Efficient photoreductive decomposition of N-nitrosodimethylamine by UV/iodide process

Transgenerational Reproductive and Developmental Toxicity Induced by N-Nitrosodimethylamine and Its Metabolite Formaldehyde in Drosophila melanogaster

N-Nitrosodimethylamine (NDMA) is a known water disinfection byproduct (DBP) characterized as a potent hepatotoxin, promutagen, and probable human carcinogen; this is because of the metabolites associated with its biotransformation. The metabolism of NDMA produces formaldehyde, another alkylating agent and DBP. Both compounds are generated from natural and anthropogenic sources, but the safety restrictions applied to NDMA do not extend to the uses of formaldehyde. Hence, potential health and ecological risks are of concern. Due to limited information on the long-term effects of exposure to these compounds at environmentally relevant concentrations, this work aimed to compare the transgenerational reproductive and developmental toxicity of separate exposures to NDMA or its metabolite formaldehyde in Drosophila melanogaster over four generations. The parental flies were fed NDMA or formaldehyde (1.19E-06 to 5 mM) for 48 h during the third larval instar. Subsequent offspring (F1-F3) were grown under compound-free conditions. In the parental generation, both exposures modified the time to emergence and reduced the number of progenies. NDMA, but not formaldehyde, was lethal, affected fertility, and weakly induced malformations. In the next generations, both exposures induced malformed flies and modified the number of offspring. Reproductive toxicity and malformations were maintained for at least three generations, suggesting that detrimental effects could extend to unexposed offspring. This is the first study reporting the associated individual transgenerational effects on reproduction and development between NDMA and its metabolite formaldehyde in D. melanogaster, highlighting the relevance of evaluating multiple generations to accurately determine the health and environmental risks of pollutants.

How I- alters UV and UV/VUV processes' redox capacities: Evidences from iodine species evolution, hydrogen peroxide formation, and oxyhalides degradation?

Although UV and/or VUV tandem I- are often proposed as advanced reduction processes (ARPs) to eliminate micropollutants by generating eaq-, the fate of I- and its byproducts formation remain to be explored. Therefore, this study investigated the iodine species evolution during UV/I- and UV/VUV/I- processes under different influencing factors. Results show that UV/VUV oxidized most of I- to IO3- whereas UV only oxidized a portion of I- to intermediate reactive iodine species (RISs, including I2, HOI, and I3-); meanwhile, substantial H2O2 was generated only in UV/VUV/I- process but not in UV/I- process, proving that UV/VUV owns stronger oxidation ability than UV alone. Spiking I- into water exerted triple-sided effects by consuming •OH, generating eaq-, and shielding light, thus complicating the systems. Holistically, increasing pH or decreasing dissolved oxygen converted oxidizing environment into reducing condition and caused less RISs formation, especially for UV/VUV/I-. For oxyhalides, neither UV/I- nor UV/VUV/I- degraded ClO4-. While UV/I- cannot remove ClO3-, UV/VUV/I- reduced ClO3- to Cl-. Expectedly, both UV/I- and UV/VUV/I- reduced BrO3- to Br- more efficiently than UV and UV/VUV, confirming that I- can enhance the reduction capacities of UV/VUV and UV technologies.

Advanced oxidation/reduction processes (AO/RPs) for wastewater treatment, current challenges, and future perspectives: a review

Advanced oxidation/reduction processes (AO/RPs) are considered as effective water treatment technologies and thus could be used to solve the problem of water pollution. These technologies of wastewater treatment involve the production of highly reactive species such as •OH, H•, e-aq, SO4•-, and SO3•-. These radicals can attack the targeted contaminants present in aqueous media and result in their destruction. The efficiency of AO/RPs is highly affected by various operational parameters such as initial concentration of contaminant, solution pH, catalyst amount, intensity of light source, nature of oxidant and reductant used, and the presence of various ionic species in aquatic media. Among AO/RPs, the solar light-based AO/RPs are most widely used nowadays for contaminant removal from aqueous media because of their high environmental friendliness and cost effectiveness. By using these techniques, almost all types of pollutants can be easily removed from aquatic media within short intervals of time, and hence, the problem of water pollution can be solved effectively. This review focuses on various AO/RPs used for wastewater treatment. The effects of different operational parameters that affect the efficiency of these processes toward contaminant removal have been discussed. Besides, challenges and future recommendations are also briefly provided for the researchers in order to improve the efficiency of these processes.

