- Email: [email protected]
Presence of aliphatic and polycyclic aromatic hydrocarbons in near-surface sediments of an oil spill area in Bohai Sea
Marine Pollution Bulletin 100 (2015) 169–175
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Presence of aliphatic and polycyclic aromatic hydrocarbons in near-surface sediments of an oil spill area in Bohai Sea Shuanglin Li a,c, Shengyin Zhang a,b,⁎, Heping Dong a,c, Qingfang Zhao a,c, Chunhui Cao b a
Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao, Shandong 266071, People's Republic of China Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou, Gansu 730000, People's Republic of China c Qingdao Institute of Marine Geology, Qingdao, Shandong 266071, People's Republic of China b
a r t i c l e
i n f o
Article history: Received 11 August 2015 Received in revised form 20 August 2015 Accepted 3 September 2015 Available online 12 September 2015 Keywords: Aliphatic hydrocarbons PAHs Near-surface sediments Oil spill Bohai Sea
a b s t r a c t In order to determine the source of organic matter and the fingerprint of the oil components, 50 samples collected from the near-surface sediments of the oil spill area in Bohai Sea, China, were analyzed for grain size, total organic carbon, aliphatic hydrocarbons (AHs), and polycyclic aromatic hydrocarbons (PAHs). The concentrations of C15–35 n-alkanes and 16 United States Environmental Protection Agency (US EPA) priority pollutant PAHs were found in the ranges of 0.88–3.48 μg g−1 and 9.97–490.13 ng/g, respectively. The terrestrial organic matters characterized by C27–C35 n-alkanes and PAHs, resulting from the combustion of higher plants, are dominantly contributed from the transportation of these plants by rivers. Marine organic matters produced from plankton and aquatic plants were represented by C17–C26 n-alkanes in AHs. Crude oil, characterized by C17–C21 n-alkanes, unresolved complex mixture (UCM) with a mean response factor of C19 n-alkanes, low levels of perylene, and a high InP/(InP + BghiP) ratio, seeped into the oceans from deep hydrocarbon reservoirs, as a result of geological faults. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Oil spills usually occur in the oceans during oil exploitation, storage, transportation, and maritime accidents (Gong et al., 2014; Mulabagal et al., 2013; Palinkas et al., 1993). It is a major environmental and financial threat to local communities, particularly if large volumes of unrefined hydrocarbons or crude oil are spilled into the sea (Graham et al., 2010; McNutt et al., 2012). In the last 10 years, the number of oil spills has increased with the rapid increase of offshore oil exploitation in China. Although the self-purifying capacity of the marine environment may dilute the spilled oil over time, seafloor sediments can accurately record massive oil spills from oil tankers and drilling platforms (Wei et al., 2015; Xu et al., 2013). Aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) present in the sediment cores have been used for the identification of the source of organic matter (OM) and reconstruction of the historical record of these hydrocarbon inputs (Lima et al., 2012; Yunker et al., 2011; Zhang et al., 2007; Zhang et al., 2013a). The shallow Bohai Sea, located in North China, is surrounded by Liaodong and Shandong peninsulas, and is connected to the northern ⁎ Corresponding author at: Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou, Gansu 730000, People's Republic of China. E-mail address: [email protected] (S. Zhang).
http://dx.doi.org/10.1016/j.marpolbul.2015.09.009 0025-326X/© 2015 Elsevier Ltd. All rights reserved.
Yellow Sea by the Bohai Strait (Fig. 1). It occupies a marine area of 77,000 km2 with an average water depth of 18 m. Several large rivers, including the Yellow River, flow into Bohai, with a total yearly runoff of 890 × 108 m3 (Sündermann and Feng, 2004). It is the second largest crude oil production base in China with more than 50 offshore platforms, which discharged approximately 9.9 million tons of petroleumcontaminated water in 2006, causing 30% of its water to fail quality standards (State Oceanic Administration, 2006). In June 2011, the most serious oil spill to date occurred on an offshore oil field, named Penglai 19-3 operated by ConocoPhillips China Inc., in Bohai Sea. The accident was caused by a geological fault that opened a near-surface reservoir during production, because of pressure from water injection. Approximately 723 barrels of oil and 2620 barrels of mineral oil-based drilling mud seeped into the sea, which led to the pollution of 840 km2 area of its surface (Liu et al., 2015). Satellite remote sensing was used to model the oil spill trajectory and to assess the damage from Penglai 19-3 (Wei et al., 2015; Xu et al., 2013). However, data on the sedimentary OM involved in this accident were not obtained earlier. Core samples were collected at 0.5 m below the seafloor (hereinafter called the near-surface sediments) in the oil spill area, which is the zone between Penglai 19-3 and other oil and gas fields. Because the sedimentation rate around 0.29 cm/a dated from 210Pb activity in the 30-cm core sample (Hu et al., 2011), these samples were expected to contain seepage hydrocarbon as well as terrigenous and marine matter with little or no anthropogenic pollution.
170
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
Fig. 1. Study area and location of sampling sites in Bohai Sea (adopted from Chu et al., 2006 and Hu et al., 2011).
The grain size, total organic carbon (TOC), AHs, and PAHs were quantified to determine the sources of OM in the sediment and to identify the fingerprint of the oil components. Moreover, characteristics of AHs and PAHs may provide a useful tool for detecting oil spills before massive hydrocarbon seepage. 2. Materials and methods 2.1. Sample collection The sampling sites (BS1–BS50) are shown in Fig. 1. In August 2012, 50 sediment cores were collected using a vibro piston corer deployed from R/V Yezhizheng of the Qingdao Institute of Marine Geology, China. This corer can obtain a 2.5- to 3.0-m core sample, via vibration, without any significant disturbance to the substrate. The sediment between 0.50 and 0.55 m of these core samples was used for analysis. All the samples were wrapped in aluminum foils and stored at −20 °C until analysis. 2.2. Analysis of grain size and TOC of sediments The grain size and TOC of the near-surface sediments were measured with a laser particle size analyzer (Mastersizer 2000, Malvern Instruments Ltd, UK) at Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, China. The 1-g sample was treated with 10% H2O2 and 0.5 mol/l HCl for 24 h to remove the OMs and biogenic carbonates, respectively. The samples were dispersed and homogenized by ultrasonic vibration for 30 s before instrumental analysis. The particle sizes were b4 μm for clay, 4–63 μm for silt, and N 63 μm for sand. The relative error of the duplicate samples was b3% (n = 4). The dried samples were treated with 4 mol/l HCl to remove carbonate, and further dried overnight at 60 °C. The carbonate-free samples were analyzed for measuring TOC using a VarioEL-III elemental
analyzer, and the average values were reported. Replicate analysis of one sample (n = 6) gave a precision of ±0.02 wt.% for TOC. 2.4. Analysis of AHs and PAHs The analysis of AHs and PAHs was performed at the Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences. Approximately 20 g of the freeze-dried, homogenized, and pulverized sediment sample was extracted with dichloromethane (DCM) in a Soxhlet apparatus for 48 h, to which activated copper was added to remove sulfur. The extracts were then reduced, hexane–exchanged, and separated on a 1:2 alumina:silica gel column. The target fraction containing AHs and PAHs was eluted with 15 ml of hexane and 20 ml of hexane:DCM (1:1, v:v). An Agilent 6890 series gas chromatograph/5975 series mass spectrometer was operated in a full-scan mode and fitted with a DB-5MS capillary column (30 m × 0.25 mm inner diameter, 0.25-μm film thickness), using helium as the carrier gas (1.0 ml/min). The samples were injected in splitless mode with a temperature of 280 °C. The oven was kept at 35 °C for 1 min, the temperature was increased from 35 to 120 °C at 10 °C/min, and then from 120 to 300 °C at 3 °C/min, with a final holding time of 30 min at 300 °C (Hu et al., 2009). The internal standard samples C24D50 (deuterated n-C24) and anthracene-d10 were used to quantify AHs and PAHs, respectively. Individual n-alkanes (C12–C35) were identified and quantified based on the molecular ion and mass to charge ratio (m/z) of 85. The unresolved complex mixture (UCM) fraction was calculated using the mean response factors of n-alkanes. The following PAHs were quantified: naphthalene (Nap), acenaphthylene (Ac), acenaphthene (Ace), fluorene (Fl), phenanthrene (Phe), anthracene (Ant), fluoranthene (Flu), pyrene (Pyr), benz[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd] pyrene (IP), dibenz[a,h]anthracene (DBA), perylene (Pery), and benzo[ghi]perylene (BghiP).
