Heavy metals in surface sediments of the intertidal Thai Binh Coast, Gulf of Tonkin, East Sea, Vietnam: distribution, accumulation, and contamination assessment

Heavy metals contamination in sediments may endanger ecosystems and human health via the food chain. In fact, there is little to no understanding about heavy metal accumulation in surface sediment of one of the most economically important marine bodies for Vietnam, the Thai Binh Coast, where five large rivers co-discharge into the Gulf of Tonkin. Twenty-seven surface sediment samples were collected from the intertidal regions and analyzed for: arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), and zinc (Zn) using inductively coupled plasma mass spectroscopy (ICP-MS). The studied area exhibited a large spatial variation in the concentration of heavy metals, e.g., the dry sediment concentration of Cd was the least (0.05–0.49 mg.kg−1), whereas that of Zn was the greatest (45.4–252 mg.kg−1). Based on the geoaccumulation index (Igeo\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${I}_{geo}$$\end{document}), most of the studied heavy metals were accumulated at low pollution levels, except four locations exhibited moderately and highly polluted levels of Hg with Igeo\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${I}_{geo}$$\end{document} Hg values from 1.92 to 2.66. However, the high contamination factor value implicated that not only Hg but also all other detected heavy metals in this area resulted from anthropogenic activities along the coast and the river upstream. This implied the need for quick action from the government. In addition, numerous analytical methods were used to see the association between metals, total organic carbon (TOC), and particle size distribution, including Pearson correlation coefficient (P) and principal component analysis (PCA). Hg demonstrates lowest connection with TOC (PHg-TOC ~ 0) but individual heavy metal correlations are largely positive, with many reaching 1.0 (e.g., PNi-Cr = 0.89, PCd-As = 0.72, PNi-Cu = 0.76, and PCu-Cr = 0.72). From the PCA diagram, we can observe that those sampling points in the positive direction of PC1 were expected to have a high concentration of Cu, Zn, As, Ni while having extremely little sand content.


Introduction
Rapid industrialization and urbanization inland and on the coast can render the intertidal zone more vulnerable to many kinds of metallic and organic pollutants (Hu et al. 2013;Gaonkar et al. 2021;Merhabi 2021). Among them, heavy metals are reported as the most hazardous in the aquatic environment and may pose a serious threat to human health, with arsenic (As), cadmium (Cd), and mercury (Hg) at the top of the hazards list (ATSDR 2019). These three metals can be released by anthropogenic activities or leached from soils, and transported by aquatic systems to the intertidal coast, and deposited on the surface sediment (Amankwaa et al. 2021). As a result, sediments can act as sources of heavy metals (El Nemr et al. 2016;Nour 2019;Shilla et al. 2019;Ye et al. 2020). It is believed that heavy metals can leach from surface sediments to enter food webs and then be biomagnified (Hosono et al. 2011;El Nemr et al. 2016;Ranjbar Jafarabadi et al. 2018;Amankwaa et al. 2021). Thus, the surface sediment quality of the intertidal coast is an essential indicator of environmental pollution (Yang et al. 2012;Zhu et al. 2012) and the potential risk to human health of aquatic produce from these areas (El Nemr et al. 2016).
Thai Binh is a deltaic coastal province in the southern part of the Red River delta, with three sides facing the river and one side facing the Gulf of Tonkin at 20°17'-20°44' north latitude and 106°06'-106°39' east longitude. Along the 59-km coastline, five rivers flow into the Gulf, namely Tra Ly, Lan, Ba Lat [Hong], Thai Binh, and Diem Ho, creating a large intertidal area of approximately 25,000 ha where saltwater from the Gulf intersects with river discharge, creating a bountiful ecosystem that is favorable for the development of aquaculture (e.g., clam, shrimp) and thus, is an economically important marine ecosystem (Ngo et al. 2018). Consequently, the intertidal region of the Thai Binh coast is exemplified the transition zone from ocean to land, where the flux of matter and energy is rapid, which has made it a site of international importance for wetland conservation (Hai et al. 2015). Therefore, information about the Thai Binh coast provides references for similar environments in other parts of the world, especially where similar aquaculture techniques may be used or under consideration.
This study assesses the accumulation of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), and zinc (Zn) in the surface intertidal sediments at some estuaries of the Thai Binh coast, the Gulf of Tonkin, Vietnam. Several indices (i.e., geoaccumulation index (I geo ) , contamination factor (CF), and the potential ecological risks ( Er i and RI)) were used to assess the current state of pollution, investigate the source of these metals, and examine the potential ecological risk.

