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N-Nitrosodimethylamine (NDMA) and its precursors in water and wastewater: A review on formation and removal
Abstract
This review summarizes major findings over the last decade related to N-Nitrosodimethylamine (NDMA) in water and wastewater. In particular, the review is focused on the removal of NDMA and of its precursors by conventional and advanced water and wastewater treatment processes. New information regarding formation mechanisms and precursors are discussed as well. NDMA precursors are generally of anthropogenic origin and their main source in water have been recognized to be wastewater discharges. Chloramination is the most common process that results in formation of NDMA during water and wastewater treatment. However, ozonation of wastewater or highly contaminated surface water can also generate significant levels of NDMA. Thus, NDMA formation control and remediation has become of increasing interest, particularly during treatment of wastewater-impacted water and during potable reuse application. NDMA formation has also been associated with the use of quaternary amine-based coagulants and anion exchange resins. UV photolysis with UV fluence far higher than typical disinfection doses is generally considered the most efficient technology for NDMA mitigation. However, recent studies on the optimization of biological processes offer a potentially lower-energy solution. Options for NDMA control include attenuation of precursor materials through physical removal, biological treatment, and/or deactivation by application of oxidants. Nevertheless, NDMA precursor identification and removal can be challenging and additional research and optimization is needed. As municipal wastewater becomes increasingly used as a source water for drinking, NDMA formation and mitigation strategies will become increasingly more important. The following review provides a summary of the most recent information available.
... Ozonation High levels of NDMA were observed after ozonation of wastewaters or highly contaminated surface waters. The currently most accepted NDMA formation pathway during ozonation at neutral and alkaline conditions involves the condensation of dimethylamine with hydroxylamine to unsymmetrical dimethylhydrazine (UDMH), which is further oxidized to NDMA [59]. Hydroxylamine may derive from the oxidation of ammonia or prior decomposition of nitrogenous organic precursors. ...
... During ozonation, high NDMA yields were observed for a limited subset of compounds. Compounds with dimethylamine bonded directly to a nitrogen atom (Group II in Fig. 7) or separated with a good leaving group (Group I in Fig. 7) were seen to form NDMA with significant molar conversion yields [59][60][61]. In case of UDMH and daminozide, it was suggested that ozone mainly attacks the unsubstituted nitrogen of UDMH or the nitrogen neighboring the carbonyl group of daminozide, forming an ozone adduct which decomposes via homolytic and heterolytic cleavage, directly yielding NDMA [4,61]. ...
... The mechanisms of NDMA formation during chlorination have not been exhaustively investigated. However, nitrosation of free dimethylamine and oxidation of UDMH [59,69,70] have been proposed. During chloramination, NDMA formation pathways involving the nucleophilic reaction of dichloramine with dimethylamine yielding chlorinated UDMH, followed by subsequent oxidation by dissolved oxygen, have been suggested [71,72]. ...
Oxidative treatment methods are valuable tools for the microbial safety of drinking water. However, the reaction of oxidants with natural substances or anthropogenic contaminants present in the raw water can potentially lead to the formation of harmful transformation products (TPs). The present paper proposes a tiered approach for the risk evaluation of TPs formed from pesticide residues during drinking water treatment. First, the concentrations of pesticide residues in raw water used for drinking water production are evaluated (step 1). Substances with a predicted concentration in raw water above 0.1 µg/L proceed further to a reactivity assessment, examining the behavior in water treatment plants (step 2). Using information available in the scientific literature, prediction of structural elements in the TPs can be made and allow a worst-case assessment based on the Threshold of Toxicological Concern (TTC) (step 3). If concerns remain, experiments may be conducted to simulate water treatment (step 4). Because of their complexity and variability, experiments for the simulation of water treatment should focus on prioritized substances of potential concern. The test conditions should be realistic (i.e., close to EU-representative conditions in waterworks) and ozonation and chlorination should be combined with pre- and post-treatment steps, as is normally the case in European waterworks. As a first screening option, we propose to test the toxicity of the reaction mixture. If the treated water shows an enhanced toxicity, further experiments can be conducted to identify and quantify the major TPs (step 5). We propose to define major TPs as substances present at more than 10% of the initially applied test substance. For major TPs, a tiered dietary risk assessment is conducted, starting with the TTC concept, and continuing with toxicity testing of the TP, according to EFSA and ECHA and internationally agreed guidance.
... Municipal wastewater discharge has been considered one of the major sources of N -nitrosamine precursors that can impact downstream source water qualities ( Krasner et al., 2013 ;Zeng et al., 2016a ;Sgroi et al., 2018 ). During biological wastewater treatment (e.g., the activated sludge (AS) process), N -nitrosamine precursors can be deactivated to different degrees, depending on wastewater treatment plants (WWTPs) and N -nitrosamine species ( Mitch and Sedlak, 2004 ;Sedlak et al., 2005 ;Krauss et al., 2010 ;Yoon et al., 2013 ;Wang et al., 2014 ). ...
... Their key physiochemical properties are shown in Appendix A Table S5. These seven N -nitrosamines are among the most frequently detected and reported N -nitrosamines in wastewater effluents and wastewater-impacted source waters ( Zeng et al., 2016a ;Sgroi et al., 2018 ). For N -nitrosamine formation tests, a NH 2 Cl stock solution was freshly prepared by adding a sodium hypochlorite solution (NaClO, ∼4000 mg Cl 2 /L) drop by drop to an ammonium chloride solution (NH 4 Cl, ∼1000 mg N/L) at pH 9 with a Cl:N mass ratio at 4:1. ...
... However, our data showed an opposite result. With the secondary effluents further purified during advanced wastewater treatment (e.g., H 2 O 2 /UV oxidation, membrane filtration processes) for potable reuse, NDMA UFC may further increase due to an enhanced removal of DOC, although NDMA FP can be apparently reduced ( Sgroi et al., 2018 ;Takeuchi et al., 2018 ). Such increases in NDMA UFC may pose further health risks, especially in reused waters, which requires further elucidation. ...
Municipal wastewater discharge is considered as one of the main sources of N-nitrosamine precursors which can impact the qualities of downstream source waters and reclaimed wastewaters for potable reuse. NNitrosamine precursors can be removed to various degrees during biological wastewater treatment (e.g., the activated sludge (AS) process). So far, little is known about the impact of the AS process on N-nitrosamine formation under practical disinfection condition (e.g., uniform formation condition (UFC)). In this study, N-nitrosamine UFC from selected model compounds, sewage components (i.e., blackwaters and greywaters) and sewage samples were comprehensively investigated during batch AS treatment tests. NNitrosodimethylamine (NDMA) formation from the tested precursor compounds (i.e., trimethylamine (TMA) and sumatriptan (SMTR)) under UFC chloramination decreased mostly after 6 or 24 h treatment with different types of AS (i.e., domestic rural AS, domestic urban AS, and textile AS), and the reductions in NDMA UFC were comparable to their NDMA formation potential (FP) reductions. In urine and feces blackwaters, NDMA UFC increased after 6 or 24 h treatment with the domestic (i.e., rural and urban) AS, while NDMA FP decreased substantially. The increases in NDMA UFC after AS treatment was presumably attributed to the removal of bulk organic matters (e.g., dissolved organic carbon (DOC)) which favored NDMA formation under UFC. On the other hand, in laundry greywaters having relatively abundant DOC, N-nitrosamine UFC was less affected by DOC removal before or after AS treatment, but decreased to similar degrees with N-nitrosamine FP. In sewage samples collected from wastewater treatment plants, N-nitrosamines UFC tended to increase or remain constant during AS treatment, despite the decreases in their FPs. These results suggest that biological wastewater treatment (e.g., the AS process) may not effectively reduce N-nitrosamine formation (e.g., measured under UFC) partially because the concurrent removal of bulk organic matters (e.g., DOC) favored N-nitrosamine formation in s econdary effluents.
... Several laboratory and pilot studies were carried out to determine factors that affect the increase or decrease of NDMA concentration in drinking water during water treatment [3]. It has been found that there are many precursors from which NA can be formed during water treatment (e.g., in the process of chlorination and even ozonation) [3,4]. Among such precursors there are aromatic amines, which, themselves, may be mutagenic, carcinogenic and toxic [5,6]. ...
... The flow rate was regulated by rotameter (6). The flat sheet membranes were posted in a tight cylindrical pressure chamber (4). The tangential inlet of the feed caused a spiral flow of liquid in the pressure chamber (4). ...
... The flat sheet membranes were posted in a tight cylindrical pressure chamber (4). The tangential inlet of the feed caused a spiral flow of liquid in the pressure chamber (4). The pressure in the chamber (4) was regulated by two valves (3). ...
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.
... One of the challenges associated with ozonation is to find the right compromise between ozone doses applied to allow the highest removal of OMPs and resulting transformation by-products (Mathon et al., 2021). Other considerations include the cost of the process, types of OMPs, solution pH and the water matrix effects (Molnar et al., 2013;Sgroi et al., 2018;Yong and Lin, 2016). Some wastewater matrices, typically represented by natural organic matter (NOM) and inorganic ions, are not suitable for ozonation. ...
... Some wastewater matrices, typically represented by natural organic matter (NOM) and inorganic ions, are not suitable for ozonation. The potential limitations include fast ozone consumption, inhibition of radical-chain reactions, and formation of unknown reaction by-products due to partial oxidation and interaction with matrix components (Gurol and Singer, 1982;Molnar et al., 2013;Sgroi et al., 2018). For example, bromide, if present in wastewater, can be transformed to bromate and N-Nitrosodimethylamine (NDMA) may also be formed by ozonation of dimethylamine (DMA) precursor (Molnar et al., 2013;Sgroi et al., 2018). ...
... The potential limitations include fast ozone consumption, inhibition of radical-chain reactions, and formation of unknown reaction by-products due to partial oxidation and interaction with matrix components (Gurol and Singer, 1982;Molnar et al., 2013;Sgroi et al., 2018). For example, bromide, if present in wastewater, can be transformed to bromate and N-Nitrosodimethylamine (NDMA) may also be formed by ozonation of dimethylamine (DMA) precursor (Molnar et al., 2013;Sgroi et al., 2018). This is, however, a very site-specific problem, but relevant because these ozonation by-products and transformation products are highly potent human carcinogen and have negative impacts on aquatic environments (Huang et al., 2019;Molnar et al., 2013). ...
The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants (WWTPs). The current strategy involves WWTPs upgrading with post-ozonation i.e., ozone (O3) and/or peroxone process (O3+H2O2). Still, ozone-based degradation of OMPs faces several challenges. For example, the degradation mechanism and kinetics of OMPs could largely be affected by water matrix compounds which include inorganic ions and natural organic matter (NOM). pH also plays a decisive role in determining the reactivity of the oxidants (O3, H2O2, andHO•), stability and speciation of matrix constituents and OMPs and thus susceptibility of OMPs to the reactions with oxidants. There have been reviews discussing the impact of matrix components on the degradation of OMPs by advanced oxidation processes (AOPs). Nevertheless, a review focusing on scavenging mechanisms, formation of secondary oxidants and their scavenging effects with a particular focus on ozonation and peroxone process is lacking. Therefore, in order to broaden the knowledge on this subject, the database ‘Web of Science’ was searched for the studies related to the ‘matrix effect on the degradation of organic micropollutants by ozone based processes’ over the time period of 2004-2021. The relevant literature was thoroughly reviewed and following conclusions were made: i) chloride has inhibitory effects if it exits at higher concentrations or as free chlorine i.e. HOCl/ClO−. ii) The inhibitory effects of chloride, bromide, HOBr/OBr− and HOCl/ClO− are dominant in neutral and alkaline conditions and may result in the formation of secondary oxidants (e.g., chlorine atoms or free bromine), which in turn contribute to pollutant degradation or form undesired oxidation by-products such as BrO3–, ClO3– and halogenated organic products. ii) NOM may induce inhibitory or synergetic effects depending on the type, chemical properties and concentration of NOM. Therefore, more efforts are required to understand the importance of pH variation as well as the effects of water matrix on the reactivity of oxidants and subsequent degradation of OMPs.
