Table 5.

Grade evaluation of heavy metal pollution in soils (mg/kg).

	Hg	Pb	Cd	Cr	As	Cu	Zn	Reference
Clear area	0.3≤	25≤	0.2≤	34≤	10≤	32≤	74≤	geochemistry background value (level I)
Passable region	0.4≤	80≤	0.3≤	50≤	15≤	124≤	106≤	Canadian Soil Quality Guidelines (level II)
Slight pollution	0.5≤	100≤	0.4≤	100≤	20≤	216≤	237≤	Soil Screening Levels (SSLs)
Moderate pollution	0.6≤	140≤	0.6≤	200≤	25≤	308≤	343≤	Soil Guideline Values (SGV)
Heavy pollution	1.0≤	240≤	0.8≤	300≤	30≤	400≤	500≤	Soil Environmental Quality Risk control standard for contamination of agricultural land (GB15618-2018)