A New Group of Heterocyclic Nitrogenous Disinfection Byproducts (DBPs) in Drinking Water: Role of Extraction pH in Unknown DBP Exploration

Revisiting the chloramination of phenolic compounds: Formation of novel high-molecular-weight nitrogenous disinfection byproducts

Disinfection is critical for ensuring water safety; however, the potential risks posed by disinfection byproducts (DBPs) have raised public concern. Previous studies have largely focused on low-molecular-weight DBPs with one or two carbon atoms, leaving the formation of high-molecular-weight DBPs (HMW DBPs, with more than two carbon atoms) less understood. This study explores the formation of HMW DBPs during the chloramination of phenolic compounds using a novel approach that combines high-resolution mass spectrometry with density functional theory (DFT) calculations. For the first time, we identified nearly 100 previously unreported HMW nitrogenous DBPs (N-DBPs), with nearly half of those being halogenated N-DBPs. These N-DBPs were tentatively identified as heterocyclic (e.g., pyrrole and pyridine analogs) and coupling heterocyclic N-DBPs. Through detailed structure analysis and DFT calculations, the key formation steps of heterocyclic N-DBPs (monochloramine-mediated ring-opening reactions of halobenzoquinones) and new bonding mechanisms (C-N, C-O, and C-C bonding) of the coupling heterocyclic N-DBPs were elucidated. The selective formation of these novel N-DBPs was significantly influenced by factors such as contact time, monochloramine dosage, pH, and bromide concentration. Our findings emphasize the occurrence of diverse HMW heterocyclic N-DBPs, which are likely toxicologically significant, underscoring the need for further research to evaluate and mitigate their potential health risks in water disinfection.

Effects of solid phase extraction conditions on molecular composition of unknown disinfection byproducts in chlorinated municipal wastewater based on FT-ICR-MS analysis

Disinfection byproducts (DBPs) have been extensively investigated during the chlorination of water and wastewater. Although over 700 DBPs have been identified, more than 50% of the total organic halogen remains unknown. Solid phase extraction (SPE) has been emerged as a popular pretreatment approach for enrichment and desalting of unknown DBPs prior to the mass spectrometry analysis. However, the effects of SPE conditions on unknown DBPs in real wastewater have not yet been reported. Herein, three factors (acid types, pH values, and sorbent types) influencing the composition of DBPs in chlorinated municipal wastewater were systematically investigated by Fourier transform ion cyclotron resonance mass spectrometry and statistical analysis. The results indicated that the number of DBPs in different SPE conditions ranged from 280 to 706, and the majority ones were Br-DBPs and CHOX compounds. Compared with H2SO4, more common DBPs were found when using HCl and HCOOH to adjust the pH values of samples. The unique DBPs extracted at pH 1.0 and 2.0 generally owned higher modified aromaticity index (AImod) value and C number than at pH 3.0. The effect of acid types on the extracted DBPs was pH dependent, and the total number of extracted DBPs increased with the increasing of pH value. In terms of sorbent types, the unique DBPs in C18 sorbent possessed low O/C ratios (O/C < 0.6), whereas the unique ones in HLB sorbent owned high O/C ratios (O/C > 0.6). Compared with C18 and HLB sorbents, the unique DBPs extracted in PPL sorbent were characterized by relatively high AImod and DBE values. Based on mass difference analysis, 1496 precursors-DBPs pairs were identified in all extracted samples, with the highest number of bromine substitution reaction. Overall, the effects of SPE conditions on the composition of unknown DBPs should not be overlooked, and the amount and diversity of DBPs may be underestimated under a single SPE condition. This study provides new methodological references for the accurate identification of unknown DBPs with different characteristics in real wastewater.

New Species and Cytotoxicity Mechanism of Halohydroxybenzonitrile Disinfection Byproducts in Drinking Water

Recently, seven dihalohydroxybenzonitriles (diHHBNs) have been determined as concerning nitrogenous aromatic disinfection byproducts (DBPs) in drinking water. Herein, eight new monohalohydroxybenzonitriles (monoHHBNs), including 3-chloro-2-hydroxybenzonitrile, 5-chloro-2-hydroxybenzonitrile, 3-chloro-4-hydroxybenzonitrile, 3-bromo-2-hydroxybenzonitrile, 5-bromo-2-hydroxybenzonitrile, 3-bromo-4-hydroxybenzonitrile, 5-iodo-2-hydroxybenzonitrile, and 3-iodo-4-hydroxybenzonitrile, were detected and identified in drinking water for the first time. Thereafter, the relative concentration-cytotoxicity contribution of each HHBN was calculated based on the acquired occurrence level and cytotoxicity data in this study, the genome-scale cytotoxicity mechanism was explored, and a quantitative structure-activity relationship (QSAR) model was developed. Results indicated that new monoHHBNs were present in drinking water at concentrations of 0.04-1.83 ng/L and exhibited higher cytotoxicity than some other monohalogenated aromatic DBPs. Notably, monoHHBNs showed concentration-cytotoxicity contribution comparable to diHHBNs, which have been previously identified as potential toxicity drivers in drinking water. Transcriptomic analysis revealed immunotoxicity and genotoxicity as dominant cytotoxicity mechanisms for HHBNs in Chinese hamster ovary (CHO-K1) cells, with potential carcinogenic effects. The QSAR model suggested oxidative stress and cellular uptake efficiency as important factors for their cytotoxicity, highlighting the importance of potential iodinated HHBNs in drinking water, such as 3,5-diiodo-2-hydroxybenzonitrile, for future studies. These findings are meaningful for better understanding the health risk and toxicological significance of HHBNs in drinking water.

