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Occurrence and Stability of Chlorophenylacetonitriles, a New Class of Nitrogenous Aromatic DBPs, in Chlorinated and Chloraminated Drinking Waters Di Zhang, Wenhai Chu, Yun Yu, Stuart W. Krasner, Yang Pan, Jun Shi, Daqiang Yin, and Naiyun Gao Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.8b00220 • Publication Date (Web): 24 May 2018 Downloaded from http://pubs.acs.org on May 24, 2018

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Environmental Science & Technology Letters

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Occurrence and Stability of Chlorophenylacetonitriles, a New Class of

2

Nitrogenous Aromatic DBPs, in Chlorinated and Chloraminated Drinking

3

Waters

4

Di Zhang†, Wenhai Chu†, ‡*, Yun Yu§, Stuart W. Krasner∥, Yang Pan⊥, Jun Shi†, Daqiang

5 6 7

Yin†, Naiyun Gao† †

State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and

Engineering, Tongji University, Shanghai, 200092, China

8 9 10

‡

11 12 13

∥La

14

* Corresponding author.

15

Address: College of Environmental Science and Engineering, Tongji University, Room 308

16

Mingjing Building, 1239 Siping Road, Yangpu District, Shanghai, 200092, China

17

Tel.: +86 021 65982691; Fax: +86 021 65986313

18

E-mail address: [email protected]; [email protected]

§

Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, P.R. China Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder,

Boulder CO, 80303, United States Verne, California 91750, United States

⊥State

Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing

University, Nanjing 210023, Jiangsu, China

1

ACS Paragon Plus Environment


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Abstract

20

2-Chlorophenylacetonitrile (2-CPAN) and 3,4-dichlorophenylacetonitrile (3,4-DCPAN),

21

representatives of a new class of nitrogenous aromatic disinfection byproducts, were first

22

identified and quantified in chlorinated and chloraminated drinking waters. The impacts of

23

pH,

24

chlorophenylacetonitriles (CPANs) were investigated. The two CPANs slightly degraded

25

with increasing pH (5-9) and chlorination doses (0-4 mg/L) after 5 days, and NH2Cl didn’t

26

cause degradation of CPANs. Among the commonly used quenching agents, the reaction

27

between sodium sulfite and CPANs was negligible, whereas the others reduced CPANs

28

by varying extents after 7 days. Notably, the two CPANs in finished water collected from

29

seven drinking water treatment plants were quantified. 2-CPAN was detected between

30

170 ng/L and 530 ng/L with a median concentration of 220 ng/L, whereas 3,4-DCPAN

31

ranged from below method detection limit (100 ng/L) up to 320 ng/L with a median

32

concentration of 130 ng/L. Moreover, cytotoxicity of the CPANs and their aliphatic

33

counterparts was determined using Chinese hamster ovary cells. The LC50 values are 133

34

µM, 83 µM, 436 µM, 260 µM, 905 µM, 4150 µM, 8900 µM for 2-CPAN, 3,4-DCPAN,

35

chloroacetonitrile, dichloroacetonitrile, chloroacetic acid, dichloroacetic acids and

36

trichloromethane, respectively. Due to the relatively high stability and high toxic potencies

37

of CPANs, the occurrence of CPANs in drinking water deserves attention.

disinfectant

residuals,

and

quenching

agents

2


on

the

stability

of

two

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Introduction

39

Disinfection of drinking water reduces microbiological risk by inactivating pathogens but

40

unintentionally increases chemical risk due to the formation of disinfection byproducts

41

(DBPs).(1) Epidemiological studies demonstrated low but significant associations

42

between chlorinated drinking water and adverse health effects including bladder cancer(2)

43

and adverse reproductive outcomes via dermal exposure as well as respiratory and

44

digestive tracts.(3, 4) Up to now, more than 600 DBPs have been identified in either

45

chlorinated or chloraminated drinking waters, (5, 6) whereas only nine of them (i.e., 4

46

trihalomethanes (THMs) and 5 haloacetic acids(HAAs)) are currently regulated by the US

47

EPA.(7) It is widely acknowledged that those regulated species are not the drivers of

48

toxicity. Accordingly, there is great interest in identifying emerging DBPs or classes of

49

DBPs that can be potential forcing agents with respect to higher cyto- and genotoxic

50

potencies. For this reason, considerable attention has been paid to the nitrogenous DBPs

