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Copper, zinc, and nickel in soil solution affected by biosolids amendment and soil management.

Introduction

Biosolids is an urban waste, production of which increases with urban expansion, with lifestyle changes, and with sewage-treatment technology advances. In the United States, for example, about 4.6 Mt of biosolids (dry matter) per annum was produced in the early 1970s (US EPA 1999). In 1998 this production was 6.9 Mt, an increase of 50%, compared with a 29% increase in population in the same period. In New Zealand the estimated biosolids production in 2006 was 240 000 t (New Zealand Ministry for the Environment 2007). Increased biosolids production requires cost-effective and environmentally friendly methods for disposal. Biosolids use on agricultural land in New Zealand has only been practised on a small scale but is expected to increase as the cost of chemical fertilisers increases.

The potential environmental and health risks from chemical contaminants (e.g. trace metals) remain a concern for biosolids use on agricultural land. Because of their toxic nature to plants, soil biota, or human beings when over-supplied, trace metals cadmium (Cd), lead (Pb), zinc (Zn), nickel (Ni), and copper (Cu) are among the most frequently investigated metal contaminants in biosolids (McBride 2003a; Shrivastava and Banerjee 2004). Guidelines have been developed in some countries to determine which biosolids can be applied to which soils at what maximum amount over a specific period of time (National Research Council 2002; Hillman et al. 2003). The underpinning scientific rationale of using total metal concentration for risk assessment, however, has been criticised for inadequacy (McLaughlin et al. 2000; McBride 2003b). Investigating the bioavailability of trace metals in soil therefore becomes an important research subject for assessing their risk associated with land use of biosolids. To this end, information is needed from long-term research on the species and dynamics of trace metals in soil solution where most soil chemical reactions and metal-biota interactions occur. Free ion activity of trace metals is considered a good indicator of bioavailability (McBride 2001; Hough et al. 2005). It is affected by environmental conditions, such as pH (McBride et al. 1997; Obrador et al. 1997; Silveira et al. 2007). The main objective of this study was to investigate the effect of biosolids amendment and soil pH change on the concentrations and species of Cu, Ni, and Zn in soil solution over the period 1997-2005.

Materials and methods

Site, soil, biosolids amendments, sampling, use of lime and sulfur for changes of soil pH, and soil solution extraction were partially described elsewhere (Percival 2003). Briefly, the field trial site is on pasture at Lincoln in the South Island of New Zealand. The soil is Templeton silt loam, classified as a Typic Immature Pallic Soil in the New Zealand Soil Classification (Hewitt 1998), equivalent to an Udic Ustochrept in Soil Taxonomy (Soil Survey Staff 1996). The trial site comprised 14 plots of 8 by 5 m. Twelve plots were separately amended twice (in early autumn 1997 and 1998) with biosolids spiked with 4 concentrations of Cu, Ni, or Zn; 1 plot was amended with unspiked biosolids; and 1 plot was a control (no biosolids). After each amendment, the plots were cultivated to 0.10m depth, and sown with a perennial ryegrass--white clover mix. The site was sprayed with herbicide just before each amendment. Post-amendment soil samples, to a depth of 0.10 m, were taken in late autumn of 1998, and yearly thereafter. Lime was applied to the plots after the 2000 sampling, raising soil pH to ~7. After the 2003 sampling, elemental sulfur was added to 2 quarters of each plot to decrease soil pH.

After soil samples were passed through a 2-mm stainless steel sieve, deionised water was added to obtain water contents of approximately -10 kPa matric potential. The soil samples were stored overnight at about 20[degrees]C to attain equilibrium between trace metals in soil solution and those on the soil particles, and then centrifuged at 10 000 r.p.m. (maximum of 16 000 RCF) to obtain soil solutions, which were filtered through 0.45 [micro]m for chemical analyses of cations, anions, and dissolved organic carbon (DOC).

Speciation was computed for Cu, Ni, and Zn in soil solution using WHAM 6.0. Inputs required by WHAM were soil solution data, including pH, the concentrations of total Cu, Ni, and Zn, cations ([Na.sup.+], [Mg.sup.2+], [Al.sup.3+], [K.sup.+], [Ca.sup.2+], [Cr.sup.3+], [Mn.sup.2+], [Fe.sup.3+], [Ni.sup.2+], [Ba.sup.2+], [Pb.sup.2+], N[H.sub.4.sup.+]), anions ([Cl.sup.-] , N[O.sub.3.sup.-], S[O.sub.4.sup.2-] , C[O.sub.3.sup.2-] , P[O.sub.4.sup.3-]), and DOC for transformation into fulvic acid. Outputs from WHAM included activities of free-metal ions ([Cu.sup.2+], [Ni.sup.2+], [Zn.sup.Z+]), metal species complexed with anions in soil solution (e.g. CuO[H.sup.+] and Cu[Cl.sup.+]), and the fraction of trace metals bound to organic matter (fulvic acid).

