Journal of Hazardous Materials 337 (2017) 115–125

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Journal of Hazardous Materials

j o ur nal ho me pa ge: www.elsev ier .com/ locate / jhazmat

nvironmental behavior of 12 UV filters and photocatalytic profile ofthyl-4-aminobenzoate

dela Jing Lia,d,1, Ziye Sanga,1, Chi-Hang Chowa, Japhet Cheuk-Fung Lawa, Ying Guoc,∗∗,.S.-Y. Leunga,b,c,∗

Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong Special Administrative RegionHKBU Institute of Research and Continuing Education, Shenzhen Virtual University Park, Shenzhen, ChinaSchool of Environment, Guangzhou Key Laboratory of Environmental Exposure and Health, Guangdong Key Laboratory of Environmental Pollution andealth, Jinan University, Guangzhou 510632, ChinaKey Laboratory of Tropical Agro-environment, Ministry of Agriculture of China, South China Agricultural University, Guangzhou 510642, China

r a p h i c a l a b s t r a c t

i g h l i g h t s

Et-PABA was not detected in any water sample.First study of the photocatalysis of Et-PABA.Eleven transformation products were identified with seven new compounds reported.Transformation products were less toxic than Et-PABA against Vibrio fischeri.Photocatalysis may be a valid resolution for Et-PABA removal.

r t i c l e i n f o a b s t r a c t

rticle history:eceived 17 November 2016eceived in revised form 27 April 2017ccepted 27 April 2017vailable online 28 April 2017

Ethyl-4-aminobenzoate (Et-PABA) is currently used as a substitute for 4-aminobenzoate (PABA) in sun-screens and anesthetic ointments. Despite its widespread use and hydrophilicity, Et-PABA has neverbeen found in environmental waters. This study, probed the occurrence of Et-PABA in both seawater anddrinking water sources in Hong Kong, and evaluated its transformation products (TPs) and environmental

∗ Corresponding author at: Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong Special Administrative Region.∗∗ Corresponding author.

E-mail addresses: yingguo2004@jnu.edu.cn (Y. Guo), s9362284@hkbu.edu.hk (K.S.-Y. Leung).1 These contributed equally to the work.

ttp://dx.doi.org/10.1016/j.jhazmat.2017.04.067304-3894/© 2017 Elsevier B.V. All rights reserved.

116 A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125

Keywords:Ethyl-4-aminobenzoateEnvironmental occurrenceTriolein-SPMDPhotocatalysisTransformation products

fate via cumulative potency and photocatalytic profile analyses. Another 11 UV filters used in skin-careproducts were also studied. Et-PABA was not detected in any water sample. Four other UV filters weredominant at ng/L level in both seawater and drinking water sources. UHPLC-QTOF-MS was used to elu-cidate the structure of TPs. With high resolution accurate mass data and fragment rationalization, 11Et-PABA TPs were characterized, including seven intermediates firstly proposed as TPs; two compoundswere reported for the first time. It is proposed that photocatalysis induces transformation pathwaysof (de)hydroxylation, demethylation and molecular rearrangement. Luminescent bacteria tests showeddecreasing toxicity with increasing irradiation of Et-PABA, suggesting that irradiation TPs are less toxicthan the parent compound. Transformation of Et-PABA appears to explain why Et-PABA has not beendetected in the natural environment.

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. Introduction

Ethyl-4-aminobenzoate (Et-PABA), a water-soluble derivativef 4-aminobenzoate (PABA) and commonly known as benzocaine,as first synthesized in 1890; it is the ethyl ester of PABA. PABA was

ne of the most widely used ingredients in sunscreen from 1943ntil the 1980s when it fell out of favor due to its potential to causeNA defects as well as allergic reactions and clothing discoloration

1]. Et-PABA is now used instead, in both sunscreens [2] and manyver-the-counter anesthetic ointments, up to a content of 20% [3].ecause it is water-soluble (958 mg/L in water at 25 ◦C) [4], Et-PABAust be entering household wastewaters and, downstream, envi-

onmental waters; however, oddly, it has not been reported and itsnvironmental fate has not been studied. Knowledge of Et-PABA’sehavior both in the environment and at wastewater treatmentlants is necessary for good environmental management of wateresources globally.

