Article pubs.acs.org/est
Transformation of 1H-Benzotriazole by Ozone in Aqueous Solution Douglas B. Mawhinney,*,† Brett J. Vanderford,† and Shane A. Snyder‡ †
Applied Research and Development Center, Southern Nevada Water Authority, P.O. Box 99954, Las Vegas, Nevada 89193-9954, United States ‡ Department of Chemical and Environmental Engineering, University of Arizona, 1133 East James E. Rogers Way, Tucson, Arizona 85721-0011, United States S Supporting Information *
ABSTRACT: Recent studies have shown that 1H-benzotriazole is a widespread contaminant of wastewater and surface water. Although disinfection by ozone has been shown to efficiently remove this compound, the transformation products have not been identified. To that end, the reaction of ozone with 1H-benzotriazole in aqueous solution has been studied in real time employing quadrupole time-of-flight mass spectrometry (Q-TOF MS) and negative electrospray ionization. The transformation products have been identified by calculating their empirical formulas using accurate mass measurements, and further confirmed by performing the reaction with stable isotope-labeled 1H-benzotriazole and measuring product ion spectra. Stable reaction products were distinguished from transient species by plotting their extracted mass profiles. The products that resulted from ozone and hydroxyl radicals in the reaction were qualitatively identified by modifying the conditions to either promote the formation of hydroxyl radicals, or to scavenge them. Based on experimental evidence, a mechanism for the direct reaction between ozone and 1H-benzotriazole is proposed that results in the formation of 1H-1,2,3-triazole-4,5-dicarbaldehyde, which has an empirical formula of C4H3O2N3. Lastly, it was confirmed that the same transformation products formed in surface water and tertiary-treated wastewater, although they were observed to degrade at higher ozone doses.
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INTRODUCTION The occurrence of contaminants of emerging concern (CECs) has been well documented in surface waters,1,2 including those used in the production of drinking water.3,4 Most of the CECs are categorized in literature by their intended use, such as pharmaceuticals and personal care products (PPCPs),5 or by their potential health effects, such as endocrine-disrupting compounds (EDCs).6 Transformation products are a class of compounds that result from the oxidation of these contaminants during wastewater and drinking water disinfection processes.7 Although many compounds display reduced bioactivity after oxidation,8,9 transformation products may display similar or increased toxicity compared to the precursor molecule.10 Due to these concerns, research directed at identifying these chemical compounds has been recently reported.10−18 Ozone has been widely used in the treatment of wastewater and in the production of drinking water.19−22 Ozone treatment of water is beneficial for a number of reasons, including disinfection and chemical oxidation processes that lead to the removal organic micropollutants.22−26 The chemistry of ozone in natural waters is dependent on a variety of parameters, such as temperature, pH, alkalinity, and DOM, which can stabilize ozone or lead to its decomposition into radical species, such as hydroxyl radicals.27 In highly purified water (i.e., laboratory reagent water) ozone decomposition into radical species can be controlled by pH adjustment and the addition of modifiers, such as hydrogen peroxide.28,29 Such approaches have been © 2012 American Chemical Society
used to study the oxidation of individual CECs by ozone and hydroxyl radicals.11,16 1H-benzotriazole (1HBT) and the tolyltriazoles have been found in wastewater and the subsequently impacted surface water.30−34 These compounds are employed to prevent metal corrosion and as UV-inhibitors, and find use in applications such as airplane deicing fluids, dishwashing detergents, and plastic formulations.35 1HBT has two pKa values (0.42 and 8.2),36 is hydrophilic (Log Kow = 1.23) and forms complexes with metals.37 1HBT has weak toxicity to humans and the environment, although it has been shown to induce an antiestrogenic response in bioassays38 and displays some toxicity in plants.35 This compound is resistant to removal by chlorination, conventional (primary and secondary) wastewater treatments, and bank filtration,39 although it is readily degraded by ozone and advanced oxidation processes (AOP). To date, the transformation products from these oxidation pathways have not been identified.39−41 The main goal of this study was to identify the major transformation products formed during the oxidation of 1HBT by ozone in aqueous solution. This was accomplished at the bench-scale by analyzing solutions of the reactants in laboratory reagent water in real time by Q-TOF MS. Deuterated 1HBT was also oxidized with ozone in order to provide further Received: Revised: Accepted: Published: 7102
