Acute oral toxicity and liver oxidant/antioxidant stress of halogenated benzene, phenol, and diphenyl ether in mice: a comparative and mechanism exploration

The lethal doses (LD₅₀s) of fluorinated, chlorinated, brominated, and iodinated benzene, phenol, and diphenyl ether in mice were ascertained respectively under the consistent condition. The acute toxicity of four benzenes orders in fluorobenzene (FB)?<?iodobenzene?<?chlorobenzene≈bromobenzene, that of four phenols orders in 4-iodophenol≈4-bromophenol?<?4-chlorophenol (4-MCP)?<?4-fluorophenol (4-MFP), and that of four diphenyl ethers orders in 4,4′-iododiphenyl ether?<?4,4′-difluorodiphenyl ether?<?4,4′-dichlorodiphenyl ether≈4,4′-dibromodiphenyl ether. General behavior adverse effects were observed, and poisoned mouse were dissected to observe visceral lesions. FB, 4-MCP, and 4-MFP produced toxic faster than other halogenated benzenes and phenols, as they had lower octanol–water partition coefficients. Pathological changes in liver and liver/kidney weight changes were also observed. Hepatic superoxide dismutase, catalase activities, and malondialdehyde level were tested after a 28-day exposure, which reflects a toxicity order basically consistent with that reflected by the LD₅₀s. By theoretical calculation and building models, the toxicity of benzene, phenol, and diphenyl ether were influenced by different structural properties.     

Thermal formation of PBDD/F from tetrabromobisphenol A--a comparison of polymer linked TBBP A with its additive incorporation in thermoplastics

For a long period, polybrominated flame retardants are under discussion because of the formation of polybrominated dibenzo-p-dioxins (PBDD)/dibenzofurans (PBDF) (PBDD/F) in case of thermal stress. Concerning polymer linked tetrabromobisphenol A (TBBP A), formation of PBDD/F was commonly presumed to be sterically hindered because of the covalent fixation into the polymer backbone. Combustion experiments with additively incorporated TBBP A compared with its polymer linkage revealed, that this assumption is incorrect and has to be revised. Under same conditions, similar PBDD/F concentrations in the range of 17.5-19.6 mg PBBD/F per kg TBBP A applied were analyzed. PBDD/F homologue distribution patterns were almost identical predominated by low brominated PBDF. These findings for PBDD/F formation have to be considered in future discussions regarding thermal stress caused by combustion or recycling processes, including other flame retardants bound in polymer matrix, e.g. polybrominated polystyrene (PS), or those with molecular structures showing less analogy to PBDD/F, like hexabromocyclododecane. The second aspect introduced, is the influence of different plastics on the formation rates of PBDD/F. In this context, combustion experiments were performed in an atmosphere consisting of synthetic air and HBr. PBDD/F concentrations were 8.47 mg/kg polyethylene, 1.67 mg/kg PS, 3.92 mg/kg phenolic resin and 18.1 mg/kg epoxy resin. Distribution patterns of PBDD/F homologues could partly be correlated with the occurrence of the precursors polybrominated benzenes and phenols.     

Hydroxylated and methoxylated polybrominated diphenyl ethers and polybrominated dibenzo-p-dioxins in red alga and cyanobacteria living in the Baltic Sea

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs) are present in the ecosystem of the Baltic Sea. OH-PBDEs are known to be both natural products from marine environments and metabolites of the anthropogenic polybrominated diphenyl ethers (PBDEs), whereas, MeO-PBDEs appear to be solely natural in origin. Polybrominated dibenzo-p-dioxins (PBDDs) are by-products formed in connection with the combustion of brominated flame retardants (BFRs), but are also indicated as natural products in a red alga (Ceramium tenuicorne) and blue mussels living in the Baltic Sea. The aims of the present investigation were to quantify the OH-PBDEs and MeO-PBDEs present in C. tenuicorne; to verify the identities of PBDDs detected previously in this species of red alga and to investigate whether cyanobacteria living in this same region of the Baltic Sea contain OH-PBDEs, MeO-PBDEs and/or PBDDs. The red alga was confirmed to contain tribromodibenzo-p-dioxins (triBDDs), by accurate mass determination and additional PBDD congeners were also detected in this sample. This is the first time that PBDDs have been identified in a red alga. The SigmaOH-PBDEs and SigmaMeO-PBDEs concentrations, present in C. tenuicorne were 150 and 4.6 ng g(-1) dry weight, respectively. In the cyanobacteria 6 OH-PBDEs, 6 MeO-PBDEs and 4 PBDDs were detected by mass spectrometry (electron capture negative ionization (ECNI)). The PBDDs and OH-PBDEs and MeO-PBDEs detected in the red alga and cyanobacteria are most likely of natural origin.     

