Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis

Marine Pollution Bulletin xxx (2014) xxx–xxx

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Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis Feng Li a,⇑, Jin-qin Lin b,c, Yan-yan Liang a, Hua-yang Gan b,c, Xiang-yun Zeng a, Zhi-peng Duan a, Kai Liang b,c, Xing Liu b,c, Zhen-hai Huo b,c, Chang-hua Wu a a b c

South China University of Technology, Guangzhou 510641, China Guangzhou Marine Geological Survey, Guangzhou 510760, China Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources, Guangzhou 510760, China

a r t i c l e

i n f o

Keywords: Potential ecological risk assessment Trace metals Coastal surface sediments Leizhou Peninsula AVS SEM

a b s t r a c t Surface sediments from the coastal area of the Leizhou Peninsula in the South China Sea were collected and analyzed and the potential ecological risks in the area were assessed based on acid-volatile sulfide (AVS) model. The AVS levels are between 0.109 and 55.6 lmol g1, with the average at 4.45 lmol g1. The high AVS-concentration zones include the aquaculture areas of Liusha Bay and the densely populated areas of Zhanjiang Bay. The simultaneously extracted metals (SEM) range from 0.026 lmol g1 to 8.61 lmol g–1, with the average at 0.843 lmol g–1. Most of high SEM-concentration stations were located in ports or aquaculture zones. Most of the coastal surface sediments of the Leizhou Peninsula (90%) had no adverse biological effects according to the criterion proposed by USEPA (2005); while adverse effects were uncertain in some stations (8%); even in 2 stations (2%) adverse biological effects may be expected. Ó 2014 Elsevier Ltd. All rights reserved.

Trace-metal toxicity has been an ecological concern because of the difficult removal of these metals from aquatic ecosystems via ecosystem self-purification. These metals can be accumulated in sediments and thus pose risks to human health and ecosystems via the food web (Lee et al., 2001). Estuarine and coastal areas are often with high population densities and intensive human activities, and the environment will face greater pressure for the anthropogenic impacts (Mucha et al., 2005; Gan et al., 2013). Most of the metals discharged have settled in the coastal sediments, since sediments are the main sink for metals in aquatic ecosystems (Wang and Chapman, 1999; Burton et al., 2005); however, when environmental conditions change, metals in sediments may release to the overlying water, making the sediments become internal pollution sources (Morse and Rickard, 2004; Morgan et al., 2012). Therefore, the potential ecological effects of trace metals in coastal sediments must be evaluated when potential risks assessment of coastal ecosystem is conducted (Zhuang and Gao, 2013). In China, the massive economic growth and urban development in the coastal areas in the last three decades have led to excessive release of waste into estuarine and coastal environments (Chen et al., 2006; Gan et al., 2013). It is necessary to investigate whether those metals in the coastal sediments have poses a threat to the health of ecosystems (Gao et al., 2013). ⇑ Corresponding author. Tel./fax: +86 02087114460. E-mail address: [email protected] (F. Li).

The acid-volatile sulfide (AVS) model has been regarded as a good approach of sediment quality assessment that could relatively evaluate potential risks of metals accurately with the additional advantages of simple operation, high efficiency and batch processing (Allen et al., 1993; Brouwer and Murphy, 1994; De Lange et al., 2008). AVS is operationally defined as the amount of sulfide that can be volatilized during extraction with cold 1 M HCl (Di Toro et al., 1990; Morse and Rickard, 2004). The metals extracted in the AVS extraction procedure (mainly including Cd, Cu, Ni, Pb and Zn), are called simultaneously extracted metals (SEM) (Di Toro et al., 1990). AVS is regarded as one of the major chemical components that control the speciation and the environmental risks of heavy metals in aquatic sediments on the basis of the fact that it will combine with divalent metals to form stable metal sulfides reducing the bioavailability of trace metals (Casas and Crecelius, 1994; Cooper and Morse, 1998). Hence, the difference between the sum of the molar concentrations of SEM and AVS was proposed as an important indicator of the bioavailability and ecological risk of trace metals (Di Toro et al., 1990; Ankley, 1996). However, many other binding phases also can remove metals from pore water to decrease the metal toxicity, consequently, Di Toro et al. (2005) proposed a revised AVS model considering the TOC, and it has been verified to be more reasonable than the previous model (De Jonge et al., 2010; Keene et al., 2010). The Leizhou Peninsula, located in Guangdong Province (Fig. 1) between Hainan Island and the Northern Beibu Gulf, is the biggest

http://dx.doi.org/10.1016/j.marpolbul.2014.04.030 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