Understanding the fate of disinfection by-products in swimming pools: current empirical and mechanistic modeling insights

Disinfecting swimming pool water plays a crucial role in preventing the spread of harmful bacteria. However, the interaction between disinfectants and precursors can lead to the formation of potentially disinfection by-products (DBPs). Prolonged exposure to these DBPs may pose health risks. This review study investigates recent research advancements concerning the formation, exposure, and regulation of DBPs within swimming pools. It also provides an overview of existing models that predict DBPs generation in pools, highlighting their limitations. The review explores the mechanisms behind DBPs formation under different disinfectant and precursor conditions. It specifically discusses two types of models that simulate the production of these by-products. Compared to drinking water, swimming pool water presents unique challenges for model development due to its complex mix of external substances, human activities, and environmental factors. Existing models can be categorized as empirical or mechanistic. Empirical models focus on water quality parameters and operational practices, while mechanistic models delve deeper into the kinetics of DBPs generation and the dynamic nature of these compounds. By employing these models, it becomes possible to minimize DBPs production, optimize equipment design, enhance operational efficiency, and manage mechanical ventilation systems effectively.

A group of emerging heterocyclic nitrogenous disinfection byproducts: Formation and cytotoxicity of halopyridinols in drinking water

Recently, a new group of halopyridinol disinfection byproducts (DBPs) was reported in drinking water. The in vivo developmental and acute toxicity assays have shown that they were more toxic than a few commonly known aliphatic DBPs such as bromoform and iodoacetic acid. However, many pyridinol DBPs with the same main structures but different halogen substitutions were still unknown due to complicated water quality conditions and various disinfection methods applied in drinking water treatment plants. Studies on their transformation mechanisms in drinking water disinfection were quite limited. In this study, comprehensive detection and identification of halopyridinols were conducted, and five new halopyridinols were first reported, including 2-chloro-3-pyridinol, 2,6-dichloro-3-pyridinol, 2-bromo-5-chloro-3-pyridinol, 2,4,6-trichloro-3-pyridinol and 2,5,6-trichloro-3-pyridinol. Formation conditions and mechanisms of the halopyridinols were explored, and results showed that chlorination promoted their formation compared with chloramination. Halopyridinols were intermediate DBPs that could undergo further transformation/degradation with increasing contact time, disinfectant dose, bromide concentration, and pH. The in vitro cytotoxicity of the halopyridinols was evaluated using human hepatocellular carcinoma cells. Results showed that the cytotoxicity of 3,5,6-trichloro-2-pyridinol was the highest (EC50 = 474.3 μM), which was 13.0 and 1.6 times higher than that of 2-bromo-3-pyridinol (EC50 = 6214.5 μM) and tribromomethane (EC50 = 753.6 μM), respectively.

The ideal model for determination the formation potential of priority DBPs during chlorination of free amino acids

Amino acids (AAs) account for about 15-35% of dissolved organic nitrogen (DON), and are known as the important precursors of nitrogenous disinfection by-products (N-DBPs). Determining the formation potential (FP) of AAs to DBPs is used to reveal the key precursors of DBPs for further control, while the ideal method for N-DBPs FP of AAs during chlorination is not revealed. In this study, the ideal FP test models for five classes of priority DBPs during chlorination of four representative AAs (accounted for about 35% of total AAs) were analyzed. For haloaldehydes (HALs), haloketones (HKs), haloacetonitriles (HANs), haloacetamides (HAMs), and halonitromethanes (HNMs), their FPs during chlorination of four AAs were 0.1-13.0, 0.01-1.1, 0.1-104, not detectable (nd)-173, and nd-0.4 μg/mg, respectively. The FPs of priority DBPs had significant deviations between different FP test models and different tested AAs. For HALs, the model, whose chlorine dosage was determined by 15 × molar concentration of AAs [Cl (mM) = 15 × M](named: model II), was the ideal model. For HKs, model II was also the ideal FP test model for AAs with ≤3 carbons, while for AAs with 4 carbons, the model, whose chlorine dosage was determined by keeping the residual chlorine at 1 ± 0.2 mg/L after 24 h of reaction (named: model 4), was the ideal model. For HANs and HNMs, model 4 was the ideal FP test model for most of the studied AAs. The performance of HAMs during chlorination of amino acids was totally different from other P-DBPs, and model 3 was recommended to be the ideal model, in which chlorine dosage was determined by 3 × mass concentration of AAs [Cl (mg/L) = X × DOC]. This study is a reference that helps researchers select an ideal model for N-DBPs FP study of AAs.

An effective and rapidly degradable disinfectant from disinfection byproducts

Chloroxylenol is a worldwide commonly used disinfectant. The massive consumption and relatively high chemical stability of chloroxylenol have caused eco-toxicological threats in receiving waters. We noticed that chloroxylenol has a chemical structure similar to numerous halo-phenolic disinfection byproducts. Solar detoxification of some halo-phenolic disinfection byproducts intrigued us to select a rapidly degradable chloroxylenol alternative from them. In investigating antimicrobial activities of disinfection byproducts, we found that 2,6-dichlorobenzoquinone was 9.0-22 times more efficient than chloroxylenol in inactivating the tested bacteria, fungi and viruses. Also, the developmental toxicity of 2,6-dichlorobenzoquinone to marine polychaete embryos decreased rapidly due to its rapid degradation via hydrolysis in receiving seawater, even without sunlight. Our work shows that 2,6-dichlorobenzoquinone is a promising disinfectant that well addresses human biosecurity and environmental sustainability. More importantly, our work may enlighten scientists to exploit the slightly alkaline nature of seawater and develop other industrial products that can degrade rapidly via hydrolysis in seawater.

