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

Abstract

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.

Natural Disinfection-like Process Unveiled in Soil Microenvironments by Enzyme-Catalyzed Chlorination

“…In practical water treatment, source water typically undergoes preprocessing, including coagulation and sedimentation, which can remove a substantial portion of high-molecular-weight DOM precursors before disinfection, , which are believed to be associated with higher degree of oxygenation and unsaturation. , This could explain the differences in the molecular properties between previously reported DBP and the organochlorine compounds observed in this study, as we used the original DOM without pretreatment. Additionally, a recent study employing 21 T FT-ICR MS demonstrated the presence of 509 DBP containing three chlorine atoms in chlorinated or chloraminated drinking water, adding support to the similarity between anthropogenic DBP and natural organochlorine compounds produced through enzymatic chlorination of DOM.…”

“…Statistical analysis showed that these compounds with more chlorine atoms were associated with a greater extent of oxidation and a lower degree of unsaturation, as indicated by the increase of the O/C wa and NOSC wa values and decrease of the DBE wa values with the number of chlorine atoms (Figure S4). This trend indicated the oxidation of DOM molecular structures along with the greater extent of chlorination in both enzymatic and abiotic reactions, which can potentially lead to the formation of low-molecular-weight halogenated aliphatic DBP. , Previous studies have identified that high-molecular-weight halogenated DBP, especially the aromatic fraction, exhibited higher developmental toxicity. ,, Therefore, the difference in the relative abundance of organochlorine compounds generated by different chlorination reactions may suggest their variations in environmental concentrations and associated risks.…”

Predicting Transformation Products during Aqueous Oxidation Processes: Current State and Outlook

“…In the past two decades, identifying transformation products induced by chemical oxidation has been an active area of research, fueled by development of sensitive high resolution mass spectrometry and protocols for the evaluation of detected features in nontarget analysis. , Considering that more than 350 000 chemicals are currently in commercial production and use, − selective screening the universe of chemicals is vital to prioritize toxicologically important chemicals and transformation products for experimental investigations as shown in the ongoing efforts to link DBPs with the toxicity. , With limited commercial availabilities of authentic standards for transformation products, a theoretical approach is critical to tentatively predict reaction products. Toward predicting oxidative transformation products, this perspective article emphasizes the key progress made in experimental measurement of kinetics and transformation products, and theoretical determination of rate constants and elucidation of reaction mechanisms.…”

MS and NMR Analysis of Isotopically Labeled Chloramination Disinfection Byproducts: Hyperlinks and Chemical Reactions

“…FT-ICR analysis of halogenated DBPs has been performed by multiple groups in recent years − and 15 N-labeling has been previously used to investigate known chloramination DBPs. , To our knowledge, this work is the first to combine the two approaches and include isotopic labeling for untargeted FT-ICR MS analysis of mixtures containing halogens.…”