Iopamidol as a Precursor to DBP Formation in Drinking Water as a Function of Natural Matter and Bromide

Iopamidol, one of the most commonly used and detected iodinated X-ray contrast media in water sources, is inert in the human body but reacts and degrades in the presence of aqueous chlorine to form highly cytotoxic/genotoxic disinfection by-products (DBPs). The objectives of this study were to investigate (1) the effect of iopamidol on the formation and speciation of DBPs in multiple source waters (SWs), (2) the formation of TOX/DBPs in SWs containing iopamidol, bromide, and chlorinated oxidants, (3) the impact of prechlorination time on TOX/DBP formation during chloramination of SWs containing iopamidol and (4) kinetic modeling of TOX, iodate, and DBP formation due to chlorination of iopamidol. SWs from Akron, Barberton, and Cleveland Water Treatment Plants containing iopamidol or iopamidol/bromide were dosed with chlorinated oxidant at pH 6.5-9.0 for 0-72 h.The study showed that the yields of either TTHMs or HAAs exhibited a strong correlation with humic, fulvic, and combined fulvic and humic fractions at pH 7.5. Similarly, the yields of TOCl/UTOCl exhibited strong correlation with SUVA254 at pH 7.5. Although iopamidol directly formed CHCl3, TCAA, and CHCl2I in chlorinated water; iopamidol exhibited minimal impact on DBP formation compared to NOM. In the presence of bromide and aqueous chlorine, iopamidol formed more DBPs. TOI loss was unaffected by the concentrations of bromide. TOCl and TOBr, respectively decreased and increased with increasing bromide concentration but was unaffected by iopamidol concentration. As bromide concentration increased the concentrations of fully brominated DBPs increased while fully chlorinated DBPs and CHCl2I decreased. CHBrClI increased with increasing bromide concentration in CSW. Also, iodo-DBPs increased with increasing iopamidol concentration.Generally, in the presence of bromide and iopamidol, lower amounts of DBPs including iodo-DBPs were formed in chloraminated SWs then chlorinated SWs. In SWs chlorinated before ammonia addition to form NH2Cl, significant amounts of iodo-DBPs were found during chloramination than prechlorination. However, CHCl3 and TCAA formation stopped after ammonia addition.The kinetic model adequately predicted TOI loss and, iodate, TOCl, and DBP formation. Since iopamidol impacted DBP formation, a limitation on the use of iopamidol in medical imaging facilities could reduce iopamidol concentrations in SWs.