Marine Pollution Bulletin xxx (2014) xxx–xxx
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Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea Xin Jiang a,b,c, Ankang Teng d, Wenzhe Xu d, Xiaoshou Liu a,⇑ a
College of Marine Life Sciences, Ocean University of China, Qingdao 266003, PR China Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, PR China c University of Chinese Academy of Sciences, Beijing 100049, PR China d Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China b
a r t i c l e
i n f o
Keywords: Heavy metals Spatial distribution Pollution assessment Yellow Sea Sediment
a b s t r a c t Heavy metal concentrations in surface sediments at 56 stations during two cruises in the Yellow Sea in summer and winter, 2011 were analyzed by inductively coupled plasma-mass spectrometry. The pollution status was assessed via the Geoaccumulation index and Hankanson potential ecological risk index. Higher concentrations of heavy metals (except for Mn) were found in the central Southern Yellow Sea and the western Northern Yellow Sea. The higher contents of Mn were much closer to Shandong Peninsula. Correlation analyses indicated that Pb, Cu, Fe, Ni, Zn and Co probably had the same origin and were controlled by grain size and total organic carbon. Pollution assessment showed that most areas of the Yellow Sea were not or lowly contaminated with the exception of the northwest and south parts of the Southern Yellow Sea showing Cd-contamination. The pollution status of the Yellow Sea in summer was worse than that in winter. Ó 2014 Elsevier Ltd. All rights reserved.
Heavy metal pollution in the aquatic environment is one of the critical issues due to the toxic and persistent characters (Zhan et al., 2010; Varol and Sßen, 2012; Gao and Chen, 2012). Heavy metal pollutants pose potential threats to ecosystems because they could be concentrated or accumulated in organisms and biomagnified at higher trophic levels (Zhan et al., 2010; Ghrefat et al., 2011; Gao and Chen, 2012), and partly converted to more toxic organic compounds (Liu et al., 2009). Heavy metals in seas originate from both natural processes and anthropogenic activities. Natural processes like atmospheric inputs and aeolian processes set the background values for heavy metals (Zhang et al., 2003). With the rapid industrialization and urbanization in coastal regions, anthropogenic inputs are the main sources of pollution in the marine environment, and heavy metals are increasingly introduced to the estuarine and coastal environments through riverine discharge and oceanic dumping (Choi et al., 2007; Zhang et al., 2012; Yuan et al., 2012). After being introduced into the aquatic environment, heavy metals from the aqueous phase eventually become deposited to sediment through physical, chemical or biological mechanisms (Zhang et al., 2007; Zhan et al., 2010; Yuan et al., 2012). ⇑ Corresponding author. Tel./fax: +86 532 82031735. E-mail address: [email protected] (X. Liu).
The Yellow Sea is a semi-enclosed epicontinental sea of the northwestern Pacific, separated from the Bohai Sea in the east. It is located between the China Mainland and the Korea Peninsula, between 31°400 N–39°500 N and 119°100 E–126°500 E. The Yellow Sea covers 380,000 km2, with an average depth of 44 m and a maximum depth of 140 m in the northern area of Cheju Island. It is divided into the Northern Yellow Sea (NYS) and the Southern Yellow Sea (SYS) by a line linking Chengshanjiao on the Shandong Peninsula and Changsan-got on the Korea Peninsula (Yang et al., 2003). The Yellow Sea receives billions of tons of particulate materials annually from both Chinese and Korean Rivers, such as the Changjiang River, Yellow River, Yalujiang River of China and the Han, Kum and Yeongsan Rivers of Korea (Qin et al., 1989). The statistics from the State Oceanic Administration, PR China (SOA, 2010, 2011, 2012, 2013) indicate that 6530, 9540, and 16,530 km2 of offshore areas of the Yellow Sea are heavily polluted (i.e. the water quality is worse than class 4) in the years of 2010, 2011, and 2012, respectively. The polluted areas of those years are significantly larger than in 2009 (2150 km2). The distribution of metals in sediments might provide evidence for human activities and their effects on ecosystems. For this reason are sediments commonly chosen as environmental indicators of the quality and potential risks within aquatic systems (Unlu et al., 2008; Luo et al., 2010; Zhan et al., 2010). The Geoaccumulation
http://dx.doi.org/10.1016/j.marpolbul.2014.03.020 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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X. Jiang et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
index and Hankanson potential ecological risk index are the most popular methods used to evaluate the ecological risk posed by heavy metals in sediments (Varol and S ß en, 2012; Li et al., 2012). Most of the existing studies, on the distribution of heavy metals in surface sediments, divided the Yellow Sea into the NYS and the SYS; however, few studies considered the Yellow Sea as a whole. Concentrations of Ni and Co and their seasonal variability are rarely studied neither. The main objectives of the present study are to determine the distribution of eight heavy metals (Pb, Cd, Cu, Fe, Ni, Mn, Zn and Co) concentrations in surface sediments of the Yellow Sea, and to assess the pollution status of this area with the Geoaccumulation index and Hankanson potential ecological risk index. The study area is located between 31°580 N–38°450 N and 121°000 E–124°400 E, near the coast of China. Sediments were collected