Spatial distribution and ecological risk assessment of

Environmental Pollution xxx (2016) 1e7

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Spatial distribution and ecological risk assessment of phthalic acid esters and phenols in surface sediment from urban rivers in Northeast China Bin Li, Ruixia Liu*, Hongjie Gao, Ruijie Tan, Ping Zeng, Yonghui Song State Key Laboratory of Environmental Criteria and Risk Assessment (SKLECRA), Chinese Research Academy of Environmental Sciences, Beijing 100012, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 February 2016 Received in revised form 10 May 2016 Accepted 11 May 2016 Available online xxx

Concentration and spatial distribution of six phthalic acid esters (PAEs) and eight phenols in sediments of urban rivers, namely the Xi River (XR) and Pu River (PR) in Shenyang city, Northeast China were investigated and the ecological risk of these target pollutants was assessed based on the risk quotient (RQ) approach. Target PAEs and phenols were detected in most of sediment samples collected from the XR and PR. The concentrations of total PAEs in sediments varied from 22.4 to 369 mg/g dw in the XR and 3.71e46.9 mg/g dw in the PR. The levels of phenols ranged from 2.72 to 106 mg/g dw in the XR and 0.811 e25.0 mg/g dw in the PR, respectively. The dominant pollutants in both XR and PR were DEHP, phenol and 4-methylphnol. The sampling locations XR1-3 in the XR suffered severe contamination from PAEs and phenols. The sites PR1 and PR6 were heavily polluted by phenols and PAEs, respectively. Almost all target PAEs and phenolic compounds in sediment of the XR exhibited medium or high ecological risk to organisms and the ecological risk in the PR mainly originated from PEAs, phenol and 4-methylphenol. These results would provide guidance for individual pollutant control and indicate that it is imperative to take some effective measures to reduce the pollution of those contaminants. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Riverine sediment Distribution Ecological risk Phthalic acid esters Phenols

1. Introduction Phthalic acid esters (PAEs) and phenols are two classes of important industrial chemicals and widely used for diverse purposes. The main application of PAEs is as plasticizers to improve the softness and flexibility of polyvinyl chloride (PVCs) materials, polyvinyl acetate, and cellulosic and polyurethane resins (Feng et al., 2002; Kawakami et al., 2011). The content of PAEs in plastic products accounts for up to 80 wt% (Rahman and Brazel, 2004). It has been reported that PAEs consumption in 2011 reached up to approximately 2.2 million tons in China (Wang et al., 2013). Nevertheless, because of the widespread application, PAEs have been considered as ubiquitous environmental pollutants and widely detected in air, water, sediments, soil and food (Blair et al., 2009; Chen et al., 2013; Fierens et al., 2012; Liu et al., 2013; Ma et al., 2013; Wang et al., 2014; Xu et al., 2014). Some PAEs and their metabolites have been also observed in wildlife and human,

* Corresponding author. E-mail address: [email protected] (R. Liu).

implicating endocrine disrupting effects, such as reproductive physiology in mammals (Hogberg et al., 2008; Martine et al., 2013; Montuori et al., 2008; Oehlmann et al., 2009). Several most commonly detected PAEs have been listed as priority pollutants by USA Environmental Protection Agency (USEPA, 2014) and also by China (Zhou et al., 1991). Phenols are important raw materials and additives for industrial purposes. Phenols can be used as precursors of synthetic chemical products such as phenolic resin, synthetic fiber and rubber, caprolactam, bisphenol A, salicylic acid and so on, as well as versatile precursor to a large collection of pharmaceuticals. China’s market demand for phenol has been rising year by year. In 2013, the supply capacity reached up to 1.5 million tons, doubled that of four years ago (Nikkei, 2014). Due to their high solubility in water and strong reactivity, phenols are extensively present in aquatic environment (Bielicka-Daszkiewicz et al., 2004). The toxicity of phenols not only hinders survival and reproduction of aquatic organisms, but also endangers human health (Davı and Gnudi, 1999; Kottuparambil et al., 2014; Wolff et al., 2015). The Xi River (XR) and Pu River (PR) are typical urban rivers in Shenyang city that is the center of economy, culture, transportation

http://dx.doi.org/10.1016/j.envpol.2016.05.022 0269-7491/© 2016 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Li, B., et al., Spatial distribution and ecological risk assessment of phthalic acid esters and phenols in surface sediment from urban rivers in Northeast China, Environmental Pollution (2016), http://dx.doi.org/10.1016/j.envpol.2016.05.022

