Reductive dechlorination for remediation of polychlorinated biphenyls

Transformation and degradation of tebuconazole and its metabolites in constructed wetlands with arbuscular mycorrhizal fungi colonization

Arbuscular mycorrhizal fungi (AMF) colonization has been used in constructed wetlands (CWs) to enhance treatment performance. However, its role in azole (fungicide) degradation and microbial community changes is not well understood. This study aims to explore the impact of AMF on the degradation of tebuconazole and its metabolites in CWs. Total organic carbon levels were consistently higher with the colonization of AMF (AMF+; 9.63- 16.37 mg/L) compared to without the colonization of AMF (AMF-; 8.79-14.48 mg/L) in CWs. Notably, tebuconazole removal was swift, occurring within one day in both treatments (p = 0.885), with removal efficiencies ranging from 94.10 % to 97.83 %. That's primarily due to rapid substrate absorption at the beginning, while degradation follows with a longer time. Four metabolites were reported in CWs first time: tebuconazole hydroxy, tebuconazole lactone, tebuconazole carboxy acid, and tebuconazole dechloro. AMF decreased the abundance of tebuconazole dechloro in the liquid phase, suggesting an inhibitory effect of AMF on dechlorination processes. Furthermore, tebuconazole carboxy acid and hydroxy were predominantly found in plant roots, with a higher abundance observed in AMF+ treatments. Metagenomic analysis highlighted an increasing abundance in bacterial community structure in favor of beneficial microorganisms (xanthomonadales, xanthomonadaceae, and lysobacter), along with a notable presence of functional genes like codA, NAD, and deaD in AMF+ treatments. These findings highlight the positive influence of AMF on tebuconazole stress resilience, microbial community modification, and the enhancement of bioremediation capabilities in CWs.

Dry dechlorination of polychlorinated biphenyls in contaminated soil by using nano-sized composite of metallic Ca/CaO and its mechanism

Soil contamination by PCBs is still known as a serious problem across the world, and the development of new technologies or the improvement of existing ones (e.g. higher efficiency, shorter processing time, lower input energy) are more and more important. Moreover, understanding the chemistry of the entire process, from a mechanistic point of view, can accelerate the process of improvement. In these circumstances, we attempted a clarification of the highly efficient degradation of PCBs by nano-sized particle of metallic Ca in CaO ("nCa") at 250 °C in dry solid state conditions. The reaction involved the hydrodechlorination, simple reduction, reductive coupling and hydroxylation processes. The detoxification efficiency reached over 99%. A tentative pathway and mechanism is proposed for explaining the final reactions products. Finally, the process was applied to real PCBs-contaminated soil, containing various amounts of PCBs, with a total success in completely eliminating the toxic polychlorinated compounds.

Chemical remediation and advanced oxidation process of polychlorinated biphenyls in contaminated soils: a review

Polychlorinated biphenyls (PCBs) are synthetic organic compounds ubiquitously distributed worldwide due to their persistence, long-range atmospheric transport, and bioaccumulation. Owing to teratogenic properties, PCBs are a global environmental problem. Different physical, biological, and chemical techniques are utilized for the remediation of PCBs. This review paper discusses the recent development in photocatalytic and chemical techniques for the remediation of PCBs in contaminated soils. In particular, the photocatalytic degradation of PCBs combined with soil washing, Fe-based reductive dichlorination, and advanced oxidation process (Fenton advance oxidation and persulfate oxidation) is discussed and reviewed in detail. The review suggested that advanced oxidation is an efficient remediation technique with 77-99% of removal efficiency of PCBs. Persulfate oxidation is the most suitable technique which could work at normal environmental conditions (such as pH, temperature, soil organic matter (SOM), etc.). Different environmental factors such as pH, temperature, and SOM affect the Fe-based reductive dechlorination and Fenton advance oxidation techniques. The surfactants and organic solvents used in soil washing combined with photocatalytic degradation affect the degradation capability of these techniques. This review will contribute to PCBs degradation by the detailed discussion of development in chemical technique future perspective and research needs.

A catalyzed method to remove polychlorinated biphenyls from contaminated transformer oil

The disposal of polychlorinated biphenyls (PCBs) as persistent organic pollutants from the environment has been normally performed by isolation from soil or water because of their biological activity and toxic potential. In the present investigation, catalytic hydrodehalogenation was used to detoxify PCBs-contaminated transformer oil. All reactions were directed on an oil containing 11.09 wt% of PCBs utilizing palladium supported on multi-walled carbon nanotubes (Pd/MWCNTs). The amount of hexa-chlorine homologues reduced considerably from 5.07% to less than 800 ppm utilizing HDC at the atmosphere of argon. Moreover, the amounts of long half-lives and bioaccumulative congener of PCB 153 decreased considerably from 3.2% to less than 200 ppm. Besides, the quantity of some environmental pollutants like PCB 105 as a mono-ortho-substituted congener decreased considerably. The significant effects of reaction time, reaction temperature, and catalyst concentration on the efficiency were confirmed and modeled through Box-Behnken design. The optimal reaction condition with an efficiency of 96.67% was 70°C, with catalyst loading of 8 wt% and reaction time of 3.23 h. Furthermore, the quantity of turnover frequency of Pd/MWCNTs showed that it has more activity than palladium-carbon active supported in the ambient pressure without utilizing hydrogen gas in transformer oil complex. The study of the kinetic model revealed that the required activation energy (of 12.99 kJ/mol) to remove PCBs from transformer oil utilizing the present catalyst was lower than other catalyzed hydrodechlorination methods.

