Halonitroalkanes, halonitriles, haloamides, and N-nitrosamines: a critical review of nitrogenous disinfection byproduct formation pathways

Synergistic oxidation and coagulation of raw water by novel Fe(II)/sulfite process: A comparative study with peroxydisulfate and peroxymonosulfate

Latest findings demonstrate that the oxidative Fe(II)/sulfite (Fe(II)/S(IV)) process can rapidly generate iron particles, holding potential for coagulation while simultaneously removing emerging contaminants. Herein, we first report the synergistic oxidation-coagulation treatment of RW by Fe(II)/S(IV) process, and compare with traditional Fe-based coagulation (FeSO4, Fe2(SO4)3), Fe(II)/PDS and Fe(II)/PMS processes. Results revealed that the Fe(II)/S(IV) process outperformed traditional Fe-based coagulants, Fe(II)/PDS and Fe(II)/PMS in removing turbidity, UV254, and DOC. For emerging contaminants removal from RW, Fe(II)/PMS showed the highest efficiency, followed by Fe(II)/PDS, while Fe(II)/S(IV) was slightly less effective, it still demonstrated a significant improvement (40 %∼65 %) over traditional coagulation processes. Moreover, the Fe(II)/S(IV) process is the most effective in reducing DBPs formation (56 %∼86 %). Although Fe(II)/PDS and Fe(II)/PMS also significantly reduce DBPs formation, their high oxidation potential at low pH generated toxic N-DBPs. Mechanistic analysis indicated that the Fe(II)/S(IV) process was most effective in removing humic substances and biopolymers. Its moderate oxidation preserved macromolecular structures, enhancing coagulation. And the hydrolysis of S(IV) generates OH⁻, promoting electrostatic neutralization and floc enlargement. Cost analysis revealed that the Fe(II)/S(IV) process is significantly more economical, with costs only 1/60 of Fe(II)/PMS. These results highlight the Fe(II)/S(IV) process as a promising and cost-effective approach to advanced water treatment.

Machine learning strategy secures urban smart drinking water treatment plant through incremental advances

The integration of machine learning into urban drinking water treatment plants (DWTPs) offers a transformative pathway to ensure drinking water safety while promoting the development of smart, low-carbon cities. However, the effectiveness of these systems is frequently hindered by challenges related to data security and reliability, including imprecise control logic, sensor inconsistencies, and data transmission errors. In this study, we introduce a novel progressive Step-by-Step (SBS) machine learning strategy, initially applied to precise disinfectant dosage control in drinking water treatment and subsequently extended to enhance the data security of the entire water supply system. Among eight evaluated methods, the deep neural network integrated with the SBS strategy demonstrated superior performance. In a real-world DWTP, the SBS model significantly outperformed manual fuzzy control, reducing disinfectant dosage by 22.0 % and effluent turbidity by 16.0 %. Furthermore, through simulations of extreme data-missing scenarios and the application of SBS-based corrections, the robustness and security of DWTPs were maintained. The integration of the SBS strategy has the potential to significantly improve emergency management in urban water systems and elevate the intelligence of water supply networks. This approach not only strengthens urban resilience but also supports the safe and sustainable evolution of smart urban water systems.

COVID-19 impacts on characterization of N-nitrosamines and their precursors during transport in sewer systems

During the COVID-19 outbreak, N-nitrosodimethylamine (NDMA) and N-nitrosomorpholine (NMOR) and their specific precursors (N,N-dimethylformamide [DMF] for NDMA and morpholine [MOR] for NMOR) were widely detected in sewerage systems of an urban area, in which chlorine-containing disinfectants were discharged with effluent of hospitals, etc. However, little is known about the effect of chlorine influx on formation and distribution of NDMA and NMOR in sewer systems in a sudden major public health event. We investigated the spatiotemporal patterns of NDMA, NMOR, DMF and MOR in influents of sewage treatment plants (STPs), as well as its upstream sewer sites during the COVID-19 pandemic. During the pandemic, there was a significant decrease of industry-related NMOR and DMF, however, with an increase of concentration (up to 243 ng/L) and detection frequency for NDMA in influents of the biggest STP in Kyoto Prefecture. Moreover, it was found that NDMA reached a maximum of 187 ng/L with 57 % detection frequency, while NMOR reached a maximum of 101 ng/L with 51 % detection frequency in the sewer systems connecting to all the STPs for service area during the pandemic. Especially, during the pandemic, concentration (median value) of NDMA increased from 40.9 ng/L with 42 % detection frequency in 2020 to 72.5 ng/L with 77 % detection frequency in 2021, which was coincident with the change of infected population. In addition, this research clearly exhibited the possibility that unintentional chlorination and nitrosation of precursors formed NDMA and NMOR in sewer systems influenced by COVID-19 pandemic. The NDMA formation was ranked according to increased concentration (median value) as follows: addition of ClO- (669 ng/L) > addition of NO2- (138 ng/L) > without addition (34.3 ng/L), while additional ClO- and NO2- did not significantly increase NMOR formation probably caused by low existence of NMOR precursors (e.g., MOR) in raw sewage. Therefore, it is necessary to make an urgent attention on environmental issues caused by high-dose chlorine-containing disinfectants residue, because increased byproducts induced by disinfectants in raw sewage caused higher risk during the future pandemic by unexpected pollution from insufficiently treated sewage (e.g. combined sewer overflow and primary effluent bypass discharge) to receiving water bodies.

Impacts of disinfection methods in a granular activated carbon (GAC) treatment system on disinfected drinking water toxicity

The efficacy of implementing granular activated carbon (GAC) treatment in combination with pre- or post-chlorination for mitigating disinfection byproducts (DBPs) in drinking water has been promising, yet its impact on water toxicity remains unclear, necessitating cost-effective and informative effect-based toxicity assessment. This study, using recently developed yeast toxicogenomic and human cell RT-qPCR assays targeting DNA and oxidative stress, compares the toxicity level and nature of water treated through a pilot-scale GAC system with post-chlorination (GAC/Cl2) or pre-chlorination upstream of GAC (Cl2/GAC/Cl2), with water treated by chloramination (Cl2/NH2Cl). Experiments were conducted at environmentally relevant bromide and iodide levels across three GAC beds. The post-chlorination with GAC generally reduces genotoxicity and oxidative stress more effectively than Cl2/NH2Cl or Cl2 treatment at ambient halide concentrations. However, pre-chlorination with GAC was inconsistent in lowering the effluent toxicity in comparison to the post-chlorination-GAC treatment, especially at high halide levels, where no toxicity reduction was observed compared to non-GAC-treated water. Correlation analysis of detected DBPs and toxicity quantifiers, along with maximum cumulative ratio analysis identifies top DBPs that contribute to the toxicity and their cumulative risks, pointing the iodinated DBPs (I-DBPs) and nitrogenous DBPs (N-DBPs) as the significant contributors to DNA and oxidative stress. The results highlight that unregulated DBPs play a critical role in water toxicity, and whole water toxicity monitoring in complement to regulated DBPs detection is needed for treatment strategies efficacy assessment to address unregulated DBPs and their health risks.

Evaluating Powdered Activated Carbon for Adsorption of Nitrogenous Organics in Water Using HDPairFinder

Amino-containing compounds are key precursors to highly toxic nitrogenous disinfection byproducts (DBPs) and odorous DBPs, posing a critical challenge for drinking water utilities. This study systematically evaluated the adsorption performance of six commercial powdered activated carbons (PACs) for removing soluble amino-containing compounds using amino acids as model compounds. Among them, PHF and AN PAC demonstrated superior removal efficiencies for six tested amino acids, ranging from 77 to 98% for PHF PAC and 83 to 96% for AN PAC. Subsequent analysis focused on PHF, AN, and HB PACs to investigate adsorption kinetics and effects of water parameters, including initial amino acid concentration, pH, and natural organic matter (NOM) on removal efficiencies. Optimal removal efficiencies were observed for PHF and AN PACs at pH levels between 6 and 8, while increased NOM levels significantly reduced amino acid adsorption. Finally, a hydrogen/deuterium isotopic labeling-based nontargeted analysis was applied to evaluate the removal of amino-containing compounds from source water (represented by Suwannee River standard reference materials). PHF exhibited the highest removal efficiency, achieving a 47% reduction in the total ion chromatogram (TIC) intensity of labeled amino-containing features, followed by AN at 21% and HB at 19%. The decrease in the TIC intensity and number of labeled amino-containing features aligned with the trends observed in adsorption, establishes a consistent ranking of PHF > AN > HB PAC. PAC can be seamlessly integrated into existing drinking water treatment processes and applied on an as-needed basis. Our results could provide valuable guidance for its effective application in water treatment plants.