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B. Li et al. / Environmental Pollution xxx (2016) 1e7

and trade in northeast of China. There are more than 1500 manufacturing enterprises around the city, where the proportions of industrial wastewater discharged into the XR and PR are up to 52.2 and 10.9%, respectively. The XR, as a main effluent canal of the city, is about 78 km long and an area of 99 km2. It is receiving a large amount of industrial wastewaters from machining, plastic, chemical with pharmaceutical plants (Guo et al., 2011; Lin et al., 2013). Some PAEs and phenols have been detected with high concentration in surface water of the XR (Li et al., 2015). The PR, inland river, is about 205 km long. With the development of industry, water quality of the PR has been severely ruined due to aggravation of water resource shortage as well as increasing of discharged effluent (Gao et al., 2015). Overall, the release of domestic and industrial wastewaters has led to the pollution from toxic and hazardous pollutants characterized by carcinogenic, teratogenic and mutagenic effects in the XR and PR, which have potential hazards to wildlife and human despite their presence in low concentration. Most of researchers have paid attentions and efforts to investigate typical toxic and hazardous compounds focusing on polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) in water basin (Liu et al., 2015). However, it is still lack of information on the pollution level of commonly used PAEs and phenols in urban rivers, particularly in the riverine sediment. As of yet, limited work has reported on the risk of PAEs and phenols exposure in the XR and PR. The aims of this study were to investigate the distribution of PAEs and phenols in sediment of the XR and PR, and then to assess their potential ecological risks. The results from this study can not only facilitate better understanding for the pollution status of PAEs and phenols, but also provide data for making countermeasure and management scheme in contaminated rivers. 2. Materials and methods 2.1. Standards and reagents Target phthalate standards were dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), diisobutyl phthalate (DiBP), di-n-octyl phthalate (DnOP) and bis(2ethylhexyl) phthalate (DEHP). The target phenols included phenol, 4-methylphenol, 2,3-dimethylphenol, 2,4-dimethylphenol, 3,5-dimethylphenol, 2,4,6-trimethylphenol, 2,4-di-tert-butylphenol and 2,6-di-tert-butyl-4-ethylphenol. The internal standard compounds were 1,4-dichlorobenzene-d4, naphthalene-d8, acenaphthene-d10. All standard compounds were supplied by Dr. Ehrenstorfer GmbH (Germany). The chromatographic-grade dichloromethane, methanol and hexane were obtained from J. T. Baker Chemical Company (USA). 2.2. Sample collection Seven and nine surface sediment samples were collected from the XR and PR in May 2014, respectively, labelled as XR1eXR7 and PR1ePR9 from upstream to downstream. Their specific geographic information was shown in Fig. 1. Each sample was collected using a precleaned stainless steel grab sampler, packed into an aluminum container, and kept in a freezer at 20 C. 2.3. Sample extraction The sediment samples were freeze-dried, ground and sieved through a 0.9 mm mesh, and stored in precleaned dark glass bottles for the subsequent extraction. Approximately 5 g of dry sample was accurately weighed, transferred into a clean 50 mL glass-centrifuge

