Chemical speciation and phytoavailability of Cr, Ni, Zn and Cu in loess amended with attapulgite-stabilized sewage sludge

Figures & data

Table 1. Physicochemical properties of the attapulgite, sewage sludge and loess.

Parameters	Attapulgite	Sewage sludge	Loess
pH(soil/water = 1:5)	8.27 (0.28)*	6.23 (0.20)	8.06 (0.07)
Electrical conductivity (EC, Ds m^−1) (soil/water = 1:5)	1.060 (0.130)	3.020 (0.120)	0.190 (0.020)
Organic carbon (%)	ND	47.3 (0.29)	0.76 (0.05)
Moisture content (%)	8.52 (3.25)	80.6 (0.36)	9.23 (1.61)
Total N (%)	0.0820 (0.0030)	3.950 (0.170)	0.0650 (0.0080)
Total P (%)	0.57 (0.02)	2.13 (0.11)	0.073 (0.012)
Total K (%)	1.65 (0.09)	0.96 (0.03)	1.06 (0.17)
Total Cr(mg kg^−1)	112 (9)	116(9)	48(5)
Total Zn(mg kg^−1)	65(3)	368 (28)	92(15)
Total Cu(mg kg^−1)	38.6 (1.8)	78.3 (3.9)	65.8(11.3)
Total Ni(mg kg^−1)	23.4 (1.0)	56.0 (3.2)	31.9(5.6)

* Values in brackets are the standard deviation of the mean of triplicate measurements. ND: not determined.

Table 2. Physicochemical properties of attapulgite-stabilized sewage sludge.

			DTPA-Cr
Treatment	pH	EC (Ds·m^−1)	mg·kg^−1	DTPA-Ni	DTPA-Zn	DTPA-Cu
SS	6.23 (0.16) f*	3.020 (0.150) a	6.65(0.38) a	3.62 (0.17) a	51.2(3.2) a	3.21(0.15) d
SA1	6.72 (0.23) e	2.460 (0.130) b	5.69(0.33) b	3.35(0.13) a	51.5 (4.4) a	3.59 (0.13) c
SA2	6.95 (0.19) de	2.110(0.200) c	6.17 (0.35)ab	2.96(0.21) b	46.7 (3.2) b	3.92 (0.17) b
SA3	7.18 (0.25) cd	1.870 (0.070) cd	5.04(0.29) bc	3.02(0.16) b	49.8 (2.4) ab	3.80 (0.26) bc
SA4	7.56 (0.27) bc	1.720 (0.090) d	3.64(0.24)d	2.94(0.18) b	47.8 (3.6) b	4.62(0.25) a
SA5	7.82 (0.32) ab	1.330 (0.080) e	4.35(0.33) c	2.90(0.12) b	43.3(2.0) c	4.73 (0.13) a
SA6	8.05 (0.16) a	1.160 (0.080) e	4.33(0.26) cd	2.37 (0.20) c	39.8 (2.8) d	3.64 (0.22) c
LSD	0.42	0.090	0.71	0.28	0.29	2.99

*Values followed by the same letter within the same column do not differ significantly at the 5% level according to the LSD test; values in brackets are the standard deviation of the mean of triplicate measurements.

Figure 1. Distribution of metals in attapulgite-stabilized sludge as a function of different treatments.

Figure 2. Dry weight yields of corn grown in loess soil receiving attapulgite-stabilized sludge.

Table 3. Heavy metal concentration in aboveground and root tissues of corn grown in soil receiving attapulgite-stabilized sludge; BF and TF of heavy metals in corn.

Treatment	Cr				Ni				Zn				Cu
	Aboveground	Root	BF	TF	Aboveground	Root	BF	TF	Aboveground	Root	BF	TF	Aboveground	Root	BF	TF
SS	3.41(0.49)a*	7.40(0.50)a	0.06	0.46	3.98(0.34)a	67.3(4.4)a	1.20	0.06	63.1(4.0)a	74.2(3.5)a	0.20	0.85	36.7(3.8)a	72.3(5.3)a	0.83	0.51
LSA1	3.26(0.59)ab	6.35(0.85)ab	0.05	0.51	3.10(0.60)bc	65.2(4.2)ab	1.19	0.05	47.8(3.6)bc	67.2(2.6)ab	0.19	0.71	29.6(2.1)b	65.0(1.6)b	0.75	0.46
LSA2	2.78(0.22)bc	5.61(0.26)bc	0.05	0.50	3.35(0.49)ab	59.2(2.7)bc	1.08	0.06	49.5(3.8)b	63.7(4.7)bc	0.18	0.78	24.6(1.6)c	58.6(3.1)bc	0.70	0.42
LSA3	2.36(0.31)cd	5.75(0.45)bc	0.05	0.41	3.37(0.38)ab	51.4(3.4)cd	0.98	0.07	42.0 (5.2)c	59.6(3.0)bcd	0.18	0.70	20.7(1.5)de	55.0(4.1)c	0.66	0.38
LSA4	1.64(0.16)e	5.38(0.11)bc	0.05	0.30	3.05(0.30)bc	53.2(8.1)cd	0.98	0.06	26.9(4.4)d	60.9(7.0)bc	0.19	0.44	22.8(2.5)cd	54.0 (3.9)c	0.66	0.42
LSA5	2.15(0.21)de	5.32(0.22)c	0.05	0.40	2.64(0.47)bc	49.7(3.6)d	0.92	0.05	28.5(2.5)d	52.7(2.2)d	0.17	0.54	19.5(2.5)de	40.3 (4.3)d	0.51	0.48
LSA6	1.78(0.24)de	4.27(0.97)d	0.04	0.42	2.53(0.21)c	34.5(2.5)e	0.64	0.07	19.1 (1.1)e	58.1(5.9)cd	0.21	0.33	17.9(2.0)e	29.1 (2.5)e	0.40	0.61
LSD	0.51	0.82			0.61	6.46			5.35	6.40			3.46	5.35

* Values followed by the same letter within the same column do not differ significantly at the 5% level.

Table 4. Correlation coefficients between the amounts of the heavy metal fractions in rhizosphere soil receiving attapulgite-stabilized sludge and in aboveground and root tissues of corn.

Content	Element	Total content	Acid-extractable	Reducible	Oxidizable	Residual
Aboveground	Cr	−0.48	0.83*	0.97**	0.81*	−0.95**
	Ni	0.51	0.86*	0.82*	0.44	−0.82*
	Zn	0.95**	0.89**	0.95**	0.96**	−0.99**
	Cu	0.81*	0.99**	0.92**	0.97**	−0.96**
Root	Cr	−0.32	0.97**	0.93**	0.84*	−0.90**
	Ni	0.66	0.95**	0.86*	0.58	−0.86*
	Zn	0.84*	0.86*	0.73	0.88**	−0.83*
	Cu	0.97**	0.89**	0.82*	0.94**	−0.82*

*Correlation is significant at the 0.05 level. **Correlation is significant at the 0.01 level.