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Journal of Arid Land  2023, Vol. 15 Issue (10): 1196-1215    DOI: 10.1007/s40333-023-0109-1     CSTR: 32276.14.s40333-023-0109-1
Research article     
Spatial distribution and ecological risk of heavy metals and their source apportionment in soils from a typical mining area, Inner Mongolia, China
XIE Shicheng1,2,3, LAN Tian4, XING An1,2,3, CHEN Chen1,2,3, MENG Chang1,2,3, WANG Shuiping1,2,3, XU Mingming1,2,3, HONG Mei1,2,3,*()
1Inner Mongolia Agricultural University, Hohhot 010018, China
2Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resources, Hohhot 010018, China
3Key Laboratory of Agricultural Ecological Security and Green Development at Universities of Inner Mongolia Autonomous Region, Hohhot 010018, China
4School of Environment, Tsinghua University, Beijing 100084, China
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Abstract  

Determining the distributions and sources of heavy metals in soils and assessing ecological risks are fundamental tasks in the control and management of pollution in mining areas. In this study, we selected 244 sampling sites around a typical lead (Pb) and zinc (Zn) mining area in eastern Inner Mongolia Autonomous Region of China and measured the content of six heavy metals, including cuprum (Cu), Zn, Pb, arsenic (As), cadmium (Cd), and chromium (Cr). The ecological risk of heavy metals was comprehensively evaluated using the Geo-accumulation index, Nemerow general pollution index, and potential ecological risk index. The heavy metals were traced using correlation analysis and principal component analysis. The results showed that the highest content of heavy metals was found in 0-5 cm soil layer in the study area. The average content of Zn, As, Pb, Cu, Cr, and Cd was 670, 424, 235, 162, 94, and 4 mg/kg, respectively, all exceeding the risk screening value of agricultural soil in China. The areas with high content of soil heavy metals were mainly distributed near the tailings pond. The study area was affected by a combination of multiple heavy metals, with Cd and As reaching severe pollution levels. The three pathways of exposure for carcinogenic and noncarcinogenic risks were ranked as inhalation>oral ingestion>dermal absorption. The heavy metals in the study area posed certain hazards to human health. Specifically, oral ingestion of these heavy metals carried carcinogenic risks for both children and adults, as well as noncarcinogenic risks for children. There were differences in the sources of different heavy metals. The tailings pond had a large impact on the accumulation of Cd, Zn, and Pb. The source of Cr was the soil parent material, the source of As was mainly the soil matrix, and the source of Cu was mainly the nearby Cu ore. The purpose of this study is to more accurately understand the extent, scope, and source of heavy metals pollution near a typical mining area, providing effective help to solve the problem of heavy metals pollution.



Key wordsheavy metal      ecological risk      Geo-accumulation index      Nemerow general pollution index      tailings pond      mining area     
Received: 20 March 2023      Published: 31 October 2023
Corresponding Authors: *HONG Mei (E-mail: nmczhm1970@126.com)
Cite this article:

XIE Shicheng, LAN Tian, XING An, CHEN Chen, MENG Chang, WANG Shuiping, XU Mingming, HONG Mei. Spatial distribution and ecological risk of heavy metals and their source apportionment in soils from a typical mining area, Inner Mongolia, China. Journal of Arid Land, 2023, 15(10): 1196-1215.

URL:

http://jal.xjegi.com/10.1007/s40333-023-0109-1     OR     http://jal.xjegi.com/Y2023/V15/I10/1196

