Environmental transformation and hazards of decachlorobiphenyl on suspended particles under sunlight irradiation.

Decachlorobiphenyl (PCB-209) can be widely detected in suspended particles and sediments due to its large hydrophobicity, and some of its transformation products may potentially threaten organisms through the food chain. Here we investigate the photochemical transformation of PCB-209 on suspended particles from the Yellow River. It was found that the suspended particles had an obvious shielding effect to largely inhibit the photodegradation of PCB-209. Meanwhile, the presence of inorganic ions (e.g. Mg2+ and NO3-) and organic matters (e.g. humic acid, HA) in the Yellow River water inhibited the reaction. The main transformation products of PCB-209 were lower-chlorinated and hydroxylated polychlorinated biphenyls (OH-PCBs), and small amounts of pentachlorophenol (PCP) and polychlorinated dibenzofurans (PCDFs) were also observed. The mechanisms of PCP formation by double •OH attacking carbon bridge and PCDFs formation by elimination reaction of ionic state OH-PCBs were proposed using theoretical calculations, which provided some new insights into the inter-transformations between persistent organic pollutants. In combination with VEGA and EPI Suite software, some intermediates such as PCDFs were more toxic to organisms than PCB-209. This study deepens the understanding of the transformation behavior of PCB-209 on suspended particles under sunlight.

Investigation of the photolysis process of benzo(a)anthracene (BaA) on polyvinyl chloride (PVC) and polystyrene (PS) microplastics: Plastics aging effect, transformation products and toxicity assessment.

Microplastics (MPs) and persistent pollutants (POPs) are new pollutants that are extensively studied worldwide. To fill the gaps that the degradation processes and mechanisms of polycyclic aromatic hydrocarbons (PAHs) on the surface of most MPs are still unclear, the photochemical transformation of benzo(a)anthracene (BaA) on polyvinyl chloride (PVC) MPs and polystyrene (PS) MPs in water were investigated and compared. The photolysis of BaA on the surface of PS in water proceeded easier than that on PVC within the 48 h irradiation period, with the pseudo-first-order rate constant of 0.0489 min-1 and 0.0181 min-1, respectively, which can be ascribed to the smaller particle size and more OH production of PS MPs. Due to the light competition between the chromophore and BaA as well as the light-shielding effect, aged MPs showed an inhibitory effect on the degradation of BaA compared with pristine MPs. For BaA/PVC MPs system, the degradation of BaA in real water was not significantly affected by coexisting ions and humic acid (HA) (p < 0.05), while slight inhibitory effect on the degradation of BaA appeared for PS MPs in different water matrices (UP: 86.97 %, YR: 84.47 %, PR: 81.42 % and HR: 83.21 %). According to the electron paramagnetic resonance (EPR) test, quenching experiment and probe experiment, the relative contribution of direct photolysis (PVC: 82.02 %; PS: 69.54 %) and indirect photolysis (PVC: 17.98 %; PS: 30.46 %) was confirmed. A total of 14 products were identified, and the product types were not affected by plastics aging. The results of the toxicity assessment indicated that although some intermediate products remained toxic to aquatic organisms, the toxicity of most products was lower than that of BaA. This study provides new insights into the environmental fate of PAHs and the role of MPs in the photolysis process of contaminants in surface water.

Photodegradation of polychlorinated biphenyls in water/nitrogen-doped silica and air/nitrogen-doped silica systems: Kinetics, mechanism and quantitative structure activity relationship (QSAR) analysis.