... The currently most accepted NDMA formation pathway during ozonation at neutral and alkaline conditions involves the condensation of dimethylamine with hydroxylamine to unsymmetrical dimethylhydrazine (UDMH), which is further oxidized to NDMA [59]. Hydroxylamine may derive from the oxidation of ammonia or prior decomposition of nitrogenous organic precursors. ...
... During ozonation, high NDMA yields were observed for a limited subset of compounds. Compounds with dimethylamine bonded directly to a nitrogen atom (Group II in Figure 7) or separated with a good leaving group (Group I in Figure 7) were seen to form NDMA with signi cant molar conversion yields [59,60,61]. In case of UDMH and daminozide, it was suggested that ozone mainly attacks the unsubstituted nitrogen of UDMH or the nitrogen neighboring the carbonyl group of daminozide, forming an ozone adduct which decomposes via homolytic and heterolytic cleavage, directly yielding NDMA [4,61]. ...
Oxidative treatment methods are valuable tools for the microbial safety of drinking water. However, the reaction of oxidants with natural substances or anthropogenic contaminants present in the raw water can potentially lead to the formation of harmful transformation products (TPs). The present paper proposes a tiered approach for the risk evaluation of TPs formed from pesticides residues during drinking water treatment.
First, the concentrations of pesticides residues in raw water used for drinking water production are evaluated (step 1). Substances with a predicted concentration in raw water above 0.1 µg/L proceed further to a reactivity assessment, examining the behaviour in water treatment plants (step 2). Using information available in the scientific literature, prediction of structural elements in the TPs can be made and allow a worst-case assessment based on the Threshold of Toxicological Concern (TTC) (step 3).
If concerns remain, experiments may be conducted to simulate water treatment (step 4). Because of their complexity and variability, experiments for the simulation of water treatment should focus on prioritized substances of potential concern. The test conditions should be realistic (i.e., close to EU-representative conditions in waterworks) and ozonation and chlorination should be combined with pre- and post-treatment steps, as is normally the case in European waterworks. As a first screening option, we propose to test the toxicity of the reaction mixture. If the treated water shows an enhanced toxicity, further experiments can be conducted to identify and quantify the major TPs (step 5). We propose to define major TPs as substances present at more than 10% of the initially applied test substance. For major TPs a tiered dietary risk assessment is conducted, starting with the TTC concept, and continuing with toxicity testing of the TP, according to EFSA and ECHA and internationally agreed guidance.
... Since these discoveries, the research on NDMA and other nitrosamines has increased around the world. More recently, researchers have reported that alternative disinfectants, including chlorine dioxide (ClO2) and ozone (O3), can also produce NDMA [11,100]. It is believed that NDMA precursors are mainly of anthropogenic origin, in contrast to other DBPs, such as THMs and HAAs, which are derived from organic matter of different environmental sources [101]. ...
... However, drinking water practices such as coagulation with PolyDADMAC have also been related to NDMA formation [102]. Algal blooms, and to a lesser degree agricultural or stormwater runoff may also be an important source of nitrosamine precursors, but likely only in very adverse conditions when a major fraction of the water supply is affected [100]. ...
Disinfection byproducts (DBPs) form after the reaction of natural and anthropogenic organic matter and other inorganic substances present in water with the disinfectants used to inactivate pathogens. This chapter provides insights into the most common DBP classes regarding their chemical properties, environmental occurrence, and the most suitable methodologies for their reliable determination in water. It includes the halogenated DBP classes trihalomethanes, haloacetic acids, haloacetaldehydes, halobenzoquinones, haloacetonitriles, halonitromethanes, haloacetamides, and the non‐halogenated DBP class nitrosamines. Liquid‐liquid extraction is the most widely used extraction method due to its simplicity, low cost, and effectiveness in simultaneously extracting various DBP classes. Linearity is obtained in most analytical approaches with the internal standard calibration method. Known DBPs represent only a small fraction of the halogenated material formed during the disinfection process. The development of target multi‐class methods is encouraged to obtain valuable information at once for many DBPs, minimizing economical and lab‐effort resources.
... N-nitrosamines constitute the class of organic nitrogen (ON) compounds that gained significant research attention owing to their highly toxic nature as well as carcinogenic properties [1][2][3][4][5]. These toxicants are primarily produced by the oxidation or nitrosation of secondary amines [6][7][8][9][10][11][12][13], and such reactions occur in the atmosphere [14][15][16], drinking water [17][18][19][20][21], organic chemical industry [5], rubber industry [22], food processing [23,24], drug synthesis [25][26][27][28][29][30][31][32], and so on. Correspondingly, nitrosamine compounds are ubiquitous, contaminating human tissues, food, water, air, soil, drugs etc, thereby posing severe health concerns [33]. ...
N- Nitrosodimethyl amine, the simplest member of the N-Nitrosamine family, is a carcinogenic and mutagenic agent that has gained considerable research interest owing to its toxic nature. Ozonation of industrially important hydrazines, such as unsymmetrical dimethylhydrazine (UDMH) or monomethylhydrazine (MMH), has been associated with NDMA formation and accumulation in the environment. UDMH/MMH - ozonation also leads to several other transformation products such as acetaldehyde dimethyl hydrazine (ADMH), tetramethyl tetra azene (TMT), diazomethane, methyl diazene, etc, which can be either precursors or competitors for NDMA formation. However, the relevant chemistry detailing the formation of these transformation products from UDMH/MMH -ozone reaction and their subsequent conversion to NDMA is not well understood. In this work, we explored the formation mechanism of ADMH and TMT from UDMH-ozonation and their further oxidation to NDMA using the second-order Moller Plesset perturbation theory employing the 6-311G(d) basis set. We have also investigated how MMH selectively forms methyl diazene and diazomethane under normal conditions and NDMA in the presence of excess ozone. Our calculations indicate that the reactions proceed via an initial H abstraction from the hydrazine –NH2 group, followed by the oxidation of the generated N-radical species. The formation of ADMH from the UDMH-ozone reaction involves an acetaldehyde intermediate, which then reacts with a second UDMH molecule to generate ADMH. The preferable attack of ozone molecule on N=C bond of ADMH generates DMAN intermediate, which subsequently undergoes oxidation to form NDMA. Unlike other transformation products, TMT formation occurs via the dimerization of DMAN. 1Though there exists an N=N bond in the TMT, which are preferable attacking sites for ozone, experimental studies show the lower yields of NDMA formation, which corroborates with the high activation barrier required for the process (42 kcal/mol). Overall, our calculated results agree well with the experimental observations and rate constants. Computational calculations bring new insights into the electronic nature and kinetics of the elementary reactions of this pathway, enabled by computed energies of structures that are not possible to access experimentally.
... Besides, NDMA is generated from low to high concentrations because it is quickly created in chemical reactions and is easily broken down by light. Anthropogenic effluents are the main precursors to NDMA (Sgroi et al., 2018). NDMA formation is also governed by pH, as the NDMA formation rate is maximum in the pH range of 7-8, which is also the pH range for WTPs (Yang et al., 2009). ...
Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at the commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.
... Among common disinfectants, chloramine leads to the highest levels of NDMA formation in water and wastewater treatment (Sgroi et al., 2018). NDMA was detected in water treatment plants that used poly-DADMAC and practised chloramination, in the range of 7-46 ng/L. ...
Disinfection by-products (DBPs) are formed through the disinfection of water containing precursors such as natural organic matter or anthropogenic compounds (e.g., pharmaceuticals and pesticides). Due to the ever increasing use of plastics, elastomers, and other polymers in our daily lives, polymer-based materials (PBMs) are detected more frequently and at higher concentrations in water and wastewater. The present review provides a comprehensive and systematic analysis of the contribution of PBMs - including elastomers, tire waste, polyelectrolytes, and microplastics - as precursors of DBPs in water and wastewater. Literature shows that the presence of PBMs can lead to the leaching of dissolved organic matter (DOM) and subsequent formation of DBPs upon disinfection in aqueous media. The quantity and type of DBPs formed strongly depends on the type of polymer, its concentration, its age, water salinity, and disinfection conditions such as oxidant dosage, pH, temperature, and contact time. DOM leaching from elastomers and tire waste was shown to form N-nitrosodimethylamine up to concerning levels of 930 ng/L and 466,715 ng/L, respectively upon chemical disinfection under laboratory conditions. Polyelectrolytes can also react with chemical disinfectants to form toxic DBPs. Recent findings indicate trihalomethanes formation potential of plastics can be as high as 15,990 µg/L based on the maximum formation potential under extreme conditions. Our analysis highlights an overlooked contribution of DOM leaching from PBMs as DBP precursors during disinfection of water and wastewater. Further studies need to be conducted to ascertain the extent of this contribution in real water and wastewater treatment plants.
... Chlorine and to a lesser extent chloramines can react with organic matter present in municipal wastewater to produce various DBPs. The wide array of formed DBPs include THMs, HAAs, and halogenated nitrogenous DBPs (Sgroi et al., 2018). Krasner et al. (2009) showed that chlorination of wastewater resulted in different DBP formation patterns depending on whether or not the treatment plant achieved good nitrification. ...
Oxidative treatment of seawater in coastal and shipboard installations is applied to control biofouling and/or minimize the input of noxious or invasive species into the marine environment. This treatment allows a safe and efficient operation of industrial installations and helps to protect human health from infectious diseases and to maintain the biodiversity in the marine environment. On the downside, the application of chemical oxidants generates undesired organic compounds, so-called disinfection by-products (DBPs), which are discharged into the marine environment. This article provides an overview on sources and quantities of DBP inputs, which could serve as basis for hazard analysis for the marine environment, human health and the atmosphere. During oxidation of marine water, mainly brominated DBPs are generated with bromoform (CHBr3) being the major DBP. CHBr3 has been used as an indicator to compare inputs from different sources. Total global annual volumes of treated seawater inputs resulting from cooling processes of coastal power stations, from desalination plants and from ballast water treatment in ships are estimated to be 470 – 800 × 10⁹ m³, 46 × 10⁹ m³ and 3.5 × 10⁹ m³, respectively. Overall, the total estimated anthropogenic bromoform production and discharge adds up to 13.5 – 21.8 × 10⁶ kg/a (kg per year) with contributions of 11.8 – 20.1 × 10⁶ kg/a from cooling water treatment, 0.89 × 10⁶ kg/a from desalination and 0.86 × 10⁶ kg/a from ballast water treatment. This equals approximately 2 – 6 % of the natural bromoform emissions from marine water, which is estimated to be 385 – 870 × 10⁶ kg/a.
... Studies have shown that dietary nitrosamines were associated with the risk of gastric cancer and other digestive system cancers ). The excessive of nitrosamines and precursors in drinking water has become an important potential health threat (Sgroi et al. 2018). Epidemiological studies have confirmed that excessive nitrosamines in food and drinking water may facilitate the risk of esophageal cancer (Huang and Yu 2018;Kaz and Grady 2014). ...
Studies have shown that environmental carcinogens exerted an important function in the high incidence of esophageal cancer (EC). Nitrosamines have been identified as important environmental carcinogens for EC. This study aimed to investigate the metabolic disturbances and new key toxicological markers in the malignant transformation process of normal esophageal epithelial cells (Het-1A) induced by MNNG (N-methyl-N′-nitro-N-nitrosoguanidine). Untargeted metabolomic and lipidomic profiling analysis by using ultra-high-performance liquid chromatography coupled with mass spectrometry (UHPLC-MS) were applied to explore the metabolic network alterations of Het-1A cells. The metabolomic results showed that significant alterations were observed in metabolic signatures between different generations (P5, P15, P25, P35) and the control cell group (P0). A total of 48 differential endogenous metabolites were screened and identified, mainly containing fatty acids, amino acids, and nucleotides. The differential metabolites were predominantly linked to the pathway of biosynthesis of unsaturated fatty acids metabolism. The cell lipidomic profiling revealed that the most differential lipids contained fatty acids (FAs), phosphatidylcholines (PC), phosphatidylethanolamines (PE), and phosphatidylserines (PS). The enrichment of the lipidomic pathway also confirmed that the lipid metabolism of biosynthesis of unsaturated fatty acids was the significant variation during the cell malignant transformation. Furthermore, we detected the expression of the upstream regulatory enzymes related to the unsaturated fatty acids to explore the regulation mechanism. The expression of stearoyl-CoA desaturase (SCD), ELOVL fatty acid elongase 1 (ELOVL1) promoted, and fatty acid desaturase 1 (FADS1) inhibited the key fatty acids of unsaturated fatty acids metabolism compared to the control cell group. Overall, our results revealed that lipid fatty acid metabolism was involved in the malignant transformation of Het-1A cells induced by MNNG and deepened the awareness of the carcinogenic mechanism of environmental exposure pollutants.
