Nontargeted Identification of an N-Heterocyclic Compound in Source Water and Wastewater as a Precursor of Multiple Nitrosamines

High Molecular-Weight Organics as Precursors for Toxic Iodinated Disinfection Byproducts during Chloramination

Iodinated DBPs (I-DBPs), many more toxic than regulated chlorinated and/or brominated DBPs, are a major challenge in the supply of safe drinking water. While over 800 DBPs have been identified, the occurrence and precursors of toxic I-DBPs remain poorly understood. Herein, natural organic matter from two raw drinking waters was fractionated using ultrafiltration membranes into different groups based on molecular weight (MW). The <1 kDa fraction exhibited the highest levels of cytotoxicity and genotoxicity after disinfection. However, in the presence of iodide, the 10-100 kDa fraction had the highest toxicity/dissolved organic carbon values. FT-ICR MS analysis showed high reactivity between hypoiodous acid and the 10-100 kDa fraction, and a shift from aromatic and unsaturated molecules to more saturated and oxidized molecules during chloramination of 10-100 kDa fraction. Based on nontarget analysis using orbitrap MS, four I-DBPs with high peak intensities during chloramination of 10-100 kDa fraction were identified and then confirmed using chemical standards: 4-hydroxy-3-iodo-5-nitrobenzonitrile, 2,4,5-triiodoimidazole, 3,5-diiodo-4-hydroxybenzonitrile, and 2,6-diiodo-4-nitrophenol. The first two have been first identified in drinking water. The concentrations of the four DBPs ranged from Collapse

Key Words

• chloramination
• cytotoxicity
• disinfection byproducts
• genotoxicity
• iodide
• molecular weight

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MESH Headings

• Disinfection
• Molecular Weight
• Halogenation
• Drinking Water
• Water Purification
• Disinfectants
• Water Pollutants, Chemical

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Grants Collapse

Affiliation(s)

Wenyuan Yang State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China Ministry of Education Key Laboratory of Yangtze River Water Environment, Tongji University, Shanghai 200092, China Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
Tom Bond Water Research Centre, Frankland Road, Swindon SN5 8YF, U.K
Chao Fang State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China Key Laboratory of Rare Earths, Ganjiang Innovation Academy, Chinese Academy of Sciences, Ganzhou, Jiangxi 341119, China
Zhenqi Du State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China Ministry of Education Key Laboratory of Yangtze River Water Environment, Tongji University, Shanghai 200092, China Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
Wenhai Chu State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China Ministry of Education Key Laboratory of Yangtze River Water Environment, Tongji University, Shanghai 200092, China Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China

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Collaborators Collapse

Combining High-Resolution Mass Spectrometry and Chemiluminescence Analysis to Characterize the Composition and Fate of Total N-Nitrosamines in Wastewater Treatment Plants

Monitoring the prevalence and persistence of N-nitrosamines and their precursors in wastewater treatment plants (WWTPs) and effluent-receiving aquatic compartments is a priority for utilities practicing wastewater recycling or exploiting wastewater-impacted source waters. In this work, we developed an analytical framework that combines liquid chromatography-high-resolution mass spectrometry (LC-HRMS) with acidic triiodide-chemiluminescence analysis to characterize the composition and fate of total N-nitrosamines (TONO) and their precursors along the treatment trains of eight WWTPs in New York. Through the parallel application of LC-HRMS and chemiluminescence methods, the TONO scores for 41 N-nitrosamines containing structurally diverse substituents on their amine nitrogen were derived based on their solid-phase extraction recoveries and conversion efficiencies to nitric oxide. Correcting the compositional analysis of TONO using the TONO scores of target N-nitrosamines refined the assessment of the reduction or accumulation of TONO and their precursors across treatment steps in WWTPs. Nontargeted analysis prioritized seven additional N-nitrosamines for confirmation by reference standards, including three previously uncharacterized species: N-nitroso-tert-butylphenylamine, N-nitroso-2-pyrrolidinmethanol, and N-nitrosodesloratadine, although they only served as minor components of TONO. Overall, our study establishes an adaptable methodological framework for advancing the quantitative and qualitative analysis of specific and unknown components of TONO across water treatment and reuse scenarios.