An intercalibration study on organobromine compounds: Results on polybrominated diphenylethers and related dioxin-like compounds

An intercalibration study on organobromine compounds has been conducted to evaluate the accuracy and reliability in the analysis of brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) and their related compounds like polybrominated and monobromo-polychlorinated dibenzodioxins and -furans (PBDDs/DFs, MoBPCDDs/DFs). This paper reports the results for these compounds in 'Mixed Standard Solutions' and 'Air-Dried Sediment'. The relative standard deviations (RSDs) for PBDEs, PBDDs/DFs and MoBPCDDs/DFs in mixed standard solutions ranged from 9% to 24%, 4% to 20% and 8% to 27%, respectively. The results of this study are better than those reported in earlier international interlaboratory studies due to general improvement in analytical methods and an increasing number of available authentic standards, particularly for PBDEs. In the analysis for higher brominated compounds such as octabromodibenzodioxin, the participants were advised to optimize the calibration curves befitting the range of concentrations found in samples because variation of relative response factors was noted. The results for 'Air-Dried Sediment' were also reasonable with RSDs from 10% to 38% for PBDEs, 8% to 38% for PBDDs/DFs and 17% to 36% for MoBPCDDs/DFs. In the sediment sample, possible errors in the sample pretreatment and/or interference by other compounds/impurities were indicated. The concentrations of pentabromodiphenylether, BDE100, varied more than the other PBDE isomers due to its poor separation in some chromatographic conditions. In addition, interference by PBDEs was observed in the analysis for PBDFs. Potential degradation/secondary formulation of PBDEs and PBDFs during the Soxhlet extraction were suggested when copper powder was added into the sediment samples. Inspite of these observations, the results in this study are better than those reported in other interlaboratory studies due to the advice given to participants for improving the results. Compared with the results for PCDDs/DFs (5-23% RSDs) and Co-PCBs (6-24% RSDs), the RSDs for most of the organobromine compounds were high, indicating an immature QA/QC approach for the analysis of PBDEs and related compounds in comparison to common chlorinated dioxins.     

Formation of chlorinated and brominated dioxins and other organohalogen compounds at the pilot incineration plant VERONA

Experiments were conducted at the VERONA pilot plant, an incineration plant with stationary grate and separate post-combustion chamber, using wood and propane as basic combustible materials and with controlled dosage of various bromine-, chlorine- and copper-containing compounds. The behaviour of the following compounds was studied in the combustion chamber, after the post-combustion chamber and after the heat exchanger: polychlorinated phenols (PCPh), polybrominated phenols (PBrPh), polychlorinated benzenes (PCBz), polybrominated benzenes (PBrBz), polychlorinated dioxins and furans (PCDD/F) and polybrominated dioxins and furans (PBDD/F). The bromine co-incineration leaded to very high bromophenol concentrations after the post-combustion chamber. The formation of brominated and mixed-halogenated phenols and the further reaction to halogenated dioxins is apparently a relevant reaction mechanism for dioxin formation in processes involving bromine. This assumption is supported by the high formation rates of PBDD/F found in the heat exchanger, which were 4-20 times higher than those of PCDD/F. Moreover, the strong correlations found between the formation rates of PCPh, PCBz and PCDD/F in the heat exchanger indicate that in addition considerable new formation of dioxins takes place through de novo synthesis. Experiments involving the variation of primary operational parameters and fuel properties have shown that the quality of post-combustion plays a much greater role than the other parameters. Furthermore, it became apparent that the congeners of the chlorophenols and of the chlorobenzenes, measured in various incineration stages, do not correlate closely with the dioxin concentrations after the heat exchanger.     

