Sources of polycyclic aromatic hydrocarbons to ... - Wiley Online Library

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, D23305, doi:10.1029/2011JD015722, 2011

Sources of polycyclic aromatic hydrocarbons to sediments of the Bohai and Yellow Seas in East Asia Tian Lin,1 Limin Hu,2 Zhigang Guo,1,3 Yanwen Qin,4 Zuosheng Yang,3 Gan Zhang,5 and Mei Zheng6 Received 2 February 2011; revised 6 October 2011; accepted 6 October 2011; published 13 December 2011.

[1] The coasts of Bohai Sea (BS) and Yellow Sea (YS) in China support almost one-quarter of its population and provide more than one-third of the national GDP. BS and YS are downwind of the Asian continental outflow in spring and winter as influenced by the East Asian monsoon. This makes the two seas important sinks of land-based pollutants associated with the Asian continental outflow. The sixteen U.S. EPA proposed priority polycyclic aromatic hydrocarbons (PAHs) in 130 surface sediment samples collected from BS and YS were measured. Combined with our previous PAH data of 90 PM2.5 samples from the upwind areas, the sources of the PAHs in BS and YS were apportioned using positive matrix factorization (PMF) modeling. Four sources were identified: petroleum residue, vehicular emissions, coal combustion and biomass burning. Petroleum residue was the dominant contributor of PAHs in the coast of the Bohai Bay probably due to Haihe River runoff, oil leakage from ships and offshore oil fields. The contribution of vehicular emissions in BS was higher than that in YS, and the reverse was true for coal combustion and biomass burning. This difference in the source patterns in the sediments of the two seas could be attributed to the different PAH emission features of the upwind area related to demographic and economic conditions, as well as the marine geography. The ratios of selected 4–6 ring PAHs in the sediments compared well with those of the PM2.5 of the upwind areas, implicating that the particle phase PAHs in the atmosphere play an important role in the source to sink process of the pyrogenic PAHs in the region. Citation: Lin, T., L. Hu, Z. Guo, Y. Qin, Z. Yang, G. Zhang, and M. Zheng (2011), Sources of polycyclic aromatic hydrocarbons to sediments of the Bohai and Yellow Seas in East Asia, J. Geophys. Res., 116, D23305, doi:10.1029/2011JD015722.

1. Introduction [2] Polycyclic aromatic hydrocarbons (PAHs) are known carcinogens and their fate has been of great interest to researchers because of their persistence in the environment. Marine sediments are usually regarded as the ultimate sink of these pollutants discharged from land-based sources either by atmospheric deposition or riverine outflows. Correlating the PAHs in the marine sediments and atmospheric 1

Department of Environmental Science and Engineering, Fudan University, Shanghai, China. 2 Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao, China. 3 College of Marine Geosciences, Ocean University of China, Qingdao, China. 4 Water Research Institute, Chinese Research Academy of Environmental Sciences, Beijing, China. 5 State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China. 6 College of Environmental Sciences and Engineering, Peking University, Beijing, China. Copyright 2011 by the American Geophysical Union. 0148-0227/11/2011JD015722

aerosols would provide much needed information on the transformation and fate of these organic pollutants in the atmospheric-marine environments. [3] Bohai Sea (BS, 77,000 km2) and Yellow Sea (YS, 400,000 km2) are a part of the East China Seas (Figure 1). Their coasts (including four provinces and two municipalities under the direct jurisdiction of the Central Government) supported almost 1/4 of the Chinese population in 2001 and provided 35% of the national GDP in 2008 (http://www. stats.gov.cn/english). According to Zhang and Tao [2009], PAH emission in China was estimated to be 114 Gg in 2004, accounting for 22% of the total PAH emission in the world, and the emission inventory of PAHs around the coasts of BS and YS was much higher than the rest of the Chinese coastal regions. Under the influence of the East Asian monsoon, BS and YS are downwind of the Asian continental outflow in spring and winter [Guo et al., 2006; Feng et al., 2007; Zhang and Gao, 2007], and large amount of dust and atmospheric pollutants are deposited in these marginal seas [Zhang et al., 1992; Primbs et al., 2007; Lang et al., 2008]. Zhang et al. [1992] reported that the atmospheric input of heavy metals such as Cu, Pb, and Co to YS is higher than those from riverine input.

