Fractionation, sources and budgets of potential harmful elements in surface sediments of the East China Sea

Marine Pollution Bulletin 68 (2013) 157–167

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Fractionation, sources and budgets of potential harmful elements in surface sediments of the East China Sea Yu Yu a,b, Jinming Song a,⇑, Xuegang Li a, Huamao Yuan a, Ning Li a a b

Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China University of Chinese Academy of Sciences, Beijing 100049, China

a r t i c l e

i n f o

Keywords: Trace element Sequential extraction Enrichment Budget Changjiang estuary East China Sea

a b s t r a c t Total concentrations, chemical fractions by BCR procedure and enrichment factors of nine potential harmful elements (V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb) in surface sediments of the East China Sea (ECS) were investigated. Spatial distributions illustrated that PHEs (potential harmful elements) were mainly from the Changjiang River and the Jiangsu coastal current, except Pb which was influenced by atmospheric input. Sediments in the ECS were moderately polluted with Cd, Pb, Zn and Cu according to their enrichment factors (EFs). Distributions of EFs and labile fractions revealed that anthropogenic Cd and Cu were mainly input though the Changjiang, Pb pollutant was delivered from the Changjiang and atmosphere, while Zn was impacted by terrestrial pollution from the Changjiang and the Hangzhou Bay. Budget calculation showed that the Changjiang contributed 82–90% of PHE influxes. Thirty-eight to 77% of PHEs were buried in sediment, mainly along the inner shelf. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.

The East China Sea (ECS) continental shelf is the largest marginal sea in the western Pacific Ocean, with a vast continental area of 0.5  1012 m2. The Changjiang River is the major source of material to the ECS (Liu et al., 2007), annually delivering 3.97  1011 kg sediment into the ECS on average from 1953 to 2009, according to the Datong Hydrological station (625 km upstream of the river mouth). A good deal of researches reveal that Zn, Cu, Pb and Cd pollution are ubiquitous in the river, lakes, intertidal zones in the Changjiang watershed, and even in suspended particulate matter (SPM) of the coastal ECS in recent decades (Hsu and Lin, 2010; Liu and Li, 2011; Zhang and Shan, 2008; Feng et al., 2004). The Changjiang River and Qiantang River annually deliver 2.4  104 and 937 t of heavy metals (Cu, Pb, Zn, Cd and Hg) on average from 2002 to 2010 into the ECS, respectively (Bulletin of China’s Marine Environmental Status of China for the year of 2002 to 2010, 2002–2010). Influenced by excess terrestrial metal input, sediments in the inshore ECS have shown evidences of Cu, Zn, Cd and Pb enrichment in recent years (Lin et al., 2002; Fang et al., 2009). However, previous studies on trace metals in the ECS mainly focused on their total concentrations in sediments (Lin et al., 2002; Fang et al., 2009). Chemical fractions of trace elements, which were effective indexes of pollution status and potential toxicity of trace metals in sediment (Backstrom et al., 2004), were rarely studied in the ECS. A procedure proposed by the Community Bureau of Reference (BCR) is commonly used to fractionate trace elements in sedi⇑ Corresponding author. Tel./fax: +86 532 82898583. E-mail address: [email protected] (J. Song).

ments. It partitions trace elements into four fractions including acid soluble (exchangeable and carbonate bound metals), reducible metals bound to Fe/Mn oxides, oxidizable (metals bound to organic matter) and residual fractions (Kazi et al., 2005). Labile fractions (acid soluble, reducible and oxidizable) are usually deemed as an indication of anthropogenic or authigenic sources of trace elements, while residual fraction represents the lithogenic part of metals (Backstrom et al., 2004; Wang et al., 2004; Zhang et al., 1990). On the other hand, larger proportion of labile fraction also indicates greater mobility and potential toxicity of trace elements in sediments (Okbah et al., 2005; Rath et al., 2009). Vanadium, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb are potential harmful elements (PHEs), which might pose harm to life with higher concentrations (N’guessan et al., 2009). In addition, these metals are the commonest pollution elements in coastal waters produced by various human activities (Buckley et al., 1995; Lambert et al., 2007). This study aimed to investigate the distributions, sources and pollution status of these elements in the ECS. Particularly, the application of chemical fractions in assessing the pollution status of PHEs and identifying the pathways of anthropogenic elements was highlighted. Thirty-five surface sediment samples (0–2 cm) were collected using a box sampler in the ECS during a cruise in May 2009 (Fig. 1). Sediments were kept in pre-cleaned polyethylene bags and frozen until lab analysis. Aliquots of sediment samples were dried at 60 °C and ground for homogenization. About 0.05 g ground sediment were digested in air tight Teflon vessel with a mixture of HF–HNO3–HClO4 at round 150 °C for

0025-326X/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2012.11.043

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34 Jia n

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JCC

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Cheju Island

ro . the C hangji ang

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A0

A1

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C1

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CDW

N 31

N

Shanghai

China

II

B1

R.

I

A4

A6

B4

B6

C3

C6

D2

D5

E2

E3

F1

F2

F3

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G1

G2

G3

G4

H1

H2

H3

H4

E6

Hangzhou Bay

30 30

F5

F6 G6

Zhejiang Pro.

20

H0

29 80

90

III

D6

100

110

120

H5

IV

KC

H6

130

E

ZFCC

TWC

East China Sea

28 119

120

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127

E Fig. 1. Sampling sites (dots) and four geographically divided regions in this study. The current system (arrows) consists of the Changjiang Dilute Water (CDW), the Jiangsu Coastal Current (JCC), the Zhejian–Fujian Coastal current (ZFCC), the Kuroshio Current (KC) and the Taiwan Warm Current (TWC) (Liu et al., 2007; Zhu et al., 2011). There are three upwelling areas (shadows) in the ECS (Youn and Kim, 2011).