onboard the vessel "Dongfanghong II" from 34 sampling stations (23 in the SYS and 11 in the NYS, Fig. 1a) during 13 to 30 June, 2011, and 22 sampling stations (16 in the SYS and 6 in the NYS, Fig. 1b) from the 20th November to 7th December, 2011. Surface sediments were taken using a stainless steel box-corer. The top 3 cm of samples were then placed in polyethylene bags, and refrigerated at 20 °C. After transport to the laboratory, samples were airdried at room temperature (20 °C), crushed, passed through a nylon sieve of 160 meshes (96 lm), homogenized, and then stored in polyethylene bags for further analysis. About 0.5 g dried sediment samples and 10 mL concentrated HNO3 were placed together in a plastic digestion tube and a microwave digestion system was used to remove any organic matters present in the sediment. The digested samples were then diluted with water to 50 mL. Sample solutions and blanks were analyzed for Pb, Cd, Cu, Fe, Ni, Mn, Zn and Co with inductively coupled plasma-mass spectrometry (ICP-MS, Optima 2100 DV ICP System, Perkin Elmer). All samples were analyzed in duplicate, and the data shown herein represent average values of the duplicates. In order to evaluate the precision, the GBW-07314 reference material (The Second Institute of Oceanography, the State Oceanic Administration of China) was measured. All plastic and glassware were pre-cleaned by soaking in HNO3 (v/v = 1:3) for at least 24 h, followed by soaking and rinsing with de-ionized water. Surfer 8.0 (Golden Software Inc., USA) was used for drawing the distribution maps of metal concentrations in surface sediments. Statistical analyses (i.e. two-tailed t test, bivariate correlation,
one-way ANOVA) were conducted with SPSS 19.0 software (SPSS Inc., USA). In this study, two methods of pollution assessment of heavy metals are conducted, the geoaccumulation index (Müller, 1969) and Hankanson potential ecological risk index (Hakanson, 1980). The geochemical background values of Cu, Pb, Zn and Cd were 15.92, 14.54, 60.00 and 0.103 lg/g, respectively (Lu and Zhu, 1987). However, the background values of other metals studied here were not available. The geoaccumulation index (Igeo) is defined by the following equation (Eq. (1)):
Igeo ¼ log2 ðC n =kBn Þ
ð1Þ
where Cn is the concentration of metals examined in sediment samples and Bn is the geochemical background value of metals. Factor k is the background matrix correction factor due to lithospheric effects, which is usually defined as 1.5 (Müller, 1969; Rubio et al., 2000; Ghrefat et al., 2011; Shafie et al., 2013). The geoaccumulation index consists of seven classes: Class 0 (practically uncontaminated): Igeo 6 0. Class 1 (uncontaminated to moderately contaminated): 0 < Igeo 61. Class 2 (moderately contaminated): 1 < Igeo 6 2. Class 3 (moderately to heavily contaminated): 2 < Igeo 6 3. Class 4 (heavily contaminated): 3 < Igeo 6 4. Class 5 (heavily to extremely contaminated): 4 < Igeo 6 5. Class 6 (extremely contaminated): Igeo > 5. The Hankanson potential ecological risk index (RI) is defined as follows (Eqs. (2)–(5)):
C if ¼
Cd ¼
Ci
ð2Þ
C in m X C if
ð3Þ
i
Eir ¼ T ir C if RI ¼
ð4Þ
m X Eir
ð5Þ
i
39° N
39° N B22 B21 B31 B23 B30 B24 B13 B25 B12 B28 B27 B05 B03 H02
H04
H06
B31 B23 B30 B25 B28
38°
37°
B08 B10 B01 H08
B13
B08
37°
B01 H08
36°
B05 B03
36°
H02
H04
H06
H09
H43 H15
H13
H15
35°
H11 HF1 H28
H21
38°
H13
34°
H25
33°
H35
35°
H11
34°
H27
H30II H35
H32 H31
H37 H38 H39 H40
33°
H32
32°
32°
H42
(a) 119°
120°
121°
122°
123°
124°
125°
31° 126° E
(b) 119°
120°
121°
122°
123°
124°
125°
31° 126° E
Fig. 1. Map of the Yellow Sea, showing the sampling stations during summer (a) and winter (b) in 2011.
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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X. Jiang et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
where Ci and C in are the concentrations of metals examined in sediment samples and the geochemical background values of metals, respectively. C if and Cd are the monomial and the polynomial contamination factors. Eir is the monomial potential ecological risk factor. T ir is the toxic-response factor for a given substance, e.g. Cu = Pb = 5, Zn = 1, Cd = 30 (Hakanson, 1980; Xu et al., 2008). RI is the sum of all risk factors for heavy metals in sediments. The relation between evaluation indices and the pollution degree and potential ecological risk are shown in Table 1. All metal concentrations in surface sediments collected from the Yellow Sea, in general, were ranked in decreasing order, as follows: Fe > Mn > Zn > Ni > Cu > Pb > Co > Cd. The concentration ranges of heavy metals in surface sediments of the Yellow Sea during summer were as follows: Pb, 4.80–21.9 lg/g; Cd, 0–8.21 lg/g; Cu, 5.93–25.7 lg/g; Fe, 0.61–2.27%; Ni, 8.43–31.1 lg/g; Mn, 84.7–1593 lg/g; Zn, 21.9–96.2 lg/g; Co, 4.11–13.0 lg/g, respectively. The concentration ranges of heavy metals during winter were as follows: Pb, 4.31–18.4 lg/g; Cd, 0–0.373 lg/g; Cu, 4.95–26.1 lg/g; Fe, 0.62–2.22%; Ni, 8.31–32.4 lg/g; Mn, 186–1334 lg/g; Zn, 18.8–82.1 lg/g; Co, 4.31–13.3 lg/g, respectively. To compare the concentrations of eight metals between summer and winter in the Yellow Sea, an independentsample t-test was conducted and the results showed no significant differences among those metals between the two seasons (p > 0.05). The range and mean concentrations of studied metals in sediments of the Yellow Sea and other representative seas are summarized in Table 2. It could be shown that the average concentrations of all studied metals in Yellow Sea sediments were within the range found in other sea areas.