Cytotoxicity of emerging halophenylacetamide disinfection byproducts in drinking water: Mechanism and prediction

Halophenylacetamides (HPAcAms) have been identified as a new group of nitrogenous aromatic disinfection byproducts (DBPs) in drinking water, but the toxicity mechanisms associated with HPAcAms remain almost completely unknown. In this work, the cytotoxicity of HPAcAms in human hepatoma (HepG2) cells was evaluated, intracellular oxidative stress/damage levels were analyzed, their binding interactions with antioxidative enzyme were explored, and a quantitative structure-activity relationship (QSAR) model was established. Results indicated that the EC50 values of HPAcAms ranged from 2353 μM to 9780 μM, and the isomeric structure as well as the type and number of halogen substitutions could obviously induce the change in the cytotoxicity of HPAcAms. Upon exposure to 2-(3,4-dichlorophenyl)acetamide (3,4-DCPAcAm), various important biomarkers linked to oxidative stress and damage, such as reactive oxygen species, 8‑hydroxy-2-deoxyguanosine, and cell apoptosis, exhibited a significant increase in a dose-dependent manner. Moreover, 3,4-DCPAcAm could directly bind with Cu/Zn-superoxide dismutase and induce the alterations in the structure and activity, and the formation of complexes was predominantly influenced by the van der Waals force and hydrogen bonding. The QSAR model supported that the nucleophilic reactivity as well as the molecular compactness might be highly important in their cytotoxicity mechanisms in HepG2 cells, and 2-(2,4-dibromophenyl)acetamide and 2-(3,4-dibromophenyl)acetamide deserved particular attention in future studies due to the relatively higher predicted cytotoxicity. This study provided the first comprehensive investigation on the cytotoxicity mechanisms of HPAcAm DBPs.

Reaction sites of pyrimidine bases and nucleosides during chlorination: A computational study

As important components of soluble microbial products in water, nucleobases have attracted much attention due to the high toxicity of their direct aromatic halogenated disinfection by-products (AH-DBPs) during chlorination. However, multiple halogenation sites of AH-DBPs pose challenges to identify them. In this study, reaction sites of pyrimidine bases and nucleosides during chlorination were investigated by quantum chemical computational method. The results indicate that the anion salt forms play key roles in chlorination of uracil, thymine, and their nucleosides, while neutral forms make predominant contributions to cytosine and cytidine. In view of both kinetics and thermodynamics, C5 is the most reactive site for uracil and thymine, N3/C5 and N3 for respective uridine and thymidine, N1/C5/N4 and N4 for respective cytosine and cytidine, whose estimated apparent rate constants kobs-est of ∼103, 103/102, 106/102/104, and 103 M-1 s-1, respectively, in consistent with the known experimental results. C6 in all pyrimidine compounds is hardly attacked by Cl+ in HOCl ascribed to its positive charge, but readily attacked by OH‾ in hydrolysis and the N1=C6 bond was found to possess the highest reactivity in hydrolysis among all double bonds. In addition, the structure-kinetic reactivity relationship study reveals a relatively strong correlation between lgkobs-est and APT charge in all pyrimidine compounds rather than FED2 (HOMO). The results are helpful to further understand the reactivity of various reaction sites in aromatic compounds during chlorination.

Molecularly imprinted polymers and porous organic frameworks based analytical methods for disinfection by-products in water and wastewater

Disinfection by-products (DBPs) with heritage toxicity, mutagenicity and carcinogenicity are one kind of important new pollutants, and their detection and removal in water and wastewater has become a common challenge facing mankind. Advanced functional materials with ideal selectivity, adsorption capacity and regeneration capacity provide hope for the determination of DBPs with low concentration levels and inherent molecular structural similarity. Among them, molecularly imprinted polymers (MIPs) are favored, owing to their predictable structure, specific recognition and wide applicability. Also, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) with unique pore structure, large specific surface area and easy functionalization, attract increasing interest. Herein, we review recent advances in analytical methods based on the above-mentioned three functional materials for DBPs in water and wastewater. Firstly, MIPs, MOFs and COFs are briefly introduced. Secondly, MIPs, MOFs and COFs as extractants, recognition element and adsorbents, are comprehensively discussed. Combining the latest research progress of solid-phase extraction (SPE), sensor, adsorption and nanofiltration, typical examples on MIPs and MOFs/COFs based analytical and removal applications in water and wastewater are summarized. Finally, the application prospects and challenges of the three functional materials in DBPs analysis are proposed to promote the development of corresponding analytical methods.

New mechanistic insights into halogen-dependent cytotoxic pattern of monohaloacetamide disinfection byproducts

As highly toxic nitrogenous disinfection byproducts (DBPs), monohaloacetamides (monoHAcAms) generally exhibited a cytotoxic rank order of iodoacetamide ˃ bromoacetamide ˃ chloroacetamide. However, the mechanisms underlying the halogen-dependent cytotoxic pattern remain largely veiled as yet. In this work, oxidative stress/damage levels in monoHAcAm-treated Chinese hamster ovary cells were thoroughly analyzed, and binding interactions between monoHAcAms and antioxidative enzyme Cu/Zn-superoxide dismutase (Cu/Zn-SOD) were investigated by multiple spectroscopic techniques and molecular docking. Upon exposure to monoHAcAms, the intracellular levels of key biomarkers associated with oxidative stress/damage, including reactive oxygen species, malondialdehyde, lactate dehydrogenase, 8-hydroxy-2-deoxyguanosine, cell apoptosis, and G1 cell cycle arrest, were all significantly increased in a dose-response manner with the same halogen-dependent rank order as their cytotoxicity. Moreover, this rank order was also determined to be applicable to the monoHAcAm-induced alterations in the conformation, secondary structure, and activity of Cu/Zn-SOD, the microenvironment surrounding aromatic amino acid residues in Cu/Zn-SOD, as well as the predicted binding energy of SOD-monoHAcAm interactions. Our results revealed that the halogen-dependent cytotoxic pattern of monoHAcAms was attributed to their differential capacity to induce oxidative stress/damage and their interaction with antioxidative enzyme, which contribute to a better understanding of the halogenated DBP-induced toxicological mechanisms.

