DNA DAMAGE AND REPAIR KINETICS IN MAMMALIAN CELLS BY REACTANTS, INTERMEDIATES AND PRODUCTS ASSOCIATED WITH THE REACTION OF COMBINED CHLORINE AND FORMALDEHYDE IN DRINKING WATER

摘要

Many U.S. facilities may switch from free chlorine to combined chlorine as a result of new regulations. Chloramination is commonly considered as a secondary disinfectant because it produces lower levels of regulated disinfection byproducts (DBPs). However, recent research has revealed that chloramination can promote formation of nitrogen-based DBPs (N-DBPs) and iodo-based DBPs (l-DBPs) and these N- DBPs and l-DBPs can be more toxic than the regulated carbon-based DBPs. CICN is one of the emerging DBPs that can form when formaldehyde reacts with monochloramine under common drinking water treatment conditions. Formaldehyde and monochloramine react quickly to form N-chloroaminomethanol, which slowly dehydrates to N-chloromethanimine, which in turn decomposes to cyanide. The deprotonated form of cyanide can react with combined chlorine species to form cyanogen chloride4. Many of these reactions are acid and/or base catalyzed and, therefore, exposure to associated reactants, intermediates and products can differ from that inferred from water samples whose pH/composition might have been altered as a result of sample preservation or during storage. The focus of this research is to investigate realistic exposure conditions and to perform genomic DNA damage and repair kinetic assays in mammalian cells to assess the genotoxicity of compounds associated with the reactions initiated by monochloramine and formaldehyde.