Occurrence of Iodophenols in Aquatic Environments and the Deiodination of Organic Iodine with Ferrate(VI)

Toxic and odorous iodophenols are commonly identified as disinfection by-products (DBPs) in drinking water. Herein, ng/L levels of iodophenols were identified in river water, wastewater treatment plant effluent, and medical wastewater, with the simultaneous identification of mu g/L to mg/L levels of iodide (I-) and total organic iodine (TOI). Oxidation experiment suggested that the I-, TOI, and iodophenols could be oxidized by ferrate [Fe(VI)], and more than 97% of TOI had been transformed into stable and nontoxic IO3-. Fe(VI) initially cleaved the C-I bond of iodophenols and led to the deiodination of iodophenols. The resulted I- was swiftly oxidized into HOI and IO3 -, with the intermediate phenolic products be further oxidized into lower molecular weight products. The Gibbs free energy change (Delta G) of the overall reaction was negative, indicating that the deiodination of iodophenols by Fe(VI) was spontaneous. In the disinfection of iodine-containing river water, ng/L levels of iodophenols and chloro-iodophenols formed in the reaction with NaClO/NH2Cl, while Fe(VI) preoxidation was effective for inhibiting the formation of iodinated DBPs. Fe(VI) exhibited multiple functions for oxidizing organic iodine, abating their acute toxicity/ cytotoxicity and controlling the formation of iodinated DBPs for the treatment of iodide/organic iodine-containing waters.

Automated summary

This study identified the presence of milligram per liter levels of iodophenols and micrograms per liter to milligrams per liter levels of iodide and total organic iodine in river water, wastewater treatment plant effluent, and medical wastewater. Oxidation experiments showed that ferrate could oxidize iodide, total organic iodine, and iodophenols, leading to their deiodination. Pre-oxidation with ferrate was effective in inhibiting the formation of iodinated disinfection by-products.