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

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

N-nitrosodimethylamine exposure to zebrafish embryos/larvae causes cardiac and spinal developmental toxicity

N-nitrosodimethylamine (NDMA), one of the new nitrogen-containing disinfection by-products, is potentially cytotoxic, genotoxic, and carcinogenic. Its potential toxicological effects have attracted a wide range of attention, but the mechanism is still not sufficiently understood. To better understand the toxicological mechanisms of NDMA, zebrafish embryos were exposed to NDMA from 3 h post-fertilization (hpf) to 120hpf. Mortality and malformation were significantly increased, and hatching rate, heart rate, and swimming behavior were decreased in the exposure groups. The result indicated that NDMA exposure causes cardiac and spinal developmental toxicity. mRNA levels of genes involved in the apoptotic pathway, including p53, bax, and bcl-2 were significantly affected by NDMA exposure. Moreover, the genes associated with spinal and cardiac development (myh6, myh7, nkx2.5, eph, bmp2b, bmp4, bmp9, run2a, and run2b) were significantly downregulated after treatment with NDMA. Wnt and TGF-β signaling pathways, crucial for the development of diverse tissues and organs in the embryo and the establishment of the larval spine, were also significantly disturbed by NDMA treatment. In summary, the disinfection by-product, NDMA, exhibits spinal and cardiac developmental toxicity in zebrafish embryos, providing helpful information for comprehensive analyses and a better understanding the mechanism of its toxicity.

Risk characterization of N-nitrosodimethylamine in pharmaceuticals

Since 2018, N-nitrosodimethylamine (NDMA) has been a reported contaminant in numerous pharmaceutical products. To guide the pharmaceutical industry, FDA identified an acceptable intake (AI) of 96 ng/day NDMA. The approach assumed a linear extrapolation from the Carcinogenic Potency Database (CPDB) harmonic-mean TD50 identified in chronic studies in rats. Although NDMA has been thought to act as a mutagenic carcinogen in experimental animals, it has not been classified as a known human carcinogen by any regulatory agency. Humans are exposed to high daily exogenous and endogenous doses of NDMA. Due to the likelihood of a threshold dose for NDMA-related tumors in animals, we believe that there is ample scientific basis to utilize the threshold-based benchmark dose or point-of-departure (POD) approach when estimating a Permissible Daily Exposure limit (PDE) for NDMA. We estimated that 29,000 ng/kg/day was an appropriate POD for calculating a PDE. Assuming an average bodyweight of 50 kg, we expect that human exposures to NDMA at doses below 5800 ng/day in pharmaceuticals would not result in an increased risk of liver cancer, and that there is little, if any, risk for any other type of cancer, when accounting for the mode-of-action in humans.

Closing Dichloramine Decomposition Nitrogen and Oxygen Mass Balances: Relative Importance of End-Products from the Reactive Nitrogen Species Pathway

In drinking water chloramination, monochloramine autodecomposition occurs in the presence of excess free ammonia through dichloramine, the decay of which was implicated in N-nitrosodimethylamine (NDMA) formation by (i) dichloramine hydrolysis to nitroxyl which reacts with itself to nitrous oxide (N2O), (ii) nitroxyl reaction with dissolved oxygen (DO) to peroxynitrite or mono/dichloramine to nitrogen gas (N2), and (iii) peroxynitrite reaction with total dimethylamine (TOTDMA) to NDMA or decomposition to nitrite/nitrate. Here, the yields of nitrogen and oxygen-containing end-products were quantified at pH 9 from NHCl2 decomposition at 200, 400, or 800 μeq Cl2·L-1 with and without 10 μM-N TOTDMA under ambient DO (∼500 μM-O) and, to limit peroxynitrite formation, low DO (≤40 μM-O). Without TOTDMA, the sum of free ammonia, monochloramine, dichloramine, N2, N2O, nitrite, and nitrate indicated nitrogen recoveries ±95% confidence intervals were not significantly different under ambient (90 ± 6%) and low (93 ± 7%) DO. With TOTDMA, nitrogen recoveries were less under ambient (82 ± 5%) than low (97 ± 7%) DO. Oxygen recoveries under ambient DO were 88-97%, and the so-called unidentified product of dichloramine decomposition formed at about three-fold greater concentration under ambient compared to low DO, like NDMA, consistent with a DO limitation. Unidentified product formation stemmed from peroxynitrite decomposition products reacting with mono/dichloramine. For a 2:2:1 nitrogen/oxygen/chlorine atom ratio and its estimated molar absorptivity, unidentified product inclusion with uncertainty may close oxygen recoveries and increase nitrogen recoveries to 98% (ambient DO) and 100% (low DO).

Patient In-Use Stability Testing of FDA-Approved Metformin Combination Products for N-Nitrosamine Impurity

Between February 2020 and January 2022, the Food and Drug Administration (FDA) recalled 281 metformin extended-release products due to the presence of N-nitrosodimethylamine (NDMA) above the acceptable daily intake (ADI, 96 ng/day). Our previous studies indicated presence of NDMA levels above ADI in both metformin immediate and extended-release products. When metformin products have NDMA impurities, it is indispensable to check for the same impurities in metformin combination products. Therefore, the objective of the present study was to evaluate in-use stability of commercial metformin combination products for NDMA. For this purpose, metformin products in combination with glyburide (GB1-GB12), glipizide (GP1-GP8), pioglitazone (P1-P3), alogliptin (A1, A2), and linagliptin (L1, L2) were repacked in pharmacy vials, stored at 30°C/75% RH for 3 months, and monitored for NDMA impurity. The NDMA level varied from 0 to 156.8 ± 32.8 ng/tablet initially and increased to 25.4 ± 5.1 to 455.0 ± 28.4 ng/tablet after 3 months of exposure to in-use condition. Initially, 18 products have NDMA level below ADI limit before exposure which decreased to 7 products (GB5, GP3, GP5, A1, A2, L1, and L2) meeting specification. In conclusion, in-use stability study provides quality and safety risk assessment of drug products where nitroso impurities are detected in the probable condition of use.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Association of N-nitrosodimethylamine exposure with cognitive impairment based on the clues of mice and humans

N-nitrosodimethylamine (NDMA) is an environmental and food contaminant, but limited data to concern whether NDMA has adverse effects on the brain. This study first determined the concentration of NDMA in foods from aquaculture markets in Shenzhen, then analyzed the effects on C57BL/6 mice and further evaluated on the urine samples of elderly Chinese residents with normal cognition (NC, n = 144), cognitive decline (CD, n = 116) and mild cognitive impairment (MCI, n = 123). The excessive rate of NDMA in foods was 3.32% (27/813), with a exceeding range of 4.78-131.00 μg/kg. Behavioral tests showed that 60 days treatment of mice with 3 mg/kg NDMA reduced cognitive performance. Cognitive impairment in human was significantly associated with sex, educational levels, length of residence in Shenzhen, household registration, passive smoking, rice, fresh vegetables, bacon products. NDMA was detected in 55.4% (212/383) of urine samples, with a median concentration of 0.23 μg/L (1.20 × 10 ^-7-157.39 μg/L). The median concentration for NC, CD and MCI were 0.32, 0.27, and 0 μg/L, respectively. The urinary NDMA concentration had a strong negative correlation with cognitive impairment (Kendall's Tau-b = -0.89, P = 0.024). The median estimated daily intake (EDI) of NDMA was determined to be 6.63 ng/kg-bw/day. Taken together, there appears to be an association between NDMA and human and murine cognition, which provides a new clue to Alzheimer's disease (AD).

