Chlorination of bisphenol S: Kinetics, products, and effect of humic acid

Accepted Manuscript Chlorination of bisphenol S: Kinetics, products, and effect of humic acid Yuan Gao, Jin Jiang, Yang Zhou, Su-Yan Pang, Jun Ma, Chengchun Jiang, Yue Yang, Zhuang-song Huang, Jia Gu, Qin Guo, Jie-Bin Duan, Juan Li PII:

S0043-1354(17)31044-8

DOI:

10.1016/j.watres.2017.12.049

Reference:

WR 13447

To appear in:

Water Research

Received Date: 9 September 2017 Revised Date:

18 December 2017

Accepted Date: 19 December 2017

Please cite this article as: Gao, Y., Jiang, J., Zhou, Y., Pang, S.-Y., Ma, J., Jiang, C., Yang, Y., Huang, Z.-s., Gu, J., Guo, Q., Duan, J.-B., Li, J., Chlorination of bisphenol S: Kinetics, products, and effect of humic acid, Water Research (2018), doi: 10.1016/j.watres.2017.12.049. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1

Chlorination of Bisphenol S: Kinetics, Products, and

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Effect of Humic Acid

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Yuan Gaoa, Jin Jianga,*, Yang Zhoua, Su-Yan Pangb,*, Jun Maa, Chengchun Jiangc,

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Yue Yangd, Zhuang-song Huanga, Jia Gua, Qin Guod, Jie-Bin Duand, and Juan Lia

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a

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Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin

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150090, China

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State Key Laboratory of Urban Water Resource and Environment, School of

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School of Municipal and Environmental Engineering, Jilin Jianzhu University,

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Changchun 130118, China

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c

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518055, China

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d

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and Technology, Harbin 150040, China

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*Corresponding Author: Prof. Jin Jiang, E-mail: [email protected];

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*Corresponding Author: Prof. Su-Yan Pang, E-mail: [email protected]

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College of Chemical and Environmental Engineering, Harbin University of Science

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School of Civil and Environmental Engineering, Shenzhen Polytechnic, Shenzhen

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Abstract

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Bisphenol S (BPS), as a main alternative of bisphenol A for the production of

20

industrial and consumer products, is now frequently detected in aquatic environments.

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In this work, it was found that free chlorine could effectively degrade BPS over a

22

wide pH range from 5-10 with apparent second-order rate constants of 7.6-435.3

23

M−1s−1.

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mono/di/tri/tetrachloro-BPS), 4-hydroxybenzenesulfonic acid (BSA), chlorinated

25

BSA (mono/dichloro-BSA), 4-chlorophenol (4CP), and two polymeric products were

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detected

27

ionization-tandem quadrupole time-of-flight mass spectrometry. Two parallel

28

transformation pathways were tentatively proposed: (i) BPS was attacked by stepwise

29

chlorine electrophilic substitution with the formation of chlorinated BPS. (ii) BPS was

30

oxidized by chlorine via electron transfer leading to the formation of BSA, 4CP and

31

polymeric products. Humic acid (HA) significantly suppressed the degradation rates

32

of BPS even taking chlorine consumption into account, while negligibly affected the

33

products species. The inhibitory effect of HA was reasonably explained by a

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two-channel kinetic model. It was proposed that HA negligibly influenced pathway i

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while appreciably inhibited the degradation of BPS through pathway ii, where HA

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reversed BPS phenoxyl radical (formed via pathway ii) back to parent BPS.

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Keywords: Bisphenol S; Chlorine; Humic acid; Electrophilic substitution; Electron

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transfer

total

of

eleven

products

including

chlorinated

BPS

(i.e.,

high

performance

liquid

chromatography

and

electrospray

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1. Introduction

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Due to the widespread occurrence of bisphenol A (BPA) and its adverse effect on

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both human and ecosystem health, organizations such as the United States

42

Environmental Protection Agency (USEPA) and the European Food Safety Authority

43

(EFSA) established a limit to BPA (Barroso 2011, Staples et al. 1998, Vandenberg et

44

al. 2007). In response to these restrictions and public pressure, bisphenol S (BPS;

45

4,4’-sulfonyldiphenol) is gradually used in replacement of BPA. BPS is commonly

46

used in epoxy glues, canned coatings, foodstuffs, and paper products (Naderi et al.

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2014). Therefore, the occurrence of BPS in the aquatic environments has been

48

documented in recent years (Liao et al. 2012, van Leerdam et al. 2014, Yamazaki et

49

al. 2015, Yang et al. 2014). For instance, Yamazaki et al. (2015) reported the

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occurrence of BPS as high as 6840 ng/L in surface water and seawater of Japan,

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China, Korea and India. Liao et al. (2012) reported that BPS was present in the

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sediment of United States, Japan, and Korea up to the concentration of 1970 ng/g dry

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weight. Unfortunately, several studies have reported that BPS has similar estrogenic

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activity and appears to be more resistant to environmental degradation as compared to

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BPA (Danzl et al. 2009, Hashimoto et al. 2001, Rochester and Bolden 2015).

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Chlorine is a globally most used chemical for water disinfection. In addition, it

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has been well documented that chlorine can react with a wide range of organic

58

contaminants especially phenolic compounds (Deborde et al. 2004, Deborde and Von

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Gunten 2008, Dodd et al. 2005, Dodd and Huang 2007, Gallard and von Gunten

60

2002a, b, Gallard et al. 2004, Gao et al. 2016, Rebenne et al. 1996). For instance, 3

ACCEPTED MANUSCRIPT Gallard et al. (2004) reported that BPA could be appreciably degraded by chlorine

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with a second-order rate constant of 58 M-1 s-1 at pH 7.0 (at 20 oC), where

63

chlorinated-BPA was generated via stepwise electrophilic substitution. In a very

64

recent work, we found that chlorine could rapidly oxidize tetrabromobisphenol A

65

(TBrBPA) via electron transfer with a second-order rate constant of 1360 M−1 s−1 at

66

pH 7.0 (at 25 oC), where oxidative product 2,6-dibromo-4-hydroxycumyl alcohol was

67

predominantly generated (Gao et al. 2016, Lin et al. 2009a, Yang et al. 2014).

