Development of Fluorescence Surrogates to ... - ACS Publications

Feb 15, 2017 - Development of Fluorescence Surrogates to Predict the. Photochemical Transformation of Pharmaceuticals in Wastewater. Effluents. Shuwen...
0 downloads 0 Views 806KB Size
Subscriber access provided by University of Newcastle, Australia

Article

Development of Fluorescence Surrogates to Predict the Photochemical Transformation of Pharmaceuticals in Wastewater Effluents Shuwen Yan, Bo Yao, Lushi Lian, Xinchen Lu, Shane A. Snyder, Rui Li, and Weihua Song Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05251 • Publication Date (Web): 15 Feb 2017 Downloaded from http://pubs.acs.org on February 15, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

Environmental Science & Technology

1 2 3 4

Development of Fluorescence Surrogates to Predict the Photochemical

5

Transformation of Pharmaceuticals in Wastewater Effluents

6

Shuwen Yan1, Bo Yao1, Lushi Lian1, Xinchen Lu1, Shane A. Snyder2, Rui Li1, and Weihua Song1,*

7 8 9

1

Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R.

10

China

11

2

12

USA

Department of Chemical & Environmental Engineering, University of Arizona, Tucson, AZ 85721,

13 14 15 16

Resubmitted to Environ. Sci. & Technol.

17 18 19 20

*Corresponding author; email: [email protected]; Tel: (+86)-21-6564-2040

21 22 1

ACS Paragon Plus Environment

Environmental Science & Technology

23

Abstract

24

The photochemical transformation of pharmaceutical and personal care products (PPCPs) in

25

wastewater effluents is an emerging concern for environmental scientists. In the current study, the

26

photodegradation of 29 PPCPs was examined in effluents under simulated solar irradiation. Direct

27

photodegradation, triplet state effluent organic matter (3EfOM*)-mediated and hydroxyl radical

28

(HO•)-mediated degradation are three major pathways in the removal process. With the

29

photodegradation of trace levels of PPCPs, the excitation-emission matrix (EEM) fluorescence

30

intensities of the effluents were also gradually reduced. Therefore, fluorescence peaks have been

31

identified, for the first time, as appropriate surrogates to assess the photodegradation of PPCPs. The

32

humic-like fluorescence peak is linked to direct photolysis-labile PPCPs, such as naproxen,

33

ronidazole, diclofenac, ornidazole, tinidazole, chloramphenicol, flumequine, ciprofloxacin,

34

methadone, and dimetridazole. The tyrosine-like EEM peak is associated with HO•/CO3•--labile

35

PPCPs, such as trimethoprim, ibuprofen, gemfibrozil, atenolol, carbamazepine, and cephalexin. The

36

tryptophan-like peak is associated with 3EfOM*-labile PPCPs, such as clenbuterol, metoprolol,

37

venlafaxine, bisphenol A, propranolol, ractopamine, salbutamol, roxithromycin, clarithromycin,

38

azithromycin, famotidine, terbutaline, and erythromycin. The reduction in EEM fluorescence

39

correlates well with the removal of PPCPs, allowing a model to be constructed. The solar-driven

40

removal of EEM fluorescence was applied to predict the attenuation of 11 PPCPs in five field

41

samples. A close correlation between the predicted results and the experimental results suggests that

42

fluorescence may be a suitable surrogate for monitoring the solar-driven photodegradation of PPCPs

43

in effluents.

44 45 46 47 2

ACS Paragon Plus Environment

Page 2 of 30

Page 3 of 30

48

Environmental Science & Technology

Introduction

49

Pharmaceuticals and personal care products (PPCPs) are a group of emerging contaminants

50

and have drawn considerable attention from environmental scientists and engineers. PPCPs are

51

primarily discharged into surface water from municipal wastewater treatment plants due to their

52

incomplete elimination by existing biological treatment processes.1-3 Consequently these

53

wastewater-derived recalcitrant micropollutants have been increasingly detected in aquatic

54

environments all over the world. The concentrations of PPCPs were reported in the range of ng L-1 to

55

µg L-1 in surface water,4, 5 which poses largely unknown long-term risks to the ecological system.

56

This fact has initiated an enormous scientific effort to understand the transformation and fate of

57

PPCPs in surface water.