Generally, sunscreens contain multiple ingredients for multi-le functions. Due to rising concern over sunburn, photoaging, skinancer and photodermatoses, skin-care products are one of theastest growing sectors of commodities. This trend is expected toontinue because the world’s coastal population—who use more ofhese products than any other sector—is expected to grow from 1.2o 5.2 billion by 2080 [5]. This is alarming because UV filters haveeen recognized as emerging contaminants (ECs), with potentialoxicities in the concentration range of other well-characterizedstrogenic chemicals [6–8]. The extremely large consumptionorldwide (10,000 tons annually) of UV filters [9] is contributing to

heir high detection frequency in various environmental matricesf fresh/sea waters [10–13], wastewaters [14–16], tap water [17],roundwater [9], sewage sludge [16,18], sediments [18,19], biota20–23] and even human bodies (i.e. urine, serum and breast milk)24–26], up to �g/L or ng/g levels [5]. Oddly, Et-PABA has nevereen reported in any environmental matrix so far, despite its com-on usage and hydrophilicity. A low Kow value of Et-PABA (1.79;

able A1 of Supplementary Materials) indicates high polarity and aendency to partition into aqueous phase.

A research group, mainly working on UV filter contaminationn surface waters, sediments and treated wastewater in Hongong, did not take Et-PABA into consideration [10,15,19]. Becauset-PABA has become so ubiquitous and because of its powerfulstrogenic activity, the current study sought to elucidate the envi-onmental occurrence of Et-PABA in Hong Kong by sampling mostoastal and drinking water sources. We also tracked 11 other UVlters, including four hitherto unstudied in Hong Kong; all 12 UVlters (Table A1 of Supplementary Materials) have never beenonitored in drinking water sources. The cumulative potency of

t-PABA and the other 11 UV filters were evaluated by a well-stablished triolein-containing semipermeable membrane deviceSPMD).

© 2017 Elsevier B.V. All rights reserved.

UV filters are supposed to be stable on exposure to UV radi-ation, but recent studies have revealed that several UV filtersare subject to undergo various transformations such as photoly-sis, biodegradation and chlorination [27–31]. A very recent studyshowed that transformation products (TPs) accounted for over 90%of the total amount of Et-PABA taken up by zebrafish embryos after96 h exposure [32]. Transformations produce byproducts that, tosome extent, can differ in their environmental behavior and ecotox-icological profile from the parent compound [31,33,34]. However,the biotic transformation kinetics of Et-PABA under UV irradiationhas not been studied. Identification and structural characterizationof the TPs formed as well as their likely influence on the ecosys-tem are necessary if we are to assess the potential environmentalimpact posed by Et-PABA and its derivatives.

This study accomplished four objectives. First, it tracked the fateand seasonal occurrence of Et-PABA and 11 other sunscreen agentsalong the Hong Kong coastline and in its drinking water resources.Second, it evaluated the tendency of these 12 UV filters to accu-mulate in the environment. Third, it characterized and identifiedthe intermediate products of Et-PABA that are produced duringits phototransformation. Finally, it clarified the toxicity of Et-PABAphotocatalytic products using the marine bacterium Vibrio fischeri.

2. Experimental

2.1. Chemicals and solvents

Standards for benzophenone-types of BP-1 (99%, China), BP-2 (97%, USA), BP-3 (100%, USA), BP-8 (98%, USA), ethylhexylmethoxycinnamate (EHMC) (100%, USA), octocrylene (OC) (100%,USA), Et-PABA (100%, USA), 4-hydroxybenzophenone (4-HB) (98%,China) and 4,4-dihydroxybenzophenone (4-DHB) (99%, China)were obtained from Sigma-Aldrich. 4-methylbenzylidene camphor(4-MBC) (>99%, China), octyl dimethyl-p-aminobenzoic acid (OD-PABA) (>95%, China) and 3-benzylidene camphor (3-BC) (90–100%,USA) were purchased from Alfa Aesar, TCI and MP Biomedicals,respectively. Detailed physicochemical characteristics of the 12UV filters are shown in Table A1. Solutions of each analyte wereprepared in pure methanol. Mixed standard solutions were madeat 10 mg/L in methanol and subsequently diluted as necessary.All standard solutions were stored in amber glass vessels at 4 ◦C.Titanium (IV) oxide of 21 nm particle size was supplied by Sigma-Aldrich (TiO2) (≥99.5%, Germany).

Solvents including Milli-Q water (18.2 M� cm, Millipore, USA),LC–MS grade methanol (Duksan Pure Chemicals, Korea), formic

acid (98–100%, International Laboratory, USA), and cyclohexane(99.5%, VWR, EC) were utilized. LC-18 solid phase extraction (SPE)cartridges (500 mg) were obtained from Supelclean (Supelco Inc.,USA).

