Liquid Chromatography–Mass Spectrometry of Emerging Disinfection By-products

Traditional methods and biosensors for detecting disinfection by-products in water: A review

In recent years, pollution caused by disinfection by-products (DBPs) has become a global concern. Initially, there were fewer contaminants, and the mechanism of their generation was unclear; however, the number of contaminants has increased exponentially as a result of rapid industrialization and numerous economic activities (e.q., during the outbreak of COVID-19 a surge in the use of chlorinated disinfectants was observed). DBP toxicity results in various adverse health effects and organ failure in humans. In addition, it profoundly affects other forms of life, including animals, plants, and microorganisms. This review comprehensively discusses the pre-treatment methods of traditional and emerging DBPs and the technologies applied for their detection. Additionally, this paper provides a detailed discussion of the principles, applicability, and characteristics of traditional large-scale instrumentation methods (such as gas/liquid/ion chromatography coupled with mass spectrometry) for detecting DBPs based on their respective detection techniques. At the same time, the design, functionality, classification, and characteristics of rapid detection technologies (such as biosensors) are also detailed and analyzed.

Facile synthesis of Ag/ZIF-8@ZIF-67 as an electrochemical sensing platform for sensitive detection of halonitrophenols in drinking water

Halonitrophenols (HNPs) are an emerging type of aromatic disinfection byproduct, with detected concentrations of ∼nmol L-1 in source water and drinking water. Currently, there are no standard methods for identifying HNPs, and most of the reported methods are time-consuming and equipment-dependent. A core-shell metal-organic framework (MOF) based electrochemical sensor (Ag/ZIF-8@ZIF-67) capable of detecting 2,6-dichloro-4-nitrophenol (2,6-DCNP) is reported in this study. The electrochemical sensor obtains the concentration of 2,6-DCNP by detecting the peak current passing through the sensor. In this sensor, Ag nanoparticles (AgNPs) play a key role in electrochemical sensing by reducing nitro groups via electron transfer, and porous structure with a large surface area is offered by ZIF-8@ZIF-67. The cyclic voltammetry (CV) response of Ag/ZIF-8@ZIF-67 was found to be approximately 1.75 times and 2.23 times greater than that of Ag/ZIF-8 and Ag/ZIF-67, respectively, suggesting an ideal synergistic effect of the core-shell structures. The Ag/ZIF-8@ZIF-67 sensor exhibited exceptional sensitivity to 2,6-DCNP, exhibiting a broad linear response range (R2 = 0.992) from 240 nmol L-1 to 288 μmol L-1 and a low detection limit of 20 nmol L-1. Furthermore, the sensor exhibited good anti-interference for isomers and common distractors in water, excellent stability and reproducibility, and high recovery in actual water samples. Our reported sensor gives a novel strategy for sensitive, selective, and in situ detection of 2,6-DCNP in practical analysis.

Identification of unknown disinfection byproducts in drinking water produced from Taihu Lake source water

Although disinfection byproducts (DBPs) in drinking water have been suggested as a cancer causing factor, the causative compounds have not yet been clarified. In this study, we used liquid chromatography quadrupole-time-of-flight spectrometry (LC-QTOF MS) to identify the unknown disinfection byproducts (DBPs) in drinking water produced from Taihu Lake source water, which is known as a convergence point for the anthropogenic pollutants discharged from intensive industrial activities in the surrounding regions. In total, 91 formulas of DBPs were discovered through LC-QTOF MS nontarget screen, 81 of which have not yet been reported. Among the 91 molecules, 56 only contain bromine, 15 only contain chlorine and 20 DBPs have both bromine and chlorine atoms. Finally, five DBPs including 2,4,6-tribromophenol, 2,6-dibromo-4-chlorophenol, 2,6-dichloro-4-bromophenol, 4-bromo-2,6-di-tert-butylphenol and 3,6-dibromocarbazole were confirmed using standards. The former three compounds mainly formed in the predisinfection step (maximum concentration, 0.2-2.6 µg/L), while the latter two formed in the disinfection step (maximum concentration, 18.2-33.6 ng/L). In addition, 19 possible precursors of the discovered DBPs were detected, with the aromatic compounds being a major group. 2,6-di-tert-butylphenol as the precursor of 4-bromo-2,6-di-tert-butylphenol was confirmed with standard, with a concentration of 20.3 µg/L in raw water. The results of this study show that brominated DBPs which are possibly formed from industrial pollutants are relevant DBP species in drinking water produced form Taihu source water, suggesting protection of Taihu Lake source water is important to control the DBP risks.