Haloketones: A class of unregulated priority DBPs with high contribution to drinking water cytotoxicity

Although unregulated aliphatic disinfection byproducts (DBPs) had a much higher concentration and cytotoxicity than known aromatic DBPs, a recent study indicated that seven classes of regulated and unregulated priority DBPs (one and two-carbon-atom DBPs) just accounted for 16.2% of disinfected water cytotoxicity in the U.S., meaning some of the highly toxic aliphatic DBPs may be overlooked. Haloketones (HKs) are an essential class of priority DBPs with a 1-100 µg/L concentration in drinking water but lack cytotoxicity data. This study investigated the cytotoxicity of seven HKs using Chinese hamster ovary (CHO) cells. The order for cytotoxicity of HKs from most to least toxic was: 1,3-dichloroacetone (LC50: 1.0 ± 0.20 μM) ≈ 1,3-dibromoacetone (1.5 ± 0.19 μM) ≈ bromoacetone (1.9 ± 0.49 μM) > chloroacetone (4.3 ± 0.22 μM) > 1,1,3-trichloropropanone (6.6 ± 0.46 μM) > 1,1,1-trichloroacetone (222 ± 7.7 μM) > hexachloroacetone (3269 ± 344 μM). The cytotoxicity of HKs was higher than most regulated and priority aliphatic DBPs in mono-halogenated, di-halogenated, and tri-halogenated categories. A prediction model of HK cytotoxicity was developed based on the quantitative structure-activity relationship (QSAR), optimizing structures and computing descriptors with Gaussian 09 W. The average concentrations of HKs in representative drinking water samples from South Carolina (U.S.) and Suzhou (China) were 12.4 and 0.9 μg/L, respectively, accounting for 18.8% and 1.7% of their specific total DBPs measured (i.e. not TOX). For South Carolina drinking water, their contributions to total calculated additive cytotoxicity of aliphatic DBPs and overall drinking water cytotoxicity were 86.7% and 14.0%, respectively, demonstrating that HKs are an essential class of overlooked DBPs with a high contribution to drinking water cytotoxicity. Our study can help to explain the conflict that why regulated and priority DBPs (except HKs) just accounted for 16% of chlorinated drinking water cytotoxicity even enough they had much higher concentration and cytotoxicity than known aromatic DBPs.

Nontargeted Analysis of Coumarins in Source Water and Their Formation of Chlorinated Coumarins as DBPs in Drinking Water

Coumarin was detected as one of the most abundant compounds by nontargeted analysis of natural product components in actual water samples prior to disinfection. More importantly, prechlorination of humic acid generated 3-hydroxycoumarin and monohydroxy-monomethyl-substituted coumarin with a total yield of ≤10.1%, which suggested the humic substance in raw water is an important source of coumarins. 7-Hydroxycoumarin, 6-hydroxy-4-methylcoumarin, 6,7-dihydroxycoumarin, and 7-methoxy-4-methylcoumarin were identified in raw water by high-performance liquid chromatography-tandem high-resolution mass spectrometry because only some coumarin standards were commercially available. Their chlorination generated monochlorinated and polychlorinated coumarins, and their structures were confirmed by the synthesized standards. These products could form at various dosages of chlorine and pH levels, and some with a concentration of 600 ng/L can be stable in tap water for days. 3,6,8-Trichloro-7-hydroxycoumarin, 3-chloro-7-methoxy-4-methylcoumarin, and 3,6-dichloro-7-methoxy-4-methylcoumarin were first identified in finished water with concentrations of 0.0670, 78.1, and 14.7 ng/L, respectively, but not in source water, suggesting that they are new DBPs formed during disinfection. The cytotoxicity of 3-chloro-7-methoxy-4-methylcoumarin in CHO-K1 cells was comparable to those of 2,6-dibromo-1,4-benzoquinone and 2,6-dichloro-1,4-benzoquinone in TIC-Tox analyses, suggesting that further investigation of their occurrence and control in drinking water systems is warranted.

What is the role of nitrate/nitrite in trace organic contaminants degradation and transformation during UV-based advanced oxidation processes?

The effectiveness of UV-based advanced oxidation processes (UV-AOPs) in degrading trace organic contaminants (TrOCs) can be significantly influenced by the ubiquitous presence of nitrate (NO3-) and nitrite (NO2-) in water and wastewater. Indeed, NO3-/NO2- can play multiple roles of NO3-/NO2- in UV-AOPs, leading to complexities and conflicting results observed in existing research. They can inhibit the degradation of TrOCs by scavenging reactive species and/or competitively absorbing UV light. Conversely, they can also enhance the elimination of TrOCs by generating additional •OH and reactive nitrogen species (RNS). Furthermore, the presence of NO3-/NO2- during UV-AOP treatment can affect the transformation pathways of TrOCs, potentially resulting in the nitration/nitrosation of TrOCs. The resulting nitro(so)-products are generally more toxic than the parent TrOCs and may become precursors of nitrogenous disinfection byproducts (N-DBPs) upon chlorination. Particularly, since the impact of NO3-/NO2- in UV-AOPs is largely due to the generation of RNS from NO3-/NO2- including NO•, NO2•, and peroxynitrite (ONOO-/ONOOH), this review covers the generation, properties, and detection methods of these RNS. From kinetic, mechanistic, and toxicologic perspectives, future research needs are proposed to advance the understanding of how NO3-/NO2- can be exploited to improve the performance of UV-AOPs treating TrOCs. This critical review provides a comprehensive framework outlining the multifaceted impact of NO3-/NO2- in UV-AOPs, contributing insights for basic research and practical applications of UV-AOPs containing NO3-/NO2-.