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LIN ET AL.: SOURCES OF PAHS TO BS AND YS SEDIMENTS

Figure 1. Map of the study area: BS1-BS71 in BS, NY1-NY32 in the Northern YS and SY1-SY27 in the Southern YS. 2 of 11

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[4] Recently, there were several reports on the distribution and source identification of the PAHs in the sediments of BS and YS [Liu et al., 2007; Qin et al., 2011]; however, there is no quantitative source apportionment for these sedimentary PAHs at the regional scale. Origins of PAHs can be categorized by using the ratios of selected PAHs that are of petrogenic and pyrogenic sources, but it is difficult to quantitatively estimate the specific contributions. The objectives of this study are to apportion the sources of the PAHs in the sediments of BS and YS using positive matrix factorization (PMF) modeling on a data set from a wellplanned 2-year sampling campaign, and to reveal the factors that influence the sources contributing to PAHs in the surface sediments in the region by combining/comparing with the results of the PM2.5 from upwind areas.

2. Materials and Methods 2.1. Sampling [5] The locations of sampling sites in BS and YS are illustrated in Figure 1. A total of 130 sediment samples were collected during 2007–2008 in two cruises, including stations SY1-SY27 and NY1-NY32 in YS, and BS1-BS71 in BS. Surface sediment samples were collected using a stainless steel box corer/or stainless steel grab sampler. The top layer/surface (0–3 cm) sediments were wrapped in aluminum foil and stored at 20°C until organic analysis. [6] In our previous studies, 90 PM2.5 samples were collected in Beijing (n = 20, summer and n = 14, winter), Changdao Island (n = 13, summer and n = 11, winter) and Qingdao (n = 16, summer and n = 16, winter). Details are provided by Feng et al. [2005, 2007] and Guo et al. [2009]. 2.2. PAHs Analysis [7] The PAH analysis procedure and QA/QC followed that described by Mai et al. [2003] and Guo et al. [2006]. Briefly, homogenized samples were freeze-dried and ground. About 10 g of the sample was spiked with a mixture of recovery standards of four deuterated PAHs. The samples were extracted with dichloromethane in a Soxhlet extractor for 72 h, with activated copper added to remove the sulfur in the samples. The extract was concentrated and fractionated using a silica-alumina (1:1) column. PAHs were eluted using 35 ml of hexane/dichloromethane (1:1). Hexamethylbenzene was added as internal standard and the mixture was reduced to 0.2 ml and subjected to GC-MSD (a HP-5972 mass spectrometer interfaced to a HP-5890 II gas chromatography) analysis. The GC was equipped with a HP-5 capillary column (25 m 0.25 mm id, film thickness 0.25 mm) with helium as carrier gas. The GC operating conditions were: held at 80°C for 5 min, ramped to 290°C at 4°C min1 and held for 30 min. The sample was injected splitless with the injector temperature at 290°C. The MSD was operated in the electron impact (EI) mode at 70 eV and the selected-ion-monitoring (SIM) mode. Procedural blanks, standard-spiked blanks, standard-spiked matrix and duplicate samples were analyzed for quality assurance and control. Sixteen U.S. EPA proposed priority PAHs were measured in this study including 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