Study areas
Every year, the Hong-Thai Binh River system discharges ~ 120 × 10 9 m 3 of water and deposits 114 × 10 6 tons of silt in coastal areas. The annual flow of water is mainly concentrated in the rainy season (300 m 3 .s −1 and 2200 m 3 . s −1 , from June to September), and just 50-300 m 3 .s −1 during the remaining months are typically low (Table S1) (Vietnam Government Portal 2010).
The coastal estuaries of the Thai Binh Province have a relatively uniform tidal regime, with the diurnal tide gradually decreasing from the north to the south. The maximum amplitude of tides ranges from 3.5 to 4.0 m, with an average of 1.7-1.9 m and a minimum of 0.3-0.5 m. The highest tide in a year can reach 4.0 m, and the lowest tide can be 0.08 m. Because of the high tide amplitude, salinity ranges from 5 ‰ to 20 ‰, and tides can result in considerably deep penetration of river mouths: 14 km for the Red River and 20 km for Tra Ly River. As shown in Table S1, the flow of rivers is lower in April than in the rainy season. During this time, the low water level facilitates seawater penetration into the land, especially saline intrusion.
Coastal flow in Thai Binh is a combination of tides, wind, waves, river flow, and the characteristics of the Gulf of Tonkin. Flows in estuarine areas are often strongly influenced by the river, whereas flow is predominantly caused by wind in the outermost sea surface. In the northeast wind field, the longshore surface current flow, influenced by the north wind, varies in a direction depending on the intensity of the river flow and the coastal terrain. The south wind is prevalent in the southeast wind field, and the surface flows along with the shore. The tidal flow and tidal composition play a decisive role in the integrated flow in the coastal area of Thai Binh.

Sampling
Sediment samples for the study were collected from 27 intertidal sites in northeast Vietnam during the dry season (i.e., April 1-10). When the tide was low (about 6-8 a.m.), samples were collected from the estuaries of the Thai Binh, Diem Ho, Tra Ly, Lan, and Hong River mouths (Ba Lat estuary) and adjacent sites (Fig. 1). For each cross section, three sampling sites, namely low, middle, and high tide marks, were obtained from inland. Specific sampling locations are shown in Fig. 1. All sediment samples were collected and carefully preserved to avoid contamination of samples. At each sampling site, five large samples were collected from a square area (each edge 20 m long), one sample from each corner, and the fifth from the intersection of the two diagonals. Each large sample consisted of three smaller samples that were collected 5 m apart. Samples were taken from a depth of 0-10 cm and stored in polyethylene bags at 4 °C until later analysis. A handheld GPS device was used to fix the sampling location. All steps were accorded to the National Technical Regulation on the use of certified reference materials (CRM) in the analysis of geology and minerals (QCVN43:2012/BTNMT 2017).

Analytical procedures
The grain-size distribution of sediments was calculated by wet sieving of sand and gravel and by using the pipetting technique for silt and clay fractions (Robert 1980). Sediment samples were placed with weighting paper and dried out at 60 °C in the oven until the weight was unchanged. Then, the dried sediments were milled to have a size < 2 mm before further measurement. Total organic carbon (TOC) of samples was calculated following the ISO 14235:1998, which is by reaction of samples with excess K 2 Cr 2 O 7 -H 2 SO 4 solution and the excess being titrated using Mohr's salt [(NH 4 ) 2 Fe (SO 4 ) 2 ]0.6H 2 O (ISO 1998). Heavy metals were extracted from accurately weighed 0.25 g sample in polyfluorocarbon tubes by wetting with 2 mL of HNO 3 , 6 mL of concentrated HCl, and 2 mL of HF (El-Sorogy et al. 2016) and allowing to stand at room temperature overnight. The next day, samples were digested under pressure using a microwave system, increasing the temperature to 180 °C in 15 min and maintaining that temperature for 30 min (QCVN43:2012/ BTNMT 2017). Solutions were allowed to cool to room temperature, then transferred to plastic volumetric cylinders and diluted to 50 mL with deionized water. According to the manufacturer's recommendations, the concentrations of As, Cd, Cr, Cu, Hg, Ni, and Zn were determined by inductive coupled plasma mass spectrometry (ICP-MS, model 7900 Agilent, USA). All digests were repeated at least twice, i.e., the values are means of at least three independent measurements. The standard deviation of independent replicate analyses was less than ± 10%. The ICP-MS was calibrated using purchased solutions of certified concentration. Accuracy was assessed using the European Commission's standard reference material BCR-277R, and the recovery of spikes of As, Cd, Cr, Cu, Hg, Ni, and Zn, and of elements in BCR-277R ranged from 90 to 110%. In all the analyses, blanks were performed and modifications were given if required. All the measurements were taken in triplicate and average results are provided.