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
171
2.3. Quality assurance/quality control A mixture of five deuterated PAHs (naphthalene-d8, acenaphthened10, phenanthrene-d10, chrysene-d12, and perylene-d12) was used as a recovery standard to monitor matrix effects and procedural performance. The recovery rate of the experiment was determined to be 91.5 ± 10%. In addition, blank and spiked blank experiments were applied as a control. In the blank experiment, there was no significant (b5%) interference of the targeted compound. 3. Results and discussion 3.1. The grain size and TOC of near-surface sediment The ranges of TOC and grain size parameters for near-surface sediments of the oil spill area are listed in Table 1. The median grain size (MZ) of near-surface sediments is in the range of 3.74–7.48 Φ, averaging 6.97 Φ. Silt and clay are found to be the predominant constituents of the near-surface sediment samples, with mean compositions of 60.86% and 28.9%, respectively. These fine-grained sediments in the oil spill area are usually observed in the central Bohai, where weaker tidal environments are dominant (Sündermann and Feng, 2004). The TOC present in the near-surface sediments is in the range of 0.05–0.60%, with an average of 0.47%. The values of TOC and MZ were slightly positively correlated (R2 = 0.48) (Fig. 2), which are found to be lower than surface sediments of marginal sea, such as the central Yellow Sea (R2 = 0.69) (Zhang et al., 2014). The correlation between TOC and MZ indicates that the distribution of OM is influenced by inputs from other possible sources, except for the dynamics of the marine environment as a predominant factor in the oil spill area. 3.2. Aliphatic hydrocarbons The n-alkanes, isoprenoids, and UCMs in AHs were analyzed using gas chromatography–mass spectrometry (GC–MS). The carbon preference indices (CPI1, CPI2) (Bray and Evans, 1961) and other deterministic ratios of isoprenoids and n-alkanes are shown in Table 2. The gas chromatograms for most samples exhibited a bimodal n-alkane distribution, with one maximum at C17 or C19 within the short-chain n-alkanes and the other maximum at C29 or C31 within the long-chain n-alkanes; however, most samples showed a maximum at C29 or C31 (Fig. 3). The average concentration of C15–35 n-alkanes was 2.15 μg g− 1 (dry weight) with a range of 0.88–3.48 μg g−1. The ratio of short- to longchain n-alkanes LMW/HMW ranged from 0.07 to 0.93, with an average of 0.28. Ranges of CPI1 and CPI2 were 0.66–1.47 and 0.95–3.35, respectively, indicating a strong odd-to-even carbon preference in the longchain n-alkanes. The sum of the most abundant n-alkanes with respect to biogenic terrestrial sources (C27, C29, C31, C33), referred to here as Alkterr, ranged from 0.20 to 0.60, with an average of 0.37 (Table 2). This Alkterr value indicates that the aquatic and other source OMs were mixed with the terrestrial OMs in the oil spill area samples. The acyclic isoprenoids pristane (Pr) and phytane (Ph) were abundant in all samples. The ranges of Pr/C17 and Ph/C18 ratios were 0.49–2.42 and 1.03–2.71, respectively. The ratio of Pr to Ph in the samples ranged from 0.30 to 1.45, with an average of 0.72 (Table 1),
Table 1 Compositions and parameters of bulk organic matter and sediment grain size in the nearsurface sediments of the oil spill area of Bohai Sea. Parameters
Minimum
Maximum
Mean
Fig. 2. Correlation analysis between the concentrations of TOC and median grain size in the oil spill area.
indicating the presence of dysoxic conditions during OM deposition. The presence of UCMs in sediments is an indicator of chronic/degraded petroleum contamination, although bacteria-derived UCMs cannot be ignored (Bouloubassi et al., 2001). The UCMs occurred as short-chain n-alkanes in all samples with a mean response factor of C19 n-alkanes (Fig. 3), and the concentrations of UCMs and C19 n-alkanes were significantly positively correlated (R2 = 0.56) (Fig. 4). The ratio of UCM to total n-alkanes (UCM/n-ALK) ranged from 1.87 to 7.03, with an average of 3.52, indicating high petroleum contamination in that area. The data sets containing Pr, Ph, individual n-alkanes, and UCMs were analyzed by principal component analysis (PCA) using SPSS 13.0 for Windows (SPSS Inc., Chicago, IL, USA) to identify the sources of AHs. The two major principal components for loading variables are shown in Fig. 5. PC1 accounted for 32% of the data variance and had a high positive loading of the combination variables of long-chain n-alkanes, attributable to terrestrial and petrogenic sources. PC2 contributed to 62% of the total variance and was distinguished by the high positive loadings of the short-chain n-alkanes (C17–C21) and UCMs, mainly attributed to marine biogenic contributions and oil contamination. The moderate-chain alkanes (C22–C26), with a positive loading on both PC1 and PC2, suggest that their origin was complex, possibly including mainly marine aquatic and minor bacterial degradation components.
Table 2 Concentrations and ratios of aliphatic hydrocarbons in the oil spill area. AH properties
Oil spill area Range
Mean
Range
Mean
Range
Mean
LMW/HMWa Pr/C17 Ph/C18 Pr/Phb CPI1c CPI2d Alkterre n-ALK (μg g−1) UCM/n-ALK
0.07–0.93 0.49–2.42 1.03–2.71 0.30–1.45 0.66–1.47 0.95–3.35 0.20–0.60 0.88–3.48 1.87–7.03
0.28 1.33 1.40 0.72 1.05 1.66 0.37 2.15 3.52
0.2–1.1 \ \ 0.9–1.9 \ 1.8–7.2 \ 1.22–5.91 0.55–10.88
0.6 \ \ 1.2
0.03–0.62 0.67–1.58 0.96–1.99 0.11–0.84 1.01–1.83 1.20–3.39 0.10–0.59 \ \
0.10 0.85 1.28 0.47 1.17 1.54 0.37 \ \
a
0.05 0 32.65 2.59 3.74
0.60 64.77 70.08 35.07 7.48
0.47 9.90 60.86 28.90 6.97
4.2 \ 3.3 7.39
Yellow Sea Zhang et al. (2014)
LMW/HMW: ∑nC21−/∑nC22+ Pr/Ph: ratio of pristane to phytane CPI1: 1/2[∑C15–21(odd carbon)/∑C14–20(even carbon) + ∑C15–21(odd carbon)/∑C16–22(even carbon)] d CPI2: 1/2[∑C25–35(odd carbon)/∑C24–34(even carbon) + ∑C25–35(odd carbon)/∑C26–36(even carbon)] e Alkterr: (C27 + C29 + C31 + C33)/∑C14–38 b
TOC (%) Sand (%) Silt (%) Clay (%) Median grain size (Φ)
BC2 Hu et al. ( 2011)
c
172
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
Fig. 4. Correlation analysis between the concentrations of UCM and C19 n-alkane in the oil spill area.
3.3. Polycyclic aromatic hydrocarbons
Fig. 3. Total ion current (TIC) of GC–MS chromatograms for (a) sediment from the oil spill area, (b) near-surface sediment from the southern Yellow Sea (Zhang, 2014), and (c) core samples from a non-oil spill area (Hu, 2011).
AHs in this study were characterized by a higher concentration of short-chain n-alkanes (LMW/HMW) and UCMs (UCM/n-ALK) than those from the surface sediments of Yellow Sea (Zhang et al., 2014). However, sediments of core BC2 and surface samples with nonseepage oil contamination from Bohai Sea, collected in August and October of 2006 (Hu et al., 2011), had higher LMW/HMW and UCM/n-ALK values, suggesting the possibility of petroleum contaminations from oil exploration, shipping activities, and river sewage. A similar distribution of UCMs is also reported in the oil spill area in the Gulf of Mexico (Abrams, 2005). As described earlier, all oil spill area samples showed significant UCMs, including short-chain n-alkanes by GC–MS, whereas the UCMs of non-oil seepage contamination sediments usually included long-chain n-alkanes. Given that the sediment was sampled at 0.5 m below the surface to avoid the mixture of anthropogenic petroleum, it is concluded that short-chain n-alkanes and UCMs with a mean response factor of C19 n-alkanes may represent oil that seeped through geological faults from deep hydrocarbon reservoirs.