Effects of ozone dose on brominated DBPs in subsequent chlor(am)ination: A comprehensive study of aliphatic, alicyclic and aromatic DBPs

Ozone‒chlor(am)ine is a commonly used combination of disinfectants in drinking water treatment. Although there are quite a few studies on the formation of some individual DBPs in the ozone‒chlor(am)ine disinfection, an overall picture of the DBP formation in the combined disinfection is largely unavailable. In this study, the effects of ozone dose on the formation and speciation of organic brominated disinfection byproducts (DBPs) in subsequent chlorination, chloramination, or chlorination‒chloramination of simulated drinking water were investigated. High-molecular-weight, aliphatic, alicyclic and aromatic brominated DBPs were selectively detected and studied using a powerful precursor ion scan method with ultra performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (UPLC/ESI-tqMS). Two groups of unregulated yet relatively toxic DBPs, dihalonitromethanes and dihaloacetaldehydes, were detected by the UPLC/ESI-tqMS for the first time. With increasing ozone dose, the levels of high-molecular-weight (m/z 300-500) and alicyclic and aromatic brominated DBPs generally decreased, the levels of brominated aliphatic acids were slightly affected, and the levels of dihalonitromethanes and dihaloacetaldehydes generally increased in the subsequent disinfection processes. Despite different molecular compositions of the detected DBPs, increasing ozone dose generally shifted the formation of DBPs from chlorinated ones to brominated analogues in the subsequent disinfection processes. This study provided a comprehensive analysis of the impact of ozone dose on the DBP formation and speciation in subsequent chlor(am)ine disinfection.

Database and review of disinfection by-products since 1974: Constituent elements, molecular weights, and structures

Since trihalomethanes were discovered in 1974, disinfection by-products (DBPs) in drinking water have attracted extensive attention. In 2011, more than 600 known DBPs were compiled; however, newly reported DBPs have not been integrated. The rapid development of mass spectrometry has led to a significant increase in the number of DBPs, therefore, there is a need to develop a database of all DBPs and their properties. Herein, a database including 6310 DBPs (651 confirmed, 1478 identified and 4142 proposed) reported between 1974 and 2022 was constructed and made available for public use at https://dbps.com.cn/main. This database can be a tool in screening new DBPs, comprehensively reviewing, and developing predictive models. In this paper, to demonstrate the functions of the database and provide useful information for this area, the origin of the collected DBPs was presented, and some basic information, including elemental composition, molecular weight, functional groups, and carbon frameworks, were comparatively analyzed. The results showed that the proportion of DBPs verified by standard compounds and frequently detected in real water is less than 7.0%, and most of DBPs remained to be identified. Approximately 88% of DBPs contain halogens, and brominated -DBPs occupied a similar ratio to chlorinated -DBPs in real water. Acids were the main functional groups of DBPs, aliphatic and aromatic compounds are the two major carbon frameworks, and the molecular weights of most DBPs ranged from 200 to 400 Da. In addition, 4142 proposed DBPs as obtained using high-resolution mass spectrometry, were characterized based on the modified van Krevelen diagram and adjusted indexes with halogens. Most of the proposed DBPs featured lignin and tannin structures, and phenolic/highly unsaturated DBPs account for the majority.

Thiol Reactome: A Nontargeted Strategy to Precisely Identify Thiol Reactive Drinking Water Disinfection Byproducts

The precise identification of predominant toxic disinfection byproducts (DBPs) from disinfected water is a longstanding challenge. We propose a new acellular analytical strategy, the 'Thiol Reactome', to identify thiol-reactive DBPs by employing a thiol probe and nontargeted mass spectrometry (MS) analysis. Disinfected/oxidized water samples had reduced cellular oxidative stress responses of 46 ± 23% in Nrf2 reporter cells when preincubated with glutathione (GSH). This supports thiol-reactive DBPs as the predominant drivers of oxidative stress. This method was benchmarked using seven classes of DBPs including haloacetonitriles, which preferentially reacted with GSH via substitution or addition depending on the number of halogens present. The method was then applied to chemically disinfected/oxidized waters, and 181 tentative DBP-GSH reaction products were detected. The formulas of 24 high abundance DBP-GSH adducts were predicted, among which nitrogenous-DBPs (11) and unsaturated carbonyls (4) were the predominant compound classes. Two major unsaturated carbonyl-GSH adducts, GSH-acrolein and GSH-acrylic acid, were confirmed by their authentic standards. These two adducts were unexpectedly formed from larger native DBPs when reacting with GSH. This study demonstrated the "Thiol Reactome" as an effective acellular assay to precisely identify and broadly capture toxic DBPs from water mixtures.

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.

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Occurrence, stability and cytotoxicity of halobenzamides: A new group of nitrogenous disinfection byproducts in drinking water

Exploring disinfection byproducts (DBPs) with adverse health effects in drinking water is a constant challenge. Halobenzamides (HBZAMs) are suspected to be a new group of nitrogenous DBPs but have not been reported in drinking water to date. In this study, by coupling SPE and UPLC‒MS/MS, a sensitive method was established to detect eight HBZAMs in drinking water with recoveries and limits of detection of 80-103% and 0.01-0.04 ng/L, respectively. Subsequently, distinct fragments of HBZAMs were extended to the development of a pseudotargeted method for the analysis of the fourteen HBZAMs that were speculated and lack chemical standards. Using the developed method, eight HBZAMs were quantified in ten drinking water samples with concentrations ranging from 2.4 to 7.2 ng/L and a detection frequency of 100%, among which five HBZAMs were stable with half-lives over 72 h under real chlorine levels. Twelve HBZAMs without standards were identified in three to ten drinking water samples with comparable levels. The cytotoxicity of eight quantified HBZAMs in CHO-K1 cells varied with disparity, in which the cytotoxicity of 3,5-DBBZAM was over 10-fold higher than that of aliphatic dichloroacetamide. Considering their diversity, toxicity and stability, the occurrence of HBZAMs in drinking water deserves attention.