tube with 20 mL of extraction solvent (a mixed solvent of acetonedichloromethane (1:2, v:v) and spiked with a known quantity of internal standard. The mixture was ultrasonicated for 30 min and centrifuged for 30 min at a speed of 3000 rpm. The supernatants were collected in a clean glass flask. The extraction procedure was repeated three times, yielding a total of 60 mL supernatant. The combined supernatant was concentrated to 3 mL by a rotary evaporator, blow-dried to 0.5 mL using high purity grade nitrogen gas and then re-dissolved in 500 mL ultrapure water for clean up by solid phase extraction (SPE). Oasis HLB (500 mg/6 mL, Waters) and Envi-18 (500 mg/6 mL, Supelco) SPE cartridges were used for clean up. The extraction method was described in our previous study in detail (Li et al., 2015). Briefly, both Oasis HLB and Envi-18 columns in series were used for achieving a good recovery for all target chemicals. The cartridges firstly cleaned by dichloromethane, methanol and ultrapure water, respectively, to remove residual impurities, subsequently preconditioned by 5 mL each of methanol and ultrapure water for Oasis HLB columns and with 5 mL of dichloromethane before methanol and ultrapure water for Envi-18 column at flowrate of 1e2 mL/min. After extraction, the columns were then rinsed with ultrapure water and evaporated to dry for 30 min. The enriched Oasis HLB and Envi-18 columns were eluted, respectively, with 15 mL of mixed dichloromethane-methanol (v:v, 7:3, 3 5 mL) and 15 mL of hexane-dichloromethane (v:v, 7:3, 3 5 mL). The elution rate was 1e2 mL/min. The eluent from Oasis HLB and Envi-18 columns was combined and evaporated to 1 mL using a rotary evaporator and nitrogen flowing, and then subjected to instrumental analysis. 2.4. Instrumental analysis The concentrations of PAEs and phenols were analyzed using an Agilent 7890B gas chromatograph (GC) coupled with an Agilent 5977A mass selective detector (MSD). A DB-5MS capillary column (Agilent, 30 m, 0.25 mm i.d., 0.25 mm film thickness) was used to separate the target substances. Helium was used as the carrier gas with a column flow rate of 1.0 mL/min in a constant-flow mode. The injector, ion source and transfer line temperatures were set at 250, 230 and 305 C, respectively. The GC oven temperature was programmed from 40 C (2 min) to 100 C at 15 C/min, increased to 300 C at 10 C/min, and held constant for 5 min. The electron impact energy was set at 70 eV, and 1 mL of each sample was injected in splitless mode. PAEs and phenols were analyzed in the selected ion monitoring mode. 2.5. Quality assurance (QA) and quality control (QC) To ensure the accuracy of extraction and analytical procedures, all data were subject to strict quality control procedures. To avoid contamination, plastic ware was excluded. The pretreatment of all samples were carried out in a super-clean workbench. Blanks covering the entire analytical procedure, including extraction, clean up procedure and GC-MS analysis, were analyzed. The results showed that very low levels of PAEs (less than 83.1 ng/g) and phenols (less for 17.0 ng/g) were found in the blank, which made a little contribution to the samples. The concentration of these pollutants in the samples was blank corrected. The limit of detection (LOD) for analytes was determined with a signal-to-noise ratio of 3:1, while the limit of quantification (LOQ) was determined with a signal-to-noise ratio of 10:1. The LOD and LOQ for target phthalates were 0.66e20 and 2.2e67 ng/g, and those of the phenols were 0.53e2.2 and 1.7e7.3 ng/g, respectively. Three matrix samples spiked with mixed standards at two levels of 500 and 1000 ng/g were run to monitor the



3

Fig. 1. Map showing sampling sites in the XR and PR in 2014.

recoveries of the analytical method. The average recoveries for the target phthalates were 83e107% with relative standard deviations (RSD) of 6e11%, which were higher than those of single Oasis HLB as SPE cartridge in previous studies (Liu et al., 2014; Zheng et al., 2014). The average recoveries for phenols were 67e112% (RSD 6e9%).

2.6. Ecological risk assessment Ecological risk assessments of PAEs and phenols were conducted according to the European Commission’s Technical Guidance Document (EC, 2003) and previous studies (Servos et al., 2003; Sirivithayapakorn and Thuyviang, 2010; Staples et al., 1998). The


4


risk quotient (RQ) was calculated as the quotient of measured environmental concentration (MEC) and predicted no effect concentration (PNEC). The detected concentrations of PAEs and phenols in sediment were regarded as the MEC (mg/kg dw). Due to the absence of toxicity data for PAEs and phenols in sediment, the equilibrium partitioning method was used for calculating PNEC of pollutants in sediment (PNECsed) (EC, 2003; Zhao et al., 2013), as expressed in Equations (1) And (2).

