Assessment of N-Oxide Formation during Wastewater Ozonation

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Assessment of N-oxide Formation during Wastewater Ozonation Sylvain Merel, Sascha Lege, Jorge Eduardo Yanez Heras, and Christian Zwiener Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b02373 • Publication Date (Web): 12 Dec 2016 Downloaded from http://pubs.acs.org on December 13, 2016

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Environmental Science & Technology

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Assessment of N-oxide Formation during

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Wastewater Ozonation

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Sylvain Merel, Sascha Lege, Jorge E. Yanez Heras, Christian Zwiener*

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Environmental Analytical Chemistry, Center for Applied Geosciences, Eberhard Karls

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University Tübingen, Hölderlinstraße 12, 72074 Tübingen, Germany.

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* Corresponding author:

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Prof. Dr. Christian Zwiener

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Environmental Analytical Chemistry

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Eberhard Karls University Tübingen

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Hölderlinstraße 12

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72074 Tübingen, Germany

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Phone: (+49) 7071-29-74702

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Email: [email protected]

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ACS Paragon Plus Environment

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ABSTRACT

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Worldwide, ozonation of secondary wastewater effluents is increasingly considered in order to

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decrease the load of organic contaminants before environmental discharge. However, despite the

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constantly growing knowledge of ozonation over the last few years, the characterization of

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transformation products (TPs) is still a major concern, particularly because such TPs might

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remain biologically active. It has been shown for selected tertiary amine pharmaceuticals that

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they react with ozone and form the corresponding N-oxides. This study therefore applies liquid

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chromatography-high resolution mass spectrometry (LC-HRMS) to assess the overall N-oxide

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formation during the pilot-scale ozonation of a secondary wastewater effluent from a major city

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in Germany. Sample analysis by LC-HRMS revealed the occurrence of 1,229 compounds,

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among which 853 were precursors attenuated by ozone and 165 were TPs. Further examination

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of precursors and TPs using Kendrick mass and Kendrick mass defect analysis revealed 34 pairs

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of precursors and products corresponding to a mono-oxygenation. Among these, 27 pairs (16%

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of all TPs) were consistent with N-oxides since the TP had a higher retention time than the

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precursor, a characteristic of these compounds. Using high resolution tandem mass spectrometry,

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10 of these N-oxides could be identified and were shown to be stable during a subsequent

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filtration step.

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Table of content illustration

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INTRODUCTION

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Nowadays tens of thousands of chemicals are commonly used by industries in order to satisfy

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the growing requirement of our society in terms of pharmaceuticals and personal care products,

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food production, housing or transportation. Generally the number of these chemicals is

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increasing and a large fraction of them will be collected in wastewater during the course of their

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life cycle. However, since conventional wastewater treatment plants are not designed to remove

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such trace organic contaminants, most of them are poorly attenuated and therefore discharged

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into receiving waters. This is creating a major environmental and public health concern.1 For

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instance, pharmaceuticals, personal care products and their metabolites have become ubiquitous

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environmental contaminants1,

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favor the emergence of bacteria resistant to antibiotics.5, 6 In addition, the effects of long term

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exposure to low doses remain largely unknown with respect to ecological and human health.

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that can affect wildlife through endocrine disruption3,

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or can

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The reduction of water contamination mostly involves the improvement of wastewater

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treatment to ensure a more efficient removal of trace organic contaminants. A major trend


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consists in upgrading conventional wastewater treatment plants with additional sorption or

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oxidation processes. Among several potential options, the implementation of ozonation is

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particularly considered since this is a well-established process in drinking water treatment and it

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has a well-proven high efficiency.7 Indeed, ozone is a strong oxidant that reacts quickly with

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aromatic, amine- and sulfur-containing compounds.8 This comprises a large number of soluble

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organic contaminants, like antibiotics,9-12 antidepressants,13 antineoplastic drugs14 and other

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pharmaceuticals.15-19 However, ozonation forms multiple transformation products8,

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that have to be characterized since they could be equally or more toxic than the parent

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compound.14

9, 13, 16, 20-25

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Among the transformation products formed during wastewater ozonation are those resulting

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from the reaction of ozone with nitrogen-containing compounds. While anilines are primarily

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degraded via an attack on the aromatic ring,8 ozone mostly reacts with other amine moieties via