Moving Beyond the Silos of Opportunistic Pathogen and Disinfection Byproduct Research to Improve Drinking Water System Management

Drinking water opportunistic pathogens (OPs) and disinfection byproducts (DBPs) both pose risks to public health, and their variable occurrence from source to tap complicates efforts to control them simultaneously. Management of OPs and DBPs is further hindered by the historical division between microbial and chemical research. This review brings together the current knowledge regarding OPs and DBPs, identifies factors that influence the occurrence of both, and highlights areas where research is needed to better understand their health risks. First, we examine the current understanding of how OPs and DBPs are jointly influenced by physicochemical parameters, source water characteristics, treatment processes including disinfection, and distribution system properties. Temperature, for example, can affect OP and DBP occurrence, where higher temperatures can promote the growth of some OPs, such as Legionella pneumophila, but temperature's effect on DBPs is species-dependent. Methods for quantifying the risks associated with OPs (quantitative microbial risk assessment) and DBPs (chemical risk assessment) are compared, finding that the numerous assumptions and data gaps associated with each method limit comparability across contaminant types. We highlight the urgent need to fill existing data gaps and develop a more unified risk framework so as to move toward holistic assessment of microbial and chemical risks. This review provides suggestions for future research, highlighting ways that researchers might utilize established practices in OP or DBP studies to further our understanding of the other. For example, analysis of source water organic matter composition, which has advanced our understanding of DBP formation, could be utilized to elucidate how source water characteristics influence OPs. This review bridges the gap between the OP and DBP disciplines, arguing that collaboration between the two is needed to address the pressing challenges facing water systems today.

Mechanistic Insights into NDMA Adsorption onto Selected Pollutants and Their Removal via Direct Rapid Sand Filtration and After Enhanced Coagulation

N-nitroso dimethylamine (NDMA), a common nitrogen disinfection by-product and carcinogen, can be removed using rapid sand filtration (RSF) after coagulation; however, its removal mechanism has not been extensively studied. This study analyzed NDMA and the water pollutant parameter removal rate change tendency in the filtrates of simulated supernatants directly and after enhanced coagulation (EC) using composite PAC/PDMDAAC that mimics treated Yangtze River water separated into blank, single-component, and mixed multi-component (MMC) water systems containing NDMA and pollutants like diatomite (DTA), humic acid salt (HAs), dimethyl amine (DMA), and ammonium nitrate (NH4NO3). Meanwhile, a correlation analysis of removal rate changes and adsorption analysis using SEM (surface morphology), polar functional groups, and zeta potentials (surface charge) were performed to obtain mechanistic insights into NDMA removal via adsorption. The results revealed that removal rates gradually increased with an increasing volume of filtrates, and there were correlations for NDMA-HAs, NDMA-DMA, NDMA-DTA, and NDMA-NH4NO3. The highest NDMA removal rates in the blank system were 10.29% using RSF directly and 12.84% after enhanced coagulation, indicating improved efficiency with coagulation. However, single and mixed systems showed that NDMA removal rate changes were enhanced by water pollutants and coagulation functions. The NDMA removal mechanism was verified, and it was revealed that the level of NDMA adsorption on water pollutants varies based on microstructure, available polar functional groups, and surface charge interactions that are strengthened by coagulation functions for improving the affinity of NDMA and pollutants on the sand surface. These findings provide new insights into NDMA removal mechanisms via adsorption and highlight the role of water pollutants and enhanced coagulation in strengthening rapid sand filtration for NDMA removal.

Formation mechanisms of carcinogenic N-nitrosamines from dissolved organic matter derived from nitrogen-containing microplastics during chloramine disinfection

The high occurrence of microplastics (MPs) in water treatment facilities may complicate the source-control of disinfection by-products. Herein, we reported that the carcinogenic N-nitrosamines, such as N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA), were generated during monochloramine disinfection of water in which nitrogen-containing microplastics (N-MPs, such as polyamide and polyacrylonitrile) were present. The precursors of NDMA and NDEA were mainly derived from the dissolved organic matter released from N-MPs (N-MP-DOM), which were characteristic of a significantly higher proportion of polar and non-cationic fractions, favouring the N-nitrosamine formation. The results of excitation-emission-matrix spectra and orbitrap-mass spectrometry indicated that the polar components were mainly CHON and highly hydrogen-saturated molecules (H/C ≥ 1.5) (such as protein-like substrates), which are potential precursors of N-nitrosamines. Further mass difference network analysis revealed that the reactions of amine and nitro/nitroso groups in the precursors made predominant contribution to the generation of N-nitrosamines. Two potent NDMA precursors bearing a (CH3)2N-R structure were identified based on the diagnostic fragments (e.g., 45.0578 Da and m/z 58.0651) and in silico fragmentation tool (MetFrag 2.2) in MS2 spectra. Our findings provide valuable insights into understanding the potential risks of N-MPs due to monochloramine disinfection in water treatment systems.

Making Waves: Formulation components used in agriculture may serve as important precursors for nitrogenous disinfection byproducts

N-Nitrosamines, many of which are carcinogenic, mutagenic, and teratogenic, are disinfection byproducts (DBPs) formed from the reaction of chloramine with nitrogenous organic compounds during water disinfection. The identification of major nitrosamine precursors is important to understand and prevent nitrosamine formation. In this analysis, we propose that efforts to identify nitrosamine precursors must look beyond conventionally evaluated active agent chemicals to consider inert or inactive chemicals as potentially relevant precursors. Using agricultural chemicals applied in the US as an example, we demonstrate that amines widely used as inactive agents in herbicide formulations (i.e., dimethylamine [DMA], a known N-nitrosamine precursor) are potentially much more important than active agent herbicides previously evaluated as potential nitrosamine precursors (i.e., the herbicides diuron or trifluralin). Accounting for use rates and nitrosamine yields, amines used in herbicide formulations represent potential nitrosamine precursor inputs to the environment that are similar in magnitude to recognized precursors like the pharmaceuticals ranitidine and metformin. Because the amounts of amines used as inert agents in herbicide formulations have increased dramatically over recent decades, particularly in certain US regions, we suggest that identification of potential nitrosamine precursors should consider variation in the inputs of both active and inactive agents over time, as well as geographical variation in use that may alter the relative importance of specific precursors in certain locations.

Overlooked risks of photoaging of nitrogenous microplastics with natural organic matter in water: Augmenting the formation of nitrogenous disinfection by-products

In aqueous environments, microplastics (MPs) undergo photoaging, releasing dissolved organic matter (DOM). Disinfection byproducts (DBPs) formation from natural organic matter (NOM) phototransformation has been reported. However, the impact of NOM on the photoaging of MPs (especially nitrogen-containing MPs) and subsequent nitrogenous DBPs (N-DBPs) formation remains unknown. Herein, this study investigated polyamide (PA) with NOM (fulvic acid [FA], humic acid [HA] and biochar-derived DOM [BDOM]) on N-DBPs formation. Results showed that the levels of the main DBPs, N-nitrosamine, formed in the FA+PA, BDOM+PA, and HA+PA systems were 3.0. 2.7 and 1.6 folds higher, respectively, compared to those in the corresponding NOM treatments. NDMA was found to be the dominant N-nitrosamine species, with the highest level of 202 ng/L, exceeding the WHO guideline of 100 ng/L. The main reactive intermediates (RIs) were 1O2 and reactive nitrogen species (RNS) during the first stage (0-3d), and •OH and RNS during the second stage (3-7d), which were confirmed by quenching experiment. For the first time, we found the formation of N-DBPs during photoaging of N-containing MPs, and proposed a two-stages, two-processes, and two-pathways theory of N-DBPs formation. This work emphasizes the importance to understand the interactions between the MPs and NOM in photoaging to better assess the risk of DBPs formation in aqueous environment.