Fig. 1. The study area and sampling stations.

peninsula in South China, covering an area of 8888 km2 and with a 1450 km long coastal line. Though regarded as the less-developed coastal areas of China, the environmental contamination and degradation in the coastal areas of this Peninsula also have been evident (Liang et al., 2006). There are sporadic studies about metals pollution the coastal areas of the Leizhou Peninsula (Guo and Huang, 2006; Yu, 2009); however, they were limited to Zhanjiang Bay and only focused on the total amount of trace metals. To date, no large-scale specialized research on trace metal pollution, particularly on SEM–AVS, has been conducted throughout the Leizhou Peninsula, mainly because of the high cost and unavailability of human resources and materials. This study aims to evaluate the ecological risk of trace metal in coastal surface sediments throughout the Leizhou Peninsula based on the AVS model. The study area is the coastal surface sediments (a shallowwater region with a depth of <6 m) throughout the Leizhou

Peninsula (Fig. 1). Sampling was conducted on May 2012 and lasted for one month. Surface sediment (0–5 cm) samples were collected in shallow water areas using a Van Veen grab sampler from a small vessel or in beach areas using a plastic spatula. Cores were obtained by using 75 mm diameter PVC liners. The PVC liners were slowly pushed into the sediment to minimize compaction. A total of 90 surface samples and 10 cores (Fig. 1) were collected. After collection, the surface sediment samples were immediately placed in plastic bags filled with N2. The bags were sealed and then placed in a box filled with ice (De Lange et al., 2008). The samples were stored at 4 °C in the laboratory for future analyses. The core samples were sealed, placed in an icebox, and then split under N2 conditions. The top layers of the core samples (0–5 cm) were obtained and used to represent the surface sediments of the corresponding stations. Thus, a total of 100 coastal surface sediments were included in this study.

Table 1 Pearson correlation coefficients between the parameters of sediment samples from Leizhou Peninsula. AVS AVS SEMCu SEMPb SEMCd SEMNi SEMZn SEM TOC a b

1 0.271b 0.388b 0.037 0.034 0.069 0.080 –

SEMCu

SEMPb

b

b

0.271 1 0.728b 0.099 0.328b 0.264b 0.291b –

0.388 0.728b 1 0.048 0.283b 0.473b 0.505b –

SEMCd 0.037 0.099 0.048 1 0.050 0.202a 0.309b –

SEMNi 0.034 0.328b 0.283b 0.050 1 0.417b 0.427b –

SEMZn 0.069 0.264b 0.473b 0.202a 0.417b 1 0.992b –

SEM 0.080 0.291b 0.505b 0.309b 0.427b 0.992b 1 –

%TOC

%Sand b

0.349 0.706b 0.628b 0.008 0.121 0.115 0.148 1

%Silt a

0.213 0.621b 0.519b 0.069 0.150 0.069 0.092 0.788b

0.163 0.628b 0.538b 0.091 0.172 0.116 0.134 0.770b

%Clay

%Water content b

0.304 0.632b 0.486b 0.067 0.114 0.026 0.051 0.780b

0.346b 0.709b 0.661b 0.218a 0.137 0.272b 0.324b –

p < 0.05. p < 0.01.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

Fig. 2. The ternary diagram showing the classification of the composition of coastal surface sediment samples collected from the Leizhou Peninsula.  ‘4’ represents the composition of coastal surface sediment in the sampling station.

AVS and SEM were determined via the purge-and-trap method (Allen et al., 1993). The concentration of AVS in the absorption solution was measured spectrophotometrically at 670 nm with

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the detect limit of 0.00016 lmol L–1. Percent recovery was estimated from the analyses of standards prepared from appropriate quantities of a standardized Na2S solution (84.7% ± 5.1%, n = 10). The SEMs of Cu, Pb, Zn, and Ni were determined using inductively coupled plasma-atomic emission spectrometry (Perkin– Elmer Optima 5300DV) with detection limits of 0.045 lmol L–1 for Cu, 0.011 lmol L–1 for Pb, 0.069 lmol L–1 for Zn, and 0.079 lmol L–1 for Ni. Cd concentration was determined using a graphite furnace (Hitachi Z-2700) with the detection limit of 0.009 nmol L–1. Certified reference materials (GSB-04-1767-2004, GSB-04-1721-2004) were used. All glassware and plasticware were cleaned by soaking in 10% HNO3 (v/v) for 24 h, followed by soaking and rinsing with deionized water (Milli-Q). All reagents used in the experiment were at least of analytical grade. The blank, replicate, and spiked samples were analyzed in each batch of test samples. The particle size distributions of all samples were determined using sieve and laser particle size analyses. Fine grain samples were directly analyzed by using a Mastersizer 2000 laser particle analyzer (Malvern Instruments Ltd., UK), which allowed measurements from 0.02 lm to 2000 lm and error repeatability of <3%. Total organic carbon (TOC) was determined using potassium dichromate oxidation–ferrous sulfate titrimetry (GAQS-IQ, 2008). Water content was gravimetrically determined by comparing the wet weight with the dry weight, which was obtained by heating an aliquot at 105 °C and repeating the post-heating measurements until a constant weight was obtained.

