Environ Sci Pollut Res DOI 10.1007/s11356-014-4059-1
APPLICATION OF SUSTAINABLE TECHNOLOGIES FOR THE REMOVAL OF ENVIRONMENTAL CONTAMINANTS BEFORE REUSE
The photosensitized oxidation of mixture of parabens in aqueous solution D. Gryglik & M. Gmurek
Received: 20 October 2014 / Accepted: 30 December 2014 # Springer-Verlag Berlin Heidelberg 2015
Abstract The work presents results of studies on the photosensitized oxidation of mixture of five parabens (methyl-, ethyl-, propyl-, n-butyl-, and benzylparaben) in aqueous solution. Aluminum phthalocyanine chloride tetrasulfonic acid and xenon lamp simulating solar radiation were used as a photosensitizer and a light source, respectively. The purpose was to investigate the influence of inhibitory effect compounds present in the mixture on the reaction rate. The influence of the addition of second photosensitizer on the parabens degradation rate was investigated. The effect of additives: tert-butanol - hydroxyl radical scavenger and sodium azide - singlet oxygen scavenger on reaction course was also determined. The transformation products formed during the photosensitized oxidation process were analyzed by UPLC-MS/MS. The efficiency of photosensitized oxidation of parabens with natural sunlight irradiation in the central Poland was checked. Keywords Parabens . Singlet oxygen . Photosensitized oxidation . Visible light . Sunlight
Introduction Surface water is a major source of drinking water in many countries over the world whereas an increasing number of
Responsible editor: Roland Kallenborn D. Gryglik (*) Faculty of Civil Engineering, Architecture and Environmental Engineering, Lodz University of Technology, Al. Politechniki 6, 90-924 Lodz, Poland e-mail: [email protected] M. Gmurek Faculty of Process and Environmental Engineering, Lodz University of Technology, ul. Wólczańska 213, 90-924 Lodz, Poland
emerging contaminants there are being detected. Among them are esters of p-hydroxybenzoic acid (Fig. 1), commonly known as parabens, the most popular preservatives used in cosmetics, drugs, food and paper products. In the early 2000s, parabens were found in over 90 % of cosmetic products (Castelain and Castelain 2012). They have high bactericidal and fungicidal efficiency (especially against molds and yeast) and low cost (Aalto et al.1953; Soni et al. 2005; Andersen 2008; Yazar et al. 2011). In mid 1950s, several studies have indicated their high stability and their lack of side effects (low toxicity) (Andersen 2008; Soni et al. 2005); however, nowadays, they are considered as “persistent pollutants” due to high toxicity to marine life (Bazin et al. 2010). Furthermore, in the 1990s of the twentieth century, there were some reports suggesting that parabens may exhibit a weak estrogenic activity and the magnitude of estrogenic effect increases with the alkyl group size (Routledge et al. 1998). This is probably due to their structural similarity to estrogens (they contain phenolic OH groups and hydrophobic fragments). As a result of that, they are included to so-called endocrine disrupting compounds (EDCs) which are defined as a class of chemicals suspected of causing negative health effects in both humans and other organisms. These compounds are continually produced and released to the environment. The main problem is that the human population is exposed to unknown doses of parabens. The general public is exposed to these chemicals through various sources - direct consuming in food or water, applying hygiene products directly onto the skin, ingesting pharmaceuticals, absorption from handling paper, and even through transdermal uptake directly from air intake via inhalation (Liao and Kannan 2014; Weschler and Nazaroff 2014). The widespread presence of parabens in the environment Presence of parabens in variety of environmental components: wastewater, rivers, and soil has been confirmed
Environ Sci Pollut Res
Fig. 1 The chemical structure of commonly used parabens
(Andersen et al. 2007). Parabens are continuously released through wastewater and transported to wastewater treatment plants (WWTPs) where they can escape conventional treatment processes leading to contamination of ground waters, rivers, lakes, and potentially drinking water resources. Albero et al. have analyzed of sewage sludge collected during 2010 in 19 wastewater treatment plants (WWTPs) located in various urban, industrial, or rural zones in Madrid. They detected methylparaben in 95 % of the WWTPs at levels between 5.1 and 26.2 ng g−1 dry weight and propylparaben in 74 % of the WWTPs at levels up to 44.1 ng g−1 dry weight. According to their calculations, parabens that reach wastewater ranged from 27 to 36,600 g per day (Albero et al. 2012). The majority of WWTPs still use conventional treatment processes so it is possible that compounds such as parabens are expected to be in drinking water resources. Additionally, it is considered that the spreading of sludge produced in WWTPs improves the fertility of agricultural soils; therefore, it is necessary to investigate the effects of parabens in the soil samples. Environmental estrogens in WWTPs effluents are well established as the principal cause of reproductive disruption in wild fish populations (Filby et al. 2007; Thorpe et al. 2009). The evidence that human exposure to parabens is widespread is that all parabens have been measured in the human body tissues. Most research has focused on the parabens determination in urine and usually involves measuring in urine the conjugated or free species of parabens or their metabolites (Ma et al. 2013; Wang et al. 2013; Shirai et al. 2013; Calafat et al. 2010; Ye et al. 2006a, b). It is often considered as a basis for assessing human exposure to parabens. Moreover, parabens have been detected in human blood (Sandanger et al. 2011), milk (Schlumpf et al. 2010), and breast tumors tissues (Darbre et al. 2004; Barr et al. 2012). It is considered that detection of free parabens in human body (especially in urine) reflects the use of personal care products containing these compounds.
The uncertainties in exposure assessment Hazard or safety issue of parabens still arouses controversy and discussions. According to Castelain and Castelain, methyl- and ethylparaben are safe to use at the maximum authorized concentrations as regards their potential hormonal
activity, whereas propyl- and butylparaben are still being investigated with regard to their effects on fertility in men exposed during early childhood (Castelain and Castelain 2012). However, the differences in the use of parabens among people (including their intake in low doses in thousands of products - in foods, medicines, and cosmetics) can be so large that no one can guarantee the safety of these chemicals. Nowadays, the occurrence of endocrine disrupting compounds (including parabens) in the aquatic environment has been recognized as an emerging worldwide issue. Question is still unresolved whether their presence, either alone or in complex mixtures, can impact on human health. It cannot be excluded that the continuous and ubiquitous input of parabens may lead to chronic low level exposure and accumulation, resulting in unpredictable negative effects on environmental health. Especially that the damages from exposure to these chemicals are not visible and they can be missed until they have affected a large number of individuals (e.g., the worldwide reduction in human sperm quality and quantity). The most studies to date concerned to single chemicals in isolation and individual chemicals alone may not reach levels needed for measurable effects in vitro. Thus, reactions and/or synergetic effects due to the simultaneous presence of various compounds in the same environment should be considered. A greater understanding of the mechanisms of interactive chemical effects is essential to fully understand the impacts of environmental mixtures for exposed organisms. (It is supported by Filby et al. studies which have demonstrated that some type of estrogen can impact differently on measures of health when it is exposed as a single chemical and when it is part of a complex mixture (Filby et al. 2007)). The real environmental impact of estrogenic chemicals needs, therefore, to take account of the total chemical load and cannot be dismissed on the basis of individual compound. It is therefore essential to investigate effective methods their removing, especially from the mixture many of them. Photosensitized oxidation process Photochemical degradation contributes to the environmental fate of many xenobiotics. A better understanding of the mechanism of this process is necessary in order to predict environmental fate and persistence of these pollutants in natural waters. Photosensitized oxidation consists in the excitation of a sensitizer by visible light to first singlet or triplet state, which can transfer electron or energy to molecular oxygen. When electron is transferred - superoxide radical anion - a precursor of free radical reactions can form. This way is called type I photooxidation. When energy is transmit - very reactive, although selective, singlet molecular oxygen is generated. This is so-called type II photooxidation.
Environ Sci Pollut Res
The possibility of the application of photosensitized oxidation in wastewater treatment has a potent advantage due to the use of easy accessible visible light (solar irradiation) and oxygen from the air.