Role of Carbonyl Compounds for N-Nitrosamine Formation during Nitrosation: Kinetics and Mechanisms

N-Nitrosamines are potential human carcinogens frequently detected in natural and engineered aquatic systems. This study sheds light on the role of carbonyl compounds in the formation of N-nitrosamines by nitrosation of five secondary amines via different pathways. The results showed that compared to a control system, the presence of formaldehyde enhances the formation of N-nitrosamines by a factor of 5-152 at pH 7, depending on the structure of the secondary amines. Acetaldehyde showed a slight enhancement effect on N-nitrosamine formation, while acetone and benzaldehyde did not promote nitrosation reactions. For neutral and basic conditions, the iminium ion was the dominant intermediate for N-nitrosamine formation, while carbinolamine became the major contributor under acidic conditions. Negative free energy changes (<-19 kcal mol-1) and relatively low activation energies (<18 kcal mol-1) of the reactions of secondary amines with N2O3, iminium ions with nitrite and carbinolamines with N2O3 from quantum chemical computations further support the proposed reaction pathways. This highlights the roles of the iminium ion and carbinolamine in the formation of N-nitrosamines during nitrosation in the presence of carbonyl compounds, especially in the context of industrial wastewater.

Compound Similarity Network as a Novel Data Mining Strategy for High-Throughput Investigation of Degradation Pathways of Organic Pollutants in Industrial Wastewater Treatment

Identification of degradation products and pathways is crucial for investigating emerging pollutants and evaluation of wastewater treatment methods. Nontargeted analysis is a powerful tool to comprehensively investigate the degradation pathways of organic pollutants in real-world wastewater samples but often generates large data sets, making it difficult to effectively locate the exact information on interests. Herein, to efficiently establish the linkages among compounds in the same degradation pathways, we introduce a compound similarity network (CSN) as a novel data mining strategy for LC-MS-based nontargeted analysis of complex wastewater samples. Different from molecular networks that cluster compounds based on MS/MS spectra similarity, our CSN strategy harnesses molecular fingerprints to establish linkages among compounds and thus is spectra-independent. The effectiveness of CSN was demonstrated by nontargeted identification of degradation pathways and products of organic pollutants in leather industrial wastewater that underwent laboratory-scale activated carbon adsorption (ACD) and ozonation treatments. Utilizing CSN in interpreting nontargeted data, we tentatively annotated 4324 compounds in the untreated leather industrial wastewater, 3246 after ACD, and 3777 after ACD/ozonation. We located 145 potential degradation pathways of organic pollutants in the ACD/ozonation process using CSN and validated 7 pathways with 15 chemical standards. CSN also revealed 5 clusters of emerging pollutants, from which 3 compounds were selected for in vitro cytotoxicity study to evaluate their potential biohazards as new pollutants. As CSN offers an efficient way to connect massive compounds and to find multiple degradation pathways in a high-throughput manner, we anticipate that it will find wide applications in nontargeted analysis of diverse environmental samples.

Plastic protective nets: A significant but neglected "reservoir" for priority chemicals as revealed by composition analysis

As chemical-intensive products, plastics are potential sources of emerging contaminants and pose risks to the ecosystem. However, knowledge on the inventory and emissions of chemicals in plastics remains scarce, prohibiting the lifecycle assessment of their environmental exposure. Herein, full compositions of plastic protective nets (PPNs, one globally used plastics) were analyzed via nontarget screening with mass spectrometry, optical emission spectrometry, infrared spectroscopy and thermogravimetric analysis. Nontarget screening identified 861 non-polymeric organic chemicals, which were classified by network-like similarity analysis into 9 communities, dominated by phthalates (PAEs), aliphatic/oxalic esters and branched alkanes. Notably, around 80.8% (696) of the chemicals were first observed in plastics, suggesting aplenty plastic additives have previously been overlooked. Quantification results indicated PPNs contained higher levels of priority chemicals, including detrimental lead (1.17 × 104 ng/g), benzotriazoles ultraviolet stabilizers (6.66 × 103 ng/g) and PAEs (1.87 × 104 ng/g) than other plastics commonly reported. Emission projections revealed that dibutyl phthalate in PPNs had an annual release (1.83 × 103 kg) comparable to that from greenhouse films in China. These findings suggest PPNs are a significant but neglected "reservoir" for priority chemicals, which could inform future research on resolving plastic compositions, so as to promote sound chemical management.