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However, the reactions of chlorine with BPS, structurally similar to BPA and

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TBrBPA (see Table S1 for their chemical structures), have not been characterized so

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far.

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Dissolved organic matter (DOM), ubiquitously existing in diverse aquatic

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environments, may exert important impacts on the transformation of contaminants in

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natural environments and engineered processes. As a competitor for oxidant, DOM

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can suppress the degradation of contaminants in numerous chemical oxidation

75

processes (Fang et al. 2014, Gallard et al. 2004, Li et al. 2017, Lu et al. 2015, Luo et

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al. 2016, Sharma et al. 2015). Another inhibitory effect of DOM has been reported to

77

take place in excited triplet states, permanganate, ferrate or enzymatic catalysis

78

oxidation (Canonica and Laubscher 2008, Feng et al. 2013, Gao et al. 2016, Leresche

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et al. 2016, Lu et al. 2015, Vione et al. 2017, Wenk et al. 2011, Wenk et al. 2015),

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where DOM can reduce the reactive intermediates formed via one electron-transfer

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back to parent contaminants. Interestingly, in our recent work, this inhibitory effect of

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DOM was also observed in chlorination of TBrBPA while not in chlorination of BPA

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(Gao et al. 2016). The contrasting effects might be related to the distinct pathways

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involved in chlorination of BPA vs TBrBPA (i.e., electrophilic substitution for BPA

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vs electron transfer for TBrBPA) (Gao et al. 2016). In this work, the transformation kinetics and products of BPS by chlorine as well

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as the effect of HA were investigated for the first time. Firstly, reaction kinetics were

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studied in synthetic buffered waters over pH range of 5-10. Secondly, transformation

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products of BPS by chlorine were identified by a high performance liquid

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chromatography and electrospray ionization-tandem quadrupole time-of-flight mass

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spectrometry (HPLC/ESI-QTOF-MS), and the tentative pathways were proposed.

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Finally, the effects of HA on the transformation of BPS by chlorine were investigated.

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2. Experimental Section

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2.1. Materials.

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BPS,

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2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid diammonium (ABTS) were

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purchased from Sigma-Aldrich. Sodium hypochlorite and sodium thiosulfate were

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purchased from Sinopharm Chemical Reagent Co. Ltd., China. All reagents used were

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of 97% purity or higher without further purification unless otherwise stated. Solutions

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were prepared in deionized water (18.2 MΩcm) from a Milli-pore system. The stock

101

solutions of chlorine were prepared by diluting a commercial solution of sodium

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hypochlorite (NaClO, 4% active chlorine) and standardized by iodometry. The stock

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solutions of HA were purified by repeated pH adjustment, filtration and precipitation

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acid

(HA;

surrogate

of

DOM),

2-methoxyphenol,

and

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following the procedure described in our previous work and its concentration was

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measured in mgC/L (Gao et al. 2016, Rebhun et al. 1998).

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2.2. Experimental procedure. Kinetic studies were performed in 50 mL conical flasks under constant stirring at

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25(±2) oC. Reactions were initiated by adding chlorine in excess (10-400 µM) into

109

pH-buffered solutions (10 mM phosphate buffer for pH 5-10) containing BPS (1 µM)

110

with/without HA (0.5-2 mgC/L). At a specific time interval, two parallel samples

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were withdrawn, and one was quenched by thiosulfate to measure residual BPS and

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the other was quenched by ABTS to measure residual chlorine (Pinkernell et al. 2000,

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Song et al. 2015). The changes of solution pH were negligible (< 0.1) during the

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kinetic runs. All the kinetic experiments were performed in triplicates and average

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data were presented. The relative standard deviations were always <10% unless

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otherwise stated.

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For products identification, a series of pH-buffered (pH 7) solutions containing

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BPS (at a relatively high concentration of 10 µM) with/without HA (0.5-5 mg C/L)

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were prepared and treated by chlorine at various doses (5-50 µM). The resulting

120

solutions were analyzed by HPLC/ESI–QTOF-MS. In addition, the evolution profiles

121

of identified products during the kinetic runs were monitored by HPLC and ESI-triple

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quadrupole mass spectrometry (HPLC/ESI−QqQ-MS) at multiple reaction monitoring

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(MRM) mode.

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2.3. Analytical Methods.

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ACCEPTED MANUSCRIPT BPS was determined using a Waters 1525 HPLC equipped with a Waters symmetry

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C18 column (4.6×150 mm, 5µm particle size), a Waters 717 autosampler, and a

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Waters 2487 dual λ detector. The mobile phase consisted of 0.1% acetic acid and

128

methanol with a ratio of 50:50 (v/v) at a flow rate of 1 mL/min. The wavelength was

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set at 260 nm.

