Insight into the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans in hazardous waste incineration and incinerators: Formation process and reduction strategy.

Incineration technology has been widely adopted to safely dispose of hazardous waste (HW). While the incineration process causes the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Due to its extreme toxicity, many scholars have been committed to determining the PCDD/F formation process and reducing emissions in incinerators. Previous studies ignored the impact of incineration and fluctuation of feeding materials on PCDD/F formation in hazardous waste incinerators (HWIs). In this study, differences in PCDD/F formation between HWIs and municipal solid waste incinerators (MSWIs) were pointed out. The incineration section in HWIs should be carefully considered. Laboratory experiments, conventional analysis and thermogravimetry experiments were conducted. An obvious disparity of PCDD/F formation between 12 kinds of HWs was found. Distillation residue was found with remarkably higher PCDD/F concentrations (11.57 ng/g). Except for the Cl content, aromatic rings and C-O bond organics were also found with high correlation coefficients with PCDD/F concentrations (>0.92). And PCDD/Fs were formed through a chlorination process and structure formation process. All of these are helpful to further understand the PCDD/F formation process during HW incineration, optimize the operation conditions in HWIs and reduce the emission pressure of PCDD/Fs in the future.

TCDD-Induced Allosteric Perturbation of the AhR:ARNT Binding to DNA.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the biological and toxicological effects of structurally diverse chemicals, including halogenated aromatic hydrocarbons. In this work, we investigate the effects of the binding of the AhR prototypical ligand, TCDD, on the stability of the AhR:ARNT complex, as well as the mechanisms by which ligand-induced perturbations propagate to the DNA recognition site responsible for gene transcription. To this aim, a reliable structural model of the overall quaternary structure of the AhR:ARNT:DRE complex is proposed, based on homology modelling. The model shows very good agreement with a previous one and is supported by experimental evidence. Moreover, molecular dynamics simulations are performed to compare the dynamic behaviour of the AhR:ARNT heterodimer in the presence or absence of the TCDD. Analysis of the simulations, performed by an unsupervised machine learning method, shows that TCDD binding to the AhR PASB domain influences the stability of several inter-domain interactions, in particular at the PASA-PASB interface. The inter-domain communication network suggests a mechanism by which TCDD binding allosterically stabilizes the interactions at the DNA recognition site. These findings may have implications for the comprehension of the different toxic outcomes of AhR ligands and drug design.

Zr-MOF-Induced Smart Accumulation Enables Surface-Enhanced Raman Spectroscopic Detection of Dioxin at ppt Level in Food Samples.

The fast and economical detection of trace polychlorinated dibenzo-p-dioxins (PCDDs) in food samples by current mass spectrum-based methods is hindered by tedious sample preparation and bulky & expensive analytical instruments. Surface-enhanced Raman spectroscopy (SERS) successfully detects many organic pollutants in foods but not dioxins because the employed metal nanoparticles weakly adsorb hydrophobic PCDDs. Herein, we report the detection of PCDDs in milk with SERS for the first time using a bifunctional substrate consisting of Au nanoparticles embedded in a zirconium-based metal-organic framework shell (AuNP/Zr-MOF). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), as the most toxic PCDD, is detected as low as 1.2 parts per trillion (ppt) in real milk samples with massive interfering substances in 30 min, which is the lowest among all reported methods. The aromatic rings of Zr-MOF promote the smart accumulation of TCDD through π-π interactions, and Au-Cl interactions drive TCDD onto Au surfaces. Zr-MOF shells with pore sizes of 12.7 and 20 Å block the accessibility of larger interfering molecules. A one-step apparatus and protocol are established to be superior to traditional methods in terms of time and cost. This work provides new insight into a rational screening method for the detection of persistent organic pollutants in a real sample matrix.

Emission reduction of PCDD/Fs by flue gas recirculation and activated carbon in the iron ore sintering.

