J Radioanal Nucl Chem (2011) 290:409–414 DOI 10.1007/s10967-011-1227-3
Contamination assessment of heavy metal in surface sediments of the Wuding River, northern China M. Longjiang • F. Qiang • M. Duowen H. Ke • Y. Jinghong
•
Received: 17 May 2011 / Published online: 10 June 2011 Ó Akade´miai Kiado´, Budapest, Hungary 2011
Abstract The heavy metal contents and the contamination levels of the surface sediments of the Wuding River, northern China, were investigated. Heavy metal concentration ranged in lg g-1: 50.15–71.91 for Cr, 408.1–442.9 for Mn, 20.11–43.59 for Ni, 17.51–20.1 for Cu, 68.32–89.57 for Zn, 0.2–0.38 for Cd and 15.08–16.14 for Pb in the Wuding River sediments. The enrichment factor (EF) and the geo-accumulation index (Igeo) demonstrated that the sediments of the Wuding River had been polluted by Cd, Cr and Ni, which mainly originated from anthropogenic sources, whereas the sediments had not been polluted by Zn, Pb, Cu and Mn, which were derived from the crust. In addition, the assessment results of EF and Igeo suggested that the sediments of the Wuding River was ‘‘moderately’’ polluted by Cd and ‘‘unpolluted to moderately’’ polluted by Cr and Ni. The elevated urban sewage discharges and agriculture fertilizers usage in river basin are the anthropogenic sources of these heavy metals in river.
M. Longjiang (&) F. Qiang Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science & Technology, Nanjing 210044, China e-mail:
[email protected] M. Longjiang F. Qiang College of Atmospheric Science, Nanjing University of Information Science & Technology, Nanjing 210044, China M. Duowen H. Ke College of Urban and Environmental Sciences, Peking University, Beijing 100871, China Y. Jinghong Department of Earth Sciences, Nanjing University, Nanjing 210093, China
Keywords The Wuding River Heavy metal Surface sediments Contamination assessment
Introduction Heavy metals are one of the serious pollutants of aquatic ecosystems, because of their environmental toxicity, persistence, and ability to be incorporated into food chains [1–4]. Over the past century, rapid industrial and urban development has added huge loads of pollutants to world rivers [5–8]. These heavy metals may be of natural source entering into the river system by weathering and erosion or anthropogenic origin due to industrial wastes, agricultural activities, as well as sewage disposal [9–12]. Heavy metals introduced into an aquatic environment can easily accumulate in the sediments [13]. As a result, the elevated heavy metals level in a river system is shown mainly by an increase in their contents in the sediments. Indeed, their occurrence in the environment results primarily from anthropogenic activities [14]. Therefore, the analysis of river sediments is a useful method to study the heavy metal pollution in an area [15]. To this day, numerous studies in heavy metal of sediments have been conducted by many researchers to understand heavy metal pollution and ecological risk in many rivers, such as the Yellow River [16], Yangtze River [7, 17], Pearl River [18, 19], Mississippi River [20], Nile River [21] and Ganges River [22], Lerma river [23, 24], Sul River [25], etc. The Wuding River is used as an important source for the public water supply in the northern Shannxi Province of China, especially the Yulin area. In recent year, economic growth and urban development in Yulin area has led to excessive release of waste into the Wuding River, although self cleaning capacity of this river is low due to low
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precipitation with only 398.4 mm/a of mean annual precipitation in this region [26]. The water quality of the Wuding River is quite important for future sustainable development of economics and society in this region for the future. However, the concentration and accumulation of heavy metals in the sediment of the Wuding River has not yet been studied. In this article, the efforts were made to evaluate the level of heavy metals in surface sediments of the Wuding River. In addition, the impacts of urban and agricultural activities on the heavy metal contamination in the Wuding River were also discussed.