58

Phototransformation driven by sunlight is one of the most important natural processes for the

59

attenuation of PPCPs in surface water.6 In general, this process includes direct and indirect

60

photodegradation.7 Direct photodegradation requires overlap between the absorption spectra of

61

PPCPs and the solar irradiation wavelengths, and as a consequence of that light absorption, PPCPs

62

undergo transformation. Indirect photodegradation is associated with triplet states of organic matter

63

(3OM*)8 and a series of reactive oxygen species (ROS), such as singlet oxygen (1O2), hydroxyl

64

radicals (HO•), superoxide anions (O2•-), carbonate radicals (CO3•-), and halogen radicals.9-15 These

65

ROS and 3OM* are capable of oxidizing a wide variety of pollutants present in wastewater effluents

66

and also facilitate the decomposition of organic matter.16-20 However, modeling the photochemical

67

transformation of PPCPs in effluent dominated waters is challenging for several reasons: 1)

68

Photodegradation involves complicated processes that are chemical structure dependent and involve

69

a variety of ROS. The complete modeling of these processes is daunting work. 2) The analysis of

70

trace amounts of PPCPs is labor intensive, time consuming, and requires costly analytic

71

instrumentation. 3) With new PPCPs constantly introduced into the market, the PPCPs of interest

72

change with time. 3

ACS Paragon Plus Environment

Environmental Science & Technology

73

The development of indicators and surrogates may be a useful approach to resolving the

74

aforementioned challenges. Numerous trace indicator compounds, including caffeine, nicotine, and

75

metformin, have been successfully used to indicate the influence of wastewater on receiving water

76

bodies.21,

77

indicator tailored to monitor the removal efficiency of trace amounts of organic contaminates (TrOCs)

78

during advanced oxidation processes (AOPs).23 Dilantin, DEET, meprobamate, and iopromide were

79

proposed as four potential indicators to assess the optimized oxidation conditions in the ozonation of

80

tertiary-treated wastewaters.24 Nevertheless, costly tandem mass spectrometry is required for

81

monitoring the trace amounts of indicator compounds, limiting the applicability of this technique.

82

Furthermore, spectroscopic parameters, including true color,25 ultraviolet absorption (UVA)24 and

83

fluorescence,26-29 were employed as surrogates to assess the elimination of PPCPs during the

84

traditional and advanced wastewater treatments. Our previous study also noted that the decrease in

85

protein-like fluorescence is well correlated with the removal of PPCPs from reverse osmosis (RO)

86

retentate via HO• oxidation.30 Spectroscopic surrogates, which are much easier to measure than

87

indicator compounds, may provide a rapid and inexpensive online method for the quantitative

88

estimation of the removal of PPCPs.

22

For advanced treatments, Lester et al. recently applied sucralose as a conservative

89

While most of the aforementioned outcomes are initiated by ozonation and AOPs, there is an

90

opportunity to apply spectroscopic surrogates to evaluate the attenuation of PPCPs in effluents under

91

solar irradiation. Both O3/AOPs and photodegradation involve ROS as key intermediates,

92

encouraging the investigation of spectroscopic surrogates for the phototransformation of PPCPs. In

93

this study, fluorescence surrogates elevated from effluent organic matter (EfOM) have been carefully

94

evaluated because they are more sensitive and specific than UVA surrogates. EfOM and PPCPs are

95

co-discharged into surface water and exposed under solar irradiation. In general, EfOM contain

96

residual natural organic matter (NOM) from the drinking water supply and soluble microbial

97

products (SMPs) contributed from biological treatment.31 As a result, the excitation-emission matrix 4

ACS Paragon Plus Environment

Page 4 of 30

Page 5 of 30

Environmental Science & Technology

98

(EEM) fluorescence of EfOM can be characterized as containing humic-like, tyrosine-like and

99

tryptophan-like peaks. Fluorescent humic acids, tyrosine and tryptophan can undergo

100

photo-transformations involving both direct and indirect photodegradation. The latter is driven by

101

3

102

EfOM and the attenuation of PPCPs may provide an alternative for the rapid monitoring of the

103

transformation of PPCPs in surface water. To the best of our knowledge, we report herein the first

104

study focused on the development of fluorescence surrogates to predict the photochemical

105

transformation of pharmaceuticals in wastewater effluents.

OM*, HO•, and 1O2 et al.32-35 The correlation between the decrease of fluorescent surrogates of

106

To test this approach, 29 PPCPs were chosen as target contaminates because they have been

107

widely detected in wastewater effluents and contain a variety of photochemical properties.36 We

108

investigated four pathways composed of direct photodegradation and indirect photodegradation

109

reactions with 3OM*, HO•/CO3•-, and 1O2. UVA and fluorescence spectroscopy were applied to

110

examine EfOM photo-transformations. Correlations between the removal of PPCPs and the changes

111

in wastewater optical properties were examined in detail.

