Preliminary assessment of heavy metal contamination in surface water ...

Front. Earth Sci. 2012, 6(1): 39–47 DOI 10.1007/s11707-012-0309-z

RESEARCH ARTICLE

Preliminary assessment of heavy metal contamination in surface water and sediments from Honghu Lake, East Central China Ying HU1,2, Shihua QI (✉)1,2, Chenxi WU2, Yanping KE1,2, Jing CHEN1,2, Wei CHEN1,2, Xiangyi GONG3 1 State Key Laboratory of Biogeology and Environmental Geology, Wuhan 430074, China 2 School of Environmental Studies, China University of Geosciences, Wuhan 430074, China 3 College of Resources and Environmental Engineering, Wuhan University of Science and Technology, Wuhan 430081, China

© Higher Education Press and Springer-Verlag Berlin Heidelberg 2012

Abstract Heavy metal concentrations in surface water and sediments collected from Honghu Lake in Hubei Province, China were analyzed, and ecological risks were evaluated according to the sediment quality guidelines. The results showed that the average concentrations of heavy metals in surface water were ranked as: As > Zn > Cu > Cr > Pb > Ni > Cd > Hg. In comparison with results reported in other rivers and the background values, The Honghu Lake was polluted by As, Cr, Pb, Cu and Ni. Most of metals might be mainly from fertilizers, industrial effluent and domestic wastewater around the lake. Heavy metals concentrations were relatively higher in the inlet area than in other areas. Negative correlations were observed between most heavy metals and pH, while a significant positive correlation was present between Zn, Cd and Pb. In the sediment core, Cu, Zn, Cr and Ni showed a decreasing trend while Cd present an increasing trend. The decrease of As, Cu, Zn, Cr and Ni in the 1990s might due to the flood event in 1998. The analysis of ecological risk assessment based on sediment quality guidelines suggested that heavy metals in most sediments from the Honghu Lake had moderate toxicity, with Cr being the highest priority pollutant. Keywords metal distribution, sediment core, ecological risk assessment, wetland

1

Introduction

Lakes are considered one of the most versatile ecosystems Received October 14, 2011; accepted November 13, 2011 E-mail: [email protected]

in the world, but they are more sensitive to environmental pollution and anthropogenic impacts (Forghani et al., 2009). Heavy metals, such as arsenic (As), mercury (Hg), cadmium (Cd), lead (Pb), and chromium (Cr), are commonly detected in lakes (Anshumali et al., 2009; Ongeri et al., 2009). Like other aquatic systems, heavy metals enter lakes through natural sources (e.g. weathering, erosion) and anthropogenic sources (e.g. mining, urban and industrial wastewater) (Zorer et al., 2008; Alhas et al., 2009). At present, heavy metal pollution has become a great environmental concern with their toxicity, persistence, bioaccumulation and biomagnification in the food chain (Li et al., 2008; Yuan et al., 2011). For human beings, lakes are important sources of water and food. Thus, heavy metals in lakes might ultimately have adverse biologic effects on human health through drinking water and consuming aquatic products (Huang et al., 2009; Zhang et al., 2009). For these reasons, it would be desirable and imperative to investigate their distribution in lakes, which can provide valuable information of heavy metal pollution and help evaluate potential environmental risks. Honghu Lake (113°12′–113°26′E and 29°40′–29°58′N), the seventh largest natural freshwater lake in China, is a unique inland freshwater lake in the middle-lower reaches of the Yangtze River. The lake covers an area of 344 km2, with an average water depth of 1.34 m. It is mainly used for aquatic cultivation, water supply, and irrigation. Due to the extensive water conservancy constructions, the Honghu Lake changed an overflowing lake to a semi-closed one during the 1950s–1970s. With rapid development of the local economy since 1980s, large amounts of wastewater from industrial, domestic and agricultural sources from Honghu City and Jianli County in Hubei Province, China was discharged into the lake. As a result, water environment in the Honghu Lake has deteriorated in terms of

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Front. Earth Sci. 2012, 6(1): 39–47

entrophication (Cheng and Li, 2006; Gui and Yu, 2008) and heavy metal pollution (Yao et al., 2009). A number of recent studies have discussed the distribution and sources of heavy metals in various freshwater systems (Chen et al., 2010; Kurun et al., 2010; Botsou et al., 2011). Some studies concerned metal distribution in the Honghu Lake have also been reported (Yao et al. 2006; Liu and Li, 2011), but little is known about the ecological risk associated with heavy metal concentrations in the sediments. The aims of this study were to: 1) investigate the contamination levels and distributions of heavy metals in surface water and sediment core from the Honghu Lake; 2) compare their concentrations with other rivers in the world and environmental quality standards, and 3) evaluate the potential toxicity of the metal concentrations based on sediment quality guidelines.

