Environmental Pollution 252 (2019) 196e204

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Environmental Pollution

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Performance of a novel magnetic solid-phase-extraction microsphere and its application in the detection of organic micropollutants in the , +

* Ying Liang a, Zekai Li a, Peng Shi a, , Chen Ling b, Xun Chen a, Qing Zhou a, Aimin Li a a State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China b Department of Environmental Engineering, Nanjing Forestry University, Nanjing, 210037, China article info abstract

Article history: Solid phase extraction has been increasingly applied for the detection of organic micropollutants (OMPs). Received 20 December 2018 However, time-consuming and high-cost disadvantages also limit the widespread use of this method, Received in revised form especially for the extraction of large-volume field water samples. In this study, a gas chromatography- 13 May 2019 mass spectrometry (GC-MS) method based on the magnetic microsphere (M150) solid-phase- Accepted 22 May 2019 extraction (MSPE) was established to investigate the OMPs in source water throughout the whole Available online 23 May 2019 Huai River. In brief, the results demonstrated that the extraction efficiency of the M150 was superior to that of C and HLB for the selected OMPs, including species of polycyclic aromatic hydrocarbons (PAHs), Keywords: 18 Magnetic solid phase extraction organochlorine pesticides (OCPs), phthalate esters (PAEs) and nitrobenzenes (NBs), and the method Organic micropollutant detection limits of M150 for these OMPs were comparable to those of C18 and HLB. The optimized Huai river conditions of extraction and elution were the 100 mg/L dosages of microspheres, extraction time of Source water 60 min and pH of 2, and the eluent with a similar polarity, hydrophobicity and molecular structure to the OMPs rendered higher elution efficiencies. A total of 21 types of OMPs affiliating to PAHs, OCPs, PAEs and NBs were detected by the established method, with the total concentrations of 505e2310 ng/L in source water of the Huai River. Spatial differences of the OMPs were also observed, demonstrating the link between pollutant profiles and geographical locations. This study provides an alternative to enrich OMPs in filed water samples, and it reveals pollutant profiles of source water throughout the whole Huai River. © 2019 Elsevier Ltd. All rights reserved.