One of the main sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the environment is the sintering of iron ore. Both flue gas recirculation (FGR) and activated carbon (AC), which have the impact of decreasing both PCDD/Fs and conventional pollutants (NOx, SO2, etc.), are significant technologies for the abatement of PCDD/Fs from the sintering exhaust gas. This work involved the first measurement of PCDD/Fs emissions during FGR and a thorough analysis of the impact of PCDD/Fs reduction following the coupling of FGR and AC technologies. According to the measured data, the ratio of PCDFs to PCDDs in the sintered flue gas was 6.8, indicating that during the sintering process, the PCDD/Fs were primarily produced by de novo synthesis. Further investigation revealed that FGR initially removed 60.7% of PCDD/Fs by returning it to the high temperature bed, and AC further removed 95.2% of the remaining PCDD/Fs through physical adsorption. While AC is better at removing PCDFs and can efficiently remove tetra-to octa-chlorinated homologs, FGR is more effective at removing PCDDs and has higher removal efficiency for hexa-to octa-chlorinated PCDD/Fs. Together, they complement each other with a removal rate of 98.1%. The study's findings are instructional for the process design of combining FGR and AC technologies to reduce PCDD/Fs in the sintered flue gas.

Suppression on PCDD/Fs formation by a novel inhibition system consisting of phosphorous-based compounds coupled with a chlorine-deactivation material.

The SN-containing inhibitors are effective for suppressing the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the post-combustion zone of municipal solid waste incineration systems, but the industrial application of the SN-containing inhibitors is restricted by the high cost and the generation of corrosive by-products (e.g., SOx). To develop cost-effective and environmentally friendly inhibitors, a new inhibition system consisting of P-based compounds (i.e., NH4H2PO4 (ADP) and KH2PO4 (PDP)) and a chlorine-deactivation material (CaO) was proposed in this study. Also, the performance of this inhibition system in terms of suppressing PCDD/Fs formation was evaluated in an experimental system which simulated PCDD/Fs generation in the post-combustion zone. Generally, the formation of PCDD/Fs was effectively suppressed by over 95 % by the mixed inhibitors (ADP/CaO and PDP/CaO) and the individual inhibitor of ADP. Based on the observation on PCDD/F-fingerprints and the chemical speciation of Cl and Cu, the mechanisms of inhibitors were identified as: (i) passivating metal catalyst by converting the speciation of Cu from chlorides and Cu2+ with high reactivities to phosphates, oxides, and Cu+ with low reactivities, and (ii) deactivating Cl by CaO to prevent the formation of organic Cl which was critical for PCDD/Fs formation. In addition, both mechanisms were supported by (i) the better performance of inhibitors on suppressing the PCDD/F-congeners formed via de novo pathway than congeners synthesized from chlorophenols and (ii) lower degrees of chlorination of PCDD/Fs for reaction systems with CaO involved than other systems.

Theoretical study on endocrine disrupting effects of polychlorinated dibenzo-p-dioxins using molecular docking simulation.

Polychlorinated dibenzo-p-dioxins (PCDDs) are hypothesized to exert their toxic effects in wildlife and humans via endocrine disruption. However, very scanty information is available on the underlying molecular interactions that trigger this disruption. In this study, molecular docking simulation was used to predict the susceptibility of 12 nuclear receptors to disruption via PCDD bindings. Findings revealed that androgen (AR and AR an), estrogen (ER α and ER ß), glucocorticoid (GR) and thyroid hormone (TR α and TR ß) receptors are the most probable protein targets that bind to PCDDs. Further molecular docking analyses showed that PCDD molecules mimic the modes of interaction observed for the co-crystallized ligands of the affected receptors, resulting in the formation of ligand-receptor complexes that were stabilized through electrostatic, van der Waals, pi-effect and hydrophobic interactions with 18, 17, 17, 16, 18, eight and four amino acid residues in the active sites of AR, AR an, ER α, ER ß, GR, TR α and TR ß respectively. The commonalities of these interacting amino acid residues with those utilized by dihydrotestosterone in AR, bicalutamide in AR an, 17ß-estradiol in ER α, 17ß-estradiol in ER ß, cortisol in GR, thyromimetic GC-1 in TR α and thyromimetic GC-1 in TR ß are 86%, 74%, 94%, 80%, 82%, 50% and 43% respectively. The results obtained in this study provide supporting evidence that PCDD molecules may interfere with the endocrine system via binding interactions with some vital amino acid residues in the binding pockets of AR, ERs, GRs and TRs.