48 h. Concentrations of nine PHEs (V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb) and Sc were determined with inductively coupled plasma-mass spectrometry (ICP-MS; Elan DRC II). A modified BCR procedure was conducted to fractionate PHEs in sediments (Kazi et al., 2005). Acid soluble, reducible and oxidizable fraction of metals were sequentially extracted with 0.11 M HAc (room temperature, 16 h), 0.5 M NH2OHHCl (pH 1.5) (room temperature, 16 h) and 30% H2O2 (twice, 85 °C, 1 h every time) followed by 1 M NH4Ac (pH 2) (room temperature, 16 h), respectively. After each step, the mixture was centrifuged for 15 min at 4000 rpm. The residual was washed with Milli-Q water, and the supernatant was discarded. Metal concentrations in extract from each step were determined using ICP-MS. Metal in residue fraction was calculated as the difference between total concentration and the sum of leachable fractions. All the chemicals and reagents used were of guarantee grade. Total organic matter (TOC) in sediment was determined with a modified Walkley–Black method (Mebius, 1960). Carbonate in sediment was extracted with 10% HAc at 100 °C for 30 min. The slurry was filtered and the content of calcium in the filtrate was determined by titration with EDTA (Moss, 1961). The relative standard deviations (RSD) for TOC and carbonate measurement were less than 5%. Wet sediment samples treated with H2O2 (10%) and HCl (1 mol/l) were disaggregated by ultrasonic, and measured for grain size with a Laser Particle Size Analyzer (Cilas 940L). All the chemicals and reagents used were at least of analytical grade. Blank, replicates and standard references were conducted to control the data quality. Blank samples were performed throughout the experiment of total concentration analysis and sequential extraction. Trace element concentrations in blank samples were below the detection limit of ICP-MS. Analytical precision was assured by duplicate analysis every 10 samples during total concentration analysis and every 8 samples during sequential extraction, with RSD less than 10% and 20%, respectively. Standard reference materials (GBW07315, GBW07316, BCR-2 and BHVO-2) were used to guarantee the accuracy of the total concentration (Table 1). The recoveries ranged from 90% to 110%. Ten samples of the residue after the sequential extraction were analyzed for metal concentrations with the same procedure as bulk concentration analysis. The recovery for sequential extraction of PHE is calculated as following (Kazi et al., 2005):

Recovery ¼ ðLacid soluble þ Creducible þ Coxidizable þ Cresidual Þ=Ctotal  100%

The recoveries for the sequential extraction ranged from 85% to 98%. Sediment grain size is a combined result of sediment input, depositional process and hydrodynamic conditions, and could be used to characterize depositional environments and sediment sources (Zhu et al., 2011). Median grain size of surface sediments in the ECS varied greatly from 1.75 to 7.68 U with a CV (coefficient of variation) of 45.8%, indicating diverse sedimentary environment in the northern ECS. Median grain size and mud content (clay and silt) displayed similar band-type distributions along the coast and they progressively decreased toward the sea (Fig. 2). Mud content decreased rapidly from more than 90% in the coast to 20–50% at 123°E, illustrating that terrestrial sediment was mainly deposited in the inner shelf west to 123°E. North to the estuary, mud content decreased southeastward from 90% in the Jiangsu coast to 20% in the northern middle shelf, revealing input of fine sediment by the JCC from old Huanghe delta. In the offshore upwelling area, sediment grain size progressively increased toward offshore reaching up to 7.7 U, with mud content increasing from 30% to 90%. High mud content and fine-grained sediment in the offshore where supply of terrestrial sediment was limited (Lim et al., 2007), indicated intense rework of sediment by offshore upwelling currents. It was noticed that, compared with less than 20% of mud in the northern middle shelf, mud content was still higher than 40% in the southern middle shelf. This distribution was attributed to more river sediment input into the southern area. TOC in surface sediments of the ECS ranged from 0.09% to 0.60% with a CV of 40.3%. The distributions of TOC resembled that of mud content, with high values off the estuary, in the Zhejiang coast and in the offshore upwelling area and very low concentrations in the northern middle shelf (Fig. 2). TOC content showed seaward decreasing trends from 0.6% in the estuary to 0.28% in the middle shelf, revealing the impact of river input on the distribution of TOC. Carbonate in sediments varied between 2.6% and 19.6%. Maximum concentration (19.6%) existed in the southeast corner of the study area (Fig. 2). From this high value center, carbonate gradually decreased northwestward to less than 6% in vast areas in the inshore and the northern ECS. Carbonate of high content in the southern middle shelf was likely of biogenic source related to the intrusion of Taiwan warm current (TWC)-a branch of the KC (Lin et al., 2002). To facilitate discussion, the investigated area is geographically divided into four regions (Fig. 1): zone-1, the estuary and

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Y. Yu et al. / Marine Pollution Bulletin 68 (2013) 157–167 Table 1 Certified and determined concentrations of trace metals (Mean ± S.D. in lg/g; n= 3) in standard reference materials: GBW07315, GBW07316, BCR-2 and BHVO-2. Element

