Non-Targeted Characterization and Hazard-Based Prioritization of Disinfection Byproducts and Co-Contaminants in U.S. Drinking Water Distribution Systems

Abstract Higher-carbon (>C2) disinfection byproducts (DBPs) remain poorly characterized in drinking water distribution systems (DWDSs) despite evidence that they may contribute substantially to drinking water toxicity. Here, we applied liquid chromatography–high-resolution mass spectrometry and non-targeted analysis to characterize >C2 DBPs and co-contaminants across 12 U.S. DWDSs spanning a range of pre-oxidation and disinfection strategies. For each DWDS, we analyzed finished drinking water and distribution system samples collected at locations representing short, medium, and long distances from the treatment plant. We identified multiple classes of >C2 DBPs, including non-halogenated and halogenated hydroxybenzoic acids, halohydroxybenzaldehydes, halonitrophenols, (halo)phenylacetamides, (halo)fumaric acids, and several emerging nitrogenous DBPs. In addition, we also detected various co-contaminants such as pesticides, pharmaceuticals, and industrial chemicals. DBPs and co-contaminants exhibited system-specific occurrence and spatial patterns, and non-halogenated hydroxybenzoic acids emerged as an overlooked and widespread class of DBPs. To support prioritization efforts, hazard data from EPA’s Hazard Comparison Module was used to develop and implement hazard-weighted prioritization metrics. This approach identified (halo)hydroxybenzoic acids, halonitrophenols, DEET, triazine herbicides, and 2-hydroxyquinoline as high-priority contaminants, indicating that both emerging DBPs and co-contaminants may contribute to mixture-level hazards in distributed drinking water. Overall, this work expands the known >C2 DBP landscape and provides a framework for prioritizing drinking water contaminants detected by non-targeted analysis.