The utility of ultraviolet beam in advanced oxidation-reduction processes: a review on the mechanism of processes and possible production free radicals

Advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) are a set of chemical treatment procedures designed to eliminate organic (sometimes inorganic) contamination in water and wastewater by producing free reactive radicals (FRR). UV irradiation is one of the factors that are effectively used in oxidation-reduction processes. Not only does the UV beam cause the photolysis of contamination, but it also leads to the product of FRR by affecting oxidants-reductant, and the pollutant decomposition occurs by FRR. UV rays produce active radical species indirectly in an advanced redox process by affecting an oxidant (O3, H2O2), persulfate (PS), or reducer (dithionite, sulfite, sulfide, iodide, ferrous). Produced FRR with high redox potential (including oxidized or reduced radicals) causes detoxification and degradation of target contaminants by attacking them. In this review, it was found that ultraviolet radiation is one of the important and practical parameters in redox processes, which can be used to control a wide range of impurities.

A review of factors affecting the formation and roles of primary and secondary reactive species in UV254-based advanced treatment processes

The presence of organic micropollutants (OMPs) in water has been threatening human health and aquatic ecosystems worldwide. Ultraviolet-based advanced treatment processes (UV-ATPs) are one of the most effective and promising technologies to transform OMPs in water; therefore, an increasing number of emerging UV-ATPs are proposed. However, appropriate selection of UV-ATPs for practical applications is challenging because each UV-ATP generates different types and concentrations of reactive species (RSs) that may not be sufficient to degrade specific types of OMPs. Furthermore, the concentrations and types of RSs are highly influenced by anions and dissolved organic matter (DOM) coexisting in real waters, making systematic understandings of their interfering mechanisms difficult. To identify and address the knowledge gaps, this review provides a comparison of the generations and variations of various types of RSs in different UV-ATPs. These analyses not only prove the importance of water matrices on formation and consumption of primary and secondary RSs under different conditions, but also highlight the non-negligible roles of optical properties and reactivities of DOM and anions. For example, different UV-ATPs may be applicable to different target OMPs under different conditions; and the concentrations and roles of secondary RSs may outperform those of primary RSs in OMP degradation for real applications. With continuous progress and outstanding achievements in the UV-ATPs, it is hoped that the findings and conclusions of this review could facilitate further research and application of UV-ATPs.

Hydrated electron based photochemical processes for water treatment

Hydrated electron (e_aq^-) based photochemical processes have emerged as a promising technology for contaminant removal in water due to the mild operating conditions. This review aims to provide a comprehensive and up-to-date summary on e_aq^- based photochemical processes for the decomposition of various oxidative contaminants. Specifically, the characteristics of different photo-reductive systems are first elaborated, including the environment required to generate sufficient e_aq^-, the advantages and disadvantages of each system, and the comparison of the degradation efficiency of contaminants induced by e_aq^-. In addition, the identification methods of e_aq^- (e.g., laser flash photolysis, scavenging studies, chemical probes and electron spin resonance techniques) are summarized, and the influences of operating conditions (e.g., solution pH, dissolved oxygen, source chemical concentration and UV type) on the performance of contaminants are also discussed. Considering the complexity of contaminated water, particular attention is paid to the influence of water matrix (e.g., coexisting anions, alkalinity and humic acid). Moreover, the degradation regularities of various contaminants (e.g., perfluorinated compounds, disinfection by-products and nitrate) by e_aq^- are summarized. We finally put forward several research prospects for the decomposition of contaminants by e_aq^- based photochemical processes to promote their practical application in water treatment.

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.

Photodegradation of F-53B in aqueous solutions through an UV/Iodide system

Advanced reduction by strong reducing hydrated electrons is a promising approach to degrade per- and polyfluoroalkyl substances (PFAS). This research aimed to investigate the effectiveness of UV/Iodide system for 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA, F-53B) degradation in aqueous solutions. Results from this work demonstrated that UV irradiation with an addition of 0.3 mM KI resulted in 55.99% degradation of F-53B within 15 min and almost 100% within 2 h. The defluorination efficiency of F-53B in the UV/Iodide system was 2.6 times higher than that in the sole UV system after 2 h of irradiation. The degradation efficiency of F-53B was not significantly affected by air purging. The defluorination efficiency with air bubbling, however, was 14.57% lower than that with nitrogen purging. The photodegradation of F-53B in the UV/Iodide system could be well described by a pseudo-first-order kinetic model. Degradation rate constant of F-53B correlated positively with the initial concentration. At 20 μg/L, the pseudo-first-order rate constant was 5.641 × 10^-2 min^-1 and the half-life was 12.29 min. Higher initial concentration also required less energy input to achieve the same degradation efficiency. The detection and identification of degradation intermediates implied that destruction of F-53B started from dechlorination and followed by continuously "flaking off" CF₂ units.