V Cr Co Ni Cu Zn Mo Cd Pb

GBW07315

GBW07316

BCR-2

BHVO-2

Certified values

Determined values

Certified values

Determined values

Certified values

Determined values

Certified values

Determined values

101 ± 8 59 ± 6 81 ± 6 167 ± 2 357 ± 20 137 ± 15 14 ± 1 0.25 37 ± 4

106 ± 5 67 ± 8 79 ± 4 156 ± 5 375 ± 18 152 ± 15 13 ± 1 0.43 ± 0.04 41 ± 3

69 ± 6 38 ± 2 53 ± 4 108 ± 9 231 ± 10 142 ± 22 5.7 ± 0.8 0.3 22 ± 5

66 ± 5 36 ± 2 50 ± 3 103 ± 6 221 ± 8 136 ± 25 5.5 ± 0.6 0.29 ± 0.3 21 ± 4

nd 18 ± 2 37 ± 3 nd 19 ± 2 127 ± 9 248 ± 17 nd 11 ± 2

nd 18 ± 1 38 ± 3 nd 24.9 ± 3 142 ± 8 283 ± 20 nd 11 ± 1

nd 280 ± 19 45 ± 3 119 ± 7 127 ± 7 103 ± 6 nd nd nd

nd 328 ± 22 46 ± 2 120 ± 5 145 ± 6 127 ± 8 nd nd nd

nd: No data.

33

32

Jia ng su Pr the C o. hangji ang R .

31

Shanghai

N

33

Jia

r the C o. hangji

32

Hangzhou Bay

ang R .

Shanghai

31

N

30

ng su P

Hangzhou Bay

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Median 120

121

122

123

124

125

Mud 126

120

121

122

33

Jia ng su Pr the C o. hangji ang

32

33

Jia ng su Pr the C o. hangji ang

32

R.

Shanghai

31

N

123

124

125

126

E

E

Shanghai

31

N

Hangzhou Bay

30

R.

Hangzhou Bay

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Carbonate

TOC 120

121

122

123

124

125

126

E

120

121

122

123

124

125

126

E

Fig. 2. Horizontal distributions of median grain size (U), mud content (clay and silt, %), total organic matter (TOC, %) and carbonate (%) of sediments in the ECS.

southward coastal waters west to 123°E where Changjiang sediment mainly deposit; zone-2, the northern ECS bound to yellow sea which is influenced by the northeastward CDW and the JCC; zone-3, fringe of the offshore upwelling areas SW to the Cheju Island; zone-4, remainder of the studied areas in the continental shelf. Concentrations of nine PHEs in four regions were presented in Table 2. Total V, Cr, Co, Ni and Pb concentrations varied relatively less with CVs lower than 20%, compared with large variations of Cu, Zn, Mo and Cd with CVs from 22.6% (Zn) to 40.9% (Cu). These elements had the highest concentrations in coastal waters (zone-1) and offshore upwelling area (zone-3), lower concentrations in the northern ECS (zone 2) and the lowest in the continental shelf

(zone-4). Spatial distributions of V, Cr, Co, Ni, Cu, Zn, Mo and Cd generally exhibited similar trends in the ECS (Fig. 3), which also resembled that of the grain size. Total concentrations of these elements distributed along the coast in a band type and decreased rapidly toward sea. The maximum concentrations were observed at station H1 in the Zhejiang coast, consistent with high mud content here (100%). High concentrations of V, Cr, Co, Ni, Cu, Zn, Mo and Cd also existed in the offshore upwelling areas, where they gradually increased toward cyclonic eddy center. These elements showed southeastward decreasing trends from the Jiangsu coast to the northern middle shelf. In agreement with the distribution of grain size, V, Cr, Co, Ni, Cu, Zn, Mo and Cd had higher concentrations in the southern shelf than in the northern part. In contrast,

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Table 2 Concentrations of trace metals (Mean ± S.D.) in the surface sediments of the ECS, suspended particulate matter (SPM) in the Changjiang and Huanghe Rivers, UCC and SPM in the coastal ECS (lg/g). Element V Cr Co Ni Cu Zn Mo Cd Pb a b c d

ECS 89.6 ± 16.8 71.4 ± 14.9 13.1 ± 1.7 30.8 ± 5.8 23.7 ± 9.8 83.8 ± 18.9 0.5 ± 0.2 0.2 ± 0.1 24.6 ± 4.5

Zone 1 105.5 ± 18.8 84.2 ± 14.0 14.9 ± 1.8 36.1 ± 6.5 33.1 ± 11.9 102.4 ± 20.3 0.6 ± 0.3 0.3 ± 0.1 28.0 ± 5.7

Zone 2 88.6 ± 7.8 71.2 ± 12.4 12.5 ± 0.9 28.7 ± 4.0 23.4 ± 6.2 76.9 ± 10.5 0.5 ± 0.1 0.2 ± 0.1 23.5 ± 1.4

Zone 3 100.5 ± 13.6 82.1 ± 9.2 14.1 ± 1.5 34.3 ± 4.4 26.8 ± 5.4 94.3 ± 16.1 0.5 ± 0.1 0.20 ± 0.0 27.3 ± 2.6

Zone 4 78.0 ± 7.4 61.4 ± 9.6 12.1 ± 1.0 27.6 ± 3.0 17.2 ± 3.1 72.9 ± 9.9 0.4 ± 0.1 0.2 ± 0.0 22.3 ± 3.2

