Quantification of Total <i>N</i>‑Nitrosamine Concentrations in Aqueous Samples via UV-Photolysis and Chemiluminescence Detection of Nitric Oxide

<i>N</i>-Nitrosamines are potent mutagens and carcinogens that can be formed during oxidative water treatment. This study describes a novel method for the determination of total <i>N</i>-nitrosamines by UV-photolysis and subsequent chemiluminescence detection of nitric oxide. Denitrosation of <i>N</i>-nitrosamines was accomplished with a microphotochemical reactor consisting of a knitted reaction coil and a low-pressure mercury lamp. The detection limits for differing <i>N</i>-nitrosamines ranged between 0.07 μM (14 pmol injected) and 0.13 μM (26 pmol injected). The nitric oxide formation from selected <i>N</i>-nitrosamines was linear (<i>R</i>² = 0.98–0.99) from 0.1 to 10 μM. The small cross-section and volume of the microphotochemical reactor used in this study was optimal to reach a sensitivity level comparable to chemical denitrosation-based methods. In addition, this method had several advantages over other similar methods: (i) compared to chemical denitrosation with copper monochloride or triiodide, the UV-photolysis does not require chemicals and is not affected by interferences of byproducts (e.g., formation of NOI), (ii) the reproducibility of replicates was enhanced compared to the triiodide-based method, and (iii) a commercially available photoreactor and NO analyzer were used. The application of this method for the determination of the <i>N</i>-nitrosamine formation potential of personal care products demonstrates its utility for assessing whether <i>N</i>-nitrosodimethylamine (NDMA) or other specific nitrosamines of current interest are dominant or minor components, respectively, of the total <i>N</i>-nitrosamine pool in technical aquatic systems or biological samples

Reaction of Ferrate(VI) with ABTS and Self-Decay of Ferrate(VI): Kinetics and Mechanisms

Reactions of ferrate­(VI) during water treatment generate perferryl­(V) or ferryl­(IV) as primary intermediates. To better understand the fate of perferryl­(V) or ferryl­(IV) during ferrate­(VI) oxidation, this study investigates the kinetics, products, and mechanisms for the reaction of ferrate­(VI) with 2,2′-azino-bis­(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and self-decay of ferrate­(VI) in phosphate-buffered solutions. The oxidation of ABTS by ferrate­(VI) via a one-electron transfer process produces ABTS^•+ and perferryl­(V) (<i>k</i> = 1.2 × 10⁶ M^–1 s^–1 at pH 7). The perferryl­(V) mainly self-decays into H₂O₂ and Fe­(III) in acidic solution while with increasing pH the reaction of perferryl­(V) with H₂O₂ can compete with the perferryl­(V) self-decay and produces Fe­(III) and O₂ as final products. The ferrate­(VI) self-decay generates ferryl­(IV) and H₂O₂ via a two-electron transfer with the initial step being rate-limiting (<i>k</i> = 26 M^–1 s^–1 at pH 7). Ferryl­(IV) reacts with H₂O₂ generating Fe­(II) and O₂ and Fe­(II) is oxidized by ferrate­(VI) producing Fe­(III) and perferryl­(V) (<i>k</i> = ∼10⁷ M^–1 s^–1). Due to these facile transformations of reactive ferrate­(VI), perferryl­(V), and ferryl­(IV) to the much less reactive Fe­(III), H₂O₂, or O₂, the observed oxidation capacity of ferrate­(VI) is typically much lower than expected from theoretical considerations (i.e., three or four electron equivalents per ferrate­(VI)). This should be considered for optimizing water treatment processes using ferrate­(VI)