Formation of PCDD/Fs from oxidation of 2-monochlorophenol over an Fe2O3/silica surface

The role of iron in surface-mediated formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from 2-chlorophenol (2-MCP) was investigated over the temperature range of 200-550 °C under oxidative conditions. In order to compare and contrast with previous work on copper and ferric oxide-mediated pyrolysis of 2-MCP, identical reaction conditions were maintained (50 ppm 2-MCP, model fly-ash particles containing 5% Fe₂O₃ on silica). Observed products included dibenzo-p-dioxin (DD), 1-monochlorodibenzo-p-dioxin (1-MCDD), dibenzofuran (DF), 4,6-dichlorodibenzofuran (4,6-DCDF), 2,4- and 2,6-dichlorophenol, 2,4,6-trichlorophenol, quinone, catechol, chloro-o-quinone, chlorocatechol and polychlorinated benzenes. Yields of DD and 1-MCDD were 2 and 5 times higher than under pyolysis conditions, respectively. Although 4,6-DCDF was the major PCDD/F product formed with a yield that was 2.5× greater than under pyrolysis, the yield of non-chlorinated DF, which was the dominant PCDD/F product under pyrolysis, decreased by a factor of 3. Furthermore, the ∼2× higher yield of PCDDs under oxidative conditions resulted in a PCDD to PCDF ratio of 0.75 compared to a relatively low ratio of 0.39 previously observed under pyrolytic conditions.     

Physicochemical properties of selected polybrominated diphenyl ethers and extension of the UNIFAC model to brominated aromatic compounds

The aqueous solubilities (S(w)) at various temperatures from 283 K to 308 K and 1-octanol/water partition coefficients (K(ow)) for four polybrominated diphenyl ethers (PBDEs: 4,4'-dibromodiphenyl ether (BDE-15), 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), and 2,2',4,4',5,5'-hexabromodiphenyl ether (BDE-153)) were measured by the generator column method. The S(w) and K(ow) data revealed the effect of bromine substitution and basic structure on S(w) and K(ow). To estimate the infinite dilution activity coefficients (gamma(i)(w,infinity)) of the PBDEs in water from the S(w) data, enthalpies of fusion and melting points for those compounds were measured with a differential scanning calorimeter. Henry's Law constants (H(w)) of the PBDEs were derived from the determined gamma(i)(w,infinity) and literature vapor pressure data. Some physicochemical characteristics of PBDEs were also suggested by comparing the present property data with that of polychlorinated dibenzo-p-dioxins, brominated phenols and brominated benzenes in past studies. Furthermore, in order to represent different phase equilibria including solubility and partition equilibrium for other brominated aromatic compounds using the UNIFAC model, a pair of UNIFAC group interaction parameters between the bromine and water group were determined from the S(w) and K(ow) data of PBDEs and brominated benzenes. The ability of the determined parameters to represent both properties of brominated aromatics was evaluated.     

Photochemical transformations of tetrabromobisphenol A and related phenols in water

A method was developed for studies of the phototransformation at UV irradiation of aqueous solutions of tetrabromobisphenol A (TBBPA), tribromobisphenol A (TriBBPA), tetrachlorobisphenol A (TCBPA), 2,4-dichlorophenol at various pHs as well as 2-chlorophenol, 2-bromophenol, 3,4-dichlorophenol and bisphenol A at pH 11. The absorbance spectra of the compounds and the emission spectra of the light-source were determined and used to calculate disappearance quantum yields of the photochemical reactions that were taking place. No major differences between the disappearance quantum yields of TBBPA and TCBPA were observed at pH 10, while the disappearance quantum yield of TriBBPA was approximately two times higher. The rate of decomposition of TBBPA was six times higher at pH 8 than at pH 6. Identification of the degradation products of TBBPA and TriBBPA, by GC-MS analysis and by comparison to synthesised reference compounds, indicated that TBBPA and TriBBPA decompose via different mechanisms. Three isopropylphenol derivatives; 4-isopropyl-2,6-dibromophenol, 4-isopropylene-2,6-dibromophenol and 4-(2-hydroxyisopropyl)-2,6-dibromophenol, were identified as major degradation products of TBBPA while the major degradation product of TriBBPA was tentatively identified as 2-(2,4-cyclopentadienyl)-2-(3,5-dibromo-4-hydroxyphenyl)propane.     