A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125 117

ong m

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Fig. 1. Spatial distribution of detected UV filters in 30 locations of the Hong K

Reagents for Microtox testing, namely osmotic adjusting solu-ion, diluent, reconstitution solution and acute reagent, wererovided by Modern Water (Guildford, UK).

.2. Sampling

Seawater samples were collected from 30 locations along theoast of Hong Kong in dry (February) and wet (August) seasons of013 (Fig. A1a of Supplementary Materials). The chosen sampling

ocations were associated with recreational activities at populareaches, namely the eastern marine waters of Sai Kung (S1–S3),ong Kong Island (S4–S10, S15, S26–S28) and the western marineater of Tuen Mun (S19, S20 and S29). Coastal areas with feweruman activities were also monitored (S11–S14, S16–S18, S21–S25

nd S30). In addition, Dongjiang River, being a key drinking waterource for Hong Kong, was sampled to assess any UV filter con-amination (DJ1–DJ6, Fig. A1b of Supplementary Materials). Wateramples from three reservoirs (i.e. Shenzhen, Kowloon and Shek

arine environment during (a) dry winter and (b) wet summer seasons, 2013.

Lei Pui) and local households were also collected. Surface waterwas sampled at 2-m depth using a Van Dorn Sampler and stored inpre-cleaned opaque polyethylene bottles sealed with screw caps at4 ◦C prior to use. Samples were filtered through 0.45 �m membranebefore treatment.

2.3. Accumulation test in triolein-SPMD

The experiment was conducted in an exposure chamber withvolume of 6.2 L. A set of 21 triolein-SPMDs each containing 0.53 mLtriolein was placed in the exposed chamber which was linked toa continuous-flow system at 15 mL/min. Concentrations for all the12 UV filters in the feeding solution were 1 �g/L. The water tem-perature was maintained at 23 ± 0.5 ◦C. The experiment lasted for

20 d. On days 0, 2, 4, 8, 12, 16 and 20, three water samples of 100 mLeach and three triolein-SPMDs were taken and processed to deter-mine concentrations of the 12 UV filters. A blank control withoutUV filter input was similarly processed on each day in parallel.

118 A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125

Table 1Mean concentrations ± S.D. of UV filters detected in Dongjiang (ng/L, n = 3), Pearl River Delta, China, 2014.

Sampling location BP-1 BP-3 BP-8 EHMC OC 4-MBC OD-PABA

DJ1 n.d. 19.64 ± 1.10 n.q. 30.85 ± 1.28 15.73 ± 1.45 16.22 ± 1.53 n.q.DJ2 n.q. 20.38 ± 2.09 n.q. 38.28 ± 2.22 19.23 ± 1.94 18.52 ± 2.15 n.q.DJ3 n.d. 23.19 ± 2.73 n.q. 14.55 ± 1.32 n.q. 18.86 ± 1.15 n.q.DJ4 n.d. 15.92 ± 1.03 n.q. 25.61 ± 2.16 18.74 ± 1.27 11.76 ± 1.18 n.d.DJ5 n.d. n.q. n.d. 14.83 ± 1.14 n.q. n.d. n.d.

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.d.: < LOD, n.q.: < LOQ.

After sampling, triolein-SPMD was first rinsed by Milli-Q water.fter soft paper drying, the membrane was dialyzed twice by soak-

ng in 40 mL cyclohexane for 24 h at room temperature. All theialysates were combined and reduced to about 1 mL using rotaryvaporation (BÜCHI Rotavapor RII, Flawil, Switzerland). The extractas concentrated under a gentle stream of nitrogen gas to near dry-ess and then re-dissolved in 1 mL methanol/Milli-Q water (1:1 v/v)

or UPLC–MS/MS analysis.

.4. Photocatalytic degradation

Irradiation experiments were carried out in a laboratory-maderradiation chamber equipped with 16 UV-C germicidal lamps inoncentric series (Sankyo G8T5, Japan; 1630 �W/cm2) on aque-us solutions, each contained in a Pyrex flask [35,36]. Schematiciagram of the laboratory-made irradiation chamber is shown inig. A2 of Supplementary Materials. Degradations were performedn 25 mL of aqueous Et-PABA solutions of 4 mg/L with varying ini-ial concentrations of TiO2. This concentration of mg/L was choseno ensure the minute TPs generated would be detectable by theHPLC-QTOF-MS. After the reaction under UV-C light at room tem-erature [36], 1-mL aliquots of sample were withdrawn at specificime intervals over a 50 h period. To remove TiO2 particles theolution samples were passed through 0.2 �m nylon membranelters and lyophilized; they were then analyzed by the appropriatenalytical technique.