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adduct formation at the lone electron pair with a subsequent O2 loss, leaving a zwitterion called

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N-oxide.8 Such N-oxides are quickly transformed into hydroxylamines for primary and

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secondary amine moieties,8 as it has been reported for metoprolol.19 In case of tertiary amines the

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N-oxides are rather stable. N-oxide formation has been increasingly reported for ozonation of

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common wastewater contaminants such as the antidepressants citalopram26 and desvenlafaxine,13

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the analgesic tramadol27 and the antibiotics clarithromycin10 and levofloxacin.11 However,

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according to experimental conditions, N-oxides 1) can be stable and remain biologically

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active,28-31 2) are reduced to the original compound or 3) are further oxidized via N-dealkylation

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or ozone reaction with other functional groups in the molecule.8, 32 Further sources of N-oxides

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in wastewater can be from human metabolism of pharmaceuticals33 and from activated sludge

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processes.34 However the potentially increased formation of N-oxides during wastewater


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ozonation should be carefully assessed, particularly when such treatment strategy becomes

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progressively more common. In water treatment, ozonation is generally followed by a

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biologically active filtration step, which has the potential to further reduce the concentration of

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biodegradable DOC fractions and TPs formed during ozonation.

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The formation of oxygenated species can be easily observed by high resolution mass

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spectrometry and Kendrick mass defect analysis. Indeed, this approach was initially developed to

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observe CH2 homologue series35 and adapted in atmospheric science to characterize the reaction

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of ozone with isoprene36 and in water science to detect the occurrence of polymer surfactants

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such as alkylphenol ethoxylates.37 Generally LC retention times of oxygenated TPs are shorter

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than the parent compounds on reversed-phase columns. In contrast, N-oxides exhibit higher

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retention times than their precursors,

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hydroxylated compounds. The objective of this study is to gain insight into transformation

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processes and TP formation during ozonation of wastewater treatment plant effluents. LC-HRMS

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data combined with Kendrick mass defect analysis and retention time shifts will be used to

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investigate removal of precursor compounds and formation of oxygenated TPs with a focus on

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N-oxides during pilot-scale wastewater ozonation and subsequent filtration.

38-41

which can be further used to distinguish them from

99 100 101

MATERIALS AND METHODS

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Chemicals. Analytical standards for lidocaine and amisulpride were purchased from TCI

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chemicals, while tramadol was from LGC Standards. Additional analytical standards for

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sulpiride, tiapride, clarithromycin N-oxide and tiapride N-oxide were from Sigma-Aldrich, and


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so was formic acid used for LC. Water and acetonitrile used as LC eluents were purchased from

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Fischer Scientific at the highest purity available.

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Sample Collection. This study was performed at a major wastewater treatment plant in Berlin,

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Germany, with a dry weather capacity higher than 40,000 m3/d. The raw wastewater effluent

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passes through bar screens, mechanical primary treatment and biological secondary treatment.

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The secondary wastewater effluent with concentration of dissolved organic carbon (DOC) of 13

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mg/L and of chemical oxygen demand (COD) of 36 mg/L was partially diverted to a pilot-scale

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ozone reactor and a flocculation filter. The mean residence time in the ozone reactor was about

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15 min during which an ozone dose of 6.4 mg/L was applied to achieve an O3/DOC ratio of 0.5.

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After the ozone reactor FeCl3 was added as coagulant (3.5 mg/L calculated as Fe). The

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subsequent flocculation filter with 1.2 m anthracite and 0.6 m sand was run at a filtration velocity

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of 5.4 m/h. The mean hydraulic residence time in the filter was therefore of about 20 min.

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Ozonation and filtration resulted in a DOC removal of 2.8 mg/L. The removal of the dissolved

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fraction of COD during ozonation was about 5 mg/L and during filtration about 4.3 mg/L. The

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betablocker metoprolol was reduced to 41 % after ozonation and to 21 % after filtration. The

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data reveal further removal in the filtration process, whereas a combination of biodegradation,

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sorption and flocculation is responsible. COD and micropollutants removal during ozonation is

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due to direct and radical mediated oxidation processes.

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To achieve the objectives of this study, time-proportional 22 h mixed samples (2 x 50 mL)

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were collected after the biological secondary treatment, after ozonation and after filtration while

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accounting for the respective hydraulic retention time.