A survey of industrial N-nitrosamine discharges in Switzerland

N-nitrosamines are formed during different industrial processes and are of significant concern due to their carcinogenic and mutagenic properties. This study reports concentrations of N-nitrosamines in eight different industrial wastewater treatment plants in Switzerland and the variability of their abundance. Only four N-nitrosamines species, N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodibutylamine (NDPA) and N-nitrosomorpholine (NMOR) were above the limit of quantification in this campaign. Remarkably high concentrations (i.e. up to 975 μg NDMA/L, 90.7 μg NDEA/L, 1.6 μg NDPA/L and 710 μg NMOR/L) of these N-nitrosamines were detected at seven of eight sites. These concentrations are two to five orders of magnitude higher than those typically detected in municipal wastewater effluents. These results suggest that industrial effluents may be a major source of N-nitrosamines. Although very high concentrations of N-nitrosamine have been detected in industrial discharges, various processes in surface water can partially mitigate their concentrations (e.g. photolysis, biodegradation and volatilization) and hence the risk to human health and aquatic ecosystems. Nevertheless, there is little information on long-term effects on aquatic organisms and therefore the discharge of N-nitrosamines to the environment should be avoided until the impact on ecosystems is assessed. During winter a less efficient mitigation of N-nitrosamines can be expected (lower biological activity, less sunlight) and therefore, emphasis should be put on this season in future risk assessment studies.

A Bioanalytical Method for Quantification of N-nitrosodimethylamine (NDMA) in Human Plasma and Urine with Different Meals and following Administration of Ranitidine

Control of N-nitrosoamine impurities is important for ensuring the safety of drug products. Findings of nitrosamine impurities in some drug products led FDA to develop new guidance providing recommendations for manufacturers towards prevention and detection of nitrosamine impurities in pharmaceutical products. One of these products, ranitidine, also had a published in vivo study, which has since been retracted by its authors, suggesting a potential for in vivo conversion of ranitidine to the probable human carcinogen, N-nitrosodimethylamine (NDMA). FDA subsequently initiated a randomized, double-blind, placebo-controlled, crossover clinical investigation to assess the potential for in vivo conversion of ranitidine to NDMA with different meals. A bioanalytical method toward characterization of NDMA formation was needed as previously published methods did not address potential NDMA formation after biofluid collection. Therefore, a bioanalytical method was developed and validated as per FDA's Bioanalytical Method Validation guidance. An appropriate surrogate matrix for calibration standards and quality control sample preparation for both liquid matrices (human plasma and urine) was optimized to minimize the artifacts of assay measurements and monitor basal NDMA levels. Interconversion potential of ranitidine to NDMA was monitored during method validation by incorporating the appropriate quality control samples. The validated methods for NDMA were linear from 15.6 pg/mL to 2000 pg/mL. Low sample volumes (2 mL for urine and 1 mL for plasma) made this method suitable for clinical study samples and helped to evaluate the influence of ranitidine administration and meal types on urinary excretion of NDMA in human subjects.

Prescription changes in patients with gastrointestinal disorders after withdrawal of ranitidine: a nationwide population-based cohort study

OBJECTIVE

Ranitidine products contain unacceptable levels of N-nitrosodimethylamine. This study aimed to investigate changes in the treatment regimen and their influencing factors after the ranitidine recall.

METHODS

This retrospective study used data from nationwide Korean claims from 2019. Patients with gastrointestinal disorders treated with ranitidine for at least a month on 25 September 2019, were selected for this study. Other histamine-2 receptor antagonists (H2RAs), proton pump inhibitors (PPIs), potassium-competitive acid blockers (PCABs), and prostaglandin E1 analogs were administered as alternatives to ranitidine. Kaplan-Meier survival and Cox proportional hazards regression analyses were performed to gauge the time until switching to alternative drugs and assess the influencing factors.

RESULTS

In total, 7502 patients were included in this study, among which 5164 (68.8%) switched from ranitidine to an alternative drug. The most prescribed alternative drugs were H2RAs, followed by PPIs, PCABs, and prostaglandin E1 analogs. Increasing age; Medical Aid insurance (MedAid); and a history of hypertension, diabetes mellitus, asthma, and osteoarthritis were associated with a higher probability of switching treatments. Patients with concomitant gastroesophageal reflux disease and peptic ulcers were more likely to switch to alternative drugs than patients with gastritis.

CONCLUSIONS

Approximately two-thirds of patients with gastrointestinal disorders switched from ranitidine to alternative drugs within 3 months after ranitidine withdrawal. The Cox regression analysis showed that age (>55 years); insurance type (MedAid); comorbidities, such as hypertension, diabetes mellitus, asthma, and osteoarthritis, and gastrointestinal disorder severity influenced the switch from ranitidine to alternative drugs.

N-Nitrosation in the absence of nitrosating agents in pharmaceuticals?

The possibility of N-Nitrosation in the absence of nitrosating agents was studied on model solutions and film coated tablets containing metformin. N-nitrosodimethylamine (NDMA) and N-nitrosation precursors (dimethylamine and nitrites) were determined using previously published fully validated analytical methods. Alternative routes to N-nitrosation were found. Dimethylamine can undergo an oxidation to nitrite in the presence of strong oxidants (e.g., H₂O₂), as was observed during wastewater treatment in several published works. The resulting nitrite can consecutively act as a nitrosating agent. We proved that the described reaction indeed leads to N-nitrosation (NDMA formation in case of dimethylamine precursor) in model solutions made of dimethylamine and H₂O₂. An experiment was designed in order to prove those reactions take place in dosage forms. Film coated tablets present a highly heterogenous system with several solid phases and low water activity, which is in stark contrast to the liquid wastewater, where this reaction was originally studied. Despite that, the described reaction took place even in the tablets, but only to a small degree. The amount formed via this alternative route corresponds to less than 10 % of the total formed NDMA. The pH optimum of this alternative route lies in the alkaline range which was confirmed by the determined NDMA concentration in model solutions. The solid phase system (i.e., tablets) was found to behave differently. The addition of Na₂CO₃ into the tablets during manufacture resulted in tablets without NDMA (c_NDMA < LOQ) even in batches spiked with both dimethylamine and H₂O₂. Thus, adjusting the pH of the solid dosage forms remains a sufficient measure of controlling N-nitrosamines in the product, even in product with limit amounts of oxidating agent (H₂O₂) and N-nitrosation precursor (dimethylamine).

Photodegradation of N-nitrosodimethylamine under 365 nm Light Emitting Diode Irradiation

The photodegradation of NDMA has been extensively investigated under the irradiation of low-pressure or medium-pressure Hg lamps and xenon lamp. However, NDMA photolysis remains unknown under 365 nm ultraviolet light-emitting diode (UV-LED) irradiation. This study conducted a comprehensive investigation on NDMA photodegradation by 365 nm UV-LED illumination. The quantum yield of NDMA photolysis under 365 nm UV-LED irradiation was determined to be 0.0312 ± 0.0047. The influence of pH on NDMA photodegradation was found to be wavelength dependent. Compared with distilled and deionized water (DDW), tap water inhibited NDMA photodegradation, but secondary wastewater effluent did not. Based on the quantification of NDMA photolysis products and pH influence, the photooxidation of the excited NDMA in the nonprotonated form was proposed to be a major pathway for NDMA photodegradation under the irradiation of UV-LED lamp at 365 nm. This study further enhances our knowledge on NDMA photodegradation. PRACTITIONER POINTS: Quantum yield of NDMA photolysis at 365 nm was determined to be 0.0312 ± 0.0047. The influence of pH on NDMA photodegradation was wavelength dependent. NDMA photodegradation was inhibited in tap water compared with that in DDW. NDMA photodegradation in SWE was similar to that in DDW. Excited nonprotonated NDMA photooxidation is a major degradation pathway.

In-use stability assessment of FDA approved metformin immediate release and extended release products for N-Nitrosodimethylamine and dissolution quality attributes

Metformin is a widely used first-line oral antidiabetic agent. TheFood and Drug Administration (FDA) confirmed the presence of the ofN-nitrosodimethylamine (NDMA) impurity, a carcinogenic, above the acceptable daily intake (ADI, 96 ng/day) in certain metformin products. The objective of the present study was to assess in-use stability of commercial metformin products for NDMA and dissolution quality attributes. Four immediate-release (M1-M4) and six extended-rerelease (M5-M10) metformin products were evaluated in the stability testing. All products were repacked in pharmacy vials and stored at 30 °C/75% RH for 12 weeks. Five products (M2, M3, M5, M7 and M10) had NDMA level above ADI limit (96 ng/day) before in-use stability exposure. NDMA in M2 (1164 ± 52.9 ng/tablet) and M3 (3776 ± 351.9 ng/tablet) products were 12 and 39 folds of ADI, respectively. Similarly, ER products, M5 (191 ± 94.1 ng/tablet), M7 (1473 ± 47.3 ng/tablet) and M10 (423 ± 55.8 ng/tablet) exhibited NDMA of 1.9, 15.3 and 4.4 folds of ADI, respectively. The impurity level significantly (p < 0.05) increased after 12-week stability exposure to 2.72, 2.47, 2.23 and 2.78 folds of initial values in M2, M3, M7 and M10. In summary, these findings suggested that carcinogenic impurity generation was affected by in-use stability condition exposure and it is expected that several more products currently in the market may also be recalled soon.

