Marine Pollution Bulletin xxx (2014) xxx–xxx
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China Zhaoyun Zhu a,b, Tieyu Wang a,⇑, Pei Wang a,b, Yonglong Lu a, John P. Giesy c a
State Key Lab of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China Graduate University of Chinese Academy of Sciences, Beijing 100049, China c Department of Veterinary Biomedical Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada b
a r t i c l e
i n f o
Keywords: PFAS Sediment Partitioning Hazard assessment South Bohai
a b s t r a c t This study investigated the concentrations and distribution of Perfluoroalkyl and polyfluoroalkyl substances (PFAS) in sediments of 12 rivers from South Bohai coastal watersheds. The highest concentrations of RPFAS (31.920 ng g1 dw) and PFOA (29.021 ng g1 dw) were found in sediments from the Xiaoqing River, which was indicative of local point sources in this region. As for other rivers, concentrations of RPFAS ranged from 0.218 to 1.583 ng g1 dw were found in the coastal sediments and from 0.167 to 1.953 ng g1 dw in the riverine sediments. Predominant PFAS from coastal and riverine areas were PFOA and PFBS, with percentages of 30% and 35%, respectively. Partitioning analysis showed the concentrations of PFNA, PFDA and PFHxS were significantly correlated with organic carbon. The results of a preliminary environmental hazard assessment showed that PFOS posed the highest hazard in the Mi River, while PFOA posed a relative higher hazard in the Xiaoqing River. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Perfluoroalkyl and polyfluoroalkyl substances (PFAS) such as perfluorocarboxylates (PFCAs) and perfluoroalkanesulfonates (PFSAs), which have been produced for more than 50 years, have emerged as a new class of global environmental pollutants since they were first reported to be widespread in the environment (Giesy and Kannan, 2001, 2002; 3M Company, 1999). The unique physicochemical properties of PFAS, such as high surface activity, thermal stability, amphiphilicity, resistance to acidic and alkaline conditions and weak intermolecular interactions, make them popular in many industrial applications (e.g., fire-fighting foams, photolithography, and pesticides) and consumer applications (e.g., shampoos, surface coatings for carpets, stain repellents for furniture, and paper products) (Kissa, 2001; Giesy and Kannan, 2001; Higgins et al., 2005; Paul et al., 2008). PFAS can be released into the environment through their production and usage. The strong C–F bond of PFAS makes them extremely resistant to hydrolysis, thermal, microbiological and photolytical degradation (Wang et al., 2009). PFAS are ubiquitous in river water, oceans, sediment, soil, and tissues of wildlife and humans (Ahrens et al., 2010a; Higgins et al., 2005;Wang et al., 2013; Giesy and Kannan, 2001; Bao et al., 2010a; Kannan et al., 2001, 2002a,b). They are potentially harmful to fresh water and marine mammals (Ishibashi et al., 2008) and have potential adverse effects in wildlife species (Hoff ⇑ Corresponding author. Tel.: +86 10 62849466. E-mail address: [email protected] (T. Wang).
et al., 2005; Fair et al., 2012; Beach et al., 2005; Newsted et al., 2005, 2008; Giesy et al., 2009). Sediment is an important sink and reservoir of persistent organic pollutants and has a large impact on their distribution, transportation, and fate in the aquatic environment (Ahrens et al., 2009; Yang et al., 2011). Some researchers reported that the only environmental sink for perfluorooctanoate (PFO, refers to PFOA & PFOS) was sediment burial and transport to the deep oceans (Prevedouros et al., 2006). The distribution of PFAS between water and sediment is considered as an important process which controls their transport and fate (Prevedouros et al., 2006; You et al., 2010). Sediment–water distribution is a complex process, depending not only on the physicochemical characteristics of the compounds but also on the sediment nature such as the organic carbon fraction (foc) (Ahrens et al., 2010b; Zhao et al., 2012). Sorption of PFAS on sediment has been studied under laboratory conditions (Higgins and Luthy, 2006), but there are few field studies focused on partitioning behavior of PFAS in aquatic environments (Ahrens et al., 2009; Zhang et al., 2012; Zhao et al., 2013). Results of studies under laboratory conditions and those observed in the field can be different (Hong et al., 2013). To gain better understanding on the fate of PFAS in the whole environment, more information of field study is necessary on partitioning behavior of PFAS. The Bohai Sea region in north China is an area where industry has been developing rapidly during the past few decades. The Bohai Sea, a semi-enclosed coastal water body with almost 40 rivers flowing directly into it, receives enormous amounts of
0025-326X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
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Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
contaminants through discharge of river water and sediment. The Bohai Sea region is currently one of the most polluted areas in China due to the industrial and agricultural activities (Hu et al., 2010; Luo et al., 2010; Naile et al., 2010; Zhao et al., 2013). Occurrence, spatial distribution, source and fate of PFAS in different matrices in estuarine and coastal areas of North Bohai Sea had been studied previously (Wang et al., 2011). Results of another study in the coastal area of Liao Dong Bay revealed that direct emission from industry parks was a major source of PFAS in soil (Wang et al., 2013). However, there are limited reports about PFAS in the southern part of the coast of the Bohai Sea compared with the northern part. Concentrations and distribution of PFAS in surface sediments from Laizhou Bay and its adjacent rivers have been measured and from that it was learned that concentrations of PFOA were extremely high in that area and might pose a potential threat for the benthic organisms (Zhao et al., 2013). Currently, there is limited information about PFAS in sediments of coastal rivers along the South Bohai coast. The present study, launched in 2008, was conducted as a systematic investigation to trace sources and fates of toxic substances in various environmental media from adjacent riverine and estuarine areas including the Yellow and Bohai Seas of China. The specific objectives of this study were to: (1) determine concentrations and spatial distribution of PFAS in sediments from coastal rivers along the south coast of the Bohai Sea; (2) identify potential sources of PFAS; and (3) conduct a screening-level ecological hazard assessment for PFAS in local aquatic ecosystems. The results of the study provide information and support for future determinations of status and trends of PFAS emissions and their management at regional and national levels. 