2

Materials and methods

2.1

Sample collection

In July 2005, water samples at 0.5 m below the water surface were collected at sampling locations shown in

Fig. 1. All of these water samples were obtained using cleaned polyethylene bottles, which were washed with hydrochloric acid and then rinsed with distilled water. Subsequently, water samples were filtered through 0.45 µm millipore filters, acidified to pH < 2 with 2 mL 6 N HCl and transported to the laboratory for analysis. During the sample collection, a global positioning system (GPS) was used to locate the sites. In addition, water temperatures and pH were measured, and electrical conductivity was analyzed by a Model 3010 portable conductivity meter. A sedimentary core (S1) for metal analysis was recovered at the central part of the Honghu Lake (113°22′18′′E, 29°51′35′′N), using a static gravity corer (5 cm i.d.). Another core was taken from the same site for dating. Each core with a length of 75 cm was sectioned at 1 cm interval. Total 150 sediment samples were obtained from the sampling site (S1). All the samples were then placed into sealed polyethylene bags and transported to the laboratory for storage at – 20°C until analysis. In the laboratory, samples were air-dried at room temperature and sieved through a 100-mesh sieve. For heavy metal analysis, 0.1 g of dry sample was digested using 10 mL HCl-HNO3-HF. Details about the procedure for the

Fig. 1 Location map of Honghu Lake and sampling sites of surface water and sediment core

Ying HU et al. Assessment of heavy metal contamination in surface water and sediments

digestion were described elsewhere (Yao et al., 2009; Bai et al., 2011). The solution was finally diluted to 25 mL with deionized distilled water. 2.2

3

Results and discussion

3.1 Distribution of heavy metals in water from Honghu Lake

Sample analysis 3.1.1

Concentrations of Pb, Cd, Ni, Cr, Cu, Zn in all samples were determined using an inductively coupled plasma mass spectrometry (ICP-MS), while As and Hg were analyzed by atomic fluorescence spectroscopy (AFS). For quality control, procedural blanks and duplicates were run every 10 samples. The standard deviations were below 10% for all elements. The detection limit for individual metal was 0.5 to 5 ng/L for a water sample and 0.005 to 1 µg/g for a sediment sample. 2.3

41

Dating

The sediment core was dated by the 210Pb method. 210Pb was measured by the analysis of the α-radioactivity of its decay product 210Po with the assumption that the two are in equilibrium (Zhang et al., 2011). Polonium isotopes were extracted, purified and plated onto a silver disk from the sample solution (in 1 N HCl) at 80°C. The counting results were corrected for the decay of 210Pb and 210Po (Hosono et al., 2010). Sedimentation rates were determined by a constant activity (CA) model (Lin et al, 1998).

Table 1

Concentration of heavy metals in surface water

Table 1 presents concentrations of heavy metals in water from the Honghu Lake. Results showed that the concentrations of heavy metals in lake water show a great variation. Generally, average concentrations of these metals in the Honghu Lake decrease with the following order: As > Zn > Cu > Cr > Pb > Ni > Cd > Hg. Chinese Environment Quality Standard for Surface Water (GB3838-2002) classified water quality into five levels (SEPA, 2002), whereas Grade 1 is the highest standard set to protect national nature reserves. According to this standard, the concentrations of heavy metals in the water of the Honghu Lake are much lower than cutoff values for the grade 1 water quality. To better understand the status of heavy metals in the study area, concentrations of these pollutants were compared with those reported in other rivers of the world (Table 2). The average concentrations of most heavy metals in the Honghu Lake are slightly higher than those in water samples from the Shur River (Karbassi et al., 2008), Rivers of Latvia (Klavinš et al., 2000) and Chaohu Lake

Concentrations of heavy metals and pH in surface water from Honghu Lake and the water quality guidelines/(µg$L–1)

