Sedimentary records of PAHs in a sediment core from tidal flat of Haizhou Bay, China

Science of the Total Environment 450–451 (2013) 280–288

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Sedimentary records of PAHs in a sediment core from tidal flat of Haizhou Bay, China Rui Zhang a, b,⁎, Fan Zhang c, Tian-Cheng Zhang a a b c

School of Geodesy and Geomatics Engineering, Huaihai Institute of Technology, Lianyungang 222005, Jiangsu Province, China State Key Laboratory of Pollution Control and Resources Reuse, Nanjing University, Nanjing 210093, China Jiangsu Marine Resources Development Research Institute, Huaihai Institute of Technology, Lianyungang 222001, Jiangsu Province, China

H I G H L I G H T S ► We have confirmed that sedimentary PAH fluxes in tidal flat from Haizhou Bay were higher than in the continental shelf. ► The accumulation rates of pyrogenic PAHs have significantly increased in the Haizhou Bay in the recent decades. ► The high molecular weight PAHs have predominated in Haizhou Bays in the recent years.

a r t i c l e

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Article history: Received 31 October 2012 Received in revised form 9 February 2013 Accepted 10 February 2013 Keywords: PAHs Sediment rates Anthropogenic input Tidal flat Principal component analysis

a b s t r a c t The concentrations and depositional fluxes of polycyclic aromatic hydrocarbons (PAHs) were investigated in a dated sediment core collected from a tidal flat in Haizhou Bay, China. The USEPA's 16 priority PAH concentrations ranged from 72.51 ng g−1 dw in 1969 to 805.21 ng g−1 dw in 2010, while the deposition fluxes were in the range of 102.36–861.02 ng cm−2 yr−1. The PAH concentrations and fluxes changed dramatically with depth, suggesting changes in energy usage and corresponding closely with the historical economic development of eastern China. The levels of PAHs slightly increased from the late 1970s, following China's “Reform and Open” policy of 1978; however, a drastic increase in the concentration of PAHs observed in 1990 was indicative of the rapid growth in coal and petroleum incomplete combustion byproducts, which was associated with the increase in economic development in this area. Furthermore, isomer ratio analysis and principle component analysis revealed the main anthropogenic pyrolytic source that causes PAH contamination in the coastal sediment. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Environmental contamination from rapid urbanization and industrialization has become a serious concern worldwide. Organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and hazardous because of their potential toxicity in aquatic environments (Gueu et al., 2007; Adams et al., 2008; Zvinowanda et al., 2009). PAHs are widely distributed in the environment and attributed mainly to combustion processes, including the burning of fossil fuels, municipal wastes and biomass (Yunker et al., 2002; Oros and Ross, 2004). Other sources include crude oil seepage and diagenesis of organic matter in anoxic sediments (Venkatesan, 1988; Lima et al., 2005). PAHs derived from combustion processes can be widely distributed into coastal environmental media via various sources, e.g., riverine runoff, atmospheric transport precipitation, sewage outfalls as well as releases from ships (Maher and Aislabie, 1992; Guo et al., 2006; Liu et al., 2012a). Coastal marine sediment is a major source and sink of PAHs (Ricking and Schulz, 2002; Guzzella et al., 2005; Peachey, 2003; Wade ⁎ Corresponding author at: School of Geodesy and Geomatics Engineering, Huaihai Institute of Technology, Lianyungang 222005, Jiangsu Province, China. Tel.: + 86 518 8589 5587. E-mail address: [email protected] (R. Zhang). 0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2013.02.029