Developing efficient and low-cost photocatalytic materials is essential for removing polychlorinated biphenyls (PCBs). In this work, the photodegradation process of fourteen representative polychlorinated biphenyls (PCBs) in both water/nitrogen-doped SiO2 (N-SiO2) and air/N-SiO2 systems was studied. The photodegradation kinetics of PCBs is consistent with the pseudo-first-order kinetic equation. The variation in the degradation effects of different PCBs in the two systems is primarily related to the position of the Cl substituent and the effective absorption wavelength range of PCBs. A total of fourteen intermediates for 4'-Dichlorobiphenyl (PCB-15), 2,2',4,4',6,6'-Hexachlorobiphenyl (PCB-155), and 2,2',3,3',4,4',5,5',6,6'-Decachlorobiphenyl (PCB-209) generated from four reaction pathways were identified based on both mass spectrometry analysis and theoretical calculations. Using the values of lnk (k denotes pseudo-first-order kinetic constants) for the 11 PCBs in the training set and the calculated molecular and structural parameters, quantitative structure-activity relationship (QSAR) models for the two systems were constructed by using multiple linear regression (MLR) method to better understand the factors affecting the photodegradation rate of PCBs. The QSAR equations were obtained with Cl atom substitution at position 3 (N3) as the main parameter, which were lnk = -1.98 - 0.19 N3 for the water/N-SiO2 system and lnk = -1.56 - 0.34 N3 for the air/N-SiO2 system, with the correlation coefficient (R2) of 0.66 and 0.73, leave-one-out cross-validation (Q2LOO) of 0.51 and 0.59, respectively, and bootstrapping validation coefficients (Q2BOOT) values of both 0.74, confirming that the models were well fitted and showed high robustness and prediction ability. This study provides valuable insights into photocatalytic degradation studies of PCBs.

Photodegradation of polycyclic aromatic hydrocarbons on soil surface: Kinetics and quantitative structure-activity relationship (QSAR) model development.

Polycyclic aromatic hydrocarbons (PAHs) have attracted much attention because of their widespread existence and toxicity. Photodegradation is the main natural decay process of PAHs in soil. The photodegradation kinetics of benzopyrene (BaP) on 16 kinds of soils and 10 kinds of PAHs on Hebei (HE) soil were studied. The results showed that BaP had the highest degradation rate in Shaanxi (SN) soil (kobs = 0.11 min-1), and anthracene (Ant) was almost completely degraded after 16 h of irradiation in HE soil. Two quantitative structure-activity relationship (QSAR) models were established by the multiple linear regression (MLR) method. The developed QSAR models have good stability, robustness and predictability. The model revealed that the main factors affecting the photodegradation of PAHs are soil organic matter (SOM) and the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (Egap). SOM can function as a photosensitizer to induce the production of active species for photodegradation, thus favoring the photodegradation of PAHs. In addition, compounds with lower Egap are less stable and more reactive, and thus are more prone to photodegradation. Finally, the QSAR model was optimized using machine learning approach. The results of this study provide basic information on the photodegradation of PAHs and have important significance for predicting the environmental behavior of PAHs in soil.

Photodegradation of 2-chlorodibenzo-p-dioxin (2-CDD) on the surface of municipal solid waste incineration fly ash: Kinetics and product analysis.

Considering that waste incineration fly ash is the main carrier of dioxins and can migrate over long distances in the atmosphere, it is of great significance to study the photochemical transformation behavior of dioxins on the surface of fly ash. In this work, 2-chlorodibenzo-p-dioxin (2-CDD) was selected to conduct a systematic photochemical study. The influence of various factors on the photodegradation of 2-CDD were first explored, and the results showed that small particle size of fly ash, low concentration of 2-CDD and appropriate level of humidity were more conducive to photodegradation, with the highest degradation percentage reaching 76%-84%. The components of fly ash (Zn (Ⅱ), Al (Ⅲ), Cu (Ⅱ) and SiO2) also had a certain promoting effect on the degradation of 2-CDD, which increases the degradation efficiency by 10%-20%, because they could act as effective photocatalysts to produce free radicals for reaction. With a higher total light exposure intensity, natural light environments led to a more complete degradation of 2-CDD than laboratory Xe lamp irradiation (90% degradation Vs. 79% degradation). Based on chemical probe and radical quenching experiment, hydroxyl radical also contributed to 2-CDD photodegradation on fly ash. A total of 16 intermediate products were detected by mass spectrometry analysis, and four initial reaction pathways of 2-CDD were speculated in the process, including dechlorination, ether bond cleavage, hydroxyl substitution, and hydroxyl addition. According to the results of density functional theory calculation, the reaction channels of ether bond cleavage and •OH attack were determined. The toxicity assessment software tool (TEST) was used to assess the toxicity and bioconcentration coefficient of reaction products, and it was found that the overall toxicity of the photodegradation products was reduced. This study would provide new insights into the environmental fate of dioxins during long-range atmospheric migration process.