January 27, 2012 May 15, 2012 May 23, 2012 May 23, 2012 dx.doi.org/10.1021/es300338e | Environ. Sci. Technol. 2012, 46, 7102−7111
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autotune program provided by the instrument manufacturer. The reaction solution was pumped at 4 mL/min from a stirred reaction container using an Agilent 1100 HPLC pump. The flow was split to 200 μL/min using a PEEK tee (IDEX Health & Science, Oak Harbor, WA, USA) prior to being combined with 300 μL/min methanol, delivered by an Agilent 1200 HPLC pump, to enhance the ionization process. The reaction solution had a transport time of about 7 s between the reaction vessel and the mass spectrometer. Details of the LC-QTOF MS method used for the analysis of reaction products in surface water and wastewater, and the LC-MS/MS method used for the quantification of glyoxylic acid are contained in the SI. The instrument was controlled from a workstation using Agilent MassHunter Data Acquisition software. This software permits autocalibration of the mass axis during data collection, which was performed using ions at m/z 112.98559 and 966.00073 from the stock reference mass solution. The data were analyzed using MassHunter Qualitative software, which permits mass spectral processing, empirical formula calculation, and a variety of other functions. Quantitative analysis of the main organic transformation products was not possible during these studies. Because standards of these compounds were not readily available, response factors in the analysis technique employed could not be determined. Furthermore, molar absorptivity values for the products are unknown, which prevented quantification through spectroscopic techniques. While standard solutions of H2O2 and quantification methods exist, the reaction rate constant with ozone is reported to be higher (70 M−1 s−1)28 than that reported for ozone and 1HBT (22 M−1 s−1)41 near the pH values employed, making accurate quantification impossible under the conditions employed. Reaction Conditions for the Laboratory Reagent Water. Initial experiments were conducted in laboratory reagent water, where reaction products were easily distinguished. Reactions were carried out in a closed, stirred amber glass reaction vessel at room temperature (22 °C) with 300 μg/ L (2.5 μM) 1HBT. The reaction solution was pumped into the mass spectrometer source and monitored until a stable signal was reached. An aliquot of the concentrated ozone solution was then added to make a final concentration of 2 mg/L (42 μM) O 3 . The reaction was followed on the QTOF mass spectrometer for at least 20 min. Additional experiments were carried out in the presence of modifiers to better understand the reaction pathways that led to the observed transformation products. The influence of pathways involving hydroxyl radicals was reduced by the addition of 100 mM tert-butanol to act as a radical scavenger, enhancing the pathways involving direct reaction with ozone. To favor the reaction pathways involving hydroxyl radicals, the reaction was carried out in a 10 mM phosphate buffer at pH = 7.8 with 0 and 11 μM H2O2. Experimental blanks were analyzed to check for interferences, and consisted of the reaction solution without 1HBT, as well as solutions of 1HBT without the addition of ozone to check for stability. Additional experimental blanks included the reaction solution with hydrogen peroxide and tert-butanol, both with and without the addition of ozone. No interferences were observed for any of the conditions. Reaction Conditions for Surface Water and TertiaryTreated Wastewater. Experiments conducted in surface water and tertiary-treated wastewater were conducted offline. No buffers or other modifiers were added in order to simulate
evidence for the identification of the reaction products. The secondary goal was to qualitatively identify which products formed from additional reactions involving radical species. This was studied by conducting the reaction at pH = 7.8 (with and without H2O2 present) to promote hydroxyl radical formation, and alternatively with tert-butanol to promote direct reaction with ozone. Reaction mechanisms are proposed based on experimental evidence and accepted ozone chemistry. Finally, the transformation products were shown to form in surface water and tertiary-treated wastewater.