Changjiang SPM 104 122 19 64.2 62.3 97.7 0.44 39.9

b

a

Huanghe SPMa 58.2 76.9 14 40.3 26.7 69.8 0.18 16.5

b

UCCc

Coastal SPMd

107 85 17 44 25 71 1.5 0.098 17

85 ± 70 100 ± 63 4.5 ± 4.5 61 ± 36 311 ± 203 180 ± 74 2.1 ± 1.6 70 ± 31

Zhang and Liu (2002). Yang et al. (2004). McLennan (2001); Taylor and McLennan (1985). Hsu and Lin (2010).

total Pb reached up to 39 and 32 lg/g in the Zhejiang coast and the northern middle shelf, respectively, but it was lower than 24 lg/g in the coastal area and the southern middle shelf. Fractionation results showed that residual fraction were the dominant form of PHE in sediment, except for Pb whose labile fraction (51%) slightly exceeded residual fraction (49%). Particularly, residual V, Cr and Mo reached up to 91 ± 3, 90 ± 4 and 89 ± 5% of bulk content, respectively. Co, Ni, Cu, Zn, Cd and Pb had larger labile fractions which accounted for 32–50, 23–51, 11–37, 17–37, 10–80 and 39–66% of their total concentrations, respectively. Their major labile fractions were reducible and oxidizable Co and Zn, oxidizable Ni and Cu, acid soluble Cd and reducible Pb. Spatial distributions of the major fractions of PHEs were depicted in Fig. 5. The distributions of residual V, Cr, Co, Ni, Cu, Zn, Mo and Cd closely resembled each other and grain size, with band-type distribution along the coast (represented by residual V and Cu in Fig. 5). In contrast, residual Pb had maximum concentration in the middle shelf of the northern ECS and then decreased toward land. Acid soluble Cd, reducible Co, Zn and Pb and oxidizable Cu exhibited typical band-type distributions. They exhibited seaward decreasing trend and high values in the offshore upwelling areas. The distributions of oxidizable Co, Ni and Zn possessed the following common features which were different from those of their residual fractions: (1) they exhibited patchy distributions; (2) they generally had high concentrations in the middle shelf out of the Hangzhou Bay and in the Zhejiang coast; (3) relatively low concentrations existed in the estuary and coastal areas. Enrichment factor of PHE is calculated as following (Abrahim and Parker, 2008):

EF ¼

ðTM=RÞsample ðTM=RÞbackground

where (TM/R)sample and (TM/R)background are the ratios of trace element to reference element in sample sediment and background soil, respectively. Trace element compositions in the upper continental crust (UCC) were used as background values (McLennan, 2001; Taylor and McLennan, 1985). Reference element for normalization should meet some requirements (Loring and Rantala, 1992; N’guessan et al., 2009): (1) the element is linearly related to the natural occurring concentrations of studied PHEs; (2) it must be conservative and not subject to biogeochemical processes; (3) it is mainly of natural origin and usually dominated by residual fraction. Sc behaves conservative and is input into ocean mainly with lithogenic aluminosilicate. Anthropogenic and authigenic inputs of Sc are typically negligible in comparison with its natural abundance in sediments (Otosaka et al., 2004). It has been successfully used as a reference element

by previous studies (Grousset et al., 1995; Zhang et al., 2007). Fig. 6 shows that Sc was strongly related to fine particles (R = 0.836, P < 0.0001, n = 35). Sc also correlated significantly with V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb (R = 0.968, 0.959, 0.911, 0.966, 0.945, 0.937, 0.821, 0.917 and 0.725, respectively, P < 0.001, n = 34). In addition, residual fraction of Sc reached up to 82.8 ± 3.2% of total content (Fig. 4), which also supported the use of Sc as a normalizing element. Results showed that EFs of V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb ranged between 1.13–1.65, 1.16–1.61, 0.99–1.65, 0.94–1.24, 0.97–2.09, 1.56–1.95, 0.34–0.84, 2.44–4.16 and 1.80–4.49, respectively. Taking EF of 1.5 as the boundary between natural crustal source and non-crustal source, i.e. anthropogenic, biogenic or diagenetic processes (Zhang and Liu, 2002), EF results revealed that V, Cr, Co, Ni and Mo at all the sampling sites were of natural occurring. Cu showed enrichment at seven stations with EFs higher than 1.5, while Zn, Cd and Pb enrichment were observed at all the stations with average EFs of 1.78, 3.11 and 2.22, respectively. About 40–50% of the sediment load in the Changjiang River deposits in the estuary, while the remaining is delivered to the ECS shelf during flood seasons, but much is resuspended and carried southward by winter storms and coastal currents (Milliman et al., 1985b). An elongated subaqueous mud wedge is formed extending from the river mouth southward off the Zhejiang and Fujian coast (Liu et al., 2007). In agreement with the dispersal of river sediment, mud content and total V, Cr, Co, Ni, Cu, Zn, Mo and Cd mainly distributed along the coast and rapidly decreased toward sea. This illustrated that sediment load from the Changjiang River was the major source of these elements in sediments. In addition, PHE compositions in zone-1 resemble that in the suspended particulate matter (SPM) of the Changjiang River (Table 2), verifying the river origins of these metals out of the estuary and in the Zhejiang coast. The JCC is another sediment source in the ECS shelf, which annually carries 1.0  1011 kg of eroded particles from the abandoned Huanghe delta into the ECS shelf (Hu and Yang, 2001). In the northern ECS, southeastward decreasing trend of mud content, V, Cr, Co, Ni, Cu, Zn, Mo and Cd verified that sediment and these elements were input from the JCC. Table 2 showed that the concentrations of trace elements in the Huanghe SPM were much lower than those in the Changjiang SPM. PHE concentrations in zone-2 ranged between those in the Changjiang and Huanghe SPM. It probably implied that sediment in the northern ECS was influenced by both the Changjiang River and the JCC. Sediment source in the offshore upwelling area is a debated issue (Lim et al., 2007; Milliman et al., 1985a; Youn and Kim, 2011). Both the old Huanghe delta and the Changjiang River or only the old Huanghe delta might be the major source of sediment to the

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32

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33

Ji a ng su

P the C ro. hangji

31

ang R .