Comprehensive binding analysis of polybrominated diphenyl ethers and aryl hydrocarbon receptor via an integrated molecular modeling approach.

Polybrominated diphenyl ethers (PBDEs) are often suspected to activate the signal transduction pathway of aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, for the induction of toxicity. Hence, the binding property of PBDEs with AhR is assumed to be associated with the ligand-dependent activation of AhR that may introduce many drug-metabolizing enzymes of genes encoding. However, the binding mechanism and the structural effect of PBDEs on their binding properties of AhR still need to be unraveled for toxicology research. A comprehensive study of the PBDEs-AhR binding mechanism was investigated using an integrated molecular modeling approach with two-dimensional quantitative structure-activity relationships (2D-QSAR), three-dimensional QSAR (3D-QSAR), and molecular docking simulation. Molecular docking revealed the differences in binding domains among 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-AhR complex and two PBDE-AhR complexes. A 2D-QSAR model was developed to analyze the overall structural effects of PBDEs on the binding affinity of AhR. It provided an insight into major physico-chemical properties by multiple linear regression based on genetic algorithm with reasonable results. The 3D-QSAR modeling discovered the detailed interaction features of binding sites, configurations and interaction fields of AhR with different PBDE ligands. This study demonstrated that the descriptors of Smin69 and MoRSEC15 were related to electronic properties and had a great effect on the relative binding affinities. The position of Br substitutions exhibited a significant influence on the interactions between AhR and PBDEs, including halogen interaction, π-S interaction, π-π stacking interaction, and hydrophobic effect. This integrated molecular modeling approach provided a comprehensive analysis of the structural effects of PBDEs on their binding properties with AhR at molecular level.

Quantum Chemical Investigation of Polychlorinated Dibenzodioxins, Dibenzofurans and Biphenyls: Relative Stability and Planarity Analysis.

All the possible polychlorinated aromatic compounds in the classes of dibenzodioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) were studied by the quantum chemical methods of HF/6-311++G(d,p), B3LYP/6-311++G(d,p), and MP2/cc-pVTZ. The calculated stabilities and structures of these compounds were compared with the available data on their abundance and toxicity. Prediction models for trends in energy and planarity among these congeners were proposed. The results discussed here can help contribute to the understanding of the role of dioxin-like compounds (DLCs) in the environment.

An aryl hydrocarbon receptor from the caecilian Gymnopis multiplicata suggests low dioxin affinity in the ancestor of all three amphibian orders.

The aryl hydrocarbon receptor (AHR) plays pleiotropic roles in the development and physiology of vertebrates in conjunction with xenobiotic and endogenous ligands. It is best known for mediating the toxic effects of dioxin-like pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). While most vertebrates possess at least one AHR that binds TCDD tightly, amphibian AHRs bind TCDD with very low affinity. Previous analyses of AHRs from Xenopus laevis (a frog; order Anura) and Ambystoma mexicanum (a salamander; order Caudata) identified three amino acid residues in the ligand-binding domain (LBD) that underlie low-affinity binding. In X. laevis AHR1ß, these are A354, A370, and N325. Here we extend the analysis of amphibian AHRs to the caecilian Gymnopis multiplicata, representing the remaining extant amphibian order, Gymnophiona. G. multiplicata AHR groups with the monophyletic vertebrate AHR/AHR1 clade. The LBD includes all three signature residues of low TCDD affinity, and a structural homology model suggests that its architecture closely resembles those of other amphibians. In transactivation assays, the EC50 for reporter gene induction by TCDD was 17.17 nM, comparable to X. laevis AhR1ß (26.23 nM) and Ambystoma AHR (34.09 nM) and dramatically higher than mouse AhR (0.13 nM), a trend generally reflected in direct measures of TCDD binding. These shared properties distinguish amphibian AHRs from the high-affinity proteins typical of both vertebrate groups that diverged earlier (teleost fish) and those that appeared more recently (other tetrapods). These findings suggest the hypothesis that AHRs with low TCDD affinity represent a characteristic that evolved in a common ancestor of all three extant amphibian groups.