.5. Analytical methods

Water samples of 100 mL were loaded onto the LC-18 SPE car-ridge at 6 mL/min after conditioning the cartridge with 3 × 3 mLf methanol followed by 3 × 3 mL Milli-Q water. Subsequent to0-min air drying of the SPE sorbent, the retained analytes wereluted with 3 mL of methanol/Milli-Q water (v/v 1:1) and another

mL methanol. The eluted enriched samples were then subjecto rotary evaporation at 60 ◦C, reduced to a volume of ca. 1 mLnd brought to complete dryness by nitrogen gas. Finally, sam-les were reconstituted with 1 mL of methanol/Milli-Q water (v/v:1) and then filtered through 0.2 �m nylon syringe filter for

nstrumental analysis by UPLC–MS/MS (Waters, MA, USA). Chro-atographic separation was performed on an ACQUITY BEH C18

olumn (50 × 2.1 mm, 1.7 �m, Waters, Ireland) using an injectionolume of 10 �L. Mobile phases were composed of water andethanol, both containing 0.05% formic acid. The flow rate was

.4 mL/min. The gradient profile started at 20% methanol, was thenamped up to 100% methanol within 8 min, kept at this condi-ion for 1 min, and then returned to the initial setup within 3 min.elected reaction monitoring (SRM) was used (Table A2). Electro-pray interface (ESI) operating in positive ionization mode was at.8 kV capillary voltage. The desolvation temperature was set at00 ◦C. Nitrogen, used as desolvation gas, and cone gas were main-

ained at flow rates of 1,000 L/h and 150 L/h, respectively. Argonas employed as collision gas at a flow rate of 0.15 mL/min.

Photocatalytic TPs of Et-PABA were analyzed by UHPLC (Agi-ent 1290 series) coupled with QTOF-MS (Agilent 6540 series)

7.81 ± 1.16 n.q. n.d. n.d.

(Agilent Technologies, Santa Clara, CA, USA). Chromatographic sep-aration was performed on an ACQUITY UPLC BEH C18 column(100 × 2.1 mm, 1.7 �m, Waters, Ireland) in the isocratic elutionmode. The mobile phase composition was set at 65% water and35% methanol for 22 min, both containing 0.1% formic acid (v/v).The flow rate was set to 0.4 mL/min and the injected volume was2 �L. Q-TOF mode was applied with ion source of Dual AJS ESIwith mass correction at reference mass of m/z 112.9855 at neg-ative mode while m/z 149.0233 at positive mode. High resolutionmass spectra (m/z 40–500) were obtained at a rate of 2 spectra persecond. TPs were screened in both positive and negative electro-spray ionization modes, though the positive mode showed higherresponses of TPs. Therefore, data derived from positive mode wereapplied for subsequent analyses. The dry gas of nitrogen flowed at8 L/min under 325 ◦C while sheath gas of nitrogen was at 8 L/minwith 350 ◦C, nebulizer was at 20 psig, fragmentor voltage was at120 V, skimmer voltage was at 65 V, octapole RFPeak voltage wasat 750 V, Vcap was to 4,000 V and the nozzle voltage was set to500 V. The instrument was operated in 4 GHz mode.

MassHunter (Agilent Technologies) was applied for instru-mental control, data acquisition and evaluation. By eliminatingbackground signals, MassHunter produced a list of chemicallydiscrete molecular features from the spectral data. The detectedcompounds were putatively characterized by candidate formulaeusing a mass accuracy limit of 5 ppm. Thereafter, molecular ionswere fragmented so as to obtain fragmentation patterns of TPs attwo collision energy of 5 V and 10 V.

2.6. Bioluminescent microtox test

According to the standard method [37], the toxicity of an unir-radiated Et-PABA solution and of aqueous samples collected atspecific irradiation intervals were examined by a Microtox Model500 analyzer (Modern Water, Guildford, UK). Bioluminescence ofthe marine bacterium V. fischeri was used when challenged withtoxic compounds. The toxicant-induced inhibition of luminescencewas measured by recording the decay after 15 min of exposure totarget solutions. Blank control without analyte was tested in par-allel to verify any influence induced by the matrix. Luminescenceinhibition (%) was calculated relative to experiment control of thediluent. Phenol was taken as positive control with an EC50 criterionset in a typical range of 13–26 mg/L for quality control.

