Dibenzo-p-dioxin Research Articles

Emission, partition, and formation pathway of polychlorinated dibenzo-p-dioxins and dibenzofurans during co-disposal of industrial waste with municipal solid waste

Growing amounts of industrial waste (IW) are being co-disposed in municipal solid waste incineration (MSWI) plants, whereas few studies have been conducted on the characterization of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during co-incineration. The emission characteristics and formation pathways of PCDD/Fs are systematically analyzed during the co-disposal of MSW and IW of the textile/food industry in a full-scale MSWI plant. The emission of toxic PCDD/Fs in the chimney (CH) is far lower than the national standard (<0.005 ng I-TEQ/Nm3) in co-disposal, as well as fly ash (FA) (<50 ng I-TEQ/kg). Co-incinerating IW of the textile industry significantly influences the PCDD/Fs (total 136 kinds of congeners) emission in boiler outlet (BO), CH and FA, while co-incinerating IW of the food industry causes less impact. IW co-disposal also enables PCDD/Fs migration from BO into FA, probably attributing to chlorine (Cl) increment in IW. Furthermore, the distribution patterns of PCDD/F isomers are analogous under MSWI and IW co-disposal conditions. De novo synthesis in all states is generally the dominant formation route of PCDD/Fs, possibly due to the longer dwell time of carbon residues, and de novo synthesis is strengthened by IW co-disposal. Chlorophenol (CP)-route synthesis and dibenzofuran (DF) chlorination contribute less, which are slightly reduced by co-incinerating IW, while dibenzodioxin (DD) chlorination is somewhat strengthened. Major air pollutants in co-disposal, including CO, NOx, HCl and particulate matter (PM) are poorly related to PCDD/Fs (−0.33 <R<0.52), while SO2 is negatively correlated with PCDD/F homologues, indicating potential suppression by sulfur (S) in IW.

Gas chromatography-triple quadrupole mass spectrometry as a cost-effective method for the determination of polychlorinated dibenzo–p-dioxins and furans in contaminated soils

The aim of this study was to evaluate the performance of gas chromatography (GC)-triple quadrupole mass spectrometry (QqQ, MS/MS) as an alternative to the standard GC-high resolution mass spectrometry (GC-HR/MS) for soils contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). GC-QqQ (MS/MS) using a dynamic multiple reaction monitoring (dMRM) mode was optimized for the quantitative analysis of 17 PCDD/Fs. A comparative study between GC-QqQ (MS/MS) and GC-HR/MS was carried out to validate the results of actual field soil samples. Although GC-HR/MS has excellent sensitivity and selectivity, the validation parameters obtained by GC-QqQ (MS/MS) also met the recommended criteria of the standard method. The results for total and I-TEQ (international toxic equivalent) value of the PCDD/F concentrations of over 86.0 pg/g and 4.3 pg I-TEQ/g, respectively, in actual field soil samples showed good agreement between the two methods, falling within ±25% relative difference. In consideration of the remediation goal (100 pg I-TEQ/g), GC-QqQ (MS/MS) can be an alternative cost-effective method for use in soil remediation research.

Biochemical and genetic characterization comparison of four extradiol dioxygenases in Rhizorhabdus wittichii RW1.

Rhizorhabdus (previously Sphingomonas) wittichii RW1 uses a diverse array of aromatic organic compounds as energy and carbon sources, including some extremely recalcitrant compounds such as dibenzo-p-dioxin and dibenzofuran. Extradiol dioxygenases play a key role in the metabolism of dibenzofuran (DBF), dibenzo-p-dioxin (DBD), PCBs, and various other aromatic compounds. In this study, a detailed kinetic analysis of four extradiol dioxygenases identified in R. wittichii RW1 (DbfB, Edo2, Edo3, and Edo4) showed all of them to be typical 2,3dihydroxybiphenyl (DHB) dioxygenases with DHB as preferred substrate (kcat/Km values of 0.13-188 (µM -1s-1)) and only slightly lower activity against trihydroxybiphenyl (THB) whereas monocyclic substrates were, to different extents, poor substrates due to high km values. All extradiol dioxygenases analyzed were subject to mechanism-based inactivation by 2,2`,3-trihydroxybiphenylether (THBE) the intermediate of DBD degradation. However, Edo4 was superior as reflected by the relatively high partition ratio and the comparably low efficiency of inactivation. Significant differences were observed with respect to their inactivation by 3-chlorocatechol. The absence of any significant mechanism-based inactivation makes Edo3 a perfect candidate for being recruited for chlorobiphenyl degradation where inactivation of extradiol dioxygenases by this intermediate creates significant metabolic problems. KEY POINTS: • Characterization of additional extradiol dioxygenases encoded by RW1 • Identification of differences in 2,2`,3-trihydroxybiphenylether transformation • Identification of differences in inhibition by 3-chlorocatechol.

