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.