Spatial Distribution and Pollution Assessment of Potentially Toxic Elements (PTEs) in Surface Sediments at the Drinking Water Source Channel of Taipu River in China

Abstract

With the integration strategy of the Yangtze River Delta rising to the height of the national strategy, it is crucial to ascertain pollution, ecological risks, and possible sources of potentially toxic elements (PTEs) in the sediments of the drinking water source channel Taipu River across the core demonstration zone. In this study, distribution, risk assessment, and source of 12 PTEs were investigated in sediment samples from the Taipu River. The concentrations of Mo, Cu, Cd, Ni, and Zn in the sediments of the Taipu River were generally 1.01–5.84 times higher than the background value of the soil from Jiangsu Province. The spatial distribution of PTEs presented differently upstream, middle, and downstream of the river. The values of $I_{geo}$ and $EF$ showed moderate pollution at individual points, mainly due to Cd, Cu, and Mo. Except for Cd, the average potential ecological risk of other elements was low. Analysis of contamination source indicated that Cr, Ni, Tl, V, As, and Co were from natural sources while Zn, Mo, Cd, Pb, and Sb were associated with industrial activities. Copper was possibly derived from historic aquaculture activities along the Taipu River. Although the concentration of PTEs is generally low, particular attention should be given to Cd, Mo, and Cu as pollution sources. The results provide guidance for controlling PTEs pollution and protecting drinking water sources in the Taipu River.

1. Introduction

River plays a pivotal role in the life of humans. It helps in irrigation, aquaculture, flood control, transportation, drinking water, and balancing the ecosystem. The river sediments are an important indicator for the assessment of the water environment due to the sediment–water interactions [1,2,3]. Aquatic sediments can act as a sink of potentially toxic elements (PTEs) by deposition [4], and a source of lithogenic or anthropogenic PTE through resuspension [5]. Due to their low solubility, PTEs, which are often derived from atmospheric deposition, surface runoff, wastewater discharge, would accumulate in river sediments. These processes include the physical (such as flocculation, precipitation, and adsorption), chemical (complexation, chelation, and ion exchange), and biological (such as absorption, metabolism, releasing). It has been reported that the concentrations of many PTEs in the sediment can generally reach tens to hundreds of times those overwater [6].

The Taipu River is an important drinking water source channel for the Yangtze River Delta Ecology and Greenery Integration Development Demonstration Zone in China. The river is an important artificially excavated channel connecting Taihu Lake and the Huangpu River. The upstream is connected with the East Taihu Lake Water Source and the East Taihu Lake Emergency Standby Water Source, and the downstream is connected with Shanghai Jinze Reservoir and Jiashan Changbaidang Drinking Water Source Protection Area. It is located in the Yangtze River Delta Ecology and Greenery Integration Development Demonstration Zone in China. It acts as an important channel for flood discharge and shipping, but also a supply for potable water sources, which requires a very high standard of water quality and ecological balance. The Taipu River flows through fifteen towns of three provinces (Jiangsu, Zhejiang, and Shanghai), which have a very dense population and developed industries including (chemical, textile, printing, and dyeing, polyester, etc.). Recently, several pollution incidents occurred in the Taipu River, such as the input of cyanobacteria from the upstream (Taihu Lake) and antimony exposure by point sources (factories and wastewater treatment plants), which have raised widespread concern. The PTEs in the Taihu Lake posed serious threats to the water supply safety downstream (Jiashan and Qingpu) [7]. For decades, the Taipu River’s different functional positions set by each administrative region have made the governance of the Taipu River a problem.

However, most of the current studies about the Taipu River focused on the conventional physicochemical parameters [8,9,10] or the PTEs concentration in water [11], while few have investigated the situation of sediments. As the major navigable and tidal watercourse, the hydrodynamic of the Taipu River changes frequently, thereby promoting the transformation of PTEs in the sediments.

In this paper, the distribution and source of PTEs in the surface sediments of the Taipu River were investigated. The enrichment level and ecological risk of the sediments were also evaluated by various methods (geoaccumulation index, enrichment factor, potential ecological risk index). With a view to protect the regional water environment and ensure the safety of upstream and downstream water supply in the Taipu River watershed, this study can provide a scientific basis for the implementation of the protection of the Taipu River’s ecology and water environment.