3. Results and discussion

3.1. Occurrence and seasonal variation of UV filters in surfacewaters

Based on standard addition technique, the current method withsample clean-up using a SPE cartridge is established and validated

for the simultaneous analysis of 12 UV filters (log Kow 1.79–6.88,Table A1 of Supplementary Materials) in the seawater/watermatrix. The limit of detection (LOD) and limit of quantification(LOQ) were as low as 2.1 and 6.4 ng/L, respectively. All the targets

A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125 119

Fig. 2. The photocatalysis of Et-PABA (4 mg/L) at different concentrations of TiO2.

Table 2Exact mass information of Et-PABA photocatalytic transformation products by using UHPLC-QTOF-MS.

Compound Chemicalformula [M+H]+

Retention time(min)

Experimentalmass [M+H]+

Exact mass [M+H]+ Mass error �m (ppm) Reference

Et-PABA C9H12NO2+ 4.913 166.0860 166.0863 −1.81 –

Aniline C6H8N+ 5.023 94.0647 94.0651 −4.25 [39]PABA C7H8NO2

+ 5.023 138.0547 138.0550 −2.17 [39]TP-120 C7H6NO+ 5.006 120.0445 120.0444 0.83 [39]TP-154 C7H8NO3

+ 1.093 154.0502 154.0499 1.95 [39]TP-136 C7H6NO2

+ 2.259 136.0397 136.0393 2.94 This workTP-152A C7H6NO3

+ 0.991 152.0344 152.0342 1.32 This workTP-152B C8H10NO2

+ 4.885 152.0707 152.0706 0.66 This workTP-168 C8H10NO3

+ 1.363 168.0656 168.0655 0.60 This work+

w9

ctwtwetticRoTlabto

Bp(

TP-182 C9H12NO3 2.234 182.0811TP-184 C8H10NO4

+ 1.059 184.0599TP-198 C9H12NO4

+ 1.414 198.0759

ere quantifiable with recoveries at 85–114% and precision over2% (Table A3 of Supplementary Materials).

Of all the samples collected from 30 locations along Hong Kong’soast, Et-PABA was not detected in any of them. While this con-radicts common sense, given the level of Et-PABA entering theseaters, it is consistent with results of other studies reported in

he literature. Biotransformation may be one explanation. A recentork found that Et-PABA could be easily biodegraded in zebrafish

mbryo producing PABA and 4-acetamidobenzoic acid as TPs, sohat the internal concentration of Et-PABA in the embryo decreasedo <10% [32]. Beside this, other biotic degradations might play a rolen the elimination of Et-PABA and the generation of relevant TPs,ontributing to Et-PABA removal from the natural environment.ecent studies have noted that direct photolysis/photocatalysisf both PABA and OD-PABA could produce diverse TPs [1,38,39].herefore, because Et-PABA is a type of p-aminobenzoic acid, it isogical to expect that it would undergo similar degradation mech-nisms and produce comparable TPs even though this has not yeteen reported. To fill this gap and test this hypothetical explana-ion, a comprehensive study of the photocatalyzed transformationf Et-PABA was undertaken and is reported here.

Seven of the 12 UV filters were above the LOD (Table A4). EHMC,P-3, OC, 4-MBC, OD-PABA and BP-8 were the dominant com-ounds, in both wet and dry seasons with detection frequenciesDFs) of 100, 100, 100, 100, 77 and 69%, respectively, indicat-

