Marine Pollution Bulletin 82 (2014) 194–200
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Heavy metals in surface sediments from nine estuaries along the coast of Bohai Bay, Northern China Guanghong Wu a,⇑, Jingmin Shang b, Ling Pan b, Zhongliang Wang a a b
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China College of Urban and Environmental Sciences, Tianjin Normal University, Tianjin 300387, China
a r t i c l e
i n f o
Keywords: Heavy metals Sewage Sediment Estuary Multivariate analysis Bohai Bay
a b s t r a c t Concentrations of heavy metals in river water and sediment were investigated in nine estuaries along the coast of Bohai Bay, Northern China. Multivariate statistical techniques such as principal component analysis and cluster analysis, in combination with metal concentration analysis and correlation analysis, were used to identify the possible sources of the metals and the pollution pattern in nine estuaries along the coast of Bohai Bay. The environmental risks of metals, evaluated by sediment quality guidelines and background values, revealed Hg contamination in the estuaries. However, levels of Cd in estuarine sediments were low, and they were less than those levels in river sediments, partly due to the high mobility and dilution of river or seawater. Cd did not contribute to sediment deposits in estuaries. High organic matter from effluents from large municipal sewage treatment plants was predominantly responsible for restricting Hg mobility from the river to Bohai Bay. Ó 2014 Elsevier Ltd. All rights reserved.
The Bohai Sea is a semi-closed ocean on the coast of Northeastern and North China. There are three major bays inside the Bohai Sea: Laizhou Bay to the south, Liaodong Bay to the north and Bohai Bay to the west. The Bohai Sea Rim area has become one of the regions of China experiencing the biggest economic boom since 2005. While enjoying rapid regional economic development, the area has been exposed to greater and greater ecological and environmental pressures (Lin et al., 2011). In recent years, water and sediment quality monitoring of heavy metals have been studied for contamination assessment in the Bohai Sea and adjacent rivers (Guo et al., 2014), and Bohai Bay was reported to be one of the most polluted bays in China (SOA, 2009). The river sediments along the coast of Bohai Bay have been contaminated by heavy metals (Shi et al., 2005; Liu et al., 2006). Hg and Cd were two common pollutants in the sediments of the Haihe River and the Beitang Wastewater Drainage River (Wu and Cao, 2010; Wu et al., 2011a,c). However, Feng et al. (2011) reported that the potential impacts of metals appeared to be low in Bohai Bay and that Bohai Bay was generally unpolluted by Cd, Cr, Cu, Ni, Pb and Zn. Gao and Li (2012) also reported that Cd, Cr, Cu, Ni, Pb and Zn in surface sediments of intertidal Bohai Bay appeared to be unpolluted or moderately polluted. Considerable decreases in heavy metal ⇑ Corresponding author. Address: Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, No. 393, Binshuixi Road, Xiqing District, Tianjin 300387, China. Tel./fax: +86 22 23766023. E-mail address: [email protected] (G. Wu). http://dx.doi.org/10.1016/j.marpolbul.2014.02.033 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.
concentrations were expected in the sediments between Bohai Bay and adjacent rivers. Estuarine sediments acted as a sink for anthropogenic contaminants. However, little attention has been paid to the sediment quality assessment of heavy metals in the estuaries along the coast of Bohai Bay. The objective of this study was to evaluate heavy metal concentration in nine estuaries of the rivers along the coast of Bohai Bay. The differences of the heavy metal concentration between the rivers and artificial rivers for wastewater drainage were revealed and the sources of heavy metals in the estuaries were identified using a multivariate analysis approach. The study would provide a window for understanding the spatial changes in heavy metal contents of sediments between Bohai Bay and adjacent rivers. The sampling sites were arranged in nine estuaries along the coast of Bohai Bay extending from the north to the south (Fig. 1): the Jiyun River (JY), Yongdingxin River (YD), Beitang Wastewater Drainage River (BT), Haihe River (HH), Dagu Wastewater Drainage River (DG), Duliujian River (DL), Qingjinghuangpaishui River (QJ), Ziyaxin River (ZY) and Beipaishui River (BP) (Fig. 1). The BT and DG rivers are two major artificial rivers for effluent discharge from large municipal sewage treatment plants (MSTPs) in Tianjin. A total of 90 sediment and 45 river water samples collected from the nine estuaries of the adjacent rivers were analysed. The surface sediment samples (n = 9 10) from the rivers were collected using a stainless steel grab sampler (20 30 30 cm). If the grab returned with a sample and coring was feasible, then
G. Wu et al. / Marine Pollution Bulletin 82 (2014) 194–200
195
Fig. 1. The study area and sampling sites.