Physiological role of isocitrate lyase in dibenzo-p-dioxin and dibenzofuran metabolism by Sphingomonas wittichii RW1

BackgroundSphingomonas wittichii RW1 is one out of three strains capable of metabolizing dioxin as a sole source for carbon and energy. Under laboratory conditions the degradation rates for these aromatics are relatively high (5 and 8 h for dibenzofuran (DBF) and dibenzo-p-dioxin (DD), respectively). However, their degradation rates are much lower in the environment due to several factors. One of these factors is the availability of other carbon sources. Acetate is a metabolized carbon source by S. wittichii RW1 and its presence in the environment would have a negative impact on DBF and DD degradation. In addition, expression of most of the genes for DBF and DD degradation were downregulated when grown on acetate compared to their growth on DBF and DD. We hypothesized that blocking the acetate utilization pathway in S. wittichii RW1 would prevent it from using acetate when present along with DD and DBF in contaminated sites. ResultsBlocking the glyoxylate shunt by deleting isocitrate lyase gene (icl) prevented the mutant strain (RW1Δicl) from using acetate as a sole carbon source thus depending on available DBF and DD in polluted sites. Our results showed that deletion of icl did not affect growth of S. wittichii RW1 on DBF and DD but blocked it from growing on acetate. ConclusionOur results introduces an engineered strain that can be used as a new candidate to clean dioxin-contaminated sites which are rich with acetate.

Agromyces and Arthrobacter isolates from surficial sediments of the Passaic River degrade dibenzofuran, dibenzo-p-dioxin and 2-monochlorodibenzo-p-dioxin

The Passaic River in New Jersey, USA is heavily polluted by chlorodibenzo-p-dioxins (CDDs). Highly chlorinated CDDs are dechlorinated by anaerobic bacteria from these sediments, producing lightly chlorinated or even non-chlorinated dibenzo-p-dioxin (DD) daughter products. Surficial Passaic River sediments were enriched under aerobic conditions and three bacterial strains (PR1, PR2 and PR3) were isolated using dibenzofuran (DF) as a model substrate. PR1 is closely related to Janibacter terrae (99.4%), a known CDD and DD degrader. PR2 and PR3 are closely related to Agromyces mediolanus (99.2%) and Arthrobacter oryzae (99.5%), respectively, which are genera not known to degrade CDDs. Janibacter PR1 grew more rapidly on DF than PR2 and PR3. The less well characterized PR2 and PR3 both degraded DD and 2-monochlorodibenzo-p-dioxin (2MCDD), at similar rates. Neither PR2 nor PR3 transformed 2,7-dichlodibenzo-p-dioxin (2,7DCDD). An angular dioxygenase 99.7% identical to that in Terrabacter sp. DBF63 was detected by PCR in Janibacter PR1 and Agromyces PR2. PCR did not detect an angular dioxygenase in Arthrobacter PR3. In this work, novel aerobic bacterial strains that can aerobically degrade the products of dechlorination were identified in surficial Passaic River sediments. The presence of these bacteria could enable an in situ treatment process that completely removes all CDDs from the sediment.