Long-Term Dechlorination of Polychlorinated Biphenyls (PCBs) in Taihu Lake Sediment Microcosms: Identification of New Pathways, PCB-Driven Shifts of Microbial Communities, and Insights into Dechlorination Potential

Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) is regarded as an alternative approach for in situ remediation and detoxification in the environment. To better understand the process of PCB dechlorination in freshwater lake sediment, a long-term (108 weeks) dechlorination study was performed in Taihu Lake sediment microcosms with nine parent PCB congeners (PCB5, 12, 64, 71, 105, 114, 149, 153, and 170). Within 108 weeks, the total PCBs declined by 32.8%, while parent PCBs declined by 84.8%. PCB dechlorinators preferred to attack meta- and para-chlorines, principally para-flanked meta and single-flanked para chlorines. A total of 58 dechlorination pathways were observed, and 20 of them were not in 8 processes, suggesting the broad spectrum of PCB dechlorination in the environment. Rare ortho dechlorination was confirmed to target the unflanked ortho chlorine, indicating a potential for complete dechlorination. PCBs drove the shifts of the microbial community structures, and putative dechlorinating bacteria were growth-linked to PCB dechlorination. The distinct jump of RDase genes ardA, rdh12, pcbA4, and pcbA5 was found to be consistent with the commencement of dechlorination. The maintained high level of putative dechlorinating phylum Chloroflexi (including Dehalococcoides and o-17/DF-1), genus Dehalococcoides, and four RDase genes at the end of incubation revealed the long-term dechlorination potential. This work provided insights into dechlorination potential for long-term remediation strategies at PCB-contaminated sites.

Insight into degradation mechanism of PCBs from thermal desorption off-gas over iron-based catalysts

Iron-based catalysts were developed to achieve the hydrodechlorination (HDC)/oxidation of polychlorinated biphenyls (PCBs) from thermal desorption off-gas, and Fe₃O₄/γ-Al₂O₃ showed higher dechlorination efficiency than Fe₂O₃/γ-Al₂O₃. The optimal Fe loading resulted in 95.5% degradation efficiency and 76.9% toxicity reduction of gaseous PCBs, and the optimal Fe₃O₄/γ-Al₂O₃ exhibited excellent stability during a 60-h test. The gas chromatography-mass spectrometry analysis of intermediate products indicated the presence of two competitive degradation pathways, namely, hydrodechlorination and oxidation with Fe₃O₄/γ-Al₂O₃ as catalyst. During the first stage (reductive dechlorination), the reductive activity of iron-based catalysts was effectively enhanced in the presence of water, which was confirmed by density functional theory (DFT) calculations. The removal of chlorine atoms was found in the order of meta > para > ortho. During the second stage (oxidation), hydroxyl and superoxide anion radicals were found to attack PCBs on the surface of Fe₃O₄/γ-Al₂O₃. This study provides an insight into the HDC and oxidation mechanism of gaseous PCBs over iron-based catalysts.

Adsorption and Reductive Defluorination of Perfluorooctanoic Acid over Palladium Nanoparticles

Per- and polyfluoroalkyl substances (PFASs) comprise a group of widespread and recalcitrant contaminants that are attracting increasing concern due to their persistence and adverse health effects. This study evaluated removal of one of the most prevalent PFAS, perfluorooctanoic acid (PFOA), in H₂-based membrane catalyst-film reactors (H₂-MCfRs) coated with palladium nanoparticles (Pd⁰NPs). Batch tests documented that Pd⁰NPs catalyzed hydrodefluorination of PFOA to partially fluorinated and nonfluorinated octanoic acids; the first-order rate constant for PFOA removal was 0.030 h^-1, and a maximum defluorination rate was 16 μM/h in our bench-scale MCfR. Continuous-flow tests achieved stable long-term depletion of PFOA to below the EPA health advisory level (70 ng/L) for up to 70 days without catalyst loss or deactivation. Two distinct mechanisms for Pd⁰-based PFOA removal were identified based on insights from experimental results and density functional theory (DFT) calculations: (1) nonreactive chemisorption of PFOA in a perpendicular orientation on empty metallic surface sites and (2) reactive defluorination promoted by physiosorption of PFOA in a parallel orientation above surface sites populated with activated hydrogen atoms (H_ads*). Pd⁰-based catalytic reduction chemistry and continuous-flow treatment may be broadly applicable to the ambient-temperature destruction of other PFAS compounds.

