Occurrence of nitrosamines and their precursors in drinking water systems around mainland China

Intake of tobacco nitrosamines of smokers in various provinces of China and their cancer risk: A meta-analysis

Nitrosamines are a class of carcinogens which have been detected widely in food, water, some pharmaceuticals as well as tobacco. The objectives of this paper include reviewing the basic information on tobacco consumption and nitrosamine contents, and assessing the health risks of tobacco nitrosamines exposure to Chinese smokers. We searched the publications in English from "Web of Science" and those in Chinese from the "China National Knowledge Infrastructure" in 2022 and collected 151 literatures with valid information. The content of main nitrosamines in tobacco, including 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosonornicotine (NNN), N-nitrosoanatabine (NAT), N-nitrosoanabasine (NAB), total tobacco-specific nitrosamines (TSNA), and N-nitrosodimethylamine (NDMA) were summarized. The information of daily tobacco consumption of smokers in 30 provinces of China was also collected. Then, the intakes of NNN, NNK, NAT, NAB, TSNAs, and NDMA via tobacco smoke were estimated as 1534 ng/day, 591 ng/day, 685 ng/day, 81 ng/day, 2543 ng/day, and 484 ng/day by adult smokers in 30 provinces, respectively. The cancer risk (CR) values for NNN and NNK inhalation intake were further calculated as 1.44 × 10-5 and 1.95 × 10-4. The CR value for NDMA intake via tobacco smoke (inhalation: 1.66 × 10-4) indicates that NDMA is similarly dangerous in tobacco smoke when compared with the TSNAs. In China, the CR values caused by average nitrosamines intake via various exposures and their order can be estimated as the following: smoke (3.75 × 10-4) > food (1.74 × 10-4) > drinking water (1.38 × 10-5). Smokers in China averagely suffer 200% of extra cancer risk caused by nitrosamines in tobacco when compared with non-smokers.

Research progress on the generation of NDMA by typical PPCPs in disinfection treatment of water environment in China: A review

The drugs and personal care products in water sources are potential threats to the ecological environment and drinking water quality. In recent years, the presence of PPCPs has been detected in multiple drinking water sources in China. PPCPs are usually stable and resistant to degradation in aquatic environments. During chlorination, chloramination, and ozonation disinfection processes, PPCPs can act as precursor substances to generate N-nitrosodimethylamine (NDMA) which is the most widely detected nitrosamine byproduct in drinking water. This review provides a comprehensive overview of the impact of PPCPs in China's water environment on the generation of NDMA during disinfection processes to better understand the correlation between PPCPs and NDMA generation. Chloramine is the most likely to form NDMA with different disinfection methods, so chloramine disinfection may be the main pathway for NDMA generation. Activated carbon adsorption and UV photolysis are widely used in the removal of NDMA and its precursor PPCPs, and biological treatment is found to be a low-cost and high removal rate method for controlling the generation of NDMA. However, there are still certain regional limitations in the investigation and research on PPCPs, and other nitrosamine by-products such as NMEA, NDEA and NDBA should also be studied to investigate the formation mechanism and removal methods.

Occurrence and fate of N-nitrosamines in full-scale domestic wastewater treatment plants and their impact on receiving waters along the Lijiang River, China

Domestic wastewaters contaminated with N-nitrosamines pose a significant threat to river ecosystems worldwide, particularly in urban areas with riparian cities. Despite widespread concern, the precise impact of these contaminants on receiving river waters remains uncertain. This study investigated eight N-nitrosamines in wastewater treatment plants (WWTPs) and their adjacent receiving river, the Lijiang River in Guilin City, Southwest China. By analyzing thirty wastewater samples from five full-scale WWTPs and twenty-three river water samples from Guilin, we quantified the mass loads of N-nitrosamines discharged into the surrounding watershed via domestic effluents. The results revealed that N-nitrosodimethylamine (10-60 ng/L), N-nitrosodiethylamine (3.4-22 ng/L), and N-nitrosopyrrolidine (not detected-4.5 ng/g) were predominant in influents, effluents, and sludge, respectively, with the overall removal efficiencies ranging from 17.7 to 65.6% during wastewater treatment. Cyclic activated sludge system and ultraviolet disinfection were effective in removing N-nitrosamines (rates of 59.6% and 24.3%), while chlorine dioxide disinfection promoted their formation. A total of 30.4 g/day of N-nitrosamine mass loads were observed in the Lijiang River water, with domestic effluents contributing about 31.3% (19.4 g/day), followed by livestock breeding wastewater (34.5%, 12.0 g/day), and unknown sources (24.7%, 7.5 g/day). These findings highlight the critical role of WWTPs in transporting N-nitrosamines to watersheds and emphasize the urgent need for further investigation into other potential sources of N-nitrosamine pollution within watersheds.

Trihalomethanes in global drinking water: Distributions, risk assessments, and attributable disease burden of bladder cancer

This study aimed to assess the global spatiotemporal variations of trihalomethanes (THMs) in drinking water, evaluate their cancer and non-cancer risks, and THM-attributable bladder cancer burden. THM concentrations in drinking water around fifty years on a global scale were integrated. Health risks were assessed using Monte Carlo simulations and attributable bladder cancer burden was estimated by comparative risk assessment methodology. The results showed that global mean THM concentrations in drinking water significantly decreased from 78.37 μg/L (1973-1983) to 51.99 μg/L (1984-2004) and to 21.90 μg/L (after 2004). The lifestage-integrative cancer risk and hazard index of THMs through all exposure pathways were acceptable with the average level of 6.45 × 10-5 and 7.63 × 10-2, respectively. The global attributable disability adjusted of life years (DALYs) and the age-standardized DALYs rate (ASDR) dropped by 16% and 56% from 1990-1994 to 2015-2019, respectively. A big decline in the attributable ASDR was observed in the United Kingdom (62%) and the United States (27%), while China experienced a nearly 3-fold increase due to the expanded water supply coverage and increased life expectancy. However, China also benefited from the spread of chlorination, which helped reduce nearly 90% of unsafe-water-caused mortality from 1998 to 2018.

hOGG1: A novel mediator in nitrosamine-induced esophageal tumorigenesis

BACKGROUND

The effect of human 8-Oxoguanine DNA Glycosylase (hOGG1) on exogenous chemicals in esophageal squamous cell carcinoma (ESCC) remain unclear. The study plans to determine hOGG1 expression levels in ESCC and possible interactions with known environmental risk factors in ESCC.

MATERIAL AND METHODS

We analyzed levels of exposure to urinary nitrosamines in volunteers from high and low prevalence areas by GC-MS. And we performed the interaction between hOGG1 gene and nitrosamine disinfection by-products by analyzing hOGG1 gene expression in esophageal tissues.

RESULTS

In ESCC, nitrosamine levels were significantly increased and hOGG1 mRNA expression levels were significantly decreased. There was a statistically significant interaction between reduced hOGG1 mRNA levels and non-tap drinking water sources in ESCC. The apparent indirect association between ESCC and NMEA indicated that 33.4% of the association between ESCC and NMEA was mediated by hOGG1.

CONCLUSION

In populations which exposed to high levels of environmental pollutants NDMA, low expression of hOGG1 may promote the high incidence of esophageal cancer in Huai'an. hOGG1 may be a novel mediator in nitrosamine-induced esophageal tumorigenesis.

A critical review of advances in tumor metabolism abnormalities induced by nitrosamine disinfection by-products in drinking water

Intensified sanitation practices amid the recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak might result in the increased release of chloramine disinfectants into surface water, significantly promoting the formation of nitrosamine disinfection by-products (DBPs) in drinking water. Unfortunately, these nitrosamine DBPs exhibit significant genotoxic, carcinogenic, and mutagenic properties, whereas chlorinating disinfectants remain in global practice. The current review provides valuable insights into the occurrence, identification, contamination status, exposure limits, and toxicity of the new unregulated disinfection by-products (nitrosamine DBPs) in drinking water. As a result, concentrations of nitrosamine DBPs far exceed allowable limits in drinking water, and prolonged exposure has the potential to cause metabolic disorders, a critical step in tumor initiation and progression. Importantly, based on recent research, we have concluded the role of nitrosamines DBPs in different metabolic pathways. Remarkably, nitrosamine DBPs can induce chronic inflammation and initiate tumors by activating sphingolipid and polyunsaturated fatty acid metabolism. Regarding amino acid and nucleotide metabolism, nitrosamine DBPs can inhibit tryptophan metabolism and de novo nucleotide synthesis. Moreover, inhibition of de novo nucleotide synthesis fails to repair DNA damage induced by nitrosamines. Additionally, the accumulation of lactate induced by nitrosamine DBPs may act as a pivotal signaling molecule in communication within the tumor microenvironment. However, with the advancement of tumor metabolomics, understanding the role of nitrosamine DBPs in causing cancer by inducing metabolic abnormalities significantly lags behind, and specific mechanisms of toxic effects are not clearly defined. Urgently, further studies exploring this promising area are needed.