112

Experimental Section

113

Chemicals. Deuterium oxide (D2O, 99.9%), furfuryl alcohol (FFA, 99%), terephthalic acid

114

(TA), isopropanol (IPA), and isoproturon (IPU) were purchased from Sigma-Aldrich and used as

115

received. 2-Hydroxyl terephthalic acid (HOTA) was synthesized using a method reported in the

116

literature.37 All PPCPs were purchased from Sigma-Aldrich or TCI Chemicals at the highest

117

available purity. The isotopic labeled compounds used as internal standards were purchased from

118

Toronto Research Chemicals. The list of PPCPs and isotopic compounds can be found in Table S1 in

119

the supporting information (SI). All solutions were prepared using Milli-Q water.

120

Tested waters. The photodegradation model was based on a typical secondary treated

121

wastewater effluent collected from a municipal sewage plant located in Jiangsu Province, China.

122

This sewage plant treats domestic sewage from the eastern district of the city of Taicang using a 5

ACS Paragon Plus Environment

Environmental Science & Technology

123

circulatory activated sludge treatment system. Samples were collected in acid-cleaned plastic

124

containers and transported to the laboratory within 2 h for preparation. The collected effluent was

125

immediately filtered through an acid-cleaned membrane (0.22 µm) to remove free bacteria and solids

126

and stored at 4 °C. The effluent for pH influence test was collected from the same facility, but 1 year

127

later. Sodium hydroxide and phosphoric acid were used to adjust pH. All water quality parameters

128

after filtration are provided in Table S2 of the SI.

129

Irradiation experiments. Photolysis experiments were conducted in a photo-reactor (Suntest

130

XLS+) with a xenon lamp. The lamp was fitted with a special quartz-glass filter to block the

131

transmission of wavelengths below 290 nm and to produce simulated natural sunlight. A temperature

132

control unit (Suncool®) was employed to fix the temperature at 25 °C. The emission spectrum for the

133

lamp, compared to natural sunlight, is shown in Figure S1 in the SI. The irradiation intensity was

134

continually measured with an online sensor and fixed at 40 W m-2 in the range of 290 - 400 nm. All

135

solutions were prepared in 200 mL cylindrical quartz glass sealed vials that allow full transmission of

136

UV light from solar irradiation. The steady-state concentrations of 1O2, HO•, and CO3•-, were

137

measured using methods reported in previous studies,38-40 and the detailed procedures are described

138

in Text S1 and Figures S2-S5 in the SI. The measurement of bimolecular reaction rate constants for

139

carbonate radicals with PPCPs was also illustrated in Text S1 of SI. UV-visible spectra were obtained

140

using a spectrophotometer (Cary 60, Agilent). The TOC content of the solutions was acquired using a

141

TOC analyzer (Shimadzu, TOC−CPH/CN). The anions were analyzed using an ion chromatograph

142

(Metrohm 883).

143

Online SPE LC-MS/MS analysis. The chemical structures of 29 PPCPs are shown in Table

144

S1 of the SI. Approximately 1 µg L-1 of each PPCP was spiked into the effluents to mimic

145

environmental concentrations. The trace levels of PPCPs were analyzed using an automated online

146

SPE system coupled to a liquid chromatography triple quadrupole mass spectrometer (LC-MS/MS,

147

Agilent 1290-6430 with Flexcube module). Only 2.0 mL of the solutions was removed at the time 6

ACS Paragon Plus Environment

Page 6 of 30

Page 7 of 30

Environmental Science & Technology

148

intervals for LC-MS/MS analysis to minimize the interference from sample collection. The detailed

149

experimental setup is described in Text S2 and Table S3 of the SI. The LC-MS/MS conditions of

150

each PPCP are also available in Table S1 in the SI. The current method is substantially time, labor,

151

and solvent efficient compared to the traditional offline SPE methods while also increasing the

152

reproducibility of analysis.41

153

EEM florescence spectroscopy experiments and parallel factor analysis (PARAFAC). All

154

3D EEM experiments were performed with a fluorescence spectrometer (Aqualog, Horriba). EEM

155

experiments consisted of 226 emission scans (250 - 620 nm) collected over excitation wavelengths

156

ranging from 240 to 600 nm at 3 nm increments. The 3D EEM data were processed with inner filter

157

correction and Rayleigh scattering elimination. Finally, 1.3 µM of quinine sulfate was used to

158

normalize the data to allow inter-laboratory comparison. In this study, parallel factor analysis

159

(PARAFAC) was used to disassemble the EEM spectra into their underlying chemical components.