2. Materials and methods 2.1. Standards and reagents 17 kinds of PFAS standards, including perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUdA), perfluorododecanoic acid (PFDoA), perfluorotridecanoic acid (PFTrDA), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDA), perfluorooctadecanoic acid (PFODA), potassium perfluorobutanesulfonate (PFBS), sodium perfluorohexanesulfonate (PFHxS), potassium perfluorooctanesulfonate (PFOS), sodium perfluorodecanesulfonate (PFDS), and 5 mass-labeled internal standards, including PFBA [1,2,3,4 13C], PFOA [1,2,3,4 13C], PFDoA [1,2 13C], PFHxS [1,2 18O] and PFOS [1,2,3,4 13C], were obtained from Wellington Laboratories with purities of >98% (Guelph, Ontario, Canada). The mixed standards were prepared in 100% methanol and stored at 4 °C. HPLC grade methanol, acetonitrile and methyl tert-butyl ether (MTBE) were purchased from J.T. Baker (Phillipsburg, NJ, USA). Ammonium acetate, anhydrous sodium sulfate and tetrabutylammonium hydrogensulfate (TBAHS) were purchased from Sigma–Aldrich Co. (St. Louis, MO, USA). Milli-Q water was obtained from a Milli-Q synthesis A10 (Millipore, Bedford, MA, USA) and used throughout the experiment. 2.2. Sediment sampling A total of 36 surface (top 1–5 cm) samples of sediment were collected from 12 typical coastal rivers, which flow into the Bohai Sea through Shandong and Hebei Provinces (Fig. 1). For each river, at least 2 sites were chosen with the first one near the coast and the other a distance of 20–30 km from the former. All surface sam-
ples were collected in September 2011 by use of a clean, stainless steel trowel, and placed in clean 250 mL, largemouth, and polypropylene (PP) bottles. Wet sediments were immediately transported to the laboratory in ice-cooled boxes and then dried in a FreeZone 2.5 Liter Benchtop Freeze Dry System (LABCONCO, Kansas City, MO), ground and homogenized with a silica mortar and pestle, sieved through a 2-mm mesh, and stored in pre-cleaned glass jars in room temperature until further analysis. 2.3. Sample extraction and instrumental analysis Detection of PFAS: Sediments were extracted according to a previously published method with minor modifications and optimizations (Naile et al., 2010; Wang et al., 2013). Briefly, a 50 ml polypropylene centrifuge tube was charged with 2.5 g homogenized sediments, which were soaked with 2 mL Milli-Q water and vortexed until the samples were visually homogenized. A 1 mL portion of 0.5 M tetrabutylammonium hydrogensulfate (TBAHS) and 2 mL of 25 mM sodium acetate were added, and spiked with 10 ng mass-labeled internal standards with vortexing. Subsequently, 5 mL of methyl tert-butyl ether (MTBE) was added and the mixture was extracted 20 min by vibration and then centrifuged at 3500 rpm for 30 min. This process of extraction with MTBE was repeated three times and the upper MTBE fraction was combined together into a 15 mL PP tube. The eluate was then evaporated to dryness under a gentle flow of high purity nitrogen, and reconstituted in 1 mL methanol, then filtered through a 0.2 mm nylon filter, transferred into a 1.5 mL PP snap top brown glass vial with polyethylene (PE) septa for HPLC analysis. The instrumental analysis was performed using a high performance liquid chromatography–negative electrospray ionization–tandem mass spectrometry system (HPLC–ESI–MS/MS) that consisted of an Agilent 1290 Infinity HPLC System coupled to an Agilent 6460 Triple Quadrupole LC/MS System (Agilent Technologies, Palo Alto, CA). The instrument conditions are listed in Table S1. Detection of organic carbon fraction (foc): The procedure used is based on a wet digestion method without heating followed by colorimetric determination (Chatterjee et al., 2009; Da Silva Dias et al., 2012). Briefly, a 0.5 g sediment sample was placed in a 100 mL Erlenmeyer flask, then 10 mL of potassium dichromate solution (0.667 mol L1) and 10 mL of sulfuric acid were added. Flasks were swirled for 5 min to homogenize the mixture. After reacting for 20 min and standing for 1 h to cool, 10 mL Milli-Q water was added to the flasks. After standing overnight (12 h), 15 mL supernatant solution was taken out and diluted to 50 mL by adding Milli-Q water. Then the solution was measured by a UV spectrophotometer under the light transmittance at 590-nm wavelength. 2.4. Quality assurance and quality control All fluorinated materials that could come into contact with the samples during sampling and extraction were removed to avoid contaminations. Nine-point external standard curves ranging from 0.01 to 100 ng mL1 were prepared for the quantification of individual PFAS with coefficients of determination (r2) for all the target analytes higher than 0.99. The limit of detection (LOD) and limit of quantification (LOQ) were defined as the peak of analyte required to yield a signal-to-noise (S/N) ratio of 3:1 and 10:1, respectively. Recoveries of internal standards spiked into sediments ranged from 73% to 119%. Concentrations of PFAS were not corrected for recoveries. Procedure blanks using anhydrous sodium sulfate as alternative of sediment were conducted with every sample set and solvent blanks using 100% methanol were run every 4–5 samples to check for carryover and background contamination. No detectable PFAS were observed over LOQ in all the procedure and
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
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Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
Fig. 1. Sampling positions of sediment in South Bohai coastal rivers.
solvent blanks. Detailed QA/QC measurements of PFAS in sediment are given in Table 1.