Experimental and Theoretical Study of the OH-Initiated Degradation of Piperidine under Simulated Atmospheric Conditions

The OH-initiated photo-oxidation of piperidine and the photolysis of 1-nitrosopiperidine were investigated in a large atmospheric simulation chamber and in theoretical calculations based on CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ quantum chemistry results and master equation modeling of the pivotal reaction steps. The rate coefficient for the reaction of piperidine with OH radicals was determined by the relative rate method to be kOH-piperidine = (1.19 ± 0.27) × 10-10 cm3 molecule-1 s-1 at 304 ± 2 K and 1014 ± 2 hPa. Product studies show the piperidine + OH reaction to proceed via H-abstraction from both CH2 and NH groups, resulting in the formation of the corresponding imine (2,3,4,5-tetrahydropyridine) as the major product and in the nitramine (1-nitropiperidine) and nitrosamine (1-nitrosopiperidine) as minor products. Analysis of 1-nitrosopiperidine photolysis experiments under natural sunlight conditions gave the relative rates jrel = j1-nitrosoperidine/jNO2 = 0.342 ± 0.007, k3/k4a = 0.53 ± 0.05 and k2/k4a = (7.66 ± 0.18) × 10-8 that were subsequently employed in modeling the piperidine photo-oxidation experiments, from which the initial branchings between H-abstraction from the NH and CH2 groups, kN-H/ktot = 0.38 ± 0.08 and kC2-H/ktot = 0.49 ± 0.19, were derived. All photo-oxidation experiments were accompanied by particle formation that was initiated by the acid-base reaction of piperidine with nitric acid. Primary photo-oxidation products including both 1-nitrosopiperidine and 1-nitropiperidine were detected in the particles formed. Quantum chemistry calculations on the OH initiated atmospheric photo-oxidation of piperidine suggest the branching in the initial H-abstraction routes to be ∼35% N1, ∼50% C2, ∼13% C3, and ∼2% C4. The theoretical study produced an atmospheric photo-oxidation mechanism, according to which H-abstraction from the C2 position predominantly leads to 2,3,4,5-tetrahydropyridine and H-abstraction from the C3 position results in ring opening followed by a complex autoxidation, of which the first few steps are mapped in detail. H-abstraction from the C4 position is shown to result mainly in the formation of piperidin-4-one and 2,3,4,5-tetrahydropyridin-4-ol, whereas H-abstraction from N1 under atmospheric conditions primarily leads to 2,3,4,5-tetrahydropyridine and in minor amounts of 1-nitrosopiperidine and 1-nitropiperidine. The calculated rate coefficient for the piperidine + OH reaction agrees with the experimental value within 35%, and aligning the theoretical numbers to the experimental value results in k(T) = 2.46 × 10-12 × exp(486 K/T) cm3 molecule-1 s-1 (200-400 K).

Functional UiO-66 for highly selective adsorption of N-nitrosodipropylamine: adsorption performance and mechanisms

N-Nitrosodipropylamine (NDPA) is a class of nitrogenous disinfection by-products (N-DBPs) with high toxicity. Although NDPA present in water bodies is at relatively low concentrations, the potential risk is high due to its high toxicity and bioaccumulation. Metal-organic frameworks (MOFs), a new type of porous material with remarkable functionality, have shown great performance in a wide variety of applications in adsorption. This is the first study investigating the adsorption of MOFs on NDPA. Herein, UiO-66 with -NH2 and imidazolium functional groups were synthesized by modifying UiO-66 after amination. Adsorption kinetics and isotherm models were used to compare the adsorption properties of the two materials for low-concentration NDPA in water. The results showed that the behavior of all the adsorbents was consistent with the Langmuir model and the pseudo-second-order model and that the adsorption was homogeneous chemisorption. The structures of the nanoparticles were characterized by FTIR, zeta potential, XRD, SEM and BET measurements. Based on the characteristics, four adsorption mechanisms, namely electron conjugation, coordination reaction, anion-π interaction, and van der Waals forces, were simultaneously involved in the adsorption. The influencing factor experiment revealed that the adsorption of UiO-66-NH2 and (I-)Meim-UiO-66 involved hydrogen bonding and electrostatic interactions, respectively.

Impact of agricultural activities on the occurrence of N-nitrosamines in an aquatic environment

N-Nitrosamines, nitroso compounds with strong carcinogenic effects on humans, have been frequently detected in natural waters. In agricultural areas, there is typically a lack of drinking water treatment processes and distribution systems. As a result, residents often consume groundwater as drinking water which may contain N-nitrosamines, necessitating the investigation of the occurrence, sources, and carcinogenic risk of N-nitrosamines within the groundwater of agricultural areas. This study identified eight N-nitrosamines in groundwater and river water in the Jianghan Plain, a famous agricultural region in central China. N-Nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosomorpholine (NMOR), N-nitrosopyrrolidine (NPYR), and N-nitrosodi-n-butylamine (NDBA) were detected in groundwater, with NDMA being the main compound detected (up to 52 ng L-1). Comparable concentrations of these N-nitrosamines were also found in river water. From laboratory experiments, we found a tremendous potential for the formation of N-nitrosamines in groundwater. Principal component analysis and multiple linear regression analysis results showed that the primary sources of N-nitrosamines in groundwater were the uses of nitrogen fertilizers and pesticides carrying specific N-nitrosamines such as NPYR. The average total carcinogenic risk values of detected N-nitrosamines were higher than the acceptable risk level (10-5), suggesting a potential carcinogenic risk of groundwater. Further research is urgently needed to minimize N-nitrosamine levels in the groundwater of agricultural areas, particularly in those where pesticides and fertilizers are heavily used.

Analysing N-nitrosamine occurrence and sources in karst reservoirs, Southwest China

N-nitrosamines in reservoir water have drawn significant attention because of their carcinogenic properties. Karst reservoirs containing dissolved organic matter (DOM) are important drinking water sources and are susceptible to contamination because of the fast flow of various contaminants. However, it remains unclear whether N-nitrosamines and their precursor, DOM, spread in karst reservoirs. Therefore, this study quantitatively investigated the occurrence and sources of N-nitrosamines based on DOM properties in three typical karst reservoirs and their corresponding tap water. The results showed that N-nitrosamines were widely spread, with detection frequencies > 85%. Similar dominant compounds, including N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosopyrrolidine, and N-nitrosodibutylamine, were observed in reservoirs and tap water, with average concentrations of 4.7-8.9 and 2.8-6.7 ng/L, respectively. The average carcinogenic risks caused by these N-nitrosamines were higher than the risk level of 10-6. Three-dimensional fluorescence excitation-emission matrix modeling revealed that DOM was composed of humus-like component 1 (C1) and protein-like component 2 (C2). Fluorescence indicators showed that DOM in reservoir water was mainly affected by exogenous pollution and algal growth, whereas in tap water, DOM was mainly affected by microbial growth with strong autopoietic properties. In the reservoir water, N-nitrosodiethylamine and N-nitrosopiperidine were significantly correlated with C2 and biological indicators, indicating their endogenously generated sources. Based on the principal component analysis and multiple linear regression methods, five sources of N-nitrosamines were identified: agricultural pollution, microbial sources, humus sources, degradation processes, and other factors, accounting for 46.8%, 36.1%, 7.82%, 8.26%, and 0.96%, respectively. For tap water, two sources, biological reaction processes, and water distribution systems, were identified, accounting for 75.7% and 24.3%, respectively. Overall, this study presents quantitative information on N-nitrosamines' sources based on DOM properties in typical karst reservoirs and tap water, providing a basis for the safety of drinking water for consumers.

Feasibility of NDEA formation control from DEDTC in chlorination/chloramination by pre-ozonation: Mechanisms and influencing factors

N-nitrosodiethylamine (NDEA), which is the most toxic nitrosamine among the 9 detected species, has been widely detected in drinking water. Amines containing diethylamine (DEA) groups in the structure would generate NDEA during the disinfection processes. The aim of this study was to evaluate the feasibility of reducing NDEA formation from a commonly used dithiocarbamate pesticide sodium diethyldithiocarbamate (DEDTC) in subsequent chlorination and chloramination by pre-ozonation. The results demonstrated that NDEA could be generated directly during ozonation, its amounts increased from 0 to 14.34 μg/L with increasing ozone dosages (0-4 mg/L), which was higher than that chlorination (2.68 μg/L) and chloramination (4.91 μg/L) when the initial concentration of DEDTC was 20 μM. Pre-ozonation significantly raised NDEA formation from 2.68 to15.32 μg/L in subsequent chlorination; and that from 4.91 to 9.54 μg/L during subsequent chloramination processes. The addition of •OH scavenger tert-butanol (tBA) increased the production of NDEA from 8.14 to 20.80 μg/L during ozonation, and that from 6.76 to17.98 μg/L in O3/HClO process, 8.74 to 17.33 μg/L in O3/NH2Cl process. Except for NO3- and CO32-, most of the co-existing substances promoted NDEA generation from DEDTC under disinfection conditions. Based on the results of Gaussian theory calculations, GC/MS and UPLC-Q-TOFMS analysis, the influencing mechanisms of pre-ozonation on NDEA generation in the subsequent disinfection process were proposed. In addition, not only acute/chronic toxicity calculation but also luminescent bacteria test was performed to assess the possibility of pre-ozonation on the risk control of DEDTC. The research results fill a gap in the control of NDEA pollution and help to develop a safer ozone oxidation technology.