Materials and methods Parabens Methylparaben (MP) (≥99 %) and propylparaben (PP) (≥99 %) were purchased from Sigma-Aldrich (Steinheim, Germany); ethylparaben (EP) (≥99 %) was bought from Aldrich Chemistry (Steinheim, Germany); butylparaben (>99 %) (ButP); and benzylparaben (BenzP) (>99 %) were obtained from Fluka (Steinheim, Germany). Sensitizers 4,4′,4″,4′″-(Porphine-5, 10, 15, 20-tetrayl) tetrakis (benzenesulfonic acid) (TPPS4) was purchased from Fluka (Steinheim, Germany). Al(III) phthalocyanine chloride tetrasulfonic acid (a mixture of regioisomers, AlPcS4) was purchased from Frontier Scientific Inc. (Logan, USA). The photochemical experiments setup was described in details in our previous work (Gryglik et al. 2009). Experiments were carried out in alkaline conditions (pH= 10.6). The reaction mixture was aerated by air bubbling which also ensured agitation of the solution. The phototransformation progress was monitored by determination of parabens concentration using a Varian 920 HPLC apparatus with diode array detector at the wavelength 256 nm. Separation was done on a Luna C18 column (3.9 mm Ą 150 mm). The mobile phase was a mixture of methanol and water (60/40v/v), and it was used with isocratic flow rate equal to 1 ml/min. The identification of photoproducts of each paraben and of the mixture was done via UPLC/Q-TOF-MS with a diode array detector (UPLC® Acquity, Synapt G2, Waters, USA). Chromatographic separation was performed on an Acquity UPLC® BEH C18 column (2 mm×150 mm×1.7 μm) at 40 °C. The mobile phase consisted of water-acetic acid (A; 100:0.1, v/v) and acetonitrile-acetic acid (B; 100:0.1, v/v) (0.35 ml/min); the gradient is presented in Table 1. The ionization mode was negative (nebulizer gas (N2), capillary needle voltage - 3 kVat 120 °C, sampling cone voltage - 40 V; extraction cone voltage - 4 V, desolvation gas (N2, 1000 dm3/h at 400 °C), cone gas flow - 100 dm3/h). Data were analyzed using Waters MassLynx software.
Results Irradiation with solar simulated light First, the optimal analysis conditions were established to gain total separation of the mixture components within 10 min of elution. Each sample was acidified to pH=6 before analysis. A sample series of chromatograms obtained during the irradiation of paraben mixture are shown in Fig. 2. The main aim of this research was to test whether the compounds present in the mixture have an inhibitory effect on the rate of decay relative to each other. Comparison of methylparaben concentration changes during the irradiation; this compound in the mixture of five parabens and alone in the presence of AlPcS4 as a sensitizer in alkaline solution (pH= 10.6) shows Fig. 3. The obtained results have shown that no significant differences in the rates of MP decay in the mixture with respect to rates observed in the individual solutions. In both cases, the complete disappearance of the initial concentration of MP occurs in the comparable period of time of approximately 150 min. The same effect was observed in case of other parabens. It seems that the presence of several parabens in the solution does not inhibit access to light or oxygen, at least under the conditions of the experiment. Additionally, it is worthy to note that the rates of degradation of all parabens in the mixture were similar (Fig. 4). In the next series of experiment, the mechanism of phototransformation process was determined. For this purpose, the mixture of parabens in alkaline solution was irradiated with various specific additives: –
In the absence of sensitizer (direct photolysis)
Table 1 Gradient of mobile phase during UPLC analysis of transformation products Eluent
0 min
2 min
3 min
5 min
7 min
10 min
14 min
A B
95 % 5%
95 % 5%
85 % 15 %
70 % 30 %
50 % 50 %
40 % 60 %
40 % 60 %
Fig. 2 A series of chromatograms obtained during the irradiation of paraben mixture with 100 W xenon lamp (initial concentration of each paraben c 0 = 8 × 10 −5 mol/dm 3, initial concentration of sensitizer cAlPcS4 =2×10−5 mol/dm3)
Environ Sci Pollut Res
Fig. 3 Changes in the relative MP concentration during the irradiation this compound in the mixture of five parabens and alone in the presence of AlPcS4 as a sensitizer in alkaline solution (pH=10.6). The source of the light was xenon arc lamp (100 W). Initial concentration of MP c 0MP = 8 × 10 −5 mol/dm 3 , initial concentration of AlPcS 4 c s = 2 × 10−5 mol/dm3, air bubbling
– – –
In the presence of AlPcS4 as a sensitizer (=photosensitized oxidation) In the presence of AlPcS4 and sodium azide as a singlet oxygen scavenger (=type I of photosensitized oxidation) In the presence of AlPcS4 and tert-butyl alcohol as a hydroxyl radical scavenger (=type II of photosensitized oxidation)
Figure 5 shows the obtained results (example for MP, but the results for other parabens were similar). As can be seen in the absence of sensitizer, the irradiation process does not cause a significant decrease in initial levels of
Fig. 5 Changes in the relative MP concentration during its irradiation in the mixture in alkaline solution (pH=10.6) with various additives. The source of the light was xenon arc lamp (100 W). Initial concentration of each paraben c0MP =8×10−5 mol/dm3, initial concentration of AlPcS4 cs =2×10−5 mol/dm3, initial concentration of sodium azide c0SA =1× 10−3 mol/dm3, initial concentration of tert-butyl alcohol c0TB =1×10 − 1 mol/dm3, air bubbling
parabens. This indicates that direct photolysis does not play a significant role in the photodegradation of substrates which is in line with expectations because the maximum of parabens absorption is below 300 nm. Total phototransformation of parabens occurs after the addition of the sensitizer. Addition of sodium azide which selectively reacts with singlet oxygen results in complete inhibition of the degradation process almost to the level of photolysis. Moreover, after the addition of hydroxyl radical scavenger—tert-butyl alcohol—the rate of substrates decay is the same as the rate of photosensitized oxidation. These effects suggest that the photooxidation of parabens proceeds entirely according to the mechanism II photooxidation by singlet oxygen route. The interesting results were obtained using two different sensitizers (TPPS4 and AlPcS4) and a mixture of them. In both cases, the concentration of the dye was equal to 2×10−5 mol/ dm3. In solution with the mixture of dyes, the concentration of each one was equal to 1×10−5 mol/dm3. The obtained results are shown in Fig. 6 (example for MP, but the results for other parabens were similar). Comparing the effect of photooxidation with using two dyes, we found that TPPS4 is a more effective sensitizer than AlPcS4 and this effect is visible even in a solution with both of them.
Irradiation with natural sunlight Fig. 4 Changes in the relative parabens concentration during their irradiation in the mixture in the presence of AlPcS4 as a sensitizer in alkaline solution (pH=10.6). The source of the light was xenon arc lamp (100 W). Initial concentration of each paraben c0 =8×10−5 mol/dm3, initial concentration of AlPcS4 cs =2×10−5 mol/dm3, air bubbling
Finally, a series of experiments were carried out in which mixture of parabens was irradiated using natural sunlight. Aluminum phthalocyanine chloride tetrasulfonic acid was
Environ Sci Pollut Res
Fig. 6 Changes in the relative MP concentration during its irradiation in the mixture in alkaline solution (pH=10.6) in the presence of different sensitizers. The source of the light was xenon arc lamp (100 W). Initial concentration of each paraben c 0MP = 8 × 10 −5 mol/dm 3 , initial concentration of sensitizers cs =2×10−5 mol/dm3, (in the mixture of dyes, their initial concentration was cs =1×10−5 mol/dm3 for each of them), air bubbling
Fig. 8 Changes in the relative MP concentration during its irradiation with natural sunlight in the mixture of parabens in alkaline solution (pH= 10.6) in the presence of sensitizer and without it. Initial concentration of each paraben c0MP =8×10−5 mol/dm3, initial concentration of AlPcS4 cs =2×10−5 mol/dm3, air bubbling
sunlight occurs very slowly. Only about 2 % reduction of MP concentration was attained after 2.5 h of reaction without sensitizer at irradiance equal to about 374.0 W/m2. No detectable degradation of substrates was observed in the dark controls. After addition of sensitizer, in nearly the same irradiation conditions and the same period of time, the initial concentration of parabens drops to undetectable value (the results for MP are shown in Fig. 8). The influence of irradiation intensity on the reaction rate is also noticeable. The increase in the light intensity increases photosensitized reactions rate. These results confirm our earlier reports, where 2-chlorophenol was degraded by photosensitized oxidation under solar irradiation (Gryglik et al. 2004).