3. Results and discussion 3.1. PFAS in sediments from South Bohai coastal rivers
2.5. Statistical analysis Statistical analysis was performed with IBM SPSS Statistics V21. Before analyzing, concentration values lower than the LOQs were set to one-half of the LOQs, andpthose lower than the LODs were ffiffiffi assigned as values of the LODs/ 2 (Bao et al., 2010a). A statistical distribution test called P–P plots was carried out to test for normality. Spatial distributions of PFAS were analyzed using ArcGIS V10.0 software (ESRI).
In sediments collected from South Bohai coastal rivers, 14 out of 17 target PFAS were quantified, including: C4–C14–PFCAs, and C4–, C6–, and C8–PFSAs. Concentrations of PFAS in sediments from South Bohai coastal rivers were generally lower than the corresponding LOQs (Table S2). The total concentrations of PFAS in surface sediments ranged from 0.098 ng g1 dw to 1.889 ng g1 dw with a mean of 0.477 ng g1 dw (except for the Xiaoqing River). The highest concentration of RPFAS (31.92 ng g1 dw) was found at the upstream location in the Xiaoqing River, and the value was approximately 2 orders of magnitude higher than the average
Table 1 Target analytes of 17 PFAS measured in this study with QA/QC information. Analyte
Acronym
MS/MS transition (m/z)
Recovery (n = 4) %Mean ± SD
LOD (ng g1)
LOQ (ng g1)
Perfluorocarboxylic acid Perfluorobutanoic acid Perfluoropentanoic acid Perfluorohexanoic acid Perfluoroheptanoic acid Perfluorooctanoic acid Perfluorononanoic acid Perfluorodecanoic acid Perfluoroundecanoic acid Perfluorododecanoic acid Perfluorotridecanoic acid Perfluorotetradecanoic acid Perfluorohexadecanoic acid Perfluorooctadecanoic acid
PFCAs PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUdA PFDoA PFTrDA PFTeDA PFHxDA PFODA
213.0 ? 263.0 ? 313.0 ? 363.0 ? 413.0 ? 463.0 ? 513.0 ? 563.0 ? 613.0 ? 662.9 ? 713.1 ? 813.0 ? 913.0 ?
- > 169.1 218.9 269.0 318.9 368.9 419.0 468.9 519.0 569.0 619.0 669.0 769.0 869.0
100 ± 5 104 ± 3 110 ± 3 96 ± 6 100 ± 11 109 ± 2 103 ± 7 90 ± 4 89 ± 4 93 ± 2 73 ± 4 73 ± 1 87 ± 5
0.02 0.01 0.004 0.006 0.002 0.002 0.004 0.008 0.004 0.006 0.006 0.006 0.006
0.1 0.03 0.01 0.02 0.01 0.01 0.01 0.02 0.01 0.02 0.02 0.02 0.02
Perfluorinated sulfonic acid Perfluorobutanesulfonat Perfluorohexanesulfonat Perfluorooctanesulfonat Perfluorodecanesulfonat
PFSAs PFBS PFHxS PFOS PFDS
299.0 ? 399.0 ? 498.9 ? 599.0 ?
80.0 80.0 80.0 79.9
119 ± 4 114 ± 8 117 ± 2 86 ± 6
0.004 0.004 0.004 0.01
0.01 0.01 0.01 0.02
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
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concentration and 16.9 times higher than the highest concentration (1.889 ng g1 dw) in the other 11 rivers. These high concentrations might be a result of receiving urban, industrial, and agricultural wastewater and sludge over the past decades (Zhao et al., 2013). The summary of PFAS concentrations in the coastal and riverine sediments are shown in Table 2. PFAS in the Xiaoqing River sediments will be discussed separately because of their high concentrations compared with the other 11 coastal rivers. In this study, the concentrations of RPFAS ranged from 0.218 ng g1 dw to 1.583 ng g1 dw (mean: 0.535 ng g1 dw) in the coastal sediments and from 0.167 ng g1 dw to 1.953 ng g1 dw (mean: 0.578 ng g1 dw) in the riverine sediments, respectively. The average concentration of RPFCAs in coastal sediments (0.259 ng g1 dw) was higher than that in the riverine sediments (0.208 ng g1 dw), while the average concentration of RPFSAs in the riverine sediments (0.370 ng g1 dw) was higher than that in the coastal sediments (0.276 ng g1 dw). The Xiaoqing River had the highest concentration of RPFAS in both coastal and riverine sediments (2.756 ng g1 dw and 31.920 ng g1 dw, respectively). Generally, the concentrations of RPFAS in riverine sediments were higher than that those in coastal sediments. Composition profiles of PFAS in the coastal and riverine sediments from South Bohai Bay are shown in Fig. 2. The dominant PFAS compound in the coastal sediments was PFOA, with a contribution of 30% to the total PFAS. Other major components were PFBS (29%), PFOS (20%), and PFBA (8%). The situation was quite different in the riverine sediments with contribution of PFOA being only 8% while contributions of PFBS, PFOS and PFBA were 35%, 27% and 15%, respectively. As for the Xiaoqing River, although concentrations of PFAS varied largely at different sampling sites along the river, PFOA was the dominant PFAS in all samples with a high contribution of over 90%. 3.2. Spatial distribution and source identification The spatial distribution of RPFAS in sediment from South Bohai coastal rivers is shown in Fig. 3. It is obvious that Xiaoqing River had the highest RPFAS (2.756–31.920 ng g1 dw) in this area, especially for the site XQ-3 (31.920 ng g1 dw), which was relatively far from the coastline. The Xiaoqing River, with a total length of 216 km and a drainage area of 10,336 km2, flows through several major cities, including Ji’nan, Zibo, Binzhou, Dongying, and Weifang in Shandong Province, China. As an important inland