Sampling sites

pH

As

Cr

Cd

Pb

Cu

Hg

Ni

Zn

H1

8.06

3.41

1.86

0.054

2.26

3.10

0.019

1.36

5.05

H2

8.10

2.26

2.05

0.029

0.67

2.02

0.005

1.22

2.00

H3

8.28

2.32

1.98

0.036

0.78

1.85

0.005

1.21

2.13

H4

8.43

3.34

1.85

0.034

2.47

2.18

0.042

1.27

2.21

H5

8.52

2.56

1.74

0.022

1.55

1.64

0.005

1.27

1.19

H6

8.39

3.26

1.92

0.026

0.34

1.44

0.005

1.15

0.94

H7

8.32

2.14

1.30

0.026

1.84

1.20

0.005

0.69

0.88

H8

8.22

1.71

1.22

0.027

2.12

0.95

0.005

0.65

0.91

H9

8.00

4.31

1.51

0.080

4.75

3.03

0.005

1.78

7.53

H10

8.48

2.37

1.41

0.045

0.25

1.29

0.018

1.28

1.40

H11

8.57

2.85

1.70

0.045

0.40

1.49

0.005

1.41

2.21

H12

8.50

3.05

1.57

0.032

0.14

2.28

0.006

1.20

1.23

H13

8.21

2.47

1.57

0.022

0.08

2.22

0.018

1.21

0.72

H14

8.08

2.61

1.96

0.022

0.03

2.28

0.005

1.14

0.84

H15

7.93

3.72

1.99

0.044

1.46

1.94

0.005

1.17

2.64

Min

7.93

1.71

1.22

0.022

0.03

0.95

0.005

0.65

0.72

Max

8.57

4.31

2.05

0.080

4.75

3.10

0.042

1.78

7.53

Mean

8.27

2.83

1.71

0.036

1.28

1.93

0.010

1.20

2.13

Ⅰ*

6–9

£50

£10

£1

£10

£10

£0.05

Note: Ⅰ*–Environmental Quality Standard for Surface Water (GB3838-2002)

£50

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Front. Earth Sci. 2012, 6(1): 39–47

(Li et al., 2011), but much lower than those reported in the Kolleru Lake (Adhikari et al., 2009), Three Gorges Reservoir (Qi et al., 2002), Danjiangkou Reservoir (Li et al., 2008) and the Yangtze River (Wu et al., 2009). When compared with background values in water from Dongting Lake (Li et al., 1986), the Honghu Lake was polluted with As, Cr, Pb, Cu and Ni, but less polluted with Cd, Hg and Zn. These results suggested that the Honghu Lake was polluted with some heavy metals. The Honghu Lake is a lowland lake, where flooding and waterlogging occur frequently. The relative high level of As in this area may be due to the landform and hydrogeological conditions. Similar result has reported in water samples from Honghu City, which provides further evidence for the high level of As (Li et al., 2010). The area where the Honghu Lake lies is one of the most important agricultural bases in China (Liu et al., 2010; Liu and Li, 2011). Fertilizers (for example, phosphate fertilizer contains heavy metals such as Cu, Ni, Cd and Pb) are used yearly on a regular basis, and this might be the reason for the presence of heavy metals (Ahmed et al., 2010; Li et al., 2011). It is reported that the amounts of fertilizer applied in the Honghu Lake Basin increased from 461 kg/hm2 in 1988 to 845 kg/hm2 in 2004 (Gui and Yu, 2008). Moreover, industrial effluent and domestic wastewater from Honghu City and Jianli County are discharged into this lake. The Honghu Lake is used for drinking water source, cultivation and irrigation. Thus, continuous monitoring is needed to the heavy metal pollution in the surface water from the Honghu Lake. 3.1.2

Spatial distribution of heavy metals in surface water

According to the spatial distribution of heavy metal concentrations in water samples from the Honghu Lake, Cr, As, Pb, Cu, Ni and Zn present similar distributions in the lake water. This is further supported by the significant correlation among these elements (R: 0.94–0.96; p < 0.05). Nevertheless, there is not so much variation in the concentration levels of Cd and Hg among the sampling

