Effects of metals on the transformation of hexabromocyclododecane (HBCD) in solvents: implications for solvent-based recycling of brominated flame retardants

Synthesis and characterization of novel guar gum based waste material derived nanocomposite for effective removal of hexabromocyclododecane and lindane

Herein, efficient degradation of hexabromocyclododecane (HBCD) and Lindane, a persistent organic pollutant using guar gum based calcium oxide doped silicon dioxide (GG-CaO@SiO2) has been reported. The nanocomposite was prepared by waste egg shell (CaO) and rice husk (SiO2) was well characterized. The maximum degradation of HBCD and Lindane were observed at 8 mg catalyst loading, neutral pH, and 2 mg L-1 of pollutant amount. The photocatalytic performance of GG-CaO@SiO2 for HBCD and Lindane photodegradation was evaluated, and it was found that the rate constant increased in the order of GG-CaO@SiO2 > CaO@SiO2 > GG. The polymeric GG-CaO@SiO2 nanocomposite showed maximum removal of both pollutants due to higher surface area (70 m2 g-1) and synergistic interactions among GG moieties. It achieved HBCD and Lindane elimination rates of 94 % and 90 % by photo-adsorptive degradation within 150 min. Meanwhile, the leaching of HBCD from expanded polystyrene (EPS) materials (0.14 ± 0.05 ppm) underwater with different time intervals and degradation of leachate HBCD were also assessed. The eradication of the pollutant manifested first-order kinetics, with the Langmuir adsorption. LC-MS analysis confirmed that GG-CaO@SiO2 effectively breaks down complex structure toxic pollutants into safer metabolites under natural sunlight exposure. The polymeric GG-CaO@SiO2 nanocomposite showed notable reusability up to ten cycle promotes sustainability.

Community reassemblies of eukaryotes, prokaryotes, and viruses in the hexabromocyclododecanes-contaminated microcosms

The microbial community in seriously contaminated environment were not well known. This research investigated the community reassemblies in microcosms made of two distinct mangrove sediments amended with high levels of hexabromocyclododecanes (HBCDs). After eight months of contamination, the transformation of HBCDs yielded various lower brominated products and resulted in acidification (pH ~2). Therefore, the degraders and dehalogenase homologous genes involved in transformation of HBCDs only presented in low abundance to avoid further deterioration of the habitats. Moreover, in these deteriorated habitats, 1344 bacterial, 969 archaeal, 599 eukaryotic (excluded fungi), 187 fungal OTUs, and 10 viral genera, were reduced compared with controls. Specifically, in two groups of microcosms, Zetaproteobacteria, Deinococcus-Thermus, Spirochaetes, Bacteroidetes, Euryarchaeota, and Ascomycota, were positively responding taxa to HBCDs. Caloneis (Bacillariophyta) and Ascomycota turned to the dominant eukaryotic and fungal taxa. Most of predominant taxa were related to the contamination of brominated flame retardants (BFRs). Microbial communities were reassembled in divergent and sediment-dependent manner. The long-term contamination of HBCDs leaded to the change of relations between many taxa, included some of the environmental viruses and their known hosts. This research highlight the importance of monitoring the ecological effects around plants producing or processing halogenated compounds.

Removal of polybrominated diphenyl ethers in high impact polystyrene (HIPS) from waste TV sets

Most studies have shown that improper disposal of e-waste can accelerate the release of high concentrations of polybrominated diphenyl ethers (PBDEs), and this situation causes environmental pollution and human health risks. The recycling technology of waste electronic plastics based on solvent processes can reduce environmental pollution and health risks from PBDEs. In this study, high impact polystyrene (HIPS) from waste TV sets was taken as the research object, and d-limonene and n-propanol were used as solvent and precipitant, respectively. We studied the relationship between the precipitation conditions and the size of precipitate particles, and the effect laws of precipitation conditions on the removal percentage of PBDEs were discussed. Transferring behavior of PBDEs during precipitation was investigated, and the parameters suitable for removing PBDEs from HIPS solution were confirmed. Results showed that lower HIPS concentration in d-limonene, lower precipitation temperature, higher mass ratio of n-propanol to HIPS solution, and greater stirring speed were conducive to form smaller and more uniform precipitate particles. All conditions (concentration, temperature, mass ratio, and stirring rate) that could increase the solubility of PBDEs in the mixed solvent of limonene and n-propanol or decrease the swelling degree of HIPS precipitate particles, or reduce the size of particles could improve the removal percentage of PBDEs. The investigated results indicated that insoluble PBDEs (e.g., decabromodiphenyl ether) transferred into the HIPS precipitate mainly through the generated crystals and then precipitated together with the HIPS particles, and soluble PBDEs (e.g., octabromodiphenyl ether) migrated into the precipitate by the solution entrained. The precipitate particles, which measured approximately 1.0 mm (on average), were obtained when the solution containing 10% of HIPS from waste TV shell was precipitated by adding n-propanol equivalent to twice the mass of the solution at 40 °C and 3000 r/min stirring speed. The total concentration of PBDEs in the precipitate particles (dried) was reduced to 2369 mg/kg, and 88.06% of the PBDEs in the original plastic solution was successfully removed by this process.