Pb, Cd, Cu, and Zn concentrations in surface sediments rarely excessed the first category standard of the China national standard – marine sediment quality (GB 18668-2002, State Oceanic Administration, PR China). However, the concentrations of Cd during summer at Station H02 and H40 were ranked second class and Station H40 exceeded the third class. The spatial distributions of heavy metals are shown in Figs. 2 and 3. The distribution of those metals in two seasons exhibited a similar pattern as follows: (1) Higher concentrations of heavy metals were generally found in the central part of the SYS and western part of the NYS, especially the north-central part of the SYS (except for Mn); (2) Away from the central area, concentrations (except for Mn) decreased along both the Korean coast and Chinese coast. This trend was quite similar to previous findings (Yuan et al., 2012). It is worthy to mention that with the exception of station H40 the concentration (8.21 lg/ g) of Cd was extremely high while the concentrations at other stations did not exceed 2.00 lg/g. However, previous studies have not reported the exception (Teng et al., 2012). The distribution of Mn showed a distinct peak approximately situated at 36°N and 122°E, much closer to Shandong Peninsula than other heavy metals. Previous studies have shown a similar phenomenon. The mechanism for such a distribution pattern is probably due to the sediments of this area being dominated by biogenic carbonate (Lin et al., 2002). The dissolved Mn could be adsorbed on, or incorporated into freshly precipitated CaCO3 in seawater (e.g. Wartel et al., 1990). Wartel et al. (1990, 1991) concluded that the adsorption on and substitution in calcite, along the French coast of the English Channel, are the major mechanisms controlling dissolved Mn in seawater. Boughriet et al. (1992) studied suspended particulate matter from the Seine Estuary and
Table 1 Corresponding relationships between evaluation indices and pollution degree and potential ecological risks. C if
Monomial contamination factor
Cd
Polynomial contamination factor
Eir
Monomial potential ecological risk factor
RI
Sum of all risk factors
0.05). Higher concentrations of heavy metals (except for Mn) were generally found in the central part of the SYS and western part of the NYS, especially the north-central part of the SYS. There was an exception for Cd that the concentration at Station H40 was extremely high. The distribution of Mn showed a distinct peak approximately situated at 36°N and 122°E, much closer to Shandong Peninsula than other heavy metals. The correlation analyses implied that Pb, Cu, Fe, Ni, Zn and Co were probably derived from the same origin and their concentrations are controlled by grain size and TOC. Both the Igeo and Hankanson potential ecological risk index indicated that most area of the Yellow Sea was uncontaminated in Pb, Cu and Zn. However, the contamination degree of Cd varied within a wide range, from moderately to heavily contaminated. The SYS close to the Shandong Peninsula was a polluted area and Station H40 was heavily polluted. The pollution status of the Yellow Sea in summer was worse than that in winter. As the main pollutant, Cd contributed more to the pollution status and potential ecological risk than other heavy metals. This study assessed the pollution status in the Yellow Sea in two methods, providing base data to environmental protection and policy planning. However, this study has shortages such as not reflecting the pollution status entirely because the background values of many heavy metals in the Yellow Sea are unavailable. Further studies are needed to determine reliable background values that could provide reference points for meaningful pollution studies in the area.
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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X. Jiang et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
Table 5 The values of Igeo, C if , Eir , Cd and RI in surface sediments in the Yellow Sea during summer. Station
B01 B03 B05 B08 B10 H02 H04 H06 H08 H11 H13 H15 H21 H28 H30II H31 H32 H35 H37 H38 H39 H40 H42 H43 HF1 B12 B13 B21 B22 B23 B24 B25 B27 B28 B30 B31
Igeo =C if =Eir Pb
Cd
Cu
Zn
0.18/1.33/6.64 1.05/0.72/3.61 1.22/0.65/3.22 1.48/0.54/2.67 1.05/0.73/3.63 1.41/0.57/2.83 0.66/0.95/4.76 0.18/1.33/6.63 0.49/1.07/5.35 0.47/1.08/5.42 0.56/1.02/5.07 1.82/0.42/2.12 0.73/0.91/4.51 0.70/0.92/4.62 0.68/0.94/4.69 0.40/1.14/5.68 0.55/1.03/5.13 1.32/0.60/3.01 1.29/0.62/3.08 1.10/0.70/3.50 0.53/1.04/5.20 0.86/0.83/4.15 0.52/1.04/5.22 0.47/1.08/5.42 0.54/1.03/5.17 1.94/0.39/1.96 1.49/0.53/2.66 2.18/0.33/1.65 1.42/0.56/2.81 0.63/0.97/4.85 0.00/1.50/7.52 0.66/0.95/4.74 1.28/0.62/3.08 1.49/0.54/2.68 0.61/0.99/4.93 0.70/0.93/4.63