Polybrominated, polychlorinated and monobromo-polychlorinated dibenzo-p-dioxins/dibenzofurans and dioxin-like polychlorinated biphenyls in marine surface sediments from Hong Kong and Korea

In this study we investigated occurrences and distribution patterns of dioxin-related compounds (DRCs) such as polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs), polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), monobromo-polychlorinated dibenzo-p-dioxins/dibenzofurans (MoBPCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) in marine surface sediments collected from the coastal waters of Hong Kong and Korea. In most sampling sites, concentrations of PCDDs were the highest, followed by DL-PCBs, PCDFs, PBDFs, PBDDs, MoBPCDDs and MoBPCDFs in this order. Levels of PBDD/Fs were generally 1-2 orders of magnitude lower than chlorinated analogues. Levels of PCDDs are higher than PCDFs in Hong Kong while levels of PBDFs are higher than PBDDs in Korea (p < 0.05). Report of PBDD/Fs and MoBPCDD/Fs in sediments from East Asian countries is novel and original. Environmental levels of PBDD/Fs are supposed to start increasing in accordance with rising production, use and disposal of brominated flame retardants (BFRs) and recycling processes of e-waste in Asian developing countries.     

Brominated phenols,anisoles, and dioxins present in blue mussels from the Swedish coastline

Introduction  

Naturally occurring hydroxylated polybrominated diphenyl ethers (OH-PBDEs), their methoxylated counterparts (MeO-PBDEs), and polybrominated dibenzo-p-dioxins (PBDDs), together with their potential precursors polybrominated phenols (PBPs) and polybrominated anisoles (PBAs), were analyzed in blue mussels (Mytilus edulis) gathered along the east coast (bordering the Baltic Sea) and west coast of Sweden (bordering the North Sea). Brown algae (Dictyosiphon foenicolaceus) and cyanobacteria (Nodularia spumigena) from the Baltic Sea, considered to be among the primary producers of these compounds, were also analyzed for comparison.     

Combustion of brominated flame retardants and behavior of its byproducts

The substance flow rate of PBDDs/DFs into flue gas and incineration residues from incineration of three types of waste samples containing brominated flame retardants were examined. The samples used consisted of PBDEs (a typical retardant), used TV casing materials (actual waste materials), and waste printed circuit boards. PBDDs/DFs concentrations in the experimental samples of PBDEs/PE, waste TV casing materials and printed circuit boards ranged between 3000 and 130,000 ng/g. These values are very high when compared to other investigations. The increase of chlorine concentration in input sample reduced the ratio of PBDDs/DFs in flue gas and raised the ratio of PCDDs/DFs. With adequate combustion control and flue gas treatment, the amount of PBDDs/DFs released from the incineration of resin containing brominated flame retardants was lower than the input amount. The presence of PBDDs/DFs in incineration residues dominated the total amount of dioxins released. When PBDDs/DFs, PCDDs/DFs and PXDDs/DFs were considered as a total, the total amount released was lower than the total amount input.     

Brominated-chlorinated diphenyl ethers formed by thermolysis of polybrominated diphenyl ethers at low temperatures

Polybrominated diphenyl ethers (PBDEs) are a group of brominated flame retardants (BFRs) used mainly as additives in different kinds of plastic material. Various PBDEs are found in all environmental compartments as well as in tissue and blood serum of animals and humans due to their persistence and tendency to bioaccumulate. Emission of PBDEs into the environment can occur during recycling of PBDE-containing plastic material or during their uncontrolled or insufficient combustion as e.g. in accidental fires or landfill fires. Under these circumstances, PBDEs can also function as precursor molecules for the formation of polybrominated dibenzodioxins (PBDDs) and dibenzofurans (PBDFs). In this study, we qualitatively investigated the reaction of two PBDE congeners, 2,2′,4,4′-tetrabromo diphenyl ether (BDE 47) and 2,2′,4,4′,5,5′-hexabromo diphenyl ether (BDE 153), as well as hexabromobenzene (HBB), a flame retardant used in the past, when exposed to temperatures between 250 °C and 500 °C. The formed reaction products were analysed by high resolution gas chromatography–low resolution mass spectrometry (HRGC-LRMS). Among others brominated–chlorinated diphenyl ethers were formed by chlorodebromination of the PBDEs. In addition, thermolysis of BDE 47 and BDE 153 in the presence of tetrachloromethane as model substance for an organic chlorine source was studied. Thermal treatment of HBB resulted in the formation of brominated–chlorinated benzenes.     

