Disinfection byproducts (DBPs), a consequence of unintended reaction between chemical disinfectants and naturally occurring organic matter, has been associated with mutagenicity, genotoxicity, carcinogenicity and developmental toxicity. Although single-chemical studies have been useful to identify these toxicity properties of individual DBP species, the adverse biological effects of DBP mixtures in disinfected water are largely unknown. Due to the more stringent Stage 2 Disinfectants/DBP Rule, many U.S. utilities have switched, or are switching from free chlorine to combined chlorine since chloramination significantly reduces the formation of regulated DBPs. However, chloramine enhances the formation of a different suite of DBPs, which could be more toxic than the regulated DBPs. For the first time we conducted a quantitative systematic analyses of toxicity from different disinfection scenarios using a filter effluent from a conventional surface water treatment plant that was either chlorinated (Cl2) or chloraminated (NH2Cl) with or without addition of 500 �g/L Br and 100 �g/L I. After 48-h reaction, the disinfected water samples were concentrated by adsorption on Amberlite XAD resins. Chronic cytotoxicity and acute genotoxicity of the DBP mixture concentrate was evaluated with mammalian cells. The cytotoxicity and genotoxicity followed the order of NH2Cl +Br- + I- > Cl2 + Br- + I- > Cl2 ~ NH2Cl. The toxicity results will be compared to the formation of total organic halide. This direct comparison using the single source water with different disinfectants and halogen precursors demonstrated that shifting the conditions for DBP formation to more brominated and iodinated analogues significantly increased mammalian cell toxicity. These potential health risks may aid the decision-making process when shifting from chlorine to chloramine disinfection.

Comparative toxicity of free and combined chlorination with different levels of halide ions

248th National Meeting (2014)

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