Degradation of Butylated Hydroxyanisole by the Combined Use of Peroxymonosulfate and Ferrate(VI): Reaction Kinetics, Mechanism and Toxicity Evaluation.

Butylated hydroxyanisole (BHA), a synthetic phenolic antioxidant (SPA), is now widely present in natural waters. To improve the degradation efficiency of BHA and reduce product toxicity, a combination of peroxymonosulfate (PMS) and Ferrate(VI) (Fe(VI)) was used in this study. We systematically investigated the reaction kinetics, mechanism and product toxicity in the degradation of BHA through the combined use of PMS and Fe(VI). The results showed that PMS and Fe(VI) have synergistic effects on the degradation of BHA. The effects of operational factors, including PMS dosage, pH and coexisting ions (Cl-, SO42-, HCO3-, K+, NH4+ and Mg2+), and different water matrices were investigated through a series of kinetic experiments. When T = 25 °C, the initial pH was 8.0, the initial BHA concentration was 100 µM, the initial concentration ratio of [PMS]0:[Fe(VI)]0:[BHA]0 was 100:1:1 and the degradation rate could reach 92.4% within 30 min. Through liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) identification, it was determined that the oxidation pathway of BHA caused by PMS/Fe(VI) mainly includes hydroxylation, ring-opening and coupling reactions. Density functional theory (DFT) calculations indicated that •OH was most likely to attack BHA and generate hydroxylated products. The comprehensive comparison of product toxicity results showed that the PMS/Fe(VI) system can effectively reduce the environmental risk of a reaction. This study contributes to the development of PMS/Fe(VI) for water treatment applications.

Enhanced permanganate oxidation of phenolic pollutants by alumina and potential industrial application.

In this study, we found that alumina (Al2O3) may improve the degradation of phenolic pollutants by KMnO4 oxidation. In KMnO4/Al2O3 system, the removal efficiency of 2,4-Dibromophenol (2,4-DBP) was increased by 26.5%, and the apparent activation energy was decreased from 44.5 kJ/mol to 30.9 kJ/mol. The mechanism of Al2O3-catalytic was elucidated by electrochemical processes, X-ray photoelectron spectroscopy (XPS) characterization and theoretical analysis that the oxidation potential of MnO4- was improved from 0.46 V to 0.49 V. The improvement was attributed to the formation of coordination bonds between the O atoms in MnO4- and the empty P orbitals of the Al atoms in Al2O3 crystal leading to the even-more electron deficient state of MnO4-. The excellent reusability of Al2O3, the good performance on degradation of 2,4-DBP in real water, the satisfactory degradation of fixed-bed reactor, and the enhanced removal of 6 other phenolic pollutants demonstrated that the KMnO4/Al2O3 system has satisfactory potential industrial application value. This study offers evidence for the improvement of highly-efficient MnO4- oxidation systems.

Assessment of the UV/DCCNa and UV/NaClO oxidation process for the removal of diethyl phthalate (DEP) in the aqueous system.

In this work, the removal and transformation process of diethyl phthalate (DEP) in UV/dichloroisocyanurate (UV/DCCNa) and UV/sodium hypochlorite (UV/NaClO) systems were compared to evaluate the application potential of UV/DCCNa technology. Compared with UV/NaClO, UV/DCCNa process has the advantage of DEP removal and caused a higher degradation efficiency (93.8%) within 45 min of oxidation in ultrapure water due to the sustained release of hypochloric acid (HOCl). Fourteen intermediate products were found by high-resolution mass spectrometry, and the transformation patterns including hydroxylation, hydrolysis, chlorination, cross-coupling, and nitrosation were proposed. The oxidation processes were also performed under quasi-realistic environmental conditions, and it was found that DEP could be effectively removed in both systems, with yields of disinfection byproduct meeting the drinking water disinfection standard (<60.0 µg/L). Comparing the single system, the removal of DEP decreased in the mixed system containing five kinds of PAEs, which could be attributed to the regeneration of DEP and the competitive effect of •OH occurred among the Dimethyl phthalate (DMP), DEP, Dipropyl phthalate (DPrP), Diallyl phthalate (DAP) and Diisobutyl phthalate (DiBP). However, a greater removal performance presented in UV/DCCNa system compared with UV/NaClO system (69.4% > 62.1%). Further, assessment of mutagenicity and developmental toxicity by Toxicity Estimation Software Tool (T.E.S.T) software indicated that UV/DCCNa process has fewer adverse effects on the environment and is a more environmentally friendly chlorination method. This study may provide some guidance for selecting the suitable disinfection technology for drinking water treatment.