Prediction of the retentions of polybrominated dibenzo-p-dioxins (PBDDs) by using the retentions of polychlorinated dibenzo-p-dioxins (PCDDs)

The retention equations In k' = A + B/T of 49 polychlorinated dibenzo-p-dioxins (PCDDs) and 4 polybrominated dibenzo-p-dioxins (PBDDs) in gas chromatography (GC) have been investigated to evaluate the properties of regression coefficients A and B. The quantitative relationships between A and B values of PCDDs and those of PBDDs are found. The regression equations derived have correlation coefficients greater than 0.997. The A, B values of any PBDD can be predicted by using the A, B values of the PCDD according to these relationships. Using these predicted A and B values, the retention times of all PBDDs can be predicted at any temperature program. It is very useful to identify the peak position of any PBDD because at present there are only a few standards of PBDDs available.     

Photocatalytic oxidation of toxic organohalides with TiO2/UV: the effects of humic substances and organic mixtures

TiO2/UV photocatalytic oxidation of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), 1,2,3-trichlorobenzene and 4-chlorophenol were examined in aqueous solution in the presence of humic substances and organic mixtures to study if the degradation rates were affected. Both commercial and natural humic substances were observed to retard the photodegradation rates, with a greater effect from the natural humic substances. Acetonitrile and isopropanol also caused significant retardation of 4-chlorophenol photodegradation. The overall retardation can be attributed to the combination of light attenuation, inhibition and competition effects. Moreover, the TiO2/UV system favors the decomposition of compounds that have stronger adsorption onto the TiO2 surface. To engineer effective treatment facilities that use the TiO2/UV system for the treatment of toxic substances in wastewater, the methodology must allow for concerns about adventitious species which are present.     

The influence of pH on the degradation of phenol and chlorophenols by potassium ferrate

This paper presents information concerning the influence of solution pH on the aqueous reaction between potassium ferrate and phenol and three chlorinated phenols: 4-chlorophenol (CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP). The redox potential and aqueous stability of the ferrate ion, and the reactivity of dissociating compounds, are known to be pH dependent. Laboratory tests have been undertaken over a wide range of pH (5.8-11) and reactant concentrations (ferrate:compound molar ratios of 1:1 to 8:1). The reactivity of trichloroethylene was also investigated as a reference compound owing to its non-dissociating nature. The extent of compound degradation by ferrate was found to be highly pH dependent, and the optimal pH (maximum degradation) decreased in the order: phenol/CP, DCP, TCP; at the optimal pH the degree of degradation of these compounds was similar. The results indicate that for the group of phenol and chlorophenols studied, the presence of an increasing number of chlorine substituent atoms corresponds to an increasing reactivity of the undissociated compound, and a decreasing reactivity of the dissociated compound.     

Fate of PBDEs during food processing: Assessment of formation of mixed chlorinated/brominated diphenyl ethers and brominated dioxins/furans

The aim of this study was to evaluate effects of food processing on PBDE levels, in particular influence of heat treatment on degradation of PBDEs, including possible formation of chlorinated diphenyl ethers or brominated dioxins/furans as degradation products. It was shown that PBDEs heated in the presence of chlorine (from either organic or inorganic sources) formed mixed chlorinated/brominated diphenyl ethers. However, no PCDEs were formed in the presence of lipids. Lipid medium increased stability of PBDEs exposed to UV irradiation. Profile of congeners formed in result of the debromination reaction was significantly different than profiles observed by some other authors in aliphatic organic solvents. Grilling processes increased concentrations (calculated on the fresh product basis) of the studied compounds by 4–8/22–34% for electric/coal grill, respectively. Depending on the congener and on the applied heat treatment, PBDE mass in pork meat after grilling dropped by 26–53%. No detectable quantities of either brominated dioxins or furans were formed during thermal processing of food containing typical levels of PBDEs.     

