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Organophosphate Triesters and Diester Degradation Products in Municipal Sludge from Wastewater Treatment Plants in China: Spatial Patterns and Ecological Implications Lingfang Fu, Bibai Du, Fei Wang, James C.W. Lam, Lixi Zeng, and Eddy Y. Zeng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04106 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on October 30, 2017

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Environmental Science & Technology

Submitted for publication in Environmental Science & Technology

Organophosphate Triesters and Diester Degradation Products in Municipal Sludge from Wastewater Treatment Plants in China: Spatial Patterns and Ecological Implications

Lingfang Fu,

†

Bibai Du,

†

Fei Wang, † James C.W. Lam, ‡ Lixi Zeng, *,† and Eddy Y.

Zeng †

†

School of Environment, Guangzhou Key Laboratory of Environmental Exposure and Health, and Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University, Guangzhou 510632, China

‡

Department of Science and Environmental Studies, The Education University of Hong Kong, Hong Kong SAR, China

*Corresponding author Dr. Lixi Zeng School of Environment, Jinan University 601 West Huangpu Avenue, Tianhe District Guangzhou 510632, China Tel: 8620-8522-6615 Fax: 8620-8522-6615 E-mail: [email protected]

ACS Paragon Plus Environment


1

ABSTRACT:

2

Little is known about the occurrences, distributions, sources and potential risks of

3

organophosphate (OP) triesters and diester degradation products in municipal sludge from

4

wastewater treatment plants (WWTPs). In this study, we conducted the first nationwide

5

survey to simultaneously determine a suite of 11 OP triesters and six diester degradation

6

products in sludge from WWTPs across China. All OP triesters were detected and three

7

diesters were for the first time identified in sludge samples. Total concentrations of OP

8

triesters and diester degradation products were in the range of 43.9–2160 ng g-1 dw and

9

17.0–1300 ng g-1 dw, respectively, indicating relatively low pollution levels in China

10

compared with several developed countries. A distinct geographical variation of higher

11

concentrations of OP triesters and diesters in East China than in Central and West China was

12

observed, suggesting that regional levels of organophosphate esters are associated with the

13

magnitudes of regional economic development. Source analysis revealed nonchlorinated OP

14

diesters are mainly derived from degradation in WWTPs, while chlorinated OP diesters were

15

largely sourced from outside WWTPs. The estimated total emission fluxes of OP triesters and

16

diesters via land-application sludge in China were approximately 330 and 134 kg yr-1,

17

respectively. Further risk assessment based on risk quotient values in sludge-applied soils

18

indicated low to medium risks for most OP triesters and diesters except tris(methylphenyl)

19

phosphate. The significant accumulation of OP triesters and widespread occurrence of diester

20

degradation products in sludge raise environmental concerns about these contaminants.

21 22 23 24 25 26 27 28 29 30


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INTRODUCTION

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Organophosphate esters (OPEs) have been extensively used as flame retarding chemicals

33

and as plasticizers and additives to plastics, lubricants, rubber products, electronic devices,

34

textiles, furniture, food packaging and hydraulic fluids.

35

polybrominated diphenyl ethers, OPEs have become one of the most frequently used

36

alternative flame retardants.

37

approximately 200 kilotons, 4 with more than 70 kilotons being produced in China. 5 Western

38

Europe, North America and China are three major consumers of flame retardants in recent

39

years, accounting for approximately 60% of global consumption.

40

OPEs produced and used worldwide have resulted in their widespread occurrence in various

41

environmental matrices,

42

linkage, OPEs can be categorized to aryl-, nonchlorinated alkyl-, chlorinated alkyl-, and

43

others.

44

hydrophobic, while chlorinated alkyl-OPEs are generally more water soluble and resistant to

45

degradation.3 Chlorinated alkyl-OPEs, including tris(2-chloroethyl) phosphate (TCEP), tris(2-

46

chloroisopropyl) phosphate (TCIPP) and tris(1,3-dichloroisopropyl) phosphate (TDCIPP)

47

have attracted increasing attention because of their carcinogenicity and neurotoxicity. 13-15

48

12

3

1, 2

With the phase-out of

The annual global production of OPEs currently reaches

1-3, 5, 7-10

as well as in remote regions.

11

6

The large amounts of

Depending on the ester

Aryl- and nonchlorinated alkyl-OPEs with higher molecular weights are more

Organophosphate triesters can be rapidly enzyme-catalyzed and metabolized to diester

49

metabolites in humans and animals.

50

than triesters and are readily excreted in urine, which often function as biomarkers of

51

exposure to OPEs.

