Concentrations and chemical forms of heavy metals in urban soils of Shanghai, China

Figures & data

Figure 1  Location of the sampling sites. QS, Qianshao Village; QY, Qinyi Village; XJ, Xijia Village; YF, Yingfang Village; ZY, Zhaoyang Village.

Table 1 General information about the sampling sites

Land-use type	Depth (cm)	Location	Crops
Reference soils
Greenhouse (n = 12)	0–15 (Topsoil)	Qinyi Village	Cucumber, alfalfa, lettuce, greengrocery, cabbage
	15–30 (Subsoil)	Yingfang Village
Orchard (n = 8)	0–15 (Topsoil)	Zhaoyang Village	Peach
	15–30 (Subsoil)	Qianshao Village	Peach
Upland (n = 4)	0–15 (Topsoil)	Qinyi Village	Alfalfa, cabbage, cauliflower
	15–30 (Subsoil)	Yingfang Village
Sewage irrigated soils
Upland (n = 6)	0–15 (Topsoil)	Xijia Village	Greengrocery, water convolvulus, cabbage, cucumber, cowpea
	15–30 (Subsoil)

Table 2 Method for sequential extraction

Fraction	Extractant	Soil : solution ratio	Condition
Water soluble (Ws-)	Deionized water	1:5	Shake 1 h
Exchangeable (Ex-)	1 mol L^−1 CH3COONH4 (pH 7)	1:10	Shake 2 h
Acid soluble (Aci-)	25 g L^−1 CH3COOH (pH 2.6)	1:10	Shake 6 h
Mn-oxide occluded (MnO-)	0.1 mol L^−1 NH2OH·HCl (pH 2)	1:50	Shake 0.5 h
Organically bound (OM-)	0.1 mol L^−1 Na4P2O7 (pH 10)	1:50	Shake 24 h
Fe-oxide occluded (FeO-)	0.175 mol L^−1 (NH4)2C2O4+0.1 mol L^−1 H2C2O4+0.1 mol L^−1 ascorbic acid (pH 3.1)	1:50	Shake 4 h, then 0.5 h in boiling water bath. Stir occasionally
Residual (Res-)	HF-HNO3-HClO4 digestion

Table 3 Mean values for the physico-chemical properties of reference soils and sewage irrigated soils from Xijia

Land-use type	Depth (cm)	EC (dS m^−1)	pH	Exchangeable bases				CEC (cmolc kg^−1)	T-N	T-C	av.P (mg kg^−1)	Sand	Silt	Clay	Texture
				K^+	Na^+	Ca^2+	Mg^2+
				(cmolc kg^−1)					(g kg^−1)			(%)
Reference soils
Greenhouse (n = 12)	0–15	0.26 a	7.62 b	2.09 a	0.66 a	18.8 b	5.33 a	14.6 a	2.77 a	24.5 a	1805 a	37.9 a	37.4 a	24.7a	L
	15–30	0.25 A	7.85 B	1.80 A	0.74 A	18.7 B	5.38 A	14.2 A	1.87 A	17.0 A	1182 A	38.8 A	36.8 A	24.4 A	L
Orchard (n = 8)	0–15	0.09 a	8.09 a	0.63 b	0.14 b	22.6 a	2.73 b	12.6 a	1.28 b	13.2 b	123 b	37.0 a	40.6 a	22.7 a	L
	15–30	0.10 A	8.15 A	0.28 B	0.25 B	23.3 A	3.03 B	13.2 A	1.50 A	14.4 A	86.7 B	36.6 A	40.8 A	22.9 A	L
Upland (n = 4)	0–15	0.09 a	7.91 ab	0.58 b	0.43 ab	18.7 b	3.58 b	13.3 a	2.01 a	16.7 b	577 b	37.8 a	37.0 a	25.2 a	L
	15–30	0.08 A	7.98 AB	0.40 B	0.37 B	19.5 B	3.51 B	13.6 A	1.37 A	13.2 A	462 B	39.3 A	36.0 A	24.8 A	L
Sewage irrigated soils (Xijia Village)
Upland (n = 6)	0–15	0.08	7.09	0.43	0.24**	14.8*	4.86*	18.5*	2.59	21.7	285*	25.5	43.4	31.6	CL
	15–30	0.06**	7.10**	0.46	0.32	13.1**	4.70*	18.4**	1.61*	16.5**	284*	27.3	42.6	30.4	CL
Means followed by the same small letter are not significantly different at a 5% level for topsoil and those followed by the same capitalized letter are not significantly different at a 5% level for subsoil according to a Tukey's test. Means followed by * and ** are significantly different from the mean values for the top and subsoil of reference upland soils at 5% and 1% levels, respectively. CEC, cation exchangeable capacity; T-C, total carbon; T-N, total nitrogen; av.P, available phosphorus.