Fig. 3. The spatial distribution of total organic carbon (TOC) in the coastal surface sediments (shallow water area with depth < 6 m).

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

The general characteristics, such as the water contents, grain sizes, and TOC concentrations, of the surface sediment samples were also determined for correlation analyses (Table 1). The ternary diagram in Fig. 2 categorized the coastal sediments of Leizhou

Peninsula using the system proposed by Shepard (1954). It reveals that the composition of the sediments belongs to 5 categories: sand (51%), clayey–silt (21%), sand–silt–clay (16%), silt–sand (11%), and sandy–silt (1%). Generally, coarse fractions accounted

Fig. 4. The spatial distribution of acid volatile sulfide (AVS) in the coastal surface sediments (shallow water area with depth < 6 m).

Table 2 Details of the 14 stations where the concentration of AVS > 10 lmol g1. Stations

Coordinates

Location

AVS (lmol g1)

Surrounding environment

1 2

BS12D147 BS12D190

109°53’02.700 E, 20°25’01.700 N 110°24’05.300 E, 21°08’1200 N

Southwest of Liusha Bay West of Zhanjiang Bay

55.6 46.2

3 4 5

BS12D138 BS12D145 BS12D202

109°47’03.900 E, 20°37’4500 N 109°52’42.900 E, 20°26’08.300 N 110°25’12.800 E, 21°10’2100 N

21.2 18.9 15.7

6 7

BS12D176 BS12D201

110°16’59.100 E, 20°53’03.500 N 110°25’08.600 E, 21°15’44.600 N

15.6 13.7

8 9

BS12D139 BS12D215

109°48’36.300 E, 20°34’31.800 N 110°27’33.100 E, 21°09’00.600 N

12.8 11.5

Aquaculture zone Aquaculture zone

10 11 12 13

BS12D165 BS12D232 BS12D127 BS12D 189

110°11’09.500 E, 110°31’18.600 E, 109°38’30.300 E, 110°22’33.900 E,

North of Wushi Bay West of Liusha Bay North of Zhanjiang Bay (Nearby Xiashan District) South of Zhanjiang Bay North of Zhanjiang Bay (Nearby downtown of Zhanjiang City) South of Wushi Bay North of Zhanjiang Bay (Southwest of Techeng Island) Haian Bay North of Zhanjiang Bay (Nanshan estuary) South of Caotan Bay South of Zhanjiang Bay (West of Naozhou Island)

Aquaculture zone Mangrove zone (artificial cultivation), Nearby the sewage outfall Aquaculture zone Aquaculture zone Mangrove zone (artificial cultivation), Nearby the sewage outfall Aquaculture zone Mangrove zone (artificial cultivation)

11.5 11.2 10.9 10.0

Aquaculture Aquaculture Aquaculture Aquaculture

Sequence

20°14’14.200 N 21°12’28.200 N 21°08’18.400 N 20°53’16.100 N

zone, nearby mangrove zone zone zone, nearby mangrove zone zone

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx Table 3 The comparison of acid-volatile sulfide (AVS), and simultaneously extracted metals (SEMa) in this study with similar studies at home and abroad. Location Present study

[SEM]a (lmol g1)

SEMZn (lmol g1)

SEMCu (lmol g1)

SEMPb (lmol g1)

SEMNi (lmol g1)

SEMCd (nmol g1)

0.026–8.606

0.022–8.212

0.001–0.161

0.001–0.185

0.001–0.069

0.03–0.826

References

Mean

0.109– 55.552 4.451

0.843

0.757

0.031

0.045

0.01

0.146

Jinzhou Bay, China

Range

3.02–126

2.9–374

–

–

–

–

–

Hansen et al. (1996)

