Photodegradation of sulfamethazine, sulfamethoxypiridazine, amitriptyline, and clomipramine drugs in aqueous media

Article abstract of DOI:10.1016/j.jphotochem.2016.12.008

The photochemical transformation of two antibacterial sulfonamides, namely sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), and two tricyclic antidepressants, namely amitriptyline (AMT) and clomipramine (CMP) were investigated. Experiments conducted in river water under artificial sunlight irradiation show an acceleration of the degradation for SMT, SMP, and CMP of a factor 1.6–7.7 by comparison to purified water. This acceleration is, at least partially, due to photosensitized reactions which can occur in river water. The photodegradation of CMP was particularly fast. In addition, no degradation was observed for AMT in purified water while photosensitized reaction occurs. Under ultra-violet (254?nm) irradiation in purified water, the four drugs were degraded. Calculated quantum yields of photodegradation were of 4.3?×?10^?3, 5.1?×?10^?3, 7.6?×?10^?3, and 65.0?×?10^?3 respectively for SMT, SMP, AMT, and CMP. UV coupled with hydrogen peroxide (UV/H₂O₂) was used as an advanced oxidation process for water depollution. The calculated second order rate constants of reaction with hydroxyl radicals were of 5.0?×?10⁹, 5.0?×?10⁹, 8.0?×?10⁹ and 9.5?×?10⁹?L?mol^?1?s^?1 for SMT, SMP, AMT and CMP, respectively. Finally, the structures of photoproducts were proposed according to LC–MS/MS analyses. The elimination of SO₂ was the main photochemical process for SMT and SMP. In the case of AMT and CMP, hydration and hydroxylation, respectively, were observed.

Full text of DOI:10.1016/j.jphotochem.2016.12.008

Accepted Manuscript
Title: Photodegradation of sulfamethazine,
sulfamethoxypiridazine, amitriptyline, and clomipramine
drugs in aqueous media
´
Author: Rania Nassar Aurelien Trivella Samia Mokh
´
Mohamad Al-Iskandarani Hele`ne Budzinski Patrick Mazellier
PII:
S1010-6030(16)30523-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2016.12.008
JPC 10463
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Journal of Photochemistry and Photobiology A: Chemistry
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Revised date:
Accepted date:
28-6-2016
29-11-2016
10-12-2016
´
Please cite this article as: Rania Nassar, Aurelien Trivella, Samia Mokh,
´
Mohamad Al-Iskandarani, Hele`ne Budzinski, Patrick Mazellier, Photodegradation
of sulfamethazine, sulfamethoxypiridazine, amitriptyline, and clomipramine drugs
in aqueous media, Journal of Photochemistry and Photobiology A: Chemistry
http://dx.doi.org/10.1016/j.jphotochem.2016.12.008
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Photodegradation of sulfamethazine, sulfamethoxypiridazine, amitriptyline,
and clomipramine drugs in aqueous media
Rania Nassar1,2, Aurélien Trivella3,4, Samia Mokh2, Mohamad Al-Iskandarani1,2, Hélène
Budzinski3,4, Patrick Mazellier3,4*
1 Faculty of Public Health I, Lebanese University, Hadath, Lebanon
2
Laboratory for Analysis of Organic Compound LACO, National Council for Scientific
Research CNRS, Lebanese Atomic Energy Commission LAEC, 11‑8281, Riad El Solh,
Beirut 1107 2260, Lebanon
3 University of Bordeaux, EPOC, L’équipe de Physico et Toxico Chimie de l’Environnement,
UMR 5805, F 33400 Talence, France
4 CNRS, EPOC, UMR 5805, F-33400 Talence, France
* Corresponding author: Patrick Mazellier,
1

Highlights
 Irradiation of selected drugs leads to the formation of several photoproducts
 The methoxy substituent is at the origin of the bathochromic shift which allows
absorption up to 380 nm for SMP while no absorption is observed above 350 nm for
SMT
 No degradation was observed for amitriptyline
 Photosensitizers enhanced the degradation of amitriptyline and clomipramine in river
water
Abstract
The photochemical transformation of two antibacterial sulfonamides, namely
sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), and two tricyclic
antidepressants, namely amitriptyline (AMT) and clomipramine (CMP) were
investigated. Experiments conducted in river water under artificial sunlight
irradiation show an acceleration of the degradation for SMT, SMP, and CMP of
a factor 1.6 to 7.7 by comparison to purified water. This acceleration is, at least
partially, due to photosensitized reactions which can occur in river water. The
photodegradation of CMP was particularly fast. In addition, no degradation was
observed for AMT in purified water while photosensitized reaction occurs.
Under ultra-violet (254 nm) irradiation in purified water, the four drugs were
degraded. Calculated quantum yields of photodegradation were of 4.3x10-3,
5.1x10-3, 7.6x10-3, and 65.0x10-3 respectively for SMT, SMP, AMT, and CMP.
UV coupled with hydrogen peroxide (UV/H2O2) was used as an advanced
2