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[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3cd]pyrene (IP), dibenz[a,h]anthracene (DBA), and benzo [ghi]perylene (BghiP). [8] A National Institute of Standards and Technology (NIST, Gaithersburg, MD) 1941 standard reference samples, standard-spiked matrix, duplicate samples and procedural blank were analyzed for quality assurance and control. Recoveries of the PAHs in the standard reference material (NIST 1941) were between 80% and 120% of the certified values. Nominal detection limits for individual PAH ranged from 0.2 to 2 ng/g (dry weight) for 10 g of sediment and 0.008–0.08 ng/m3 for 500 m3 of atmospheric aerosols [Mai et al., 2003]. PAHs except AC and ACE were detected in all sediment samples. There were 26 (12%) samples where AC was below the detection limit and 27 (12%) samples for ACE. PAH recoveries of the standard-spiked matrix ranged from 85 to 95%, the paired duplicate samples agreed to within 15% of the measured values (n = 12), and the targeted compounds were not detected in procedural blank (n = 12). The average surrogate recoveries were 65 6% for naphthalene-d8, 68 6% for acenaphthene-d10, 97 10% for phenanthrene-d10 and 91 15% for perylene-d12, respectively. The final concentrations of PAHs were not corrected for the recoveries. 2.3. PMF Modeling [9] PMF was developed in the early 1990s and has been often applied to atmospheric, and temporal distributed data sets. Compared to chemical mass balance, PMF can be used for source apportionment without source profile information. This advantage makes PMF well suited for studies of the source apportionment of pollutants in sediments and atmospheric aerosols. In recent years, PMF has been successfully applied to spatially distributed data sets to apportion the sources of PAHs in sediments [Sofowote et al., 2008; Stout and Graan, 2010]. [10] Detailed concept and application of PMF source apportionment has been described in EPA PMF 3.0 Fundamentals & User Guide (www.epa.gov/heasd/products/pmf). In principle, the PMF model is based on the following equation: Xij ¼

p X

Lik Fkj þ Rij

k¼1

where Xij is the concentration of the jth congener in the ith sample of the original data set; Aik is the contribution of the kth factor to the ith sample; Fkj is the fraction of the kth factor arising from congener j; and Rij is the residual between the measured Xij and the estimated Xij using p principal components. Q¼

P n X m X Xij p

k¼1

i¼1 j¼1

2 Aik Fkj

Sij

where Sij is the uncertainty of the jth congener in the ith sample of the original data set containing m congeners and n samples. Q is the weighted sum of squares of differences between the PMF output and the original data set. One of the objectives of PMF analysis is to minimize the Q value. [11] Before the analysis, undetectable value (dull value) was replaced with concentration value of one half the

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Figure 2. Comparison of 2–3 ring PAH concentrations and 4–6 ring PAH concentrations in the sediments in (a) BS and (b) YS.

method detection limit. Uncertainty file should be provided in the model as an estimate of the confidence level for each value. In this study, an uncertainty of 20% was adopted based on the results from regularly analyzing the standard reference material [Mai et al., 2003].

3. Results and Discussion 3.1. Concentrations and Compositions of PAHs in Sediments [12] The PAH concentration ranged from 30 to 537 ng/g (average 160 114 ng/g, n = 130). The concentrations of the individual PAH at each sampling site are shown in auxiliary material Data Set A1.1 The PAH concentrations in BS decreased from the nearshore area (BS1-BS23) to the open sea (BS24-BS71). This may be partially influenced by large regional river runoffs such as Haihe River [Qin et al., 2011]. High concentrations were observed in the central YS (NY18-NY19 and SY12-SY15) (Figure 1 and Data Set A1) where the sediments contained a high proportion of finegrained particles and organic carbon, which can absorb or retain more of these organic pollutants [Hu et al., 2011]. The PAH concentrations in this study are close to those measured in the Adriatic Sea (24.1–501.1 ng/g, n = 23) [Magi et al., 2002], northern South China Sea (138–498 ng/g for 25 PAHs, n = 25) [Chen et al., 2006], South-Western Barents Sea (with an average around 200 ng/g, n = 13) [Boitsov et al., 2009]. [13] In Figure 2, the samples from BS are distinctly clustered into two groups characterized by 2–3 ring PAHs in the nearshore area of the Bohai Bay and 4–6 ring PAHs in the open sea of BS. The ratios of the 2–3 ring to the 4–6 ring PAHs are >1 in the majority of the samples in the nearshore Bohai Bay, suggesting PAH contamination from petrogenic sources; while in the open sea of BS, pyrogenic source is indicated by the 1) that showed the maximum percentage of the total variance of the data set were used as the factors. The two PCs accounted for 66% and 22% of the total variation. PCA was used to divide the samples into groups which had similar