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Liquid Chromatography. Each sample collected was aliquoted for triplicate analysis. After

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centrifugation at 6,000 rpm for 10 minutes in order to remove suspended solids, samples were

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analyzed by liquid chromatography and in triplicates. Using a 1260 infinity device from Agilent

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Technologies and without previous enrichment, 100 µL of sample were injected on a reversed

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phase C18 column (Agilent Poroshell 120 with 2.1 mm internal diameter, 100 mm length and 2.7

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µm particle size) at a temperature of 40°C. Analytes were eluted with a gradient of 0.4 ml/min of

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water and acetonitrile (both acidified with 0.1% formic acid) similar to that previously described

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in peer-reviewed literature for non-target screening of contaminants in wastewater.13,

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Briefly, the fraction of acetonitrile was kept at 5% for 1 min, linearly increased to 90% within

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the next 14 minutes, then set to 100% and held for 3 minutes. Before analyzing the next sample,

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fraction of acetonitrile was returned to 5% and the column was allowed to equilibrate for 7 min.

42, 43

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Time of Flight Mass Spectrometry. Following chromatographic separation, the compounds

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occurring in the sample were detected by high resolution mass spectrometry, using a 6550

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quadrupole-time of flight (QTOF) instrument from Agilent Technologies. Analytes were ionized

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by positive electrospray (ESI+), applying 12 L/min sheath gas (N2) at 400°C, 16 L/min drying

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gas (N2) at 150°C, 35 psi as nebulizer pressure, 3 kV as capillary voltage and 300 V as nozzle

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voltage. Initially, only MS data were acquired by monitoring m/z in the range 50-1,000 at a rate

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of three spectra/sec. In a second step, MS/MS data were acquired for the selected pairs of

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precursor/N-oxide. The precursor ion [M+H]+ was selected by the quadrupole with an isolation

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width of ± 0.65 u, and successively fragmented using N2 as collision gas with three different

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collision energies set at 10 V, 20 V and 40 V.

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Data Processing. The large amount of data obtained from high resolution mass spectrometry

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was processed as described in a previous study43 and through five successive phases summarized

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in Figure S1 of the supporting information. Briefly, in the first phase, a deconvolution of the total

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ion chromatogram of each sample was performed using the “Molecular Feature Extraction”

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algorithm from the MassHunter software (Agilent Technologies). The algorithm reported a

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compound if a chromatographic peak is recognized with a specific accurate mass (m/z) and with

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at least two isotopes (e.g. from

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charge carriers. The algorithm binned ionization isomers (e.g. ions [M+H]+ and [M+Na]+) and

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isotope signals to a single compound characterized by its accurate mass, abundance, retention

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time and isotope pattern. In the second phase, these lists of compounds obtained from the

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algorithm were imported into the “Mass Profiler Professional” software (Agilent Technologies)

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for further statistical analysis. While compounds that did not occur in three out of three replicates

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were discarded, a T-test (p-value < 0.05) was performed to compare the samples collected before

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and after ozonation. Compounds with a lower peak area after ozonation were considered as

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precursors while those with a higher peak area were considered as transformation products (TPs).

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In the third phase the measured accurate masses of precursors and TPs were converted to

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Kendrick masses (KM) with oxygen as the reference element (Eq. 1) and the respective Kendrick

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mass defect (KMD) was calculated (Eq. 2). Then, precursors and their oxygenated species were

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distinguished among all pairs of precursors/TPs since their KM was shifted by a multiple of 16

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(Eq. 3) while their KMD was the same (Eq. 4). Subsequently, N-oxides were distinguished from

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the remaining oxygenated species through their increased retention time compared to their

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respective precursors. In the fourth phase, precursors and their N-oxides were tentatively

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identified based on their accurate mass and a compound database (STOFF-IDENT,44 and Agilent

13

C) to limit artifacts. H and Na were considered as potential


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ForTox library). Finally, the fifth phase confirmed the identification by high resolution tandem

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mass spectrometry.