Dechlorination of short-chain chlorinated paraffins by the metal sodium dispersion method

Short-chain chlorinated paraffins (SCCPs) are listed in Annex A (elimination) of the Stockholm Convention on persistent organic pollutants, and products containing SCCPs require detoxification. In the present study, the metal sodium (Na) dispersion method was applied to a wax sample containing SCCPs (58%, C₁₀-C₁₃ and Cl₅-Cl₉) to assess the dechlorination effect. Effective dechlorination of SCCPs was confirmed using 2-L and 20-L reaction systems. The initial concentrations of the wax (5, 10, 20, 30%), reaction time (10, 30, 60, 120, 180 min), and the ratios of the amount of Na dispersion and the initial amount of the wax containing SCCPs (Na/wax ratios; 3.9, 4.4, 5.2) were tested. The destruction efficiency of SCCPs was over 99.999% after 10 min of reaction at 90 °C under several conditions. The initial concentrations of the wax and the Na/wax ratios did not affect the results. The ultralow SCCP contents in exhaust gas from the reaction tank demonstrated a destruction removal efficiency of over 99.999999%. Trace levels of polychlorinated dibenzo-p-dioxins and furans, dioxin-like polychlorinated biphenyls, hexachlorobenzene, and pentachlorobenzene in the wax sample and treated materials (oil, water, and gas) met various regulatory values or exhibited the same levels as the environmental background. After dechlorination of the SCCPs, the main reaction products in the reaction liquid and final oil phase were identified as aliphatic compounds. The metal Na dispersion method was found to be an effective and decontaminated destruction technique for application to SCCPs in liquid-like samples with no formation of hazardous organic byproducts.

Comparison of decabromodiphenyl ether degradation in long-term operated anaerobic bioreactors under thermophilic and mesophilic conditions and the pathways involved

Anaerobic digestion of decabromodiphenyl ether was carried out and compared in two continuously stirred anaerobic bioreactors for 210 days under thermophilic and mesophilic conditions. Results show that the degradation of decabromodiphenyl ether followed the first-order reaction kinetics, which exhibited a higher removal rate in the thermophilic reactor when compared to the mesophilic one, reaching its maximum of 1.1 μg·day^-1. The anaerobic digestion of decabromodiphenyl ether was found to involve the replacement of bromines from polybrominated diphenyl ether by hydrogen atoms, gradually forming nona-, octa- and hepta-brominated diphenyl ether, respectively. Under the thermophilic condition, the reactors were dominated by Bacillus sp. and Methanosarcina sp. with high bioactivity and high concentrations of debromination microorganisms.

Degradation of PCB67 in soil using the heterogenous Fenton process induced by montmorillonite supported nanoscale zero-valent iron

Montmorillonite supported nanoscale zero-valent iron (MMT-nZVI) was prepared and proved to be able to induce the heterogenous Fenton process for better removal of 2,3',4,5-tetrachlorobiphenyl (PCB67) in a long-term polluted soil. PCB67 removal depended highly on the dosages of MMT-nZVI and H₂O₂, and the initial pH, with the highest removal rate of 76.38% at conditions of H₂O₂ 45.99 g·kg^-1, MMT-nZVI 29.88 g·kg^-1 and initial pH 3.5 after 80 min of reaction. Furthermore, PCB67 could be removed in a wider pH range (from 3.5 to near neutrality), with a loss of 13.6% in removal rate at neutral pH. With an activation energy of 21.4 kJ·mol^-1, the degradation of PCB67 was an endothermic and diffusion-controlled process and followed the pseudo-first-order kinetics. That Fe²⁺ was supplied through aerobic corrosion of MMT-nZVI to activate H₂O₂ for·OH production was the possible mechanism of PCB67 degradation, leading to complete mineralization of PCB67 through two proposed pathways, with the intermediates of ethylbenzene and 3-hepten-2-one, as well as dibutyl phthalate and butyl acetate respectively.

Dechlorination of 2,4,4'-trichlorobiphenyl by magnetoferritin with different loading factors

Polychlorinated biphenyls are synthetic industrial organic substances. These persistent pollutants occur in nature causing high ecological risks and damage to human health. Magnetoferritin nanoparticles composed of apoferritin protein shell surrounding synthetically prepared iron-based nanoparticles seem to be a promising candidate for polychlorinated biphenyls elimination. Properties of magnetoferritin, as a redox activity, a biocompatible character, high application possibilities and a close relationship with the human body promoted ours in vitro investigation of the magnetoferritin catalytic activity in the presence of representative 2,4,4'-trichlorobiphenyl. Basic physico-chemical properties of magnetoferritin were determined by ultraviolet and visible spectrophotometry, dynamic light scattering, zeta potential measurements, superconducting quantum interference device magnetometry and atomic force microscopy. The remediation effect of magnetoferritin on 2,4,4'-trichlorobiphenyl was demonstrated by the use of gas chromatography in combination with infrared spectroscopy.