Insight into suppression of dibutyl phthalate on DOM removal during municipal sewage treatment using fluorescence spectroscopy with PARAFAC and moving-window 2D-COS

Dibutyl phthalate (DBP) has been widely detected in municipal and industrial wastewater, which could indirectly inhibit pollutant removals, especially degradation of dissolved organic matter (DOM). Here, the inhibition of DBP on DOM removal from wastewater in pilot-scale A2O-MBR system was investigated by fluorescence spectroscopy with two-dimensional correlation (2D-COS) and structural equation modeling (SEM). Seven components were extracted from DOM using parallel factor analysis, i.e., tryptophan-like (C1 and C2), fulvic-like (C4), tyrosine-like (C5), microbial humic-like (C6) and heme-like (C7). The tryptophan-like had a blue-shift at DBP occurrence, defined as blue-shift tryptophan-like (C3). DBP with 8 mg L^-1 exhibited a stronger inhibition on removals of DOM fractions, extraordinarily tyrosine-like and tryptophan-like in anoxic unit than DBP of 6 mg L^-1 by moving-window 2D-COS. The indirect removals of C1 and C2 through the C3 removal were more strongly inhibited by 8 mg L^-1 DBP than those by 6 mg L^-1 DBP, while the former exhibited a weaker inhibition on the direct degradation of C1 and C2 than the latter via SEM. Based on metabolic pathways, abundances of key enzymes secreted by microorganism in anoxic unit, degrading tyrosine-like and tryptophan-like, were higher in wastewater with 6 mg L^-1 DBP than those with 8 mg L^-1 DBP. These could provide a potential approach for online monitoring of DBP concentrations in wastewater treatment plants, which could rectify operating parameters, and then enhance the treatment efficiencies.

Hydroxylation of some emerging disinfection byproducts (DBPs) in water environment: Halogenation induced strong pH-dependency

In this work, the hydroxylation mechanisms and kinetics of some emerging disinfection byproducts (DBPs) have been systematically investigated through theoretical calculation methods. Five chlorophenols and eleven halogenated pyridinols were chosen as the model compounds to study their pH-dependent reaction laws in UV/H₂O₂ system. For the reactions of HO^• with 37 different dissociation forms, radical adduct formation (RAF) was the main reaction pathway, and the reactivity decreased with the increase of halogenation degree. The k_app values (at 298 K) increased with the increase of pH from 0 to 10, and decreased with the increase of pH from 10 to 14. Compared with phenol, the larger the chlorination degree in chlorophenols was, the stronger the pH sensitivity of the k_app values; compared with chlorophenols, the pH sensitivity in halogenated pyridinols was further enhanced. As the pH increased from 2 to 10.5, the degradation efficiency increased at first and then decreased. With the increase of halogenation degree, the degradation efficiency range increased, the pH sensitivity increased, the optimal degradation efficiency slightly increased, and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental compounds. These findings provided meaningful insights into the strong pH-dependent hydroxylation of emerging DBPs on molecular level.

Comparative cytotoxicity analyses of disinfection byproducts in drinking water using dimensionless parameter scaling method: Effect of halogen substitution type and number

Up to date, over 700 disinfection byproducts (DBPs) have been detected and identified in drinking water. It has been recognized that cytotoxicity of DBPs varied significantly among groups. Even within the same group, cytotoxicity of different DBP species was also different due to different halogen substitution types and numbers. However, it is still difficult to quantitatively determine the inter-group cytotoxicity relationships of DBPs under the effect of halogen substitution in different cell lines, especially when a large number of DBP groups and multiple cytotoxicity cell lines are involved. In this study, a powerful dimensionless parameter scaling method was adopted to quantitatively determine the relationship of halogen substitution and the cytotoxicity of various DBP groups in three cell lines (i.e., the human breast carcinoma (MVLN), Chinese hamster ovary (CHO), and human hepatoma (Hep G2) cell cytotoxicity) with no need to consider their absolute values and other influences. By introducing the dimensionless parameters D_{x-orn-species}^cellline and D¯_{x-orn-species}^cellline, as well as their corresponding linear regression equation coefficients k_typeornumber^cellline and k¯_typeornumber^cellline, the strength and trend of halogen substitution influences on the relative cytotoxic potency could be determined. It was found that the effect of halogen substitution type and number on the cytotoxicity of DBPs followed the same patterns in the three cell lines. The CHO cell cytotoxicity was the most sensitive cell line to evaluate the effect of halogen substitution on the aliphatic DBPs, whereas the MVLN cell cytotoxicity was the most sensitive cell line to evaluate the effect of halogen substitution on the cyclic DBPs. Notably, seven quantitative structure activity relationship (QSAR) models were established, which could not only predict the cytotoxicity data of DBPs, but also help to explain and verify the patterns of halogen substitution effect on cytotoxicity of DBPs.