Graphical abstract
... Nitrites, destroying vitamins A and B in the body, can react with secondary and tertiary amines to form carcinogenic, teratogenic, and mutagenic compounds called N-nitrosamines [17]. Nitrosamines produce nitrosate from nitrite under acidic conditions in the stomach, reacting with secondary amines [18,19]. N-Nitroso dimethylamine (NDMA) is a member of the N-nitrosamine group, highly soluble in water. ...
The present study was conducted to investigate the concentration of nitrate in drinking water resources and its carcinogenic risk in the southern provinces of Iran in 2020. Raw data of nitrate concentrations were obtained from wastewater and water Company of each province, and Mont Carlo Simulation (MCS) was considered 10‐5 for estimating human carcinogenic risk. Our results demonstrated that in the drinking water resources of Khuzestan and Fars provinces, the nitrate level was 59 and 72 mg/L, respectively, higher than the World Health Organization (WHO) recommendation. The calculated carcinogenic risk of nitrate for Khuzestan and Fars provinces were higher than the range set by WHO and Health Canada, 8.8 × 10⁻⁵ and 1.3 × 10⁻⁵, respectively. Exposure to an unacceptable nitrate level through drinking water can affect blood carrying oxygen and cause methemoglobinemia and a significant relationship with gastrointestinal cancer spread.
... However, ozonation of wastewater or highly contaminated surface water can also generate significant levels of NDMA. 16 White has reported and published that N-nitrosodimethylamine (NDMA) is a hepatotoxic agent and carcinogen contaminant in commonly used medications such as valsartan, losartan, irbesartan, and ranitidine. [17] It can be argued that a patient suffering from Type 2 diabetes is more at risk for hepatotoxicity from the impurity NDMA because of the pathogenesis of Type 2 diabetes mellitus. ...
Minority patients taking prescription drugs for diabetes mellitus and hypertension are sick and vulnerable. They should not be subjected to poor quality medications that can make them worse. The purpose of this review is to present data fortifying an argument that Covid-19 will continue to disproportionally effect minorities who suffer with Type 2 Diabetes Mellitus, Hypertension, and GI ulcer disease by limiting drug safety for pharmaceuticals that are imported from oversea manufacturers even after the pandemic is over. As a foundation an overview of the Food and Drug Administration (FDA) overseas inspection process that have been validated by previously published reports will be offered to accent the procedural process. Limitations and challenges to the overseas drug inspection process as documented by congressional leadership and the FDA are offered. An accurate scientific description of N-nitrosodimethylamine (NDMA) will be presented to emphasize its danger to these patients. Five key points or initiatives recently published by the FDA to assist in food and drug safety from overseas manufacturers during the Covid-19 pandemic will be presented
... Previous studies have shown that NDMA cannot be degraded by chlorine and became accumulated as a final product (Mitch and Sedlak, 2002). NDMA can be formed from a variety of precursors such as amines, amine-based polymers and humus in the water treatment disinfection process by reacting with chlorine (Sgroi et al., 2018). Amine derivatives in algae such as proteins and nucleic acids will first react with oxidants to form intermediates. ...
The effects of chlorine dosage, reaction time, algae concentration, and cell components, including extracellular organic matter (EOM), intracellular organic matter (IOM) and cell debris (CD), were evaluated on the formation of nitrosamines (NAs), including N-Nitrosodimethylamine (NDMA), -Nitrosomethylethylamine (NMEA), N-Nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA), N-Nitrosopyrollidine (NPyr), during the chlorination of Microcystis aeruginosa (M. aeruginosa) and Cyclotella meneghiniana (C. meneghiniana) in drinking water treatment. In addition, the NAs formation from Chlorophyll-a and Microcystin-LR (MC-LR) chlorination was investigated. The results showed that NDMA was the most dominant product of two algae, while only a small yield of NPyr, NMEA and NDBA was generated with NDPA as the least. The nitrosamines formation potential (NAsFP) of M. aeruginosa was positively correlated with the chlorine concentration, while the highest NAsFP of C. meneghiniana was observed at 10 mg/L chlorine. With the increase of reaction time, the NAsFP from C. meneghiniana was higher than M. aeruginosa. The NAs formation enhanced with the increase of cell concentration. Moreover, the impacts of cellular components on the NAsFP followed the order of CD > IOM > EOM and IOM > EOM > CD for M. aeruginosa and C. meneghiniana, respectively. The results indicated that proteins and soluble microbial products (SMPs) were the main cellular components to contribute to NAs formation and IOM was the primary source of NAs precursor for both algae. Chlorination of Chlorophyll-a and MC-LR showed that chlorophyll-a formed only a small yield of NDMA and NDBA, while MC-LR made a more significant contribution to the types of NAs.
... The side reaction of chlorination of TCs impacted the DMA separation (Fig. S1). As reported in published studies, the DMA separation was viewed as a directed way to form NDMA (Sgroi et al., 2018), thus DMA as a model precursor in many researches had a relatively high NDMA conversion (Andrzejewski et al., 2008;. Reaction involved the adjacent group of carbon atom which is next to the DMA group has a subtle impact on the formation of nitrosamine (Le Roux et al., 2012). ...
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.
... Some investigations indicated that a portion of high nitrosamine FP concentrations in drinking water can be attributed to anthropogenic pollution in source waters. (Krasner et al., 2008;Bei et al., 2016b;Sgroi et al., 2018;Luo et al., 2020). Besides the role of emerging DBPs formed by disinfection, nitrosamines have also been detected as contaminants present in source waters at the level of tens of nanograms per liter (Wang et al., 2016;Qiu et al., 2019Qiu et al., , 2020, and their removal in drinking water treatment process is limited (Plumlee et al., 2008;Qiu et al., 2020). ...
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.
N-nitrosamines (NAs), and N-nitrosodimethylamine (NDMA) in particular, are hazardous disinfection byproducts (DBPs) relevant when wastewater impacts drinking water sources and, in water reuse practices. Our study investigates the concentrations of NDMA and five additional NAs and their precursors in industrial wastewater effluents. Aiming to identify potential differences between industrial typologies, wastewaters from 38 industries belonging to 11 types of the UN International Standard Industrial Classification of All Economic Activities system (ISIC) were analysed. Results show that the presence of most NAs and their precursors cannot be linked to a specific industry type as these were in general very different within the classes. Nevertheless, N-nitrosomethylethylamine (NMEA) and N-nitrosopiperidine (NPIP) as well as precursors for N-nitrosodiethylamine (NDEA), NPIP and N-nitrosodibuthylamine (NDBA) could be rank with different concentrations between ISIC classes (p-value < 0.05). Specific industrial wastewater with notable high concentrations of NAs and their precursors were identified too. The effluents with the highest concentration of NDMA belong to the ISIC C2011 class (Manufacture of basic chemical), while the effluents with the highest concentration of NDMA precursors were from the ISIC C1511 class (Tanning and dressing of leather; dressing and dyeing of fur). Other relevant NAs found were NDEA in ISIC class B0810 (Quarrying of stone, sand, and clay) and ISIC class C2029 (Manufacture of other chemical products).
Anion exchange resin is responsible for removing harmful anionic contaminants in drinking water treatment, but it may become a significant source of precursors for disinfection byproducts (DBPs) by shedding material during application without proper pretreatment. Batch contact experiments were performed to investigate the dissolution of magnetic anion exchange resins and their contribution to organics and DBPs. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) released from the resin were highly correlated with the dissolution conditions (contact time and pH), in which 0.7 mg/L DOC and 0.18 mg/L DON were distributed at exposure time of 2 h and pH 7. The formation potential of four DBPs in the shedding fraction was also revealed that trichloromethane (TCM), dichloroacetonitrile (DCAN), nitrosodimethylamine (NDMA), and dichloroacetamide (DCAcAm) concentrations could reach 21.4, 5.1, 12.1 μg/L, and 69.6 ng/L, respectively, which was consistent with the release of DOC and DON. Furthermore, the hydrophobic DOC that preferred to detach from the resin mainly originated from the residues of crosslinkers (divinylbenzene) and porogenic agents (straight-chain alkanes) detected by LC-OCD and GC-MS. Nevertheless, pre-cleaning inhibited the leaching of the resin, among which acid-base and ethanol treatments significantly lowered the concentration of leached organics, and formation potential of DBPs (TCM, DCAN, and DCAcAm) below 5 μg/L and NDMA dropped to 10 ng/L.
N-nitrosamines have recently attracted attention as a class of disinfection byproducts and are also a hot spot in environmental studies. Current N-nitrosamine analytical methods typically involve manual solid phase extraction (SPE) of samples followed by quantitative analysis using liquid chromatography-mass spectrometry (LCMS), which is time-consuming and may also fail to eliminate complex matrix effects. Size exclusion chromatography (SEC) is a technique that can separate compounds according to their molecular size. For the first time, this study developed an Online-SPE/SEC/LCMS quantitative analysis method to detect and analyze nine common N-nitrosamine disinfection byproducts in wastewater plant tailwater, including N-dimethylnitrosamine (NDMA) and N-nitrosodiethylamine (NDEA), etc. The samples of 1.0 mL can be directly injected after the simple 0.22 μm membrane filtration. This method reports the combination of SPE, SEC, and RP C18 columns to achieve several functions in a processing time of 20 min, including online enrichment, desalination, and matrix separation for the first time. The method provides good linearity (R2 > 0.999), recoveries ranging from 91.67% to 105.88%, relative standard deviation (RSD) lower than 4.17%, and the limits of detection (LOD) are 0.12–6.60 ng/L. This method alleviates tedious human labor and can effectively overcome the matrix effect (ME < 20%). This method allows for the accurate quantitative analysis of N-nitrosamines with high compatibility in wastewater plant tailwater, rivers, and lakes with a high background matrix. Interested researchers can also use this method as a reference in the online analysis of other specific pollutants after necessary optimization. It can also be utilized for non-targeted screening and targeted analysis of contaminants in water with a wide range of applications, giving valuable information for environmental monitoring.
N-Nitrosamines are considered highly carcinogenic and genotoxic compounds, which are formed in water largely due to chloramination or chlorination disinfection in the presence of ammonia. N-nitrosodimethylamine has particularly attracted interest due to its high carcinogenicity. This review seeks to provide a synopsis of the present state of knowledge on the occurrence, toxicity, and analysis of N-nitrosamines in African surface and drinking water and highlights limitations and future directions. Solid phase extraction is preferred for nitrosamines in water, whilst analysis is mainly based on GC-MS or LC-MS. Extensive research into the distribution and potential impacts of N-nitrosamines in water has not yet been achieved on the African continent. There is a need for comprehensive research towards the development of sensitive but facile analytical methods for N-nitrosamines, and the monitoring thereof in African water matrices, particularly in drinking water, in order to better assess potential human health implications.
N-nitrosodimethylamine (NDMA) is a disinfection byproduct that forms at the presence of an organic nitrogen precursor. Doxylamine, an antihistaminic pharmaceutical, is a precursor of NDMA and has been shown to form NDMA in the presence of chloramine. In this study, the effect of Doxylamine as an NDMA precursor has been further studied during chloramination. The end product and byproducts during chloramination were investigated using a high-resolution mass spectrometer by taking samples at different time intervals. Results suggest that NDMA is not the only end product forming during chloramination of Doxylamine and several transformation products that do not end up as NDMA may form. A group of these transformation products have been selected based on their relative amounts during chloramination with time and notated as Focus Tentative Transformation Products (FTTPn). The identification of these byproducts will make it easier to study the conditions during chloramination that may favor these "known" transformation products with the use of less sophisticated analytical instruments. Then, it might lead to the establishment of chloramination protocols that will minimize the formation of NDMA from its precursors.