Heavy metal analysis
Materials and methods
Contamination assessment methods
Study area
In order to evaluate anthropogenic impact of the metals, the enrichment factor (EF) and the geo-accumulation index (Igeo), were calculated for the metal concentration obtained in sediments at each site. The enrichment factor (EF), is commonly defined as a ratio of the metal element against a reference element. This reference element is often a conservative one, such as the commonly used elements Al, Fe, Ti, Mn, Sc, K, etc. [7, 8, 30, 31]. In this study, scandium (Sc) is expected to be a conservative element and may be chosen as the reference element. This element has been already used for calculating anthropogenic metal enrichments in the literature [8, 32]. We calculated the EF by using the following equation:
The Wuding River, which is important one of tributaries of the middle reach of the Yellow River, lies in Yulin area of northern Shannxi Province, China (Fig. 1). The Wuding River, which has the length of 491 km and cover an area of 30 261 km2, originates in the Baiyu Mountains of Shannxi Province, and flows through Jinbian, Hengshan, Yulin, Mizhi, Zizhou, Suide County, and finally enters the Yellow River (Fig. 1). The Wuding River Basin, is exposed to an extra-tropical semi-arid continently monsoon climate. The mean annual air temperature ranges from 7.6 to 9.6 °C over the entire basin. The mean annual precipitation is only 398.4 mm/a, but 75% of the annual precipitation occurs during the flood season from June to September, especially July and August. Furthermore, vegetation is sparse and soil is loose in this drainage basin due to low precipitation and relative higher evaporation. These make soil erosion is rather serious with 7,075 t/km2a of mean annual soil erosion modulus, and about 76.5 percent of entire basin is eroded. The Wuding River, including major tributaries such as Lu River, Yuxi River and Dali River yielded 25.2 9 106 t/a of sediments and transported into the Yellow River [27, 28]. Samples The location of the sampling sites is plotted in Fig. 1. The surface sediment samples were collected in June 2009 from five locations along lower reach of the Wuding River, Northern China. Five sites, including sites S1, S2, S3, S4 and S5, were selected for sampling. For the purpose of avoiding the effects of grain-size, the sediments were scooped up by plastic spade from the upper 3 to 5 cm of the modern floodplain, where the size of the sediments is silty sand. The samples were kept in plastic sacks and transported to the laboratory within days and air dried prior to the analysis.
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All of the samples for the chemical analysis were powdered in an agate mortar. About 100 mg fractions of powdered sediment were digested according to the method referred by Jiang [29]. Heavy metal element analysis included Cr, Mn, Ni, Cu, Zn, Cd and Pb was conducted by high-resolution inductively coupled plasma mass spectroscopy (HRICPMS) at the State Key Laboratory for Mineral Deposits Research of Nanjing University. The analytical precision was estimated to be \10% according to duplicate analysis of samples and standards.
EF ¼
ðCX =CSc Þsample ðCX =CSc ÞUCC
Where (Cx/CSc)Sample is a ratio of concentration of the metal to Sc in the samples of interest, whereas (Cx/CSc)UCC is the ratio of the upper continental crust (UCC) value of metal to Sc. The UCC values utilized were [33] in lg g-1: 11.0 for Sc, 35.0 for Cr, 600 for Mn, 20.0 for Ni, 25.0 for Cu, 71.0 for Zn, 0.098 for Cd and 20.0 for Pb, respectively. In general, an value of EF close to 1 indicates that a given metal may be entirely from crustal materials or natural weathering processes, while EF values greater than 1.5 denotes that a significant portion of trace metal is delivered from non-crustal materials, thus anthropogenic sources become an important contributor [34, 35]. The geo-accumulation index (Igeo), originally defined by Mu¨ller [36], is a quantitative measure of the metal pollution in aquatic sediments [7, 9, 35]: Igeo ¼ log2
ðC n Þ ð1:5Bn Þ
Where Cn is the measured concentration of the examined metal (n) in the sediment, and Bn is the geochemical background concentration of the metal (n). Factor 1.5 was utilized to minimize the effect of possible variations in the
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Fig. 1 Sampling locations of the Wuding River, northern China
background values because of lithogenic effects [36]. Here, Bn is the background concentration of element n in the UCC [33].
