Assessment of heavy metal pollution in Red River surface sediments

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Surface sediment samples were collected from upstream down to the subaqueous delta of the Red River in Viet- nam to assess heavy metal pollution. Sediment ...
MPB-07957; No of Pages 7 Marine Pollution Bulletin xxx (2016) xxx–xxx

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Assessment of heavy metal pollution in Red River surface sediments, Vietnam Thi Thu Hien Nguyen a,b, Weiguo Zhang a,⁎, Zhen Li c, Jie Li d, Can Ge a, Jinyan Liu a, Xuexin Bai a, Huan Feng e, Lizhong Yu a a

State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China Institute of Geography, Vietnam Academy of Science and Technology, Hanoi, Vietnam School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8P5C2, Canada d Yunnan Institute of Environmental Science, Kunming 650034, China e Department of Earth and Environmental Studies, Montclair State University, NJ 07043, USA b c

a r t i c l e

i n f o

Article history: Received 27 June 2016 Received in revised form 8 August 2016 Accepted 13 August 2016 Available online xxxx Keywords: Heavy metal pollution Sediment The Red River

a b s t r a c t Surface sediment samples were collected from upstream down to the subaqueous delta of the Red River in Vietnam to assess heavy metal pollution. Sediment Cr and V concentrations are strongly correlated with Al, Fe, Mn and total organic carbon concentrations, as well as particle size, suggesting that these two metals are derived primarily from natural sources and enriched in the fine fraction of sediments. In contrast, Cu, Cd, Pb, Ni and Zn concentrations show weaker correlations with particle size, with very high concentrations observed at several sites in the upper reach of the river, pointing to anthropogenic input as a possible source of these heavy metals. Enrichment factors (EF) of Cu, Cd, Pb, Ni and Zn suggest that heavy metal pollution is present in sediments with significantly high values in the upstream. The data analysis indicates that Cd, Cu and Pb are the dominant pollutants in the Red River, with their concentrations reaching moderate to serious pollution levels. © 2016 Elsevier Ltd. All rights reserved.

Heavy metal pollution in many river systems of the world is a common environmental problem due to rapid population growth, industrialization and economic development (Förstner, 1981; Hudson-Edwards et al., 2001; Staley et al., 2015). River sediments tend to be the repository of heavy metals which are potential secondary source of metal pollutants to the overlying aquatic systems (Adams et al., 1992). Heavy metals are non-degradable and toxic, and as such, heavy metal pollution in river sediments is drawing global attention (Soares et al., 1999; Fu et al., 2012; Shafie et al., 2014; Nan et al., 2016). Water pollution in Vietnam has been increasing over the last 30 years. In particular, downstream reaches of rivers, lakes and canals in urban areas are the most polluted (WEPA, 2011). The Red River, which originates from China, is the second largest river in Vietnam. The Red River has two major tributaries, the Da River and the Lo River, which have their head sources in China (Fig. 1). It plays an important role in the economic, cultural and social life of the Vietnamese people. With a population density varying from 80 to N 1000 inhabitants/km2 in different sectors of its watershed, the Red River system is a typical example of a subtropical system experiencing rapid increasing population pressure (Le et al., 2010). Driven by urbanization, industrialization and the intensified use of agrochemicals, a large amount of waste water containing heavy metals is discharged into the Red River system. For example, arsenic concentration in the Red River in Hanoi exceeded the WHO ⁎ Corresponding author. E-mail address: [email protected] (W. Zhang).

provisional guideline value of 10 μg/L (Berg et al., 2001). Heavy metal pollution is therefore becoming a critical issue in the Red River water management. Understanding the status of heavy metal pollution in the Red River is critical for remediating pollutants in the environment. There have been several heavy metal pollution studies in the Red River delta (Ho and Egashira, 2000; Phuong et al., 2010; Thuong et al., 2013). Coastal environmental research requires knowledge about the source, transport and fate of the contaminant in the riverine, estuarine and coastal system. However, a source-to-sink analysis for heavy metal pollution in the Red River sediments is still quite limited. In this study, heavy metal distributions in the Red River sediments are investigated from its upper reach down to the subaqueous delta. The purpose of this study is to gain a better understanding of environmental status of the Red River due to sediment heavy metal pollution. The catchment of the Red River is dominated by Paleozoic sedimentary rocks together with metamorphic and igneous rocks distributed along the main stream and in the Lo River basin (Borges and Huh, 2007). The river basin is within a subtropical monsoon climate region with a mean annual rainfall of 1590 mm. The wet season (May–October) accounts for 85–95% of the total annual rainfall. Mean annual temperature in the upstream region ranges from 14 to 16 °C in winter to 26– 27 °C in summer, and 17 to 30 °C in the delta area, which is slightly higher than that in inland (Le et al., 2007). Thao River, which is the main stream of the Red River in the upstream, is the major source of sediments. Contribution of sediments from the Da River is minor due to the closure of the Hoa Binh Dam in 1989 (Fig. 1). According to the