Oxidations of the antitubercular drug isoniazid (INH) and its analogy hydrazides, nicotinic hydrazide (NH), picolinoyl hydrazide (PH), and benzohydrazide (BH), by ClO2 were investigated with a focus on the kinetics and reaction mechanisms. In buffered solutions of a wide pH range (from 0.51 to 10.35), the oxidation reactions strictly followed the second-order kinetics, and the apparent second-order rate constant kapp versus pH profiles were established at 25.0 oC and 1.0 M ionic strength. Excess ClO2 could rapidly oxidize the hydrazides to their corresponding aryl acids which were identified by mass spectrometry. For each of the hydrazides, the proposed reaction mechanism involves parallel rate-determining reactions between ClO2 and various protolysis species of the hydrazide, rendering two types of hydrazyl free radicals; the free radicals are quickly oxidized by 3 more equivalents of ClO2 to aryl acids. The derived rate constants for the rate-determining reactions revealed that for each hydrazide a huge reactivity difference existed among the protolysis species (> 10⁸ times) and that the enolate form (or its resonant structures) was extremely reactive. Two possible modes of electron transfer in the rate-determining reactions are discussed based on the observed reaction characters. In buffered solution of pH 7.0 and 25.0 oC, the measured values of kapp are 6.20 x 10⁴, 7.8 x 10³, 2.57 x 10³, and 1.83 x 10³ M–1 s–1 for INH, NH, PH, and BH, respectively, imparting an important data set as a reference to the water treatment. This work may open a new door for resolving water pollution caused by INH and its derivatives.
Dimethylamine (DMA) and diethylamine (DEA) as precursors for the formation of potentially N-nitrosamines are widespread in the environment, and the removal of these disinfection byproduct precursors from water is of great significance to control the quality of drinking water. In this study, a three-dimensional hierarchical NiLa-layered double hydroxide/biochar nanocomposite (NiLa-LDH/BC) was prepared to remove them from a synthetic solution and real surface water. NiLa-LDH nanoplatelets endowed the biochar with an improved porous structure, high functional groups, and more active metal sites. NiLa-LDH/BC exhibited a high DMA and DEA adsorption capacity of 46.45 and 40.10 mg g⁻¹, which is 6.31 and 7.85 times higher than that of BC, respectively. A fixed-bed column experiment revealed that NiLa-LDH/BC could last for ∼1860 to 2400 bed volumes (BVs) before a breakthrough occurred (approximately 9 times higher than that of BC). In addition, the leaching test and regeneration and toxicity test of Daphnia magna demonstrate the high stability (over 88% adsorption capacity after seven adsorption-desorption cycles), extremely low metal leaching (<0.01 mg g⁻¹), and low toxicity (24h-EC50and 48h-EC50of the NiLa-LDH/BC leachates were 13.07 and 6.33%, respectively). According to material characterization, the main removal mechanism of DMA and DEA by NiLa-LDH/BC was electrostatic attraction, hydrogen bonding, and complexation. Density functional theory calculations were also applied to evaluate the DMA and DEA adsorption performance of materials. Overall, this study indicated that three-dimensional hierarchical NiLa-LDH/BC can be promising in highly efficient removal of N-nitrosamine precursors from real surface water.
Reactive nitrogen species (RNS) pose a potential risk to drinking water quality because they react with organic compounds to form toxic byproducts. Since the discovery of RNS formation in sunlit surface waters, these reactive intermediates have been detected in numerous sunlit natural waters and engineered water treatment systems. This critical review summarizes what is known regarding RNS, including their formation, contributions to contaminant transformation, and products resulting from RNS reactions. Reaction mechanisms and rate constants have been described for nitrogen dioxide (˙NO2) reacting with phenolic compounds. However, significant knowledge gaps remain regarding reactions of RNS with other types of organic compounds. Promising methods to quantify RNS concentrations and reaction rates include the use of selective quenchers and probe compounds as well as electron paramagnetic resonance spectroscopy. Additionally, high resolution mass spectrometry methods have enabled the identification of nitr(os)ated byproducts that form via RNS reactions in sunlit surface waters, UV-based treatment systems, treatment systems that employ chemical oxidants such as chlorine and ozone, and certain types of biological treatment processes. Recommendations are provided for future research to increase understanding of RNS reactions and products, and the implications for drinking water toxicity.
Magnetic nanocatalysts are garnering attention for development of greener catalytic processes due to their ease of recovery from a reaction medium. This book delves into a variety of magnetic nanocatalysts, their use in the industrial context, and recyclability. Topics covered include wastewater treatment, drug delivery, and industrial catalysis; another available volume focuses on the use of magnetic nanocatalysts in synthetic appliances and transformations.
Explores magnetic nanocatalysts, their use in synthesis, and their recyclability for more sustainable processes.
Contains chapters on their use in environmental remediation and catalytic processes.
Viability of a single-step mixotrophic algal wastewater treatment (A-WWT) system in delivering discharge-quality effluent has been previously demonstrated. This report presents inactivation performance of the A-WWT system and compares it with that of high-rate algal ponds, activated sludge, and membrane bioreactors. Log reduction per unit energy input/volume of wastewater by the A-WWT system is shown to range 6.4–14.6 m³/kWh, while that in the above alternatives ranged 1.3–3.5 m³/kWh. Pathogenicity and virulence of the algal effluent and the potential for formation of disinfection byproducts (DBPs) under chlorination are discussed. Concentrations of seven of the common nitrogenous DBPs in the algal effluent were <50 ng/L.
The presence of dissolved organic nitrogen (DON) in biological nutrient removal (BNR) effluent has led to increased concern about its adverse effects on wastewater discharge and reuse applications. Previous studies have demonstrated efficient biological inorganic nitrogen removal in BNR under low dissolved oxygen (DO) conditions; however, information on DON is scarce. This study investigated low-DO effects on DON and N-nitrosodimethylamine (NDMA) precursor concentrations in BNR effluents. Identical BNR reactors consisting of an external real-time DO intelligent control system were operated at three different DO concentrations (0.3, 1.0, and 4.0 mgO2/L). Surprisingly, significantly higher values of effluent DON (p<0.05, t-test) and NDMA precursors (p<0.01, t-test) were observed at lower DO levels. Ultrahigh-resolution mass spectrometry analysis showed that molecules produced by microbes at low-DO levels exhibited high proteins/amino sugars-like and low normal oxidation state of carbon characteristics, which possibly acted critical roles in NDMA formation. Furthermore, path analysis by partial least-squares path modeling suggested that NDMA formation potential had strong associations with microbe-DON network stability of microbe-DON co-occurrence interactions (r=0.979, p<0.01). These results highlight the necessity of reconsidering the feasibility of BNR systems operating at low-DO concentrations considering the adverse effects of DON on wastewater discharge and reuse applications.
This study assessed the efficacy of laboratory and pilot-scale (1) UV photolysis, (2) combined UV and hydrogen peroxide oxidation (UV/H2O2), (3) granular activated carbon (GAC) adsorption, and (4) UV/H2O2 followed by GAC, for simultaneous removal of contaminants of emerging concerns (CECs) in water. Five globally relevant CECs from five different contaminant classes were selected as target CECs to represent the wide range, i.e., N-nitrosodimethylamine (NDMA) as a disinfection by-product, trimethoprim (TMP) as a pharmaceutical, triclosan (TCS) as a personal care product, atrazine (ATZ) as a herbicide, and estrone (E1) as a steroid hormone. Highly photosensitive compounds like NDMA and TCS were easily degraded by UV (>75%) and UV/H2O2 (>80%) with direct photolysis as the main removal mechanism. Their removal efficiencies were less affected by the presence of other CECs and the water matrix than the other CECs. The effects of competitive adsorption among CECs and the water matrix was more profound for moderately hydrophobic or less hydrophilic compounds, e.g., TMP, ATZ, and E1. The laboratory-scale results showed the application of a single treatment could not efficiently remove the target CECs. Hence the combination of treatments was employed in the pilot-scale experiments, which assessed the effectiveness of UV/H2O2 (1000 mJ/cm² and 4 mg/L H2O2) followed by GAC (empty bed contact time 3.5–28 min) in removing target CECs at their environmentally relevant concentrations. Our findings suggest that UV/H2O2 followed by GAC would serve as an excellent multi-barrier for efficiently removing a wide range of CECs in water.
Pre-oxidation have been widely applied in drinking water treatment plants with micro-polluted water as water sources. In this study, the effects of three commonly used oxidants (ozone, chlorine, and potassium permanganate) on disinfection by-products (DBPs) formation from micro-polluted water during subsequent chlorination and chloramination were investigated. Moreover, the toxicities of treated water were also compared. In addition, principal component analysis was applied to clarify the main components that contributed to DBPs generation. The results demonstrated that all the selected oxidants could reduce DBPs to some extent, but the species and amounts were quite different. Pre-KMnO4 greatly reduced haloacetic acid (HAAs) formation in subsequent chloramination; the removal rate reached up to 45.2%. Pre-HClO could produce trihalomethane (THMs) and HAAs directly, and its effect on DBPs reduction during subsequent disinfection processes was limited. Pre-O3 performed best on N, N-dimethyl nitrosamine (NDMA) reduction during subsequent chloramination; the corresponding removal rates were 49.7%. In addition, pre-O3 significantly reduced UV254 and SUVA. Pre-KMnO4 transferred more organic matter to cationic components (24%), while the highest polar component augmentation was observed during pre-HClO (15%). Based on the analysis of total toxicity of formed DBPs, pre-O3 performed best on toxicity reduction no matter subsequent chlorination or chloramination, which decreased by 25.8% and 46.4%, respectively. The principal component analysis showed that DBPs has a weak correlation with regular water quality parameters, but related with specific organic fractions. The results of this paper had significant guidance for the selection of pre-oxidation methods in drinking water treatment plants for this kind of water sources.
This review summarizes major findings over the last decade related to N-nitrosodimethylamine (NDMA) formed upon ozonation, which was regarded as highly toxic and carcinogenic disinfection by-products. The reaction kinetics, chemical yields and mechanisms were assessed for the ozonation of potential precursors including dimethylamine (DMA), N,N-dimethylsulfamide, hydrazines, N-containing water and wastewater polymers, dyes containing a dimethylamino function, N-functionalized carbon nanotubes, guanidine, and phenylurea. The effects of bromide on the NDMA formation during ozonation of different types of precursors were also discussed. The mechanism for NDMA formation during ozonation of DMA was re-summarized and new perspectives were proposed to assess on this mechanism. Effect of hydroxyl radicals (•OH) on NDMA formation during ozonation was also discussed due to the noticeable oxidation of NDMA by •OH. Surrogate parameters including nitrate formation and UV254 after ozonation may be useful parameters to estimate NDMA formation for practical application. The strategies for NDMA formation control were proposed through improving the ozonation process such as ozone/hydrogen peroxide, ozone/peroxymonosulfate and catalytic ozonation process based on membrane pores aeration (MEMBRO3X).
Bromate, a regulated disinfection byproduct, forms during the ozonation of bromide through reactions with both ozone and hydroxyl radical. In this study, preformed monochloramine was evaluated for use as a bromate suppression method in pilot testing of wastewater reuse with an average bromide concentration of 422±20 µg/L. A dose of 3 mg/L NH2Cl-Cl2 decreased bromate formation by an average of 82% and was sufficient to keep bromate below the MCL at ozone doses up to 8.6 mg/L (1.2 O3:TOC). Removal of 1,4-dioxane through ozonation decreased with increasing NH2Cl dose, confirming that monochloramine suppresses bromate formation, at least in part, by acting as a hydroxyl radical scavenger. This may negatively impact oxidation objectives of ozonation in reuse applications. Increasing monochloramine contact time did not improve bromate suppression, indicating that monochloramine probably did not mask bromide as NHBrCl or other haloamines prior to ozonation. However, NHBrCl and NH2Br may be formed from reactions between HOBr and NH2Cl and excess free ammonia during ozonation. NDMA was formed by ozonation at concentrations up to 79 ng/L and was not enhanced by NH2Cl addition.