Co-disposal of incineration fly ash and sewage sludge via hydrothermal treatment combined with pyrolysis: Cl removal and PCDD/F detoxification.

In this study, the incineration fly ash (IFA) of municipal solid waste (MSW) and municipal sewage sludge (MSS) was synergistically subjected to hydrothermal treatment coupled with pyrolysis (HTP). The regulation of Cl removal and the destruction and detoxification of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) were investigated. The results demonstrated that during hydrothermal treatment (HTT), the Cl removal rate increased with temperature, most of the soluble chlorides were removed, and the acid dissolution of Cl in the hydro-residue was significantly reduced. At hydrothermal temperatures exceeding 180 °C, the variation in the Cl removal rate decreased. Although a certain quantity of PCDD/Fs dissolved in the hydrothermal liquid, the total destruction rate achieved by HTT remained more than 90%. The detoxification rate did not exceed 60% owing to the formation of low-chlorinated PCDD/Fs. Subsequent pyrolysis of the hydro-residue further improved the Cl removal rate, which increased with pyrolysis temperature; the Cl content of pyro-char was reduced to 1.8% and that of the leached acid was less than 0.5 mg/g at 800 °C. In addition, PCDD/Fs in tar and pyrolysis gas were not detected under optimal conditions; the PCDD/F concentration of pyro-char was reduced to 0.17 ng I-TEQ/kg. The destruction and detoxification efficiencies of PCDD/Fs reached 98.49% and 92.50%, respectively. Thus, the method of HTP was conducive to the co-disposal of IFA and MSS.

Electrophilic chlorination of dibenzo-p-dioxin and dibenzofuran over composite copper and iron chlorides and oxides in combustion flue gas.

Dibenzo-p-dioxin (DD) and dibenzofuran (DF) chlorination mediated by Cu and Fe chlorides can make a direct contribution to the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in combustion flue gas. In this study, a kind of composite Cu and Fe chlorides and oxides (CuFe9O9.5Cl10) was prepared by impregnating oxides with HCl solution to imitate the coexistence status of Cu and Fe species in combustion flue gas. Composite CuFe9O9.5Cl10 was active in promoting the electrophilic chlorination of DD/DF at 150-300 °C, with the highest activity at 200 °C. DD/DF chlorination could occur under inert atmosphere, and 5% O2 atmosphere was most favorable for DD/DF chlorination. Electrophilic chlorination of DD/DF primarily favored at 2,3,7,8 positions. Hybridization of Cu and Fe chlorides and oxides not only decreased the starting temperature and activation energy of DD/DF chlorination, but also induced a synergistic effect for accelerating the chlorination of DD/DF. The measured activities of composite CuFe9O9.5Cl10 for promoting the chlorination of DD/DF were near to those of composite Cu chloride and oxide (CuO0.2Cl1.6), whereas 2 orders of magnitude higher than those of composite Fe chloride and oxide (FeO0.3Cl2.4). Comparison of PCDD/F congener distribution patterns indicated that DD/DF chlorination should be a main source of Cl1-3DFs and Cl1-2DDs in combustion flue gases.

The Ah Receptor: Adaptive Metabolism, Ligand Diversity, and the Xenokine Model.

The Ah receptor (AHR) has been studied for almost five decades. Yet, we still have many important questions about its role in normal physiology and development. Moreover, we still do not fully understand how this protein mediates the adverse effects of a variety of environmental pollutants, such as the polycyclic aromatic hydrocarbons (PAHs), the chlorinated dibenzo-p-dioxins ("dioxins"), and many polyhalogenated biphenyls. To provide a platform for future research, we provide the historical underpinnings of our current state of knowledge about AHR signal transduction, identify a few areas of needed research, and then develop concepts such as adaptive metabolism, ligand structural diversity, and the importance of proligands in receptor activation. We finish with a discussion of the cognate physiological role of the AHR, our perspective on why this receptor is so highly conserved, and how we might think about its cognate ligands in the future.