et al., 2008; Peng et al., 2008). In aquatic environments, PAHs tend to adhere to particulate matter because of their hydrophobic nature and are finally deposited in the underlying sediments of lakes, estuaries and tidal flats (Tolosa et al., 2004). These accumulated pollutants can exert a significant impact on coastal environmental quality. The lipophilic nature and low chemical and biological degradation rates of PAHs have led to their accumulation in sediment-dwelling organisms and their subsequent biomagnification up the food chain. Because sediment deposition continues over time, the sediments can act as geochronometers to trace and reconstruct general environmental changes over time (Lima et al., 2003). Studies focused on PAHs in the water column and in core sediments can lead to a better understanding of PAH cycles in top-to-bottom processes and in historical trends, thus many studies on the concentration and distribution of PAHs have been conducted in estuaries and coastal areas around the world in the recent years (Adams et al., 1992; Wu et al., 2001; Liu et al., 2005; Guo et al., 2006, 2007; Taskin et al., 2011). In China, several studies were also conducted in the Pearl River Estuary (Luo et al., 2006; Mai et al., 2001; Liu et al., 2005; Peng et al., 2008), Yangtze Estuary (Liu et al., 2000; Xu et al., 2001), East China Sea continental shelf (Guo et al., 2006, 2007; Liu et al., 2012a, 2012b) and other developed coastal regions. Haizhou Bay lies on the western margin of the South Yellow Sea, near the city of Lianyungang, and receives water inflow from the Linhong

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River (Fig. 1). The bay is shaped like a trumpet and has an area of approximately 876.39 km2. The length of the coastline is 86.81 km, and its maximum width is approximately 42 km. Lianyungang Harbor, a natural deep-water harbor, is located on the southeast side of Haizhou Bay and is one of the most important harbors in China because it serves Europe, America, the Middle East, and Northeast and Southeast Asia, and is therefore an important logistics and transport center. In the past, the regions near Haizhou Bay experienced significant economic development. During that period, municipal domestic sewage and industrial waste water were either discharged directly into the sea along the Linhong River and the coastal line or discharged after simple aerobic treatment. Therefore, domestic and industrial garbage has accumulated in the coastal zone, which has caused a large amount of landfill leachate to flow along the tidal flat into the sea. According to the recent reports, the Linhong River carried 2.26 × 108 t of domestic sewage and industrial wastewater in 2010 (EPAL, 2011; OFBL, 2011), and a considerable

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portion of this wastewater was deposited and accumulated in the tidal flat creating a sink of toxic chemical pollution. A few environmental studies have determined the trace metal concentrations, the accumulation rates of contamination, the extent of contamination and the pollution history of Haizhou Bay (Zhang et al., 2008, 2013). Furthermore, researchers have shown that the coastal tidal flats of Haizhou Bay appear to be heavy metal sinks, and the release of pollutants from these contaminated sediments has a negative impact on the water quality of the bay (Zhang et al., 2013); however, data on the environmental occurrence of PAHs in Haizhou Bay are scarce. This gap needs to be filled in order for an effective environmental policy to be built upon a sound scientific knowledge of the sources, distribution mechanisms, potential risks and actual dangers of these contaminants to human and environmental health (Piazza et al., 2009). Moreover, the levels and orientation of industrialized development near Haizhou Bay in Lianyungang with similar natural environments provide an interesting contrast for

Fig. 1. Sampling site map.