Unraveling the chemodiversity of halogenated disinfection by-products formed during drinking water treatment using target and non-target screening tools

To date, there is no analytical approach available that allows the full identification and characterization of highly complex disinfection by-product (DBP) mixtures. This study aimed at investigating the chemodiversity of drinking water halogenated DBPs using diverse analytical tools: measurement of adsorbable organic halogen (AOX) and mass spectrometry (MS)-based target and non-target analytical workflows. Water was sampled before and after chemical disinfection (chlorine or chloramine) at four drinking water treatment plants in Sweden. The target analysis had the highest sensitivity, although it could only partially explain the AOX formed in the disinfected waters. Non-target Fourier transform ion cyclotron resonance (FT-ICR) MS analysis indicated that only up to 19 Cl and/or Br-CHO formulae were common to all disinfected waters. Unexpectedly, a high diversity of halogenated DBPs (presumed halogenated polyphenolic and highly unsaturated compounds) was found in chloraminated surface water, comparable to that found in chlorinated surface water. Overall, up to 86 DBPs (including isobaric species) were tentatively identified using liquid chromatography (LC)-Orbitrap MS. Although further work is needed to confirm their identity and assess their relevance in terms of toxicity, they can be used to design suspect lists to improve the characterization of disinfected water halogenated mixtures.

The identification of halogenated disinfection by-products in tap water using liquid chromatography-high resolution mass spectrometry

In this paper, a comprehensive method for the identification of the unknown halogenated DBPs (X-DBPs, X = Cl, Br, and I) in the tap water of Wuhan, China via liquid chromatography-high resolution mass spectrometry (LC-HRMS) was developed. 123 X-DBPs were identified through the stepwise procedure, 94 of them were newly identified, and 3 of them were confirmed by standards. Most X-DBPs were aliphatic compounds and highly unsaturated and phenolic compounds, some X-DBPs contained multiple halogen atoms and rich in carboxyl groups, such as C₂H₂O₂BrCl, C₂H₂O₂Br₂, and C₂H₂O₂ClI. It was worth noting that the concentration of some X-DBPs had the same trend with time. Most Cl-DBPs remained stable and I-DBPs were detected occasionally by monitoring the change of concentration of these X-DPBs with the time during three consecutive months. The results demonstrate that the proposed method could provide valuable molecular formula and structure information on unknown multiple halogenated DBPs, or be used for the identification of other multiple halogenated organic compounds in different media.

Identification of novel disinfection byproducts in pool water: Chlorination of the algaecide benzalkonium chloride

The maintenance of public swimming pools requires numerous technological steps. One of the most important issues involves microbiological safety. Benzalkonium chloride (BAC) encompasses homologous alkylbenzyldimethylammonium chlorides with various alkyl chains, in particular C12 and C14, and is known as a popular algaecide for keeping water clean. In addition to BAC, NaOCl and UV-irradiation are also used to treat pool water as additional technological steps. Therefore, BAC itself can become a precursor of disinfection byproducts (DBPs). High-performance liquid chromatography - tandem mass spectrometry (HPLC-MS/MS), with accurate mass measurements, has allowed the discovery of several groups of DBPs that are related to BAC in public pool water in Arkhangelsk (Russia). These DBPs include numerous isomeric monochlorinated derivatives ([C₂₁H₃₇ClN]⁺ and [C₂₃H₄₁ClN]⁺), hydroxyl derivatives ([C₂₁H₃₈NO]⁺ and [C₂₃H₄₂NO]), carbonyl ([C₂₁H₃₆NO]⁺ and [C₂₃H₄₀NO]⁺), and dicarbonyl derivatives ([C₂₁H₃₄NO₂]⁺ and [C₂₃H₃₈NO₂]⁺). In addition, chlorinated alcohols, ketones and ketoalcohols of BAC were also detected, including [C₂₁H₃₅ClNO]⁺, [C₂₁H₃₇ClNO]⁺ and [C₂₁H₃₅ClNO₂]⁺ for BAC-12; and [C₂₃H₃₉ClNO]⁺, [C₂₃H₄₁ClNO]⁺ and [C₂₃H₃₉ClNO₂]⁺ for BAC-14. MS/MS allowed reliable elucidation of the structures of novel DBPs, proving that chlorination starts via radical substitution in the long aliphatic chains of BAC. UV-irradiation dramatically accelerates the reaction completely destroying the original compounds in less than an hour, while the array of the intermediate products remains the same as in the dark. The formation of other DBPs proceeds due to further reactions of these primary products. The concentrations of novel DBPs in pool water reach μg L^-1 levels. These conclusions were proved by conducting model reactions of BAC with NaOCl.

Emerging Polar Phenolic Disinfection Byproducts Are High-Affinity Human Transthyretin Disruptors: An in Vitro and in Silico Study