Kinetics of Inactivation of Waterborne Enteric Viruses by Ozone

Ozone is an effective disinfectant against all types of waterborne pathogens. However, accurate and quantitative kinetic data regarding virus inactivation by ozone are scarce, because of the experimental challenges associated with the high reactivity of ozone toward viruses. Here, we established an experimental batch system that allows tailoring and quantifying of very low ozone exposures and simultaneously measuring virus inactivation. Second-order ozone inactivation rate constants (<i>k</i>_O₃‑virus) of five enteric viruses [laboratory and two environmental strains of coxsackievirus B5 (CVF, CVEnv1, and CVEnv2), human adenovirus (HAdV), and echovirus 11 (EV)] and four bacteriophages (MS2, Qβ, T4, and Φ174) were measured in buffered solutions. The <i>k</i>_O₃‑virus values of all tested viruses ranged from 4.5 × 10⁵ to 3.3 × 10⁶ M^–1 s^–1. For MS2, <i>k</i>_O₃‑MS2 depended only weakly on temperature (2–22 °C; <i>E</i>_a = 22.2 kJ mol^–1) and pH (6.5–8.5), with an increase in <i>k</i>_O₃‑MS2 with increasing pH. The susceptibility of the selected viruses toward ozone decreases in the following order: Qβ > CVEnv2 > EV ≈ MS2 > Φ174 ≈ T4 > HAdV > CVF ≈ CVEnv1. On the basis of the measured <i>k</i>_O₃‑Virus and typical ozone exposures applied in water and wastewater treatment, we conclude that ozone is a highly effective disinfectant for virus control

MEMBRO₃X, a Novel Combination of a Membrane Contactor with Advanced Oxidation (O₃/H₂O₂) for Simultaneous Micropollutant Abatement and Bromate Minimization

Ozonation is a water treatment process for disinfection and/or micropollutant abatement. However, ozonation of bromide-containing water leads to bromate (BrO₃^–) formation, a potential human carcinogen. A solution for mitigating BrO₃^– formation during abatement of micropollutants is to minimize the ozone (O₃) concentration. This can be achieved by dosing ozone in numerous small portions throughout a reactor in the presence of H₂O₂. Under these conditions, O₃ is rapidly consumed to form hydroxyl radical (^<b>•</b>OH), which will oxidize micropollutants. To achieve this goal, a novel process (“MEMBRO₃X”) was developed in which ozone is transferred to the water through the pores of polytetrafluoroethylene (PTFE) hollow fiber membranes. When compared to the conventional peroxone process (O₃/H₂O₂), the MEMBRO₃X process shows better performance in terms of micropollutant abatement and bromate minimization for groundwater and surface water treatment. For a groundwater containing 180 μg/L bromide, a 95% abatement of the ozone-resistant probe compound <i>p</i>-chlorobenzoic acid yielded <0.5 μg/L BrO₃^–, whereas in the conventional peroxone process, 8 μg/L BrO₃^– was formed. In addition, the efficacy of the MEMBRO₃X process was demonstrated with river water and lake water

Enhanced Chlorine Dioxide Decay in the Presence of Metal Oxides: Relevance to Drinking Water Distribution Systems

Chlorine dioxide (ClO₂) decay in the presence of typical metal oxides occurring in distribution systems was investigated. Metal oxides generally enhanced ClO₂ decay in a second-order process via three pathways: (1) catalytic disproportionation with equimolar formation of chlorite and chlorate, (2) reaction to chlorite and oxygen, and (3) oxidation of a metal in a reduced form (e.g., cuprous oxide) to a higher oxidation state. Cupric oxide (CuO) and nickel oxide (NiO) showed significantly stronger abilities than goethite (α-FeOOH) to catalyze the ClO₂ disproportionation (pathway 1), which predominated at higher initial ClO₂ concentrations (56–81 μM). At lower initial ClO₂ concentrations (13–31 μM), pathway 2 also contributed. The CuO-enhanced ClO₂ decay is a base-assisted reaction with a third-order rate constant of 1.5 × 10⁶ M^–2 s^–1 in the presence of 0.1 g L^–1 CuO at 21 ± 1 °C, which is 4–5 orders of magnitude higher than in the absence of CuO. The presence of natural organic matter (NOM) significantly enhanced the formation of chlorite and decreased the ClO₂ disproportionation in the CuO–ClO₂ system, probably because of a higher reactivity of CuO-activated ClO₂ with NOM. Furthermore, a kinetic model was developed to simulate CuO-enhanced ClO₂ decay at various pH values. Model simulations that agree well with the experimental data include a pre-equilibrium step with the rapid formation of a complex, namely, CuO-activated Cl₂O₄. The reaction of this complex with OH^– is the rate-limiting and pH-dependent step for the overall reaction, producing chlorite and an intermediate that further forms chlorate and oxygen in parallel. These novel findings suggest that the possible ClO₂ loss and the formation of chlorite/chlorate should be carefully considered in drinking water distribution systems containing copper pipes