used as a photosensitizer. The experiments were run in glass tube reactor of the capacity 0.5 dm3 (Fig. 7). The reaction mixture was aerated by air bubbling which also ensured agitation of the solution. The spectrum of light was collected with an Oceans Optics USB 4000 fiber optic spectrometer with an approximate resolution of 0.4 nm. The open field experiments using sunlight were run in central Poland in various illumination conditions, on sunny and cloudy days. Figure 8 shows the changes of the relative MP concentration for process carried out under direct solar radiation in dependance on light intensity. The results show that the direct photolysis of paraben mixture in alkaline solution under irradiation of natural
UPLC-MS/MS identification of phototransformation products
Fig. 7 The picture of the reactor used in outdoor experiments
The transformation products (TPs) formed during the photosensitized oxidation process were analyzed by UPLC-MS/MS. The intermediates were identified by interpretation of fragment ions and product ion scan. The spectra of parent compounds were obtained of [M-H]− at m/z 151.0404 (tR 7.32 min), m/z 165.0576 (tR 8.18 min), m/z 179.0702. (tR 8.98 min), m/z 193.0883 (tR 9.88 min), m/z 227.0687 (tR 9.93 min) for MP, EP, PP, ButP, and BenzP, respectively. The EI mass spectra of parabens are shown in Fig. 9. The peak of p-hydroxybenzoic acid (p-HBA), the product of hydrolysis appears at the first sample with the retention time at 5.52 min (m/z 137.0251) (Fig. 10a). After 20 min of photodegradation, the new peaks corrected with TPs can be observed. As can be seen on Fig. 10b and c, the height of TPs peaks is two order lower than parabens. According to the
Environ Sci Pollut Res Fig. 9 High-resolution MS spectrum in negative ion mode of parent compounds and transformation products
Environ Sci Pollut Res Fig. 10 Evolution of a UPLC chromatograms during photosensitized oxidation of the parabens mixture, b kinetic of photodegradation of parabens, c and phototransformation products (TPs) formed upon photodegradation
peaks, height can be supposed that the concentration of TPs is low. Kinetic profile of TPs during irradiation time indicates that photoproducts are formed at the beginning and after some time undergo degradation. After 180 min of photodegradation, both parent compounds as well as its photoproducts were almost completely removed. In order to get more information about the observed TPs, UPLC/Q-TOF-MS/MS have been used for its identification. Monohydroxylation has been found to be the major reaction pathway for the formation of byproducts for the reaction of 1 O2 with parabens. The performed experiments indicated that in the mixture of parabens after 20 min of treatment, the
formation of six phototransformation products can be observed. TP1 with the mass 153.0187 m/z [M-H]−, suggesting the hydroxylation of p-hydroxybenzoic acid. The TP2, TP3, TP4, TP5, and TP6 with the mass: 167.0350 m/z [M-H]− (tR 6.23 min), 181.0472 m/z [M-H] (tR 7.17 min), 195.0667 m/z [M-H] (tR 8.02 min), 209.0796 m/z [M-H] (tR 8.71 min), 243.0661 m/z [M-H] (tR 8.88 min), indicating monohydroxylation of the parabens (Fig. 9, Table 2). The fragmentation of all these compounds allowed to identify that for parabens, the addition of –OH group was onto aromatic ring (main fragment ions of hydroxylated parabens are found as 153.0187, 108.0218 m/z [M-H]−).
Environ Sci Pollut Res Table 2
Characterization of parent compounds as well as transformation products detected by UPLC-MS/MS Main compounds (identify by standards) No.
compounds
1
methylparaben (MP)
t R, min
theoretic monoisotopic mass, Da
detected monoisotopic mass, Da
7.32
151.0407
151.0404
supposed structure O
O
-
CH3
O
CH3
2
ethylparaben (EP)
8.18
165.0557
165.0576
O
O
-
O
3
propylparaben (PP) 8.98
179.0714
179.0702
O
CH3
O
-
O
4
butylparaben (ButP)
9.88
193.0870
193.0883 O
CH3
O
-
O
5
benzylparaben (BenzP)
9.93
227.0714
227.0687
O
-
O
O
Transformation products No.
compounds p-hydroxybenzoic acid (pHBA) a
detected theoretic t R, monoisotopic monoisotopic min mass, Da mass, Da 5.52
137.0244
supposed structure O
137.0251
OH
-
O
HO
TP1
TP2
3,4dihydroxybenzoic acid a methyl dihydroxybenzoate
4.48
153.0193
153.0187
O
OH
-
OH
6.23
167.0350
167.0350
O
-
O
O
CH3
O
TP3
ethyl dihydroxybenzoate
CH3
OH
7.17
181.0506
181.0472
O
O
-
O
TP4
propyl dihydroxybenzoate
OH
8.02
195.0663
195.0667
O
-
CH3 O O
CH3
TP5
butyl dihydroxybenzoate
8.71
209.0891
OH
209.0796 O
-
O O
TP6
hydroxyl-benzyl, 8.88 p-hydroxybenzoate
243.0663
OH
243.0661 O
a
-
O O
Confirmed by the standard
Environ Sci Pollut Res
Discussion 1. The obtained results indicate a great potential of sunlightmediated photodegradation in the removal of water pollutants in the middle latitude. There are many publications on the photodegradation of xenobiotics (especially pharmaceuticals, endocrine disruptors, or pesticides) in the aquatic environment. Most of them concern the photodegradation using UV light and the type of TiO2/ ZnO photocatalysts (Kamaraj et al. 2014; Maroga et al. 2015) or photo-Fenton and UV/H2O2 (Cavalcante et al. 2013). However, studies on photosensitized oxidation process in the presence of visible light absorbing sensitizers are becoming more and more popular but they are still limited, particularly with the use of natural sunlight. It is known that the processes of photosensitized degradation play a major role in the self-purification of natural water. Many studies have shown that a significant role in these processes plays dissolved natural organic matter (Remucal 2014; Vialaton and Richard 2002). It contains chromophores which are effective as a sensitizer and can act both by the radical pathway and by the generation of singlet oxygen. It is widely demonstrated that indirect photolysis of organic pollutants in water solutions undergoes both by type I and type II photooxidation mechanism. The predominance of one of them is dependent on the chemical structure of substrate, the reaction conditions and presence of other substances in solution (especially in natural water samples) (Remucal 2014; Zuo et al. 2013; Vialaton and Richard 2002). 2. Our research confirmed that photosensitized oxidation is an effective method in the removal of parabens from water during visible light irradiation in the presence of sensitizer. Additionally, our scavenging experiments suggest that the mixture of parabens in water solution is completely oxidized by the reaction with singlet oxygen during an exposure to solar simulated light in the presence of sensitizer. Chen at al. (2013b) obtained other results when they studied direct and indirect photodegradation of estriol in w a t e r s o l u t i o n s . T h e y f o u n d th a t t h e d i r e c t photodegradation of substrate was relatively slow under direct irradiation of sunlight and simulated solar light whereas the addition of sensitizers (humic acids) significantly enhanced the degradation. In contrast to our results, their studies with using specific quenchers confirmed a major role in the degradation of the substrate radical mechanism (type I photooxidation). In another studies, Chen et al. (2013a) carried out a series of experiments to investigate the photosensitized degradation mechanism of β-blocker timolol in the presence of fulvic acid (FA) under simulated sunlight. Their results suggested that only half of the substrate photodegradation was attributed to the reaction with 1O2.
The second route of photodegradation proceeded via the reactions with 3FA. 3. One of the purposes of our work was to investigate the influence of inhibitory effect compounds present in the mixture on the degradation rate. The obtained results have shown that no significant differences in the rates of parabens decay in the mixture with respect to rates observed in the individual solutions. It seems that the presence of several parabens in the solution does not inhibit access to light or oxygen, at least under the conditions of the experiment. According to our knowledge, there are no studies on the removal of parabens mixture by photosensitized oxidation in aqueous solution. There are, however, some reports about degradation of a mixture of parabens by other methods. Tay et al. (2010) used the high oxidation potential of ozone to decompose of solution containing methyl-, ethyl-, propyl-, butyl-, and benzylparaben. Authors put emphasis on the kinetics of the reaction and do not make the comparison the rate of substrate degradation in the mixture and in individual solutions. Recently, another group of scientists (Domínguez et al. 2014) studied the degradation rates and removal efficiencies of mixture of methyl-, ethyl-, propyl-, and butylparaben using H2O2/Fe2+ advanced oxidation process. In their studies, the simultaneous optimization of the parabens removal was achieved depending on the initial concentrations of hydrogen peroxide and Fe2+ ion. The elimination of the same parabens from water solution in presence of Fe(III)-citrate circumneutral pH was examined by Feng et al. (2014). In their research, the effect of formic acid, acetic acid, oxalic acid, malonic acid, succinic acid, and fulvic acid on the photodegradation of parabens by Fe(III)-citrate was investigated. From this article, you can conclude that only individual solutions of parabens were tested. 4. The photoproducts of parabens degradation were identified an d th e d egra datio n p athway was prop ose d. Monohydroxylation has been found to be the major reaction pathway for the formation of byproducts for the reaction of 1O2 with parabens. The main transformation product formed during the photosensitized oxidation of paraben mixture was p-hydroxybenzoic acid. Similar results obtained Feng et al. (2014) and Steter et al. (2014) when analyzing different methods of parabens decomposition.
Conclusions It was confirmed that singlet oxygen is an effective oxidant in the degradation of paraben mixture in water during visible light irradiation in the presence of sensitizer. The obtained
Environ Sci Pollut Res
results indicate a strong dependence of the decay rate of substrates on light intensity as well as the additives of second photosensitizer. The experiments confirmed that singlet oxygen route is the major pathway of parabens degradation. No significant differences in the rates of parabens decay in the mixture in relation to the decay rate of the individual solutions were observed; thereby, there was found neither the enhancement nor inhibition effect of several substrates in the solution. Monohydroxylation has been found to be the major reaction pathway for the formation of byproducts for the reaction of 1 O2 with parabens. The main transformation product formed during the photosensitized oxidation of paraben mixture was p-hydroxybenzoic acid. The results collected during the investigation of photosensitized oxidation of parabens using solar irradiation indicate a great potential of sunlight-mediated photodegradation in the removal of water pollutant in the middle latitude. The application of photosensitized oxidation in elimination of hazardous pollutants from water environment seems attractive due to the possibility of the use of two inexhaustible resources: oxygen from the air and photons from solar radiation. Phototransformation processes in natural aqueous environment have been studied for many years, and the results shown above could advance scientific knowledge in this area, especially from the point of view the role of sunlight in self-purification processes in water. Acknowledgments Marta Gmurek acknowledges the support from Foundation for Polish Science within the START scholarship. Conflict of interest The authors declare that there is no any actual or potential conflict of interest including any financial, personal, or other relationships with other people or organizations within 3 years of beginning the submitted work that could inappropriately influence, or be perceived to influence, their work.