Synthesis and evaluation of Fe3O4-impregnated activated carbon for dioxin removal

Polychlorinated dibenzo-p-dioxins and -furans (PCDD/PCDFs) are highly toxic organic pollutants in soils and sediments which persist over timescales that extend from decades to centuries. There is a growing need to develop effective technologies for remediating PCDD/Fs-contaminated soils and sediments to protect human and ecosystem health. The use of sorbent amendments to sequester PCDD/Fs has emerged as one promising technology. A synthesis method is described here to create a magnetic activated carbon composite (AC-Fe3O4) for dioxin removal and sampling that could be recovered from soils using magnetic separation. Six AC-Fe3O4 composites were evaluated (five granular ACs (GACs) and one fine-textured powder AC(PAC)) for their magnetization and ability to sequester dibenzo-p-dioxin (DD). Both GAC/PAC and GAC/PAC-Fe3O4 composites effectively removed DD from aqueous solution. The sorption affinity of DD for GAC-Fe3O4 was slightly reduced compared to GAC alone, which is attributed to the blocking of sorption sites. The magnetization of a GAC-Fe3O4 composite reached 5.38 emu/g based on SQUID results, allowing the adsorbent to be easily separated from aqueous solution using an external magnetic field. Similarly, a fine-textured PAC-Fe3O4 composite was synthesized with a magnetization of 9.3 emu/g.

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.

Synergistic effect of mixed Cu and Fe oxides and chlorides on electrophilic chlorination of dibenzo-p-dioxin and dibenzofuran

The direct chlorination of dibenzo-p-dioxin (DD) and dibenzofuran (DF) is an important source of dioxins in combustion flue gas. The chlorination reaction mainly occurs via electrophilic substitution induced by Cu and Fe chlorides, which must cohabit on particulate matters in mixed state. To explore the mechanism for DD/DF chlorination in real combustions flue gas, 8 kinds of CuO/Fe2O3/CuCl2/FeCl3 composites impregnated onto silica powder were prepared to simulate the coexisting state of Cu and Fe species in combustion flue gas. Mixed Cu and Fe oxides and chlorides induced a significant synergistic effect on electrophilic chlorination of DD/DF. The efficiencies of DD/DF chlorination over composites containing both Cu and Fe species were 1–2 orders of magnitude higher than those over composites containing only Fe species at 250 °C. CuCl2 species were highly active sites for electrophilic chlorination. FeCl3 acted as an excellent promoter to accelerate DD/DF chlorination over CuCl2 species. The elevated proportion of Cu and Fe oxides was also favora ble for electrophilic chlorination. Compared with DF, DD was more prone to be chlorinated. Chlorine substitution primarily occurred at 2, 3, 7 and 8 positions of DD and DF. Furthermore, the possible mechanism for synergistic effect on electrophilic chlorination of DD/DF was speculated.

Mechanistic aspects of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) formation from chlorine bleaching of non-wood pulp

Chlorine bleaching of non-wood pulp can produce and release polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) into environment. In this study, a series of chlorination experiments were conducted to explore the source, formation pathway and formation kinetics of Cl1−8DD/Fs during the chlorine bleaching of wheat straw pulp. The 13C isotope-labeling experiment verified that PCDD/Fs could not be formed from the chlorination of phenols in pulp. Above 80% of the observed PCDFs originated from the direct chlorination of dibenzofuran (DBF) in unbleached wheat straw pulp, while approximately 60% of the observed PCDDs came from the chlorination of nonextractable precursors in the pulp. The yield of total PCDFs was 2 orders of magnitude higher than that of total PCDDs. The kinetic study indicated that DBF was more easily chlorinated than dibenzo-p-dioxin (DBD) in the pulp solution. Pseudo-first-order reaction kinetic equations fitted the formation and degradation of PCDD/Fs well. The direct chlorination of DBD/F primarily preferred a selective pattern at the 2 position, followed by the 8, 7 and 3 positions. A higher content of DBF in unbleached pulp led to a higher yield of 2,3,7,8-Cl4DF. Finally, the practical implication for dioxin formation control was discussed.

Enhanced photocatalytic reduction for the dechlorination of 2-chlorodibenzo-p-dioxin by high-performance g-C3N4/NiO heterojunction composites under ultraviolet-visible light illumination

