Brominated dibenzodioxines

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). 

PCDDs, PCDFs, and PCBs are chemically classified as halogenated aromatic hydrocarbons. The chlorinated and brominated dibenzodioxins and dibenzofurans are classified as tricyclic aromatic compounds with similar physical and chemical properties, and both classes are similar structurally. Certain PCBs (the so-called coplanar or mono-ortho coplanar congeners) are also structurally and conforma-tionally similar. The most widely studied of these compounds is TCDD this compound, often called simply dioxin, represents the reference compound for this class. 

On a pilot scale (Figure 20.2) several process parameters such as temperamre, residence time and rotation speed and modes have been optimized. The temperature has been varied between 250 and 550°C. The residence time was between 1 and 4 h. The bromine content of aU products was determined and especially the amount of brominated dibenzodioxins and furans in the residue fractions was determined and correlated with temperature. 

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... 

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. 

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). 

An analogous series of dibenzodioxin relative retention time standards were prepared from dibenzodioxin (DBD) using Fe°/Br2 and the same procedure used to brominate the ether and the furan. The DBD itself was prepared by refluxing ortho-chlorophenol with NaOH. 

H. Thoma, G. Hauschulz, E. Knorr and O. Hutzinger, "Polybrominated Dibenzofurans (PBDF) and Dibenzodioxins (PBDD) from the Pyrolysis of Neat Brominated Diphenylethers, Biphenyls and Plastic Mixtures of these Compounds,"Chemosphere, JJi, 277(1987). 

Buser, H.R. Rapid photol34ic decomposition of brominated and brominated/chlorinated dibenzodioxins and dibenzofurans, Chemosphere, 17(5) 899-903, 1988. 

Dumler R, Thoma H, Lenoir D, et al. 1989b. Thennal formation of polybrominated dibenzodioxins (PBDD) and dibenzofurans (PBDF) from bromine containing flame retardants. Chemosphere 19(l-6) 305-308. 

Incubation in soils showed that polybrominated biphenyls were resistant to degradation, but were apparently not taken up by plants or leached into groundwater [261]. Commercial formulations of brominated aromatic flame retardants had variable composition some contained highly brominated phenols, but no evidence of contamination with dibenzodioxins and dibenzofurans was found [198]. 

BuserHR. 1987. Brominated and brominated/chlorinated dibenzodioxins and dibenzofurans Potential environmental contaminants. Chemosphere 16 713-732. 

In response to the continuing discovery of the persistence, bioaccumulative properties, and toxicity of POPs, regional, national and international policies ban the intentional production of compounds, such as polychlorinated biphenyls (PCBs), several organochlo-rine pesticides, such as mirex and dieldrin, and the brominated flame retardants poly-brominated diphenyl ethers (penta-BDE and octa-BDE, and most recently, deca-BDE). Policies and programs have also targeted the unintentional production and release of POPs such as polychlorinated dibenzodioxins and furans (PCDD/Fs). Evidence of the success of these policies has been seen in immediate reductions of air concentrations, followed by declining concentrations in water bodies, soils, biota and our food supplies... 

UBA (Federal Environmental Agency)(1989) [Stat of facts. Polybrominated dibenzodioxins (PBDD) - Polybrominated dibenzofurans (PBDF). Second supplement Polybrominated biphenyls.] In Polybrominated dibenzodioxins and dibenzofurans (PBDD/ PBDF) from brominated flame retardants. Report of the working group on brominated flame retardants to the Environment Minister Conference. Bonn, Tederal Ministry for the Environment, Nature Conservation and Nuclear Safety, pp 95-97 (in German)... 

Figure 5.18 Relation between the excretion rate constant ( 2) and octanol-water partition coefficient (ATd,oct) for polyhalogenated hydrocarbons chlorinated dibenzofurans O, chlorinated dibenzodioxins O, brominated biphenyls T, chlorinated naphthalenes , brominated benzenes , chlorinated biphenyls , chlorinated benzenes. [Reproduced with permission from A. Opperhuizen and D. T. H. M. Sijm, Environ. Toxicol. Chem. 9, 175 (1990). Copyright SETAC, Pensacola, FL, USA.]...

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