oxidation process for water depollution. The calculated second order rate
constants of reaction with hydroxyl radicals were of 5.0x109, 5.0x109, 8.0x109
and 9.5x109 L mol-1 s-1 for SMT, SMP, AMT and CMP, respectively. Finally,
the structures of photoproducts were proposed according to LC-MS/MS
analyses. The elimination of SO2 was the main photochemical process for SMT
and SMP. In the case of AMT and CMP, hydration and hydroxylation,
respectively, were observed.
Keywords: antibacterial sulfonamides, tricyclic antidepressant, photodegradation, artificial
sunlight, UV irradiation.
1. Introduction
Medicine residues are organic micropollutants of great interest due to their extensive use and
their increasing occurrence in the aquatic environment [1]. These residues potentially impact
water quality, ecosystems, and human health [2]. Some of these pharmaceutical compounds
are not completely removed by waste water treatment plants [3,4]. Drugs most frequently
found in wastewater are antibiotics, antacids, steroids, antidepressants, analgesics, anti-
inflammatories, antipyretics, beta-blockers, lipid-lowering drugs, tranquilizers, and stimulants
[5]. Potential health effects and acute toxicity of those micropollutants are not always well
known. For example, one of the major concerns of antibiotic residues in the environment
involves the development of resistant bacteria [6]. Polluted water can generally be treated
efficiently by biological treatment plants, and by using adsorbents or conventional chemical
treatments (chlorination, ozonation …). However, these procedures are occasionally not able
3

to degrade pollutants to the levels required by law or essential for the subsequent use of the
effluent [3].
Ultraviolet (UV) treatment of water is being used for disinfection of wastewater and drinking
water in North America, Europe, and numerous countries around the world [1]. This
technique is very effective in advanced water treatment technologies [7]. Furthermore,
advanced oxidation processes, in particular UV irradiation coupled with hydrogen peroxide
(UV/H2O2), are very effective in the oxidation of numerous organic and inorganic compounds
●
[8]. These processes are all based on the generation of highly reactive free radicals (HO●, O2
●
-, HO2 ) [9-11]. During UV/H2O2 treatment, oxidation occurs mainly by HO● radicals which
react unselectively with organic contaminants. Second order reaction rate constants in the
order of 108-1010 L mol-1 s-1 have been reported for many organic compounds [12].
The aims of the present study were to evaluate the photodegradation kinetic constants of
sulfamethazine (SMT), sulfamethoxypyridazine (SMP), amitriptyline (AMT), and
clomipramine (CMP) antibiotic and antidepressant compounds by irradiating them in different
water matrices by means of simulated sunlight and a UV source (254 nm) alone or coupled
with hydrogen peroxide. Quantum yields of direct photodegradation were also calculated for
the four compounds under a 254 nm irradiation. Pharmaceutical compounds SMT and SMP
were chosen due to their massive use in veterinary medicine [13]. AMT and CMP drugs were
chosen for their use in human medicine [14]. Their presence in ground [15], surface [16,17]
and drinking [18] waters was reported. Finally, the structural characterization of the
degradation products formed during UV irradiation was performed by means of LC-MS/MS
analyses.
4