Polychlorinated dibenzo-p-dioxins (PCDDs), characterized by their high persistency and bioaccumulation, are widely detected in the environment. In this study, high-performance g-C3N4/NiO heterojunctions were fabricated to degrade 2-chlorodibenzo-p-dioxin (2-CDD) under ultraviolet-visible (UV–vis) light illumination. Experiments revealed that the pure g-C3N4 and range of g-C3N4/NiO heterojunctions were synthesized by the mixing and heating method, and then were characterized by XRD, TEM, XPS and PL etc. The composites exhibited enhanced dechlorination activities under anoxic conditions. After comparison, the g-C3N4/NiO (4:6) showed optimal dechlorination performance such that 70.4% of 2-CDD was removed within 8 h and 52.3% of 2-CDD was transformed to dibenzo-p-dioxin (DD), about fourfold higher than the pristine g-C3N4. The transformation of 2-CDD was accompanied by the resale of Cl ion, and the additional oxygen was proven to be able to consume electrons and hydrogen ions, thus greatly inhibiting the degradation of PCDD in systems. The g-C3N4/NiO (4:6) can be reused at least seven times, and the mechanism was proposed in detail to promote photoinduced electrohole separation and provide active sites. This study extends the use range of g-C3N4/NiO heterojunctions and develops a new technology to degrade PCDDs with striking activity and stability.

Destruction of dioxin and furan pollutants via electrophilic attack of singlet oxygen

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) remain of particular concern owing to their extensive toxicity towards health and accumulation in the environment. Atmospheric oxidation (by ambient oxygen molecules) of this class of persistent environmental pollutants has little to no kinetic feasibility due to very sizable activation energies in the entrance channel. The current control measures involve energy-intensive source incineration of contaminated materials at high temperatures as high as 850 °C. This study finds an alternative low-energy approach of destroying dioxin-like compounds, proposing that advanced oxidation by highly reactive singlet oxygen (O21Δg, originated from chemical, surface-mediated and photochemical processes) can initiate low-temperature remediation of these pollutants. This contribution completes the first milestone in mapping out the mechanisms of the electrophilic addition of singlet oxygen to unsubstituted and chlorinated dibenzo-p-dioxin (DBD) and dibenzofuran (DBF) structures, according to density functional theory DFT-B3LYP method in conjunction with the 6–311+g(d,p) basis set, as well as energy refinements based on the approximate spin-projection scheme. The [2+2]-cycloaddition mechanism appears dominant for singlet oxidation of dibenzo-p-dioxin with a fitted rate constant of k(T) = 5.01 × 10−14 exp(-98000/RT). On the other hand, the addition of singlet oxygen to the aromatic ring of dibenzofuran primarily transpires via [4+2]-cycloaddition channel with a fitted rate constant of k(T) = 2.16 × 10−13 exp(-119000/RT). The results suggest that application of singlet oxygen can reduce the energy cost of recycling halogenated and flame retarded materials.

Mechanistic studies on the dibenzofuran and dibenzo‑p‑dioxin formation reactions from anthracene

Polychlorinated dibenzo‑p‑dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic, carcinogenic and mutagenic to humans. As precursors of PCDD/Fs, dibenzofuran (DF) and dibenzo‑p‑dioxin (DD) have received considerable public and scientific attention. To reduce the emission of PCDD/Fs, it is critical to explore the formation mechanisms of DF and DD. The present study delineated the DF and DD formation mechanisms from anthracene partial oxidation with the aid of high-accuracy quantum chemistry calculations. The rate constants of crucial elementary steps were obtained utilizing canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) correction. The results indicate that anthracene could be important precursor of DF and DD, because of the potential barriers for all the major elementary reactions are lower than 33.54kcalmol−1. This work also reveals that water molecule plays an important catalytic effect during the formation of both DF and DD by lowering the barriers of about 27.24kcalmol−1. For the water-assisted formation pathway, DF is the dominate product of anthracene partial oxidation with the highest barrier of 30.45kcalmol−1. For the non-water-assisted formation pathway, DD is the dominate product with the highest barrier of 33.54kcalmol−1.

Suppressing formation pathway of PCDD/Fs by S-N-containing compound in full-scale municipal solid waste incinerators

The emission of polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) is a serious concern from municipal solid waste incineration (MSWI). The utilization of inhibitor is an effective method to inhibit the formation of PCDD/Fs. In the present study, the thiourea is used as an effective inhibitor in two full-scale MSW incinerators, and the suppression mechanisms are investigated in detail. After the injection of thiourea, the total PCDD/Fs emission factor decreases from 6.19 and 7.89 mg/t MSW (0.13 and 0.18 mg I-TEQ/t MSW) to 1.35 and 1.34 mg/t MSW (0.029 and 0.026 mg I-TEQ/t MSW), respectively for incinerator A and B. In the post-combustion zone, the contribution of three pathways on PCDD/Fs formation is found to be in the order of de novo synthesis > chlorophenol (CP) route formation > chlorination of dibenzofuran (DF) and dibenzodioxin (DD). The S and N in thiourea poison the catalytic metals, thus significantly hindering the de novo synthesis of PCDD/Fs. Since metal catalysts for precursor-formation are not as crucial as for de novo synthesis, the thiourea has less suppression effect on CP-route synthesis, which is identified from the reduction of signal intensity of CP-route congeners. In addition, the chlorination of DF/DD is also observed to be suppressed, indicating the transformation of Cl2 to less activate HCl caused by thiourea. This study provides a robust basis to promote the industrial application of inhibitor to control the emissions of PCDD/Fs from MSW incinerator.

