Urban topsoil is the most frequent interface between human society and natural environment. The accumulation of heavy metals in the urban topsoil has a direct effect on residents' life and health. The geochemical baseline of heavy metals is an objective description of the general level of heavy metals in the urban topsoil. Meanwhile, the determination of geochemical baseline is necessary for regional environmental management, especially in coal cities prone to heavy metal pollution. Heavy metal pollution has become an environmental problem in Fuxin City, China for a long time. To establish the geochemical baseline of heavy metals in the topsoil of Fuxin City and to evaluate the ecological risk of the topsoil, we collected 75 topsoil samples (0-20 cm) and analyzed the concentrations of Cu, Ni, Zn, Pb, Cr, Cd, Hg and As through X-ray fluorescence spectrometry, atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry. We determined the geochemical baseline of heavy metals in the topsoil of Fuxin City by using iteration removal, box-whisker plot, cumulative frequency curve and reference metal normalization; evaluated the contamination risk and ecological risk of the topsoil by using the baseline factor index, Nemerow index and Hakanson potential ecological risk index; and identified the source category of heavy metals in the topsoil by using a pedigree clustering heatmap. Results showed that the geochemical baseline values were 42.86, 89.34, 92.23, 60.55, 145.21, 0.09, 0.08 and 4.17 mg/kg for Cu, Ni, Zn, Pb, Cr, Cd, Hg and As, respectively. The results of Nemerow index and Hakanson potential ecological risk index indicated that the urban topsoil in the study area was slightly contaminated and suffering low potential ecological risk. The main contaminated areas dominated in the middle part and northeast part of the study area, especially in the western Haizhou Strip Mine. The result of baseline factor index indicated that Hg and Cd were the major pollution elements. Using a pedigree clustering heatmap, we divided the sources of these heavy metals into three types: type I for Ni and Cr, largely represented the enrichment of heavy metals from natural sources; type II for Cu, Pb, Zn, Cd and As, mainly represented the enrichment of heavy metals from anthropogenic sources; and type III for Hg, represented the form of both natural and anthropogenic inputs.
ZHANG Hua, YU Miao, XU Hongjia, WEN Huan, FAN Haiyan, WANG Tianyi, LIU Jiangang. Geochemical baseline determination and contamination of heavy metals in the urban topsoil of Fuxin City, China. Journal of Arid Land, 2020, 12(6): 1001-1017.
Fig. 1Sampling sites and distribution in the urban topsoil of Fuxin City
Functional area
Item
Cu (mg/kg)
Ni (mg/kg)
Zn (mg/kg)
Pb (mg/kg)
Cr (mg/kg)
Cd (mg/kg)
Hg (mg/kg)
As (mg/kg)
Whole study area
Minimum
20.00
38.50
40.17
27.85
75.26
0.02
0.03
0.73
Maximum
156.58
207.45
510.16
168.95
1095.42
1.18
0.64
8.40
Average
45.13
91.84
107.96
63.15
162.50
0.13
0.11
4.36
CV (%)
36.54
36.23
61.51
32.31
73.01
132.05
93.08
53.67
Traffic area
Minimum
29.56
51.08
41.78
34.35
98.53
0.05
0.03
1.32
Maximum
72.70
146.16
279.58
168.95
239.47
1.18
0.44
8.40
Average
48.84
95.03
117.18
69.01
148.47
0.28
0.12
5.33
CV (%)
20.60
28.73
49.37
44.97
29.32
120.72
82.48
38.84
Industrial mining area
Minimum
26.36
44.79
49.01
39.92
104.00
0.03
0.04
0.94
Maximum
156.58
186.23
334.21
112.33
276.42
0.21
0.64
8.11
Average
50.22
91.31
120.67
60.96
146.69
0.10
0.16
4.65
CV (%)
58.45
42.36
53.62
30.55
28.95
45.96
92.00
46.96
Commercial area
Minimum
32.75
48.72
75.52
27.85
75.26
0.03
0.06
1.00
Maximum
73.50
121.01
200.05
128.11
197.05
0.18
0.57
8.09
Average
47.24
76.01
110.82
62.63
152.08
0.11
0.13
4.83
CV (%)
27.03
31.90
29.74
33.14
25.02
31.74
94.97
46.60
Residential area
Minimum
27.16
51.86
44.56
43.63
87.58
0.03
0.04
0.73
Maximum
57.52
136.73
510.16
77.98
186.79
0.15
0.24
8.28
Average
39.20
95.24
103.77
62.32
127.95
0.07
0.09
4.10
CV (%)
17.93
28.35
106.10
13.79
25.96
50.56
53.56
64.62
Green space area
Minimum
20.00
38.50
40.17
31.56
106.74
0.02
0.03
1.38
Maximum
51.93
207.45
141.40
77.05
1095.42
0.21
0.16
6.22
Average
40.16
101.63