Insights into enhanced oxidation of benzophenone-type UV filters (BPs) by ferrate(VI)/ferrihydrite: Increased conversion of Fe(VI) to Fe(V)/Fe(IV).

In this work, the oxidation performance of a new ferrate(VI)/ferrihydrite (Fe(VI)/Fh) system was systematically explored to degrade efficiently six kinds of benzophenone-type UV filters (BPs). Fe(VI)/Fh system not only had a superior degradation capacity towards different BPs, but also exhibited higher reactivity over a pH range of 6.0-9.0. The second-order kinetic model successfully described the process of BP-4 degradation by heterogeneous Fh catalyzed Fe(VI) system (R2 = 0.93), and the presence of Fh could increase the BP-4 degradation rate by Fe(VI) by an order of magnitude (198 M-1·s-1 v.s. 14.2 M-1·s-1). Remarkably, there are higher utilization efficiency and potential of Fe(VI) in Fe(VI)/Fh system than in Fe(VI) alone system. Moreover, characterization and recycling experiments demonstrated that Fh achieved certain long-term running performance, and the residual Fe content of solution after clarifying process meet World Health Organization (WHO) guidelines for drinking water. The contributions of reactive species could be ranked as Fe(V)/Fe(IV) > Fe(VI) > â€¢OH. Fe(IV)/Fe(V) were the dominant species for the enhanced removal in the Fe(VI)/Fh system, whose percentage contribution (72 %-36 %) were much higher than those in Fe(VI) alone system (5 %-17 %). However, the contribution of Fe(VI) in oxidizing BP-4 should not be underestimated (20 %-56 %). These findings reasonably exploit available Fh resources to reduce the relatively high cost of Fe(VI), which offers a proper strategies for efficient utilization of high-valent iron species and may be used as a highly-efficient and cost-effective BPs purification method.

Enhanced removal of bisphenol S in ozone/peroxymonosulfate system: Kinetics, intermediates and reaction mechanism.

The degradation process of bisphenol S (BPS) in ozone/peroxymonosulfate (O3/PMS) system was systematically explored. The results showed that the removal efficiency of BPS by O3 could be significantly improved with addition of PMS. Compared with ozonation alone, the pseudo-first-order constant (kobs) was increased by 2-5 times after adding 400 µM PMS. In O3/PMS system, accelerated removal of BPS was observed under neutral and alkaline conditions. The removal efficiency of BPS reached 100% after 40 s of reaction at pH 7.0, with the kobs of 0.098 s-1. Moreover, Cu2+ had a catalytic effect on the O3/PMS system, because it could catalyze the decomposition of ozone and PMS to produce •OH and SO4•-, respectively. Electron paramagnetic resonance illustrated that •OH and SO4•- were the reactive species in O3/PMS system. Twelve intermediates were identified by mass spectrometry, and the degradation reactions in O3/PMS system mainly included hydroxylation, sulfate addition, polymerization and ß-scission. Finally, the toxicity of the products was evaluated by the EOCSAR program. Our results introduce an efficient method for BPS removal and would provide some guidance for the development of O3-based advanced oxidation technology.

Insights into the photocatalytic degradation of hydrophobic organic contaminants on the surface of nitrogen doped silica: New findings of the formation of silicon-based substitution products.