ship-transport river in Shandong Province and the only discharge channel of wastewater in Ji’nan city, the Xiaoqing River receives all kinds of wastewater and sludge. Although control measures like building more municipal sewage treatment plants and sewage interception facilities were carried out in recent years, there were still huge amounts of sewage and garbage pouring into the Xiaoqing River. The high concentrations of PFAS in sediments of this river might result from upstream transportation, tributaries of industrial discharge as well as local release of garbage and wastewater from human activities along the river. The relatively high concentrations of RPFAS in Jiaolai River sediment (0.404– 1.638 ng g1 dw) might be from the upper stream historically industrial wastewater discharge, such as iron ore plants and chemical fiber factories. Site ZW-3 in Zhangwei River was found to have a higher value of RPFAS (1.889 ng g1 dw) in sediment compared to other sampling sites in this river, indicating a potential point source at this site. According to the existing environmental situation of this sampling site, the most possible source might be paper manufacturing factories at south of this sampling position, since PFOS-substances derived from perfluorooctane sulfonyl fluoride (POSF) and their simple derivatives were widely used in paper treatment in China (Xie et al., 2013). Similar results were found on the estuary of both the Mi (site MR-1, 0.863 ng g1 dw) and Wang Rivers (site WR-1, 1.511 ng g1 dw). There was direct discharge of wastewater from a fertilizer factory and salt fields around site MR-1, which could be the sources of PFAS. The industry park located near site WR-1 could also be the source of PFAS. The major discharging river in this area was the Yellow River, which from 1919 to 2008 had discharged approximately 12.7 108 t a1 sediment into the Bohai Sea (Mu et al., 2012). Comparing to its adjacent rivers, the Yellow River had lower concentrations of RPFAS in sediments. One reason might be that the riverbed of the Yellow River in Shandong Province is rather high. Therefore it is unlikely to receive sewage from local facilities. The other reason might be that the water and sediment regulation conducted on the Yellow River every year since 2002 increased erosion in the downstream part of the Yellow River, carrying most of the surface sediment into the Bohai Sea (Li, 2004; Yao et al., 2009; Wang et al., 2010). The much higher discharge of the Yellow River than those of other rivers in this study would lead to more dilution, which could also be an explanation of this phenomenon. Generally speaking, concentrations of RPFAS in sediment at inland riverine locations were higher than those in coastal sediment because of the scouring and dilution of tidal currents and waves, and explanations have been found for
Table 2 PFAS concentrations in sediments from South Bohai coastal rivers (ng g1 dw). Coastal sediment (n = 13)
PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUdA PFDoA PFTrDA PFTeDA PFBS PFHxS PFOS RPFCAs RPFSAs RPFAS a
Riverine sediment (n = 20)
Xiaoqing River sediment (n = 3)
Mean
Max
Min
Median
Mean
Max
Min
Median
Estuary (n = 1)
Riverine (n = 2)
0.043 – 0.006 – 0.158 0.017 0.011 0.010 0.004 – – 0.158 0.009 0.107 0.259 0.276 0.535
0.121 – 0.043 0.006 1.049 0.080 0.025 0.034 0.013 – – 0.348 0.028 0.188 1.143 0.462 1.583
–a – – – 0.005 0.002 – – – – – 0.036 – 0.061 0.044 0.102 0.218
0.029 – 0.004 – 0.071 0.009 0.012 – – – – 0.111 – 0.098 0.133 0.258 0.442
0.089 – 0.004 – 0.044 0.016 0.020 0.020 0.005 – – 0.204 0.010 0.155 0.208 0.370 0.578
0.452 0.013 0.031 0.008 0.221 0.087 0.067 0.084 0.027 0.009 0.009 1.695 0.074 0.435 0.775 1.796 1.953
– – – – 0.005 0.002 – – – – – 0.012 – 0.027 0.053 0.114 0.167
0.038 – – – 0.027 0.009 0.015 – – – – 0.098 – 0.109 0.115 0.259 0.358
0.035 0.010 0.040 0.034 2.452 0.005 0.017 – 0.004 – – 0.070 – 0.082 2.604 0.152 2.756
0.155 0.133 0.208 0.153 12.988 0.052 0.089 0.120 0.106 0.040 0.017 0.141 0.046 0.101 14.061 0.288 14.350
0.315 0.225 0.392 0.307 29.021 0.178 0.245 0.319 0.352 0.127 0.059 0.106 0.098 0.176 31.540 0.380 31.920
‘‘–’’ means data below limitation of detection.
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
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Fig. 2. Composition of PFAS in Xiaoqing River (Part A) and percentage composition of PFAS in coastal sediments and riverine sediments (Part B).
Fig. 3. Spatial distributions of RPFAS in sediments from South Bohai coastal rivers.