2. Materials and methods
2.1 Chemicals
High purity standards of sulfamethazine (SMT, ≥ 99 %), sulfamethoxypyridazine (SMP, ≥
97 %), amitriptyline (AMT, ≥ 98 %), clomipramine (CMP, ≥ 98 %), and hydrogen peroxide
(30%, w/w) were purchased from Sigma-Aldrich.
HPLC grade solvents (water, methanol - MeOH, and acetonitrile - ACN) were supplied from
Sigma-Aldrich. For each drug, stock solutions were prepared at a concentration of 100 mg L-1
in purified water using a Millipore device (resistivity 18.2 MΏ cm, DOC < 0.1 mg L-1). The
solutions were stored in dark at 4 °C until use. All the experiments have been performed at pH
6.1.
River water was sampled three times from the "Isle" in Périgueux (France) in July 2012, May
2013 and May 2014 (7.8 < pH < 8.0; total organic carbon (TOC): 0.2 mg L-1). The river water
was filtered with a 0.45 µm membrane prior to use for photochemical experiments. One liter
of the river water was acidified with 5 mL of sulfuric acid (7.5 M) for measurement of the
permanganate index (6.2, 3.1 and 2.5 mg O2 L-1 in July 2012, and May 2013 and 2014).
Drug concentrations used for photodegradation kinetics and photoproducts identification
experiments were in the range 0.3-0.5 µmol L-1 and 30-35 µmol L-1, respectively.
2.2 UV-Visible spectroscopy
UV-Vis spectra were recorded on a Shimadzu double-beam spectrophotometer (UV-1800),
using either 1 or 5 cm quartz cells (Hellma Analytics, QS). Baselines (purified water) and
spectra were recorded at room temperature with a 1-nm resolution.
Molar absorption coefficients of each drug were calculated using solutions with
concentrations ranging from 1.8 µM to 5.6 µM. Absorbance of solutions were measured using
a 1-cm cell.
2.3 LC-UV and LC-MS/MS analyses
5

The concentration of target drugs at different irradiation times was quantified by liquid
chromatography (Agilent, 1100 series) coupled with UV detection (LC-UV). UV absorption
of SMT and SMP was recorded at 260 nm, that of AMT at 240 nm, and that of CMP at 230
nm. A Nucleosil C18 5 µm-100 Å column (250 mm × 4.6 mm) was used for SMT and SMP
analyses. A Nucleosil C18 Nautilus column (same packing material) was used for AMT and
CMP analyses. The flow rate was set to 1 mL min-1. Solvent A was MeOH and solvent B
purified water. SMT and SMP analyses were performed from a mobile phase composed of
65% of A. In the case of AMT and CMP analyses, the mobile phase was prepared from 50%
of A and 50% of B adjusted to pH 3 by adding 10 mM of formic acid. All the experiments
were performed in isocratic mode. The sample injection volume was set to 20 µL for SMT
and SMP, and to 50 µL for AMT and CMP.
The structural identification of photoproducts was carried out with an Agilent 1200 LC
system (Agilent Technologies, USA) coupled to an Agilent 6410 triple quadrupole mass
spectrometer (LC-MS/MS). The eluents and columns used for the separation of the parent
compound and its photoproducts were the same as those of LC-UV analyses. The flow rate
was set to 0.6 mL min-1. Detection was performed with an electrospray ionization (ESI)
source operating in positive mode. The following conditions were set: source temperature 450
°C, capillary voltage 3000 V. The collision energy was adjusted from 5 to 30 V to obtain the
fragmentation patterns when performing product ion scans. Nitrogen was used as collision gas
and nebulization gas at 30 and 40 psi, respectively.
2.4 Irradiation experiments
UV irradiation (254 nm) experiments were performed in purified water. The irradiation setup
was a batch photoreactor (volume of irradiated solution: 2 L, optical path length: 3.6 cm). The
lamp (Vilber-Lourmat T6C-254 nm, low pressure Hg lamp 6 W) was located at the center of
the reactor, in a quartz sleeve. The photon fluence rate (I0) was evaluated by hydrogen
6

peroxide actinometry [19]. A value of 1.36x10-6 E L-1 s-1 was obtained. Hydrogen peroxide
concentration was measured by the Ti-complexometry method described by Eisenberg [20].
Simulation of natural sunlight was carried out using a Suntest CPS instrument from Atlas
Material Testing Technology (Chicago, Illinois, USA), equipped with a xenon arc lamp and
UV-IR filters ( ≥ 290 nm). The emitted UV-Visible wavelengths ranged from 290 to 800
nm. Irradiance was set to 250 W m-2. Drug solutions were prepared in purified and river
waters and transferred into 12 mL glass tubes (optical pathlength: 1.5 cm). Before irradiation,
aliquots of 1 mL of each spiked sample were taken off and stored in the dark (aluminum
wrapped vials) at room temperature (26 °C). For dark control experiments, non-irradiated
samples were wrapped in aluminum foil and dropped off into the sample compartment in the
same conditions than unwrapped samples. Drugs were irradiated in the Suntest over a period
of 7 hours. Aliquots of 1 mL were withdrawn for analysis at scheduled time intervals.
2.4 Reaction rate constants and photodegradation quantum yields
2.4.1 Direct photolysis
The degradation pattern of target drugs (D) was adjusted to the pseudo-first order kinetic
model, which assumes a decrease of the concentration through time proportional to the
concentration remaining in the matrix. The model follows equation (1):
ln([D]/[D]0) = - kapp t (1)
where [D]0 and [D] are the drug concentrations (mol L-1) respectively before and during
irradiation, kapp is the apparent first order reaction rate constant (s-1), and t is the irradiation
time (s).
Aqueous solutions of target drugs (0.3 ≤ [D] ≤ 0.8 µmol L-1) were irradiated at 254 nm. A
disappearance of the organic compound is observed according to the reaction:
h
D → degradation products
with -d[D]/dt = ϕ(D) I0(1-10-A)
(2)
7