Pollution assessment criteria
This study used the standards on sediment quality established by Ontario Canada's Ministry of the Environment (OCME 2008) and the Environmental Protection Agency (EPA), USA (USEPA 1992;Long et al. 1995). The ratings for these parameters are shown in Table 1.

Assessment of heavy metal contamination in sediment by using indicators.
The I geo , potential ecological risk of a single element (Er i ) , and potential toxicity response index for various heavy metals in the sediments (RI) were used to assess the cumulative origin of heavy metals in the intertidal sediments. The chosen indicators supported each other to compensate for their disadvantages. Briefly, I geo shows us how high the heavy metal level is in the study area compared to the base level in the earth's crust. I geo previously has a factor of 1.5, which is a background matrix correction factor designed to reduce the influence of any changes in the baseline due to lithological changes in sedimentary rocks. CF, on the other hand, compares heavy metal concentrations to their typical composition in rocks without using a correction factor. However, CF is utilized together with the response coefficient for the toxicity of heavy metals to calculate Er i . It is worth noting that the toxicity of each heavy metal varies. This means that even at low concentrations, metals can pose more significant environmental risks. Finally, the RI provides a comprehensive view of all metals found in the study area's sediments. This is critical because, while the area is not significantly contaminated individually, the aggregate of all metals has various consequences.

The geoaccumulation index (I geo )
I geo is a quantitative measurement of the level of contamination in sediments and freshwater environments. I geo is calculated by comparing the total metal content in a sample with the base value of the metal (in this study, heavy metal content in the earth's crust was used as the base value); thus, an increase in the present level is predicted to be due to human activity affecting the natural environment. This index was calculated after Muller (1969), and after that, it has been successfully applied by many researchers (Muller 1969;El-Sorogy et al. 2016;Beata et al. 2018;Dash et al. 2021). The index was calculated as Eq. (1): where C n is the total measured concentration of the metal n (Table S2), and B n is the geochemical background of the metal n obtained from Turekian Karl's measurements (Turekian et al. 1961). Factor 1.5 is a background matrix correction factor proposed to minimize the impact of possible changes on the baseline because of lithological changes in sedimentary rocks. According to (Loska et al. 1997), the classification of the sediment pollution level is as follows: I geo ≤ 0 (unpolluted); 0 < I geo < 1 (unpolluted to moderately polluted); 1 < I geo < 2 (moderately polluted); 2 < I geo < 3 (moderately to strongly polluted); 3 < I geo < 4 (strongly polluted); 4 < I geo < 5 (strongly to extremely polluted); and 5 < I geo (extremely polluted).