N-nitrosamines induced gender-dimorphic effects on infant rats at environmental levels

The safety of drinking water has always been a concern for people all over the world. N-nitrosamines (NAs), a kind of nitrogenous disinfection by-products (N-DBPs), are generally detected as a mixture in drinking water at home and abroad. Studies have shown that individual NAs posed strong carcinogenicity at high concentrations. However, health risks of NAs at environmental levels (concentrations in drinking water) are still unclear. Therefore, the potential health risks of environmentally relevant NAs exposure in drinking water needs to be conducted. In this study, blood biochemical analysis and metabolomics based on nuclear magnetic resonance (NMR) were performed to comprehensively investigate NAs induced metabolic disturbance in infant rats at environmental levels. Results of blood biochemical indices analysis indicated that AST in the serum of male rats in NAs-treated group exhibited a significant gender-specific difference. Multivariate statistics showed that two and eight significantly disturbed metabolic pathways were identified in the serum samples of NAs-treated male and female rats, respectively. In the urine samples of NAs-treated female rats, glycine, serine, and threonine metabolism pathway was significantly disturbed; while three significantly disturbed metabolic pathways were found in the urine of NAs-treated male rats. Finally, results of spearman correlation coefficients suggested that the disturbances of metabolism profile in serum and urine were correlated with changes in the gut microbiota (data derived from our published paper). Data presented here aimed to generate new health risk data of NAs mixture exposure at environmental levels and provide theoretical support for drinking water safety management. ENVIRONMENTAL IMPLICATION: N-nitrosamines (NAs) are a kind of nitrogenous disinfection by-products (N-DBPs) generated during drinking water disinfection processes. Herein, health risks of NAs at environmental levels (concentrations in drinking water) are investigated using blood biochemical analysis and nuclear magnetic resonance (NMR)-based metabolomics. Results confirmed NAs induced gender-specific on the metabolism in rat and the disturbances of metabolism profile in serum and urine were correlated with changes in the gut microbiota. Data presented here aimed to generate new health risk data of NAs mixture exposure at environmental levels and provide theoretical support for drinking water safety management.

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.

Occurrence of N-nitrosodimethylamine in roasted Alaska pollock fillets during processing and storage and preliminary cancer risk assessment

BACKGROUND

Dried and salt-fermented fish products are important sources of N-nitrosodimethylamine (NDMA) exposure for human. As a potent carcinogen, NDMA was frequently detected in roasted Alaska pollock fillet products (RPFs), which is among the most common fish products in China. Until now, the occurrence and development of NDMA and its precursors (nitrites, nitrates and dimethylamine) in RPFs during processing and storage were not well elucidated, and safety evaluation of this fish product is also urgently needed.

RESULTS

The presence of precursors in the raw material was verified and significant increase of nitrates and nitrites during processing was observed. NDMA was found generated during pre-drying (3.7 μg kg-1 dry basis) and roasting (14.6 μg kg-1 dry basis) process. Continuous increase in NDMA content can also be found during storage, especially at higher storage temperature. The 95th percentile of Monte Carlo simulated cancer risk (3.73 × 10-5 ) surpassed the WHO threshold (1.00 × 10-5 ) and sensitivity analysis implies the risk was mainly attributable to NDMA level in RPFs.

CONCLUSION

The occurrence of NDMA in RFPs was mainly a result of endogenous factors originating in Alaska pollock during processing and storage rather than exogenous contamination, and temperature played a pivotal role. The preliminary risk assessment results suggest that long-term consumption of RPFs would impose potential health risks for consumers. © 2023 Society of Chemical Industry.

RAE1 promotes nitrosamine-induced malignant transformation of human esophageal epithelial cells through PPARα-mediated lipid metabolism

Esophageal cancer (EC) is the sixth cause of cancer-related deaths and still is a significant public health problem globally. Nitrosamines exposure represents a major health concern increasing EC risks. Exploring the mechanisms induced by nitrosamines may contribute to the prevention and early detection of EC. However, the mechanism of nitrosamine carcinogenesis remains unclear. Ribonucleic acid export 1 (RAE1), has an important role in mediating diverse cancer types, but, to date, there has been no study for any functional role of RAE1 in esophageal carcinogenesis. Here, we successfully verified the nitrosamine-induced malignant transformation cell (MNNG-M) by xenograft tumor model, based on which it was found that RAE1 was upregulation in the early stage of nitrosamine-induced esophageal carcinogenesis and EC tissues. RAE1 knockdown led to severe blockade in G2/M phase and significant inhibition of proliferation of MNNG-M cells, whereas RAE1 overexpression had the opposite effect. In addition, peroxisome proliferator-activated receptor-alpha (PPARα), was demonstrated as a downstream target gene of RAE1, and its down-regulation reduced lipid accumulation, resulting in causing cells accumulation in the G2/M phase. Mechanistically, we found that RAE1 regulates the lipid metabolism by maintaining the stability of PPARα mRNA. Taken together, our study reveals that RAE1 promotes malignant transformation of human esophageal epithelial cells (Het-1A) by regulating PPARα-mediated lipid metabolism to affect cell cycle progression, and offers a new explanation of the mechanisms underlying esophageal carcinogenesis.

Critical Role of Trichloramine Interaction with Dichloramine for N-Nitrosamine Formation during Breakpoint Chlorination

Breakpoint chlorination is prevalent in drinking water and potable reuse water treatment. Breakpoint chlorination enhances the formation of N-nitrosamines through reactions that form nitrosating agents. The most recent study suggests that nitroxyl (HNO) can react with free chlorine (HOCl) to form the nitrosyl chloride (ClNO) nitrosating agent but has not experimentally verified its importance in breakpoint chlorination. This study first assessed the formation of N-nitrosamines from model N-chloro-alkylamine precursors when they were added to a mixture of HOCl and HNO-derived nitrosating agents generated by chlorinating hydroxyurea. Results demonstrated negligible N-nitrosamine formation. Instead, we observed that the interaction of NCl3 with NHCl2 (total Cl2/total N molar ratio = 2.4-3:1) produced an intermediate capable of nitrosating N-chloro-alkylamines to N-nitrosamines at yields 8-fold higher to those observed in NHCl2 treatment alone, within a very short timescale (<3 min). We examined the stoichiometry of the reaction of NCl3 with NHCl2 using a UV-spectrum-based approach. Nitrosyl chloride was proposed as the key intermediate, likely formed alongside the reformation of NHCl2. Further isotopic experiments, byproduct measurements, and kinetic modeling supported the hypotheses. Modeling indicated that the reaction of NCl3 with NHCl2 explained ∼75% of NDMA formation during breakpoint chlorination. Because NCl3 is mainly derived from the reaction of HOCl with NHCl2, controlling NHCl2 (e.g., with additional treatment) is critical for minimizing nitrosamine formation in waters where breakpoint chlorination occurs.

Antiviral agents and disinfectants for foot‑and‑mouth disease (Review)

Fluorouracil, 5-azacytidine, 6-azauridine, ribavirin, favipiravir (T-705) and its derivative (T-1105) exhibit anti-foot-and-mouth disease virus (FMDV) effects. In particular, T-1105 exhibits promising results when administered to guinea pigs orally, and pigs in their feed. FMDV is excreted in the early stages of infection in aerosols and oral or nasal droplets from animals. T-1105 along with the FMDV vaccine can be used to combat foot-and-mouth disease (FMD) epidemics. Several studies have shown that sodium hypochlorous solutions are widely used to inactivate viruses, including FMDV. However, these solutions must be stored under cool and dark conditions to maintain their virucidal effects. Interestingly, a study indicated that the virucidal activity of a calcium bicarbonate solution with a mesoscopic structure (CAC-717) did not decrease after storage at room temperature for at least four years outside direct sunlight. Numerous lessons acquired from the 2010 FMD outbreak in Japan are relevant for the control of COVID-19. However, the widespread use of chlorite can cause environmental issues. Chlorite can be combined with nitrogen to produce chloramine or N-nitrosodimethylamine, which plays a role in carcinogenesis. Therefore, risk assessments should be conducted in aquatic environments. Moreover, there is a need to develop nonchlorine disinfectants that can be used during epidemics, including FMD. The approach of 'One Health' should be shared between the public health and veterinary fields to improve the management of viral outbreaks, including those due to FMD.