Laizhou Bay, China

Range Mean Range Mean

1.22–7.60 2.99 0.71–11.03 4.05

0.20–0.74 0.45 0.10–0.57 0.32

0.064–0.278 0.165 0.052–0.216 0.137

0.051–0.310 0.166 0.026–0.247 0.109

0.014–0.097 0.044 0.01–0.067 0.039

0.033–0.138 0.074 0.013–0.046 0.034

1.1–3.3 2.0 0–1.3 0.7

Gao et al. (2013)

Zhangzi Island, China

Range

AVS (lmol g1)

Shen’ao Bay, China

Range

0.04–39.09

–

–

–

–

–

–

Du et al. (2011)

Zhangjiang Estuary, Fujian, China

Range

0.2–12.5

1.4–2.1

0.731–1.391

0.152–0.324

0.115–0.197

0.095–0.207

0.623–1.690

Liu et al. (2010)

Douro Estuary, Portugal

Range Mean

0.004–2.8 0.932

0.12–1.7 0.624

– –

– –

– –

– –

– –

Mucha et al. (2005)

Guadalete River Estuary, Spain

Range

0.594– 1.136

0.308–0.981

–

–

–

–

–

Campana et al. (2005)

Guanabara bay, Brazil

Range

97–187

3.5–6.2

–

–

–

–

–

Machado et al. (2004)

Note: ‘‘–’’ refer to no data (Not available in the original paper). a The sum of the SEMZn, SEMPb, SEMNi, SEMCu, and SEMCd.

Fig. 5a. The spatial distribution of acid-extracted metals (SEMPb, SEMCd, SEMNi, SEMZn, SEMCu) and SEM (The sum of the SEMZn, SEMPb, SEMNi, SEMCu, and SEMCd) in the coastal surface sediments (shallow water area with depth <6 m). SEM (The sum of the SEMZn, SEMPb, SEMNi, SEMCu, and SEMCd).

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

for the larger proportion of in sediments samples from the Leizhou Peninsula. The TOC concentrations in the sediment are shown in Fig. 3. The values ranged from 0.01% to 1.35%, with an average of 0.41%. The highest TOC content was obtained in BS12D190 in Zhanjiang Bay, which is a sediment sample collected from the estuary of a creek discharging large amount of domestic sewage rich in organic matter. Silt and clay were both significantly and positively correlated with the TOC, whereas sand was negatively correlated with the TOC (Table 1). These results indicate that the TOC contents were usually lower in sediments with coarser components (Gao et al., 2013). However, the situations of station BS12D141 were a bit different, where gravel and sand accounted for 54.5% in the composition of the sediment (gravel 21.8%, sand 32.7%, silt 34.0%, clayer 11.5%), whereas TOC content is still relatively high (1.05%). The AVS concentrations in the surface sediment samples from the Leizhou Peninsula were shown in Fig. 4. The AVS concentrations in the Leizhou Peninsula sediments ranged from 0.109 lmol g1 to 55.6 lmol g1, with an average of 4.45 lmol g1. The highest AVS (55.6 lmol g1) was recorded in station BS12D147 in Liusha Bay, a famous aquaculture area for both shellfish and fish. It has been reported that aquaculture may accelerate sulfur accumulation (Asami et al., 2005; Wang et al., 2006), hence, it may be reasonable to link the high concentration of AVS with the aquaculture in this bay, which is the biggest pearl hatchery, breeding, and processing base in China. This might result from two reasons: the organic matter (including the compound of C, N, P, S) will

accumulate in sediments because of large amounts of uneaten food and fish feces produced by intensive fish farming (Yokoyama et al., 2004); the process of sulfate reduction will accelerate in the anaerobic conditions rich in organic matter (Asami et al., 2005; Wang et al., 2006). The anaerobic conditions are more often occur in the surface sediments in aquaculture zones where the cages hinder the water exchange and oxygen usually deplete by organ matter. Last but not least, the problem of excessive aquaculture is popular in the Leizhou Peninsula, which makes the situations even worse. Take Liusha Bay for instance, it has been reported in October 2011 by Guangdong TV that a large number farmed fish was dead because of high-density aquaculture combined with poor weather conditions (Guangdong TV, 2011). Sediment AVS concentrations of >10 lmol g1 were determined in 13 stations, mainly from the aquaculture zones and sewage-discharge zones (Table 2), indicating anthropogenic activity have closely been associated with the increase of AVS concentrations. There are 3 stations located in the intertidal zone, and their concentrations of AVS are relatively low. The sediment collected from station BS12D135 (the intertidal zone) has been identified the lowest AVS concentration (0.109 lmol g1) in all the samples in this study. Low AVS concentrations also have been found in two other sediment samples from the intertidal zone (BS12D148, 2.64 lmol g–1; BS12D223 1.27 lmol g–1), whose concentrations are both lower than the average value. The AVS concentration of the intertidal sediment was low, possibly because the surface sediments, which were under aerobic conditions for a long period,