where ϕ(D) is the quantum yield of degradation at 254 nm, I0 is the photon fluence rate of the
irradiation source (I0 = 1.36x10-6 E L-1 s-1), and A is the absorbance at 254 nm.
Working concentrations were chosen such as the absorbance at 254 nm is lower than 0.02
(hyper dilute medium). Thus, the rate of photodegradation of D can be simplified from (2) to
(3):
-d[D]/dt = 2.303 A ϕ(D) I0
(3)
Eq. (3) indicates that the photodegradation of D follows to an apparent first order kinetics law.
Thus, the expression of the monochromatic quantum yield is:
ϕ(D) = kapp / (2.303 I0 ɛD ℓ)
(4)
where ϕ(D) is the quantum yield of degradation at 254 nm, kapp is the apparent first order
reaction rate constant (s-1), I0 is the photon fluence rate of the irradiation source, ɛD is the
molar absorption coefficient of the drug at 254 nm, and ℓ is the internal radius of the reactor
minus the radius of the monochromatic lamp (the UV source was placed at the center of the
reactor).
2.4.2 Photosensitized reactions.
The UV irradiation (λ = 254 nm) of hydrogen peroxide in aqueous solution leads to the
production of hydroxyl radicals (HO●) following the reaction:
h
H2O2 → 2 HO●
with d[HO●]/dt = 2 ϕH2O2 Ia
(5)
where -d[HO●]/dt is the rate of formation of HO● radicals (mol L-1 s-1), ϕH2O2 is the hydrogen
peroxide quantum yield of photodegradation at 254 nm (ϕH2O2 = 0.5, [21]), and Ia is the rate of
light absorption (E L-1 s-1).
Aqueous solutions of D were irradiated in the presence of large amounts of hydrogen
peroxide ([H2O2]0 = 0.05, 0.08, 0.10 and 0.20 mol L-1) at 254 nm. No change in D
concentration was observed in the presence of such excess of hydrogen peroxide but in the
absence of UV light meaning that no dark reaction occurred. In the time scale of experiments,
8

the concentration of hydrogen peroxide was shown to remain almost constant: [H2O2]t /
[H2O2]0 > 0.98. Under UV irradiation the following reactions occur:
kH2O2
●
HO● + H2O2 → HO2 + H2O
-d[H2O2]/dt = kH2O2 [H2O2] [HO●] (6)
-d[D]/dt = kD [D] [HO●] (7)
kD
HO● + D → degradation products
At a given time, the steady-state concentration of hydroxyl radicals is given by the Eq. 8:
[HO●] = (2 ϕH2O2 × Ia) / (kH2O2 [H2O2]0 + kD [D]0)
(8)
where [HO●] is the hydroxyl radical concentration (mol L-1), Ia is the rate of light absorption
(E L-1 s-1), kH2O2 is the second order rate constant of reaction of hydrogen peroxide with
hydroxyl radicals (kH2O2 = 2.7×107 L mol-1 s-1, [21]), [H2O2]0 is the concentration of hydrogen
peroxide before irradiation (mol L-1), kD is the second order rate constant of reaction of the
drug with hydroxyl radicals (L mol-1 s-1), and [D]0 is the concentration of the drug before
irradiation (mol L-1).
●
Reactions of HO2 with D can be neglected in our conditions due to the well-known lower
reactivity of this radical compared to HO● radicals.
If hydrogen peroxide concentration is high enough (A254nm > 2), it is considered that the
incident light is completely absorbed by hydrogen peroxide. Moreover, the decrease in H2O2
concentration is low (< 5%) in the time scale of the experiments and kH2O2 [H2O2]0 >> kD [D]0
even if a value of kD of 1010 is considered. Then, the expression of Eq. 8 can be simplified:
[HO●] = 2 ϕH2O2 × I0 / (kH2O2 [H2O2]0)
The D disappearance as a function of time can be written according to relations 7 and 9:
-ln ([D]/[D]0) = 2 kD ϕH2O2 I0 t / (kH2O2 [H2O2]0) (10)
(9)
The plot of ln ([D]/[D]0) as a function of reaction time allows the determination of the second
order rate constant of reaction between the drug and hydroxyl radicals (kD).
9