Status of disinfection byproducts research in India

India faces high incidents of waterborne disease outbreaks owing to their limited access to safe drinking water. In many ways, the effort to improve the quality of drinking water is performed, and it has been keenly monitored. Among those, the disinfection of drinking water is considered a necessary and important step as it controls the microbial population. Chlorination is the most practiced (greater than 80%) disinfection process in India, and it is known to generate various disinfection byproducts (DBPs). Although the toxicity and trend of DBPs are regularly monitored and investigated in most countries, still in India, the research is at the toddler level. This review summarizes i) the status of drinking water disinfection in India, ii) types of disinfection processes in centralized water treatment plants, iii) concentrations and occurrence patterns of DBPs in a different region of India, iv) a literature survey on the toxicity of DBPs, and v) removal methodologies or alternative technologies to mitigate the DBPs formation. Overall, this review may act as a roadmap to understand the trend of disinfection practices in India and their impacts on securing the goal of safe drinking water for all.

Control of N-nitrosodimethylamine (NDMA) formation from N,N-dimethylhydrazine compounds by ozone-based advanced oxidation processes

N-nitrosodimethylamine (NDMA) is formed during ozonation of model compounds with dimethylhydrazine groups, such as daminozide (DMZ) and 2-furaldehyde 2,2-dimethylhydrazone (2-F-DMH) at pH 7 with yields of 100 % and 87 %, respectively. In this study, ozone/hydrogen peroxide (O₃/H₂O₂) and ozone/peroxymonosulfate (O₃/PMS) were investigated to control NDMA formation, and O₃/PMS (50-65 %) was more effective than O₃/H₂O₂ (10-25 %) with a ratio of H₂O₂ or PMS to O₃ of 8:1. The reaction of PMS or H₂O₂ to decompose ozone could not compete with the ozonation of model compound because of the high second-order rate constants of the ozonation of DMZ (5 ×10⁵ M^-1 s^-1) or 2-F-DMH (1.6 ×10⁷ M^-1 s^-1). The R_ct value of the sulfate radical (SO₄^•-) showed a linear relationship with NDMA formation, indicating that SO₄^•- significantly contributed to its control. NDMA formation could be further controlled by injecting small quantities of ozone numerous times to minimize the dissolved ozone concentration. The effects of tannic acid, bromide and bicarbonate on NDMA formation were also investigated during ozonation, O₃/H₂O₂, and O₃/PMS processes. Bromate formation was more pronounced in the O₃/PMS process than in the O₃/H₂O₂ process. Therefore, in practical applications of O₃/H₂O₂ or O₃/PMS processes, the generation of NDMA and bromate should be detected.

Study on characteristic and mechanism involved in the formation of N-nitrosodimethylamine precursors during microbial metabolism of amino acids

Amino acid metabolism by microorganisms is a new but important pathway for the formation of NDMA precursors in water. We investigated the properties of nitrosamine precursors produced through microbial metabolism of amino acids by polarity rapid assessment method and molecular weight fractionation by ultrafiltration method. The PRAM results showed that the positively charged fraction and the non-polar fraction accounted for most (45 %-79 % and 6 %-82 %, respectively) of the NDMA precursors. The MW fractionation results also indicate the dominant precursors had MWs <1 kDa or over 10 kDa. NDMA precursors produced through amino acid metabolism were identified and quantified. Dimethylamine, N-methyl-alanine and alanine methyl ester were produced during the metabolism of alanine and peptone. Together, N-methyl-alanine and dimethylamine averagely contributed 24 % (12 %-44 %) of the NDMA precursors in the alanine medium. The NDMA precursor formation pathway during alanine metabolism involves the methylation of alanine to form N-methyl-alanine and the decomposition of alanine anabolism products to form dimethylamine. Nitrosamine precursors are generally formed through anabolism or methylation, but biogenic amines or NH₃ can be produced through catabolism before nitrosamine precursor synthesis. Microbial community analysis was performed and Ralstonia was found to be a likely key genus contributing to NDMA precursor formation during alanine metabolism.

Influencing pathways and toxicity changes of pre-ozonation on carcinogenic NDEA formation from greenhouse gas adsorbent DEAPA in subsequent disinfection processes

This study was to evaluate the feasibility of controlling carcinogenic nitrosodiethylamine (NDEA) formation from greenhouse gas adsorbent 3-diethylaminopropylamine (DEAPA) by pre-O₃ in subsequent chlorination/chloramination processes. The result indicated that the NDEA yields (0.4 %) during chlorination was 1.3 times of that during chloramination (0.3 %); pre-oxidation with 4 mg/L O₃ significantly cut down its formation; the reduction rates were up to 67.5 and 48.5 %, respectively. OH scavenger greatly augmented the final NDEA amount from 1.86 to 5.05 μg/L during ozonation, while its roles on subsequent processes differed with disinfection methods as well as O₃(g) dosages. Most of co-existed substances inhibited NDEA generation, except NO₂^-, CO₃^2- and SO₄^2-, which slightly promoted during ozonation. Basing on Gaussian calculation, GC/MS and UPLC-Q-TOF-MS analysis, the influencing mechanisms of pre-O₃ on NDEA formation in subsequent disinfection processes were proposed. In addition, the calculated toxicity analysis as well as the whole toxicity was applied to evaluate the possibility of pre-O₃ on risk control.

Peroxymonosulfate activated by composite ceramic membrane for the removal of pharmaceuticals and personal care products (PPCPs) mixture: Insights of catalytic and noncatalytic oxidation

A composite manganese-based catalytic ceramic membrane (Mn-CCM) was developed by a solid-state sintering method, and its effectiveness toward activation of peroxymonosulfate (PMS) for the degradation of 11 pharmaceutical and personal care products (PPCPs) mixture was tested. The optimized Mn-CCMs/PMS system showed remarkable degradation efficiencies for PPCPs mixture with total removal >90% in ultrapure water, river water and natural organic matter (NOM) solution. The Mn-CCMs/PMS system showed the contribution of different phenomena in PPCPs removal in the order of catalytic oxidation (54.7%, Mn-CCMs/PMS) > noncatalytic oxidation (42.3%, PMS oxidation) > adsorption (3.0%, by Mn-CCMs). The singlet oxygen (¹O₂) was the dominant reactive oxygen specie for the degradation of PPCPs in all water matrices proved by the quenching experiments and electro-paramagnetic resonance (EPR) spectroscopy. The extraordinary stability of Mn-CCMs for the activation of PMS has been noted in terms of repeatability experiments for PPCPs degradation with fewer leaching of Mn (1.9 to 3.6 µg/L). Mineralization was achieved in the range of 28-65% for different water matrices. The toxicity of the PPCPs mixture was reduced by 85.9%. The Mn-CCMs/PMS system showed a reduction (25-100%) in precursors of different carbon- and nitrogen-based disinfection by-products. This study found the Mn-CCMs/PMS system as a feasible purification unit for removing trace concentrations of PPCPs (ng/L) in real drinking water matrices.

Maternal exposure to nitrosamines in drinking water during pregnancy and birth outcomes in a Chinese cohort

Maternal exposure to regulated disinfection by-products (DBPs) during pregnancy has been linked with adverse birth outcomes. However, no human studies have focused on drinking water nitrosamines, a group of emerging unregulated nitrogenous DBPs that exhibits genotoxicity and developmental toxicity in experimental studies. This cohort study included 2457 mother-infant pairs from a single drinking water supply system in central China, and maternal trimester-specific and entire pregnancy exposure of drinking water nitrosamines were evaluated. Multivariable linear and Poisson regression models were used to estimate the associations between maternal exposure to nitrosamines in drinking water and birth outcomes [birth weight (BW), low birth weight (LBW), small for gestational age (SGA) and preterm delivery (PTD)]. Elevated maternal N-nitrosodimethylamine (NDMA) exposure in the second trimester and N-nitrosopiperidine (NPIP) exposure during the entire pregnancy were associated with decreased BW (e.g., β = -88.6 g; 95% CI: -151.0, -26.1 for the highest vs. lowest tertile of NDMA; p for trend = 0.01) and increased risks of PTD [e.g., risk ratio (RR) = 2.16; 95% CI: 1.23, 3.79 for the highest vs. lowest tertile of NDMA; p for trend = 0.002]. Elevated maternal exposure of N-nitrosodiethylamine (NDEA) in the second trimester was associated with increased risk of SGA (RR = 1.80; 95% CI: 1.09, 2.98 for the highest vs. lowest tertile; p for trend = 0.01). Our study detected associations of maternal exposure to drinking water nitrosamines during pregnancy with decreased BW and increased risks of SGA and PTD. These findings are novel but require replication in other study populations.