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An ABSciex Triple TOF X500 coupled with an AB Sciex Exion LC was used for

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HPLC/ESI–QTOF-MS analysis. An ABSciex QTrap 5500 MS combined with an

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Agilent 1260 HPLC was used for HPLC/ESI-QqQ-MS analysis. HPLC separation

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was performed on a Waters XBridge C18 column (3.0 × 100 mm, 2.5 µm particle

134

size). The gradient mobile phase consisted of acetonitrile/deionized water containing

135

0.1% formic acid (A/B) at a flow rate of 0.4 mL/min, which linearly increased from

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5% A to 95% A in the first 20 min and kept for 10 min, then went back to 5% A for

137

15 min for re-equilibration. The MS instrumental parameters were listed as follows:

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source temperature, 500

139

arbitrary units; gas I, 50 arbitrary, gas II, 55 arbitrary units; declustering potential

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(DP), -40 ∼ -120 V; collision energy (CE), -10 ∼-50 V; scan range (m/z), 100−800.

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C; negative ion spray voltage, -4500V; curtain gas, 35

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o

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The DOC content of HA stock solution was determined using Analytikjena Multi

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N/C 3100. UV–vis absorbance was measured by a Varian Cary 300 spectrometer.

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Solution pH was measured with Leici PHS–3C pH-meter (Shanghai INESA Scientific

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Instrument Co.Ltd). The concentration of chloride was measured by using a Dionex

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ICS 3000 on an AS19-HC column.

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3. Results and Discussion 7

ACCEPTED MANUSCRIPT 3.1. Reaction Kinetics

148

The time course profiles of BPS loss in the presence of excess chlorine exhibited

149

pseudo first-order kinetics over the pH range of 5-10 (see SI Figure S1a for example).

150

Moreover, the measured pseudo first-order rate constants showed a linear correlation

151

with varying chlorine concentrations (see SI Figure S1b for example). Therefore, the

152

reactions of chlorine with BPS were first-order with respect to each reactant. The

153

apparent second-order rate constants (kapp) could be accordingly determined and

154

shown in Figure 1. As can be seen, kapp exhibited a strong pH dependency. In other

155

word, kapp substantially increased from 7.6(±0.2) to 435.3(±13.1) M-1s-1 with pH

156

increasing from 5 to 8 and then decreased to 11.9(±0.4) M-1s-1 as pH further increased

157

to 10 (SI Table S2). Similar bell-shaped pH-rate profiles were also observed in

158

previous studies on the reactions of chlorine and phenolics (e.g., phenol, BPA,

159

TBrBPA, triclosan, and 4-n-nonylphenol), which were reasonably explained by the

160

combined effects of chlorine speciation and phenolic speciation as a function of pH

161

(Deborde et al. 2004, Deborde and Von Gunten 2008, Gallard and von Gunten 2002a,

162

b, Gallard et al. 2004, Lee and Von Gunten 2012, Mackie et al. 2017, Rebenne et al.

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1996). The dissociation of phenolics (pKa1,BPS=7.42, pKa2,BPS=8.03, eqs 1-2) can result

164

in the increase of kapp as the dissociating forms exhibit stronger reactivity towards

165

chlorine (Choi and Lee 2017). The dissociation of HOCl to OCl- (pKa,HOCl = 7.54, eq 3)

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can lead to the decrease of kapp due to the much lower reactivity of OCl- as compared

167

to HOCl (i.e., the contribution of OCl- was considered to be negligible)

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a1 ¾® BPS ¬¾¾¾ BPS- +H+ (1)

K

8

ACCEPTED MANUSCRIPT 2+ BPS- ¬¾¾¾® ¾ BPS +H (2) Ka2

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K

a Cl ® H + +OClHOCl ¬¾ ¾¾¾ ¾

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(3)

Recently, Lau et al. (2016) reported that Cl2 and ClO2 might take participate in

172

chlorination of phenolics (e.g., phenol and 2,4-dichloropheonol) in acid solutions (pH

173

< 6) containing high concentrations of chloride (>1mM). In addition, the involvement

174

of Cl2 and ClO2 species could result in the reaction order with respect to HOCl

175

approaching to 2. Considering the relatively low chloride concentration introduced by

176

chlorine stock solution into reaction solutions, it seemed likely that Cl2 and ClO2

177

negligibly contributed to the overall reaction. Moreover, the first-reaction-order

178

relative to HOCl in chlorination of BPS (SI Figure S1b) further precluded the

179

involvement of Cl2 and ClO2 species. Therefore, the following reactions (eqs 4-6)

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were initially proposed to explain the pH-rate profile in chlorination of BPS.

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BPS+HOCl → product k1

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BPS- +HOCl → product k2

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k3

(6)

The apparent second-order rate constant could be expressed as follows:

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(5)

BPS2- +HOCl → product

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(4)

k app =

+

3

3

2

k1  H +  + k 2 K a 1  H +  + k 3  H +  K a1 K a2 +

2

+

 H  + ( K a1 + K aCl )  H  + ( K a1 K aCl + K a1 K a2 )  H  + K a1 K a2 K aCl

(7)

The species-specific second-order rate constants were calculated according to

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nonlinear least-squares regressions. The fit between experimental data and eq 7 was

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satisfactory (Figure 1), further validating the assumption that HOCl was the primary

189

oxidant. The values of k1, k2, and k3 were calculated to be 25(± 8) M-1 s-1, (1.5 ± 0.6) ×

190

102 M-1 s-1, and (4.0 ± 0.14) × 103 M-1 s-1, respectively. A similar difference in 9

ACCEPTED MANUSCRIPT species-specific second-order rate constants (i.e., k3 >k2 >k1 ) was also observed in

192

chlorination of BPA (Gallard et al. 2004). These findings could be attributed to the

193

much higher activating effect of hydroxyl groups after their deprotonation (i.e., the

194

dissociated forms exhibited higher reactivity towards HOCl) (Deborde et al. 2004,

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Gallard et al. 2004, Gao et al. 2016).

