Although >700 disinfection by-products (DBPs) have been identified to date, most DBPs in drinking water are still unknown. Identifying unknown DBPs is an important step for improving drinking water quality because known DBPs do not fully account for the adverse health effects noted in epidemiologic studies. Using gas chromatography high-resolution mass spectrometry, six chloro-and bromo-halocyclopentadienes (HCPDs) were identified in chlorinated and chloraminated drinking water via nontarget analysis; five HCPDs are reported for the first time as new alicyclic DBPs. Formation pathways were also proposed. Simulated disinfection experiments with Suwannee River natural organic matter (NOM) confirm that NOM is a precursor for these new DBPs. Further, HCPDs are more abundant in chlorinated drinking water (real and simulated) when compared to chloraminated drinking water due to the higher reactivity of chlorine. Of these new DBPs, 1,2,3,4,5,5-hexachloro-1,3-cyclopentadiene is approximately 100,000× more toxic (in vivo) than regulated trihalomethanes (THMs) and haloacetic acids (HAAs) and 20−2000× more toxic than halobenzoquinones, halophenols, and halogenated pyridinols using the available median lethal dose (LD 50 ) and concentration for 50% of maximal effective concentration (EC 50 ) of DBPs to aquatic organisms. The predicted bioconcentration factors of these HCPDs range from 384 to 3980, which are 2−3 orders of magnitude higher than those for regulated and priority DBPs (including THMs, HAAs, halobenzoquinones, haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, iodo-THMs, and iodo-HAAs). Thus, HCPDs are an important emerging class of DBPs that should be studied to better understand their impact on drinking water quality and long-term human health exposure.

Due to their elevated concentrations in drinking water, compared to other emerging environmental contaminants, disinfection byproducts (DBPs) have become a global concern. To address this, we have created a simple and sensitive method for simultaneously measuring 9 classes of DBPs. Haloacetic acids (HAAs) and iodo-acetic acids (IAAs) are determined using silylation derivatization, replacing diazomethane or acidic methanol derivatization with a more environmentally friendly and simpler treatment process that also offers greater sensitivity. Mono-/di-haloacetaldehydes (mono-/di-HALs) are directly analyzed without derivatization, along with trihalomethanes (THMs), iodo-THMs, haloketones, haloacetonitriles, haloacetamides, and halonitromethanes. Of the 50 DBPs studied, recoveries for most were 70–130%, LOQs for most were 0.01–0.05 μg/L, and relative standard deviations were <30%. We subsequently applied this method to 13 home tap water samples. Total concentrations of 9 classes of DBPs were 39.6–79.2 μg/L, in which unregulated priority DBPs contributed 42% of total DBP concentrations and 97% of total calculated cytotoxicity, highlighting the importance of monitoring their presence in drinking water. Br-DBPs were the dominant contributors to total DBPs (54%) and total calculated cytotoxicity (92%). Nitrogenous DBPs contributed 25% of total DBPs while inducing 57% of total calculated cytotoxicity. HALs were the most important toxicity drivers (40%), particularly four mono-/di-HALs, which induced 28% of total calculated cytotoxicity. This simple and sensitive method allows the synchronous analysis of 9 classes of regulated and unregulated priority DBPs and overcomes the weaknesses of some other methods especially for HAAs/IAAs and mono-/di-HALs, providing a useful tool for research on regulated and unregulated priority DBPs.