Seasonal variability, predictive modeling and health risks of N-nitrosamines in drinking water of Shanghai

The prevalence of carcinogenic N-nitrosamines in drinking water is of significant concern. In the present study, eight N-nitrosamines from three representative drinking water treatment plants (DWTPs) in Shanghai, China were monitored for an entire year to evaluate their seasonal variability, probabilistic cancer risk and the resulting disease burden. The possibility of employing routinely monitored water quality parameters as predictors of N-nitrosamines was also examined. The results showed that the Taipu River-fed reservoir suffered more serious N-nitrosamine contamination than the Yangtze River-fed reservoirs. Winter witnessed higher levels of N-nitrosamines in both source and finished water. N-nitrosamine concentrations increased from source water to finished water in autumn or winter, but no spatial variations were observed in summer. The total lifetime cancer risk (LCR) posed by N-nitrosamines in finished water was within the acceptable range (1.00 × 10^-6 to 1.00 × 10^-4), with N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) being the main contributors. Winter and autumn were found to have higher total LCR values. The average individual disability-adjusted life years (DALYs) lost was 4.43 × 10^-6 per person-year (ppy), exceeding the reference risk level (1.00 × 10^-6 ppy). Liver cancer accounted for 97.1 % of the total disease burden, while bladder and esophagus cancers made a little contribution (2.9 %). A multiple regression model was developed to estimate the total N-nitrosamines in finished water as a function of water quality parameters, and the R² value was 0.735. This study not only provides fundamental data for public health policy development, but also reveals the necessity to incorporate a seasonal control strategy in DWTPs to minimize the associated health risks induced by N-nitrosamines.

Development of multi-residue gas chromatography coupled with mass spectrometry methodologies for the measurement of 15 chemically different disinfection by-products (DBPs) of emerging concern in drinking water from two different Portuguese water treatment plants

In water treatment plants (WTPs), chemical agents, such as chlorine and ozone, might react with organic matter and anthropogenic contaminants, forming a high diversity of disinfection by-products (DBPs). Due to the potential toxicological effects, the identification of unregulated DBPs (UR-DBPs) is critical to help water managers in the selection of effective water treatment processes, contributing to improving water safety plans. Given the limited validated analytical methods to detect UR-DBPs, here we developed new multi-residue gas chromatography coupled with mass spectrometry methodologies for the detection and quantification of 15 UR-DBPs, including aldehydes, haloketones (HKs), nitrosamines and alcohols, in drinking water matrices. Solid-phase extraction (SPE), for the nitrosamine group, and solid-phase micro extraction (SPME), for the remaining DBPs, were used as sample preparation methods. The developed methodologies allowed the quantification of target UR-DBPs at trace concentration levels (ng L^-1), with method quantification limits (MQLs) ranging from 14.4 ng L^-1 to 26.0 ng L^-1 (SPE-GC-MS) and 2.3 ng L^-1 and 1596 ng L^-1 (SPME-GC-MS). The methods were applied to different drinking water matrices, considering distinct delivery points of EPAL - Empresa Portuguesa das Águas Livres WTPs. Overall, the aldehyde group, represented by decanal, nonanal and 2-ethylheaxanal, showed the highest occurrence, followed by HKs and nitrosamines. The results of this study suggested that the formation of these UR-DBPs should be further monitored in WTPs.

Transformation mechanism and fate of dissolved organic nitrogen (DON) in a full-scale drinking water treatment

Dissolved organic nitrogen (DON) has attracted much attention in drinking water treatment due to its potential to produce nitrogenous disinfection by-products (N-DBPs). This work was designed to explore the transformation and fate of DON and dissolved inorganic nitrogen (DIN) in drinking water treatment. The changes of DON and formation of N-DBPs were evaluated along the water treatment route (i.e., pre-ozonation and biological-contact oxidation, delivery pipes' transportation, coagulation-sedimentation, sand filtration, post-ozonation, biological activated carbon, ultrafiltration and disinfection) of drinking water treatment plant (DWTP). The transformation mechanism of DON was comprehensively investigated by molecular weight fractionation, three-dimensional fluorescence, LC-OCD (Liquid Chromatography-Organic Carbon Detection), total free amino acids. A detailed comparison was made between concentrations and variations of DON and DIN affected by seasons in the drinking water treatment. Regardless of seasonal variation in raw water concentration, the DON removal trends between different treatment processes remain constant in the present study. Compared to other treatment processes, pre-ozonation and coagulation-sedimentation exhibited the dominant DON removal in different seasons, i.e., 11.13%-14.45% and 14.98%-22.49%, respectively. Contrary, biological-contact oxidation and biological activated carbon negatively impacted the DON removal, in which DON increased by 1.76%-6.49% in biological activated carbon. This may be due to the release of soluble microbial products (SMPs) from bacterial metabolism, which was further validated by the rise of biopolymers in LC-OCD.

Quality assessment and prediction of municipal drinking water using water quality index and artificial neural network: A case study of Wuhan, central China, from 2013 to 2019

The sanitary security of drinking water is closely related to human health, but its quality assessment mainly focused on limited types of indicators and relatively restricted time span. The current study was aimed to evaluate the long-term spatial-temporal distribution of municipal drinking water quality and explore the origin of water contamination based on multiple water indicators of 137 finished water samples and 863 tap water samples from Wuhan city, China. Water quality indexes (WQIs) were calculated to integrate the measured indicators. WQIs of the finished water samples ranged from 0.24 to 0.92, with the qualification rate and excellent rate of 100 % and 96.4 %, respectively, while those of the tap water samples ranged from 0.09 to 3.20, with the qualification rate of 99.9 %, and excellent rate of 95.5 %. Artificial neural network model was constructed based on the time series of WQIs from 2013 to 2019 to predict the water quality thereafter. The predicted WQIs of finished and tap water in 2020 and 2021 qualified on the whole, with the excellent rate of 87.5 % and 92.9 %, respectively. Except for three samples exceeding the limits of free chlorine residual, chloroform and fluoride, respectively, the majority of indicators reached the threshold values for drinking. Our study suggested that municipal drinking water quality in Wuhan was generally stable and in line with the national hygiene standards. Moreover, principal component analysis illustrated that the main potential sources of drinking water contamination were inorganic salts and organic matters, followed by pollution from distribution systems, the use of aluminum-containing coagulants and turbidity involved in water treatment, which need more attention.

Pilot Study of Pollution Characteristics and Ecological Risk of Disinfection Byproducts in Natural Waters in Hong Kong

Increased disinfection efforts in various parts of China, including Hong Kong, to prevent the spread of the novel coronavirus may lead to elevated concentrations of disinfectants in domestic sewage and surface runoff in Hong Kong, generating large quantities of toxic disinfection byproducts. Our study investigated the presence and distribution of four trihalomethanes (THMs), six haloacetic acids (HAAs), and eight nitrosamines (NAMs) in rivers and seawater in Hong Kong. The concentrations of THMs (mean concentration: 1.6 µg/L [seawater], 3.0 µg/L [river water]), HAAs (mean concentration: 1.4 µg/L [seawater], 1.9 µg/L [river water]), and NAMs (mean concentration: 4.4 ng/L [seawater], 5.6 ng/L [river water]) did not significantly differ between river water and seawater. The total disinfection byproduct content in river water in Hong Kong was similar to that in Wuhan and Beijing (People's Republic of China), and the total THM concentration in seawater was significantly higher than that before the COVID-19 pandemic. Among the regulated disinfection byproducts, none of the surface water samples exceeded the maximum index values for THM4 (80 μg/L), HAA5 (60 μg/L), and nitrosodimethylamine (100 ng/L) in drinking water. Among the disinfection byproducts detected, bromoform in rivers and seawater poses the highest risk to aquatic organisms, which warrants attention and mitigation efforts. Environ Toxicol Chem 2022;41:2613-2621. © 2022 SETAC.