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understanding pollutant sources and distribution mechanisms in an aquatic environment. This study aims to (1) delineate the temporal trends of concentrations and fluxes of PAHs in tidal flats of Haizhou Bay, determined by 210Pb dating in a sedimentary core; (2) elucidate anthropogenic impacts on the marine environment in Haizhou Bay in recent years; and (3) trace potential input sources of PAHs. 2. Materials and methods 2.1. Sample collection A sediment core was collected from the south tidal flat of Haizhou Bay, near the Linhong River estuary in April 2010; the location is shown in Fig. 1. The core, labeled LH4, was 65 cm in length and 7.5 cm in diameter. In the laboratory, the core was subsampled at 1 cm intervals. The samples were packed in aluminum foil and stored at −20 °C until analysis. 2.2. PAH analysis The PAH analysis procedure followed the procedure described by Grimalt et al. (2004). Homogenized core samples were freeze-dried and ground. Approximately 3–5 g of the sample was spiked with a mixture of recovery standards of two deuterated PAHs (phenanthrene-d10 and perylene-d12). The samples were sonic extracted with dichloromethane methanol (2:1) for 20 min; this procedure was repeated three times. The extract was vacuum evaporated to approximately 10 ml and hydrolyzed overnight with 20 ml of 6% KOH in methanol. The neutral fractions were recovered with n-hexane and fractionated with an alumina silica (1:1) column. The PAHs were eluted with 30 ml of hexane/dichloromethane (1:1). The PAH fraction was concentrated to 0.5 ml in isooctane prior to GC–MS analysis. PAHs in all samples and procedure blanks were analyzed using a gas chromatograph (GC) with an ion-trap mass spectrometer (MS) (Finnigan Trace GC/PolarisQ). A 30 m×250 mm i.d. HP-5MS capillary column was used for separation. High-purity helium was used as a carrier gas at a constant flow rate of 1.0 ml min−1. Each sample was analyzed using splitless injection and 70-eV electron impact (EI) ionization. When the MS uses an ion-trap as a mass separator, the MS–MS mode can be used to achieve high sensitivity. The temperature of the injector was 250 °C, and the temperature of the transfer line was 280 °C. The oven-temperature program for PAHs was adjusted to the following parameters: the column was held at 50 °C for 2 min before the temperature was increased to 180 °C at a rate of 20 °C min−1; the temperature was then increased at 4 °C min−1 up to 250 °C, then increased to 280 °C at a rate of 2 °C min−1and held for 2 min. Finally, the temperature was brought to 300 °C at a rate of 10 °C min−1 and then held for 5 min. Sixteen United States Environmental Protection Agency (US EPA) priority PAHs were measured: naphthalene (Nap), acenaphthylene (Ac), acenaphthene (Ace), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fluo), pyrene (Pyr), benz[a]anthracene (BaA), chrysene(Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3cd]pyrene (Inp), dibenz[a,h]anthracene (DBA), and benzo[ghi]perylene (BghiP). Procedural blanks, standard-spiked blanks, and standard-spiked matrices were analyzed for quality assurance and control. Recovery for field samples was 103±15% for phenanthrene-d10 and 83±12% for perylene-d12. The quantification limit for individual PAH species was set at three times the detected amount in the procedural blank. In addition, 30% of field samples were analyzed in duplicate, and the relative standard deviation for individual PAHs was less than 13%. PAH concentrations were not recovery corrected.

was recorded. The sample in the container was dried at 60 °C for two days to a constant weight in an oven. After cooling for approximately 30 min in a desiccator, the sample was re-weighed. The water content of the sample was calculated according to the following Eq. (1) (Gouleau et al., 2000): wc ¼

mw−md  100% md

ð1Þ

where wc represents water content (%), mw represents net mass of the wet sample (g), and md represents net mass of the dry sample (g). The dry density of the sediment can be calculated according to Eq. (2): ρsed ¼

ρr  ρw wc  ρr þ ρw

ð2Þ

where ρsed represents the density of the dry sediment (g cm−3), ρr is the density of rocks (2.67 g cm−3), and ρw is the density of water (1 g cm−3). 2.4. Sediment core dating 210

Pb was determined by alpha counting of the 210Po deposited onto Ag discs (Flynn, 1968) by using 209Po as a yield tracer. The sediment was dissolved by adding a mixture of 1:1:0.5 HNO3 +HCl +HF to 2 g of sediment and heating to 200 °C overnight in closed Teflon®PFA containers. Counting was conducted by computerized multichannel α-spectrometry with gold-silicon surface barrier detectors. The vertical distributions of excess 210Pb for the LH4 core are shown in Fig. 2. The supported 210Pb activity (derived from the decay of its effective parent, 226Ra, in the seabed) is determined by measuring 210Pb activity at the bottom of a core with low accumulation rates. However, the bottom depth of our cores did not reach the depth of supported 210Pb activity; thus, the supported 210Pb activity was approximately 1 dpm g−1, as shown in previous studies (Zhang et al., 2008). The excess 210Pb activity (210Pbex, the activity particles attained while sinking through the water column) was calculated by subtracting the supported activity from the total activity. The excess 210 Pb activities were shown to exponentially decrease with depth (Fig. 2 and Supplementary material Table S1), suggesting a constant deposition of excess 210Pb over time at these sites.

2.3. Measurement of the sediment dry density To measure the water content of the sediment, approximately 5 g of the sediment was placed in a pre-weighed crucible, and the total mass

Fig. 2. Depth profiles of excess 210Pb (210Pbex) of core LH4, an exponential decreasing trend with depth of excess 210Pb.