Nanoporous metal-polymer composite membranes for organics separations and catalysis

Metallic thin-film composite membranes are produced by sputtering metal films onto commercial polymer membranes. The separations capability of the membrane substrate is enhanced with the addition of a 10 nm Ta film. The addition of a tantalum layer decreases the molecular weight cutoff of the membrane from 70 kDa dextran (19 nm) to below 5 kDa (6 nm). Water flux drops from 168 LMH/bar (LMH: liters/meters2/hour) (polymer support) to 8.8 LMH/bar (Ta composite). A nanoporous layer is also added to the surface through Mg/Pd film deposition and dealloying. The resulting nanoporous Pd is a promising catalyst with a ligament size of 4.1 ± 0.9 nm. The composite membrane's ability to treat water contaminated with chlorinated organic compounds (COCs) is determined. When pressurized with hydrogen gas, the nanoporous Pd composite removes over 70% of PCB-1, a model COC, with one pass. These nanostructured films can be incorporated onto membrane supports enabling diverse reactions and separations.

Recent advances in the removal of persistent organic pollutants (POPs) using multifunctional materials:a review

Persistent organic pollutants (POPs) have gained heightened attentions in recent years owing to their persistent property and hazard influence on wild life and human beings. Removal of POPs using varieties of multifunctional materials have shown a promising prospect compared with conventional treatments. Herein, three main categories, including thermal degradation, electrochemical remediation, as well as photocatalytic degradation with the use of diverse catalytic materials, especially the recently developed prominent ones were comprehensively reviewed. Kinetic analysis and underlying mechanism for various POPs degradation processes were addressed in detail. The review also systematically documented how catalytic performance was dramatically affected by the nature of the material itself, the structure of target pollutants, reaction conditions and treatment techniques. Moreover, the future challenges and prospects of POPs degradation by means of multiple multifunctional materials were outlined accordingly. Knowing this is of immense significance to enhance our understanding of POPs remediation procedures and promote the development of novel multifunctional materials.

Defunctionalisation catalysed by boron Lewis acids

Selective defunctionalisation of organic molecules to valuable intermediates is a fundamentally important transformation in organic synthesis. Despite the advances made in efficient and selective defunctionalisation using transition-metal catalysis, the cost, toxicity, and non-renewable properties limit its application in industrial manufacturing processes. In this regard, boron Lewis acid catalysis has emerged as a powerful tool for the cleavage of carbon-heteroatom bonds. The ground-breaking finding is that the strong boron Lewis acid B(C6F5)3 can activate Si-H bonds through η1 coordination, and this Lewis adduct is a key intermediate that enables various reduction processes. This system can be tuned by variation of the electronic and structural properties of the borane catalyst, and together with different hydride sources high chemoselectivity can be achieved. This Perspective provides a comprehensive summary of various defunctionalisation reactions such as deoxygenation, decarbonylation, desulfurisation, deamination, and dehalogenation, all of which catalysed by boron Lewis acids.

Promoted liquid-phase hydrodechlorination of chlorophenol over Raney Ni via controlling base: Performance, mechanism, and application

The potential effect of base on Raney Ni-catalyzed hydrodechlorination (HDC) of chlorophenol was studied. Compared to weak inorganic bases, strong inorganic bases (NaOH and KOH) and triethylamine (Et₃N) were more favorable to promote Raney Ni-catalyzed HDC reaction. Moreover, a stoichiometric amount of NaOH/Et₃N was found to be optimal for the HDC reaction, and up to 100% conversion of 4-chlorophenol was achieved within 30 min. Catalyst characterization (SEM, EDXS, and XRD) combined with ICP-OES analysis were introduced to better understand the mechanism for the promoted effect of base on the HDC reaction. The results showed that the optimal amount of strong inorganic bases and Et₃N efficiently eliminated HCl corrosion to Raney Ni, greatly reduced the active phase Ni and Al leaching, and avoided collapse of the catalyst framework. Based on the mechanism, the best bases and their optimal amount were developed for further disposal of polychlorinated phenols, and excellently stepwise HDC of polychlorinated phenols was achieved. Recycling tests showed that Raney Ni could be reused at least 5 times for the HDC reaction with the stoichiometric amount of NaOH, which was a promising option for the HDC of wastewater containing chlorophenols over Raney Ni.

Dechlorination and conversion mechanism of trichlorobenzene as a model compound of chlorine-containing wastes by different base-catalyzed combinations

