No abstract

Polybrominated diphenyl ethers (PBDEs) are widely used as additive flame retardants in, for example, textiles, computers, television sets, and other electrical appliances. PBDEs are ubiquitous environmental contaminants, present also in humans. The environmental levels of the PBDEs are, however, still in general lower than those of polychlorinated biphenyls (PCBs). However, while the levels of PCBs generally are decreasing, those of the PBDEs are increasing in, for example, human milk. In the present study 32 individual PBDE congeners were synthesized and characterized. Physicochemical parameters including melting points and UV, 1H NMR, and mass spectra are reported. Twenty-nine monobrominated to heptabrominated diphenyl ethers were synthesized by the coupling between four diphenyliodonium salts and nine phenolates. One tetrabromodiphenyl ether and two hexabromodiphenyl ethers were synthesized by bromination of two different PBDEs. Twenty-one of the PBDEs and two of the iodonium salts, 2,2‘,4,4‘-tetrabromodiphenyliodonium chloride and 3,3‘,4,4‘-tetrabromodiphenyliodonium chloride, are to the authors' knowledge described for the first time. These synthesized reference compounds will aid in the identification and quantification of PBDEs present in environmental samples and will allow further assessment of PBDE toxicity.

A growing number of studies have reported phenolic halogenated compounds (PHCs) that are retained in the blood of humans and wildlife. These PHCs may be industrial chemicals; metabolites thereof, as in the case with polychlorobiphenylols (OH-PCBs); or of natural origin. The present study was aimed to identify hitherto unknown PHCs in human plasma with chemical structures that are consistent to PHCs known to possess endocrine-disrupting activity. For this purpose, samples of blood plasma from 10 randomly selected male blood donors from Sweden were pooled and analyzed by GC/ECD and GC/MS. Brominated, bromochlorinated, and chlorinated methyl derivatives of phenols and OH-PCBs were synthesized to be used as authentic reference standards. More than 100 PHCs were indicated in the plasma, and among those a total of 9 monocyclic brominated or chlorinated phenol-, guaiacol-, and/or catechol-type compounds were identified as their methylated derivatives. The two major compounds were 2,4,6-tribromophenol and pentachlorophenol. Thirty-eight OH-PCB congeners were structurally identified on two GC columns of different polarity. The origin of the OH-PCB metabolites in the context of their parent PCB congeners are suggested. Other PHCs identified in the male plasma were Triclosan (5-chloro-2-[2,4-dichlorophenoxy] phenol), a common bactericide; 4-hydroxy-heptachlorostyrene, a metabolite of octachlorostyrene; and 3,5-dibromo-2-(2,4-dibromophenoxy)phenol, a natural compound and a potential metabolite of polybrominated diphenyl ethers.

To predict the persistency of a chemical in the environment, the chemical's physical-chemical properties and its reactivity in the environment need to be known or at least estimated. The partitioning of a chemical can be described on the basis of its water solubility, its octanol/water partitioning coefficient, and its vapor pressure. The mechanisms by which a chemical can be transformed may be categorized as being hydrolysis, oxidation, reduction, and photolysis. This study establishes a method for estimating the relative susceptibility of some potential environmental pollutants to undergo hydrolysis reactions. The method used the second-order rate constant for the reaction with sodium methoxide in methanol/N,N-dimethylformamide (DMF) as an indicator of relative susceptibility toward hydrolysis. The decabromodiphenyl ether is rapidly hydrolyzed, that is, undergoes nucleophilic aromatic substitution, while the rate of reaction of less brominated diphenyl ethers decreased by roughly a factor of 10 for each decrease in the level of bromination. Hexachlorobenzene was found to have a similar rate to a nonabromodiphenyl ether. 2,2-Bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT) was transformed to 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (DDE) immediately under these conditions, while DDE showed no apparent reaction. The results show that chemicals that can undergo elimination reactions are rapidly transformed, as are perhalogenated chemicals that can undergo substitution reactions. These chemicals are not likely to persist in the environment, while those that did not show any observable reactivity under similar hydrolytic conditions may persist for a very long time.