Formation Mechanisms of Iodinated Disinfection By-Products from X-Ray Contrast Media

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In this cooperative project, the mechanisms will be elucidated and a kinetic model will be designed for the formation of iodinated disinfection by-products (iodo-DBPs) when chlorinated oxidants (i.e., chlorine and chloramines) react with iodinated X-ray contrast media (ICM) or their biological transformation products (TPs). ICM and their TPs are capable of passing biological barriers, as well as to some extent, sorptive barriers, such as activated carbon. ICM have been detected in several U.S. and European surface waters up to several μg/L, as well as in drinking water up to several 100 ng/L. ICM TPs were detected in ground water and drinking water up to 500 ng/L. Disinfection with chlorinated oxidants leads to the transformation only of selected ICM to form highly toxic, low molecular weight DBPs, such iodo-acids and iodo-trihalomethanes (iodo-THMs). In preliminary experiments, only iopamidol was significantly transformed, while diatrizoate, iohexol, iomeprol and iopromide were not significantly oxidized by HOCl. For this U.S.-German initiative, reaction pathways and the kinetic parameters will be elucidated for the oxidant reactions with ICM. Furthermore, the chemical structures of higher molecular weight and lower molecular weight ICM oxidation products will be identified, and the influence of treatment conditions (i.e., pH, natural organic matter [NOM], and bromide concentrations) on iodo-DBP formation will be determined. Additionally, the toxicity of these reaction mixtures will be assessed to determine whether oxidant reactions with ICM result in increased toxicity caused by DBPs.