References Aalto TR, Firman MC, Rigler NE (1953) p-Hydroxybenzoic acid esters as preservatives. J Am Pharm Assoc Am PharmAssoc (Baltim) 42(8):449–457 Albero B, Pérez RA, Sánchez-Brunete C, Tadeo JL (2012) Occurrence and analysis of parabens in municipal sewage sludge from wastewater treatment plants in Madrid (Spain). J Hazard Mater 239–240: 48–55 Andersen FA (2008) Final report on the safety assessment of methylparaben, ethylparaben, isopropylparaben, isobutylparaben and benzylparaben as used in cosmetic products. Int J Toxicol 27(suppl 4):1–82 Andersen HR, Lundsbye M, Wedel HV, Eriksson E, Ledin A (2007) Estrogenic personal care products in a greywater reuse system. Water Sci Technol 56:45–49 Barr L, Metaxas G, Harbach CA, Savoy LA, Darbre PD (2012) Measurement of paraben concentrations in human breast tissue at serial locations across the breast from axilla to sternum. J Appl Toxicol 32(3):219–232
Bazin I, Gadal A, Touraud E, Roig B (2010) Hydroxy benzoate preservatives (parabens) in the environment: data for environmental toxicity assessment. In: Fatta-Kassinos D, Bester K, Kummerer K (eds) Xenobiotics in the urban water cycle: mass flows, environmental processes, mitigation and treatment strategies. Part II. Springer, Netherlands, pp 245–257 Calafat AM, Ye X, Wong LY, Bishop AM, Needham LL (2010) Urinary concentrations of four parabens in the U.S. population: NHANES 2005–2006. Environ Health Perspect 118(5):679–685 Castelain F, Castelain M (2012) Parabens: a real hazard or a scare story? Eur J Dermatol 22(6):723–727 Cavalcante RP, da Rocha Sandim L, Bogo D, Barbosa AML, Osugi ME, Blanco M, de Oliveira SC, de Fatima Cepa Matos M, Machulek A Jr, Ferreira VS (2013) Application of Fenton, photo-Fenton, solar photo-Fenton and UV/H2O2 to degradation of the antineoplastic agent mitoxantrone and toxicological evaluation. Environ Sci Pollut Res 20:2352–2361 Chen Y, Liang Q, Zhou D, Wang Z, Tao T, Zuo Y (2013a) Photodegradation kinetics, products and mechanism of timolol under simulated sunlight. J Hazard Mater 252–253:220–226 C h e n Y, Z h a n g K , Z u o Y ( 2 0 1 3 b ) D i r e c t a n d i n d i r e c t photodegradation of estriol in the presence of humic acid, nitrate and iron complexes in water solutions. Sci Total Environ 463– 464:802–809 Darbre PD, Aljarrah A, Miller WR, Coldham NG, Sauer MJ, Pope GS (2004) Concentrations of parabens in human breast tumours. J Appl Toxicol 24:5–13 Domínguez JR, Muñoz MJ, Palo P, González T, Peres JA, Cuerda-Correa EM (2014) Fenton advanced oxidation of emerging pollutants: parabens. Int J Energy Environ Eng 5:89–98 Feng X, Chen Y, Fang Y, Wang X, Wang Z, Tao T, Zuo Y (2014) Photodegradation of parabens by Fe(III)-citrate complexes at circumneutral pH: matrix effect and reaction mechanism. Sci Total Environ 472:130–136 Filby AL, Neuparth T, Thorpe KL, Owen R, Galloway TS, Tyler CR (2007) Health impacts of estrogens in the environment, considering complex mixture effects. Environ Health Perspect 115(12):1704– 1710 Gryglik D, Miller JS, Ledakowicz S (2004) Solar energy utilization in degradation of 2-chlorophenol by immobilized photosensitizers. Sol Energy 77(5):615–623 Gryglik D, Lach M, Miller JS (2009) The aqueous photosensitized degradation of butylparaben. Photochem Photobiol Sci 8:549–555 Kamaraj M, Ranjith KS, Rajeshwari S, Rajendra KRT, Hasna AS (2014) Photocatalytic degradation of endocrine disruptor Bisphenol-A in the presence of prepared CexZn1−xO nanocomposites under irradiation of sunlight. J Environ Sci. Article in press Liao C, Kannan K (2014) Concentrations and composition profiles of parabens in currency bills and paper products including sanitary wipes. Sci Total Environ 475:8–15 Ma WL, Wang L, Guo L, Liu LY, Qi H, Zhu NZ, Gao CJ, Li JF, Kannan K (2013) Urinary concentrations of parabens in Chinese young adults: implications for human exposure arch. Environ Contam Toxicol 65:611–618 Maroga MV, Héquet V, Andrès Y, Gru Y, Colin R, Doña-Rodríguez JM, Pastrana-Martínez LM, Silva AMT, Leleu M, Tindall AJ, Mateos S, Falaras P (2015) Photocatalytic degradation of estradiol under simulated solar light and assessment of estrogenic activity. Appl Catal B Environ 162:437–444 Remucal CK (2014) The role of indirect photochemical degradation in the environmental fate of pesticides: a review. Environ Sci Process Impacts 16:628–653 Routledge EJ, Parker J, Odum J, Ashby J, Sumpter JP (1998) Some alkyl hydroxy benzoate preservatives (parabens) are estrogenic. Toxicol Appl Pharmacol 153(1):12–19
Environ Sci Pollut Res Sandanger TM, Huber S, Moe MK, Braathen T, Leknes H, Lund E (2011) Plasma concentrations of parabens in postmenopausal women and self-reported use of personal care products: the NOWAC postgenome study. J Expo Sci Environ Epidemiol 21(6):595–600 Schlumpf M, Kypke K, Wittassek M, Angerer J, Mascher H, Mascher D, Vökt C, Birchler M, Lichtensteiger W (2010) Exposure patterns of UV filters, fragrances, parabens, phthalates, organochlor pesticides, PBDEs, and PCBs in human milk: Correlation of UV filters with use of cosmetics. Chemosphere 81(10):1171–1183 Shirai S, Suzuki Y, Yoshinaga J, Shiraishi H, Mizumoto Y (2013) Urinary excretion of parabens in pregnant Japanese women. Reprod Toxicol 35:96–101 Soni MG, Carabin IG, Burdock GA (2005) Review: safety assessment of esters of p-hydroxybenzoic acid (parabens). Food Chem Toxicol 43(7):985–1015 Steter JR, Rocha RS, Dionísio D, Lanza MRV, Motheo AJ (2014) Electrochemical oxidation route of methyl paraben on a borondoped diamond anode. Electrochim Acta 117:127–133 Tay KS, Rahman NA, Mhd. Abas RB (2010) Kinetic studies of the degradation of parabens in aqueous solution by ozone oxidation. Environ Chem Lett 8:331–337 Thorpe KL, Maack G, Benstead R, Tyler CR (2009) Estrogenic wastewater treatment works effluents reduce egg production in fish. Environ Sci Technol 43(8):2976–2982
Vialaton D, Richard C (2002) Phototransformation of aromatic pollutants in solar light: photolysis versus photosensitized reactions under natural water conditions. Aquat Sci 64:207–215 Wang L, Wu Y, Zhang W, Kannan K (2013) Characteristic profiles of urinary p-hydroxybenzoic acid and its esters (parabens) in children and adults from the United States and China. Environ Sci Technol. doi:10.1021/es304659r Weschler CJ, Nazaroff WW (2014) Dermal uptake of organic vapors commonly found in indoor air. Environ Sci Technol 48(2):1230–1237 Yazar K, Johnsson S, Lind ML, Boman A, Liden C (2011) Preservatives and fragrances in selected consumer-available cosmetics and detergents. Contact Dermatitis 64(5):265–272 Ye X, Bishop AM, Reidy JA, Needham LL, Calafat AM (2006a) Parabens as urinary biomarkers of exposure in humans. Environ Health Perspect 114(12):1843–1846 Ye X, Kuklenyik Z, Bishop AM, Needham LL, Calafat AM (2006b) Quantification of the urinary concentrations of parabens in humans by on-line solid phase extraction-high performance liquid chromatography-isotope dilution tandem mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci 844:3–9 Zuo Y, Zhang K, Zhou S (2013) Determination of estrogenic steroids and microbial and photochemical degradation of 17a-ethinylestradiol (EE2) in lake surface water, a case study. Environ Sci Process Impacts 15:1529–1535
APPLICATION OF SUSTAINABLE TECHNOLOGIES FOR THE REMOVAL OF ENVIRONMENTAL CONTAMINANTS BEFORE REUSE
The photosensitized oxidation of mixture of parabens in aqueous solution D. Gryglik & M. Gmurek
Received: 20 October 2014 / Accepted: 30 December 2014 # Springer-Verlag Berlin Heidelberg 2015
Abstract The work presents results of studies on the photosensitized oxidation of mixture of five parabens (methyl-, ethyl-, propyl-, n-butyl-, and benzylparaben) in aqueous solution. Aluminum phthalocyanine chloride tetrasulfonic acid and xenon lamp simulating solar radiation were used as a photosensitizer and a light source, respectively. The purpose was to investigate the influence of inhibitory effect compounds present in the mixture on the reaction rate. The influence of the addition of second photosensitizer on the parabens degradation rate was investigated. The effect of additives: tert-butanol - hydroxyl radical scavenger and sodium azide - singlet oxygen scavenger on reaction course was also determined. The transformation products formed during the photosensitized oxidation process were analyzed by UPLC-MS/MS. The efficiency of photosensitized oxidation of parabens with natural sunlight irradiation in the central Poland was checked. Keywords Parabens . Singlet oxygen . Photosensitized oxidation . Visible light . Sunlight