Water disinfection and disinfection by products

For ecological safety and public health, it is essential to identify the causes of pollution in water sources and the effects of both natural and human activities. A class of secondary pollutants known as disinfection byproducts (DBPs) is produced when water is treated with disinfectant. Global problems include DBP formation, monitoring, and health effects in drinkable water. Because of the negative health effects of drinking chlorinated water and some DBPs, water manufacturers have made an attempt to balance pathogen elimination with DBP monitoring. The primary obstacles to managing DBPs are their low concentrations and the viability of their extensive use from a technical and economic perspective. Adsorption on activated carbons, ion exchange, membrane processes, and reducing precursors like NOMs are some of the techniques that may be used in controlling DBPs. The application of both new and conventional disinfection technologies in the removal of ARB and ARGs is also summarized in this review, with an emphasis on bacterial inactivation mechanisms like ozonation, chlorination, ultraviolet (UV), sunlight, sunlight-dissolved organic matter (DOM), and photocatalysis/photoelectrocatalysis (PEC).

Occurrence, fate, and transport of N-nitrosamines and precursors in sewage treatment plants and receiving rivers in a highly urbanized basin

N-nitrosamines (NAs), highly carcinogenic disinfection by-products, were frequently detected in raw sewage, sewage treatment plants (STPs), and receiving rivers. This study investigated five NAs, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosomorpholine (NMOR), N-nitrosodi-n-butylamine (NDBA), and N-nitrosopiperidine (NPIP), and their formation potentials (FPs) in a highly urbanized basin. The results showed that total NAs and their FPs ranged from 101 to 141 ng/L and 72.6-203 ng/L in the influent, implying that NAs and their FPs in the raw sewage might be affected by the sewage type, especially for NDMA (up to 103 ng/L) influenced by industrial wastewater. NDMA FP was positively correlated with NH4+, TN, and TOC, while NDMA, NDEA, and NDEA FP were strongly associated with heavy metals, especially Hg, implying factories using Hg as potential sources. The biological treatment effectively removed NAs in STPs, but NMOR showed the weakest biological removal. In addition, the removal efficiency of NDMA was related to the type of biological treatment in the following order: Modified anaerobic-anoxic-oxic-membrane-bioreactor (Modified AAO-MBR) (81.2%) > AAO (60.1%) > Oxidation ditch (53.3%) > UNITANK (46.5%) > Modified AAO (25.8%). After treatment, total NAs (mainly NDMA and NMOR) in the effluent still ranged from 7.09 to 31.8 ng/L. In the receiving rivers, although NMOR was mainly photodegraded, Patescibacteria discharged from STPs was the first time to be identified as a potential contributor for NMOR. NDMA was primarily degraded through photodegradation and biodegradation, NDMA FP was probably biodegraded, with Proteobacteria probably contributing to the biodegradation of NDMA and NDMA FP.

Haloacetamides exacerbate non-alcoholic fatty liver disease induced by a high-fat diet in C57BL/6J mice

Obesity, a significant global health issue, heightens the risk of non-alcoholic fatty liver disease (NAFLD). Its interaction with environmental pollutants might exacerbate NAFLD's severity. Haloacetamides (HAcAms), a group of emerging nitrogenous disinfection byproducts (DBPs) and potent oxidative stressors, are found in chlorinated drinking water. Since oxidative stress is associated with HAcAms-DBP cytotoxicity and a key factor in NAFLD pathogenesis, we hypothesize that HAcAms-DBPs could exacerbate liver injury and NAFLD, particularly with high-fat diets. This study examined HAcAms-DBPs' impact on liver lipid metabolism in mice treated with 1 to 100 times the background drinking water level (13.05 µg/L) for up to 16 weeks of oral administration. Compared to a high-fat-only group, mice co-exposed to a high-fat diet and HAcAms-DBPs for 16 weeks had elevated serum alanine transaminase, aspartate transaminase, triglyceride, hepatic lipid aggregation, and inflammation response. Under high-fat conditions, background drinking water levels of HAcAms significantly upregulated liver Acetyl-CoA carboxylase 1, fatty acid synthase, peroxisome proliferator-activated receptor gamma (PPARγ), PPARγ coactivator-1α, glucose transporter 1 and 4 protein expression in C57BL/6J mice; 10 times background significantly increased expression of inflammatory marker tumor necrosis factor and liver fibrosis marker protein alpha-smooth muscle actin; 100 times further increased both liver damage and markers of early non-alcoholic steatohepatitis phenotypes like steatosis and lobular inflammation. HAcAms-DBPs plus high-fat conditions worsened liver damage. The possible health risks of NAFLD induced by HAcAms in obese individuals deserve further study.

Involvement of inorganic nitrogen species (NOX- (x = 2, 3)) in the degradation of organic contaminants in environmental waters via UV irradiation or chemical oxidation: A dual-edged approach

OH-mediated advanced oxidation processes (AOPs) are widely used in wastewater treatment and drinking water purification. Recently, an increasing number of studies have indicated that common inorganic nitrogen ions can efficiently generate •OH under UV irradiation, demonstrating strong performance in the degradation of various contaminants. Conversely, the presence of inorganic nitrogen ions in UV or other oxidation processes dramatically increases the yield of toxic nitro (so)-aromatic products and the formation potential of nitrogenous disinfection by-products with high genotoxicity and cytotoxicity. This suggests that the presence of inorganic nitrogen ions in water and wastewater treatment is a 'double-edged sword', offering both benefits and potential harms. Herein, we systematically review the dual roles of inorganic nitrogen ions in contaminant degradation and nitrogenous by-product formation. First, the degradation kinetics of the UV/NOx- (x = 2, 3) and oxidant/NO2- processes are summarized for various contaminants. The pseudo-first-order rate constants (kpfo) of contaminant degradation in the UV/NO3- system range from 10-3 to 10-1min-1, while those in the UV/NO2- and peracetic acid/NO2- system vary from 10-3 to 102min-1 and 10-2 to 10-1min-1, respectively. Moreover, the properties of the water matrix (i.e., pH and O2) play a crucial role in the degradation kinetics by influencing the concentrations and distribution of reactive nitrogen species (RNS), as well as the morphology of the contaminants. Second, this review provides a general overview of the sources and properties of key RNS, including •NO2, ONOO-/ONOOH, and free nitrous acid (FNA), which are closely associated with the formation of nitrogenous by-products. Finally, the formation pathways of nitro (so)-aromatic products and nitrogenous disinfection by-products are discussed. These pathways are driven either by RNS alone or by the combination of RNS with reactive oxygen species (ROS).

Dissolved inorganic nitrogen as an overlooked precursor of nitrogenous disinfection byproducts - A critical review

Aquatic nitrogenous compounds can be classified as dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN), including ammonia, nitrite, nitrate, and inorganic chloramines. The occurrence of nitrogenous disinfection byproducts (N-DBPs) in water, such as haloacetonitriles (HANs), halonitromethanes (HNMs), haloacaetamides (HAcAms), and nitrosamines (NAs), has attracted considerable attention due to their higher toxicity than regulated carbonaceous analogues. While numerous studies have investigated the contributions of DON to N-DBP formation, relatively fewer studies have explored DIN as N-DBP precursors, although DINs are sometimes evaluated as influencing factors. Through a literature review and data mining, this study delves into the existing body of evidence that analyze the contributions of different forms of DIN to N-DBP generation. The results showed that ammonia and nitrite can enhance trichloronitromethane (TCNM) and nitrodimethylamine (NDMA) formation in conventional chlorination and chloramination processes, nitrate can promote HNM formation in ultraviolet-based processes, and monochloramine can increase HAN, HAcAm, HNM, and NDMA formation in most disinfection scenarios. Notably, some experiments demonstrated that the yields of dichloroacetonitrile (DCAN) and TCNM can be higher from reactions involving nitrogen-free organic precursors and DIN than those involving DON and nitrogen-free disinfectant, suggesting that the relative importance of DON and DIN in forming N-DBP in real water remains unresolved. These insights thus underscore DIN as a non-negligible precursor in N-DBP formation and call for more attention to water management strategies for DIN.