sites, indicating Cd and Hg have different geochemical behavior in this aquatic system. The relative higher level of heavy metals was observed in the inlet area (H1, H9 and H15) since pollution sources are around these sites. Among these sampling sites, site H9 exhibits the highest water concentrations of As, Cd, Pb, Ni and Zn, which is close to Jianli County and the entry of the Yangtze River. There are two possible reasons that might explain the high concentration of these heavy metals at this site. The first possibility is that agricultural runoff and wastewater from the surrounding area was discharged into the Honghu Lake. On the other hand, it may be due to inflows from the Yangtze River. This is further supported by the fact that concentrations of Zn, Cu, Cd, Ni, Cr and As in the Yangtze River are higher than in the Honghu Lake (Wu et al., 2009). The relative low concentrations of heavy metals were observed at sites H8 and H10. Site H8 is at the wetland protection area, where wastewater discharge is forbidden by the government. Site H10 is close to the Xintan drainage sluice, where is far away from the inlet area and water exchange ability is strong. Pearson correlation is used to evaluate the co-variance of heavy metals (Li et al., 2011). The correlation coefficients for heavy metals and pH in the surface water samples (Table 3) present a positive correlation among Cd, Cu, Ni, Zn and As, among Pb, Cu, Ni and Cd, among Ni, Zn and Cu. High correlations among these metals in the water might indicate their same origin or similar enrichment mechanism (Nguyen et al., 2009). There is a strong positive correlation among Pb, Cd and Zn, suggesting that the anthropogenic sources of these metals are closely related in the water from the Honghu Lake. However, negative correlations were found between pH and As, Cr, Cd, Pb, Cu, Ni or Zn, with the correlation coefficients being – 0.31, – 0.27, – 0.33, – 0.38, – 0.51, – 0.09 and – 0.48, respectively. As shown in Table 1, pH values are lower at sites H1, H9, H15 where the concentrations of these metals are higher compared to other sites. This provides further support by the fact that negative

Average concentrations of heavy metals in water from other rivers over the world/(µg$L–1)

Table 2 Sites

As

Kolleru Lakea) Dongting Lakeb)

0.9 c)

Three Gorges Reservoir

Cr

Cd

Pb

Cu

n.d.

36

16

24

0.89

0.06

1

1

0.025

10.129

1.125

3.244

6.463

0.018

0.02

0.2

1

0.3

10

1.17

10.59

13.32

1.73

2.02

0.026

0.116

0.771

Rivers of Latviad) e)

Danjiangkou Reservoir

11.08

6.29

f)

Shur River

Chaohu Lakeg) h)

0.73

0.89

0.01

2

0.5

0.07

0.2

1.8

20.9

4.7

55.1

10.7

This study

2.83

1.71

0.036

1.28

1.93

Zn

0.4

4 30.636

0.688 0.36

13.2

Ni

n.d.

1.55

Yangtze Riveri)

Background value

Hg

0.010

1.09

7.59

0.3

10

13.4

9.4

1.20

2.13

Note: n.d. means not detected; a) Adhikari et al. (2009); b) Niao et al. (1990); c) Qi et al. (2002); d) Klavinš et al. (2000); e) Li et al. (2008); f) Karbassi et al. (2008); g) Li et al. (2011); h) Li et al. (1986); i) Wu et al. (2009)


43

Pearson correlation coefficients of heavy metals and pH values in the surface water from Honghu Lake (n = 15)

Table 3 Parameters

pH

pH

1.00

As

Cr

Cd

Pb

Cu

Hg

Ni

As

– 0.31

1.00

Cr

– 0.27

0.31

Cd

– 0.33

0.70*

– 0.07

1.00

Pb

– 0.38

0.50

– 0.24

0.67*

1.00

Cu

– 0.51

0.69*

0.37

0.54*

0.38

1.00

Hg

0.17

0.17

0.04

0.040

0.15

0.24

1.00

Ni

– 0.09

0.73*

0.35

0.70*

0.28

0.69*

0.15

1.00

Zn

– 0.48

0.74*

0.07

0.93**

0.78**

0.72*

0.06

0.71*

Zn

1.00

1.00

Notes: 2-tailed test of significance is used; * correlation is significant at the 0.05 level; ** correlation is highly significant at the 0.01 level

correlations between pH and heavy metals were observed. 3.2 3.2.1

Heavy metals in the sediment core from Honghu Lake 210

Pb Chronology

As shown in Fig. 2, sediments of the Honghu Lake have 210 Pbex activities which range from 0.45 to 24.67 dpm/g with a mean of 8.54 dpm/g. The 210Pbex activity is higher in the top layer than in the downward section. 210Pbex shows sharp peaks at 2 and 21 cm from the top of the core, suggesting anthropogenic activities may have resulted in significant increase of the 210Pb activity due to the rapid development of industry and agriculture. At depths of 27– 60 cm, a simple exponential decrease of 210Pbex with depth was observed. Below the depth of 60 cm, the concentration of 210Pbex presents an increase trend. The vertical distribution of 210Pbex in this core indicates that the accumulation rate varies greatly. Assuming that sediment mixing is restricted to the surface mixed layer, the leastsquare fits for the logarithmic decrease of the 210Pbex activity give a sedimentation rate of 0.44 cm/a. Thus the section of 27–60 cm sediment represents about 75 years of deposition. The average accumulation rate in the Honghu Lake is higher than that obtained from Jiaozhou Bay (Dai et al., 2007). It might be related to the high content of