Introduction Surface water is a major source of drinking water in many countries over the world whereas an increasing number of
Responsible editor: Roland Kallenborn D. Gryglik (*) Faculty of Civil Engineering, Architecture and Environmental Engineering, Lodz University of Technology, Al. Politechniki 6, 90-924 Lodz, Poland e-mail: [email protected] M. Gmurek Faculty of Process and Environmental Engineering, Lodz University of Technology, ul. Wólczańska 213, 90-924 Lodz, Poland
emerging contaminants there are being detected. Among them are esters of p-hydroxybenzoic acid (Fig. 1), commonly known as parabens, the most popular preservatives used in cosmetics, drugs, food and paper products. In the early 2000s, parabens were found in over 90 % of cosmetic products (Castelain and Castelain 2012). They have high bactericidal and fungicidal efficiency (especially against molds and yeast) and low cost (Aalto et al.1953; Soni et al. 2005; Andersen 2008; Yazar et al. 2011). In mid 1950s, several studies have indicated their high stability and their lack of side effects (low toxicity) (Andersen 2008; Soni et al. 2005); however, nowadays, they are considered as “persistent pollutants” due to high toxicity to marine life (Bazin et al. 2010). Furthermore, in the 1990s of the twentieth century, there were some reports suggesting that parabens may exhibit a weak estrogenic activity and the magnitude of estrogenic effect increases with the alkyl group size (Routledge et al. 1998). This is probably due to their structural similarity to estrogens (they contain phenolic OH groups and hydrophobic fragments). As a result of that, they are included to so-called endocrine disrupting compounds (EDCs) which are defined as a class of chemicals suspected of causing negative health effects in both humans and other organisms. These compounds are continually produced and released to the environment. The main problem is that the human population is exposed to unknown doses of parabens. The general public is exposed to these chemicals through various sources - direct consuming in food or water, applying hygiene products directly onto the skin, ingesting pharmaceuticals, absorption from handling paper, and even through transdermal uptake directly from air intake via inhalation (Liao and Kannan 2014; Weschler and Nazaroff 2014). The widespread presence of parabens in the environment Presence of parabens in variety of environmental components: wastewater, rivers, and soil has been confirmed
Environ Sci Pollut Res
Fig. 1 The chemical structure of commonly used parabens
(Andersen et al. 2007). Parabens are continuously released through wastewater and transported to wastewater treatment plants (WWTPs) where they can escape conventional treatment processes leading to contamination of ground waters, rivers, lakes, and potentially drinking water resources. Albero et al. have analyzed of sewage sludge collected during 2010 in 19 wastewater treatment plants (WWTPs) located in various urban, industrial, or rural zones in Madrid. They detected methylparaben in 95 % of the WWTPs at levels between 5.1 and 26.2 ng g−1 dry weight and propylparaben in 74 % of the WWTPs at levels up to 44.1 ng g−1 dry weight. According to their calculations, parabens that reach wastewater ranged from 27 to 36,600 g per day (Albero et al. 2012). The majority of WWTPs still use conventional treatment processes so it is possible that compounds such as parabens are expected to be in drinking water resources. Additionally, it is considered that the spreading of sludge produced in WWTPs improves the fertility of agricultural soils; therefore, it is necessary to investigate the effects of parabens in the soil samples. Environmental estrogens in WWTPs effluents are well established as the principal cause of reproductive disruption in wild fish populations (Filby et al. 2007; Thorpe et al. 2009). The evidence that human exposure to parabens is widespread is that all parabens have been measured in the human body tissues. Most research has focused on the parabens determination in urine and usually involves measuring in urine the conjugated or free species of parabens or their metabolites (Ma et al. 2013; Wang et al. 2013; Shirai et al. 2013; Calafat et al. 2010; Ye et al. 2006a, b). It is often considered as a basis for assessing human exposure to parabens. Moreover, parabens have been detected in human blood (Sandanger et al. 2011), milk (Schlumpf et al. 2010), and breast tumors tissues (Darbre et al. 2004; Barr et al. 2012). It is considered that detection of free parabens in human body (especially in urine) reflects the use of personal care products containing these compounds.
The uncertainties in exposure assessment Hazard or safety issue of parabens still arouses controversy and discussions. According to Castelain and Castelain, methyl- and ethylparaben are safe to use at the maximum authorized concentrations as regards their potential hormonal
activity, whereas propyl- and butylparaben are still being investigated with regard to their effects on fertility in men exposed during early childhood (Castelain and Castelain 2012). However, the differences in the use of parabens among people (including their intake in low doses in thousands of products - in foods, medicines, and cosmetics) can be so large that no one can guarantee the safety of these chemicals. Nowadays, the occurrence of endocrine disrupting compounds (including parabens) in the aquatic environment has been recognized as an emerging worldwide issue. Question is still unresolved whether their presence, either alone or in complex mixtures, can impact on human health. It cannot be excluded that the continuous and ubiquitous input of parabens may lead to chronic low level exposure and accumulation, resulting in unpredictable negative effects on environmental health. Especially that the damages from exposure to these chemicals are not visible and they can be missed until they have affected a large number of individuals (e.g., the worldwide reduction in human sperm quality and quantity). The most studies to date concerned to single chemicals in isolation and individual chemicals alone may not reach levels needed for measurable effects in vitro. Thus, reactions and/or synergetic effects due to the simultaneous presence of various compounds in the same environment should be considered. A greater understanding of the mechanisms of interactive chemical effects is essential to fully understand the impacts of environmental mixtures for exposed organisms. (It is supported by Filby et al. studies which have demonstrated that some type of estrogen can impact differently on measures of health when it is exposed as a single chemical and when it is part of a complex mixture (Filby et al. 2007)). The real environmental impact of estrogenic chemicals needs, therefore, to take account of the total chemical load and cannot be dismissed on the basis of individual compound. It is therefore essential to investigate effective methods their removing, especially from the mixture many of them. Photosensitized oxidation process Photochemical degradation contributes to the environmental fate of many xenobiotics. A better understanding of the mechanism of this process is necessary in order to predict environmental fate and persistence of these pollutants in natural waters. Photosensitized oxidation consists in the excitation of a sensitizer by visible light to first singlet or triplet state, which can transfer electron or energy to molecular oxygen. When electron is transferred - superoxide radical anion - a precursor of free radical reactions can form. This way is called type I photooxidation. When energy is transmit - very reactive, although selective, singlet molecular oxygen is generated. This is so-called type II photooxidation.
Environ Sci Pollut Res
The possibility of the application of photosensitized oxidation in wastewater treatment has a potent advantage due to the use of easy accessible visible light (solar irradiation) and oxygen from the air.