The 16 United States Environmental Protection Agency (US EPA) priority pollutant PAHs and perylene, from 20 selected samples, were quantified to identify hydrocarbon contamination from oil spills (Table 3). The total concentration of the 16 US EPA priority pollutant PAHs ranged from 9.97 to 490.13 ng/g, with an average of 107.27 ng/g. The concentrations of the 16 PAHs in the oil spill area were higher than those of the sedimentary PAHs in Yellow River (range: 31–133 ng/g, mean: 76.8 ng/g) (Li et al., 2006), northern Yellow Sea (range: 27–110 ng/g, median: 51 ng/g) (Li et al., 2002), and south China Sea (range: 28–109 ng/g, median: 57 ng/g) (Liu et al., 2012); similar to those of the BC-2 core sample from Bohai Sea (range: 53.3–186 ng/g, mean: 103) (Hu et al., 2011); and lower than those in the surrounding rivers such as Hai River (mean: 64 ng/g) (Shi et al., 2005) and Daliao River system (range: 61.9–840.5 ng/g, mean: 287.3 ng/g) (Guo et al., 2007). Sediments in this study did not have a higher concentration of AHs and PAHs than those from the non-oil spill area, mainly because of the following reasons: (1) when a vast amount of crude oil seeped through the major faults into sea water, only a relatively small amount of oil spread slowly into the sediment via micro faults and (2) the spilled oil was likely deposited in sandy sediment rather than muddy sediment, and the selected muddy samples had sufficient OM for organic geochemistry analysis.
Fig. 5. Factor loadings of n-alkanes and UCMs in the sediment samples.
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
173
Table 3 Concentrations (ng/g dry weight) of PAHs in the oil spill area. Concentration (ng/g) and ratios
Minimum
Maximum
Mean
Variance
Naphthalene (Nap) Acenaphthene (Acy) Acenaphthylene (Ace) Fluorene (Flu) Phenanthrene (Phe) Anthracene (Ant) Fluoranthene (Flt) Pyrene (Pyr) Benzo[a]anthracene (BaA) Chrysene (Chr) Benzo[b]fluoranthen (BbF) Benzo[k]fluoranthen (BkF) Benzo[a]pyrene (BaP) Indeno[1,2,3-cd]pyrene (InP) Indeno[1,2,3-cd]pyrene (DBA) Benzo[ghi]perylene (BghiP) Perylene ΣEPAPAHs Perylene/ΣPAHs (%)
0.00 0.00 0.00 0.09 4.18 0.09 1.46 1.50 0.26 0.74 0.25 0.24 0.06 0.11 0.01 0.36 2.56 9.97 5.44
0.34 0.20 0.16 9.74 160.31 7.00 66.68 78.49 15.04 34.45 23.16 15.54 5.53 7.63 4.64 32.07 103.09 490.13 42.77
0.04 0.03 0.03 0.43 18.80 0.69 11.94 14.40 2.38 6.56 4.94 3.62 0.82 1.23 0.63 4.77 17.58 88.72 18.58
0.09 0.06 0.05 2.27 34.87 1.44 13.76 15.93 3.13 7.28 5.27 3.42 1.36 1.66 1.19 7.11 25.39 101.01 10.77
Perylene was one of the most abundant nonalkylated PAHs found in the oil spill area sediment, contributing 5.44–42.77% (mean: 18.58%) of the total PAHs (Perylene/ΣPAHs, Table 2). High levels of perylene were also present in sediments collected from the southern Yellow Sea, China (range: 6.40–88.85%, mean: 39.38%) (Zhang et al., 2013b) and Emerald Peak Lake, Taiwan (60–98%) (Cheng-Wei et al., 2011). In most of these sediments, perylene contributed N 10% of the total PAHs, suggesting a short-term diagenetic process as the predominant source of perylene (Tissier and Saliot, 1983). By contrast, Wakeham et al. (1980) found that 1–4% perylene relative to the total nonalkylated PAHs was a typical value for combustion/pyrolysis sources of surface sediment. Marynowski et al. (2015) reported that perylene is found at relatively high concentrations in samples with a vitrinite reflectance (Rr) maturation of b 0.6%, whereas its abundance rapidly decreases for 0.6–0.7% Rr. In samples with N0.7% Rr, perylene disappears completely. The concentrations of perylene in our samples were found to be lower than those from the southern Yellow Sea, although they developed in a similar depositional environment by a high sediment load from a large river. The relatively low percentage of perylene as a fraction of the total nonalkylated PAHs may reflect a significant amount of oil with little perylene overprinted from terrestrial OM. Combinations of PAH isomer pair ratios, such as Fluo/(Fluo + Pyr), Ant/(Ant + Phe), BaA/(BaA + Chr), and InP/(InP + BghiP) (Yunker et al., 2002), have been used to determine PAH compositions and their possible sources (Fig. 6). Most of the PAH ratios in this study indicate that the presence of PAH is mainly due to mixed sources of combustion and petroleum, and all samples suggest petroleum as an important source of PAH, particularly for InP and BghiP in the oil spill area (Fig. 6). The low Ant/(Ant + Phe) ratios could be attributed to a faster degradation of Ant than Phe during transport (Wang et al., 2010). Similarly, the Fluo/(Fluo + Pyr) and BaA/(BaA + Chr) ratios indicate coal and biomass combustion as major sources, although no sample was present in the combustion area of the three plots (Fig. 6), which was distinct from sedimentary PAHs in core BC-2 of the nonseepage oil spill area. Therefore, the overprinting oil spilled from deep reservoirs could significantly alter the biogenic PAH isomers of OM in sediments near spill areas. 3.4. Mixed-source model for OM The mixed-source model for OM in the near-surface sediments could be established by the distribution of AHs and PAHs, as well as the bulk geochemical parameters (TOC, grain size). It is evident from Fig. 7 that there are three main OM sources for the near-surface sediments in the oil spill area: (1) terrestrial OM from the surrounding river input,
Fig. 6. PAH cross-plots for the following ratios: (a) Ant/(Ant + Phe) (m/z 178), (b) BaA/ (BaA + Chr) (m/z 228), and (c) InP/(InP + BghiP) vs. Fluo/(Fluo + Pyr). Source boundary lines are based on Yunker et al. (2002).
which is characterized by C27–C35 long-chain n-alkanes and PAHs from combustion of higher plants; (2) marine OM produced from plankton or aquatic plants, represented by C17–C26 short-chain n-alkanes; (3) crude oil seeped through geological faults from deep hydrocarbon reservoirs, which is characterized by C17–C21 shortchain n-alkanes, UCM with a mean response factor of C19 n-alkanes, high levels of BghiP, and low levels of perylene.
174
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
Fig. 7. Mixed-source model for organic matter in the oil spill area of Bohai Sea.
Although the sediments in this area experienced a serious oil spill in 2006, the OMs present in the near-surface sediments are predominantly sourced from terrestrial higher plants, and their AHs show higher values of CPI2 and Alkterr, as well as a high proportion of long-chain n-alkanes. The marine plankton or aquatic plants also have an appreciable contribution to the sediments, particularly for C22–C26 n-alkanes of AHs. Because the molecular weight of spilled oil has overprinted on the primary OM in the near-surface sediment, the compositions of AHs and PAHs have been altered into the feature as mentioned earlier. 4. Conclusions The grain size, TOC, AHs, and PAHs of near-surface sediments of the oil spill area were analyzed to determine the source of OM. Although the concentrations of AHs were not significantly higher than those of core sediment from a non-oil spill area, the levels of short-chain n-alkanes, UCMs, and EPA 16 priority pollutant PAHs were higher than the nonoil spilled surface sediment developed in a similar semi-closed marginal sea shelf. Sediments of the oil spill area have mixed biogenic and petroleum sources characterized by high levels of UCMs associated with short-chain n-alkanes, low levels of perylene, as well as a high InP/(InP + BghiP) ratio. The following are the three main OM sources for the near-surface sediments in the oil spill area: (1) terrestrial OM from the surrounding river input, (2) marine OM produced from plankton or aquatic plants, and (3) crude oil seeped through geological faults from deep hydrocarbon reservoirs. However, the OMs in this near-surface sediment are predominantly sourced from terrestrial vascular plants, and the marine plankton or aquatic plants also have an appreciable contribution to the sediments. The compositions of AHs and PAHs have been altered as the molecular weight of spilled oil has overprinted on the primary OM in the near-surface sediment. Acknowledgments This study was financially supported by the Special Program of Ministry of Land and Resources of the People's Republic of China (Grant No. 201211060), National Natural Science Foundation of China (Grant No. 41503048), and the Key Laboratory Project of Gansu Province (Grant No. 1309RTSA041). The authors extend their special thanks to Chief Editor Dr Charles Sheppard for thorough and constructive reviews that greatly improved the clarity and quality of this article. References Abrams, M.A., 2005. Significance of hydrocarbon seepage relative to petroleum generation and entrapment. Mar. Pet. Geol. 22, 457–477. Bouloubassi, I., Fillaux, J., Saliot, A., 2001. Hydrocarbons in surface sediments from the Changjiang (Yangtze river) estuary, East China Sea. Mar. Pollut. Bull. 42, 1335–1346.