52

as

53

photodegradation

54

phosphate (DPHP), are more toxic than their parent compounds. 20 In cities, most released OP

55

triesters and diester degradation products are commonly collected in sewer systems and

56

accumulated in municipal wastewater treatment plants (WWTPs)

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that OP triesters were detected in influents of WWTPs at µg L-1 levels 29-32, 34, 35. WWTPs are

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therefore considered as major sinks and perhaps degradation sites. Studies on the behavior of

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OPEs in WWTPs indicate that nonchlorinated alkyl- and aryl-OPEs can be partly degraded

60

by activated sludge treatment

microbial

17

3, 10, 16-26

These diester metabolites are more hydrophilic

OP diesters can also be generated via other degradation pathways such

metabolism/biotransformation,

base-catalyzed

hydrolysis

27

and

28

. It should be emphasized that some OP diesters, such as diphenyl

12, 29, 31, 32, 34, 36

29-33

. It has been reported

, while chlorinated alkyl-OPEs are poorly



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removed even in the advanced oxidation processes

62

alkyl-OPEs, ultimately end up in sludge

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wastewater-derived OPEs and their degradation products locally 37. However, up to now, only

64

limited studies have reported one or several selected OPEs in sludge at a regional level 12, 30,

65

33, 37-39

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diesters in sludge 12, 33. Although OP triesters and diester as emerging global contaminants in

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humans have been widely examined

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and potential risks in abiotic matrices such as sludge at a large geographical scale still remain

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unknown.

32

. Most OPEs, particularly chlorinated

31, 32, 36

. So sludge is an excellent medium to trace

. Among these studies, only two demonstrated the presence of both OP triesters and

3, 10, 17-19, 21-25

, their co-occurrence, distributions, sources

70

To fill the above-mentioned knowledge gap, we conducted the first nationwide survey to

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simultaneously determine a suite of OP triesters and diester degradation products in sludge

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from WWTPs in 36 cities across China. The aims were to (1) examine the geographical

73

distribution patterns and potential sources of currently used OP triesters and their diester

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degradation products; (2) better understand the behavior and fate of the target compounds in

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WWTPs and the ambient environment and (3) evaluate the environmental emissions and

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potential ecological risks via land-application of sludge in China.

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MATERIALS AND METHOD

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Chemicals and Materials

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Eleven target OP triesters,

40

i.e., tris(propyl) phosphate (TPP), tris(butyl) phosphate

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(TNBP),

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tris(2-ethylhexyl) phosphate (TEHP), TCEP, TCIPP, TDCIPP, tris(phenyl) phosphate

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(TPHP), tris(methylphenyl) phosphate (TMPP) and 2-ethylhexyl diphenyl phosphate

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(EHDPP) were purchased from Dr. Ehrenstorfer (Augsburg, Germany). Six OP diesters,

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including di-n-butyl phosphate (DNBP) for parent TNBP, bis(2-butoxyethyl) phosphate

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(BBOEP) for parent TBOEP, bis(2-chloroethyl) phosphate (BCEP) for parent TCEP,

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bis(2-chloroisopropyl) phosphate (BCIPP) for parent TCIPP, bis(1,3-dichloroisopropyl)

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phosphate (BDCIPP) for parent TDCIPP and diphenyl phosphate (DPHP) for parent TPHP

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were studied. DNBP, BBOEP, BCEP, BCIPP and BDCIPP were purchased from Toronto

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Research Chemicals (North York, Canada), and DPHP was purchased from Tokyo Chemical

tris(isobutyl)

phosphate

(TIBP),

tris(2-butoxyethyl)


phosphate

(TBOEP),

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Industry (Tokyo, Japan). Detailed information on their molecular formula/weight and

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physicochemical parameters is listed in Table S1. Internal standards: TNBP-d27, TDCIPP-d15,

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TPHP-d15 and DPHP-d10 were obtained from Cambridge Isotope Laboratories (Andover, MA,

93

USA). Stock solutions of the target analytes were prepared in acetonitrile and stored at -20 °C.

94

Methanol, acetonitrile, ethyl acetate and cyclohexane of high-performance liquid

95

chromatography grade were acquired from Oceanpak (Gothenburg, Sweden).

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Field Sampling

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A total of 64 sewage sludge samples from WWTPs in 36 cities across China (Figure S1)

98

were collected from October 2010 to May 2011. Details about the secondary treatment

99

technologies, sewage sources and treatment capacities for the WWTPs have been published

100

previously 41, as well as presented in Table S2. Freshly digested sludge 0.5–1.0 kg wet weight

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from secondary clarifier in each WWTPs was collected after the dewatering process. Wet

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sludge samples were packed in aluminum foil, sealed in ziplock bags, and transported

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immediately to laboratory, where they were freeze-dried, homogenized, sieved through 100

104

mesh sieve and then stored at -20 °C before extraction.

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Sample Extraction and Cleanup

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Sample extraction procedure for OP triesters was adopted from previous studies with

107

moderate modifications.