Unveiling the optical and molecular characteristics of aging microplastics derived dissolved organic matter transformed by UV/chlor(am)ine oxidation and its potential for disinfection byproducts formation

The investigations into the existence and behavior of microplastics (MPs) in water environment were widely conducted, while the characteristics of dissolved organic matter derived from MPs (MPs-DOM) during advanced oxidation have garnered comparatively little attention. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was employed along with multiple statistical analyses to gain a deeper understanding of the conversion of MPs-DOM in UV/chlor(am)ine advanced oxidation processes (AOPs). The diverse treatments exhibited varying degrees of augmentation in both aging and fragmentation of MPs with the order of UV/Cl2 > UV > UV/NH2Cl. The fragmentation degree of MPs upon two UV-based AOPs (UV-AOPs) was dependent on their monomer chemical structure. The highest TOC values of three MPs-DOM were observed after UV/Cl2 AOP and the lowest after UV/NH2Cl AOP. Polyvinyl chloride (PVC) displayed a greater release of MPs-DOM under varying leaching conditions. UV/Cl2 AOP favored the reaction with saturated MPs-DOM, while UV/NH₂Cl AOP reduced unsaturated MPs-DOM, alleviating disinfection byproducts (DBPs) formation after chlorination. The precursors generated by UV/Cl₂ AOP owned lower H/C, higher modified aromatic index (AImod), and lower molecular weight (MW) products after chlorination. PVC-DOM with fewer CH₂ groups was more reactive. -H₂O, +O and -CH₂ reactions dominated in PVC-DOM (CHO compounds), while -2H, +O, -CH₂ did in PVC-DOM (CHON compounds). The dominant chlorine addition/substitution reactions occurred in PVC-DOM treated by UV/Cl₂ AOP, identifying 195 Cl-DBPs with 220 precursor-product pairs. Mass difference analyses showed that +2H and +O reactions were the most frequent of the 24 reaction types.

Reactive Nitrogen Species Generated from Far-UVC Photolysis of Nitrate Contribute to Pesticide Degradation and Nitrogenous Byproduct Formation

Climate change has resulted in increased use of pesticides and fertilizers in agriculture, leading to elevated pesticide and nitrate levels in aquatic ecosystems that receive agricultural runoff. In this study, we demonstrate that far-UVC (UV222) photolysis of nitrate rapidly degrades four pesticides in surface water, with a degradation rate constant 37.1-144.75 times higher than that achieved by UV254 photolysis of nitrate. The improved pesticide degradation is due not only to the enhanced direct photolysis by UV222 compared to UV254 but also to the increased generation of hydroxyl radicals (HO•) and reactive nitrogen species (e.g., NO2• and ONOO-) in the UV222/nitrate process. We determined the innate quantum yields of nitrate photolysis at 222 nm and incorporated these values into a kinetic model, allowing for the accurate prediction of nitrate photodecay and reactive species generation. While reactive nitrogen species predominantly contribute to pesticide degradation in the UV222/nitrate process, they also lead to the formation of nitration byproducts. Using stable isotope-labeled nitrate (15NO3-) combined with mass spectrometry, we confirmed that the nitration byproducts are formed from the reactive nitrogen species generated from nitrate photolysis. Additionally, we demonstrate that the UV222/nitrate process increases the formation potential of highly toxic nitrogenous chlorinated products (e.g., trichloronitromethane) during postchlorination in real surface water.

Computational Studies of Nucleophilic Substitution at Nitrogen Center: Reactions of NH2Cl with HO-, CH3O- and C2H5O. Chemphyschem 2024;25:e202400365. [PMID: 38923666 DOI: 10.1002/cphc.202400365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The atomic-level mechanisms of the nucleophilic substitution reactions at the nitrogen center (SN2@N) were investigated for the reactions of chloramine (NH2Cl) with the alkoxide ions (RO-, where R=H, CH3, and C2H5) using DFT and MP2 methods. The computed potential energy profiles for the SN2@N pathways involving the back-side attack of the nucleophiles show the typical double-well potential with submerged barriers similar to the SN2 reactions at the carbon center (SN2@C). However, the pre-reaction and post-reaction complexes are, respectively, the N-H⋅⋅⋅O and N-H⋅⋅⋅Cl hydrogen-bonded intermediates, which are different from those generally seen in SN2@C reactions. The SN2@N pathways involving front-side attack of the nucleophiles have high-energy barriers. The potential energy surfaces (PESs) along the proton-transfer pathways were flat. In addition to the proton-transfer and SN2 pathways, we also observed a new path for the methoxide and ethoxide nucleophiles where a hydride-transfer from the nucleophile to chloramine resulted in the products Cl-+R'CHO+NH3, (R'=H, CH3), and was the most exoergic. A comparison of the energetics obtained used different DFT and MP2 methods with that of the benchmark coupled-cluster methods reveals that CAM-B3LYP best describes the PESs.

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

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

Chlorination of Biopterin in Water: Deciphering the Kinetics, Disinfection Byproducts, and Toxicity

Pterins, including biopterin prevalent during cyanobacterial blooms, are nitrogen-containing heterocyclic compounds ubiquitous in both natural and engineered environments. However, their roles and associated human risks in water treatment remain poorly understood. This study systematically investigated the kinetics, disinfection byproducts (DBPs), and toxicity of biopterin in chlorination. For deciphering the reaction kinetics, 1,3,5-trimethoxybenzene proved to be a more effective chlorine quencher than the commonly used reducing agents, as it preserved N-chlorinated intermediates without reversing them back to biopterin. The pH-dependent kinetics demonstrated that both chlorine and biopterin species had a significant influence on the reaction rates, with deprotonated biopterin exhibiting a markedly higher reactivity toward HClO/ClO-. Based on time-of-flight mass spectrometry, ten transformation products (TPs) including seven halogenated N-Cl ones, have been identified for the first time. These cyclic TPs were transformed into various aliphatic carbonaceous and nitrogenous DBPs during the subsequent chlorination process. Notably, theoretical predictions and the luminescent bacteria assay confirmed potential higher toxicities of these products than biopterin. These findings highlight the potential risks of pterins during water disinfection and provide a reference framework for accurately revealing the chlorination behavior of emerging nitrogenous chemicals.

Combination of oxidative and reductive effects of phenolic compounds on the degradation of aniline disinfection by-products by free radicals

In this study, we selected 13 phenolic compounds containing -COOH, -CHO, -OH, and -COCH3 functional groups as model compounds for dissolved organic matter (DOM), and explored the redox reactions during the co-degradation of phenolic compounds with aniline disinfection by-products (DBPs) at the molecular level. When phenolic compounds and aniline DBPs were degraded, phenoxy radicals and aniline radicals were the most important intermediates. Phenoxy radicals can degrade aniline DBPs via hydrogen atom abstraction (HAA) reactions, and the reaction rates were related to the reduction potentials of the compounds. Compounds containing electron-withdrawing groups were more likely to oxidize aniline DBPs. Aniline DBPs were more easily degraded by phenoxy radicals when they contained electron-donating groups, and the increase in the number of chlorine atoms inhibited the reaction rates of aniline DBPs degradation by phenoxy radicals. Although phenolic compounds can reduce aniline DBPs, there was no significant correlation between the reaction rates and the reduction potentials of the compounds. Considering the redox effects of phenolic compounds on aniline DBPs, co-degradation simulations showed that phenolics inhibited the degradation efficiency of aniline DBPs. This work provided new insights into the transformation mechanisms and degradation efficiencies of DOM and aniline DBPs when they were co-degraded.