0.71/2.45/73.49 0.16/1.67/50.18 0.27/1.24/37.25 1.97/0.38/11.48 0.04/1.54/46.22 3.28/14.58/437.31 3.40/15.86/475.91 0.79/2.59/77.82 1.10/3.21/96.35 2.01/6.04/181.14 0.87/2.75/82.47 0.33/1.88/56.51 1.64/4.68/140.28 1.03/3.07/91.95 0.75/2.52/75.44 0.10/2.10/89.96 1.33/3.78/113.40 1.03/3.07/92.03 0.92/2.85/85.39 0.90/2.81/84.23 0.92/2.83/84.89 5.73/79.72/2391.61 0.76/2.55/76.36 1.36/3.85/115.57 0.21/1.74/52.20 /0.00/0.00 4.97/0.05/1.44 /0.00/0.00 4.96/0.05/1.45 0.26/1.25/37.52 0.53/2.17/65.14 1.15/0.68/20.28 1.37/0.58/17.40 0.38/1.15/34.61 0.30/1.84/55.22 0.38/1.16/34.68
0.07/1.57/7.87 1.08/0.71/3.56 1.37/0.58/2.91 1.06/0.72/3.60 0.99/0.76/3.79 1.23/0.64/3.20 0.37/1.16/5.80 0.11/1.62/8.08 0.02/1.48/7.39 0.38/1.16/5.78 0.41/1.13/5.65 1.81/0.43/2.13 0.06/1.57/7.84 0.68/0.94/4.68 0.65/0.96/4.79 0.33/1.19/5.98 0.36/1.17/5.84 1.04/0.73/3.65 0.74/0.90/4.50 1.35/0.59/2.94 0.44/1.11/5.53 0.96/0.77/3.85 0.47/1.08/5.40 0.21/1.30/6.51 0.53/1.04/5.21 1.95/0.39/1.94 2.01/0.37/1.86 1.94/0.39/1.96 1.15/0.67/3.37 0.28/1.24/6.19 0.62/0.98/4.87 0.40/1.14/5.68 0.89/0.81/4.05 1.67/0.47/2.36 0.18/1.33/6.63 0.58/1.00/5.01
0.10/1.60/1.60 0.95/0.78/0.78 1.32/0.60/0.60 1.41/0.57/0.57 1.29/0.62/0.62 1.54/0.52/0.52 0.89/0.81/0.81 0.39/1.15/1.15 0.44/1.11/1.11 0.57/1.01/1.01 0.77/0.88/0.88 2.01/0.37/0.37 0.94/0.78/0.78 0.67/0.94/0.94 0.59/0.10/0.10 0.58/1.00/1.00 0.69/0.93/0.93 1.25/0.63/0.63 1.22/0.64/0.64 1.38/0.58/0.58 0.85/0.83/0.83 0.89/0.81/0.81 0.72/0.91/0.91 0.38/1.15/1.15 0.52/1.05/1.05 1.97/0.38/0.38 1.95/0.39/0.39 2.04/0.37/0.37 1.40/0.57/0.57 0.66/0.95/0.95 1.03/0.74/0.74 0.75/0.89/0.89 1.31/0.60/0.60 1.74/0.45/0.45 0.69/0.93/0.93 0.83/0.85/0.85
Cd
RI
6.95 3.89 3.07 2.21 3.64 16.30 18.79 6.68 6.87 9.29 5.77 3.11 7.93 5.87 5.41 6.33 6.91 5.03 5.01 4.67 5.81 82.13 5.58 7.39 4.86 1.16 1.34 1.09 1.85 4.41 5.38 3.65 2.61 2.61 5.08 3.93
89.60 58.13 43.99 18.34 54.26 443.85 487.28 93.68 110.19 193.35 94.07 61.14 153.42 102.19 85.92 102.61 125.31 99.32 93.61 91.24 96.46 2400.41 87.89 128.64 63.62 4.29 6.35 3.97 8.19 49.51 78.27 31.59 25.13 40.09 67.71 45.16
Table 6 The values of Igeo, C if , Eir , Cd and RI in surface sediments in the Yellow Sea during winter. Station
B01 B03 B05 B08 H02 H04 H06 H08 H09 H11 H13 H15 H25 H27 H32 H35 B13 B23 B25 B28 B30 B31
Igeo =C if =Eir Pb
Cd
Cu
Zn
0.24/1.27/6.33 1.06/0.72/3.59 1.04/0.73/3.66 1.30/0.61/3.04 1.70/0.46/2.32 1.05/0.72/3.62 0.58/1.00/5.00 0.62/0.97/4.87 0.56/1.02/5.10 0.70/0.92/4.62 0.79/0.87/4.34 2.34/0.30/1.48 1.94/0.39/1.96 1.02/0.74/3.70 0.66/0.95/4.76 1.51/0.53/2.63 1.61/0.49/2.46 0.50/1.06/5.30 0.56/1.02/5.10 1.61/0.49/2.46 0.60/0.99/4.95 0.84/0.84/4.18
0.74/2.50/74.91 0.03/1.54/46.10 0.00/1.50/44.85 1.96/0.38/11.53 1.65/0.48/14.36 0.57/1.01/30.22 0.04/1.54/46.16 0.27/1.25/37.42 1.27/0.62/18.72 2.96/0.19/5.80 0.87/0.82/24.60 1.51/0.53/15.79 4.97/0.05/1.44 3.97/0.10/2.87 1.26/0.63/18.77 11.17/0.00/0.02 1.15/0.68/20.33 0.24/1.77/53.22 0.09/1.59/47.76 0.20/1.30/39.08 1.27/3.62/108.66 0.73/2.49/74.65
0.13/1.64/8.20 1.06/0.72/3.60 0.78/0.87/4.36 0.95/0.78/3.89 1.10/0.70/3.50 0.45/1.10/5.48 0.09/1.59/7.96 0.12/1.38/6.91 0.23/1.28/6.41 0.38/1.15/5.76 0.40/1.14/5.68 2.27/0.31/1.56 1.78/0.44/2.19 0.75/0.89/4.46 0.39/1.15/5.73 0.97/0.77/3.83 1.29/0.61/3.06 0.18/1.32/6.61 0.24/1.27/6.34 1.69/0.46/2.32 0.08/1.42/7.08 0.56/1.02/5.09
0.13/1.37/1.37 1.28/0.62/0.62 1.14/0.68/0.68 1.51/0.53/0.53 1.77/0.44/0.44 1.19/0.66/0.66 0.44/1.11/1.11 0.48/1.08/1.08 0.42/1.12/1.12 0.49/1.07/1.07 0.70/0.92/0.92 2.26/0.31/0.31 1.64/0.48/0.48 1.10/0.70/0.70 0.97/0.77/0.77 1.48/0.54/0.54 1.59/0.50/0.50 0.68/0.94/0.94 0.73/0.90/0.90 1.76/0.44/0.44 0.64/0.97/0.97 0.90/0.80/0.80
Cd
RI
6.77 3.59 3.78 2.30 2.08 3.49 5.24 4.68 4.05 3.34 3.75 1.45 1.36 2.43 3.49 1.83 2.28 5.09 4.78 2.70 6.99 5.15
90.81 53.91 53.55 18.98 20.60 39.98 60.23 50.27 31.35 17.25 35.55 19.14 6.07 11.74 30.02 7.01 26.35 66.07 60.10 44.30 121.65 84.73
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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X. Jiang et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx 39° N
39° N
38°
38°
1 0 6 37°
-1
37° 5
36°
35°
-2 36°
4
-3
3
-4
35°
-5
2 34°
34° -6
1 33°
-7
33°
0
-8 32°
-10
32°
(a) 119°
120°
121°
122°
123°
124°
125°
(b)
31° 126° E
119°
120°
121°
122°
123°
124°
125°
-9 -10
31° 126° E
Fig. 4. The Igeo spatial distribution of Cd in surface sediments in the Yellow Sea during summer (a) and winter (b).
39° N
39° N
38°
38°
37°
37°
64
2000 1000
36°
36° 32
600 35°
35°
300
16 34°
33°
32°
(a) 119°
120°
121°
122°
123°
124°
125°
34° 8
0
(b)
31°
126° E
119°
120°
121°
122°
123°
124°
125°
150
33°
0
32°
-150
31°
126° E
Fig. 5. The spatial distribution of Cd (a) and RI (b) in surface sediments in the Yellow Sea during summer.
Acknowledgments This study was funded by a Grant to X.S.L. (No. 41006081) from the National Natural Science Foundation of China (NSFC). We are grateful to ‘‘NSFC Open Cruises for Bohai and Yellow Seas Marine Scientific Research’’ and crew members of the vessel ‘‘Dongfanghong II’’. Prof. Hans-U. Dahms is thanked for critical comments to an earlier version of the manuscript.