Results and discussion

Metal concentrations in soil and soil solution

Total trace metal concentrations in soil are still used in environmental regulations and guidelines for assessing the suitability of biosolids disposal on land. For example, the guidelines for the safe application of biosolids to land in New Zealand (New Zealand Water & Wastes Association 2003) set the limit or ceiling concentrations of trace metals in soils at 100 mg Cu, 60 mg Ni, and 300 mg Zn/kg. Table 1 shows the total concentrations of Cu, Ni, and Zn in soils (0-0.10m) following biosolids amendment. Metal concentrations in the soil plots before biosolids amendment were not determined; however, the control plot could be used as an approximation of the baseline concentrations. A wide range of Cu, Ni, and Zn concentrations, including below, close to, and above the limit concentrations of the New Zealand guidelines, was found in plots amended with metal-spiked biosolids.

Table 2 shows pH values and concentrations of Cu, Ni, and Zn in soil solutions from the trial plots. These data, together with the concentrations of DOC and cations and anions, were used for computing Cu, Ni, and Zn species. Biosolids amendment increased Cu, Ni, and Zn concentrations in soil solutions (1998)--the more metal spiked into biosolids, the higher its concentration in soil solution. Zinc and Ni concentrations were higher than that of Cu, which may be related to the weaker adsorption of Zn and Ni than Cu by soil organic matter and clays, and the high Zn concentration in biosolid-amended soil. This trend remained in the next 2 years (1999-2000). The pH values of soil solutions in 2000, however, were lower than previous years. Thus, after the 2000 sampling, lime was applied to increase soil pH to ~7 (Table 3).

Effects of pH on metal concentrations and speciation in soil solution

Total concentration is a 'capacity' measure of a trace metal reservoir in soil, potentially to supply the metal to soil solution for its depletion. Because trace metals in soil exist in many different solid phases with variable solubility, total concentration is often a poor indicator of bioavailability and toxicity. Researchers are therefore moving towards an approach based on the 'intensity', or the bioavailable species of metals in soil solution, to aid the development of ecological and environmental effects-based regulations and guidelines to assess the risks associated with waste disposal on land and trace metal contamination in soil. Free ions of trace metals have been suggested as a better analogue of intensity and the major determinant of bioavailability (Parker et al. 1995; Sauve et al. 1998; Vulkan et al. 2000). They can be computed by several models, of which GEOCHEM, MINTEQ, NICA-Donnan, and WHAM are the most frequently used (Dudal and Gerard 2004). These models, however, could produce discrepant results from the same set of input data. For example, WHAM was reported to overestimate Cu complexation with dissolved organic matter (Cloutier-Hurteau et al. 2007) or to underestimate the free Cu ion concentration by 1-2 orders of magnitude (Guthrie et al. 2005). Discrepant results have also been noted when comparing the free ion activity directly determined with that computed from the models (Ge et al. 2005). The discrepancy might be related to the variations in thermodynamic and kinetic data used by the models, the diversity of natural organic matter in water and soil solution, and the differences in the organic matter being accounted for in the models.

A recently proposed indicator of extraneous trace metals in relation to their ecotoxicological effects is the critical concentration of the metals in soil and soil solution, as summarised by De Vries et al. (2007). Critical concentration is dependent on soil and soil solution chemistry, of which pH and organic matter concentration are of particularly importance. In their review, De Vries et al. (2007) calculated, for example, the critical concentrations of Cd, Pb, Cu, and Zn in soil solution in relation to pH and DOC. Using Cu as an example, at pH 5 and DOC 35 mg/L, its calculated critical concentration in soil solution is ~26 [micro]g/L. This value is higher than the Cu concentration in the control plot (10 [micro]g/L), but lower than those in soil solution (DOC 38-45 mg/L) after application of biosolids (1998): 90 [micro]g/L for plot Cul, 133 [micro]g/L for Cu2, 163 [micro]g/L for Cu3, and 252 [micro]g/L for Cu4 (Table 2). Similarly, Zn concentrations in soil solutions of 2489 [micro]g/L for plot Zn1, 4539 [micro]g/L for Zn2, 9587 [micro]g/L for Zn3, and 3109 [micro]g/L for Zn4 in 1998 are much higher than the critical concentration (~75 [micro]g/L at pH 5 and DOC 35 mg/L) reported by De Vries et al. (2007). This suggests an ecotoxicological effect may occur in plots amended by Zn-spiked biosolids, although it was not determined in this research. Zinc concentration in soil solution from the control plot (57 [micro]g/L), however, was lower than its critical concentration.