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KM = measured accurate mass * 16 / 15.99491

(Eq. 1)

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KMD = KM – nominal KM

(Eq. 2)

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KMTP = n*16 + KMprecursor

(Eq. 3)

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KMDTP = KMDprecursor ± 2 mDa

(Eq. 4)

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Where: KM is the Kendrick mass (oxygen as reference element) calculated from the measured

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accurate mass; KMD is the Kendrick mass defect; nominal KM is the nominal Kendrick mass

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(KM rounded to the closest integer); KMTP is the Kendrick mass of the transformation product;

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KMprecursor is the Kendrick mass of the precursor; KMDTP is the Kendrick mass defect of the

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transformation product and KMDprecursor is the Kendrick mass defect of the precursor.

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RESULTS AND DISCUSSION

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Assessment of matrix effects during analysis. The extent of matrix effects on quantification

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was assessed by spiking three stable isotopes of caffeine, diclofenac and amitriptyline into all

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samples. The results (Fig. S2) show the high stability of the retention time throughout the

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analysis and recoveries in the range between 85% and 115% for all compounds and across all

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samples. Therefore, matrix effects could be neglected and signal abundances of single

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compounds can be directly compared.

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Overall impact of ozonation on water composition. Ozonation of the secondary wastewater

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effluent had a significant impact on the overall water composition assessed by non-targeted

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screening of organic contaminants, as shown in Figure 1. Indeed, a total of 1,229 compounds

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were detected, among which 1,097 occurred in the secondary effluent and 599 after ozonation.


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The distribution of these compounds in a Venn diagram further reveals that 630 compounds were

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attenuated below detection limits by ozonation while 132 products were formed. The remaining

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467 compounds which co-occurred before and after ozonation represent 1) contaminants that

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were not attenuated, 2) contaminants partially attenuated or 3) compounds already occurring

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before ozonation and which are further increased. For instance, the antibiotic clarithromycin and

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its main human metabolite, N-desmethyl-clarithromycin,45 both occur in wastewater.42 However,

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the concentration of N-desmethyl-clarithromycin could increase after ozonation since it is also

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formed by the reaction of ozone with the residual clarithromycin.10 Similarly, citalopram N-

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oxide and N-desmethyl-citalopram are two major human metabolites of the antidepressant

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citalopram which can also be formed by ozonation of the residual drug.26

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The comparison of samples before and after ozonation by a T-test (p-value < 0.05) statistically

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subdivided the overall 1,229 compounds into 853 precursors (decreasing abundance), 165 TPs

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(increasing abundance) and 211 resistant compounds (stable abundance). Previous research on

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wastewater analysis with a similar non-target screening method reported several thousands of

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statistically significant compounds, with a number of TPs similar or higher than the number of

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precursors.43 However, the lower number of compounds reported in this study resulted from the

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absence of sample enrichment. In fact, sample enrichment was avoided on purpose in order to

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minimize bias due to any loss of analyte during solid phase extraction or increased ion

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suppression due to the higher concentration of contaminants in the extracts. As a result, this

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study focuses exclusively on the most abundant organic contaminants and their related ozonation

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TPs which were particularly scrutinized in order to identify precursors forming potential

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oxygenated species and most particularly N-oxides.

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Formation of oxygenated species. The precursors and TPs found by the T-Test were paired

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according to their respective KM and KMD for oxygen homologs. Related pairs of precursors

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and oxygenated species are characterized by the same KMD. This led to the overall observation

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of 60 potential oxygenated species for 99 precursors (Table 1 and Figure S3). Among the

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oxygenated species formed during ozonation of the secondary wastewater effluent, the majority

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(56%) are mono-oxygenated species. These TPs are consistent with mono-hydroxylation which

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is a common degradation pathway during ozonation of a wide range of wastewater contaminants,

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particularly those with reactive aromatic rings.8 For instance, hydroxylation resulting from

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ozonation has been observed for the antibiotics amoxicillin46 and sulfamethoxazole,47 the anti-

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inflammatory drug diclofenac,18 the beta blocker metoprolol,23 or the antibacterial triclosan.21

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However, mono-oxygenated species can also result from N-oxide formation due to oxidation of

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compounds with a tertiary amine moiety,8 as previously described for several pharmaceuticals

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commonly found in wastewater.9, 10, 13, 27, 48 Also poly-oxygenated species were formed (Table 1).

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These TPs are consistent with multiple hydroxylation23 or a combination of hydroxylation with

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N-oxide formation. However, this study will focus on assessing N-oxide formation among mono-

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oxygenated species.