51

in recent years, (8-13) including N-nitrosamines, cyanogen halides, haloacetonitriles

52

(HANs), haloacetamides (HAMs),(14) and halonitromethanes.(15) Another class of

53

emerging DBPs of increasing concern are the aromatic ones. For instance,

54

halobenzoquinones, (16, 17) dihalo-4-hydroxybenzaldehydes, dihalo-4-hydroxybenzoic

55

acids, dihalo-salicylic acids and trihalo-phenols were successively identified in disinfected

56

waters.(18, 19) More importantly, these newly identified halogenated aromatics have been

57

demonstrated to be more toxic than those aliphatic DBPs based on the marine polychaete

58

Platynereis dumerilii bioassay.(20) In the meanwhile, dihalonitrophenols, including

59

dibromonitrophenol (21), and diiodo-4-nitrophenol (22-24) were identified in simulated tap

3



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water as an emerging group of DBPs with both nitrogenous and aromatic properties. It is

61

likely that these halogenated nitrogenous aromatic compounds may present significantly

62

higher toxic potency than either the nitrogenous or the aromatic analogs, and thus

63

becoming one of the driving forces to the toxicity of disinfected water.

64

In this study, we report the identification and quantification of a new class of nitrogenous

65

aromatic DBPs, chlorophenylacetonitriles (CPANs), in real finished water collected from

66

seven drinking water treatment plants (DWTPs). One of the objectives of this study was to

67

develop an analytical method for the quantification of CPANs in drinking waters, by

68

optimizing sample pH and the selection of quenching agent to prevent CPAN degradation

69

during sample storage. Another key objective of this study was to evaluate the impacts of

70

pH and different disinfectant types on the stability of CPANs to examine the potential

71

association between CPAN occurrence and different disinfection scenarios (i.e.,

72

chlorination vs. chloramination). Lastly, the mammalian cell chronic cytotoxicity of CPANs

73

was determined using Chinese hamster ovary (CHO) cells (25) and was compared to that

74

of their aliphatic analogs (i.e., chloroacetonitrile [MCAN] and dichloroacetonitrile [DCAN])

75

as well as to that of the regulated trichloromethane (TCM), chloroacetic acid (MCAA), and

76

dichloroacetic acid (DCAA) to understand their potential hazards to public health.

77

Materials and Methods

78

Chemicals and Materials.

79

2-CPAN

80

2,6-dichlorophenylacetonitrile (2,6-DCPAN, 98%) standards (Table S1) and methyl

81

tert-butyl ether (MtBE) were purchased from Aladdin Industrial Inc. (Shanghai, China).

(98%),

3,4-DCPAN

(98%),

4-chlorophenylacetonitrile

4


(4-CPAN,98%),

Page 5 of 19


82

2,3-dichlorophenylacetonitrile (2,3-DCPAN,98%) was obtained from TCI Industrial Inl.

83

(Shanghai, China). 2,4-dichlorophenylacetonitrile (2,4-DCPAN, 98%) standard was

84

supplied by Macklin (Shanghai, China). All other chemicals were obtained from

85

Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and were of analytical grade

86

unless otherwise noted.

87

Finished Water Samples.

88

Finished waters were collected from seven surface DWTPs. Treatment processes applied

89

at each plant and major characteristics of each water including pH, DOC, NH4+-N,

90

disinfectant doses, and disinfectant contact times are listed in Table S2. Upon collection,

91

residual disinfectant was measured using a portable photometer (HACH Pocket

92

Colorimeter™ II, USA) and was quenched with 120% of the stoichiometric amount of

93

sodium sulfite (10 mg/L) and sample pH was adjusted to 7 using phosphate buffer.

94

Samples were analyzed for CPANs within 24 hours after quenching. Other details

95

regarding sample collection and water quality characterization are available in the SI.

96

Bench-scale CPAN Stability Tests.

