Concentrations, distribution and sources of polychlorinated dibenzo¡ce:italic¿p¡/ce:italic¿-dioxins and dibenzofurans and dioxin-like polychlorinated biphenyls in coastal sediments from Xiamen, China Minggang Cai, Qingquan Hong, Jionghui Sun, Kristina Sundqvist, Karin Wiberg, Kai Chen, Yun Wang, Cangrong Qiu, Shuiying Huang PII: DOI: Reference:
S0304-4203(16)30057-3 doi: 10.1016/j.marchem.2016.05.008 MARCHE 3372
To appear in:
Marine Chemistry
Received date: Revised date: Accepted date:
15 October 2015 24 May 2016 24 May 2016
Please cite this article as: Cai, Minggang, Hong, Qingquan, Sun, Jionghui, Sundqvist, Kristina, Wiberg, Karin, Chen, Kai, Wang, Yun, Qiu, Cangrong, Huang, Shuiying, Concentrations, distribution and sources of polychlorinated dibenzo-¡ce:italic¿p¡/ce:italic¿dioxins and dibenzofurans and dioxin-like polychlorinated biphenyls in coastal sediments from Xiamen, China, Marine Chemistry (2016), doi: 10.1016/j.marchem.2016.05.008
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ACCEPTED MANUSCRIPT Concentrations, distribution and sources of polychlorinated dibenzo-p-dioxins and dibenzofurans and dioxin-like polychlorinated biphenyls in coastal sediments from Xiamen, China a, b, c,*
Minggang Cai
, Qingquan Hongc, Jionghui Sunc, Kristina Sundqvistd, Karin Wiberg d, f, Kai
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Chenb, Yun Wangc, Cangrong Qiuc, Shuiying Huangc
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a State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, PR China
b Coastal and Ocean Management Institute, Xiamen University, Xiamen 361005, PR China c College of Ocean and Earth Science, Xiamen University, Xiamen 361005, PR China
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d Department of Chemistry, Umeå University, Umeå SE-901 87, Sweden f Department of Aquatic Science and Environmental Assessment, Swedish University of
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Agricultural Sciences, Uppsala SE-750 07, Sweden
Abstract
Xiamen and its surroundings are representative areas suffering from intense anthropogenic
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turbulence and contamination in southeast coast of China during rapid industrialization and
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urbanization period, thus relevant organic pollutants research is necessary to assess the coastal environmental quality and generate management strategy. Contamination status of polychlorinated
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dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) was investigated for 7 surface sediment samples collected in these areas in January, 2007. The given data were used to evaluate the contamination and their potential risks of the pollutants. Concentrations of PCDD/Fs were in the range of 60 to 4089 pg·g-1 (dry weight) with an
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average of 1706 pg·g-1 and DL-PCBs in the range of 3 to 76 pg·g-1 with an average of 28 pg·g-1. Octa-chlorinated dibenzo-p-dioxin (OCDD) and PCBs 105 and 118 were the main congeners of the PCDD/F and DL-PCB, respectively. The toxicity equivalent concentrations (TEQs) were in the range of 0.15 to 5.2 pg·g-1 (average 3.0 pg·g-1) for PCDD/Fs, while in the range of < limit of quantitation (LOQ) to 0.09 pg·g-1 (average 0.05 pg·g-1) for DL-PCBs. Congener pattern analysis showed a dominance of OCDD, suggesting main sources were current or historical use of chlorophenol, current use of dioxin contaminated pesticides or atmospheric deposition. Due to the current levels of PCDD/Fs and DL-PCBs in this area, it is necessary to further research their biogeochemical processes and ecological influences in the future.
Keywords: PCDD/Fs, DL-PCBs, WHO-TEQ, sediments, Xiamen, Southeast China
*
Corresponding author. E-mail:
[email protected]. Phone: +86 592 2886188.