Materials and methods Parabens Methylparaben (MP) (≥99 %) and propylparaben (PP) (≥99 %) were purchased from Sigma-Aldrich (Steinheim, Germany); ethylparaben (EP) (≥99 %) was bought from Aldrich Chemistry (Steinheim, Germany); butylparaben (>99 %) (ButP); and benzylparaben (BenzP) (>99 %) were obtained from Fluka (Steinheim, Germany). Sensitizers 4,4′,4″,4′″-(Porphine-5, 10, 15, 20-tetrayl) tetrakis (benzenesulfonic acid) (TPPS4) was purchased from Fluka (Steinheim, Germany). Al(III) phthalocyanine chloride tetrasulfonic acid (a mixture of regioisomers, AlPcS4) was purchased from Frontier Scientific Inc. (Logan, USA). The photochemical experiments setup was described in details in our previous work (Gryglik et al. 2009). Experiments were carried out in alkaline conditions (pH= 10.6). The reaction mixture was aerated by air bubbling which also ensured agitation of the solution. The phototransformation progress was monitored by determination of parabens concentration using a Varian 920 HPLC apparatus with diode array detector at the wavelength 256 nm. Separation was done on a Luna C18 column (3.9 mm Ą 150 mm). The mobile phase was a mixture of methanol and water (60/40v/v), and it was used with isocratic flow rate equal to 1 ml/min. The identification of photoproducts of each paraben and of the mixture was done via UPLC/Q-TOF-MS with a diode array detector (UPLC® Acquity, Synapt G2, Waters, USA). Chromatographic separation was performed on an Acquity UPLC® BEH C18 column (2 mm×150 mm×1.7 μm) at 40 °C. The mobile phase consisted of water-acetic acid (A; 100:0.1, v/v) and acetonitrile-acetic acid (B; 100:0.1, v/v) (0.35 ml/min); the gradient is presented in Table 1. The ionization mode was negative (nebulizer gas (N2), capillary needle voltage - 3 kVat 120 °C, sampling cone voltage - 40 V; extraction cone voltage - 4 V, desolvation gas (N2, 1000 dm3/h at 400 °C), cone gas flow - 100 dm3/h). Data were analyzed using Waters MassLynx software.
Results Irradiation with solar simulated light First, the optimal analysis conditions were established to gain total separation of the mixture components within 10 min of elution. Each sample was acidified to pH=6 before analysis. A sample series of chromatograms obtained during the irradiation of paraben mixture are shown in Fig. 2. The main aim of this research was to test whether the compounds present in the mixture have an inhibitory effect on the rate of decay relative to each other. Comparison of methylparaben concentration changes during the irradiation; this compound in the mixture of five parabens and alone in the presence of AlPcS4 as a sensitizer in alkaline solution (pH= 10.6) shows Fig. 3. The obtained results have shown that no significant differences in the rates of MP decay in the mixture with respect to rates observed in the individual solutions. In both cases, the complete disappearance of the initial concentration of MP occurs in the comparable period of time of approximately 150 min. The same effect was observed in case of other parabens. It seems that the presence of several parabens in the solution does not inhibit access to light or oxygen, at least under the conditions of the experiment. Additionally, it is worthy to note that the rates of degradation of all parabens in the mixture were similar (Fig. 4). In the next series of experiment, the mechanism of phototransformation process was determined. For this purpose, the mixture of parabens in alkaline solution was irradiated with various specific additives: –
In the absence of sensitizer (direct photolysis)
Table 1 Gradient of mobile phase during UPLC analysis of transformation products Eluent
0 min
2 min
3 min
5 min
7 min
10 min
14 min
A B
95 % 5%
95 % 5%
85 % 15 %
70 % 30 %
50 % 50 %
40 % 60 %
40 % 60 %
Fig. 2 A series of chromatograms obtained during the irradiation of paraben mixture with 100 W xenon lamp (initial concentration of each paraben c 0 = 8 × 10 −5 mol/dm 3, initial concentration of sensitizer cAlPcS4 =2×10−5 mol/dm3)
Environ Sci Pollut Res
Fig. 3 Changes in the relative MP concentration during the irradiation this compound in the mixture of five parabens and alone in the presence of AlPcS4 as a sensitizer in alkaline solution (pH=10.6). The source of the light was xenon arc lamp (100 W). Initial concentration of MP c 0MP = 8 × 10 −5 mol/dm 3 , initial concentration of AlPcS 4 c s = 2 × 10−5 mol/dm3, air bubbling
– – –
In the presence of AlPcS4 as a sensitizer (=photosensitized oxidation) In the presence of AlPcS4 and sodium azide as a singlet oxygen scavenger (=type I of photosensitized oxidation) In the presence of AlPcS4 and tert-butyl alcohol as a hydroxyl radical scavenger (=type II of photosensitized oxidation)
Figure 5 shows the obtained results (example for MP, but the results for other parabens were similar). As can be seen in the absence of sensitizer, the irradiation process does not cause a significant decrease in initial levels of
Fig. 5 Changes in the relative MP concentration during its irradiation in the mixture in alkaline solution (pH=10.6) with various additives. The source of the light was xenon arc lamp (100 W). Initial concentration of each paraben c0MP =8×10−5 mol/dm3, initial concentration of AlPcS4 cs =2×10−5 mol/dm3, initial concentration of sodium azide c0SA =1× 10−3 mol/dm3, initial concentration of tert-butyl alcohol c0TB =1×10 − 1 mol/dm3, air bubbling
parabens. This indicates that direct photolysis does not play a significant role in the photodegradation of substrates which is in line with expectations because the maximum of parabens absorption is below 300 nm. Total phototransformation of parabens occurs after the addition of the sensitizer. Addition of sodium azide which selectively reacts with singlet oxygen results in complete inhibition of the degradation process almost to the level of photolysis. Moreover, after the addition of hydroxyl radical scavenger—tert-butyl alcohol—the rate of substrates decay is the same as the rate of photosensitized oxidation. These effects suggest that the photooxidation of parabens proceeds entirely according to the mechanism II photooxidation by singlet oxygen route. The interesting results were obtained using two different sensitizers (TPPS4 and AlPcS4) and a mixture of them. In both cases, the concentration of the dye was equal to 2×10−5 mol/ dm3. In solution with the mixture of dyes, the concentration of each one was equal to 1×10−5 mol/dm3. The obtained results are shown in Fig. 6 (example for MP, but the results for other parabens were similar). Comparing the effect of photooxidation with using two dyes, we found that TPPS4 is a more effective sensitizer than AlPcS4 and this effect is visible even in a solution with both of them.
Irradiation with natural sunlight Fig. 4 Changes in the relative parabens concentration during their irradiation in the mixture in the presence of AlPcS4 as a sensitizer in alkaline solution (pH=10.6). The source of the light was xenon arc lamp (100 W). Initial concentration of each paraben c0 =8×10−5 mol/dm3, initial concentration of AlPcS4 cs =2×10−5 mol/dm3, air bubbling
Finally, a series of experiments were carried out in which mixture of parabens was irradiated using natural sunlight. Aluminum phthalocyanine chloride tetrasulfonic acid was
Environ Sci Pollut Res
Fig. 6 Changes in the relative MP concentration during its irradiation in the mixture in alkaline solution (pH=10.6) in the presence of different sensitizers. The source of the light was xenon arc lamp (100 W). Initial concentration of each paraben c 0MP = 8 × 10 −5 mol/dm 3 , initial concentration of sensitizers cs =2×10−5 mol/dm3, (in the mixture of dyes, their initial concentration was cs =1×10−5 mol/dm3 for each of them), air bubbling
Fig. 8 Changes in the relative MP concentration during its irradiation with natural sunlight in the mixture of parabens in alkaline solution (pH= 10.6) in the presence of sensitizer and without it. Initial concentration of each paraben c0MP =8×10−5 mol/dm3, initial concentration of AlPcS4 cs =2×10−5 mol/dm3, air bubbling
sunlight occurs very slowly. Only about 2 % reduction of MP concentration was attained after 2.5 h of reaction without sensitizer at irradiance equal to about 374.0 W/m2. No detectable degradation of substrates was observed in the dark controls. After addition of sensitizer, in nearly the same irradiation conditions and the same period of time, the initial concentration of parabens drops to undetectable value (the results for MP are shown in Fig. 8). The influence of irradiation intensity on the reaction rate is also noticeable. The increase in the light intensity increases photosensitized reactions rate. These results confirm our earlier reports, where 2-chlorophenol was degraded by photosensitized oxidation under solar irradiation (Gryglik et al. 2004).