Fig. 1 Location of the study area (a) and spatial distribution of sampling sites (b)
Ei r Potential ecological risk level RI Potential ecological risk level
<40 Low ecological risk <150 Low ecological risk
40-80 Moderate ecological risk 150-300 Moderate ecological risk
80-160 Considerable ecological risk 300-600 Considerable ecological risk
160-320 Very high ecological risk >600 Very high ecological risk
>320 Serious ecological risk
Table 1 Classification of potential ecological risk
Fig. 2 Content of cuprum (Cu; a), lead (Pb; b), zinc (Zn; c), arsenic (As; d), chromium (Cr; e), cadmium (Cd; f), at different soil depths. The bar chart and the width of violin chart represent the frequency of the data. The black dots represent the medians. The bars represent the 95% confidence interval.
Fig. 3 Soil pH (a) and electrical conductivity (EC; b) at different soil depths. The bar chart and the width of violin chart represent the frequency of the data. The black dots represent the medians. The bars represent the 95% confidence interval.
Fig. 4 Spatial distribution of the content of Pb (a), Zn (b), Cu (c), As (d), Cr (e), and Cd (f) at 0-5 cm soil depth
Fig. 5 Spatial distribution of heavy metals pollution level at 0-5, 5-10, 10-20 cm soil depths based on the Geo-accumulation index (Igeo). (a1-a3), Pb; (b1-b3), Zn; (c1-c3), Cu; (d1-d3), As; (e1-e3), Cd; (f1-f3), Cr.
Fig. 6 Nemerow general pollution index (PN) of heavy metals at 0-5 (a), 5-10 (b), 10-20 (c) cm soil depths
Fig. 7 Pollution distribution map based on potential ecological risk index (RI) at 0-5 (a), 5-10 (b), 10-20 (c) cm soil depths
Heavy
metal
RfDing
mg/(kg•d)
RfDder
mg/(kg•d)
RfDinh mg/(kg•d) HQing HQder HQinh
Child Adult Child Adult Child Adult
Cu 4.0×10-2 1.2×10-2 - 1.6×10-4 9.2×10-5 3,8×10-7 3.2×10-7 3.8×10-9 8.6×10-9
Zn 3.0×10-1 6.0×10-2 - 6.4×10-4 3.8×10-4 1.6×10-6 1.3×10-6 1.5×10-8 3.5×10-8
As 3.0×10-4 1.2×10-4 3.5×10-6 3.4×10-4 2.0×10-4 8.3×10-7 7.0×10-7 8.2×10-9 1.8×10-8
Pb 3.5×10-3 5.3×10-4 8.2×10-5 1.8×10-4 1.0×10-4 4.3×10-7 3.6×10-7 4.3×10-9 9.6×10-9
Cd 1.0×10-3 1.0×10-5 2.4×10-6 2.3×10-6 1.4×10-6 5.7×10-9 4.8×10-9 5.6×10-11 1.3×10-10
HI - - - 1.2 7.0×10-1 8.2×10-3 6.9×10-3 2.4×10-3 5.4×10-3
Table 2 Assessment of reference dose (RfD) values and noncarcinogenic health risks of different exposure pathways of soil heavy metals in different populations
Heavy
metal
CRing CRder CRinh
Child Adult Child Adult Child Adult
As 3.4×10-4 2.0×10-4 8.3×10-7 7.0×10-7 8.2×10-9 1.8×10-8
Pb 1.8×10-4 1.0×10-4 4.3×10-7 3.6×10-7 4.3×10-9 9.6×10-9
Cd 2.3×10-6 1.4×10-6 5.7×10-9 4.8×10-9 5.6×10-11 1.3×10-10
Table 3 Assessment of carcinogenic health risks of different exposure pathways of soil heavy metals in different populations
Cu Zn Cr As Cd Pb EC pH
Cu 1.000
Zn 0.351** 1.000
Cr 0.103 -0.355** 1.000
As 0.196** 0.199** -0.097 1.000
Cd 0.583** 0.411** 0.116 0.485** 1.000
Pb 0.532** 0.331** 0.214** 0.491** 0.840** 1.000
EC 0.382** 0.366** -0.134* 0.138* 0.282** 0.229** 1.000
pH -0.202** -0.370** 0.226** -0.045 -0.115 -0.059 -0.476** 1.000
Table 4 Spearman correlation analysis of heavy metals and soil physical-chemical parameters
PC Initial eigenvalue Sum of squared loadings
Eigenvalue Explain variance (%) Cumulative variance (%) Eigenvalue Explain variance (%) Cumulative variance (%)
1 2.583 43.054 43.054 2.583 43.054 43.054
2 1.436 23.937 66.991 1.436 23.937 66.991
3 0.814 13.566 80.557 0.814 13.566 80.557
4 0.575 9.580 90.137
5 0.327 5.449 95.586
6 0.265 4.414 100.000
Table 5 Principal component analysis (PCA) of heavy metals in soils of the study area
Fig. 8 Principal component analysis (PCA) of heavy metals in soils of the study area. PC, principal component.
Fig. 9 Cluster analysis of heavy metals in soils of the study area
Fig. S1 Spatial distribution of the content of lead (Pb; a), zinc (Zn; b), cuprum (Cu; c), arsenic (As; d), chromium (Cr; e), and cadmium (Cd; f)
Fig. S2 Spatial distribution of the content of Pb (a), Zn (b), Cu (c), As (d), Cr (e), and Cd (f) at 10-20 cm soil depth
Fig. S3 Percentage of the geo-accumulation index (Igeo) at 0-5 (a), 5-10 (b), and 10-20 (c) cm soil depths
Fig. S4 Percentage of the potential ecological risk factor of a single heavy metal (Ei r) at 0-5 (a), 5-10 (b), and 10-20 (c) cm soil depths
Fig. S5 Percentage of potential ecological risk index (RI) at 0-5 (a), 5-10 (b), and 10-20 (c) cm soil depths
Soil depth (cm) Parameter Cu (mg/kg) Pb (mg/kg) Zn (mg/kg) As (mg/kg) Cr (mg/kg) Cd (mg/kg) pH EC (μS/cm) Elevation (m)
0-5 Mean 163 235 671 425 95 4 7.7 415 747
Median 105 101 366 119 64 2 8.0 213 748
Minimum 3 0 18 6 9 0 2.5 57 703
Maximum 1025 2943 5654 8840 462 87 8.5 3098 788
SD 163 373 841 933 83 8 0.9 482 20
CV (%) 100 159 125 220 87 187 11.7 116 3
Exceeding standard rate (%) 53 34 58 78 10 73
5-10 Mean 162 200 200 354 88 3 7.7 455 747
Median 86 80 358 105 59 1 7.9 235 748
Minimum 1 1 8 2 11 0 2.4 37 703
Maximum 2776 1757 6037 6458 306 20 8.6 2841 788
SD 258 294 886 741 67 3 1.0 488 20
CV (%) 159 147 444 209 76 125 12.4 107 3
Exceeding standard rate (%) 49 29 56 73 6 66
10-20 Mean 138 168 620 257 91 4 7.6 557 747
Median 73 70 304 61 62 1 7.9 302 748
Minimum 0 1 0 2 10 0 2.7 33 703
Maximum 1924 1497 5207 5985 2015 416 8.8 2713 788
SD 198 257 828 656 142 30 0.9 546 20
CV (%) 144 153 134 256 155 722 12.3 98 3
Exceeding standard rate (%) 41 23 52 64 5 62
Table S1 Statistical analysis results of soil heavy metal content
Soil depth (cm) Ei r RI
Cu Zn Cr As Cd Pb
0-5 10 2 1 160 209 7 388
5-10 9 2 1 132 123 6 273
10-20 8 2 1 95 182 4 291
Table S2 Mean value of Ei r and RI of soils at different depths
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