Dibenzodioxins

These are probably ubiquitous in the environment, and their biodegradability has been extensively examined. This will not be discussed in detail here, and attention will be drawn merely to a few investigations that illustrate important aspects. 

Chlorinated dioxins occur in atmospheric deposition (Koester and Hites 1992), and will thereby enter the terrestrial environment and watercourses. The degradation of tetrachloro- through octa-chlorodibenzo[l,4]dioxins has been examined in low-nitrogen medium by Phanerochaete sor-dida YK-624 (Takada et al. 1996). All the compounds were extensively degraded, and the ring fission of 2,3,7,8-tetra- and octachlorodibenzo[l,4]dioxin produced 4,5-di- and tetrachlorocatechol. These results established important evidence for the biodegradability of even highly chlorinated dibenzodioxins. 

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Some hquid defoamers are preemulsified relatives of paste defoamers. In addition to the fatty components mentioned above, kerosene [8008-20-6] or an organic cosolvent such as 2-propanol have been used to enhance stabiUty of the oil—water emulsion and the solubiUty of the defoamer s active ingredients. These cosolvents are used less frequently as concerns increase about volatile organic emissions (VOCs) from the paper machine. Additionally, the use of ultrapure mineral oil in defoamers has become commonplace. Concern about the creation of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) in the pulping process has led to the discovery of unchlorinated precursor molecules, especially in recycled mineral oil and other organic cosolvents used in defoamer formulations (28). In 1995 the mineral oil that is used is essentially free of dibenzodioxin and dibenzofuran. In addition, owing to both the concern about these oils and the fluctuating cost of raw materials, the trend in paper machine defoamers is toward water-based defoamers (29). 

Dibenzo[b,/][l,5]diazocine, tetrahydro-conformation, 7, 704 Dibenzo[b,/][l,4]diazocinediones synthesis, 7, 675 Dibenzodioxin, 2,7-dichloro-toxicity, 3, 992 Dibenzodioxin, hexachloro-toxicity, 3, 992 Dibenzodioxin, octachloro-toxicity, 3, 992... 

Dibenzo[6,e][l,4]dioxin, 2-nitro-bromination, 3, 974 cleavage reactions, 3, 973 Dibenzo[b,e][l,4]dioxin, 2,3,7,8-tetrachloro-synthesis, 3, 985 toxicity, 3, 992 Dibenzodioxins... 

SW-846, is used to measure emissions of semivolatile principal organic constituents. Method 0010 is designed to determine destruction and removal efficiency (DRE) of POHCs from incineration systems. The method involves a modification of the EPA Method 5 sampling train and may be used to determine particulate emission rates from stationary sources. The method is applied to semivolatile compounds, including polychlorinated biphenyls (PCBs), chlorinated dibenzodioxins and dibenzofurans, polycyclic organic matter, and other semivolatile organic compounds. 

Ecological danger of polychlorinated dibenzodioxines and dibenzofurans 97MI26, 97MI45, 98MI33, 98MI34. 

In general, capillary gas chromatography provides enough resolution for most determinations in environmental analysis. Multidimensional gas chromatography has been applied to environmental analysis mainly to solve separation problems for complex groups of compounds. Important applications of GC-GC can therefore be found in the analysis of organic micropollutants, where compounds such as polychlorinated dibenzodioxins (PCDDs) (10), polychlorinated dibenzofurans (PCDFs) (10) and polychlorinated biphenyls (PCBs) (11-15), on account of their similar properties, present serious separation problems. MDGC has also been used to analyse other pollutants in environmental samples (10, 16, 17). 

As shown by several investigations [91], the bromine-rich polybromide phase by itself is hardly flammable and fireextinguishing properties have been reported occasionally. The formation of polybrominated dibenzo-dioxins (PBrDD) and furans (PBrDF) due to the plastic-containing housing of a zinc-flow battery cannot be totally neglected in the case of a fire, but their concentrations are far away from the tetrachloro dibenzodioxine (TCDD) toxic equivalents even in a worst-case scenario. 