Fluorescence and molecular weight dependence of disinfection by-products formation from extracellular organic matter after ultrasound irradiation

Algal blooms have a negative impact on the safety of drinking water. Ultrasonic radiation technology is an "environment-friendly" technology that is widely used in algae removal. However, this technology leads to the release of intracellular organic matter (IOM), which is an important precursor of disinfection by-products (DBPs). This study investigated the relationship between the release of IOM in Microcystis aeruginosa and the generation of DBPs after ultrasonic radiation as well as analyzed the generation mechanism of DBPs. Results showed that the content of extracellular organic matter (EOM) in M. aeruginosa increased in the order of 740 kHz >1120 kHz >20 kHz after 2 min of ultrasonic radiation. Organic matter with a molecular weight (MW) greater than 30 kDa increased the most, including protein-like, phycocyanin (PC) and chlorophyll a, followed by small-molecule organic matter less than 3 kDa, mainly humic-like substances and protein-like. DBPs with an organic MW range of less than 30 kDa were dominated by trichloroacetic acid (TCAA), while those with an MW greater than 30 kDa had the highest trichloromethane (TCM) content. Ultrasonic irradiation changed the organic structure of EOM, affected the amount and type of DBPs, and tended to generate TCM.

Developmental toxicity of 2-bromoacetamide on peri- and early post-implantation mouse embryos in vitro

2-bromoacetamide (BAcAm), a new class of disinfection by-products (DBPs), is widely detected in drinking water across the world. Reports of the high cytogenetic toxicity of BAcAm have aroused public attention concerning its toxic effects on early embryonic development. In this study, we optimized an in vitro culture (IVC) system for peri- and early post-implantation mouse embryos and used this system to determine the developmental toxicity of BAcAm. We found that exposure to BAcAm caused a reduction in egg cylinder formation rate and abnormal lineage differentiation in a dose-dependent manner. Transcriptomic analysis further revealed that BAcAm exposure at early developmental stages altered the abundance of transcripts related to a variety of biological processes including gene expression, metabolism, cell proliferation, cell death and embryonic development, thus indicating its toxic effects on embryonic development. Thus, we developed a robust tool for studying the toxicology of chemicals at the early stages of embryonic development and demonstrated the developmental toxicity of BAcAm in the early embryonic development of mammals.

Identification of Toxicity Forcing Agents from Individual Aliphatic and Aromatic Disinfection Byproducts Formed in Drinking Water: Implications and Limitations

Recently, a study found that aromatic DBP fractions dominate the overall toxicity of chlorinated drinking water. However, key toxicity drivers have not been reported via comprehensive evaluation based on the formation of aliphatic and aromatic DBPs in drinking water. In this study, the occurrence of 37 aliphatic and 19 aromatic DBPs in drinking samples with different water characteristics collected in a Chinese megacity was explored. According to the individual DBP concentrations and cytotoxicity potencies as well as the "TIC-Tox" method, haloacetonitriles and halonitrophenols were found to be the toxicity drivers among the measured aliphatic and aromatic DBPs, respectively. However, when aromatic and aliphatic DBPs are taken into consideration together, aliphatic DBPs were calculated to present higher toxicity contribution than aromatic DBPs, which is inconsistent with the previous study. TOX showed significant positive correlations with most aliphatic DBPs but no aromatic DBPs, and the overall toxicity of the water sample concentrates is significantly related to the total calculated cytotoxicity and aliphatic DBPs, suggesting that current selected aromatic DBPs are insufficient to represent the overall aromatic DBPs. UV254 and DOC rather than SUVA are better surrogates for predicting DBP formation potential for DOM with a lower humification degree as indicated by fluorescence results.

Occurrence and Cytotoxicity of Aliphatic and Aromatic Halogenated Disinfection Byproducts in Indoor Swimming Pool Water and Their Incoming Tap Water

Disinfection byproducts (DBPs) in swimming pool water are of wide concern for public health. In this study, the occurrence of five categories of aliphatic halogenated DBPs, i.e., trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloketones (HKs), and six categories of aromatic halogenated DBPs, i.e., halophenols (HPs), halonitrophenols (HNPs), halohydroxy-benzaldehydes (HBALs), halohydroxybenzoic acids (HBAs), halobenzoquinones (HBQs), and haloanilines (HAs), was examined in seven indoor swimming pool water and their incoming tap water. The correlations between the DBP concentrations and water quality parameters were explored. Moreover, the cytotoxicity of the aliphatic and aromatic halogenated DBPs was tested with human hepatoma (HepG2) cells, and the concentration-cytotoxicity contributions of different DBP categories were calculated. The results demonstrate that 24 aliphatic (5 THMs, 8 HAAs, 5 HANs, 4 HNMs, and 2 HKs) and 50 aromatic halogenated DBPs (9 HPs, 8 HNPs, 9 HBALs, 8 HBAs, 11 HBQs, and 5 HAs) were present in the swimming pool water, among which 41 aromatic halogenated DBPs were detected in swimming pool water for the first time. The average concentrations of the five categories of aliphatic halogenated DBPs in the swimming pool water were in the order of HAAs > HANs > HKs > THMs > HNMs, while those in their incoming tap water were in the order of THMs > HAAs > HKs > HANs > HNMs. The average concentrations of the aromatic halogenated DBPs in the swimming pool water were significantly lower than those of the aliphatic halogenated DBPs, following the order of HBQs > HPs > HBAs > HBALs > HAs > HNPs, while those in their incoming tap water were in the order of HBALs > HBQs > HPs > HBAs > HAs > HNPs. The average concentration-cytotoxicity contributions of different DBP categories in the swimming pool water followed the order of HAAs > HANs > HNMs > HKs > HBQs > THMs > HPs > HNPs > HBAs > HBALs > HAs, with HAAs, HANs, and HNMs possessing the main concentration-cytotoxicity contributions (93.2% in total) among all DBP categories.