Membrane distillation for achieving high water recovery for potable water reuse

Achieving high water recovery using reverse osmosis membranes is challenging during water recycling because the increased concentrations of organics and inorganics in wastewater can cause rapid membrane fouling, necessitating frequent cleaning using chemical agents. This study evaluated the potential of membrane distillation to purify reverse osmosis-concentrated wastewater and achieve 98% overall water recovery for potable water reuse. The results indicate that membrane fouling during membrane distillation treatment was low (4% reduction in permeability) until 98% water recovery. In contrast, membrane fouling during reverse osmosis treatments was high (73% reduction in permeability) before reaching 90% water recovery. Furthermore, membrane distillation showed superior performance in removing dissolved ions (99.9%) from wastewater as compared with reverse osmosis (98.9%). However, although membrane distillation removed most trace organic chemicals tested in this study, a negligible rejection (11%) was observed for N-nitrosodimethylamine, a disinfection byproduct regulated in potable water reuse. In contrast, RO treatment exhibited a high removal of N-nitrosodimethylamine (70%). Post-treatment (e.g., advanced oxidation) after reverse osmosis and membrane distillation may be needed to comply with the N-nitrosodimethylamine regulations. Overall, the membrane distillation process had the capacity to purify reverse osmosis concentrate with insignificant membrane fouling.

Isolation of N-nitrosodimethylamine from drug substances using solid-phase extraction-liquid chromatography-tandem mass spectrometry

N-Nitrosodimethylamine (NDMA) has been detected in some drug substances and pharmaceutical products containing sartans, ranitidine and metformin, and a potential risk of NDMA contamination exists in other drug substances and their pharmaceutical products. To quantitate NDMA in various drugs having diverse physicochemical properties, a specific, sensitive, and reliable analytical method is required, in addition to methods that can be applied to a class of nitrosamines. We aimed to develop an off-line isolation method for NDMA in drug substances using SPE for quantification with LC-APCI-MS/MS. Impediments to accurate quantitation of NDMA in drug substances using LC-MS/MS and insufficient durability of the system are attributed to the extremely large amounts of active pharmaceutical ingredients (APIs) in sample solutions in comparison to the trace amount of NDMA. A reduced retention of NDMA and/or decreased separation from other substances in LC, matrix effect in MS detection, and undesirable contamination of instruments with API and other substances may be occasionally encountered, all of which consequently result in deterioration of system performance and generation of unreliable data, even in the cases where a divert valve is configured between the column and ion source of the MS instrument. To address these problems, an off-line NDMA isolation methodology from APIs exhibiting diverse physicochemical properties, namely ranitidine hydrochloride (ranitidine), metformin hydrochloride (metformin), nizatidine, valsartan, and telmisartan, was developed. The applicability of the method was confirmed by batch analysis of metformin and ranitidine. Furthermore, contrary to previous reports, NDMA was found to be stable over a wide pH range. The proposed methodology and data from this study would contribute to the control of NDMA contamination in various drugs to realize the safe delivery of pharmaceuticals to patients.

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

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

Motivation of reactive oxidation species in peracetic acid by adding nanoscale zero-valent iron to synergic removal of spiramycin under ultraviolet irradiation: Mechanism and N-nitrosodimethylamine formation potential assessment

In this study, nanoscale zero-valent iron (nZVI) was added to motivate the functions of all the reactive oxidation species in peracetic acid (PAA) mixture under ultraviolet (UV) irradiation, and to enhance the removal of spiramycin, which is a typical precursor of N-nitrosodimethylamine (NDMA). Spiramycin (≤ 10 mg/L) could be completely removed within 20 min under the conditions of an initial pH of 4.0, a nZVI dose of 0.02 g/L and a PAA dose of 3.0 mg/L; additionally, 95.8% and 78.8% of PAA and H₂O₂ were consumed during the process. Electron paramagnetic resonance analysis and quenching experiments confirmed that 52.4% and 44.8% of spiramycin removal was contributed by hydroxyl radical (•OH) and carbon-centered radicals (R-C•), respectively; and Fe²⁺ released from nZVI played a critical role in radicals generation. Four degradation pathways of spiramycin were proposed and verified by the density of functional theory analysis. 65.2% of the NDMA formation potential (FP) was reduced after the reaction, and its residual was mainly contributed by the undegraded intermediate of dimethylamine. The results of multiple characterizations and continuous degradation experiments indicated that nZVI was stable in the system as the removal of spiramycin was hardly influenced even if reused three times. The nZVI/UV/PAA process is a promising advanced oxidation technology not only for the removal of refractory NDMA precursors (such as spiramycin) but also for significantly lowering the NDMA FP.

Pretreatment with Ranitidine Bismuth Citrate May Improve Success Rates of Helicobacter pylori Eradication: A Prospective, Randomized, Controlled and Open-Label Study

Effective Helicobacter pylori (H. pylori) eradication is a major public health concern; however, eradication failure rates with the standard triple therapy remain high. We aimed to investigate the effectiveness and tolerability of ranitidine bismuth citrate (RBC) pretreatment before standard triple therapy for H. pylori eradication. A prospective, randomized, controlled, and open-label clinical trial was conducted from June to December 2019. H. pylori eradication rate, safety, and tolerability were compared between the standard treatment group (esomeprazole, amoxicillin, and clarithromycin for 7 days) and RBC pretreatment group (RBC for 2 weeks before standard triple therapy). This trial ended earlier than estimated owing to the N-nitrosodimethylamine concerns with ranitidine. Success rates of H. pylori eradication were 80.9% and 67.3% in the RBC pretreatment (n = 47) and standard treatment (n = 52) (p = 0.126) groups, respectively. Our trial was discontinued earlier than planned; however, a statistical significance would be achieved by expansion of our data (p = 0.031) if patient enrollment numbers reached those initially planned. Adverse event rates were comparable between groups (25.5% in the pretreatment group vs. 28.8% in the standard treatment group), without serious event. Tolerability was excellent in both groups, recorded as 97.9% and 100% in the pretreatment and standard treatment groups, respectively. Compared with the standard triple regimen, RBC pretreatment for 2 weeks may achieve higher H. pylori eradication rates, with excellent safety and tolerability. However, this study necessitates further validation as it was discontinued early owing to the N-nitrosodimethylamine issues of ranitidine.

Betulinic acid abates N-nitrosodimethylamine-induced changes in lipid metabolism, oxidative stress, and inflammation in the liver and kidney of Wistar rats

N-nitrosamines have been linked with cancer in humans due to their presence in drinking water and diets. This study evaluated the role of betulinic acid (BA) in abating oxidative stress, inflammation, and hyperlipidemia in rats treated with N-nitrosodimethylamine (NDMA). Twenty-four male rats were assigned into four equal groups. Group I served as the control, Group II received BA (25 mg/kg), Group III received NDMA (5 mg/kg) and, Group IV received BA (25 mg/kg) and NDMA (5 mg/kg). Results showed that the administration of NDMA significantly (p < 0.05) elevated malondialdehyde in the liver and kidney relative to controls. Activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase, and the level of glutathione were significantly (p < 0.05) decreased by NDMA, while treatment with BA elevated the activities of these enzymes in the liver and kidney. The BA lowered serum interleukin-6 and tumor necrosis factor-alpha levels against the NDMA effect. Furthermore, NDMA increased hepatic and renal triglyceride while phospholipids levels were decreased. NDMA significantly modulated the activities of drug-metabolizing enzymes (aniline hydroxylase, aminopyrine-N-demethylase, and uridyldiphosphoglucuronyltransferase), while BA was able to restore these enzymes to values close to controls. Histology revealed the presence of infiltration and fibroplasia in the liver, while cortical degeneration was noticed in the kidney in NDMA-administered rats. These lesions were reduced in the NDMA rats treated with BA. The findings suggest that BA improves NDMA-induced damage in the liver and kidney of rats through reactions that can be linked with antioxidant, anti-inflammatory, and lipid-lowering pathways.