In this work, nitrogen-doped SiO2 (N-SiO2) was successfully synthesized to develop an "adsorption-photocatalytic degradation" water purification technology to remove hydrophobic organic contaminants (HOCs). As a representative of HOCs, decabromodiphenylethane (DBDPE) could be efficiently degraded under simulated sunlight after adsorption on the surface of N-SiO2. Due to the generation of reactive oxygen species (ROS) and silicon-based radicals, the photodegradation rate of DBDPE on water-SiO2 interface was 1.5-fold higher than that in water. Furthermore, the transformation pathways of DBDPE on N-SiO2 surface were compared with that in water. Bond breaking and debromination reactions were the common pathways, while hydroxylation and silicon-based substitution reactions were the specific transformation pathways for DBDPE on the surface of N-SiO2. Density functional theory (DFT) calculation was used to reveal the generation mechanism of silicon-based radicals and determine the rationality of the involvement of silicon-based radicals in DBDPE transformation. The energy barriers of silicon-based substitution reaction were comparable to that of hydroxylation and debromination reactions, which confirmed the plausibility of the generation of silicon-based substitution products. This study provides an efficient method for the disposal of HOCs, which also gives some new insights into the conversion mechanism of organic pollutants mediated by silicon-based radicals.

Promoting Effect of Silver Oxide Nanoparticles on the Oxidation of Bisphenol B by Ferrate(VI).

Bisphenol B (BPB, 2,2-bis(4-hydroxyphenyl) butane), as a substitute for bisphenol A, has been widely detected in the environment and become a potential threat to environmental health. This work found that silver oxide nanoparticles (Ag2O) could greatly promote the removal of BPB by ferrate (Fe(VI)). With the presence of 463 mg/L Ag2O, the amount of Fe(VI) required for the complete removal of 10 µM BPB will be reduced by 70%. Meanwhile, the recyclability and stability of Ag2O have been verified by recycling experiments. The characterization results and in situ electrochemical analyses showed that Ag(II) was produced from Ag(I) in the Fe(VI)-Ag2O system, which has a higher electrode potential to oxidize BPB to enhance its removal. A total of 13 intermediates were identified by high-resolution mass spectrometry, and three main reaction pathways were proposed, including oxygen transfer, bond breaking, and polymerization. Based on the toxicity assessment through the ECOSAR program, it is considered that the presence of Ag2O reduced the toxicity of BPB oxidation intermediates to aquatic organisms. These results would deepen our understanding of the interaction between Fe(VI) and Ag2O, which may provide an efficient and environmentally friendly method for water and wastewater treatment.

Oxidative degradation and possible interactions of coexisting decabromodiphenyl ether (BDE-209) on polystyrene microplastics in UV/chlorine process.

This work was to investigate the transformation of coexisting decabromodiphenyl ether (BDE-209) on microplastics and their possible interactions in UV/chlorine process. Compared with pristine microplastics, the highly aged polystyrene (PS) showed an inhibitory effect on degradation of BDE-209. Increasing initial concentration of BDE-209 on PS inhibited degradation, while the chlorine concentration and pH did not affect the final degradation efficiency. Moreover, the presence of NO3-, SO42-, HCO3- and HA in water was unfavorable for BDE-209 degradation. According to the experimental and calculation results, the contribution to the degradation of BDE-209 was ranked as direct photolysis > HO• > •Cl in the UV/ chlorine system. Chlorination products released by PS during UV/chlorination were detected. Four possible reaction pathways of BDE-209 were proposed, which mainly involved debromination, hydroxylation, chlorine substitution, cleavage of ether bond, and intramolecular elimination of HBr. It was worth noting that PS microplastics not only inhibited the degradation of BDE-209, but also affected the type and abundance of its transformation products. Meanwhile, interaction products of PS and BDE-209 were determined, which was attributed to reactions of PS-derived radicals with •Br/•C6Br5 and •Cl. Results of toxicity evaluation showed that the introduction of carbon-halogen bonds, especially C-Br bond, increased the toxicity of chain scission products of PS. This work provides some new insights into transformation, interaction, and associated ecological risks of coexisting microplastics and surface adsorbed contaminants in the UV/chlorine process of drinking water treatment plants (DWTPs) and wastewater treatment plants (WWTPs).

Insights into oxidation of pentachlorophenol (PCP) by low-dose ferrate(VI) catalyzed with α-Fe2O3 nanoparticles.