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Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea Xin Jiang a,b,c, Ankang Teng d, Wenzhe Xu d, Xiaoshou Liu a,⇑ a
College of Marine Life Sciences, Ocean University of China, Qingdao 266003, PR China Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, PR China c University of Chinese Academy of Sciences, Beijing 100049, PR China d Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China b
a r t i c l e
i n f o
Keywords: Heavy metals Spatial distribution Pollution assessment Yellow Sea Sediment
a b s t r a c t Heavy metal concentrations in surface sediments at 56 stations during two cruises in the Yellow Sea in summer and winter, 2011 were analyzed by inductively coupled plasma-mass spectrometry. The pollution status was assessed via the Geoaccumulation index and Hankanson potential ecological risk index. Higher concentrations of heavy metals (except for Mn) were found in the central Southern Yellow Sea and the western Northern Yellow Sea. The higher contents of Mn were much closer to Shandong Peninsula. Correlation analyses indicated that Pb, Cu, Fe, Ni, Zn and Co probably had the same origin and were controlled by grain size and total organic carbon. Pollution assessment showed that most areas of the Yellow Sea were not or lowly contaminated with the exception of the northwest and south parts of the Southern Yellow Sea showing Cd-contamination. The pollution status of the Yellow Sea in summer was worse than that in winter. Ó 2014 Elsevier Ltd. All rights reserved.
Heavy metal pollution in the aquatic environment is one of the critical issues due to the toxic and persistent characters (Zhan et al., 2010; Varol and Sßen, 2012; Gao and Chen, 2012). Heavy metal pollutants pose potential threats to ecosystems because they could be concentrated or accumulated in organisms and biomagnified at higher trophic levels (Zhan et al., 2010; Ghrefat et al., 2011; Gao and Chen, 2012), and partly converted to more toxic organic compounds (Liu et al., 2009). Heavy metals in seas originate from both natural processes and anthropogenic activities. Natural processes like atmospheric inputs and aeolian processes set the background values for heavy metals (Zhang et al., 2003). With the rapid industrialization and urbanization in coastal regions, anthropogenic inputs are the main sources of pollution in the marine environment, and heavy metals are increasingly introduced to the estuarine and coastal environments through riverine discharge and oceanic dumping (Choi et al., 2007; Zhang et al., 2012; Yuan et al., 2012). After being introduced into the aquatic environment, heavy metals from the aqueous phase eventually become deposited to sediment through physical, chemical or biological mechanisms (Zhang et al., 2007; Zhan et al., 2010; Yuan et al., 2012). ⇑ Corresponding author. Tel./fax: +86 532 82031735. E-mail address: [email protected] (X. Liu).
The Yellow Sea is a semi-enclosed epicontinental sea of the northwestern Pacific, separated from the Bohai Sea in the east. It is located between the China Mainland and the Korea Peninsula, between 31°400 N–39°500 N and 119°100 E–126°500 E. The Yellow Sea covers 380,000 km2, with an average depth of 44 m and a maximum depth of 140 m in the northern area of Cheju Island. It is divided into the Northern Yellow Sea (NYS) and the Southern Yellow Sea (SYS) by a line linking Chengshanjiao on the Shandong Peninsula and Changsan-got on the Korea Peninsula (Yang et al., 2003). The Yellow Sea receives billions of tons of particulate materials annually from both Chinese and Korean Rivers, such as the Changjiang River, Yellow River, Yalujiang River of China and the Han, Kum and Yeongsan Rivers of Korea (Qin et al., 1989). The statistics from the State Oceanic Administration, PR China (SOA, 2010, 2011, 2012, 2013) indicate that 6530, 9540, and 16,530 km2 of offshore areas of the Yellow Sea are heavily polluted (i.e. the water quality is worse than class 4) in the years of 2010, 2011, and 2012, respectively. The polluted areas of those years are significantly larger than in 2009 (2150 km2). The distribution of metals in sediments might provide evidence for human activities and their effects on ecosystems. For this reason are sediments commonly chosen as environmental indicators of the quality and potential risks within aquatic systems (Unlu et al., 2008; Luo et al., 2010; Zhan et al., 2010). The Geoaccumulation
http://dx.doi.org/10.1016/j.marpolbul.2014.03.020 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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index and Hankanson potential ecological risk index are the most popular methods used to evaluate the ecological risk posed by heavy metals in sediments (Varol and S ß en, 2012; Li et al., 2012). Most of the existing studies, on the distribution of heavy metals in surface sediments, divided the Yellow Sea into the NYS and the SYS; however, few studies considered the Yellow Sea as a whole. Concentrations of Ni and Co and their seasonal variability are rarely studied neither. The main objectives of the present study are to determine the distribution of eight heavy metals (Pb, Cd, Cu, Fe, Ni, Mn, Zn and Co) concentrations in surface sediments of the Yellow Sea, and to assess the pollution status of this area with the Geoaccumulation index and Hankanson potential ecological risk index. The study area is located between 31°580 N–38°450 N and 121°000 E–124°400 E, near the coast of China. Sediments were collected onboard the vessel "Dongfanghong II" from 34 sampling stations (23 in the SYS and 11 in the NYS, Fig. 1a) during 13 to 30 June, 2011, and 22 sampling stations (16 in the SYS and 6 in the NYS, Fig. 1b) from the 20th November to 7th December, 2011. Surface sediments were taken using a stainless steel box-corer. The top 3 cm of samples were then placed in polyethylene bags, and refrigerated at 20 °C. After transport to the laboratory, samples were airdried at room temperature (20 °C), crushed, passed through a nylon sieve of 160 meshes (96 lm), homogenized, and then stored in polyethylene bags for further analysis. About 0.5 g dried sediment samples and 10 mL concentrated HNO3 were placed together in a plastic digestion tube and a microwave digestion system was used to remove any organic matters present in the sediment. The digested samples were then diluted with water to 50 mL. Sample solutions and blanks were analyzed for Pb, Cd, Cu, Fe, Ni, Mn, Zn and Co with inductively coupled plasma-mass spectrometry (ICP-MS, Optima 2100 DV ICP System, Perkin Elmer). All samples were analyzed in duplicate, and the data shown herein represent average values of the duplicates. In order to evaluate the precision, the GBW-07314 reference material (The Second Institute of Oceanography, the State Oceanic Administration of China) was measured. All plastic and glassware were pre-cleaned by soaking in HNO3 (v/v = 1:3) for at least 24 h, followed by soaking and rinsing with de-ionized water. Surfer 8.0 (Golden Software Inc., USA) was used for drawing the distribution maps of metal concentrations in surface sediments. Statistical analyses (i.e. two-tailed t test, bivariate correlation,
one-way ANOVA) were conducted with SPSS 19.0 software (SPSS Inc., USA). In this study, two methods of pollution assessment of heavy metals are conducted, the geoaccumulation index (Müller, 1969) and Hankanson potential ecological risk index (Hakanson, 1980). The geochemical background values of Cu, Pb, Zn and Cd were 15.92, 14.54, 60.00 and 0.103 lg/g, respectively (Lu and Zhu, 1987). However, the background values of other metals studied here were not available. The geoaccumulation index (Igeo) is defined by the following equation (Eq. (1)):
Igeo ¼ log2 ðC n =kBn Þ
ð1Þ
where Cn is the concentration of metals examined in sediment samples and Bn is the geochemical background value of metals. Factor k is the background matrix correction factor due to lithospheric effects, which is usually defined as 1.5 (Müller, 1969; Rubio et al., 2000; Ghrefat et al., 2011; Shafie et al., 2013). The geoaccumulation index consists of seven classes: Class 0 (practically uncontaminated): Igeo 6 0. Class 1 (uncontaminated to moderately contaminated): 0 < Igeo 61. Class 2 (moderately contaminated): 1 < Igeo 6 2. Class 3 (moderately to heavily contaminated): 2 < Igeo 6 3. Class 4 (heavily contaminated): 3 < Igeo 6 4. Class 5 (heavily to extremely contaminated): 4 < Igeo 6 5. Class 6 (extremely contaminated): Igeo > 5. The Hankanson potential ecological risk index (RI) is defined as follows (Eqs. (2)–(5)):
C if ¼
Cd ¼
Ci
ð2Þ
C in m X C if
ð3Þ
i
Eir ¼ T ir C if RI ¼
ð4Þ
m X Eir
ð5Þ
i
39° N
39° N B22 B21 B31 B23 B30 B24 B13 B25 B12 B28 B27 B05 B03 H02
H04
H06
B31 B23 B30 B25 B28
38°
37°
B08 B10 B01 H08
B13
B08
37°
B01 H08
36°
B05 B03
36°
H02
H04
H06
H09
H43 H15
H13
H15
35°
H11 HF1 H28
H21
38°
H13
34°
H25
33°
H35
35°
H11
34°
H27
H30II H35
H32 H31
H37 H38 H39 H40
33°
H32
32°
32°
H42
(a) 119°
120°
121°
122°
123°
124°
125°
31° 126° E
(b) 119°
120°
121°
122°
123°
124°
125°
31° 126° E
Fig. 1. Map of the Yellow Sea, showing the sampling stations during summer (a) and winter (b) in 2011.
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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where Ci and C in are the concentrations of metals examined in sediment samples and the geochemical background values of metals, respectively. C if and Cd are the monomial and the polynomial contamination factors. Eir is the monomial potential ecological risk factor. T ir is the toxic-response factor for a given substance, e.g. Cu = Pb = 5, Zn = 1, Cd = 30 (Hakanson, 1980; Xu et al., 2008). RI is the sum of all risk factors for heavy metals in sediments. The relation between evaluation indices and the pollution degree and potential ecological risk are shown in Table 1. All metal concentrations in surface sediments collected from the Yellow Sea, in general, were ranked in decreasing order, as follows: Fe > Mn > Zn > Ni > Cu > Pb > Co > Cd. The concentration ranges of heavy metals in surface sediments of the Yellow Sea during summer were as follows: Pb, 4.80–21.9 lg/g; Cd, 0–8.21 lg/g; Cu, 5.93–25.7 lg/g; Fe, 0.61–2.27%; Ni, 8.43–31.1 lg/g; Mn, 84.7–1593 lg/g; Zn, 21.9–96.2 lg/g; Co, 4.11–13.0 lg/g, respectively. The concentration ranges of heavy metals during winter were as follows: Pb, 4.31–18.4 lg/g; Cd, 0–0.373 lg/g; Cu, 4.95–26.1 lg/g; Fe, 0.62–2.22%; Ni, 8.31–32.4 lg/g; Mn, 186–1334 lg/g; Zn, 18.8–82.1 lg/g; Co, 4.31–13.3 lg/g, respectively. To compare the concentrations of eight metals between summer and winter in the Yellow Sea, an independentsample t-test was conducted and the results showed no significant differences among those metals between the two seasons (p > 0.05). The range and mean concentrations of studied metals in sediments of the Yellow Sea and other representative seas are summarized in Table 2. It could be shown that the average concentrations of all studied metals in Yellow Sea sediments were within the range found in other sea areas.