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ACCEPTED MANUSCRIPT 1. Introduction The coast and estuary are subjected to numerous disturbances, among which chemical pollution is a major concern, and increasing attention has been paid to the occurrence of persistent
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organic pollutants (POPs) in recent years. Polychlorinated dibenzo-p-dioxins and dibenzofurans
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(PCDD/Fs) are hydrophobic organic contaminants (HOCs) comprising 210 congeners. Among them, the seventeen 2,3,7,8-substituted congeners are widely recognized by the scientific
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community as compounds of the most toxicity and strong ability to bioaccumulation (Schulz-Bull et al., 1995; Roscales et al., 2016). They are not only harmful to the nerve, immune, endocrine and reproductive systems, but are also considered teratogenic, mutagenic and carcinogenic (Zheng et al., 2008). PCDD/Fs are formed unintentionally during a number of anthropogenic activities, such
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as incomplete combustion of solid waste, chemical manufacturing, use of herbicide and pesticides (e.g. Pentachlorophenol), disposal of sewage sludge and vehicle exhaust (Cappelletti et al., 2014; Korhonen et al., 2013). Another well-known group of HOCs is the polychlorinated biphenyls
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(PCBs) (Ko et al., 1995). Among these congeners, 12 compounds are chemically and toxicologically similar to 2,3,7,8-tetraclorodibenzo-p-dioxin (2,3,7,8-TCDD), which are referred to as dioxin-like PCBs (DL-PCBs, also called non-ortho PCBs) (Hui et al., 2009; Nune et al., 2011;
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Shen et al., 2009). High persistence of PCDD/Fs and DL-PCBs, combined with low vapor
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pressures, results in ubiquitously occurrence and accumulation in different carbonaceous environmental matrixes, such as soil, sediment and biota (Venkatesan et al., 1999).
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PCDD/Fs and DL-PCBs enter coastal aquatic environments via different ways, such as direct/indirect discharges, riverine inputs and atmospheric deposition (Verta et al., 2007). Due to their hydrophobic characteristic, PCDD/Fs and DL-PCBs strongly adsorb to suspended particle and settle into the sediments in the aquatic environment, as a result, the sediments become the
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major sink for such pollutants in estuaries and coastal areas. On the one hand, PCDD/Fs in coastal sediments can reenter the overlaying water by resuspension of sediments and subsequent desorption processes. Besides, the uptake by benthic organism could result in the accumulation in the food web. Once present in food webs, these compounds would bioaccumulate and biomagnify, reaching higher concentrations in species at upper trophic levels and intake by human (Nunes et al., 2011). Thus the studies of trace organic contaminants such as PCDD/Fs and DL-PCBs in coastal environments, especially in estuarine systems, are significantly important since these areas are biologically productive and receive pollutant inputs from land-based sources continuously (Maskaoui, 2002). Over the past few years, many studies focusing on PCDD/Fs or DL-PCBs have been conducted in different coastal sea areas and estuaries around the world (Birch et al., 2007; Howell et al., 2011; Ishaq et al., 2009; Kannan et al., 2007; Salo et al., 2008; Sundqvist et al., 2010; Verta et al., 2007). In China, studies have been carried out for estuaries such as the Yellow River Estuary (Hui et al., 2009), Yangtze River Estuary (Hui et al., 2009; Wen et al., 2008), Pearl River Delta (Zhang et al., 2009) and other coastal sea areas such as Hong Kong (Mũller et al., 2002), 2
ACCEPTED MANUSCRIPT Bohai Bay (Hu et al., 2005), Jiaozhou Bay (Pan et al., 2008) and the Yellow Sea (Pan et al., 2010). Xiamen and its surrounding sea areas are typical sea-land interface and estuarine zone, whose environmental stress caused by modern industrial and agricultural development has been greatly enhanced. Moreover, this estuary connects the Jiulong River basin and Taiwan Strait, which means
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the organic contaminants could be transported to the East China Sea by currents (Wu et al., 2007).
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Although studies have been conducted to understand the anthropogenic impacts on the coastal environment in China (Cai et al., 2016), it is urgent to evaluate the status of the persistent organic
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pollutants in this area for management purposes in Jiulong River Estuary and its adjacent areas. Several researches have focused on the pollution of OCPs, PCBs (Maskaoui et al., 2005) and PAHs (Maskaoui et al., 2002) in sediments in this area. There were petroleum and organochlorine
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contamination in the estuary area, which got more and more serious in recent years (Maskaoui et al., 2005). However, there is no published data regarding PCDD/Fs levels, and the information on DL-PCBs contamination about sediment samples is scarcely available in this study area.