196

3.2. Quantitative Structure–Activity Relationship

197

In previous work, Lee and Von Gunten (2012) established a quantitative

198

structure–activity relationship (QSAR) for the species-specific rate constants of HOCl

199

and phenolate ions (e.g., dissociated forms of chlorophenols, bromophenols, triclosan,

∑σ

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−

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and 4-n-nonylphenol), where

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among Hammett σ constants (i.e., σ, σ+, and σ-) (eq 8).

was the best substituent descriptor variable

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o ,m , p

log k H O C l = 4.46 ( ± 0.15 ) − 4.90 ( ± 0.44 ) ∑ σ

− o ,m , p

(8)

The phenolics used to obtain the QSAR (eq 8) almost all undergo chlorine

204

electrophilic substitution, as demonstrated in many studies on chlorinated products of

205

these phenolic compounds (Deborde and Von Gunten 2008, Hu et al. 2002, Lee and

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Morris 1962, Rule et al. 2005). Due to the complex structure of BPS, the Hammett

207

constants for BPS substituents were unavailable in literature. So, a structural

208

approximation was used to estimate the Hammett substituent constants (SI Table S1).

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This is based on the principle that the inductive/resonance effects of atoms in

210

substituents are weakened with increasing distance of the atoms from a reaction center.

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In previous work, this structural approximation has been well applied to estimate the

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ACCEPTED MANUSCRIPT Hammett σ constants for structurally complex compounds (e.g., BPA and

213

17a-ethinylestradiol) and their rate constants could be predicted from the developed

214

QSARs by using the estimated Hammett constants (Lee and Von Gunten 2012). In the

215

case of BPA, the substituent of 4-C(CH3)2-C6H4OH was approximated to be

216

4-C(CH3)2-CH3 and thus the structure of BPA was approximated to be

217

4-isopropylphenol (Lee and Von Gunten 2012). Similar to the case of BPA, the

218

structure of BPS was approximated to be 4-(methylsulfonyl)phenol (SI Table S1).

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Accordingly, the species-specific rate constants of fully-dissociated BPA and BPS

220

could be predicted by eq 8 from their Hammett σ- constants (-0.13 for BPA and 1.13

221

for BPS) (Lee and Von Gunten 2012). Lee and von Gunten (2012) reported that the

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species-specific rate constant of fully-dissociated BPA could be also well predicted by

223

the QSAR (eq 8). This was consistent with two independent studies, where BPA was

224

transformed by chlorine via electrophilic substitution pathway as confirmed by the

225

formation of chlorinated BPA (Gallard et al. 2004, Hu et al. 2002). However,

226

according to eq 8, the value of k3 for BPS was predicted to be in the range of

227

0.019-0.37 M-1 s-1, at least four orders of magnitude lower than the experimental one

228

(4.0 ± 0.14) × 103 M-1 s-1. A similar result was also obtained in a recent study on

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chlorination of TBrBPA, and the underestimation was explained by that TBrBPA was

230

transformed by chlorine via electron transfer rather than electrophilic substitution as

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confirmed by product analysis (Gao et al. 2016). So, it seemed likely that oxidative

232

pathway might be also involved in chlorination of BPS leading to the underestimation

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ACCEPTED MANUSCRIPT of k3 by the QSAR (eq 8), possibly due to the withdrawing effect of sulfur in BPS

234

structure (see the following section).

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3.3. Identification of Transformation Products

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Figure 2 showed the HPLC/ESI-QTOF-MS chromatogram of a sample containing

237

BPS treated by chlorine at pH 7. As can be seen, six new peaks appeared as compared

238

to the control one. Product I eluting at 19.31 min had a molecular ion of 282.983. On

239

the basis of its accurate mass and isotopic pattern (SI Figure S2), the molecular

240

formula of product I was assigned as C12H8SO4Cl (i.e., [C12H9SO4Cl-H]-). It was

241

further proposed to be mono-chloro BPS in accordance with its major fragments ions

242

of 18 (H2O), 36 (HCl), 126 (C6H3ClO) and 157(C6H5SO3) (SI Figure S3). Products II

243

and III eluting at 20.46 and 20.71 min had the same molecular ion of 316.944,

244

indicating they were structural isomers. Their molecular ions displayed isotopic

245

patterns identical to the molecular formula of C12H7SO4Cl2 (i.e., [C12H8SO4Cl2-H]-)

246

(SI Figure S4). The fragment ions of product II in the product ion spectra apparently

247

included m/z 36 (HCl), 157 (C6H5SO3,) 160 (C6H2Cl2O) (SI Figure S5). So, product II

248

was supposed to be 2,6-dichloro-BPS. Product III was suggested to be

249

2,6’-dichloro-BPS in accordance with its fragment ions of 36 (HCl), 126 (C6H3ClO),

250

and 191 (C6H4SO3Cl) (SI Figure S6). Product IV at 21.12 min had a molecular ion of

251

126.996 corresponding to molecular formula of C6H4OCl (i.e., [C6H5OCl-H]-) (SI

252

Figure S7). It was further assigned to be 4-chlorophenol (4CP) according to its

253

fragment ions of 36 (HCl) and 91 (C6H3O), which was confirmed by its analytical

254

standard (SI Figure S8). Product V at 21.80 min had a molecular ion of 350.905,

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ACCEPTED MANUSCRIPT corresponding to molecular formula of C12H6SO4Cl3 (i.e., [C12H7SO4Cl3-H]-) (SI

256

Figure S9). It was further supposed to be trichloro-BPS on the basis of fragment ions

257

of 36 (HCl), 126(C6H3ClO), 160 (C6H2Cl2O), and 191 (C6H4SO3Cl) (SI Figure S10).