Changes in levels of N-nitrosamine formed from amine-containing compounds during chloramination via photocatalytic pretreatment with immobilized TiO2: Effect of source water and pH

We investigated the effectiveness of photocatalytic pretreatment (PCP) of precursors in minimizing the formation potentials (FPs) of carcinogenic nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodiethanolamine (NDELA), during water chloramination. A steel mesh substrate with immobilized TiO₂ was highly efficient at mitigating nitrosamine formation and removing targeted precursors such as ranitidine, nizatidine, trimebutine, triethanolamine, and metoclopramide. Compared to UVC/H₂O₂, PCP under UVA irradiation (intensity of 0.67 mW cm^-2) was more effective for reducing nitrosamine-FPs during post-chloramination. However, the PCP efficacies varied with the water source, pretreatment pH, and irradiation time. For example, PCP of eutrophic water increased the NDMA-FPs, but produced notable reductions (up to 99%) for NDELA- and NDEA-FPs. Shorter irradiation times, up to 15 min, increased the NDELA-FP in triethanolamine, and the NDMA-FP in nizatidine and trimebutine. However, the nitrosamine-FP decreased by > 50% after PCP at a pH > 5.6, following irradiation for 120 min. Oxygen addition, N-de(m)ethylation, and N-dealkylation were responsible for decreasing nitrosamine-FPs via the destruction of key moieties; this has been elucidated by mass spectroscopy. This study suggests that PCP could be used as an alternative strategy for minimizing nitrosamine-FPs during water treatment.

The fate and transformation of iodine species in UV irradiation and UV-based advanced oxidation processes

Iodinated disinfection byproducts (I-DBPs) formed in water treatment are of emerging concern due to their high toxicity and the tase-and-odor problems associated with iodinated trihalomethanes (I-THMs). Iodoacetic acid and dichloroiodomethane are currently regulated in Shenzhen, China and the Ministry of Health of the People's Republic of China has also been considering regulating I-DBPs. Iodide (I^-), organoiodine compounds (e.g., iodinated X-ray contrast media [ICM]), and iodate (IO₃^-) are the three common iodine sources in aquatic environment that lead to I-DBP formation. While UV irradiation effectively inactivate a wide range of microorganisms in water, it induces the transformation of these iodine sources, enabling the formation of I-DBPs. This review focuses on the fate and transformation of these iodine sources in UV-based water treatment (i.e., UV irradiation and UV-based advanced oxidation processes [UV-AOPs]) and the formation of I-DBPs in post-disinfection. I^- released in UV-based treatments of ICM and can be oxidized in subsequent disinfection to hypoiodous acid (HOI), which reacts with natural organic matter (NOM) to produce I-DBPs. Both UV and UV-AOPs are not able to fully mineralize ICM and completely oxidize the released I^- to (except UV/O₃). Results reveal that UV and UV-AOPs are adequate for I-DBP degradation but require high UV doses. While the ideal I-DBP mitigation strategy awaits to be developed, understanding their sources and formation pathways aids in informed selections of water treatment processes, empowers water suppliers to meet drinking water standards, and minimizes consumers' exposure to I-DBPs.

Photodegradation pathway of iodate and formation of I-THMs during subsequent chloramination in iodate-iodide-containing water