HDPairFinder: A data processing platform for hydrogen/deuterium isotopic labeling-based nontargeted analysis of trace-level amino-containing chemicals in environmental water

The combination of hydrogen/deuterium (H/D) formaldehyde-based isotopic methyl labeling with solid-phase extraction and high-performance liquid chromatography-high resolution mass spectrometry (HPLC-HRMS) is a powerful analytical solution for nontargeted analysis of trace-level amino-containing chemicals in water samples. Given the huge amount of chemical information generated in HPLC-HRMS analysis, identifying all possible H/D-labeled amino chemicals presents a significant challenge in data processing. To address this, we designed a streamlined data processing pipeline that can automatically extract H/D-labeled amino chemicals from the raw HPLC-HRMS data with high accuracy and efficiency. First, we developed a cross-correlation algorithm to correct the retention time shift resulting from deuterium isotopic effects, which enables reliable pairing of H- and D-labeled peaks. Second, we implemented several bioinformatic solutions to remove false chemical features generated by in-source fragmentation, salt adduction, and natural 13C isotopes. Third, we used a data mining strategy to construct the AMINES library that consists of over 38,000 structure-disjointed primary and secondary amines to facilitate putative compound annotation. Finally, we integrated these modules into a freely available R program, HDPairFinder.R. The rationale of each module was justified and its performance tested using experimental H/D-labeled chemical standards and authentic water samples. We further demonstrated the application of HDPairFinder to effectively extract N-containing contaminants, thus enabling the monitoring of changes of primary and secondary N-compounds in authentic water samples. HDPairFinder is a reliable bioinformatic tool for rapid processing of H/D isotopic methyl labeling-based nontargeted analysis of water samples, and will facilitate a better understanding of N-containing chemical compounds in water.

Molecularly imprinted polymer sheathed mesoporous silica tube as SPME fiber coating for determination of tobacco-specific nitrosamines in water

Tobacco-specific nitrosamines (TSNAs) are probably carcinogenic disinfection byproducts eliciting health risk concerns. The determination and surveillance of TSNAs in water is still cumbersome due to the lack of advanced sample preparation methods. Herein, we prepared a solid phase microextraction (SPME) fiber coated with the molecularly imprinted polymer (MIP) sheathed mesoporous silica tube (MST) composite material, and developed a highly efficient, selective, and sensitive method for the determination of five TSNAs in water. Benefiting from the TSNAs-specific recognition of MIP and the increased specific surface area derived from MST, the MIP@MST fiber exhibited excellent extraction performance for TSNAs, which was much superior to the commercially available SPME fibers. By coupling to high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), the outstanding analytical merits such as low method detection limits (ranging 0.1-6.7 ng L-1) and good reproducibility (intra-fiber and inter-fiber relative standard deviations ranging 4.1 %-11.6 % and 3.5 %-12.2 %, respectively) were achieved with the consumption of 8 mL water sample and 100 μL methanol solvent in 50 min. The feasibility of the SPME-HPLC-MS/MS method was demonstrated in tap water and chloraminated source water, with relative recoveries for the five TSNAs ranging from 85.2 % to 108.5 %. In result, none of the TSNAs were found in the tap water samples, while 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-Butanol (NNAL) were detected in the chloraminated source water samples. The rapid and convenient SPME-HPLC-MS/MS method developed in this study offers a powerful tool for monitoring TSNAs in water.

Cytotoxicity of nitrogenous disinfection byproducts: A combined experimental and computational study