Bray, E., Evans, E., 1961. Distribution of paraffins as a clue to recognition of source beds. Geochim. Cosmochim. Acta 22, 2–15. Cheng-Wei, F., Shiue, J., Cheng-Yi, W., Cheng-Yu, W., 2011. Perylene dominance in sediments from a subtropical high mountain lake. Org. Geochem. 42. Chu, Z., Sun, X., Zhai, S., Xu, K., 2006. Changing pattern of accretion/erosion of the modern Yellow River (Huanghe) subaerial delta, China: based on remote sensing images. Mar. Geol. 227, 13–30. Gong, Y., Zhao, X., Cai, Z., O'Reilly, S.E., Hao, X., Zhao, D., 2014. A review of oil, dispersed oil and sediment interactions in the aquatic environment: influence on the fate, transport and remediation of oil spills. Mar. Pollut. Bull. 79, 16–33. Graham, W.M., Condon, R.H., Carmichael, R.H., D'Ambra, I., Patterson, H.K., Linn, L.J., Hernandez Jr., F.J., 2010. Oil carbon entered the coastal planktonic food web during the Deepwater Horizon oil spill. Environ. Res. Lett. 5, 045301. Guo, Z., Lin, T., Zhang, G., Zheng, M., Zhang, Z., Hao, Y., Fang, M., 2007. The sedimentary fluxes of polycyclic aromatic hydrocarbons in the Yangtze River Estuary coastal sea for the past century. Sci. Total Environ. 386, 33–41. Hu, L., Guo, Z., Feng, J., Yang, Z., Fang, M., 2009. Distributions and sources of bulk organic matter and aliphatic hydrocarbons in surface sediments of the Bohai Sea, China. Mar. Chem. 113, 197–211. Hu, L., Guo, Z., Shi, X., Qin, Y., Lei, K., Zhang, G., 2011. Temporal trends of aliphatic and polyaromatic hydrocarbons in the Bohai Sea, China: evidence from the sedimentary record. Org. Geochem. 42, 1181–1193. Li, B., Wu, Y., Zhang, J., 2002. Distribution and source of polycyclic aromatic hydrocarbons(PAHs) in surface sediment of the northern Yellow Sea. China Environ. Sci. 22, 429–432. Li, G., Xia, X., Yang, Z., Wang, R., Voulvoulis, N., 2006. Distribution and sources of polycyclic aromatic hydrocarbons in the middle and lower reaches of the Yellow River, China. Environ. Pollut. 144, 985–993. Lima, M.B., Feitosa, E.A., Emídio, E.S., Dórea, H.S., Alexandre, M.R., 2012. Distribution and sources of aliphatic hydrocarbons in surface sediments of Sergipe River estuarine system. Mar. Pollut. Bull. 64, 1721–1725. Liu, L.-Y., Wang, J.-Z., Wei, G.-L., Guan, Y.-F., Zeng, E., 2012. Polycyclic aromatic hydrocarbons (PAHs) in continental shelf sediment of China: implications for anthropogenic influences on coastal marine environment. Environ Pollut 167, 155–217. Liu, X., Guo, J., Guo, M., Hu, X., Tang, C., Wang, C., Xing, Q., 2015. Modelling of oil spill trajectory for 2011 Penglai 19-3 coastal drilling field, China. Appl. Math. Model. 39, 5331–5340. Marynowski, L., Smolarek, J., Hautevelle, Y., 2015. Perylene degradation during gradual onset of organic matter maturation. Int. J. Coal Geol. 139, 17–25. McNutt, M.K., Camilli, R., Crone, T.J., Guthrie, G.D., Hsieh, P.A., Ryerson, T.B., Savas, O., Shaffer, F., 2012. Review of flow rate estimates of the Deepwater Horizon oil spill. Proc. Natl. Acad. Sci. 109, 20260–20267. Mulabagal, V., Yin, F., John, G.F., Hayworth, J.S., Clement, T.P., 2013. Chemical fingerprinting of petroleum biomarkers in Deepwater Horizon oil spill samples collected from Alabama shoreline. Mar. Pollut. Bull. 70, 147–154. Palinkas, L.A., Petterson, J.S., Russell, J., Downs, M.A., 1993. Community patterns of psychiatric disorders after the Exxon Valdez oil spill. Am. J. Psychiatr. 150, 1517–1523. Shi, Z., Tao, S., Pan, B., Fan, W., He, X., Zuo, Q., Wu, S., Li, B., Cao, J., Liu, W., 2005. Contamination of rivers in Tianjin, China by polycyclic aromatic hydrocarbons. Environ. Pollut. 134, 97–111. Sündermann, J., Feng, S., 2004. Analysis and modelling of the Bohai sea ecosystem—a joint German–Chinese study. J. Mar. Syst. 44, 127–140. Tissier, M., Saliot, A., 1983. Pyrolytic and naturally occurring polycyclic aromatic hydrocarbons in the marine environment, advances in organic geochemistry. Wiley, Chichester, pp. 268–278. Wakeham, S.G., Schaffner, C., Giger, W., 1980. Polycyclic aromatic hydrocarbons in recent lake sediments—II. Compounds derived from biogenic precursors during early diagenesis. Geochim. Cosmochim. Acta 44, 415–429. Wang, W., Simonich, S.L.M., Xue, M., Zhao, J., Zhang, N., Wang, R., Cao, J., Tao, S., 2010. Concentrations, sources and spatial distribution of polycyclic aromatic hydrocarbons in soils from Beijing, Tianjin and surrounding areas, North China. Environ. Pollut. 158, 1245–1251. Wei, L., Hu, Z., Dong, L., Zhao, W., 2015. A damage assessment model of oil spill accident combining historical data and satellite remote sensing information:
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175 a case study in Penglai 19-3 oil spill accident of China. Mar. Pollut. Bull. 91, 258–271. Xu, Q., Li, X., Wei, Y., Tang, Z., Cheng, Y., Pichel, W.G., 2013. Satellite observations and modeling of oil spill trajectories in the Bohai Sea. Mar. Pollut. Bull. 71, 107–116. Yunker, M.B., Macdonald, R.W., Vingarzan, R., Mitchell, R.H., Goyette, D., Sylvestre, S., 2002. PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Org. Geochem. 33, 489–515. Yunker, M.B., Macdonald, R.W., Snowdon, L.R., Fowler, B.R., 2011. Alkane and PAH biomarkers as tracers of terrigenous organic carbon in Arctic Ocean sediments. Org. Geochem. 42, 1109–1146. Zhang, J., Wu, Y., Jennerjahn, T.C., Ittekkot, V., He, Q., 2007. Distribution of organic matter in the Changjiang (Yangtze River) Estuary and their stable carbon and nitrogen
175
isotopic ratios: Implications for source discrimination and sedimentary dynamics. Mar. Chem. 106. Zhang, R., Zhang, F., Zhang, T.-C., 2013a. Sedimentary records of PAHs in a sediment core from tidal flat of Haizhou Bay, China. Sci. Total Environ. 450–451, 280–288. Zhang, S.-y., Li, S.-l., Dong, H.-p., Zhao, Q.-f., Shi, J.-a., Zhang, Z.-n., 2013b. Distribution and source identification of polycyclic aromatic hydrocarbon of surface sediments from the center part of South Yellow Sea, China. China Environ. Sci. 7, 020. Zhang, S., Li, S., Dong, H., Zhao, Q., Lu, X., Shi, J.a., 2014. An analysis of organic matter sources for surface sediments in the central South Yellow Sea, China: evidence based on macroelements and n-alkanes. Mar. Pollut. Bull. 88, 389–397.