PNECsed ¼

Ksuspwater PNECwater 1000 4:6 RHOsusp

Ksuspwater ¼ Fwatersusp þ Fsolidsusp Focsusp

(1) Koc RHOsolid 1000 (2)

where PNECsed and PNECwater were the PNECs in sediment (dry weight) (mg/kg dw) and in water (mg/L); RHOsusp and RHOsolid were densities of wet suspended matter and the solid phase, valued 1150 and 2500 in kg/m3, respectively; Fwater-susp and Fsolid-susp were the volume fractions of water and solid in suspension, defined as 0.9 and 0.1 in m3/m3; Foc-susp was the mass fraction of organic carbon in suspension, assigned as 0.1 in kg/kg; Koc was the partition coefficient of organic carbon-water (L/kg) and obtained from the database of software EPI suite v4.10. The PNECwater values were calculated from the lowest acute toxicity data (EC50 or LC50) of three aquatic organisms: fish, daphnia magna and algae, divided by an assessment factor (AF) (usually 1000) or for chronic toxicity, using no observed effect concentration (NOEC) divided by AF values that were defined as 100 if one long-term NOEC was available, 50 when two NOECs were available and 10 when NOECs from the three trophic levels were available (EC, 2003; Kosma et al., 2014). The different acute and chronic toxicity data were obtained from the EPA ECOTOX database, as shown in Table 1. The different ecological risk levels were established as follows: low risk to organisms for RQ value lower than 0.1, medium risk for value between 0.1 and 1, and high risk for value higher than 1 (Hernando et al., 2006; Verlicchi et al., 2012).

3. Results and discussion 3.1. Distribution of PAEs in the XR and PR The concentration ranges of DMP, DEP, DiBP, DBP, DnOP, DEHP and total PAEs (S6PAEs) in the sediment samples from the XR and

PR were presented in Table 2. The concentrations of S6PAEs in the PR were detected in the range of 3.71e46.9 mg/g dw (mean value at 13.9 mg/g dw). As for the XR, the concentrations were about 10 times higher than those in the PR, varying from 22.4 to 369 mg/g dw (mean value at 188 mg/g dw). The spatial distribution of S6PAEs was shown in Fig. 2. In the XR, the highest concentrations of S6PAEs occurred in the upstream (sites XR1-3), with the concentration higher than 300 mg/g dw. Of these sites, XR1 was located 100 m downstream of Xiannvhe Wastewater Treatment Plant (WWTP), which is one of the biggest WWTPs in Shenyang, inevitably receiving domestic and various industrial wastewater containing PAEs and phenols. The sites XR2 and XR3 were situated the downstream of Economic and Technological Development Zone (ETDZ) in Shenyang, the largest ETDZ in China where there are a variety of industrial clusters such as equipment manufacturing, automobile, pharmaceutical, food and packaging, textile, printing and dyeing industries. The pollution levels of PAEs in sites XR6 and XR7 were higher than 100 mg/g dw, which was due to wastewater discharge from surrounding chemical reagent factories or fine chemical mills, where some of PAEs were manufactured or used as additives for plastic production. In the XR, the mean concentrations of individual PAEs descended in the order: DEHP (180.0 mg/g dw) > DnOP (4.28 mg/g dw) > DiBP (2.02 mg/g dw) > DBP (1.28 mg/g dw) > DMP (0.161 mg/g dw) > DEP (0.169 mg/g dw). The most abundant PAEs was DEHP with the proportion accounting for 82.5e96.9% of S6PAEs, followed by DnOP (1.36e10.7%). This result was consistent with the findings in previous studies (Srivastava et al., 2010; Wang et al., 2006, 2008), where DEHP and DnOP were the dominant components in sediments. In the PR, the highest concentration of S6PAEs was observed in the site PR6 (as shown in Fig. 2). The serious PAEs pollution in this site mainly originated from Vegetables Planting Base (VPB) nearby, where a massive plastic film containing PAEs was used for adjusting temperature of vegetable greenhouse and PAEs in the plastic films were released into the water with surface runoff. Relatively high concentrations of S6PAEs were also observed in the sampling sites PR1 (15.9 mg/g dw), PR5 (15.1 mg/g dw), PR7 (11.1 mg/g dw) and PR9 (11.9 mg/g dw), which were possibly attributed to the development in Puhe New District. The order of average concentration for individual PAEs was similar to that in the XR, i. e. DEHP (12.3 mg/g dw) > DnOP (0.95 mg/g dw) > DiBP (0.30 mg/g dw) > DBP (0.25 mg/g dw) > DEP (0.06 mg/g dw) > DMP (0.04 mg/g dw). The major PAEs pollution in the PR was also from DEHP and DnOP, accounting for 65.3e95.1% and 3.16e25.1% of S6PAEs, respectively. These results