several anomalous points opposite to this trend. However, the distribution of PFAS in the coastal environment is influenced by many factors, such as partitioning behaviors between sediment and water (Higgins and Luthy, 2006), the deposition of volatile compounds in the air (Dreyer et al., 2009), and the transport of PFAS in water (Ahrens et al., 2009). Thus, more information is needed to identify sources of PFAS in sediment of South Bohai coastal rivers. 3.3. Comparison of PFAS in sediments with other Asian countries PFOA and PFOS were the most frequently detected PFAS compounds in the environment. Their concentrations in other coastal and riverine sediments in China and other Asian countries were compared in this study (Table 3). Compared with other riverine and coastal sediments in China, concentrations of PFOS in sediments from South Bohai coastal rivers, excluding the Xiaoqing River, (0.03–0.36 ng g1 dw) were comparable to those found in the Daliao River system of northeast China (0.06–0.37 ng g1 dw)
(Bao et al., 2009) and Yangtzi River Estuary, Shanghai (n.d.– 0.46 ng g1 dw) (Bao et al., 2010b), but lower than those observed in North Bohai coastal rivers (n.d.–1.97 ng g1 dw) (Wang et al., 2011b), Laizhou Bay rivers (
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China Zhaoyun Zhu a,b, Tieyu Wang a,⇑, Pei Wang a,b, Yonglong Lu a, John P. Giesy c a
State Key Lab of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China Graduate University of Chinese Academy of Sciences, Beijing 100049, China c Department of Veterinary Biomedical Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada b
a r t i c l e
i n f o
Keywords: PFAS Sediment Partitioning Hazard assessment South Bohai
a b s t r a c t This study investigated the concentrations and distribution of Perfluoroalkyl and polyfluoroalkyl substances (PFAS) in sediments of 12 rivers from South Bohai coastal watersheds. The highest concentrations of RPFAS (31.920 ng g1 dw) and PFOA (29.021 ng g1 dw) were found in sediments from the Xiaoqing River, which was indicative of local point sources in this region. As for other rivers, concentrations of RPFAS ranged from 0.218 to 1.583 ng g1 dw were found in the coastal sediments and from 0.167 to 1.953 ng g1 dw in the riverine sediments. Predominant PFAS from coastal and riverine areas were PFOA and PFBS, with percentages of 30% and 35%, respectively. Partitioning analysis showed the concentrations of PFNA, PFDA and PFHxS were significantly correlated with organic carbon. The results of a preliminary environmental hazard assessment showed that PFOS posed the highest hazard in the Mi River, while PFOA posed a relative higher hazard in the Xiaoqing River. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Perfluoroalkyl and polyfluoroalkyl substances (PFAS) such as perfluorocarboxylates (PFCAs) and perfluoroalkanesulfonates (PFSAs), which have been produced for more than 50 years, have emerged as a new class of global environmental pollutants since they were first reported to be widespread in the environment (Giesy and Kannan, 2001, 2002; 3M Company, 1999). The unique physicochemical properties of PFAS, such as high surface activity, thermal stability, amphiphilicity, resistance to acidic and alkaline conditions and weak intermolecular interactions, make them popular in many industrial applications (e.g., fire-fighting foams, photolithography, and pesticides) and consumer applications (e.g., shampoos, surface coatings for carpets, stain repellents for furniture, and paper products) (Kissa, 2001; Giesy and Kannan, 2001; Higgins et al., 2005; Paul et al., 2008). PFAS can be released into the environment through their production and usage. The strong C–F bond of PFAS makes them extremely resistant to hydrolysis, thermal, microbiological and photolytical degradation (Wang et al., 2009). PFAS are ubiquitous in river water, oceans, sediment, soil, and tissues of wildlife and humans (Ahrens et al., 2010a; Higgins et al., 2005;Wang et al., 2013; Giesy and Kannan, 2001; Bao et al., 2010a; Kannan et al., 2001, 2002a,b). They are potentially harmful to fresh water and marine mammals (Ishibashi et al., 2008) and have potential adverse effects in wildlife species (Hoff ⇑ Corresponding author. Tel.: +86 10 62849466. E-mail address: [email protected] (T. Wang).
et al., 2005; Fair et al., 2012; Beach et al., 2005; Newsted et al., 2005, 2008; Giesy et al., 2009). Sediment is an important sink and reservoir of persistent organic pollutants and has a large impact on their distribution, transportation, and fate in the aquatic environment (Ahrens et al., 2009; Yang et al., 2011). Some researchers reported that the only environmental sink for perfluorooctanoate (PFO, refers to PFOA & PFOS) was sediment burial and transport to the deep oceans (Prevedouros et al., 2006). The distribution of PFAS between water and sediment is considered as an important process which controls their transport and fate (Prevedouros et al., 2006; You et al., 2010). Sediment–water distribution is a complex process, depending not only on the physicochemical characteristics of the compounds but also on the sediment nature such as the organic carbon fraction (foc) (Ahrens et al., 2010b; Zhao et al., 2012). Sorption of PFAS on sediment has been studied under laboratory conditions (Higgins and Luthy, 2006), but there are few field studies focused on partitioning behavior of PFAS in aquatic environments (Ahrens et al., 2009; Zhang et al., 2012; Zhao et al., 2013). Results of studies under laboratory conditions and those observed in the field can be different (Hong et al., 2013). To gain better understanding on the fate of PFAS in the whole environment, more information of field study is necessary on partitioning behavior of PFAS. The Bohai Sea region in north China is an area where industry has been developing rapidly during the past few decades. The Bohai Sea, a semi-enclosed coastal water body with almost 40 rivers flowing directly into it, receives enormous amounts of
0025-326X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
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Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