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Assessment of N-oxide formation. The application of a retention time filter indicated that

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79% (27 out of 34) of mono-oxygenated species formed during ozonation of the secondary

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wastewater are potential N-oxides, which are characterized by retention times higher than the

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precursors (Table 1). Moreover, these potential N-oxides also represent 16% (27 out of 165) of

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the overall ozonation TPs. Therefore, additional analysis was performed in an attempt to confirm

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the identity of such N-oxides.


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The precursors identified with a confidence level of 1 or 249, 50 were the antipsychotic drugs

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sulpiride, tiapride and amisulpride, the antihistamine diphenhydramine, the antidepressants

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venlafaxine and citalopram, the pain medication tramadol, the local anesthetic lidocaine, the

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antibiotic clarithromycin and its metabolite clindamycin sulfoxide (Table 2). Identification was

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based on matches with authentic standards or the ForensicTox MS/MS library (Figures S4-S14).

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For these ten compounds, the occurrence of the corresponding N-oxides after ozonation could be

249

verified with a confidence level 1 (Figure 2, Figures S15-S17), 2a or 2b (Figures S18-S30).

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Whenever neither standards nor MS/MS spectra were available, for example for sulpiride N-

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oxide, the identity of the compound was deduced by diagnostic evidence based on MS/MS

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fragments as shown in Figure 3. While three product ions were common to sulpiride and its N-

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oxide and confirmed their similar structure, two other product ions from sulpiride associated with

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the tertiary amine moiety had their m/z shifted by 15.995 with sulpiride N-oxide, which is

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consistent with the addition of oxygen on the amine. Finally, a last piece of evidence supporting

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the identification of N-oxides is the calculated LogD values. For all the precursors previously

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identified, LogD values were calculated at pH 2.7 (pH of the eluent) according to the public web

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resource developed by ChemAxon,51 and so was done for the corresponding N-oxides and

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hydroxyl products. While higher LogDs are associated with higher retention times on reversed-

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phase separation, the positive LogD shifts of the N-oxides and the negative LogD shifts of the

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hydroxylated compounds tend to confirm the identification of TPs as N-oxides rather than

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hydroxylated products.

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Overall, 37% of the potential N-oxides from the mono-oxygenated TPs (10 out of 27) could be

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identified. The other 17 compounds remain potential N-oxides but no tentative identity could be

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assigned. This is mostly attributed to the inability to identify a precursor based on MS/MS


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spectra in libraries. In fact, secondary wastewater effluent is a complex matrix that is likely to

267

contain unknown tertiary amines, such as metabolites of pharmaceuticals not yet identified or

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included in compound libraries. Besides the N-oxides identified in this study, previous research

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has also shown the potential N-oxide formation from other common wastewater contaminants,

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including cetirizine, fexofenadine, hydrochlorothiazide, pargyline, deprenyl and pheniramine.20,

271

34

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pre-concentration) their N-oxide formation could not be assessed during pilot-scale ozonation.

273

However, N-oxides associated with these non-detected compounds further strengthen the

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relevance of N-oxide formation during ozonation.

Since these precursors were not detected in this study (potentially due to the absence of sample

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The 10 N-oxide precursors identified in this study were almost totally transformed during

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ozonation (Table 2). While their N-oxides were not detected in the secondary wastewater

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effluent (Figure 4), they were detected with a substantial abundance after ozonation (peak area

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normalized to the peak area of the precursor). Some of these N-oxides were previously reported

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to be formed during other processes, such as activated sludge treatment.34 However ozone tends

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to yield a higher formation of N-oxides. For instance, while venlafaxine and lidocaine formed

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respectively 5% and 19% of N-oxide during wastewater treatment with activated sludge, they

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formed respectively 16% and 38% of N-oxide after ozonation.

283

The assumption of N-oxides representing 16% of the overall ozonation TPs should be

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considered as conservative. Indeed, N-oxides might also occur for poly-oxygenated species. For

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instance, clindamycin sulfoxide N-oxide observed after ozonation can be a mono-oxygenated

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species of the precursor clindamycin sulfoxide, but it can be also considered as a di-oxygenated

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species of the precursor clindamycin (Fig. S27). However, N-oxides among poly-oxygenated


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species were not further investigated in this study and will require further research since the rule

289

of increasing retention time cannot be applied in this case.