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Based on 210Pbex activities, the constant initial concentration (CIC) model was used to calculate sedimentation rates. The CIC model has been successfully applied in other studies of estuaries and intertidal mudflats (Andersen et al., 2000; Sanders et al., 2010). For this model, the 210Pbex activity (Az) at any sediment layer (z) with age (t) is simply expressed as: −λt

Az ¼ A0  e

−λz=S

¼ A0  e

ð3Þ

where A0 is the 210Pbex at the sediment–water interface, λ is the radioactive decay constant for 210Pb (0.03114 yr−1), and S is the sedimentation rate (cm yr−1). Using Eq. (3), the sedimentation rate (S) was determined by the slope of 210Pbex profiles using least squares regression; however, a number of studies have shown that the compaction on sediment layers may cause an incorrect depth (z) (Lu, 2007). An alternative method, which expresses 210Pbex as a function of mass depth (m: g cm−2), eliminates this compaction effect (Lu, 2007). Thus, Eq. (3) can be rewritten as: −λt

Am ¼ A0  e

−λm=r

¼ A0  e

ð4Þ

where m is mass depth of the cumulative dry weight (g cm−2) at the sediment layer (z), r is the sediment accumulation rate (g cm−2 yr−1), Am is the 210Pbex at the sediment layer (m), and A0 is the 210Pbex at the sediment–water interface layer. From Eq. (4), the sediment accumulation rate (r) was determined by the slope of 210Pbex profiles using least squares regression. Finally, the 210Pb chronologies of both methods were compared to derive the final chronologies. The results of both methods were consistent; the compaction effect was not significant in the 210Pb chronologies in this core. The result of sediment core chronology was therefore unique and was analyzed using the least squares regression from Eq. (3). By using the CIC model, the mean sedimentation rate was calculated to be 1.5 cm yr −1 for core LH4. The sediments in these cores have accumulated during the last 40 yr at a constant sedimentation rate. The deepest layer at a depth of 63 cm in core LH4 was estimated to have been deposited in 1965; therefore, this core was expected to contain records related to the anthropogenic impact of pollutants from Lianyungang. The average depositional rate was determined to be 1.5 cm yr −1, which is consistent with that reported by Zhang et al. (2008). The PAH flux was estimated from the following equation: F ¼ S  ρi  C i

ð5Þ

where F is the PAH flux (ng cm−2 yr−1), Ci is the PAH concentration at i depth (ng g−1), ρi is the dry bulk density of i depth (g cm−3) and S is the sediment rate (cm yr−1).

2.5. Statistical analysis In the present study, correlation analysis was performed to obtain information about the interrelationships between PAHs and historical economic data. To assess the possible sources of PAHs, as well as to verify the contribution of distinct sources to the sediment subsamples, a principal component analysis (PCA) was performed. The varimax rotation method was chosen in the PCA for all variables to maximize factor variance and to simplify the columns of the factor matrix. An eigenvalue over unity was used as the test for the factors. The computer package SPSS (version20.0) was employed to perform the statistical analyses. Two-sided p valuesb 0.05 were considered significantly.