3. Results and discussion
3.1 UV-Vis absorption spectra
Fig.
1
shows the UV-Vis absorption spectra of sulfamethazine (SMT),
sulfamethoxypyridazine (SMP), amitriptyline (AMT) and clomipramine (CMP) in aqueous
solutions at pH 6.1. UV-Vis spectra display maxima at 240 (1.7x104 L mol-1 cm-1) and 263
nm (1.8x104 L mol-1 cm-1) for SMT, and 263 nm (1.8x104 L mol-1 cm-1) for SMP (Fig. 1a).
SMT and SMP have a common absorption maximum at 263 nm due to their structural
similarities, especially the substituted benzene cycle which is present in both structures.
Differences can be observed from the pyrimidine (SMT) and pyridazine (SMP) cycles and the
nature of their substituents. In particular, the methoxy group is at the origin of a bathochromic
shift of the * transition of the substituted pyridazine cycle [22,23] and this one allows
absorption up to 380 nm for SMP while no absorption is observed above 350 nm for SMT.
UV-Vis absorption spectra of AMT and CMP are totally different despite their structural
similarities (Fig. 1b). Maxima of absorption are located at 210 (3.5x104 L mol-1 cm-1) and 240
nm (1.2x104 L mol-1 cm-1) for AMT, and 220 (2.1x104 L mol-1 cm-1), 253 (6.8x103 L mol-1
cm-1) and 280 nm (5.8x103 L mol-1 cm-1) for CMP. Moreover, AMT do not absorb above 290
nm while CMP absorbs light up to 320 nm. These spectral differences can be explained by the
presence of a chlorine atom and especially a nitrogen atom located in the CMP tricyclic part
which induce n* transitions. In addition, the heteroatoms are responsible for bathochromic
shifts of the * bands. To a lesser extent, the increase conjugation in the AMT structure
also induced a bathochromic shift of the * transitions.
3.2 Kinetic data and quantum yields
Kinetic data and quantum yields obtained under simulated solar light and UV irradiation are
gathered in Table 1. The photodegradation of SMT, SMP, AMT and CMP under artificial
sunlight irradiation was studied in purified and river waters. SMT, SMP and CMP
10

decomposition followed a pseudo-first order kinetics in the two aqueous matrices while AMT
was not degraded after seven hours of irradiation in purified water. This latter result is in line
with the absence of absorption above 290 nm on the UV-Vis spectrum of AMT (Fig. 1b). For
the same duration of irradiation, AMT was not degraded in the river water. SMT and SMP
degradation rate constants measured in purified water were respectively of 1.1x10-3 and
0.9x10-3 min-1. The two sulfonamides disappeared with comparable kinetics upon irradiation
under the used lamp.CMP degradation was fast by comparison with sulfonamides. The
degradation rate constant was of 18.2x10-3 min-1. In river water, an increase of the rate
constants was observed for the three degraded drugs. The photochemical transformation of
SMP (kR = 6.9x10-3 min-1) was 1.9 fold faster than that of SMT (kR = 3.7x10-3 min-1). The
observed differences between the two aqueous media can be assigned not only to the presence
of photosensitizers in river water [24] but also to the change of protonation state (SMT: pKa1
= 2.8 and pKa2 = 7.0, and SMP: pKa1 = 2.2 and pKa2 = 7.3). In fact, the experiments were
carried out in purified water at pH 6.1 and in river water at pH 7.8. The change in protonation
state of the sulfonamide compounds can induce modifications of UV-Vis absorption and
could be, at least partially, at the origin of the acceleration of the degradation. In 2011, Baeza
and Knappe [25] studied the effect of pH on SMT photolysis rate and the results show that the
anionic form photolyzed more rapidly than the neutral one. The quantum yield values were
calculated at 254 nm to be 2.8 ×10-3, 8.7 ×10-3 and 8.4 ×10-3 respectively at pH 3.6, 7.85 and
9.7. In 2012, García-Galán et al. [26] reported the behavior of SMT under artificial solar light
irradiation in both purified water and in reclaimed wastewater, in order to compare the
influence of dissolved organic matter. First order rate constants of 1.8×10-3 and 2.3×10-3 min-
1
were determined in purified water and waste water, respectively. García-Galán et al.
explained that dissolved organic matter contained in the matrix could have acted as a catalyst
for this sulfonamide compound. The photolysis kinetics of SMP was evaluated by Khaleel et
11