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The aim of the present study was to investigate the levels of the 17 PCDD/Fs and 12 DL-PCBs in surface sediments of Jiulong River Estuary and Western Xiamen Bay, to evaluate their ecological risk by World Health Organization (WHO) -TEQ and to analyze their possible
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sources. Since organic carbon content and grain size of sediments are important in controlling the distribution and bioavailability of HOCs (Hung et al., 2010), the relationship between the
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sediment composition and the compounds were also studied. Only when the levels of PCDD/Fs and DL-PCBs are determined, can the coastal environmental quality be assessed for generating
stability.
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management strategy in this area since it is closely related to human health and ecosystem
2. Materials and Methods
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2.1 Study area
Xiamen, which has an area of about 1 700 km2 and population of over 3.5 million, is an important port city located in the southeast coast of China. The Jiulong River is the second largest river in Fujian Province, China, with a length of 285 km and a drainage area of 14 741 km2. During its course, it supports over five million inhabitants and runs through highly agricultural areas before reaching the estuary and Western Xiamen Bay, which is the most developed area in Fujian Province. However, due to the policy of reform and opening implementation and rapid economic development since 1980s, the Jiulong River basin and the Western Xiamen Bay are subjected to strong anthropogenic stress. The main pollution sources are wastewaters, most resulting from high population density through domestic sewage (partially untreated) and industrial activities (e.g. paper mill and fertilizer plant) through industrial sewage. This basin also receives agricultural runoff from 2 700 km2 of agricultural land, which requires the use of great amounts of fertilizers and pesticides (Zhang et al., 2002).
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ACCEPTED MANUSCRIPT 2.2 Sampling In January 2007, surface sediment samples were collected in seven locations from the coastal sea area of Xiamen, China, with stations 1 and 5-7 in the Jiulong River Estuary and stations 2-4 in the Western Xiamen Bay (Figure 1). Sediment samples (0-5 cm) were collected using a
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solvent-rinsed stainless steel grab sampler. Samples were freeze-dried, grounded with a pestle and
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mortar, wrapped in pre-baked aluminum foil, and then stored at -20°C until chemical analysis in
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laboratory.
2.3 Chemicals
Methanol, dichloromethane, n-hexane and toluene were purchased from Burdick and Jackson
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(Muskegon, USA), dehydrated Na2SO4, silica (0.063-0.200 mm) and tetradecane were obtained from Fluka (Germany), Celite 545 from Fluka (Switzerland), AX21 carbon from Anderson Development (USA), and granulated copper (−10+40 Mesh) from Sigma Aldrich (USA). The 13
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C-labelled recovery standards, internal standards and quantification standard were all from
Cambridge Isotope Laboratories (Andover, USA) or Wellington Laboratories (New Zealand).
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2.4 Sample treatment and Instrumental analysis
The extraction, clean up and instrumental analysis were carried out at Umeå University,
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Sweden, and details of the methods used were described elsewhere (Sundqvist et al., 2009a). Briefly, homogenized sediment samples (15-20 g) were Soxhlet extracted in cellulose thimbles 13
C-labeled PCDD/Fs and DL-PCBs as recovery
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using toluene for 24 h after being spiked with
standards. Tetradecane was added as a keeper, and then the solvent was exchanged to n-hexane and concentrated to ~1 mL. Clean-up and fractionation were carried out by column chromatography using three different columns. The first one was a multilayer silica column filled
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with (from bottom to top): glass wool, 3 g KOH-silica, 1.4 g neutral silica, 4 g of 40% H2SO4-silica and 3 g dehydrated Na2SO4. This was followed by the treatment with activated copper granules turnings. It was prerinsed with twice the volume of n-hexane and eluted with 100 mL n-hexane. The extracts were then rotary evaporated to ~1 mL. The fractionation column was filled with a mixture of activated AX21 carbon and Celite 545 (7.9:92.1). Before use, the column was
washed
with
4
dichloromethane/n-hexane
mL
dichloromethane/methanol/toluene
(v:v=1:1).