Table 4 Mean values of total heavy metal concentrations for reference soils and sewage irrigated soils from Xijia Village

Land-use type	Depth (cm)	Cd	Zn	Cu	Pb	Cr	Mn	Ni	As	Hg
		(mg kg^−1)
Reference soils
Greenhouse (n = 12)	0–15	0.19 b	150 a	39.0 a	27.0 a	88.2 a	576 a	29.4 a	9.72 a	0.19 a
	15–30	0.14 AB	127 A	32.3 A	28.0 A	82.8 A	550 B	29.9 A	9.66 B	0.17 AB
Orchard (n = 8)	0–15	0.10 c	93.0 b	26.9 b	27.0 a	74.7 b	638 a	31.0 a	11.3 a	0.09 b
	15–30	0.10 B	91.6 B	27.6 A	26.6 A	78.6 A	649 A	32.1 A	12.5 A	0.13 B
Upland (n = 4)	0–15	0.26 a	123 ab	34.2 ab	29.4 a	84.8 ab	565 a	32.1 a	10.1 a	0.17 ab
	15–30	0.20 A	122 AB	33.7 A	29.8 A	81.4 A	581 AB	32.7 A	10.1 AB	0.26 A
Sewage irrigated soils (Xijia Village)
Upland (n = 6)	0–15	2.15**	455**	78.0*	45.0**	159**	531	41.6*	13.4*	0.51**
	15–30	1.98**	414**	69.5*	41.0*	140**	504	40.8*	12.4	0.51**
Means followed by the same small letter are not significantly different at a 5% level for topsoil and those followed by the same capitalized letter are not significantly different at a 5% level for subsoil according to a Tukey's test. Means followed by * and ** are significantly different from the mean values for the top and subsoil of reference upland soils at 5% and 1% levels, respectively.

Figure 2  Total concentrations of Zn and Cd in sewage irrigated soils from Xijia Village. 2, 10, 20 and R refer to soils sampled at 2, 10 and 20 m from the open canal and reference samples. (▒), topsoil; (□) subsoil, and the dotted line represents the permissible value set by the Chinese Environmental Quality Standard (GB15618-1995). Bars on the top right represent the least significant differences (LSD) at the 95% level for comparison between distance from the abandoned canal (left) and depth (right).

Figure 3  The 0.1 mol L−1 HCl extractable fraction of Zn and Cd in sewage irrigated soils from Xijia Village and reference upland soils. 2, 10, 20 and R refer to soils sampled at 2, 10 and 20 m from the open canal and reference samples. (▒), topsoil; (□) subsoil. Bars on the top right represent the least significant differences (LSD) at the 95% level for comparison between distance from the abandoned canal (left) and depth (right).

Table 5 Correlation coefficients between concentrations of metal fractions and soil properties of sewage irrigated soils from Xijia Village

Metal	Fractions	Total metal	pH	K^+	T-N	T-C	av.P
Zn	0.1 mol L^−1 HCl extractable	0.97**	−0.84*	−0.80	NS	0.81	0.87*
	Ws-	NS	NS	NS	0.85*	0.77	NS
	Ex-	0.89*	−0.83*	NS	0.81	NS	0.77
	Aci-	0.94**	−0.77	−0.81	NS	NS	0.86*
	MnO-	0.98**	−0.79	−0.81	NS	NS	NS
	OM-	0.89**	NS	−0.82*	NS	NS	0.91*
	FeO-	0.99**	−0.83*	−0.83*	NS	NS	0.82*
Cd	0.1 mol L^−1 HCl extractable	0.99**	−0.81*	−0.86	NS	NS	0.85*
	Ws-	0.79	−0.83*	NS	NS	NS	NS
	Ex-	0.93**	−0.80	−0.86*	NS	NS	0.88*
	Aci-	0.93**	NS	−0.89*	NS	NS	0.83*
	MnO-	0.95**	−0.78	−0.81	NS	NS	NS
	OM-	NS	NS	NS	NS	NS	NS
	FeO-	0.91*	NS	−0.86*	NS	NS	0.92**
*P < 0.05;
**P < 0.01; NS, not significant at a 10% level (n = 6). T-C, total carbon; T-N, total nitrogen; av.P, available phosphorus.

Figure 4  Fractionation of Zn in sewage irrigated soils from Xijia Village and reference upland soils. *Concentration below the detection limit (0.01 mg kg−1). 2, 10, 20 and R refer to soils sampled at 2, 10 and 20 m from the open canal and reference samples. (▒), topsoil; (□) subsoil. Bars on the top right represent the least significant differences (LSD) at the 95% level for comparison between distance from the abandoned canal (left) and depth (right). An anova was not conducted for the Ws-fraction because of a lack of data.

Figure 5  Fractionation of Cd in sewage irrigated soils from Xijia Village and reference upland soils. *Concentration below the detection limit (2 mg kg−1 for Ws-Cd, and 0.01 mg kg−1 for OM- and Res-Cd). 2, 10, 20 and R refer to soils sampled at 2, 10 and 20 m from the open canal and reference samples. (▒), topsoil; (□) subsoil. Bars on the top right represent the least significant differences (LSD) at the 95% level for comparison between distance from the abandoned canal (left) and depth (right). An anova was not conducted for the Ws-, OM-, FeO- and Res-fractions because of a lack of data.