Chloramination of iodide-containing waters: Formation of iodinated disinfection byproducts and toxicity correlation with total organic halides of treated waters

The formation of iodinated disinfection byproducts (I-DBPs) in drinking waters is of a concern due to their higher cyto- and genotoxicity than their chlorinated and brominated analogues. This study investigated the formation of I-DBPs under chloramination conditions using preformed chloramine and associated cyto- and geno-toxicities obtained with Chinese Hamster Ovary (CHO) cell assay. Cyto- and geno-toxicity of the samples were also calculated using DBP toxicity index values and correlated with total organic halide (TOX) formation. In low iodide (I^-) (0.32 μM, 40 μg L⁻¹) water, increasing dissolved organic carbon (DOC) concentration of selected waters from 0.1 to 0.25 mg L⁻¹ increased the formation of iodinated trihalomethanes (I-THMs), while further increases from 0.25 to 4 mg L⁻¹ produced an opposite trend. In high iodide water (3.2 μM, 400 μg L⁻¹), increasing DOC from 0.5 to 4 mg L⁻¹ gradually increased the I-THM formation, while a decrease was observed at 5.4 mg L⁻¹ DOC. Iodoform was the most influenced species from the changes in DOC concentration. While increasing the initial iodide concentration from 0 to 5 μM increased the formation of iodoform, it did not make any considerable impact on the formation of other I-THMs. The measured cytotoxicity of samples was significantly correlated with increasing DOC concentration. Unknown TOCl and TOI showed a high correlation with measured cytotoxicity, while calculated total organic chlorine (TOCl) and total organic iodine (TOI) did not correlate. The comparison of measured and calculated cytotoxicity values showed that the calculated values do not always represent the overall cytotoxicity, since the formation of unknown DBPs are not taken into consideration during the toxicity calculations.