108

different from that for triesters. Detailed sample extraction and cleanup procedures are

109

presented in the Supporting Information (SI).

110

UPLC-MS/MS Analysis

32, 42

The procedure used to extract samples for OP diesters was

111

Analyte concentrations were measured using an ultra-performance liquid chromatography

112

(Nexera X2, Shimadzu) coupled to a tandem mass spectrometer (Triple Quad™ 5500 System,

113

AB SCIEX) based on previously reported methods with some optimizations.

114

information with regard to UPLC and MS/MS parameters (Table S3) is given in the SI.

115

Quality Assurance and Quality Control

43-46

Detailed

116

Strict quality controls were implemented to ensure accurate quantification of these target

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compounds. All glassware was soaked in a phosphate-free cleaning agent (decon90) for 12 h

118

and then rinsed thoroughly with deionized water. After drying carefully, the glassware was

119

solvent rinsed, then heated at 450 °C overnight prior to use. For the evaluation of extraction



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efficiency, sludge samples were randomly chosen for the fourth extraction after the first three

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extraction cycles, and the target compounds were undetected in the fourth extraction, which

122

indicated high efficiencies of the first three extractions for sludge samples. One procedure

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blank sample was included in every batch of 10 samples to monitor the blank contamination.

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Most analytes in the blanks were under the limit of detection except TIBP and TPHP (Table

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S4), and therefore the two OP triester concentrations were corrected by the blank.

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Randomly selected sludge samples (n = 6) were fortified with known concentrations of

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OPEs (5–25 ng) for determination of matrix effect (for details see SI).

128

was within 91–107%, and thus the potential over/underestimation of concentrations could be

129

excluded. Matrix spike recovery was examined in matrix spike sample and matrix spike

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duplicate according to U.S. EPA method.

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analytes and internal standards (IS) were between 67-99% and 74-104%, respectively.

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Accuracy and precision were evaluated by fortification of samples (n = 6) with native and

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internal standards, and analysis of those samples through the entire procedure. 12 For accuracy,

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the deviations of IS-corrected quantitative results from the known values were ≤ 15%. For

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precision, the relative standard deviations (RSDs) in duplicate sample tests were ≤ 10%.

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Recoveries of TNBP-d27, TDCIPP-d15, TPHP-d15 and DPHP-d10 in all field samples (n = 64)

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were 73 ± 6%, 84 ± 17%, 101 ± 10% and 78 ± 13%. The method quantification limits (MQLs)

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of the analytes were calculated as a signal-to-noise ratio of 10, which were from 0.09 (DPHP)

139

to 3.76 ng g-1 (TCIPP). Detailed data are presented in Table S4. Concentrations below MQLs

140

were replaced by half of the MQLs, and all data were log-transformed for statistical analysis

141

using IBM SPSS Statistics 20.0 (IBM Corp, 1989−2011). Eight-point calibration curves were

142

established at the range of 0.50–500 ng mL-1 with regression coefficient r2 > 0.995.

143

Ecological Risk Assessment

144 145

146

47

12

The matrix effect

Average matrix spike recoveries (n = 6) of target

The risk assessment in sludge-applied soils was performed using risk quotient (RQ) values, which are expressed as: RQ =

PEC soil PNEC soil

147

where PNECsoil is defined as the predicted no effect concentration on organisms and often

148

derived from no observed effect concentration (NOEC) in the laboratory. PECsoil was


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149

estimated as the concentration of contaminant in agricultural soil from one year after

150

sludge-dose application

151

based on the commonly recommended criteria: high risk (RQ ≥ 1.0), medium risk (0.1 ≤ RQ

152

< 1.0) and low risk (0.01 ≤ RQ < 0.1) 48, 49.

153

48

. The maximum probable risk of ecological effects was evaluated

In this study, the PNECsoil values for TCEP, TCIPP, TDCIPP, TPHP, TMPP and EHDPP

154

refer to the data from European Commission

155

triesters and diesters were estimated as a quotient of toxicological relevant concentration

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LC50 and an assessment factor (f) using the formula: PNECsoil = LC50 / f, where f was 1000 51,

157

52

158

TEHP, DNBP, BBOEP, BCEP and DPHP was used for PNECsoil calculation 53.

159 160

50

, while the PNECsoil values for other OP

. For this purpose, the LC50 for earthworm associated with TPP, TNBP, TIBP, TBOEP,

The PECsoil values in sludge-applied soils were determined according to the European Commission Technical Guidance Document (TGD) on Risk Assessment 48, 51: PEC soil =

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Csludge × APPLsludge DEPTH soil × RHO soil

162

where Csludge (g/kg dw) is the measured concentration of target compound in sludge;

163

APPLsludge is the application rate of dry sludge into agricultural soils (usually 0.50 kg m-2 yr-1);

164

DEPTHsoil is the mixing depth (usually 0.20 m for agricultural soils); and RHOsoil is the bulk

165

density of wet soil (usually 1.5 × 103 kg m-3 for agricultural soils).

