Decomposition of Total Organic Halogen Formed during Chlorination: The Iceberg of Halogenated Disinfection Byproducts Was Previously Underestimated

Nitrogen-containing disinfection byproducts (N-DBPs) are highly toxic DBPs in drinking water. Though, under normal conditions, NO3 – could not directly participate in disinfection reactions to generate N-DBPs, here, we first found that NO3 – could promote the formation of N-DBPs in corroded iron drinking water pipes. The coexistence of corrosion produced Fe(II) and iron oxides is a critical condition for the transformation of N species; meanwhile, most of the newly generated N-DBPs had aromatic fractions. The Fe–O–C bond formed between iron corrosion products and natural organic matter promoted electron transfer for the N transformation with pyrrolic N as the intermediate N species. Density functional calculation confirmed that the coexistence of Fe(II) and iron oxides effectively reduced the Gibbs free energy for NO3 – reduction. ΔG of the key rate-determining step from NO* to NOH* decreased from 1.55 eV on FeOOH to 1.35 eV on Fe(II)+FeOOH. In addition, the large decrease of cell viability of the water samples from 74.3% to 45.4% further confirmed the formation of highly toxic N-DBPs. Thus, in a drinking water distribution system with corroded iron pipes, the low toxic NO3 – may increase toxicity risks via N-DBP formation.

Section: Resultsmentioning

confidence: 99%

NO₃^– Promotes Nitrogen-Containing Disinfection Byproduct Formation in Corroded Iron Drinking Water Pipes

Zhuang

Shi

2023

“…It is crucial to determine adequate quenching agent and dose to achieve simultaneous disinfection termination and DBP preservation. Commonly used quenching agents (i.e., ascorbic acid, sodium thiosulfate, and sodium sulfite) might degrade the DBPs in the range of 18–100%. − However, it was found that ammonium chloride, as the quenching reagent, could achieve a minor or no degradation of target DBPs within 48 h . Therefore, samples were quenched with ammonium chloride at a molar ratio of 1:1.3 free chlorine to quenching agent and then acidified to pH 3.0–5.0 using sulfuric acid.…”

Section: Methodsmentioning

confidence: 99%

Widespread Antioxidants during Storm Events Could Serve as Precursors of Regulated, Priority, and New Disinfection Byproducts

Yang,

Fang,

Hong

et al. 2024

Self Cite

Widely used antioxidants can enter the environment via urban stormwater systems and form disinfection byproducts (DBPs) during chlorination in downstream drinking water processes. Herein, we comprehensively investigated the occurrence of 39 antioxidants from stormwater runoff to surface water. After a storm event, the concentrations of the antioxidants in surface water increased by 1.4-fold from 102−110 ng/L to 128−139 ng/L. Widespread antioxidants during the stormwater event could transform into toxic DBPs during disinfection. Moreover, the yields of trihalomethanes, haloacetaldehydes, haloacetonitriles (HANs), and halonitromethanes during the chlorination of widely used antioxidants considerably increased with an increasing chlorine dose and contact time. Specifically, the yields of dichloroacetonitrile during the chlorination of diphenylamine (DPA) and N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) were higher than those of most reported amino acid precursors, indicating that DPA and 6PPD might be important precursors of HANs. Exploring the intermediates using GC × GC-time-of-flight high-resolution mass spectrometry helped reveal potential pathways from DPA to HANs, whose formation could be attributed to the intermediate carbazole and indole moieties detected in this study. This study provides insights into the transport and transformation of commonly used antioxidants in a water environment and during water treatment processes, highlighting the potential risks of anthropogenic pollutants from a DBP perspective.

“…Because of the complexity of DBPs and the fact that numerous DBPs are still unknown, total organic halogen (TOX) has been used as a surrogate indicator to represent all halogenated organic DBPs in chlorinated drinking water. 31,66,67,69,70 In addition, studies have reported that for the same source water, the TOX concentration generally correlates positively with the toxicity of a chlorinated drinking water sample, 4,65,66,71,72 indicating that TOX may be a suitable indicator to represent or predict the toxicity of DBP mixtures in a water sample.…”

Section: ■ Introductionmentioning

confidence: 99%

“…This study was therefore designed to (1) quantify the contributions of NOM and pharmaceuticals to the overall formation of halogenated DBPs; (2) establish a kinetic model for predicting the halogenated DBP formation and the relative contributions in chlorination of source waters containing both NOM and pharmaceuticals; and (3) evaluate the developmental toxicity of NOM- and pharmaceutical-derived DBPs and their combined effects on the overall developmental toxicity of DBP mixtures. Because of the complexity of DBPs and the fact that numerous DBPs are still unknown, total organic halogen (TOX) has been used as a surrogate indicator to represent all halogenated organic DBPs in chlorinated drinking water. ,,,, In addition, studies have reported that for the same source water, the TOX concentration generally correlates positively with the toxicity of a chlorinated drinking water sample, ,,,, indicating that TOX may be a suitable indicator to represent or predict the toxicity of DBP mixtures in a water sample.…”

Section: Introductionmentioning

confidence: 99%

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

Han

Zhang

et al. 2023

Pharmaceuticals have been considered a priority group of emerging micropollutants in source waters in recent years, while their role in the formation and toxicity of disinfection byproducts (DBPs) during chlorine disinfection remains largely unclear. In this study, the contributions of natural organic matter (NOM) and pharmaceuticals (a mixture of ten representative pharmaceuticals) to the overall DBP formation and toxicity during drinking water chlorination were investigated. By innovatively “normalizing” chlorine exposure and constructing a kinetic model, we were able to differentiate and evaluate the contributions of NOM and pharmaceuticals to the total organic halogen (TOX) formation for source waters that contained different levels of pharmaceuticals. It was found that at a chlorine contact time of 1.0 h, NOM (2 mg/L as C) and pharmaceuticals (total 0.0062–0.31 mg/L as C) contributed 79.8–99.5% and 0.5–20.2%, respectively, of TOX. The toxicity test results showed that the chlorination remarkably increased the toxicity of the pharmaceutical mixture by converting the parent compounds into more toxic pharmaceutical-derived DBPs, and these DBPs might contribute significantly to the overall developmental toxicity of chlorinated waters. This study highlights the non-negligible role of pharmaceuticals in the formation and toxicity of overall DBPs in chlorinated drinking water.