Chlorine-containing organic waste (COWs) is a big threat for the waste incineration because of the dioxin generation and equipment corrosion. Recently, dechlorination and detoxification of COWs is emergent in order to lower the environmental risk and treatment costs. In this study, base-catalyzed decomposition processes with different hydroxides, hydrogen donors, and catalysts were conducted for pre-treatment of COWs to reduce organic chlorine content, with the TCB as a model compound and industrial rectification residues for verification. Results showed that maximum chlorine retention efficiency (CRE) of four alkalis followed the order of KOH > NaOH-KOH > NaOH > Mg(OH)₂, which were 98.3%, 93.4%, 97.2%, and 1.5%, respectively, and could be expressed as an apparent first-order reaction. The differences were resulted from the varying ionic potentials of the metal cations. Hydrogen donors (glycol, glycerol, paraffin oil, and PEG 200) acted as effective dechlorination regents follow the order of PEG > glycol > paraffin oil > glycerol. In addition, Fe, Ni, Cu, and activated carbon catalysts increased the CRE by 68.9% to 92.4%, 91.9%, 89.2%, and 73.3%, respectively. Residue analysis through X-ray diffraction and Fourier transform infrared spectroscopy revealed that KCl, sodium oxalate, and phenol were the main products and a plausible stepwise dechlorination pathway was proposed. The effectiveness of three optimized combinations including NaOH/PEG, KOH/PEG, and NaOH-KOH/PEG (with the Fe catalyst) was confirmed by using them for dechlorinating rectification residues, and they restrained 98.2%, 91.2%, and 94.6% of the chlorine, respectively. The organochlorine content decreased from 19.2 to 1.8% within 180 min, while inorganic chorine content increased from 1.5 to 18.9%, indicating the potential for COWs dechlorination.

Performance and toxicity assessment of nanoscale zero valent iron particles in the remediation of contaminated soil: A review

Nanoscale zero valent iron (nZVI) particles have been studied in recent years as a promising technology for the remediation of contaminated soil. Although the potential benefits of nZVI are considerable, there is a distinct need to identify possible risks after environmental exposure to nZVI. This work firstly introduced the remediation of nZVI for heavy metals and chlorinated organic compounds in contaminated soil. And the corresponding stabilization mechanisms were discussed. We also highlighted the factors affecting nZVI reactivity, including nZVI surface area, nZVI stabilizers, soil pH, soil organic matter and soil types. In addition, this review shows a critical overview of the current understanding of toxicity of nZVI particles to soil bacteria and fungi. The toxicity mechanisms, cellular defenses behaviors and the factors affecting the toxicity of nZVI were summarized. Finally, the remaining barriers to be overcome in materials development for environment application are also discussed.

Base-catalysed decomposition of polychlorinated biphenyls in transformer oils by mixture of sodium hydroxide, glycerol and iron

In this research, a method based on base-catalysed decomposition (BCD) was developed using sodium hydroxide and glycerol for dechlorination of transformer oils with low levels of polychlorinated biphenyls (PCBs). PCB removal and dechlorination efficiencies were measured by gas chromatography and the silver nitrate titration method, respectively. PCB dechlorination and removal efficiencies after 4 h at 250°C and in the presence of iron were 97.4% and 99.8%, respectively. However, in the absence of iron the same efficiencies were calculated to be 79.4 and 99.7%, respectively. The dielectric loss factor of oil refined at 250°C was 0.0064 and did not meet the required standards to be reused in the transformers. However, that refined at 200°C satisfied the standards with acceptable conversion rates. Use of iron, besides increasing conversion rates, changed the mechanism of the reaction from nucleophilic substitution to a combination of hydrodechlorination and nucleophilic substitution. In the presence of iron, highly chlorinated PCBs were converted to less chlorinated PCBs, and this caused the concentration of less chlorinated PCBs to reach a peak and then decline thereafter. The production of PCB 36 confirmed this. However, in the absence of iron particles, all changes in the PCB concentration curves were downward.

Photodegradation behaviors of polychlorinated biphenyls in methanol by UV-irradiation: Solvent adducts and sigmatropic arrangement

This study has investigated the photolysis of polychlorinated biphenyls (PCBs) in methanol solution under UV irradiation. The results showed that the PCBs containing ortho-chlorine can generate both hydroxylated and methoxylated PCBs (HO-PCBs and MeO-PCBs), while the PCBs with a meta-chlorine but without ortho-chlorine can only generate MeO-PCBs as the only solvent adducts. No solvent adducts were detected during the photochemical reaction of 4-chlorobiphenyl (PCB-3), indicating the para-chlorine cannot be attacked by solvent molecule to form correspondent solvent adducts. The sigmatropic rearrangement was found during the photochemical reaction of ortho-substituted PCBs, but cannot occur in the reaction of PCBs with only meta- or para-chlorine, indicating that ortho-chlorine played a vital role in the sigmatropic rearrangement reaction. In addition, the seteric hindrance can also lead to the generation of sigmatropic rearrangement products. The effect of solvent was investigated in the case of photochemical reaction of 2-chlorobiphenyl (PCB-1), the results showed that sigmatropic rearrangement can occur in different solvents, and corresponding solvent adducts were generated in the photochemical reaction of PCB-1 in different solvents.

