This study investigated the degradation and deactivation of an extracellular ampicillin resistance gene (ampR) encoded in plasmid pUC19 during exposure to UV254, •OH (generated by UV>290/H2O2), and ...combined exposure to UV254 and •OH (and/or SO4•−) using UV254/H2O2 and UV254/S2O82−. The degradation rates of ampR measured by quantitative polymerase chain reaction increased with increasing target amplicon length (192–851 bps). The rate constants for the degradation of pUC19 (2686 bps) were calculated as 0.26 cm2/mJ for UV254 and 1.5 × 1011 M−1s−1 for •OH, based on the degradation rates of ampR amplicons and assuming an equal sensitivity of DNA damage across the entire plasmid. DNA repair-proficient Escherichia coli (E. coli) AB1157 strain (wild-type) and its repair-deficient mutants including AB1886 (uvrA−), AB2463 (recA−), AB2480 (uvrA−, recA−), and DH5α (recA−, endA−) were applied as recipient cells in gene transformation assays. Results suggested that the elimination efficiency of transforming activity during UV254 and •OH exposure was dependent on the type of DNA repair genes in recipient E. coli strains. Losses of transforming activity were slower than the degradation of pUC19 by a factor of up to ∼5 (for E. coli DH5α), highlighting the importance of DNA repair in recipient cells. The degradation rates of ampR amplicons were much larger (by a factor of ∼4) in UV254/H2O2 and UV254/S2O82− than UV254 direct photolysis, indicating the significant contribution of •OH and SO4•− to the gene degradation. Not only UV254 and SO4•−, but also •OH contributed to the degradation of ampR during UV254/S2O82−, which was attributed to the conversion of SO4•− to •OH and a 10-fold larger reactivity of •OH towards ampR as compared to SO4•−. However, the enhanced gene degradation by radicals did not lead to a faster elimination of gene transforming activity during UV254/H2O2 and UV254/S2O82−, suggesting that UV254- and radical-induced DNA damage were not additive in their contributions to losses of gene transforming activity. Wastewater effluent organic matter (EfOM) accelerated the degradation of ampR during UV254 irradiation by means of reactive species production through indirect photolysis reactions, whereas EfOM mainly acted as a radical scavenger during UV254/H2O2 and UV254/S2O82− treatments.
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•Degradation and deactivation kinetics of a plasmid-encoded resistance gene (ampR).•Individual vs combined effect of UV254 and radicals (•OH, SO4•−) on ampR•Slower gene deactivation rate than the plasmid degradation due to DNA damage repair.•UV- and radical-induced DNA damage are not additive in causing gene deactivation.•Effluent organics as photo-sensitizers or radical scavengers for ampR degradation.
•38 oxidation products were tentatively identified from tire-derived 6-PPD in the lab.•Most of them were also found in snow from roads, primarily in particle fraction.•Load of 6-PPD and TPs in ...municipal wastewater peaked during rainfall and snowmelt.•6-PPD and 6-PPDQ of minor importance in WWTP effluent.