The contamination factor (CF) and the potential ecological risks ( Er i and RI)
CF is used to evaluate the contamination of heavy metals in sediments and is calculated by the ratio of the concentration of each metal in sediment to its base value. Formula (2) is as follows (Hakanson 1980): n is the heavy metal content of the studied sediment, whereas B n is the heavy metal content in the substrate (Table S2), after accounting for the average content in the shale (Turekian et al. 1961). Pollutants are classified into four levels: CF < 1 (low CF ); 1 ≤ CF < 3 (moderate CF ); 3 ≤ CF < 6 (considerable CF ); and 6 ≤ CF (very high CF).
Er i is the potential ecological risk factor of single metal i. The calculation of Er i is deduced as follows: where Tr i is the response coefficient for the toxicity of the i th heavy metal. The corresponding Tr i listed values are as follows: Hg = 40, Cd = 30, As = 10, Cu = Ni = 5, Cr = 2, and Zn = 1 (El Nemr et al. 2016); CF i is the contamination factor which calculated in Eq. (2). The levels of impact of the element on the sediment environment were as follows: Er i < 40 (low potential ecological (1) risk), 40 ≤ Er i < 80 (moderate potential ecological risk), 80 ≤ Er i < 160 (considerable potential ecological risk), 160 ≤ Er i < 320 (high potential ecological risk), and Er i ≥ 320 (serious ecological risk). Finally, RI was obtained using Eq. (4).

Statistical analysis
Multivariate statistical techniques, including Pearson correlation matrix (PCM) and principal component analysis (PCA), were performed using OriginPro 2021 learning edition (OriginLab Corporation, Northampton, MA, USA) software packages. PCA is a strong pattern recognition approach that seeks to explain the variation of a large set of inter-correlated variables (Ranjbar Jafarabadi et al. 2018). It denotes the connection of variables, therefore decreasing the dimensionality of the data collection. PCA was conducted on the raw data set of heavy metals, TOC content, and grain components of the sediments in this work. The loading from PCA analysis provides information on the correlation between variables. Besides, their contribution to modeling and their effect on sample cluster separation also can be obtained.

Heavy metals and TOC distribution in sediment
The results of some heavy metals and TOC content in sediments on the Thai Binh coast are summarized in Table 2. Besides, the spatial variations of seven metals are represented in Table S2, Figure S1. The spatial distribution of the seven heavy metals in sediments is shown in Figure S1 and Table S2. According to the ATSDR (ATSDR 2019), we divided the metals into two groups associated with their toxicity, including group I is with lower toxicity (i.e., Cu, Cr, Ni, and Zn) and group II is with higher toxicity (i.e., As, Cd, and Hg).
The concentrations of the group I element were varied 8.65-71.9; 24.6-62.3; 11.2-43.7; and 45.4-252 mg.kg −1 for Cu, Cr, Ni, and Zn, respectively ( Table 2). The concentration of metals in decreasing order from the highest to lowest was as follows: Zn > Cu > Cr > Ni; this finding is in agreement with that of previous studies (Phuong et al. 2010;Tue et al. 2012;Ho et al. 2013). By comparing the concentrations of Zn, Cu, Cr, and Ni with the OCME guidelines (Table 1), we found that three locations (TT24, TT14, and TT4) had the lowest level of Zn pollution. However, only TT24 and TT24 ranged between effects range low (ERL)-effects range medium (ERM) according to the US EPA 1998. Most of the locations were polluted by the three remaining metals at the lowest level with the exception of TT8 for Ni, TT21 for Ni, and TT8, TT21, and TT23 for Cu. Following the criteria by both the OCME and EPA (Table 1), no probable or severe effect could be detected. As also indicated in Table 2, the group I element was still in the range of the national standard limit. However, Ni and Cu were already passed the threshold of ERL value according to US EPA. Regarding group II, we found that they were present at a considerably toxic level with some noticeable points. The concentration of Cd in the studied areas was lower than the lowest effect level according to the OCME, and the effect of this metal was rarely observed according to the EPA USA 1998 criterion (Table 1). On the other hand, As and Hg contamination in these areas varied. The mean of the As and Hg concentration, respectively, were 15.36 mg.kg −1 and 0.98 mg.kg −1 (Table 2). Such high concentrations have been seemingly predicted on the basis of statistics on the concentrations of metals in surface waters or in sediments from inland areas (Asian Development Bank 2007). In more detail, the highest concentration of As was 26.3 mg.kg −1 at the sampling station TT4, and this concentration had not yet reached the level of severe impact. All samples were affected by As at the lowest level, and the concentration of As was between the ERL-ERM values. The concentration of Hg in sediments at some stations was particularly high. For example, the Hg concentration at the TT9 was 3.79 mg. kg −1 of dry sediment; stations 12 and 22 (TT12 and TT22) had the same concentration of 2.28 mg.kg −1 of dry sediment (Table S1). Those stations including (TT8, TT9, TT12, TT22) with Hg concentrations larger than 2.00 mg.kg −1 indicated that they had reached a level of severity according to the Ontario provincial sediment quality guidelines, and frequent effects could be observed (Table 1 and Table S2). Table 3 shows comparisons of heavy metal concentrations in the Thai Binh coast area with those in other referenced locations. The results showed that the concentrations range of As, Cd, Cu, Cr, Hg, Ni, and Zn in the research area were comparable to those found in the other locations indicated. The average metal concentrations in the research region, on the other hand, were significantly higher than those on the coast of the Mekong River. The major cause of the difference in concentration was the obvious anthropogenic activities (Liang et al. 2019;Dang Hoai et al. 2020). Compared to Duyen Hai Seaport, Hg concentration in this research seems significantly high, which can be explained only by human influence.