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Presence of aliphatic and polycyclic aromatic hydrocarbons in near-surface sediments of an oil spill area in Bohai Sea Shuanglin Li a,c, Shengyin Zhang a,b,⁎, Heping Dong a,c, Qingfang Zhao a,c, Chunhui Cao b a
Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao, Shandong 266071, People's Republic of China Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou, Gansu 730000, People's Republic of China c Qingdao Institute of Marine Geology, Qingdao, Shandong 266071, People's Republic of China b
a r t i c l e
i n f o
Article history: Received 11 August 2015 Received in revised form 20 August 2015 Accepted 3 September 2015 Available online 12 September 2015 Keywords: Aliphatic hydrocarbons PAHs Near-surface sediments Oil spill Bohai Sea
a b s t r a c t In order to determine the source of organic matter and the fingerprint of the oil components, 50 samples collected from the near-surface sediments of the oil spill area in Bohai Sea, China, were analyzed for grain size, total organic carbon, aliphatic hydrocarbons (AHs), and polycyclic aromatic hydrocarbons (PAHs). The concentrations of C15–35 n-alkanes and 16 United States Environmental Protection Agency (US EPA) priority pollutant PAHs were found in the ranges of 0.88–3.48 μg g−1 and 9.97–490.13 ng/g, respectively. The terrestrial organic matters characterized by C27–C35 n-alkanes and PAHs, resulting from the combustion of higher plants, are dominantly contributed from the transportation of these plants by rivers. Marine organic matters produced from plankton and aquatic plants were represented by C17–C26 n-alkanes in AHs. Crude oil, characterized by C17–C21 n-alkanes, unresolved complex mixture (UCM) with a mean response factor of C19 n-alkanes, low levels of perylene, and a high InP/(InP + BghiP) ratio, seeped into the oceans from deep hydrocarbon reservoirs, as a result of geological faults. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Oil spills usually occur in the oceans during oil exploitation, storage, transportation, and maritime accidents (Gong et al., 2014; Mulabagal et al., 2013; Palinkas et al., 1993). It is a major environmental and financial threat to local communities, particularly if large volumes of unrefined hydrocarbons or crude oil are spilled into the sea (Graham et al., 2010; McNutt et al., 2012). In the last 10 years, the number of oil spills has increased with the rapid increase of offshore oil exploitation in China. Although the self-purifying capacity of the marine environment may dilute the spilled oil over time, seafloor sediments can accurately record massive oil spills from oil tankers and drilling platforms (Wei et al., 2015; Xu et al., 2013). Aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) present in the sediment cores have been used for the identification of the source of organic matter (OM) and reconstruction of the historical record of these hydrocarbon inputs (Lima et al., 2012; Yunker et al., 2011; Zhang et al., 2007; Zhang et al., 2013a). The shallow Bohai Sea, located in North China, is surrounded by Liaodong and Shandong peninsulas, and is connected to the northern ⁎ Corresponding author at: Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou, Gansu 730000, People's Republic of China. E-mail address: [email protected] (S. Zhang).
http://dx.doi.org/10.1016/j.marpolbul.2015.09.009 0025-326X/© 2015 Elsevier Ltd. All rights reserved.
Yellow Sea by the Bohai Strait (Fig. 1). It occupies a marine area of 77,000 km2 with an average water depth of 18 m. Several large rivers, including the Yellow River, flow into Bohai, with a total yearly runoff of 890 × 108 m3 (Sündermann and Feng, 2004). It is the second largest crude oil production base in China with more than 50 offshore platforms, which discharged approximately 9.9 million tons of petroleumcontaminated water in 2006, causing 30% of its water to fail quality standards (State Oceanic Administration, 2006). In June 2011, the most serious oil spill to date occurred on an offshore oil field, named Penglai 19-3 operated by ConocoPhillips China Inc., in Bohai Sea. The accident was caused by a geological fault that opened a near-surface reservoir during production, because of pressure from water injection. Approximately 723 barrels of oil and 2620 barrels of mineral oil-based drilling mud seeped into the sea, which led to the pollution of 840 km2 area of its surface (Liu et al., 2015). Satellite remote sensing was used to model the oil spill trajectory and to assess the damage from Penglai 19-3 (Wei et al., 2015; Xu et al., 2013). However, data on the sedimentary OM involved in this accident were not obtained earlier. Core samples were collected at 0.5 m below the seafloor (hereinafter called the near-surface sediments) in the oil spill area, which is the zone between Penglai 19-3 and other oil and gas fields. Because the sedimentation rate around 0.29 cm/a dated from 210Pb activity in the 30-cm core sample (Hu et al., 2011), these samples were expected to contain seepage hydrocarbon as well as terrigenous and marine matter with little or no anthropogenic pollution.
170
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
Fig. 1. Study area and location of sampling sites in Bohai Sea (adopted from Chu et al., 2006 and Hu et al., 2011).
The grain size, total organic carbon (TOC), AHs, and PAHs were quantified to determine the sources of OM in the sediment and to identify the fingerprint of the oil components. Moreover, characteristics of AHs and PAHs may provide a useful tool for detecting oil spills before massive hydrocarbon seepage. 2. Materials and methods 2.1. Sample collection The sampling sites (BS1–BS50) are shown in Fig. 1. In August 2012, 50 sediment cores were collected using a vibro piston corer deployed from R/V Yezhizheng of the Qingdao Institute of Marine Geology, China. This corer can obtain a 2.5- to 3.0-m core sample, via vibration, without any significant disturbance to the substrate. The sediment between 0.50 and 0.55 m of these core samples was used for analysis. All the samples were wrapped in aluminum foils and stored at −20 °C until analysis. 2.2. Analysis of grain size and TOC of sediments The grain size and TOC of the near-surface sediments were measured with a laser particle size analyzer (Mastersizer 2000, Malvern Instruments Ltd, UK) at Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, China. The 1-g sample was treated with 10% H2O2 and 0.5 mol/l HCl for 24 h to remove the OMs and biogenic carbonates, respectively. The samples were dispersed and homogenized by ultrasonic vibration for 30 s before instrumental analysis. The particle sizes were b4 μm for clay, 4–63 μm for silt, and N 63 μm for sand. The relative error of the duplicate samples was b3% (n = 4). The dried samples were treated with 4 mol/l HCl to remove carbonate, and further dried overnight at 60 °C. The carbonate-free samples were analyzed for measuring TOC using a VarioEL-III elemental
analyzer, and the average values were reported. Replicate analysis of one sample (n = 6) gave a precision of ±0.02 wt.% for TOC. 2.4. Analysis of AHs and PAHs The analysis of AHs and PAHs was performed at the Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences. Approximately 20 g of the freeze-dried, homogenized, and pulverized sediment sample was extracted with dichloromethane (DCM) in a Soxhlet apparatus for 48 h, to which activated copper was added to remove sulfur. The extracts were then reduced, hexane–exchanged, and separated on a 1:2 alumina:silica gel column. The target fraction containing AHs and PAHs was eluted with 15 ml of hexane and 20 ml of hexane:DCM (1:1, v:v). An Agilent 6890 series gas chromatograph/5975 series mass spectrometer was operated in a full-scan mode and fitted with a DB-5MS capillary column (30 m × 0.25 mm inner diameter, 0.25-μm film thickness), using helium as the carrier gas (1.0 ml/min). The samples were injected in splitless mode with a temperature of 280 °C. The oven was kept at 35 °C for 1 min, the temperature was increased from 35 to 120 °C at 10 °C/min, and then from 120 to 300 °C at 3 °C/min, with a final holding time of 30 min at 300 °C (Hu et al., 2009). The internal standard samples C24D50 (deuterated n-C24) and anthracene-d10 were used to quantify AHs and PAHs, respectively. Individual n-alkanes (C12–C35) were identified and quantified based on the molecular ion and mass to charge ratio (m/z) of 85. The unresolved complex mixture (UCM) fraction was calculated using the mean response factors of n-alkanes. The following PAHs were quantified: naphthalene (Nap), acenaphthylene (Ac), acenaphthene (Ace), fluorene (Fl), phenanthrene (Phe), anthracene (Ant), fluoranthene (Flu), pyrene (Pyr), benz[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd] pyrene (IP), dibenz[a,h]anthracene (DBA), perylene (Pery), and benzo[ghi]perylene (BghiP).