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EXPERIMENTAL SECTION Chemicals. 1H-Benzotriazole, CAS 95-14-7, (>99%, Fluka) and potassium indigo sulfonate were purchased from Sigma Aldrich Corp (St. Louis, MO, USA). 1H-Benzotriazole-d4 was purchased from Toronto Research Chemicals (98%, 99% isotopic purity, North York, ON, CA). tert-Butanol (99.5%, Acros Extra Pure) was purchased from Thermo Fisher Scientific (Waltham, MA, USA). Methanol (Honeywell, GCMS grade) was obtained from VWR (West Chester, PA, USA). The solutions used for tuning and calibrating the mass spectrometer were standard solutions (G1969-85000 and 85001) supplied by the instrument manufacturer (Agilent Technologies, Santa Clara, CA, USA). Laboratory reagent water was produced in-house using a Millipore (Billerica, MA, USA) water purification system with UV treatment and had a minimum resistivity of 18.2 MΩ·cm. Ozone Preparation. Ozone was produced with a DEL Ozone (San Luis Obispo, CA, USA) LC-7 generator for the experiments performed in laboratory reagent water. Ozone was produced with an Ozonia CFS-1A (Dubendorf, Switzerland) generator for the experiments conducted at basic pH, surface water, and tertiary-treated wastewater, and for the quantification of glyoxylic acid. The inlet of the generator was supplied with 15 psi of 99.5% oxygen from a compressed gas cylinder, and outlet of the ozone generator was attached to a jacketed glass vessel (Allen Scientific Glass, Boulder, CO, USA) using PTFE tubing (Figure SI-1 in the Supporting Information (SI)). The reactor was cooled to 1−2 °C using a VWR 1327 recirculating chiller. The gas output from the generator was bubbled through laboratory reagent water in the vessel using a gas dispersion tube, and subsequently routed through two gas washing bottles in series containing 50 mM potassium iodide solution to help remove excess ozone. The generator, vessel, and scrubbers were contained within a chemical hood to prevent exposure of laboratory personnel to ozone. The concentration of the ozone in solution was measured immediately before each experiment using a Perkin-Elmer Lambda 45 UV−vis spectrometer (Waltham, MA, USA), and was generally ∼20 mg/L for the DEL Ozone generator and ∼80 mg/L for the Ozonia generator. The indigo method42 was used for measuring residual ozone concentration during the reaction with 1HBT. Briefly, an aliquot of the reaction solution is mixed with the indigo solution, and the residual ozone reacts with indigo trisulfonate. The concentration of ozone is calculated from the loss of indigo, which is measured by its absorbance at 600 nm using a Hach DR 2000 spectrophotometer (Loveland, CO, USA). Instrumental Analysis. Mass spectral analysis was performed on an Agilent 6510 quadrupole time-of-flight (QTOF) mass spectrometer (Santa Clara, CA, USA) using a setup similar to that in Vanderford et al.13 The instrument was calibrated daily using the suggested calibration solution and 7103
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Figure 1. Behavior of 1HBT and the transformation products formed in the reaction of 1HBT and ozone. (A) Extracted mass profiles of 1HBT at m/z 118, and the transformation product at m/z 124. (B) Magnified view showing the extracted mass profiles of the lower-intensity transformation products, emphasizing the formation of the species at m/z 150 prior to the formation of the species at m/z 124. Reaction temperature: 22 °C; reaction pH: ∼5.5. Residual ozone concentration as measured by the indigo method (mg/L): 0.5 min (t0), 2.2; 0.9 min, 1.9; 11 min, 0.65; 20 min, 0.27; and 30 min, 0.14.