http://dx.doi.org/10.1016/j.marpolbul.2016.08.030 0025-326X/© 2016 Elsevier Ltd. All rights reserved.

Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030

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T.T.H. Nguyen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

Fig. 1. Map of the study area (a), with the sampling sites detailed in (b). The inset map in (b), map (c), shows the sampling sites in the subaqueous delta.

Food and Agriculture Organization classification system, soils in the upper basin of the Red River are typically Acrisols and Ferrasols (Gong, 1999), and the river is named after the red color of the eroded laterite soils. At present, the main outlet of the Red River is the Ba Lat mouth, which releases 38% of the fluvial sediment (Fig. 1) (Duc et al., 2007). Geomorphologically, the subaqueous delta is divided into an erosional shoreface zone (water depth b 5 m), a delta front at the Ba Lat mouth, and a prodelta zone (water depth 5–30 m) (van den Bergh et al., 2007). Sand dominates in the shoreface zone, while silt and clayey silt are dominant in the delta front and prodelta zone, respectively (Duc et al., 2007). A total of 50 surface sediment samples were collected using a plastic sampler or a grab sampler between 2007 and 2015 (Fig. 1). In 2007, fourteen samples were collected at Sites F27–F31, and F38–F46 on the river bank along the main channel of the Red River, and eighteen surface sediment samples were collected in the subaqueous delta, respectively. In 2014, sixteen samples were collected at Sites SH1, SH3, SH5–SH9, ND1–ND3, ND5 and ND7. Six samples were collected at Sites YB2–YB7 in 2015. All the sediment samples were dried at 40 °C, then disaggregated prior to the analysis. Sites F27–F38 are located in the upper and middle sections of the Red River. Downstream below Site F39, the river branches into several distributaries, which belong to the Red

River delta plain. Sites S1, T1, T8 and T9 are within the shoreface zone (b5 m), while the other sites (i.e., S3, S6–S13, T2 and T4–T7) are in the pro-delta zone (N 5 m). For heavy metal analysis, sediment samples were digested using a mixture of concentrated HF–HClO4–HNO3 acids, following the method described in Zhang et al. (2009). The samples were then analyzed for Cd, Cu and Pb concentrations using a graphite furnace atomic absorption spectrometer (Perkin Elmer A Analyst 800), and for Al, Fe, Cr, Mn, Ni, V and Zn concentrations using Inductively Coupled PlasmaOptical Emission Spectrometer (iCAP™ 7400 ICP-OES Analyzer). The reagent blanks were monitored throughout the analysis. China Stream Sediment Reference Material (GSD9, now named GBW07309), issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, was analyzed along with the samples for quality assurance purposes. The analytical results of metal concentrations for GSD9 were within the range of the certified values and the analytical precision was better than 10% based on the replicate analysis for each batch of samples. Total organic carbon (TOC) was determined by titration with FeSO4 after digestion with K2Cr2O7–H2SO4 solution (Lu, 2000). Data on particle size distributions of the samples are cited from work done by Nguyen et al. (2016).

Table 1 Heavy metal concentrations in sediments of the Red River, Vietnam (unit % for Al and Fe, while mg·kg−1 for the other elements). Al

Fe

Mn

Cd

Cr

Red River sediment Min-Max Mean ± SD Red River bank Subaqueous delta (b5 m) Subaqueous delta (N5 m) Soil, Red River delta Suspended sediment Ba Lat estuary Cam River Upper Continental Crust