contaminants through discharge of river water and sediment. The Bohai Sea region is currently one of the most polluted areas in China due to the industrial and agricultural activities (Hu et al., 2010; Luo et al., 2010; Naile et al., 2010; Zhao et al., 2013). Occurrence, spatial distribution, source and fate of PFAS in different matrices in estuarine and coastal areas of North Bohai Sea had been studied previously (Wang et al., 2011). Results of another study in the coastal area of Liao Dong Bay revealed that direct emission from industry parks was a major source of PFAS in soil (Wang et al., 2013). However, there are limited reports about PFAS in the southern part of the coast of the Bohai Sea compared with the northern part. Concentrations and distribution of PFAS in surface sediments from Laizhou Bay and its adjacent rivers have been measured and from that it was learned that concentrations of PFOA were extremely high in that area and might pose a potential threat for the benthic organisms (Zhao et al., 2013). Currently, there is limited information about PFAS in sediments of coastal rivers along the South Bohai coast. The present study, launched in 2008, was conducted as a systematic investigation to trace sources and fates of toxic substances in various environmental media from adjacent riverine and estuarine areas including the Yellow and Bohai Seas of China. The specific objectives of this study were to: (1) determine concentrations and spatial distribution of PFAS in sediments from coastal rivers along the south coast of the Bohai Sea; (2) identify potential sources of PFAS; and (3) conduct a screening-level ecological hazard assessment for PFAS in local aquatic ecosystems. The results of the study provide information and support for future determinations of status and trends of PFAS emissions and their management at regional and national levels. 2. Materials and methods 2.1. Standards and reagents 17 kinds of PFAS standards, including perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUdA), perfluorododecanoic acid (PFDoA), perfluorotridecanoic acid (PFTrDA), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDA), perfluorooctadecanoic acid (PFODA), potassium perfluorobutanesulfonate (PFBS), sodium perfluorohexanesulfonate (PFHxS), potassium perfluorooctanesulfonate (PFOS), sodium perfluorodecanesulfonate (PFDS), and 5 mass-labeled internal standards, including PFBA [1,2,3,4 13C], PFOA [1,2,3,4 13C], PFDoA [1,2 13C], PFHxS [1,2 18O] and PFOS [1,2,3,4 13C], were obtained from Wellington Laboratories with purities of >98% (Guelph, Ontario, Canada). The mixed standards were prepared in 100% methanol and stored at 4 °C. HPLC grade methanol, acetonitrile and methyl tert-butyl ether (MTBE) were purchased from J.T. Baker (Phillipsburg, NJ, USA). Ammonium acetate, anhydrous sodium sulfate and tetrabutylammonium hydrogensulfate (TBAHS) were purchased from Sigma–Aldrich Co. (St. Louis, MO, USA). Milli-Q water was obtained from a Milli-Q synthesis A10 (Millipore, Bedford, MA, USA) and used throughout the experiment. 2.2. Sediment sampling A total of 36 surface (top 1–5 cm) samples of sediment were collected from 12 typical coastal rivers, which flow into the Bohai Sea through Shandong and Hebei Provinces (Fig. 1). For each river, at least 2 sites were chosen with the first one near the coast and the other a distance of 20–30 km from the former. All surface sam-
ples were collected in September 2011 by use of a clean, stainless steel trowel, and placed in clean 250 mL, largemouth, and polypropylene (PP) bottles. Wet sediments were immediately transported to the laboratory in ice-cooled boxes and then dried in a FreeZone 2.5 Liter Benchtop Freeze Dry System (LABCONCO, Kansas City, MO), ground and homogenized with a silica mortar and pestle, sieved through a 2-mm mesh, and stored in pre-cleaned glass jars in room temperature until further analysis. 2.3. Sample extraction and instrumental analysis Detection of PFAS: Sediments were extracted according to a previously published method with minor modifications and optimizations (Naile et al., 2010; Wang et al., 2013). Briefly, a 50 ml polypropylene centrifuge tube was charged with 2.5 g homogenized sediments, which were soaked with 2 mL Milli-Q water and vortexed until the samples were visually homogenized. A 1 mL portion of 0.5 M tetrabutylammonium hydrogensulfate (TBAHS) and 2 mL of 25 mM sodium acetate were added, and spiked with 10 ng mass-labeled internal standards with vortexing. Subsequently, 5 mL of methyl tert-butyl ether (MTBE) was added and the mixture was extracted 20 min by vibration and then centrifuged at 3500 rpm for 30 min. This process of extraction with MTBE was repeated three times and the upper MTBE fraction was combined together into a 15 mL PP tube. The eluate was then evaporated to dryness under a gentle flow of high purity nitrogen, and reconstituted in 1 mL methanol, then filtered through a 0.2 mm nylon filter, transferred into a 1.5 mL PP snap top brown glass vial with polyethylene (PE) septa for HPLC analysis. The instrumental analysis was performed using a high performance liquid chromatography–negative electrospray ionization–tandem mass spectrometry system (HPLC–ESI–MS/MS) that consisted of an Agilent 1290 Infinity HPLC System coupled to an Agilent 6460 Triple Quadrupole LC/MS System (Agilent Technologies, Palo Alto, CA). The instrument conditions are listed in Table S1. Detection of organic carbon fraction (foc): The procedure used is based on a wet digestion method without heating followed by colorimetric determination (Chatterjee et al., 2009; Da Silva Dias et al., 2012). Briefly, a 0.5 g sediment sample was placed in a 100 mL Erlenmeyer flask, then 10 mL of potassium dichromate solution (0.667 mol L1) and 10 mL of sulfuric acid were added. Flasks were swirled for 5 min to homogenize the mixture. After reacting for 20 min and standing for 1 h to cool, 10 mL Milli-Q water was added to the flasks. After standing overnight (12 h), 15 mL supernatant solution was taken out and diluted to 50 mL by adding Milli-Q water. Then the solution was measured by a UV spectrophotometer under the light transmittance at 590-nm wavelength. 2.4. Quality assurance and quality control All fluorinated materials that could come into contact with the samples during sampling and extraction were removed to avoid contaminations. Nine-point external standard curves ranging from 0.01 to 100 ng mL1 were prepared for the quantification of individual PFAS with coefficients of determination (r2) for all the target analytes higher than 0.99. The limit of detection (LOD) and limit of quantification (LOQ) were defined as the peak of analyte required to yield a signal-to-noise (S/N) ratio of 3:1 and 10:1, respectively. Recoveries of internal standards spiked into sediments ranged from 73% to 119%. Concentrations of PFAS were not corrected for recoveries. Procedure blanks using anhydrous sodium sulfate as alternative of sediment were conducted with every sample set and solvent blanks using 100% methanol were run every 4–5 samples to check for carryover and background contamination. No detectable PFAS were observed over LOQ in all the procedure and
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
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Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
Fig. 1. Sampling positions of sediment in South Bohai coastal rivers.
solvent blanks. Detailed QA/QC measurements of PFAS in sediment are given in Table 1.