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
171
2.3. Quality assurance/quality control A mixture of five deuterated PAHs (naphthalene-d8, acenaphthened10, phenanthrene-d10, chrysene-d12, and perylene-d12) was used as a recovery standard to monitor matrix effects and procedural performance. The recovery rate of the experiment was determined to be 91.5 ± 10%. In addition, blank and spiked blank experiments were applied as a control. In the blank experiment, there was no significant (b5%) interference of the targeted compound. 3. Results and discussion 3.1. The grain size and TOC of near-surface sediment The ranges of TOC and grain size parameters for near-surface sediments of the oil spill area are listed in Table 1. The median grain size (MZ) of near-surface sediments is in the range of 3.74–7.48 Φ, averaging 6.97 Φ. Silt and clay are found to be the predominant constituents of the near-surface sediment samples, with mean compositions of 60.86% and 28.9%, respectively. These fine-grained sediments in the oil spill area are usually observed in the central Bohai, where weaker tidal environments are dominant (Sündermann and Feng, 2004). The TOC present in the near-surface sediments is in the range of 0.05–0.60%, with an average of 0.47%. The values of TOC and MZ were slightly positively correlated (R2 = 0.48) (Fig. 2), which are found to be lower than surface sediments of marginal sea, such as the central Yellow Sea (R2 = 0.69) (Zhang et al., 2014). The correlation between TOC and MZ indicates that the distribution of OM is influenced by inputs from other possible sources, except for the dynamics of the marine environment as a predominant factor in the oil spill area. 3.2. Aliphatic hydrocarbons The n-alkanes, isoprenoids, and UCMs in AHs were analyzed using gas chromatography–mass spectrometry (GC–MS). The carbon preference indices (CPI1, CPI2) (Bray and Evans, 1961) and other deterministic ratios of isoprenoids and n-alkanes are shown in Table 2. The gas chromatograms for most samples exhibited a bimodal n-alkane distribution, with one maximum at C17 or C19 within the short-chain n-alkanes and the other maximum at C29 or C31 within the long-chain n-alkanes; however, most samples showed a maximum at C29 or C31 (Fig. 3). The average concentration of C15–35 n-alkanes was 2.15 μg g− 1 (dry weight) with a range of 0.88–3.48 μg g−1. The ratio of short- to longchain n-alkanes LMW/HMW ranged from 0.07 to 0.93, with an average of 0.28. Ranges of CPI1 and CPI2 were 0.66–1.47 and 0.95–3.35, respectively, indicating a strong odd-to-even carbon preference in the longchain n-alkanes. The sum of the most abundant n-alkanes with respect to biogenic terrestrial sources (C27, C29, C31, C33), referred to here as Alkterr, ranged from 0.20 to 0.60, with an average of 0.37 (Table 2). This Alkterr value indicates that the aquatic and other source OMs were mixed with the terrestrial OMs in the oil spill area samples. The acyclic isoprenoids pristane (Pr) and phytane (Ph) were abundant in all samples. The ranges of Pr/C17 and Ph/C18 ratios were 0.49–2.42 and 1.03–2.71, respectively. The ratio of Pr to Ph in the samples ranged from 0.30 to 1.45, with an average of 0.72 (Table 1),
Table 1 Compositions and parameters of bulk organic matter and sediment grain size in the nearsurface sediments of the oil spill area of Bohai Sea. Parameters
Minimum
Maximum
Mean
Fig. 2. Correlation analysis between the concentrations of TOC and median grain size in the oil spill area.
indicating the presence of dysoxic conditions during OM deposition. The presence of UCMs in sediments is an indicator of chronic/degraded petroleum contamination, although bacteria-derived UCMs cannot be ignored (Bouloubassi et al., 2001). The UCMs occurred as short-chain n-alkanes in all samples with a mean response factor of C19 n-alkanes (Fig. 3), and the concentrations of UCMs and C19 n-alkanes were significantly positively correlated (R2 = 0.56) (Fig. 4). The ratio of UCM to total n-alkanes (UCM/n-ALK) ranged from 1.87 to 7.03, with an average of 3.52, indicating high petroleum contamination in that area. The data sets containing Pr, Ph, individual n-alkanes, and UCMs were analyzed by principal component analysis (PCA) using SPSS 13.0 for Windows (SPSS Inc., Chicago, IL, USA) to identify the sources of AHs. The two major principal components for loading variables are shown in Fig. 5. PC1 accounted for 32% of the data variance and had a high positive loading of the combination variables of long-chain n-alkanes, attributable to terrestrial and petrogenic sources. PC2 contributed to 62% of the total variance and was distinguished by the high positive loadings of the short-chain n-alkanes (C17–C21) and UCMs, mainly attributed to marine biogenic contributions and oil contamination. The moderate-chain alkanes (C22–C26), with a positive loading on both PC1 and PC2, suggest that their origin was complex, possibly including mainly marine aquatic and minor bacterial degradation components.
Table 2 Concentrations and ratios of aliphatic hydrocarbons in the oil spill area. AH properties
Oil spill area Range
Mean
Range
Mean
Range
Mean
LMW/HMWa Pr/C17 Ph/C18 Pr/Phb CPI1c CPI2d Alkterre n-ALK (μg g−1) UCM/n-ALK
0.07–0.93 0.49–2.42 1.03–2.71 0.30–1.45 0.66–1.47 0.95–3.35 0.20–0.60 0.88–3.48 1.87–7.03
0.28 1.33 1.40 0.72 1.05 1.66 0.37 2.15 3.52
0.2–1.1 \ \ 0.9–1.9 \ 1.8–7.2 \ 1.22–5.91 0.55–10.88
0.6 \ \ 1.2
0.03–0.62 0.67–1.58 0.96–1.99 0.11–0.84 1.01–1.83 1.20–3.39 0.10–0.59 \ \
0.10 0.85 1.28 0.47 1.17 1.54 0.37 \ \
a
0.05 0 32.65 2.59 3.74
0.60 64.77 70.08 35.07 7.48
0.47 9.90 60.86 28.90 6.97
4.2 \ 3.3 7.39
Yellow Sea Zhang et al. (2014)
LMW/HMW: ∑nC21−/∑nC22+ Pr/Ph: ratio of pristane to phytane CPI1: 1/2[∑C15–21(odd carbon)/∑C14–20(even carbon) + ∑C15–21(odd carbon)/∑C16–22(even carbon)] d CPI2: 1/2[∑C25–35(odd carbon)/∑C24–34(even carbon) + ∑C25–35(odd carbon)/∑C26–36(even carbon)] e Alkterr: (C27 + C29 + C31 + C33)/∑C14–38 b
TOC (%) Sand (%) Silt (%) Clay (%) Median grain size (Φ)
BC2 Hu et al. ( 2011)
c
172
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
Fig. 4. Correlation analysis between the concentrations of UCM and C19 n-alkane in the oil spill area.
3.3. Polycyclic aromatic hydrocarbons
Fig. 3. Total ion current (TIC) of GC–MS chromatograms for (a) sediment from the oil spill area, (b) near-surface sediment from the southern Yellow Sea (Zhang, 2014), and (c) core samples from a non-oil spill area (Hu, 2011).
AHs in this study were characterized by a higher concentration of short-chain n-alkanes (LMW/HMW) and UCMs (UCM/n-ALK) than those from the surface sediments of Yellow Sea (Zhang et al., 2014). However, sediments of core BC2 and surface samples with nonseepage oil contamination from Bohai Sea, collected in August and October of 2006 (Hu et al., 2011), had higher LMW/HMW and UCM/n-ALK values, suggesting the possibility of petroleum contaminations from oil exploration, shipping activities, and river sewage. A similar distribution of UCMs is also reported in the oil spill area in the Gulf of Mexico (Abrams, 2005). As described earlier, all oil spill area samples showed significant UCMs, including short-chain n-alkanes by GC–MS, whereas the UCMs of non-oil seepage contamination sediments usually included long-chain n-alkanes. Given that the sediment was sampled at 0.5 m below the surface to avoid the mixture of anthropogenic petroleum, it is concluded that short-chain n-alkanes and UCMs with a mean response factor of C19 n-alkanes may represent oil that seeped through geological faults from deep hydrocarbon reservoirs.