Transformation of HBCDs by Rhodococcus sp. stu-38

1,2,5,6,9,10-Hexabromocyclododecanes (HBCDs) are brominated flame retardants causing serious environmental pollution. HBCDs in the environment could be transformed to various products. Identification of transformation products has been performed using various mass-spectrometric techniques. However, bacterial transformation of HBCDs yielding low-level products was not well studied. In this paper, a Rhodococcus strain stu-38 which could stereoselectively transform HBCDs in mineral salt medium, seawater, and growth medium was isolated. Seven potential biotransformation products of HBCDs were identified by using GC-MS. These products, including brominated alkenes, dibromocyclododecadiene and bromocyclododecatriene; brominated alkenols, bromocyclododecadienol and bromocyclododecatrienol; fully debrominated compounds, cyclododecadiendiol, 1,2-epoxy-5,9-cyclododecadiene, and cyclododecadienol, were presented in rather low level which could lead to false negative results. The low-level transformation products should not be ignored because their toxicity was less assessment. This research highlighted identification of the low-level transformation products to reveal the complicated stereoselective biotransformation of HBCDs.

Novel trends in the thermo-chemical recycling of plastics from WEEE containing brominated flame retardants

The amount of plastics from waste electric and electronic equipment (WEEE) has enormously increased nowadays, due to the rapid expansion and consumption of electronic devices and their short lifespan. This, in combination with their non-biodegradability, led to the need to explore environmentally friendly solutions for their safe disposal. One main obstacle when recycling plastics from WEEE is that they usually comprise harmful additives such as brominated flame retardants (BFRs) that need to be removed before or during their recycling. This paper reviews existing techniques for the recycling of plastics from WEEE and focuses specifically on the advantages, disadvantages, and challenges of pyrolysis as an environmentally friendly method for the production of value-added materials (monomers, hydrocarbons, phenols, etc.). Current technological trends available for the recycling of plastics containing brominated flame retardants are reviewed in an attempt to provide insights for future research on the sustainable management of plastics from WEEE. Emphasis is given on conventional pyrolysis, where a pretreatment step for the debromination of products is applied. This is required since brominated compounds treated at high temperatures may result in the production of harmful to health compounds such as dioxins. All current pretreatment methods (solvent extraction, supercritical fluid technology, etc.) are presented and compared in detail. Co-pyrolysis is also investigated, as it seems to be a very interesting approach, since no catalysts or solvents are used, and at the same time, more plastic wastes can be consumed as feedstock. Furthermore, catalytic pyrolysis along with key parameters, such as the type of the catalyst or pyrolysis temperature, are fully analyzed. Catalysts affect the products' distribution and enhance the removal of bromine from pyrolysis oils. Finally, an emerging technique, that of microwave-assisted pyrolysis, is also highlighted, as it offers many advantages over conventional pyrolysis. Of course, there are some impediments, such as the operational costs or other difficulties as regards the industrial implementation of the mentioned techniques that need to be overcome through future works.

Chemical Recycling of WEEE Plastics—Production of High Purity Monocyclic Aromatic Chemicals

More than 200 kg real waste electrical and electronic equipment (WEEE) shredder residues from a German dismantling plant were treated at 650 °C in a demonstration scale thermochemical conversion plant. The focus within this work was the generation, purification, and analysis of pyrolysis oil. Subsequent filtration and fractional distillation were combined to yield basic chemicals in high purity. By means of fractional distillation, pure monocyclic aromatic fractions containing benzene, toluene, ethylbenzene, and xylene (BTEX aromatics) as well as styrene and α-methyl styrene were isolated for chemical recycling. Mass balances were determined, and gas chromatography–mass spectrometry (GC-MS) as well as energy dispersive X-ray fluorescence (EDXRF) measurements provided data on the purity and halogen content of each fraction. This work shows that thermochemical conversion and the subsequent refining by fractional distillation is capable of recycling WEEE shredder residues, producing pure BTEX and other monocyclic aromatic fractions. A significant decrease of halogen content (up to 99%) was achieved with the applied methods.