Dioxin leaching risk assessment through selected soils by estimating distribution coefficient and breakthrough curves.

From health and environmental point of views, dioxins are important due to their toxicity and persistence. Dioxins have the potential to reside in the environment for longer time if sorbed onto the clay and organic content of the soil matrix. Their transport or leaching under certain environmental conditions such as preferential flow can increase the risk of groundwater contamination. In the current study, breakthrough curves (BTCs) against time were plotted for selected dioxin transport prediction; based on measured distribution coefficient (Kd), dispersion coefficient (D), and retardation factor (R). Three representative soil series named Burhan, Warsak, and Kunda were selected. For dibenzo-p-dioxin (DD), Kd values followed the order as: Burhan> Warsak > Kunda, while for 2-chloro dibenzo-p-dioxin (2 Cl-DD), Kd values followed an order as: Kunda > Burhan > Warsak. Dioxin transport was measured at two different linear velocities (20 and 50cmday-1). Attainment of equilibrium was verified to be dependent upon the Kd, R, D, and chlorination on dioxin. Kunda series with low OM (0.6%), clay (0.2%), and R (377) was found to have relatively high DD transport potential under normal velocity, due to high dispersion values for its sandy nature. Under the steady or preferential flow conditions, all the plots obtained were identical irrespective of soil type and dioxin nature.

Photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin by Pd modified g-C3N4 photocatalysts under UV–vis irradiation: Efficacy, kinetics and mechanism

Polychlorinated dibenzo-p-dioxins (PCDDs), as a group of notorious anthropogenic environmental toxicants, are arguably ubiquitous in nature. In this study, we investigated the photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin (2-CDD) over Pd/g-C3N4 catalysts under UV–vis irradiation. The g-C3N4 and a series of Pd/g-C3N4 catalysts were prepared by thermal polymerization and mechanical mixing-illumination method and characterized by XRD, TEM, BET, SEM and UV–vis DRS analyses. Among all the samples, the Pd/g-C3N4 (5 wt%) yielded the optimal dechlorination activity with a total 2-CDD conversion of 54% within 4 h, and 76% of those converted 2-CDD were evolved to dibenzo-p-dioxin (DD). The kinetics of dechlorination could be described as pseudo-first-order decay model (R2 > 0.84). Corresponding rate constants (k) increased from 0.052 to 0.17 h−1 with Pd contents up to 5 wt% and decreased to 0.13 h−1 with a 10 wt% of Pd. The enhanced activities originated from the surface plasmonic resonance (SPR) effect of Pd nanoparticles and the formation of Schottky barrier between Pd and g-C3N4, which extend the spectrum responsive range and suppress the charge recombination of g-C3N4. This is the first report on the photocatalytic reductive removal of PCDDs and may provide a new approach for PCDDs pollution control.

Sampling and analyses of polychlorinated dibenzo dioxins (PCDDs) and polychlorinated dibenzo furans (PCDFs) emissions in South Africa: A practitioner’s guide

Dioxins and furans are toxic chemicals. A draft report released for public comment in September 1994 by the US Environmental Protection Agency clearly describes dioxin as a serious public health threat. The public health impact of dioxins may rival the impact that dichlorodiphenyltrichloroethane (DDT) had on public health in the 1960’s. According to the United States Environmental Protection Agency(USEPA) report, not only does there appear to be no “safe” level of exposure to dioxin, but levels of dioxin and dioxin-like chemicals have been found in the general US population that are “at or near levels associated with adverse health effects.” With this in mind the purpose of this paper is to provide an overview of the current dioxin and furan emissions from industry in South Africa, in terms of compliance with the relevant emission limit values (ELVs) and the current challenges faced with the monitoring and analysis thereof.