Table 1 PNECsed of PAEs and phenols (EC, 2003). Chemical

Fish L(E)C50

DMP DEP DBP DiBP DnOP DEHP phenol 4-methylphenol 2,3-dimethylphenol 2,4-dimethylphenol 3,5-dimethylphenol 2,4,6-trimethylphenol 2,4-di-tert-butylphenol 2,6-di-tert-butyl-4-ethylphenol

29,000 29,000 350 900 e 160 70 5000 14,000 1500 22,000 13,000 e e

Daphnia magna

Algae

NOEC

L(E)C50

NOEC

L(E)C50

NOEC

3200 3200 25 e e 300 118 e e 398 e e e e

33,000 45,900 500 3000 e 133 961 1400 18,692 2100 22,113 3400 e e

1700 1700 260 e e 77 160 1000 e 810 e 100 e e

33,300 33,300 210 e e 100 229,000 7800

10,000 10,000 210 e e e 94,110 e 50,000 50,000 50,000 e e e

e e 17,000 e e

AF

50 50 50

100 100 100 1000 10 1000 100

PNECwater (mg/L)

lg(Koc)

PNECsed (mg/g dw)

34 34 0.5

1.60 1.84 3.14 3.14 4.38 4.94 1.90 2.70 2.70 2.70 2.83 2.91 3.96 4.45

0.26 0.36 0.07

0.77 0.7 10 14 39.8 22 1

6.71 0.01 0.54 0.75 2.14 1.57 0.08

Note: e, no reported data.



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Table 2 Concentrations of 6 PAEs and 8 phenols congeners in sediment of the XR and PR (mg/g dw). Analytes

Xi river

Pu river Mean

SD

Range

Mean

SD

DMP DEP DBP DiBP DnOP DEHP S6PAEs

0.046e0.266 0.127e0.197 0.469e2.43 0.414e4.35 2.20e8.30 18.5e355 22.4e369

0.169 0.161 1.28 2.02 4.27 180 188

0.082 0.026 0.668 1.50 2.20 135 139

0.014e0.053 0.051e0.060 0.158e0.304 0.131e0.404 0.801e1.47 2.33e44.5 3.71e46.9

0.042 0.056 0.246 0.303 0.943 12.2 13.9

0.012 0.003 0.045 0.083 0.194 12.0 12.3

phenol 4-methylphenol 2,3-dimethylphenol 2,4-dimethylphenol 3,5-dimethylphenol 2,4,6-trimethylphenol 2,4-di-tert-butylphenol 2,6-di-tert-butyl-4-ethylphenol S8Phenol

0.634e34.8 0.658e66.9 0.068e0.111 0.286e2.15 0.207e0.268 0.078e0.112 0.410e1.10 0.023e0.027 2.72e106

12.1 23.2 0.080 0.609 0.246 0.092 0.751 0.025 37.1

11.4 26.0 0.013 0.630 0.021 0.011 0.259 0.001 35.5

0.192e20.1 0.168e4.30 0.027e0.031 0.113e0.153 0.080e0.116 0.030e0.056 0.183e0.403 0.009e0.011 0.811e25.0

3.02 1.11 0.028 0.124 0.091 0.037 0.279 0.010 4.37

6.48 1.45 0.001 0.012 0.011 0.008 0.060 0.000 7.45

400 360 320 100 80 60 40 20 0

DEHP DnOP DiBP DBP DEP DMP

XR1

XR2

XR3

XR4

105 90 75

Xi River

2,6-di-tert-butyl-2-ethylphenol 2,4-di-tert-butylphenol 2,4,6-trimethylphenol 3,5-dimethylphenol 2,4-dimethylphenol 2,3-dimethylphenol 4-methylphenol phenol

Xi River

30

XR5

XR6

52 48

XR7

Pu River

15

Concentration (μg/g dw)

Concentration (μg/g dw)

Range

20 10 0

XR1 27 24 21

10

4

5

2

XR2

XR3

XR4

XR5

XR6

XR7

Pu River

0

0

PR1

PR2

PR3

PR4

PR5

PR6

PR7

PR8

PR9

Sampling site

PR1

PR2

PR3

PR4

PR5

PR6

PR7

PR8

PR9

Sampling site

Fig. 2. Distribution of PAEs in different sampling sites from the XR and PR.