Table 1. Measured m/z, Molecular Mass, Calculated Mass, Accuracy, the Calculated Empirical Formula, and the Double Bond Equivalent for the Transformation Products of 1HBT Formed upon the Addition of Ozone and No Modifiersa product
measured m/z (u)
molecular mass (u)
calculated mass (u)
accuracy (ppm)
empirical formula
double bond equivalent
deuterated product
124 142 150 154 166
124.01502 142.02531 150.03057 154.02551 166.02548
125.02230 143.03259 151.03785 155.03279 167.03276
125.02253 143.03309 151.03818 155.03309 167.03309
1.8 3.5 2.2 2.0 2.0
C4H3N3O2 C4H5N3O3 C6H5N3O2 C5H5N3O3 C6H5N3O3
5 4 6 5 6
C4HD2N3O2 C4H3D2N3O3 C6HD4N3O2 C5H2D3N3O3 C6H2D3N3O3
a
The corresponding products from deuterated 1HBT are also presented. It should be noted that the empirical formulas are for the neutral molecule.
conditions encountered in drinking water treatment plants and wastewater treatment plants. The surface water sample was collected at Lake Mead near Las Vegas, NV, and the tertiarytreated wastewater sample was collected following a membrane bioreactor (MBR) at a wastewater treatment plant located in
Las Vegas, NV. The surface water quality parameters were as follows: pH 7.7; alkalinity (as HCO3), 137 mg/L; total organic carbon (TOC), 2.4 mg/L; TDS, 582 mg/L. The wastewater quality parameters were the following: pH 7.4: alkalinity (as CaCO3), 100 mg/L: dissolved organic carbon (DOC), 6.0 mg/ 7104
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Figure 2. Extracted mass profiles of the transformation products in the presence of 100 mM tert-butanol at pH = ∼5.5. Initial O3 concentration: 2 mg/L; initial 1HBT concentration: 300 μg/L; reaction temperature: 22 °C.
and are known to be nonspecific oxidants, reacting with compounds that ozone does not.44 1HBT reacts rapidly with hydroxyl radicals (rate constant ∼1 × 1010 41), therefore small amounts formed in the laboratory reagent water could affect the transformation products formed. To reduce these reactions, the hydroxyl radicals were scavenged by carrying out the reaction in 100 mM tert-butanol,45 which has been used by other researchers for such experiments.11,16 Under these reaction conditions, only the transformation product at m/z 124 was still formed, along with the species at m/z 150 and 142 (in Figure 2A). Similar to the reaction conditions without tert-butanol, these species displayed relatively low intensity compared to the species at m/z 124, which could indicate either low yields of these products, or relatively poor ionization efficiency. The species at m/z 154 and 166 did not form, indicating that their formation involved reactions with radicals. The reaction was also carried out at pH = 7.8 with 0 (Figure 3A) and 11 μM H2O2 (SI Figure SI-2) in order to enhance the formation of hydroxyl radicals. The degradation of 1HBT proceeded quickly under both conditions, being decomposed by more than 90% in less than 1 min, and all transformation products were found to be transient with lifetimes of less than 1 min. The product at m/z 150 became the most intense, while a single new species at m/z 148 was also identified and formed at higher relative concentrations in the presence of H2O2. All of the products formed at relatively low intensity compared to that of 1HBT (with the exception of m/z 142), and were further decomposed into species that were not amenable to this method of measurement. The relatively fast degradation of the 1HBT can be explained through the reaction of hydroxyl radicals, where a reaction rate constant of 0.62−1.7 × 1010 M−1 s−1 has been reported.41 This was confirmed by reactions conducted at pH = 7.8 in the presence of 100 mM tert-butanol (Figure 3B), where the extracted mass profiles more closely resembled those at lower pH values. The reaction did appear to occur at a faster rate under these conditions, likely due to activation of the benzo-ring due to the deprotonation of the
L; TDS, 1100 mg/L. Both samples were collected in baked amber glass bottles, transported immediately to the laboratory, and cooled to 4 °C. After warming to room temperature, aliquots were transferred to amber glass vials without filtration and spiked with 300 μg/L 1HBT. Ozone additions were made at 0, 0.8, 2, 4, 8, and 16 mg/L, and the vials were capped, vortexed, and held for a minimum of 30 min prior to analysis. To keep the concentration of 1HBT consistent, the amount of the water matrix was varied relative to the amount of ozone solution dosed, to make a final volume of 10 mL.