surface sample would be obtained by carefully inserting a 5 cm diameter PVC tube into the core. The sediments in the cores were sectioned at required interval (0–25 cm) and were placed in polyethylene bags. Sediment samples were air-dried at room temperature in the laboratory, passed through a 100-mesh nylon sieve and then thoroughly homogenised and kept in a silica gel desiccator until analysis. The river water samples (n = 9 5) were collected into polyethylene bottles and acidified with HNO3 to keep the dissolved metals in solution after filtration with a 0.45-lm membrane filter. Heavy metals in the sediment samples were digested using the US EPA method 3052. Cd, Cr, Pb, Cu, Zn and Ni were determined by inductively coupled plasma mass spectrometry (ICP-MS, Elan 9000) directly when the solution was limpid. Cold vapour atomic fluorescence spectroscopy (CVAFS) was applied for the determination of Hg and As. All chemicals used in the experiment were guaranteed reagent grade. Blank determinations were performed for each set of analysis using the same reagents. Sediment samples
Table 1 Recovery of sediment certified reference materials (Sediment GBW-07310). Certified value (mg kg Hg Cd Pb As Cr Cu Zn Ni
0.28 ± 0.04 1.12 ± 0.12 27 ± 3 25 ± 4 136 ± 15 22.6 ± 2 46 ± 5 30 ± 3
1
)
Mean (mg kg 0.26 ± 0.05 1.2 ± 0.06 30 ± 5 29.9 ± 5 131 ± 9 24.7 ± 4 55 ± 9 35 ± 2
1
)
Recovery (%) 92.8 107.1 110.4 119.5 96.8 109.3 119.6 117.3
were analysed in three replicates for which the relative standard deviations (%RSDs) were less than 11.2%. The experimental approach to the detection limit was estimated as 6). The Igeo values for the studied heavy metals were determined for the superficial sediments of the nine estuaries. Cd and As contamination levels were low (mean Igeo 6 0); Pb, Cr, Cu, Ni and Zn contamination levels were low to moderate (0 < mean Igeo 6 1); and Hg contamination levels were moderate to high (2 < mean Igeo 6 3). The JY, HH, DG and BT rivers were founded to have high values of CF and Igeo. The accumulation of Hg in the sediments was observed and was consistent with the results of heavy metal pollution in water. The results indicated that the amount of Hg discharged from Tianjin industrial activity was
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still a significant contributor and contributed to the role of urban environments as diffuse sources of Hg. Several previous studies revealed that Hg, Cd and Pb were found in high contamination levels; Zn, Cu, Cr and Ni were found in moderate contamination levels ; and As was not found in the river sediments (Wu and Cao, 2010; Wu et al., 2011a,c). However, evaluation of CF in the sediments of adjacent estuaries in Bohai Bay revealed that the highest value was obtained only for Hg. A comparison of CF in the rivers to CF in the estuaries revealed low Cd and As contamination levels. Conversely, several previous studies indicated high mobilisation of Cd in the sediments of the Haihe River through sequential selective extraction (Wu et al., 2011a; Gao and Chen, 2012). Over 31% of the total Cd in the Haihe River sediment was found to be associated with the exchangeable form, indicating the significant remobilisation of Cd (Wu et al., 2011a). Meanwhile, the highest percentage of acid soluble Cd, up to 60.3%, was observed with a mean of 48% in the Bohai Bay sediments (Gao and Chen, 2012). The estuary sediments were not enriched with Cd compounds, which was partly due to the high mobility and dilution of river or sea water. Table 4 summarises the Pearson’s correlation coefficients for OM, TN, TP and heavy metals (Hg, Cd, Pb, As, Cr, Cu, Ni and Zn). TN was significantly correlated with TP (r = 0.81, n = 90), Hg was significantly correlated with OM (r = 0.79, n = 90), TN (r = 0.79, n = 90), and TP (r = 0.92, n = 90). Pb was significantly correlated with As (r = 0.79, n = 90), Cr (r = 0.80, n = 90) and Ni (r = 0.93, n = 90). Ni was significantly correlated with Cr (r = 0.94, n = 90) and Pb (r = 0.93, n = 90). Household, livestock and agricultural runoff are major sources of nitrogen from human activities, and household and livestock have contributed to an increase in anthropogenic phosphorus (Huang et al., 2006). TN and TP were significantly correlated with each other (r = 0.81, n = 90), indicating that TN and TP came mainly from sewage discharge, which was generated by human activities such as washing, cooking and using the toilet. Sewage effluent was becoming an environmental issue as it flowed into rivers in Tianjin. Rivers such as DG and BT served as recipient rivers for effluents from large MSTPs. Effluent from Jizhuangzi (JZ, since 1986) and Xianyanglu (XY, since 2005) MSTPs flowed into the DG River, and effluents from Dongjiao (DJ, since 1993) and Beicang (BC, since 2006) MSTPs flowed into the BT and YD Rivers, respectively (Fig. 1). The estuaries received untreated domestic discharge and both treated