The
analytes
were
(15:4:1) eluted
and
with
1
mL
40
mL
dichloromethane/n-hexane (v:v=1:1; poly- and mono-ortho PCBs; fraction 1) and 40 mL toluene (reversed elution; PCDD/Fs and non-ortho PCBs; fraction 2). The final clean-up step was yet another multilayer silica column consisting of (bottom to top): 0.1 g KOH-silica, 0.2 g neutral silica, 0.1 g of 40% H2SO4-silica and 0.1 g dehydrated Na2SO4, and the analytes were eluted with 10 mL n-hexane. Before instrumental analysis, 13C-labelled internal standards were added and the solvent was reduced to ~40 µL (tetradecane). Steel and glass equipment was pre-cleaned with distilled water and organic solvents, and the 4
ACCEPTED MANUSCRIPT cellulose thimbles were pre-extracted with toluene for 8 hours prior to use. Copper granules were activated with HCl and then washed with water, methanol, dichloromethane and n-hexane. Instrumental analysis was performed with a Hewlett Packard 5890 gas chromatograph coupled to a VG 70-250S high resolution mass spectrometer (GC-HRMS). The GC was equipped
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with a DB5 capillary column (60 m ×0.25 mm, i.d., 0.25 μm, Agilent Technologies, USA), and
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the HRMS was a double focusing magnet sector mass spectrometer that operated in the EI+ selected ion monitoring (SIM) mode. Samples were injected splitless at an injector temperature of
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280°C (2 μL, splitless time: 2 min). Helium carrier gas was at 18 psi and the transfer line temperature and ion source temperature were both 250°C, and the electron energy was 35 eV. The temperature program of the oven was as follows: held at 200°C (for fraction 2) or 190°C (for
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fraction 1) for 2 min, increased by 3°C min-1 to 300°C and held for 10 min. Particle size distribution was analyzed at Xiamen University using a Mastersizer 2000 (Malvern Instruments Ltd., UK). Based on a previous study in the Baltic Sea that implies a
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significant relationship between the sediment organic content and Loss of Ignition (LOI) (Sundqvist et al., 2009a), LOI is used in this study to explore the relationship of organic content with PCDD/Fs and DL-PCBs. Dried sediments were heated at 550°C for 4 h and the LOI were
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calculated as the difference of the weight before and after heating.
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2.5 Quality Assurance and Quality Control The laboratory blanks were included at a percentage rate of one blank for every 4 field
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samples. As a result, laboratory blank generally contained 0-9 % of the PCDD/Fs amounts measured in samples and 0-7% of the DL-PCBs (Table 1). The exceptions for 1,2,3,7,8,9-hexa-CDF and PCB 169 were mainly due to the low content in the samples. Recoveries were calculated as the overall recovery from the pretreatment process and the
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instrumental analysis. They ranged from 92 to 105% with an average of 101% for PCDD/Fs and 89 to 112% with a mean of 97% for DL-PCBs.