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RESULTS AND DISCUSSION O3 + 1H-Benzotriazole. The progress of the reaction between ozone and 1HBT was monitored in real time using the Q-TOF MS operating in time-of-flight mode. The reaction began immediately after the addition of ozone, as indicated by the loss of intensity for 1HBT at m/z 118 in Figure 1A, which appeared to be consistent with the reported reaction rate constant near this pH of 22.0 ± 2.0 M−1 s−1 and the concentrations employed.40 The most intense reaction product at m/z 124 (Figure 1A and Table 1) begins to form shortly after the addition of ozone. However, upon closer inspection of the extracted mass profiles of the products, it was found to be preceded by the formation of the lower intensity product at m/ z 150 (Figure 1B and Table 1). Three other transformation products then began to form at m/z 142, 154, and 166 (Figure 1B and Table 1). These are at relatively low intensity compared to the species at m/z 124, which could indicate either low yields of these products, or relatively poor ionization efficiency. The residual ozone concentration was monitored, and dropped from 2.2 to 0.14 mg/L over the course of the experiment. This is likely due to multiple reactions with 1HBT, spontaneous decomposition, and solution degassing to the headspace of the reaction container. Ozone decomposes in aqueous solution to form a variety of radical species, including hydroxyl radicals.28,43 Hydroxyl radicals form from the reaction of ozone with hydroxide ions, 7105
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Figure 3. Behavior of transformation products of 1HBT formed in the presence of modifiers. Initial O3 concentration: 2 mg/L; initial 1HBT concentration: 300 μg/L; reaction temperature: 22 °C. (A) Extracted mass profiles of the transformation products formed in phosphate buffer at pH = 7.8. (B) Extracted mass profiles of the transformation products formed in phosphate buffer at pH = 7.8 with 100 mM tert-butanol.
in m/z due to the presence of deuterium. An example of this is presented in Figure 4, where an overlay of mass spectra clearly shows the transformation product at m/z 124 is shifted to m/z 126 in the case of the deuterated 1HBT. Those products that resulted through reactions with ozone only should only have deuterium present, while those that involved reaction with water or hydroxyl radicals may have incorporated hydrogen. The empirical formulas determined from the accurate mass data are shown in Table 1 for the corresponding products. It should
triazole ring. Whereas the reaction of 1HBT with hydroxyl radicals should be studied in more detail, it is beyond the scope of this manuscript. O3 + 1H-Benzotriazole-d4. The reaction between ozone and 1H-benzotriazole-d4, where the hydrogen located on the carbon ring has been replaced with deuterium, was also investigated. The results of this reaction were used to help elucidate the reaction mechanism. Because the labeled molecule reacts via the same mechanism as the native compound, the reaction products will be the same with the exception of a shift 7106
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Figure 4. Overlayed mass spectra demonstrating the transformation product at m/z 124 is shifted to m/z 126 when the reaction is performed with 1HBT-d4. Ozone dose: 2 mg/L; reaction temperature: 22 °C; reaction pH: ∼5.5.