2. Materials and Methods

2.1. Study Area and Sediment Sampling

The Taipu River belongs to the river network area of the Taihu Lake Basin. With a length of 57 km, it connects Taihu Lake, which is the third-largest freshwater lake, and the largest river in Shanghai, the Huangpu River. In addition, it is closely related to the surrounding water network, including 205 small/medium size lakes, and affected by the inflow of tributaries on both sides of the river. The average flux was 300 m³/s, and the flow rate was 0.03–0.33 m/s [12]. The bottom of the Taipu River is relatively flat, mostly covered by loose Quaternary layers, and the exposed area of bedrock is small. Sediment accumulation rate was about 4.2 cm/a [13]. This investigation conducted intensive sampling of the Taipu River, focusing on the intersection of the main tributaries and regional functional areas.

The sampling sites were recorded with a GPS and shown in Figure 1. From September to October 2018, 25 surface sediment samples (0–15 cm) were collected using a grab sampler, numbered TP1 to TP25. Before being kept in polyethylene Ziploc bags, the stones, animals, plants, debris, and the parts that were in contact with the sampler were carefully removed. Prior to storage at 4 °C, the samples were then taken back to the laboratory, freeze-dried at −20 °C, ground, sorted through 20 mesh and 200 mesh nylon sieves for the analysis of the particle size (20 mesh) and PTEs (200 mesh).

2.2. Analysis of PTE Concentration in Sediments

The concentration of PTEs was analyzed on an aliquot (0.1 g) of the pretreated sample digested by 1.0 mL HCl, 4.0 mL HNO₃, 1.0 mL HF, and 1.0 mL H₂O₂ in Teflon vessels in a microwave digestion system. After digestion (heating to 180 °C for 10 min prior to maintaining at 180 °C for 20 min) and cooling, the digestion vessels were placed in an electric hot plate heating (DKQ-1800, China), keeping at 150 °C to drive away HF. The digest was made up to 50 mL with 5% HNO₃ before analysis. The concentrations of Cr, Ni, Cu, Zn, Mo, Cd, Tl, Pb, V, Co, As and Sb were determined using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS, NexIon300X, PerkinElmer, Waltham, MA, USA).

2.3. Quality Control

The quality assurance and quality control (QA/QC) procedures were performed by setting blank and quality control samples for each batch of sediment samples. In the analysis of the total amount of PTEs, the certified reference materials (GBW07408, National Research Center of Certified Reference Materials of China, Beijing, China) were used for the quality control of the digestion process. The results showed that the reference materials recovery rate is within 88–109%. Sediment samples (every 5 samples) were analyzed in parallel during the digestion, and the relative error was below 6%. The total amounts were determined by ICP-MS, and each sample was repeatedly determined 3 times with relative standard deviation (RSD) < 10.8%, which insured the precision of the results. The internal standard method was applied, with Ge (10 μg/L), In (5 μg/L), and Bi (5 μg/L) as internal standard substances to correct the response signal to eliminate Instrument drift and matrix effects.

2.4. Sediment Characterization

The sediment pH values and the total organic carbon (TOC) were measured using the methods of Soil Determination of pH Potentiometry (HJ 962-2018, China) [14] and Soil Determination of Organic Carbon Combustion Oxidation Nondispersive Infrared Absorption (HJ695-2014, China) [15], respectively. The particle size was analyzed by laser diffraction (GB/T 12763.8-2007, China) [16].

2.5. Risk Assessment Methods

2.5.1. Geoaccumulation Index ($I_{geo}$)

Geoaccumulation index ($I_{geo}$) was introduced to assess the risk of trace elements in sediment samples collected [17]. $I_{geo}$ is defined by the following equation:

$$I_{geo}={\log }_2\left[C_n/\left(k\times B_n\right)\right],$$

(1)

where $C_n$ represents the concentration of elements tested in sediment samples, and $B_n$ is the geochemical background concentration of the element (n), employing the deep soil environmental background concentrations in Jiangsu Province; the values are shown in Table S4. The constant of 1.5 acts as the background matrix correction due to lithospheric effects to minimize the variation of background values. The seven pollution grades of $I_{geo}$ are shown in Supplementary Materials Table S1.