3. Results and Discussion 3.1 Concentrations of PCDD/Fs and DL-PCBs The concentrations of the 2,3,7,8-substituted PCDD/Fs (n=17) and the DL-PCBs (n=12) are shown in Table 2 and Figure 2 as dry weight (d.w.). The ∑PCDD/F concentrations (the sum of the 17 PCDD/F congeners) in the surface sediments varied from 60 to 4089 pg·g-1 d.w. with an average value of 1706 pg·g-1 d.w.. The dominant congeners were OCDD followed by 1,2,3,4,6,7,8-hepta-CDD for dioxins, and 1,2,3,4,6,7,8-hepta-CDF for furans. The ∑DL-PCB concentrations ranged from 3 to 76 pg·g-1 d.w. and averaged 28 pg·g-1 d.w. with the dominant congeners being PCB 118 followed by PCB 105 in the whole study area. The highest concentrations of the 2,3,7,8-substituted PCDD/Fs and the DL-PCBs were both found in station 5, while two inner stations in Jiulong River Estuary had apparent low ∑DL-PCB concentrations (3.1 5
ACCEPTED MANUSCRIPT to 4.8 pg·g-1 d.w.). Generally, both ∑PCDD/F and ∑DL-PCB concentrations did not show any overall spatial distribution trends, since the study area is influenced by various agriculture and industrial activities, with different point and non-point sources. In the Western Xiamen Bay, station 2 showed a higher concentration of PCDD/Fs than stations 3 and 4. Considering that there
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is a sewage treatment plant serving the downtown in the vicinity of station 2, this relatively high
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level of PCDD/Fs may be related to its considerable discharge. Similarly, elevated levels and distribution patterns of PAHs and PCBs in the Western Xiamen Bay were also observed by
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Maskaoui et al. (2002, 2005), which implied potential similar sources from the adjacent coast around the Western Xiamen Bay. Extremely low levels of both ∑PCDD/F and ∑DL-PCB in station 6 were found. This is probably due to the high portion of coarse gravel and sand (totally
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accounted for more than 98% of the sediments), which have the lower sorption capacity to accumulate the particle-reactive PCDD/Fs and DL-PCBs (Hung et al., 2010). In station 7, the ∑ DL-PCB level was abnormally low compared to ∑PCDD/F, which may be attributed to the
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illegal use of pentachlorophenol as pesticide and subsequent contamination of the PCDD/Fs in the adjacent zone. A previous study showed slight PCBs pollution in this natural mangrove forest, which suggested that the forest could prevent the PCBs contamination (Zhao et al., 2012). The
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distribution in the Jiulong River Estuary was different from those of PAHs and PCBs (Maskaoui et
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al., 2002, 2005). This may be due to the potential point source and/or different controlling mechanisms. However, we cannot draw a conclusion as limited research concerning the sources/sinks and the controlling mechanisms have been conducted.
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The concentrations of PCDD/Fs and DL-PCBs in sediments were presented in Table 3. This provides a global perspective of the pollution status of Xiamen coastal areas and allows a comparison between Xiamen coastal areas and other regions from the rest of the world. The levels
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of ∑PCDD/F and ∑DL-PCB in this study area were comparable with that of less disturbed coastal and estuarine areas, e.g., Bohai Bay in China (Hu et al., 2005), Oder River Estuary in Baltic Sea (Dannenberger et al., 1997), and Casco Bay in USA (Wade et al., 1997) (Table 3). However, they were relatively lower than those in the intensively polluted areas including Hong Kong in China (Mũller et al., 2002), Masan Bay in Korea (Kannan et al., 2007), Grenlandsfjords in Norway (Ishaq et al., 2009) and Lake Superior and Huron in Canada (Shen et al., 2009), which may indicate that Xiamen coastal areas are not obviously polluted by intensive industry. However, potential sources from agriculture should be focused on because of the ataxic usage of pesticides.
3.2 Toxic equivalents (TEQs) of PCDD/Fs and DL-PCBs Total WHO-TEQ values were calculated by multiplying the absolute concentration of each isomer by a toxicity equivalency factor (TEF) proposed by the WHO in 2005 to represent the toxic or biological effects (Figure 3) (Van den Berg et al., 2006). The TEQ values ranged from 0.15 to 5.2 pg g-1 d.w. for PCDD/Fs and from PCDFs>DL-PCBs, indicating that PCDD/Fs are the major contributors to the total
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TEQ for surface sediments in this area.
∑DL-PCB
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3.3 Influence of grain size and organic carbon content on the concentrations of ∑PCDD/F and
Organic carbon content and grain size are considered to be important factors controlling PCDD/Fs and PCBs levels in sediments, since organic carbon content acts as important sorbent
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for the pollutants and the fine sediment particles possess relatively high concentrations of pollutants (Lee et al., 2006; Persson et al., 2002). In the current study, LOI values were applied to explore the relationship between organic matter and PCDD/Fs and DL-PCBs levels. The LOI values ranged from 0.83% to 8.1% of dry weight. A strong positive Pearson correlation was obtained between LOI and ∑PCDF with a correlation coefficient of 0.908 (p