The antiozonant N-phenyl-N’-(1,3-dimethylbutyl)-p-phenylenediamine (6-PPD) is added to tires to increase their lifetime and is emitted with tire and road wear particles into the environment. Recently, one of its transformation products (TPs), 6-PPD quinone (6-PPDQ), has gained attention due to its toxicity towards coho salmon. In this study, the abiotic oxidative transformation of 6-PPD is investigated by a series of ozonation experiments in the lab followed by analysis of TPs using liquid chromatography-high resolution-mass spectrometry (LC-HRMS). A total of 38 TPs were detected and tentatively identified, which were formed either directly from 6-PPD or via 6-PPDQ as intermediate. A suspect screening by LC-HRMS showed 32 of these TPs to occur in snow collected from urban roads as surrogate of road-runoff, where 6-PPDQ, 4-aminodiphenylamine (4-ADPA), TP 213, and TP 249 were the most prominent besides 6-PPD. More than 90% of the total load of 6-PPD and its TPs was found in the particulate fraction of snow. Thus, retaining the particulate fraction of road runoff before its discharge into surface water would substantially reduce the emission of 6-PPD and many of its TPs. Some TPs prevailed in the water phase of the snow due to their higher polarity. A total of 13 TPs were detected by suspect screening in the dissolved phase of a wastewater treatment plant (WWTP) influent. Their total load was markedly enhanced during a day of snowmelt (approx. 1100 g/d) and rainfall (approx. 2000 g/d) compared to dry weather (approx. 190 g/d). 6-PPD and 6-PPDQ contributed to less than 1% to this total load in the water phase (estimated concentrations of max 0.1 µg/L). The elimination of the estimated total loads of 6-PPD related TPs from the water phase in WWTP ranged from 22 to 67% depending on weather conditions. Eventually TP 249, 4-ADPA and TP 259_2 dominated in WWTP effluent (estimated concentration from 0.5 up to 2 µg/L). Thus TP 249 and TP 259_2 are, likely, the most specific and stable TPs of 6-PPD to be determined in the environment.
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High resolution mass spectrometry (HRMS) coupled to either gas chromatography or reversed-phase liquid chromatography is the generic method to identify unknown disinfection byproducts (DBPs) but can ...easily overlook their highly polar fractions. In this study, we applied an alternative chromatographic separation method, supercritical fluid chromatography-HRMS, to characterize DBPs in disinfected water. In total, 15 DBPs were tentatively identified for the first time as haloacetonitrilesulfonic acids, haloacetamidesulfonic acids, and haloacetaldehydesulfonic acids. Cysteine, glutathione, and p-phenolsulfonic acid were found as precursors during lab-scale chlorination, with cysteine providing the highest yield. A mixture of the labeled analogues of these DBPs was prepared by chlorination of 13C3-15N-cysteine and analyzed using nuclear magnetic resonance spectroscopy for structural confirmation and quantification. A total of 6 drinking water treatment plants utilizing various source waters and treatment trains produced sulfonated DBPs upon disinfection. Those were widespread in the tap water of 8 cities across Europe, with estimated concentrations up to 50 and 800 ng/L for total haloacetonitrilesulfonic acids and haloacetaldehydesulfonic acids, respectively. Up to 850 ng/L haloacetonitrilesulfonic acids were found in 3 public swimming pools. Considering the stronger toxicity of haloacetonitriles, haloacetamides, and haloacetaldehydes than the regulated DBPs, these newly found sulfonic acid derivatives may also pose a health risk.
A recent investigation has demonstrated that peroxymonosulfate (PMS), a peroxide commonly applied as a radical precursor during advanced oxidation processes (AOPs), can degrade organic contaminants ...without the involvement of radicals. However, little is known about this non-radical reaction mechanism. In this study, the reactivity of PMS with several nitrogenous compounds was investigated. Fluoroquinolone antibiotics (except for flumequine) were rapidly degraded by direct PMS oxidation, followed by aliphatic amines (e.g., metoprolol and venlafaxine) and nitrogenous heterocyclic compounds (e.g., adenine and caffeine) at pH 8. The degradation rate of fluoroquinolones followed a second-order kinetic and was highly pH and structure-dependent. Unlike the radical-based AOPs, the direct degradation of contaminants by PMS was less influenced by the scavenging effect of the water matrix. High-Resolution Mass Spectrometry (HRMS) analysis demonstrated that the piperazine ring of fluoroquinolones was the main reaction site. Results showed that the direct electron-transfer from nitrogenous moieties (piperazine ring) to PMS can produce amide and aldehyde compounds. An amide-containing transformation product of ciprofloxacin (m/z 320), showing the highest signal intensity on HRMS, was previously recorded during ozonation. Moreover, the hydroxylamine analogue of ciprofloxacin and enrofloxacin N-oxide were tentatively identified, and the formation of the latter was not impacted by the dissolved oxygen in water. These results suggested that PMS also reacts with nitrogenous compounds via oxygen transfer pathway. Agar disk-diffusion tests indicated that PMS treatment efficiently removed the antibacterial activity of ciprofloxacin with the complete degradation of parent antibiotic, except for the transformation products in an earlier stage, which might still exert antibacterial potency.