Fig. 2

Profiles of 210Pbex activity for the S1 from Honghu Lake

suspended particles that were carried by rivers, flooding streams, surface runoff flowing into this lake (Al-Masri et al., 2002). 3.2.2

Historical trends of heavy metals in the sediment core

Concentrations of heavy metals in the S1 from the Honghu Lake present the following variation (Fig. 3). Overall, the drastic changes were observed in the 0–30 cm section in comparison to deeper sediments. Increase of Cd in the top 30 cm of the profiles reflects that this metal in the sediments might originate from the anthropogenic activities around the Honghu Lake due to the rapid industrial development and urbanization. Industry sources, agricultural runoff in some heavily polluted soils resulting from the intensive use of phosphate fertilizer contained Cd might be the main reason for Cd pollution in the Honghu Lake (Ahmed et al., 2010). However, concentrations of Zn, Cu, Cr and Ni in the top layer show the same decreasing trend compared to those in the sub-surface layer. The similar distribution patterns are most likely related to their similar geochemical behavior, which is consistent with the strong correlations among these elements (R: 0.94–0.96; p < 0.01). Cu, Ni and Zn are frequently associated in sediments as authigenic sulfide minerals (Ahmed et al., 2010). Hg, As and Pb show different distributions in comparison with the heavy metals mentioned above. As shown in Fig. 3, the levels of all metals had almost no obvious change in the pre-1950s. Concentrations of all metals decreased in the 1950s, especially for Cu, Zn, Cr and Ni. Obvious decreases in concentration of Zn, Cu, Cr and Ni were also found in the 1970s. Xintan drainage sluice, built in 1958, blocked the connection between the lake and the Yangtze River. In the 1970s, Luoshan main canal and Four-lake main canal were also built. The facts suggest that these metals might be associated with hydraulic construction, which is likely to reduce pollution input into the lake. Elevated Hg, Cd, As and Cu concentrations were observed in the 1974. These increases in heavy metal contents suggest there might be an increase

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Front. Earth Sci. 2012, 6(1): 39–47

Fig. 3 Vertical distribution of heavy metals in the sediment core (S1) of Honghu Lake

in pollutant input into the lake through industrial sources and other sources. High concentrations of Cd, As, Cu, Zn,

Ni and Pb were observed in the 1990s. After this period, these metals decreased sharply until 2000. A heavy flood


45

happened in the Yangtze River in 1998, which could produce dilution effects that resulted in the decreases of these pollutants. After the 2000, Pb showed an increasing trend in concentration, while concentrations of Cu, Zn, Cr and Ni showed decreasing trends. The Honghu Lake is a key producing area for freshwater fish and an ideal habitat for migratory birds. To restore the ecosystem, the Honghu Lake Wetland Protection and Restoration Demonstration Project (HLWPRDP) has been implemented since 2004. In this program, waste treatment was enforced by the government, and the amount of industrial waste discharged was reduced. The decrease trend of these metals reflected the result of environmental regulation by the local government. However, the increase of Pb concentration was observed in this time, which might be the atmospheric deposit from coal burning of power generation plants and lead-gasoline used in vehicle (Yao et al., 2009; Liu et al., 2011).

Nasir, 2010). From Table 4, it is evident that the concentrations of Hg and Cd in more than 90% samples are below ERL, representing a range with which biologic effects occur rarely. More than 60% sediments with respect to Cu, Ni and Zn are greater than TEL but less than PEL, suggesting that adverse biological effect could occasionally be observed. Cr and Pb in more than 80% sediment samples and As in 22.7% samples exceed PEL, representing that adverse biologic effects could frequently occur. TUs of heavy metals were calculated (Fig. 4), which was ranked as: Cr > Pb > As > Ni > Zn > Cu > Hg > Cd. This shows that Cr is the highest priority pollutant (25.5%3.0%) while Cd is the least significant one (2.2%0.9%). The total TU of all heavy metals in 94.7% sediment samples is higher than 4, indicating the presence of moderate toxicity (Pedersen et al., 1998; Bai et al., 2011).