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3. Results and discussions 3.1. Down-core flux and concentration variation of 16 PAHs The sedimentary flux and concentration profiles of the 16 PAHs in the sediment core are shown in Fig. 3 and listed in the Supplementary material Table S1. The individual PAH sedimentary flux was calculated from the corresponding concentration, average sedimentary rate, and dry density of the sediment. The total concentrations of PAHs ranged from 72.51 to 805.21 ng g − 1dry weight (dw). The PAH concentrations in the core were higher than those detected in the Pearl River Estuary (59–330 ng g−1 dw) (Liu et al., 2000; Liu et al., 2005), central continental shelf of the East China Sea (27–132 ng g−1 dw) (Guo et al., 2006), the Bohai Sea (97–205 ng g −1 dw) (Hu et al., 2010) and the South Yellow Sea (26–203 ng g−1 dw) (Liu et al., 2012a, 2012b), but were lower than those in the Changjiang River Estuary (80–11740 ng g−1 dw) (Liu et al., 2000) and the Yellow Sea (470–3800 ng g−1 dw) (Wu et al., 2001). Depositional fluxes of the total PAHs ranged from 102.36 to 861.02 ng cm−2 yr−1, which were higher concentrations compared with those in cores collected from the Yellow Sea (53–218 ng cm−2 yr−1) (Liu et al., 2012a), the East China Sea (115–408 ng cm−2 yr−1) (Guo et al., 2007) and the Pearl River Estuary (15–95 ng cm−2 yr−1) (Liu et al., 2005), indicating more inputs occurred in this coastal area. The surface samples showed higher concentration/flux values for the 16 PAHs. The highest concentration of the total PAHs in the tidal flat of Haizhou Bay was nearly two times lower than that from the Changjiang River Estuary, and the highest depositional PAH flux was higher by a factor of 3 (Guo et al., 2006). These results indicate that the amount of PAHs in the tidal flat of Haizhou Bay was relatively higher and that those contaminants that enter the marine environment and partition to particles are ultimately deposited in sediments that can be both a sink and a source of organic pollutants. PAHs, which mainly originated from the incomplete combustion of fossil fuels, are also good tracers of anthropogenic activities. Lianyungang city has had remarkable economic development in the last two decades and has become a new economic growth area in eastern China. In this study, regional socioeconomic data were used to determine the relationship between PAH pollution and historical economic development. The concentration profiles of the 16 PAHs showed small fluctuations from the 1960s to the 1970s (Fig. 3). After the establishment of the People's Republic of China in 1949, China entered a period of reconstruction and rapid economic development. The presence of a small peak associated with PAH concentrations in the sediment core in 1971 might be associated with the short-term economic development in China. An increase of total PAH concentrations from 72.51 to 112.58 ng g−1 was recorded by sediment (Fig. 3). Previously reported results from mud of the East China Sea indicated an increase in PAHs of 33% from 1963 to 1973 (Guo et al., 2006), which is similar with to the results of the present study. The Cultural Revolution period in China was from 1966 to 1976. At that time, economic development was disrupted, and industrial production was reduced during this political movement. Many factories were severely damaged, and China's economy again became stagnant. Consequently, a slight decrease in PAH concentration in the early 1970s was observed (see Fig. 3). The lowest concentration, 89 ng g−1 dw, was recorded in the 1973 layer; however, an increase in PAH levels beginning in 1973 likely corresponds to the commencement of oil and coal productions. A similar increase was also detected in the late 1970s in the sediment cores from the Changjiang River Estuary and the Yellow Sea (Guo et al., 2007; Liu et al., 2012a). The total PAH concentration profiles closely coincided with the historical economic development of this region. A significant increase in total PAH concentrations occurred in the late 1970s (Fig. 3). With the initiation of the “Reform and Open” policy in 1978, the resuscitation of China's economy, accompanied by urbanization and industrialization, resulted in rising energy consumption and consequently increased PAH

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Fig. 3. Down-core concentrations and fluxes of the 16 USEPA priority PAHs in LH4.

emissions (Liu et al., 2005) which is consistent with the rapid increase in PAH concentrations from the late 1970s until 1983. However, the total PAH concentrations gradually decreased from 253.74 ng g−1 dw in 1983 to 228.27 ng g−1 dw in 1990. The PAH fluxes ranged from 316.13 to 248.33 ng cm−2 yr−1, which reflected the stagnancy of Lianyungang's economy in the late 1980s. Since 1991, economic growth has been rising (Supplementary material Fig. S1). The total PAH concentrations rose until they reached the surface maximum, with a 70% increase from 228.27 to 805.21 ng g−1 dw, reflecting the increase in demand for energy from fossil fuels and coal. The trends of PAH concentration profiles in this study are not similar to previously reported sediment cores from the East China Sea (Guo et al., 2006) and the Pearl River Delta (Peng et al., 2008), in which the PAH concentrations show a sustained increase since 1978. The difference in the vertical PAH profile patterns between Haizhou Bay and other regions may reflect different levels of economic development in China. In addition, the accumulation of PAHs in Haizhou Bay reflects the local economic development in Lianyungang, including north Jiangsu Province. It is more meaningful to assess the changes in PAH concentrations in terms of deposition flux, which reflects not only source emissions but also the sedimentary rate and sediment dilution in aquatic environments (Lima et al., 2003). As shown in Fig. 3a, the variations of sedimentary flux were similar to the profiles of the total PAH concentrations in this sediment core. These trends further illustrated the differences in the economic development stages in this area. To further assess the impact of rapid economic development on the local environment, the relationship between the time-dependent fluxes of total PAHs and gross domestic product (GDP) in Lianyungang (SBL, 2011) was examined during the period of 1978–2010 (Supplementary material Fig. S1). The total PAH fluxes and the regional GDP development exhibited strong correlations (R2 =0.91, n =24, pb 0.01). A strong correlation was also observed between historical rural populations and the PAH concentrations, as well as the total PAH fluxes from 1969 to 2010 (R2 =0.85 n=31, pb 0.01) (Supplementary material Fig. S1), which is consistent with the level of PAH emissions from the combustion of domestic coal and biomass (80% of total emissions). Interestingly, a sharp decrease in total PAH flux appeared from 1996 (734.42 ng cm−2 yr−1) to 2004 (604.58 ng cm−2 yr−1). This decrease reflects the trend that the household energy usage structure in China evolved over time: domestic coal was replaced with natural gas since the early 1990s; thus, there was a decreasing proportion of energy from coal combustion and an increasing proportion from cleaner energy sources, such as natural gas and liquefied