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 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.
N-nitrosamines (NAs), a class of emerging nitrogenous disinfection byproducts, have been detected remarkably in drinking/reclaimed water. There is a significant risk of excessive levels of NAs in the chlorination of the polluted source water, especially in the direct chlorination of nitrite-enriched groundwater. Considering the co-pollution of nitrite and micro-organic pollutants on groundwater, experiments were conducted on chlorination of nitrite-enriched water with precursor of antibiotics, and it was confirmed that the Cl2: N (molar ratio of chlorine to nitrite), contacting time, pH, and DO appreciably influenced the NAs formation potential. The molecular electric potential revealed that different dissociation status of precursors has a specific correlation with NAs formation potential (FP). The nitrite significantly increased the NAs FP because the reactive nitrogen species (RNS) formed in the oxidation process from nitrite to nitrate. Sequences of transformation products are determined to support the RNS promoted hypothesis of N-nitrosodimethylamine (NDMA) formation mechanism; furthermore, theoretical investigation in the reaction of dimethylamine (DMA) with different RNS verified the above hypothesis.
N -Nitrosodimethylamine (NDMA) is a nitrogenous disinfection by-product (DBP) that has been included in drinking water regulations worldwide because of its carcinogenicity and hazardousness. Anticipating the NDMA formation potential (FP) of...
We investigated the effectiveness of photocatalytic pretreatment (PCP) of precursors in minimizing the formation potentials (FPs) of carcinogenic nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodiethanolamine (NDELA), during water chloramination. A steel mesh substrate with immobilized TiO2 was highly efficient at mitigating nitrosamine formation and removing targeted precursors such as ranitidine, nizatidine, trimebutine, triethanolamine, and metoclopramide. Compared to UVC/H2O2, PCP under UVA irradiation (intensity of 0.67 mW cm⁻²) was more effective for reducing nitrosamine-FPs during post-chloramination. However, the PCP efficacies varied with the water source, pretreatment pH, and irradiation time. For example, PCP of eutrophic water increased the NDMA-FPs, but produced notable reductions (up to 99%) for NDELA- and NDEA-FPs. Shorter irradiation times, up to 15 min, increased the NDELA-FP in triethanolamine, and the NDMA-FP in nizatidine and trimebutine. However, the nitrosamine-FP decreased by >50% after PCP at a pH > 5.6, following irradiation for 120 min. Oxygen addition, N-de(m)ethylation, and N-dealkylation were responsible for decreasing nitrosamine-FPs via the destruction of key moieties; this has been elucidated by mass spectroscopy. This study suggests that PCP could be used as an alternative strategy for minimizing nitrosamine-FPs during water treatment.
Carcinogenic N, N-Dimethylnitrosamine (NDMA) has been reported to generate significantly during ozonation of fuel additive unsymmetrical dimethylhydrazine (UDMH), the combined ozone/Peroxy-Monosulfate (O3/PMS) technology was tried for reducing its formation in this study. The influence of PMS dosages, ozone concentrations, pH, Br⁻ and humic acid (HA) on NDMA formation from UDMH were investigated. In addition, the reduction mechanisms were explored by intermediates identification and Gaussian calculation. The results demonstrated that O3/PMS technology was effective on NDMA reduction, reaching an efficiency of 81% with 80 μM PMS. Higher NDMA reduction rates were achieved by O3/PMS with increasing pH within the scope of research (from 5 to 9), achieving a maximum of 69.9% at pH 9. The presence of bromide ion facilitated NDMA generation during ozonation, but the reduction efficiency by O3/PMS slightly improved from 66.3% to 70.6%. The presence of HA reduced NDMA formation in O3/PMS system. The contribution of SO4•− on NDMA reduction accounted for ~64%, which was higher than that of •OH (41.4%); however, its promotion role on conversing UDMH to NDMA was lower than O3. Therefore, the technology could reduce NDMA formation effectively. In addition, the results of Gaussian calculation manifested that the N atom in -NH2 group of UDMH was easily attacked not only by •OH but also by O3, so it is the key path that determines final NDMA formation. This study would provide reference for reducing NDMA formation during ozonation of UDMH-containing water matrixes.
Ensuring safe water supply for communities across the United States is a growing challenge due to aging infrastructure, impaired source water, strained community finances, etc. In 2019, about 6% of public water utilities in the U.S. had a health-based violation. Due to the high risk of exposure to various contaminants in drinking water, point-of-use (POU) drinking water treatment is rapidly growing in popularity in the U.S. and beyond. POU treatment technologies include various combinations of string-wound sediment filters, activated carbon, modified carbon, ion exchange and redox media filters, reverse osmosis membranes, and ultraviolet lamps depending on the contaminants of concern. While the technologies are well-proven, highly commoditized, and cost-effective, most systems offer little in the way of real-time performance monitoring or interactive technology like other smart home appliances (e.g., thermostats, smoke detectors, doorbells, etc.). Herein, we review water quality regulations and violations in the U.S. as well as state-of-the-art POU technologies and systems with an emphasis on their effectiveness at removing the contaminants most frequently reported in notices of violations. We conclude by briefly reviewing emerging smart water technologies and the needs for advances in the state-of-the-art technologies. The smartness of commercially available POU water filters is critiqued and a definition of smart water filter is proposed.
Background
In 2019, the United States Food and Drug Administration detected above-regulation levels of the human carcinogen N-nitrosodimethylamine (NDMA) in ranitidine, resulting in a complete removal of the medication from the market. NDMA is known to cause gastrointestinal malignancies in animal models.
Aim
To determine if patients who were receiving ranitidine have a higher risk of developing cancers of the digestive tract compared to patients taking other anti-reflux medications.
Methods
Using the nationwide database IBM Explorys, patients taking ranitidine were compared to patients on either famotidine or omeprazole. Incidence data of new malignancies of the oesophagus, stomach, liver, pancreas, and colon/rectum were obtained in 1-year intervals for up to 10 years. Two multivariable logistic regression models were used to calculate odds ratios (ORs), one adjusting for common risk factors for each cancer studied, and the other for demographic factors.
Results
Patients on ranitidine who were compared to patients on famotidine had ORs of 0.51(95% CI 0.43-0.60), 0.43(95% CI 0.36-0.51), 0.39(95% CI 0.36-0.41), 0.54(95% CI 0.49-0.62), and 0.46(95% CI 0.43-0.49) of developing oesophageal, gastric, hepatocellular, pancreatic, and colorectal cancers, respectively (P < 0.001). Patients on ranitidine compared to omeprazole had ORs of 0.62(95% CI 0.52-0.72), 0.58(95% CI 0.49-0.68), 0.81 (95% CI 0.76-0.86), 0.68(95% CI 0.60-0.76), and 0.66(95% CI 0.62-0.70) of developing oesophageal, gastric, hepatocellular, pancreatic, and colorectal cancers respectively (P < 0.001).
Conclusions
Use of ranitidine was not associated with an increased odds of developing gastrointestinal malignancies compared to omeprazole or famotidine use.
Disinfection is an essential process for both potable water and wastewater treatment plants. However, disinfection byproducts (DBPs) like trihalomethanes (THMs), haloacetonitriles (HANs), and nitrosamines (NOAs) are formed when organic matter precursors react with disinfectants such as chlorine, chloramine, and ozone. Formation of DBPs is strongly associated with the type of water source, type of disinfectant, and organic matter concentration, which can have seasonal variation. In this study, water samples were collected from 20 different intra-watershed locations, which included urban runoff (with and without the influence of unsheltered homeless populations), wastewater effluent discharges, and a large, terminal reservoir that serves as the local drinking water source. Samples were collected on dry and rainy days, which represent seasonal samples. DBP formation potential (FP) tests were conducted at consistent pH, contact time, and temperature. THMs, NOAs, and HANs were analyzed by gas chromatography-mass spectrometry (GC-MS). The FP tests performed on these water samples revealed that chlorine formed the highest THM concentrations, while THM concentrations were low for the ozone FP test as expected. Chloramine produced the greatest HAN concentrations, with dichloroacetonitrile representing the highest concentration. With respect to sample type, more DBPs were formed at the non-wastewater-impacted runoff sites as compared to the wastewater effluent discharge sites. With respect to TOC levels, rain event samples for all locations had higher TOC concentrations compared to dry sampling days. Similarly, rain event samples showed increased DBP formation; a significant amount of precursors for THMs was found in runoff waters that were influenced by wastewater effluent discharges and unsheltered homeless locations (concentration of total THMs for chlorine FP test was >200 µg/L). Therefore, urban runoff waters should be considered as potential sources of DBP precursors to drinking water source waters, and runoff water is prone to seasonal variation.
PolyDiallyldimethyl Ammonium Chloride (PolyDADMAC) is the most commonly used polymer at drinking water treatment plants and has the potential to form nitrosamines, like N-Nitrosodimethylamine (NDMA), if free polymer is present...
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 five N-nitrosamines were found below the risk level.
N-nitrosamines are contaminants of emerging concern, and controlling these chemicals in potable water and recycled water for potable reuse has become important for protecting public health. This study aimed to evaluate the influence of the alkyl chain lengths of N-nitrosamine precursors (secondary and tertiary amines) on the formation of N-nitrosamines via chloramination. The molar conversion efficiency from dimethylamine, an N-nitrosodimethylamine (NDMA) precursor, to NDMA (0.67%) was greater than that from diethylamine, an N-nitrosodiethylamine (NDEA) precursor, to NDEA (0.38%). Similarly, the molar conversion efficiency from trimethylamine to NDMA (0.92%) was greater than from triethylamine to NDEA (0.33%). Interestingly, a considerable difference in molar conversion efficiencies were observed for tertiary amines with the N,N-dialkyl-α-arylamine structure: the molar conversion efficiencies from N,N-dimethylbenzylamine and N,N-diethylbenzylamine to NDMA and NDEA were 50.2% and 1.7%, respectively. These results indicate that amines with ethyl groups have lower potentials for producing the corresponding N-nitrosamines than those with methyl groups. These differences in yields between amines with methyl and ethyl groups can be explained by the difference in electron density in the nitrogen atom of the amine, which influences the protonation of the amine and stabilization of intermediate species. These findings could be useful for enhancing source control of water and wastewater by regulating runoff or industrial wastewater containing high concentrations of specific N-nitrosamine precursors.
Removal of nitrosamines from water intended for consumption is an important topic due to the carcinogenic risks they pose to human health. In this study, we measure and compare nitrosamine removal by four individuals and three combinations of water treatments applied in situ as a pilot study and in the laboratory. Of the two advanced oxidation processes tested, UV irradiation at a wavelength of 254 nm was more effective in nitrosamine removal than ozonation; however, the efficacy of UV photolysis required a high dose (>635 mJ/cm²) for sufficient (>90 %) removal of the contaminants. The biological activated carbon (BAC) process was also effective at removing nitrosamines, most of which were adsorbed onto the carbon. A small fraction (<10 %) of nitrosamines were removed through biodegradation. Nanofiltration membranes were limited in removing nitrosamines, particularly N-nitrosodimethylamine, which is hydrophilic. Employing either UV or BAC treatments can warrant a high degree of elimination of nitrosamines; however, desorption of nitrosamines from BAC can occur due to variations in the quality of source water and the types of carbon filters used. Combined treatments using both UV and BAC processes offer promising alternative strategies for removing nitrosamines when treating water for human consumption.