160

The algorithm used was the N-way Toolbox for MATLAB®.42 The number of components

161

(fluorophores) that best fit a model for each set of 3D EEM spectra was determined by minimizing

162

the sum of squared residuals. The model was validated with the core consistency diagnostic provided

163

in the N-way toolbox and split-half analysis.

164

Field studies for fluorescence surrogates. Five field samples were collected from local

165

rivers (Suzhou River, Huangpu River, Xietang River, Longhuagang River, and Shagang River, all

166

located in Shanghai, China), which are dominated by wastewater effluents. The water quality

167

parameters are provided in Table S2 of the SI. Field samples were enriched by SPE after 5 h of

168

irradiation in the solar simulator and analyzed using LC-MS/MS (Text S3 of the SI). Only 11 of 29

169

PPCPs were quantified in this experiment, and their concentrations are shown in Table S4 of the SI.

170

The corresponding decrease of EEM fluorescence was then used to predict the photo-attenuation of

171

PPCPs.

172

Results and Discussion 7

ACS Paragon Plus Environment

Environmental Science & Technology

Page 8 of 30

173

Grouping PPCPs on the basis of their photochemical properties. In this study, 29 PPCPs

174

were selected because they are widely identified in effluents and surface waters. The initial

175

experiment was conducted in Milli-Q water at pH 7.0 under simulated solar irradiation. The

176

first-order degradation rates of PPCPs were measured as kDI, which represents the attenuation of

177

PPCPs under direct photodegradation. The kDI of PPCPs ranged from 5×10-4 to 4.6 h-1, indicating the

178

noteworthy diversity of PPCPs involved in direct photodegradation. In the presence of wastewater

179

effluents, the first-order degradation rates of PPCPs were observed as kEw, which represents the

180

integrated degradation rates from both direct and indirect photodegradation. In this study, kEw are

181

observed in the range from 2×10-2 to 8.3 h-1. Furthermore, a series of enhancing/quenching

182

experiments were performed to assess the role of ROS in indirect photodegradation. To explore the

183

role of 1O2, the effluent was freeze dried and redissolved in D2O because 1O2 has a longer life time

184

due to the isotopic effect.43 IPA (0.2 mM) was employed to minimize the effect of HO•, and the

185

first-order degradation rates are denoted as kIPA. In the IPA spiked effluents, not only were the steady

186

state concentrations of HO• sharply decreased but the effects of CO3•- were also minimized because

187

most of the CO3•- originates from HO• through one electron oxidation of bicarbonate.44 Furthermore,

188

argon saturated effluents were irradiated to enhance the 3OM* effect because dissolved oxygen can

189

act as a 3OM* quencher and yield 1O2.45 The first-order degradation rates of argon-saturated effluents

190

are referred to as kAr.

191

As shown in Eq. 1, kEw includes direct photodegradation (kDI) and indirect photodegradation.

192

The indirect photodegradation is further classified into the contributions of HO•, CO3•-, 3OM* and

193

1

194

O2.  =  +  • +  • +  ∗ +   

(1)

195

All tested PPCPs were classified into three groups based on their photochemical properties, namely,

196

Group I: direct photodegradation dominated; Group II: HO•/CO3•- dominated; and Group III: 3OM*

197

dominated. As illustrated in Figure S6, 1O2 has minor effects on the photochemical transformation of 8

ACS Paragon Plus Environment

Page 9 of 30

Environmental Science & Technology

198

the tested PPCPs, therefore it was not considered as a dominated group. The photochemical features

199

of each group are following:

200

Group I: Figure 1a demonstrates that the direct photodegradation contribution ( ) for the

201

group I compounds is greater than 50%, indicating that they are labile to direct photolysis. Group I

202

includes naproxen, methadone, ronidazole, dimetridazole, diclofenac, ornidazole, tinidazole,

203

chloramphenicol, flumequine, and ciprofloxacin. Their half-lives in the effluent were measured from

204

0.08 to 3 h with a median half-life of 0.6 h. Dimetridazole is employed as an example, as illustrated

205

in Figure 2a. The pseudo first-order decay rates (k) of dimetridazole did not alter significantly under

206

five experimental conditions, including Di-H2O, effluent, 1O2 enhanced (effluent/D2O), HO•/CO3•-

207

scavenged (effluent/IPA), and 3OM* enhanced (argon saturated effluent). These results indicated that

208

direct photodegradation is the dominant process. The other degradation profiles for the group I

209

compounds can be found in Figure S6 in the SI. The results indicate that direct photodegradation is a

