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Environmental Technology
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Degradation in chlorinated water of the UV filter 4-
tert-butyl-4′-methoxydibenzoylmethane present in
commercial sunscreens
Diana M.A. Cristaa, Margarida S. Mirandab & Joaquim C.G. Esteves da Silvaa
a Centro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade
de Ciências, Universidade do Porto, Porto, Portugal
b Centro de Geologia da Universidade do Porto, Faculdade de Ciências, Universidade do
Porto, Porto, Portugal
Accepted author version posted online: 17 Nov 2014.Published online: 09 Dec 2014.
To cite this article: Diana M.A. Crista, Margarida S. Miranda & Joaquim C.G. Esteves da Silva (2014): Degradation
in chlorinated water of the UV filter 4-tert-butyl-4′-methoxydibenzoylmethane present in commercial sunscreens,
Environmental Technology, DOI: 10.1080/09593330.2014.988184
To link to this article: http://dx.doi.org/10.1080/09593330.2014.988184
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Environmental Technology, 2014
http://dx.doi.org/10.1080/09593330.2014.988184
Degradation in chlorinated water of the UV filter 4-tert-butyl-4-methoxydibenzoylmethane
present in commercial sunscreens
Diana M.A. Cristaa, Margarida S. Mirandaband Joaquim C.G. Esteves da Silvaa∗
aCentro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Porto,
Portugal; bCentro de Geologia da Universidade do Porto, Faculdade de Ciências, Universidade do Porto, Porto, Portugal
(Received 26 May 2014; accepted 11 November 2014)
4-tert-Butyl-4-methoxydibenzoylmethane (BMDM) is a widely used ultraviolet A filter. In this work, we have studied the
effect of chlorine and dissolved organic matter (DOM) concentrations on the stability of UV filter (BMDM) present in
two commercial sunscreen cream formulations in water. An experimental design was used to assess the effect of the two
experimental factors on the degradation of BMDM. Higher concentrations of chlorine lead to higher degradation percentages
of BMDM and higher concentrations of DOM inhibit its degradation. Moreover, a mono and a dichloro derivate of BMDM
were identified as by-products.
Keywords: sunscreen creams; UV filters; 4-tert-butyl-4-methoxydibenzoylmethane; chlorine; chlorination by-products
1. Introduction
The increasing awareness of the harmful effects of solar
UV radiation on human skin has resulted in the increase
in the production and use of sunscreen cream formula-
tions. These commercial products contain UV filters that
absorb, reflect and scatter UV radiation therefore prevent-
ing sunburn, photo-ageing and ultimately skin diseases
such as skin cancer. UV filters can be classified into two
types: inorganic (also regarded as physical) UV filters,
which reflect and scatter radiation and organic (considered
chemical) UV filters, which absorb the UV radiation. The
organic UV filters comprise various classes of compounds
and the most common being the para-aminobenzoates, sal-
icylates, cinnamates, benzophenones, dibenzoylmethanes,
camphor derivatives and benzimidazoles.[1] In general
these compounds possess one or more benzenic moieties
conjugated with electron-releasing and electron-accepting
groups in either ortho or para positions therefore allowing
an efficient electronic delocalization and rendering them a
specific maximum absorbance wavelength. UV filters are
added to sunscreen creams and other personal care prod-
ucts in concentrations in general not higher than 10% as
some of them have shown toxic effects.[2]
The increased production and use of UV filters has
led to increased inputs into the environment and this fact
prompted UV filters to be considered environmental pollu-
tants in the same group of emerging pollutants classified as
pharmaceuticals and personal care products.[3–7]UVfil-
ters may enter the environment through direct and indirect
*Corresponding author. Email: jcsilva@fc.up.pt
sources.[8] The direct sources are the washing off during
bathing activities in seas, lakes, rivers and swimming
pools as well as industrial wastewater discharges. Indi-
rect inputs are related to domestic wastewater discharges
(during showering, clothes washing and urine excretion)
and via wastewater treatment plants. Several papers have
already reported the presence of UV filters in surface
bathing waters (rivers, lakes and seawater), in sewage
water (untreated and treated sewage effluents), in sludge
and in swimming pools.[9]
However, the behaviour and fate of UV filters after
they enter the aquatic environment are largely unknown.