32

Shanghai

N

Jia ng su P the C ro. hangji ang

31

R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Cr

V 120

121

122

123

124

125

126

120

121

122

33

32

N

33

Ji a ng su

P the C ro. hangji an

31

123

124

125

g R.

32

Shanghai

N

Ji a ng s

uP the C ro. hangji a

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Co 120

121

122

123

124

125

Ni 126

120

121

122

E 33

32

N

126

E

E

31

124

125

126

E 33

Jia n

gs uP the C ro. hangji an

123

g R.

32

Shanghai

N

Jia ng s

uP the C ro. hangji a

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Zn

Cu 120

121

122

123

124

125

126

E

120

121

122

123

124

125

126

E

Fig. 3. Horizontal distributions of PHEs in surface sediments of the ECS (lg/g).

upwelling area (Milliman et al., 1985a; Youn and Kim, 2011). In zone-3, PHE compositions seemed to resemble those in the Changjiang SPM. However, higher element concentrations might also result from hydrological sorting by upwelling currents. V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb in the ECS had significant correlations with sediment grain size (R = 0.794, 0.793, 0.775, 0.839, 0.775, 0.808, 0.630, 0.720 and 0.649, respectively, P < 0.001, n = 35), revealing that the distributions of PHEs in the ECS were a combined result of sediment source and hydrodynamic conditions. Nevertheless, one thing could be certain that the supply of terrestrial sediment was limited in the offshore upwelling area in view of low sedimentation rate here (<0.2–0.5 cm/a) (Lim et al., 2007). In zone-4, sediments had the lowest PHE concentrations. It was consistent with

much less terrestrial sediment input and the coarsest grain size in relict region (Hu and Yang, 2001). High proportion of residual fraction implied that V, Cr, Co, Ni, Cu, Zn, Mo and Cd in the ECS were majorly of natural lithogenic origin. And these residual elements were also from the Changjiang and the JCC sediment load according to their unanimously seaward decreasing trends. In addition, good linear correlations existed between residual metals and median grain size with R 0.621, 0.640, 0.496, 0.605, 0.627 and 0.631 and 0.562 (P < 0.001, n = 32) for V, Cr, Co, Ni, Cu, Zn and Mo, respectively, and 0.385 (P < 0.05, n = 32) for Cd, verifying the common source between residual fraction and fine terrestrial sediment and also the grain size effects on residual metals.

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33

32

N

Jia n

33

P the C ro. hangji

31

Ji a ng s

gs u

ang R .

uP the C ro. hangji a

32

Shanghai

N

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

Mo 120

121

122

123

124

125

29

126

Cd 120

121

122

123

E

124

125

126

E 33

32

N

Ji a ng s

uP the C ro. hangji a

31

ng R.

Shanghai Hangzhou Bay

30 Zhejiang Pro.

29

Pb 120

121

122

123

124

125

126

E Fig. 3. (continued)

Total Pb concentrations reached 32 lg/g in the northern middle shelf where much less terrestrial sediment was supplied with mud content lower than 20%. High content of total Pb resulted from high concentration of residual Pb (Figs. 3 and 5). Different from other residual PHEs, residual Pb nearly had no linear correlation with sediment grain size. The reason was likely that Pb was from other sources rather than natural aluminosilicate mineral input, for example, anthropogenic input (Lin et al., 2002). Furthermore, low concentrations of Pb in coastal areas indicated that Pb of high content in the middle shelf was supplied by atmospheric input instead of terrestrial delivery. Pb pollution has been widely observed in sediments, resulting from excessive atmospheric delivery of Pb induced by various human activities (Komarek et al., 2008; Marx et al., 2010; Siver and Wizniak, 2001). The cycling of Pb in the ECS has been influenced by excess atmospheric delivery from mainland China (Lin et al., 2000). Therefore, total and residual Pb in the northern middle shelf most likely originated from atmospheric input. In contrast, low Pb concentrations in the Jiangsu coast and off the estuary (<24 lg/g) were likely caused by the dilution of Pb-depleted particles from the JCC (16.5 lg/g). As for the reason why atmospheric Pb was related to residual Pb in sediment, this needs further study about the chemical fractions of aerosol Pb. But At least, there is another evidence of this association. Gao and Chen (2012) found that residual Pb closely correlated with EFs of Pb in sediments. This meant that excess Pb in sediment was associated with residual Pb and be of atmospheric origin given that residue fraction of river source represented its natural crustal part. Labile fraction of PHE reveals the potential for anthropogenic disturbance to PHEs in sediments (Backstrom et al., 2004). Enrich-

Fig. 4. Fractions of PHEs in sediments of the ECS.

ment factor provides a quantitative way to assess the pollution status of PHE in sediment (Abrahim and Parker, 2008). EF results showed that V, Cr, Co, Ni and Mo in sediment were basically of natural occurring, in agreement with with high proportion of residual fraction of V, Cr and Mo. Sediment were moderately contaminated by Cu, Zn, Cd and Pb which also had higher proportions of labile fractions. These contaminated elements were consistent with those in previous studies in the Changjiang watershed and the

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33

32

N

33

Ji a ng su

P the C ro. hangji

31

ang R .