290 291

Fate of N-oxides during filtration. After ozonation, an additional treatment by filtration was

292

applied, which resulted in further changes in the water composition presented in a heat map of a

293

hierarchical cluster analysis (Fig. S31). The clusters show compounds which are removed during

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filtration like ozonation products and the beta-blocker atenolol (known for its biodegradability on

295

trickling filters),52 those which are released into the water and a large fraction of ozonation

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products which reveal stable during filtration. Compound and COD removal of 4.3 mg/L suggest

297

biodegradation processes during filtration, but they work with limited efficiency as the stability

298

of ozonation products reveal. Also N-oxides formed during ozonation were very poorly retained

299

or transformed during the filtration process (Table 2). Therefore, the effect of filtration on the

300

overall water composition should be further studied in more detail. However, this is out of the

301

scope of this study on N-oxides as ozonation TPs.

302 303

Implications for wastewater treatment. Advanced oxidation processes are increasingly

304

considered to upgrade conventional wastewater treatment and to decrease the load of

305

contaminants discharged to the environment. This study confirms that ozonation of secondary

306

wastewater effluents efficiently decreases the concentration of common micro-pollutants.

307

However, a substantial fraction of these compounds containing a tertiary amine moiety appears

308

to react with ozone to yield quaternary N-oxides by a formal addition of oxygen. In this study,

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potential N-oxides represented 16% (27 out of 165) of the total TPs observed after ozonation.

310

Ten N-oxides were identified, while 17 remain potential N-oxides without any tentative


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identification. There were no further accurate mass matches of precursors in compound libraries,

312

which underlines the need for enhanced compound libraries.53 The estimation of N-oxides

313

representing 16% of the overall TPs is conservative since it does not account for N-oxides in

314

poly-oxygenated species and those eluting earlier than their precursors. These cases were shown

315

to occur and will be examined in future studies.

316

The hydroxylation of water contaminants, often considered in degradation studies, was shown

317

to represent only a small fraction of mono-oxygenated ozonation TPs compared to N-oxide

318

formation based on our analysis using KMD and positive RT shifts. A sub-structure search for

319

compounds with a tertiary amine moiety in the publicly available database STOFF-IDENT44

320

resulted in over 1,300 hits for possible N-oxide precursors. This reveals a rather large potential

321

of wastewater contaminants to form N-oxides. However, N-oxide formation is pH dependent,

322

since ozone does not react rapidly with a protonated tertiary amine.17, 19, 24, 25 Therefore, among

323

all potential compounds in the wastewater effluent, only those with a deprotonated tertiary amine

324

at the pH of wastewater would be the principal N-oxide precursors during ozonation.

325

Since the N-oxides were not removed by a following filtration step in this work and since they

326

can be reduced to reform the native compound,34 these observations have significant implications

327

for the application of ozonation in wastewater treatment. While ozonation efficiently eliminates

328

the native contaminant, the N-oxides formed should be further characterized since some were

329

also shown to remain biologically active.

330

analyzed by suitable bioassays to assess the impact of ozonation on the biological activity. In

331

addition, the formation of N-oxides should be further assessed with higher ozone doses as they

332

might be further degraded. Finally, the occurrence and fate of N-oxides in river water should be

333

particularly considered when ozonation is applied in wastewater treatment.

28-31

Therefore, ozonated samples should also be


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334 335

ASSOCIATED CONTENT

336

Supporting Information. The supporting information includes 31 figures showing a workflow

337

for compound identification, the investigation of matrix effects, a Kendrick mass plot, mass

338

spectra and fragmentation pathways of precursors and N-oxides, and the effect of ozonation and

339

filtration on water composition by cluster analysis. This material is available free of charge via

340

the Internet at http://pubs.acs.org.

341 342 343

ACKNOWLEDGMENT

344

The authors thank the staff of Berlin Wasserbetriebe and Kompetenz Zentrum Wasser Berlin,

345

Germany, for providing the samples used in this study. The German Federal Environmental

346

Foundation (Deutsche Bundesstiftung Umwelt, DBU) is gratefully acknowledged for funding the

347

Ph.D. scholarship of Sascha Lege (Nr. 20013/277) and the German Research Foundation (DFG)

348

for funding the project ZW 73/14.

349 350

ABBREVIATIONS

351

LC, liquid chromatography; MSMS, tandem mass spectrometry; TP, transformation product;

352

DOC, dissolved organic carbon.