and untreated industrial effluents from their tributaries. Sediments in the rivers and estuaries were contaminated by MSTP effluent. Hg was significantly correlated with OM, TN and TP, which indicated that Hg was easily deposited on sediments with organic matter and nutrients. These results also support the previous studies that much of the Hg present in the solid fraction was associated with OM, which was one of the most important factors that influenced distributions of Hg in sediments (Ramalhosa et al., 2006); high concentrations of dissolved organic matter in the water column might increase Hg sequestration process by sediments (Chakraborty et al., 2014). Organic matter in sediment represented the sum of various organic compounds. Soluble organic matter may provide a substrate with enormous surface area by concentrating on the finer sediment size fractions and potentially acting as a ‘‘concentrator’’ for Hg and other organic-associated elements, which play the most important role in the distribution of Hg in sediment (Sanei and Goodarzi, 2006). Soils in Tianjin were contaminated with atmospheric Hg deposition (Wang et al., 2005); sediments in the rivers and estuaries might become an important sink for Hg compounds. Rivers act as depositional areas, trapping and retaining sediments and organic matter, along with associated contaminants such as Hg and nutrients, from their catchments. Relatively high Hg contents in
Table 5 Results of the PCA for data of surface sediments (PCA loadings >0.4 are shown in bold). Eigenvalues, percent of variance and eigenvectors are given for the first three principal components (PC1–PC3).
Eigenvalues % of variance Cumulative % Eigenvectors pH OM TN TP Hg As Cd Cr Pb Cu Zn Ni
PC1
PC2
PC3
5.6 46.5 46.5
3.2 26.7 73.2
1.6 13.4 86.6
0.81 0.66 0.69 0.98 0.74 0.26 0.51 0.04 0.74 0.73 0.81 0.65
0.34 0.60 0.27 0.02 0.45 0.72 0.16 0.97 0.48 0.22 0.31 0.75
0.25 0.30 0.54 0.11 0.39 0.43 0.70 0.03 0.41 0.26 0.30 0.04
river and estuary sediments revealed that huge amounts of Hg were stored in sediments deposited. Moderate contamination elements such as Pb, Cr and Ni exhibited significant correlations with each other, which indicated that they had common behaviours or sources. Principal component analysis (PCA) was performed to group the pollutants (heavy metals and OM, TN and TP) and the estuaries in order to identify the differences in the contamination levels of heavy metals in nine estuaries. By extracting the eigenvalues and eigenvectors from the correlation matrix, three significant principal components were determined, and the percentage of the total variance they obtained are shown in Fig. 2; additional details are shown in Table 5. Three significant components that generated approximately 86.6% of the total variance were obtained. The first two eigenvalues generated 73.2% of the total variance, indicating that they were the most important factors. The first factor generated 46.5% of the total variance and had the greatest weights (>0.70) for TP, Hg, Cu, and Zn, and moderate weights for OM, TN, and Ni. This factor represented anthropogenic sources, which were mainly derived from sewage effluent. Hg may be incorporated into the sediment combined with domestic sources. Guentzel (2009) reported that Hg was significantly correlated with total organic carbon in the water samples, and Hg was associated with organic matter in water bodies throughout the South Carolina. Eutrophication could also enhance the sediment to accumulate organic matter-bound Hg in the estuary, Southeast Brazil (Machado et al., 2008). Factor two accounted for 26.7% of the total variance and had the greatest weights for Cr, As and Ni, and a moderate weight for Pb. The third factor (eigenvalue = 1.6) generated approximately 13.6% of the total variance and had a strong weight for Cd, and moderate weights for As and TN. Ni, TN, Pb, and As had loadings of more than 0.4 in both components and seemed to have a combination of the two anthropogenic sources. PCA results showed that three PCs represented the geochemical variability in the sediments of adjacent estuaries of Bohai Bay: PC1, the sewage discharge and Hg contamination; PC2, heavy metals such as Cr and Pb pollution from industry; and PC3, agricultural pollution and Cd contamination. Fig. 2b presents a plot of the three REGR factor scores that clearly revealed these relationships among the nine rivers. Three groups were established that differed significantly (P < 0.05), one comprised the DG River, another comprised the BT River, and another comprised seven rivers. Significant correlations among the JY, YD, HH, DL, QJ, BP and ZY rivers suggested that they had a common or combined pollutant. No significant correlations
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Fig. 3. Hierarchical dendrogram for the pollutants (a: Variables) and rivers (b: Cases) obtained using Ward’s clustering method.