al. [16]. The first order rate constant was determined in purified water to be 52×10-3 min-1, i.e.
58 fold higher than that determined in our study. This difference can be explained by the use
of a medium-pressure mercury lamp as irradiation source. AMT was persistent after 7 hours
of irradiation in river water but 50% of degradation was obtained after 2 days of irradiation
(data not shown). CMP degradation rate constant was evaluated as 28.9x10-3 min-1, almost 2
times higher than in purified water. In the case of AMT (pKa = 9.41) and CMP (pKa = 9.28),
only neutral forms are present in both aqueous matrices, thus we can confirm that
photosensitizers have enhanced their degradation in river water.
Under 254 nm irradiation, the degradation of the four drugs was observed in purified water.
The quantum yields were of 4.3x10-3, 5.1x10-3, 7.6x10-3, and 65.0x10-3 for SMT, SMP, AMT
and CMP, respectively (Table 1). The photoreaction efficiency is close for SMT and SMP
drugs while a factor 8.6 separates the values obtained for AMT and CMP. Following
irradiation at 254 nm, the pseudo-first order rate constants of degradation were of 57.3x10-3
and 66.0x10-3 min-1 for SMT and SMP, respectively. In the case of AMT and CMP the
constants were of 39.9x10-3 and 367.8x10-3 min-1. Among the four drugs, a significantly faster
degradation of CMP was observed. This result was also obtained from simulated solar light
irradiation experiments. This difference can be explained by the lone-pairs of electrons of the
chlorine atom. Indeed, this atom has a mesomeric effect which allows to release the electron-
pairs to participate to the conjugation with the π electrons of the benzene ring. This effect
could enhance the photolytic reactivity of CMP as explained by Lian et al. [27] in the case of
sulfachloropyridazine. The photochemical transformation of AMT at a concentration of 1
µmol L-1 was investigated in ultrapure water at 20°C using a low pressure mercury lamp ( =
254 nm) by Real et al. [28]. The value obtained for the quantum yield was close to our value.
In the framework of water depollution, the UV/H2O2 advanced oxidation process was used.
The selected drugs were oxidized using ultraviolet coupled to hydrogen peroxide at
12

concentrations ranging from 0.03 to 0.20 mol L-1. The calculated second order rate constants
were of 5.0x109, 5.0x109, 8.0x109, and 9.5x109 L mol-1 s-1 for SMT, SMP, AMT and CMP,
respectively (Table 1). The presence of H2O2 enhanced the degradation rates. This effect is
attributed to the photodegradation of H2O2, which generates hydroxyl radicals which can
oxidize drugs. The second order rate constants (kD) are in the same order of magnitude with
those reported previously for other pharmaceutical compounds [18, 28]. The effects of pH and
H2O2 concentration on SMT degradation was evaluated by Beaza and Knappe [25], pH
affected direct photolysis rates but had little effect on the hydroxyl radical oxidation rate. In
fact, kD value obtained in this study was of 5.6×109 L mol-1 s-1 at pH 7.85 which is similar to
that obtained in our study (5.0×109 Lmol-1 s-1) at pH 6.1.
3.3 Photoproduct structures identification
Irradiation of the drugs at 254 nm in the absence of hydrogen peroxide leads to the formation
of several photoproducts. The evolution of the concentration of the parent compounds and of
photoproducts peak areas as a function of irradiation time are displayed Fig. 2. The
sulfonamide drugs yield to the formation of four photoproducts from SMT and two
photoproducts from SMP. Three photoproducts are observed from AMT and one from CMP.
LC-MS/MS analyses were performed in positive mode and results are gathered in Table 2.
Photodegradation of SMT produced 4 major photoproducts; SMT-1 and SMT-2 with the same
m/z (215), and SMT-3 and SMT-4 with m/z of 124.1 and 295.1, respectively (Table 2). The
photoproducts are more polar than SMT except SMT-2 (Figure 2). SMT-1 and SMT-2 are
formed just at the beginning of the reaction while SMT-3 and SMT-4 start appearing after few
minutes of irradiation. The maximal peaks area of the four photoproducts are obtained after
70 minutes of irradiation. The determined elemental composition for SMT-1 and SMT-2 was
C12H15N4. These compounds are formed from SO2 elimination which is the main
photochemical transformation process. On the basis of the MS/MS fragmentation patterns, the
13