182.0812 −0.55 This work184.0604 −2.72 This work198.0761 −1.01 This work

ing their extensive consumption in Hong Kong. A work focusingmainly on Hong Kong Island and Sai Kung showed compara-ble DF in EHMC (93%), BP-3 (95%), OC (100%) and BP-8 (88%)[10]. The maximum mean concentrations were found for EHMC(192 ng/L), BP-3 (82 ng/L), OC (64 ng/L) and 4-MBC (75 ng/L) incurrent work, and these values are within the detecting range of39–6,812 ng/L reported earlier [10]. The detected levels of OD-PABA, BP-8 and BP-1 (11–46 ng/L) were slightly lower than thosefound by Tsui et al. [10], namely (64–182 ng/L). Additionally, otherUV filters, i.e. BP-4, butyl methoxydibenzoylmethane (BMDM),isoamyl p-methoxycinnamate (IAMC), ethylhexyl salicylate (EHS)and homosalate (HMS) were also detected in the Hong Kong marineenvironment (24–2,812 ng/L) [10]. Such wide ranges of so manydifferent UV filters suggest diverse human input, possibly becausethere are no particular regulations on UV filters in commercialproducts in this region. Actually, these UV filters have been globallydetected up to �g/L level, and levels correlate positively with highconsumption volume of UV filters regionally [40,41]. It is worthnoting that EHMC is typically the filter found with the highest con-centration in diverse matrices, e.g. seawater [10], wastewater [15],sediment [16,19], marine organisms [42] and even breast milk [43].

Personal care products (PCPs) are considered a key source of EHMCexposure [41] with its use frequency above 90% of products in China[44]. Because of its lipophilic properties (log Kow 5.80, Table A1 ofSupplementary Materials) and potential risks related to multiple

120 A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125

Fig. 3. Accurate MS/MS spectra and fragmentation routes for Et-PABA and its seven transformation products (TP-136, TP-152A, TP-152B, TP-168, TP-182, TP-184, TP-198);mass deviations from theoretical m/z values are indicated in brackets.

A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125 121

Fig. 3. (Continued)

122 A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125

s of Et

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wloswHubpawhwsS

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Fig. 4. Proposed transformation pathway

ormonal activities [5,45,46], EHMC deserves more attention intudies to determine its behavior and fate in the environment.

All detected UV filters showed marginally higher levels in theet season which is also the summer, thereby correlating with a

arger consumption of PCPs-containing sunscreens (Fig. 1). Beachesf Sai Kung and Hong Kong Island, popular for sun-bathing andnorkeling on the coral reefs (S1, S2, S5 and S26), and vicinity (S6),ere subject to the most UV filters pollution. All the locations nearong Kong Island (S5–S10, S15, S26–S28, serving highly dense pop-lation) showed relatively high levels of UV filters, which can belamed on both direct (recreational activities) and indirect anthro-ogenic inputs (sewage discharge). These sites, with few waterctivities but adjacent to estates and ports (S13, S16 and S23–S25),ere moderately polluted possibly due to UV filters release fromousehold wastewater. The less polluted areas are either free fromater recreational activities (S11, S12, S14, S17 and S18) or are open

ea (S22 and S30) facing the Pearl River Delta and the South Chinaea.

Hong Kong, with a population density of 6,300/km2 [47], gets itsrinking water mainly from the Dongjiang River (>80%), a tributaryf the Pearl River Delta. Fast-track and large-scale urban develop-ent during the last three decades has caused noticeable pollution

n this area, e.g. metals and persistent organic pollutants (POPs)48,49]. Thus, the water quality of the Dongjiang River has become a

reat concern. The present study indicates that EHMC (15–38 ng/L)s still the most abundant UV filter in the Dongjiang River, followedy BP-3, OC and 4-MBC (Table 1). Relatively higher levels of theV filters were observed in the main river of Dongjiang (DJ1, DJ2

-PABA under photocatalytic degradation.

and DJ3), which receives heavy population from Huizhou City. Sim-ilarly, several UV filters/stabilizers (BPs and benzotriazoles) werefound in sediments and sludge up to thousands of ng/g concentra-tions along the Songhua River in North China [18]. Although noneof the 12 UV filters was found in the water samples collected fromthe reservoirs and household tap water (data not shown), the largeamounts of these compounds being produced and used in Chinamean that they may require good management to prevent adverseenvironmental consequences in the future. Preserving sufficientsafe drinking water supplies is key to supporting domestic eco-nomic growth as well as bolstering the efforts of China to protectthe global environment.

Once in the water, components released from sunscreens mayaccumulate in different environmental compartments dependingon the influence of physicochemical properties and biological pro-cesses [32]. Given the facts of UV filters’ extensive application,wide environmental detection, and multiple hormonal activities,it is critical to evaluate their cumulative potency for better riskassessment and management in the long term.

