Full Characterization of the UV Hydrodebromination Products of the Current-Use Brominated Flame Retardants Hexabromobenzene, Pentabromotoluene, and Pentabromoethylbenzene

Abstract

UV transformation was studied with three structurally closely related current-use brominated flame retardants (cuBFRs), i.e., hexabromobenzene (HBB), pentabromotoluene (PBT), and pentabromoethylbenzene (PBEB). Irradiation in toluene and benzotrifluoride (BTF) showed pseudo-first-order kinetics. Repeated high-performance liquid chromatographic (HPLC) fractionation, available reference standards, dedicated syntheses, gas chromatography with mass spectrometry (GC/MS), GC separation on two different phases including retention time rules based on dipole interactions, and proton magnetic resonance spectroscopy ( 1 H NMR) evaluation enabled a full structural characterization of all 22 transformation products formed by hydrodebromination. In addition to pentabromobenzene (only transformation product with five bromine), tetra-and tribrominated transformation products were predominantly formed in the case of all three cuBFRs. Hydrodebromination was favored by bromine removal from positions with a high Br density. Br → H exchange was about 3 times faster in positions flanked by two vicinal Br atoms. This favored pathway explained why hydrodebromination sharply dropped at the level of tribrominated cuBFRs because readily degradable precursors were no more available at this point. Hence, a full degradation of tribrominated and lower-brominated transformation products may only be achieved in combination with a different process such as microbial transformation.

Temporal Trends and Suspect Screening of Halogenated Flame Retardants and Their Metabolites in Blubbers of Cetaceans Stranded in Hong Kong Waters during 2013–2020

“…PBBz, TeBBz, and TrBBz were reported to be the step-by-step debromination products of HBBz under abiotic/biotic degradation/metabolism conditions. 13 , 49 , 50 No significant correlation was found between the concentrations of PBBz/TeBBz/TrBBz and HBBz in either porpoise or dolphin blubber samples, suggesting that the source of TrBBz/TeBBz/PBBz and HBBz is different in the investigated samples, and the debromination of HBBz may not be the main source of PBBz, TeBBz, and TrBBz in the investigated marine mammals. PBBz is widely used in polymeric materials, electronic equipment, and household furniture and has become ubiquitous in the aquatic environment and biota owing to relatively high bioaccumulation potential, while reports on the direct production and use of TrBBz and TeBBz are lacking.…”

“…Combined with HBBz quantified via target analysis, in total, four bromobenzenes were found in the cetacean bubbler samples in this study. PBBz, TeBBz, and TrBBz were reported to be the step-by-step debromination products of HBBz under abiotic/biotic degradation/metabolism conditions. ,, No significant correlation was found between the concentrations of PBBz/TeBBz/TrBBz and HBBz in either porpoise or dolphin blubber samples, suggesting that the source of TrBBz/TeBBz/PBBz and HBBz is different in the investigated samples, and the debromination of HBBz may not be the main source of PBBz, TeBBz, and TrBBz in the investigated marine mammals. PBBz is widely used in polymeric materials, electronic equipment, and household furniture and has become ubiquitous in the aquatic environment and biota owing to relatively high bioaccumulation potential, while reports on the direct production and use of TrBBz and TeBBz are lacking. ,, The developed industry and high population density of the PRD may promote the wide production and use of PBBz, and the presence of PBBz in marine mammals can mainly be attributed to the direct emission from the PRD rather the degradation/debromination of HBBz.…”

Photodegradation Kinetics and Solvent Effect of New Brominated Flame Retardants (NBFRS) in Liquid Medium

“…Photodegradation has more efficient performance compared with microbial degradation with slow degradation rate [ 20 , 21 ]. At present, some researchers have conducted preliminary studies on the photodegradation of NBFRs, mainly from two aspects: on the one hand, the effects of experimental conditions, including light conditions, environmental media [ 22 , 23 ] and the degradation kinetics of NBFRs [ 24 , 25 ]; on the other hand, the degradation pathway and degradation mechanism of NBFRs [ 26 , 27 ]. It can be found that organic solvents can be used to simulate the composition of environmental media [ 28 ], and research on the transformation of NBFRs in different polar solvents is conducive to analyzing their degradation characteristics in the actual environment.…”