97

Firstly, the impact of pH on the stability of CPANs was investigated in phosphate buffered

98

solutions (10 mM) at pH 5, 6, 7, 8 and 9. The initial concentration of individual CPAN was

99

100 µg/L. At prescribed reaction times, samples were extracted immediately for residual

100

CPANs without the addition of any preservatives. Secondly, the stability of CPANs was

101

further evaluated at pH 7 in the presence of different types of disinfectants. Chlorination of

102

CPANs was conducted by adding sodium hypochlorite (NaOCl) stock solution into

103

buffered CPAN solutions (initial CPAN concentration was 100 µg/L) at doses of 1, 2, and 4 5



104

mg/L as Cl2. Chloramination was carried out by adding preformed monochloramine

105

(NH2Cl) to CPAN solutions at doses of 1, 2, 4 and 8 mg/L as Cl2. NH2Cl was prepared by

106

slowly adding NaOCl into an ammonium chloride solution at Cl:N molar ratio of 1:1.2, and

107

pH of both solutions was adjusted to 8.5 before mixing. The actual concentrations of

108

NaOCl and NH2Cl stock solutions were standardized using a portable photometer (HACH

109

Pocket Colorimeter™ II, USA). After dosing with Cl2 or NH2Cl, samples were stored

110

without headspace in 500 mL bottles in dark at 25.0 ± 0.5 °C. Aliquots of sample were

111

taken at prescribed reaction times and were analyzed right away for residual disinfectant

112

as well as CPAN concentrations. Finally, the impact of quenching agents on the loss of

113

CPANs over sample holding time was investigated. Five commonly used quenching

114

agents (200 µM), including sodium sulfite (Na2SO3), sodium thiosulfate (Na2S2O3),

115

ascorbic acid, ammonium chloride (NH4Cl), and sodium arsenite (NaAsO2) were

116

individually added to a CPAN solution (0.6 µM of either 2-CPAN or 3,4-DCPAN) at pH 7

117

and CPAN concentrations were quantified after 7 days. In the meanwhile, the control

118

experiment was performed also at pH 7 without the presence of any quenching agents.

119

Analytical Methods.

120

The identification and quantification of CPANs were conducted using a high-sensitivity gas

121

chromatography-mass spectrometer (GC-MS) (Shimadzu-QP2020, Japan) in electron

122

ionization (EI) mode. The identity of each CPAN was confirmed using reference standard

123

based on both retention time and parent as well as daughter ions. The method detection

124

limits (MDLs) were 100 ng/L for both 2-CPAN and 3,4-DCPAN. Detailed information

125

regarding the quantification of CPANs is provided in the SI. 6


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126

CHO Cell Chronic Cytotoxicity Determinations.

127

The cytotoxicity of CPANs and the corresponding HANs (i.e., MCAN and DCAN), HAAs

128

(i.e., MCAA and DCAA) and TCM were determined. The CHO-K1 cell line was purchased

129

from ATCC (CCL-61). The CHO cell cytotoxicity assay quantitatively measures the

130

reduction in cell density as a function of DBP concentration after 72-hour incubation.

131

Cytotoxicity of each DBP was determined according to published instructions.(25)

132

Dose-response curves were fitted via nonlinear least-squares regression and LC50 values

133

(the concentration of each toxicant that induced a 50% reduction in the density of CHO

134

cells compared to the negative control) were inferred.(25) Details of the CHO cell

135

cytotoxicity analysis are referred to the SI.

136

Results and Discussion

137

Identification and Confirmation of CPANs.

138

The detection of CPANs in chlorinated and chloraminated finished waters by liquid-liquid

139

extraction/GC-MS technique was the starting point of this investigation. When finished

140

water collected from DWTP 1 was first screened by GC-MS in scan mode, two of the

141

unknown peaks (Figure 1a) were suspected to belong to organic halogens because of

142

their typical mass spectra that were affected by chlorine isotopes (Figure S1). More

143

importantly, neither of the two unknown peaks was observed in the source water from the

144

same DWTP (Figure 1b). Then more finished water samples from different treatment

145

plants were collected and unknowns A and B were found to be generally present in those

146

samples (Figure S2). This indicated that these two unknowns were being formed as a

147

result of drinking water disinfection. Through a quick search of the National Institute of 7



Page 8 of 19

148

Standards and Technology (NIST) library, unknowns A and B were tentatively identified as

149

chlorophenylacetonitrile

150

well-matched mass spectra shown in Figure S1. Since chlorophenylacetonitrile has three

151

constitutional isomers and dichlorophenylacetonitrile has six, it is important to clarify which

152

of the two isomers were responsible for peaks A and B in Figure 1a. Among the six