1. Introduction humans and animals (la Farre et al., 2008), and producing carci- nogenic effects (Zhang et al., 2013b). However, it is difficult to Water pollution has drawn increasing public attention with detect these OMPs directly with techniques such as gas or liquid urbanization and industrialization. Numerous organic micro- chromatography when they appear in extremely low concentra- pollutants (OMPs), including polycyclic aromatic hydrocarbons tions and complex matrices. Thus, the extraction and enrichment of (PAHs), organochlorine pesticides (OCPs), phthalate esters (PAEs), OMPs are key steps that have been widely applied prior to instru- and nitrobenzenes (NBs), have been detected in drinking water mental analysis. sources (Vieno et al., 2007; Huerta-Fontela et al., 2011), and they Solid-phase-extraction (SPE) has been increasingly applied in have been suggested to pose potentially high risks to humans and the field of trace OMP detection due to its low solvent consumption ecosystems despite their low concentrations, such as leading to and simple operation (Yilmazcan et al., 2015), but it also has the microbial resistance (Jiang et al., 2013), affecting reproductive disadvantages of being time consuming and needing a high development, nervous system and immune system functions in compression pressure when extracting trace OMPs from large- volume water samples (Zhang et al., 2010). Magnetic solid-phase- extraction (MSPE), which can overcome the drawbacks of the + This paper has been recommended for acceptance by Dr. Sarah Harmon. classic SPE method, has gained increasing attention (Sen et al., * Corresponding author.State Key Laboratory of Pollution Control and Resource 2006; Aguilar-Arteaga et al., 2010; Chen et al., 2011). At the same Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, time, a series of magnetic sorbents, including magnetic hemi- 210023, China. micelles (Li et al., 2013), silicon-based magnetic materials (Guan E-mail address: [email protected] (P. Shi). https://doi.org/10.1016/j.envpol.2019.05.115 0269-7491/© 2019 Elsevier Ltd. All rights reserved. Y. Liang et al. / Environmental Pollution 252 (2019) 196e204 197 et al., 2010; Zhai et al., 2010), magnetic carbon (Zhang et al., 2010) water, ultrapure water and methanol in sequence before sampling, and magnetic polymer materials (Li et al., 2010; Meng et al., 2011), and then 5 L of water samples were collected from each sampling have been synthesized and applied in the extraction or adsorption location. The pH of water samples was adjusted to below 2.0 by of OMPs in real water. In our previous study, a new MSPE micro- adding 5 mL of concentrated hydrochloric acid, and then the sam- sphere (M150) was also successfully developed by using membrane ples were transported to the laboratory within 4 h at 4 C. Subse- emulsification, suspension polymerization and post-crosslinking quently, water impurities were removed by 0.45-mm glass fiber reaction technologies and applied to adsorb OMPs, including car- filters. The filtered water was stored at 4 C in 1-L brown glass bamazepine, atrazine (Zhang et al., 2013a), p-nitrophenol, and containers to avoid light before further treatments. Chromatograms chlorotetracycline (Ma et al., 2014), in simulated water, and opti- of the blank samples spiked with OMPs were presented in Fig. S1. mized solution and sample volumes, pH and salinity for 8 target OMPs (Zhang et al., 2013a). However, the extraction performance of 2.3. Sample extraction methods the M150 has only been examined for limited types of OMPs at relatively high concentrations and thus needs to be investigated for To compare the extraction performances of C18 (500 mg, 6 mL, broad-spectrum OMPs at trace levels. In addition, the Huai River is CNW Inc., Germany), HLB (200 mg, 6 mL, Waters Inc., U.S.) and one of the seven major rivers in China and flows through the most M150 materials for the selected OMPs, 0.1 mg/L of these OMPs was densely populated areas in China. Severe water pollution of the spiked into ultrapure water as the simulated water samples and river with multiple types of OMPs was reported in previous studies then extracted according to a series of procedures. Elution condi- (Zhang et al., 2014; Zhao et al., 2016; Zhao et al., 2017). In recent tions, including the elution type (DCM, EA, DCM and EA mixture decades, the Chinese government has implemented strict regula- (volume ratio is 1:1), Hex, CYH) and volume (3 mL, 6 mL, 9 mL and tion policies for improving the water quality of this river, and the 12 mL), were optimized by single factor and orthogonal design concentrations of ammonia nitrogen and chemical oxygen demand experiments. have significantly decreased since then (Zhai et al., 2014). However, For the MSPE extraction, M150 microspheres were ultrasoni- few studies investigated the OMP levels in source water throughout cally cleaned in EA for 20 min. Then, a designated amount of M150 the whole Huai River basin. was immersed in 1 L of water samples. The samples were shaken in In this work, we first optimized the extraction and elution pa- a constant-temperature incubator at 288 K for a certain time, and rameters of the M150 for OMPs, including important species of then the microspheres were magnetically separated from the water PAHs, OCPs, PAEs and NBs, and then compared the extraction per- matrix and transferred into an empty cartridge with a sieve plate to formance with commercially available extraction materials (C18 and prevent runoff of the microspheres. Analytes were eluted with HLB). A rapid and efficient M150-GC-MS (gas chromatography different types and volumes of elution solvents. The eluent was first coupled with mass spectrometry) method was successfully estab- concentrated to 2e3 mL using a rotary evaporator and then further lished and applied to investigate the selected OMPs in source water blown to dryness under a gentle nitrogen (99.999% pure) flow. of the whole Huai River basin. Overall, this study may provide us Subsequently, the analytes were re-dissolved in 1.0 mL of the DCM with an alternative method for OMP detection and a complete and EA mixture (volume ratio is 1:1). Finally, the concentrated profile of OMP pollution in source water throughout the Huai River solution was loaded into a 2-mL sampler vial for OMPs determi- basin. nation before analysis. In addition, C18 and HLB cartridges were placed on a vacuum 2. Materials and methods manifold and conditioned sequentially with 10 mL of DCM, 10 mL of MeOH and 5 mL of ultrapure water. Then, 1 L of water sample was 2.1. Standards and reagents fed to the cartridge at a flow rate of 10 mL/min. After extraction, the cartridge was washed with 10 mL of Milli-Q water and dried with a A total of 22 kinds of OMPs, including 6 PAHs, 6 OCPs, 5 PAEs and gentle stream of nitrogen gas (99.999% pure) for 5 min. Analytes 5 NBs, were all purchased from the J&K Scientific LTD., Co. were eluted with the same solvents used in cartridge activation and (Shanghai, China). Methanol (MeOH), dichloromethane (DCM), conditioning. Then the eluent was first concentrated to 2e3mL ethyl acetate (EA), n-hexane (Hex) and cyclohexane (CYH) were of using a rotary evaporator and then further blown to dryness under HPLC grade and supplied by Merck Company (Darmstadt, Ger- a gentle nitrogen flow. Finally, the analytes were re-dissolved with many). The full and abbreviated names, purity, CAS number and 1 mL of the DCM and EA mixture and then transferred to a 2-mL supplier of each compound are provided in Supplementary Data sampler vial before analysis. All the extraction and elution pro- Table S1. The preparation of M150 microspheres and physico- cedures were conducted by an automatic SPE instrument (Ther- chemical parameters was described in our previous study (Zhang mofisher, Auto trace 280, U.S.). et al., 2013a), and described in Text S1. In brief, M150 micro- spheres were prepared via membrane emulsification-suspension 2.4. Instrumental analysis polymerization and post-crosslinking reactions, and then oleic acid was used to modify the Fe3O4 nanoparticles, which enhanced All the OMPs were analyzed by a TRACE ULTRA GC and an ISQ the lipophilicity and monodispersity of the magnetite MS (Thermo Fisher, U.S.) with a TG-5 MS capillary column (Thermo nanoparticles. Scientific, 30 m 0.25 mm i.d. 0.25 mm) according to a previous study (Shi et al., 2018). In brief, the injector was set at 280 Cina 2.2. Sample collection and pretreatment splitless injection mode, and 1 mL of sample was injected for each run. The carrier gas was ultra-pure helium (99.99% pure) at a As shown in Fig. 1, a total of 18 water samples were collected constant flow rate of 1.0 mL/min. The oven temperature programs across the whole Huai River basin. Among the sampling locations, for different types of OMPs, temperatures of the transfer line and 3, 4 and 3 sampling locations lie in the upstream, midstream and the ion source are listed in Supplementary Data Text S2. The mass downstream of the Huai River, respectively. In addition, 8 samples spectrometer was operated at 70 eV in EI and SIM modes, and the were collected from the four main tributaries of the Huai River, selected ions for determining each OMP was listed in Table S2. namely, the Shaying River, Guo River, Xinyi River and Jinghang Acenaphthene-d10, chrysene-d12, di-n-butyl phthalate-d4, bis(2- River (Fig. 1). All the sampling bottles were rinsed with distilled ethylhexyl) phthalate-3,4,5,6-d4 and parathion-d 10 were used as 198 Y. Liang et al. / Environmental Pollution 252 (2019) 196e204

