Iodide promotes bisphenol A (BPA) halogenation during chlorination: Evidence from 30 X-BPAs (X = Cl, Br, and I)

As a well known endocrine-disrupting and model chemical, bisphenol A (BPA) may pose a serious threat to human health, since it and its disinfection by-products (DBPs) have been detected in drinking water , urine, human colostrum, adipose tissue , and placenta samples. Although chlorinated BPAs (Cl-BPAs) and iodinated BPAs (I-BPAs) have been well studied, brominated BPAs (Br-BPAs), and mixed halogenated DBPs like bromo-iodo-BPAs (Br-I-BPAs), and bromo-chloro-iodo-BPAs (Cl-Br-I-BPAs) are less well understood. Notably, the role of iodide (I - ) during chlorination is not well understood, since the studies of the I-DBPs mainly focus on their genotoxicity and cytotoxicity. To understand the formation mechanisms of halogenated bisphenol A (HBPs) during chlorination with bromide (Br - ) and/or I - , and the role of I - during chlorination, three set of reactions were performed in the laboratory (“BPA + chlorine + Br - ”, “BPA + chlorine + I - ” and “BPA + chlorine + Br - +I - ” assigned as group A, B and C respectively). Thirty HBPs were identified and 18 of them were never reported before. I - increases the transformation rate of BPA into HBPs as I-BPAs act as intermediate HBPs during chlorination that easily react with HClO/ClO - and HBrO/BrO - to form Cl-BPAs and Br-BPAs. HIO/IO - showed higher reactivity towards BPA and HBPs than that of HBrO/BrO - and HClO/ClO - . The recycling of I - was observed in the reactions of “BPA + chlorine + I - ” and “BPA + chlorine + Br - +I - ”, which may explain why I - can induce BPA to transform into HBPs and suggests that I - may act as a catalyst during the BPA chlorination reactions. The reaction pathways are proposed which present the reactions of BPA and HBPs with HClO/ClO - , HBrO/BrO - , and HIO/IO - , as well as the recycling of I - . This study describes the potential DBP formation and transformation mechanisms of BPA and its 16 alternatives, as well as the role of I - on the transformation of phenol compounds during chlorination.