Antimicrobial Effectiveness of Innovative Photocatalysts: A Review

Waterborne pathogens represent one of the most widespread environmental concerns. Conventional disinfection methods, including chlorination and UV, pose several operational and environmental problems; namely, formation of potentially hazardous disinfection by-products (DBPs) and high energy consumption. Therefore, there is high demand for effective, low-cost disinfection treatments. Among advanced oxidation processes, the photocatalytic process, a form of green technology, is becoming increasingly attractive. A systematic review was carried out on the synthesis, characterization, toxicity, and antimicrobial performance of innovative engineered photocatalysts. In recent decades, various engineered photocatalysts have been developed to overcome the limits of conventional photocatalysts using different synthesis methods, and these are discussed together with the main parameters influencing the process behaviors. The potential environmental risks of engineered photocatalysts are also addressed, considering the toxicity effects presented in the literature.

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

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 non-target 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 (LD50) and concentration for 50% of maximal effective concentration (EC50) 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.

Occurrence and transformation of newly discovered 2-bromo-6-chloro-1,4-benzoquinone in chlorinated drinking water

Halobenzoquinones (HBQs) have been reported as an emerging category of disinfection byproducts (DBPs) in drinking water with relatively high toxicity, and the previously reported HBQs include 2,6-dichloro-1,4-benzoquinone, 2,3,6-trichloro-1,4-benzoquinone, 2,6-dichloro-3-methyl-1,4-benzoquinone, 2,6-dibromo-1,4-benzoquinone, 2,6-diiodo-1,4-benzoquinone, 2-chloro-6-iodo-1,4-benzoquinone, and 2-bromo-6-iodo-1,4-benzoquinone. In this study, another HBQ species, 2-bromo-6-chloro-1,4-benzoquinone (2,6-BCBQ), was newly detected and identified in drinking water. The occurrence frequency and levels of 2,6-BCBQ were investigated, and its cytotoxicity was evaluated. Since the formed 2,6-BCBQ was found to be not stable in chlorination, its transformation kinetics and mechanisms in chlorination were further studied. The results reveal that 2,6-BCBQ was generated from Suwannee River humic acid with concentrations in the range of 4.4-47.9 ng/L during chlorination within 120 h, and it was present in all the tap water samples with concentrations ranging from 1.5 to 15.7 ng/L. Among all the tested bromochloro-DBPs, 2,6-BCBQ showed the highest cytotoxicity on the human hepatoma cells. The transformation of 2,6-BCBQ in chlorination followed a pseudo-first-order decay, which was significantly affected by the chlorine dose, pH, and temperature. Seven polar chlorinated and brominated intermediates (including HBQs, halohydroxybenzoquinones, and halohydroxycyclopentenediones) were detected in chlorinated 2,6-BCBQ samples, according to which the transformation pathways of 2,6-BCBQ in chlorination were proposed. Besides, four trihalomethanes and four haloacetic acids were also generated during chlorination of 2,6-BCBQ with molar transformation percentages of 1.6-13.7%.

Research Progress of the Endocrine-Disrupting Effects of Disinfection Byproducts

Since 1974, more than 800 disinfection byproducts (DBPs) have been identified from disinfected drinking water, swimming pool water, wastewaters, etc. Some DBPs are recognized as contaminants of high environmental concern because they may induce many detrimental health (e.g., cancer, cytotoxicity, and genotoxicity) and/or ecological (e.g., acute toxicity and development toxicity on alga, crustacean, and fish) effects. However, the information on whether DBPs may elicit potential endocrine-disrupting effects in human and wildlife is scarce. It is the major objective of this paper to summarize the reported potential endocrine-disrupting effects of the identified DBPs in the view of adverse outcome pathways (AOPs). In this regard, we introduce the potential molecular initiating events (MIEs), key events (KEs), and adverse outcomes (AOs) associated with exposure to specific DBPs. The present evidence indicates that the endocrine system of organism can be perturbed by certain DBPs through some MIEs, including hormone receptor-mediated mechanisms and non-receptor-mediated mechanisms (e.g., hormone transport protein). Lastly, the gaps in our knowledge of the endocrine-disrupting effects of DBPs are highlighted, and critical directions for future studies are proposed.

Effect of ammonia on acute toxicity and disinfection byproducts formation during chlorination of secondary wastewater effluents

Ammonia nitrogen (NH₃-N) significantly affects the occurrence of disinfection byproducts (DBPs) and residual chlorine in chlorinated wastewater, thereby affecting the acute toxicity to aquatic organisms. In this paper, the formation of thirty-five halogenated DBPs and the changes in acute toxicity of luminescent bacteria and zebrafish embryos were evaluated after chlorination of seven secondary wastewater effluents with different NH₃-N concentrations. Results showed that NH₃-N significantly reduced the formation of most DBPs by 82-100%. The acute toxicity was enhanced after chlorination and increased linearly with increasing NH₃-N concentration for luminescent bacteria (r = 0.986, p < 0.05) and zebrafish embryos (r = 0.972, p < 0.05) due to the coexistence of DBPs and monochloramine. According to the toxicity classification system of wastewater, the fitting results indicated that the toxicity level was acceptable for chlorinated wastewater with NH₃-N concentration below 1.00 mg-N/L. DBPs might be the main toxicant to luminescent bacteria in the wastewater with low NH₃-N concentrations (0.06-0.31 mg-N/L), which accounted for 68-97% of the toxicity contribution. By contrast, monochloramine contributed over 80% to the toxicity of luminescent bacteria and zebrafish embryos in the wastewater with high NH₃-N concentrations (2.66-7.17 mg-N/L). Compared to chlorination, chlorine dioxide and ultraviolet disinfection unaffected by NH₃-N could reduce acute toxicity by nearly 100%, primarily due to the lack of residual disinfectant. In view of the high toxicity caused by chlorination, chlorination-dechlorination or chlorine dioxide and UV disinfection are highly recommended for the treatment of wastewater with high NH₃-N concentration.