N-nitrosodimethylamine (NDMA) is a carcinogenic disinfection by-product from water chloramination. Despite the identification of numerous NDMA precursors, essential parts of the reaction mechanism such as the incorporation of molecular O2 are poorly understood. In laboratory model systems for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the stoichiometries of monochloramine (NH2Cl) and aqueous O2 consumption, derived ¹⁸O-kinetic isotope effects (¹⁸O-KIE) for the reactions of aqueous O2, and studied the impact of radical scavengers on NDMA formation. While the molar NDMA yields from five N,N-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O2 per N,N-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small ¹⁸O-KIEs between 1.0026±0.0003 and 1.0092±0.0009 found for all precursors as well as completely inhibited NDMA formation in the presence of radical scavengers (ABTS and trolox) imply that O2 reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH2Cl and N-peroxyl radicals from the reaction of aminyl radicals with aqueous O2 are part of the NDMA formation mechanism.
Nitrosamines are toxic and emerging disinfection byproducts. In this study, three drinking water treatment plants (DWTPs) in southern Taiwan treating the same source water in Gaoping River with comparable technologies were selected. The objective was to evaluate the formation and fates of six nitrosamines and their formation potentials (FPs) from a surface water source to drinking water. Albeit decreased further downstream in the river, four nitrosamine-FPs were observed in the source water due to anthropogenic pollution in the upstream areas. In the DWTPs, nitrosamines were formed and NDMA was the main species. While high organic carbon concentrations indicated elevated nitrosamine-FPs in the source water, NDMA formation in the DWTPs was more positively associated with reductions of water parameters that quantify organic matters with double bonded ring structures. Although precursor removal via pre-oxidation is a viable approach to limit nitrosamine formation during post-disinfection, this study clearly indicates that a great portion of NDMA in treated water has been formed in the 1st oxidation step of drinking water treatment. The pre-oxidation simulations in the lab demonstrated the impact of pre-chlorination on nitrosamine formation. Given the limited removal in conventional treatment processes, avoiding nitrosamine-FPs in sources and/or nitrosamine formation during pre-oxidation become important issues to control the threats of nitrosamines in drinking water. Under current circumstance in which pre-oxidation is widely used to optimize the treatment effectiveness in many DWTPs, its adverse effect by forming nitrosamines needs to be carefully minimized and using technologies other than pre-chlorination (e.g., pre-ozonation) may be considered.
UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (~5.5) coupled with the effective rejection of NH4+ promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H+ ↔ NHCl2 + NH4+. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.
The impact of fouling substances on the rejection of four N-nitrosamines by a reverse osmosis (RO) membrane was evaluated via a systematic characterisation of individual organic fractions in a secondary wastewater effluent and the deployment of a novel high-performance liquid chromatography-photochemical reaction-chemiluminescence (HPLC-PR-CL) analytical technique. The HPLC-PR-CL analytical technique allowed for a systematic examination of the correlation between the fouling level and the permeation of N-nitrosamines in the secondary wastewater effluent and synthetic wastewaters through an RO membrane. Membrane fouling caused by the secondary wastewater effluent led to a notable decrease in the permeation of N-nitrosodimethylamine (NDMA) while a smaller but nevertheless discernible decrease in the permeation of N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR) and N-nitrosomorpholine (NMOR) was also observed. The decrease in N-nitrosamine permeation became insignificant after membrane permeability decreased by approximately 30%. Fluorescence spectrometry analysis revealed that major foulants in the secondary wastewater effluent were humic and fulvic acid-like substances. Analysis using the size exclusion chromatography technique also identified polysaccharides and proteins as additional fouling substances. Thus, further examination was conducted using solutions containing model foulants (i.e., sodium alginate, bovine serum albumin, humic acid and two fulvic acids). Similar to the secondary wastewater effluent, membrane fouling with fulvic acid solutions resulted in a decrease in N-nitrosamine permeation. In contrast, membrane fouling with the other model foulants resulted in an increase in N-nitrosamine permeation. Overall, these results suggest that the impact of fouling on the permeation of N-nitrosamines by RO is governed by specific small organic fractions (e.g. fulvic acid-like organics) in the secondary wastewater effluent.
Water treatment combining advanced oxidative processes with subsequent exposure to biological activated carbon (BAC) holds promise for the attenuation of recalcitrant pollutants. Here we contrast oxidation and subsequent biofiltration of treated wastewater effluent employing either ozone or UV/H2O2 followed by BAC during pilot-scale implementation. Both treatment trains largely met target water quality goals by facilitating the removal of a suite of trace organics and bulk water parameters. N-nitrosodimethylamine (NDMA) formation was observed in ozone fed BAC columns during biofiltration and to a lesser extent in UV/H2O2 fed columns and was most pronounced at 20 min of empty bed contact time (EBCT) when compared to shorter EBCTs evaluated. While microbial populations were highly similar in the upper reaches, deeper samples revealed a divergence within and between BAC filtration systems where EBCT was identified to be a significant environmental predictor for shifts in microbial populations. The abundance of Nitrospira in the top samples of both columns provides an explanation for the oxidation of nitrite and corresponding increases in nitrate concentrations during BAC transit and support interplay between nitrogen cycling with nitrosamine formation. The results of this study demonstrate that pretreatments using ozone versus UV/H2O2 impart modest differences to the overall BAC microbial population structural and functional attributes, and further highlight the need to evaluate NDMA formation prior to full-scale implementation of BAC in potable reuse applications.
Ozonation followed by biological activated carbon (O3/BAC) is being considered as a key component of reverse osmosis-free advanced treatment trains for potable wastewater reuse. Using a laboratory-scale O3/BAC system treating two nitrified wastewater effluents, this study characterized the effect of different ozone dosages (0-1.0 mg O3/mg dissolved organic carbon) and BAC empty bed contact times (EBCT; 15-60 minutes) on the formation after chlorination or chloramination of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), 8 N-nitrosamines, and bromate. DBP concentrations were remarkably similar between the two wastewaters across O3/BAC conditions. Ozonation increased bromate, TCNM and N-nitrosodimethylamine, but ozonation was less significant for other DBPs. DBP formation generally decreased significantly with BAC treatment at 15 minute EBCT, but little further reduction was observed at higher EBCT where low dissolved oxygen concentrations may have limited biological activity. The O3/BAC-treated wastewaters met regulatory levels for trihalomethanes (THMs), haloacetic acids (HAAs), and bromate, although N-nitrosodimethylamine exceeded the California Notification Level in one case. Regulated THMs and HAAs dominated by mass. When DBP concentrations were weighted by measures of their toxic potencies, unregulated haloacetonitriles, haloacetaldehydes and haloacetamides dominated. Assuming toxicity is additive, the calculated DBP-associated toxicity of the O3/BAC-treated chloraminated effluents were comparable or slightly higher than those calculated in a recent evaluation of Full Advanced Treatment trains incorporating reverse osmosis.
N-nitrosamines are potent mutagens and carcinogens that can be formed during oxidative water treatment. This study describes a novel method for the determination of total N-nitrosamines by UV-photolysis and subsequent chemiluminescence detection of nitric oxide. Denitrosation of N-nitrosamines was accomplished with a microphotochemical reactor consisting of a knitted reaction coil and a low-pressure mercury lamp. The detection limits for differing N-nitrosamines ranged between 0.07 μM (14 pmol injected) and 0.13 μM (26 pmol injected). The nitric oxide formation from selected N-nitrosamines was linear (R(2)=0.98-0.99) from 0.1 and 10 μM. The small cross-section and volume of the microphotochemical reactor used in this study was optimal to reach a sensitivity level comparable to chemical denitrosation-based methods. In addition, this method had several advantages over other similar methods: (i) compared to chemical denitrosation with copper monochloride or triiodide, the UV-photolysis doesn't require chemicals and is not affected by interferences of by-products (e.g. formation of NOI), (ii) the reproducibility of replicates was enhanced compared to the triiodide-based method and iii a commercially available photoreactor and NO analyzer were used. The application of this method for the determination of the N-nitrosamine formation potential of personal care products demonstrates its utility for assessing whether N-nitrosodimethylamine (NDMA) or other specific nitrosamines of current interest are dominant or minor components, respectively, of the total N-nitrosamine pool in technical aquatic systems or biological samples.
A comparison of loadings of N-nitrosamines and their precursors from different source water categories is needed to design effective source water blending strategies. Previous research using Formation Potential (FP) chloramination protocols (high dose and prolonged contact times) raised concerns about precursor loadings from various source water categories, but differences in the protocols employed rendered comparisons difficult. In this study, we applied Uniform Formation Condition (UFC) chloramination and ozonation protocols mimicking typical disinfection practice to compare loadings of ambient specific and total N-nitrosamines as well as chloramine-reactive and ozone-reactive precursors in 47 samples, including 6 pristine headwaters, 16 eutrophic waters, 4 agricultural runoff samples, 9 stormwater runoff samples, and 12 municipal wastewater effluents. N-Nitrosodimethylamine (NDMA) formation from UFC and FP chloramination protocols did not correlate, with NDMA FP often being significant in samples where no NDMA formed under UFC conditions. N-Nitrosamines and their precursors were negligible in pristine headwaters. Conventional, and to a lesser degree, nutrient removal wastewater effluents were the dominant source of NDMA and its chloramine- and ozone-reactive precursors. While wastewater effluents were dominant sources of TONO and their precursors, algal blooms, and to a lesser degree agricultural or stormwater runoff, could be important where they affect a major fraction of the water supply.
Nanofiltration (NF) is a promising technology for removing precursors of disinfection byproducts (DBPs) from source waters prior to oxidant addition in water treatment. The aims of this study were to investigate (i) the removal efficiencies of N-nitrosodimethylamine (NDMA), halonitromethane (HNM), and trihalomethane (THM) precursors by NF membranes from different source water types (i.e. surface water, wastewater impacted surface water, and municipal and industrial wastewater treatment effluents), (ii) the impact of membrane type, and (iii) the effects of background water components (i.e., pH, ionic strength, and Ca²⁺) on the removal of selected DBP precursors from different source waters. The results showed the overall precursor removal efficiencies were 57–83%, 48–87%, and 72–97% for NDMA, HNM, and THM precursors, respectively. The removal of NDMA precursors decreased with the increases in average molecular weight cut off and negative surface charge of NF membranes tested, while the removal of THM precursors was slightly affected. pH changes increased the removal of NDMA precursors, but pH did not affect the removal of THM and HNM precursors in municipal WWTP effluent. On the other hand, pH changes had little or no effect on DBP removal from industrial WWTP effluent. In addition, regardless of the membrane type or background water type/characteristics, ionic strength did not show any impact on DBP precursor removals. Lastly, an increase in Ca²⁺ concentration enhanced the removal of NDMA precursors while a slight decrease and no effect was observed for THM and HNM precursors, respectively, in municipal WWTP effluent.
Compounds with N,N-dimethylhydrazine moieties ((CH3)2N-N-) form N-nitrosodimethylamine (NDMA) during ozonation, but the relevant reaction chemistry is hitherto poorly understood. This study investigated the reaction kinetics and mechanisms of NDMA formation during ozonation of unsymmetrical dimethylhydrazine (UDMH) and daminozide (DMZ) as structural model N,N-dimethylhydrazine compounds. The reaction of ozone with these NDMA precursor compounds was fast, and kO3 at pH 7 was 2 × 10⁶ M⁻¹ s⁻¹ for UDMH and 5 × 10⁵ M⁻¹ s⁻¹ for DMZ. Molar NDMA yields (i.e., Δ[NDMA]/Δ[precursor] × 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O3]0/[precursor]0) of ≥4 in the presence of tert-butanol as hydroxyl radical ([radical dot]OH) scavenger. The molar NDMA yields decreased significantly in the absence of tert-butanol, indicating [radical dot]OH formation and its subsequent reaction with the parent precursors forming negligible NDMA. The k[radical dot]OH at pH 7 was 4.9 × 10⁹ M⁻¹ s⁻¹ and 3.4 × 10⁹ M⁻¹ s⁻¹ for UDMH and DMZ, respectively. Reaction mechanisms are proposed in which an ozone adduct is formed at the nitrogen next to N,N-dimethylamine which decomposes via homolytic and heterolytic cleavages of the –N⁺-O-O-O⁻ bond, forming NDMA as a final product. The heterolytic cleavage pathway explains the significant [radical dot]OH formation via radical intermediates. Overall, significant NDMA formation was found to be unavoidable during ozonation or even O3/H2O2 treatment of waters containing N,N-dimethylhydrazine compounds due to their rapid reaction with ozone forming NDMA with high yield. Thus, source control or pre-treatment of N,N-dimethylhydrazine precursors and post-treatment of NDMA are proposed as the mitigation options.