Most studies have focused on the stability of the UV fil-
ters in water and the formation of photoproducts.[10]In
the case of swimming pool water other environmental
concerns come into play as chlorine-based disinfectants,
loosely referred simply as chlorine, react with the organic
matter, natural and human, present in the same pool water
producing a variety of chlorinated organic compounds
(disinfection by-products, DBPs) whose toxic effects are
of primary concern.[11,12] Although some papers have
reported the detection of UV filters in swimming pools,[8]
the number of papers that reported the fate of UV filters in
chlorinated waters is rather scarce.[13–16]
Dibenzoylmethane derivatives constitute an impor-
tant family of organic ultraviolet A filters used in
many commercial sunscreen cream formulations. The
most widely used dibenzoylmethane is 4-tert-butyl-4-
methoxydibenzoylmethane (BMDM) (tradenames avoben-
© 2014 Taylor & Francis
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2D.M.A. Crista et al.
H
3
CO
O O
H
t-BuH
3
CO
O O
t-Bu
enol keto
Figure 1. The enol and keto tautomers of UV filter 4-tert-butyl-4-methoxydibenzoylmethane.
zone, Parsol 1789, Eusolex 9020). It exists in two tau-
tomeric forms (Figure 1): the enol-tautomer (or enol
form); and the keto-tautomer (or keto form).[1] However,
in sunscreen formulations, BMDM exists predominantly in
the enol form which has a wavelength of maximum absorp-
tion ranging from 350 to 365 nm depending on the solvent
used.[17]
BMDM has already been detected in surface waters
in concentrations of about 20 ng/L and is known to suf-
fer degradation in aqueous solutions.[8,9,16,18,19] Huong
et al.[18] have found that under irradiation in aqueous solu-
tion, the enol form of BMDM tautomerizes to the keto
form and is also fully photodegraded. The authors iden-
tified various photoproducts: substituted benzoic acids,
benzils, dibenzoyl methanes and dibenzoyl ethanes. Some
of these compounds were also previously proposed.[19]
These authors argued that the formation of these photo-
products involves primary αbond cleavages of carbonyl
groups of the 1,3-diketo form, followed by hydrogen
abstraction and/or oxidation or radical recombination. In a
study by Santos et al. [16] it was found that BMDM reacts
in chlorinated aqueous solutions leading to the formation
of chlorinated by-products that were tentatively identified
as mono- and dichloro-substituted compounds that resulted
from an electrophilic substitution of one or two hydrogen
atoms in the benzene rings by one or two chlorine atoms.
This study also assessed the effect of the following exper-
imental factors: pH, temperature, chlorine concentration,
dissolved organic matter (DOM) concentration and artifi-
cial sunlight irradiation on the degradation of BMDM.[16]
The majority of the studies on UV filters degradation
in chlorinated water (such as the one performed by San-
tos et al. [16]) were done with pure aqueous solutions
of the UV filters and, up to the authors knowledge, no
degradation study was done with commercial sunscreen
cream formulations. This work was aimed at determining
the stability of BMDM inserted in two commercial sun-
screen cream formulations in aqueous solution containing
chlorine and DOM. With this study we intend to under-
stand the behaviour of UV filter BMDM when included
in a sunscreen cream with other compounds such as other
organic and inorganic UV-filters and preservatives thus
approaching the real situation.
In order to verify if these two experimental factors
affect the stability of BMDM a factorial analysis strategy
was used.[20–23] A central composite experimental design
response surface methodology was selected to study the
effect of chlorine concentration and DOM concentration
on the degradation percentage of BMDM. To identify the
chlorinated by-products of BMDM incorporated in the two
sunscreens, a liquid–liquid extraction step was performed
before analysis by LC–MS.