Nitrite, biogenic amines and volatile N-nitrosamines in commercial Chinese traditional fermented fish products

To examine the safety of Chinese traditional fermented fish products (CTFPs) available on the Chinese market, nitrite, nitrate, biogenic amines (BAs) and volatile N-nitrosamines (VNAs) content in 33 commercial CTFPs from different provinces was investigated. The mean content of nitrite and nitrate wase 0.63 and 749.5 mg/kg, respectively. Concerning the occurrence of BAs, the accumulation in all CTFPs samples remained at low levels, whereas only in one sample from Guangxi the histamine content exceeded the critical level (50 mg/kg). In addition, six types of VNAs, including N-nitrosodimethylamine (NDMA), N-nitrosoethylmethylamine, N-nitrosopiperidine, N-nitrosopyrrolidine, N-nitrosomorpholine and N-nitrosodiphenylamine, were detected in a high number of samples. The NDMA content in 36.4% of the samples and the total VNAs content in about 63.6% of the samples were unacceptable. Principal component analysis indicated that the accumulation of NDMA and total VNAs was closely related with the content of histamine, tyramine and nitrate.

Effect of Ranitidine Intake on the Risk of Gastric Cancer Development

Gastric cancer is one of the most prevalent cancers globally, with high mortality, particularly in East Asia. Certain ranitidine products contain potentially carcinogenic N-nitrosodimethylamine. We investigated the potential association between gastric cancer risk and ranitidine intake using a nationwide cohort, extracted from the Korean National Health Insurance Service. In this longitudinal study, we employed a 1:1 propensity score matching according to sociodemographic factors. A total of 40,887 subjects were enrolled, of which 906 developed gastric cancer during the follow-up period. We investigated gastric cancer events during the follow-up period using the survival analysis, log-rank test, and Cox proportional hazards regression models to estimate incidence, survival rate, and hazard ratio. The incidence of gastric cancer was 67,422; 67,470; and 67,444 person-years in the control, other histamine-2 blockers, and ranitidine groups, respectively. Because the adjusted hazard ratio of gastric cancer was 0.98 and 1.01 in the other histamine-2 blockers and ranitidine groups, respectively, we could not calculate the likelihood of gastric cancer development in the ranitidine group. Ranitidine intake did not significantly increase the incidence of gastric cancer. Therefore, the relative risk of gastric cancer may be low in patients taking ranitidine products in South Korea.

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

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

Enhanced removal of oxytetracycline by UV-driven advanced oxidation with peracetic acid: Insight into the degradation intermediates and N-nitrosodimethylamine formation potential

In this study, UV-driven advanced oxidation with peracetic acid (PAA) was adopted to enhance the removal of oxytetracycline (OTC) as well as to lower the formation potential of N-nitrosodimethylamine (NDMA). Results implied that the combination of UV and PAA had a synergetic effect on both the removal and mineralization of OTC. OTC (≤5 mg L^-1) could be completely removed in 45 min in the UV/PAA system under the conditions of an initial pH of 7.10 and a PAA dose of 5 mg L^-1; additionally, 50.9% of mineralization rate of OTC was obtained. Electron paramagnetic resonance analysis and quenching experiments indicated that ·OH was the main oxidizer for the removal of OTC, while UV, PAA and carbon-centered radicals (R-C·) also participated in its removal. During the degradation of OTC, 31 kinds of degradation intermediates were traced, and 20 kinds of them were first detected in the UV/PAA system. OTC was removed through five pathways, and the hydroxylation pathway was involved in nearly the entire degradation period. The NDMA formation potential decreased by 65.8% after the reaction, and residual dimethylamine accounted for 15.1% of its total composition. The proposed UV/PAA process is a promising method not only for the removal of refractory antibiotics but also for controlling the formation of NDMA.

Performance and mechanism of nickel hydroxide catalyzed reduction of N-nitrosodimethylamine by iron

Since iron (Fe) was first proven to have a strong reduction ability, it has been successfully applied to remove pollutants from water. In this study, nickel hydroxide (Ni(OH)₂), a catalyst commonly used in hydrogen evolution reactions, was added to improve the activity of Fe to remove N-nitrosodimethylamine (NDMA). The results showed that with the increasing Ni(OH)₂ dosages, the reactions accelerated. The NDMA removal rates increased when the pH value was 6 or 7. Further, when the dissolved oxygen concentration was in the range of 0-12.0 mg∙L^-1, it had little effect on the Fe/Ni(OH)₂ system, and all the reactions obeyed pseudo-first-order kinetics. 1,1-dimethylhydrazine and dimethylamine were formed during NDMA degradation. The capture of active substances and electron spin resonance method confirmed that the main active species were active hydrogen atoms, which participated in the removal of NDMA. Ni(OH)₂ acting as a catalyst was confirmed using wide-angle X-ray diffraction, X-ray photoelectron spectroscopy and Ni²⁺ dissolution. Further, catalytic hydrogenation was proposed as the main removal mechanism as Ni(OH)₂ promotes the corrosion of Fe and dissociation of water, thereby generating more active hydrogen atoms. In addition, Ni(OH)₂ may activate both Fe and NDMA. This technique could be employed as an alternative for NDMA reduction and expand the application field of Ni(OH)₂.

Implications of an epidemiological study showing an association between in utero NDMA exposure and childhood cancer

Exposure to N-nitrosodimethylamine (NDMA) has recently been linked to a childhood cancer cluster in Wilmington, MA, which is home to the Olin Chemical Superfund Site. When it was discovered in the 1990's that 22 children in a town of under 22,000 people got cancer, the community took action and pressed for an investigation into the possibility that chemicals from the Olin Chemical site had contaminated their water. This led to the eventual discovery that NDMA was present in the town water supply. NDMA has long been known for its potent carcinogenicity in animal models, and so the community pointed to NDMA as a possible cause. This led to an investigation by the Massachusetts Department of Public Health, which, in 2021, released its findings showing an association between NDMA exposure in utero and childhood cancer. The mission of the NIEHS Superfund Research Program is to protect human health from hazardous substances. In 2017, in response to community concerns, a team at MIT created the MIT Superfund Research Program Center with a focus on research related to NDMA. Just 1 week prior to the release of the Department of Public Health study, the MIT Superfund Research Program Center published a manuscript in Cell Reports that identifies the Alkyladenine DNA glycosylase (AAG) as a possible genetic susceptibility factor. This commentary provides an author's perspective on the context and implications of this and related research.

The Overactivation of NADPH Oxidase during Clonorchis sinensis Infection and the Exposure to N-Nitroso Compounds Promote Periductal Fibrosis

Clonorchis sinensis, a high-risk pathogenic human liver fluke, provokes various hepatobiliary complications, including epithelial hyperplasia, inflammation, periductal fibrosis, and even cholangiocarcinogenesis via direct contact with worms and their excretory-secretory products (ESPs). These pathological changes are strongly associated with persistent increases in free radical accumulation, leading to oxidative stress-mediated lesions. The present study investigated C. sinensis infection- and/or carcinogen N-nitrosodimethylamine (NDMA)-associated fibrosis in cell culture and animal models. The treatment of human cholangiocytes (H69 cells) with ESPs or/and NDMA increased reactive oxidative species (ROS) generation via the activation of NADPH oxidase (NOX), resulting in augmented expression of fibrosis-related proteins. These increased expressions were markedly attenuated by preincubation with a NOX inhibitor (diphenyleneiodonium chloride) or an antioxidant (N-acetylcysteine), indicating the involvement of excessive NOX-dependent ROS formation in periductal fibrosis. The immunoreactive NOX subunits, p47^phox and p67^phox, were observed in the livers of mice infected with C. sinensis and both infection plus NDMA, concomitant with collagen deposition and immunoreactive fibronectin elevation. Staining intensities are proportional to lesion severity and infection duration or/and NDMA administration. Thus, excessive ROS formation via NOX overactivation is a detrimental factor for fibrogenesis during liver fluke infection and exposure to N-nitroso compounds.