Solvent effects on quantitative analysis of brominated flame retardants with Soxhlet extraction

Reliable quantifications of brominated flame retardants (BFRs) not only ensure compliance with laws and regulations on the use of BFRs in commercial products, but also is key for accurate risk assessments of BFRs. Acetone is a common solvent widely used in the analytical procedure of BFRs, but our recent study found that acetone can react with some BFRs. It is highly likely that such reactions can negatively affect the quantifications of BFRs in environmental samples. In this study, the effects of acetone on the extraction yields of three representative BFRs [i.e., decabrominated diphenyl ether (decaBDE), hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA)] were evaluated in the Soxhlet extraction (SE) system. The results showed that acetone-based SE procedure had no measureable effect for the recovery efficiencies of decaBDE but could substantially lower the extraction yields for both TBBPA and HBCD. After 24 h of extraction, the recovery efficiencies of TBBPA and HBCD by SE were 93 and 78% with acetone, 47 and 70% with 3:1 acetone:n-hexane, and 82 and 94% with 1:1 acetone:n-hexane, respectively. After 72 h of extraction, the extraction efficiencies of TBBPA and HBCD decreased to 68 and 55% with acetone, 0 and 5% with 3:1 acetone/n-hexane mixtures, and 0 and 13% with 1:1 acetone/n-hexane mixtures, respectively. The study suggested that the use of acetone alone or acetone-based mixtures should be restricted in the quantitative analysis of HBCD and TBBPA. We further evaluated nine alternative solvents for the extraction of the three BFRs. The result showed that diethyl ether might be reactive with HBCD and may not be considered as the alternative to acetone used solvents for the extraction of HBCD.

Catalytic dehydrochlorination of lindane by nitrogen-containing multiwalled carbon nanotubes (N-MWCNTs)

This paper reports a nonreductive dechlorination pathway (dehydrochlorination) of lindane in the presence of N-MWCNTs (CNT-N1 and CNTN2) under environmentally relevant conditions. The enhanced catalytic dehydrochlorination at mild pH values (7.0-9.0) was mainly attributed to the Lewis base nature of nitrogen functional groups on the surface of N-MWCNTs, based on FT-IR spectra, X-ray photoelectron spectroscopy and CO₂-TPD profile. Amine and pyridinic nitrogen species were inferred as the main basic sites that were responsible for the dehydrochlorination of lindane. The concentration of lindane was unchanged in homogenous alkaline aqueous solutions at pH7.0 and 8.0 within 6 d, and up to 89.5% of lindane remained at pH9.0. In sharp contrast, the reaction rate constant (k_obs) increased from 0.024 to 0.876 d^-1 with the increasing pH from 7.0 to 9.0 when CNT-N2 catalyst was used. All lindane was transformed in the presence of CNT-N2 at pH9.0, leading to a much greater k_obs as compared to that obtained in homogenous solution (0.876 vs 0.019 d^-1). Even at neutral pH condition, the k_obs obtained in the presence of CNT-N2 was higher than that observed in weakly alkaline solution (0.024 d^-1 at pH7.0 vs 0.019 d^-1 at pH9.0). γ-1,3,4,5,6-pentachlorocyclohexene and trichlorobenzene isomers were detected as the intermediate and final products, respectively. It might be inferred that amine and pyridinic nitrogen species could attack the hydrogen atom attached to the β‑carbon, and the dehydrochlorination of lindane followed a β-elimination mechanism. This study provides an alternative dechlorination way for making lindane less toxic and better biodegradable under mild conditions, which is beneficial for complete mineralization of lindane when coupled with microbial degradation.

Abiotic transformation of hexabromocyclododecane by sulfidated nanoscale zerovalent iron: Kinetics, mechanism and influencing factors

