Halogenation of Bisphenol-A, Triclosan, and Phenols in Chlorinated Waters Containing Iodide

Free chlorine reacts with the iodide (I-) present in disinfected waters to produce free iodine. Past research has indicated that this nonchlorinated oxidant exhibits greater reactivity and potentially produces more toxic byproducts than free chlorine alone. In this study, we examined the reactivity of the phenolic compounds 2,4-dichlorophenol, triclosan, and bisphenol A in chlorinated waters containing I-. The free iodine mediated reactions were probed as a function of the initial I- concentration and the solution pH. Over the pH range of 5.5 to 10 for an initial I- concentration of 10 mu M, the observed transformation kinetics of 2,4-dichlorophenol were generally 2-15x faster than reactions with free chlorine alone, while for triclosan and bisphenol A the free iodine mediated transformations were approximate to 3-20x and approximate to 230-660x faster, respectively. A comprehensive reaction model that simultaneously accounts for free chlorine and free iodine reactivity in these systems was developed to determine second order rate constants for the chlorinated and iodinated oxidants. For all test compounds, iodinated daughter products are rapidly produced when free chlorine reacts in the presence of I-.