Degradation kinetics and disinfection by-products formation of benzophenone-4 during UV/persulfate process

The degradation kinetics, reaction pathways, and disinfection by-products formation of an organic UV filter, benzophenone-4 (BP4) during UV/persulfate oxidation were investigated. BP4 can hardly be degraded by UV alone, but can be effectively decomposed by UV/persulfate following pseudo-first order kinetics. BP4 degradation rate was enhanced with increasing persulfate dosage and decreasing pH from 8 to 5. However, the degradation rate of BP4 at pH 9 was higher than that at pH 8 because of the presence of phenolic group in BP4 structure. and SO 4 - ⋅ were confirmed as the major contributors to BP4 decomposition in radical scavenging experiments, and the second-order rate constants between HO ⋅ and BP4 as well as those between SO 4 - ⋅ and BP4 were estimated by establishing and solving a kinetic model. The presence of B r - and humic acid inhibited the decomposition of BP4, while N O 3 - promoted it. The mineralisation of BP4 was only 9.1% at the persulfate concentration of 50 μM. Six degradation intermediates were identified for the promulgation of the reaction pathways of BP4 during UV/persulfate oxidation were proposed as a result. In addition, the formation of DBP in the sequential chlorination was evaluated at different persulfate dosages, pH values, and water matrix. The results of this study can provide essential knowledge for the effective control of DBP formation with reducing potential hazard to provide safe drinking water to the public.

Non-target analysis of organic pollutants in oil-production wastewater treatment stations and surrounding soils: Their profiles, electro-transformation, and environmental risks

Although pollution during crude oil production has been paid attention, there is lack of studies on organic pollutants generated/emitted from oil-production wastewater (OPW) treatment processes, especially advanced oxidation process. Based on GC-Q-Orbitrap-HRMS, the present study performed non-target analysis of volatile/semi-volatile organic compounds in physical and electro-oxidation units of OPW treatment stations located in Shengli Oilfield of China. Overall, 64-227 organic compounds were respectively identified in different units, and electro-oxidation was found elevating (by 2.7-66 times) specie numbers (25-71) of CHO, CHNO and halogenated compounds as well as inducing generation of 38 alkanes and 6 alkyl-PAHs in wastewater, indicating the important roles of reactive oxygen and halogen species in pollutant transformation. In soils (n = 22) closed to OPW treatment stations, 580 compounds were identified with hydrocarbons (45%), esters (24.3%), and others (30.7%, including aldehydes, ketones, phenols, amines, nitriles and heteroatomic compounds), while esters had largest concentration contribution (up to 53.0%) to total compounds. The calculated hazard quotients (HQ) showed 55 compounds in OPW effluents and 314 compounds in soils having medium-high risks, considerable portions of which (23.6% for effluent and 12.7% for soil) were generated from electro-oxidation process, especially including esters and halogenated hydrocarbons, highlighting the contribution of OPW electro-oxidation treatment to ecological risk in oil-production areas.

Occurrence and Ecological Risk Assessment of Highly Toxic Halogenated Byproducts during Chlorination Decolorization of Textile Printing and Dyeing Wastewater

Textile printing and dyeing wastewater is a substantial source of highly toxic halogenated pollutants because of the chlorination decolorization. However, information on the occurrence and fate of the highly toxic halogenated byproducts, which are produced by chlorination decolorization of the textile printing and dyeing wastewater, is very limited. In this study, the occurrence of six categories of halogenated byproducts (haloacetic acids (HAAs), haloacetonitriles (HANs), N-nitrosamines (NAs), trihalomethanes, halogenated ketones, and halonitromethanes) was investigated along the full-scale treatment processes of textile printing and dyeing wastewater treatment plants. Furthermore, the ecological risk of the halogenated byproducts was evaluated. The results showed that the total concentration of halogenated byproducts increased significantly after chlorination. Large amounts of HAAs (average 122.1 μg/L), HANs (average 80.9 μg/L), THMs (average 48.3 μg/L), and NAs (average 2314.3 ng/L) were found in the chlorinated textile wastewater, and the results showed that the generations of HANs and NAs were positively correlated with the BIX and β/α index, indicating that the HANs and NAs might form from the microbial metabolites. In addition, HAAs and HANs exhibited high ecological risk quotients (>1), suggesting their high potential ecological risk. The results also demonstrated that most halogenated byproducts could be effectively removed by reverse osmosis treatment processes except NAs, with a lower removal rate of 18%. This study is believed to provide an important theoretical basis for controlling and reducing the ecological risks of halogenated byproducts in textile printing and dyeing wastewater effluents.

Reactivity, Pathways, and Iodinated Disinfection Byproduct Formation during Chlorination of Iodotyrosines Derived from Edible Seaweed

Iodine derived from edible seaweed significantly enhances the formation of iodinated disinfection byproducts (I-DBPs) during household cooking. Reactions of chlorine with monoiodotyrosine (MIT) and diiodotyrosine (DIT) derived from seaweed were investigated. Species-specific second-order rate constants (25 °C) for the reaction of hypochlorous acid with neutral and anionic MIT were calculated to be 23.87 ± 5.01 and 634.65 ± 75.70 M-1 s-1, respectively, while the corresponding rate constants for that with neutral and anionic DIT were determined to be 12.51 ± 19.67 and 199.12 ± 8.64 M-1 s-1, respectively. Increasing temperature facilitated the reaction of chlorine with MIT and DIT. Based on the identification of 59 transformation products/DBPs from iodotyrosines by HPLC/Q-Orbitrap HRMS, three dominant reaction pathways were proposed. Thermodynamic results of computational modeling using density functional theory revealed that halogen exchange reaction follows a stepwise addition-elimination pathway. Among these DBPs, 3,5-diiodo-4-hydroxy-benzaldehyde and 3,5-diiodo-4-hydroxy-benzacetonitrle exhibited high toxic risk. During chlorination of MIT and DIT, iodinated trihalomethanes and haloacetic acids became dominant species at common cooking temperature (80 °C). These results provide insight into the mechanisms of halogen exchange reaction and imply important implications for the toxic risk associated with the exposure of I-DBPs from household cooking with iodine-containing food.

Halogenation of Anilines: Formation of Haloacetonitriles and Large-Molecule Disinfection Byproducts

Aniline-related structures are common in anthropogenic chemicals, such as pharmaceuticals and pesticides. Compared with the widely studied phenolic compounds, anilines have received far less assessment of their disinfection byproduct (DBP) formation potential, even though anilines and phenols likely exhibit similar reactivities on their respective aromatic rings. In this study, a suite of 19 aniline compounds with varying N- and ring-substitutions were evaluated for their formation potentials of haloacetonitriles and trihalomethanes under free chlorination and free bromination conditions. Eight of the aniline compounds formed dichloroacetonitrile at yields above 0.50%; the highest yields were observed for 4-nitroaniline, 3-chloroaniline, and 4-(methylsulfonyl)aniline (1.6-2.3%). Free bromination generally resulted in greater haloacetonitrile yields with the highest yield observed for 2-ethylaniline (6.5%). The trihalomethane yields of anilines correlated with their haloacetonitrile yields. Product analysis of aniline chlorination by liquid chromatography-high-resolution mass spectrometry revealed several large-molecule DBPs, including chloroanilines, (chloro)hydroxyanilines, (chloro)benzoquinone imines, and ring-cleavage products. The product time profiles suggested that the reaction pathways include initial ring chlorination and hydroxylation, followed by the formation of benzoquinone imines that eventually led to ring cleavage. This work revealed the potential of aniline-related moieties in micropollutants as potent precursors to haloacetonitriles and other emerging large-molecule DBPs with the expected toxicity.