Assessment of heavy metal contamination in sediment by using indicators
Geoaccumulation ( I geo ) Figure 2 presents the calculated I geo values for As, Cd, Cu, Cr, Ni, Zn, and Hg in the studied area. The mean I geo values of the sediments of the intertidal surface of the coastal area of Thai Binh province with the elements As, Cd, Cu, Cr, Hg, Ni, and Zn were − 0.43, − 0.99, − 0.90, − 1. 80, 0.21, − 1.94, and − 0.73, respectively (Table S3). Based on these values, the cumulative level of heavy metal was as follows: Hg > As > Zn > Cu > Cd > Cr > Ni. Comparing with the standards defined earlier, we concluded that most of the heavy metals at studied stations, which present the intertidal surface sediment, were not contaminants according to the previously defined criteria. Except for TT2, TT8,  The box-and-whisker plot of I geo TT11, TT12, TT22, TT26, they were moderately polluted, and TT9 was from moderately to strongly polluted. The explanation for this phenomenon could be from the clam and shrimp culture of people in the studied area. It was reported that before every new growing season, growing ponds were rinsed with chemicals to kill fungi and viruses such as Falizan and Sinment (GAE 2016). Unfortunately, such fungicides contain some amount of Hg. Other researchers reported that some pollutants originated from industrial waste, sewage runoff, and agricultural discharge accumulated in sediment could be released and affected the marine ecosystem (He et al. 2021;Tham et al. 2021). Therefore, there is a need for a better policy and more examination from the government.

Contamination factor
The CF indicated the metal pollution of sediments at different levels (Fig. 3). The highest value of CF Hg of approximately 9.47 was at station 9 (Table S4), which indicated that Hg was a very high CF at this station. No other report concurs with this unexpected value. Therefore, careful evaluation is required to assess this factor in the studied area. Moreover,stations 4,11,14,16,22,[24][25][26] were moderately contaminated by As and Zn, according to CF. The effect trend of I geo was repeated, and the CF of the studied heavy metal decreased as follows: Hg > As > Zn > Cu > Cd > Cr > Ni. There were differences in the CF value between heavy metals because of feature activities along the river basin. However, these generally high CF values at all the studied locations implicated that not only Hg, as discussed above, was polluted by human activities, but also the other heavy metal. This intertidal ecosystem may be critically affected by anthropogenic contamination such as mining from upstream.