32

Shanghai

N

Jia ng s

uP the C ro. hangji a

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Residual V 120

121

122

123

124

125

126

Residual Cu 120

121

122

33

32

N

33

Ji a ng su

P the C ro. hangji an

31

g R.

32

Shanghai

N

uP the C ro. hangji a

31

126

ng R.

Hangzhou Bay

30 Zhejiang Pro.

29

29

Residual Pb 120

121

122

123

124

125

Acid soluble Cd

126

120

121

122

E

N

125

Shanghai

Zhejiang Pro.

32

124

Jia ng s

Hangzhou Bay

30

33

123

E

E

Ji a ng su P the C ro. hangji ang

31

123

124

125

126

E 33

32

R.

Shanghai

N

Jia ng su P the C ro. hangji ang

31

R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Reducible Co 120

121

122

123

124

125

126

E

Reducible Zn 120

121

122

123

124

125

126

E

Fig. 5. Spatial distributions of the major chemical fractions of PHEs in sediments of the ECS.

ECS (Fang et al., 2009, 2004; Lin et al., 2002; Liu and Li, 2011; Zhang and Shan, 2008). Pollution status and anthropogenic sources of these elements were discussed in the following with a combination of EFs and chemical fractions. Cd enrichment was observed at all the stations with the EFs higher than 2. However, it should be noticed that Cd is a nutrient type metal and could be delivered to sediment with marine organic matter (Tribovillard et al., 2006). Biogenic Cd is often associated with calcium organisms and biogenic carbonate in sediments (Lin et al., 2002). However, the EFs (Cd) and acid soluble Cd-the major labile fraction of Cd exhibited distinct distributions with carbonate.

EFs of Cd and acid soluble Cd mainly concentrated along the inner shelf while maximum carbonate located in the southern middle shelf (Figs. 2, 5 and 7). Therefore, excess Cd in the ECS was not caused by biogenic input, but terrestrial pollution. In addition, a significant correlation between acid soluble Cd and residual Cd (R = 0.465, P < 0.001, n = 31) verified the terrestrial origin of acid soluble Cd mainly from the Changjiang and the JCC. Excess input of Cd into water induced by phosphorus fertilizer has been widely reported (Lambert et al., 2007; Zhang and Shan, 2008). Increasing use of phosphorus fertilizer in agriculture has caused elevated Cd content in sediments of the Changjiang watershed (Zhang and

164

Y. Yu et al. / Marine Pollution Bulletin 68 (2013) 157–167

33

32

N

33

Ji a ng su

P the C ro. hangji

31

ang R .

Jia ng s

uP the C ro. hangji a

32

Shanghai

N

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Oxidizable Cu

Reducible Pb 120

121

122

123

124

125

126

120

121

122

123

E 33

32

N

33

Ji a ng su

P the C ro. hangji an

31

124

125

126

E

g R.

Jia ng s

uP the C ro. hangji a

32

Shanghai

N

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

Oxidizable Ni

Oxidizable Co 120

121

122

123

124

125

126

120

121

122

123

E

124

125

126

E 33

32

N

Ji a ng s

uP the C ro. hangji a

31

ng R.

Shanghai Hangzhou Bay

30 Zhejiang Pro.

29

Oxidizable Zn 120

121

122

123

124

125

126

E Fig. 5. (continued)

Shan, 2008). This study revealed that sediments in the ECS, especially those in the coastal area, were polluted with anthropogenic Cd mainly from the Changjiang River. Previous studies have reported Cu enrichment of lake sediments in the Changjiang watershed and of sediments in the inshore ECS, probably resulting from painting industry, mining and waste discharge (Fang et al., 2009; Liu and Li, 2011). In this study, EF distributions presented moderate Cu contamination in coastal sediment (Fig. 7). Analogous to Cd, EFs (Cu) and oxidizable Cu (major species of labile Cu) exhibited typical band-type distribution along the coast. In addition, oxidizable Cu significantly correlated with residual Cu and median grain size with R 0.856 and 0.701 (P < 0.001,

n = 33), respectively. These results implied that anthropogenic Cu was mainly input through terrestrial sediment load. This was consistent with previous report that the Changjiang River was the major source of pollutants in the ECS (Huh and Chen, 1999). High EFs of Pb (2.1–4.5) located in the northern middle shelf. Pb enrichment in this area likely resulted from atmospheric input of Pb pollutant as suggested by the distributions of total and residual Pb. High proportion of labile Pb (39–66%) also revealed great potential of anthropogenic input of Pb. Reducible Pb, the major species of labile Pb, was likely of terrestrial source from the Changjiang and the JCC according to its seaward decreasing distribution (Fig. 5). However, reducible Pb nearly had no correlation

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Y. Yu et al. / Marine Pollution Bulletin 68 (2013) 157–167

Fig. 6. Relationship between Sc (lg/g) and mud content (%) in sediments of the ECS.

with sediment grain size (R = 0.114, P > 0.5, n = 32). Thus, it might be influenced by other processes besides terrestrial aluminosilicate mineral input, for example, authigenic processes. Lead was reported to have strong affinity to particles with aluminosilicates and manganese oxides (Lin et al., 2000). Dissolved Pb in water from aerosol deposition could be scavenged by Mn oxides, whose seaward decreasing trend in the ECS might contribute to the similar distribution of reducible Pb (Lin et al., 2002). Additionally, reducible Pb could be released from sediment in reducing conditions, especially in the hypoxia zone off the Changjiang estuary in summer (Song, 2009).