Fig. 3. Distribution of phenols in different sampling sites from the XR and PR.

indicated that the PAEs pollution in the XR was much severer than that in the PR.

dw for the remaining phenols. Of these pollutants, the predominant phenolic compounds were phenol and 4-methylphenol, with the concentrations ranging from 0.634 to 34.8 mg/g dw and 0.658e66.9 mg/g dw, respectively. The proportions of phenol and 4methylphenol to S8phenols were 37.6% and 48.3%, respectively. Higher concentrations of phenol were observed in the sites XR1 (34.8 mg/g dw), XR2 (19.7 mg/g dw) and XR7 (15.9 mg/g dw). The serious pollution of 4-methylphenol occurred in the sites XR1 (66.9 mg/g dw), XR2 (14.3 mg/g dw), XR3 (59.4 mg/g dw) and XR7 (17.0 mg/g dw). Very similar spatial distribution has been found between the pollution levels of PAEs and phenolic compounds, indicating that both pollutants might be subjected to the same contamination sources. In the PR, the highest concentration of S8phenols was found in the sampling site PR1, followed by site PR4, where some pharmaceutical and chemical factories were situated along the river and wastewater containing phenolic compounds used as raw materials or additives for production might be discharged into the river. The mean concentration of phenolic congeners in all sampling sites was 3.02 mg/g dw for phenol, 1.11 mg/g dw for 4-methylphenol, 0.279 mg/ g dw for 2,4-di-tert-butylphenol, 0.124 mg/g dw for 2,4dimethylphenol and below 0.100 mg/g for the remaining phenols.

3.2. Distribution of phenols in the XR and PR The level ranges and mean concentrations of phenol, 4methylphenol, 2,3-dimethylphenol, 2,4-dimethylphenol, 3,5dimethylphenol, 2,4,6-trimethylphenol, 2,4-di-tert-butylphenol, 2,6-ditert-butyl-4-ethylphenol and total phenols (S8phenols) in sediment samples from the XR and PR were given in Table 2. The concentration of S8phenols in sediments varied from 2.72 to 106 mg/g dw (mean concentration at 37.1 mg/g dw) in the XR and 0.81e25.0 mg/g dw (mean concentration at 4.37 mg/g dw) in the PR, respectively. In the XR, the severely contaminated sites by phenols were located in the upstream (XR1-3), with the concentration of S8phenols ranging from 35.8 to 106 mg/g dw and the downstream of the river (site XR7) with the concentration of 34.3 mg/g dw (Fig. 3). The individual phenols were found in all sampling sites with mean concentration of 23.2 mg/g dw for 4-methylphenol, 12.1 mg/g dw for phenol, 0.751 mg/g dw for 2,4-di-tert-butylphenol, 0.609 mg/g dw for 2,4-dimethylphenol and lower than 0.500 mg/g


6


High risk

Medium risk

Low risk

DMP DEP DBP DEHP phenol

—

4-methylphenol 2,3-dimethylphenol 2,4-dimethylphenol 3,5-dimethylphenol 2,4,6-trimethylphenol Sampling site

XR1 XR2 XR3 XR4 XR5 XR6 XR7 PR1 PR2 PR3 PR4 PR5 PR6 PR7 PR8 PR9

Note: —, no MEC Fig. 4. Calculated risk quotient (RQ) for the PAEs and phenols in surface sediment of the XR and PR.