Results and discussion Heavy metal concentration in surface sediments Descriptive statistics including the total, mean, maximum, minimum and standard deviation values for the surface sediments from the Wuding River are presented in Table 1. The ranges of heavy metals in sediments were: 50.15– 71.91 lg g-1 for Cr, 408.1–442.9 lg g-1 for Mn, 20.11– 43.59 lg g-1 for Ni, 17.51–20.1 lg g-1 for Cu, 68.32–89. 57 lg g-1 for Zn, 0.2–0.38 lg g-1 for Cd and 15.08–16. 14 lg g-1 for Pb. The mean heavy metal concentrations followed the order; Mn [ Zn [ Cr [ Ni [ Cu [ Pb [ Cd for the sediments from the Wuding River. As a result, the Mn and Zn concentrations showed higher levels in the sediments, whereas Pb and Cd exhibited the lowest. The maximum value of Mn was 442.9 lg g-1, while the minimum value of Cd was only 0.2 lg g-1. In this study, UCC values are selected for the background values. Compared with UCC background values, we can clearly find that the values of Mn, Cu and Pb are lower than the UCC values, respectively, while Cr, Ni, Zn and Cd concentrations are enriched in the Wuding River sediments with respect to the UCC, respectively. Cr concentrations in the sediments of the Wuding River vary from 50.15 to 71.91 lg g-1, with an average of 60.71 lg g-1, which is higher than the Cr UCC background values
(35.0 lg g-1) [33]. The average Cr concentration for the sediments is 1.7 times the UCC background values. Ni concentrations range from 20.11 to 43.59 lg g-1, which are 1.0–2.2 times the Ni UCC background values (20.0 lg g-1) [33]. The average Zn concentration is 76.55 lg g-1, with a range from 68.32 to 89.57 lg g-1. Most concentrations are exceeding Zn UCC background values (71.0 lg g-1) [33]. Although the Cd concentrations for the sediments are lowest, with an average of only 0.3 lg g-1, which is more than three times Cd UCC background values (0.098 lg g-1) [33]. These demonstrate that the Wuding River basin has accumulated a considerable amount of these metals from anthropogenic sources in recent years. In general, the elevated heavy metal concentrations are mainly due to anthropogenic sources including mining, municipal waste water, fertilizers and pesticides used in agricultural activities [10–12, 37]. However, no noticeable industrial facilities were identified along the Wuding River. Cd concentration enrichment in sediments may be mainly attributed to urban sewage, fertilizers and road traffic. In addition, rapid urban development along the banks of the Wuding River seemed to have increased sewage discharge, which had led to Cr and Ni influx elevated in the river. Therefore, it is of major concern to monitor the level of contamination of these heavy metals along the Wuding River. The comparison of heavy metal concentrations in the sediments from other rivers with the Wuding River is listed in Table 2. As shown in Table 2, the concentrations of heavy metals gotten in surface sediments in this study were generally similar or lower than those reported for other rivers, including the Yangtze River [38], Yellow River [39], Kumho
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Table 1 Heavy metal contents in surface sediments collected from different sites of the Wuding River Station
Chromium (lg g-1)
Manganese (lg g-1)
Nickel (lg g-1)
Copper (lg g-1)
Zinc (lg g-1)
Cadmium (lg g-1)
Lead (lg g-1)
S1
64.57
442.9
34.80
20.10
89.57
0.29
16.14
S2
57.89
435.1
27.87
19.38
72.85
0.26
15.68
S3
50.15
429.0
21.84
18.57
72.35
0.20
15.47
S4
71.91
419.3
43.59
19.43
79.64
0.37
15.65
S5
59.02
408.1
20.11
17.51
68.32
0.38
15.08
Maximum
71.91
442.9
43.59
20.10
89.57
0.38
16.14
Minimum Mean
50.15 60.71
408.1 426.86
20.11 29.64
17.51 19.00
68.32 76.55
0.20 0.30
15.08 15.60
