Table 7.

Pollution grade classification of the SPIs in soil (N = 1822).

Pollution Degree	Cr (%)	Pb (%)	Cd (%)	Hg (%)	As (%)	Cu (%)	Zn (%)	Ni (%)
Safety	99.40	99.95	92.86	66.68	100	95.88	98.63	92.04
Slight pollution	0	0.05	6.75	20.09	0	3.90	1.26	7.24
Mild pollution	0	0	0.27	6.59	0	0.22	0.05	0.27
Moderate pollution	0	0	0	5.76	0	0	0.05	0.33
Severe pollution	0	0	0.11	0.88	0	0	0	0.11
Polluted	0.60	0.05	7.14	33.32	0	4.12	1.37	7.96