Recent studies showed that sulfidated nanoscale zerovalent iron (S-nZVI) is a better reducing agent than nanoscale zerovalen iron (nZVI) alone for reductive dechlorination of several organic solvents such as trichloroethylene (TCE) due to the catalytic role of iron sulfide (FeS). We measured the rates of transformation of hexabromocyclododecane (HBCD) by S-nZVI and compared them to those by FeS, nZVI, and reduced sulfur species. The results showed that: i) HBCD (20 mg L^-1) was almost completely transformed by S-nZVI (0.5 g L^-1) within 12 h; ii) the reaction with β-HBCD was much faster than with α- and γ-HBCD, suggesting the diastereoisomeric selectivity for the reaction by S-nZVI; and iii) the reaction with S-nZVI was 1.4-9.3 times faster than with FeS, S^2- and nZVI, respectively. The study further showed that the HBCD reaction by S-nZVI was likely endothermic, with the optimal solution pH of 5.0, and could be slowed in the presence of Ca²⁺, Mg²⁺, NO₃^-, HCO₃^- and Cl^-, and by increasing ionic strength, solvent content and initial HBCD concentration, or decreasing the S-nZVI dosage. GC-MS analysis showed that tetrabromocyclododecene and dibromocyclododecadiene were the products. XPS spectra indicated that both Fe(II) and S(-II) on the S-nZVI surface were oxidized during the reaction, suggesting that FeS might act as both catalyst and reactant. The study not only demonstrated the superiority of S-nZVI over other well-known reactive reagents, but also provided insight to the mechanisms of the reaction.

Levels and distribution of hexabromocyclododecane and its lower brominated derivative in Japanese riverine environment

Hexabromocyclododecane (HBCD) and its lower brominated derivatives were measured in both surface water and sediment samples from three Japanese rivers; Tsurumi River, Yodo River, and Kuzuryu River. The concentration level of ∑HBCD (sum of α-, β-, and γ-HBCD) was in the order of Kuzuryu>Yodo>Tsurumi Rivers, reflective of the different emission sources for each basin. The highest ∑HBCD concentration (7800 ng g(-1)dw) was detected in the sediment sample from the Kuzuryu River that receives effluents from textile industries, which use HBCD in flame retardant finishes. A different diastereomeric pattern of α-, β-, and γ-HBCD of each river was investigated, indicating the level of HBCD in these rivers is directly influenced by emission source. Enantiomer fractions of HBCDs in water and sediment samples were also determined. Racemic mixtures were observed in the water samples, whereas enantiomeric enrichment of (-) γ-HBCD and (+) α-HBCD was observed in the sediment samples. Some lower brominated HBCD derivatives such as pentabromocyclododecenes were detected in both the water and sediment samples, and their concentration ranged from below the detection limit to 15 ng L(-1) and 20 ng g(-1)dw, respectively.

Removal of brominated flame retardant from electrical and electronic waste plastic by solvothermal technique

Brominated flame retardants (BFRs) in electrical and electronic (E&E) waste plastic are toxic, bioaccumulative and recalcitrant. In the present study, tetrabromobisphenol A (TBBPA) contained in this type of plastic was tentatively subjected to solvothermal treatment so as to obtain bromine-free plastic. Methanol, ethanol and isopropanol were examined as solvents for solvothermal treatment and it was found that methanol was the optimal solvent for TBBPA removal. The optimum temperature, time and liquid to solid ratio for solvothermal treatment to remove TBBPA were 90°C, 2h and 15:1, respectively. After the treatment with various alcohol solvents, it was found that TBBPA was finally transferred into the solvents and bromine in the extract was debrominated catalyzed by metallic copper. Bisphenol A and cuprous bromide were the main products after debromination. The morphology and FTIR properties of the plastic were generally unchanged after the solvothermal treatment indicating that the structure of the plastic maintained after the process. This work provides a clean and applicable process for BFRs-containing plastic disposal.

Transformation of tetrabromobisphenol A in the presence of different solvents and metals

Solvent-based separation method is presumably an efficient and environmentally beneficial approach for elimination of brominated flame retardants (BFRs) from waste electrical and electronic equipment (WEEE). The overall goal of this study was to evaluate possible effects of organic solvent on the behavior of BFRs during solvent-based processing of WEEE. We initiated a set of batch experiments for examining the rates and possible pathways of transformation of a representative BFR (tetrabromobisphenol A, TBBPA) using acetone, toluene, and methanol as the solvents. Our results showed that toluene and methanol had no effect on the transformation of TBBPA, but approximately 20% of TBBPA (100 mg L(-1)) was transformed by acetone within 2 h at 50°C. Analysis of the products with GC-MS showed that two high-molecular-weight products (MW=586) were major products of the transformation reactions. The role of acetone as a reactant in the transformation of TBBPA was further validated with dueterated acetone. In addition, the effects of co-existing metals in WEEE (i.e., Zn, Cu, and Ni) on the transformation of TBBPA in the solvent systems were investigated. These metals tested were found to greatly enhance the rates of TBBPA transformation. The metal facilitated solvent reactions with TBBPA may lower the extractability of TBBPA by formation of larger and less soluble products, hence potentially increasing the cost for separating the chemical from WEEE.