Organophosphate Triesters and Diester Degradation Products in

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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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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]

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ABSTRACT:

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

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

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

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

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

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

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

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

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

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

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

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magnitudes of regional economic development. Source analysis revealed nonchlorinated OP

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

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

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

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

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

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

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degradation products in sludge raise environmental concerns about these contaminants.

21 22 23 24 25 26 27 28 29 30

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Environmental Science & Technology

INTRODUCTION

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

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

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textiles, furniture, food packaging and hydraulic fluids.

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

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alternative flame retardants.

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

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

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years, accounting for approximately 60% of global consumption.

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

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environmental matrices,

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

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others.

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

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

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

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

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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

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metabolites in humans and animals.

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

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exposure to OPEs.

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as

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photodegradation

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

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

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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

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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

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. 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

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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

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

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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.

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. 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

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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

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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,

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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)

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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,

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

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

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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)

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

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

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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

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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

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moderate modifications.

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

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presented in the Supporting Information (SI).

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UPLC-MS/MS Analysis

32, 42

The procedure used to extract samples for OP diesters was

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Analyte concentrations were measured using an ultra-performance liquid chromatography

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

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

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

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Quality Assurance and Quality Control

43-46

Detailed

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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

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

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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

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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).

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

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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)

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

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

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

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

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Ecological Risk Assessment

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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

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

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

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

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sludge-dose application

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

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

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. The maximum probable risk of ecological effects was evaluated

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

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refer to the data from European Commission

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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,

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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

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

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

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

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

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RESULTS AND DISCUSSION

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Concentrations, Spatial Distribution and Composition Profiles of OP Triesters in

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Nationwide Sludge

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

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

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

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

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

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

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

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

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

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Sludge with predominant industrial inputs generally contained higher OPE levels than

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domestic sludge

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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

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

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

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less developed region. 38

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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

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

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dw and range: 1185–13370 ng g-1 dw)

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1000–20000 ng g-1 dw)

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dw).

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

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report,

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

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

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

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

12

30

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, 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

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

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

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

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

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

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

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

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

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

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

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

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

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pattern.

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

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

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

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

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

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

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

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

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

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

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Similarly, two other alkyl-OPEs, TBOEP (