Improvement of reporter gene assay for highly sensitive dioxin detection using protoplastic yeast with inactivation of CWP and PDR genes.

A yeast reporter gene assay system with improved performance for dioxin detection was established. Since yeast reporter gene assays are relatively simple, easy to handle, and inexpensive, they have been used for various assessments of environmental contaminants. We previously constructed a yeast assay strain expressing the aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (Arnt) carrying the lacZ reporter gene, for detection of dioxins. In the present study, genes encoding cell wall mannoproteins and ATP-binding cassette transporters in the yeast assay strains were deleted in order to increase the substance influx and prevent its efflux. We also established an assay procedure for protoplasts of these yeasts. These modifications improved the detection limit 40-fold and reduced the duration of the assay by 40%. By combining the yeast protoplast and a rapid sample preparation technique using disposal multilayer solid-phase extraction columns to remove unintended aryl hydrocarbons, this yeast reporter gene assay system detected the ligand activities of dioxins and related compounds in 1 g of forest soil containing dioxins at a concentration 10 times lower than the Japanese environmental standard for dioxins in soil.

Alteration in formation behaviors of chloroaromatic precursors of PCDD/Fs: An experimental study on the effect of extrinsic and intrinsic oxygen on chlorination.

Due to the promotion on Cl radical generation by enhanced oxidation, chlorination of hydrocarbon intermediates becomes a potential formation path for chloroaromatic precursors of PCDD/Fs (polychlorinated dibenzo-p-dioxins and dibenzofurans) in both MSW (municipal solid waste) incineration and gasification-combustion processes, in which intrinsic oxygen might have a significant effect on the competition between oxidation and chlorination. Thus, chlorination of benzene and phenol was experimentally studied on a homogeneous flow reaction system. Effects of temperature and ER (equivalence ratio) were assessed, and comparison was carried out to clarify the alteration in formation behaviors of chloroaromatics by extrinsic and intrinsic oxygen. At 600 °C, chlorobenzenes were already largely formed in benzene chlorination, and the addition of extrinsic oxygen barely affected it. On the contrary, with intrinsic oxygen, phenol tended to decompose to light compounds. With rising temperature, oxidation was promoted and extrinsic oxygen strongly inhibited the formation of chloroaromatics in benzene chlorination at 900 °C and higher temperature. For phenol chlorination, chlorobenzenes were still rarely generated. However, high proportions of octachloronaphthalene and octachlorodibenzofuran were observed, due to the enhancement in polymerization by high temperature. When increasing ER, oxidative decomposition was also promoted in both the chlorination of benzene and phenol. Extra extrinsic oxygen led to a further reduction of chloroaromatics during benzene chlorination, and till ER = 1.0 at 1000 °C, comparable performance to intrinsic oxygen could be achieved in the control of chloroaromatics. Based on these results, formation pathways of the major chloroaromatics from chlorination, oxidation and polymerization were summarized, and the roles of extrinsic and intrinsic oxygen in altering their formation behaviors were revealed.

Simultaneous quantification of humic acid-water and silanized glass-water partition constants for PCBs, PCDDs and OCDF.

Super-hydrophobic organic contaminants (SHOCs) such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and octachlorodibenzofuran (OCDF) can sorb to dissolved hydrophobic materials including humic acids (HAs), enhancing their apparent aqueous solubility and potentially resulting in increased groundwater contamination and offsite transport. To manage risks associated with transport of and contamination by SHOCs, modelling approaches incorporating partitioning data, i.e. dissolved organic carbon-water partition constants (KDOC), are necessary. Measurement of KDOC can however be compromised by SHOC sorption to glassware surfaces leading to an overestimation of experimental values resulting in larger KDOC. A method for simultaneous derivation of KDOC and glass-water partition constants (KGW) is described. It involves a mass balance approach combined with HA as a co-solvent at various concentrations and accounts for SHOC losses to silanized glassware. Measured log KDOC values ranged from 5.28 to 7.64 for tetra- to decachlorinated PCBs, 6.67 to 7.93 for tetra- to octachlorinated PCDDs and 8.20 for OCDF. These data were linear functions of log KOW and consistent with relationships reported for more polar compounds. Log KGW (mm3 mm-2) values (1.62 to 4.06 for PCBs, 2.96 to 3.90 for PCDDs, 3.77 for OCDF) were one order of magnitude greater compared to literature PCB borosilicate glass-water partition constants. Techniques such as those presented in this work present simple, versatile means to provide prediction of the SHOC proportion remaining in aqueous solutions after loss to glassware that was inversely related to container surface area/volume ratio and log KOW in our study.

