated that the (001) face showed the crucial influence on oxyanions adsorption amount. These findings demonstrated the important role of crystal face composition in goethite's adsorption ability, and provided a theoretical explanation for the variations of oxyanions adsorption amount on different SSA goethite.

Facet-Dependent Competitive Adsorption Mechanisms of Chromate and Oxalic Acid on γ-FeO(OH) Nanocrystals.

Facet-dependent toxic metal adsorption of iron oxides widely occurred in natural environments. It is known that organic acids can alter the adsorption behaviors of trace elements by cooperative or competitive effects. However, the coadsorption mechanisms of the specific facets are still not fully understood. In the current investigation, Cr(VI) adsorption onto the lepidocrocite (γ-FeO(OH))-exposed facets in the presence of oxalic acid (OA) was studied using macroexperiments, in situ attenuated total reflectance Fourier transform infrared spectroscopy, X-ray adsorption fine structure, and density functional theory calculations. Rod-like lepidocrocite (R-LEP) with a high ratio of {001}/{010} facet showed excellent Cr(VI) adsorption capacity than that of plate-like lepidocrocite (P-LEP, the dominant facet is {010}) in the absence/presence of OA. Interestingly, OA reacted with R-LEP would be easier to diminish Cr(VI) adsorption than with P-LEP. The competitive adsorption occurred on the {001} facet due to the formation of inner-sphere OA configurations (monodentate mononuclear and bidentate mononuclear structures) and a bidentate binuclear Cr(VI) complex. However, OA coordinated with {010} facets via the outer-sphere complexes, while Cr(VI) could form a protonated monodentate binuclear configuration. These observations suggest that the competitive adsorption processes between OA and Cr(VI) exhibit facet dependence. Furthermore, lepidocrocite-exposed facets determine the interfacial interactions and geochemical behaviors of Cr(VI) in polluted environments.

Application of apatite particles for remediation of contaminated soil and groundwater: A review and perspectives.

With rapid industrial development and population growth, the pollution of soil and groundwater has become a critical concern all over the world. Yet, remediation of contaminated soil and water remains a major challenge. In recent years, apatite has gained a surging interest in environmental remediation because of its high treatment efficiency, low cost, and environmental benignity. This review summarizes recent advances in: (1) natural apatite of phosphate ores and biological source; (2) synthesis of engineered apatite particles (including stabilized or surface-modified apatite nanoparticles); (3) treatment effectiveness of apatite towards various environmental pollutants in soil and groundwater, including heavy metals (e.g., Pb, Zn, Cu, Cd, and Ni), inorganic anions (e.g., As oxyanions and F-), radionuclides (e.g., thorium (Th), strontium (Sr), and uranium (U)), and organic pollutants (e.g., antibiotics, dyes, and pesticides); and (4) the removal and/or interaction mechanisms of apatite towards the different contaminants. Lastly, the knowledge or technology gaps are identified and future research needs are proposed.

Validation of quenching effectiveness and pollutant degradation ability of singlet oxygen through model reaction system.

Quenching method is widely used to assess the contribution of specified reactive species through the probe inhibition efficiency (IE) caused by adding excessive quencher. However, for reactive species with weak ability such as singlet oxygen (1O2), the quenching results are prone to ambiguity. In this study, an 1O2 system using furfuryl alcohol (FFA) as a probe was successfully constructed by methylene-blue-N vis-photosensitization, to discuss the quenching, interference elimination and pollutant degradation ability of 1O2. Inhibition of FFA transformation caused by both quenching and interrupting of 1O2 production was found. The quenching is affected by quencher dosage and ability, which depends on the second-order-rate constant (k). A high k means a strong ability, and less dosage is required to achieve the same IE. Comparison between the calculated ratio of reactive species consumed by quencher and experimental IE helps to judge the interruption of 1O2 production. None of the organic-solvents (methanol, ethanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, tetrahydrofuran, acetonitrile, acetone and chloroform) scavenged 1O2, which would be used as screening-agent for other reactive species (e.g., hydroxyl radicals) that would interrupt 1O2 contribution assessment. Besides, 1O2 was powerless to degrade most selected pollutants. These results encourage proper use of quenchers and better experimental design.

Enhanced arsenic(III) sequestration via sulfidated zero-valent iron in aerobic conditions: Adsorption and oxidation coupling processes.

