Formation of DBPs and halogen-specific TOX in the presence of iopamidol and chlorinated oxidants

Abstract

Iopamidol is a known direct precursor to iodinated and chlorinated DBP formation; however, the influence of iopamidol on both iodo/chloro-DBP formation has yet to be fully investigated. This study investigated the effect of iopamidol on the formation and speciation of halogen-specific total organic halogen (TOX), as well as iodo/chloro-DBPs, in the presence of 3 source waters (SWs) from Northeast Ohio and chlorinated oxidants. Chlorination and chloramination of SWs were carried out at pH 6.5-9.0 and, different iopamidol and dissolved organic carbon (DOC) concentrations. Total organic iodine (TOI) loss was approximately equal (22-35%) regardless of SW. Total organic chlorine (TOCl) increased in all SWs and was substantially higher in the higher SUVA₂₅₄ SWs. Iopamidol was a direct precursor to chloroform (CHCl₃), trichloroacetic acid (TCAA), and dichloroiodomethane (CHCl₂I) formation. While CHCl₃ and TCAA exhibited different formation trends with varying iopamidol concentrations, CHCl₂I increased with increasing iopamidol and DOC concentrations. Low concentrations of iodo-acids were detected without discernible trends. Total trihalomethanes (THMs), total haloacetic acids (HAAs), TOCl, and unknown TOCl (UTOCl) were correlated with fluorescence regional volumes and SUVA₂₅₄. The yields of all these species showed a strong positive correlation with fulvic, humic, and combined humic and fulvic regions, as well as SUVA₂₅₄. Iopamidol was then compared to the 3 SWs with respect to DBP yield. Although the SUVA₂₅₄ of iopamidol was relatively high, it did not produce high yields of THMs and HAAs compared to the 3 SWs. However, chlorination of iopamidol did result in high yields of TOCl and UTOCl.

Keywords: Aqueous chlorine; Disinfection byproducts; Iopamidol; Monochloramine; Natural organic matter; Total organic halogen.