Photodegradation of novel brominated flame retardants (NBFRs) in a liquid system: Kinetics and photoproducts

Abstract

The photolysis of four typical NBFRs decabromodiphenyl ethane (DBDPE), bis(2-ethylhexyl) tetrabromophthalate (TBPH), pentabromotoluene (PBT) and hexabromobenzene (HBB) were first explored under different sources of light, two temperatures, organic solvents and the presence of humic substance (HS). Degradation could be described by pseudo-first-order kinetic model. Under different irradiation sources, the degradation rates were in order of UVC (0.0616–0.137 min−1) > UVB (0.0348–0.0810 min−1) > sunlight (0.0102–0.0370 min−1) > UVA (almost no degradation). Under UVB irradiation, the half-life of NBFRs was the lowest in tetrahydrofuran (6.16–22.77 min), and the longest (93.42–>120 min) in acetone, indicating that organic solvents greatly affected the degradation kinetics. HS could influence the degradation, and DBDPE or TBPH respectively declined 13.92–30.68% and 12.17–59.41% at 240 min, while the degradation of PBT and HBB were highly inhibited. TBPH photolysis was affected by humic acid (HA) or fulvic acid (FA) concentration, but DBDPE degradation barely showed significant difference (p < 0.05) in the presence of 1 and 10 mg L−1 of HA. Photolytic products of the four NBFRs were identified by GC-NCI/EI-MS, indicating that the photodegradation process was mainly stepwise debromination from high- down to low-bromine-substituted NBFRs. 2,4,6-triBT and 2,4,5-triBT were identified as products of PBT. PBB, 1,2,4,5-tetraBB, 1,2,4-triBB, 1,3,5-triBB and 1,3/1,2-diBB were identified as products of HBB. Our observations could provide a few insights into the removal of NBFRs in a liquid environment.