showed different origins, and they indicated that the rivers had different pollutants than other estuaries. The contents were standardised using z-scores; then the Euclidean distances among the values for the pollutant (heavy metals, OM, TN and TP) were calculated. Hierarchical clustering for the variables and cases were performed using Ward’s method. The cluster has three overall subgroups in Fig. 3a: the first contained Zn, Ni, and Cu, which showed moderate contamination; the second contained Hg, which showed very high contamination; and the third included Cd, Pb, As, Cr, which showed relatively low pollution. Hg enrichment was evident in the estuaries. This could be attributed to both the direct discharges from point sources, such as rivers carrying contaminant, and the relatively constant sedimentation conditions. Clusters 1 and 2 were mainly influenced by sewage discharge and agricultural pollution; cluster 3 was mainly affected by industrialisation. The clustering confirmed the results of the PCA. The estuaries were clustered in four separate groups in Fig. 3b: the first contained the YD, BP and QJ Rivers; the second contained the ZY, BT and JY Rivers; the third included only the HH River; and the fourth included only the DG River. Fig. 3b presents a plot of the polluted estuaries as HH and DG, which clearly revealed the differences among the nine estuaries in Bohai Bay. DG River was a major artificial river for effluent discharge from JZ MSTP and XY MSTP in Tianjin. Domestic and industrial waste from Tianjin has reached the HH River for a long time. Although wastewater produced in the urban districts of the basin has been redirected to sewage plants since 2000, more than 3.4 105 million tons of waste continue to be discharged into the lower reaches of the river. Therefore, the amount of heavy metal contamination in DG and HH Rivers was different from that of other rivers. We investigated heavy metals and OM, TN and TP in the sediments in nine estuaries along the coast of Bohai Bay, Northern China. It was concluded that the sediments were slightly to moderately contaminated with the studied metals, with the exception of highly contaminated levels of Hg. Pb, Cr and Cd, which were found to have anthropogenic origin (wastewater drainage); Cu, Zn and Ni
were mainly influenced by sewage discharge; and As originated from natural sources. Hg mainly came from industrial activities, and in combination with domestic sources, it was stored in river and estuary sediments deposited with organic matter, whereas Cd was not enriched in the estuary and Bohai Bay sediments, but high Cd contents were found in the river sediments, which may due to the high mobility of Cd and dilution of river or sea water. The high concentration of OM, high mobility of Cd and significant anthropogenic sewage input may explain the surprisingly homogeneous Hg and heterogeneous Cd contents found in sediments between the rivers and the estuaries. This study reveals that anthropogenic processes and metal behaviour in the environment are the major factors for heavy metal pollution in estuaries, and Hg is a global pollutant that affects human and ecosystem health. A better understanding of river Hg inputs to the estuaries and their historical trends is needed. Acknowledgements This work was financially supported by the Key Laboratory for Ecological Environment in Coastal Areas, State Oceanic Administration of China (201111). References Chakraborty, P., Sharma, B., Babua, P.V.R., Yao, K.M., Jaychandran, S., 2014. Impact of total organic carbon (in sediments) and dissolved organic carbon (in overlying water column) on Hg sequestration by coastal sediments from the central east coast of India. Mar. Pollut. Bull. 79, 342–347. Chen, J.S., Zhou, J.Y., 1992. Study of Heavy Metals in Water Environment of China. Environmental Sciences Press of China, Beijing (in Chinese). Feng, H., Jiang, H., Gao, W., Weinstein, M.P., Zhang, Q., Zhang, W., Yu, L., Yuan, D., Tao, J., 2011. Metal contamination in sediments of the western Bohai Bay and adjacent estuaries, China. J. Environ. Manage. 92, 1185–1197. Gao, X., Chen, C.T.A., 2012. Heavy metal pollution status in surface sediments of the coastal Bohai Bay. Water Res. 46, 1901–1911. Gao, X., Li, P., 2012. Concentration and fractionation of trace metals in surface sediments of intertidal Bohai Bay, China. Mar. Pollut. Bull. 64, 1529–1536. Guentzel, J.L., 2009. Wetland influences on mercury transport and bioaccumulation in South Carolina. Sci. Total Environ. 407, 1344–1353.