2.5.2. Enrichment Factor ($EF$)

Enrichment factor ($EF$) is a useful index in diagnosing the degree of anthropogenic PTEs pollution [18]. The enrichment factors for the tested PTEs in the sediments are calculated choosing Fe as the element of normalization since the Fe input is dominated vastly by its natural sources [19,20]. The formula applies is as follows:

$$EF=\frac{C_n/C_{ref}}{B_n/B_{ref}} ,$$

(2)

where C_n represents the element concentration in the sediment, and $C_{ref}$ represents the concentration of the reference element used. $B_n$ and $B_{ref}$ represent the background concentrations of PTEs and the reference element, respectively. Table S2 shows the factor standard of different levels.

2.5.3. Potential Ecological Risk Index ($RI$)

The potential ecological risk index ($RI$) was proposed by [21] and can be used to comprehensively evaluate the ecological risks of PTEs and their impacts on biology [22]. The equations used to calculate RI were as follows:

$$E_r^i=T_r^i\times \frac{C_n^i}{C_0^i} ,$$

(3)

$$RI={\displaystyle \sum }_{i=1}^n{E}_r^i ,$$

(4)

where ${\mathrm{C}}_n^i$ is the content of element i, $C_0^i$ is the background value for the metal i, $E_r^i$ is the potential ecological risk factor of the monomial element, and $T_r^i$ is the toxicity coefficient; its values for Cr, Ni, Cu, Zn, Mo, Cd, Pb, V, Co, As, and Sb are 2, 5, 5, 1, 1, 30, 5, 10, 2, 5, and 10, respectively. $RI$ is the sum of potential ecological risk for all the elements. As shown in Table S3, the values of $E_r^i$ can be divided into five categories, and $RI$ values can be divided into four categories.

2.6. Data Analysis

Microsoft Excel 2016 (Microsoft, Redmond, WA, USA), Origin 2018 (OriginLab, Northampton, MA, USA), SPSS 25.0 (IBM, Chicago, IL, USA), and Arc GIS 10.6 (ESRI, Redlands, CA, USA) were used for data processing and drawing of charts and graphs. Microsoft Excel 2016 and Origin 2018 were used for data collation and charting, respectively. Pearson correlation analysis and principal component analysis (PCA) were conducted within SPSS 25.0. ArcGIS 10.6 was applied to map the sampling area, and Kriging interpolation was used to analyze and represent the spatial distribution of PTEs graphically.

3. Results and Discussion

3.1. Sediment Characterization

The pH, particle size distribution, and total organic carbon of surface sediments are shown in

Table 1. Physicochemical properties data for surface sediment in the Taipu River.

Physicochemical Index	Max	Min	Median	Average	Standard Deviation	Variable Coefficient
pH	8.81	6.48	7.86	7.65	0.56	0.074
TOC(g/kg)	49.23	3.73	10.21	12.60	9.66	0.77
Clay (<4 μm) (%)	75.47	7.35	18.09	24.93	18.40	0.74
Silt (4–63 μm) (%)	79.10	24.53	68.9	63.22	14.85	0.23

. The pH values of surface sediments in the Taipu River range between 6.48 and 8.81, with an average pH of 7.65, showing slight alkalinity. The values of total organic carbon (TOC) range from 3.73 to 49.23 g kg⁻¹, and average at 12.60 g/kg. The variation coefficient of the pH values is 0.074, indicating a low spatial variability in alkalinity and acidity, while the higher variation coefficients of TOC (0.77) and the particle size (0.74 and 0.23) imply the more obvious spatial variabilities in the study area. In addition, the mean silt content of samples collected is much greater than clay.

3.2. PTEs Concentration

The amounts of Cr, Ni, Cu, Zn, Mo, Cd, Tl, Pb, V, Co, As, and Sb in the surface sediments of samples collected in the Taipu River are shown in

Table 2. The content of PTEs in the surface sediments of the Taipu River (mg/kg).

