3 research outputs found
Comparison studies of the mechanistic formation of polyhalogentaed dibenzo-p-dioxins and furans from the thermal degradation of 2-bromophenol and 2-chlorophenol
Emissions of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) from hazardous waste incinerators, and many other sources for combustion have been considered environmentally hazardous and a major health threat. Recently, a growing number of materials containing brominated hydrocarbons, commonly used flame retardants, have been disposed in municipal and hazardous waste incinerators. This results in the increased potential for formation of PBDD/Fs and other hazardous combustion by-products. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. In fact, studies have shown that brominated phenols form higher yields of PBDD/Fs than the analogous chlorinated phenols form PCDD/Fs. For this study, the individual homogeneous, gas-phase oxidative and pyrolytic thermal degradations of 2-bromophenol and 2-chlorophenol were studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000°C. In addition, 50:50 mixture of 2-chlorophenol and 2-bromophenol with a combined concentration of 88 ppm was studied under similar conditions. Also in order to compare previous work with 2-chlorophenol, the surface catalyzed gas-phase reactions for 2-bromophenol to form PBDD/Fs are described over a temperature range from 250 to 550°C. The results are compared and contrasted with each other in order to understand the roles oxygen, chlorine and bromine play in the formation of PCDD/Fs and PBDD/Fs. Reaction pathways to PCDD/F and PBDD/F products as well as all other products detected are proposed that are consistent with the experimental data for each condition. The presence of oxygen increases the formation of PBDFs and PCDFs. Presence of bromine increases the concentration of Cl radicals which in turn increases chlorination and formation of 4,6-dichlorodibenzofuran (4,6-DCDF). However the yields of the PCDFs and PBDFs are considerably less with the presence of both bromine and oxygen. The pool of ·OH and concentration of the chlorine atoms is reduced and thus prevents these furans from becoming major products
Monohydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) and Dihydroxylated Polybrominated Biphenyls (Di-OH-PBBs): Novel Photoproducts of 2,6-Dibromophenol
Hydroxylated polybromodiphenyl ethers
(OH-PBDEs) are emerging aquatic
pollutants, but their origins in the environment are not fully understood.
There is evidence that OH-PBDEs are formed from bromophenols, but
the underlying transformation processes remain unknown. Here, we investigate
if the photoformation of OH-PBDEs from 2,6-dibromophenol in aqueous
solution involves 2,6-bromophenoxyl radicals. After the UV irradiation
of an aqueous 2,6-dibromophenol solution, HPLC–LTQ-Orbitrap
MS and GC–MS analysis revealed the formation of a OH-PBDE and
a dihydroxylated polybrominated biphenyl (di-OH-PBB). Both dimeric
photoproducts were tentatively identified as 4′-OH-BDE73 and
4,4′-di-OH-PBB80. In addition, three debromination products
(4-OH-BDE34, 4′-OH-BDE27, and 4,4′-di-OH-PBBs) were
observed. Electron paramagnetic resonance spectroscopy revealed the
presence of a 2,6-dibromophenoxyl radical with a six-line spectrum
(a<sup>H</sup> (2 <i>meta</i>) = 3.45 G, a<sup>H</sup> (1 <i>para</i>) = 1.04 G, <i>g</i> = 2.0046) during irradiation
of a 2,6-dibromophenol solution in water. The 2,6-dibromophenoxyl
radical had a relatively long half-life (122 ± 5 μs) according
to laser flash photolysis experiments. The <i>para–para</i> C–C and O–<i>para</i>-C couplings of these
2,6-dibromophenoxyl radicals are consistent with the observed formation
of both dimeric OH-PBDE and di-OH-PBB photoproducts. These findings
show that bromophenoxyl radical-mediated phototransformation of bromophenols
is a source of OH-PBDEs and di-OH-PBBs in aqueous environments that
requires further attention
Evaluation of Common Use Brominated Flame Retardant (BFR) Toxicity Using a Zebrafish Embryo Model
Brominated flame retardants (BFRs) are used to reduce the flammability of plastics, textiles, and electronics. BFRs vary in their chemical properties and structures, and it is expected that these differences alter their biological interactions and toxicity. Zebrafish were used as the model organism for assessing the toxicity of nine structurally-diverse BFRs. In addition to monitoring for overt toxicity, the rate of spontaneous movement, and acetylcholinesterase and glutathione-S-transferase (GST) activities were assessed following exposure. The toxicities of BFRs tested can be ranked by LC50 as tetrabromobisphenol A (TBBPA) < 4,4′-isopropylidenebis[2-(2,6-dibromophenoxyl)ethanol] (TBBPA-OHEE) < Pentabromochlorocyclohexane (PBCH) < 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) < hexabromocyclododecane (HBCD) < hexabromobenzene (HBB) < Tetrabromophthalic anhydride (PHT4). No adverse effect was observed in di(2-ethylhexyl) tetrabromophthalate (TBPH) or dibromoneopentyl glycol (DBNPG)-treated embryos. The rate of spontaneous movement was decreased in a concentration-dependent manner following exposure to four of the nine compounds. GST activity was elevated following treatment with PBCH, TBBPA, HBCD, and HBB. The results indicate that exposure to several BFRs may activate an antioxidant response and alter behavior during early development. Some of the BFRs, such as TBBPA and TBBPA-OHEE, induced adverse effects at concentrations lower than chemicals that are currently banned. These results suggest that zebrafish are sensitive to exposure to BFRs and can be used as a comparative screening model, as well as to determine alterations in behavior following exposure and probe mechanisms of action