33

32

N

Jia n

Zn is a common pollution element induced by human activities such as painting industry, mining, and urban life (Buckley et al., 1995). Zn contamination has been found in the tidal flat sediment of the Changjiang estuary and the SPM in the coastal water (Feng et al., 2004; Hsu and Lin, 2010). Zn enrichment in the SPM in the coastal water was probably related to pollutant input from the Hangzhou Bay and Zhejiang coast (Hsu and Lin, 2010). Reducible and oxidizable were major labile forms of Zn in sediments. Reducible Zn generally decreased from land toward sea and had significant correlations with residual Zn (R = 0.506, P < 0.005, n = 33). These results indicated that reducible Zn was mainly from terrestrial sediment load. In contrast, oxidizable Zn showed distribution different from residual Zn and did not correlated with sediment grain size. Oxidizable Zn likely has other source instead of river input. High content of oxidizable Zn in the southern shelf probably resulted from anthropogenic input from heavily polluted Hangzhou Bay and economically-developed Zhejiang Province (Fig. 5) (Hsu and Lin, 2010; Wang et al., 2008). Nevertheless, oxidizable Zn might be also related to authigenic deposition with organic matter (Tribovillard et al., 2006). Good correlations between oxidizable Zn and TOC (R = 0.505, P < 0.005, n = 34) likely indicated that the distribution of oxidizable Zn was influenced by organic matter. Budgets of PHEs in sediments of the studied areas (122–125°E, 29–32.5°N) were calculated. Major influxes of sediment and trace elements in the ECS included sediment load from the Changjiang River, the JCC and atmosphere. Sediment influxes from the Changjiang River and the JCC are 3.97  1011 and 1.0  1011 kg/a, respectively (Data from Datong Station; Hu and Yang, 2001). PHE

33 gs u

P the C ro. hangji an

31

g R.

32

Shanghai

N

Ji a ng s

uP the C ro. hangji a

31

ng R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

EF(Pb)

EF(Cd) 120

121

122

123

124

125

126

120

121

122

33

32

N

Jia n

33 gs uP

the C ro. hangji

31

123

124

125

126

E

E

ang R .

32

Shanghai

N

Jia ng su P the C ro. hangji ang

31

R.

Shanghai

Hangzhou Bay

Hangzhou Bay

30

30 Zhejiang Pro.

Zhejiang Pro.

29

29

EF(Zn) 120

121

122

123

124

125

EF(Cu) 126

120

121

122

E Fig. 7. Horizontal distributions of enrichment factors for Cd, Pb, Zn and Cu.

123

E

124

125

126

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Y. Yu et al. / Marine Pollution Bulletin 68 (2013) 157–167

Table 3 Fluxes of sediment and trace metals in the ECS. Flux

Sediment flux (108 t/a)

V (t/a)

Cr (t/a)

Co (t/a)

Ni (t/a)

Cu (t/a)

Zn (t/a)

Changjiang JCC Atmosphere

3.97 1 –

41288 5820 107.51

48434 7690 16.48

7543 1400 4.95

25487 4030 17.2

24733 2670 860.07

Sedimentation Zone-1 Zone-2 Zone-3

2.31 1.17 0.17

24371 10366 1719

19450 8330 1404

3442 1463 241

8339 3358 587

3.65

36455

29185

5146

12284

Total

compositions in SPM of the Changjiang and Huanghe River were presented in Table 2. Dry deposition fluxes of soluble V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb from atmosphere into the southern ECS are reported as 1.5, 0.23, 0.069, 0.24, 12, 19, 0.027, 0.19 and 2.5 lg/m2/d, respectively (Hsu and Lin, 2010). Fluxes of total PHEs from atmosphere were calculated by dividing the fluxes of soluble species by the solubility of these elements (Hsu and Lin, 2010). A mass accumulation rate of 0.75 g/cm2/a was used to calculate sediment accumulation in zone-1 (122–123°E, 29–31.5°N) (Huh and Su, 1999). Sedimentation rate on the border between the ECS and the Yellow Sea ranges from 0.1 to 0.5 cm/a (Li et al., 2002b). Sedimentation rate in station A6 is determined to be 0.18 cm/a (Yu et al., 2012). Thus sedimentation rates of 0.3 cm/a and 0.18 cm/a were employed to calculate sediment accumulation in zone 2 (122–124.5°E/31.5–32.5°N) and zone-3 (124.5–125°E/31–32.5°N), respectively. Sedimentation in zone 4 was not included considering much less terrestrial sediment input and strong winnowing in the relict area (Zhu et al., 2011; Hu and Yang, 2001). The results allowed 2.31  108 t/a of sediment accumulations along the coast, 1.17  108 t/a in the northern ECS and 0.17  108 t/a in the margin of offshore upwelling area. Sediment accumulation along the coast accounted for 58% of the annual sediment load from the Changjiang River, which was in agreement with previous studies (Milliman et al., 1985b). In addition, sediment accumulation in the northern ECS and offshore upwelling areas is also reasonable in view of sediment load from the JCC. PHE concentrations in surface sediments were used to calculate sedimentation fluxes of PHEs. As was shown in Table 3, the Changjiang River was the major source of sediment to the ECS, accounting for 80% of total sediment input assuming that atmospheric input could be neglected. About 46% of total sediment load was deposited in inshore area, 23% in the northern ECS and 3.5% in the offshore upwelling waters. Accordingly, PHEs were mainly from the Changjiang River, which contributed 82–90% of total metal input. Atmospheric fluxes of Cu, Zn, Cd and Pb accounted for 3%, 3%, 7% and 1% of their total influx, respectively, which were much higher than the proportions of other elements (<0.2%). This probably suggested the pollution of Cu, Zn, Cd and Pb from atmosphere. Thirty-eight to seventy-seven percent of trace elements were finally deposited, among which 27– 52% deposited in inshore area, 10–22% in the northern ECS and 2– 4% in the offshore upwelling area. Among the nine elements, Ni, Cu, Cd and Pb had relatively low proportions of sedimentation (42%, 38%, 47% and 55%, respectively). In agreement with their high proportions of labile fractions, low burial efficiency of Ni, Cu, Cd and Pb probably resulted from the regeneration of these elements from sediment or suspended particles. Distributions of EFs of Cd and Zn illustrated that terrestrial pollutant dispersed over a large extent along the shelf of the ECS (Fig. 7), although the majority of terrestrial sediment was deposited in the inner shelf east to 123°E (Milliman et al., 1985b). Excess Cd, Zn and Pb in offshore sediments might originate from the dispersal of terrestrial sediment, atmospheric input or scavenging input from water by carbonate, Fe/Mn oxides or organic matter (Lin