Determination of dimethylamine and nitrite in pharmaceuticals by ion chromatography to assess the likelihood of nitrosamine formation

Since July 2018 several drugs have been recalled due to contamination with N-nitrosodimethylamine (NDMA), a probable human carcinogen. Dimethylamine (DMA) and nitrite are precursors in the formation of NDMA. In this study, ion chromatography (IC) methods were developed for the determination of these two precursors in drug substances and drug products. Two methods were developed to determine DMA in two drug products using a cation exchange separation coupled to suppressed conductivity detection. The limit of detection of DMA is < 1 μg/g of active pharmaceutical ingredient (API) for both methods. Nitrite was determined using an anion exchange separation coupled with UV absorbance detection. The limit of detection of nitrite was 0.918 μg/g API. The developed methods were successfully applied to DMA and nitrite determinations in five drug products including metformin, losartan, ranitidine, Nytol, and Benadyrl, and two drug substances (APIs), losartan potassium and metformin hydrochloride. Some samples contained nitrite and DMA at detectable levels. Dimethylamine and nitrite recovery from pharmaceutical samples ranged from 96.0-104 %. The developed methods should be useful for the rapid screening and quantification of nitrite and DMA in pharmaceuticals and in-process samples to assess the likelihood of NDMA formation. The methods for DMA should be applicable to other amines to assess the likelihood of the formation of other nitrosamines in pharmaceutical products.

Contribution of N,N-dimethylformamide to formation of N-nitrosodimethylamine by chloramination in sewage treatment plants and receiving rivers

The contribution of specific precursors to N-nitrosodimethylamine formation potential (NDMA FP) upon chloramination depends not only on their NDMA molar yields but also on their concentrations in the actual environment. We investigated the seasonal and diurnal patterns of the NDMA precursor N,N-dimethylformamide (DMF) and NDMA FP in the Yodo River basin, Japan, by examining water samples taken from inside the basin's largest sewage treatment plant (STP) as well as samples from five final effluents from four STPs, two main stream sites, and two tributary sites in the same basin. DMF and NDMA FP were found to be high in influent (raw sewage), and were found to be mostly removed during the STP treatment processes (especially with biological treatment). Nevertheless, DMF was found in concentrations of 0.06 to 31.7 µg/L in chlorinated effluents and in receiving rivers, while NDMA FP was detected in concentrations of 3.57 to 306 ng/L. Thus, STPs were shown to be an important source of DMF and NDMA FP to rivers. A strong positive correlation between NDMA FP and DMF was confirmed in the receiving river (K-M), indicating that DMF was an important NDMA precursor in the Yodo River basin. The contribution of DMF to NDMA FP was 15.8±11.2% (n = 4) in summer and 82.1±10.2% (n = 4) in winter in the main stream (site K-M) of the river due to insufficient dilution of chlorinated effluents from the largest STP. From the viewpoint of NDMA and NDMA FP control at downstream sites, monitoring and control of DMF at upstream sites are important.

Phenylurea herbicide degradation and N-nitrosodimethylamine formation under various oxidation conditions: Relationships and transformation pathways

Four phenylurea herbicides (PUHs) were assessed for degradation and transformation into N-nitrosodimethylamine (NDMA) under three oxidation conditions (chlorine (Cl₂), chlorine dioxide (ClO₂), and ozone (O₃)) from an aqueous solution. Removal ratios correlated with the numbers of halogen elements contained in PUHs (isoproturon ₍₀₎ > chlorotoluron _{(1 Cl)} > diuron _{(2 Cl)} > fluometuron _(3 F)), and the degradation efficiencies of oxidants from fastest to slowest were: O₃, ClO₂, and Cl₂. NDMA can be generated directly from the ozonation of PUHs. Further, compared with chloramination alone, ozonation prominently promoted NDMA formation potential (NDMA-FP) during post-chloramination, and NDMA-FPs increased approximately 23-68 times than those during ozonation only at 2.5 mg/L O₃ over 10 min; molar yields of NDMA from highest to lowest were 11.1% (isoproturon), 1.17% (chlorotoluron), 1.0% (diuron), and 0.73% (fluometuron). The PUH degradation kinetics data during ozonation agreed with the pseudo-first-order model. The rate constant k_obs were 0.31 × 10^-3-19.8 × 10^-3 s^-1. The k_obs and removal ratios of PUHs during ozonation partially scaled with the mass, LogK_ow, and Henry's constants of PUHs. Comparisons of measured NDMA-FPs with calculated NDMA-FPs from residual PUH after oxidation showed that the intermediates produced during ozonation facilitated NDMA-FPs; this contribution was also observed for chlorotoluron and isoproturon during ClO₂ oxidation. Examination of reaction mechanisms revealed that tertiary amine ozonation, N-dealkylation, hydroxylation, the cleavage of N-C bonds, ammonification, and nitrification occurred during the ozonation of PUHs, and the dimethylamine (DMA) functional groups could be decomposed directly and transformed into NDMA via the formation of the intermediate unsymmetrical dimethylhydrazine. NDMA is also formed from the reaction between DMA and phenylamino-compounds. Clarifying primary degradation products of PUHs and transformation pathways of NDMA during oxidation processes is useful to optimize treatment processes for water supplies.

Application of capillary electrophoresis-nano-electrospray ionization-mass spectrometry for the determination of N-nitrosodimethylamine in pharmaceuticals

After a presence of highly hepatotoxic and potentially carcinogenic N-nitrosodimethylamine was detected in certain lots of sartan, ranitidine, metformin, and other pharmaceuticals, local regulatory authorities issued recalls of suspected products, and concerns of the pharmacotherapy safety were widely discussed. Since then, testing of a representative sample of each produced lot of these pharmaceuticals is required as a part of quality control processes. Hence, an interface-free CE-nanoESI system coupled with MS detection was employed for the development of a simple and economical method for quantitative detection of this contaminant in the valsartan drug substances and finished formulations used as model matrices. In this arrangement, a fused-silica capillary was used as both a separation column and a nanoESI emitter providing high ionization efficiency and sensitivity. The optimized procedure was found to have sufficient selectivity, linearity, accuracy, and precision. The established LOD and LOQ values were 0.3 and 1.0 ng/mL, respectively. The practical applicability of the method was tested by analyses of commercially available Valsacor^® tablets. The results obtained prove that the developed procedure represents a promising alternative to currently available GC- and LC-based methods. Furthermore, after an adjustment of the separation conditions, the CE-nanoESI/MS system can be conceptually used for the determination of NDMA in other suspected pharmaceuticals.

A novel CWPO/H2O2/VUV synergistic treatment for the degradation of unsymmetrical dimethylhydrazine in wastewater

In this paper, the catalytic wet peroxide oxidation (CWPO) combined with vacuum ultraviolet (VUV) irradiation was developed to mineralize the wastewater with high concentration of unsymmetrical dimethylhydrazine (UDMH), especially to decompose the main byproduct of UDMH decomposition, N-nitrosodimethylamine (NDMA). CuO-NiO-MgO/γ-Al₂O₃ was used as the catalyst and H₂O₂ as the resources of ⋅ O H . Fourier Transform Infrared spectroscopy (FT-IR), X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX) were employed to evaluate the structure of the catalyst. The treatment performances such as the UDMH degradation efficiency, chemical oxygen demand (COD) removal efficiency, and the concentration of N-nitrosodimethylamine (NDMA) were investigated in the treating process. The optimal conditions were obtained based on the results of single-factor experiments including parameters such as the initial UDMH concentration, catalyst dosage, initial pH, H₂O₂ dosage and temperature. The comprehensive results indicated that CWPO/H₂O₂/VUV process presented remarkable treatment performance to the reaction conditions with about 100% UDMH conversion efficiency, 95.02% COD removal efficiency and approximately 100% UDMH removal within 30 min.