258

Product VI eluting at 23.05 min had a molecular ion of 384.866, exhibiting isotopic

259

patterns identical to the molecular formula of C12H5SO4Cl4 (i.e., [C12H6SO4Cl4-H]-)

260

(SI Figure S11). It was further assigned to be tetrachloro-BPS in accordance with its

261

fragment ions of 36 (HCl), 160 (C6H2Cl2O), and 225 (C6H2SO3Cl) (SI Figure S12).

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It should be noted that not all transformation products could be detected as

263

chromatographic peak by visual inspection against the baseline of the chromatogram

264

because of their different abundances and response values (Baena-Nogueras et al.

265

2017, Gulde et al. 2016). Therefore, the Analytics software (AB Sciex) was further

266

applied to pick up possible products through suspect analysis on the basis of accurate

267

mass measurement, specific fragments, as well as comparison of theoretical and

268

measured isotopic patterns. As a consequence, additional five products (VII-XI) were

269

identified. Products VII and VIII were isomeric dimers of BPS. Product IX was

270

assigned to be 4-hydroxybenzenesulfonic acid (BSA), which was further confirmed

271

by its analytical standards. Products X and XI were proposed to be mono- and

272

dichloro-BSA, respectively. In order to confirm this, transformation products of BSA

273

treated by chlorine were detected and the chromatogram was shown in SI Figure S13,

274

where products X and XI were obvious. In summary, a total of eleven products were

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identified in chlorination of BPS and their detailed information including retention

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277

in Table 1.

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3.4. Proposed Reaction Pathways

279

On the basis of identified products, transformation pathways for chlorination of BPS

280

were tentatively proposed as shown in Figure 3. BPS was initially attacked by

281

chlorine substitution with the formation of monochloro-BPS (product I), which

282

subsequently underwent stepwise substitution reactions leading to the generation of

283

di/tri/tetrachloro-BPS (products II, III, V, and VI). Similar chlorine electrophilic

284

substitution was also reported in chlorination of BPA (Gallard et al. 2004). This

285

transformation pathway (pathway i) is consistent with the fact that electrophilic

286

substitution is a main chlorination pathway for aromatic rings (Deborde and Von

287

Gunten 2008, Gallard et al. 2004, Lee and Morris 1962). In addition, an oxidative

288

pathway (pathway ii) was proposed to account for the formation of 4CP (product VI),

289

dimers (prdocuts VII and VIII) and BSA (product IX): the phenol moiety of BPS was

290

initially oxidized by chlorine with the formation of a phenoxy radical R1. Then radical

291

R1 coupled to each other with the formation of dimers (products VII and VIII), or

292

cleavaged to release R2 radical and R3 cation. Subsequently, R2 radical was further

293

transformed to 4CP (product IV). R3 intermediate underwent substitution reactions to

294

generate BSA (product IX), which might be further attacked by chlorine substitution

295

with the generation of chlorinated BSA (product X and XI). Similar transformation

296

pathway ii was also reported in TBrBPA oxidation by chlorine (Gao et al. 2016).

297

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EP

TE D

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276

Kuruto-Niwa

et

al.

(2005)

reported 14

that

chlorinated

BPS

(i.e.,

ACCEPTED MANUSCRIPT mono/di/tri/tetrachloro-BPS) showed a substantially lower estrogenic activity

299

compared to BPS using a green fluorescent protein expression system, in contrast to

300

the findings that chlorinated BPA exhibited higher estrogenic activity compared to

301

parent BPA. In addition, the estrogenic activity of 4-CP was found to be very low as

302

reported by Nishihara et al. (2000). By testing the estrogenic activity of more than 500

303

chemicals, Nishihara et al. (2000) concluded that the estrogen activity of substituent

304

phenolics was positively related to their hydrophobic moiety at the para-position. So,

305

several oxidative products of BPS by chlorine (e.g., BSA and its chlorinated

306

derivatives) are expected to show an appreciably low estrogenic activity due to

307

hydrophilicity of sulfonic group. Therefore, it seems likely that chlorine treatment

308

may also eliminate estrogenic activity induced by BPS, which warrants further

309

verification by laboratory tests.

310

3.5. Effect of HA on Chlorination of BPS

311

3.5.1. Effect of HA on Reaction Kinetics.

312

Kinetic experiments were conducted to assess the effect of HA (0.5-2mgC/L) during

313

chlorination (30 µM) of BPS (1 µM) at an environmentally relevant pH 7. Figure 4

314

exhibited the time course profiles of BPS degradation and chlorine loss, respectively.

315

As can be seen, the presence of HA appreciably suppressed the degradation of BPS.

316

With the concentration of HA increasing from 0 to 2 mg C/L, the extent of BPS loss

317

greatly decreased from 86% to 46% at 15 minute. HA could competitively consume

318

oxidant thus leading to the decrease of degradation rates (Gallard et al. 2004, Yang et

AC C

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298

15

ACCEPTED MANUSCRIPT 319

al. 2014). In order to account for this effect, eq 9 was introduced to quantify the

320

kinetics Ct

321

C0

=exp{ -k

t 0

HOCl dt }

(9)

where Ct was the concentration of BPS at a specific time t, C0 was the initial

323

concentration of BPS, and

324

over time (i.e., chlorine exposure). It was found that the predictions made according to

325

eq 9 considerably overestimated the level of BPS loss in the presence of HA (SI

326

Figure 14). In addition, the transformation rate constants (k) at different

327

concentrations of HA could be obtained by eq 9. As shown in Figure 5, the rate

328

constants (k) decreased with the increase of HA concentration. Similar inhibition was

329

also observed in chlorination of TBrBPA, which was reasonably explained by the fact

330

that TBrBPA phenoxyl radicals formed by one-electron chlorine oxidation were

331

competitively reduced back to its parent by HA. Interestingly, it was also found that

332

HA had negligible influence on the degradation of BPA by chlorine, where the

333

reaction proceeded via chlorine electrophilic substitution (Gao et al. 2016).