petroleum gas. These changes in PAH flux suggest that the PAHs in sediments were mainly derived from anthropogenic sources. 3.2. PAH compositions Fig. 4 describes the variation in PAH categories in the studied sediment core. According to their molecular weights and their sources of origin, the 16 PAHs were grouped separately into 2 + 3 rings, including Nap, Ac, Ace, Flu, Phe and Ant; 4 rings, including Fluo, Pyr, BaA and Chr; and 5 + 6 rings, including BbF, BkF, BaP, InP, DBA and BghiP. After 1970, the percentage of low molecular weight PAHs (2+ 3 rings) to total PAHs gradually decreased to 7.0%. In contrast, the percentage of high molecular weight (5+ 6 ring) PAHs to total PAHs increased from a percentage of 33% in 1969 to the current value of 55%, with a steep increase in the ratio of high molecular weight PAHs to total PAHs starting in 1980. Apart from petrogenic sources, low molecular weight PAHs with a 2 + 3 ring typically originate from low to moderate temperature combustion processes, including biomass and coal burning in homes and small factories (Mai et al., 2003; Guo et al., 2006, 2007; Wang et al., 2009). High molecular weight (5+ 6 rings) PAHs are the byproducts of high-temperature combustion involving coal and petroleum, such as combustion processes in power plants, factories, automotive engines, and gas-fired cooking appliances (Khalili et al., 1995; Harrison et al., 1996; Guo et al., 2007). Consequently, the change in PAH compositions from low molecular weight to high molecular weight PAHs reflects Lianyungang's inevitable transformation from an agricultural economy to an industrial economy, which is more evident after the late 1970s. The PAH species Flu, Phe, Ant, Fluo, Pyr, BaA, Chr, BbF, BkF, DBA, InP, BghiP, and BaP are important tracers for PAH source identification because of their stability and abundance in the environment (Guo et al., 2006). The profiles of the selected PAH concentrations in the sediment core from the tidal flat of Haizhou Bay are shown in Fig. 5. The figure shows that the concentrations of Flu and Phe increase rapidly after the early 1990s. Flu and Phe are mainly from low and moderate temperature combustion processes, such as biomass burning and domestic coal burning with a minority of Flu and Phe originating from petrogenic sources (Khalili et al., 1995; Harrison et al., 1996; Wang et al., 2009). In addition, the increase in population resulted in an increase in energy consumption, combustion processes and PAH emissions (Liu et al., 2012a); therefore, the trends observed for the Flu and Phe profiles may be related to the population growth in Lianyungang (Supplementary material Fig. S1). Similar trends of Flu and Phe were also observed in Donghu Lake of

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285

Fig. 4. Vertical variations of relative abundance of PAHs in the sediment from tidal flat of Haizhou Bay.