Industrial disposal processes for treatment of polychlorinated dibenzo-p-dioxins and dibenzofurans in municipal solid waste incineration fly ash.

Hazardous waste disposal is a serious environmental concern in China. Therefore, in this study, industrial trials were conducted in a low-temperature thermal degradation facility, a tunnel kiln, and a shaft kiln to effectively treat dioxins in municipal solid waste incineration (MSWI) fly ash. The results indicated that the low-temperature thermal degradation facility efficiently decomposed polychlorinated dibenzo-p-dioxins and dibenzofurans in the MSWI fly ash. Additionally, the concentrations of dioxins in the treated fly ash and exhaust gas were lower than the suggested standard limits and the degradation ratio of dioxins was ∼99%. Therefore, treated fly ash characterized by acceptable dioxin risks could be utilized for the production of non-fired building materials. The results from the tunnel kiln indicated complete decomposition of the dioxins in the firing and insulating sections. However, the addition of fly ash in the tunnel kiln increased the concentration of dioxins in the flue gas. This can be primarily attributed to the heterogeneous catalytic synthesis reaction in the low-temperature section of the tunnel kiln. The results from the shaft kiln indicated degradation of at least 22% of the dioxins in the ash. The dioxin concentration in the flue gas was lower than the national standard while that in the clinker was within a reasonable limit. Furthermore, the environmental risks were significantly reduced at fly ash addition ratios lower than 3%.

Bioaccumulation of PCDD/Fs in foodstuffs near Bien Hoa and Da Nang airbases: assessment on sources and distribution.

In this survey, food items were collected from vicinities of Bien Hoa and Da Nang airbase and determined for polychloro-dibenzo-dioxins and polychloro-dibenzo-furans (PCDD/Fs) to assess their accumulation, distribution in the local food items, and risk of PCDD/F exposure through consumption of the local foods. Dioxin compounds were determined using isotope dilution method which is slightly modified from US-EPA method 1613B. The dioxin concentration was the highest in fish followed by eggs, chicken, meat (pork and beef), and vegetables. Particularly, in Bien Hoa airbase, the mean concentrations of dioxin on TEQ and lipid basis (except for vegetables) were 26 pg/g for fish, 13 pg/g for eggs, 20 pg/g for chicken, 4.5 pg/g for meat, and 0.34 pg/g fresh wt for vegetables. In Da Nang airbase, the mean levels of dioxin on TEQ and lipid basis were slightly lower, 12.9 pg/g for fish, 8.7 pg/g for eggs, 5.9 pg/g for chicken, 6.7 pg/g for meat, and 0.17 pg/g for vegetables. It has been interesting to observe that free-range chicken expose to higher level of dioxin than caged chicken. In some free-range chicken, the portion of 2,3,7,8-TCDD was relatively high and implying recent exposure to dioxin.

A stable zirconium based metal-organic framework for specific recognition of representative polychlorinated dibenzo-p-dioxin molecules.