Pb, Cd, Cu, and Zn concentrations in surface sediments rarely excessed the first category standard of the China national standard – marine sediment quality (GB 18668-2002, State Oceanic Administration, PR China). However, the concentrations of Cd during summer at Station H02 and H40 were ranked second class and Station H40 exceeded the third class. The spatial distributions of heavy metals are shown in Figs. 2 and 3. The distribution of those metals in two seasons exhibited a similar pattern as follows: (1) Higher concentrations of heavy metals were generally found in the central part of the SYS and western part of the NYS, especially the north-central part of the SYS (except for Mn); (2) Away from the central area, concentrations (except for Mn) decreased along both the Korean coast and Chinese coast. This trend was quite similar to previous findings (Yuan et al., 2012). It is worthy to mention that with the exception of station H40 the concentration (8.21 lg/ g) of Cd was extremely high while the concentrations at other stations did not exceed 2.00 lg/g. However, previous studies have not reported the exception (Teng et al., 2012). The distribution of Mn showed a distinct peak approximately situated at 36°N and 122°E, much closer to Shandong Peninsula than other heavy metals. Previous studies have shown a similar phenomenon. The mechanism for such a distribution pattern is probably due to the sediments of this area being dominated by biogenic carbonate (Lin et al., 2002). The dissolved Mn could be adsorbed on, or incorporated into freshly precipitated CaCO3 in seawater (e.g. Wartel et al., 1990). Wartel et al. (1990, 1991) concluded that the adsorption on and substitution in calcite, along the French coast of the English Channel, are the major mechanisms controlling dissolved Mn in seawater. Boughriet et al. (1992) studied suspended particulate matter from the Seine Estuary and
Table 1 Corresponding relationships between evaluation indices and pollution degree and potential ecological risks. C if
Monomial contamination factor
Cd
Polynomial contamination factor
Eir
Monomial potential ecological risk factor
RI
Sum of all risk factors
0.05). Higher concentrations of heavy metals (except for Mn) were generally found in the central part of the SYS and western part of the NYS, especially the north-central part of the SYS. There was an exception for Cd that the concentration at Station H40 was extremely high. The distribution of Mn showed a distinct peak approximately situated at 36°N and 122°E, much closer to Shandong Peninsula than other heavy metals. The correlation analyses implied that Pb, Cu, Fe, Ni, Zn and Co were probably derived from the same origin and their concentrations are controlled by grain size and TOC. Both the Igeo and Hankanson potential ecological risk index indicated that most area of the Yellow Sea was uncontaminated in Pb, Cu and Zn. However, the contamination degree of Cd varied within a wide range, from moderately to heavily contaminated. The SYS close to the Shandong Peninsula was a polluted area and Station H40 was heavily polluted. The pollution status of the Yellow Sea in summer was worse than that in winter. As the main pollutant, Cd contributed more to the pollution status and potential ecological risk than other heavy metals. This study assessed the pollution status in the Yellow Sea in two methods, providing base data to environmental protection and policy planning. However, this study has shortages such as not reflecting the pollution status entirely because the background values of many heavy metals in the Yellow Sea are unavailable. Further studies are needed to determine reliable background values that could provide reference points for meaningful pollution studies in the area.
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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Table 5 The values of Igeo, C if , Eir , Cd and RI in surface sediments in the Yellow Sea during summer. Station
B01 B03 B05 B08 B10 H02 H04 H06 H08 H11 H13 H15 H21 H28 H30II H31 H32 H35 H37 H38 H39 H40 H42 H43 HF1 B12 B13 B21 B22 B23 B24 B25 B27 B28 B30 B31
Igeo =C if =Eir Pb
Cd
Cu
Zn
0.18/1.33/6.64 1.05/0.72/3.61 1.22/0.65/3.22 1.48/0.54/2.67 1.05/0.73/3.63 1.41/0.57/2.83 0.66/0.95/4.76 0.18/1.33/6.63 0.49/1.07/5.35 0.47/1.08/5.42 0.56/1.02/5.07 1.82/0.42/2.12 0.73/0.91/4.51 0.70/0.92/4.62 0.68/0.94/4.69 0.40/1.14/5.68 0.55/1.03/5.13 1.32/0.60/3.01 1.29/0.62/3.08 1.10/0.70/3.50 0.53/1.04/5.20 0.86/0.83/4.15 0.52/1.04/5.22 0.47/1.08/5.42 0.54/1.03/5.17 1.94/0.39/1.96 1.49/0.53/2.66 2.18/0.33/1.65 1.42/0.56/2.81 0.63/0.97/4.85 0.00/1.50/7.52 0.66/0.95/4.74 1.28/0.62/3.08 1.49/0.54/2.68 0.61/0.99/4.93 0.70/0.93/4.63
0.71/2.45/73.49 0.16/1.67/50.18 0.27/1.24/37.25 1.97/0.38/11.48 0.04/1.54/46.22 3.28/14.58/437.31 3.40/15.86/475.91 0.79/2.59/77.82 1.10/3.21/96.35 2.01/6.04/181.14 0.87/2.75/82.47 0.33/1.88/56.51 1.64/4.68/140.28 1.03/3.07/91.95 0.75/2.52/75.44 0.10/2.10/89.96 1.33/3.78/113.40 1.03/3.07/92.03 0.92/2.85/85.39 0.90/2.81/84.23 0.92/2.83/84.89 5.73/79.72/2391.61 0.76/2.55/76.36 1.36/3.85/115.57 0.21/1.74/52.20 /0.00/0.00 4.97/0.05/1.44 /0.00/0.00 4.96/0.05/1.45 0.26/1.25/37.52 0.53/2.17/65.14 1.15/0.68/20.28 1.37/0.58/17.40 0.38/1.15/34.61 0.30/1.84/55.22 0.38/1.16/34.68