Species and Sex Differences in the Morphogenic Response of Primary Rodent Neurons to 3,3'-Dichlorobiphenyl (PCB 11)

PCB 11 is an emerging global pollutant that we recently showed promotes axonal and dendritic growth in primary rat neuronal cell cultures. Here, we address the influence of sex and species on neuronal responses to PCB 11. Neuronal morphology was quantified in sex-specific primary hippocampal and cortical neuron-glia co-cultures derived from neonatal C57BL/6J mice and Sprague Dawley rats exposed for 48 h to vehicle (0.1% DMSO) or PCB 11 at concentrations ranging from 1 fM to 1 nM. Total axonal length was quantified in tau-1 immunoreactive neurons at day in vitro (DIV) 2; dendritic arborization was assessed by Sholl analysis at DIV 9 in neurons transfected with MAP2B-FusRed. In mouse cultures, PCB 11 enhanced dendritic arborization in female, but not male, hippocampal neurons and male, but not female, cortical neurons. In rat cultures, PCB 11 promoted dendritic arborization in male and female hippocampal and cortical neurons. PCB 11 also increased axonal growth in mouse and rat neurons of both sexes and neuronal cell types. These data demonstrate that PCB 11 exerts sex-specific effects on neuronal morphogenesis that vary depending on species, neurite type, and neuronal cell type. These findings have significant implications for risk assessment of this emerging developmental neurotoxicant.

Considerations on the mechanism of Ca/ethanol/Pd/C assisted hydrodechlorination of chlorinated aromatic substrates

In order to elucidate the metal-alcohol hydrodechlorination reaction mechanism, several experiments using chloroanisoles as substrates were performed. Thus, chloroanisoles were stirred at 60 °C for 2 h with a mixture of Ca, methanol and various reduction catalysts. The use of deuterated methanol and zeta potential experiments offered supplementary informations, pointing toward a probable radicalic mechanism that occurs on Ca and Pd/C surfaces.

Application of microwave irradiation for the removal of polychlorinated biphenyls from siloxane transformer and hydrocarbon engine oils

The removal of polychlorinated biphenyls (PCBs) both from siloxane transformer oil and hydrocarbon engine oil was investigated through the application of microwave (MW) irradiation and a reaction system based on polyethyleneglycol (PEG) and potassium hydroxide. The influence of the main reaction parameters (MW irradiation time, molecular weight of PEG, amount of added reactants and temperature) on the dechlorination behavior was studied. Promising performances were reached, allowing about 50% of dechlorination under the best experimental conditions, together time and energy saving compared to conventional heating systems. Moreover, an interesting dechlorination degree (up to 32%) was achieved for siloxane transformer oil when MW irradiation was employed as the unique driving force. To the best of our knowledge, this is the first time in which MW irradiation is tested as the single driving force for the dechlorination of these two types of PCB-contaminated oils.

Application of aluminum-supported Pd, Rh, and Rh-Pd nanoparticles in supercritical carbon dioxide system for hydrodebromination of polybrominated diphenyl ethers

Al-powder-supported Pd, Rh, and Rh-Pd catalysts were synthesized through a spontaneous redox reaction in aqueous solutions. These catalysts hydrodebrominated 4- and 4,4'-bromodiphenyl ethers in supercritical carbon dioxide at 200 atm CO2 containing 10 atm H2 and 80 °C in 1 h. Diphenyl ether was the major product of Pd/Al. Rh/Al and Rh-Pd/Al further hydrogenated two benzene rings of diphenyl ether to form dicyclohexyl ether. The hydrogenolysis of CO bonds on diphenyl ether over Rh/Al and Rh-Pd/Al was observed to generate cyclohexanol and cyclohexane (<1%). With respect to hydrodebromination efficiency and catalyst stability, Rh-Pd/Al among three catalysts is suggested to be used for ex situ degradation of polybrominated diphenyl ethers in supercritical carbon dioxide.

Degradation of lindane and hexachlorobenzene in supercritical carbon dioxide using palladium nanoparticles stabilized in microcellular high-density polyethylene

Palladium nanoparticles stabilized in microcellular high-density polyethylene prepared through supercritical foaming, supercritical impregnation, and H2 reduction are used for the hydrodechlorination of lindane and hexachlorobenzene in supercritical carbon dioxide below 100 °C. Both lindane and hexachlorobenzene can be almost 100% transformed to cyclohexane in 1 h. Reaction intermediates, such as lower chlorinated products or benzene, are not observed or exist in trace amount indicating that most of them may undergo reactions without leaving the metal surface.

Enhanced anaerobic dechlorination of polychlorinated biphenyl in sediments by bioanode stimulation

The application of a low-voltage electric field as an electron donor or acceptor to promote the bioremediation of chlorinated organic compounds represents a promising technology meeting the demand of developing an efficient and cost-effective strategy for in situ treatment of PCB-contaminated sediments. Here, we reported that bioanode stimulation with an anodic potential markedly enhanced dechlorination of 2,3,4,5-tetrachlorobiphenyl (PCB 61) contained in the sediment at an electronic waste recycling site of Qingyuan, Guangdong, China. The 110-day incubation of the bioanode with a potential poised at 0.2 V relative to saturated calomel electrode enabled 58% transformation of the total PCB 61 at the initial concentration of 100 μmol kg(-1), while only 23% was reduced in the open-circuit reference experiment. The introduction of acetate to the bioelectrochemical reactor (BER) further improved PCB 61 transformation to 82%. Analysis of the bacterial composition showed significant community shifts in response to variations in treatment. At phylum level, the bioanode stimulation resulted in substantially increased abundance of Actinobacteria, Bacteroidetes, and Chloroflexi either capable of PCB dechlorination, or detected in the PCB-contaminated environment. At genus level, the BER contained two types of microorganisms: electrochemically active bacteria (EAB) represented by Geobacter, Ignavibacterium, and Dysgonomonas, and dechlorinating bacteria including Hydrogenophaga, Alcanivorax, Sedimentibacter, Dehalogenimonas, Comamonas and Vibrio. These results suggest that the presence of EAB can promote the population of dechlorinating bacteria which are responsible for PCB 61 transformation.