3. Results and discussion 3.1. PFAS in sediments from South Bohai coastal rivers
2.5. Statistical analysis Statistical analysis was performed with IBM SPSS Statistics V21. Before analyzing, concentration values lower than the LOQs were set to one-half of the LOQs, andpthose lower than the LODs were ffiffiffi assigned as values of the LODs/ 2 (Bao et al., 2010a). A statistical distribution test called P–P plots was carried out to test for normality. Spatial distributions of PFAS were analyzed using ArcGIS V10.0 software (ESRI).
In sediments collected from South Bohai coastal rivers, 14 out of 17 target PFAS were quantified, including: C4–C14–PFCAs, and C4–, C6–, and C8–PFSAs. Concentrations of PFAS in sediments from South Bohai coastal rivers were generally lower than the corresponding LOQs (Table S2). The total concentrations of PFAS in surface sediments ranged from 0.098 ng g1 dw to 1.889 ng g1 dw with a mean of 0.477 ng g1 dw (except for the Xiaoqing River). The highest concentration of RPFAS (31.92 ng g1 dw) was found at the upstream location in the Xiaoqing River, and the value was approximately 2 orders of magnitude higher than the average
Table 1 Target analytes of 17 PFAS measured in this study with QA/QC information. Analyte
Acronym
MS/MS transition (m/z)
Recovery (n = 4) %Mean ± SD
LOD (ng g1)
LOQ (ng g1)
Perfluorocarboxylic acid Perfluorobutanoic acid Perfluoropentanoic acid Perfluorohexanoic acid Perfluoroheptanoic acid Perfluorooctanoic acid Perfluorononanoic acid Perfluorodecanoic acid Perfluoroundecanoic acid Perfluorododecanoic acid Perfluorotridecanoic acid Perfluorotetradecanoic acid Perfluorohexadecanoic acid Perfluorooctadecanoic acid
PFCAs PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUdA PFDoA PFTrDA PFTeDA PFHxDA PFODA
213.0 ? 263.0 ? 313.0 ? 363.0 ? 413.0 ? 463.0 ? 513.0 ? 563.0 ? 613.0 ? 662.9 ? 713.1 ? 813.0 ? 913.0 ?
- > 169.1 218.9 269.0 318.9 368.9 419.0 468.9 519.0 569.0 619.0 669.0 769.0 869.0
100 ± 5 104 ± 3 110 ± 3 96 ± 6 100 ± 11 109 ± 2 103 ± 7 90 ± 4 89 ± 4 93 ± 2 73 ± 4 73 ± 1 87 ± 5
0.02 0.01 0.004 0.006 0.002 0.002 0.004 0.008 0.004 0.006 0.006 0.006 0.006
0.1 0.03 0.01 0.02 0.01 0.01 0.01 0.02 0.01 0.02 0.02 0.02 0.02
Perfluorinated sulfonic acid Perfluorobutanesulfonat Perfluorohexanesulfonat Perfluorooctanesulfonat Perfluorodecanesulfonat
PFSAs PFBS PFHxS PFOS PFDS
299.0 ? 399.0 ? 498.9 ? 599.0 ?
80.0 80.0 80.0 79.9
119 ± 4 114 ± 8 117 ± 2 86 ± 6
0.004 0.004 0.004 0.01
0.01 0.01 0.01 0.02
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
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Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
concentration and 16.9 times higher than the highest concentration (1.889 ng g1 dw) in the other 11 rivers. These high concentrations might be a result of receiving urban, industrial, and agricultural wastewater and sludge over the past decades (Zhao et al., 2013). The summary of PFAS concentrations in the coastal and riverine sediments are shown in Table 2. PFAS in the Xiaoqing River sediments will be discussed separately because of their high concentrations compared with the other 11 coastal rivers. In this study, the concentrations of RPFAS ranged from 0.218 ng g1 dw to 1.583 ng g1 dw (mean: 0.535 ng g1 dw) in the coastal sediments and from 0.167 ng g1 dw to 1.953 ng g1 dw (mean: 0.578 ng g1 dw) in the riverine sediments, respectively. The average concentration of RPFCAs in coastal sediments (0.259 ng g1 dw) was higher than that in the riverine sediments (0.208 ng g1 dw), while the average concentration of RPFSAs in the riverine sediments (0.370 ng g1 dw) was higher than that in the coastal sediments (0.276 ng g1 dw). The Xiaoqing River had the highest concentration of RPFAS in both coastal and riverine sediments (2.756 ng g1 dw and 31.920 ng g1 dw, respectively). Generally, the concentrations of RPFAS in riverine sediments were higher than that those in coastal sediments. Composition profiles of PFAS in the coastal and riverine sediments from South Bohai Bay are shown in Fig. 2. The dominant PFAS compound in the coastal sediments was PFOA, with a contribution of 30% to the total PFAS. Other major components were PFBS (29%), PFOS (20%), and PFBA (8%). The situation was quite different in the riverine sediments with contribution of PFOA being only 8% while contributions of PFBS, PFOS and PFBA were 35%, 27% and 15%, respectively. As for the Xiaoqing River, although concentrations of PFAS varied largely at different sampling sites along the river, PFOA was the dominant PFAS in all samples with a high contribution of over 90%. 3.2. Spatial distribution and source identification The spatial distribution of RPFAS in sediment from South Bohai coastal rivers is shown in Fig. 3. It is obvious that Xiaoqing River had the highest RPFAS (2.756–31.920 ng g1 dw) in this area, especially for the site XQ-3 (31.920 ng g1 dw), which was relatively far from the coastline. The Xiaoqing River, with a total length of 216 km and a drainage area of 10,336 km2, flows through several major cities, including Ji’nan, Zibo, Binzhou, Dongying, and Weifang in Shandong Province, China. As an important inland