153

commercially available CPAN standards, including 2-CPAN, 4-CPAN, 2,3-DCPAN,

154

2,4-DCPAN, 2,6-DCPAN and 3,4-DCPAN, 2-CPAN and 3,4-DCPAN matched unknowns A

155

and B, respectively in both retention times (Figure 1c) and mass spectra (Figure S1). To

156

further confirm these two CPANs, 2-CPAN and 3,4-DCPAN standard solutions were

157

spiked into the finished water sample from DWTP 1 at concentration of 10 µg/L and the

158

responses of unknowns A and B were amplified (Figure 1d). For these reasons, unknowns

159

A and B were identified and verified as 2-CPAN and 3,4-DCPAN, respectively. It needs to

160

note that the other CPAN isomers (i.e., 4-CPAN, 2,3-DCPAN, 2,4-DCPAN, 2,6-DCPAN)

161

were not detected in any of the finished water samples either due to their low level of

162

occurrence that the method was not sensitive enough to capture, or to their absence as

163

drinking water disinfection products.

164 165 166 167

[Figure 1. GC chromatograms of finished (a) and source water (b) from drinking water treatment

168

The Impact of pH on the Stability of 2-CPAN and 3,4-DCPAN.

169

Aside from the identification of 2-CPAN and 3,4-DCPAN as a new class of DBPs in

170

disinfected drinking waters, the understanding of their stability under relevant treatment

171

conditions is also of great importance. The hydrolysis of 2-CPAN and 3,4-DCPAN was first

and

dichlorophenylacetonitrile,

respectively

based

on

plant 1(DWTP 1); 2-CPAN, 4-CPAN, 2,3-DCPAN, 2,4-DCPAN, 2,6-DCPAN and 3,4-DCPAN standard compounds (c); finished water from DWTP 1 spiked with 10 µg/L 2-CPAN and 3,4-DCPAN (d).]

8


Page 9 of 19


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investigated at pH 5-9 and residual CPAN concentrations were monitored over time as

173

shown in Figure 2. Both 2-CPAN and 3,4-DCPAN were stable at pH 5, 6 and 7 with less

174

than 15% degradation after 5 days of incubation. In general, the hydrolysis rates of both

175

2-CPAN and 3,4-DCPAN slightly increased with increasing pH and were the highest at pH

176

9, resulting in approximately 25% decrease in concentration after 5 days (Figure 2). Also

177

compared in Figure 2 is the hydrolysis of their corresponding aliphatic nitriles, MCAN and

178

DCAN, under the same pH conditions. Both monochloronitriles were stable across the

179

wide pH range (i.e., pH 5-9). At any given pH, 2-CPAN didn’t show significantly higher or

180

lower stability than MCAN (Figure 2a). Note, MCAN was rarely detected in drinking water

181

with 50th percentile value of 0 µg/L and maximum value of 0.9 µg/L. This compares to 1.0

182

µg/L 50th percentile value and maximum value of 12 µg/L for DCAN.(1) The real

183

comparison between CPANs and HANs should be based on DCAN, which is the most

184

predominant species of HANs. Compared to 3,4-DCPAN, DCAN was more susceptible to

185

hydrolysis especially under slightly alkaline conditions (i.e., pH 8 and 9, Figure 2b).(26,

186

27). The higher stability of CPANs compared to their aliphatic counterparts (i.e., DCAN)

187

can be probably explained by a higher electron density on their nitrile carbon due to the

188

presence of the benzene ring, which inhibits the hydrolysis reaction at the nitrile

189

group.(28-31)

190 191 192 193 194 195 196

[Figure 2. The stability of CPANs. Figure 2a and 2b present the hydrolysis of 2-CPAN (a) and 3,4-DCPAN (b) at pH 5, 6, 7, 8 and 9. Figure 2c and 2d present the stability of 2-CPAN (c) and 3, 4-DCPAN (d) in the presence of Cl2 at pH 7. Initial 2-CPAN and 3,4-DCPAN concentrations were both 100 µg/L. Initial Cl2 doses were 0, 1, 2, 4 mg/L as Cl2. The hydrolysis of MCAN (Figure 2a) and DCAN (Figure 2b) at different pHs, and the chlorination rates of MCAN (Figure 2c) and DCAN (Figure 2d) at pH 7 with different Cl2 doses, were calculated according to Yu & Reckhow, 2015. (27). The error bars in all the figures represent the relative standard deviation of three replicates.]

9



197

Stability of CPANs in the presence of Residual Disinfectants.