	Average	Median	Min–Max	Detection Limit	Standard Deviation	Variable Coefficient (%)	Background
Cr	58.2	57.9	35.6–85.3	0.11	11.88	20.4	77.8
Ni	27.6	28.1	10.88–46.9	0.67	8.26	30.0	26.7
Cu	27.5	23.3	8.53–130.2	0.06	23.3	83.7	22.3
Zn	71.7	67.1	26.8–143.1	0.05	28.7	40.1	62.6
Mo	0.460	0.433	0.222–0.963	0.02	0.19	41.9	0.3
Cd	0.107	0.081	0.021–0.455	0.09	0.087	81.5	0.126
Tl	0.435	0.423	0.291–0.617	0.08	0.088	20.2	0.439
Pb	19.1	18.4	12.03–27.5	0.03	4.41	23.1	26.2
V	77.1	77.2	45.8–116.5	0.12	17.1	22.2	83.4
Co	11.78	12.58	5.48–18.9	0.15	3.04	25.8	12.6
As	8.39	8.33	2.70–22.5	0.11	4.04	48.2	10
Sb	1.013	0.950	0.549–1.717	0.67	0.321	31.7	1.04

. Due to the strong regionality with the environmental sediment background, this study compared PTEs concentrations with the Jiangsu Province soil environmental background value (hereinafter referred to as the background value) to analyze the environmental pollution status of PTEs in the sediments of the Taipu River [23]. The maximum detection values of all PTEs at the sampled points exceed the background values. The maximum contents of Cu, Cd, and Mo are 130.2 mg/kg, 0.455 mg/kg, and 0.963 mg/kg, respectively, which are 5.84, 3.65, and 3.2 times of the background values, indicating severe enrichment in the Taipu River sediments. The average contents of Mo, Cu, Zn, and Ni surpass the background values, which are 1.53, 1.15, 1.23, and 1.03 times the background value, respectively. The median values of three elements (Ni, Zn, and Mo) exceed the background values, while Cu and Co are equivalent to the background values. As to the variation coefficients of element concentrations, discrepancies also are exhibited. Copper and chromium are more than 80%, indicating that the distribution of Cu and Cd in the Taipu River sediment has been highly uneven. The concentration variation coefficients of Zn, Mo, and As range from 40.1% to 48.2%, and that of other elements (Cr, Ni, Tl, Pb, V, Co, and Sb) range from 20.2% to 31.7%.

Compared with other water source rivers (such as Huangpu River and Biliuhe Reservoir), the overall pollution levels of various elements in the sediments of the Taipu River are lower (Table S5). As regards other important tributaries in the Yangtze River Basin (such as Xiangjiang River, Zijiang River, and Dadu River), the PTE contents in the Taipu River demonstrate light pollution. Except for Cd, the PTE concentrations in the Taipu River are higher than in the Liaohe River, while these are lower than in the Jialu River (Huaihe River Basin) and the Haihe River, apart from As. The contents of Cu, Pb, and Cd are below records in the rivers of the other countries, such as Vaigai River (India), and Bangshi River and Somesu Mic River (Romania); nevertheless, the contents of Cu, Pb, Zn, and Mo exceed the values of Chenab River, Pakistan.

3.3. Spatial Distribution

From upstream to downstream of the Taipu River (Figure 2), the spatial variation trends of the elements in the surface sediment samples are different, with significant fluctuations. The concentrations of Zn and Mo upstream are significantly higher than those in the middle and downstream, and high concentration sites are at TP2, TP3, TP5, TP8, and TP9. The element As is mainly concentrated midstream, and its maximum concentration is at TP13. Cu (TP11), Cd, and Pb (TP5, TP8, TP13) are higher in a few sites in the middle and upstream, and the values in other positions remained uniform. The spatial distribution of Ni, Cr, Tl, V, and Co are similar; their concentration in the middle and downstream is higher than upstream, but the three sites (TP3, TP8, and TP9) upstream also show high values. Sb shows a high concentration upstream and downstream but a low concentration midstream. The distribution of the sites generally shows that multiple elements are highly enriched at TP3, TP5, and TP8, indicating that these sites will become the main focus of environmental management.

3.4. Pollution and Risk Assessment

3.4.1. Pollution Degree Assessment

The geoaccumulation index ($I_{geo}$) results of Cr, Ni, Cu, Zn, Mo, Cd, Tl, Pb, V, Co, As, and Sb in the surface sediments of the Taipu River are shown in Figure 3a. Overall, the $I_{geo}$ values of all PTEs are below zero, showing unpolluted conditions. Spatial distribution characteristics of enrichment for differing elements are various, with individual elements enriched seriously within the region. The $I_{geo}$ values of Cr, Tl, Pb, V, Co, Ni, As, Zn, and Sb are greater than zero at some points, and thus, the overall pollution accumulation of these PTEs is low. Mo and Cd show uncontaminated to moderately polluted conditions at TP5 and TP8, and Cu is moderately polluted at TP11. These results may be related to the large number of industries distributed at TP5 and TP8. TP11 is located at the junction of the Taipu River and the Jinghang Grand Canal. The surrounding domestic and industrial pollutants carried by the Beijing–Hangzhou Canal may have caused the accumulation of elements.