This study investigated the mechanisms of mixed IO₃^-/I^- system under UV irradiation in drinking water and compared the iodinated trihalomethanes (I-THMs) formation of a mixed IO₃^-/I^- system to that of single I^- and IO₃^- systems during subsequent chloramination. The effects of initial I^-/IO₃^- molar ratio, pH, and UV intensity on a mixed IO₃^-/I^- system were studied. The introduction of I^- enhanced the conversion rate of IO₃^- to reactive iodine species (RIS). Besides, IO₃^- degradation rate increased with the increase of initial I^- concentration and UV intensity and the decrease of pH value. In a mixed IO₃^-/I^- system, IO₃^- could undergo direct photolysis and photoreduction by hydrated electron (e_aq^-). Moreover, the enhancement of I-THM formation in a mixed IO₃^-/I^- system during subsequent chloramination was observed. The I-THM yields in a mixed IO₃^-/I^- system were higher than the sum of I-THMs produced in a single IO₃^- and I^- systems at all the evaluated initial I^- concentrations and pH values. The difference between I-THM formation in a mixed IO₃^-/I^- system and the sum of I-THMs in a single IO₃^- and I^- systems increased with the increase of initial I^- concentration. As the initial pH decreased from 9 to 5, the difference of I-THM yields enhanced, while the total I-THM yield of a mixed IO₃^-/I^- system and single I^- and IO₃^- systems decreased slightly. Besides, IO₃^--I^--containing water with DOC concentration of 2.5-4.5 mg-C/L, which mainly contained humic-acid substances, had a higher risk in I-THMs formation than individual I^--containing and IO₃^--containing water.

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.

Chemical profiling of liposoluble liquid smokes obtained from Eucalyptus wood tar: confirmation of absence of polycyclic aromatic hydrocarbons

Liposoluble liquid smoke (LS) preparations are versatile food additives used worldwide. The objective of the present work was to characterise the chemical composition of four types of industrial liposoluble LS currently used as the basis for the production of commercial smoke flavourings. The LS was obtained by vacuum fractional distillation from a raw pyrolysis oil (raw LS) obtained primarily from eucalyptus wood tar. The raw LS and the four LS flavourings obtained therefrom were analysed by gas chromatography/mass spectrometry (GC/MS) to characterise the main groups of components. Additional analyses were carried out to evaluate the occurrence of PAHs (polycyclic aromatic hydrocarbons) in the samples, as the producer claimed that these samples are free of PAHs. The main chemical components characterised in the LS were organic acids, aldehydes, esters, furans, pyrans and phenols, with phenolic compounds being the major chemical group. For the four LS tested samples, no PAHs could be detected with the method employed, which could indicate that the industrial processing was able to effectively remove this harmful class of compounds, or at least decrease its concentrations to levels below the limits of detection of the method of analysis.

Enhancing photo-degradation of ciprofloxacin using simultaneous usage of eaq- and OH over UV/ZnO/I- process: Efficiency, kinetics, pathways, and mechanisms

The aim of this study is to develop the process relies on the UV irradiation of ZnO and I^-, i.e. UV/ZnO /I^- (UZI), to create both oxidizer and reducer agents simultaneously for photo-degradation of the Ciprofloxacin (CIP). This paper shows that while applying UV irradiation, UV/ZnO and UV/I^- for 20 min can lead to achieve 37.5%, 58.12%, and 61.4% photo-degradation of 100 mg L^-1 CIP at pH 7, respectively. Moreover, the UZI treatment can provide 91.54% photo-degradation efficiency. The LC-MS analysis of the UZI effluent indicates that 10 min process was adequate to degrade CIP into simple ring-shaped metabolites while 15 min treatment, mostly of CIP intermediates were linear and biodegradable organic compounds. Furthermore, fourteen little fragments were identified in the CIP photo-degradation via UZI, during the photoreaction time of 2.5 to 20 min. Then, a pseudo first-order kinetics equation was utilized to model the observed photo-degradation process. Finally, the computational results show that the increased concentration of the CIP solution from 100 to 400 mg L^-1 decreases the observed rate constant (k_obs) from 0.4125 to 0.2189 min^-1 while increases the photoreaction rate (r_obs) from 41.25 to 87.56 mg L^-1 min^-1.

Reagent-free and pH-independent degradation of N-nitrosamines using electrons generated via corona discharge at ambient pressure

Traditional degradation methods for N-nitrosamines are either confined with acid solution or required for additional chemical reagents to guarantee high reaction efficiency. Herein, we demonstrate a facile and effective way for reagent-free and pH-independent degradation of N-nitrosamines, which was induced by free electrons generated via corona discharge at ambient pressure. The highly reactive free electron is produced in situ and responsible for degradation of three N-nitrosamines, which was also theoretically confirmed. N-nitrosamines were believed to be reduced by electrons and to form the radical anion, which underwent a selectively heterolytic cleavage of the N-NO bonds to form the corresponding secondary amines as the degradation products.