Wuhan City (Wang et al., 2009). A strong correlation was found between the size of the rural population of Lianyungang and total PAHs with R 2 = 0.86, n = 11 and p b 0.01 from 1995 to 2010. Moreover, a strong correlation existed between PAH concentrations and historical energy consumption in Lianyungang over the same period with R 2 = 0.71, n = 11, and p b 0.01 (Supplementary material Fig. S1) (SBL, 2011). Fluo and Pyr are chemical tracers for coal and petroleum combustions (Guo et al., 2006). Since 1970, their concentrations gradually increased to the present levels (Fig. 4). These concentration profiles correlate with the increasing demand for energy from coal and petroleum

in Lianyungang. Previous studies have confirmed that BaA and Chr were dominant in the emissions of petroleum and its combustion process (Sicre et al., 1987; Guo et al., 2006). In contrast to the aforementioned PAH species, the concentrations of BaA + Chr showed slight increases in the 1980s, which correlate with the increasing energy demand for coal and petroleum after the initiation of “Reform and Open” in China. BaA + Chr concentrations also exhibited a noticeable increase since 1990, with peak values in surface sediments (Fig. 5), which reflects the rapid industrialization in Lianyungang. Additionally, a strong correlation was found between gross industrial and agricultural products (GIAP) and total PAHs with R 2 = 0.81, n = 15 and

Fig. 5. Temporal trends of selected PAH levels at the sediment core from tidal flat of Haizhou Bay.

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p b 0.01 (Supplementary material Fig. S1). Moreover, the quantity of the remaining high molecular weight PAHs increased rapidly after 1990, which corresponds with regional economic development. Furthermore, InP and BghiP, which usually act as tracers for vehicular exhaust (Harrison et al., 1996; Guo et al., 2006; Mai et al., 2003; Wang et al., 2010), increased markedly since 1990 (Fig. 5), which chronicles the sharp increase in vehicles in Lianyungang; however, the InP and BghiP concentrations showed a decreasing trend after 1997 (Fig. 5). The sea dike is a non-permeable structure and marks the northern boundary of Lianyungang Harbor, which is used by many ships and boats. This sea dike hampers the currents and suspended sediments that flow from Lianyungang Harbor to Haizhou Bay (Gong et al., 2002); thus, InP and BghiP, which originate from the combustion in gasoline engines of boats in the harbor, are prevented from flowing into the bay. The declines in the InP and BghiP concentrations in the sediment may therefore be attributed to the construction of the sea dike. 3.3. Sources of PAHs Previous studies have reported ratios of individual PAHs with similar molecular weights that can have been used as indexes for source apportionment (Khalili et al., 1995; Yunker et al., 1999, 2002; Mandalakis et al., 2005; Zhang et al., 2005). Fluo/(Fluo+ Pry) ratios b 0.4 indicate petrogenic sources, and those between 0.4 and 0.5 indicate liquid fossil fuel combustion, while ratios >0.5 are characteristics of coal or biomass combustion (Yunker et al., 1999, 2002). InP/(InP+ BghiP) ratios b0.2 indicate possible petrogenic sources, those between 0.2 and 0.5 indicate liquid fossil fuel combustion, and ratios >0.5 are presumed to mean that a pyrogenic source was dominant (Yunker et al., 1999, 2002). The Fluo/(Fluo+ Pry), BaA/(BaA+ Chr), and InP/(InP+ BghiP) ratios in the sediment core are shown in Fig. 6. The Fluo/(Fluo+ Pry) ratios were in the range 0.54–0.63, and the InP/(InP+ BghiP) ratios were 0.46– 0.64. These results suggest that pyrolytic PAHs in the tidal flat of Haizhou Bay were mainly derived from coal, grass, and wood combustion. Fluo/(Fluo+ Pry) showed a decreasing trend since the late 1980s, implying an increase in the introduction of PAHs into Haizhou