2. Methodology
2.1. Reagents
Two commercial sunscreen creams (S1 and S2) were used
for this study. Both sunscreen creams have a sun protec-
tion factor of 30 and the qualitative composition of the
sunscreens is
S1 – butyl methoxydibenzoylmetane, ethylhexyl salicylate,
octocrylene, titanium dioxide, ethylhexyl triazone,
drometrizole trisiloxane, bis-ethylhexyloxyphenol
methoxyphenyl triazine and terephthalylidene dicam-
phor sulphonic acid;
S2 – butyl methoxydibenzoylmethane, ethylhexyl salicy-
late, disodium EDTA, titanium dioxide, octocrylene,
ethylhexyl triazone, drometrizole trisiloxane and bis-
ethylhexyloxyphenol methoxyphenyl triazine.
A commercial sodium hypochlorite (NaClO) solution
with a chlorine content of 4% was used. This solution was
stored at a temperature of 4 °C and its exact concentra-
tion was periodically determined by iodometric titration
using a standard procedure. Deionized water (conductivity
<0.1 μS cm−1) was used in all experiments. The methanol
used as eluent for chromatographic analysis was liquid
chromatographic grade and was bought from Merck. DOM
was mainly composed of fulvic acids extracted from mate-
rials present in a pinewood soil.[24–26] Ethyl acetate was
used in the liquid–liquid extraction.
2.2. Degradation experiments
An initial solution was prepared with the sunscreen creams
S1 and S2 in 100 mL of deionized water and the final con-
centrations were adjusted to be about 2000–3000 mg/L.
The sunscreen formulation was not immediately com-
pletely soluble in water. Indeed, under the experimental
conditions used, the concentration of BMDM in the aque-
ous phase was steadily increasing. The solutions were kept
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Environmental Technology 3
in constant stirring for about 24 h in order to assure that
all BMDM was solubilized in water. During this time,
HPLC–UV–DAD analysis were done in order to monitor
the UV filter peak area. Solutions were prepared by dilution
of the initial solution to about 100 mg/L and with differ-
ent concentrations of chlorine (from 0.189 to 2.311 mg/L)
and DOM (from 0.757 to 9.243 mg/L), in order to per-
form the study presented in Section 2.5. At a fixed reaction
time of 20 min an aliquot of the reaction mixture was
taken and the samples were then immediately analysed by
HPLC–UV–DAD. All solutions were kept in constant stir-
ring. The reactions were evaluated at room temperature
(25.0 ±0.1 °C).
2.3. Identification of chlorination by-products
The identification of the chlorination by-products was per-
formed using reaction conditions similar to those used
in the degradation study using sunscreen S1. The chlo-
rine and DOM concentrations used in this study were the
most favourable to a higher UV filter degradation: 2.3 and
0.8 mg/L, respectively. After 24 h, the water samples
(100 mL) were concentrated by liquid–liquid extraction
with ethyl acetate (3 ×20 mL). Then, the organic solvent
was evaporated and 1.5 mL of methanol was added to the
final residue for LC–MS analysis.
2.4. Chromatographic conditions
The degradation of the UV filter in aqueous solution in
the presence of chlorine and DOM was studied by HPLC–
UV–DAD. The chromatographic system was constituted
by a isocratic pump (Hewlett-Packard 1100 Series, Boe-
blingen, Germany), a manual sample injection valve with
a 20 μL loop (Rheodyne 7725i, Rohnert Park, USA), a
silica-based C18 reversed-phase column (Hypersil GOLD
column 150 mm ×2.1 mm; particle size 5.0 μm; pore
diameter 175 Å; Thermo Scientific, USA) and a photo-
diode array detector (UV 6000LP with a 50 mm Ligh-
Pipe flow cell, Thermo Scientific, San Jose, USA). The
mobile phase was composed of methanol and water (80%:
20%, v/v). Elutions were performed at a constant flow rate
(0.25 mL/min) under isocratic conditions. Absorbance was
monitored at a total scan mode from 210 to 600 nm. The
system was controlled by Xcalibur version 1.4 SR.