Liming increased soil solution pH from 4.52-4.67 in 2000 to 6.88-7.28 in 2001. This was accompanied by a decrease in Cu, Ni, and Zn concentrations in soil solution in 2001-03, the extent of which was profound for Zn (Table 2). Indeed, Zn concentrations in plots amended with metal-spiked biosolids were similar to that in the control plot before liming. Thus, maintaining a near neutral pH would be of practical importance in soil management to reduce Cu, Ni, and Zn concentrations in solution and thus decrease their bioavailability and potential to leach.

Figures 1-3 show the free metal ion activities ([Cu.sup.2+], [Ni.sup.2+], [Zn.sup.2+]) in soil solution. Biosolids amendment increased [Cu.sup.2+], [Ni.sup.2+], and [Zn.sup.2+ ]in soil solution in 1998, the extent of which was in agreement with the amount of the metal spiked into biosolids. The much higher [Zn.sup.2+] than [Cu.sup.2+] in soil solution suggests Zn is loosely bound by solid phases in soil and anions in soil solution, whereas Cu is tightly bound. In the next 2 years, free metal activities were similar to those in 1998. However, data from 2001 show that liming decreased [Cu.sup.2+], [Zn.sup.2+,] and [Ni.sup.2+] by orders of magnitude 3, 2, and 1, respectively. As the pH of soil solution declined in 2002 and 2003, [Cu.sup.2+] activity rebounded rapidly; [Zn.sup.2+] and [Ni.sup.2+] were less sensitive than [Cu.sup.2+] to the change in pH of soil solution.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The proportions of Cu, Ni, and Zn species in soil solution were variable (Table 4). Ionic [Cu.sup.2+] only accounted for small percentages of the metal in soil solution, except in 1998 when spiked Cu probably was not completely adsorbed by organic matter and minerals in soil. A large proportion of Cu in soil solution was bound to dissolved organic matter (represented by fulvic acid in WHAM model). In 2001, almost 100% of Cu was organic-bound. This may be due to the very high DOC concentrations in soil solutions (78.1-106.3, average 89 mg/L) after liming to raise the pH. Nickel and Zn differed from Cu in that large percentages existed as free ions, although in 2001, when pH was near neutral and DOC concentration was high, the percentages of free ions were lower. This difference helps explain why Ni and Zn had much higher free ion activities than Cu (Figs 1-3) even when their concentrations in soil solution were of the same order of magnitude after liming. Nickel and Zn also formed complexes with dissolved organic matter, but these species only accounted for small percentages of Ni and Zn in soil solution, except in 2001 when soil solution had high concentration of DOC and thus provided more organic ligands to form complexes with Ni and Zn. The WHAM model is sensitive to DOC, and an assumptions is often made that 65% of the DOC is 'active', i.e. behaves as isolated humic substances such as fulvic acid (Guthrie et al. 2005) for complexation with metals.

The large effect of liming on the concentrations and free ion activities of Cu, Ni, and Zn prompted a further action in soil management practice, this time by decreasing soil pH through the addition to the soil plots of elemental sulfur, which naturally oxidised to become sulfate. Sulfur decreased soil solution pH (2004-05 data), and in some plots the reduction was clear, resulting in an increase of Cu and Zn concentrations in soil solutions from the plots. The changes in free ion activities of Cu and Zn were more significant than the changes in their concentrations. This is in agreement with research indicating that pH is crucial in affecting metal sorption by soils (Yuan and Lavkulich 1997) and in regulating the bioavailability of trace metals in soil solution (Obrador et al. 1997).