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•The reactivity of peroxymonosulfate with nitrogenous compounds were compared.•A product with an amide group had the highest intensity on mass spectrometry.•N-oxide was tentatively identified from enrofloxacin.•Reaction mechanism includes the electron and oxygen transfer pathways.•Ciprofloxacin by-products in earlier stages exerted antibacterial potency.
•Suspect/non-target screening of ozonated wastewater effluent for ozonation products•Supercritical fluid chromatography-SFC vs. reversed-phase liquid chromatography•Hydrophilic and small ozonation ...products are detected by SFC-MS•Dual-media filter removes these ozonation products primarily by adsorption•Metformin forms some ozonation products that escape from post-treatment
Ozonation is an important process to further reduce the trace organic chemicals (TrOCs) in treated municipal wastewater before discharge into surface waters, and is expected to form products that are more oxidized and more polar than their parent compounds. Many of these ozonation products (OPs) are biodegradable and thus removed by post-treatment (e.g., aldehydes). Most studies on OPs of TrOCs in wastewater rely on reversed-phase liquid chromatography- mass spectrometry (RPLC-MS), which is not suited for highly polar analytes. In this study, supercritical fluid chromatography combined with high resolution MS (SFC-HRMS) was applied in comparison to the generic RPLC-HRMS to search for OPs in ozonated wastewater treatment plant effluent at pilot-scale. While comparable results were obtained from these two techniques during suspect screenings for known OPs, a total of 23 OPs were only observed by SFC-HRMS via non-targeted screening. Several SFC-only OPs were proposed as the derivatives of methoxymethylmelamines, phenolic sulfates/sulfonates, and metformin; the latter was confirmed by laboratory-scale ozonation experiments. A complete ozonation pathway of metformin, a widespread and extremely hydrophilic TrOC in aquatic environment, was elaborated based on SFC-HRMS analysis. Five of the 10 metformin OPs are reported for the first time in this study. Three different dual-media filters were compared as post-treatments, and a combination of sand/anthracite and fresh post-granular activated carbon proved most effective in OPs removal due to the additional adsorption capacity. However, six SFC-only OPs, two of which originating from metformin, appeared to be persistent during all post-treatments, raising concerns on their occurrence in drinking water sources impacted by wastewater.
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Water treatment utilities are diversifying their water sources and often rely on waters enriched in nitrogen-containing compounds (e.g., ammonia, organic nitrogen such as amino acids). The ...disinfection of waters exhibiting high levels of nitrogen has been associated with the formation of nitrogenous disinfection byproducts (N-DBPs) such as haloacetonitriles (HANs) and haloacetamides (HAcAms). While the potential precursors of HANs have been extensively studied, only few investigations are available regarding the nature of HAcAm precursors. Previous research has suggested that HAcAms are hydrolysis products of HANs. Nevertheless, it has been recently suggested that HAcAms can be formed independently, especially during chloramination of humic substances. When used as a disinfectant, monochloramine can also be a source of nitrogen for N-DBPs. This study investigated the role of aromatic organic matter in the formation of N-DBPs (HAcAms and HANs) upon chloramination. Formation kinetics were performed from various fractions of organic matter isolated from surface waters or treated wastewater effluents. Experiments were conducted with 15N-labeled monochloramine (15NH2Cl) to trace the origin of nitrogen. N-DBP formation showed a two-step profile: (1) a rapid formation following second-order reaction kinetics and incorporating nitrogen atom originating from the organic matrix (e.g., amine groups); and (2) a slower and linear increase correlated with exposure to chloramines, incorporating inorganic nitrogen (15N) from 15NH2Cl into aromatic moieties. Organic matter isolates showing high aromatic character (i.e., high SUVA) exhibited high reactivity characterized by a major incorporation of 15N in N-DBPs. A significantly lower incorporation was observed for low-aromatic-content organic matter. 15N-DCAcAm and 15N-DCAN formations exhibited a linear correlation, suggesting a similar behavior of 15N incorporation as SUVA increases. Chloramination of aromatic model compounds (i.e., phenol and resorcinol) showed higher HAcAm and HAN formation potentials than nitrogenous precursors (i.e., amino acids) usually considered as main precursors of these N-DBPs. These results demonstrate the importance of aromatic organic compounds in the formation of N-DBPs, which is of significant importance for water treatment facilities using chloramines as final disinfectant.