3.3 Ecological risk assessment of heavy metals in the sediment core

4

Numerical sediment quality guidelines (SQGs) have been widely applied to evaluate the degree to which the concentrations of heavy metals might adversely affect aquatic organisms (Harikumar and Nasir, 2010; Bai et al., 2011). In this study, the sediment quality guidelines are developed for freshwater ecosystems to determine the ecotoxicological potential of heavy metal pollution in the sediment core from the Honghu Lake (MacDonald et al., 2000). This method provides two sets of concentrations: the effect range low (ERL)/effect range median (ERM) and the threshold effect level (TEL)/probable effect level (PEL). The ERL and TEL represent chemical concentrations below which adverse effects would be rarely observed. While the ERM and PEL are concentrations above which adverse effects are likely to occur (Bai et al., 2011). Furthermore, the potential acute toxicity of pollutants in sediments can be estimated as the sum of the toxic units (TUs), which is defined as the ratio of the determined concentration to PEL value (Harikumar and Table 4 Elements

Conclusions

The study of the distribution of heavy metals in surface water and the sediment core from the Honghu Lake suggests that the lake is facing heavy metal pollution. In surface water, abundances of heavy metals in water were ranked as: As > Zn > Cu > Cr > Pb > Ni > Cd > Hg. Some heavy metals exceeded background values, indicating that the Honghu Lake is polluted with some heavy metals. Concentrations of heavy metals in the inlet area were higher than those in other areas in the lake. The spatial distribution of these metals indicated that they might be related to fertilizers, industrial effluent and domestic wastewater around the lake. Lower pH values were observed at sampling sites where the concentrations of these metals were higher. This was consistent with the negative correlation between pH and most metals. 210 Pb chronology revealed that the average sedimentation rate of S1 from the Honghu Lake is 0.44 cm/a. In the sediment core, the drastic changes were observed in the top layer (0–30 cm) in comparison to the deeper layer. Increase of Cd concentration in the top 30 cm of the profiles

Risk assessment of heavy metals in the sediment core Guidelines/(µg$g–1) TEL

PEL

ERL

Frequency/% ERM

< TEL

TEL-PEL

> PEL

< ERL 100

As

5.9

17

33

85

0

77.3

22.7

Cr

37.3

90

80

145

0

17.3

82.7

5

9

94.7

5.3

0

36

35

110

0

12.0

88.0

197

70

390

5.3

94.7

0

100 100

Cd

0.596

Pb

18

Cu

35.7

Hg

0.174

Ni

35

Zn

123

3.53

0.486 91.3 315

0.15

1.3

100

10.7 100 2.7

ERL-ERM

> ERM

0

0

89.3

0

0

0

97.3

0

0

0

0

0

0

0

30

50

4.0

96.0

0

1.3

29.3

69.4

120

270

37.3

62.7

0

33.3

66.7

0

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Front. Earth Sci. 2012, 6(1): 39–47

Fig. 4 TUs

Contributions of respective heavy metal to the sum of

reflected that this metal in the sediments might originate from the anthropogenic activities. Decrease in concentration of Cu, Zn, Cr and Ni was likely associated with the HLWPRDP. Pb in sediments might be from atmospheric deposit of coal burning, and lead-gasoline used in vehicle. The potential acute toxicity of pollutants in most sediments suggested that heavy metal concentrations in the Honghu Lake should be of moderate concern, and Cr was the highest priority pollutant. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Grant No. 41073070) and the Research Fund for the Doctoral Program of Higher Education, China (No. 20090145110004). The authors are grateful to acknowledge the State Laboratory of Biogeology and Environmental Geology. The authors also would like to appreciate the reviewers for their suggestions.

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Dr. Shihua Qi is a professor in the School of Environmental Studies, China University of Geosciences, Wuhan, China. He obtained his B.S. degree in Geochemistry, Wuhan College of Geology, received his M.S. degree in Geochemistry and Ph.D. in Paleontology and Stratigraphy from China University of Geosciences. His current research focuses on fate and behaviour of environmental organic pollutants and persistent organic pollutants, environmental geochemistry and remote sensing applications to environment. He holds three patents and has published more than 150 refereed journal articles and conference papers.