Determination, synthesis and survey of iodinated trihalomethanes in water treatment processes

Trihalomethanes (THMs) are formed as a result of the interaction of free aqueous chlorine, used as a disinfectant in drinking water, with the organic matter in raw water. Although chlorinated, brominated and chlorobromotrihalomethanes are the most common disinfection by-products reported, iodinated trihalomethanes (ITHMs) can be formed when iodide is present in raw water. ITHMs have been usually associated with several medicinal or pharmaceutical taste and odor events in drinking water. For instance, the odor and taste threshold concentrations of iodoform are 0.02 and 5 μg/l, respectively. Different analytical techniques have been studied to identify these compounds but their quantitative determination has not been performed due to the lack of commercial standards. In this study ITHMs (CHCl2I, CHClI2, CHBr2I, CHBrI2 and CHBrClI) have been synthesized in order to evaluate headspace (HS), purge and trap (P&T), closed loop stripping analysis (CLSA) and liquid–liquid extraction (LLE) as analytical methods for determination. HS and LLE were followed by gas chromatography and electron capture detector (GC/ECD); whereas P&T and CLSA with gas chromatography and mass spectrometry (GC/MS). The most appropriate method, LLE/GC/ECD, was applied to evaluate the stability of ITHMs in water (ultrapure, raw and treated water) in order to confirm their presence in tap water. Ascorbic acid was the quenching reagent chosen to avoid free chlorine at the time of sample collection. Finally, samples from the different stages of the treatment plant in Barcelona (NE Spain) were analyzed. Only three (CHCl2I, CHBrClI and CHBr2I) of the six ITHMs were identified and determined, at average levels lower than 1μg/l, in sand filtered and ozonated waters. No ITHMs were identified in distribution system water.