ship-transport river in Shandong Province and the only discharge channel of wastewater in Ji’nan city, the Xiaoqing River receives all kinds of wastewater and sludge. Although control measures like building more municipal sewage treatment plants and sewage interception facilities were carried out in recent years, there were still huge amounts of sewage and garbage pouring into the Xiaoqing River. The high concentrations of PFAS in sediments of this river might result from upstream transportation, tributaries of industrial discharge as well as local release of garbage and wastewater from human activities along the river. The relatively high concentrations of RPFAS in Jiaolai River sediment (0.404– 1.638 ng g1 dw) might be from the upper stream historically industrial wastewater discharge, such as iron ore plants and chemical fiber factories. Site ZW-3 in Zhangwei River was found to have a higher value of RPFAS (1.889 ng g1 dw) in sediment compared to other sampling sites in this river, indicating a potential point source at this site. According to the existing environmental situation of this sampling site, the most possible source might be paper manufacturing factories at south of this sampling position, since PFOS-substances derived from perfluorooctane sulfonyl fluoride (POSF) and their simple derivatives were widely used in paper treatment in China (Xie et al., 2013). Similar results were found on the estuary of both the Mi (site MR-1, 0.863 ng g1 dw) and Wang Rivers (site WR-1, 1.511 ng g1 dw). There was direct discharge of wastewater from a fertilizer factory and salt fields around site MR-1, which could be the sources of PFAS. The industry park located near site WR-1 could also be the source of PFAS. The major discharging river in this area was the Yellow River, which from 1919 to 2008 had discharged approximately 12.7 108 t a1 sediment into the Bohai Sea (Mu et al., 2012). Comparing to its adjacent rivers, the Yellow River had lower concentrations of RPFAS in sediments. One reason might be that the riverbed of the Yellow River in Shandong Province is rather high. Therefore it is unlikely to receive sewage from local facilities. The other reason might be that the water and sediment regulation conducted on the Yellow River every year since 2002 increased erosion in the downstream part of the Yellow River, carrying most of the surface sediment into the Bohai Sea (Li, 2004; Yao et al., 2009; Wang et al., 2010). The much higher discharge of the Yellow River than those of other rivers in this study would lead to more dilution, which could also be an explanation of this phenomenon. Generally speaking, concentrations of RPFAS in sediment at inland riverine locations were higher than those in coastal sediment because of the scouring and dilution of tidal currents and waves, and explanations have been found for
Table 2 PFAS concentrations in sediments from South Bohai coastal rivers (ng g1 dw). Coastal sediment (n = 13)
PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUdA PFDoA PFTrDA PFTeDA PFBS PFHxS PFOS RPFCAs RPFSAs RPFAS a
Riverine sediment (n = 20)
Xiaoqing River sediment (n = 3)
Mean
Max
Min
Median
Mean
Max
Min
Median
Estuary (n = 1)
Riverine (n = 2)
0.043 – 0.006 – 0.158 0.017 0.011 0.010 0.004 – – 0.158 0.009 0.107 0.259 0.276 0.535
0.121 – 0.043 0.006 1.049 0.080 0.025 0.034 0.013 – – 0.348 0.028 0.188 1.143 0.462 1.583
–a – – – 0.005 0.002 – – – – – 0.036 – 0.061 0.044 0.102 0.218
0.029 – 0.004 – 0.071 0.009 0.012 – – – – 0.111 – 0.098 0.133 0.258 0.442
0.089 – 0.004 – 0.044 0.016 0.020 0.020 0.005 – – 0.204 0.010 0.155 0.208 0.370 0.578
0.452 0.013 0.031 0.008 0.221 0.087 0.067 0.084 0.027 0.009 0.009 1.695 0.074 0.435 0.775 1.796 1.953
– – – – 0.005 0.002 – – – – – 0.012 – 0.027 0.053 0.114 0.167
0.038 – – – 0.027 0.009 0.015 – – – – 0.098 – 0.109 0.115 0.259 0.358
0.035 0.010 0.040 0.034 2.452 0.005 0.017 – 0.004 – – 0.070 – 0.082 2.604 0.152 2.756
0.155 0.133 0.208 0.153 12.988 0.052 0.089 0.120 0.106 0.040 0.017 0.141 0.046 0.101 14.061 0.288 14.350
0.315 0.225 0.392 0.307 29.021 0.178 0.245 0.319 0.352 0.127 0.059 0.106 0.098 0.176 31.540 0.380 31.920
‘‘–’’ means data below limitation of detection.
Please cite this article in press as: Zhu, Z., et al. Perfluoroalkyl and polyfluoroalkyl substances in sediments from South Bohai coastal watersheds, China. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2013.12.042
Z. Zhu et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
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Fig. 2. Composition of PFAS in Xiaoqing River (Part A) and percentage composition of PFAS in coastal sediments and riverine sediments (Part B).
Fig. 3. Spatial distributions of RPFAS in sediments from South Bohai coastal rivers.
several anomalous points opposite to this trend. However, the distribution of PFAS in the coastal environment is influenced by many factors, such as partitioning behaviors between sediment and water (Higgins and Luthy, 2006), the deposition of volatile compounds in the air (Dreyer et al., 2009), and the transport of PFAS in water (Ahrens et al., 2009). Thus, more information is needed to identify sources of PFAS in sediment of South Bohai coastal rivers. 3.3. Comparison of PFAS in sediments with other Asian countries PFOA and PFOS were the most frequently detected PFAS compounds in the environment. Their concentrations in other coastal and riverine sediments in China and other Asian countries were compared in this study (Table 3). Compared with other riverine and coastal sediments in China, concentrations of PFOS in sediments from South Bohai coastal rivers, excluding the Xiaoqing River, (0.03–0.36 ng g1 dw) were comparable to those found in the Daliao River system of northeast China (0.06–0.37 ng g1 dw)
(Bao et al., 2009) and Yangtzi River Estuary, Shanghai (n.d.– 0.46 ng g1 dw) (Bao et al., 2010b), but lower than those observed in North Bohai coastal rivers (n.d.–1.97 ng g1 dw) (Wang et al., 2011b), Laizhou Bay rivers (
