Project title: Iodinated Trihalomethane Exposure Potential from Point-of-Use Water Treatment
Completed in: 2010
Chlorination and chloramination are oft-used techniques in water treatment throughout the United States to provide potable water to its citizens. As such the disinfection byproducts (DBPs) produced by such a process are closely regulated by the United States Environmental Protection Agency (US EPA) due to evidence related to human health risks as a result of exposure to these compounds. In contrast, iodine tablets are an oft-used technique to eliminate Giardia lamblia and bacteria when potable water is unavailable. However, the DBPs, produced by this method, specifically iodo-trihalomethanes (iodo-THMs) and iodo-haloacetic acids (iodo-HAAs) are not regulated. While, iodo-THM formation has been known since the mid-1970s to occur during iodine treatment processes, little data exists to inform the public of their potential exposures. Recently, iodo-DBPs have been detected in drinking water treatment plant effluents where an iodide-rich source water was treated with chloramine disinfection. Furthermore, a recently published study indicates that iodinated DBPs may exhibit greater mammalian cell genotoxicity and cytotoxicity than their chlorinated and brominated counterparts. To further investigate iodinated DBP formation, 1) sampling and analysis were conducted to measure iodoform formation upon iodine treatment of water 2) a study was initiated to determine the occurrence of iodinated THM in finished waters at a municipal water treatment facility utilizing chloramine disinfection. To observe iodoform formation, water samples were collected from surface waters across the state of Washington, USA. At all sampled locations, formation of iodoform was expected due to reaction of free iodine with dissolved organic carbon (DOC) in the source water. However, the level to which the byproducts will form was unknown. To determine the occurrence of iodinated THMS as a result of chloramination, water from a municipal drinking water treatment facility in the state of Washington was analyzed. The chloraminated municipal drinking water enabled analysis for a mix of iodinated THMs: bromodiiodomethane (CHBrI2), dichloroiodomethane (CHCl2I), bromochloroiodomethane (CHBrClI), dibromoiodomethane (CHBr2I), chlorodiiodomethane (CHClI2) in addition to analysis of iodoform or triiodomethane (CHI3). The samples were analyzed by solid-phase extraction-gas chromatography/mass spectrometry (SPE-GC/MS). The levels of detected iodo-THM were then compared to toxicity and genotoxicity data for iodo-DBPs. The results were also compared to US EPA designated Maximum Contaminant Level (MCL) value for regulated THMs, using appropriate scaling factors to account for different toxicity of iodo-THMS in comparison to their chlorinated and brominated analogues. The results of this study can inform the public of their possible exposure to iodo-THMS and their potential disease risk associated with the exposures.