Detection and Stability of Cyanogen Bromide and Cyanogen Iodide in Drinking Water

This study systematically summarized the factors affecting the stability of CNXs, providing a reference for better control and elimination of CNXs. A method for the detection of CNBr and CNI in solution was established using a liquid–liquid extraction/gas chromatography/electron capture detector. Specifically, the method was used to investigate the stability of CNBr and CNI in drinking water, especially in the presence of chlorine and sulfite, and it showed good reproducibility (relative standard deviation <3.05%), high sensitivity (method detection limit <100 ng/L), and good recovery (91.49–107.24%). Degradation kinetic studies of cyanogen halides were conducted, and their degradation rate constants were detected for their hydrolysis, chlorination, and sulfite reduction. For hydrolysis, upon increasing pH from 9.0 to 11.0, the rate constants of CNCl, CNBr, and CNI changed from 8 to 155 × 10−5 s−1, 1.1 to 34.2 × 10−5 s−1, and 1.5 to 6.2 × 10−5 s−1, respectively. In the presence of 1.0 mg/L chlorine, upon increasing pH from 7.0 to 10.0, the rate constants of CNCl, CNBr, and CNI changed from 36 to 105 × 10−5 s−1, 15.8 to 49.0 × 10−5 s−1, and 1.2 to 24.2 × 10−5 s−1, respectively. In the presence of 3 μmol/L sulfite, CNBr and CNI degraded in two phases. In the first phase, they degraded very quickly after the addition of sulfite, whereas, in the second phase, they degraded slowly with rate constants similar to those for hydrolysis. Owing to the electron-withdrawing ability of halogen atoms and the nucleophilic ability of reactive groups such as OH− and ClO−, the rate constants of cyanogen halides increased with increasing pH, and they decreased in the order of CNCl > CNBr > CNI during hydrolysis and chlorination. The hydrolysis and chlorination results could be used to assess the stability of cyanogen halides in water storage and distribution systems. The sulfite reduction results indicate that quenching residual oxidants with excess sulfite could underestimate the levels of cyanogen halides, especially for CNBr and CNI.

Formation and Cytotoxicity of Halophenylacetamides: A New Group of Nitrogenous Aromatic Halogenated Disinfection Byproducts in Drinking Water

Nitrogenous aromatic halogenated disinfection byproducts (DBPs) in drinking water have received considerable attention recently owing to their relatively high toxicity. In this study, a new group of nitrogenous aromatic halogenated disinfection byproducts, halophenylacetamides (HPAcAms), were successfully identified for the first time in both the laboratory experiments and realistic drinking water. The formation mechanism of HPAcAms during chlorination of phenylalanine in the presence of Br^- and I^-, occurrence frequencies, and concentrations in authentic drinking water were investigated, and a quantitative structure-activity relationship (QSAR) model was developed based on the acquired cytotoxicity data. The results demonstrated that HPAcAms could be formed from phenylalanine in chlorination via electrophilic substitution, decarboxylation, hydrochloric acid elimination, and hydrolysis. The HPAcAm yields from phenylalanine were significantly affected by contact time, pH, chlorine dose, and temperature. Nine HPAcAms with concentrations in the range of 0.02-1.54 ng/L were detected in authentic drinking water samples. Most tested HPAcAms showed significantly higher cytotoxicity compared with dichloroacetamide, which is the most abundant aliphatic haloacetamide DBP. The QSAR model demonstrated that the cellular uptake efficiency and the polarized distributions of electrons of HPAcAms play essential roles in their cytotoxicity mechanisms.

Comparative Toxicity Analyses from Different Endpoints: Are New Cyclic Disinfection Byproducts (DBPs) More Toxic than Common Aliphatic DBPs?

In recent years, dozens of halogenated disinfection byproducts (DBPs) with cyclic structures were identified and detected in drinking water globally. Previous in vivo toxicity studies have shown that a few new cyclic DBPs possessed higher developmental toxicity and growth inhibition rate than common aliphatic DBPs; however, in vitro toxicity studies have proved that the latter exhibited higher cytotoxicity and genotoxicity than the former. Thus, to provide a more comprehensive toxicity comparison of DBPs from different endpoints, 11 groups of cyclic DBPs and nine groups of aliphatic DBPs were evaluated for their comparative in vitro and in vivo toxicity using human hepatoma cells (Hep G2) and zebrafish embryos. Notably, results showed that the in vitro Hep G2 cytotoxicity index of the aliphatic DBPs was nearly eight times higher than that of the cyclic DBPs, whereas the in vivo zebrafish embryo developmental/acute toxicity indexes of the cyclic DBPs were roughly 48-50 times higher than those of the aliphatic DBPs, indicating that the toxicity rank order differed when different endpoints were applied. For a broader comparison, a Pearson correlation analysis of DBP toxicity data from nine different endpoints was conducted. It was found that the observed Hep G2 cytotoxicity and zebrafish embryo developmental/acute toxicity in this study were highly correlated with the previously reported in vitro CHO cytotoxicity and in vivo toxicity in aquatic organisms (P < 0.01), respectively. However, the observed in vitro toxicity had no correlation with the in vivo toxicity (P > 0.05), suggesting that the toxicity rank orders obtained from in vitro and in vivo bioassays had large discrepancies. According to the observed toxicity data in this study and the candidate descriptors, two quantitative structure-activity relationship (QSAR) models were established, which help to further interpret the toxicity mechanisms of DBPs from different endpoints.