Irrespective of the biosolids amendment and soil management practices, [Cu.sup.2+], [Ni.sup.2+], and [Zn.sup.2+] in soil solution in 2005 were close to 1997 baseline results before biosolids amendment (Figs 1-3), which is of significance for further investigation on land applications of biosolids. The results suggest that in a soil with medium organic carbon content (23.8g/kg in 1997 and 31.9g/kg in 2005, both mean values of 14 plots) and with pH maintained near neutral, [Cu.sup.2+], [Ni.sup.2+], and [Zn.sup.2+] in soil solution 8 years after the first application of biosolids seem not to be a great concern. Even though total Cu and Zn concentrations in soil amended by metal-spiked biosolids were equal to, or exceeded, the limits set by NZ guidelines for biosolids disposal, their free ion activities in soil solution were little different from the baseline values. At near-neutral pH, Cu and Zn concentration and activity in the soil were low. Nickel concentration and activity were higher than baseline values, but they were within the same order of magnitude.

The anticipated increase in biosolids use on agricultural land require better understanding of the potential health and environmental effects of contaminants in biosolids. In this regard, long-term research relevant to the local environmental conditions is particularly important. Previous research on biosolids, however, has often been of short-term nature and has not taken into account the changes in soil properties due to soil management practice. Through this research, started in 1997, we have accumulated data on the concentrations and activities of Cu, Ni, and Zn in soil solution from biosolids-amended soil, and gained knowledge about how pH affects the concentrations and activities. These will help assess the bioavailability of the metals and refine the New Zealand guidelines for safe use of biosolids on land.

Conclusions

Increased use of biosolids on agricultural land calls for better understanding of the benefits and the associated environmental risks of the practice, which requires data from long-term research on trace metals. This study shows that the concentrations and free ion activities of Cu, Ni, and Zn in soil solution increased with the addition of these metals to the soil. Copper in soil solution largely existed as Cu-humic complexes, whereas [Ni.sup.2+] and [Zn.sup.2+] were the major metals species in soil solution. Because pH greatly affected the concentrations and activities of Cu, Ni, and Zn in soil solution, their bioavailability can be managed by changing the pH of the soil. Indeed, when soil pH was kept near neutral, [Cu.sup.2+] and [Zn.sup.2+] in soil solution were similar to their baseline values, even though the biosolids amendment increased their total concentrations in soil to levels above, or close to, the limits set by the New Zealand guidelines.

Acknowledgements

This research was funded by the New Zealand Foundation for Research, Science and Technology via a grant to ESR (Environmental Science & Research). Data for 1997-2003 were collected by my colleague Dr H. J. Percival before he retired. Constructive comments and suggestions from anonymous reviewers are greatly appreciated.

Manuscript received 24 July 2008, accepted 20 January 2009

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Guodong Yuan

Landcare Research, PB 11052, Palmerston North, New Zealand. Email: yuang@landcareresearch.co.nz
Table 1. Properties of soils from trial plots, following biosolids
amendment (1998) Cu, Ni, and Zn concentrations were determined by
X-ray fluorescence

Plot Treatment Carbon Cu Ni Zn
 (mg/kg)

Control No biosolids 23.3 4 14 49
Unspiked Biosolids 23.9 15 15 73
Cu1 Spiked biosolids 27.1 69 15 84
Cu2 Spiked biosolids 31.2 87 20 81
Cu3 Spiked biosolids 28.3 117 17 80
Cu4 Spiked biosolids 28.8 181 l7 75
Ni1 Spiked biosolids 26.1 17 26 70
Ni2 Spiked biosolids 29.4 20 38 80
Ni3 Spiked biosolids 25.3 22 47 69
Ni4 Spiked biosolids 27.3 20 58 69
Zn1 Spiked biosolids 26.9 15 15 140
Zn2 Spiked biosolids 29.1 29 14 224
Zn3 Spiked biosolids 28.4 21 16 294
Zn4 Spiked biosolids 25.0 16 14 296
Baseline (A) 23.8

(A) Carbon content was mean value for 14 plots before biosolids
amendment.