Phenolic disinfection byproducts (phenolic-DBPs) have been identified in recent years. However, the toxicity data for phenolic-DBPs are scarce, hampering their risk assessment and the development of regulations on the acceptable concentration of phenolic-DBPs in water. In this study, the binding potency and underlying interaction mechanism between human transthyretin (hTTR) and five groups of representative phenolic-DBPs (2,4,6-trihalo-phenols, 2,6-dihalo-4-nitrophenols, 3,5-dihalo-4-hydroxybenzaldehydes, 3,5-dihalo-4-hydroxybenzoic acids, halo-salicylic acids) were determined and probed by competitive fluorescence displacement assay integrated with in silico methods. Experimental results implied that 2,4,6-trihalo-phenols, 2,6-dihalo-4-nitrophenols, and 3,5-dihalo-4-hydroxybenzaldehydes have a high binding affinity with hTTR. The hTTR binding potency of the chemicals with electron-withdrawing groups on their molecular structures were higher than that with electron-donor groups. Molecular modeling methods were used to decipher the binding mechanism between model compounds and hTTR. The results documented that ionic pair, hydrogen bonding and hydrophobic interactions were dominant interactions. Finally, a mechanism-based model for predicting the hTTR binding affinity was developed. The determination coefficient ( R²), leave-one-out cross validation Q² ( Q_LOO²), bootstrapping coefficient ( Q_BOOT²), external validation coefficient ( Q_EXT²) and concordance correlation coefficient ( CCC) of the developed model met the acceptable criteria ( Q² > 0.600, R² > 0.700, CCC > 0.850), implying that the model had good goodness-of-fit, robustness, and external prediction performances. All the results indicated that the phenolic-DBPs have the hTTR disrupting effects, and further studies are needed to investigate their other mechanism of endocrine disruption.

Formation, Identification, and Occurrence of New Bromo- and Mixed Halo-Tyrosyl Dipeptides in Chloraminated Water

Dipeptides are widely present in surface water and serve as precursors to form disinfection byproducts (DBPs) during disinfection (e.g., chloramination). Bromide (Br^-) and iodide (I^-) are common in many source waters, enhancing Br- and I-DBP formation. Recently Cl-, I-, and Cl-I-dipeptides were identified after chloramination of tyrosyl dipeptides in the presence of I^- and were detected in authentic disinfected drinking water samples. However, the formation and occurrence of Br- and mixed halogen (Cl, Br, and/or I)-dipeptides in disinfected water have not been studied. Here we investigated the formation of halogenated dipeptides from three aromatic dipeptides, phenylalanylglycine (Phe-Gly), tyrosylalanine (Tyr-Ala), and tyrosylglycine (Tyr-Gly), under chloramination in the presence of Br^- and I^- at environmentally relevant levels ([Br^-] and [I^-], 0 and 0 μg L^-1, 6 and 30 μg L^-1, 30 and 30 μg L^-1, 150 and 30 μg L^-1, 300 and 30 μg L^-1, and 900 and 30 μg L^-1, respectively). For the first time, N-Br- and N,N-di-Br- as well as N-Br- N-Cl- and N-Br-3-I-tyrosyl dipeptides were identified using infusion electrospray quadrupole time-of-flight mass spectrometry. Tyrosyl dipeptides produced N-Cl-, 3-I-/3,5-di-I-, and N-Cl-3-I-tyrosyl dipeptides, while Phe-Gly formed only N-Cl-/ N, N-di-Cl-Phe-Gly. To determine halogenated dipeptides in authentic water samples, we developed a new method of solid phase extraction and high-performance liquid chromatography with quadrupole ion trap mass spectrometry using reaction monitoring. 3,5-Di-I-Tyr-Ala and N-Br-Tyr-Ala were detected in treated water but not in the corresponding raw water, warranting further investigation into the occurrence of halogenated peptides in other drinking water systems.

Evaluating the Comparative Toxicity of DBP Mixtures from Different Disinfection Scenarios: A New Approach by Combining Freeze-Drying or Rotoevaporation with a Marine Polychaete Bioassay

The unintended formation of disinfection byproducts (DBPs) may compromise the safety of drinking water. Since no specified DBPs have been found to be responsible for the overall adverse effects and over half of total organic halogen (TOX) remains unidentified, DBP mixture toxicity is gaining increasing interest as a potential indicator of how risky drinking water might be. In this study, a new approach to evaluating the toxicity of drinking water DBP mixtures was developed by combining freeze-drying or rotoevaporation pretreatment with an in vivo high-salinity-tolerance bioassay with the embryos of a marine polychaete Platynereis dumerilii. The DBP recoveries by freeze-drying or rotoevaporation were compared with those by commonly applied liquid-liquid-extraction (LLE). For drinking water subjected to typical disinfection processes (i.e., chlorination, chloramination, chlorine dioxide treatment, and ozonation with or without postchlorination), LLE led to the lowest TOX recovery (11-18%) and the loss of all inorganic DBPs, while freeze-drying and rotoevaporation recovered 28-58% and 35-61% of TOX, respectively, and effectively recovered 81-99% and 85-104% of inorganic DBPs, respectively. Thus, LLE caused an underestimation of the toxicity of DBP mixtures compared with freeze-drying and rotoevaporation. Besides, the comparative toxicity varied significantly for water samples pretreated with different methods due to the effect of inorganic DBPs and a synergistic effect of organic and inorganic DBPs. The new approach revealed that the bromide-rich source water disinfected with ozone caused the highest developmental toxicity, followed by those disinfected with chlorine, chlorine dioxide, and chloramine in that order.