Similar to the XR, the dominant pollutants in the PR were also phenol (0.192e20.1 mg/g dw) and 4-methylphenol (0.175e4.30 mg/g dw). The proportions of both phenol and 4-methylphenol to S8phenols varied from 16.4 to 80.4% (mean value at 34.3%) and 17.0e53.9% (mean value at 29.3%), respectively. 3.3. Ecological risk assessment High concentrations of PAEs and phenols, in particular DEHP, phenol and 4-methyphenol, have been found in sediment samples from the XR and PR (Table 2). These contaminants would cause adverse ecological impacts. The ecological risk assessment of these contaminants in sediments was carried out based on the calculated RQ values. The acute or chronic toxicity data (LC50, EC50 and NOEC) of PAEs and phenols applied in this study were presented in Table 1. As shown in Fig. 4, the RQ values of DBP, DEHP, phenol and 4methylphenol in the XR ranged from 6.70 to 34.7, 2.75 to 52.9, 63.4 to 3478 and 1.22 to 124 among different sampling sites, respectively, which indicated that the XR suffered serious ecological risk from these contaminants. As to 2,4,6-trimethylphenol, of seven sampling sites five posed a high risk and two sites showed medium risk. DMP and 2,4-dimethylphenol displayed high risk only in one site and medium risk in six sampling sites. DEP, 2,3dimethylphenol and 3,5-dimethylphenol exhibited medium or low risk in most of sampling locations. The results suggested that the majority of target PAEs and phenolic compounds in the XR had medium or high ecological risk to organisms, implicating that it is imperative to take some effective measures to reduce the pollution of those contaminants. In the PR, the RQ values of DBP and phenol were also higher than 1 in all sampling locations, with ranges from 2.26 to 4.34 and 19.2 to 2009, respectively. DEHP and 4-methylphenol posed high or medium risk to organisms in nine sampling sites. DMP, DEP and 2,4,6trimethylphenol in all locations indicated medium risk apart from DMP in the site PR8. 2,3-dimethylphenol, 2,4-dimethylphenol and 3,5-dimethylphenol exhibited low risk in the PR. These results indicated that the ecological risk of the PR mainly derived from PEAs, phenol and 4-methylphenol. This would be useful guidance for individual pollutant control. Nevertheless, due to lack of appropriate test systems and standardized risk assessment guidelines of chemicals in sediment, as well as eco-toxicological data of PAEs and phenols for benthic organisms, there would be some limitations using equilibrium

partitioning method to calculate PNECsed for risk assessment, in which a number of assumptions were presented, such as equally sensitive to the chemicals between sediment and water organisms, thermodynamic equilibrium for chemical concentration in diverse phases, available partition coefficients and so on. Thus, further research might be needed to establish the real risks of PAEs and phenolic compounds to benthic organisms. 4. Conclusion The distributions of PAEs and phenols in the XR and PR were investigated and the ecological risk was evaluated in this study. The results revealed that both the XR and the PR were subjected to contamination by PAEs and phenols. Of six PAEs and eight phenols, DEHP, phenol and 4-methylphenol were the most abundant pollutants in the XR and PR. The pollution levels of PAEs and phenols in the XR were approximately 10 times higher than those in the PR. The seriously contaminated sites were XR1-3 (from PAE and phenols) in the XR and PR1 (from phenols) and PR6 (from PAEs) in the PR. The ecological risk assessment showed that DBP, DEHP, phenol, 4-methylphenol and 2,4,6-trimethylphenol in the XR, as well as DBP and phenol in the PR would have a high ecological risk to relevant organisms. Thus, it is imperative to control the discharge of toxic sewage into the rivers so as to reduce the potential risks from PAEs and phenols in the XR and PR. Disclosure of potential conflicts of interest This manuscript has been seen by all co-authors and its submission has been approved by all co-authors. All the authors declare that there is no conflict of interest. Acknowledgements This work was supported by the National Natural Science Foundation of China (No.21277133). References Bielicka-Daszkiewicz, K., De˛ bicka, M., Voelkel, A., 2004. Comparison of three derivatization ways in the separation of phenol and hydroquinone from water samples. J. Chromatogr. A 1052, 233e236. Blair, J.D., Ikonomou, M.G., Kelly, B.C., Surridge, B., Gobas, F.A., 2009. Ultra-trace determination of phthalate ester metabolites in seawater, sediments, and biota


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