8.10
13.60
9.70
0.99
8.34
0.08
0.38
SDa a
Standard deviation
Table 2 Comparison of heavy metal contents in river sediments from the Wuding River and other rivers River Heavy Metal (lg g-1) Wuding River China (n = 5) this study Cr
60.71
Mn
426.86
Ni
29.64
Yangtze River China (n = 36) Yang [38] 87.82 – 40.91
Yellow River China (n = 16) Liu [39]
Kumho River Korea (n = 11) Kim [9]
85.48 54.59 –
Ganges River India (n = 17) Singh [40]
Almendares River, Cuba (n = 15) Susana [41]
Bouregreg river, Morocco (n = 9) Bounouira [42]
99.7
148
114.31
71.31
–
1806
–
742.11
97.6
48
–
29.58
– 36
Lerma river, Moxico (n = 8) Tejeda [43] – 472
Cu
19.00
51.64
55.63
125
55
158.31
22.39
Zn
76.55
140.27
49.12
298
107
261.74
119.76
Cd
0.30
1.53
1.67
0.6
2.46
0.49
–
149
22
92.58
–
27
Pb
15.6
45.18
– 18.61
River of Korea [9], Ganges River of India [40] Almendares River of Cuba [41], Bouregreg river of Morocco [42] and Lerma river of Moxico [43], which had been polluted by the heavy metal in various degree. In general, Mn concentration in the sediments is produced principally by natural contributions whereas the Cu, Zn, Cr, and Pb concentrations are originated principally by anthropogenic contributions. Heavy metal contamination assessment For the purpose of understanding the heavy metal enrichment in the surface sediments of the Wuding River, EF and Igeo have been worked for all the heavy metals studied. In fact, the EF and Igeo methods have been widely used to study sources and contamination level of heavy metals in riverine [8, 9, 19], lacustrine [11, 44], estuarine and coastal environments [7, 34, 35], as well as roadway dust [45, 46], etc. The EF and Igeo of different heavy metals in surface sediments from the Wuding River are listed in Table 3 and 4, respectively. The heavy metal EF in surface sediments was calculated with respect to their natural abundance in the UCC, with Sc
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as the reference element. As described in Table 3, EF for Cd was highest, ranging from 2.56 to 4.64, with an average of 3.71. The EF for Cr and Ni was from 1.79 to 2.53 and 1.09 to 2.68, with averages of 2.12 and 1.83, respectively, while the EF values for Zn, Pb, Cu and Mn were either close to or less than 1 (Table 3). Thus, the mean EF values of these metals were in the order: Cd [ Cr [ Ni [ 1.5 [ Zn [ 1 [ Pb & Cu & Mn [ 0.5. Based on the study carried out by Zhang and Liu [34], when an EF value is between 0.5 and 1.5, it suggests that the metal may be entirely from crustal materials or natural weathering processes, while an EF is greater than 1.5, it suggests that a significant portion of the metal has originated from noncrustal or anthropogenic processes [34]. Generally, present study showed that the sediments from the Wuding River are seen to be polluted with Cd followed by Cr and Ni, which had anthropogenic origins, while Zn, Pb, Cu and Mn were derived from the crust. For specific stations, the EF values of Cd and Cr were higher than 1.5 for all sampling stations, suggesting that these metals in the surface sediments of all sites had anthropogenic origins, while EF values of Zn, Pb, Cu and Mn were lower 1.5 for all
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Table 3 Enrichment factor (EF) of different heavy metals in surface sediments from the Wuding River Station
EF (Cr)
EF (Mn)
EF (Ni)
EF (Cu)
EF (Zn)
EF (Cd)
EF (Pb)
S1
2.40
0.96
2.27
1.05
1.64
3.88
1.05
S2
2.06
0.90
1.74
0.97
1.28
3.25
0.98
S3
1.79
0.89
1.36
0.93
1.27
2.56
0.96
S4
2.53
0.86
2.68
0.96
1.38
4.64
0.96
S5
1.84
0.74
1.09
0.76
1.05
4.22
0.82
Maximum
2.53
0.96
2.68
1.05
1.64
4.64
1.05
Minimum
1.79
0.74
1.09
0.76
1.05
2.56
0.82
Mean
2.12
0.87
1.83
0.93
1.32
3.71
0.96
