Iodinated X-ray contrast media (ICM) as precursors to disinfection byproduct (DBP) formation and enhanced toxicity as a function of pH and chlorinated oxidant

The objective of this study was to investigate the formation of iodinated disinfection by-products (iodo-DBPs) and mammalian cell cyto/genotoxicity in the presence of iodinated x-ray contrast media (ICM), chlorinated oxidants, and natural organic matter (NOM).The ICM chosen as the source of iodide for these experiments were iopamidol and iohexol.The experiments were conducted with aqueous chlorine or monochloramine as the chlorinated oxidant.The experiments were conducted at pH 6.5 -9.0.The NOM concentration was constant [DOC] = 5.57 mg/L.Chloroform formation in the presence of iopamidol, a regulated DBP, was highest at pH 9.0 with aqueous chlorine (up to 4014 nM) and pH 6.5 with monochloramine (up to 56 nM).Additionally, dichloroiodomethane followed a similar trend in the presence of iopamidol with concentrations in the chlorine experiments forming up to 650 nM and the monochloramine experiments forming up to 52 nM.Trichloroacetic acid (TCAA) formation generally decreased as pH increased; however, iopamidol significantly contributes to TCAA formation at pH 7.5 disrupting the normally observed TCAA formation trend in the presence of NOM.Toxicity of the iopamidol transformation in the presence of chlorinated oxidants and NOM was also investigated.The cytotoxicity index (CTI) values were highest for chlorine (i.e., 21.0) and monochloramine (i.e., 16.5) when compared to control experiments without iopamidol.Genotoxicity index (GTI) values were highest for chlorine (i.e., 7.1) and monochloramine (i.e., 3.5) when compared to control experiments.Iohexol DBP experiments resulted in an enhanced formation of iv chloroform, while very little dichloroiodomethane formed, and the TCAA formation observed was comparable to the chlorinated source water controls.With iohexol as the iodide source, the CTI and GIT values were highest with aqueous chlorine at 21.6 and 3.8, respectively, when compared to control experiments without iohexol present.Iopamidol acts as a precursor to DBP formation, while also enhancing mammalian cell cytotoxicity and genotoxicity after chlorine or chloramine disinfection.While iohexol formed regulated and unregulated DBPs, it also enhanced mammalian cell cytotoxicity and genotoxicity, though to a lesser extent than iopamidol.