210

major contributor to the degradation of this group, referred as the “direct photolysis-labile group.” As

211

previous studies have reported, all group I compounds present either significant UV absorption that

212

overlaps with the solar irradiation spectrum and/or high quantum yield to be decomposed.7, 46

213



Group II: Excluding group I compounds, other compounds are labile to indirect photolysis (>

214

50%), as shown in Figure 1a. To explore the indirect photodegradation mechanism, IPA was applied

215

to minimize the effects of HO• and associated CO3•-, and the contribution of HO•/CO3•- can be

216

calculated as

217

gemfibrozil, carbamazepine, ibuprofen, and cephalexin, belong to group II, and HO•/CO3•- is

218

responsible for more than 50% of their indirect photodegradation. Gemfibrozil, as an example from

219

this group, is shown in Figure 2b. The half-lives of the compounds in group II were measured from 5

220

to 35 h, with a median of 26 h. These values present the longest half-lives among all three groups,

221

demonstrating that group II compounds are relatively photo-resistant. On the basis of the

222

photochemical features within this group, it is referred to as the “HO•/CO3•--labile group.”

  

, as

shown in Figure 1b. Six pharmaceuticals, including trimethoprim, atenolol,

9

ACS Paragon Plus Environment

Environmental Science & Technology

Page 10 of 30

223

Furthermore, the contributions of CO3•- for photodegradation of group II were determined

224

based on an assessment of the steady-state concentrations of CO3•- and bimolecular reaction rate

225

constants with PPCPs. As illustrated in Table S5, the CO3•- reaction rate constants varied from < 105

226

to 107 M-1s-1, which are notably lower than the HO• reaction rate constants (~109 M-1s-1). Although

227

[CO3•-]ss (6.7 × 10-14 M) was one order magnitude higher than [HO•]ss (1.2 × 10-15 M), CO3•- still

228

played a minor role in the photodegradation of group II compounds at neutral pH.

229

Group III: The rest of the PPCPs can be classified as group III, including clenbuterol,

230

metoprolol, venlafaxine, bisphenol A, propranolol, ractopamine, salbutamol, roxithromycin,

231

clarithromycin, azithromycin, famotidine, terbutaline, and erythromycin. Their half-lives were

232

measured in the range of 0.8 to 12 h, with a median half-life of 4 h. These compounds are degraded

233

more slowly than the compounds of group I and faster than those of group II. One of the most

234

obvious characteristics of group III compounds is that their kAr was 2-fold higher than their kEw.

235

Erythromycin, as a model compound, is shown in Figure 2c. The enhanced degradation effect of

236

argon-saturated conditions was calculated as

237

to degradation, this group was referred to as the “3OM*-labile group.” The primary step of 3OM*

238

reaction with group III compounds has been proposed as electron transfer or hydrogen abstraction

239

processes, which mainly occurs at electron donor groups.

240

    

. Considering the notable contribution of 3OM*

Our aforementioned grouping principle is in close agreement with previous studies,7,

47

241

although most of them focused on the solar-driven attenuation of PPCPs in NOM-enriched solutions.

242

In contrast to natural waters, effluents present considerably higher levels of nitrate ion, which is an

243

important photosensitizer for HO• generation; therefore, the contribution of HO• in the effluent may

244

be more substantial than in the NOM-enriched solutions.

245

Phototransformation of EEM spectra of EfOM. In addition to the photodegradation of

246

PPCPs, the progressive changes in the fluorescence spectra of effluents were investigated. As

247

illustrated in Figure S7 in the SI, the EEM spectra of the effluents undergo considerable alteration 10

ACS Paragon Plus Environment

Page 11 of 30

Environmental Science & Technology

248

during the simulated solar irradiation. Considering the possible overlap and interference among

249

different fluorescence peaks, PARAFAC was used as a mathematical tool to disambiguate the

250

fluorescence EEM spectra into several individual fluorescent components that are independent from

251

each other. As illustrated in Figure 3, all emission loadings of components are unimodal. The single

252

emission maxima suggests that the model was successful at grouping the fluorophores present into

253

groups with similar molecular structure and/or fluorescence properties even though the model was

254

not constrained to do this. The model was split-half validated and contained three components; each

255

component consisted of a pair of well-rounded symmetrical peaks, with fluorescence located at the

256

same λem but two different λex. Furthermore, each component was located at the shortest λex peak that

257

had the highest fluorescence intensity, as described for pure compounds and recommended for

258

PARAFAC modeling.48 Based on the profile of the EEM spectra,31 three peaks were identified: a

259

tyrosine-like peak (λex/λem: