Halocyclopentadienes: An Emerging Class of Toxic DBPs in Chlor(am)inated Drinking Water

Abstract

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.

Uncovering an Emerging Group of Halogenated Nucleobase-Derived Disinfection Byproducts in Drinking Water: Prioritization of the Highly Cytotoxic 2-Chloroadenine

“…The detection frequencies of the five identified nucleobases were in the range of 73–100% (Table ), of which 5-chlorouracil, 6-chlorouracil and 5-bromouracil were 100%. The concentrations of the five halogenated nucleobases in drinking water ranged from n.d. to 22.2 ng/L (Table ), which were at a comparable level with some other emerging DBPs, such as haloquinone cloroimides (HQCs, up to 20.3 ng/L), halonaphthoquinones (HNQs, up to 136.7 ng/L), and halocyclopentadienes (HCPDs, up to 153 ng/L) . Notably, 5-bromouracil was the only Br-DBP among these five detectable species.…”

“…The concentrations of the five halogenated nucleobases in drinking water ranged from n.d. to 22.2 ng/L (Table 2), which were at a comparable level with some other emerging DBPs, such as haloquinone cloroimides (HQCs, up to 20.3 ng/L), 39 halonaphthoquinones (HNQs, up to 136.7 ng/L), 35 and halocyclopentadienes (HCPDs, up to 153 ng/L). 40 Notably, 5-bromouracil was the only Br-DBP among these five detectable species. The concentrations of Br − in samples H and I (53.1− 68.1 μg/L) were much higher than the other samples, which may be because the source water was affected by seawater.…”

Unravelling High-Molecular-Weight DBP Toxicity Drivers in Chlorinated and Chloraminated Drinking Water: Effect-Directed Analysis of Molecular Weight Fractions

“…Continued efforts have been made to identify unknown DBPs in drinking water, especially for the toxicity drivers. − The identification of unknown DBPs and corresponding toxicity assessments significantly enriched the knowledge of unknown TOX. One of the tricky challenges in the assessment of complex drinking water mixtures is the identification of those DBPs that contribute significantly to observed toxicity.…”

Contributions of Pharmaceuticals to DBP Formation and Developmental Toxicity in Chlorination of NOM-containing Source Water

“…During disinfection, chlorine can react with natural organic matter (NOM) in source waters to form chlorinated disinfection byproducts (DBPs). − When bromide is present in source water, it can be oxidized by hypochlorous acid/hypochlorite (HOCl/OCl – ) to hypobromous acid/hypobromite (HOBr/OBr – ). Compared with HOCl/OCl – , HOBr/OBr – is more reactive in substitution reactions with NOM to form brominated DBPs. − Many DBPs have been shown to be cytotoxic, genotoxic, mutagenic, and developmentally toxic. ,− Epidemiological studies have linked long-term exposure to disinfected drinking water to adverse health effects (e.g., colorectum and bladder cancers). − Numerous efforts have been made in recent decades to investigate the formation of NOM-derived halogenated DBPs during drinking water disinfection. ,− Apart from NOM, micropollutants in drinking water sources may also serve as DBP precursors, whereas their role is much less addressed in the literature.…”