Chlorination by-products were identified by using a
LC–MS system composed of a HPLC pump (Finnigan
Surveyor LC Pump Plus), an autosampler (Finnigan Sur-
veyor Autosampler Plus) and a photodiode array detector
equipped with a Light Pipe flow cell (Finnigan Surveyor
PDA Plus Detector) (all instrumentation from Thermo
Electron Corporation, Waltham, USA), together with a
silica-based C18 reversed-phase column (Performance
RP-18E column 4.6 mm ×100 mm; macropore size
2 mm; micropore size 13 nm; Merck Chromolith HPLC
columns, Darmstadt, Germany). The mobile phase
consisted of LC–MS grade acetonitrile and deionized water
(80:20 v/v). Elution was performed at a constant flow rate
of 0.3 mL/min under isocratic conditions and absorbance
was monitored at a total scan mode from 200 to 600 nm.
The mass spectrometer was a Finnigan LCQ Deca XP
Max (Thermo Electron Corporation, Waltham, USA) cou-
pled to the HPLC system. This device was equipped with
an electrospray interface as the ionization source and a
quadrupole ion trap for MS experiments, and was oper-
ated in the positive ion mode between m/z150 and 1000
with the following conditions: spray voltage, 5.0 kV; cap-
illary voltage, 4.0 V and capillary temperature, 325 °C. The
system was controlled by Xcalibur version 1.4 SR.
2.5. Study of the effect of chlorine and DOM
concentrations on BMDM degradation
Experimental design formulation and the corresponding
analysis of the effects (ANOVA) and response surface cal-
culations were done using The Unscramble v9.2 (CAMO
PROCESS AS, Oslo, Norway). A response surface central
composite experimental design was used for the analysis
of two factors (design variables) (chlorine concentration
|Cl|and DOM concentration |DOM|) and one non-design
variable (percentage of BMDM degradation). The temper-
ature (25.0 ±0.1 °C) and the concentration of the initial
sunscreen solution (100 mg/L) were kept constant during
the experiments. All experiments were performed in dupli-
cate with five central points – the total number of design
samples per design was 21.
3. Results and discussion
Contrary to pure BMDM, and as expected, the sunscreen
formulation was not readily soluble in water. This result
shows the protective effect of the other constituents of the
sunscreen in the aqueous solubilization of the UV filter and
its subsequent degradation.
3.1. Study of the effect of chlorine and DOM
concentrations
A two-level central composite design with five levels for
each factor was built. The selected factors and their levels
are listed in Table 1. In this study, we have analysed the
effect of two factors: |Cl|and |DOM|on the degradation
Table 1. Factors and corresponding levels
under research in the central composite design.
|Cl|(mg/L) |DOM|(mg/L)
0.189 0.757
0.500 2.000
1.250 5.000
2.000 8.000
2.311 9.243
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4D.M.A. Crista et al.
Table 2. ANOVA of the system response obtained for the BMDM degradation percentage using a
Composite Central experimental design of the influence of chlorine and DOM concentrations (sunscreen S1).
ANOVA (RMultiple =0.950)
Effect SS d.f. MS F-ratio (p-value) β(SD)b
Model 3.432 ×1035 6.863 ×10234.523 (0.0000)
Error 2.982 ×10215 19.880
Adjusted total 3.730 ×10320 1.865 ×102
Factor
Intercept 4.584 ×1031 4.584 ×103230.607 (0.0000) 30.280 1.994
|Cl|1.203 ×1031 1.203 ×10360.497 (0.0000) 11.560 1.486
|DOM|1.299 ×1031 1.299 ×10365.323 (0.0000) −3.003 0.372
|Cl|×|DOM|2.565 ×1021 2.565 ×10212.903 (0.0027) −4.530 1.261
|Cl|×|Cl|5.633 ×1021 5.633 ×10228.334 (0.0001) −5.910 1.110
|DOM|×|DOM|1.981 1 1.981 0.0997 (0.7566) 0.350 1.110
Model check
Main 2.501 ×1032 1.251 ×103
Int 2.565 ×1021 2.565 ×10212.903 (0.0027)
Int +Squ 6.738 ×1022 3.369 ×10216.947 (0.0001)
Squ 6.738 ×1022 3.369 ×10216.947 (0.0001)
Error 2.982 ×10215 19.880
Lack of fit
Lack of fit 2.711 ×1023 90.364 40.009 (0.0000)
Pure error 27.103 12 2.259
Total error 2.982 ×10215 19.880
Note: RMultiple, multiple correlation; SS, sum of squares; d.f., degrees of freedom; MS, mean squares; F-ratio,
Fisher ratio; p-value, probability value (p) for a 5% significance level; β, beta-regression coefficient; (SD)b,
standard deviation of β; Main, main effects; Int., interactions effects, Squ., square effects.