Rational design of nanomaterials for water treatment

The ever-increasing human demand for safe and clean water is gradually pushing conventional water treatment technologies to their limits. It is now a popular perception that the solutions to the existing and future water challenges will hinge upon further developments in nanomaterial sciences. The concept of rational design emphasizes on 'design-for-purpose' and it necessitates a scientifically clear problem definition to initiate the nanomaterial design. The field of rational design of nanomaterials for water treatment has experienced a significant growth in the past decade and is poised to make its contribution in creating advanced next-generation water treatment technologies in the years to come. Within the water treatment context, this review offers a comprehensive and in-depth overview of the latest progress in rational design, synthesis and applications of nanomaterials in adsorption, chemical oxidation and reduction reactions, membrane-based separation, oil-water separation, and synergistic multifunctional all-in-one nanomaterials/nanodevices. Special attention is paid to the chemical concepts related to nanomaterial design throughout the review.

Treatment of a suspension of PCB contaminated soil using iron nanoparticles and electric current

Contaminated soils and sediments with polychlorinated biphenyls (PCB) are an important environmental problem due to the persistence of these synthetic aromatic compounds and to the lack of a cost-effective and sustainable remediation technology. Recently, a new experimental setup has been proposed using electrodialytic remediation and iron nanoparticles. The current work compares the performance of this new setup (A) with conventional electrokinetics (setup B). An historically contaminated soil with an initial PCB concentration of 258 μg kg(-1) was treated during 5, 10, 20 and 45 d using different amounts of iron nanoparticles in both setups A and B. A PCB removal of 83% was obtained in setup A compared with 58% of setup B. Setup A also showed additional advantages, such as a higher PCB dechlorination, in a shorter time, with lower nZVI consumption, and with the use of half of the voltage gradient when compared with the traditional setup (B). Energy and nZVI costs for a full-scale reactor are estimated at 72 € for each cubic meter of PCB contaminated soil treated on-site, making this technology competitive when compared with average off-site incineration (885 € m(-3)) or landfilling (231 € m(-3)) cost in Europe and in the USA (327 USD m(-3)).

Synergistical enhancement by Ni2+ and Tween-80 of nanoscale zerovalent iron dechlorination of 2,2',5,5'-tetrachlorinated biphenyl in aqueous solution

Effective dehalogenation by nanoscale zerovalent iron (nZVI) has been reported. In this study, the effects of Ni(2+), Cu(2+) ions, and the nonionic surfactant Tween-80 on dechlorination of 2,2',5,5'-tetrachlorinated biphenyl (PCB-52) by nZVI were investigated in aqueous solution. The rate of dechlorination was significantly enhanced by Ni(2+), while Cu(2+) had a less significant catalytic effect. Ni(2+) and Tween-80 used in combination synergistically enhanced dechlorination of PCB-52 by nZVI, although the enhancement by Tween-80 was inhibitory in the presence of Cu(2+) and insignificant in the absence of both metal ions. Congener specificity in the dechlorination pathway resulted from the preferential retention of ortho-chlorine, which restricted the formation of environmentally toxic coplanar PCB congeners. The application of nZVI dehalogenation enhanced by Ni(2+) and Tween-80 is a promising technique for posttreatment of PCB-contaminated soil washing solutions.

Thermal desorption of PCBs from contaminated soil using nano zerovalent iron

In this study, thermal desorption was combined with the addition of nano zerovalent iron (nZVI) to remediate polychlorinated biphenyl (PCB)-contaminated soil collected from a storage point for PCB-contaminated capacitors and transformers. The thermal desorption test conditions were varied from 300 to 600 °C, both with blank soil and with 100 mg of nZVI added. Next, the effect of the amount of nZVI added (0, 20, 40, 100, 200 mg) was investigated by thermal treatment at 400 °C. The test results show that thermal desorption eliminates most of the PCB load and that the presence of nZVI clearly enhances thermal desorption. After thermal treatment at 400 °C, a removal efficiency of 94.2 % was reached, with the use of 200 mg of nZVI. At 600 °C, the PCB removal efficiency after 1 h attained 98.35 % with 100 mg of nZVI and 97.40 % without nZVI. The presence of nZVI effectively decreased both the sum and the WHO-TEQ value of the 12 dl-PCBs.

