Chlorination decreases acute toxicity of iodophenols through the formation of iodate and chlorinated aliphatic disinfection byproducts.

Highly toxic iodinated phenolic by-products were frequently detected in the oxidative treatment and disinfection of iodine-containing water. Herein, it was found that three model iodinated phenolic disinfection byproducts (DBPs), 2-iodophenol, 4-iodophenol and 2,4,6-triiodophenol, were reactive with HOCl, and the reaction rate constants (at pH 7.0 and 25℃) were 1.86 ×10, 1.62 ×10 and 7.5 ×10 Ms, respectively. When HOCl was in excess (HOCl/iodophenol = 40/1, [iodophenol] = 20 μM), acute toxicity of water sample containing iodophenols could be largely eliminated (> 85%), with the conversion of iodophenols into stable and non-toxic iodate (IO) and iodinated and chlorinated aliphatic DBPs. Besides IO, seven kinds of aromatic intermediate products including iodophenols, chloroiodophenols, iodoquinones, chloroiodoquinones, chloroquinones, chlorophenols, and coupling products were detected. C-I bond of iodophenols was cleaved in the reaction and the resulted aromatic products were further transformed into chlorinated aliphatic DBPs [trichloromethane (TCM), trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), and chloral hydrate (CH)] (mg/L level) and iodinated trihalomethanes (μg/L level). HOCl was effective for converting iodophenols into IO and less toxic chlorinated aliphatic DBPs. Considering that chlorine was widely used as disinfectant, transformation and toxicity alteration of emerging DBPs during chlorination/booster chlorination warrant further investigations.