Carbon, Hydrogen, and Nitrogen Isotope Fractionation Trends in <i>N</i>‑Nitrosodimethylamine Reflect the Formation Pathway during Chloramination of Tertiary Amines

Assessing the precursors and reactions leading to the carcinogenic <i>N</i>-nitrosodimethylamine (NDMA) during drinking water disinfection is a major challenge. Here, we investigate whether changes of ¹³C/¹²C, ²H/¹H, and ¹⁵N/¹⁴N ratios of NDMA give rise to isotope fractionation trends that can be used to infer NDMA formation pathways. We carried out compound-specific isotope analysis (CSIA) of NDMA during chloramination of four tertiary amines that produce NDMA at high yields, namely ranitidine, 5-(dimethylaminomethyl)furfuryl alcohol, <i>N,N</i>-dimethylthiophene-2-methylamine, and <i>N,N</i>-dimethylbenzylamine. Carbon and hydrogen isotope ratios of NDMA function as fingerprints of the N­(CH₃)₂ moiety and exhibit only minor isotope fractionation during the disinfection process. Nitrogen isotope ratios showed that NH₂Cl is the source of the N atom of the nitroso group. The large enrichment of ¹⁵N in NDMA was indicative of the isotope effects pertinent to bond-cleavage and bond-formation reactions during chloramination of the tertiary amines. Correlation of δ¹⁵N versus δ¹³C values of NDMA resulted in trend lines that were not affected by the type of tertiary amine and treatment conditions, suggesting that the observed C and N isotope fractionation in NDMA may be diagnostic for NDMA precursors and formation pathways during chloramination

Probing the Photosensitizing and Inhibitory Effects of Dissolved Organic Matter by Using <i>N</i>,<i>N</i>‑dimethyl-4-cyanoaniline (DMABN)

Dissolved organic matter (DOM) can act as a photosensitizer and an inhibitor in the phototransformation of several nitrogen-containing organic contaminants in surface waters. The present study was performed to select a probe molecule that is suitable to measure these antagonistic properties of DOM. Out of nine studied nitrogen-containing aromatic compounds, 4-cyanoaniline, <i>N</i>,<i>N</i>-dimethyl-4-cyanoaniline (DMABN), sotalol (a β-blocker) and sulfadiazine (a sulfonamide antibiotic) exhibited a marked photosensitized transformation that could be substantially inhibited by addition of phenol as a model antioxidant. The photosensitized transformation of DMABN, the selected probe compound, was characterized in detail under UV-A and visible irradiation (λ > 320 nm) to avoid direct phototransformation. Low reactivity of DMABN with singlet oxygen was found (second-order rate constant <2 × 10⁷ M^–1 s^–1). Typically at least 85% of the reactivity of DMABN could be inhibited by DOM or the model antioxidant phenol. The photosensitized transformation of DMABN mainly proceeded (>72%) through demethylation yielding <i>N</i>-methyl-4-cyanoaniline and formaldehyde as primary products. In solutions of standard DOM extracts and their mixtures the phototransformation rate constant of DMABN was shown to vary nonlinearly with the DOM concentration. Model equations describing the dependence of such rate constants on DOM and model antioxidant concentrations were successfully used to fit experimental data

Enhanced Bromate Formation during Chlorination of Bromide-Containing Waters in the Presence of CuO: Catalytic Disproportionation of Hypobromous Acid