87.36
60.84
237.28
0.09
0.06
2.88
CV (%)
22.30
39.48
28.35
24.45
100.42
64.24
48.63
57.24
Distribution pattern
L
N
L
L
L
L
L
L
Background value of Liaoning Provincea
19.80
25.60
63.50
21.40
57.90
0.11
0.04
8.80
Table 1 Concentrations of heavy metals in the urban topsoil of Fuxin City
Fig. 2Geochemical baseline values calculated by the box-whisker method
Fig. 3Geochemical baseline values calculated by the cumulative frequency curve
Element
Al
Fe
Ti
Rb
Regression equation
R2
P
Cu
-0.256*
0.272*
-0.340**
-0.200
y= -59.97x+70.54
0.99
0.00
Ni
0.073
0.314**
0.132
-0.007
y= -27.12x+5.65
0.92
0.00
Zn
-0.444**
0.093
-0.268*
-0.284*
y= -31.05x+320.33
0.98
0.00
Pb
0.057
0.079
0.315**
0.042
y= -15.08x+52.60
0.89
0.01
Cr
0.107
0.566**
0.275*
-0.016
y= -52.81x-7.97
0.98
0.00
Cd
-0.457**
0.016
-0.278*
-0.321**
y= -0.04x+0.38
0.97
0.00
Hg
-0.306**
-0.265*
-0.108
-0.038
y= -0.03x+0.29
0.96
0.00
As
-0.179
0.060
-0.328**
-0.148
y= -16.52x+11.28
0.99
0.00
Table 2 Correlation coefficients and regression equations of inert element and active element
Element
Cumulative frequency curve
Reference metal normalization (mg/kg)
Box- Whisker (mg/kg)
Iteration removal (mg/kg)
Final value (mg/kg)
Background value of Liaoning Province (mg/kg)
First bend (mg/kg)
Second bend (mg/kg)
Baseline value (mg/kg)
Cu
59.25
44.93
42.08
44.93
42.34
42.08
42.86
19.80
Ni
97.50
93.06
84.62
93.06
92.33
87.35
89.34
25.60
Zn
110.00
105.47
87.87
105.47
86.77
88.82
92.23
63.50
Pb
50.25
59.09
58.73
59.09
60.80
63.56
60.55
21.40
Cr
141.00
161.51
140.01
161.51
141.63
137.69
145.21
57.90
Cd
0.10
0.11
0.09
0.11
0.08
0.08
0.09
0.11
Hg
0.09
0.10
0.07
0.10
0.07
0.07
0.08
0.04
As
7.30
4.25
3.88
4.25
4.95
3.58
4.17
8.80
Table 3 Geochemical baseline values computed by various methods in the urban topsoil of Fuxin City
Sampling site
Cu (mg/kg)
Ni (mg/kg)
Zn (mg/kg)
Pb (mg/kg)
Cr (mg/kg)
Cd (mg/kg)
Hg (mg/kg)
As (mg/kg)
Reference
Baotou, Inner Mongolia
20.37
17.98
61.42
23.52
118.47
-
-
8.65
Zhu et al. (2016)
Bayan Obo, Inner Mongolia
26.46
29.16
76.71
29.07
124.37
-
-
16.09
Zhu et al. (2016)
Dexing, Jiangxi
58.90
-
138.54
54.61
72.87
0.37
0.100
14.00
Liu et al. (2014)
Urumqi, Xinjiang
94.54
43.28
294.47
53.53
54.28
1.17
-
-
Wei et al. (2010)
Zigong, Sichuan
23.10
24.50
62.00
28.20
66.40
0.18
0.037
3.86
Li et al. (2012)
Chengdu, Sichuan
-
32.00
535.00
281.00
110.00
2.94
0.630
28.60
Shi et al. (2012)
Tongling, Anhui
47.70
25.20
113.00
39.00
73.50
0.33
0.051
24.30
Jia et al. (2019)
Suzhou, Anhui
16.97
-
48.66
19.43
65.22
-
-
9.07
Gao et al. (2018)
Yanzhou, Shandong
34.34
33.27
89.86
27.39
75.27
0.14
0.069
7.77
Zhang (2007)
Fuxin, Liaoning
42.86
89.34
92.23
60.55
145.21
0.09
0.080
4.17
This study
Table 4 Comparison of geochemical baseline value with other literature
Fig. 4Pi (contamination index) values for heavy metals in the urban topsoil of Fuxin City
Functional area
PN value
RI value
Range
Mean
Rating range
Range
Mean
Rating range
Whole study area
0.80-9.56
1.96
Precaution-seriously
56.63-483.98
131.54
Low-considerable
Traffic area
1.12-9.56
2.93
Slightly-seriously
77.39-483.98
186.78
Moderately-considerable
Industrial mining area
1.11-6.09
2.04
Slightly-seriously
95.49-381.92
148.22
Low-considerable
Commercial area
1.11-5.33
1.66
Slightly-seriously
89.26-324.03
132.03
Low-considerable
Residential area
1.10-4.07
1.53
Slightly-seriously
63.59-154.11
98.54
Low-moderately
Green space area
0.80-5.50
1.64
Precaution-seriously
56.63-159.19
92.12
Low-moderately
Table 5PN (Nemerow index) and RI (Hakanson potential ecological risk index) values for heavy metals in the urban topsoil of Fuxin City
Fig. 5Spatial distribution of PN (Nemerow index) value in the urban topsoil of Fuxin City
Fig. 6Spatial distribution of RI (Hakanson potential ecological risk index) value in the urban topsoil of Fuxin City
Fig. 7Pedigree clustering heatmap of heavy metals in the urban topsoil of Fuxin City. The color key represents a weighted value of each element concentration. A high color key value represents the severe enrichment (such as red), whereas a low value represents the low enrichment (such as purple).
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