Current regulations intended to limit disinfection byproducts (DBPs) are focused on trihalomethanes (THMs) and haloacetic acids (HAAs), the most chemically-stable of the known DBPs. By placing limits on these end products of the reaction of chlorine with natural organic matter (NOM), regulators are encouraging utilities to distribute water that is “younger”. This less-highly disinfected water has higher levels of intermediates that fall along the trajectory between NOM and THMs & HAAs. As an alternative, some utilities have moved to chloramines which tend to result in partial halogenation as compared to free chlorine. The end result is often higher levels of many nitrogenous DBPs, iodinated DBPs and hypo-halogenated compounds. A wide range of toxicity assays have been used to help inform the relative risks of exposure to these DBPs. Because the aforementioned intermediates (i.e., N-DBPs, I-DBPs and DBPs with incomplete halogenation) are more toxic than the regulated endpoints of disinfection, there is a risk that we are elevating the overall toxicity of drinking water.<br/>In this study we look at several trajectories of DBP compounds from initial products through various intermediates and finally to the regulated end product. Combining kinetic models and compound-specific toxicity data, we propose an overall toxicity profile for each of these scenarios. We then discuss alternative control strategies that would better minimize the assessed toxicity.

Toxicity profiles and metastable disinfection byproducts

253rd National Meeting (2017)

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