Figure 3b presents the values of $EFs$ of PTEs studied. According to previous research, enrichment factor values below 1.5 indicate that elements originate from crustal materials or natural processes, while values higher than 1.5 suggest anthropogenic sources [24]. In general, among the analyzed 12 PTEs, the average $EF$ is between 0.83 and 1.67, of which Cu, Mo, and Zn reveal more elevated enrichment. The highest $EF$ value of a single element in all samples occurs at TP11, reaching 8.95 for Cu, which indicates moderately severe enrichment. The $E{F}_{Cu}$ values of the four sites (TP9, TP13, TP11, and TP14) are all higher than 1.5, implying minor enrichment caused by human activities in the area. The high $EF$ value of the second enriched metal element Mo is mainly concentrated upstream and midstream. In addition, the $EF$ for Cd is above 2 in both TP5 and TP8, showing minor enrichment. The enrichment factors for Cd are above 2 in both TP5 and TP8 sites, showing minor enrichment. This indicates that the sediment enrichment factors for Cu, Mo, and Cd are mainly caused by anthropogenic impact. The $EF$ values of Zn, Co, As, Sb, and Ni are higher than 1.5 in some points, which indicates that the enrichment of these elements is affected by anthropogenic activities. $E{F}_{Tl}$ and $E{F}_V$ are less than 1.5, implying their natural enrichment. The low $EF$ value (<1.0) indicates that Cr and Pb originate from natural processes such as soil and lithospheric weathering.

Variability in background values of PTEs in soils and sediments as a result of uneven distribution of natural PTEs has been reported in various studies [25,26]. A single threshold value, which is often determined as an average/medium value in the area, may lead to an under/overestimation of the pollution level [27]. Therefore, in this study, the uncertainty of the $I_{geo}$ and $EF$ results were assessed by comparing those based on background values of adjacent study areas (Figures S1 and S2). Under the background values of the three provinces, the elements with significant differences in the proportion of $I_{geo}$ pollution levels are Cu, Zn, Mo, and Cd. The unpolluted to moderately polluted concentrations of Cu (28%) and Cd (28%) in Zhejiang Province are significantly higher than the other two provinces, while Zn and Mo concentrations are higher in Jiangsu Province. The $EF$ values of all PTEs basically show differences under different background values. In general, Zhejiang Province has a higher proportion of minor enrichment, especially in Cr, Cu, Cd, Pb, V, and As. Determination of sediment background values in the study area is necessary to provide a more accurate assessment in the future.

3.4.2. Environmental Risk Assessment

The potential ecological risk index of PTEs in the surface sediments of the Taipu River is shown in Figure 4. The potential ecological risk level of almost all elements is low risk ($E_r^i$ < 30). Only Cd exhibits a certain ecological risk at a few sites. In terms of a single PTE, the $E_r^i$ value of Cd at TP3, TP5, TP9, TP13, and TP22 ranges from 30 to 60, which indicates moderate risk, and the $E_r^i$ value at TP8 is between 60 and 120, indicating considerable risk. These are basically in line with the pollution level results obtained by $I_{geo}$ and $EF$; the difference in some elements (Mo and Cu) may be caused by the toxicity coefficient. As regards the comprehensive potential ecological risk index ($RI$), the value is 80 < $RI$ < 160 at TP3, TP5, TP9, TP11, TP13, and TP22, which is a moderate risk level, while in TP8, it indicates a considerable risk. Other sampling sites in the study area are at low potential ecological risk. According to the above analysis, the ecological risk grades from small to large are Zn < Cr < V < Pb < Co < Ni < Cu < As < Sb < Cd.

3.5. Source Apportionment

The PCA was used to distinguish the pollution sources of PTEs in the sediments (Figure 5). The Kaiser–Meyer–Olkin (KMO) test value is 0.779, and the Bartlett sphericity test value P (corresponding to 0.000) is below 0.05, indicating that the data is suitable for principal component analysis. Three principal components loaded with eigenvalues >1 were extracted. which together explain 91.006% of the concentrations of these PTEs. PC1 explains 46.576% of the total variation, and it shows high loadings of Cr, Ni, Tl, V, Co, and As. PC2 explains 33.699% of the total variation, with the higher loadings of Zn, Mo, Cd, Pb, and Sb. Moreover, PC3 explains the lowest percentage (10.732%) of the total variance, and it merely loads with Cu.

