Collaborative Research: Effects of Drinking Water Disinfection Conditions, Water Age and Nitrification on Aromatic and Protein/Lipid-Derived DBPs

Chlorine disinfection of drinking water has played a critical role in preventing outbreaks of waterborne diseases. Unfortunately, chlorine also reacts with dissolved organic matter in water supplies to form chlorinated byproducts. Consumer exposure to these byproducts is associated with slightly increased health risks. Drinking water regulations thus balance the need to reduce consumer exposure while maintaining effective disinfection. In the past, these regulations have focused on controlling the accumulation of small molecule end products that form as chlorine progressively breaks down dissolved organic matter. However, recent research has indicated that the larger byproducts formed during the process may be more important drivers of toxicity. The goal of this collaborative study by a chemist and a toxicologist is to compare the concentrations and contributions to toxicity of the large intermediate byproducts compared to smaller end products. The study will target water samples collected from drinking water utilities from different sources that use different disinfection techniques. The results of this project will be used to develop guidance to utilities on which disinfection conditions and techniques result in the formation of byproducts contributing to toxicity. The results also will benefit society by helping regulators identify byproducts that can serve as improved metrics of consumer exposure, thus contributing broadly to public health. Drinking water regulations have focused on trihalomethanes (THMs) and haloacetic acids (HAAs) as metrics of disinfection byproduct (DBP) exposure since the 1970s. Research over the past two decades has shifted to other unregulated 1-2 carbon DBPs such as haloacetonitriles that may contribute more to the toxicity of disinfected waters due to their greater cytotoxic and genotoxic potencies. While 1-2 carbon DBPs accumulate as terminal products, the higher molecular weight intermediate DBPs formed from the initial chlorine reactions with organic matter have received less attention. Recent research has indicated that these intermediate DBPs contribute more to the toxicity of disinfected drinking water. This project will compare the concentrations and contributions to toxicity of several novel classes of intermediate DBPs (halogenated phenols, proteins, and lipids) versus 1-2 carbon DBPs under different disinfection scenarios. The first objective is to compare DBP classes during chlorine/chloramine disinfection versus granular activated carbon (GAC) treatment followed by chlorine disinfection. The second objective is to assess how the formation of these DBP classes is affected by water age and water source (e.g., pristine source water, algal-impacted water, and wastewater-impacted water). The third objective is to assess whether nitrifying biofilms in chloraminated distribution systems increase the formation of these DBP classes by emitting DBP precursors. A fundamental assumption behind the current use of THMs and HAAs as metrics of DBP exposure is that their formation correlates with the toxicity drivers in disinfected waters. This study will test this assumption. The results will benefit society by providing information to regulators to assess whether alternative metrics of DBP exposure are needed to more accurately assess toxicity and whether efforts to reduce THM/HAA concentrations effectively reduce health impacts associated with DBP exposure. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.