166

RESULTS AND DISCUSSION

167

Concentrations, Spatial Distribution and Composition Profiles of OP Triesters in

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Nationwide Sludge

169

All the target OPEs (triesters) were detected in most sludge samples (Table 1). The total

170

concentration of 11 OPEs (sum of which is designated as ∑11OPE thereafter) ranged from

171

43.9 to 2160 ng g-1 dry weight (dw) with an average value of 303 ng g-1 dw, indicating

172

considerable variability among the WWTPs. The maximum and minimum concentrations of

173

OPEs were found at WWTPs located in Zhejiang province of East China and Yunnan

174

province of West China, respectively. The WWTPs under investigation mainly treat domestic

175

wastewater or mixed domestic/industrial wastewater (Table S2). The highest ∑11OPE

176

concentration from East China may be attributed to the high industrial output in this region as



177

corroborated by a large portion (70%) of industrial wastewater in the WWTP influents.

178

Sludge with predominant industrial inputs generally contained higher OPE levels than

179

domestic sludge

180

lower than that previously reported in two relatively more economically developed regions of

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China, i.e., 699 ng g-1 dw with a range of 204–4100 ng g-1 dw in Beijing 33 and 420 ng g-1 dw

182

with a range of 96.7–1313 ng g-1 dw in the Pearl River Delta (PRD), 37 but higher than that

183

found in Henan Province (mean: 170 ng g-1 dw and range: 38.6–508 ng g-1 dw), where is a

184

less developed region. 38

185

37

. The national average concentration of sludge OP triesters in China was

Sludge ∑11OPE

concentrations in China were at least ten times lower than those in

186

Sweden (mean: 4239 ng g-1 dw and range: 620–6900 ng g-1 dw), 31 Spain (mean: 4476 ng g-1

187

dw and range: 1185–13370 ng g-1 dw)

188

1000–20000 ng g-1 dw)

189

dw).

190

consumptions of OPEs in China compared with these developed countries. According to a

191

report,

192

production in 2008, while Europe and the United States took up 40% and 35%, respectively.

193

These results implied that elevated sludge levels of ∑11OPE in developed countries were

194

likely associated with more frequently industrial activity together with larger consumption of

195

OPEs, but population density of WWTP location was another potential factor. 55

12

30

32

, Germany (only TCIPP detected over a range of

and U.S. (mean: 11800 ng g-1 dw and range: 4110–20200 ng g-1

The relatively low levels of ∑11OPE in China were consistent with the relatively low

54

the amount of OPEs consumed in China accounted for only 7% of the global

196

Of all target OP triesters, TNBP, TIBP, TCEP, TPHP and TMPP were detected in all

197

sludge samples, whereas TBOEP (98.4%), TCIPP (95.3%), EHDPP (93.8%), TDCIPP

198

(90.6%), TEHP (81.2%) and TMPP (76.6%) were partially detectable. In Sweden, Germany

199

and Spain 30-32, EHDPP, TCIPP, TBOEP and TEHP were the abundant compounds in sludge.

200

Some previous studies in China indicated that the predominant compounds of OP triesters

201

were TEHP and TMPP in Beijing 33, TBOEP and TPHP in the Pearl River Delta 37, and TCEP,

202

TBOEP and TCIPP in Henan province 38. In the present study, TIBP, TBOEP, TCEP, TCIPP

203

and TMPP contributed comparably (11.1−14.4%) to ∑11OPE (Table 1), which were identified

204

as the dominant compounds. Generally, sludge samples from the same province/municipality

205

were similar in the composition profile of OPEs, but variations among different regions were

206

observed (Figure S2). Differences in composition profiles of sludge OPEs between different


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207

regions in China and between China and other countries may be attributed to varying use

208

pattern.

209

There is still a lack of environmental data for OPEs in sludge among different countries

210

worldwide. We compared individual OP triester concentration with the reported data from

211

Sweden, Spain, Canada, U.S. and Germany (Table S5). In the present study, TPP was

212

detected in 49 of 64 samples with the concentration of < MQL–8.77 ng g-1 dw. The lowest

213

concentration and percentage composition for TPP (Table 1) could be partly attributed to its

214

low logKow and preferential partitioning in the aqueous phase, while production volume,

215

usage period, and stability were also related to sludge TPP level. The concentrations of TNBP

216

and TIBP in nationwide sludge samples from China were 2.97–430 and 6.25–387 ng g-1 dw,

217

respectively, comparable to those previously reported in Beijing and Henan Province

218

but lower than those detected in sludge from Sweden 31, Spain

219

Similarly, two other alkyl-OPEs, TBOEP (

Organophosphate Triesters and Diester Degradation Products in

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