Fig. 5b. SEMPb.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

have been eroded by seawater under strong hydrodynamic conditions. The sediment AVS concentration may vary with factors such as Eh, presence of clay, and other variables, which affect the rate of sulfate reduction (Prica et al., 2008). The correlation matrix for the sediment components in this study are shown in Table 1. The AVS concentration is significantly and positively correlated with the TOC (r = 0.349, p < 0.01), clay (r = 0.304, p < 0.01), and water content (r = 0.346, p < 0.01) but is negatively correlated with sand (r = 0.213, p < 0.05), suggesting less coarse sediment fractions, higher TOCs and higher water contents, favor AVS formation in general. Table 3 presents the comparison between the AVS concentrations of this study and the results of the similar studies at home and abroad. Compared with the other coastal areas of China, the AVS concentrations in this study varied in a range that was similar with Shen’ao Bay (Du et al., 2011); wider than the range of values for sediments in Laizhou Bay and Zhangzi Island (Gao et al., 2013), Zhangjiang Estuary (Liu et al., 2010); while narrower than Jinzhou Bay (Hansen et al., 1996). Table 3 also shows that the average of AVS in this study is at the same level with Laizhou Bay and Zhangzi Island (Gao et al., 2013). The comparison results with the study areas at abroad show that the range of AVS in this study is wider than those in Douro Estuary in Portugal (Mucha et al., 2005) and Guadalete River estuary in Spain (Campana et al., 2005), while narrower than that of Guanabara Bay in Brazil (Machado et al., 2004). In addition, the mean AVS concentration

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in this study is higher than obtained in Douro Estuary, Portugal (Mucha et al., 2005). Fig. 5a shows that the SEM (which is the sum of the Cu, Zn, Pb, Cd, and Ni concentrations) in the coastal surface sediments, ranging from 0.026 lmol g–1 to 8.61 lmol g–1, with the average at 0.843 lmol g–1. Zn was the major component in the total amount of SEM, accounting for approximately 65.5–99.0% with the average of 84.7%, whereas the contribution of Cd to SEM was less than 1%. The above results are consistent with those results of Gao et al. (2013) and Zhuang and Gao (2013). The concentrations of the acid-extracted trace metals that contribute to SEM are ranked in the following order: Zn > Cu > Pb > Ni  Cd (Figs. 5b–5f). As is shown in Table 1, the significant correlations between metals and physical–chemical parameters of sediments revealed that general characteristics, such as the grain size distribution, TOC and water content probably played important roles in controlling the behaviors of metals in the coastal surface sediments of Leizhou Peninsula. However, the situation is not same when the various metals were specified. TOC content, water content and the grain size distribution appeared to significantly affect the concentrations of Cu and Pb, while the concentrations of Zn, Cd, Cu and Pb appeared to be strongly influenced by water content. Significant correlations also were evident between the five metals (Table 1), indicating that these metals were associated with each other and might have common anthropogenic and natural sources in the sediments (Zhuang and Gao, 2013; Li et al., 2013).

Fig. 5c. SEMCd.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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The lowest value (0.026 lmol g–1) of SEM was identified in station BS12D135 (109°450 4.000 E, 20°450 47.000 N), located in the outer edge of Qishui Bay where anthropogenic impact is relatively low, hence, it was chosen to be the reference site. Sediment SEM concentrations of >2 lmol g1 were listed and compared with the reference station in Table 4 to identify the occurrence of pollution. It can been seen from Table 4 that their concentrations are much higher than the reference site (from 91 to 331 times), identifying the existence of metals pollution in Leizhou Peninsula. It is noted that SEM concentrations in aquaculture area are frequently high similar to the distribution of AVS. The highest SEM concentration was obtained from station BS12D145 located in Liusha Bay where the highest value of AVS also has been identified. The high concentrations were also observed in stations BS12D146 and BS12D139 located in aquaculture zone, where SEM concentrations were 3.97 and 3.90 lmol g–1, respectively. Significant positive correlations between AVS and SEMCu and SEMPb (Table 1) implied that they might have similar formative and existing conditions and that AVS was an important carrier for SEM (Zhuang and Gao, 2013). Hence the cause of high concentrations in aquaculture areas might be similar to the cause of AVS to some degree. In addition, it has been reported that fish drug containing hazard materials including metals such as Cu, and Pb, have often been excessively used in aquaculture (Sutherland et al., 2007; Mendiguchía et al., 2006; Cai et al., 2010). Given this, the abuse of fish drug and the