used as a photosensitizer. The experiments were run in glass tube reactor of the capacity 0.5 dm3 (Fig. 7). The reaction mixture was aerated by air bubbling which also ensured agitation of the solution. The spectrum of light was collected with an Oceans Optics USB 4000 fiber optic spectrometer with an approximate resolution of 0.4 nm. The open field experiments using sunlight were run in central Poland in various illumination conditions, on sunny and cloudy days. Figure 8 shows the changes of the relative MP concentration for process carried out under direct solar radiation in dependance on light intensity. The results show that the direct photolysis of paraben mixture in alkaline solution under irradiation of natural
UPLC-MS/MS identification of phototransformation products
Fig. 7 The picture of the reactor used in outdoor experiments
The transformation products (TPs) formed during the photosensitized oxidation process were analyzed by UPLC-MS/MS. The intermediates were identified by interpretation of fragment ions and product ion scan. The spectra of parent compounds were obtained of [M-H]− at m/z 151.0404 (tR 7.32 min), m/z 165.0576 (tR 8.18 min), m/z 179.0702. (tR 8.98 min), m/z 193.0883 (tR 9.88 min), m/z 227.0687 (tR 9.93 min) for MP, EP, PP, ButP, and BenzP, respectively. The EI mass spectra of parabens are shown in Fig. 9. The peak of p-hydroxybenzoic acid (p-HBA), the product of hydrolysis appears at the first sample with the retention time at 5.52 min (m/z 137.0251) (Fig. 10a). After 20 min of photodegradation, the new peaks corrected with TPs can be observed. As can be seen on Fig. 10b and c, the height of TPs peaks is two order lower than parabens. According to the
Environ Sci Pollut Res Fig. 9 High-resolution MS spectrum in negative ion mode of parent compounds and transformation products
Environ Sci Pollut Res Fig. 10 Evolution of a UPLC chromatograms during photosensitized oxidation of the parabens mixture, b kinetic of photodegradation of parabens, c and phototransformation products (TPs) formed upon photodegradation
peaks, height can be supposed that the concentration of TPs is low. Kinetic profile of TPs during irradiation time indicates that photoproducts are formed at the beginning and after some time undergo degradation. After 180 min of photodegradation, both parent compounds as well as its photoproducts were almost completely removed. In order to get more information about the observed TPs, UPLC/Q-TOF-MS/MS have been used for its identification. Monohydroxylation has been found to be the major reaction pathway for the formation of byproducts for the reaction of 1 O2 with parabens. The performed experiments indicated that in the mixture of parabens after 20 min of treatment, the
formation of six phototransformation products can be observed. TP1 with the mass 153.0187 m/z [M-H]−, suggesting the hydroxylation of p-hydroxybenzoic acid. The TP2, TP3, TP4, TP5, and TP6 with the mass: 167.0350 m/z [M-H]− (tR 6.23 min), 181.0472 m/z [M-H] (tR 7.17 min), 195.0667 m/z [M-H] (tR 8.02 min), 209.0796 m/z [M-H] (tR 8.71 min), 243.0661 m/z [M-H] (tR 8.88 min), indicating monohydroxylation of the parabens (Fig. 9, Table 2). The fragmentation of all these compounds allowed to identify that for parabens, the addition of –OH group was onto aromatic ring (main fragment ions of hydroxylated parabens are found as 153.0187, 108.0218 m/z [M-H]−).
Environ Sci Pollut Res Table 2
Characterization of parent compounds as well as transformation products detected by UPLC-MS/MS Main compounds (identify by standards) No.
compounds
1
methylparaben (MP)
t R, min
theoretic monoisotopic mass, Da
detected monoisotopic mass, Da
7.32
151.0407
151.0404
supposed structure O
O
-
CH3
O
CH3
2
ethylparaben (EP)
8.18
165.0557
165.0576
O
O
-
O
3
propylparaben (PP) 8.98
179.0714
179.0702
O
CH3
O
-
O
4
butylparaben (ButP)
9.88
193.0870
193.0883 O
CH3
O
-
O
5
benzylparaben (BenzP)
9.93
227.0714
227.0687
O
-
O
O
Transformation products No.
compounds p-hydroxybenzoic acid (pHBA) a
detected theoretic t R, monoisotopic monoisotopic min mass, Da mass, Da 5.52
137.0244
supposed structure O
137.0251
OH
-
O
HO
TP1
TP2
3,4dihydroxybenzoic acid a methyl dihydroxybenzoate
4.48
153.0193
153.0187
O
OH
-
OH
6.23
167.0350
167.0350
O
-
O
O
CH3
O
TP3
ethyl dihydroxybenzoate
CH3
OH
7.17
181.0506
181.0472
O
O
-
O
TP4
propyl dihydroxybenzoate
OH
8.02
195.0663
195.0667
O
-
CH3 O O
CH3
TP5
butyl dihydroxybenzoate
8.71
209.0891
OH
209.0796 O
-
O O
TP6
hydroxyl-benzyl, 8.88 p-hydroxybenzoate
243.0663
OH
243.0661 O
a
-
O O
Confirmed by the standard
Environ Sci Pollut Res
Discussion 1. The obtained results indicate a great potential of sunlightmediated photodegradation in the removal of water pollutants in the middle latitude. There are many publications on the photodegradation of xenobiotics (especially pharmaceuticals, endocrine disruptors, or pesticides) in the aquatic environment. Most of them concern the photodegradation using UV light and the type of TiO2/ ZnO photocatalysts (Kamaraj et al. 2014; Maroga et al. 2015) or photo-Fenton and UV/H2O2 (Cavalcante et al. 2013). However, studies on photosensitized oxidation process in the presence of visible light absorbing sensitizers are becoming more and more popular but they are still limited, particularly with the use of natural sunlight. It is known that the processes of photosensitized degradation play a major role in the self-purification of natural water. Many studies have shown that a significant role in these processes plays dissolved natural organic matter (Remucal 2014; Vialaton and Richard 2002). It contains chromophores which are effective as a sensitizer and can act both by the radical pathway and by the generation of singlet oxygen. It is widely demonstrated that indirect photolysis of organic pollutants in water solutions undergoes both by type I and type II photooxidation mechanism. The predominance of one of them is dependent on the chemical structure of substrate, the reaction conditions and presence of other substances in solution (especially in natural water samples) (Remucal 2014; Zuo et al. 2013; Vialaton and Richard 2002). 2. Our research confirmed that photosensitized oxidation is an effective method in the removal of parabens from water during visible light irradiation in the presence of sensitizer. Additionally, our scavenging experiments suggest that the mixture of parabens in water solution is completely oxidized by the reaction with singlet oxygen during an exposure to solar simulated light in the presence of sensitizer. Chen at al. (2013b) obtained other results when they studied direct and indirect photodegradation of estriol in w a t e r s o l u t i o n s . T h e y f o u n d th a t t h e d i r e c t photodegradation of substrate was relatively slow under direct irradiation of sunlight and simulated solar light whereas the addition of sensitizers (humic acids) significantly enhanced the degradation. In contrast to our results, their studies with using specific quenchers confirmed a major role in the degradation of the substrate radical mechanism (type I photooxidation). In another studies, Chen et al. (2013a) carried out a series of experiments to investigate the photosensitized degradation mechanism of β-blocker timolol in the presence of fulvic acid (FA) under simulated sunlight. Their results suggested that only half of the substrate photodegradation was attributed to the reaction with 1O2.
The second route of photodegradation proceeded via the reactions with 3FA. 3. One of the purposes of our work was to investigate the influence of inhibitory effect compounds present in the mixture on the degradation rate. The obtained results have shown that no significant differences in the rates of parabens decay in the mixture with respect to rates observed in the individual solutions. It seems that the presence of several parabens in the solution does not inhibit access to light or oxygen, at least under the conditions of the experiment. According to our knowledge, there are no studies on the removal of parabens mixture by photosensitized oxidation in aqueous solution. There are, however, some reports about degradation of a mixture of parabens by other methods. Tay et al. (2010) used the high oxidation potential of ozone to decompose of solution containing methyl-, ethyl-, propyl-, butyl-, and benzylparaben. Authors put emphasis on the kinetics of the reaction and do not make the comparison the rate of substrate degradation in the mixture and in individual solutions. Recently, another group of scientists (Domínguez et al. 2014) studied the degradation rates and removal efficiencies of mixture of methyl-, ethyl-, propyl-, and butylparaben using H2O2/Fe2+ advanced oxidation process. In their studies, the simultaneous optimization of the parabens removal was achieved depending on the initial concentrations of hydrogen peroxide and Fe2+ ion. The elimination of the same parabens from water solution in presence of Fe(III)-citrate circumneutral pH was examined by Feng et al. (2014). In their research, the effect of formic acid, acetic acid, oxalic acid, malonic acid, succinic acid, and fulvic acid on the photodegradation of parabens by Fe(III)-citrate was investigated. From this article, you can conclude that only individual solutions of parabens were tested. 4. The photoproducts of parabens degradation were identified an d th e d egra datio n p athway was prop ose d. Monohydroxylation has been found to be the major reaction pathway for the formation of byproducts for the reaction of 1O2 with parabens. The main transformation product formed during the photosensitized oxidation of paraben mixture was p-hydroxybenzoic acid. Similar results obtained Feng et al. (2014) and Steter et al. (2014) when analyzing different methods of parabens decomposition.
Conclusions It was confirmed that singlet oxygen is an effective oxidant in the degradation of paraben mixture in water during visible light irradiation in the presence of sensitizer. The obtained
Environ Sci Pollut Res
results indicate a strong dependence of the decay rate of substrates on light intensity as well as the additives of second photosensitizer. The experiments confirmed that singlet oxygen route is the major pathway of parabens degradation. No significant differences in the rates of parabens decay in the mixture in relation to the decay rate of the individual solutions were observed; thereby, there was found neither the enhancement nor inhibition effect of several substrates in the solution. Monohydroxylation has been found to be the major reaction pathway for the formation of byproducts for the reaction of 1 O2 with parabens. The main transformation product formed during the photosensitized oxidation of paraben mixture was p-hydroxybenzoic acid. The results collected during the investigation of photosensitized oxidation of parabens using solar irradiation indicate a great potential of sunlight-mediated photodegradation in the removal of water pollutant in the middle latitude. The application of photosensitized oxidation in elimination of hazardous pollutants from water environment seems attractive due to the possibility of the use of two inexhaustible resources: oxygen from the air and photons from solar radiation. Phototransformation processes in natural aqueous environment have been studied for many years, and the results shown above could advance scientific knowledge in this area, especially from the point of view the role of sunlight in self-purification processes in water. Acknowledgments Marta Gmurek acknowledges the support from Foundation for Polish Science within the START scholarship. Conflict of interest The authors declare that there is no any actual or potential conflict of interest including any financial, personal, or other relationships with other people or organizations within 3 years of beginning the submitted work that could inappropriately influence, or be perceived to influence, their work.