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•Haloacetamide formation kinetics follow two pathways during chloramination.•Fast incorporation of organic nitrogen from NOM follows second-order kinetics.•A slower step incorporates inorganic nitrogen from NH2Cl in aromatic moieties.•High SUVA organic matter shows major incorporation of inorganic nitrogen.•Chloramination of phenol and resorcinol exhibits high N-DBP formation potentials.
In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/H2O2 and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions ...of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO4•−) were determined for the first time. Experiments were conducted in buffered pure water and wastewater effluent with spiked TOrCs. UV/PDS degraded all TOrCs more efficiently than UV/H2O2 in buffered pure water due to the higher yield of SO4•− than that of hydroxyl radical (•OH) at the same initial molar dose of PDS and H2O2, respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/H2O2 in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/H2O2 was more efficient in degrading compounds with lower reactivity to SO4•−. The fluence-based rate constants (kobs−UV/H2O2) of TOrCs in wastewater effluent linearly increased as a function of initial H2O2 dose during UV/H2O2, possibly due to the constant scavenging impact of the wastewater matrix on •OH. However, exponential increase of kobs−UV/PDS with increasing PDS dose was observed for most compounds during UV/PDS, suggesting the decreasing scavenging effect of the water matrix (electron-rich site of effluent organic matter (EfOM)) after initial depletion of SO4•− at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/H2O2 compared to aromatic protein and soluble microbial product-like fluorophores. In contrast, UV/PDS efficiently degraded all identified fluorophores and showed less selectivity toward the fluorescent EfOM components. Removal pattern of TOrCs during pilot-scale UV/PDS was consistent with lab-scale experiments, however, overall removal rates were lower due to the presence of higher concentration of EfOM and nitrite.
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•A comparative investigation on the efficiency of UV/H2O2 and UV/PDS.•Degradation kinetics of 12 trace organic chemicals.•Higher steady state concentration of SO4•− compared to •OH in pure water.•Selective property of SO4•− favouring oxidation of electron-rich organic moieties.•Pilot-scale validation of UV/PDS in wastewater treatment plant effluent.
The potential formation of nitrogenous disinfection byproducts (N-DBPs) was investigated from the chloramination of nitrogenous and non-nitrogenous aromatic compounds. All molecules led to the ...formation of known N-DBPs (e.g., dichloroacetonitrile, dichloroacetamide) with various production yields. Resorcinol, a major precursor of chloroform, also formed di/trichloroacetonitrile, di/trichloroacetamide, and haloacetic acids, indicating that it is a precursor of both N-DBPs and carbonaceous DBPs (C-DBPs) upon chloramination. More detailed experiments were conducted on resorcinol to understand N-DBPs formation mechanisms and to identify reaction intermediates. Based on the accurate mass from high resolution Quadrupole Time-of-Flight GC–MS (GC–QTOF) and fragmentation patterns from electronic impact and positive chemical ionization modes, several products were tentatively identified as nitrogenous heterocyclic compounds (e.g., 3-chloro-5-hydroxy-1H-pyrrole-2-one with dichloromethyl group, 3-chloro-2,5-pyrroledione). These products were structurally similar to the heterocyclic compounds formed during chlorination, such as the highly mutagenic MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) or halogenated pyrroles. To our knowledge, this is the first time that the formation of halogenated nitrogenous heterocyclic compounds is reported from chloramination process. The formation of these nitrogenous byproducts during chloramination might be of concern considering their potential toxicity.
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