3.2. Accumulation of triolein-SPMD

The passive sampling device, triolein-SPMD, is designed for inte-grative sampling of nonpolar organic chemicals from water; it has

been used to sample POPs and ECs of brominated flame retardants,UV filters and perfluorinated compounds in lakes, rivers and theocean [50–52]. Because of the validity of its results and ease in han-dling, SPMD was used to assess the cumulative potency of these 12

A.J. Li et al. / Journal of Hazardous Materials 337 (2017) 115–125 123

tion o

Um(oOtiir

oiclbwcostT

3

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Fig. 5. Inhibition (%) of the luminescence of bacteria Vibrio fischeri as a func

V filters in this study. Results show that SPMD-derived bioaccu-ulation (log BCF) was lower than expected from log Kow values

Table A1 of Supplementary Materials), a result in line with previ-us findings [50]. The estimated log BCFs for 3-BC, BP-3, 4-MBC,D-PABA, OC, BP-8 and EHMC were relatively high, suggesting

heir potential for accumulation in biota. The cumulative capac-ty estimated by SPMD agrees with the bioaccumulation tendencyn marine organisms, with EHMC, OD-PABA, BP-8, OC and BP-3 atelatively high levels of 14–51 ng/g (dw) [42].

In fact, the actual bioaccumulation level should depend on notnly BCF but also the environmental presence of a compound andts degradable potency. Balmer et al. [50] found that UV filter con-entration was lower in fish than in SPMDs exposed in the sameake, and proposed further metabolism of the compound in theiota as an explanation. This suggestion has been verified by recentork on Et-PABA biodegradation in zebrafish embryo [32]. Con-

erns over degradation of UV filters are actually increasing becausef TPs produced, some of which might have unexpected and unde-irable environmental consequence [31,53,54]. Thus, elucidation ofransformation mechanism in UV filters and identification of theirPs has become a necessity.

.3. Degradation of Et-PABA by photolysis and photocatalysis

As shown in Fig. 2, direct photolysis without a TiO2 catalysts responsible for maximum 17% of Et-PABA degradation for aime period of 50 h. The degradation rate increases remarkably atiO2 concentration up to 80 mg/L (88% of Et-PABA degraded), asxpected, confirming the positive influence of the increased num-er of TiO2 active sites on the process kinetics. At higher catalyst

oading a decreasing trend of Et-PABA degradation was observedt the reactions from 40 to 50 h. Similar observations have beeneported for UV filter photocatalysis of 4-MBC and azo dye of Pro-ion Red [33,55]. An increase in catalyst loading may cause lightcattering and a screening effect, and thereby reduce the specificctivity of the catalyst due to the blockage of photons from reachinghe photocatalysts in the inner zone [56–58]. Therefore, an iden-ification study of Et-PABA TPs was carried out upon TiO2 initialoading of 80 mg/L after 50 h UV-C exposure.

Samples were examined by UHPLC-QTOF-MS in scan mode andcreened for potential TPs using MassHunter software. Molecularormulae for the detected TPs were deduced from the accurate

ass measurements. High mass accuracy measurements of the

f the photocatalytic treatment time in Et-PABA (3 �g/L at TiO2 of 126 �g/L).

fragment ions contributed to the high confidence in the TPs identifi-cation. A total of 11 TPs were identified for Et-PABA photocatalysis,matching the proposed molecular formulas within 5 ppm of massmeasurement error (Table 2; Fig. A3 of Supplementary Materials).Of these 11, four TPs are known compounds (i.e. aniline and PABA)or reported fragment ions (i.e. TP-120 and TP-154) [39]; two (TP-136 and TP-152A) have molecular structures firstly identified in thecurrent study; the remaining five (i.e. TP-152B, TP-168, TP-182, TP-184 and TP-198) presented identical structures in SciFinder but arefirstly proposed as TPs.

To elucidate the structure of the photocatalytic TPs, MS/MS spec-tra of the parent compound and its seven photocatalytic byproductsare recorded (Fig. 3) and a pathway of their evolution is pro-posed (Fig. 4). It is inferred that Et-PABA was firstly transformedto TP-182 and TP-198 by (di)hydroxylation. MS/MS fragmenta-tion yielded a fragment ion at m/z 136.0397 (C7H6NO2

+) andm/z 152.0349 (C7H6NO3

+) from TP-182 and TP-198, respectively,revealing that hydroxylation reaction occurred in the aromaticmoiety. By demethylation, the above three compounds were fur-ther degraded to TP-152B, TP-168 and TP-184, respectively, whichwere characterized by their structural-diagnostic ions of m/z120.0447 (C7H6NO+), m/z 136.0392 (C7H6NO2