Nitrosamine formation driven by electrochemical chlorination of urine-containing source waters: Effects of operational conditions

We investigated the formation of nitrosamines from urine during electrochemical chlorination (EC) using dimensionally stable anodes. Short-term electrolysis (< 1 h) of urine at 25 mA cm-2 generated seven nitrosamines (0.1-7.4 µg L-1), where N-nitrosodimethylamine, N-nitrosomethylethylamine, and N-nitrosodiethylamine were predominant with concentrations ranging from 1.2 to 7.4 µg L-1. Mechanistic studies showed that the formation kinetics of nitrosamines was influenced by urine aging and composition, with fresh urine generating the highest levels (0.9-5.8 µg L-1) compared with aged, centrifuged, or filtered urine (0.2-4.1 µg L-1). Concurrently, studies on urine pretreatment through filtration and centrifugation underscored the significance of nitrogenous metabolites (such as protein-like products and urinary amino acids) and particle-associated humic fractions in nitrosamine formation during EC of urine. This finding was confirmed through chromatographic and spectroscopic studies utilizing LCOCD, Raman spectra, and 3DEEM fluorescence spectra. Parametric studies demonstrated that the ultimate [nitrosamines] increased at a pH range of 4.5-6.2, and with increasing [bromide], [ammonium], and current density. Conversely, sulfate and carbonate ions inhibited nitrosamine formation. Moreover, the implications of EC in urine-containing source waters were evaluated. The results indicate that regardless of the urine source (individual volunteers, septic tank, swimming pool, untreated municipal wastewater), high levels of nitrosamines (0.1-17.6 µg L-1) were generated, surpassing the potable reuse guideline of 10 ng L-1. Overall, this study provides insights to elucidate the mechanisms underlying nitrosamine formation and optimize the operating conditions. Such insights facilitate suppressing the generation of nitrosamine byproducts during electrochemical treatment of urine-containing wastewater.

Probing nitro(so) and chloro byproducts and their precursors in natural organic matter during UV/NH2Cl treatment by FT-ICR MS with machine learning insights

The UV/monochloramine (UV/NH2Cl) process, while efficiently eliminating micropollutants, produces toxic byproducts. This study utilized Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to investigate molecular-level changes in natural organic matter (NOM) and to disclose formation pathways of nitro(so) and chloro byproducts in the UV/NH2Cl process. The UV/NH2Cl process significantly increased the saturation and oxidation levels and altered the elemental composition of NOM. Using 15N labeling and a screening workflow, nitro(so) byproducts with nitrogen originating from inorganic sources (i.e., reactive nitrogen species (RNS) and/or NH2Cl) were found to exhibit total intensities comparable to those from NOM. RNS, rather than NH2Cl, played a significant role in incorporating nitrogen into NOM. Through linkage analysis, nitro(so) addition emerged as an important reaction type among the 25 reaction types applied. By using phenol as a representative model compound, the nitro byproducts were confirmed to be mainly generated through the oxidation of nitroso byproducts instead of nitration. Machine learning and SHAP analysis further identified the major molecular indices distinguishing nitro(so) and chloro precursors from non-precursors. This study enhances our fundamental understanding of the mechanisms driving the generation of nitro(so) and chloro byproducts from their precursors in complex NOM during the UV/NH2Cl process.

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.

Nontargeted Analysis of Reactive Nitrogenous Compounds in Suwannee River Standard Reference Materials and Authentic River Water Samples

Concerns over toxic nitrogenous disinfection byproducts (N-DBPs) necessitate identifying their precursors in source water. Natural organic amino compounds are known precursors to N-DBPs. Three Suwannee River (SR) standard reference materials (SRMs), humic acids (HA), fulvic acids (FA), and natural organic matter (NOM), are commonly used to study DBP formation, but the chemical makeup of amino compounds in SRSRMs remains largely unknown. To address this, we combined stable hydrogen/deuterium isotope labeling, HDPairFinder bioinformatics, and nontargeted high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS) to characterize these compounds in SRSRMs. This method classifies reactive amines, provides accurate masses and MS/MS spectra, and quantifies intensities. We identified 2707 high-quality features with primary and/or secondary amines in SRSRMs and 75% of them having an m/z < 300. Across all three SRSRMs, 327 amino features were detected, while 856, 794, and 200 unique features were found in SRNOM, SRHA, and SRFA, respectively. In North Saskatchewan River (NSR) samples, a total of 6449 amino features were detected, 818 of them matched those in SRSRMs, and 87% of them were different between the two rivers. Using chemical standards, we confirmed 10 compounds and tentatively identified 5 more. This study highlights similarities and differences in reactive N-precursors in SRSRMs and local river water, enhancing the understanding of geo-differences in reactive N-precursors in different source waters.

Complex impact of metals on the fate of disinfection by-products in drinking water pipelines: A systematic review

Metals in the drinking water distribution system (DWDS) play an important role on the fate of disinfection by-products (DBPs). They can increase the formation of DBPs through several mechanisms, such as enhancing the proportion of reactive halogen species (RHS), catalysing the reaction between natural organic matter (NOM) and RHS through complexation, or by increasing the conversion of NOM into DBP precursors. This review comprehensively summarizes these complex processes, focusing on the most important metals (copper, iron, manganese) in DWDS and their impact on various DBPs. It organizes the dispersed 'metals-DBPs' experimental results into an easily accessible content structure and presents their underlying common or unique mechanisms. Furthermore, the practically valuable application directions of these research findings were analysed, including the toxicity changes of DBPs in DWDS under the influence of metals and the potential enhancement of generalization in DBP model research by the introduction of metals. Overall, this review revealed that the metal environment within DWDS is a crucial factor influencing DBP levels in tap water.

Widespread Antioxidants during Storm Events Could Serve as Precursors of Regulated, Priority, and New Disinfection Byproducts

Widely used antioxidants can enter the environment via urban stormwater systems and form disinfection byproducts (DBPs) during chlorination in downstream drinking water processes. Herein, we comprehensively investigated the occurrence of 39 antioxidants from stormwater runoff to surface water. After a storm event, the concentrations of the antioxidants in surface water increased by 1.4-fold from 102-110 ng/L to 128-139 ng/L. Widespread antioxidants during the stormwater event could transform into toxic DBPs during disinfection. Moreover, the yields of trihalomethanes, haloacetaldehydes, haloacetonitriles (HANs), and halonitromethanes during the chlorination of widely used antioxidants considerably increased with an increasing chlorine dose and contact time. Specifically, the yields of dichloroacetonitrile during the chlorination of diphenylamine (DPA) and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) were higher than those of most reported amino acid precursors, indicating that DPA and 6PPD might be important precursors of HANs. Exploring the intermediates using GC × GC-time-of-flight high-resolution mass spectrometry helped reveal potential pathways from DPA to HANs, whose formation could be attributed to the intermediate carbazole and indole moieties detected in this study. This study provides insights into the transport and transformation of commonly used antioxidants in a water environment and during water treatment processes, highlighting the potential risks of anthropogenic pollutants from a DBP perspective.

Iodide enhances degradation of histidine sidechain and imidazoles and forms new iodinated aromatic disinfection byproducts during chlorination

Peptide-bound histidines and imidazoles are important constituents of dissolved organic matter in water, and understanding the formation of halogenated disinfection byproduct (DBP) formation from these compounds during disinfection is important for ensuring a safe drinking water supply. Previous studies suggested that histidine has low reactivity with chlorine only; this study indicates that iodide substantially enhances histidine reactivity with the disinfectant at a time scale from days to hours. Mono- and di-iodinated histidines were identified as dominant transformation products with cumulative molar yields of 3.3 % at 6 h and they were stable in water over 7 days. These products were formed via electrophilic substitution of iodine to imidazole ring when hypoiodous acid reacted with histidine sidechain. Bromide minimally influenced the formation yields of these iodinated products, and higher pH increased yields up to 12 % for pH in the range 5-9. The cumulative concentration of low-molecular-weight DBPs, such as trihalomethanes and haloacetic acids, was less than 0.3 % under the same conditions. Similar iodinated imidazole analogs were also identified from other imidazoles (i.e., imidazole-carboxylic and phenyl-imidazole-carboxylic acids). This study demonstrated that peptide-bound histidine and imidazoles can serve as important precursors to iodinated aromatic DBPs, facilitating the identification of less-known iodinated DBPs.

Unexpected weakened formation of disinfection byproducts and enhanced production of halates by cupric oxide during chlorination of peptide-bound aspartic acid

Under the condition that the residual chlorine is guaranteed, the biofilm still thrives in drinking water distribution systems through secreting a large number of extracellular polymeric substances (EPS), in which protein components are the primary precursor of disinfection byproducts (DBPs), mostly in the form of combined amino acids. The aim of this study is to investigate the action of CuO on the formation of halates (XO3-, ClO3- and BrO3-) and DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as protein surrogate. The presence of CuO promoted the self-decay rather than TAsp-induced decay of oxidants, resulting in an increase in XO3- yield and a decrease in DBPs yield. It was CuO-induced weaker production of cyanoacetic acid and 3-oxopropanoic acid that induced the decreased yields of HANs and THMs, respectively. The FTIR and Raman spectra indicate a weak complexation between CuO and TAsp. Given this, the CuO-HOX/OX- complexes were inferred to be reactive to HOX/OX- but less reactive to TAsp. The study helps to better understand the formation of XO3- and DBPs during the chlorination of EPS, and propose precise control strategies when biofilm boosts in water pipes.