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Guo, L., Wu, G., Shan, J., 2014. State of toxic metals in the Bohai Sea, China: a review. Mar. Environ. Sci. 33 (1), 194–201 (in Chinese). Huang, Q., Shen, H., Wang, Z., Liu, X., Fu, R., 2006. Influences of natural and anthropogenic processes on the nitrogen and phosphorus fluxes of the Yangtze Estuary, China. Reg. Environ. Change 6, 125–131. Legorburu, I., Rodríguez, J.G., Borja, Á., Menchaca, I., Solaun, O., Valencia, V., Galparsoro, I., Larreta, J., 2013. Source characterization and spatio–temporal evolution of the metal pollution in the sediments of the Basque estuaries (Bay of Biscay). Mar. Pollut. Bull. 66, 25–38. Lin, L., Liu, Y., Chen, J., Zhang, T., Zeng, S., 2011. Comparative analysis of environmental carrying capacity of the Bohai Sea Rim area in China. J. Environ. Monitor. 13, 3178–3184. Liu, L., Li, F., Xiong, D., Song, C., 2006. Heavy metal contamination and their distribution in different size fractions of the surficial sediment of Haihe River, China. Environ. Geol. 50, 431–438. Machado, W., Santelli, R.E., Loureiro, D.D., Oliveira, E.P., Borges, A.C., Ma, V.K., Lacerda, L.D., 2008. Mercury accumulation in sediments along an eutrophication gradient in Guanabara Bay, Southeast Brazil. J. Brazil Chem. Soc. 19 (3), 569–575. Meng, W., Qin, Y., Zheng, B., Zhang, L., 2008. Heavy metal pollution in Tianjin Bohai Bay, China. J. Environ. Sci.-China 20, 814–819. NOAA (National Oceanic and Atmospheric Administration), 1999. Sediment Quality Guidelines developed for the National Status and Trends Program , (accessed 01.12.13). Ramalhosa, E., Segade, S.R., Pereira, E., Vale, C., Duarte, A., 2006. Mercury cycling between the water column and surface sediments in a contaminated area. Water Res. 40, 2893–2900. Sanei, H., Goodarzi, F., 2006. Relationship between organic matter and mercury in recent lake sediment: the physical-geochemical aspects. Appl. Geochem. 21 (11), 1900–1912.
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Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Heavy metals in surface sediments from nine estuaries along the coast of Bohai Bay, Northern China Guanghong Wu a,⇑, Jingmin Shang b, Ling Pan b, Zhongliang Wang a a b
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China College of Urban and Environmental Sciences, Tianjin Normal University, Tianjin 300387, China
a r t i c l e
i n f o
Keywords: Heavy metals Sewage Sediment Estuary Multivariate analysis Bohai Bay
a b s t r a c t Concentrations of heavy metals in river water and sediment were investigated in nine estuaries along the coast of Bohai Bay, Northern China. Multivariate statistical techniques such as principal component analysis and cluster analysis, in combination with metal concentration analysis and correlation analysis, were used to identify the possible sources of the metals and the pollution pattern in nine estuaries along the coast of Bohai Bay. The environmental risks of metals, evaluated by sediment quality guidelines and background values, revealed Hg contamination in the estuaries. However, levels of Cd in estuarine sediments were low, and they were less than those levels in river sediments, partly due to the high mobility and dilution of river or seawater. Cd did not contribute to sediment deposits in estuaries. High organic matter from effluents from large municipal sewage treatment plants was predominantly responsible for restricting Hg mobility from the river to Bohai Bay. Ó 2014 Elsevier Ltd. All rights reserved.
The Bohai Sea is a semi-closed ocean on the coast of Northeastern and North China. There are three major bays inside the Bohai Sea: Laizhou Bay to the south, Liaodong Bay to the north and Bohai Bay to the west. The Bohai Sea Rim area has become one of the regions of China experiencing the biggest economic boom since 2005. While enjoying rapid regional economic development, the area has been exposed to greater and greater ecological and environmental pressures (Lin et al., 2011). In recent years, water and sediment quality monitoring of heavy metals have been studied for contamination assessment in the Bohai Sea and adjacent rivers (Guo et al., 2014), and Bohai Bay was reported to be one of the most polluted bays in China (SOA, 2009). The river sediments along the coast of Bohai Bay have been contaminated by heavy metals (Shi et al., 2005; Liu et al., 2006). Hg and Cd were two common pollutants in the sediments of the Haihe River and the Beitang Wastewater Drainage River (Wu and Cao, 2010; Wu et al., 2011a,c). However, Feng et al. (2011) reported that the potential impacts of metals appeared to be low in Bohai Bay and that Bohai Bay was generally unpolluted by Cd, Cr, Cu, Ni, Pb and Zn. Gao and Li (2012) also reported that Cd, Cr, Cu, Ni, Pb and Zn in surface sediments of intertidal Bohai Bay appeared to be unpolluted or moderately polluted. Considerable decreases in heavy metal ⇑ Corresponding author. Address: Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, No. 393, Binshuixi Road, Xiqing District, Tianjin 300387, China. Tel./fax: +86 22 23766023. E-mail address: [email protected] (G. Wu). http://dx.doi.org/10.1016/j.marpolbul.2014.02.033 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.