structures of SMT-1 and SMT-2 were proposed (Scheme 1). The SMT-3 photoproduct is
constituted of the pyrimidine part of SMT but can also be formed from the SMT-2 product.
The corresponding elemental composition was assigned to C6H10N3 which would correspond
to 4,6-dimethylpyrimidine-2-amine. This structure was found by García Galán et al. [28].
Finally, SMT-4 is issued from the hydroxylation of SMT. The hydroxyl group was located on
the benzene cycle due to the formation of the 186 fragment which corresponds to the SO2-
NH-C6H7N2 moiety. Similarly, SMT-4 was detected in the study with the fungus T. versicolor
[29] verified by the transition 295→108.
During SMP degradation, photoproducts show m/z of 215.0 (SMP-1), 216.1 (SMP-2) and
126.0 (SMP-3). SMP-1 is more polar than SMP and reached its maximal area after 50 minutes
of irradiation while SMP-2 is less polar than the parent compound and reached its maximal
area after about 150 minutes of irradiation. SMP-1 (C11H11N4O) arises after extraction of SO2
then elimination of H2 from the parent drug. The compound lost CH3OH (-32) to give a
fragment at m/z 183. Two alternative structures were proposed on this basis (Scheme 2). The
fragmentation pattern of SMP-2 (m/z=216, C11H12N4O) was not helpful to identify its
structure. The structure of SMP-3, detected in LC-MS experiments only, corresponds to 4-
methoxy-2-amino pyrimidine with a m/z of 126.0. The structure was proposed by Chuang et
al. [30].
Photochemical transformation of AMT produced 3 major products upon irradiation at 254 nm,
AMT-1 with a m/z of 296.1, AMT-2 and AMT-3 with m/z of 314.2. The photoreactivity of
AMT is associated to successive hydrations leading to +18 for AMT-1 (C20H28NO) and then
+36 for AMT-2 and AMT-3 (C20H28NO2). The fragmentation spectra do not give information
allowing the localization of the positions of the OH groups. Benitez et al. proposed a
photoproduct structure in the case of nortriptyline hydration which has a similar structure to
14

AMT [31]. Thehydration reaction was located on the unsaturation of the lateral chain. On this
basis, structures were proposed for the photoproducts of AMT (Scheme 3).
The photodegradation of CMP leads to only one product (CMP-1, m/z = 297.2). This
compound, which is more polar than CMP, appeared from the first minute of reaction and
reached its maximal area after 5 minutes. CMP-1 (C20H25N2O) is generated from a
nucleophilic substitution reaction, i.e. the chlorine atom was replaced by an OH group. This
hypothesis is confirmed by the degradation pattern.
4. Conclusion
The photodegradation of SMT, SMP, AMT and CMP was investigated in purified and river
water under simulated solar light irradiation in order to evaluate their environmental fate in
surface water. It has been demonstrated that SMT and SMP were partially degraded after
seven hours of irradiation while CMP degradation was especially fast due to the presence of
the chlorine atom. At the opposite, AMT shows no light absorption above 290 nm and thus
was not degraded in purified water. Its photosensitized degradation was observed in river
water. The presence and persistence of these contaminants in surface water constitute a
potential risk for human health. For example, the antibiotics may lead to antibacterial
resistance, a threat to public health worldwide.
The four drugs were irradiated at 254 nm and their photoproducts were identified. The results
showed that UV water treatment was effective to degrade these drugs basing to the rate
constant values, however their degradation yielded several photoproducts with unknown
toxicity. LC-MS/MS analyses allowed to identify the photoproduct structures generated under
UV irradiation in purified water. The results showed that SMT and SMP have a common
pathway of degradation. Their photoproducts were formed after SO2 elimination. However,
the hydroxylated product was observed from SMT degradation only. In the case of AMT and
15

CMP, photo-oxidation processes were observed but the involved mechanisms were different
due to the presence of a chlorine atom in the CMP structure and unsaturation on the lateral
chain of AMT. Finally, the advanced oxidation process UV/H2O2 leaded to complete
degradation of the drugs, however a toxicity study will help to confirm that this process could
be used for water decontamination.
ACKNOWLEDGEMENTS
The collaboration of the UMR EPOC-LPTC from France, the Laboratory for Analysis of
Organic Compound (LACO), and the Lebanese Atomic Energy Commission LAEC (LACO-
CLEA) from Lebanon is gratefully acknowledged. Thanks also go to Dr. Ahmad Rifaei for
his information in LC-MS/MS analysis and to Prof. Dr. Bilal Nsouli for his support. This
study also benefitted from supports from the French National Research Agency (ANR) as part
of the Investments for the Future Program, within the Cluster of Excellence COTE (ANR-10-
LABX-45).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at
16