Bromate (BrO₃^–) in drinking water is traditionally seen as an ozonation byproduct from the oxidation of bromide (Br^–), and its formation during chlorination is usually not significant. This study shows enhanced bromate formation during chlorination of bromide-containing waters in the presence of cupric oxide (CuO). CuO was effective to catalyze hypochlorous acid (HOCl) or hypobromous acid (HOBr) decay (e.g., at least 10⁴ times enhancement for HOBr at pH 8.6 by 0.2 g L^–1 CuO). Significant halate concentrations were formed from a CuO-catalyzed hypohalite disproportionation pathway. For example, the chlorate concentration was 2.7 ± 0.2 μM (225.5 ± 16.7 μg L^–1) after 90 min for HOCl (<i>C</i>_o = 37 μM, 2.6 mg L^–1 Cl₂) in the presence of 0.2 g L^–1 CuO at pH 7.6, and the bromate concentration was 6.6 ± 0.5 μM (844.8 ± 64 μg L^–1) after 180 min for HOBr (<i>C</i>_o = 35 μM) in the presence of 0.2 g L^–1 CuO at pH 8.6. The maximum halate formation was at pHs 7.6 and 8.6 for HOCl or HOBr, respectively, which are close to their corresponding p<i>K</i>_a values. In a HOCl–Br^––CuO system, BrO₃^– formation increases with increasing CuO doses and initial HOCl and Br^– concentrations. A molar conversion (Br^– to BrO₃^–) of up to (90 ± 1)% could be achieved in the HOCl–Br^––CuO system because of recycling of Br^– to HOBr by HOCl, whereas the maximum BrO₃^– yield in HOBr–CuO is only 26%. Bromate formation is initiated by the formation of a complex between CuO and HOBr/OBr^–, which then reacts with HOBr to generate bromite. Bromite is further oxidized to BrO₃^– by a second CuO-catalyzed process. These novel findings may have implications for bromate formation during chlorination of bromide-containing drinking waters in copper pipes

Chlorination of Iodide-Containing Waters in the Presence of CuO: Formation of Periodate

It has been shown previously that the disproportionation of halogen-containing oxidants (e.g., HOCl, HOBr, and ClO₂) is enhanced by a CuO-catalyzed process. In this study, the transformation of iodine during chlorination in the presence of CuO was investigated. There is no significant enhancement of the disproportionation of hypoiodous acid (HOI) in the presence of CuO. The formation rate of iodate (IO₃^–) in the CuO–HOCl–I^– system significantly increased when compared to homogeneous solutions, which was ascribed to the activation of HOCl by CuO enhancing its reactivity toward HOI. In this reaction system, iodate formation rates increase with increasing CuO (0–0.5 g L^–1) and bromide (0–2 μM) doses and with decreasing pH (9.6–6.6). Iodate does not adsorb to the CuO surfaces used in this study. Nevertheless, iodate concentrations decreased after a maximum was reached in the CuO–HOCl–I^–(−Br^–) systems. Similarly, the iodate concentrations decrease as a function of time in the CuO–HOCl–IO₃^– or CuO–HOBr–IO₃^– system, and the rates increase with decreasing pH (9.6–6.6) due to the enhanced reactivity of HOCl or HOBr in the presence of CuO. It could be demonstrated that iodate is oxidized to periodate by a CuO-activated hypohalous acid, which is adsorbed on the CuO surface. No periodate could be measured in filtered solutions because it was mainly adsorbed to CuO. The adsorbed periodate was identified by scanning electron microscopy plus energy dispersive spectroscopy and X-ray photoelectron spectroscopy

Trafiklagstiftning och barn

<i>N</i>-Nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct from water chloramination. Despite the identification of numerous NDMA precursors, essential parts of the reaction mechanism such as the incorporation of molecular O₂ are poorly understood. In laboratory model systems for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the stoichiometries of monochloramine (NH₂Cl) and aqueous O₂ consumption, derived ¹⁸O-kinetic isotope effects (¹⁸O-KIE) for the reactions of aqueous O₂, and studied the impact of radical scavengers on NDMA formation. Although the molar NDMA yields from five <i>N</i>,<i>N</i>-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O₂ per <i>N</i>,<i>N</i>-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small ¹⁸O-KIEs between 1.0026 ± 0.0003 and 1.0092 ± 0.0009 found for all precursors as well as completely inhibited NDMA formation in the presence of radical scavengers (ABTS and trolox) imply that O₂ reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH₂Cl and <i>N</i>-peroxyl radicals from the reaction of aminyl radicals with aqueous O₂ are part of the NDMA formation mechanism