353 354 355

REFERENCES


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511 512


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513


FIGURES

514 515

Figure 1. Overall impact of ozonation on water composition.

516 517 518 519 520 521 522


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523 524

Figure 2. Identification of N-oxides by LC-MS/MS analysis based on analytical standards

525

(Retention time differences between analytes and standards were below 0.05 min; identification

526

is based on a minimum of 7 common MS/MS fragments for analytes and standards).


22

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527 528

Figure 3. Identification of sulpiride N-oxide by diagnostic evidence based on MS/MS fragments.

529


23


Page 24 of 30

530 531

Figure 4. Extracted ion chromatograms show the relative abundance of selected precursors and

532

N-oxides before ozonation, after ozonation and after biofiltration.

533 534 535 536 537 538 539 540 541 542 543


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544

TABLES

545

Table 1. Assessment of the formation potential of oxygenated species and N-oxides during

546

wastewater ozonation. Precursors and oxygenated species are paired based on the same KMD

547

without restriction, precursor/(N-)oxide pairs were selected by KMD and a positive retention

548

time shift.

Number of Precursors → Oxygenated species oxygenation (without restriction) 1 42 → 34

Precursors → (N-)Oxides (RTprecursor < RToxide) 27 → 27

2

26 → 21

5→7

3

19 → 12

1→1

4

18 → 11

4→3

5

3→2

-

All

99 → 60

39 → 37

549 550


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Table 2. Overview on identification and occurrence of precursors and their respective N-oxides.

Precursor

N-oxide Relative abundance in water*

Identity

Relative abundance in water*

Identity

Name

Formula

Level**

Untreated

Ozonated

Filtered

Level**

LogD shift

RT-shift (min)

Untreated

Ozonated

Filtered

Sulpiride

C15H23N3O4S

1

100%

n.d.

n.d.

2b

1,5

1,73

n.d.

45%

45%

Tiapride

C15H24N2O4S

1

100%

n.d.

1%

1

1,51

0,57

n.d.

50%

51%

Lidocaine

C14H22N2O

1

100%

n.d.

6%

2a

1,52

0,91

n.d.

38%

39%

Amisulpride

C17H27N3O4S

1

100%

n.d.

1%

2a

1,5

0,34

n.d.

20%

20%

Tramadol

C16H25NO2

1

100%

11%

11%

1

1,5

0,27

n.d.

31%

32%

Venlafaxine

C17H27NO2

2a

100%

15%

15%

2a

1,5

0,38

n.d.

16%

16%

Diphenhydramine

C17H21NO

2a

100%

n.d.

n.d.

2b

1,5

0,34

n.d.

141%

144%

Citalopram

C20H21FN2O

2a

100%

5%

21%

2b

1,5

0,19

n.d.

82%

88%

Clarithromycin

C38H69NO13

1

100%

n.d.

1%

1

1,51

0,32

n.d.

61%

63%

Clindamycin sulfoxide

C18H33N2O6SCl

2b

100%

n.d.

n.d.

2b

1,51

0,35

n.d.

21%

29%

* Peak area normalized to the abundance of the precursor in the untreated water, where n.d. stands for not detected. ** According to peer-reviewed literature49, 50. Level 1 implies identification with an analytical standard showing less than 0.05 min difference in retention time and a minimum of 2 common product ions. Level 2a implies identification with a spectral library and a minimum of 3 common product ions. Level 2b implies identification by diagnostic evidence based on mass fragments with a minimum of 3 annotated product ions.


26

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Figure 1. Overall impact of ozonation on water composition. 76x74mm (96 x 96 DPI)



Figure 2. Identification of N-oxides by LC-MS/MS analysis based on analytical standards (Retention time differences between analytes and standards were below 0.05 min; identification is based on a minimum of 7 common MS/MS fragments for analytes and standards). 160x111mm (96 x 96 DPI)


Page 28 of 30

Page 29 of 30


Figure 3. Identification of sulpiride N-oxide by diagnostic evidence based on MS/MS fragments. 160x198mm (96 x 96 DPI)



Figure 4. Extracted ion chromatograms show the relative abundance of selected precursors and N-oxides before ozonation, after ozonation and after biofiltration. 160x98mm (96 x 96 DPI)


Page 30 of 30

Assessment of N-Oxide Formation during Wastewater Ozonation

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