Dioxins are prominent members of the class of polychlorinated hydrocarbons that also includes diben-zofuran, biphenyls and others. Dioxins are highly toxic environmental contaminants. Like others small planar xenobiotics, some dioxins bind with high affinity to the arylhydrocarbon (Ah) receptor. Dioxins activate the receptor over a long time period, but are themselves poor substrates for the enzymes which are induced via the Ah-receptor. These properties of the dioxins and related xenobiotics may be important for the toxicity of these compounds. Dioxins like 2,3,7,8-tetrachloro-p-dibenzodioxin can cause persistent dermatosis, like chloracne and may have other neurotoxic, immunotoxic and carcinogenic effects. 

The fate of aromatic bromine compounds such as brominated dibenzodioxins occurring on fly ash of municipal waste incinerators has been deduced from appropriate laboratory experiments. Stereoselective, first order ipso-substitution of bromine by chlorine is observed. 

Photochemical degradation of brominated dibenzodioxins and fiirans has been studied. Decay of these compounds under environmental conditions is much faster compared to the chlorine analogues due to the higher values for the quantum yields of the bromine compounds. 

During incineration of 1 in the polymeric matrix debromination/hydrogenation occur in addition to cyclization process. Tetrabrominated dibenzofuran isomers are the most abundant products formed in the temperature range between 300° or 400° (Figure 6 shows Br-composition at 300° - 800°C). Incineration at 400°C gives tetrabromo-benzofurans in yields up to 13 % (Fig. 6). Besides of PBDF, brominated dibenzodioxins are also formed, but to a much lesser extent (30-90 ppm) (ref. 11). 

It is possible that brominated dibenzodioxins and -furans are formed in trace levels during the preparation of technical bromoether products 1-2- Dumler (ref. 12) and others (ref. 17) have found PBDD/F in the ppm range in commercial samples of decabromodiphenyl ether. A more recent and advanced study has been... 

Aromatic bromine compounds can be formed and transformed during various thermal processes, like aromatic chlorine compounds (ref. 22). Brominated dibenzodioxins and -furans and mixed brominated/chlorinated compounds have been detected in trace levels in the fly ash of a municipal waste incinerator (ref. 23).Chlorine is generally abundant compared to the bromine of typical municipal waste the chlorine vs. bromine ratio is in the range of 250 1. 

These results show the fate of aromatic bromine compounds during municipal waste incineration bromine is exchanged by chlorine on the surface of fly ash at the electrostatic precipitator at 250-3(X)°C. But the toxic potential at brominated dibenzodioxins and furans is not reduced by these transformations. The increase of PCDD/F concentration in MWI by adding bromine compounds has been pointed out by Lahl and coworkers (ref. 26). 

Photolysis of all brominated dibenzodioxins investigated occurs very fast in n-hexane. The rate of degradation of all compounds follows a good first-order kinetic scheme. In Table 4 the calculated first order rate constants k are summarised along with the quantum-yields. The corresponding results for three brominated dibenzofurans are also included. 

Table 4. Photolysis constants (k) and Quantum Yields (O) of Brominated Dibenzodioxins and furans in n-Hexane as Solvent. A and B are replicates. 

The reaction products formed in the photolysis of all these brominated dibenzodioxins have been determined with dependence on time. In general, consecutive substitution of bromine by hydrogen does occur, this is shown below for photolysis of 1,2,3,4-TBDD (Fig. 11). 

This reaction has been also described for low chlorinated dibenzodioxins. Assuming an identical MS response factor for monoBrDD and monobromohydroxy-biphenyl ether (monoBrDPE) a quantification study shows that monoBrDPE is much more stable towards photolysis compared to monoBrDD, because it accumulates in the mixture of the reaction products. For the dibrominated dibenzodioxins the same reaction (ether fission) is observed but to a minor extent. With triBrDD and higher brominated BrDD no diaryl-ether products are observed at all. 

The use of aromatic brominated compounds as flame retardants has been a potential source of environmental contamination. Incomplete incineration of these compounds and wastes (plastics, textiles, oils etc...) containing brominated flame retardants caused formation of brominated/chlorinated dibenzodioxines (PBDDs/ PCDDs) and dibenzofurans (PCDFs/PBDFs) (refs. 1 - 4). 

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