334

Considering the two-channel pathways involved in chlorination of BPS, we

335

tentatively proposed that HA inhibited the degradation of BPS by chlorine via

336

electron transfer (pathway ii), similar to the case of TBrBPA. In parallel, HA had

337

negligible effect on the depletion of BPS transformed via electrophile substitution

338

(pathway i), similar to the case of BPA.

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322

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HOCl dt was the chlorine concentration integrated

339

A two-channel kinetic model was accordingly introduced to further characterize the

340

effect of HA. Contaminants (P) was transformed by chlorine with the formation of 16

ACCEPTED MANUSCRIPT intermediate P1 (via electron transfer) with a yield r and P2 (via electrophilic

342

substitution) with a yield (1-r) (eq 10). P1 would be competitively reduced by HA to

343

its original form P (eq 11), in addition to its further irreversibly transformation (eq

344

12).

RI PT

341

P+chlorine → rP1 +(1-r)P2 (10) k4

345

P1 +HA → P (11) k5

P1 → Products k6

347

(12)

SC

346

The reactions 10 and 11 were both second-order to reactants, where k4 represented the

349

rate constants in the absence of HA (eq 10), and k5 was the rate constants for the

350

reaction of intermediate P1 with HA (eq 11). k6 was the first-order rate constant for eq

351

12. Therefore, kinetic equations 13 and 14 could be obtained to describe the

352

degradation rate for P and the formation rate for P1, respectively. dP dt

356 357

358

(13)

=rk4 P chlorine -k6 P1 -k5 P1 HA

(14)

By making a steady-state assumption for [P1], eq 15 could be obtained:

EP

355

d P1 dt

dP

AC C

354

=k4 P chlorine -k5 P1 HA

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353

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348

dt

=k4 1-r+ k

rk6 5

P chlorine

HA +k6

(15)

Therefore, the rate constant in the presence of HA could be described as eq 16 kHA =k4 1-r+ k

rk6 5

HA +k6

= k4 1-r+ k5 k6

r HA +1

(16)

359

As can be seen in Figure 5, the two-channel kinetic model (eq 16) could fit the

360

experimental data well. The values of r and k5/k6 was estimated to 0.64(±0.02) and

361

1.66(±0.18), respectively. These results indicated that the contribution of electron

17

ACCEPTED MANUSCRIPT 362

transfer and electrophilic substitution pathway to BPS degradation was around 64%

363

and 36%, respectively.

364

3.5.2. Effect of HA on Products Formation. (i) products analysis. The effect of HA on the products formation during

366

chlorination of BPS was also investigated. No additional products were detected in the

367

presence of HA compared to the case in the absence of HA (data not shown). This

368

finding was similar to the scenario of chlorination of TBrBPA, where HA had

369

negligible impact on the products species either (Gao et al. 2016). The influence of

370

HA on products formation during oxidation processes (e.g., permanganate, ferrate,

371

and enzymatic catalysis) was also investigated in previous work but confounding

372

effects were reported (Gao et al. 2016, Li et al. 2017, Lu et al. 2015, Lu and Huang

373

2009, Lu et al. 2017). For instance, Li et al. (2017) reported that HA negligibly

374

influenced the products species in soybean-catalyzed oxidation of triclosan. On the

375

contrary, Feng et al. (2013) reported that HA affected the products species in

376

laccase-catalyzed oxidation of TBrBPA, where additional new products with large

377

molecular ions were detected in the presence of HA. It seemed likely that the effect of

378

HA on the products species was complex, which might be associated with the nature

379

of HA and the experimental conditions.

SC

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TE D

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AC C

380

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365

Due to the complexity of HA molecular structure, model compounds with defined

381

structures were used to further explore the effect of HA. In previous work,

382

2-methoxyphenol was commonly used to mimic HA (Li et al. 2017, Lu and Huang

383

2009, Lu et al. 2017). For instance, Lu and Huang (2009) reported that the presence of 18

ACCEPTED MANUSCRIPT 2-methoxyphenol in laccase-catalysis oxidation of acetaminophen led to the formation

385

of a new product, resulting from the coupling of 2-methoxyphenol and

386

acetamionphenol phenoxy radicals. Similarly, cross-coupling products were also

387

detected in soybean peroxidase-catalysis oxidation of triclosan. In this work, a new

388

product with a molecular ion of 371.059 was detected when 2-methoxyphenol was

389

present during chlorination of BPS. This new product was likely generated from cross

390

coupling of BPS and 2-methoxyphenol phenoxy radicals (SI Figure 15). This finding

391

in turn confirmed the occurrence of oxidative pathway during chlorination of BPS.

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384

Interestingly, several studies reported that co-solvent methanol could affect the

393

product species during BPA or TBrBPA oxidation (e.g., by permanganate, ferrate,

394

manganese dioxide or enzymatic catalysis oxidation), which was also verified in this

395

work (SI Table S3) (Feng et al. 2013, Gao et al. 2016, Yang et al. 2014). Carbocation

396

intermediates of 4-isopropylphenol or 2,6-dibromo-4-isopropylphenol formed during

397

BPA or TBrBPA oxidation, underwent substitution reactions with methanol (other

398

than

399

2,6-dibromo-hydroxy-isopropyl methanol (SI Table S3). Similarly, a new product

400

with a molecular ion of 187.007 was detected in chlorination of BPS when methanol

401

was present. This new product was suggested

402

benzenesulfonate (SI Figure 16), which was derived from the substitution reaction of

403

methanol and R3 intermediate. This finding confirmed again the occurrence of

404

oxidative pathway during chlorination of BPS.