Determination of N-nitrosodimethylamine in Ranitidine Dosage Forms by ESI-LC-MS/MS; Applications for Routine Laboratory Testing

A practical high-performance liquid chromatography-mass spectrometry method was developed for the analysis of N-nitrosodimethylamine (NDMA) characterized as an impurity, in combination with reports of the carcinogen found in ranitidine samples. After simple extraction of ranitidine samples, all compounds were analyzed with a high-performance liquid chromatography-mass spectrometry. Sensitivity was enhanced by employing the ten-way valve switching technology, which was examined to allow NDMA to enter the mass spectrometry and cut out the ranitidine samples extremely. A good linear relationship was observed within 3-100 ng·mL^-1 (r = 0.9992). The validated approach was effectively used to evaluate the NDMA contents in ranitidine samples in circulation, which revealed a difference among 21 batches. Quantitative determination of NDMA was within the scope of 3.38-57.05 ng·mL^-1. Moreover, the contamination levels of NDMA in seven batches of products from six manufacturers were listed to exceed the acceptable daily intake. The sensitive method was verified to be appropriate to determine NDMA, even with low contents of NDMA in ranitidine products; the analysis of the selected samples reveals that some samples exceeded the national limit requirements. Therefore, it is worthwhile to conduct comprehensive quality control of the other drugs containing NDMA.

Insight into the formation of N-nitrosodimethylamine in metformin products

An effective analytical method for the quantification of N-nitrosodimethylamine (NDMA) using a liquid chromatography coupled with tandem mass spectrometry was developed and applied to a process optimization study of the production of metformin film coated tablets in order to identify the key factors behind the NDMA formation in metformin products. The method uses a linear gradient elution with mobile phases 0.1 % formic acid in water for chromatography and methanol for chromatography and a column Acquity UPLC HSS T3 1.8 μm. The use of the tandem mass spectrometry in a positive ion mode with an atmospheric pressure chemical ionization allows for the use of an isotopically labelled internal standard and an external calibration standard. The method was validated according to the guidelines of International Council for Harmonization in terms of limit of detection and quantification, linearity, precision, accuracy and method selectivity. To further justify the effectiveness of the method, a comparison between two laboratories was performed using a linear regression testing. Both methods give comparable results. 469 samples of both metformin active pharmaceutical ingredient and film coated tablets were analysed and the key factors behind NDMA formation were identified. Hypotheses explaining the mechanism were formulated and confronted with measurements and scientific literature. Protective measures to prevent NDMA contamination in metformin products were drawn.

Surface modification of coconut shell activated carbon for efficient solid-phase extraction of N-nitrosodimethylamine from water

A practical and cheap methodology in modifying commercial coconut shell activated carbon for solid-phase extraction of N-nitrosodimethylamine in water was developed through an understanding of activated carbon surface chemistry. In comparison with commercial activated carbon, extraction recoveries by activated carbon treated with sulfuric acid decreased by 50%, while those of activated carbon heated at 800°C improved by more than 100%. Acid treatment increased the oxygen content on the carbon's surface. In contrast, heat treatment decreased the surface oxygen content, resulting in a more hydrophobic surface, which favoured adsorption and extraction of N-nitrosodimethylamine. The influence of different activated carbon sizes, amount of modified activated carbon, and pH on the N-nitrosodimethylamine recoveries was assessed and compared with the commercial solid-phase extraction cartridge. The recommended amount of powder activated carbon treated at 800°C was 3 g to yield an optimum recovery of 130%, which was superior to the commercial solid-phase extraction cartridges. The method validation results confirmed the high accuracy, reproducibility, and precision of the method. The study indicated that chemisorption plays a significant role in the adsorption of N-nitrosodimethylamine on activated carbon, and the optimization of its surface chemistry can enhance N-nitrosodimethylamine adsorption/extraction from water.

[Ultrasonic assisted-dispersive solid-phase extraction for rapid enrichment of N-nitrosodimethylamine in water]

OBJECTIVE

a novel and rapid analytical method was established for the extraction of N-nitrosodimethylamine in large-volume water samples.

METHODS

Pretreatment was on the basis of ultrasonic-assisted-dispersed solid phase extraction. Coco housing activated carbon was incorporated into the water samples, and the rapid enrichment of N-nitrosodimethylamine was realized by implementing ultrasonic-assisted dispersion. After that, the suspension was filtered by suction, and the residue was eluted by dichloromethane. The eluate was collected and then concentrated to dry using rotary evaporation. Ultra-high performance liquid chromatography tandem mass spectrometer, which equipped with atmospheric pressure chemical ionization source was employed for determination under the multiple reaction monitoring mode.

RESULTS

Limit of detection and quantification for N-nitrosodimethylamine in 500 mL water was 2. 0 ng/mL and 6. 0 ng/mL, respectively. Throughout the validation, good linearity with R~2&gt;0. 999 were achieved with the range from 0. 5 ng/mL to 150. 0 ng/mL. Satisfactory recovery(95. 7%-100. 8%) and inter-day reproducibility(&lt;4. 2%) were obtained by three-level spiking experiments in different water matrices. Finally, the established method was applied for analysis of 48 real samples, the detectable concentrations of positive samples were in the range of &lt;2. 0 ng/L to 14. 4 ng/L.

CONCLUSION

Compared with the traditional solid-phase extraction method, this method ology showed the characteristics of rapid and more efficient, and could save at least 50% of the pretreatment time. Meanwhile, the result of method ology validation were satisfactory.

UV/sulfite chemistry to reduce N-nitrosodimethylamine formation in chlor(am)inated water

The disinfection by-product N-nitrosodimethylamine (NDMA) is a major concern in water quality management due to its carcinogenicity. Thus, a proper pretreatment is necessary to mitigate NDMA formation upon periodic chloramination by removing precursors, such as ranitidine (RNT). This study investigated the effect of UV/sulfite pretreatment on NDMA formation from an RNT-spiked tap and chloraminated synthetic swimming pool (SSP) water. At UVC intensity of 2.1 mW cm^-2 and 0.5 mM of sulfite, UV/sulfite chemistry showed complete degradation of 20 µM RNT within 30 min. It was found that SO₄^•- primarily reduced the NDMA formation potential (FP) of RNT, while hydrated electrons effectively mitigated the pre-formed NDMA in the SSP water. The UV/sulfite pretreatment alleviated NDMA formation during post-chloramination (24 h) by up to 82%, outperforming the commonly employed advanced oxidation processes such as UV/H₂O₂. However, in the presence of bromide ions, the effectiveness of UV/sulfite pretreatment was seriously deteriorated, although the bromide ion itself was found to inhibit the NDMA formation from RNT especially at pH < 8 during chloramination. Mass spectrometric analysis indicated that the NDMA-FP of RNT could be removed by UV/sulfite principally via N-methylation, dealkylation, and oxygen transfer pathways. Consequently, UV/sulfite could be used as an alternative unit process for water treatment with reduced NDMA formation.

Field demonstration of N-Nitrosodimethylamine (NDMA) treatment in groundwater using propane biosparging

N-Nitrosodimethylamine (NDMA) is found in groundwater and drinking water from industrial, agricultural, water treatment, and military/aerospace sources, and it must often be treated to part-per-trillion (ng/L) concentrations. The most effective remedial technology for NDMA in groundwater is pump-and-treat with ultraviolet irradiation (UV), but this approach is expensive because it requires ex situ infrastructure and high energy input. The objective of this project was to evaluate an in situ biological treatment approach for NDMA. Previous laboratory studies have revealed that propane-oxidizing bacteria are capable of biodegrading NDMA from μg/L to low ng/L concentrations (Fournier et al., 2009; Webster et al., 2013). During this field study, air and propane gas were sparged into an NDMA-contaminated aquifer for more than 1 year. Groundwater samples were collected throughout the study from a series of monitoring wells within, downgradient, and sidegradient of the zone of influence of the biosparge system. Over the course of the study, NDMA concentrations declined by 99.7% to >99.9% in the four monitoring wells within the zone of influence of the biosparge system, reaching low ng/L concentrations whereas the control well declined by only 14%. Pseudo first-order degradation rate constants for NDMA in system monitoring wells ranged from ∼0.019 day ^-1 to 0.037 day ^-1 equating to half-lives ranging from 19 to 36 days. Native propanotrophs increased by more than one order of magnitude in the propane-impacted wells but not in the control well. The field data show for the first time that propane biosparging can be an effective in situ approach to reduce the concentrations of NDMA in a groundwater to ng/L concentrations.