be noted that one proton is added to indicate the neutral form of the molecule. Proposed Mechanism for Direct Reaction with Ozone. The reaction of 1H-benzotriazole with ozone proceeds readily, as can be seen in the extracted mass profile in Figures 1A and 3B. As shown in Figure 5, (1) ozone initially reacts with the benzo-moiety, and likely proceeds through the formation of a primary ozonide, (2) Creigee intermediate46 and (3) reaction with water to form the hydroxyperoxide species.47,48 Unfortunately, the hydroxyperoxide species is not observed, and may either be short-lived under these conditions, or readily decomposed in the ionization process. This species then (4) decomposes through a loss of H2O2,47 and forms the product at m/z 150. The remaining accessible carbon−carbon double bond then (5) undergoes a rapid reaction with ozone, proceeding through the pathway similar to that outlined above, (6) to form the main transformation product at m/z 124 and glyoxylic acid. This mechanism is supported by the extracted mass profile of m/z 150, which shows that it begins to form rapidly prior to the product at m/z 124. The rate of formation then appears to slow, which can be explained by a second reaction with ozone to form the species at m/z 124, which prevents the continued increase in concentration of species at m/z 150. Eventually, there is a loss of intensity for species at m/z 150, as the 1HBT is depleted and the remainder is converted to the species at m/z 124. This pathway is also supported by the results of the reaction performed with labeled 1HBT, where the species at m/ z 150 retains all four deuterium atoms, and then loses two in the formation of the product at m/z 124. Furthermore, the
formation of glyoxylic acid was confirmed by LC-MS/MS experiments (SI), where it was found to form at 61% of the expected yield. It should be noted that the yield is complicated by the fact that additional studies confirmed that glyoxylic acid is also decomposed under these reaction conditions (SI Figure SI-3). Therefore, it can be concluded that this is a major pathway for the reaction of ozone with 1HBT. The formation of the product at m/z 142 (Table 1) involves the removal of two carbon atoms from 1HBT, and, with deuterium-labeled 1HBT, the incorporation of two hydrogen atoms. This transformation product was observed when the reaction was performed with ozone and in the presence of tertbutanol, but not at pH = 7.8 with or without H2O2. When it was subjected to MS/MS experiments, the main product ion was at m/z 124, indicating a loss of water (SI Figure SI-4). Considering the m/z ratios of the remaining product ions match those of the transformation product at m/z 124, the main product ion likely contains the same structure. Therefore, it is proposed that the species at m/z 142 forms by the hydration of an aldehyde group in the transformation product at m/z 124 to form 4-(dihydroxymethyl)-1H-1,2,3-triazole-5carbaldehyde (SI Figure SI-4). This reaction is known to occur readily at room temperature from oxygen isotope exchange experiments with similar aldehyde-containing compounds.49 Because the final product at m/z 124 was degraded quickly in the experiments conducted pH = 7.8 without tert-butanol, the product at m/z 142 did not have sufficient time to form. Proposed Mechanisms for Reactions Involving Radical Species. The remaining transformation products are formed more slowly and in relatively low abundance in the 7107
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Figure 5. Proposed mechanism for the direct reaction of ozone and 1HBT to form the products at m/z 150 and m/z 124.
ring is transformed into a quinone structure. Reaction (7) represents a series of steps to the formation of a phenolic group from the aromatic structure.52 In reaction (9), O2•− is formed from the decomposition of O3 by HO2−, which is present in solution containing H2O2 at appropriate pH values, or through the reaction of O3 with OH−.28 Similar reaction mechanisms have been proposed for the ozonation of phenol in aqueous solution.47 Because this product was not observed in the reaction of 1HBT with ozone in laboratory reagent water, this indicates that any that did form was short-lived. It is likely that the formation of this product is simply not favored under these conditions due to the kinetically unfavorable conditions for hydroxyl radical formation.28 Reaction Products Involving Both Ozone and Radical Species. The product at m/z 154 clearly involves both a direct reaction of 1HBT with ozone and with radical species, given its lack of formation in the presence of tert-butanol, and the incorporation of hydrogen into the corresponding product from labeled 1HBT. However, the exact pathway is not clearly understood at this time and is the subject of future work. A
reaction with ozone (Figure 1B) in laboratory reagent water. Because the transformation products at m/z 148 and 166 were not formed in the presence of tert-butanol, it may be concluded they are formed through radical pathways. However, because all of the reaction conditions resulted in transformation products at m/z 150, there are likely multiple species at this m/z. Under conditions that favor hydroxyl radical pathways, the species at m/z 150 and 166 are most likely the result of the incorporation of oxygen onto the benzo-ring50,51 by hydroxyl radical reactions. Under the reaction conditions where both ozone and hydroxyl radical pathways are present, the signal at m/z 150 is also due to the previously discussed product (Figure 5). Under both reaction conditions, the signal at m/z 166 is likely only due to phenolic species. The product at m/z 148, only observed to form at pH = 7.8 with and without H2O2, cannot be explained by simple addition of oxygen to the carbon ring. The empirical formula was calculated to be C6H3N3O2, with an accuracy of 2.2 ppm and a DBE of 7. The mechanism in Figure 6 is proposed to explain the transformation product at m/z 148, in which the carbon 7108
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Figure 6. Proposed reaction mechanism for the transformation product at m/z 148 formed in the presence of ozone at pH = 7.8 with and without hydrogen peroxide.