Table 2. The pH and metal concentrations ([micro]M) of soil
solution from trial plots

n.d., Not determined because of solution spill

Plot 1997 (A) 1998 1999 2000 2001

 pH

Control 5.10 4.93 5.41 4.54 7.28
Unspiked 4.98 5.04 5.16 4.52 7.21
Cu1 4.94 5.02 5.05 4.57 7.12
Cu2 5.11 5.06 5.01 4.58 7.21
Cu3 4.93 4.84 5.01 4.62 7.12
Cu4 5.00 4.76 5.23 4.64 6.92
Ni1 4.93 4.85 5.04 4.55 6.88
Ni2 5.18 5.18 5.02 4.67 7.18
Ni3 4.98 5.00 5.33 4.55 7.00
Ni4 4.95 4.88 4.98 4.64 6.94
Zn1 4.83 4.93 5.01 4.57 7.04
Zn2 4.90 4.95 5.07 4.62 7.09
Zn3 5.10 4.80 5.00 4.64 6.98
Zn4 5.05 4.77 4.98 4.52 7.16

 Cu

Control 0.36 0.16 0.51 0.38 0.20
Unspiked 0.25 0.44 0.53 0.72 0.31
Cu1 0.27 1.42 1.03 1.53 1.10
Cu2 0.38 2.09 1.73 2.05 1.84
Cu3 0.23 2.56 2.63 3.62 2.34
Cu4 0.19 3.97 3.73 3.93 2.36

 Ni

Control 0.12 0.05 0.14 0.05 0.03
Unspiked 0.15 0.19 0.28 0.17 0.02
Ni1 0.08 2.27 4.06 2.73 0.57
Ni2 0.09 3.31 4.86 2.56 0.91
Ni3 0.09 9.87 10.22 8.18 1.63
Ni4 0.11 13.17 10.79 8.52 2.22

 Zn

Control 1.03 0.87 2.37 1.35 0.12
Unspiked 2.45 3.47 4.94 3.67 0.10
Zn1 1.33 38.08 35.63 29.06 0.42
Zn2 1.10 69.43 80.29 58.11 0.54
Zn3 1.10 146.66 87.32 76.46 0.88
Zn4 0.95 475.61 198.81 214.10 2.94

Plot 2002 2003 2004 2005

 pH

Control 6.94 6.68 6.70 6.34
Unspiked 6.81 6.78 6.28 6.35
Cu1 6.65 6.40 6.29 6.36
Cu2 6.51 6.50 5.53 6.31
Cu3 6.61 6.36 6.14 6.35
Cu4 6.46 6.60 6.39 6.78
Ni1 6.80 6.41 6.08 6.27
Ni2 7.00 6.89 5.94 6.47
Ni3 7.27 6.84 6.17 5.80
Ni4 6.69 6.81 6.64 6.18
Zn1 6.67 6.30 6.62 6.16
Zn2 7.02 6.84 6.53 6.71
Zn3 7.14 7.00 6.28 6.55
Zn4 6.99 6.83 6.46 6.45

 Cu

Control 0.26 0.19 0.33 1.04
Unspiked 0.34 0.25 0.38 0.60
Cu1 0.87 0.76 0.83 1.68
Cu2 1.17 0.94 1.32 0.99
Cu3 2.08 1.51 n.d. 0.85
Cu4 2.08 1.87 2.75 2.28

 Ni

Control 0.09 0.05 0.09 0.05
Unspiked 0.09 0.07 0.09 0.05
Ni1 0.34 0.31 0.22 0.17
Ni2 0.55 0.34 0.36 0.24
Ni3 0.95 0.80 0.95 0.73
Ni4 1.30 0.94 0.77 0.73

 Zn

Control 0.12 0.08 0.15 0.96
Unspiked 0.12 0.08 0.15 0.29
Zn1 0.30 0.24 0.31 1.01
Zn2 0.22 0.28 0.15 0.70
Zn3 0.47 0.40 0.61 1.01
Zn4 1.52 0.84 2.91 2.92

(A) Before biosolids amendment.

Table 3. The pH of soils from trial plots

Baseline pH in 1997 before biosolids amendment was 5.64
(mean value of 14 plots)

Plot 1998 1999 2000 2001

Control 5.49 5.61 5.49 6.88
Unspiked 5.49 5.51 5.46 6.81
Cu1 5.50 5.52 5.50 6.89
Cu2 5.54 5.66 5.66 6.99
Cu3 5.37 5.50 5.54 7.12
Cu4 5.34 5.48 5.44 6.90
Ni1 5.48 5.48 5.39 6.72
Ni2 5.76 5.75 5.70 6.99
Ni3 5.48 5.55 5.54 6.83
Ni4 5.39 5.48 5.47 6.78
Zn1 5.43 5.43 5.43 6.71
Zn2 5.42 5.48 5.51 7.12
Zn3 5.41 5.57 5.59 7.08
Zn4 5.07 5.32 5.32 6.70