Fig. 1. Overview map of sampling locations of water samples along the Huai River.

internal standards to calibrate the standard curves. Each sample 3. Results and discussion was collected, extracted and analyzed in triplicate to ensure repeatability and accuracy. Procedural blanks of each run were 3.1. Optimization of extraction and elution procedures of M150 conducted to guarantee no background contamination, and the contamination was negligible in this study. Limit of quantification Both extraction and elution procedures can affect the recoveries (LOQ) of each compound was detailed in Table S3. The mean re- of analytes from water by extraction materials. Our previous work covery rate (n ¼ 3) of each OMP was also calculated according to has proven that a dynamic-elution method is superior to the our previous study (Li et al., 2018), and expressed as the shaking-elution method (Zhang et al., 2013a). In this work, the mean ± standard deviation. elution type and volume of the eluting solvents were both opti- mized. Fig. 2 shows that the elution efficiency of the DCM and EA mixture (volume ration is 1:1) was better for the majority of PAHs 2.5. Statistical analysis with the same elution volume compared with the other three types of elution solvents. Among the four elution solvents, Hex is a The method detection limit (MDL) of each OMP by different nonpolar solvent, while DCM and EA are weakly polar solvents. extraction methods was calculated by Eq. (1) according to the re- Based on the principle of similarity and intermiscibility, the elution sults of the 7 parallel samples. efficiency of DCM and EA for PAHs should be higher than that of Hex, and the mixture has a wider extraction range, resulting in a high elution performance on PAH contaminants. Similarly, the best MDL ¼ St(n-1,1-alpha¼0.99) Eq. 1 elution solvents for OCPs, PAEs and NBs were EA, DCM and CYH, respectively (Fig. 2). These results show that the elution solvent where t(n-1,1-alpha¼0.99) is the value of 99% confidence when the degree of freedom is (n-1), n is the number of parallel samples and with similar polarity, hydrophobicity and molecular structure to fi S is the standard deviation of repeated analysis. Water samples the OMPs may render high elution ef ciencies. As shown in Fig. S2, were prepared by adding 5 ng/L of each OMP to ultrapure water, it is easy to understand that the more elution volumes used, the fi with the pH adjusted below 2.0, and then extracted as previously better elution ef ciency we get. When the elution solvent volume described. increased from 3 mL to 12 mL, the recovery rates of these OMPs In addition, heatmap analysis of the total concentrations of peaked. Further increase of the elution volume led to no obvious OMPs in different samples was performed by R software (version increase of the recovery rates (Fig. S2). Therefore, 12 mL was 3.3.2) with the Vegan package. Cluster analysis was also performed adopted as the optimized elution volume in the following to group the patterns of OMP composition of each sample using experiments. PAST (PAleontological Statistics) software (University of Oslo, Nor- For the amount of M150 used for the extraction, the recoveries way). All the data was expressed as the mean ± standard deviation of all four types of OMPs increased with the amount of magnetic in this study. materials. The highest recoveries of these OMPs were observed Y. Liang et al. / Environmental Pollution 252 (2019) 196e204 199