Mo (t/a)

Cd (t/a)

Pb (t/a)

38787 6980 1361.78

1.94

174.7 18 13.62

15840 1650 179.18

7646 2738 458

23654 8997 1613

138.6 58.5 8.6

69.3 23.4 3.4

6468 2750 467

10842

34264

205.7

96.1

9684

et al., 2000; Tribovillard et al., 2006). Furthermore, it is worth noticing that pollution elements including Cu, Zn and Pb had much lower concentrations and EFs in sediments than those in the coastal SPM reported by Hsu and Lin (2010) (Table 2). This phenomenon was also observed in the Changjiang River (Zhang and Liu, 2002). In addition, Liu and Li (2011) found that sediment of the lakes in the Changjiang region was mainly of natural occurring while lake water showed heavy metal pollution. Therefore, sediment seemed to be less sensitive to metal pollution than water and SPM did. This might be due to high self-purification capacity of marine system, in which dissolution of metals from SPM and sediment in early diagenesis and material exchange between contaminated particles and clean ocean water frequently happened. The dissolution of metals was also verified by low bury percentage of PHEs in the ECS. In conclusion, combined application of EFs and chemical fractionations was an effective way to evaluate the pollution status of sediment and identify pathways of anthropogenic input of PHEs. Acknowledgements This research was supported by the Natural Science Foundation of China for Creative Research Groups (No. 41121064), the National Basic Research Program (973) of China (No. 2011CB403602) and the National Natural Science Foundation of China (No. 40906056). References Abrahim, G.M.S., Parker, R.J., 2008. Assessment of heavy metal enrichment factors and the degree of contamination in marine sediments from Tamaki Estuary, Auckland, New Zealand. Environ. Monit. Assess. 136, 227–238. Backstrom, M., Karlsson, S., Allard, B., 2004. Metal leachability and anthropogenic signal in roadside soils estimated from sequential extraction and stable lead isotopes. Environ. Monit. Assess. 90, 135–160. Buckley, D.E., Smith, J.N., Winters, G.V., 1995. Accumulation of contaminant metals in marine sediments of Halifax Harbour, Nova Scotia: environmental factors and historical trends. Appl. Geochem. 10, 175–195. Bulletin of China’s Marine Environmental Status of China for the year of 2002–2010. State Oceanic Administration, People’s Republic of China, 2002–2010. (in Chinese). Fang, T.H., Li, J.Y., Feng, H.M., Chen, H.Y., 2009. Distribution and contamination of trace metals in surface sediments of the East China Sea. Mar. Environ. Res. 68, 178–187. Feng, H., Han, X.F., Zhang, W.G., Yu, L.Z., 2004. A preliminary study of heavy metal contamination in Yangtze River intertidal zone due to urbanization. Mar. Pollut. Bull. 49, 910–915. Gao, X., Chen, C.-T.A., 2012. Heavy metal pollution status in surface sediments of the coastal Bohai Bay. Water Res. 46, 1901–1911. Grousset, F.E., Quetel, C.R., Thomas, B., Donard, O.F.X., Lambert, C.E., Guillard, F., Monaco, A., 1995. Anthropogenic vs lithogenic origins of trace-elements (as, Cd, Pb, Rb, Sb, Sc, Sn, Zn) in water column particles – northwestern mediterraneansea. Mar. Chem. 48, 291–310. Hu, D.X., Yang, Z.S., 2001. Key Processes of the Ocean Flux in the EAST China Sea. Ocean Press, Beijing. Hsu, S.C., Lin, F.J., 2010. Elemental characteristics of surface suspended particulates off the Changjiang estuary during the 1998 flood. J. Mar. Syst. 81, 323–334. Huh, C.A., Chen, H.Y., 1999. History of lead pollution recorded in East China Sea sediments. Mar. Pollut. Bull. 38, 545–549. Huh, C.A., Su, C.C., 1999. Sedimentation dynamics in the East China Sea elucidated from Pb-210, Cs-137 and Pu-239, Pu-240. Mar. Geol. 160, 183–196. Kazi, T.G., Jamali, M.K., Kazi, G.H., Arain, M.B., Afridi, H.I., Siddiqui, A., 2005. Evaluating the mobility of toxic metals in untreated industrial wastewater

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