High-molecular-weight by-products of chlorine disinfection

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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.

Section: Materials and Methodsmentioning

confidence: 99%

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

Han

Zhang

et al. 2023

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“…115,116 Due to the differences in the elemental composition, hydrophilicity, and structure of AOM and natural organic matter (NOM), the type and concentration of DBPs produced by the chlorination of AOM are different from those of NOM. 116 Liu et al compared DBP formation from AOM and NOM and found that algae-laden waters formed less known DBPs (e.g., trihalomethanes (THMs), haloacetonitriles (HANs), and haloacetic acids (HAAs)) than NOM under practical treatment conditions. 80 However, chlorination of MCs was found to enhance their cytotoxicity and genotoxicity, indicating the formation of highly toxic algal-derived DBPs.…”

Section: Toxicitymentioning

confidence: 99%

“…Oxidation of algae-laden water releases intracellular algal organic matter (AOM) into the water as a result of oxidant-induced cell lysis . AOM is composed of protein, carbohydrate, lipid, and nucleic acid structures, and its hydrophilic fraction is resistant to removal through coagulation-sedimentation-filtration processes. , Due to the differences in the elemental composition, hydrophilicity, and structure of AOM and natural organic matter (NOM), the type and concentration of DBPs produced by the chlorination of AOM are different from those of NOM . Liu et al compared DBP formation from AOM and NOM and found that algae-laden waters formed less known DBPs (e.g., trihalomethanes (THMs), haloacetonitriles (HANs), and haloacetic acids (HAAs)) than NOM under practical treatment conditions .…”

Section: Transformation Of Algal Toxins In Oxidation/disinfection Pro...mentioning

confidence: 99%

Transformation of Algal Toxins during the Oxidation/Disinfection Processes of Drinking Water: From Structure to Toxicity

Dong,

Aziz,

Richardson

2023

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With the increase of algal blooms worldwide, drinking water resources are threatened by the release of various algal toxins, which can be hepatotoxic, cytotoxic, or neurotoxic. Because of their ubiquitous occurrence in global waters and incomplete removal in conventional drinking water treatment, oxidation/disinfection processes have become promising alternative treatment options to destroy both the structures and toxicity of algal toxins. This Review first summarizes the occurrence and regulation of algal toxins in source water and drinking water. Then, the transformation kinetics, disinfection byproducts (DBPs)/ transformation products (TPs), pathways, and toxicity of algal toxins in water oxidation/disinfection processes, including treatment by ozonation, chlorination, chloramination, ultraviolet-based advanced oxidation process, and permanganate, are reviewed. For most algal toxins, hydroxyl radicals (HO • ) exhibit the highest oxidation rate, followed by ozone and free chlorine. Under practical applications, ozone and chlorine can degrade most algal toxins to meet water quality standards. However, the transformation of the parent structures of algal toxins by oxidation/disinfection processes does not guarantee a reduction in toxicity, and the formation of toxic TPs should also be considered, especially during chlorination. Notably, the toxicity variation of algal toxins is associated with the chemical moiety responsible for toxicity (e.g., Adda moiety in microcystin-LR and uracil moiety in cylindrospermopsin). Moreover, the formation of known halogenated DBPs after chlorination indicates that toxicity in drinking water may shift from toxicity contributed by algal toxins to toxicity contributed by DBPs. To achieve the simultaneous toxicity reduction of algal toxins and their TPs, optimized oxidation/disinfection processes are warranted in future research, not only for meeting water quality standards but also for effective reduction of toxicity of algal toxins.

“…While >700 low-molecular-weight DBPs have been identified, the molecular composition of high-molecular-weight DBPs (>C 2 ) remains poorly understood. 31 Liquid chromatography−mass spectrometry (LC-MS) based methods, using softer ionization methods (e.g., electrospray ionization (ESI)) and high-resolution MS (HRMS), have heightened the possibilities for the detection of unknown DBPs. With increased use of LC-MS, more and more hydrophilic, highmolecular-weight DBPs have been identified, broadening our understanding of the physical and chemical characteristics of DBPs in drinking water.…”

Section: ■ Introductionmentioning

confidence: 99%

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

Dong

Cuthbertson

Plewa

et al. 2023

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As disinfection byproducts (DBPs) are ubiquitous sources of chemical exposure in disinfected drinking water, identifying unknown DBPs, especially unknown drivers of toxicity, is one of the major challenges in the safe supply of drinking water. While >700 low-molecular-weight DBPs have been identified, the molecular composition of high-molecular-weight DBPs remains poorly understood. Moreover, due to the absence of chemical standards for most DBPs, it is difficult to assess toxicity contributions for new DBPs identified. Based on effect-directed analysis, this study combined predictive cytotoxicity and quantitative genotoxicity analyses and Fourier transform ion cyclotron resonance mass spectrometry (21 T FT-ICR-MS) identification to resolve molecular weight fractions that induce toxicity in chloraminated and chlorinated drinking waters, along with the molecular composition of these DBP drivers. Fractionation using ultrafiltration membranes allowed the investigation of <1 kD, 1–3 kD, 3–5 kD, and >5 kD molecular weight fractions. Thiol reactivity based predictive cytotoxicity and single-cell gel electrophoresis based genotoxicity assays revealed that the <1 kD fraction for both chloraminated and chlorinated waters exhibited the highest levels of predictive cytotoxicity and direct genotoxicity. The <1 kD target fraction was used for subsequent molecular composition identification. Ultrahigh-resolution MS identified singly charged species (as evidenced by the 1 Da spacing in 13C isotopologues), including 3599 chlorine-containing DBPs in the <1 kD fraction with the empirical formulas CHOCl, CHOCl2, and CHOCl3, with a relative abundance order of CHOCl > CHOCl2 ≫ CHOCl3. Interestingly, more high-molecular-weight CHOCl1–3 DBPs were identified in the chloraminated vs chlorinated waters. This may be due to slower reactions of NH2Cl. Most of the DBPs formed in chloraminated waters were composed of high-molecular-weight Cl-DBPs (up to 1 kD) rather than known low-molecular-weight DBPs. Moreover, with the increase of chlorine number in the high-molecular-weight DBPs detected, the O/C ratio exhibited an increasing trend, while the modified aromaticity index (AImod) showed an opposite trend. In drinking water treatment processes, the removal of natural organic matter fractions with high O/C ratio and high AImod value should be strengthened to minimize the formation of known and unknown DBPs.