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.

Computational-aided analysis of the pathway and mechanism of dichloroacetonitrile formation from phenylalanine upon chloramination

Dichloroacetonitrile (DCAN) is an emerging disinfection by-product (DBP) that is widespread in drinking water. However, the pathway for DCAN formation from aromatic amino acids remains unclear, leading to a lack of an understanding of its explicit fate during chloramination. In this study, we investigated the specific formation mechanism of DCAN during the chloramination of phenylalanine based on reaction kinetics and chemical thermodynamics. The reason for differences between aldehyde and decarboxylation pathways was explained, and kinetic parameters of the pathways were obtained through quantum chemistry calculations. The results showed that the reaction rate constant of the rate-limiting step of the aldehyde pathway with 1.9 × 10-11 s-1 was significantly higher than that of decarboxylation (3.6 × 10-16 s-1 M-1), suggesting that the aldehyde pathway is the main reaction pathway for DCAN formation during the chloramination of phenylalanine to produce DCAN. Subsequently, theoretical calculations were performed to elucidate the effect of pH on the formation mechanism, which aligned well with the experimental results. Dehydrohalogenation was found to be the rate-limiting step under acidic conditions with reaction rate constants higher than those of the rate-limiting step (expulsion of amines) under neutral conditions, increasing the rate of DCAN formation. This study highlights the differences in DCAN formation between the decarboxylation and aldehyde pathways during the chloramination of precursors at both molecular and kinetic levels, contributing to a comprehensive understanding of the reaction mechanisms by which aromatic free amino acids generate DCAN.

N-nitrosamines in electroplating and printing/dyeing industrial wastewater treatment plants: Removal efficiency, environmental emission, and the influence on drinking water

The discharge of industrial wastewater containing high concentrations of N-nitrosamines to the aquatic environment can impair downstream source waters and pose potential risks to human health. However, the transport and fate of N-nitrosamines in typical industrial wastewater treatment plants (IWWTPs) and the influence of these effluents on source water and drinking water are still unclear. This study investigated nine N-nitrosamines in four full-scale electroplating (E-) and printing/dyeing (PD-) IWWTPs, two drinking water treatment plants (DWTPs) in the lower reaches of these IWWTPs, and the corresponding tap water in South China. The total concentrations of N-nitrosamines (∑NAs) were 382-10,600, 480-1920, 494-789, and 27.9-427 ng/L in influents, effluents, source water, and tap water, respectively. The compositions of N-nitrosamine species in different influents varied a lot, while N-nitrosodi-n-butylamine (NDBA) and N-nitrosodimethylamine (NDMA) dominated in most of the effluents, source water, and tap water. More than 70 % N-nitrosamines were removed by wastewater treatment processes used in E-IWWTPs such as ferric-carbon micro-electrolysis (Fe/C-ME), while only about 50 % of N-nitrosamines were removed in PD-IWWTPs due to the use of chlorine reagent or other inefficient conventional processes such as flocculation by cationic amine-based polymers or bio-contact oxidation. Therefore, the mass fluxes of N-nitrosamines discharged from these industrial wastewaters to the environment in the selected two industrial towns were up to 14,700 mg/day. The results based on correlation and principal component analysis significantly demonstrated correlations between E-and PD-effluents and source water and tap water, suggesting that these effluents can serve as sources of N-nitrosamines to local drinking water systems. This study suggests that N-nitrosamines are prevalent in typical IWWTPs, which may infect drinking water systems. The findings of this study provide a basis data for the scientific evaluation of environmental processes of N-nitrosamines.

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.

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.

Chlorination of Aromatic Amino Acids: Elucidating Disinfection Byproducts, Reaction Kinetics, and Influence Factors

In the face of ongoing water pollution challenges, the intricate interplay between dissolved organic matter and disinfectants like chlorine gives rise to potentially harmful disinfection byproducts (DBPs) during water treatment. The exploration of DBP formation originating from amino acids (AA) is a critical focus of global research. Aromatic DBPs, in particular, have garnered considerable attention due to their markedly higher toxicity compared to their aliphatic counterparts. This work seeks to advance the understanding of DBP formation by investigating chlorination disinfection and kinetics using tyrosine (Tyr), phenylalanine (Phe), and tryptophan (Trp) as precursors. Via rigorous experiments, a total of 15 distinct DBPs with accurate molecular structures were successfully identified. The chlorination of all three AAs yielded highly toxic chlorophenylacetonitriles (CPANs), and the disinfectant dosage and pH value of the reaction system potentially influence chlorination kinetics. Notably, Phe exhibited the highest degradation rate compared to Tyr and Trp, at both the CAA:CHOCl ratio of within 1:2 and a wide pH range (6.0 to 9.0). Additionally, a neutral pH environment triggered the maximal reaction rates of the three AAs, while an acidic condition may reduce their reactivity. Overall, this study aims to augment the DBP database and foster a deeper comprehension of the DBP formation and relevant kinetics underlying the chlorination of aromatic AAs.

How to achieve adequate quenching for DBP analysis in drinking water?

Quenching is an important step to terminate disinfection during preparation of disinfected water samples for the analysis of disinfection byproducts (DBPs). However, an incomplete quenching might result in continued reactions of residual chlorine, whereas an excessive quenching might decompose target DBPs. Therefore, an adequate quenching to achieve simultaneous disinfection termination and DBP preservation is of particular importance. In this study, the two-stage reaction kinetics of chlorine and three commonly used quenching agents (i.e., ascorbic acid, sodium thiosulfate, and sodium sulfite) were determined. Stopping quenching during the first stage prevented interactions of residual chlorine with natural organic matter. Complete quenching was achieved by minimizing the quenching time for ascorbic acid and sodium sulfite, while limiting the quenching time to less than 3 min for sodium thiosulfate. At the optimized quenching times, the molar ratios (MRs) of quenching agent to chlorine were 1.05, 1.10, and 0.75 for ascorbic acid, sodium sulfite, and sodium thiosulfate, respectively. The destructive effects of the three quenching agents on total organic halogen (TOX) followed the rank order of ascorbic acid (33.7-64.8 %) < sodium sulfite (41.6-72.8 %) < sodium thiosulfate (43.3-73.2 %), and the destructive effects on aliphatic DBPs also followed the rank order of ascorbic acid (29.5-44.5 %) < sodium sulfite (34.9-51.9 %) < sodium thiosulfate (46.9-53.2 %). For total organic chlorine (TOCl) and aliphatic DBPs, the quenching behavior itself had more significant destructive effect than the quenching agent type/dose and quenching time, but for total organic bromine (TOBr), the destructive effect caused by quenching agent type/dose and quenching time was more significant. High-dose, long-duration quenching enhanced the reduction of TOX, but had little effect on aliphatic DBPs. Additionally, the three quenching agents reduced the levels of halophenols (except for tribromophenol), while maintained or increased the levels of tribromophenol, halobenzoic/salicylic acids, and halobenzaldehydes/salicylaldehydes. To achieve adequate quenching for overall DBP analysis in chlorinated water samples, it is recommended to use ascorbic acid at a quenching agent-to-chlorine MR of 1.0 for a quenching time of < 0.5 h.

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-.