Plot 2002 2003 2004 2005

Control 7.02 6.90 6.89 6.58
Unspiked 6.98 6.87 6.81 6.41
Cu1 6.75 6.75 6.76 6.46
Cu2 6.88 6.68 6.92 6.47
Cu3 6.93 6.80 6.82 6.61
Cu4 6.79 6.81 6.84 6.57
Ni1 6.80 6.76 6.81 6.33
Ni2 7.07 6.88 6.89 6.51
Ni3 7.03 6.77 6.68 6.30
Ni4 6.65 6.83 6.84 6.29
Zn1 6.79 6.62 6.83 6.37
Zn2 7.00 6.89 7.02 6.61
Zn3 7.06 6.93 6.93 6.62
Zn4 6.83 6.78 6.89 6.51

Table 4. Cu, Ni, and Zn species as percentages of their concentrations
in soil solution

Species include free metal ions ([Cu.sup.2+], [Ni.sup.2+],
[Zn.sup.2+]), metal ions bound with fulvic acid, and ion pairs of
the metals with anions (not shown in the table). 0, Values between
0.01 and 0.03

Plot 1997 (A) 1998 1999 2000 2001

 [Cu.sup.2+]

Control 5 37 5 11 0
Unspiked 7 33 8 11 0
Cul 17 37 10 l4 0
Cu2 11 38 10 8 0
Cu3 6 42 12 14 0
Cu4 5 45 14 14 0

 Fulvic acid

Control 93 44 92 82 100
Unspiked 91 47 88 83 100
Cul 77 39 84 77 100
Cu2 84 35 83 87 100
Cu3 91 26 80 78 100
Cu4 93 22 76 78 100

 [Ni.sup.2+]

Control 67 67 61 62 26
Unspiked 69 63 6l 61 29
Nil 68 64 60 61 37
Ni2 66 64 56 61 34
Ni3 69 61 61 62 34
Ni4 67 62 61 64 36

 Fulvic acid

Control 10 1 5 4 20
Unspiked 8 1 4 4 19
Nil 8 1 3 3 18
Ni2 7 1 4 5 22
Ni3 8 1 5 5 23
Ni4 9 1 4 5 24

 [Zn.sup.2+]

Control 64 67 59 61 25
Unspiked 66 63 60 60 26
Znl 65 58 58 58 29
Zn2 68 54 58 59 21
Zn3 65 50 57 60 26
Zn4 65 42 54 56 24

 Fulvic acid

Control 14 1 7 5 42
Unspiked 11 2 7 5 37
Znl 12 1 5 6 36
Zn2 6 l 5 6 56
Zn3 9 1 5 5 48
Zn4 11 1 5 4 39

Plot 2002 2003 2004 2005

 [Cu.sup.2+]

Control 2 6 0.1 1
Unspiked 1 4 0.2 1
Cul 3 16 0.2 2
Cu2 10 14 0.8 1
Cu3 5 13 0.3
Cu4 7 13 0.2 1

 Fulvic acid

Control 84 77 100 97
Unspiked 91 78 99 97
Cul 92 3 100 95
Cu2 60 66 99 98
Cu3 81 5 99
Cu4 76 49 100 97

 [Ni.sup.2+]

Control 39 59 47 56
Unspiked 43 56 53 55
Nil 47 55 57 57
Ni2 40 49 54 52
Ni3 38 51 53 54
Ni4 44 53 48 56

 Fulvic acid

Control 1 1 24 5
Unspiked 2 1 17 5
Nil 3 1 14 5
Ni2 1 1 13 6
Ni3 2 1 23 3
Ni4 2 1 21 5

 [Zn.sup.2+]

Control 43 60 40 54
Unspiked 45 58 48 53
Znl 45 56 40 54
Zn2 43 55 40 48
Zn3 43 49 48 50
Zn4 40 55 49 51

 Fulvic acid

Control 3 2 37 9
Unspiked 5 2 26 9
Znl 5 1 39 7
Zn2 5 1 35 14
Zn3 5 1 25 11
Zn4 4 1 40 12

(A) Baseline data before biosolids amendment.
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Article Details
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Author:Yuan, Guodong
Publication:Australian Journal of Soil Research
Article Type:Report
Geographic Code:8AUST
Date:May 1, 2009
Words:5363
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