Fig. 2. Recoveries of polycyclic aromatic hydrocarbons (PAHs) (A), organochlorine pesticides (OCPs) (B), phthalate esters (PAEs) (C), and nitrobenzenes (NBs) (D) under different elution solvents. Four elution solvents, including dichloromethane (DCM), ethyl acetate (EA), dichloromethane and ethyl acetate mixture (volume ration is 1:1) (DCM þ EA) and n- Hexane (Hex), were investigated. n-Hexane is replaced by cyclohexane (CYH) during the elution of NBs. when over 80 mg/L magnetic materials were used (Fig. 3A). the pH of 2, and the recoveries gradually decreased when Considering the runoff of the magnetic materials and probably increasing the pH from 2 to 12. However, the recoveries for OCPs higher concentrations of OMPs in some specific water samples, we and NBs showed insignificant variations when increasing the pH selected 100 mg/L as the commonly-used dosage. This dosage is from 2 to 12 (Fig. 3C). Thus, the pH of 2 was selected as the opti- lower than some similar materials used in previous studies, such as mum value for the following experiment. For the water volume, the magnetic titanium oxide nanoparticles (200 mg/L) (Li et al., 2013), recoveries of all OMPs had an insignificant decrease when the mixed hemimicelles materials (160 mg/L) (Li et al., 2007) and water volume increased from 1 L to 10 L (Fig. 3D), indicating that magnetic nanoparticles (400 mg/L) (Cai et al., 2015). For the the water volume had no significant influence on the extraction extraction time, the recoveries of all four types of OMPs increased efficiency of the M150. A previous study also demonstrated that the by prolonging the extraction time and reached the maximum in salinity and volume had insignificant influences on the extraction 60 min (Fig. 3B). Thus, the optimal extraction time was 60 min. The of the 8 target OMPs (Zhang et al., 2013a), which is generally extraction time of M150 was longer than that of the magnetic ti- consistent with this study. In summary, the optimized extraction tanium oxide nanoparticles (20 min) (Li et al., 2013) and magnetic conditions, including the dosages of microspheres, extraction time, nanoparticles (5 min) (Cai et al., 2015) due to its relatively large size, and pH of samples were 100 mg/L, 60 min, and 2, respectively. The but the recycling and separation of M150 was much easier and optimized results of the extraction and elution procedures were faster than that of the nanoparticles. Despite this, the extraction applied in the following sample analyses. time of M150 was still faster than that of common SPE procedures when extracting large-volume water samples, with a sampling 3.2. Comparison of C18, HLB and M150 performances speed of 10 mL/min. Overall, the small particle size and the large pore diameter of M150 resulted in fast diffusion from the solution To compare the extraction performances of C18, HLB and M150 to the interaction sites on the microspheres, which contributed to a materials, the recoveries and MDLs of these materials for all the rapid extraction process. In addition, the recoveries of different selected OMPs were detected and calculated in this study. Fig. 4 types of OMPs showed different trends when the pH increased shows the recoveries (A) and MDLs (B) of these targeted OMPs. In from 2 to 12. The highest recoveries for PAHs and PAEs occurred at general, the recoveries of C18, HLB, and M150 materials for PAHs 200 Y. Liang et al. / Environmental Pollution 252 (2019) 196e204