high-density aquaculture could contribute a lot to the accumulation of metals in aquaculture zones. The results of SEM content in the Leizhou Peninsula also were compared with the coastal areas at home and abroad, as revealed in Table 3. It can be seen in Table 3 that the mean SEM content in this study is similar to those of Douro Estuary in Portugal (Mucha et al., 2005), Laizhou Bay and Zhangzi Island in China (Gao et al., 2013); while the range of SEM in this study is wider than the aforementioned studies. In fact, that the variation degree of SEM in the Leizhou Peninsula is in second place in terms of all the studies listed in Table 3, being next only to that of Jinzhou Bay (Hansen et al., 1996). Table 5 compares the sediment values with the sediment quality standards of several countries, including the USA (Long et al., 1995; Buchman, 2008), Australia and New Zealand (Hübner et al., 2009), and China (SOAPRC, 2002). The results show that except for Zn and Pb in a few stations, metals concentrations are relatively low in most of the stations. Generally speaking, Zn pollution is more obvious than Pb. As is shown in Table 5, there are only 2 stations (stations BS12D145 and BS12D186, located in Zhanjiang Bay and Liusha Bay, respectively) exceeding the threshold effects level (TEL, SQGs of Australian and New Zealand), while the concentrations of Zn exceed the standards of TEL in seven stations, among which 2 stations (BS12D137 and BS12D145) were also over than the standards of PEL (SQGs of Australian and New Zealand). The

Fig. 5d. SEMNi.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

comparing results with SQGs of USA indicated that Zn concentrations were exceed the standard of ERL in 6 stations, among which 1 station (BS12D145) was also greater than the standards of ERM. The results of comparing with SQGs of China show that the Zn concentration in 6 stations was over than the standard of first class, among which 2 stations (BS12D137 and BS12D145) were also exceed the standards of second class. It is worth mentioning that all of the stations whose metal concentrations exceeded the above standards were located in ports or aquaculture zones. These results were consistent with the water quality monitoring and analysis results by the environmental monitoring stations of Zhanjiang (Yu, 2009), whose results identified the Pb and Zn pollution after analyzing the surface and bottom layers of water collected from Zhanjiang Bay from April 2002 to April 2007. In general, the pollution sources of coastal area caused by anthropogenic impact could roughly be divided into four categories: waste water and garbage discharged by coastal area; upstream pollutants brought by the river; pollutants by aquaculture; pollutants by ships. In the past decades, environmental management of ports has been ignored in the Leizhou Peninsula. Wastewater and garbage produced around the ports have been discharged into the waters, even worse, some dangerous solid waste in the trash also have been discharged into the sea because garbage classification is not implemented in the China. Furthermore metals pollution by discarded batteries is worth mentioning, including batteries mixed with discarded garbage and batteries used in the

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ships (Guo and Huang, 2006; Yu, 2009). For decades, the battery recycling has not been carried out yet, and most of the used batteries have been discarded directly, carrying large amount of metals into the ecosystem. Take station BS12D137 for example, it is located in the outer edge of Caotan Bay (far from the land). Although there are no obvious pollution sources nearby, the concentration of SEM is up to 6.20 lmol g–1; thus it is inferred that the abnormal high concentration of metals may be linked with the batteries discarded by ships. The ships could be one of the important sources of Zn in the Leizhou Peninsula especially as far as ports are concerned. Since Zn is widely applied in the anticorrosion of hull, its concentration in seawater may increase because of seawater-induced erosion and Zn in water will eventually settle down in sediments. In addition, organic matter from wastewater may hasten the accumulation of metals in sediments because of the adsorption, and flocculation effects (Machado et al., 2004; Li et al., 2013) and it is partly verified by the significant correlation between TOC content and metals in Table 1. In addition to untreated domestic wastewater, the discharged wastewater rich in organic matter also includes the discharge of waters produced by intensive shrimp ponds with high levels of nutrients and suspended solids (Burford et al., 2003), and they also contribute to the metals pollution in this study. With the in-depth understanding of metals pollution, the idea has been widely accepted that metals concentrations in sediments alone do not suffice for the evaluation of bioavailability/toxicity or

Fig. 5e. SEMZn.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

Fig. 5f. SEMCu.