Oxidation processes and me

This publication summarizes my journey in the field of chemical oxidation processes for water treatment over the last 30+ years. Initially, the efficiency of the application of chemical oxidants for micropollutant abatement was assessed by the abatement of the target compounds only. This is controlled by reaction kinetics and therefore, second-order rate constant for these reactions are the pre-requisite to assess the efficiency and feasibility of such processes. Due to the tremendous efforts in this area, we currently have a good experimental data base for second-order rate constants for many chemical oxidants, including radicals. Based on this, predictions can be made for compounds without experimental data with Quantitative Structure Activity Relationships with Hammet/Taft constants or energies of highest occupied molecular orbitals from quantum chemical computations. Chemical oxidation in water treatment has to be economically feasible and therefore, the extent of transformation of micropollutants is often limited and mineralization of target compounds cannot be achieved under realistic conditions. The formation of transformation products from the reactions of the target compounds with chemical oxidants is inherent to oxidation processes and the following questions have evolved over the years: Are the formed transformation products biologically less active than the target compounds? Is there a new toxicity associated with transformation products? Are transformation products more biodegradable than the corresponding target compounds? In addition to the positive effects on water quality related to abatement of micropollutants, chemical oxidants react mainly with water matrix components such as the dissolved organic matter (DOM), bromide and iodide. As a matter of fact, the fraction of oxidants consumed by the DOM is typically > 99%, which makes such processes inherently inefficient. The consequences are loss of oxidation capacity and the formation of organic and inorganic disinfection byproducts also involving bromide and iodide, which can be oxidized to reactive bromine and iodine with their ensuing reactions with DOM. Overall, it has turned out in the last three decades, that chemical oxidation processes are complex to understand and to manage. However, the tremendous research efforts have led to a good understanding of the underlying processes and allow a widespread and optimized application of such processes in water treatment practice such as drinking water, municipal and industrial wastewater and water reuse systems.

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.

Copper ion affects oxidant decay and combined aspartic acid transformation during chlorination in water pipes: Differentiated action on the yield of trihalomethanes and haloacetonitriles

The chlorination of extracellular polymeric substances (EPS) secreted by biofilm often induces the formation of high-toxic disinfection byproducts (DBPs) in drinking water distribution systems. The protein components in EPS are the main precursors of DBPs, which mostly exist in the form of combined amino acids. The paper aimed to study the action of a pipe corrosion product (Cu2+) on the formation of DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as a precursor. Cu2+ mainly promoted the reaction of oxidants with TAsp (i.e., TAsp-induced decay) to produce DBPs, rather than self-decay of oxidants to generate BrO3‒ and ClO3‒. Cu2+ increased THMs yield, but decreased HANs yield due to the catalytic hydrolysis. Cu2+ was more prone to promote the reaction of TAsp with HOCl than with HOBr, leading to a DBPs shift from brominated to chlorinated species. The chemical characterizations of Cu2+-TAsp complexations demonstrate that Cu2+ combined with TAsp at the N and O sites in both amine and amide groups, and the intermediate identification suggests that Cu2+ enhanced the stepwise chlorination process by promoting the substitution of chlorine and the breakage of CC bonds. The effect of Cu2+ on THMs yield changed from promoting to inhibiting with the increase of pH, while that on HANs yield was inhibiting regardless of pH variation. Additionally, the impact of Cu2+ on the formation of DBPs was also affected by Cu2+ dose, Cl2/C ratio and Br- concentration. This study helps to understand the formation of EPS-derived DBPs in water pipes, and provides reference for formulating control strategies during biofilm outbreaks.

Spatiotemporal dynamics of dissolved organic matter and disinfection by-products formation potential of Shengzhong Lake in southwest China

The quality and quantity of dissolved organic matter (DOM) in lakes as well as its environmental effects associated with the unintended disinfection by-products (DBPs) have received continuous attention. This work investigated the spatiotemporal dynamics of DOM in Shengzhong Lake in southwest China and the formed DBPs during the chlorine disinfection process. The results showed that lake water in summer had significantly higher dissolved oxygen and dissolved organic carbon than that in winter. In contrast, DOM in winter demonstrated an obviously higher aromaticity and molecular weight than that in summer. Four fluorescence components, i.e., terrestrial humic-like substances (C1), protein-like substances (C2), and microbial humic-like substances (C3 and C4), were identified, and their relative abundance followed in the order of C3 > C4 > C2 > C1 in winter and C4 > C3 > C1 > C2 in summer. The formation potential of trihalomethanes and haloacetic acids in winter was higher and lower than that in summer, which was mainly ascribed to the content of aromatic and hydrophobic substances. Compared to the significant seasonal dynamic, the spatial variation of DOM and the formed DBPs was not obvious. This work sheds light on the spatial-temporal distribution of DOM and the potentially formed DBPs in Shengzhong Lake, and will be helpful for understanding the biogeochemical cycle of carbon and assessing the drinking water safety.

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.

Aging of polystyrene microplastics by UV/Sodium percarbonate oxidation: Organic release, mechanism, and disinfection by-product formation

The occurrence and transformation of microplastics (MPs) in environment has attracted considerable attention. However, the release characteristics of MP-derived dissolved organic matter (MP-DOM) under oxidation conditions and the effect of DOM on subsequent chlorination disinfection by-product (DBP) still lacks relevant information. This study focused on the conversion of polystyrene microplastics (PSMPs) in the advanced oxidation of ultraviolet-activated sodium percarbonate (UV/SPC-AOP) and the release characteristics of MP-DOM. The DBP formation potential of MP-DOM was also investigated. As a result, UV/SPC significantly enhanced the aging and fragmentation of PSMPs. Under UV irradiation, the fluorescence peak intensity and position of humus-like and protein-like components of MP-DOM were correlated with SPC concentration. The aging MP suspension was analyzed by gas chromatography-mass spectrometry (GC-MS), and various alkyl-cleavage and oxidation products were identified. Quenching experiments and electron paramagnetic resonance (EPR) detection confirmed that carbonate and hydroxyl radicals jointly dominated the conversion of PSMPs. The formation of DBP was related to the components of MP-DOM. Overall, these results help to understand the aging behavior of MPs in AOP. Moreover, MP-DOM released by MPs after AOP oxidation may be a precursor of DBPs, which deserved more attention.

Photochemical Transformation of Dissolved Organic Matter in Surface Water Augmented the Formation of Disinfection Byproducts

Sunlight may lead to changes in disinfection byproducts (DBPs) formation potentials of source water via transforming dissolved organic matter (DOM); however, the underlying mechanisms behind these changes remain unclear. This work systematically investigated the effect of photochemical transformation of DOM from reservoir water (DOMRe) and micropolluted river water (DOMRi) after 36 h of simulated sunlight irradiation (equivalent to one month under natural sunlight) on DBPs formation. Upon irradiation, high molecular weight (MW) and aromatic molecules tended to be mineralized or converted into low-MW and highly oxidized (O/C > 0.5) ones which might react with chlorine to generate high levels of DBPs, resulting in an elevation in the yields (μg DBP/mg C) of almost all the measured DBPs and the quantities of unknown DBPs in both DOM samples after chlorination. Additionally, DOMRi contained more aromatic molecules susceptible to photooxidation than DOMRe. Consequently, irradiated DOMRi exhibited a greater increase in the formation potentials of haloacetonitriles, halonitromethanes, and specific regulated DBPs, with nitrogenous DBPs being responsible for the overall rise in the calculated cytotoxicity following chlorination. This work emphasized the importance of a comprehensive removal of phototransformation products that may serve as DBPs precursors from source waters, especially from micropolluted source waters.

Perspectives and understanding on the occurrence, toxicity and abatement technologies of disinfection by-products in drinking water

Disinfection by-products (DBPs) are one of the significant emerging contaminants that have caught the attention of researchers worldwide due to their pervasiveness. Their presence in drinking water, even in shallow concentrations (in levels of parts per billion), poses considerable health risks. Therefore, it is crucial to understand their kinetics to understand better their formation and persistence in the water supply systems. This manuscript demonstrates different aspects of research carried out on DBPs in the past. A systematic approach was adopted for the bibliographical research that started with choosing appropriate keywords and identifying the most relevant manuscripts through the screening process. This follows a quantitative assessment of the extracted literature sample, which included the most productive and influential journal sources, the most widely used keywords, the most influential authors active in the research domain, the most cited articles, and the countries most actively engaged in the research field. Critical observations on the literature sample led to the qualitative assessment, wherein the past and current research trends were observed and reported. Finally, we identified the essential gaps in the available literature, which further led to recommending the course ahead in the research domain. This study will prove fruitful for young and established researchers who are or wish to work in this emerging field of research.