Bay through petroleum combustion. As a result of the rapid economic development in Lianyungang, petroleum product consumption increased dramatically, which was reflected in the depositional records in the East China Sea and the Changjiang Estuary as well as Dong Lake in central China (Guo et al., 2006, 2007; Yang et al., 2011). The ratios of InP/(InP + BghiP) also emphasized this characteristic energy consumption. As shown in Fig. 6, the ratios just above 0.5 reflect coal as the dominant pyrolytic source of PAHs in this area. PCA was used for source apportionment. Based on the loading of the 16 measured PAHs in all sediment samples, two principal components, PC1 and PC2, were identified and accounted for 80.1% and 8.6%, respectively, of the total variance (Fig. 7). Moreover, PCA was used for sediment samples from a depth of 40.5 cm to the surface, which revealed that PAH concentrations have increased rapidly since 1983. Two principal components were also identified (Supplementary material Fig. S2), which were similar to those detected in the results from all samples. Because of insufficient data, however, no principal component was extracted in the samples from depths of 62.5 cm– 40.5 cm, where a gradual increase in PAH concentrations was observed. PC2 showed a negative loading of 2–3 ring PAHs including Nap, Ac, and Acy, suggesting a combination of petrogenic and low moderate temperature pyrolytic sources (Mai et al., 2003; Guo et al., 2006). In addition, PC1 showed a significant positive loading of 4–6 ring PAHs, including Flu, Phe, Ant, Fluo, Pry, BaA, Chr, BbF, BkF, BaP, BghiP, DBA and InP, which may be attributed to a combination of high temperature combustion and pyrolytic processes (Mai et al., 2003; Guo et al., 2006). This loading is in agreement with Lianyungang's change in energy structure. In the past two decades there has been an increase in oil consumption in this area, but the main energy source in Lianyungang is still coal (Supplementary material Fig. S1). Biomass burning is still an important energy source in the villages in northern China (Guo et al., 2006). This is similar to the results in East China Sea (Guo et al., 2006, 2007), but is different from the other developed countries, for example, Japan (Ishitake et al., 2007), the United States (Lima et al., 2003) and Europe (Fernandez et al., 2000). The energy usage structure in other developed countries,

Fig. 6. Source identification using PAH ratios; Fluo/(Fluo + Pyr) b 0.4 = petrogenic source (I), 0.4–0.5 = liquid fossil fuel combustion (II), >0.5 = coal, grass or wood combustion (III); InP/(InP + BghiP) b0.2 = petrogenic (I), 0.2–0.5 = liquid fossil fuel combustion (II), >0.5 = coal, grass and wood combustion (III); BaA/(BaA + Chr) b 0.2 = petrogenic source (I), 0.2–0.35 = liquid fossil fuel combustion (II), >0.35 = coal, grass or wood combustion (III) (Yunker et al., 2002; Mai et al., 2003; Guo et al., 2006).

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Fig. 7. Principal component analysis of PAHs.

because of the replacement of coal with oil initiated since the 1950s, led to a decrease in coal combustion and an increase in oil as an energy source (Fernandez et al., 2000; Lima et al., 2003; Ishitake et al., 2007). In contrast, the main energy source in Lianyungang has been, and still is mainly coal although the usage of petroleum has greatly increased since the 1990s (Supplementary material Fig. S1). These data reinforce the assertion that the majority of PAHs in the sediment originate from coal and biomass combustions. 4. Conclusion PAHs in the coastal Haizhou Bay sediment core have been successfully used to track the economic development stages of Lianyungang of eastern China over a period of four decades. The significant increase in 16 PAH concentrations and fluxes after the 1990s closely correlated with the substantial economic development that occurred in this region during that time. In this sediment core, high molecular weight PAH concentrations have gradually increased since the late 1960s, whereas low molecular weight PAH concentrations have declined during this period. The PAH diagnostic ratios indicate that PAHs in the sediments of Haizhou Bay originated predominantly from the combustion of coal and biomass, and the contribution of petroleum combustion to PAH deposition is increasing. PAHs in the study area were dominantly from pyrolytic sources, as assessed by PCA. Conflicts of interest statement The authors declared that they have no conflicts of interest to this work. Acknowledgments This work was financially supported by the Priming Scientific Research Foundation for the Junior Teachers in Huaihai Institute of Technology (no. KQ09041), Natural Science Foundation of Huaihai Institute of Technology (no. Z2011001) and Open Fund of State Key Laboratory of Pollution Control and Resources Reuse (no. PCRRF11024). Editor Professor Eddy Zeng and the anonymous reviewers are sincerely appreciated for their critical reviews that greatly improved this manuscript.

Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.scitotenv.2013.02.029.

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