A balancing act: Optimizing free chlorine contact time to minimize iodo-DBPs, NDMA, and regulated DBPs in chloraminated drinking water

Many drinking water treatment plants in the U.S. have switched from chlorination to chloramination to lower levels of regulated trihalomethane (THM) and haloacetic acid (HAA) disinfection byproducts (DBPs) in drinking water and meet the current regulations. However, chloramination can also produce other highly toxic/carcinogenic, unregulated DBPs: iodo-acids, iodo-THMs, and N-nitrosodimethylamine (NDMA). In practice, chloramines are generated by the addition of chlorine with ammonia, and plants use varying amounts of free chlorine contact time prior to ammonia addition to effectively kill pathogens and meet DBP regulations. However, iodo-DBPs and nitrosamines are generally not considered in this balancing of free chlorine contact time. The goal of our work was to determine whether an optimal free chlorine contact time could be established in which iodo-DBPs and NDMA could be minimized, while keeping regulated THMs and HAAs below their regulatory limits. The effect of free chlorine contact time was evaluated for the formation of six iodo-trihalomethanes (iodo-THMs), six iodo-acids, and NDMA during the chloramination of drinking water. Ten different free chlorine contact times were examined for two source waters with different dissolved organic carbon (DOC) and bromide/iodide. For the low DOC water at pH 7 and 8, an optimized free chlorine contact time of up to 1 h could control regulated THMs and HAAs, as well as iodo-DBPs and NDMA. For the high DOC water, a free chlorine contact time of 5 min could control iodo-DBPs and NDMA at both pHs, but the regulated DBPs could exceed the regulations at pH 7.

Effects of seasons and parts on volatile N-nitrosamines and their exposure and risk assessment in raw chicken and duck meats

The N-nitrosamine (NA) concentrations and types in raw chicken and duck meats of different parts and seasons were estimated by headspace solid-phase micro-extraction with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The exposure level and hazard quotient of each detected volatile N-nitrosamine (VNA) were conducted. The selected chicken and duck samples were contaminated by VNAs to some extent. The major types and contents of VNAs in different parts of chicken and duck meats varied seasonally. For chicken samples, the order of the total VNA concentrations was as follows: autumn > spring > winter > summer. For duck samples, the order was changed as follows: winter > autumn > summer > spring (thigh samples) and autumn > spring > winter > summer (breast samples). The estimated exposure levels for adults caused by duck consumption were slightly higher than those by chickens, which was consistent with the tendency in 2-3 years old children. According to the linear regression correlation between the 10% benchmark dose limit (BMDL₁₀) and subtriplicate of median lethal dose (LD₅₀), BMDL₁₀ values of each VNA were calculated. Due to this hypothesis, the risk assessments of each detected VNA and total VNAs posed by consuming chicken and duck meats in Tianjin, China were of low concern.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-021-05195-1.

Reactive oxygen species-mediated activation of NLRP3 inflammasome associated with pyroptosis in Het-1A cells induced by the co-exposure of nitrosamines

Nitrosamines were a class of important environmental carcinogens associated with digestive tract neoplasms. As the early toxic effect of nitrosamines, inflammatory response participated in the malignant transformation of cells and promoted the occurrence and development of tumors. However, the role of NLRP3 inflammasome in the nitrosamines-induced inflammatory response was unclear. In this study, the human esophageal epithelial cells (Het-1A) were used to explore potential mechanisms of the activation of NLRP3 inflammasome under co-exposure to nine nitrosamines commonly found in drinking water at the doses of 0, 4, 20, 100, 500, and 2500 ng/mL. The results showed that nitrosamines stimulated activation of the NLRP3 inflammasome and induced cellular oxidative damage in a dose-dependent manner. Pretreatment of reactive oxygen species scavenger N-acetyl-L-cysteine (NAC), particularly mitochondrial reactive oxygen species (mtROS) scavengers Mito-TEMPO, effectively inhibited the activation of NLRP3 inflammasome, suggesting that nitrosamines could mediate the activation of NLRP3 inflammasome via mtROS. Furthermore, we found that nitrosamines co-exposure also promoted cell pyroptosis through the NLRP3/caspase-1/GSDMD pathway, which was demonstrated by adding the caspase-1 inhibitor Z-YVAD-FMK and constructing NLRP3 downregulated Het-1A cell line. This study revealed the underlying mechanism of the activation of NLRP3 inflammasome initiated by nitrosamines co-exposure and provided new perspectives on the toxic effects of nitrosamines.

N-nitrosodimethylamine formation during oxidation of N,N-dimethylhydrazine compounds by peroxymonosulfate: Kinetics, reactive species, mechanism and influencing factors

This study found that peroxymonosulfate (PMS) oxidation without activation has the potential to generate a suspected human carcinogen, N-nitrosodimethylamine (NDMA), in water containing N,N-dimethylhydrazine compounds. Considerable amounts of NDMA formed from three compounds by PMS oxidation were observed. 1,1,1',1'-Tetramethyl-4,4'-(methylene-di-p-phenylene) disemicarbazide (TMDS), which is an industrial antiyellowing agent and light stabilizer, was used as a representative to elucidate the kinetics, transformation products, mechanism and NDMA formation pathways of PMS oxidation. TMDS degradation and NDMA formation involved direct PMS oxidation and singlet oxygen (¹O₂) oxidation. The oxidation by PMS/¹O₂ was pH-dependent, which was related to the pH-dependent characteristics of the reactive oxygen species and intermediates. The degradation mechanism of TMDS mainly included the side chain cleavage, dealkylation, and O-addition. NDMA was generated from TMDS mainly via O-addition and 1,1-dimethylhydrazine (UDMH) generation. The cleavage of amide nitrogen in O-addition products and primary amine nitrogen in UDMH are likely the key steps in NDMA generation. The results emphasized that the formation of harmful by-products should be taken into account when assessing the feasibility of PMS oxidation.

The genotoxic potential of mixed nitrosamines in drinking water involves oxidative stress and Nrf2 activation

Nitrosamine by-products in drinking water are designated as probable human carcinogens by the IARC, but the health effects of simultaneous exposure to multiple nitrosamines in drinking water remain unknown. Genotoxicity assays were used to assess the effects of both individual and mixed nitrosamines in finished drinking water produced by a large water treatment plant in Shanghai, China. Cytotoxicity and genotoxicity were measured at 1, 10-, 100- and 1000-fold actual concentrations by the Ames test, Comet assay, γ-H2AX assay, and the cytokinesis-block micronuclei assay; oxidative stress and the Nrf2 pathway were also assessed. Nitrosamines detected in drinking water included NDMA (36.45 ng/L), NDPA (44.68 ng/L), and NEMA (37.27 ng/L). Treatment with a mixture of the three nitrosamines at 1000-fold actual drinking-water concentration induced a doubling of revertants in Salmonella typhimurium strain TA100, DNA and chromosome damage in HepG2 cells, while 1-1000-fold concentrations of compounds applied singly lacked these effects. Treatment with 100- and 1000-fold concentrations increased ROS, GSH, and MDA and decreased SOD activity. Thus, nitrosamine mixtures showed greater genotoxic potential than that of the individual compounds. N-Acetylcysteine protected against the nitrosamine-induced chromosome damage, and Nrf2 pathway activation suggested that oxidative stress played pivotal roles in the genotoxic property of the nitrosamine mixtures.

UV/chlorinated cyanurates as an emerging advanced oxidation process for drinking water and potable reuse treatments

Chlorinated cyanurates, prepared by application of hypochlorite to cyanuric acid at different ratios, have been commonly employed for disinfection. Combining UV with chlorinated cyanurates (UV/Cl-cyanurates) can be a novel and effective advanced oxidation process (AOP) because (1) Cl-cyanurates structurally resemble chlorinated amides that feature low reactivity with radicals, and (2) Cl-cyanurates, which bear multiple -Cl, may exhibit high molar absorptivity at 254 nm due to red-shifting absorption. Those chemiphysical properties of Cl-cyanurates may facilitate oxidant photolysis rate and lower radical scavenging rates in an AOP, thereby increasing steady-state concentrations of radicals. In this study, UV spectra measured for Cl-cyanurates highlighted molar absorptivities at 254 nm (∼200 M^-1cm^-1) much higher than free chlorine or H₂O₂, while k_•OH determined using competition kinetics suggests low •OH reactivity (<1.95 × 10⁷ M^-1s^-1) for Cl-cyanurates. Photolysis of Cl-cyanurates forms •Cl (i.e., Cl-N cleavage), and •Cl converts to •OH; formation of •OH during a UV/Cl-cyanurates AOP was evaluated using terephthalate as a probe compound. Experiments systematically investigated the effects of pH, Cl₂ dosage, and cyanuric concentration (three key factors affecting the equilibrium concentrations of chlorinated-cynaurate species) on the efficacy of removing three indicator contaminants by UV/Cl-cyanurates AOP. UV/Cl-cyanurates AOP conducted in phosphate buffers or authentic surface waters highlighted efficiencies up to 170% higher than UV/Cl₂ AOP at neutral pH when the same dosage of oxidants was employed, and the presence of certain levels of background ammonia or chloramines further enhanced its performance. Transformation of cyanuric acid or Cl-cyanurates by reacting with radicals during a UV/Cl-cyanurates AOP treatment was minimum. Toxicity assay indicated that UV/Cl-cyanurates AOP treated water was comparable or less toxicity than UV/H₂O₂ or UV/Cl₂ AOP treated water, and the initial cost estimate indicates UV/Cl-cyanurates AOP is potentially a cost-effective alternative AOP.

