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

Metformin as an Emerging Pollutant in the Aquatic Environment: Occurrence, Analysis, and Toxicity

The use of human and veterinary drugs has led to the accumulation of pharmaceuticals in various aquatic environments at progressively increasing levels, exhibiting strong ecological risks. Metformin is widely used as a first-line prescription drug for the treatment of type 2 diabetes mellitus as well as a livestock drug. Unlike other drugs, metformin is not metabolized in the body, and almost all of its intake is excreted and released into the aquatic environment via urine and feces, causing adverse effects on aquatic ecosystems. This review provides an overview of the occurrence and detection of metformin in the aquatic environment and its toxic effects on different aquatic organisms (fish, daphnia, rotifers, chlorella). Metformin has been documented in a variety of aqueous environments such as wastewater, surface water, and groundwater as well as drinking water. The wide distribution of metformin in the aqueous environment calls for the development of more accurate detection methods. This paper reviews detection methods for metformin in the aqueous environment and evaluates their advantages and disadvantages. Toxicity studies have shown that metformin can cause adverse reactions in fish, such as oxidative stress, genotoxicity, disruption of intestinal flora, and morphological alterations; it also affects the growth and reproduction of small aquatic organisms. Knowledge gaps in the field of metformin research were assessed, and future research priorities were identified.

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.

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

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

Oxidation of amine-based pharmaceuticals with unactivated peroxymonosulfate: Kinetics, mechanisms, and elimination efficiency of NDMA formation

Amine-based pharmaceuticals are a significant class of N-nitrosodimethylamine (NDMA) precursors. This study investigated the use of unactivated peroxymonosulfate (PMS) to control amine-based pharmaceuticals and their NDMA formation potential. Kinetic analysis and product identification revealed that sumatriptan and doxylamine primarily underwent reactions at their tertiary amine group, while ranitidine and nizatidine had both tertiary amine and thioether group as reaction sites. The NDMA formation from sumatriptan and doxylamine during post-chloramination was significantly reduced with the abatement of the parent contaminants, while the formation of NDMA remained high even if full abatement of ranitidine and nizatidine was achieved. Product formation kinetics and reference standard tests revealed the great contribution of transformation products to NDMA formation. Ranitidine could be oxidized to sulfoxide-type product ranitidine-SO and N-oxide type product ranitidine-NO. Ranitidine-SO exhibited a high NDMA yield comparable to that of ranitidine (>90%), while ranitidine-NO showed a low NDMA yield (2%). With further oxidation of ranitidine-SO at the tertiary amine group, NDMA formation was reduced by more than 90%. The underlying mechanism for the importance of the tertiary amine group in NDMA formation was demonstrated by quantum chemical calculation. These findings underscore the potential of PMS pre-oxidation on NDMA control.

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

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

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

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

Exploring Br-'s roles on non-brominated NDMA formation during ozonation: Reactive oxygen species contribution and brominated intermediate path validation

Bromide ions (Br^-) affected non-brominated nitroso-dimethylamine (NDMA) formation during ozonation, but the mechanism is still unclear. 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene) di-semicarbazide (TMDS) was chosen to further probe this problem. The results indicated that low levels of Br^- (≤20 μM) enhanced NDMA from 3.27 to 7.56 μg/L, while its amount slightly dropped to 6.22 μg/L raising Br^- to 100 μM. It was experimentally verified that intermediates 1,1-dimethylsemicarbazide (DMSC) and 1,1-dimethylhydrazine (UDMH) played important roles on promoting NDMA generation, whose contribution rates were 40.2% and 32.2%, respectively. The brominated substances with higher NDMA molar yields were detected. ∙OH reduced NDMA formation without Br^-, while it played promotion role with Br^-; the corresponding contribution rates were - 26.9% and 29.2%, respectively. No matter with or without Br^-, both ∙O₂^- and ^lO₂ brought a boost to NDMA formation, their contribution ratios were 34.9% and 58.1% without Br^-, while raised significantly to 64.6% and 81.5% when Br^- existed. Br^- not only facilitated NDMA formation, but also benefited the degradation of TMDS. Based on the calculation results and intermediates detected, the influence mechanisms of Br^- were proposed. The results would provide theoretical basis and technical guarantee for treating NDMA precursors and bromide co-existing water in the future.

Wastewater bacteria remediating the pharmaceutical metformin: Genomes, plasmids and products

Metformin is used globally to treat type II diabetes, has demonstrated anti-ageing and COVID mitigation effects and is a major anthropogenic pollutant to be bioremediated by wastewater treatment plants (WWTPs). Metformin is not adsorbed well by activated carbon and toxic N-chloro derivatives can form in chlorinated water. Most earlier studies on metformin biodegradation have used wastewater consortia and details of the genomes, relevant genes, metabolic products, and potential for horizontal gene transfer are lacking. Here, two metformin-biodegrading bacteria from a WWTP were isolated and their biodegradation characterized. Aminobacter sp. MET metabolized metformin stoichiometrically to guanylurea, an intermediate known to accumulate in some environments including WWTPs. Pseudomonas mendocina MET completely metabolized metformin and utilized all the nitrogen atoms for growth. Pseudomonas mendocina MET also metabolized metformin breakdown products sometimes observed in WWTPs: 1-N-methylbiguanide, biguanide, guanylurea, and guanidine. The genome of each bacterium was obtained. Genes involved in the transport of guanylurea in Aminobacter sp. MET were expressed heterologously and shown to serve as an antiporter to expel the toxic guanidinium compound. A novel guanylurea hydrolase enzyme was identified in Pseudomonas mendocina MET, purified, and characterized. The Aminobacter and Pseudomonas each contained one plasmid of 160 kb and 90 kb, respectively. In total, these studies are significant for the bioremediation of a major pollutant in WWTPs today.

