The standard value of soil heavy metals contents (mg/kg).

Table 2: The standard value of soil heavy metals contents (mg/kg).

Heavy metal	Degree	Primary Standard		Secondary Standard		Tertius Degree
Heavy metal	pH	Natural background value	< 6.5	6.5-7.5	> 7.5	> 6.5
	Cd	0.2	0.3	0.3	0.6	1
	Cu	35	50	100	100	400
	Ni	40	40	50	60	200
	Pb	35	250	300	350	500
	Cr	Cr	150	200	250	300
	Mn			1500
	Co			40
	Se			1