Formation of brominated by-products during the degradation of tetrabromobisphenol S by Co2+/peroxymonosulfate oxidation

Abstract

Tetrabromobisphenol S (TBBPS), an emerging brominated flame retardant, can cause neurotoxic and cytotoxic effects to human physiology. In this study, the degradation of TBBPS in Co2+ activated peroxymonosulfate (PMS) oxidation process was explored. In particular, brominated by-products formed during the degradation of the TBBPS were examined. It was found that TBBPS could be effectively removed in the Co2+/PMS oxidation process. The pseudo-first-order rate constants were 0.13 min−1 at 0.2 mM PMS and 0.5 μM Co2+ initially. It appeared that TBBPS degradation occurred via ▪ and HO attacks, but ▪ played a dominant role. The presence of natural organic matter (NOM) greatly inhibited the transformation of the TBBPS, which can be explained by the scavenging of the radical species. ▪ β-Scission, debromination, and cross-coupling were identified as the main reaction pathways of TBBPS degradation in the Co2+/PMS system. Further oxidation and ring-opening of the intermediates generated brominated by-products including bromoform, monobromoacetic acid, and dibromoacetic acid. The formation of the brominated by-products increased gradually in approximately 48 h. But, the presence of NOM reduced the yields of the brominated -by-products. The findings of this study indicate that organic bromine contaminants can be effectively removed but lead to brominated by-products in the activated PMS oxidation process, which should be taken into consideration when ▪-based oxidation technology is applied.