198

For drinking water distribution, it is important that a disinfectant residual is maintained in

199

the network in order to prevent microbial regrowth. DBPs may continue to form or

200

simultaneously degrade depending on which reaction (i.e., formation vs. degradation)

201

becomes more predominant in the presence of disinfectant residuals. Therefore, it is

202

pivotal to examine if there’s any reaction between CPANs and Cl2 or NH2Cl that may

203

impact their occurrence in distribution systems. For this reason, the stability of both

204

2-CPAN and 3,4-DCPAN was assessed at pH 7 with varying doses (1, 2, and 4 mg/L as

205

Cl2) of Cl2 (Figure 2) and preformed NH2Cl (Figure S3), respectively. Neither 2-CPAN

206

(Figure 2c) nor 3,4-DCPAN (Figure 2d) underwent significant degradation at pH 7 in the

207

presence of Cl2 up to 4 mg/L as Cl2. However, the degradation of both CPANs exhibited

208

certain dependence on chlorine dose. Both CPAN degradation rates slightly increased

209

with increasing chlorine dose, even though no appreciable amount of difference was

210

observed between samples that were chlorinated and the control (i.e., without the dose of

211

chlorine). NH2Cl didn’t cause additional degradation of both 2-CPAN and 3,4-DCPAN

212

other than CPAN hydrolysis up to an initial NH2Cl dose of 8 mg/L as Cl2. 2-CPAN was

213

slightly less stable than MCAN (Figure 2c). Only for water with long residence time and

214

high chlorine dose, the difference in their stability will be significant. As shown in Figure 2d,

215

compared to the aliphatic DCAN, 3,4-CPAN is relatively more stable in the presence of

216

either Cl2 or NH2Cl.

10


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Occurrence of CPANs in Finished Drinking Water.

218

Occurrence of 2-CPAN and 3,4-DCPAN was determined in real finished waters collected

219

from seven surface DWTPs. Prior to sample analysis, pH was optimized, and quenching

220

agent was carefully selected to prevent CPAN loss during sample holding before analysis.

221

As is suggested by CPAN hydrolysis experiment, CPANs were relatively stable under

222

ambient pH (i.e., pH 7) up to 5 days. Therefore, sample pH was adjusted to 7 upon

223

collection. More importantly, the effects of five commonly used quenching agents (i.e.,

224

sodium sulfite, sodium thiosulfate, ascorbic acid, ammonium chloride, and sodium

225

arsenite) on CPAN stability at pH 7 was investigated (Figure S4). Sodium sulfite was

226

found to be the most suitable for CPAN analysis, which didn’t result in significant

227

degradation of either 2-CPAN or 3,4-DCPAN (< 5%) compared to the control. In contrast,

228

ascorbic acid caused the concentrations of 2-CPAN to decrease by 90% after 7 days. As

229

shown in Figure S5, 2-CPAN was detected in all seven finished water samples and its

230

concentration ranged from 170 ng/L to 530 ng/L, with a median concentration of 220 ng/L.

231

On the other hand, 3,4-DCPAN was detected in five of the seven plant effluents and its

232

concentration ranged from 100 ng/L to 320 ng/L, with a median of 130 ng/L. In all seven

233

samples, 2-CPAN concentration was always higher than that of 3,4-DCPAN. Moreover,

234

both CPANs occurred consistently at higher levels in chlorinated than in chloraminated

235

finished waters (Figure S5). This indicates that CPANs is more likely to be produced

236

during chlorination than during chloramination with a median concentration of 230 ng/L for

237

2-CPAN and 170 ng/L for 3,4-DCPAN during chlorination, and a median concentration of

238

190 ng/L for 2-CPAN and below detection limit (100 ng/L) for 3,4-DCPAN during 11



239

chloramination. This is probably because chlorine is more likely than chloramine to react

240

with potential aromatic precursors to form CPANs due to its stronger electrophilic

241

substitution ability.(32)

242

CHO Cell Cytotoxicity of CPANs.