Carcinogenic nitrosamines have received much attention due to their formation in CO2 capture processes and probable emission into the atmosphere. Fortunately, nitrosamines are decomposed by exposure to UV irradiation. This may be an effective strategy to degrade nitrosamines, forming more benign products in the process. In this work, UV photolysis was used to examine the degradation kinetics and fate of nitrosamines (i.e., N-nitrosodiethylamine (NDEA), N-nitrosodibutylamine (NDBA), N-nitrosodimethylamine (NDMA), N-nitrosodiethanolamine (NDELA), and N-nitrosopyrrolidine (NPYR)) in water at 40°C. Nearly all nitrosamines were decomposed within the first 10 min of photodegradation using 4 W, low pressure Hg lamp. Pseudo-first order reaction rate constants were 1.8 × 10-2, 2.6 × 10-2, 2.6 × 10-2, 2.3 × 10-2, and 1.4 × 10-2 L/W-min for NDEA, NDBA, NDMA, NDELA, and NPYR, respectively. There was minimal change in total organic carbon (TOC) and total nitrogen (TN), suggesting negligible loss of nitrosamines and photodegradation products by evaporation.
Wastewater-derived organic nitrogen (org-N) can act as both nutrients and carcinogenic nitrogenous disinfection byproduct precursors. In this study, the concentration, composition, bioavailability, and N-nitrosodimethylamine (NDMA) formation potential of particulate organic nitrogen (PON) from three different municipal wastewater treatment plants were characterized and compared with that of effluent dissolved organic nitrogen (DON). The average effluent PON and DON concentrations ranged from 0.09 to 0.55 mg N/L and from 0.91 to 1.88 mg N/L, respectively. According to principal component analysis, org-N composition and characterization differed in PON and DON samples (n = 20). Compared with DON, PON tended to be enriched in protein and nucleic acids, and showed a more proteinaceous character. Composition of org-N functional groups estimated from the X-ray photoelectron spectroscopy N 1s spectra indicate no significant differences in the molecular weight distribution of the protein-like materials between PON and DON. Moreover, PON exhibited a significantly higher bioavailability (61.0 ± 13.3%) compared to DON (38.5 ± 12.4%, p ˂ 0.05, t-test) and a significantly higher NDMA yields (791.4 ± 404.0 ng/mg-N) compared to DON (374.8 ± 62.5 ng/mg-N, p ˂ 0.05, t-test). Accordingly, PON contributed to approximately 12.3–41.7% of the total bioavailable org-N and 22.0–38.4% of the total NDMA precursors in wastewater effluents. Thus, the potential adverse effects of PON on wastewater discharge and reuse applications should not be overlooked, even though it only accounted for 7.4–26.8% of the total effluent org-N.
A fast and reliable analytical technique was evaluated and validated for determination of N-nitrosodimethylamine (NDMA) formation and rejection by reverse osmosis (RO) membranes in potable water reuse applications. The analytical instrument used in this study is high-performance liquid chromatography (HPLC), photochemical reaction (PR) and chemiluminescence (CL) - namely HPLC-PR-CL. Results reported here show that HPLC-PR-CL can be used to measure NDMA with a similar level of accuracy compared to conventional and more time-consuming techniques using gas chromatography and tandem mass spectrometry detection in combination with solid phase extraction. Among key residual chemicals (i.e. monochloramine, hydrogen peroxide and hypochlorite) in reclaimed wastewater, hypochlorite was the only constituent that interfered with the determination of NDMA by HPLC-PR-CL. However, hypochlorite interference was eliminated by adding ascorbic acid as a reducing agent. Direct injection of ultrafiltration (UF)-treated wastewater samples into HPLC-PR-CL also resulted in an underestimation of the NDMA concentration possibly due to interference by organic substances in the UF-treated wastewater. Accurate determination of NDMA concentrations in UF-treated wastewater was achieved by reducing the sample injection volume from 200 to 20 μL, though this increased the method detection limit from 0.2 to 2 ng/L. In contrast, no interference was observed with RO permeate. These results suggest that RO membranes could remove part of substances that interfere with the NDMA analysis by HPLC-PR-CL. In addition, RO treatment experiments demonstrated that HPLC-PR-CL was capable of evaluating near real-time variation in NDMA rejection by RO.
The removal of N-nitrosodimethylamine (NDMA) formation potential through a membrane bioreactor (MBR) coupled to a nanofiltration (NF) pilot plant that treats urban wastewater is investigated. The results are compared to the fate of the individual NDMA precursors detected: azithromycin, citalopram, erythromycin, clarithromycin, ranitidine, venlafaxine and its metabolite o-desmethylvenlafaxine. Specifically, the effect of dissolved oxygen in the aerobic chamber of the MBR pilot plant on the removal of NDMA formation potential (FP) and individual precursors is studied.
During normal aerobic operation, implying a fully nitrifying system, the MBR was able to reduce NDMA precursors above 94%, however this removal percentage was reduced to values as low as 72% when changing the conditions to minimize nitrification. Removal decreased also for azithromycin (68–59%), citalopram (31–17%), venlafaxine (35–15%) and erythromycin (61–16%) on average during nitrifying versus non-nitrifying conditions. The removal of clarithromycin, o-desmethylvenlafaxine and ranitidine could not be correlated with the nitrification inhibition, as it varied greatly during the experiment time. The MBR pilot plant is coupled to a nanofiltration (NF) system and the results on the rejection of both, NDMA FP and individual precursors, through this system was above 90%.
Finally, results obtained for the MBR pilot plant are compared to the percentage of removal by a conventional full scale biological wastewater treatment plant (WWTP) fed with the same influent. During aerobic operation, the removal of NDMA FP by the MBR pilot plant was similar to the full scale WWTP.
Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) and epichlorohydrin-dimethylamine (Epi-DMA), are commonly used by water utilities to enhance removal of particles and dissolved organic matter (DOM) from raw waters. Unfortunately, chloramination of waters treated with quaternary ammonium polymers leads to the formation of carcinogenic N-nitrosodimethylamine (NDMA). In this study, two approaches were developed to modify polyDADMAC and Epi-DMA to inhibit N-nitrosamine formation. The first approach involved treatment of polymers with methyl iodide (MeI), an alkylating agent, to convert polymer-bound tertiary amine groups to less chloramine-reactive quaternary ammonium groups. The second approach involved synthesis of polymers bearing less chloramine-reactive quaternary ammonium groups with dipropylamino (DPA) substituents. Treatment with MeI reduced NDMA formation from polymers by ∼75%, while synthesis of DPA-based polymers eliminated NDMA formation and formed N-nitrosodipropylamine, which is 10-fold less carcinogenic than NDMA, at 20-fold lower yields. Bench-scale jar tests demonstrated that both MeI-treated and DPA-based polymers achieved similar removal of particles and DOM as the original polyDADMAC and Epi-DMA at both low and high doses, but formed significantly less N-nitrosamines. This work demonstrates two approaches for modifying quaternary ammonium cationic polymers, which may enable water utilities to meet potential future regulations on N-nitrosamines while maintaining polymer usage to meet existing regulations.
N-Nitrosamines (NAs) in drinking water have attracted considerable attention in recent years due to their high carcinogenicity, frequent occurrence, and their potential regulation. During the past three years, we have collected about 164 water samples of finished water, tap water, and source water from 23 provinces, 44 cities from large cities to small towns, and 155 sampling points all over China. The occurrence of NAs in the finished and tap water was much higher in China than that in the U.S. Nine NAs were measured and NDMA had the highest concentration. The occurrence of NDMA was in 33% of the finished waters of water treatment plants and in 41% of the tap waters. The average NDMA concentration in finished and tap waters was 11 and 13 ng/L, respectively. Formation potentials (FPs) of source waters were examined with an average NDMA FP of 66 ng/L. Large variations in NA occurrence were observed geographically in China and temporally in different seasons. The Yangtze River Delta area, one sub-area in East China, had the highest concentrations of NAs, where the average NDMA concentrations in the finished and tap water were 27 and 28.5 ng/L, respectively, and the average NDMA FP in the source water was 204 ng/L. NA control may be achieved by applying breakpoint free chlorination and/or advanced treatment of ozone - granular activated carbon process to remove the NA precursors before disinfection.
Removal of N-nitrosodimethylamine (NDMA) in drinking water treatment poses a significant technical challenge due to its small molecular size, high polarity and water solubility, and poor biodegradability. Degradation of NDMA and its precursor, dimethylamine (DMA), was investigated by adsorbing them from aqueous solution using porous mineral sorbents, followed by destruction under microwave irradiation. Among the mineral sorbents evaluated, dealuminated ZSM-5 exhibited the highest sorption capacities for NDMA and DMA, which decreased with the density of surface cations present in the micropores. In contrast, the degradation rate of the sorbed NDMA increased with the density of surface cations under microwave irradiation. Evolutions of the degradation products and C/N ratio indicate that the sorbed NDMA and DMA could be eventually mineralized under continuous microwave irradiation. The degradation rate was strongly correlated with the bulk temperature of ZSM-5 and microwave power, which is consistent with the mechanism of pyrolysis caused by formation of micro-scale “hot spots” within the mineral micropores under microwave irradiation. Compared to existing treatment options for NDMA removal, microporous mineral sorption coupled with microwave-induced degradation has the unique advantages of being able to simultaneously remove NDMA and DMA and cause their full mineralization, and thus could serve as a promising alternative method.
Distribution system storage facilities are a critical, yet often overlooked, component of the urban water infrastructure. This study showed elevated concentrations of N-nitrosodimethylamine (NDMA), total N-nitrosamines (TONO), regulated trihalomethanes (THMs) and haloacetic acids (HAAs), 1,1-dichloropropanone (1,1-DCP), trichloroacetaldehyde (TCAL), haloacetonitriles (HANs), and haloacetamides (HAMs) in storage facility waters undergoing nitrification as compared to non-nitrifying waters within 15 storage facilities in five different chloraminated drinking water distribution systems. The concentrations of NDMA, TONO, HANs, and HAMs in the nitrifying waters further increased upon application of simulated distribution system chloramination. The addition of a nitrifying biofilm sample collected from a nitrifying facility to its non-nitrifying influent water led to increases in N-nitrosamine and halogenated DBP formation, suggesting the release of precursors from nitrifying biofilms. Periodic treatment of nitrifying facilities with breakpoint chlorination (BPC) temporarily suppressed nitrification and reduced precursor levels for N-nitrosamines, 1,1-DCP, TCAL, HANs, and HAMs, as reflected by lower concentrations of these DBPs measured after re-establishment of a chloramine residual within a facility than prior to BPC treatment. However, BPC promoted halogenated DBP formation while a free chlorine residual was maintained. Strategies that minimize application of free chlorine while preventing nitrification are needed to control DBP precursor release in the nitrifying storage facilities.
N-Nitrosodimethylamine (NDMA) is a disinfection by-product (DBP) that is potentially carcinogenic and has been found to occur in drinking water treatment systems impacted with treated wastewater. A major gap in NDMA research is an understanding of the persistence of wastewater-derived precursors within the natural environment. This research sought to fill this knowledge gap by surveying NDMA precursors across the length of a wastewater effluent-dominated wash. Significant precursor reduction (17%) was found to occur from introduction into the wash to a point 9 h downstream. This reduction translates into a half-life of roughly 32 h for bulk NDMA precursors. Further laboratory experiments examining rates of photolysis, biodegradation and loss to sediments, illustrated that both photolytic and biological degradation were effective removal mechanisms for NDMA precursors. Loss to sediments that were acquired from the wash did not appear to reduce NDMA precursors in the water column, although a control conducted with DI water provided evidence that significant NDMA precursors could be released from autoclaved sediments (suggesting that sorption does occur). Microbial experiments revealed that microbes associated with sediments were much more effective at degrading precursors than microbes within the water column. Overall, this study demonstrated that natural processes are capable of attenuating NDMA precursors relatively quickly within the environment, and that utilities might benefit from maximizing source water residency time in the environment, prior to introduction into treatment plants.