possible structure is proposed in SI Figure SI-5 that fits both the calculated empirical formula and DBE. Oxidation of 1HBT by Ozone in Surface Water and Tertiary-Treated Wastewater. The real-time screening method employed laboratory reagent water in order to eliminate interferences during the initial screening of transformation products. These ideal conditions are certainly not representative of those found in the disinfection stages of drinking water treatment plants or wastewater treatment plants, where parameters such as dissolved organic carbon, pH, and others strongly influence the chemistry of ozone. To understand if the same transformation products are formed in the presence of these more complicated matrices, representative samples were collected, spiked with 1HBT, and subjected to increasing doses of ozone. The resulting solutions were subjected to analysis using LC-Q-TOF MS, which showed that those transformation products identified by the real-time screening method also formed in these matrices. Table 2 shows the degradation of 1HBT, the production of transformation products at various ozone doses, and their subsequent degradation at high ozone doses. This indicates that these transformation products are likely to be present in wastewater effluents and some drinking waters, unless sufficient ozone doses are applied, and they warrant further studies to reveal their toxicological relevance. Further studies are needed to understand if these transformation products are resistant to chlorination. Method Limitations. The methods employed in this work had several limitations that should be clarified. The real-time analysis setup was designed to qualitatively determine reaction products and reaction sequence. It has not been fully characterized for precise quantitative measurements, and therefore inter- and intraday reproducibility has not been determined. Additionally, further studies are needed to fully characterize the reaction of 1HBT solely with hydroxyl radicals. This was not a goal of the present study, and as such, the reactions were conducted with ozone in excess. Different reaction pathways and products are likely to result under
Table 2. Integrated Area of the Chromatographic Peaks for 1HBT and Transformation Products at Different Ozone Doses in Surface Water and Tertiary-Treated Wastewatera surface water O3 dose (mg/L)
1HBT (counts)
m/z 124 (counts)
0 0.8 2 4 8 16
950000 440000 18000 0 0 0
0 0 0 110000 16000 150000 270000 0 12000 72000 0 0 0 0 0 0 0 0 tertiary-treated wastewater
O3 dose (mg/L)
1HBT (counts)
m/z 124 (counts)
m/z 148 (counts)
0 0.8 2 4 8 16
1100000 790000 450000 70000 0 0
0 18000 36000 110000 33000 0
0 8400 27000 0 0 0
a
m/z 148 (counts)
m/z 150 (counts)
m/z 154 (counts)
m/z 166 (counts)
0 2200 1900 0 0 0
0 4600 8000 9200 3800 0
m/z 150 (counts)
m/z 154 (counts)
m/z 166 (counts)
0 32000 76000 24000 0 0
0 0 3000 3000 0 0
0 4800 15000 19000 16000 0
Reaction temperature: 22°C.
conditions where hydroxyl radicals are the major or only oxidant present.
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ASSOCIATED CONTENT
S Supporting Information *
Additional figures and methods details. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. 7109
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