TE D

392

to

generate

4-hydroxy-isopropyl

AC C

EP

water)

19

methanol

or

to be 4-hydroxy-methyl

ACCEPTED MANUSCRIPT (ii) products evolution. The time course profiles of transformation products of BPS

406

by chlorine in the absence vs presence of HA were comparatively monitored by the

407

HPLC/ESI-QqQ-MS at MRM mode (Figure 6). In the absence of HA, the

408

consecutive formation of chlorinated BPS (generated through chlorine electrophilic

409

substitution pathway) was followed by their decay as a function of time, where

410

mono/di/tri/tetrachloro-BPS reached their maxima at about 5, 8, 15, and 35 min,

411

respectively. As the reaction proceeded, tetrachloro-BPS became the only chlorinated

412

BPS congeners. 4CP (generated via electron transfer pathway) was gradually

413

accumulated within 15 min and then declined. The maximum yield of 4CP was

414

quantified by the authentic standard to be about ~2% with respect to BPS loss.

415

Unfortunately, the response values of BSA and polymeric products (also generated

416

via electron transfer pathway) were too low and thus the formation dynamics of BSA

417

and its chlorinated products as well as the two dimers were not followed.

TE D

M AN U

SC

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405

In the presence of HA, the formation of monochloro-BPS was also followed by its

419

decay along with the reaction time but the occurrence of its maxima was prolonged to

420

about 25 min. Dichloro-BPS and trichloro-BPS were gradually generated and then

421

reached plateaus, while tetrachloro-BPS was negligibly generated. In particular, the

422

maximum yield of monochloro-BPS was calculated to be ~0.53 by using peak areas

423

(i.e., dividing its peak area by the decreased peak area of BPS) due to the lack of

424

authentic standard, which was higher than that obtained in the absence of HA (~0.40).

425

Along with reaction time, 4CP slowly accumulated to a plateau and its maximum

426

yield was calculated to be about ~1.1%, lower than that obtained in the absence of HA

AC C

EP

418

20

ACCEPTED MANUSCRIPT (~2%). These findings that HA increased the yield of monochloro-BPS and decreased

428

the yield of 4CP were in consistent with the conclusion deduced from the two-channel

429

model, where BPS was transformed by two parallel pathways and HA could inhibit

430

the degradation of BPS via electron transfer pathway.

431

4. Conclusion

432

This work firstly investigated the transformation of BPS by chlorine including

433

kinetics, products, mechanism, and the effect of HA. The following conclusions were

434

obtained, which might improve the understanding of chlorine chemistry in water

435

treatment:

M AN U

SC

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427

Chlorine could effectively degrade BPS over a wide pH range from 5-10 with the

437

apparent second-order rate constants of 7.6-435.3 M−1s−1.With a typical chlorine

438

residual concentration of 2 mg/L, the half life time of BPS was calculated to be

439

around 0.94-3.2 min at pH 7-8.

440

Eleven products including chlorinated BPS (i.e., mono/di/tri/tetrachloro-BPS),

441

4CP, BSA, chlorinated BSA (i.e., mono/dichloro-BSA) and two dimers were

442

detected by HPLC/ESI–QTOF-MS. It was proposed that BPS was transformed by

444 445

EP

AC C

443

TE D

436

chorine via two parallel pathways including chlorine electrophile substitution and electron transfer pathways. The inhibitory effect of HA on BPS degradation was reasonably explained by a

446

two-channel kinetic model, where HA negligibly influenced electrophile

447

substitution while appreciably inhibited the degradation of BPS through electron

448

transfer via reversing BPS phenoxyl radical back to parent BPS. 21

ACCEPTED MANUSCRIPT HA had negligible impact on the product species in chlorination of BPS.

450

However, in the presence of 2-methoxyphenol, a new additional product was

451

generated via cross coupling of BPS and 2-methoxyphenol phenoxy radicals. In

452

the case of co-solvent methanol, 4-hydroxy-methyl benzenesulfonate derived

453

from the substitution reaction of methanol and an intermediate was generated.

RI PT

449

Acknowledgments

455

This work was supported by the National Natural Science Foundation of China

456

(51578203); the Funds of the State Key Laboratory of Urban Water Resource and

457

Environment (HIT, 2016DX13); and the Foundation for the Author of National

458

Excellent Doctoral Dissertation of China (201346).

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459

22

ACCEPTED MANUSCRIPT 460

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461

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Canonica, S. and Laubscher, H. (2008) Inhibitory effect of dissolved organic matter on triplet-induced Choi, Y.J. and Lee, L.S. (2017) Partitioning Behavior of Bisphenol Alternatives BPS and BPAF Compared to BPA. Environmental Science & Technology 51(7), 3725-3732.

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electrospray tandem mass spectrometry. Journal of Chromatography A 1328, 26-34.

