Prevalence of emerging disinfection byproducts iodinated nucleosides in coastal drinking water

Halogenated nucleic acids have been proposed as candidate disinfection byproducts (DBPs) of health concern, while iodinated nucleosides have not been reported yet despite their potential toxicity. This study established an analytical method for iodinated nucleosides using solid-phase extraction and vacuum centrifugal concentration coupled with ultra-performance liquid chromatography-tandem mass spectrometry. The method achieved recoveries of 58.0%-112% for 12 targeted iodinated nucleosides, with limits of detection and quantification in the ranges of 0.16-0.54 ng/L and 0.53-1.79 ng/L, respectively. Using this method, all 12 iodinated nucleosides were detected in drinking water samples collected from ten coastal cities in China, with the concentration of a single species reaching 29.1 ng/L and a maximum total concentration of 145 ng/L. In addition to iodine substitution at nucleobases, iodination at riboses was observed for the first time. The concentrations of iodinated ribonucleosides were generally higher than those of iodinated deoxyribonucleosides, and iodination at C8 of purines and C5 of pyrimidines was the dominant form. The IC₅₀ values in CHO-K1 cells ranged widely from 77.37 μM to 2235 μM, and iodination at the 5'-position of the ribose moiety generally conferred higher cytotoxicity compared to iodination at nucleobases. 5'-I-5'-dA was pinpointed as a potential priority compound by integrating environmental concentrations and cytotoxicity. These findings provide the first evidence for the occurrence of iodinated nucleosides in coastal drinking water and highlight their intrinsic cytotoxicity and potential contribution to DBP-associated toxicity.