Simultaneous Adsorption and Electrochemical Reduction of N-Nitrosodimethylamine Using Carbon-Ti4O7 Composite Reactive Electrochemical Membranes

This study focused on synthesis and characterization of Ti₄O₇ reactive electrochemical membranes (REMs) amended with powder-activated carbon (PAC) or multiwalled carbon nanotubes (MWCNTs). These composite REMs were evaluated for simultaneous adsorption and electrochemical reduction of N-nitrosodimethylamine (NDMA). The carbon-Ti₄O₇ composite REMs had high electrical conductivities (1832 to 2991 S m^-1), where carbon and Ti₄O₇ were in direct electrical contact. Addition of carbonaceous materials increased the residence times of NDMA in the REMs by a factor of 3.8 to 5.4 and therefore allowed for significant electrochemical NDMA reduction. The treatment of synthetic solutions containing 10 μM NDMA achieved >4-log NDMA removal in a single pass (liquid residence time of 11 to 22 s) through the PAC-REM and MWCNT-REM with the application of a -1.1 V/SHE cathodic potential, with permeate concentrations between 18 and 80 ng L^-1. The treatment of a 6.7 nM NDMA-spiked surface water sample, under similar operating conditions (liquid residence time of 22 s), achieved 92 to 97% removal with permeate concentrations between 16 and 40 ng L^-1. Density functional theory calculations determined a probable reaction mechanism for NDMA reduction, where the rate-limiting step was a direct electron transfer reaction.

UV Sensitization of Nitrate and Sulfite: A Powerful Tool for Groundwater Remediation

Groundwater contamination by nitrate and organic chemicals (for example, 1,4-dioxane) is a growing worldwide concern. This work presents a new approach for simultaneously treating nitrate and 1,4-dioxane, which is based on the ultra-violet (UV) sensitization of nitrate and sulfite, and the production of reactive species. Specifically, water contaminated with nitrate and 1,4-dioxane is irradiated by a UV source (<250 nm) at relatively high doses, to sensitize in situ nitrate and generate OH•. This leads to the oxidation of 1,4-dioxane (and other organics) and the (undesired) production of nitrite as an intermediate. Subsequently, sulfite is added at an optimized time-point, and its UV sensitization produces hydrated electrons that react and reduces nitrite. Our results confirm the effectivity of the proposed treatment: UV irradiation of nitrate (at >5 mg N/L) efficiently degraded 1,4-dioxane, while producing nitrite at levels higher than its maximum contaminant level (MCL) of 1 mg N/L in drinking water. Adding sulfite to the process after 10 min of irradiation reduces the concentration of nitrite without affecting the degradation rate of 1,4-dioxane. The treated water contained elevated levels of sulfate; albeit at much lower concentration than its MCL. Treating water contaminated with nitrate and organic chemicals (often detected concomitantly) typically requires several expensive treatment processes. The proposed approach presents a cost-effective alternative, employing a single system for the treatment of nitrate and organic contaminants.

Ruthenium Catalysts for the Reduction of N-Nitrosamine Water Contaminants

N-Nitrosamines have raised extensive concern due to their high toxicity and detection in treated wastewater and drinking water. Catalytic reduction is a promising alternative technology to treat N-nitrosamines, but to advance this technology pathway, there is a need to develop more-efficient and cost-effective catalysts. We have previously discovered that commercial catalysts containing ruthenium (Ru) are unexpectedly active in reducing nitrate. This study evaluated supported Ru activity for catalyzing reduction of N-nitrosamines. Experiments with N-nitrosodimethylamine (NDMA) show that contaminant is rapidly reduced on both commercial and in-house prepared Ru/Al₂O₃ catalysts, with the commercial material yielding an initial metal weight-normalized pseudo-first-order rate constant ( k₀) of 1103 ± 133 L·g_Ru^-1·h^-1 and an initial turnover frequency (TOF₀) of 58.0 ± 7.0 h^-1. NDMA is reduced to dimethylamine (DMA) and ammonia end-products, and a small amount of 1,1-dimethylhydrazine (UDMH) was detected as a transient intermediate. Experiment with a mixture of five N-nitrosamines spiked into tap water (1 μg L^-1 each) demonstrates that Ru catalysts are very effective in reducing a range of N-nitrosamine structures at environmentally relevant concentrations. Cost competitiveness and high catalytic activities with a range of contaminants provide a strong argument for developing Ru catalysts as part of the water purification and remediation toolbox.