In this study, the catalytic performance of α-Fe2O3 nanoparticles (nα-Fe2O3) in the low-dose ferrate (Fe(VI)) system was systematically studied through the degradation of pentachlorophenol (PCP). Based on the established quadratic functions between nα-Fe2O3 amount and observed pseudo first-order rate constant (kobs), two linear correlation equations were offered to predict the optimum catalyst dosage and the maximum kobs at an applied Fe(VI) amount. Moreover, characterization and cycling experiments showed that nα-Fe2O3 has good stability and recyclability. According to the results of reactive species identification and quenching experiment and galvanic oxidation process, the catalytic mechanism was proposed that Fe(III) on the surface of nα-Fe2O3 may react with Fe(VI) to enhance the generation of highly reactive Fe(IV)/Fe(V) species, which rapidly extracted a single electron from PCP molecule for its further reaction. Besides, two possible PCP degradation pathways, i.e., single oxygen transfer mediated hydroxylation and single electron transfer initiated polymerization were proposed. The formation of coupling products that are prone to precipition and separation was largely improved. This study proved that nα-Fe2O3 can effectively catalyze PCP removal at low-dose Fe(VI), which provides some support for the application of Fe(VI) oxidation technology in water treatment in the context of low-carbon emissions.

Comparative study on the removal of 1- naphthol and 2-naphthol by ferrate (VI): Kinetics, reaction mechanisms and theoretical calculations.

In this study, the oxidation of 1-naphthol (1-NAP) and 2-naphthol (2-NAP) by Fe(VI) was investigated. The impacts of operating factors were investigated through a series of kinetic experiments, including Fe(VI) dosages, pH and coexisting ions (Ca2+, Mg2+, Cu2+, Fe3+, Cl-, SO42-, NO3- and CO32-). Almost 100% elimination of both 1-NAP and 2-NAP could be achieved within 300 s at pH 9.0 and 25 °C. Cu2+ could significantly improve the degradation efficiency of 1-NAP and 2-NAP, but the impacts of other ions were negligible. The liquid chromatography-mass spectrometry was used to identify the transformation products of 1-NAP and 2-NAP in Fe(VI) system, and the degradation pathways were proposed accordingly. Electron transfer mediated polymerization reaction was the dominant transformation pathway in the elimination of NAP by Fe(VI) oxidation. After 300 s of oxidation, heptamers and hexamers were found as the final coupling products during the removal of 1-NAP and 2-NAP, respectively. Theoretical calculations demonstrated that the hydrogen abstraction and electron transfer reaction would easily occur at the hydroxyl groups of 1-NAP and 2-NAP, producing NAP phenoxy radicals for subsequent coupling reaction. Moreover, since the electron transfer reactions between Fe(VI) and NAP molecules were barrierless and could occur spontaneously, the theoretical calculation results also confirmed the priority of coupling reaction in Fe(VI) system. This work indicated that the Fe(VI) oxidation was an effective way for removing naphthol, which may help us understand the reaction mechanism between phenolic compounds with Fe(VI).

Insights into manganese(VII) enhanced oxidation of benzophenone-8 by ferrate(VI): Mechanism and transformation products.

Benzophenones (BPs) are commonly used as UV filters in cosmetics and plastics products and are potentially toxic to the environment. This paper presents kinetics and products of BPs oxidation by ferrate(VI) (FeO42-, Fe(VI)) promoted by permanganate (Mn(VII)) . Degradation of 10.0 µM 2,2'-dihydroxy-4-methoxybenzophenone (BP-8)were determined under different experimental conditions ([Mn(VII)] = 0.5-1.5 µM, [Fe(VI)] = 50-150 µM, and pH = 7.0-10.0). The addition of Mn(VII) traces to Fe(VI)-BP-8 solution enhanced kinetics and efficiency of the removal. Similar enhanced removals were also seen for other BPs (BP-1, BP-3, and BP-4) under optimized conditions. The second-order rate constants (k, M-1s-1) of the degradation of BPs showed positive relationship with the energy of the highest occupied orbital (EHOMO). The possible interaction between Mn(VII) and BP-8 and the enhanced generation of Fe(V)/Fe(IV) and •OH was proposed to facilitate the oxidation of the target benzophenone, supported by in-situ electrochemical measurements, theoretical calculations and reactive species quenching experiments. Thirteen oxidation products of BP-8 suggested hydroxylation, bond breaking, polymerization and carboxylation steps in the oxidation. Toxicity assessments by ECOSAR program showed that the oxidized intermediate products posed a tapering ecological risk during the degradation process. Overall, the addition of Mn(VII) could improve the oxidation efficiency of Fe(VI).