Metabolomics-based molecular signatures reveal the toxic effect of co-exposure to nitrosamines in drinking water

Nitrosamines, a group of emerging nitrogenous pollutants, are ubiquitously found in the drinking water system. However, less is known about how systemic biological responses resist or tolerate nitrosamines, especially long-term co-exposure at low concentrations. In this study, untargeted metabolomics was used to investigate the metabolic perturbations in human esophageal epithelial Het-1A cells induced by a mixture of nine common nitrosamines in drinking water at environmentally relevant, human-internal-exposure, and genotoxic concentrations. Generally, the disrupted metabolic spectrum became complicated with nitrosamines dose increasing. Notably, two inflammation-associated pathways, namely, cysteine (Cys) and methionine (MET) metabolism, and nicotinate and nicotinamide metabolism, changed significantly under the action of nitrosamines, even at the environmentally relevant level. Furthermore, targeted metabolomics and molecular biology indicators in cells were identified in mice synchronously. For one thing, the up-regulated Cys and MET metabolism provided methyl donors for histone methylation in the context of pro-inflammatory response. For another, the down-regulated NAD⁺/NADH ratio inhibited the deacetylation of NF-кB p65 and eventually activated the NF-кB signaling pathway. Taken collectively, the metabolomics molecular signatures were important indicative markers for nitrosamines-induced inflammation. The potential crosstalk between the inflammatory cascade and metabolic regulation also requires further studies. These findings suggest that more attention should be paid to long-term co-exposure at low concentrations in the control of nitrosamines pollution in drinking water. Additionally, this study also highlights a good prospect of the combined metabolomic-molecular biology approach in environmental toxicology.

Characterization of nitrosamines and nitrosamine precursors as non-point source pollutants during heavy rainfall events in an urban water environment

N-nitrosodimethylamine (NDMA) and N-nitrosomorpholine (NMOR) and their specific precursors (N,N-dimethylformamide [DMF] for NDMA and morpholine [MOR] for NMOR) were widely identified in runoff of urban area around the southern Lake Biwa basin, Japan. It was thought that this runoff might constitute a non-point source of the four compounds in rivers and sewage treatment plants (STPs) during heavy rainfall events. We investigated the spatiotemporal patterns of NDMA, NMOR, DMF and MOR in runoff and rivers in rainy days. NDMA and NMOR were detected in concentrations of up to 295 ng/L, while DMF and MOR were detected in concentrations of up to 33.7 µg/L. Continuous sequential sampling over periods of 24 or 48 h at the largest STP in the study area revealed that the four compounds in the primary effluent (PE) each had higher mass fluxes during heavy rainfall events than on dry days. This phenomenon might be contributed to non-point sources (e.g., runoff) from infiltration/inflow related to rainwater into sanitary sewers. Moreover, the four compounds were confirmed to have higher mass fluxes in the final effluent of the STP during periods of PE bypass (1.3-1.7 times for NDMA, NMOR, and MOR; over 200 times for DMF; on average) than that on dry days because of increasing inflow during heavy rain than during periods without PE bypass in dry weather.

Predictable Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry Fragmentation of Ozone-Reactive N-Nitrosodimethylamine Precursors Coupled with In Silico Fragmentation and Ion Mobility-Quadrupole Time-of-Flight Facilitates Their Identification in Sewage

This study investigated the liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS) fragmentation of 10 potent model ozone (O₃)-reactive N-nitrosodimethylamine (NDMA) precursors bearing (CH₃)₂N-N or (CH₃)₂N-(SO₂)-N. Fragments (m/z 61.0766, 60.0688 Da loss, and 72.0688 Da loss) were discovered as pertinent diagnostic fragments for precursors bearing (CH₃)₂N-N, whereas a loss of 108.0119 Da was consistent for precursors bearing (CH₃)₂N-S(O₂)-N. Using the fragments as structural hints on a sewage fraction with a high concentration of O₃-reactive precursors, peaks of precursors sharing m/z 61.0766, a 60.0688 Da loss, or both were flagged. Then, using in silico fragmenters and (CH₃)₂N-N as a substructure filter on online-chemical structure databases, we identified PubChem's compound identifier (PCCID) 141210417 and 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene)disemicarbazide (TMDS). TMDS was confirmed using an authentic standard, and ion mobility (IM)-QTOF/MS confirmed its rider peak as PCCID 141210417. PCCID 141210417 is an isomer of TMDS, and its environmental occurrence is associated with technical-grade TMDS and industrial effluents. The estimated contribution of TMDS to the total NDMA formation potential of the sewage fraction was 20-24%, which was suggestive of the significance of PCCID 141210417 and other precursors.

Cyclic coupling of photocatalysis and adsorption for completely safe removal of N-nitrosamines in water

The incomplete removal of N-nitrosamines in water through current degraded techniques and the carcinogenicity of N-nitrosamines call for alternative complete and safe removal approaches. Here, we describe a cyclic coupling process of photocatalysis and adsorption enabling N-nitrosamines in water thoroughly and safely removed. Among them, the immobilized TiO2/Ti photocatalyst degraded N-nitrosamines into primary and secondary amines up to 100% by attacking on nitrosyl nitrogen via •OH originated from its nanowire film morphology. Furthermore, the affinity of HY zeolite to primary and secondary amines led to efficient adsorption through corresponding to Lagergren adsorption rate equation of second order. And then the cyclic coupling process of photocatalysis and adsorption realized complete and safe removal of N-nitrosamines with various concentration ranging from 0.1 mM to 1 mM in water, significantly higher than the existing reports on the removal rate of N-nitrosamines and the formation potential of N-nitrosamines. This study will lead to new avenues for complete and safe eliminaton of hardly degradable hazardous substances in water.

Long-term monitoring and risk assessment of N-nitrosamines in the finished water of drinking water treatment plants in South Korea

Approximately 99.1% of South Koreans have access to drinkable tap water from river basins. Due to such a high access rate, the South Korean government has been running, since 2013, a long-term program for monitoring the quality of tap water for drinking. Under this program, the maximum allowed concentrations of N-nitroso-di-n-methylamine (NDMA) and N-nitrosomethylethylamine (NMEA) are defined and applied. In this study, the data from this monitoring program were used to investigate the changes in six N-nitrosamine substances in the finished water of 33 drinking water treatment plants (DWTPs) in South Korea from 2013 to 2020, based on time and location. The effect of the applied water treatment steps on the appearance of N-nitrosamines was analyzed. The excess cancer risk (ECR) due to the oral intake of these substances was assessed. The results before the maximum allowed concentrations of NDMA and NMEA were defined showed that the oral intake ECR of these substances exceeded the carcinogenesis risk of one per one million people per year. After the maximum allowed concentrations of the substances were applied, the concentrations of the substances in the finished water of the DWTPs significantly dropped. The drinking water treated through sand filtration, and then with granular activated carbon, showed the highest efficiency in preventing the appearance of NDMA. Considering the potency of N-nitrosamines in tap water for drinking, the levels of these substances in the finished water of DWTPs in South Korea should be continuously monitored.

Removal of Organic Compounds with an Amino Group during the Nanofiltration Process

The research covered the process of nanofiltration of low molecular weight organic compounds in aqueous solution. The article presents the results of experiments on membrane filtration of compounds containing amino groups in the aromatic ring and comparing them with the results for compounds without amino groups. The research was carried out for several commercial polymer membranes: HL, TS40, TS80, DL from various manufacturers. It has been shown that the presence of the amino group and its position in relation to the carboxyl group in the molecule affects the retention in the nanofiltration process. The research also included the oxidation products of selected pharmaceuticals. It has been shown that 4-Amino-3,5-dichlorophenol—a oxidation product of diclofenac and 4-ethylbenzaldehyde—a oxidation product of IBU, show poor separation efficiency on the selected commercial membranes, regardless of the pH value and the presence of natural organic matter (NOM). It has been shown that pre-ozonation of natural river water can improve the retention of pollutants removed.

Disinfection by-product (DBP) research in China: Are we on the track?

Disinfection by-products (DBPs) formed during water disinfection has drawn significant public concern due to its toxicity. Since the first discovery of the trihalomethanes in 1974, continued effort has been devoted on DBPs worldwide to investigate the formation mechanism, levels, toxicity and control measures in drinking water. This review summarizes the main achievements on DBP research in China, which included: (1) the investigation of known DBP occurrence in drinking water of China; (2) the enhanced removal of DBP precursor by water treatment process; (3) the disinfection optimization to minimize DBP formation; and (4) the identification of unknown DBPs in drinking water. Although the research of DBPs in China cover the whole formation process of DBPs, there is still a challenge in effectively controlling the drinking water quality risk induced by DBPs, an integrated research framework including chemistry, toxicology, engineering, and epidemiology is especially crucial.