concentrations were expected in the sediments between Bohai Bay and adjacent rivers. Estuarine sediments acted as a sink for anthropogenic contaminants. However, little attention has been paid to the sediment quality assessment of heavy metals in the estuaries along the coast of Bohai Bay. The objective of this study was to evaluate heavy metal concentration in nine estuaries of the rivers along the coast of Bohai Bay. The differences of the heavy metal concentration between the rivers and artificial rivers for wastewater drainage were revealed and the sources of heavy metals in the estuaries were identified using a multivariate analysis approach. The study would provide a window for understanding the spatial changes in heavy metal contents of sediments between Bohai Bay and adjacent rivers. The sampling sites were arranged in nine estuaries along the coast of Bohai Bay extending from the north to the south (Fig. 1): the Jiyun River (JY), Yongdingxin River (YD), Beitang Wastewater Drainage River (BT), Haihe River (HH), Dagu Wastewater Drainage River (DG), Duliujian River (DL), Qingjinghuangpaishui River (QJ), Ziyaxin River (ZY) and Beipaishui River (BP) (Fig. 1). The BT and DG rivers are two major artificial rivers for effluent discharge from large municipal sewage treatment plants (MSTPs) in Tianjin. A total of 90 sediment and 45 river water samples collected from the nine estuaries of the adjacent rivers were analysed. The surface sediment samples (n = 9 10) from the rivers were collected using a stainless steel grab sampler (20 30 30 cm). If the grab returned with a sample and coring was feasible, then
G. Wu et al. / Marine Pollution Bulletin 82 (2014) 194–200
195
Fig. 1. The study area and sampling sites.
surface sample would be obtained by carefully inserting a 5 cm diameter PVC tube into the core. The sediments in the cores were sectioned at required interval (0–25 cm) and were placed in polyethylene bags. Sediment samples were air-dried at room temperature in the laboratory, passed through a 100-mesh nylon sieve and then thoroughly homogenised and kept in a silica gel desiccator until analysis. The river water samples (n = 9 5) were collected into polyethylene bottles and acidified with HNO3 to keep the dissolved metals in solution after filtration with a 0.45-lm membrane filter. Heavy metals in the sediment samples were digested using the US EPA method 3052. Cd, Cr, Pb, Cu, Zn and Ni were determined by inductively coupled plasma mass spectrometry (ICP-MS, Elan 9000) directly when the solution was limpid. Cold vapour atomic fluorescence spectroscopy (CVAFS) was applied for the determination of Hg and As. All chemicals used in the experiment were guaranteed reagent grade. Blank determinations were performed for each set of analysis using the same reagents. Sediment samples
Table 1 Recovery of sediment certified reference materials (Sediment GBW-07310). Certified value (mg kg Hg Cd Pb As Cr Cu Zn Ni
0.28 ± 0.04 1.12 ± 0.12 27 ± 3 25 ± 4 136 ± 15 22.6 ± 2 46 ± 5 30 ± 3
1
)
Mean (mg kg 0.26 ± 0.05 1.2 ± 0.06 30 ± 5 29.9 ± 5 131 ± 9 24.7 ± 4 55 ± 9 35 ± 2
1
)
Recovery (%) 92.8 107.1 110.4 119.5 96.8 109.3 119.6 117.3
were analysed in three replicates for which the relative standard deviations (%RSDs) were less than 11.2%. The experimental approach to the detection limit was estimated as 6). The Igeo values for the studied heavy metals were determined for the superficial sediments of the nine estuaries. Cd and As contamination levels were low (mean Igeo 6 0); Pb, Cr, Cu, Ni and Zn contamination levels were low to moderate (0 < mean Igeo 6 1); and Hg contamination levels were moderate to high (2 < mean Igeo 6 3). The JY, HH, DG and BT rivers were founded to have high values of CF and Igeo. The accumulation of Hg in the sediments was observed and was consistent with the results of heavy metal pollution in water. The results indicated that the amount of Hg discharged from Tianjin industrial activity was