Cu

Ni

Pb

Zn

V

Reference

12–122 38 ± 17 37 ± 20 21 ± 4 44 ± 3

27–188 66 ± 28 68 ± 32 32 ± 5 71 ± 7 45.89 129 81.59 92 ± 15 20

40–287 127 ± 50 127 ± 57 64 ± 8 144 ± 12 109.14 179 134.38 178 ± 31 71

46–140 97 ± 27 88 ± 21 61 ± 10 126 ± 8

This study

mg·kg−1

% 2.62–8.92 6.30 ± 1.71 6.06 ± 1.67 3.92 ± 0.07 7.58 ± 0.06

1.51–5.66 3.76 ± 0.99 3.84 ± 1.05 2.08 ± 0.04 4.07 ± 0.02

258–1240 806 ± 236 826 ± 262 474 ± 144 856 ± 59

9.85

5.46

5.36 ± 0.87 8.04

3.62 ± 0.35 827 ± 94 3.5 600

0.06–1.40 0.35 ± 0.27 0.46 ± 0.28 0.08 ± 0.02 0.18 ± 0.04 0.21 0.59 0.4 0.098

23.88–113.08 85.71 ± 23.75 81.69 ± 25.40 59.91 ± 10.27 102.29 ± 4.75 137.22 160 66.95 90 ± 11 35

20–332 83 ± 55 98 ± 63 26 ± 5 63 ± 11 58.14 94 73.49 82 ± 16 25

100 38 ± 6 20

60

Phuong et al. (2010) Gaillardet et al. (1999) Nguyen et al. (2011) Ho et al. (2013) Taylor and McLennan, 1995

Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030

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Fig. 2. Spatial variations of heavy metals and total organic carbon (TOC). The fluvial samples are arranged in an order from upstream down to the coast. Values of Cr and V increase gradually from upstream down to the river mouth. The concentrations of Cu, Cd, Pb, Ni and Zn do not exhibit simple trends. In the subaqueous delta, Cr, Ni, Zn, Cu, Cd and Pb show minor spatial variations. The subaqueous delta samples are grouped into shoreface (water depth b5 m) and prodelta (water depth N5 m) zones. In general, higher heavy metal concentrations occur in sediments from deeper water (N5 m) than those in the shallow water (b5 m).

Fig. 3. Spatial variation of particle size composition of the river bank and subaqueous sediments. Clearly, sediments from the prodelta zones have the highest clay fraction on average.

Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030

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Table 2 Statistical results from principal component analysis (PCA).

TOC Al Cd Cr Cu Fe Mn Ni Pb V Zn

Clay

Silt

Sand

TOC

Al

Cd

Cr

Cu

Fe

Mn

Ni

Pb

V

Zn

0.64 0.76 –0.17 0.75 –0.06 0.54 0.48 0.53 0.33 0.89 0.49

0.76 0.72 0.16 0.66 0.26 0.67 0.73 0.55 0.46 0.74 0.56

–0.76 –0.79 –0.03 –0.75 –0.14 –0.66 –0.67 –0.58 –0.44 –0.86 –0.57

1.00 0.59 –0.02 0.51 0.14 0.51 0.51 0.42 0.41 0.68 0.46

1.00 0.12 0.93 0.12 0.90 0.80 0.61 0.52 0.92 0.73

1.00 0.22 0.94 0.43 0.51 0.34 0.75 0.03 0.67

1.00 0.19 0.91 0.79 0.71 0.58 0.90 0.79

1.00 0.39 0.53 0.37 0.75 0.12 0.65

1.00 0.92 0.68 0.66 0.81 0.84

1.00 0.65 0.70 0.74 0.82

1.00 0.52 0.64 0.64

1.00 0.52 0.90

1.00 0.70

1.00

Rotated loading matrix (VARIMAX Gamma = 1.000) PC1 PC2 V 0.95 0.15 Sand –0.94 –0.08 Clay 0.92 –0.10 Al 0.91 0.23 Cr 0.86 0.32 Silt 0.84 0.20 TOC 0.75 0.05 Fe 0.75 0.53 Mn 0.69 0.61 Ni 0.63 0.42 Cd –0.10 0.98 Cu –0.02 0.94 0.39 0.83 Pb Zn 0.59 0.75 Eigenvalues 8.81 2.76 % total variance 62.92 19.68 % cumulative 62.92 82.60 Bold type indicates significance at p b 0.01.

Fig. 4. Scatter plot of Al content versus (a) clay, (b) TOC, (c) V, (d) Cr, (e) Ni, (f) Zn, (g) Pb, (h) Cd, and (k) Cu. In (b), (e) and (f), the R2 values are calculated without the samples in the circles.

Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030

T.T.H. Nguyen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

Heavy metal concentrations in the Red River sediments are summarized in Table 1 and Fig. 2. The average concentrations of heavy metals in sediments are in decreasing order of V N Zn N Cu N Cr N Pb N Ni N Cd (Table 1). Heavy metal concentrations in the Red River sediments in this study are comparable to those in Ba Lat Estuary sediments (Nguyen et al., 2011), Cam River (one of Red River distributaries) (Ho et al., 2013), and soils of the Red River delta (Phuong et al., 2010), but lower than those in the suspended sediments of the Red River (Gaillardet et al., 1999). They are higher in comparison to heavy metals in the upper continental crust (Table 1). Concentrations of Cr and V increase gradually from upstream to the river mouth. The concentrations of Cu, Cd, Pb, Ni and Zn do not exhibit simple trends. These metals show pronounced higher values at Sites F31 and F34 in the upstream. Spatial variations are observed for Cr, V, Ni, Zn, Cu, Cd, and Pb in the subaqueous delta. In general, sediments from deeper water (N 5 m) have higher heavy metal concentrations than those in the shallow water (b5 m) (Fig. 2). Particle size, clay mineralogy, iron oxides and TOC are important factors controlling heavy metal concentrations (Förstner, 1981; Singh et al., 1999; Du Liang et al., 2007, 2009). Normally, fine-grained sediments with higher clay mineral, iron oxides and TOC contents show higher heavy metal concentration (Förstner, 1981; Schropp et al., 1990; Zhang et al., 2001; Du Liang et al., 2007, 2009). Variations of Al, Fe, Mn and TOC concentrations show similar trends as observed in the mean particle size (Figs. 2 and 3), indicating the correlations of clay mineral, Fe/Mn oxides and TOC with fine sediments (Table 2). Correlation analysis reveals diverse relationships between particle size and heavy metal contents (Table 2). There are significant correlations (p b 0.01) between V and Cr and the fine fraction (clay and silt), while Ni and Zn exhibit weaker correlations with the fine fraction. However, if the

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samples with high concentrations of these metals (e.g., Ni at Sites F27, F29 and F31; Zn at Sites F31 and F34) are removed, then, concentrations of Ni and Zn are significantly (p b 0.01) correlated with Al content (Fig. 4), suggesting that except for a few sites, V, Cr, Ni and Zn are largely controlled by the fine sediments, i.e., a primary natural source. Since Cu, Cd and Pb are poorly correlated with particle size, there could be other factors influencing their concentrations such as anthropogenic input. Heavy metals were categorized into three groups by cluster analysis (Fig. 5). The first group includes Cu and Cd, then Al, Fe, Mn, V, Cr, Zn, Pb and clay for the second group, while the third group includes Ni. The results indicate that fine particles with higher clay minerals, Fe/Mn oxides and TOC content are the major carriers for transporting Cr and V. This implies that concentrations of these metals are mainly controlled by particle size as a result of natural weathering processes. High concentrations of Cr and V are generally found at sites with high percentages of clay fraction from upstream to the subaqueous delta of the Red River (Figs. 2 and 3). Due to the increasing trend of clay fraction from upstream down to the coast, Cr and V also follow the same pattern. So do Al and Fe. However, variations in Pb, Cd, Cu and Zn concentrations in the sediments do not follow the clay fraction change. Concentrations of these metals, therefore, cannot be simply explained by change in particle size. Sorting of particle size during sediment transportation is not the only process affecting concentrations of Pb, Zn, Cd and Cu in the Red River sediments. To further identify possible sources of heavy metals in sediments, principal component analysis (PCA) was performed on Cr, Ni, Zn, V, Cu, Cd, Pb, Al, Fe, Mn and TOC concentrations (Table 2). The extracted two components with Eigen values N1 explain 82.60% of the total variance. The first principal component (PC1) accounts for 62.92% of total variance, showing high positive loadings of Al (0.91), Fe (0.75), Cr

Cluster tree 0

5

10

15

20

25

Cu Cd Zn Pb Cr Al V Mn Fe Clay TOC Slit Ni Sand Fig. 5. Hierarchical cluster analysis shows tha association among particle size and geochemical compositions in the Red River sediments.

Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030

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for the purpose, which is expressed as follows (Salomons and Förstner, 1984; Sinex and Wright, 1988):

Table 3 Enrichment factor (EF) of heavy metals for the Red River sediments.

EF (Cr) EF (Ni) EF(V) EF (Zn) EF (Cu) EF (Cd) EF (Pb)

Min

Max

Mean ± S.D.