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591 592 593 594 595 596 597 598 599 600 601 602 603 604

26

ACCEPTED MANUSCRIPT

Table1. Products of BPS transformed by chlorine Found at mass

Formular

BPS

17.77

249.0224

C12H10SO4

20.71

316.9444

C12H9SO4Cl

C12H8SO4Cl2

316.9445

C12H8SO4Cl2

21.12

AC C

IV

126.9957

Proposed structural

-1.2

O S O

HO

-0.9

O S

OH

O

-1.0

Cl 2

HO

3

1

4

6

5

O S O

3'

2'

4'

1'

5'

OH

6'

Cl

-0.8

Cl 2

HO

1.0

3

1

4

6

C6H5OCl

OH

Cl HO

EP

III

20.46

282.9835

M AN U

II

19.31

TE D

I

Mass Error(ppm)

RI PT

Retention time

SC

Product number

HO

5

O S O

3'

2'

4'

1'

5'

6'

Cl

Cl

OH

ACCEPTED MANUSCRIPT

VII

18.76

20.08

497.0363

SC

384.8666

C12H7SO4Cl3

C12H6SO4Cl4

C24H18S2O4

497.0366

C24H18S2O8

-0.7

Cl

Cl O S O

HO

7.81

AC C

IX

172.9915

OH Cl

-0.5

Cl

Cl O HO

S O

OH

Cl

-1.4

Cl

O S O

HO

OH HO

O S

OH

O

-0.8

O S O

HO

EP

VIII

23.05

350.9055

M AN U

VI

21.80

TE D

V

RI PT

Table1(continuted)

OH O

O S O

OH

C6H6SO8

0.5

O HO S O

OH

ACCEPTED MANUSCRIPT

Table1(continuted)

-0.6

RI PT

SC

C6H4SO4Cl2

M AN U

240.9131

C6H5SO4Cl

TE D

16.46

206.9523

EP

XI

13.60

AC C

X

-1.4

O HO S O O HO S O

Cl OH

Cl OH Cl

ACCEPTED MANUSCRIPT

500

RI PT

300

-1 -1

kapp(M s )

400

SC

200

0 5

6

M AN U

100

7

8

9

10

pH

Figure 1. pH dependency of apparent second-order rate constants for the reactions of

AC C

EP

the model fit by eq 7.

TE D

chlorine with BPS. Symbols represent measured data and the dashed line represents

ACCEPTED MANUSCRIPT

RI PT

BPS

2

SC

1

6

M AN U

5

﹡

﹡

﹡

TE D

3 4

Figure 2. The HPLC/ESI–QTOF-MS chromatogram of a sample containing BPS treated by chlorine. Asterisks represent the impurities.

AC C

EP

Experimental condition: [BPS] = 10 µM, [chlorine] = 30 µM, and pH 7.

ACCEPTED MANUSCRIPT

Cl O S O

OH

RI PT

HO Cl

II

Cl

chlorine

OH

HO

Cl

I

O HO

S O

OH

Cl

Cl OH

O S O

HO

Cl

OH

Cl

Cl

VI

V

Cl

OH

III

O

BPS

chlorine HO

O S

HO

O

O

R1

EP

HO

H2O

S O

HO

O S O

O S O

O

O S OH O

HO

R3

HO

Cl

IV

R2

O

Electron transfer

TE D

HO

AC C

HO

O S

Cl

O S O

SC

HO

Cl

M AN U

Electrophilic substitution

O S O

HO

O S OCH3 O

HO

O S O

self-coupling

O

HO

VII

or

OH O S O

Cl

O HO S O

OH

X

IX CH3OH

Cl

O HO S O

OH Cl

XI

HO

OH

O S O

O

O S O

OH

VIII

OH

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Figure 3. The proposed pathway for the reaction of chlorine with BPS.

[chlorine]t/[chlorine]0

0.8 0.6

HA=0mgC/L HA=0.5mgC/L HA=1mgC/L HA=2mgC/L

0.2 0.0

0

5

0.8 0.6

0.2 0.0

10

Time(min)

15

(b)

0.4

M AN U

0.4

TE D

[BPS]t/[BPS]0

1.0

(a)

SC

1.0

RI PT

ACCEPTED MANUSCRIPT

0

HA=0mgC/L HA=0.5mgC/L HA=1mgC/L HA=2mgC/L

5

10

15

Time(min)

AC C

1 µM, [chlorine] = 30 µM, and pH 7.

EP

Figure 4. The time course profiles of BPS degradation (a) and chlorine loss (b) at different HA concentrations. Experimental condition: [BPS]=

RI PT

ACCEPTED MANUSCRIPT

SC M AN U

90

-1

k(M s-1)

120

30 0.0

TE D

60

0.5

1.0

2

R =0.99

1.5

2.0

EP

HA (mgC/L)

AC C

Figure 5. HA concentration dependency of measured second-order rate constants for the reaction of chlorine (30 µM) with BPS (1 µM) at pH 7. Symbols represent measured data and the dashed line represents the model fit by eq 16.

0

0 0

25

50

75

100

3

1

0

0

25

-2

SC

2

20000

TE D

Time (min)

product I product II product III product IV product V

concentration (×10 µΜ)

1 20000

40000

M AN U

40000

60000

-2

2

80000

Area

Area

60000

(b)

3

concentration (×10 µΜ)

product I product II product III product IV product V product VI

(a)

80000

RI PT

ACCEPTED MANUSCRIPT

0 50

75

100

Time (min)

Figure 6. The evolution profiles of identified products of BPS by the treatment of chlorine in the absence (a) and presence of HA (b).

AC C

EP

Experimental condition: [BPS]= 1 µM, [chlorine] = 30 µM, [HA] = 2 mgC/L, and pH 7

ACCEPTED MANUSCRIPT Highlights: BPS could be effectively degraded by chlorine over pH of 5-10 (kapp 7.6-435.3 M−1s−1) A total of eleven products were detected by HPLC/ESI-QTOF-MS

RI PT

Two parallel pathways (electrophilic substitution & electron transfer) were proposed Inhibitory effect of HA on degradation was explained by a two-channel kinetic model

AC C

EP

TE D

M AN U

SC

HA had negligible effect on product species in chlorination of BPS