The 16 United States Environmental Protection Agency (US EPA) priority pollutant PAHs and perylene, from 20 selected samples, were quantified to identify hydrocarbon contamination from oil spills (Table 3). The total concentration of the 16 US EPA priority pollutant PAHs ranged from 9.97 to 490.13 ng/g, with an average of 107.27 ng/g. The concentrations of the 16 PAHs in the oil spill area were higher than those of the sedimentary PAHs in Yellow River (range: 31–133 ng/g, mean: 76.8 ng/g) (Li et al., 2006), northern Yellow Sea (range: 27–110 ng/g, median: 51 ng/g) (Li et al., 2002), and south China Sea (range: 28–109 ng/g, median: 57 ng/g) (Liu et al., 2012); similar to those of the BC-2 core sample from Bohai Sea (range: 53.3–186 ng/g, mean: 103) (Hu et al., 2011); and lower than those in the surrounding rivers such as Hai River (mean: 64 ng/g) (Shi et al., 2005) and Daliao River system (range: 61.9–840.5 ng/g, mean: 287.3 ng/g) (Guo et al., 2007). Sediments in this study did not have a higher concentration of AHs and PAHs than those from the non-oil spill area, mainly because of the following reasons: (1) when a vast amount of crude oil seeped through the major faults into sea water, only a relatively small amount of oil spread slowly into the sediment via micro faults and (2) the spilled oil was likely deposited in sandy sediment rather than muddy sediment, and the selected muddy samples had sufficient OM for organic geochemistry analysis.
Fig. 5. Factor loadings of n-alkanes and UCMs in the sediment samples.
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
173
Table 3 Concentrations (ng/g dry weight) of PAHs in the oil spill area. Concentration (ng/g) and ratios
Minimum
Maximum
Mean
Variance
Naphthalene (Nap) Acenaphthene (Acy) Acenaphthylene (Ace) Fluorene (Flu) Phenanthrene (Phe) Anthracene (Ant) Fluoranthene (Flt) Pyrene (Pyr) Benzo[a]anthracene (BaA) Chrysene (Chr) Benzo[b]fluoranthen (BbF) Benzo[k]fluoranthen (BkF) Benzo[a]pyrene (BaP) Indeno[1,2,3-cd]pyrene (InP) Indeno[1,2,3-cd]pyrene (DBA) Benzo[ghi]perylene (BghiP) Perylene ΣEPAPAHs Perylene/ΣPAHs (%)
0.00 0.00 0.00 0.09 4.18 0.09 1.46 1.50 0.26 0.74 0.25 0.24 0.06 0.11 0.01 0.36 2.56 9.97 5.44
0.34 0.20 0.16 9.74 160.31 7.00 66.68 78.49 15.04 34.45 23.16 15.54 5.53 7.63 4.64 32.07 103.09 490.13 42.77
0.04 0.03 0.03 0.43 18.80 0.69 11.94 14.40 2.38 6.56 4.94 3.62 0.82 1.23 0.63 4.77 17.58 88.72 18.58
0.09 0.06 0.05 2.27 34.87 1.44 13.76 15.93 3.13 7.28 5.27 3.42 1.36 1.66 1.19 7.11 25.39 101.01 10.77
Perylene was one of the most abundant nonalkylated PAHs found in the oil spill area sediment, contributing 5.44–42.77% (mean: 18.58%) of the total PAHs (Perylene/ΣPAHs, Table 2). High levels of perylene were also present in sediments collected from the southern Yellow Sea, China (range: 6.40–88.85%, mean: 39.38%) (Zhang et al., 2013b) and Emerald Peak Lake, Taiwan (60–98%) (Cheng-Wei et al., 2011). In most of these sediments, perylene contributed N 10% of the total PAHs, suggesting a short-term diagenetic process as the predominant source of perylene (Tissier and Saliot, 1983). By contrast, Wakeham et al. (1980) found that 1–4% perylene relative to the total nonalkylated PAHs was a typical value for combustion/pyrolysis sources of surface sediment. Marynowski et al. (2015) reported that perylene is found at relatively high concentrations in samples with a vitrinite reflectance (Rr) maturation of b 0.6%, whereas its abundance rapidly decreases for 0.6–0.7% Rr. In samples with N0.7% Rr, perylene disappears completely. The concentrations of perylene in our samples were found to be lower than those from the southern Yellow Sea, although they developed in a similar depositional environment by a high sediment load from a large river. The relatively low percentage of perylene as a fraction of the total nonalkylated PAHs may reflect a significant amount of oil with little perylene overprinted from terrestrial OM. Combinations of PAH isomer pair ratios, such as Fluo/(Fluo + Pyr), Ant/(Ant + Phe), BaA/(BaA + Chr), and InP/(InP + BghiP) (Yunker et al., 2002), have been used to determine PAH compositions and their possible sources (Fig. 6). Most of the PAH ratios in this study indicate that the presence of PAH is mainly due to mixed sources of combustion and petroleum, and all samples suggest petroleum as an important source of PAH, particularly for InP and BghiP in the oil spill area (Fig. 6). The low Ant/(Ant + Phe) ratios could be attributed to a faster degradation of Ant than Phe during transport (Wang et al., 2010). Similarly, the Fluo/(Fluo + Pyr) and BaA/(BaA + Chr) ratios indicate coal and biomass combustion as major sources, although no sample was present in the combustion area of the three plots (Fig. 6), which was distinct from sedimentary PAHs in core BC-2 of the nonseepage oil spill area. Therefore, the overprinting oil spilled from deep reservoirs could significantly alter the biogenic PAH isomers of OM in sediments near spill areas. 3.4. Mixed-source model for OM The mixed-source model for OM in the near-surface sediments could be established by the distribution of AHs and PAHs, as well as the bulk geochemical parameters (TOC, grain size). It is evident from Fig. 7 that there are three main OM sources for the near-surface sediments in the oil spill area: (1) terrestrial OM from the surrounding river input,
Fig. 6. PAH cross-plots for the following ratios: (a) Ant/(Ant + Phe) (m/z 178), (b) BaA/ (BaA + Chr) (m/z 228), and (c) InP/(InP + BghiP) vs. Fluo/(Fluo + Pyr). Source boundary lines are based on Yunker et al. (2002).
which is characterized by C27–C35 long-chain n-alkanes and PAHs from combustion of higher plants; (2) marine OM produced from plankton or aquatic plants, represented by C17–C26 short-chain n-alkanes; (3) crude oil seeped through geological faults from deep hydrocarbon reservoirs, which is characterized by C17–C21 shortchain n-alkanes, UCM with a mean response factor of C19 n-alkanes, high levels of BghiP, and low levels of perylene.
174
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175
Fig. 7. Mixed-source model for organic matter in the oil spill area of Bohai Sea.
Although the sediments in this area experienced a serious oil spill in 2006, the OMs present in the near-surface sediments are predominantly sourced from terrestrial higher plants, and their AHs show higher values of CPI2 and Alkterr, as well as a high proportion of long-chain n-alkanes. The marine plankton or aquatic plants also have an appreciable contribution to the sediments, particularly for C22–C26 n-alkanes of AHs. Because the molecular weight of spilled oil has overprinted on the primary OM in the near-surface sediment, the compositions of AHs and PAHs have been altered into the feature as mentioned earlier. 4. Conclusions The grain size, TOC, AHs, and PAHs of near-surface sediments of the oil spill area were analyzed to determine the source of OM. Although the concentrations of AHs were not significantly higher than those of core sediment from a non-oil spill area, the levels of short-chain n-alkanes, UCMs, and EPA 16 priority pollutant PAHs were higher than the nonoil spilled surface sediment developed in a similar semi-closed marginal sea shelf. Sediments of the oil spill area have mixed biogenic and petroleum sources characterized by high levels of UCMs associated with short-chain n-alkanes, low levels of perylene, as well as a high InP/(InP + BghiP) ratio. The following are the three main OM sources for the near-surface sediments in the oil spill area: (1) terrestrial OM from the surrounding river input, (2) marine OM produced from plankton or aquatic plants, and (3) crude oil seeped through geological faults from deep hydrocarbon reservoirs. However, the OMs in this near-surface sediment are predominantly sourced from terrestrial vascular plants, and the marine plankton or aquatic plants also have an appreciable contribution to the sediments. The compositions of AHs and PAHs have been altered as the molecular weight of spilled oil has overprinted on the primary OM in the near-surface sediment. Acknowledgments This study was financially supported by the Special Program of Ministry of Land and Resources of the People's Republic of China (Grant No. 201211060), National Natural Science Foundation of China (Grant No. 41503048), and the Key Laboratory Project of Gansu Province (Grant No. 1309RTSA041). The authors extend their special thanks to Chief Editor Dr Charles Sheppard for thorough and constructive reviews that greatly improved the clarity and quality of this article. References Abrams, M.A., 2005. Significance of hydrocarbon seepage relative to petroleum generation and entrapment. Mar. Pet. Geol. 22, 457–477. Bouloubassi, I., Fillaux, J., Saliot, A., 2001. Hydrocarbons in surface sediments from the Changjiang (Yangtze river) estuary, East China Sea. Mar. Pollut. Bull. 42, 1335–1346.