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still a significant contributor and contributed to the role of urban environments as diffuse sources of Hg. Several previous studies revealed that Hg, Cd and Pb were found in high contamination levels; Zn, Cu, Cr and Ni were found in moderate contamination levels ; and As was not found in the river sediments (Wu and Cao, 2010; Wu et al., 2011a,c). However, evaluation of CF in the sediments of adjacent estuaries in Bohai Bay revealed that the highest value was obtained only for Hg. A comparison of CF in the rivers to CF in the estuaries revealed low Cd and As contamination levels. Conversely, several previous studies indicated high mobilisation of Cd in the sediments of the Haihe River through sequential selective extraction (Wu et al., 2011a; Gao and Chen, 2012). Over 31% of the total Cd in the Haihe River sediment was found to be associated with the exchangeable form, indicating the significant remobilisation of Cd (Wu et al., 2011a). Meanwhile, the highest percentage of acid soluble Cd, up to 60.3%, was observed with a mean of 48% in the Bohai Bay sediments (Gao and Chen, 2012). The estuary sediments were not enriched with Cd compounds, which was partly due to the high mobility and dilution of river or sea water. Table 4 summarises the Pearson’s correlation coefficients for OM, TN, TP and heavy metals (Hg, Cd, Pb, As, Cr, Cu, Ni and Zn). TN was significantly correlated with TP (r = 0.81, n = 90), Hg was significantly correlated with OM (r = 0.79, n = 90), TN (r = 0.79, n = 90), and TP (r = 0.92, n = 90). Pb was significantly correlated with As (r = 0.79, n = 90), Cr (r = 0.80, n = 90) and Ni (r = 0.93, n = 90). Ni was significantly correlated with Cr (r = 0.94, n = 90) and Pb (r = 0.93, n = 90). Household, livestock and agricultural runoff are major sources of nitrogen from human activities, and household and livestock have contributed to an increase in anthropogenic phosphorus (Huang et al., 2006). TN and TP were significantly correlated with each other (r = 0.81, n = 90), indicating that TN and TP came mainly from sewage discharge, which was generated by human activities such as washing, cooking and using the toilet. Sewage effluent was becoming an environmental issue as it flowed into rivers in Tianjin. Rivers such as DG and BT served as recipient rivers for effluents from large MSTPs. Effluent from Jizhuangzi (JZ, since 1986) and Xianyanglu (XY, since 2005) MSTPs flowed into the DG River, and effluents from Dongjiao (DJ, since 1993) and Beicang (BC, since 2006) MSTPs flowed into the BT and YD Rivers, respectively (Fig. 1). The estuaries received untreated domestic discharge and both treated and untreated industrial effluents from their tributaries. Sediments in the rivers and estuaries were contaminated by MSTP effluent. Hg was significantly correlated with OM, TN and TP, which indicated that Hg was easily deposited on sediments with organic matter and nutrients. These results also support the previous studies that much of the Hg present in the solid fraction was associated with OM, which was one of the most important factors that influenced distributions of Hg in sediments (Ramalhosa et al., 2006); high concentrations of dissolved organic matter in the water column might increase Hg sequestration process by sediments (Chakraborty et al., 2014). Organic matter in sediment represented the sum of various organic compounds. Soluble organic matter may provide a substrate with enormous surface area by concentrating on the finer sediment size fractions and potentially acting as a ‘‘concentrator’’ for Hg and other organic-associated elements, which play the most important role in the distribution of Hg in sediment (Sanei and Goodarzi, 2006). Soils in Tianjin were contaminated with atmospheric Hg deposition (Wang et al., 2005); sediments in the rivers and estuaries might become an important sink for Hg compounds. Rivers act as depositional areas, trapping and retaining sediments and organic matter, along with associated contaminants such as Hg and nutrients, from their catchments. Relatively high Hg contents in
Table 5 Results of the PCA for data of surface sediments (PCA loadings >0.4 are shown in bold). Eigenvalues, percent of variance and eigenvectors are given for the first three principal components (PC1–PC3).