Nitrogenous disinfection byproducts (N-DBPs), such as halocetamides (HAcAms), haloacetonitriles (HANs) and halonitromethanes (HNMs), are emerging DBPs in drinking water. They are more toxic than currently regulated DBPs, attracting more attention to their toxic effects and mechanism. In this study, human embryonic kidney (HEK) 293T cells were employed to explore the cytotoxicity of 29 N-DBPs. The influence of molecular structures and different halogenations on cytotoxicity has been comparatively analyzed. As toxicity is the downstream of chemico-biological interactions, the thiol reactivity of 29 N-DBPs has thus been evaluated by using glutathione (GSH) as a model nucleophile, which is the most prevalent cellular thiol and acts as an antioxidant to protect cells by detoxifying electrophilic compounds. Results show that the cytotoxicity of N-DBPs follows by the order of HAcAms > HANs > HNMs, which is different from their reactivity with GSH (the median of k_GSH ranks as HNMs > HAcAms > HANs). However, a significant correlation (p < 0.001) between log k_GSH and log IC₅₀ (concentration causing 50% inhibition) has been respectively observed for HAcAms and HANs subset and HNMs subset, indicating such chemical reaction is a probable trigger for these DBPs to result in cytotoxicity. Finally, two separate quantitative structure - activity relationship (QSAR) models based on HANs & HAcAms subset and HNMs subset have been developed for estimating IC₅₀ values. The good statistical performance makes the models possible to quickly and accurately predict IC₅₀ values of other N-DBPs, providing basic data for their health risk assessment and greatly reducing in vivo and in vitro experiments.

Integration of solid phase extraction with HILIC-MS/MS for analysis of free amino acids in source water

Amino acids (AAs) are prevalent in source water, particularly during spring run-off. Monitoring of amino acids in source water is desirable for water treatment plants (WTP) to indicate changes in source water quality. The objective of this study was to establish analytical procedures for reliable monitoring of amino acids in source water. Therefore, we examined two different methods, large volume inject (LVI) and solid phase extraction (SPE), for sample preparation prior to HILIC-MS/MS. The LVI-HILIC-MS/MS method can provide fast and sensitive detection for clean samples, but suffers from matrix effects, resulting in irreproducible separation and shortening column lifetime. We have demonstrated that SPE was necessary prior to HILIC-MS/MS to achieve reproducible and reliable quantification of AAs in source water. A natural heterocyclic amine 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCCA) was also included in the method to indicate changes in other natural nitrogenous compounds in source water. The SPE-HILIC-MS/MS method was able to achieve limits of detection from 2.6-3400 ng/L for the amino acids and MTCCA with RSDs (n=3) of 1.1%-4.8%. As well, retention times (RT) of the analytes were reproducible with variation less than 0.01 min (n=3) through the entire project. We further applied the SPE-HILIC-MS/MS method to determine AAs in authentic source water samples collected from two drinking water treatment plants (WTPs) during the 2021 spring run-off season. The results support that the SPE-HILIC-MS/MS method does not require derivatization and can provide reliable, accurate, and robust analysis of AAs and MTCCA in source water, supporting future monitoring of source water quality.

Preparation of flower-like molybdenum disulfide for solid-phase extraction of N-nitrosoamines in environmental water samples

In this paper, a flower-like molybdenum disulfide material was prepared by hydrothermal method and was first used as adsorbents in the solid-phase extraction process for enriching N-nitrosoamines. Molybdenum disulfide exhibited three-dimensional petal-like microspheres with about 500 nm in diameter. The relevant analyte extraction and elution parameters (sample volumes, solution pH, washing solvents, elution solvents, and elution volumes) were optimized to improve the solid-phase extraction efficiency. The solid-phase extraction process coupled with high-performance liquid chromatography-tandem mass spectrometry for determining N-nitrosoamines in environmental water samples was established. The limits of detection were in the range of 0.01-0.05 ng/mL. The satisfactory recoveries (68.9-106.1%) were obtained at three different spiked concentrations (2, 5, and 8 ng/mL) in water samples, and the relative standard deviations were between 1.96 and 8.38%. This proposed method not only showed high sensitivity and good reusability but also provided a new adsorbent for enriching trace N-nitrosoamines in environmental water samples.

Analytical discovery of water disinfection byproducts of toxicological relevance: highlighting halobenzoquinones

Analytical advancement enables discoveries in water research, and challenges in the identification and determination of a wide range of trace level toxic compounds in water drives the development of new analytical platforms and tools. The identification of toxic disinfection byproducts (DBPs) in disinfected drinking water is an excellent example. Water disinfection is necessary to protect the public from waterborne disease. However, an unintentional consequence is the formation of DBPs resulting from reactions of disinfectants with natural organic matter in source water. To date, regulated DBPs do not account for the increased bladder cancer risk estimated in epidemiological studies. The majority of halogenated DBPs remain unidentified and the discovery of unknown DBPs of toxicological relevance continues to be a major focus of current water research. This review will highlight halobenzoquinones as a class of DBPs that serves as an example of analytical development and toxicological studies. We will feature recent trends and gaps in analytical technologies for identification of unknown DBPs and bioassays for evaluation of the toxicological effects of specific DBPs and their mixtures.