Long-term potential of in situ chemical reduction for treatment of polychlorinated biphenyls in soils

Polychlorinated biphenyls (PCBs) are well-known for being hydrophobic and persistent in the environment. Although many treatment approaches have been demonstrated to result in degradation of PCBs in water or water/cosolvent systems, few examples exist where such approaches have been applied successfully for PCB degradation in soil-water systems. A possible explanation for the limited treatment of PCBs in soil-water systems is that reactants that are capable of degrading PCBs in the aqueous phase are unlikely to persist long enough to achieve meaningful treatment of slowly-desorbing PCBs associated with the soil phase. To investigate this explanation, laboratory studies were conducted to evaluate chemical reductants, including zero valent metals, palladium (Pd) catalyst, and emulsified zero valent iron (EZVI), for dechlorination of PCBs in the presence and absence of soil. In the absence of soil, Pd-catalyzed treatments (Pd with electrolytic ZVI or iron/aluminum alloy) achieved rapid destruction of a model PCB congener, 2-chlorobiphenyl, with half-lives ranging from 43 to 110 min. For treatment of soils containing Aroclor 1248 at an initial concentration of approximately 1,500 mg kg(-1), Pd-catalyzed treatments achieved no measurable enhancement over the background PCB depletion rate (i.e., that measured in the untreated control) of 5.3 mg kg(-1)week(-1). In the presence of soils, EZVI was the only approach evaluated that resulted in a clear enhancement in PCB dechlorination rates. EZVI achieved PCB concentration reductions of greater than 50% at an average rate of 19 mg kg(-1)week(-1). The results suggest that slow PCB desorption limits treatment effectiveness in soils.

Reactivity of polychlorinated biphenyls in nucleophilic and electrophilic substitutions

To explain the chemical reactivity of polychlorinated biphenyls in nucleophilic (S(N)) and electrophilic (S(E)) substitutions, quantum chemical calculations were carried out at the B3LYP/6-31G(d) level of the Density Functional Theory in gas phase. Carbon atomic charges in biphenyl structure were calculated by the Atoms-in-Molecules method. Chemical hardness and global electrophilicity index parameters were determined for congeners. A comparison of calculated descriptors and experimental data for congener reactivity in the S(N) and S(E) reactions was made. It is shown that interactions in the S(N) mechanism are reactions of the hard acid-hard base type, these are the most effective in case of highly chlorinated substrates. To explain the congener reactivity in the SE reactions, correct descriptors were not established. The obtained results can be used to carry out chemical transformations of the polychlorinated biphenyls in order to prepare them for microbiological destruction or preservation.

Improved 4-chlorophenol dechlorination at biocathode in bioelectrochemical system using optimized modular cathode design with composite stainless steel and carbon-based materials

This study developed and optimized a modular biocathode materials design in bioelectrochemical system (BES) using composite metal and carbon-based materials. The 4-chlorophenol (4-CP) dechlorination could be improved with such composite materials. Results showed that stainless steel basket (SSB) filled with graphite granules (GG) and carbon brush (CB) (SSB/GG/CB) was optimum for dechlorination, followed by SSB/CB and SSB/GG, with rate constant k of 0.0418 ± 0.0002, 0.0374 ± 0.0004, and 0.0239 ± 0.0002 h(-1), respectively. Electrochemical impedance spectroscopy (EIS) demonstrated that the composite materials with metal can benefit the electron transfer and decrease the charge transfer resistance to be 80.4 Ω in BES-SSB/GG/CB, much lower than that in BES-SSB (1674.3 Ω), BES-GG (387.3 Ω), and BES-CB (193.8 Ω). This modular cathode design would be scalable with successive modules for BES scale-up, and may offer useful information to guide the selection and design of BES materials towards dechlorination improvement in wastewater treatment.

Novel Fe-Pd/SiO2 catalytic materials for degradation of chlorinated organic compounds in water

Novel reactive materials for catalytic degradation of chlorinated organic compounds in water at ambient conditions have been prepared on the basis of silica-supported Pd-Fe nanoparticles. Nanoscale Fe-Pd particles were synthesized inside porous silica supports using (NH4)3[Fe(C2O4)3] and [Pd(NH3)4]Cl2 or Pd acetate as reaction precursors. According to temperature programmed reduction (TPR) studies, Pd introduction decreased the reduction temperature of the supported Fen+ species and nearly complete reduction with H2 was observed at 400 °C. The successful surface loading with Pd was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Characterization of the samples by X-ray diffraction (XRD) and X-ray absorption near-edge structure + extended X-ray absorption fine structure (XANES + EXAFS) verified the presence of highly dispersed Pd0, Pdx Fe1–x and Fe0 phases. Reduction of the supported precursors in hydrogen resulted in materials that were highly active in perchloroethene (PCE) degradation and 2-chlorobiphenyl (2-ClBP) dechlorination. It was found that highly dispersed amorphous Fe-Pd bimetallic nanoparticles on silica support showed superior catalytic activity against PCE dechlorination in comparison to the free-standing Fe-Pd nanoparticles. For the samples with the same Fe content, the conversion of chlorinated organics as well as the stability increased with the Pd loading, e.g., the most effective degradation of PCEs and 2-ClBP was achieved at a Pd loading of 2.3–3.2 wt. %.