Table 4 The 7 stations where the concentration of [SEM]a>2 lmol g1.

a

Sequence

Stations

Coordinates

1 2 3 4 5 6 7

BS12D145 BS12D137 BS12D146 BS12D139 BS12D138 BS12D128 BS12D206

109°520 42.900 E, 109°430 42.700 E, 109°530 05.400 E, 109°480 36.300 E, 109°470 03.900 E, 109°390 38.500 E, 110°250 30.600 E,

20°260 08.300 N 21°190 38.800 N 20°270 16.800 N 20°340 31.800 N 20°370 45.000 N 20°590 04.400 N 20°360 46.200 N

Location

[SEM]a (lmol g1)

Comparison with the Reference site (times)

Liusha Bay Caotan Bay Liusha Bay Wushi Bay Wushi Bay Jianghong Bay Jinhe Bay

8.61 6.20 3.97 3.90 3.46 3.20 2.37

331 239 153 150 133 123 91

The sum of the SEMZn, SEMPb, SEMNi, SEMCu, and SEMCd.

Table 5 The comparison of metals concentrations in the coastal surface sediment in Leizhou Peninsula with the sediment quality guidelines. References

Cu (lmol g1)

Pb (lmol g1)

Range of this study

–

0–0.161

0.001–0.185

0.030–0.826

0–0.069

0.022–8.212

Average of this study

–

0.031

0.046

0.146

0.009

0.761

TEL (Threshold effects level) PEL (Probable effect levels)



SQGs of Australian and New Zealand (Hübner et al., 2009)

0.294 1.700

0.146 (2) 0.541

6.049 37.452

0.271 0.729

1.897 (7N) 4.145 (24)

ERL (Effects range low) ERM (Effect range median)

 SQGs of USA (Long et al., 1995; Buchman, 2008))

0.535 4.249

0.225 1.052

10.675 85.401

0.356 0.879

2.294 (6H) 6.271 (1I)

The first class The second class The third class



0.551 1.574 3.148

0.290 0.627 1.207

4.448 13.344 44.480

– – –

2.294 (6) 5.353 (2}) 9.177

SQGs of China (SOAPRC, 2002)

Cd (nmol g1)

Ni (lmol g1)

Zn (lmol g1)

Note: Proposed by ANZECC (Australian and New Zealand Environment and Conservation Council). Proposed by NOAA (National Oceanic and Atmospheric Administration, USA). Proposed by SOAPRC (State Oceanic Administration People’s Republic of China). 2 Pb concentration in 2 stations exceed TEL. 7N Zn concentration in 7 stations exceed TEL. 24 Zn concentration in 2 stations exceed PEL. 6H Zn concentration in 6 stations exceed ERL. 1I Zn concentration in 1 stations exceed ERM. 6 Zn concentration in 6 stations exceed the first class (SQGs of China). 2 } Zn concentration in 2 stations exceed the second class (SQGs of China).

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

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F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx Table 6 The criteria used in this study and the classification results. Sediment quality guideline

Classification

Criterion used to determine classification

References

Number of stations

[SEM]–[AVS]

Category 1 Category 2 Category 3

[SEM]–[AVS] > 5 [SEM]–[AVS] = 0 to 5 [SEM]–[AVS] < 0

USEPA (2004)

0 22 78

([SEM]–[AVS])/fOC

Category 1 Category 2 Category 3

([SEM]–[AVS])/fOC > 3000 ([SEM]–[AVS])/fOC = 130–3000 ([SEM]–[AVS])/fOC < 130

USEPA (2005)

2 9 89

([SEM]–[AVS])/fOC

Category 1 Category 2 Category 3

([SEM]–[AVS])/fOC>3400 ([SEM]–[AVS])/fOC=150–3400 ([SEM]–[AVS])/fOC<150

Di Toro et al. (2005)

2 8 90

Note: [SEM]–[AVS] unit: lmol g1 (dry weight); ([SEM]–[AVS])/fOC unit: lmol g1 OC (dry weight).