0.07/1.57/7.87 1.08/0.71/3.56 1.37/0.58/2.91 1.06/0.72/3.60 0.99/0.76/3.79 1.23/0.64/3.20 0.37/1.16/5.80 0.11/1.62/8.08 0.02/1.48/7.39 0.38/1.16/5.78 0.41/1.13/5.65 1.81/0.43/2.13 0.06/1.57/7.84 0.68/0.94/4.68 0.65/0.96/4.79 0.33/1.19/5.98 0.36/1.17/5.84 1.04/0.73/3.65 0.74/0.90/4.50 1.35/0.59/2.94 0.44/1.11/5.53 0.96/0.77/3.85 0.47/1.08/5.40 0.21/1.30/6.51 0.53/1.04/5.21 1.95/0.39/1.94 2.01/0.37/1.86 1.94/0.39/1.96 1.15/0.67/3.37 0.28/1.24/6.19 0.62/0.98/4.87 0.40/1.14/5.68 0.89/0.81/4.05 1.67/0.47/2.36 0.18/1.33/6.63 0.58/1.00/5.01
0.10/1.60/1.60 0.95/0.78/0.78 1.32/0.60/0.60 1.41/0.57/0.57 1.29/0.62/0.62 1.54/0.52/0.52 0.89/0.81/0.81 0.39/1.15/1.15 0.44/1.11/1.11 0.57/1.01/1.01 0.77/0.88/0.88 2.01/0.37/0.37 0.94/0.78/0.78 0.67/0.94/0.94 0.59/0.10/0.10 0.58/1.00/1.00 0.69/0.93/0.93 1.25/0.63/0.63 1.22/0.64/0.64 1.38/0.58/0.58 0.85/0.83/0.83 0.89/0.81/0.81 0.72/0.91/0.91 0.38/1.15/1.15 0.52/1.05/1.05 1.97/0.38/0.38 1.95/0.39/0.39 2.04/0.37/0.37 1.40/0.57/0.57 0.66/0.95/0.95 1.03/0.74/0.74 0.75/0.89/0.89 1.31/0.60/0.60 1.74/0.45/0.45 0.69/0.93/0.93 0.83/0.85/0.85
Cd
RI
6.95 3.89 3.07 2.21 3.64 16.30 18.79 6.68 6.87 9.29 5.77 3.11 7.93 5.87 5.41 6.33 6.91 5.03 5.01 4.67 5.81 82.13 5.58 7.39 4.86 1.16 1.34 1.09 1.85 4.41 5.38 3.65 2.61 2.61 5.08 3.93
89.60 58.13 43.99 18.34 54.26 443.85 487.28 93.68 110.19 193.35 94.07 61.14 153.42 102.19 85.92 102.61 125.31 99.32 93.61 91.24 96.46 2400.41 87.89 128.64 63.62 4.29 6.35 3.97 8.19 49.51 78.27 31.59 25.13 40.09 67.71 45.16
Table 6 The values of Igeo, C if , Eir , Cd and RI in surface sediments in the Yellow Sea during winter. Station
B01 B03 B05 B08 H02 H04 H06 H08 H09 H11 H13 H15 H25 H27 H32 H35 B13 B23 B25 B28 B30 B31
Igeo =C if =Eir Pb
Cd
Cu
Zn
0.24/1.27/6.33 1.06/0.72/3.59 1.04/0.73/3.66 1.30/0.61/3.04 1.70/0.46/2.32 1.05/0.72/3.62 0.58/1.00/5.00 0.62/0.97/4.87 0.56/1.02/5.10 0.70/0.92/4.62 0.79/0.87/4.34 2.34/0.30/1.48 1.94/0.39/1.96 1.02/0.74/3.70 0.66/0.95/4.76 1.51/0.53/2.63 1.61/0.49/2.46 0.50/1.06/5.30 0.56/1.02/5.10 1.61/0.49/2.46 0.60/0.99/4.95 0.84/0.84/4.18
0.74/2.50/74.91 0.03/1.54/46.10 0.00/1.50/44.85 1.96/0.38/11.53 1.65/0.48/14.36 0.57/1.01/30.22 0.04/1.54/46.16 0.27/1.25/37.42 1.27/0.62/18.72 2.96/0.19/5.80 0.87/0.82/24.60 1.51/0.53/15.79 4.97/0.05/1.44 3.97/0.10/2.87 1.26/0.63/18.77 11.17/0.00/0.02 1.15/0.68/20.33 0.24/1.77/53.22 0.09/1.59/47.76 0.20/1.30/39.08 1.27/3.62/108.66 0.73/2.49/74.65
0.13/1.64/8.20 1.06/0.72/3.60 0.78/0.87/4.36 0.95/0.78/3.89 1.10/0.70/3.50 0.45/1.10/5.48 0.09/1.59/7.96 0.12/1.38/6.91 0.23/1.28/6.41 0.38/1.15/5.76 0.40/1.14/5.68 2.27/0.31/1.56 1.78/0.44/2.19 0.75/0.89/4.46 0.39/1.15/5.73 0.97/0.77/3.83 1.29/0.61/3.06 0.18/1.32/6.61 0.24/1.27/6.34 1.69/0.46/2.32 0.08/1.42/7.08 0.56/1.02/5.09
0.13/1.37/1.37 1.28/0.62/0.62 1.14/0.68/0.68 1.51/0.53/0.53 1.77/0.44/0.44 1.19/0.66/0.66 0.44/1.11/1.11 0.48/1.08/1.08 0.42/1.12/1.12 0.49/1.07/1.07 0.70/0.92/0.92 2.26/0.31/0.31 1.64/0.48/0.48 1.10/0.70/0.70 0.97/0.77/0.77 1.48/0.54/0.54 1.59/0.50/0.50 0.68/0.94/0.94 0.73/0.90/0.90 1.76/0.44/0.44 0.64/0.97/0.97 0.90/0.80/0.80
Cd
RI
6.77 3.59 3.78 2.30 2.08 3.49 5.24 4.68 4.05 3.34 3.75 1.45 1.36 2.43 3.49 1.83 2.28 5.09 4.78 2.70 6.99 5.15
90.81 53.91 53.55 18.98 20.60 39.98 60.23 50.27 31.35 17.25 35.55 19.14 6.07 11.74 30.02 7.01 26.35 66.07 60.10 44.30 121.65 84.73
Please cite this article in press as: Jiang, X., et al. Distribution and pollution assessment of heavy metals in surface sediments in the Yellow Sea. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.020
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X. Jiang et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx 39° N
39° N
38°
38°
1 0 6 37°
-1
37° 5
36°
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-2 36°
4
-3
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-4
35°
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2 34°
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1 33°
-7
33°
0
-8 32°
-10
32°
(a) 119°
120°
121°
122°
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124°
125°
(b)
31° 126° E
119°
120°
121°
122°
123°
124°
125°
-9 -10
31° 126° E
Fig. 4. The Igeo spatial distribution of Cd in surface sediments in the Yellow Sea during summer (a) and winter (b).
39° N
39° N
38°
38°
37°
37°
64
2000 1000
36°
36° 32
600 35°
35°
300
16 34°
33°
32°
(a) 119°
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34° 8
0
(b)
31°
126° E
119°
120°
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123°
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150
33°
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32°
-150
31°
126° E
Fig. 5. The spatial distribution of Cd (a) and RI (b) in surface sediments in the Yellow Sea during summer.
Acknowledgments This study was funded by a Grant to X.S.L. (No. 41006081) from the National Natural Science Foundation of China (NSFC). We are grateful to ‘‘NSFC Open Cruises for Bohai and Yellow Seas Marine Scientific Research’’ and crew members of the vessel ‘‘Dongfanghong II’’. Prof. Hans-U. Dahms is thanked for critical comments to an earlier version of the manuscript.
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