1.0 1.5 1.7 1.4 1.7 1.2 1.6

2.0 7.4 2.6 4.5 17.9 19.3 10.5

1.5 ± 0.2 2.5 ± 0.9 2.1 ± 0.2 2.2 ± 0.6 4.5 ± 3.3 4.8 ± 3.6 4.3 ± 1.5

(0.86), V (0.95), and TOC (0.75), and medium loadings of Mn (0.69) and Ni (0.63). This suggests that these heavy metals are primarily from natural sources. The second principal component (PC2) accounts for 19.68% of the total variance, showing high positive loadings of Cd (0.98), Cu (0.94), Pb (0.83), and Zn (0.75). This may imply anthropogenic sources, such as local traditional rural handicraft production villages. The high Cu content may be caused by smelting activities in the traditional copper casting village, mechanical engineering and agrochemicals/phosphate fertilizers. Cd is used for industrial purposes (e.g., plating and metal casting). There are many traditional villages along the Red River, such as chemical and fertilizer factory near Site F34, carpentry handicraft village near Site SH5, phosphorous fertilizer factory near Site F38, traditional lacquer handicraft village near Site F40, and a copper casting handicraft village near Site F42. Normally, Zn occurs together with Cu in bronze and brass or with Pb in batteries. Waste waters from these manufacturing industries have been discharged into rivers and polluted the river during the transport. Results from this study agree with previous reports (Trinh and Wada, 2004; Nguyen et al., 2006; Ngoc et al., 2009; Phuong et al., 2010). To minimize the effect of particle size and determine the impact of anthropogenic sources, metal enrichment factor (EF) is usually used



EF ¼

Me Al sample  Me Al background

:

where (Me/Al)Sample is the metal to Al ratio in the samples; (Me/ Al)Background is the metal to Al ratio in the background. There is scanty information about heavy metal background values in the Red River. Therefore, we adopted the values of upper continental crust (Taylor and McLennan, 1995) as the background values, which are (in mg·kg– 1 ): 80,400 for Al; 60 for V; 20 for Ni; 20 for Pb; 71 for Zn; 25 for Cu; 0.098 for Cd. For Cr, the updated value of 73 mg·kg−1 was used (Hu and Gao, 2008). This approach has been widely used to determine the sources and contamination of trace metals in riverine, estuarine and coastal environments (Sinex and Wright, 1988; Feng et al., 2004; Zhang et al., 2007, 2009; Zhu et al., 2011). The estimated heavy metal enrichment factors in Red River sediments are shown in Table 3 and Fig. 6. Typically, an EF value of b1.5 suggests a dominance of natural source (Zhang and Liu, 2002). Han et al. (2006) suggest EF N 2 as an indicator of pollution. In this study, EF values for Cr are found to be b2 (EF b2), suggesting that Cr contamination may not be a major concern in the Red River. The EF values of Ni, V, Zn, Cu, Cd and Pb are N 2 (EF N2), indicating existence of heavy metal contamination in the Red River. These results are comparable to those reported for the Ba Lat estuary, where heavy metal concentrations increased from core bottom to 50 cm of depth, and then, varied slightly to the surface (Nguyen et al., 2011). Their result suggests that the degree of heavy metal pollution has been rising with socioeconomic development and population growth (Nguyen et al., 2011). In the Red River, the mean EF values ranked in the order of Cd N Cu N Pb N Ni N Zn N V N Cr.

Fig. 6. Spatial variations of EF values for the Red River sediments. The EF values for heavy metals are higher in the fluvial part than those in the subaqueous delta sediments. The EF values for Zn, Pb, Ni, Cu and Cd display decreasing trend from upstream to river mouth. It means that heavy metal pollution is more serious in the upstream.

Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030

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In general, the EF values of heavy metals are higher in the fluvial plain section compared to the subaqueous delta. The EF values of Zn, Pb, Ni, Cu and Cd display decreasing trends from the upstream to the river mouth, indicating that heavy metal pollution is more pronounced in the upstream especially at Sites F31 and F34. These sites are located near chemical and fertilizer manufacturing industries and ore (Cu, Pb and Zn) mining facilities. Sediments from the delta plain and subaqueous deltas are relatively not contaminated. This could be attributed to the downstream dilution by sediments from the less polluted tributaries such as Da and Lao Rivers. Therefore, the upstream anthropogenic heavy metal impact becomes less significant (Chen et al., 2004). In summary, this study shows that heavy metal concentrations in the Red River sediments are influenced by both particle size and anthropogenic input. The results indicate that Cr and V in the Red River sediments are primarily derived from natural sources such as weathering processes. In contrast, Pb, Cd, Cu and Zn concentrations are influenced by anthropogenic source input. Nickel (Ni) pollution is found to be limited in the upstream. In general, sediments show a decreasing trend of metal pollution from the upstream down to the subaqueous delta possibly due to the dilution of natural or less-polluted sediment input from the tributaries. Acknowledgments The authors would like to thank Dr. Bruce J. Richardson and an anonymous reviewer whose comments and suggestions have improved the quality of an early version of this manuscript. This study was supported in part by the National Natural Science Foundation of China (41271223), and the State Key Laboratory Special Fund of China (2012KYYW01). We thank Prof. Fanuel Kapute for language improvement and Dr. XuanPhong Dang for his assistance in the field work. References Adams, W.J., Kimerle, R.A., Barnett Jr., J.W., 1992. Sediment quality and aquatic life assessment. Environ. Sci. Technol. 26 (10), 1864–1875. Berg, M., Tran, H.C., Nguyen, T.C., Pham, H.V., Schertenleib, R., Giger, W., 2001. Arsenic contamination of groundwater and drinking water in Vietnam: a human health threat. Environ. Sci. Technol. 35 (13), 2621–2626. Borges, J., Huh, Y., 2007. Petrography and chemistry of the bed sediments of the Red River in China and Vietnam: provenance and chemical weathering. Sediment. Geol. 194 (3), 155–168. Chen, Z.Y., Saito, Y., Kanai, Y., Wei, T.Y., Li, L.Q., Yao, H.S., Wang, Z.H., 2004. Low concentration of heavy metals in the Yangtze estuarine sediments, China: a diluting setting. Estuar. Coast. Shelf Sci. 60 (1), 91–100. Du Liang, G., Vandecasteele, B., Grauwe, P.D., Moors, W., Lesage, E., Meers, E., Tack, F.M.G., Verloo, M.G., 2007. Factor affecting metal concentrations in the upper sediment layer of intertidal reed beds along the river Scheldt. J. Environ. Monit. 9, 449–455. Du Liang, G., Rinklebe, J., Vandecasteele, B., Meers, E., Tack, F.M.G., 2009. Trace metal behavior in estuarine and riverine floodplain soils and sediments: a review. Sci. Total Environ. 407 (13), 3972–3985. Duc, D.M., Nhuan, M.T., Ngoi, C.V., Nghi, T., Tien, D.M., van Weering, T.C.E., van den Bergh, G.D., 2007. Sediment distribution and transport at the nearshore zone of the Red River delta, northern Vietnam. J. Asian Earth Sci. 29 (4), 558–565. Feng, H., Han, X., Zhang, W., Yu, L., 2004. A preliminary study of heavy metal contamination in Yangtze River intertidal zone due to urbanization. Mar. Pollut. Bull. 49, 910–915. Förstner, U., 1981. Metal Pollution in Aquatic Environment. Springer-Verlag, New York (475 pp.). Fu, K.D., Su, B., He, D.M., Lu, X.X., Song, J.Y., Huang, J.C., 2012. Pollution assessment of heavy metals along the Mekong River and dam effects. J. Geogr. Sci. 22 (5), 874–884. Gaillardet, J., Dupré, B., Allègre, C.J., 1999. Geochemistry of large river suspended sediments: silicate weathering or recycling tracer? Geochim. Cosmochim. Acta 63 (23– 24), 4037–4051. Gong, Z.T., 1999. Chinese Soil Taxonomy: Theory, Method and Application (in Chinese). Science Press, Beijing, China (903 pp.). Han, Y.M., Du, P.X., Cao, J.J., Posmentier, E.S., 2006. Multivariate analysis of heavy metal contamination in urban dusts of Xi'an, central China. Sci. Total Environ. 355 (1–3), 176–186. Ho, H.H., Swennen, R., Cappuyns, V., Vassilieva, E., Neyens, G., Rajabali, M., Tran, T.V., 2013. Assessment on pollution by heavy metals and arsenic based on surficial and core

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Please cite this article as: Nguyen, T.T.H., et al., Assessment of heavy metal pollution in Red River surface sediments, Vietnam, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.030