Fig. 3. Recoveries of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), phthalate esters (PAEs), and nitrobenzenes (NBs) based on different amount of microspheres (A), extraction time (B), pH (C) and sample volume (D). were 77.72e90.66%, 77.62e97.23% and 80.5e96.63%, respectively However, the MDLs of M150 for all the detected OMPs were still less (Fig. 4A). For all the detected PAHs, except for BaP, the recoveries of than 3.9 ng/L, which is considered a low level. Therefore, these M150 were higher than those of C18, which was partially supported results reveal the feasibility and high precision of the method. by our previous study (Zhou et al., 2015). Moreover, the recoveries Overall, the extraction efficiency of M150 was superior to that of of M150 materials for OCPs were all above 80.84%, which were C18 and HLB cartridges for the selected OMPs, while the MDLs of higher than those obtained by the C18 (76.99e91.72%) and HLB M150 for these OMPs were comparable to those of C18 and HLB. (72.49e97.02%). For all selected PAEs, the recoveries of these three MSPE, based on magnetic materials, has begun to be widely applied materials showed little difference, in the range of 78.89e97.65%, in OMP detection. For instance, Yu et al. (2018) adopted porphyrin- 77.53e93.92%, and 80.45e97.71%, respectively (Fig. 4A). For NBs, based magnetic nanocomposites and detected 15 PAHs with the recoveries of M150 materials were all above 90% except for NB, acceptable recoveries (73.7e107.1%) from the River in which was much higher than that of C18 (52.21e87.31%) and com- China. Yazdanfar et al. (2018) developed a highly sensitive solid- parable to those of HLB (89.75e94.81%). The recovery of M150 for phase-dispersive microextraction method based on magnetic car- NB was 84.41%, slightly lower than that of C18 (87.63%) and HLB bon nanocomposites for the extraction and determination of 16 (93.39%) (Fig. 4A). Although the recoveries of both C18 and HLB PAHs in real environmental samples, including tap water, sea water, extraction materials were considered satisfactory, M150 had a waste water, sewage, and soil samples. better enrichment performance than C18 and HLB for most of the selected OMPs, demonstrating that M150 has an advantage over 3.3. Occurrence and total concentrations of OMPs in the Huai River commercial C18 and HLB materials in the extraction of most OMPs. For the MDLs of M150, 6 OMPs had the lowest MDLs, while 7 OMPs Fig. 5 shows the occurrence of OMPs in source water of the had the highest MDLs, indicating that the M150 materials had no whole Huai River, and the detailed concentrations of individual fi signi cant superiority over commercial C18 and HLB (Fig. 4B). contaminants are listed in Supplementary Data Table S4. In brief, a Y. Liang et al. / Environmental Pollution 252 (2019) 196e204 201

Fig. 5. Occurrences and concentrations of organic micropollutants (OMPs) in the source water from the Huai River.

g-BHC can be attributed to the recent usage of lindane (Walker et al., 1999). Results showed that g-BHC is the predominant spe- cie among the different isomeride of lindane (Fig. S3), suggesting lindane is still in use, although they have been forbidden in China for many years. Fig. 4. Recoveries (A) and method detection limits (B) for the organic micropollutants Fortunately, the PAE pollution in the HuaiP River was much better (OMPs) with the optimized extraction and elution procedures of C18, HLB and M150. than that in other areas in China. The PAEs in the Huai River ranged from 164.37 ng/L to 662.55 ng/L, withP a mean value of total of 21 types of OMPs, including 6 PAHs, 5 OCPs, 5 PAEs and 5 327.49 ng/L, which was much lower than the PAEs in several NBs, were all detected in water samples of the Huai River by our cities from Jiangsu Province (Li et al., 2012). The concentrations of established method, with the highest concentrations of 538.66 ng/ the detectable NBs in this study ranged from 30.43 ng/L to 1323.77 ng/L, with a mean value of 170.91 ng/L. The concentrations L, 320.05 ng/L, 662.55 ng/L and 1323.77 ng/L,P respectively. of the detected NBs were higher than those in the surface water Compared with the total concentration of PAHsP ( PAHs) detected in the surface water at home and abroad, the PAHs in the Huai from the Yangtze River (55.2 ng/L) and the (6.5 ng/L) River were similar to those of the major rivers in China but were (Gao et al., 2008). However, the concentrations of NBs were lower higher than those in areas with higher urbanization levels, such as than those in the surface water from the southern part of the Huai > samples from the in Zhejiang Province with the River Basin ( 10 mg/L) and the (17.26 mg/L) (He et al., mean concentration of 162.8 ng/L (Chen et al., 2007). Nap is the 2006). predominant PAH specie and similar with the samples from the main stream of Yangtze River in Wuhan section (Feng et al., 2007). 3.4. Spatial distribution of OMPs in the Huai River However, the levels of same PAHs subtypes were far higher than those of foreign rivers, such as the Mississippi River (0.58e12.7 ng/ Cluster analyses were performed to characterize the spatial L) in theP U.S. (Mitra and Bianchi, 2003). distribution of different types of OMPs in the source water along The OCPs in the Huai River Basin ranged from 98.01 ng/L to the Huai River. Fig. 6A shows that the PAHs profiles of the surface 320.05 ng/L, with a mean value of 181.67 ng/L. The concentrations water samples from the downstream (Down-1, Down-3) and its of the detectable OCPs in this study were much higher than the tributaries (Xinyi, Jinghang) generally clustered together, as did the same OCPs species in the drinking water from cities along the samples from upstream and midstream of the Huai River. It can be Chinese coastland of the Yellow Sea (0e104.67 ng/L) (Li et al., 2018) concluded that the distribution of PAHs in the Huai River is related and those in the source water from the Yangtze River and Tai lake to the spatial location and river water systems because there are (0.2e168.84 ng/L) (Shi et al., 2018). Moreover, the predominance of significant differences regarding the PAH types and abundances in b-BHC indicates no fresh inputs of BHCs, while a high percentage of varied river systems. In addition, it can be speculated that there are 202 Y. Liang et al. / Environmental Pollution 252 (2019) 196e204