243

The cytotoxicity of 2-CPAN, 3,4-DCPAN and the corresponding HANs, HAAs and TCM

244

were determined using CHO cell assay (Figure 3, Table S3). The LC50 values for 2-CPAN,

245

3,4-DCPAN, MCAN, DCAN, MCAA, DCAA and TCM were 148 µM, 83 µM, 436 µM, 260

246

µM, 905 µM, 415 µM, 8900 µM, respectively (Table S3). It is obvious in Figure 3 that the

247

cytotoxicity of these tested compounds is in the following hierarchy: 3,4-DCPAN >

248

2-CPAN > DCAN > MCAN > MCAA > DCAA > TCM. The cytotoxicity follows a decreasing

249

order from DCAN to MCAN, MCAA, DCAA, and eventually to TCM, which is consistent

250

with what was indicated by a previous study.(25) However, there were offsets in the

251

absolute LC50 values between this and the previous study (25) due to the use of different

252

strains. CHO cell line AS52, clone 11-4-8 was used in the previous study and CHO K1 cell

253

line (ATCC, CCL-61) was used in this study. The two aromatic nitriles were approximately

254

one order of magnitude more toxic compared to their aliphatic counterparts (i.e., MCAN

255

and DCAN) and about two orders of magnitude more potent than the regulated MCAA and

256

DCAA. TCM is the least cytotoxic and is 60 and 108 times less toxic than 2-CPAN and

257

3,4-DCPAN, respectively.

258 259

[Figure 3. CHO cell cytotoxicity analysis of 2-CPAN, 3,4-DCPAN, MCAN, DCAN, MCAA, DCAA, and

260

Implications.

261

2-CPANs and 3,4-DCPAN, representatives of a new class of nitrogenous aromatic

TCM.]

12


Page 12 of 19

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262

DBPs, were quantified in finished water at ng/L levels in both chlorinated and

263

chloraminated systems. However, compared to DCAN, CPANs were much more stable

264

under the same pH conditions, both with and without the presence of Cl2 or NH2Cl.

265

Perhaps most importantly, CPANs are more cytotoxic than the corresponding HANs and

266

HAAs. CPANs are therefore of high risks due to their high stability, as well as higher

267

toxicity.

268

Supporting Information

269

Further information on materials, sample preparation, and toxicity assays are available

270

free of charge via the Internet at http://pubs.acs.org.

271

Acknowledgements

272

This work was supported by the National Natural Science Foundation of China (NO.

273

51578389; 51778445), the National Major Science and Technology Project of China (NO.

274

2015ZX07406004-3, 2017ZX07201005), the Shanghai City Youth Science and

275

Technology Star Project (NO. 17QA1404400), and State Key Laboratory of Pollution

276

Control and Resource Reuse Foundation (NO. PCRRE16009) and Fundamental

277

Research Funds for the Central Universities. We also sincerely thank Michael J. Plewa

278

(University of Illinois at Urbana-Champaign) for helpful suggestions on toxicity evaluation

279

and Paul Westerhoff (Arizona State University) for helpful communications on N-DBPs.

280 281

The authors declare no competing financial interest.

282 283 284 285 286 287 288 289 290 291

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Figure 1. GC chromatograms of finished (a) and source water (b) from drinking water treatment plant 1(DWTP 1); 2-CPAN, 4-CPAN, 2,3-DCPAN, 2,4-DCPAN, 2,6-DCPAN and 3,4-DCPAN standard compounds (c); finished water from DWTP 1 spiked with 10 µg/L 2-CPAN and 3,4-DCPAN (d). 220x190mm (150 x 150 DPI)



Figure 2.The stability of CPANs. Figure 2a and 2b present the hydrolysis of 2-CPAN (a) and 3,4-DCPAN (b) at pH 5, 6, 7, 8 and 9. Figure 2c and 2d present the stability of 2-CPAN (c) and 3, 4-DCPAN (d) in the presence of Cl2 at pH 7. Initial 2-CPAN and 3,4-DCPAN concentrations were both 100 µg/L. Initial Cl2 doses were 0, 1, 2, 4 mg/L as Cl2. The hydrolysis of MCAN (Figure 2a) and DCAN (Figure 2b) at different pHs, and the chlorination rates of MCAN (Figure 2c) and DCAN (Figure 2d) at pH 7 with different Cl2 doses, were calculated according to Yu & Reckhow, 2015. (27). The error bars in all the figures represent the relative standard deviation of three replicates. 284x215mm (300 x 300 DPI)


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Figure 3. CHO cell cytotoxicity analysis of 2-CPAN, 3,4-DCPAN, MCAN, DCAN, MCAA, DCAA, and TCM. 235x188mm (300 x 300 DPI)


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