Photochemical transformation of anthracene (ANT) in surface soil: Chlorination and hydroxylation.

To reveal the fate of anthracene (ANT) in soil, the photodegradation behavior of ANT was systematically studied using SiO2 to simulate a soil environment. Under xenon lamp irradiation, more than 90% of ANT loaded on SiO2 could be removed after 240 min. Moreover, the effects of water content, chloride ions (Cl-) and humic acid (HA) were examined. It was found that the presence of water and HA can significantly inhibit the photolysis of ANT on SiO2, while the addition of chloride alone has no obvious effect. However, when water is present, the inhibition effect of chloride became more obvious. According to radical quenching experiments and electron paramagnetic resonance (EPR) spectra, hydroxyl radicals (•OH) and chlorine radicals (Cl•) were formed in the system. Possible reaction pathways were speculated based on products identified by mass spectrometry. ANT was attacked by •OH to form hydroxylated products, which can be further hydroxylated and oxidized with the final formation of ring-opening products. ANT directly excited by light may also react with Cl• to produce chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs). Finally, the experimental results were verified on real soil. This study provides important information for understanding the photochemical transformation mechanism of ANT at the soil/air interface.

Simulation and risk assessment of arsenic by Hydrus-3D and CalTOX in a typical brownfield site.

Accurate quantification of arsenic migration and accumulation in brownfield site is critical for environmental management and soil remediation. However, the researches simulating arsenic in brownfield site in China are limited due to sparse data and complex migration behaviors. In this study, we simulated historic arsenic contamination using Hydrus-3D in an abandoned brownfield site in Hebei, China, from 1972 to 2019. Atmospheric discharge, wastewater leakage, solid waste discharge and tank leakage were calculated according to the factory processes for model simulation. Based on the results of Hydrus-3D, we assessed health risk of arsenic in this site. The results showed that total arsenic input to the soil surface from 4 pathways was 24.6 tons, the solid waste discharge was the highest contributor. The accumulation process mainly occurred in the unsaturated zone due to clay and silty clay absorbed arsenic and thus slow down the migration process. While in the saturation zone, abundant groundwater promoted migration of arsenic, resulting in widespread distribution of contaminated area. The model results represented good performance between simulated and measured values. Sensitivity analysis indicated that adsorption constant and water conductivity were the most influential parameters. Heath risk assessment showed that arsenic contamination continues to threaten resident health.

Degradation of Bisphonel AF (BPAF) by zero-valent iron activated persulfate: Kinetics, mechanisms, theoretical calculations, and effect of co-existing chloride.

The removal of Bisphonel AF (BPAF) by zero-valent iron activated persulfate (Fe0/PS) system was systematically evaluated in this work. 30.0 µM BPAF was removed by 94.4% in 60 min of treatment under optimal conditions of pH = 3.0 and [PS] = [Fe0] = 3.0 mM. Cl- significantly accelerated the removal of BPAF, resulting from accelerated Fe2+ release and reactive chlorine species (RCS) formation. Liquid chromatography-time-of-flight-mass spectrometry identified thirteen degradation products, and bond breaking, coupling reactions, hydroxylation and sulfate addition were considered as the major transformation pathways. When Cl- was present, six new chlorinated byproducts were also generated. Based on density functional theory (DFT) calculations, the occurrence of radical addition reactions was verified and the preferential reaction channels were determined. Significantly BPAF degradation products were less toxic, according to toxicity assessment by the ECOSAR program. Moreover, a high removal efficiency of BPAF (>90%) was also obtained in the three actual water matrixes. The present work demonstrates the feasibility of Fe0/PS system for treating BPAF, which could also provide new insights into the influence of coexisting Cl- on the environmental fate of organic pollutants in sulfate radicals based advanced oxidation processes.