Table 3.

Physicochemical properties and background concentrations of metals in the different soils.

Soil No.	Location	Coordinates	pH	OC (g·kg−1)	CaCO3 (g·kg−1)	CEC (cmol·kg−1)	Clay (%)	Background Cd (mg·kg−1)	Background Pb (mg·kg−1)	Background Cr (mg·kg−1)	Background As (mg·kg−1)	Background Hg (mg·kg−1)	Soil qualitya
1	Hunan	26°45′ N, 110°52′ E	4.90	9.00	0.00	10.85	42.91	0.19	28.74	49.69	16.59	0.08	I
2	Chongqing	29°48′ N, 106°24′ E	5.74	10.14	0.00	21.34	24.96	0.20	38.46	31.01	4.15	0.06	II
3	Yunnan	24°52′ N, 102°49′ E	5.92	19.87	0.00	11.10	27.52	0.30	42.51	53.74	8.71	0.09	II
4	Jiangxi	28°12′ N, 116°56′ E	6.01	6.78	0.00	8.70	36.51	0.18	34.75	44.81	11.64	0.07	I
5	Anhui	31°55′ N, 117°11′ E	6.25	11.62	0.00	19.08	16.84	0.11	30.17	36.96	8.34	0.07	I
6	Heilongjiang	45°40′ N, 126°37′ E	6.27	20.70	0.00	28.59	19.33	0.24	44.79	54.22	9.03	0.06	II
7	Jilin	43°31′ N, 124°48′ E	6.82	19.05	0.00	31.11	30.18	0.14	44.73	35.07	11.13	0.08	II
8	Shaanxi	34° 17′ N, 108° 01′ E	7.90	9.56	35.60	22.37	26.01	0.24	37.40	58.27	13.44	0.09	II
9	Henan	35° 00′ N, 113° 41′ E	8.07	10.32	27.50	16.01	18.18	0.23	36.12	50.97	9.22	0.09	II
10	Xinjiang	43°56′ N, 87°16′ E	8.12	11.27	15.06	25.25	9.57	0.20	40.87	73.42	10.82	0.07	II
11	Shanxi	37°22′ N, 112°28′ E	8.24	13.44	25.15	16.80	17.74	0.23	38.58	52.78	9.75	0.10	II
12	Tianjin	38°45′ N, 117°06′ E	8.29	12.77	53.57	24.67	7.59	0.22	39.75	46.26	12.26	0.06	II
13	Gansu	38°52′ N, 100°26′ E	8.37	11.18	38.51	11.23	6.66	0.21	36.86	79.17	13.94	0.09	II
14	Shandong	37°27′ N, 116°30′ E	8.65	6.87	31.69	13.09	17.11	0.26	36.02	59.86	8.29	0.07	II
15	Inner Mongolia	41°33′ N, 110°01′ E	8.80	9.45	11.51	11.61	10.51	0.22	40.80	66.00	7.24	0.07	II

^aClassification of soil quality based on GB15618-1995 (China). Grade I: natural background level; Grade II: lightly polluted, safe for agricultural production and human health.