Fig. 6. Cluster analysis dendrogram of polycyclic aromatic hydrocarbons (PAHs) (A), organochlorine pesticides (OCPs) (B), phthalates (PAEs) (C) and nitrobenzenes (NBs) (D) in the source water from the Huai River based on Bray-Curtis similarity index. strong PAH emission sources near the two main tributaries Shaying not related to those of the other sites as shown in Fig. 6C, indicating and Guo because all sitesP with the highest concentrations of PAHs that strong emission sources may exist in this area. The average clustered together. The PAHs decreased with the dilution of the concentrations of PAEs in upstream and midstream were 277.95 ng/ water flow, which may be mainly resulted from the absence of new L and 273.05 ng/L, respectively (Fig. S4). While in the downstream emission sources. of the Huai River, the average concentrations of PAEs was Similar results were observed regarding the spatial distribution 420.24 ng/L, which was higher than the samples from the Shaying of OCPs. Concentrations of OCPs in the two main tributaries were River and the Guo River, with average concentrations of 303.57 ng/L over 240 ng/L, which were higher than those in the mainstream. and 361.89 ng/L, respectively (Fig. S4). As shown in Fig. 6C, sam- Sampling sites in the Shaying River and the Guo River generally pling sites in the mainstream of the Huai River behind Mid-4 clustered together as displayed in Fig. 6B. Both the Shaying River clustered together, indicating that the pollution of PAEs in down- and the Guo River flow through areas with frequent agricultural stream of the Huai River was more serious. Considering the production and widespread use of fertilizers and pesticides (Wang booming industry in the northern part of Jiangsu Province, the two et al., 2009). Additionally, the release of pesticide pollutants in tributaries including the Jinghang River and the Xinyi River are sediments may be responsible for the high concentration of OCPs in supposed to be contaminated by various OMPs. Different types of the source water of the two tributaries, which was also reported in leading industries, such as beverage, textile, chemical, and phar- a previous study (Li et al., 2018). Moreover, the concentration of maceutical factories, occupy the dominant position of the local OCPs gradually decreased from Mid-2 to Mid-4, while a sharp in- industry, and all these industries are capable of generating large crease was observed in Down-1, indicating that new sources of the amounts of PAEs (Huang et al., 2004), which may be an important OCPs may exist in this area. Fig. 6B shows that samples from the reason for the higher concentration of PAEs in the source water of upstream and downstream were separated, reflecting the different downstream of the Huai River and its tributaries in Jiangsu types of pollution sources. Province. The spatial distribution of PAEs was distinctly different from The concentration of NBs in the main stream of the Huai River those of PAHs and OCPs. The sample Guo-2 had the highest con- was relatively constant, except for the samples of Mid-4 (677.55 ng/ centration of 662.55 ng/L, and the PAE distribution in this site was L) and Down-1 (1323.77 ng/L). However, samples from the Y. Liang et al. / Environmental Pollution 252 (2019) 196e204 203 downstream of the river reverted to a lower level (30.43e43.57 ng/ the separation and the preconcentration of pollutants in water samples. Trac. e L). It is worth nothing that the concentration of m-C-NB increased Trends Anal. Chem. 30, 1095 1108. Chen, Y., Zhu, L., Zhou, R., 2007. 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