+), and m/z 152.0339(C7H6NO3

+) correspondingly. A further demethylation of TP–152 Band TP-168 led to the formation of PABA and TP-154. Under UV-C irradiation, PABA is suggested to form TP-154 by hydroxylation,which is different from TPs proposed from PABA photolysis by sim-ulated solar irradiation using a xenon lamp [1,38]. Continuously,PABA and TP-154 produced TP-120 and TP-136, respectively, bydehydroxylation and molecular rearrangement. The presence inMS2 spectrum of the structural-diagnostic ions of m/z 120.0450(C7H6NO+) and m/z 108.0449 (C6H6NO+) is crucial for the structureattribution of TP-136. The pathway ultimately produced TP-152A,which was proposed to be a TP of TP-136 or TP-184. Hypothetically,Et-PABA photocatalysis is initiated by hydroxylation and demethy-lation, and sustained through dehydroxylation and rearrangementof molecule to form more stable products.

Thus far, the hypothesis has been verified that transformationof Et-PABA when photo-irradiated explains why Et-PABA has notbeen detected in water samples where it should, logically, occur.

In this case, evaluation of the risk caused by the Et-PABA TPs is ofgreat importance in defining its environmental safety in the longrun.

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24 A.J. Li et al. / Journal of Hazard

.4. Toxicity evaluation of Et-PABA and its TPs

The original Et-PABA compound showed estrogenic activityoward both rainbow trout estrogen receptor and human estro-en receptor [59]. The environmental toxicity of the TPs of-aminobenzoic acid remains to be explored, even though pho-olytic TPs of both OD-PABA and PABA have been clarified [1,38,39].

hether Et-PABA photocatalysis produces TPs even more toxichan the parent compound is unknown, just as whether photolysisan remove toxic Et-PABA is still unknown. Thus, to address theseuestions, a preliminary assessment of irradiated Et-PABA solutionas evaluated by Microtox assay.

To quantify photocatalytic-related toxicity of Et-PABA, photo-atalytic samples were collected at defined intervals and analyzedased on the luminescence inhibition (%) to the marine bacterium. fischeri. An environmentally relevant level of Et-PABA at 3 �g/Las used. A blank control with no Et-PABA was run in parallel. Thendings of the Microtox test display a pattern of decreasing toxicity

or Et-PABA irradiated TPs (Fig. 5). At the beginning, Et-PABA witho irradiation showed an inhibition of 22% in the bacteria lumines-ence, which is comparable with 4-MBC inhibition of 16% [33]. Theoxicity was reduced remarkably with reduction of the parent sub-tance and formation of TPs. At 12 h of exposure, no toxicity wasresent relative to the blank control, indicating decreased toxicity

nduced by photolytic TPs of Et-PABA. This shows that photoly-is/photocatalysis may be a valid treatment for removing Et-PABAesidue from the environment with few undesirable consequences.

. Conclusions

Using SPE-UPLC–MS/MS to determine Et-PABA and the other 11UV filters simultaneously in a water matrix was demonstrated tobe an accurate method. Et-PABA was not detected in any watersample. Four UV filters, namely EHMC, BP-3, OC and 4-MBC, wereboth dominant in Hong Kong coastal water and drinking waterfrom the Dongjiang River.SPMD can be used to estimate the potential for accumulation ofUV filters; its results represent a valid basis for risk assessment.Significant formation of 11 TPs was recognized during photo-catalysis of Et-PABA. Seven were firstly proposed as TPs whiletwo others were newly identified. To our knowledge, Et-PABAphotocatalysis and the identification of its TPs are reported forthe first time here.With regard to Et-PABA photocatalysis, toxicity as revealed by theMicrotox assay showed a decreasing trend. Thus, photocatalysismay be a satisfactory remedial means to remove Et-PABA fromdrinking water sources.

cknowledgements

We thank the Science, Technology and Innovation Commis-ion of Shenzhen (JCYJ20150630164505506) for the financialupport. Kelvin S.–Y. Leung also thanks the grants from the inter-nstitutional Collaborative Research Scheme (RC-ICRS/14-15/02)nd Faculty of Science (FRG2/15-16/069), Partner State Key Lab-ratory of Environmental and Biological Analysis (SKLP 1617 P03),ong Kong Baptist University. Z. −Y. Sang, J.C.-F. Law and C.-H.how gratefully acknowledge their receipt of postgraduate stu-entships from the University Grants Committee.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.jhazmat.2017.04.67.

aterials 337 (2017) 115–125

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