Influence of combustion conditions on yields of solvent-extractable anhydrosugars and lignin phenols in chars: Implications for characterizations of biomass combustion residues

Anhydrosugars, such as levoglucosan and its isomers (mannosan, galactosan), as well as the solvent-extractable lignin phenols (methoxylated phenols) are thermal degradation products of cellulose/hemicellulose and lignin, respectively. These two groups of biomarkers are often used as unique tracers of combusted biomass inputs in diverse environmental media. However, detailed characterization of the relative proportion and signatures of these compounds in highly heterogeneous plant-derived chars are still scarce. Here we conducted a systematic study to investigate the yields of solvent-extractable anhydrosugars and lignin phenols in 25 lab-made chars produced from different plant materials under different combustion conditions. Solvent-extractable anhydrosugars and lignin phenols were only observed in chars formed below 350 °C and yields were variable across different combustion temperatures. The yields of mannosan (M) and galactosan (G) decreased more rapidly than those of levoglucosan (L) under increasing combustion severity (temperature and duration), resulting in variable L/M and L/(M + G) ratios, two diagnostic ratios often used for identification of combustion sources (e.g. hardwoods vs. softwoods vs. grasses). Our observations thus may provide an explanation for the wide ranges of values reported in the literature for these two ratios. On the other hand, the results of this study suggest that the ratios of the major solvent-extractable lignin phenols (vanillyls (V), syringyls (S), cinnamyls (C)) provide additional source reconstruction potential despite observed variations with combustion temperature. We thus propose using a property-property plot (L/M vs. S/V) as an improved means for source characterization of biomass combustion residues. The L/M-S/V plot has shown to be effective in environmental samples (soil organic matter, atmospheric aerosols) receiving substantial inputs of biomass combustion residues.     

A standardized method for assessment of oxidative transformations of brominated phenols in water

The term persistence has been used to confusion since it is used as a conceptual parameter without a uniform definition. Work is therefore being done in order to unite ideas and describe persistence based on the chemical reactivity and chemico-physical properties of compounds via investigation of the main degradation pathways in the environment; photolysis, hydrolysis-substitution-elimination (hse), oxidation, reduction and radical reactions. The present work is focused on developing a method to determine oxidative degradation rates of chemicals and thereby measurement of their susceptibility to undergo oxidation reactions. The method based on potassium permanganate works well for water soluble compounds and is easy, robust, inexpensive and reproducible. By using the method and varying the analysed substances, the degradation rates for brominated phenols, two chlorinated phenols and high volume production compounds such as tetrabromobisphenol A (TBBPA), tetrachlorobisphenol A (TCBPA) and bisphenol A (BPA) have been determined at pH 7.6+/-0.2. The reaction rates of the two halogenated BPA's are particularly fast, giving half-lives in seconds. The other test compounds have slower reaction rates but easily measured under the reaction conditions applied. The reactions are temperature dependent. There is evidence that pK(a) and the substitution pattern of the halogens affects the rate of the reactions. The method is robust and applicable for reaction rate constant measurements of present and potential future environmental contaminants.     

Pyrolysis and GC/MS-analysis of brominated flame retardants in on-line operation

Flame retardants such as brominated diphenyl ethers (Bromkal 70-5-DE, FR 300 BA), 2,4,6-tribromophenol, pentabromophenol and hexabromobiphenyl were pyrolyzed at 600°C, 700°C, 800°C and 900°C in absence of oxygen in a SGE pyrojector, and the residues were analyzed by means of GC/MS in on-line operation. The pyrolysis of Bromkal 70-5-DE hereby yielded bromobenzenes (PBBz), bromophenols (PBP) and brominated dibenzofurans (PBDF). PBBz, bromonaphthalenes (PBN) and PBDF could be detected in the FR 300 BA pyrolysate, whereas brominated benzenes and dibenzodioxins formed during the pyrolysis of 2,4,6-tribromophenol. Unlike the pyrolysis of 2,4,6-tribromophenol, pentabromophenol pyrolysis produced mainly bromobenzenes along with traces of bromonaphthalenes, bromodioxins and bromodiphenyl ethers. The pyrogram of hexabromobiphenyl showed bromobenzenes and brominated biphenyls as key pyrolysate components.