N-nitrosamines and their precursors are significant concerns for utilities exploiting wastewater-impacted water supplies, particularly those practicing potable reuse of wastewater. Previous efforts to identify specific precursors in municipal wastewater accounting for N-nitrosamine formation have met with limited success. As an alternative, we quantified the relative importance of greywater (i.e., shower, kitchen sink, bathroom washbasin and laundry) and blackwater (i.e., urine and feces) streams in terms of their loadings of ambient specific and total N-nitrosamines and chloramine-reactive and ozone-reactive N-nitrosamine precursors to domestic sewage. Accounting for the volume fractions of individual greywater and blackwater streams, laundry water represented the most significant source of N-nitrosamines and their precursors, followed by shower water and urine. Laundry water was particularly important for ozone-reactive N-nitrosamine precursors, accounting for ~98% of N-nitrosodimethylamine (NDMA) precursors and ~70% of precursors for other uncharacterized N-nitrosamines. For the other greywater streams, consumer products contributed additional N-nitrosamines and precursors, but the remarkable uniformity across different products suggested the importance of common macroconstituents. Consumption of a standard dose of the antacid, ranitidine, substantially increased NDMA and its chloramine-reactive precursors in urine. Nevertheless, nearly 40% of the American population would need to consume ranitidine daily to match the NDMA loadings from laundry water.
Some N-nitrosamines (NAs) have been identified as emerging disinfection by-products during water treatment. Thus, it is essential to understand the characteristics of the NA precursors. In this study, the polarity rapid assessment method (PRAM) and the classical resin fractionation method were studied as methods to fractionate the NA precursors during drinking water treatment. The results showed that PRAM has much higher selectivity for NA precursors than the resin approach. The normalized N-nitrosodimethylamine formation potential (NDMA FP) and N-nitrosodiethylamine (NDEA) FP of four resin fractions was at the same level as the average yield of the bulk organic matter whereas that of the cationic fraction by PRAM showed 50 times the average. Thus, the cationic fraction was shown to be the most important NDMA precursor contributor. The PRAM method also helped understand which portions of the NA precursor were removed by different water treatment processes. Activated carbon (AC) adsorption removed over 90% of the non-polar PRAM fraction (that sorbs onto the C18 solid phase extraction [SPE] cartridge) of NDMA and NDEA precursors. Bio-treatment removed 80–90% of the cationic fraction of PRAM (that is retained on the cation exchange SPE cartridge) and 40–60% of the non-cationic fractions. Ozonation removed 50–60% of the non-polar PRAM fraction of NA precursors and transformed part of them into the polar fraction. Coagulation and sedimentation had very limited removal of various PRAM fractions of NA precursors.
N-nitrosodimethylamine (NDMA) is an emerging disinfection by-product, and we show that use of chlorine dioxide (ClO2) has the potential to increase NDMA formation in waters containing precursors with hydrazine moieties. NDMA formation was measured after oxidation of 13 amines by monochloramine, ClO2 and pre-treatment with ClO2 followed by post-monochloramination. Daminozide, a plant growth regulator, was found to yield 5.01±0.96% NDMA upon reaction with ClO2, although no NDMA was recorded during chloramination. The reaction rate was estimated to be ~0.0085 s-1 and based upon our identification by mass spectrometry spectra of intermediates the reaction likely proceeds via the hydrolytic release of unsymmetrical dimethylhydrazine (UDMH), with the hydrazine structure a key intermediate in NDMA formation. The presence of UDMH was confirmed by gas chromatography-mass spectrometry (GC-MS) analysis. For 10 of the 13 compounds, ClO2 pre-oxidation reduced NDMA yields compared with monochloramination alone, which is explained by our measured release of DMA. This work shows potential pre-oxidation strategies to control NDMA formation may not impact all organic precursors uniformly, so differences might be source specific depending upon occurrence of different precursors in source waters. For example, daminozide is a plant regulator so drinking water that intakes heavily influenced by upstream agricultural runoff could be at risk.
Utilities using chloramines need strategies to mitigate nitrosamine formation to meet potential future nitrosamine regulations. The ability to reduce NDMA formation under typical post-chloramination conditions of pretreatment with ultraviolet light from a low pressure mercury lamp (LPUV), free chlorine (HOCl), ozone (O3), and UV light from a medium pressure mercury lamp (MPUV) were compared at exposures relevant to drinking water treatment. The order of efficacy after application to waters impacted by upstream wastewater discharges was O3 > HOCl ≈ MPUV > LPUV. NDMA precursor abatement generally did not correlate well between oxidants, and waters exhibited different behaviors with respect to pH and temperature, suggesting a variety of source-dependent NDMA precursors. For wastewater-impacted waters, the observed pH dependence for precursor abatement suggested the important role of secondary or tertiary amine precursors. Although hydroxyl radicals did not appear to be important for NDMA precursor abatement during O3 or MPUV pretreatment, the efficacy of MPUV correlated strongly with dissolved organic carbon concentration (p = 0.01), suggesting alternative indirect photochemical pathways. The temperature dependences during pre- and post-disinfection indicated that NDMA formation is likely to increase during warm seasons for O3 pretreatment, decrease for HOCl pretreatment, and remain unchanged for MPUV treatment, although seasonal changes in source water quality may counteract the temperature effects. For two waters impacted by relatively high polyDADMAC coagulant doses, pretreatment with HOCl, O3, and MPUV increased NDMA formation during post-chloramination. For O3 pretreatment, hydroxyl radicals likely led to precursor formation from the polymer in the latter tests. MPUV treatment of polymer-impacted water increased subsequent NDMA formation through an indirect photochemical process. Many factors may mitigate the importance of this increased NDMA formation, including the low polyDADMAC doses typically applied, and simultaneous degradation of watershed-associated precursors.
Copyright © 2015 [The Author/The Authors]. Published by Elsevier Ltd.. All rights reserved.
The formation of nitrosamines in drinking water was first reported in the early 1990s. These compounds are classified as probable human carcinogens, so their control presents a challenge to authorities in providing a safe water supply to the public. Generally, nitrosamines in water supplies are the result of disinfection by chlorine or chloramines, and the standard control strategy has been to minimize their formation by changing treatment processes, often including the addition of an ultraviolet irradiation stage. This problem has now been exacerbated by the discovery that high levels of N-nitrosodimethylamine (NDMA) in newly constructed pipelines result from NDMA leaching from the rubber sealing rings used to connect the pipes. This study strongly suggests that NDMA and other nitrosamines could be present for several years in distribution systems with rubber components. Furthermore, the occurrence of nitrosamines in drinking water was independent of both the type and presence of disinfectant.2011
N-Nitrosodimethylamine (NDMA) is a probable human carcinogen that forms in drinking water as a disinfection byproduct. Several specific precursor chemicals present during chloramination are known but cannot account for the total observed NDMA formation potential (FP) in drinking waters. We discovered a pharmaceutical precursor of NDMA with high FP using a liquid chromatography/quadrupole/time-of-flight mass spectrometry (LC/QTOF-MS) screening procedure. The pharmaceutical methadone, which is used to mitigate heroin withdrawal symptoms and is also prescribed for chronic pain, contains a dimethylisopropylamine functional group that reacts to form large amounts of NDMA upon chloramination. In this study, methadone had a molar NDMA yield ranging from 23 to 70% depending on chloramine dose (1–150 mg of Cl2/L) and was responsible for between 1 and 10% of NDMA FP in most raw surface waters in which it was detected and up to 62% of NDMA FP in wastewater. Samples with higher methadone concentrations had greater NDMA FP. We measured a median methadone concentration of 23 ng/L with a range of 1–2256 ng/L among detections, which was consistent with high occurrence rates and environmental persistence for methadone in the published literature for surface waters and wastewaters. A literature review of methadone use, metabolism, and fate in the United States resulted in a prediction of low nanogram per liter levels of methadone-associated NDMA FP at drinking water treatment plants (DWTPs) downstream of communities using methadone. Medicinal use of methadone potentially displaces and transforms the health risks associated with heroin use by individuals to possible cancer risk for populations served by downstream DWTPs. This work is among the first to contrast known public health benefits of pharmaceutical-taking patients against the potential exposure of millions of people to physiologically relevant levels of carcinogenic NDMA in chloraminated drinking water.
Wildfire occurrence and intensity are increasing worldwide causing severe disturbances to forest watersheds used for potable water supply. The effects of wildfire on drinking water quality are not well understood, especially in terms of terrestrial dissolved organic matter (DOM) and DOM-associated formation of disinfection byproducts (DBP). As the forest floor layer is a major source of terrestrial DOM, we investigated characteristics and DBP formation of water extractable organic matter (WEOM) from the 0-5 cm depth of non-burned detritus (control) and burned detritus with black ash (moderate severity) and white ash (high severity) associated with the 2013 Rim Fire in California. Spectroscopic results suggested that the aromaticity of WEOM followed white ash > control > black ash and fluorescence region II (excitation 220-250 nm; emission 330-380 nm) of the emission-excitation-matrix was identified as a potential burn severity indicator. Compared to the control, WEOM from white and black ashes had lower reactivity in forming trihalomethanes (55%-of-control) and haloacetic acids (67%-of-control), but higher reactivity in forming the more carcinogenic haloacetonitrile after chlorination (244%-of-control) and N-nitrosodimethylamine after chloramination (229%-of-control). There was no change in reactivity for chloral hydrate formation, while WEOM from black ash showed a higher reactivity for haloketone formation (150%-of-control). Because wildfire consumed a large portion of organic matter from the detritus layer, there was lower water extractable organic carbon (27%-of-control) and organic nitrogen (19%-of-control) yields in ashes. Consequently, the wildfire caused an overall reduction in water extractable terrestrial DBP precursor yield from detritus materials.
During ozonation of drinking water, the fungicide metabolite N,N-dimethylsulfamide (DMS) can be transformed into a highly toxic product, N-nitrosodimethylamine (NDMA). We used quantum chemical computations and stopped-flow experiments to evaluate a chemical mechanism proposed previously to describe this transformation. Stopped-flow experiments indicate a pKa = 10.4 for DMS. Experiments show that hypobromous acid (HOBr), generated by ozone oxidation of naturally occurring bromide, brominates the deprotonated DMS(-) anion with a near-diffusion controlled rate constant (7.1 ± 0.6 × 10(8) M(-1) s(-1)), forming Br-DMS(-) anion. According to quantum chemical calculations, Br-DMS has a pKa ∼ 9.0 and thus remains partially deprotonated at neutral pH. The anionic Br-DMS(-) bromamine can react with ozone with a high rate constant (10(5±2.5) M(-1) s(-1)), forming the reaction intermediate (BrNO)(SO2)N(CH3)2(-). This intermediate resembles a loosely bound complex between an electrophilic nitrosyl bromide (BrNO) molecule and an electron-rich dimethylaminosulfinate ((SO2)N(CH3)2(-)) fragment, based on inspection of computed natural charges and geometric parameters. This fragile complex undergoes immediate (10(10±2.5) s(-1)) reaction by two branches: an exothermic channel that produces NDMA, and an entropy-driven channel giving non-NDMA products. Computational results bring new insights into the electronic nature, chemical equilibria, and kinetics of the elementary reactions of this pathway, enabled by computed energies of structures that are not possible to access experimentally.
Elevated concentrations of N-nitrosodimethylamine (NDMA) were detected in a distribution system during routine monitoring. The high concentrations were localized, and a temporary storage tank was suspected to be the source of the problem. Samples of the gaskets used in the construction of the temporary tank were gathered and subjected to bench-scale tests. These tests demonstrated that the gaskets, when exposed to system water, did produce NDMA as well as other nitrosamines. Chloramine did not contribute to NDMA or N-nitrosodi-n-butylamine (NDBA) leaching from gasket material. 2014