Occurrence and Mammalian Cell Toxicity of Iodinated Disinfection Byproducts in Drinking Water

An occurrence study was conducted to measure five iodo-acids (iodoacetic acid, bromoiodoacetic acid, (Z)-3-bromo-3-iodo-propenoic acid, (E)-3-bromo-3-iodo-propenoic acid, and (E)2-iodo-3-methylbutenedioic acid) and two iodo-trihalomethanes (iodo-THMs), (dichloroiodomethane and bromochloro-iodomethane) in chloraminated and chlorinated drinking waters from 23 cities in the United States and Canada. Since iodoacetic acid was previously found to be genotoxic in mammalian cells, the iodo-acids and iodo-THMs were analyzed for toxicity.A gas chromatography (GC)/negative chemical ionization-mass spectrometry (MS) method was developed to measure the iodo-acids; iodo-THMs were measured using GC/high resolution electron ionization-MS with isotope dilution. The iodo-acids and iodo-THMs were found in waters from most plants, at maximum levels of 1.7 mu g/L (iodoacetic acid), 1.4 ug/L (bromoiodoacetic acid), 0.50 mu g/L ((Z)-3-bromo-3-iodopropenoic acid), 0.28 mu g/L ((E)-3-bromo-3-iodopropenoic acid), 0.58 mu g/L ((E)-2-iodo-3-methylbutenedioic acid), 10.2 mu g/L (bromochloroiodomethane), and 7.9 mu g/L(dichloroiodomethane). Iodo-acids and iodo-THMs were highest at plants with short free chlorine contact times (<1 min), and were lowest at a chlorine-only plant or at plants with long free chlorine contact times (>45 min). Iodide levels in source waters ranged from 0.4 to 104.2 ug/L(when detected), but there was not a consistent correlation between bromide and iodide. The rank order for mammalian cell chronic cytotoxicity of the compounds measured in this study, plus other iodinated compounds, was iodoacetic acid > (E)-3-bromo-2-iodopropenoic acid > iodoform > (E)-3-bromo-3-iodo-propenoic acid > (Z)-3-bromo-3-iodo-propenoic acid > diiodoacetic acid > bromoiodoacetic acid > (E)-2-iodo-3-methylbutenedioic acid > bromodiiodomethane > dibro-moiodomethane > bromochloroiodomethane approximate to chlorodi-iodomethane > dichloroiodomethane. With the exception of iodoform, the iodo-THMs were much less cytotoxic than the iodo-acids. Of the 13 compounds analyzed, 7 were genotoxic; their rank order was iodoacetic acid >> diiodoacetic acid > chlorodiiodomethane > bromoiodoacetic acid > E-2-iodo-3-methylbutenedioic acid > (E)-3-bromo-3-iodo-propenoic acid > (E)-3-bromo-2-iodopropenoic acid. In general, compounds that contain an iodo-group have enhanced mammalian cell cytotoxicity and genotoxicity as compared to their brominated and chlorinated analogues.