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Figure 5. Comparison of selected PAH concentrations of the 130 sediment samples in the two seas with 90 upwind PM2.5 samples, that is (a) PHE and ANT, (b) FLU and PYR, (c) BaA and CHR, and (d) IP and BghiP.

sample scores. There were three clusters based on the two PC scores of each sample, and the compounds that separated the sediments and the PM2.5 were PHE, IP and BghiP. The PCA sample scores with the typical PAH compositions of PM2.5 and sediment samples showed that the sediment samples contained more 2–3 ring PAHs (in particular, PHE) than the upwind PM2.5 samples (Figure 6). The 2–3 ring PAHs are mostly associated with petroleum residue. In addition, the gas phase PAHs were considered as potentially important contributors of 2–3 ring PAHs in the open sea sediments. The gas phase PAHs are dominated by 2– 3 ring PAHs (85%), and 2–3 ring PAHs have relative high water solubility [Wania and Mackay, 1996; Van Jaarsveld et al., 1997]. Tsapakis et al. [2003, 2006] found that gas phase PAHs were significant contributors of 2–3 ring PAHs in the water by air-water exchange. The contribution of gaseous or dissolved 2–3 ring PAHs in sediments is interface exchange limited (air-water exchange or water-sediment exchange) before transporting through the water column and

sinking in the sediments. Most of the dissolved gaseous PAHs are more efficiently removed from the water column via uptake and metabolism in the aquatic food web than by sedimentation [Arzayus et al., 2001; Tsapakis et al., 2006]. By contrast, the 4–6 ring PAHs in particles are less degradable in the water column, and they are more effectively transported and eventually incorporated into the sediments, to be associated with the organic fine particles [Lipiatou et al., 1993; Dachs et al., 1996; Tsapakis et al., 2003]. Thus, the water column process and hydrological environments have less impact on the particulate-origin PAHs in the sediments. [25] However, the photolysis degradation of the particlephase PAHs during atmospheric transport and PAH fractionation in the water column should still be mentioned in the fate of PAHs in the marine environment [Witt, 2002; Hafner and Hites, 2003; Stubbins et al., 2010]. Additionally, the accumulation and fate of the particle-associated PAHs in sediments in highly dynamic coastal regions could

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Figure 6. (a) PCA for PAHs in sediment samples from BS and YS (n = 130) and PM2.5 samples (n = 90) in upwind areas based on sample scores. (b) Typical PAH composition in PM2.5 samples. Typical PAH composition in sediment sample in (c) YS and (d) Bohai Bay (B1-B23).

also be modified by water currents and the re-suspension of deposited PAHs.

4. Conclusions [26] This study showed that the pyrogenic 4–6 ring PAHs were the major compounds in the sediments of the open sea of BS and YS; while 2–3 PAHs derived from the petroleum residue was the dominant contributor in the nearshore area of the Bohai Bay. Relating the PAHs distribution data obtained from the sediments of two seas to the upwind PM2.5 data, it is suggested that the atmospheric deposition of aerosols is the dominant source of the 4–6 ring PAHs in sediments of the open sea, and the particle phase PAHs in the atmosphere play a dominant role in the source to sink process of the pyrogenic PAHs in the open sea of BS and entire YS. [27] PMF and PCA successfully source apportioned the combined PAHs data that are of different nature (sediments

and aerosols) and the methods complemented each other well, thus yielding more confidence and, perhaps, better interpretation of the source to fate of these pollutants in the region. [28] Acknowledgments. This work was supported by the Natural Science Foundation of China (NSFC) (40776062), and the National Basic Research Program of China (973) (2007CB407306 and 2005CB422304). We are most grateful to Ming Fang of the Hong Kong University of Science and Technology for his invaluable advices and comments in finalizing the manuscript, and the original PAH data of PM2.5 samples in Beijing. We wish to thank the crew of R/V Dong Fang Hong 2 of the Ocean University of China for collecting the sediment samples. The anonymous reviewers are sincerely appreciated for their constructive comments that greatly improved this work.

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