Sulfidated zero-valent iron (S-ZVI) has shown significant potential for the removal of arsenic(III). However, little attention has been paid to the mechanism of As(III) sequestration enhancement and how the phase transformation for S-ZVI strengthens this process in aerobic conditions. In this work, sulfidated ZVI was created by ball-milling (S-ZVIbm) and liquid-mixing (S-ZVIlm) of ZVI with elemental sulfur(S0) to investigate the performance and mechanisms of As(III) sequestration in air-saturated water. Sulfidation was found to significantly enhance the As(III) removal rate constant, which was 2.8 âˆ¼ 6.7 times (S-ZVIbm) and 3.1 âˆ¼ 17.1 times (S-ZVIlm) higher than that without sulfidation. FeS was identified as the predominant sulfur species in the S-ZVI samples using S K-edge XANES spectra. The enhanced electron transfer and ZVI corrosion after sulfidation were verified via electrochemical tests. XANES and Mössbauer spectra suggested that lepidocrocite(γ-FeOOH) was the predominant corrosion product generated on the ZVI surface with the presence of oxygen, and DFT calculations further confirmed the improved performance of γ-FeOOH for As(III) sequestration. Besides, As(III) oxidation occurred dominantly on the heterogeneous surface rather than in solution, and the As(III) sequestration pathway of adsorption followed by oxidation was proposed. This study provides new insight into the enhanced As(III) sequestration by S-ZVI in aerobic conditions.

Divergent repartitioning of antimony and arsenic during jarosite transformation: A comparative study under aerobic and anaerobic conditions.

Jarosite is the host mineral of Sb(V) and As(V) in mining environments. However, the repartitioning of Sb and As during its transformation is poorly understood. Additionally, the mutual effect between the redistribution behavior of As and Sb during jarosite conversion remains unclear. Here, we investigated the transformation of Sb(V)-, As(V)- and Sb(V)-As(V)-jarosite at pH 5.5 under aerobic and anaerobic conditions without a reductant. The results indicated that co-precipitated Sb(V) promotes jarosite dissolution, and the final products were mainly goethite and hematite. In contrast, the co-precipitated As(V) retarded jarosite dissolution and altered the transformation pathway, mainly forming lepidocrocite, which might be attributed to the formation of As-Fe complexes on the jarosite surface. The inhibiting or promoting effect increased with the increase in co-precipitated As or Sb concentration. In the treatment with Sb(V)-As(V)-jarosite, the inhibition effect of co-precipitated As(V) on mineral dissolution was predominant, but the end-products were mainly goethite and hematite. Compared with the aerobic system, the dissolution and transformation of jarosite in treatments in the anaerobic system occurred faster, although without a reductant, which was possibly associated with the reduced CO2 content in the reaction solutions after degassing. In all treatments, the release of Sb(aq) and As(aq) into the solution was negligible during jarosite transformation. The transformation processes drove As into the surface-bound exchangeable and poorly crystalline phases, while Sb was typically redistributed in the poorly crystalline phase. During the transformation of Sb(V)-As(V)-jarosite, the co-existence of As significantly increased the proportion of Sb distributed on the solid surface and in the poorly crystalline phase. These findings are valuable for predicting the long-term fate of Sb and As in mining environments.

Interaction between Phthalate Ester and Rice Plants: Novel Transformation Pathways and Metabolic-Network Perturbations.

Our understanding is limited concerning the interaction mechanism between widespread phthalate esters and staple crops, which have strong implications for human exposure. Therefore, this study was aimed at illuminating the transformation pathways of di-n-butyl phthalate (DnBP) in rice using an untargeted screening method. UPLC-QTOF-MS identified 16 intermediate transformation products formed through hydroxylation, hydrolysis, and oxidation in phase I metabolism and further by conjugation with amino acids, glutathione, and carbohydrates in phase II metabolism. Mono-2-hydroxy-n-butyl phthalate-l-aspartic acid (MHBP-asp) and mono-2-hydroxy-n-butyl phthalate-d-alanyl-ß-d-glucoside (MHBP-ala-glu) products were observed for the first time. The proteomic analysis demonstrated that DnBP upregulated the expression of rice proteins associated with transporter activity, antioxidant synthesis, and oxidative stress response and downregulated that of proteins involved in photosynthesis, photorespiration, chlorophyll binding, and mono-oxygenase activity. Molecular docking revealed that DnBP can affect protein molecular activity via pi-sigma, pi-alkyl, and pi-pi interactions or by forming carbon-hydrogen bonds. The metabolomic analysis showed that key metabolic pathways including citrate cycle, biosynthesis of aminoacyl-tRNA, and metabolism of amino acids, sphingolipids, carbohydrates, nucleotides, and glutathione were activated in rice plants exposed to DnBP and its primary metabolite mono-n-butyl phthalate (MnBP). Furthermore, exposure to 80 ng/mL MnBP significantly perturbed the metabolic profile and molecular function in plants, with downregulation of the levels of beta-alanine (0.56-fold), cytosine (0.48-fold), thymine (0.62-fold), uracil (0.48-fold), glucose (0.59-fold), and glucose-1-phosphate (0.33-fold), as well as upregulation of the levels of l-glutamic acid (2.97-fold), l-cystine (2.69-fold), and phytosphingosine (38.38-fold). Therefore, the degradation intermediates of DnBP pose a potentially risk to plant metabolism and raise concerns for crop safety related to plasticizer pollution.