Chemiresistive Carbon Nanotube Sensors for N-Nitrosodialkylamines

N-Nitrosamines are environmental genotoxicants that are widely encountered in air, water, and food. Contamination of indoor and outdoor air with N-nitrosamines has been reported on many occasions. Conventional detection of airborne N-nitrosamines requires sophisticated instrumentation, field sampling, and laboratory analysis. Herein, we report ultrasensitive carbon nanotube based chemiresistive sensors utilizing a cobalt(III) tetraphenylporphyrin selector element for the detection of N-nitrosamines. Concentrations as low as 1 ppb N-nitrosodimethylamine, N-nitrosodiethylamine, and N-nitrosodibutylamine were detected. We also demonstrate the integration of these sensors with a field deployable sensing node wherein the sensor response can be read online remotely.

Oxidation of Citalopram with Sodium Hypochlorite and Chlorine Dioxide: Influencing Factors and NDMA Formation Kinetics

The highly prescribed antidepressant, citalopram, as one of newly emerging pollutants, has been frequently detected in the aquatic environment. Citalopram oxidation was examined during sodium hypochlorite (NaOCl) and chlorine dioxide (ClO₂) chlorination processes since conventional wastewater treatment plants cannot remove citalopram effectively. Citalopram has been demonstrated to form N-nitrosodimethylamine (NDMA) during chlorination in our previous study. Further investigation on NDMA formation kinetics was conducted in the present study. Influences of operational variables (disinfectant dose, pH value) and water matrix on citalopram degradation, as well as NDMA generation, were evaluated. The results indicated high reactivity of citalopram with NaOCl and ClO₂. NDMA formation included two stages during CIT oxidation, which were linear related with reaction time. NaOCl was more beneficial to remove CIT, but it caused more NDMA formation. Increasing disinfectant dosage promoted citalopram removal and NDMA formation. However, no consistent correlation was found between citalopram removal and pH. Contrary to the situation of citalopram removal, NDMA generation was enhanced when citalopram was present in actual water matrices, especially in secondary effluent. DMA, as an intermediate of citalopram chlorination, contributed to NDMA formation, but not the only way.

Lesson Learnt from Recall of Valsartan and Other Angiotensin II Receptor Blocker Drugs Containing NDMA and NDEA Impurities

The presence of N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) impurities in angiotensin II receptor blocker (ARB) drugs containing tetrazole ring has triggered worldwide product recalls. The purpose of this article is to identify the potential gap area in current pharmaceutical industry practice that might have led to the NMDA and NDEA impurities escaping the drug manufacturer's and FDA's attention. The impact of process change was not adequately assessed by the manufacturer of contaminated APIs (active pharmaceutical ingredients), and potential for generation of mutagenic or other toxic impurities was not considered. The safety and risk associated with a chemical synthetic process was also not evaluated. This is primarily due to current industry practice which focuses on controlling the impurities above reporting threshold. ICH Q3A and FDA guidance on genotoxic and carcinogenic impurities in drug substances and products need to be integrated so that the ICH Q3A decision tree (attachment 3) begins by checking whether the synthetic process has been evaluated for the potential to generate toxic impurities. The compliance with ICH Q3A limits should be carried out only after the process has been determined to be safe without the risk of generating mutagenic and carcinogenic impurities.

Formation of N-nitrosodimethylamine by chloramination of anthropogenic nitrogenous compounds with dimethylamine monitored by Japanese water authorities

Pollutant release and transfer registers (PRTRs) compounds accidentally released to source waters can be important precursors of the carcinogenic N-nitrosodimethylamine (NDMA) during drinking water treatment. The NDMA formation potentials (NDMAFPs) of 31 anthropogenic nitrogenous compounds with dimethylamine (DMA) moiety on the Japanese PRTR and the registered precursors listed by the Ministry of Health, Labour and Welfare of Japan are investigated as well as influencing factors (i.e., NH₂Cl dose and water matrices) on the NDMAFPs of precursors. Tertiary amines with aryl groups β-positioned to the nitrogen atom of the DMA moiety formed high concentrations of NDMA (35-51%) during chloramination. Moreover, dimethylcarbamoyl chloride (DMCCl) was considered a new NDMA precursor with NDMAFP of 1.1%, higher than DMA, a traditional NDMA precursor. Excessive NH₂Cl dose enhanced the NDMA formation, and the NDMAFP of DMCCl significantly decreased in river water; the effect of the matrix in river water varied and was compound-specific. Among the selected nitrogenous compounds, NDMAFPs of 15 excessed the current guideline concentration for NDMA in Japan (100 ng/L) assuming an accidental release of 0.144 mg C/L (the concentration in previous Japanese water quality accident in May 2012), and 2-(dimethylaminomethyl) thiophene (DMAMT) showed the highest NDMAFP at 58 μg/L.

Lower molecular weight fractions of PolyDADMAC coagulants disproportionately contribute to N-nitrosodimethylamine formation during water treatment

N-nitrosodimethylamine (NDMA) is a chloramine disinfection by-product, and its formation in drinking waters can increase due to the addition of cationic polydiallyldimethylammonium chloride (polyDADMAC). PolyDADMAC is a cationic polymer added as a coagulant or coagulant aid to enhance turbidity removal during sedimentation and filtration. This paper answers two central questions to understanding the nature of the NDMA precursors in polyDADMAC. First, what is the reactivity of different molecular weight (MW) fractions of polyDADMAC with chloramines? NDMA formation potential (NDMAFP) and kinetic experiments with chloramines were conducted for non-fractionated (raw) and size-excluded fractions (<3K, 3-10K, and >10K Da.) of polyDADMAC. The lower MW fraction (<3K Da.) of polyDADMAC solutions was responsible for forming 64 ± 6% of the NDMA, despite containing only 8.7 and 9.8% of the carbon or nitrogen present in the bulk polymer. The chloramine demand kinetics of the lowest MW fraction were also >2× faster than the higher MW fractions. Therefore, in a water treatment application the lower MW polyDADMAC likely contributes to most of the NDMA attributed to the use of polyDADMAC. The second question was: can ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR) be used to characterize the molecular structures in polyDADMAC that react with chloramines? A peak for ¹H NMR dimethylamine (DMA), a known low MW NDMA precursor, was found in a commercial polyDADMAC solution and decreased upon chloramination. The estimated DMA alone could not account for the observed NDMAFP, indicating the presence of other low MW precursors. Diffusion order spectroscopy (DOSY) NMR also showed multiple lower MW organics in polyDADMAC that change upon chloramination, including a 1.5× decrease in MW, suggesting chloramines cleave CC or CN bonds. These reactions may produce intermediates responsible for NDMA formation. Polymer manufacturers could use NMR to synthesize polyDADMAC with less DMA and other low MW compounds that produce NDMA upon chloramination.

Inhibitory effects on N-nitrosodimethylamine formation by decrease of salted-fermented fish products and increase of condiments in kimchi

Ethanol extracts from developed kimchi condiments (KME, KMEE) and mixtures of sub-ingredients (ME, MEE) showed high nitrite scavenging activity. ME was able to scavenge 89% of total nitrite at 50 mg/mL ME and pH 1.2. The nitrite scavenging abilities of KME and KMEE were significantly higher than in ethanol extract from the control condiment. The inhibitory effects on N-nitrosodimethylamine (NDMA) formation by decrease of salted-fermented fish products (Jeot-gal) and increase of condiments in the composition of kimchi were investigated. The modified kimchi (KM) was prepared with new condiments, which included new sub-ingredients and reduced Jeot-gal. The NDMA and its precursor levels were significantly decreased in KM compared with those in the control kimchi (KC). The KM also obtained higher sensory scores than KC. Therefore, the increase of sub-ingredients and reduction of Jeot-gal in kimchi would be recommended for production of reduced-NDMA kimchi while maintaining or even enhancing flavor profiles.