SDa
0.33
0.08
0.65
0.10
0.22
0.82
0.08
a
Standard deviation
Table 4 Geoaccumulation index (Igeo) of heavy metal in surface sediments from the Wuding River Station
Igeo (Cr)
Igeo (Mn)
Igeo (Ni)
Igeo (Cu)
Igeo (Zn)
Igeo (Cd)
Igeo (Pb)
S1
0.30
-1.02
0.21
-0.90
-0.25
0.99
-0.89
S2
0.14
-1.05
-0.11
-0.95
-0.55
0.80
-0.94
S3
-0.07
-1.07
-0.46
-1.01
-0.56
0.45
-0.96
S4
0.45
-1.10
0.54
-0.95
-0.42
1.33
-0.94
S5
0.17
-1.14
-0.58
-1.10
-0.64
1.37
-0.99
Maximum
0.45
-1.02
0.54
-0.90
-0.25
1.37
-0.99
Minimum
-0.07
-1.14
-0.58
-1.10
-0.64
0.45
-0.89
Mean
0.20
-1.08
-0.08
-0.98
-0.48
0.99
-0.94
SDa
0.19
0.05
0.46
0.08
0.15
0.38
0.04
a
Standard deviation
sampling stations except for Zn in station S1, showing that these metals in the surface sediments of all sites derived mainly from natural processes related to the exposure of material from the earth crust. However, EF values of Ni were higher than 1.5 in S1, S2 and S4 stations, suggesting point sources of Ni at these points of the Wuding River. As shown in Table 4, the Igeo values calculated for heavy metal concentrations from this study were -0.07 to 0.45 for Cr, -1.14 to -1.02 for Mn, -0.58 to 0.54 for Ni, -1.10 to -0.90 for Cu, -0.64 to -0.25 for Zn, 0.45 to 1.37 for Cd and -0.99 to -0.89 for Pb. The average Igeo values was 0.2 for Cr, -1.08 for Mn, -0.08 for Ni, -0.98 for Cu, -0.48 for Zn, 0.99 for Cd and -0.94 for Pb (Table 4). The Igeo values includes seven grades, from 0 (non-contaminate) until 6 (very strong) [47]. According to this scale described by Mu¨ller [47], the present study results suggested that the Wuding River was ‘‘moderately’’ polluted by Cd and ‘‘unpolluted to moderately’’ polluted by Cr, whereas this river have not been polluted overall by these metals of Zn, Pb, Cu and Mn. However, the Igeo values of Ni in stations S1 (0.21) and S4 (0.54) suggested that S1and S4 were ‘‘unpolluted to moderately’’ polluted
by Ni. In summary, the contamination assessment results are in concordance with those of EF.
Conclusions The ranges of heavy metals in the surface sediments from the Wuding River were: 50.15–71.91 lg g-1 for Cr, 408.1–442.9 lg g-1 for Mn, 20.11–43.59 lg g-1 for Ni, 17.51–20.1 lg g-1 for Cu, 68.32–89.57 lg g-1 for Zn, 0.2–0.38 lg g-1 for Cd and 15.08–16.14 lg g-1 for Pb. The mean Mn, Cu and Pb concentrations are lower than the UCC values, respectively, while Cr, Ni, Zn, and Cd mean concentrations are enriched in the Wuding River sediments with respect to the UCC, respectively. The enrichment factor and Igeo demonstrated that the sediments of the Wuding River had been polluted by Cd, Cr and Ni, which mainly originated from anthropogenic sources, whereas the sediments had not been polluted by Zn, Pb, Cu and Mn, which were derived from the crust. The assessment results of EF and Igeo indicated the Wuding River sediments was ‘‘moderately’’ polluted by Cd and ‘‘unpolluted to moderately’’ polluted by Cr and Ni.
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These elevated heavy metal concentrations could be related to land-based sources of pollution in the Wuding River basin, mainly including: (1) the elevated urban sewage discharges with the development of the cities along the banks of the Wuding River, (2) agricultural practices, especially the fertilizers usage. Acknowledgments This study was supported by National Natural Science Youth Foundation of China (NO: 40901012),National Science and Technology Support Program of China (NO: 2010BAK67B02) and National Natural Science Foundation of China (NO: 40671016). The authors sincerely thank the editor for the helpful suggestions and comments which significantly improved our manuscript.
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