Table 3. ANOVA of the system response obtained for the BMDM degradation percentage using a Composite
Central experimental design of the influence of chlorine and DOM concentrations (sunscreen S2).
ANOVA (RMultiple =0.950)
Effect SS d.f. MS F-ratio (p-value) β(SD)b
Model 3209 5 641.790 26.854 (0.000)
Error 358.489 15 23.899
Adjusted total 3567 20 178.372
Factor
Intercept 8921 1 8921 373.279 (0.000) 42.240 2.186
|Cl|1271 1 1271 53.169 (0.000) 11.882 1.630
|DOM|986.933 1 986.933 41.296 (0.000) −2.618 0.407
|Cl|×|DOM|407.551 1 407.551 17.053 (0.001) −5.710 1.383
|Cl|×|Cl|11.018 1 11.018 0.461 (0.508) 0.827 1.217
|DOM|×|DOM|517.891 1 517.891 21.670 (0.000) 5.666 1.217
Model check
Main 2258 2 1129
Int 407.552 1 407.552 17.053 (0.001)
Int +Squ 543.767 2 271.883 11.376 (0.001)
Squ 543.767 2 271.883 11.376 (0.001)
Error 358.489 15 23.899
Lack of fit
Lack of fit 293.322 3 97.774 18.004 (0.000)
Pure error 65.167 12 5.431
Total error 358.489 15 23.899
Note: See footnote of Table 2.
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Environmental Technology 5
(a)
(b)
Figure 2. Response surface of BMDM degradation percentage (from sunscreen cream S1 (a) and from sunscreen cream S2 (b)) obtained
with the central composite experimental design for chlorine concentration vs. DOM concentration.
percentage of BMDM used in two commercial sunscreen
creams. The temperature was kept constant at room tem-
perature (25.0 ±0.1 °C). Results of the ANOVA analysis
are presented in Table 2for sunscreen cream S1 and Table
3for sunscreen cream S2.
From the analysis of Tables 2and 3it is possible
to conclude that the model is valid for two studied sun-
screen creams (F-value =34.523 and F-value =26.854,
respectively) for a significance level of 5% (α=0.05) the
theoretical F-value of the model is 2.901.
For BMDM in sunscreen cream S1, the statisti-
cally significant variables to affect its degradation per-
centage were the linear terms of chlorine concentra-
tion (F-value =60.497) and DOM concentration (F-
value =65.323). The quadratic term of chlorine concen-
tration (|Cl|×|Cl|)(F-value =28.334) and the cross-
product term (interaction between |Cl|×|DOM|) (with
F-value =12.903) are also significant to the degradation
of BMDM. The theoretical F-value for the factors is 4.543.
The quadratic term of DOM concentration was found to
be not significant. The β-regression coefficients and the
correspondent standard deviations for the significant terms
are: |Cl|, (11.6 ±1.5); |DOM|,−(3.0 ±0.4); |Cl|×|Cl|,
−(5.9 ±1.1) and |Cl|×|DOM|,−(4.5 ±1.3). Figure
2(a) shows the response surface of the percentage of
BMDM degradation as a function of the chlorine concen-
tration |Cl|and DOM concentration |DOM|for BMDM
in sunscreen cream S1. This figure clearly shows that
higher degradation percentages of BMDM were obtained
at higher chlorine concentration values and at lower DOM
concentration values. The decrease in the degradation per-
centage of BMDM at higher DOM concentration values
can be explained by a competition process between the UV
filter and DOM for the available chlorine thus decreasing
the degradation of the UV filter.
For BMDM in sunscreen cream S2, the linear terms
of chlorine concentration (F-value =53.169) and DOM
concentration (F-value =41.296) are significant to the
degradation of BMDM (theoretical F-value =4.543).