Bray, E., Evans, E., 1961. Distribution of paraffins as a clue to recognition of source beds. Geochim. Cosmochim. Acta 22, 2–15. Cheng-Wei, F., Shiue, J., Cheng-Yi, W., Cheng-Yu, W., 2011. Perylene dominance in sediments from a subtropical high mountain lake. Org. Geochem. 42. Chu, Z., Sun, X., Zhai, S., Xu, K., 2006. Changing pattern of accretion/erosion of the modern Yellow River (Huanghe) subaerial delta, China: based on remote sensing images. Mar. Geol. 227, 13–30. Gong, Y., Zhao, X., Cai, Z., O'Reilly, S.E., Hao, X., Zhao, D., 2014. A review of oil, dispersed oil and sediment interactions in the aquatic environment: influence on the fate, transport and remediation of oil spills. Mar. Pollut. Bull. 79, 16–33. Graham, W.M., Condon, R.H., Carmichael, R.H., D'Ambra, I., Patterson, H.K., Linn, L.J., Hernandez Jr., F.J., 2010. Oil carbon entered the coastal planktonic food web during the Deepwater Horizon oil spill. Environ. Res. Lett. 5, 045301. Guo, Z., Lin, T., Zhang, G., Zheng, M., Zhang, Z., Hao, Y., Fang, M., 2007. The sedimentary fluxes of polycyclic aromatic hydrocarbons in the Yangtze River Estuary coastal sea for the past century. Sci. Total Environ. 386, 33–41. Hu, L., Guo, Z., Feng, J., Yang, Z., Fang, M., 2009. Distributions and sources of bulk organic matter and aliphatic hydrocarbons in surface sediments of the Bohai Sea, China. Mar. Chem. 113, 197–211. Hu, L., Guo, Z., Shi, X., Qin, Y., Lei, K., Zhang, G., 2011. Temporal trends of aliphatic and polyaromatic hydrocarbons in the Bohai Sea, China: evidence from the sedimentary record. Org. Geochem. 42, 1181–1193. Li, B., Wu, Y., Zhang, J., 2002. Distribution and source of polycyclic aromatic hydrocarbons(PAHs) in surface sediment of the northern Yellow Sea. China Environ. Sci. 22, 429–432. Li, G., Xia, X., Yang, Z., Wang, R., Voulvoulis, N., 2006. Distribution and sources of polycyclic aromatic hydrocarbons in the middle and lower reaches of the Yellow River, China. Environ. Pollut. 144, 985–993. Lima, M.B., Feitosa, E.A., Emídio, E.S., Dórea, H.S., Alexandre, M.R., 2012. Distribution and sources of aliphatic hydrocarbons in surface sediments of Sergipe River estuarine system. Mar. Pollut. Bull. 64, 1721–1725. Liu, L.-Y., Wang, J.-Z., Wei, G.-L., Guan, Y.-F., Zeng, E., 2012. Polycyclic aromatic hydrocarbons (PAHs) in continental shelf sediment of China: implications for anthropogenic influences on coastal marine environment. Environ Pollut 167, 155–217. Liu, X., Guo, J., Guo, M., Hu, X., Tang, C., Wang, C., Xing, Q., 2015. Modelling of oil spill trajectory for 2011 Penglai 19-3 coastal drilling field, China. Appl. Math. Model. 39, 5331–5340. Marynowski, L., Smolarek, J., Hautevelle, Y., 2015. Perylene degradation during gradual onset of organic matter maturation. Int. J. Coal Geol. 139, 17–25. McNutt, M.K., Camilli, R., Crone, T.J., Guthrie, G.D., Hsieh, P.A., Ryerson, T.B., Savas, O., Shaffer, F., 2012. Review of flow rate estimates of the Deepwater Horizon oil spill. Proc. Natl. Acad. Sci. 109, 20260–20267. Mulabagal, V., Yin, F., John, G.F., Hayworth, J.S., Clement, T.P., 2013. Chemical fingerprinting of petroleum biomarkers in Deepwater Horizon oil spill samples collected from Alabama shoreline. Mar. Pollut. Bull. 70, 147–154. Palinkas, L.A., Petterson, J.S., Russell, J., Downs, M.A., 1993. Community patterns of psychiatric disorders after the Exxon Valdez oil spill. Am. J. Psychiatr. 150, 1517–1523. Shi, Z., Tao, S., Pan, B., Fan, W., He, X., Zuo, Q., Wu, S., Li, B., Cao, J., Liu, W., 2005. Contamination of rivers in Tianjin, China by polycyclic aromatic hydrocarbons. Environ. Pollut. 134, 97–111. Sündermann, J., Feng, S., 2004. Analysis and modelling of the Bohai sea ecosystem—a joint German–Chinese study. J. Mar. Syst. 44, 127–140. Tissier, M., Saliot, A., 1983. Pyrolytic and naturally occurring polycyclic aromatic hydrocarbons in the marine environment, advances in organic geochemistry. Wiley, Chichester, pp. 268–278. Wakeham, S.G., Schaffner, C., Giger, W., 1980. Polycyclic aromatic hydrocarbons in recent lake sediments—II. Compounds derived from biogenic precursors during early diagenesis. Geochim. Cosmochim. Acta 44, 415–429. Wang, W., Simonich, S.L.M., Xue, M., Zhao, J., Zhang, N., Wang, R., Cao, J., Tao, S., 2010. Concentrations, sources and spatial distribution of polycyclic aromatic hydrocarbons in soils from Beijing, Tianjin and surrounding areas, North China. Environ. Pollut. 158, 1245–1251. Wei, L., Hu, Z., Dong, L., Zhao, W., 2015. A damage assessment model of oil spill accident combining historical data and satellite remote sensing information:
S. Li et al. / Marine Pollution Bulletin 100 (2015) 169–175 a case study in Penglai 19-3 oil spill accident of China. Mar. Pollut. Bull. 91, 258–271. Xu, Q., Li, X., Wei, Y., Tang, Z., Cheng, Y., Pichel, W.G., 2013. Satellite observations and modeling of oil spill trajectories in the Bohai Sea. Mar. Pollut. Bull. 71, 107–116. Yunker, M.B., Macdonald, R.W., Vingarzan, R., Mitchell, R.H., Goyette, D., Sylvestre, S., 2002. PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Org. Geochem. 33, 489–515. Yunker, M.B., Macdonald, R.W., Snowdon, L.R., Fowler, B.R., 2011. Alkane and PAH biomarkers as tracers of terrigenous organic carbon in Arctic Ocean sediments. Org. Geochem. 42, 1109–1146. Zhang, J., Wu, Y., Jennerjahn, T.C., Ittekkot, V., He, Q., 2007. Distribution of organic matter in the Changjiang (Yangtze River) Estuary and their stable carbon and nitrogen
175
isotopic ratios: Implications for source discrimination and sedimentary dynamics. Mar. Chem. 106. Zhang, R., Zhang, F., Zhang, T.-C., 2013a. Sedimentary records of PAHs in a sediment core from tidal flat of Haizhou Bay, China. Sci. Total Environ. 450–451, 280–288. Zhang, S.-y., Li, S.-l., Dong, H.-p., Zhao, Q.-f., Shi, J.-a., Zhang, Z.-n., 2013b. Distribution and source identification of polycyclic aromatic hydrocarbon of surface sediments from the center part of South Yellow Sea, China. China Environ. Sci. 7, 020. Zhang, S., Li, S., Dong, H., Zhao, Q., Lu, X., Shi, J.a., 2014. An analysis of organic matter sources for surface sediments in the central South Yellow Sea, China: evidence based on macroelements and n-alkanes. Mar. Pollut. Bull. 88, 389–397.