Sphingomonas wittichii Strain RW1 Genome-Wide Gene Expression Shifts in Response to Dioxins and Clay.

Sphingomonas wittichii strain RW1 (RW1) is one of the few strains that can grow on dibenzo-p-dioxin (DD). We conducted a transcriptomic study of RW1 using RNA-Seq to outline transcriptional responses to DD, dibenzofuran (DF), and the smectite clay mineral saponite with succinate as carbon source. The ability to grow on DD is rare compared to growth on the chemically similar DF even though the same initial dioxygenase may be involved in oxidation of both substrates. Therefore, we hypothesized the reason for this lies beyond catabolic pathways and may concern genes involved in processes for cell-substrate interactions such as substrate recognition, transport, and detoxification. Compared to succinate (SUC) as control carbon source, DF caused over 240 protein-coding genes to be differentially expressed, whereas more than 300 were differentially expressed with DD. Stress response genes were up-regulated in response to both DD and DF. This effect was stronger with DD than DF, suggesting a higher toxicity of DD compared to DF. Both DD and DF caused changes in expression of genes involved in active cross-membrane transport such as TonB-dependent receptor proteins, but the patterns of change differed between the two substrates. Multiple transcription factor genes also displayed expression patterns distinct to DD and DF growth. DD and DF induced the catechol ortho- and the salicylate/gentisate pathways, respectively. Both DD and DF induced the shared down-stream aliphatic intermediate compound pathway. Clay caused category-wide down-regulation of genes for cell motility and chemotaxis, particularly those involved in the synthesis, assembly and functioning of flagella. This is an environmentally important finding because clay is a major component of soil microbes’ microenvironment influencing local chemistry and may serve as a geosorbent for toxic pollutants. Similar to clay, DD and DF also affected expression of genes involved in motility and chemotaxis.

Nanoparticular surface-bound PCBs, PCDDs, and PCDFs-a novel class of potentially higher toxic POPs.

In a previous study, Env Sci Poll Res:1-7, 2015 showed that polychlorinated biphenyls (PCBs), polychlorinated dibenzo dioxins (PCDDs), and polychlorinated dibenzo furanes (PCDFs) are found in commercially available (nano) particular titanium dioxide as a result of the fabrication. Here, we give a brief perspective and reason the toxicity of these new classes of persistent organic pollutants (POPs) by reviewing also their nanoparticular properties, such as surface-to-volume ratio, photocatalytic activity, polarity shifts, and stealth effect. These insights point towards a new class of POPs and toxicologic effects, which are related to the size but not a result of nanotechnology itself. We pave the way to the understanding of until now unresolved very complex phenomena, such as the indoor exposure, formation, and transformation of POP and sick-building syndrome. This is a fundamental message for nanotoxicology and kinetics and should be taken into account when determining the toxicity of nanomaterials and POPs separately and as a combination.

Mechanistic studies on the dibenzofuran and dibenzo-p-dioxin formation reactions from o-benzyne precursor

All the homogeneous formation mechanisms of dibenzo-p-dioxin (DD) and dibenzofuran (DF) from o-benzyne are predicted using the M06-2X-GD3, a method based on density functional theory. We find products arising from bimolecular reactions of o-benzyne with phenyl, phenoxy and phenylperoxy radicals to evolve in facile and exothermic mechanisms to yield DD and DF. Accordingly, these reaction channels are suitable for the specific flame or post-flame areas, in which oxidizing agents are insufficient to oxidize organic compounds completely. The activation enthalpies for all the elementary reactions are lower than 31.27kcal/mol, except the dehydration–cyclization reaction of D3—67.65kcal/mol, and thus these reactions are easy to occur. 2-Phenoxy-phenyl (B1) could be an important intermediate during the formation of PCDFs, because each of the follow-up elementary reactions is a rapid and spontaneous process, i.e. with a low potential barrier and negative reaction Gibbs energy.

Monitoring of Polychlorinated Dibenzo (p) Dioxins and Furans in Cement Kiln Emission Using Different Kinds of Fuel

Monitoring of Polychlorinated Dibenzo (p) Dioxins and Furans in Cement Kiln Emission Using Different Kinds of Fuel