Brominated biphenyls, highly

These observations indicate three possible reasons for the low accumulation of highly brominated biphenyls and benzenes in juvenile Atlantic salmon ... 

Low water solubility, possibly acting in conjunction with low membrane permeability, appears to be the main reason for the lack of accumulation of highly brominated biphenyls and hexabromobenzene from water by juvenile Atlantic salmon. 

The use of brominated biphenyls has been examined to induce dechlorination of highly chlorinated biphenyls including the hepta-, hexa-, and pentachloro congeners (Bedard et al. 1998). Di- and tri-bromo congeners were the most effective and were themselves reduced to biphenyl. This is noted again in Chapter 8, Section 8.2A.2. 

Highly brominated biphenyls and diphenyl ethers have been manufactured as flame-retardants, and the diphenyl ethers have apparently become environmental contaminants (references in Sellstrom et al. 1998 see also Chapter 3, Section 3.6.3). One of the reasons for concern is the formation of polybrominated dibenzofurans and dibenzo[-l,4]-dioxins (although not 2,3,7,8-tetra-bromdibenzo[-l,4]-dioxin) during subsequent incineration (Buser 1986). Mixed cultures of organisms isolated from sediments contaminated with PCBs and PBBs were shown to debrominate PBBs under anaerobic conditions (Morris et al. 1992), and the dominant congener — 2,4,5,2,4, 5 -hexabro-mobiphenyl — could be successively debrominated to 2,2,-dibromobiphenyl. On the other hand, in sediments from the most heavily contaminated site containing contaminants in addition to PBBs, very little debromination occurred and the recalcitrance was attributed to the toxicity of the other contaminants (Morris et al. 1993). 

Obtain the energy of each cation that might be generated by electrophilic addition of Br to biphenyl (biphenyl+Br+). Which one is most stable Are there others of comparable stability Examine the structure of the most stable cation(s), and draw all of the resonance contributors needed to describe this ion(s). Predict the product(s) of biphenyl bromination. Will the reaction be highly selective, moderately selective or unselective ... 

De la Mare and Maxwell199 measured the rate of bromination of biphenyl by hypobromous acid in 75 % aqueous acetic acid, in some cases catalysed by perchloric acid, at temperatures between —3.78 and +20.1 °C. They showed that whereas when mineral acid is present the brominating species is Br+ (or a solvate), in the absence of mineral acid it is BrOAc which is a highly reactive brominating species giving Ea = 7.9 (this value is only approximate since it also includes a contribution from bromination by HOBr), and the appropriate kinetic equation is then... 

In 1979, it was stated that poiybrominated aromatic ethers have received little attention (ref. 1). That statement is still applicable. Analyses to characterize this class of commercial flame retardants have been performed using UV (refs. 1-2), GC (refs. 1-6), and GC-MS (refs. 1-4). The bromine content of observed peaks was measured by GC-MS, but no identification could be made. The composition of poiybrominated (PB) diphenyl ether (DPE) was predicted from the expected relationship with polyhalogenated biphenyl, a class which has received extensive attention. NMR (refs. 3-6) was successfully used to identify relatively pure material which had six, or fewer, bromine atoms per molecule. A high performance liquid chromatography (HPLC) method described (ref. 1) was not as successful as GC. A reversed phase (RP) HPLC method was mentioned, but no further work was published. 

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

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]. 

The uptake of some brominated benzenes and polybrominated biphenyls in fish (Atlantic salmon) was investigated in 1976 for the first time in a static test by Zitko and Hutzinger [250]. After 96 hours, they found no uptake of hexabro-mobenzene (HBB) from water or food in Salmo salar. The fish contained 2.3% hexane-extractable fat. The polybrominated biphenyls were accumulated to a lower extent than the polychlorinated biphenyls. Zitko and Hutzinger [250] suggested that HBB with a high molecular weight of 552 can not be taken up by fish. They concluded also that it is possible that HBB can be taken up by fish but that this compound may be converted into a non-extractable form in fish. Experiments with C-labeled HBB are required to determine its fate. But as far as we know, no bio concentration experiments with C-labeled HBB and fish were conducted. 

A recent method of detection is electron capture negative ionisation (ECNI) as ionization technique in combination with GC-MS analysis. This method is advantageous because it offers a high sensitivity for compounds with four or more bromine atoms [36]. The sensitivity of ECNI for these compounds is approximately 10 times higher than with the use of an electron capture detector (ECD) [5]. In the analytical method which was developed to quantitate PCBs and PBBs in human serum, GC/ECD was used [30]. Because the response, and therefore the sensitivity, of the ECD depends on the position of the halogen on the biphenyl nucleus as well as the number of halogen atoms, it is necessary to run a standard for each compound to be determined [2], The use of narrow bore (0.15 mmi.d.) capillary columns is advised to obtain the required resolution [5]. 

A second group of specific xenobiotics in Teltow Canal sediments are halogenated aromatics. Several chlorinated and brominated mono- and diaromatic hydrocarbons were detected in high amounts within the extractable organic matter as reported previously (Schwarzbauer et al. 2001). The halogenated arenes identified in the hydrolysis extracts included mono- and dichlorinated naphthalenes 12+13. mono- and dihrominated naphthalenes 14+15. tetra- to hexachlorinated biphenyls (PCB) and 2,4,6-tribomoaniline. The peak pattern of the chlorinated naphthalenes was similar to the congener distribution in technical mixtures e.g. Halowax 1000 (Falandysz 1998). 

Brominated flame retardants (BFRs) are a structurally diverse group of compounds including aromatics, cyclic aliphatics, phenolic derivatives, ahphatics, and phthahc anhydride derivatives (Figure 31.3). The most common BFRs are tetrabromobisphenol A (TBBPA), polybrominated diphenyl ethers (PBDE), hexabromocyclododecane (HBCD), and polybrominated biphenyls (PBB). The primary use of TBBPA is as reactive additive in epoxy resin circuit boards, while decabromodiphenyloxide (DBDO) is primarily used in high impact polystyrene for electronic enclosures. PBDEs are typically used as the additive type of flame retardant in high impact polystyrene, acrylonitrile butadiene styrene, flexible polyurethane foam, textile coatings, wire and cable insulation and electrical connectors. 

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