Nitrite ion mitigates the formation of N-nitrosodimethylamine (NDMA) during chloramination of ranitidine

Ranitidine (RNT) has been an important tertiary amine precursor of N-nitrosodimethylamine (NDMA) in chlorine-based water treatment, due to reaction with monochloramine (NH₂Cl) with exceptionally high molar yields up to 90%. This study examined the effects of nitrite ions (NO₂^-) on the kinetics of NDMA formation during the chloramination of RNT under variable concentrations of dissolved oxygen (DO, 0.7-7.5mg/L), RNT (5-30μM), NH₂Cl (5-20mM), NO₂^- or NO₃^- (0-2mM) and pH (5.6-8.6). In the absence of the NO₂^-, the ultimate molar yield of NDMA after 6h of reaction was primarily influenced by [DO] and pH, while marginally affected by initial [RNT] and [NH₂Cl]. A kinetic model, prepared in accordance with the reaction sequence of NDMA formation, suggested that the rate determining step was accelerated with increasing [NH₂Cl]₀, [DO], and pH. A Kinetic study together with ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometer (UPLC-Q-TOF MS) and gas chromatography (GC)/TOF MS analyses in parallel demonstrated that the nitrite ion inhibited the nucleophilic substitution of the terminal amine on NH₂Cl, and reduced the pseudo-steady state concentration of N-peroxyl radicals, significantly decreasing the ultimate yields of NDMA.

Factors affecting N-nitrosodimethylamine formation from poly(diallyldimethyl-ammonium chloride) degradation during chloramination

Poly(diallyldimethylammonium chloride) (polyDADMAC) has been shown to be an important precursor of the probable human carcinogen N-nitrosodimethylamine (NDMA) when in contact with chloramine. In this study, we conducted an orthogonal experiment design to evaluate the effects of pH values, ammonia, bromide, natural organic matter (NOM) and monochloramine dosages on the formation of NDMA from polyDADMAC during chloramination. Meanwhile, single-factor experiments of pH, bromide and NOM prove the results of orthogonal experiment. The results supported that pH was the most critical factor affecting NDMA formation from polyDADMAC during chloramination, and the highest NDMA formation from polyDADMAC occurred at pH near 7 due to released DMA from polyDADMAC degradation and the critical importance of low concentrations of dichloramine in water. In the presence of excess bromide, the NDMA formation was enhanced significantly at all different pH values owing to bromochloramine, which has higher electronegativity of the brominated nitrogen atom than monochloramine or dichloramine. The NDMA formation from polyDADMAC in the presence of NOM was 41.7% lower than NDMA formation in the absence of NOM. The overwhelming majority of NDMA formation from polyDADMAC under simulated conditions was lower than the current advisory levels (i.e. 9 ng l-1 in Ontario, 10 ng l-1 in California).

Effects of inoculating autochthonous starter cultures on N-nitrosodimethylamine and its precursors formation during fermentation of Chinese traditional fermented fish

This study investigated the effects of Lactobacillus plantarum 120, Saccharomyces cerevisiae 2018 and Staphylococcus xylosus 135 inoculation on N-nitrosodimethylamine (NDMA) and its precursors formation, and on microbiological characteristics of Chinese traditional fermented fish products (CTFPs). The results indicated that three strains could directly degrade NDMA in culture broth, and the highest degradation rate was observed in L. plantarum 120. The lactic acid bacteria counts in samples inoculated with L. plantarum 120 and mixed starter cultures were significantly (P < 0.05) higher than the others during the initial and middle fermentation stages (≤3 weeks). The final contents of total volatile base nitrogen, trimethylamine, dimethylamine, nitrite and NDMA in inoculated samples were significantly (P < 0.05) lower than those in spontaneous fermentation samples. According to these results, the inoculation with autochthonous starter cultures was a promising method to inhibit the NDMA and its precursors accumulation in CTFPs during fermentation process.

Online monitoring of N-nitrosodimethylamine rejection as a performance indicator of trace organic chemical removal by reverse osmosis

The security of recycled water quality in potable reuse can be enhanced by improving the credibility of reverse osmosis (RO) treatment for the removal of trace organic chemicals (TOrCs). This study evaluated the potential of online monitoring of N-nitrosodimethylamine (NDMA) before and after RO treatment as a surrogate indicator for TOrC removal by RO. This pilot-scale study monitored NDMA concentrations in RO feedwater (ultrafiltration-treated wastewater) and RO permeate every 22 min using novel online NDMA analyzers-high-performance liquid chromatography followed by photochemical reaction and chemiluminescence detection. NDMA rejection by RO varied considerably in response to changes in operating conditions (permeate flux and feedwater temperature). A high linear correlation between NDMA rejection and the rejection of six other TOrCs was observed. The linear correlation was also identified for an RO membrane damaged with chlorine. The correlation between another potential surrogate indicator (conductivity rejection) and TOrC rejection was relatively low. NDMA, which is the smallest compound among regulated TOrCs, revealed rejections lower than the other TOrCs, indicating that NDMA rejection can be a conservative surrogate indicator capable of predicting changes in TOrC removal.

High rejection reverse osmosis membrane for removal of N-nitrosamines and their precursors

Direct potable reuse is becoming a feasible option to cope with water shortages. It requires more stringent water quality assurance than indirect potable reuse. Thus, the development of a high-rejection reverse osmosis (RO) membrane for the removal of one of the most challenging chemicals in potable reuse - N-nitrosodimethylamine (NDMA) - ensures further system confidence in reclaimed water quality. This study aimed to achieve over 90% removal of NDMA by modifying three commercial and one prototype RO membrane using heat treatment. Application of heat treatment to a prototype membrane resulted in a record high removal of 92% (1.1-log) of NDMA. Heat treatment reduced conductivity rejection and permeability, while secondary amines, selected as N-nitrosamine precursors, were still well rejected (>98%) regardless of RO membrane type. This study also demonstrated the highly stable separation performance of the heat-treated prototype membrane under conditions of varying feed temperature and permeate flux. Fouling propensity of the prototype membrane was lower than a commercial RO membrane. This study identified a need to develop highly selective RO membranes with high permeability to ensure the feasibility of using these membranes at full scale.

Biological treatment of N-nitrosodimethylamine (NDMA) and N-nitrodimethylamine (NTDMA) in a field-scale fluidized bed bioreactor

The ex situ treatment of N-nitrosodimethylamine (NDMA) and N-nitrodimethylamine (NTDMA) in groundwater was evaluated in a field-scale fluidized bed bioreactor (FBR). Both of these compounds, which originally entered groundwater at the test site from the use of liquid rocket propellant, are suspected human carcinogens. The objective of this research was to examine the application of a novel field-scale propane-fed fluidized bed bioreactor as an alternative to ultraviolet irradiation (UV) for treating NDMA and NTDMA to low part-per-trillion (ng/L) concentrations. Previous laboratory studies have shown that the bacterium Rhodococcus ruber ENV425 can biodegrade NDMA and NTDMA during growth on propane as a primary substrate and that the strain can effectively reduce NDMA concentrations in propane-fed bench-scale bioreactors of different design. R. ruber ENV425 was used as a seed culture for the FBR, which operated at a fluidization flow of ∼19 L-per-min (LPM) and received propane, oxygen, and inorganic nutrients in the feed. The reactor effectively treated ∼1 μg/L of influent NDMA to effluent concentrations of less than 10 ng/L at a hydraulic residence time (HRT) of only 10 min. At a 20 min HRT, the FBR reduced NDMA to <4.2 ng/L in the effluent, which was the discharge limit at the test site where the study was conducted. Similarly, NTDMA was consistently treated in the FBR from ∼0.5 μg/L to <10 ng/L at an HRT of 10 min or longer. Based on these removal rates, the average NDMA and NTDMA elimination capacities achieved were 2.1 mg NDMA treated/m³ of expanded bed/hr of operation and 1.1 mg NTDMA treated/m³ of expanded bed/hr of operation, respectively. The FBR system was highly resilient to upsets including power outages. Treatment of NDMA, but not NTDMA, was marginally affected when trace co-contaminants including trichloroethene (TCE) and trichlorofluoromethane (Freon 11) were initially added to feed groundwater, but performance recovered over a few weeks in the continued presence of these compounds. Strain ENV425 appeared to be replaced by native propanotrophs over time based on qPCR analysis, but contaminant treatment was not diminished. The results suggest that a FBR can be a viable alternative to UV treatment for removing NDMA from groundwater.