References Aalto TR, Firman MC, Rigler NE (1953) p-Hydroxybenzoic acid esters as preservatives. J Am Pharm Assoc Am PharmAssoc (Baltim) 42(8):449–457 Albero B, Pérez RA, Sánchez-Brunete C, Tadeo JL (2012) Occurrence and analysis of parabens in municipal sewage sludge from wastewater treatment plants in Madrid (Spain). J Hazard Mater 239–240: 48–55 Andersen FA (2008) Final report on the safety assessment of methylparaben, ethylparaben, isopropylparaben, isobutylparaben and benzylparaben as used in cosmetic products. Int J Toxicol 27(suppl 4):1–82 Andersen HR, Lundsbye M, Wedel HV, Eriksson E, Ledin A (2007) Estrogenic personal care products in a greywater reuse system. Water Sci Technol 56:45–49 Barr L, Metaxas G, Harbach CA, Savoy LA, Darbre PD (2012) Measurement of paraben concentrations in human breast tissue at serial locations across the breast from axilla to sternum. J Appl Toxicol 32(3):219–232
Bazin I, Gadal A, Touraud E, Roig B (2010) Hydroxy benzoate preservatives (parabens) in the environment: data for environmental toxicity assessment. In: Fatta-Kassinos D, Bester K, Kummerer K (eds) Xenobiotics in the urban water cycle: mass flows, environmental processes, mitigation and treatment strategies. Part II. Springer, Netherlands, pp 245–257 Calafat AM, Ye X, Wong LY, Bishop AM, Needham LL (2010) Urinary concentrations of four parabens in the U.S. population: NHANES 2005–2006. Environ Health Perspect 118(5):679–685 Castelain F, Castelain M (2012) Parabens: a real hazard or a scare story? Eur J Dermatol 22(6):723–727 Cavalcante RP, da Rocha Sandim L, Bogo D, Barbosa AML, Osugi ME, Blanco M, de Oliveira SC, de Fatima Cepa Matos M, Machulek A Jr, Ferreira VS (2013) Application of Fenton, photo-Fenton, solar photo-Fenton and UV/H2O2 to degradation of the antineoplastic agent mitoxantrone and toxicological evaluation. Environ Sci Pollut Res 20:2352–2361 Chen Y, Liang Q, Zhou D, Wang Z, Tao T, Zuo Y (2013a) Photodegradation kinetics, products and mechanism of timolol under simulated sunlight. J Hazard Mater 252–253:220–226 C h e n Y, Z h a n g K , Z u o Y ( 2 0 1 3 b ) D i r e c t a n d i n d i r e c t photodegradation of estriol in the presence of humic acid, nitrate and iron complexes in water solutions. Sci Total Environ 463– 464:802–809 Darbre PD, Aljarrah A, Miller WR, Coldham NG, Sauer MJ, Pope GS (2004) Concentrations of parabens in human breast tumours. J Appl Toxicol 24:5–13 Domínguez JR, Muñoz MJ, Palo P, González T, Peres JA, Cuerda-Correa EM (2014) Fenton advanced oxidation of emerging pollutants: parabens. Int J Energy Environ Eng 5:89–98 Feng X, Chen Y, Fang Y, Wang X, Wang Z, Tao T, Zuo Y (2014) Photodegradation of parabens by Fe(III)-citrate complexes at circumneutral pH: matrix effect and reaction mechanism. Sci Total Environ 472:130–136 Filby AL, Neuparth T, Thorpe KL, Owen R, Galloway TS, Tyler CR (2007) Health impacts of estrogens in the environment, considering complex mixture effects. Environ Health Perspect 115(12):1704– 1710 Gryglik D, Miller JS, Ledakowicz S (2004) Solar energy utilization in degradation of 2-chlorophenol by immobilized photosensitizers. Sol Energy 77(5):615–623 Gryglik D, Lach M, Miller JS (2009) The aqueous photosensitized degradation of butylparaben. Photochem Photobiol Sci 8:549–555 Kamaraj M, Ranjith KS, Rajeshwari S, Rajendra KRT, Hasna AS (2014) Photocatalytic degradation of endocrine disruptor Bisphenol-A in the presence of prepared CexZn1−xO nanocomposites under irradiation of sunlight. J Environ Sci. Article in press Liao C, Kannan K (2014) Concentrations and composition profiles of parabens in currency bills and paper products including sanitary wipes. Sci Total Environ 475:8–15 Ma WL, Wang L, Guo L, Liu LY, Qi H, Zhu NZ, Gao CJ, Li JF, Kannan K (2013) Urinary concentrations of parabens in Chinese young adults: implications for human exposure arch. Environ Contam Toxicol 65:611–618 Maroga MV, Héquet V, Andrès Y, Gru Y, Colin R, Doña-Rodríguez JM, Pastrana-Martínez LM, Silva AMT, Leleu M, Tindall AJ, Mateos S, Falaras P (2015) Photocatalytic degradation of estradiol under simulated solar light and assessment of estrogenic activity. Appl Catal B Environ 162:437–444 Remucal CK (2014) The role of indirect photochemical degradation in the environmental fate of pesticides: a review. Environ Sci Process Impacts 16:628–653 Routledge EJ, Parker J, Odum J, Ashby J, Sumpter JP (1998) Some alkyl hydroxy benzoate preservatives (parabens) are estrogenic. Toxicol Appl Pharmacol 153(1):12–19
Environ Sci Pollut Res Sandanger TM, Huber S, Moe MK, Braathen T, Leknes H, Lund E (2011) Plasma concentrations of parabens in postmenopausal women and self-reported use of personal care products: the NOWAC postgenome study. J Expo Sci Environ Epidemiol 21(6):595–600 Schlumpf M, Kypke K, Wittassek M, Angerer J, Mascher H, Mascher D, Vökt C, Birchler M, Lichtensteiger W (2010) Exposure patterns of UV filters, fragrances, parabens, phthalates, organochlor pesticides, PBDEs, and PCBs in human milk: Correlation of UV filters with use of cosmetics. Chemosphere 81(10):1171–1183 Shirai S, Suzuki Y, Yoshinaga J, Shiraishi H, Mizumoto Y (2013) Urinary excretion of parabens in pregnant Japanese women. Reprod Toxicol 35:96–101 Soni MG, Carabin IG, Burdock GA (2005) Review: safety assessment of esters of p-hydroxybenzoic acid (parabens). Food Chem Toxicol 43(7):985–1015 Steter JR, Rocha RS, Dionísio D, Lanza MRV, Motheo AJ (2014) Electrochemical oxidation route of methyl paraben on a borondoped diamond anode. Electrochim Acta 117:127–133 Tay KS, Rahman NA, Mhd. Abas RB (2010) Kinetic studies of the degradation of parabens in aqueous solution by ozone oxidation. Environ Chem Lett 8:331–337 Thorpe KL, Maack G, Benstead R, Tyler CR (2009) Estrogenic wastewater treatment works effluents reduce egg production in fish. Environ Sci Technol 43(8):2976–2982
Vialaton D, Richard C (2002) Phototransformation of aromatic pollutants in solar light: photolysis versus photosensitized reactions under natural water conditions. Aquat Sci 64:207–215 Wang L, Wu Y, Zhang W, Kannan K (2013) Characteristic profiles of urinary p-hydroxybenzoic acid and its esters (parabens) in children and adults from the United States and China. Environ Sci Technol. doi:10.1021/es304659r Weschler CJ, Nazaroff WW (2014) Dermal uptake of organic vapors commonly found in indoor air. Environ Sci Technol 48(2):1230–1237 Yazar K, Johnsson S, Lind ML, Boman A, Liden C (2011) Preservatives and fragrances in selected consumer-available cosmetics and detergents. Contact Dermatitis 64(5):265–272 Ye X, Bishop AM, Reidy JA, Needham LL, Calafat AM (2006a) Parabens as urinary biomarkers of exposure in humans. Environ Health Perspect 114(12):1843–1846 Ye X, Kuklenyik Z, Bishop AM, Needham LL, Calafat AM (2006b) Quantification of the urinary concentrations of parabens in humans by on-line solid phase extraction-high performance liquid chromatography-isotope dilution tandem mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci 844:3–9 Zuo Y, Zhang K, Zhou S (2013) Determination of estrogenic steroids and microbial and photochemical degradation of 17a-ethinylestradiol (EE2) in lake surface water, a case study. Environ Sci Process Impacts 15:1529–1535