Simultaneous Determination for Nine Kinds of N-Nitrosamines Compounds in Groundwater by Ultra-High-Performance Liquid Chromatography Coupled with Triple Quadrupole Mass Spectrometry

The ability to effectively detect N-nitrosamine compounds by liquid chromatography-tandem mass spectrometry presents a challenge due to the problems of high detection limits and difficulty in simultaneous N-nitrosamine compound detection. In order to overcome these limitations, this study reduced the detection limit of N-nitrosamine compounds by applying n-hexane pre-treatment to remove non-polar impurities before the conventional process of column extraction. In addition, ammonium acetate was used as the mobile phase to enhance the retention of nitrosamine target substances on the chromatographic column, with formic acid added to the mobile phase to improve the ionization level of N-nitrosodiphenylamine, to achieve the simultaneous detection of multiple N-nitrosamine compounds. Applying these modifications to the established detection method allowed the rapid and accurate detection of N-nitrosamine in water within 12 min. The linear relationship, detection limit, quantification limit and sample spiked recovery rate of nine types of nitrosamine compound were investigated, showing that the correlation coefficient ranged from 0.9985-0.9999, while the detection limits of the instrument and the method were 0.280-0.928 µg·L^-1 and 1.12-3.71 ng·L^-1, respectively. The spiked sample recovery rate ranged from 64.2-83.0%, with a standard deviation of 2.07-8.52%, meeting the requirements for trace analysis. The method was applied to the detection of N-nitrosamine compounds in nine groundwater samples in Wuhan, China, and showed that the concentrations of N-nitrosodimethylamine and NDEA were relatively high, highlighting the need to monitor water bodies with very low levels of pollutants and identify those requiring treatment.

Metformin Contamination in Global Waters: Biotic and Abiotic Transformation, Byproduct Generation and Toxicity, and Evaluation as a Pharmaceutical Indicator

Metformin is the first-line antidiabetic drug and one of the most prescribed medications worldwide. Because of its ubiquitous occurrence in global waters and demonstrated ecotoxicity, metformin, as with other pharmaceuticals, has become a concerning emerging contaminant. Metformin is subject to transformation, producing numerous problematic transformation byproducts (TPs). The occurrence, removal, and toxicity of metformin have been continually reviewed; yet, a comprehensive analysis of its transformation pathways, byproduct generation, and the associated change in adverse effects is lacking. In this review, we provide a critical overview of the transformation fate of metformin during water treatments and natural processes and compile the 32 organic TPs generated from biotic and abiotic pathways. These TPs occur in aquatic systems worldwide along with metformin. Enhanced toxicity of several TPs compared to metformin has been demonstrated through organism tests and necessitates the development of complete mineralization techniques for metformin and more attention on TP monitoring. We also assess the potential of metformin to indicate overall contamination of pharmaceuticals in aquatic environments, and compared to the previously acknowledged ones, metformin is found to be a more robust or comparable indicator of such overall pharmaceutical contamination. In addition, we provide insightful avenues for future research on metformin.

Formation mechanism and control strategies of N-nitrosodimethylamine (NDMA) formation during ozonation

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).

Performance of high temperature phase-stable high entropy oxide (MgCuMnCoFe)O x in catalytic wet air oxidation of chloroquine phosphate

With the continuous spread of COVID-19, the water pollution problems caused by the abuse of chloroquine phosphate (CQP) as an antiviral drug have attracted wide attention. The cubic Fm-3m spinel high entropy oxide (HEO)-(MgCuMnCoFe)O _x was prepared by coprecipitation method as the catalytic wet air oxidation (CWAO) catalyst to treat CQP simulated wastewater. Through electron spin resonance (ESR) analysis, HEO will stimulate the production of superoxide radical (·O₂ ^-) and hydroxyl radical (·OH) in the wet air oxidation (WAO) process, which accelerates the degradation and mineralization of CQP. Through response surface method (RSM) optimization, the optimal degradation conditions of CQP in CWAO were proposed: initial oxygen pressure of 15 bar, catalyst dosage of 1.4 g/L and temperature of 230 °C. The advantages of HEO in CWAO were analyzed by principal component analysis (PCA). The degradation mechanism of CQP in CWAO by (MgCuMnCoFe)O _x were explored. This work provides a new idea for the rapid development of HEO in the field of environmental catalysis.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-022-07271-z.

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

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