Fig. 6. The spatial distribution of [SEM]–[AVS] (the difference between [SEM] and AVS) in the coastal surface sediments (shallow water area with depth < 6 m). ⁄ [SEM] = SEMZn + SEMPb + SEMNi + SEMCu + SEMCd.

pollution status across sediments (Luoma, 1989; Long et al., 1995). It has been demonstrated that the AVS model can be used as an indicator of the degree of pollution of sediment for a wide range of sediment types that involve freshwater and seawater (Di Toro et al., 1990; Ankley, 1996). In its early edition, this model has been proposed the potential ecological risk can be predicted on the basis of SEM–AVS (Casas and Crecelius, 1994; Hansen et al., 1996; Grabowski et al., 2001). According to this model, when SEM– AVS < 0 (on a molar basis), a low probability of toxicity would be expected because there is enough combining phase for reacting with metals to form insoluble sulfides which are non-bioavailable for benthic organisms (Di Toro et al., 1990; De Jonge et al., 2010).

On the contrary, when SEM–AVS > 0, the excess fraction of the divalent metals may potentially exist as free metal ions in the pore water and become potentially toxic to the aquatic life. One criterion for assessing the sediment quality on the basis of SEM–AVS has been proposed by USEPA in 2004. Based on this criterion, the sediment samples can be divided into the three following categories: Category 1, adverse effects on aquatic life is probable when SEM–AVS > 5; Category 2, adverse effects on aquatic life are possible when 0 < SEM–AVS < 5; and Category 3, no indication of adverse effects when SEM–AVS < 0 (USEPA, 2004). However, not all sediments with [SEM]–[AVS] > 0 can cause increased toxicity because there are many other metal-binding phases in sediments,

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

12

F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

Fig. 7. The spatial distribution of ([SEM]–[AVS])/foc in the coastal surface sediments (shallow water area with depth < 6 m).

such as TOC (Burton et al., 2005; Di Toro et al., 2005). Hence, a complementary evaluation method taking into account the TOC concentrations in sediments was proposed (USEPA, 2005; Di Toro et al., 2005). The 3 criteria all have been introduced in this study, as have been listed in Table 6. Figs. 6 and 7 show the spatial distribution of [SEM]–[AVS] and ([SEM]–[AVS])/foc in the coastal surface sediments in the Leizhou Peninsula. According to this criterion of [SEM]–[AVS] (USEPA, 2004), 22 station (22%) fell in Category 2, which means its adverse biological effects are uncertain, while it had probable adverse effect on aquatic life; the other sites (78%) might have no adverse effect (Table 5, Fig. 6). But based on the criterion of ([SEM]–[AVS])/fOC (USEPA, 2005; Di Toro et al., 2005), the number of the stations which have no adverse effect is bigger: 89% and 90% (Fig. 7), because the binding phase of organic matter mediate bioavailability of metals. Besides, the evaluation results of the criterion of USEPA (2005) and Di Toro et al. (2005) had slight difference. 9 stations fell in Category 2 according to the criterion by USEPA (2005), while the number is 8 according to the criterion by Di Toro et al. (2005). It was noted that adverse biological effects may be expected in 2 stations as is shown in Fig. 7: BS12D146, located in Liusha Bay, and BS12D137, located in Caotan Bay. The coastal surface sediments from Leizhou Peninsula were collected and analyzed for AVS and SEM to assess the sediment quality on the basis of the AVS model. The high AVS-concentration zones include the aquaculture areas of Liusha Bay and the densely populated areas of Zhanjiang Bay. Most of high SEM-concentration stations are located in ports or aquaculture zones. In conclusion,

most of the coastal surface sediments of the Leizhou Peninsula (90%) had no adverse biological effects according to the criterion proposed by USEPA (2005); while adverse effects are uncertain in some stations (8%), even in 2 stations (2%) adverse biological effects may be expected. Despite the underdevelopment of industry in the Leizhou Peninsula, anthropogenic influences, such as excessive aquaculture, disorder of abandoning the garbage and discharging sewage, poor management of ports have increased the metals concentrations in coastal sediments and posed a threat to the ecosystem. Acknowledgements This study was funded by the China Geological Survey (Grant No. 1212010914020), the National Natural Science Foundation of China (Grant No. 41001341), and the Natural Science Foundation of Guangdong Province, China (Grant No. 9151401501000015). We would also like to thank Dr. Han-ying Dong, Dr. Hai-tao Zhang, Juan-ding Yu, and colleagues from the Zhanjiang Institute of Geological Engineering Exploration for their help in field-sample collection and analysis. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.marpolbul.2014. 04.030.

Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030

F. Li et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

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Please cite this article in press as: Li, F., et al. Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM–AVS analysis. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.04.030