Polychlorinated dibenzo-p-dioxins (PCDDs), as a class of persistent and highly toxic organic pollutants, have been posing a great threat to human health and the environment. The sensing of these compounds is important but challenging. Here, we report a highly stable zirconium-based metal-organic framework (MOF), Zr6O4(OH)8(HCOO)2(CPTTA)2 (BUT-17) with one-dimensional hexagonal channels and phenyl-rich pore surfaces for the recognition and sensing of two representative PCDDs, 2,3-dichlorodibenzo-p-dioxin (BCDD) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), based on the fluorescence quenching. BUT-17 exhibits high sensing ability with the detection limits as low as 27 and 57 part per billion toward BCDD and TCDD, respectively, and is very selective as well without the interference of similar compounds. The recognition of BUT-17 toward BCDD is demonstrated by single-crystal structure of its guest-loaded phase, in which the fluorescence-quenched complexes form between the adsorbed BCDD molecules and the MOF host through π-π stacking and hydrogen bonding interactions.

PCDD/PCDFs and PCBs in the irrigation water in Egypt: levels, patterns, and potential sources.

The contamination levels of PCDD/PCDFs in irrigation water are the most rarely studied throughout the world. The major problem in Egypt is the lack of studies and statistics about these contaminants of POPs in irrigation water. Therefore, this study is the first comprehensive report to elucidate the estimation and sources of PCDD/PCDFs and PCBs in irrigation water from Egypt and rare for worldwide may provide a reference to future studies of POPs compounds in irrigation water of Egypt. A total of 24 irrigated water samples were collected from different irrigation canals which are adjacent to industrial areas from six Egyptian governorates (Bani Swef, El-Giza, El-Sharkeya, El-Menoufeya, El-Gharbeya, and Alexandria). The study shows that irrigation water canals were contaminated with low levels of PCDDs/PCDFs, which were 0.95 pgWHO-TEQ/l, and the total of PCDD/PCDFs and dl-PCBs were 2.06 pgWHO-TEQ/l with contamination ranging between 0.88 to 2.97 pgWHO-TEQ/l while the levels of indicator PCBs were 18.52 ng/l and ranged between 0.39 to 165.6 ng/l. The most predominant dioxins congeners were HpCDD, OCDD, HpCDF, and OCDF while for dl-PCBs were PCB105 and PCB118, and for ndl-PCBs was PCB138. The areas with recent urbanization and industrialization were more contaminated with PCBs than the unindustrialized area. Lightly to moderately chlorinated congeners dominated the PCB profiles. The major sources for these contaminants were fire bricks followed by textile industries closer to the located sampling sites. The detected pattern was found to be similar to the patterns reported in the air by other studies. Although the concentrations of the studied POPs are found to be low in irrigated water, it may be considered as a potential source of soil pollution due to their accumulation process in the agricultural land and may lead to risk on human health by consuming the agricultural products irrigated by contaminated water.

The effect of the transition from elemental chlorine bleaching to chlorine dioxide bleaching in the pulp industry on the formation of PCDD/Fs.

The article reviews the transition from bleaching kraft pulp with elemental chlorine to bleaching with chlorine dioxide with respect to formation of chlorinated dioxins and furans (PCDD/Fs). New data is also presented for bleaching with 100% chlorine dioxide and the effect of elemental chlorine impurities. The typical fingerprint of PCDD/Fs in pulp bleached with elemental chlorine was unique compared to all other sources such as incineration and metallurgic processes. 2,3,7,8-TCDD and 2,3,7,8-TCDF were the dominating congeners formed during the period pulp was bleached with elemental chlorine. Elimination of unchlorinated precursors lowered, but did not eliminate, the formation of 2,3,7,8-TCDD and 2,3,7,8-TCDF. The formation of 2,3,7,8-TCDD and 2,3,7,8-TCDF increases exponentially with the amount of elemental chlorine used. Replacing elemental chlorine with chlorine dioxide (with levels of elemental chlorine contamination of <0.3% in the chlorine dioxide) in pulp bleaching eliminates the formation of 2,3,7,8-TCDD and 2,3,7,8-TCDF. PCDD/Fs can also be found in background levels in ecosystems, food, soil and air as well as in unbleached pulp, bleached pulp, and paper and fiber products. Thus, the only way to determine if PCDD/Fs are present from bleaching is to make a full congener analysis and compare to known sources and processes as well as to laboratory blanks and unbleached reference samples.