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20

Figures
30
40
35
30
25
20
15
10
5
a
b
25
20
15
10
5
0
0
200
300
400
200
250
300
350
Wavelength (nm)
Wavelength (nm)
Fig. 1 UV-Vis absorption spectra in aqueous solution at pH 6.1 of (a) SMT (dashed line) and
SMP (plain line), and (b) AMT (dotted line) and CMP (plain line).
21

SMP (10.5 min)
SMP-1 (6.9 min)
SMP-2 (11.6 min)
500
400
300
200
100
0
20
15
10
5
1000
800
600
400
200
0
16
12
8
SMT (10.1 min)
SMT-1 (4.9 min)
SMT-2 (13.1 min)
SMT-3 (5.7 min)
SMT-4 (6.9 min)
4
0
0
0
50
100
150
200
0
50
100
Time (min)
150
200
Time (min)
400
30
1
10
8
CMP (10.0 min)
CMP-1 (3.4 min)
AMT (13.5 min)
AMT-1 (7.7 min)
AMT-2 (5.1 min)
AMT-3 (3.6 min)
0.8
300
200
100
0
20
10
0
0.6
0.4
0.2
0
6
4
2
0
0
100
200
300
0
2
4
6
Time (min)
Time (min)
Fig. 2 Evolution of drug concentrations and of photoproduct areas as a function of irradiation
(254 nm) time.
22

Schemes
Scheme 1 Structures of SMT and of its products generated under UV irradiation in purified
water.
Scheme 2 Structures of SMP and of its products under UV irradiation in purified water.
23

Scheme 3 Structures of AMT and of its products generated under UV irradiation in purified
water.
Scheme 4 Structures of CMP and of its product generated under UV irradiation in purified
water.
24

Tables
Table 1 First order degradation rate constants in purified (kP, min-1) and river (kR, min-1)
waters obtained under simulated solar light irradiation. Quantum yields of photodegradation
(ф254nm), first order degradation rate constants (kUV, min-1) obtained under irradiation at 254
nm, and second order degradation rate constant (kD, L mol-1 s-1).
kP×10-3
1.1 ± 1.1
0.9 ± 3.0
ND
kR×10-3
3.7 ± 4.2
6.9 ± 5.0
ND
kUV×10-3
kD×109
ф
254 nm×10-3
SMT
SMP
AMT
CMP
4.3 ± 0.1
5.1 ± 0.1
7.6 ± 0.2
65.0 ± 0.02
57.3 ± 2.2
66.0 ± 1.3
39.9 ± 5.6
5.0 ± 0.1
5.0 ± 0.4
8.0 ± 0.3
18.2 ± 3.3
28.9 ± 2.4
367.8 ± 30.1 9.5 ± 0.1
ND: not degraded
25

Table 2 LC-MS/MS ESI+ analyses of SMT, SMP, AMT and CMP drugs and their
photoproducts.
Name
m/z
Formula
Fragments (relative intensity)
SMT
279.1
215.1
215.1
124.1
295.1
281.0
215.0
216.1
126.0
278.1
296.1
314.2
314.2
315.1
297.2
C12H15N4O2S
C12H15N4
C12H15N4
SMT-1
SMT-2
SMT-3
SMT-4
SMP
SMP-1
SMP-2
SMP-3
AMT
AMT-1
AMT-2
AMT-3
CMP
215 (100), 173 (10)
215 (100), 198 (20),108 (40)
124 (100), 107 (80), 82 (28), 67 (33)
295 (100), 186 (30), 124 (75)
C6H10N3
C12H15N4O3S
C11H13N4O3S
C11H11N4O
C11H12N4O
C5H8N3O
215 (100), 200 (30), 183 (15), 145 (20)
216 (100), 187 (20), 173 (15), 147 (12)
126 (100), 111 (23)
C20H24N
C20H26NO
C20H28NO2
C20H28NO2
C19H24ClN2
C20H25N2O
296 (28), 278 (100)
314 (100), 296 (25), 58 (12)
314 (100), 270 (15)
CMP-1
86 (100), 58 (40)
26