Impact of coal power generation on the characteristics and risk of heavy metal pollution in nearby soil

Figures & data

Figure 1. The location of the seven national large-scale CPBs.

Figure 2. The location and distribution of Xilin Gol CPB.

Figure 3. The locations of sampling sites in Xilinhot CPB.

Table 1. The classification of contamination levels based on Geo-accumulation index ($I_{geo}$).

$I_{geo}$	Soil quality
$I_{geo}$≤ 0	Uncontaminated
0 <$I_{geo}$≤ 1	Slightly contaminated
1 <$I_{geo}$≤ 3	Moderately contaminated
3 <$I_{geo}$≤ 5	Strongly contaminated
5 <$I_{geo}$	Extremely contaminated

Table 2. The classes of revised Nemerow integrated pollution index (RNIPI).

RNIPI	Soil quality
RNIPI<0	non-contaminated
0≤ RNIPI<0.5	slightly contaminated
0.5≤ RNIPI<1	slightly to moderately contaminated
1≤ RNIPI<2	moderately contaminated
2≤ RNIPI<3	moderately to strongly contaminated
3≤ RNIPI<4	strongly contaminated
4≤ RNIPI<5	strongly to extremely contaminated
5≤ RNIPI	extremely contaminated

Table 3. The classifications of potential ecological risk factor ($E_r^i$) and potential ecological risk index (RI).

$E_r^i$	Risk level	$RI$	Risk level
<30	Low	<150	Low
30–60	Moderate	150–300	Moderate
60–120	Moderate to high	300–600	High
120–240	High	≥600	Extremely high
≥240	Extremely high

Table 4. The statistical analysis of heavy metals in soil samples.

	As	Pb	Cu	Zn	Mn	Cd	pH
Max (mg﹒kg^−1)	47.00	10.96	23.55	50.70	464.67	2.20	8.37
Min (mg﹒kg^−1)	4.39	0.60	5.58	10.36	163.75	0.20	7.50
Median (mg﹒kg^−1)	24.48	5.36	11.73	23.44	287.54	1.19	8.01
Mean (mg﹒kg^−1)	25.13	5.67	12.42	23.21	291.29	1.11	8.01
Standard Deviation (mg﹒kg^−1)	11.51	2.90	3.74	7.75	72.48	0.46	0.19
Coefficient of Variation	45.79%	51.04%	30.10%	33.37%	24.88%	41.62%	2.35%
Xilin Gol background value (Gu, Zhang, and Bai 1995)	5.70	17.08	10.18	32.40	330.00	0.026	8.30
National Standard – Risk screening value	60.00	800.00	18000.00	300.00	/	65.00	/

Risk screening value is adopted from Soil Environmental Quality Risk Control Standard for Soil Contamination of Development Land (GB 36600–2018) Class II Land, and Zn not covered in that standard is adopted from Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15818–2018).

Table 5. Geo-accumulation index values and potential ecological risk factor values of the six heavy metals.

Method	As		Pb		Cu		Zn		Mn		Cd
	index	level	index	level	index	level	index	level	index	level	index	level
$I_{geo}$	1.38	Moderately contaminated	−2.45	Uncontaminated	−0.36	Uncontaminated	−1.14	Uncontaminated	−0.81	Uncontaminated	4.65	Strongly contaminated
$E_r^i$	44.09	Moderate risk	1.66	Slight risk	6.10	Slight risk	0.72	Slight risk	0.88	Slight risk	1276.43	Extremely high risk

Table 6. Characteristics of spatial distribution and potential ecological risk of heavy metals.

Method	Open pit mine waste dump		Suburb		Urban		Power plant		Overall
	index	level	index	level	index	level	index	level	index	level
RNIPI	2.93	moderately to strongly contaminated	3.20	strongly contaminated	3.76	strongly contaminated	3.67	strongly contaminated	3.30	Strongly contaminated
RI	997.56	extremely high risk	1160.10	extremely high risk	1847.50	extremely high risk	1712.70	extremely high risk	1329.88	extremely high risk

Figure 4. RNIPI values of all the 34 samples.

Figure 5. RI values of all the 34 samples.

Table 7. The results of factor analysis after rotation for the maximum variance.

Elements	Factor 1	Factor 2
Mn	0.865	/
As	−0.813	0.409
Cu	0.71	/
pH	0.701	/
Pb	−0.692	0.467
Zn	0.591	/
Cd	/	0.943
Eigenvalues	3.236	1.408
% of Variance	46.22%	20.11%

Figure 6. Cluster analysis of six heavy metals and pH.

Table 8. Pearson’s correlation analysis of six heavy metals and pH.

	As	Pb	Cu	Zn	Mn	Cd	pH
As	1
Pb	0.657**	1
Cu	−0.709**	−0.515**	1
Zn	−0.508**	−0.325	0.27	1
Mn	−0.647**	−0.465**	0.557**	0.397*	1
Cd	0.302	0.351*	−0.156	−0.053	0.114	1
pH	−0.382*	−0.514**	0.292	0.262	0.514**	0.043	1

**At 0.01 level (two sides) significantly correlated.

*At 0.05 level (two sides) significantly correlated.

Figure 7. The release mechanism of heavy metals in the production process of CPB.

Figure 8. The location of a power plant, residential area, and tourist park in the study area.

Gu, Y., T. Zhang, and H. Bai. 1995. “Qualitative Classification of Soil Background Value in Inner Mongolia.” Inner Mongolia Environmental Protection 7: 6–9.

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