Er i and RI
As shown in Fig. 4 and Table S5, the Er i and RI values of most of the sediment samples in the research area were lower than 40 and 150, respectively. This reflects that the Thai Binh coastal region generally poses a low potential ecological risk for most of the detected metals. However, a few stations pose a high risk. TT2, TT3, TT8-TT12, TT15, TT17, TT22, TT25, and TT26 had higher than the moderate ecological risk for Hg, and the same condition was observed in TT11 for Cd. TT8, TT9, TT12, and TT22 stations had reached a severely potential risk position for Hg. The concentration of Hg in this region showed a similar trend but with higher values than those reported by (Wang et al. 2013;Zhuang and Gao 2015;El Nemr et al. 2016). Regular monitoring and assessment should be conducted  Table 4 shows the Pearson's correlation coefficients (P) of seven heavy metals, TOC, and grain size proportion in sediments with statistical significance at p < 0.05. Individual heavy metal correlations are mainly positive, with several nearing 1.0 (e.g., P Ni-Cr = 0.89, P Cd-As = 0.72, P Ni-Cu = 0.76, and P Cu-Cr = 0.72). The amount of heavy metal contamination can be revealed by a substantial positive association between metal (i.e., As, Cd, Cu, Zn, and Ni) and total organic carbon (TOC). Hg exhibited the lowest relationship with total organic carbon (P Hg-TOC < 0). There were significant variations in the Pearson correlation values between individual metals such as Cu, Pb, Zn, Cd, and Cr along the Thai Binh estuary. TOC has a strong correlation with clay and silt. The small size of clay and silt may carry TOC better than large size (i.e., sand). The particle size decreased with an increase in the distance of the sampling location from the estuary because large particles were difficult to be flown far away. All stations contained sand (40.2-95.3%), and small-sized particles were present in relatively small proportions; however, the higher their concentration, the higher the TOC concentration (Tyson 1995). TOC is a critical indicator for   (Tham et al. 2021). The TOC concentration in some stations was low (< 1.0% of dry sediment Table S2), suggesting that TOC was mainly of marine origin (Youssef and El-Said 2011). On the contrary, TT4 was reported with a TOC concentration of 5.47%, which highly suggested it may come from the continent. Generally, at the sampling sites near major estuaries (TT1-TT3, TT7, TT13, TT25), surface sediments had a relatively high concentration of heavy metals. This may be attributed to the interaction of the sea with a high amount of matter from the continent (Youssef and El-Said 2011;Wang et al. 2013). However, considering that only reason, we cannot explain for the TT4 or the TT22 where many heavy metals have the highest concentration among this study. One possible explanation is the flow rate of the river. Table S1 shows that Ba Lat or Hong estuary has a considerably high flow rate. As a result, water can flow further, and then, the tidal brings it back to be more settled on both sides of the estuary. The other explanation is from human activities such as aquacultural. Therefore, a synergy of many processes should be considered to provide a better understanding (Bryan and Langston 1992). Besides, other indices (e.g., I geo ) are also important because considering a single metal does not describe the real potential risk of the studied area. Another reason may from the two large town in the study area (Fig. 1). The people living along the sampling area are mostly fishermen. Because of the ideal hydrological conditions, people have produced shrimp and oysters in this area for years and now. Farming methods in the past, on the other hand, were backward. People wash the pond after each farming and make use of various antifungal, antimicrobial medications, some of which include mercury. This might possibly be one of the explanations for the exceptionally high mercury levels in some places.

Discussion
The top two PCA axes' eigenvalues accounted for 72.12% of the overall variance (Table S6). Except for sand and Hg, all other parameters were positively linked with PC1 (Table S7), while Cu and Hg were positively associated with PC2 (r = 0.42 for Cu and r = 0.79 for Hg). From the PCA diagram, we can see that those locations in the positive direction of PC1 were likely to have a high concentration of Cu, Zn, As, Ni while having very low sand content. The explanation can be from the hydrology condition; low hydrology ineffectively dilutes heavy metals. Besides, those locations on the upper right of the diagram, particularly samples TT9 and TT12, were highly polluted with Hg indicates the presence of Hg contamination sources related to it. In fact, the Thai Binh province has a relatively poor waste treatment system, including solid waste and wastewater. Furthermore, the overuse of pesticides and fungicides, as mentioned in Sect. 3.2.1, makes the pollution situation in this study area more severe.

Conclusions
The ecological risk of As, Cd, Cu, Cr, Hg, Ni, and Zn in 27 surface coastal sediment samples collected from the Thai Binh coast, the Gulf of Tonkin, Vietnam, in 2017 was evaluated using different analysis methods, namely I geo , CF, Er i , and RI. Zn was the dominant heavy metal in sediment samples. However, its concentration was presented as a low pollution risk. The concentration of the studied heavy metal was sequenced as Zn > Cu > Cr > Ni > As > Hg > Cd. According to the I geo value, except for Hg, the levels of detected metals in the Thai Binh coast were relatively low. CF indicates that most of the sediment deposition was drastically affected by anthropogenic activities. The Er i and RI indicate that heavy metals in sediments did not pose any ecological risk except for Hg.