PC1 components are identified as natural sources, as the average concentrations of Cr, Ni, Tl, V, As, and Co are lower than or equivalent to the background value. Cr, Ni, Tl, and V are the only elements related to particle size (Table S6). Some studies assert that Cr, Ni, Tl, V, Pb, and Co are mainly controlled by the parent material and the soil-forming process [28]. The correlation coefficients of the five elements in PC2 are all >7, and the $I_{geo}$ and $EF$ values of Zn, Mo, and Cd reach the maximum at TP5 and TP8, indicating that these elements may originate from the same source to a greater extent. A large number of metal casting, textile, printing and dyeing, chemical fiber, and other industries are distributed near TP5 and TP8. Cd, Cu, Mo, Pb, and Sb are common elements in wastewater from these industries [29,30,31,32,33,34]. In summary, PC2 components are considered industrial sources. The only contributing element of PC3 is Cu. In aquaculture activities with a long history along the Taipu River, copper sulfate (CuSO₄) algaecides or parasiticides are used to control the outbreak of cyanobacteria [35]. In Han’s study, with the CuSO₄·5H₂O-amended, pond sediment had a high total Cu concentration of 172.5 mg/kg, and four to five times higher than the data measured in the nonamended pond sediment, demonstrating an apparent copper accumulation [36]. Based on this, it can be denoted that PC3 might be mainly associated with the nearby aquaculture activities, especially the frequent addition of copper sulfate.

4. Conclusions

(1) The average contents of PTEs Cr, Ni, Cu, Zn, Mo, Cd, Tl, Pb, V, Co, As, and Sb in the surface sediments of the Taipu River are 58.2 ± 11.9 mg/kg, 27.6 ± 8.3 mg/kg, 27.5 ± 23.0 mg/kg, 71.7 ± 28.7 mg/kg, 0.457 ± 0.192 mg/kg, 0.107 ± 0.087 mg/kg, 0435 ± 0.088 mg/kg, 19.1 ± 4.41 mg/kg, 77.1 ± 17.11 mg/kg, 11.8 ± 3.04 mg/kg, 8.4 ± 4.04 mg/kg, 1.01 ± 0.321 mg/kg. The concentrations of Mo, Cu, Cd, Ni, and Zn are generally higher than the soil background value from Jiangsu Province, and other elements fluctuate around the background value. Compared with other rivers at domestic and abroad, the surface sediments of the Taipu River are slightly polluted. Spatially, Zn, Mo, and Sb have higher concentrations upstream, while As concentrations are enriched in the middle reaches, and the characteristic elements downstream are Ni, Cr, Tl, V, Co, and Sb.

(2) In the pollution assessment, based on deep soil background values, the $I_{geo}$ values of Mo and Cd show uncontaminated to moderately polluted conditions at TP5 and TP8, while Cu is moderately polluted at TP11. $EF$ indicates that Zn (TP5), Mo (TP2, TP3, TP5, TP8, TP11, TP22), and Cd (TP5, TP8) are slightly or moderately enriched at some sites, while Cu shows moderately severe enrichment ($EF=8.95$) at TP11. In the risk assessment, the potential ecological risk of almost all elements is low, and only Cd has moderate risk and considerable risk in individual sites. A comprehensive evaluation of $RI$(168.37) revealed a moderate risk level at TP8. Determination of sediment background values in the study area is necessary to provide a more accurate assessment in the future.

(3) The analysis of contamination sources indicated that Cr, Ni, Tl, V, As, and Co derived from natural sources. Zn, Mo, Cd, Pb, and Sb are considered to have originated from industrial sources, which may be associated with industrial activities. Copper, independent of other elements, possibly derived from the long historic aquaculture activities along the Taipu River.

(4) In this study, the concentrations of 12 PTEs are generally low, but there may be potential risks at individual sites. For the safety of water quality in the upper and lower reaches of the Taipu River, it is recommended that managers particularly consider Cd, Mo, and Cu levels.