Formation of N-nitrosodimethylamine (NDMA) from tetracycline antibiotics during the disinfection of ammonium-containing water: The role of antibiotics dissociation and active chlorine species

N-nitrosodimethylamine (NDMA), a nitrosamine, is a typical nitrogenous disinfection byproduct. In this study, NDMA formation potential and mechanism, from tetracycline and oxytetracycline (as model precursors) in an ammonium-contaminating water, were investigated. The results indicated that both monochloramine and dichloramine played a vital role in NDMA formation. Additionally, the determination of NDMA formation potential (NDMA FP) at a wide range of pH showed that the unprotonated tetracycline tended to have a higher NDMA conversion ratio. We also found that the dissociation of hydroxyl on the meta-position of dimethylamine group promoted on NDMA formation. The detection of significant intermediate products showed that N-chloro unsymmetrical dimethylhydrazine (UDMH-Cl) and sequences of chlorine substitution products were key intermediates, indicating that NDMA formation occurred via the UDMH mechanism pathway. These results improve the knowledge on NDMA formation mechanism and the control strategies during the disinfection of ammonium-containing water.

NDMA formation during ozonation of metformin: Roles of ozone and hydroxyl radicals

Metformin, a high-consumed pharmaceutical for diabetes, has been reported to generate carcinogenic nitroso-dimethylamine (NDMA) during treatment of its containing wastewater. However, whether it would produce NDMA during ozonation or not is unclear, let alone discriminate roles of ozone (O₃) and hydroxyl radicals (OH). In this paper, effects of ozonation on NDMA formation from metformin were investigated, roles of O₃ and OH were also distinguished by adding tert-butyl alcohol (tBA) as OH scavenger. Moreover, various influencing factors and reaction mechanisms were demonstrated. The results indicated that NDMA could be directly formed from metformin during ozonation, the addition of OH scavenger significantly enhanced its formation (0-46.2 ng/L vs 0-139.1 ng/L). The formation of NDMA by O₃ and OH was more affected by bromide and HCO₃^- than those with only O₃; while the impacts of pH and sulphate on the latter were more notable. No matter without/with tBA in the solution, the formed NDMA during ozonation of metformin increased with raising pH (from 5 to 9) and achieved the maximum 69.6 ng/L and 235.9 ng/L at pH 9, respectively; small amount of bromide (0.1 μM) promoted NDMA production, high levels of bromide (10 μM) inhibited its formation; the existence of HCO₃^- enhanced the amounts of NDMA from 44.5 to 73.5 ng/L (raised by 65.2%) by O₃ and OH and from 102.9 to 130 ng/L with only O₃ (raised by 26.3%); with the addition of sulphate, NDMA concentration raised by 43.8% by O₃ and OH, while the value was high up to 134.6% with only O₃. Based on the result of UPLC-Q-TOF and density functional theory, the oxidation intermediates were identified and possible transformation pathways of metformin during ozonation were proposed. The findings in this paper would provide reference when treating metformin-containing water in future.

The characteristic of N-nitrosodimethylamine precursor release from algal organic matter and degradation performance of UV/H2O2/O3 technology

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/H₂O₂/O₃ was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/H₂O₂/O₃ is higher than by UV/H₂O₂ or UV/O₃ which can reach 95% at the UV dose of 400 mJ/cm². An alkaline environment reduces the oxidation efficiency of UV/H₂O₂/O₃ technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO₃^-, SO₄^2-, Cl^- and NO₃^- are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/H₂O₂/O₃ is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/H₂O₂/O₃ was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components.

Enhanced coagulation for mitigation of disinfection by-product precursors: A review

The unintended formation of disinfection by-products (DBPs) has received considerable attention as it may pose risks to human health. Coagulation is the most common process for removing particulates as well as dissolved organic matter (DOM) (i.e., DBP precursors) during drinking water and wastewater treatments. With the improvement of water quality standards and the increased fluctuation in source water quality, conventional coagulation becomes challenging. Thus, significant efforts have been made to enhance coagulation to promote the removal of DOM in source water and mitigate the formation of DBPs in drinking water. This review provides a brief summary of the properties of DBP precursors and summarizes the effectiveness of enhanced coagulation involving three types of coagulants (metal-based coagulants, organic polymers, and organic-inorganic hybrid coagulants) in controlling the formation of DBPs during chlor(am)ination disinfection. Metal-based coagulants can achieve a reduction in DBP formation potential of approximately 20%-60% in natural water under enhanced coagulation conditions. Both the organic polymers (used as coagulant aids) and novel hybrid coagulants increase the removal of DOM and exhibit high potential for mitigating DBP formation. In addition, integrated treatments combining coagulation with other treatment processes (e.g., oxidation, membrane filtration, ion exchange, and adsorption) to enhance DBP precursor removal are evaluated in terms of performance, mechanisms, and features. Advanced treatments, such as membrane filtration and activated carbon adsorption, are effective coagulation-assisted processes, and can further control chlorinated DBPs; however, the elevated formation of bromate or highly brominated DBPs is of particular concern.

Occurrence and fate of N-nitrosamines in three full-scale drinking water treatment systems with different treatment trains

The occurrence of mutagenic and carcinogenic N-nitrosamines in drinking water is of great concern. In this study, dynamics and removal of nine N-nitrosamines in three drinking water treatment systems of a southern city of China are monitored during one year of sampling. The impacts of physicochemical treatment units on the removal and generation of N-nitrosamines were evaluated. The O₃ and KMnO₄ based pre-oxidation units have caused an increase in N-nitrosamines concentration, with O₃ showing the substantial generation of N-nitrosamines. The carbon filter and ultrafiltration membrane units were found effective in removing N-nitrosamine precursors. These drinking water treatment systems have been useful in removing N-nitrosamine precursors; meanwhile, a slight decrease was found in already formed N-nitrosamines concentration. However, N-nitrosomorpholine (NMOR) and N-nitrosodiphenylamine (NDPhA) were found resistant toward all kinds of physicochemical treatments, and negligible changes in concentration were noted in all drinking water treatment systems. The distribution networks in the city provided an effective contact period to residual chlorine and precursors, which caused an increase in N-nitrosamines concentration. Overall, N-nitrosodimethylamine (NDMA) and N-nitroso-diethylamine (NDEA) have been found near the cancer risk threshold (10^-6) in all of the drinking water treatment systems, while the remaining seven N-nitrosamines were found below the risk level.

Quantitative analysis of source and fate of N-nitrosamines and their precursors in an urban water system in East China

The source and fate of N-nitrosamines and their precursors in terms of formation potential (FP) was investigated quantitatively in the city level for the first time. Different sources of nitrosamines and their precursors were investigated in one city in the Yangtze River delta, China. The source water located downstream of the city contained 8.4 ng/L of N-nitrosodimethyamine (NDMA) and 153 ng/L of NDMA FP. The contribution of each discharge source was evaluated based on the concentration, the river water flux, and the amount of wastewater discharges. Textile printing and dyeing wastewater, and electroplating industrial wastewater contained high concentration of nitrosamines and were important discharge sources. Taking NDMA and NDMA FP attenuation by photolysis and biodegradation into consideration, the mass load calculation showed upstream surface water brought about 13 ± 4% of NDMA and 21 ± 3% of NDMA FP to downstream source water. Local wastewater discharges contributed 30 ± 8% of NDMA and 17 ± 2% of NDMA FP to downstream source water. Endogenous formation via amino acids metabolism could contribute 36% of NDMA FP (maximum) to downstream source water. Overall, this study provides a protocol for quantitative evaluation of the nitrosamine contribution to urban water supply from different contamination sources.

The Occurrence of N-nitrosodimethylamine (NDMA) in Swimming Pools: An Overview

The occurrence of several disinfectant byproducts has been investigated in swimming pools. Until now, there are only a few studies on nitrosamine, particularly N-nitrosodimethylamine in swimming pool water. This could be due to the lack of a suitable method that is sensitive enough for the measurement of N-nitrosodimethylamine in pool waters. Other disinfectant byproducts formed in pool water widely documented are trihalomethanes, haloacetic acids, halonitromethanes, and chloramines but inadequate information on N-nitrosodimethylamine. This paper provides a review of the nitrogenous disinfectant byproduct in swimming pools and its health implications. Anthropogenic substances introduced by swimmers such as sweat, lotions, and urine contribute to the formation of N-nitrosodimethylamine. The reaction of secondary amines such as dimethylamine with mono/dichloroamines produced dimethyl hydrazine and further undergo oxidation to form N-nitrosodimethylamine. The reaction of chlorine and other disinfectants with these anthropogenic sources in swimming pools cause cancer and asthma in human tissues. Thus, the assessment of N-nitrosodimethylamine in the swimming pool is less well documented. Therefore, the health consequences, mutagenic, and genotoxic potentials of N-nitrosodimethylamine should be the focus of more research studies.