Eigenvalues % of variance Cumulative % Eigenvectors pH OM TN TP Hg As Cd Cr Pb Cu Zn Ni
PC1
PC2
PC3
5.6 46.5 46.5
3.2 26.7 73.2
1.6 13.4 86.6
0.81 0.66 0.69 0.98 0.74 0.26 0.51 0.04 0.74 0.73 0.81 0.65
0.34 0.60 0.27 0.02 0.45 0.72 0.16 0.97 0.48 0.22 0.31 0.75
0.25 0.30 0.54 0.11 0.39 0.43 0.70 0.03 0.41 0.26 0.30 0.04
river and estuary sediments revealed that huge amounts of Hg were stored in sediments deposited. Moderate contamination elements such as Pb, Cr and Ni exhibited significant correlations with each other, which indicated that they had common behaviours or sources. Principal component analysis (PCA) was performed to group the pollutants (heavy metals and OM, TN and TP) and the estuaries in order to identify the differences in the contamination levels of heavy metals in nine estuaries. By extracting the eigenvalues and eigenvectors from the correlation matrix, three significant principal components were determined, and the percentage of the total variance they obtained are shown in Fig. 2; additional details are shown in Table 5. Three significant components that generated approximately 86.6% of the total variance were obtained. The first two eigenvalues generated 73.2% of the total variance, indicating that they were the most important factors. The first factor generated 46.5% of the total variance and had the greatest weights (>0.70) for TP, Hg, Cu, and Zn, and moderate weights for OM, TN, and Ni. This factor represented anthropogenic sources, which were mainly derived from sewage effluent. Hg may be incorporated into the sediment combined with domestic sources. Guentzel (2009) reported that Hg was significantly correlated with total organic carbon in the water samples, and Hg was associated with organic matter in water bodies throughout the South Carolina. Eutrophication could also enhance the sediment to accumulate organic matter-bound Hg in the estuary, Southeast Brazil (Machado et al., 2008). Factor two accounted for 26.7% of the total variance and had the greatest weights for Cr, As and Ni, and a moderate weight for Pb. The third factor (eigenvalue = 1.6) generated approximately 13.6% of the total variance and had a strong weight for Cd, and moderate weights for As and TN. Ni, TN, Pb, and As had loadings of more than 0.4 in both components and seemed to have a combination of the two anthropogenic sources. PCA results showed that three PCs represented the geochemical variability in the sediments of adjacent estuaries of Bohai Bay: PC1, the sewage discharge and Hg contamination; PC2, heavy metals such as Cr and Pb pollution from industry; and PC3, agricultural pollution and Cd contamination. Fig. 2b presents a plot of the three REGR factor scores that clearly revealed these relationships among the nine rivers. Three groups were established that differed significantly (P < 0.05), one comprised the DG River, another comprised the BT River, and another comprised seven rivers. Significant correlations among the JY, YD, HH, DL, QJ, BP and ZY rivers suggested that they had a common or combined pollutant. No significant correlations
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Fig. 3. Hierarchical dendrogram for the pollutants (a: Variables) and rivers (b: Cases) obtained using Ward’s clustering method.
showed different origins, and they indicated that the rivers had different pollutants than other estuaries. The contents were standardised using z-scores; then the Euclidean distances among the values for the pollutant (heavy metals, OM, TN and TP) were calculated. Hierarchical clustering for the variables and cases were performed using Ward’s method. The cluster has three overall subgroups in Fig. 3a: the first contained Zn, Ni, and Cu, which showed moderate contamination; the second contained Hg, which showed very high contamination; and the third included Cd, Pb, As, Cr, which showed relatively low pollution. Hg enrichment was evident in the estuaries. This could be attributed to both the direct discharges from point sources, such as rivers carrying contaminant, and the relatively constant sedimentation conditions. Clusters 1 and 2 were mainly influenced by sewage discharge and agricultural pollution; cluster 3 was mainly affected by industrialisation. The clustering confirmed the results of the PCA. The estuaries were clustered in four separate groups in Fig. 3b: the first contained the YD, BP and QJ Rivers; the second contained the ZY, BT and JY Rivers; the third included only the HH River; and the fourth included only the DG River. Fig. 3b presents a plot of the polluted estuaries as HH and DG, which clearly revealed the differences among the nine estuaries in Bohai Bay. DG River was a major artificial river for effluent discharge from JZ MSTP and XY MSTP in Tianjin. Domestic and industrial waste from Tianjin has reached the HH River for a long time. Although wastewater produced in the urban districts of the basin has been redirected to sewage plants since 2000, more than 3.4 105 million tons of waste continue to be discharged into the lower reaches of the river. Therefore, the amount of heavy metal contamination in DG and HH Rivers was different from that of other rivers. We investigated heavy metals and OM, TN and TP in the sediments in nine estuaries along the coast of Bohai Bay, Northern China. It was concluded that the sediments were slightly to moderately contaminated with the studied metals, with the exception of highly contaminated levels of Hg. Pb, Cr and Cd, which were found to have anthropogenic origin (wastewater drainage); Cu, Zn and Ni
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