Regarding second-order factors, the (|DOM|×|DOM|)
(F-value =21.670) is also significant to the degrada-
tion of BMDM. Another important interaction seems
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6D.M.A. Crista et al.
(a)
(b) (c)
Figure 3. (a) LC chromatogram of the solution resultant from reaction between sunscreen and chlorine; (b) MS spectra referring to the
monochloro-by-product of BMDM and (c) MS spectra referring to the dichloro-by-product of BMDM.
to be (|Cl|×|DOM|) (with F-value =17.053). The
β-regression coefficients and the correspondent stan-
dard deviations for these terms are: |Cl|, (11.9 ±1.6);
|DOM|,−(2.6 ±0.4); |DOM|×|DOM|,(5.7±1.2) and
|Cl|×|DOM|,−(5.7 ±1.4). Figure 2(b) shows the
response surface of the percentage of BMDM degrada-
tion as a function of the chlorine concentration and DOM
concentration. This figure also clearly shows that higher
degradation percentages of BMDM can be obtained at
higher chlorine concentration values and at lower DOM
concentration values.
The response of BMDM included in the two sunscreen
creams in the presence of chlorine and DOM is very similar
and in agreement with a previous report where the UV-
filter alone was studied.[16]
3.2. Identification of chlorinated by-products
LC chromatogram and MS spectra obtained from the
mixture resulting from the reaction of BMDM present
Table 4. LC–MS results from the analysis of the chlo-
rinated by-products of BMDM.
Retention
time (min) Molecular ion
(m/z)Proposed molecular
formula
4.67 345.13 C20H21O3Cl
9.10 381.93 C20H20O3Cl2
in the sunscreen cream with chlorine and DOM in
the dark are given in the Figure 3. Retention times
and the respective ions in the MS spectra of the
BMDM chlorination by-products are shown in Table 4.
By interpretation of the mass spectra, it was possi-
ble to tentatively identify two chlorinated by-products
(see Figure 4for the possible chlorinated by-products
formed). The compound appearing at retention time 4.67
min exhibited a molecular ion at m/z=345.13, which cor-
responds to a monochloro-by-product with molecular for-
mula C20H21 O3Cl (two possible monochloro-by-products
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Environmental Technology 7
H
3
CO
O O
H
t-Bu
H
3
CO
O O
H
t-Bu
Cl-BMDM
Cl
2
-BMDM
Cl
Cl
Cl
H
3
CO
O O
H
t-Bu
Cl
or
Figure 4. Structural formula of the chlorinated by-products of BMDM: two possible monochloro-by-products (Cl-BMDM) and one
possible dichloro-by-product (Cl2-BMDM).
are: 4-tert-butyl-3-chloro-4-methoxydibenzoylmethane or
4-tert-butyl-5-chloro-4-methoxydibenzoylmethane). The
compound appearing at retention time 9.10 min exhib-
ited a molecular ion at m/z=381.93, which corre-
sponds to a dichloro-by-product with a molecular formula
C20H20 O3Cl2(one possible dichloro-by-product is 4-tert-
butyl-3,5-dichloro-4-methoxydibenzoylmethane).
4. Conclusion
With this study, it was possible to conclude that the UV fil-
ter BMDM introduced in commercial sunscreen creams is
also degraded in the presence of chlorine and DOM. How-
ever, the UV filter included in the sunscreen formulation
shows an apparent reduced water solubility that may result
in a decreased degradation.
Higher concentrations of chlorine lead to higher degra-
dation percentages of BMDM and higher concentrations of
DOM inhibit BMDM degradation. From the reaction of the
two sunscreens with chlorine, two by-products were iden-
tified: a mono- and a dichloro-substituted compound that
result from substitution of one or two hydrogen atoms in
the benzenic rings by one or two chlorine atoms.
The importance of this study results from the fact that
it does not occur under model conditions, when a BMDM
standard is mixed with chlorine in pure water, but also
occurs when a BMDM containing sunscreen is used. Con-
sequently, in aquatic systems disinfected with chlorine,
such as in swimming pools, where people used sunscreens
for sun radiation protection, the presence of the UV filter
and its DBPs are expected to be present in the water.
Disclosure statement
No potential conflict of interest was reported by the authors.
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