Effect of treated zeolite, iron waste, and liming on phytoavailability of Zn, Cu, and Ni in long-term biosolids-amended soils.
The intensive use of sewage sludge (biosolids) as a soil amendment can result in the accumulation of heavy metals in the soil. Heavy metals remain in the soil for many years (Alloway and Jackson 1991) and are a potential cause of phytotoxicity or entry of metals into the food chain (Cunningham et al. 1975). Soil--plant transfer of trace elements is a part of the natural cycling of chemical elements (Kabata-Pendias 2004). The risk to both the environment and human health of a given heavy metal is a function of its mobility and phytoavailability.
Several techniques have been proposed to manage or remediate metal-contaminated soils. One of these, chemical immobilisation, is an in situ remediation method in which inexpensive materials are added to contaminated soil to reduce the solubility of heavy metal contaminants, which then may alleviate environmental risk (Pierzyuski and Schwab 1993; Brown et al. 1996). The success of chemical immobilisation can be evaluated by its ability to reduce contaminant phytoavailability and human exposure to heavy metals in contaminated soils. The application of soil amendments to immobilise heavy metals is a promising technology to meet requirements for environmentally sound and cost-effective remediation (Friesl et al. 2004).
The technique involves addition of chemicals to contaminated soil to reduce the solubility of metals through metal sorption and/or precipitation reactions. Decreased metal solubility and mobility will reduce heavy metal phytoavailability and metal transport from contaminated soils to surface and ground water (Vangronsveld and Cunningham 1998). Immobilisation can be accomplished by adding either natural or synthetic chemicals to the soil. Treatment additives fall into 2 classes: strongly adsorbing and weakly adsorbing. Strongly adsorbing insoluble chemicals, once added and distributed throughout the soil, will not migrate down through the soil to groundwater, and metals will be adsorbed, complexed, or chelated by the additive. Weakly adsorbing chemical additives will cause metals to precipitate, or will complex or chelate metals, and then become attached to the soil structure (Sims et al. 1986).
Addition of liming materials to maintain or increase soil pH levels is a common method for attempting to minimise heavy metal phytoavailability in soils receiving biosolids. However, in time, natural re-acidification of soils may lead to a remobilisation of metals (Lombi et al. 2003). Other potential amendments designed to increase the metal sorption capacity of the soil may not necessarily be affected by re-acidification. Two potential amendments available in New Zealand are natural zeolite and iron waste from the steel-making industry.
Zeolites are crystalline, porous 3-dimensional aluminosilicates of the alkali (mainly Na and K) and alkaline-earth (mainly Ca) metals. Their crystal structure is based on a 3 dimensional framework of (SiAl)[0.sub.4] tetrahedra (Armbruster and Gunter 2001) and they have a relatively high cation exchange capacity (Blanchard et al. 1984). The use of zeolites for pollution control depends on their ion-exchange capabilities. In addition, incorporation of zeolites into soils causes a general alkalisation of the treated soils, which may also help to reduce metal mobility and phytotoxicity (Edwards et al. 1999). New Zealand Natural Zeolite Ltd produces about 9000t of zeolite annually from 3 deposits near Ngakuru in the North Island. The most common minerals present in the deposits are mordenite, clinoptilolite, laumonite, and wairakite.
Iron-containing industrial wastes are also potentially low-cost adsorbents for heavy metal remediation. Hydrous oxides of iron are known to form several different types of surface complexes with trace metals (Spadini et al. 1994). Generally, industrial wastes are generated as byproducts. Since these materials are locally available in large quantities, they are relatively inexpensive. The New Zealand steel industry generates around 180 000 t/year of iron waste products which require disposal or re-use.
The effects of both zeolites and iron-containing materials on metal solubility and phytoavailability in contaminated soils have been examined in several laboratory, glasshouse, and field studies (e.g. Mench et al. 2000; Knox et al. 2001). However, the results of such studies appear to be quite variable, and are clearly site-specific, material-specific, and metal-specific.
The objective of this study was to examine the potential of New Zealand natural zeolite, and iron waste produced in New Zealand, for remediating heavy metal contamination in biosolids-amended soils, both without, and in combination with, a liming material. Evaluation of the various treatments was carried out by examining effects on metal (Cu, Ni, and Zn) phytoavailability to plants (sunflower, Helianthus annuus L.), and on soil metal solubility as assessed by extraction with dilute calcium nitrate solution.
Materials and methods
Two bulk samples of soil were obtained from sites on the Bromley sewage treatment farm, Christchurch, New Zealand. The soils on the Bromley farm are described as Kairaki complex soils (Kear et al. 1967); however, because of their considerable disturbance by human activity, they are classified as Anthropic Soils (Hewitt 1993). The paddocks on this farm have received long-term applications of dried and liquid biosolids at different rates since the late 1960s and the soils are contaminated with a range of heavy metals at varying concentrations. Soils were sampled from the 0-150mm layer using a shovel, collecting material from several locations at each of the 2 sites. The soils were mixed thoroughly in a concrete mixer and then sieved in a field-moist condition to pass through a 4-mm stainless steel sieve. The samples were then air-dried at 20[degrees]C in a drying cabinet. Subsamples were taken and ground to pass through a 2-mm stainless steel sieve prior to laboratory analysis. The bulk soils were stored in polyethylene bags at 4[degrees]C until used in the pot experiments.
Properties of the 2 soil samples are shown in Table 1. Total soil C and N were determined using a LECO CNS 2000 analyser, oxide AI and Fe by acid oxalate extraction (Blakemore et al. 1987), soil pH in water as described by Blakemore et al. (1987), and soil texture by the pipette method (Day 1965). Total soil metal concentrations were determined using the acid digestion procedure of Kovacs et al. (2000), with determination of metals in the digests by atomic absorption spectrophotometry. Both samples of soil contain concentrations of Cu, Ni, and Zn well in excess of normal background concentrations for soils of the Canterbury region (Percival et al. 1996). The total Cu and Zn concentrations in one of the samples (referred to hereafter as the highly contaminated soil) are both above the current guideline limits (100mg/kg for Cu and 300mg/kg for Zn, New Zealand Water and Waste Association 2003) for biosolids-amended soils (Table 1). The second sample (referred to hereafter as the moderately contaminated soil) has lower concentrations of Cu, Ni, and Zn, but the Zn concentration is still above the guideline limit.
Three types of soil amendment were used in this study: zeolite, iron waste, and a liming material [Ca[(OH).sub.2]].
The natural zeolite came from the Twist Road deposit, Ngakuru, New Zealand. The composition of the zeolite included mordenite (65-95%), smectite (5-20%), opal C (<5%), and K feldspar (5-20%).The zeolite as received was treated with NaCl to convert it to the homoionic sodium form. The treatment consisted of immersing 120g zeolite in 1000mL 2u NaCl solution, and then heating at 53[degrees]C for 36h. The material was then oven-dried at 100[degrees]C and finely ground using a coffee blender. The NaCl treatment was based on the findings of previous studies that the sodium ion is the most effective exchangeable ion for heavy metal removal (Blanchard et al. 1984; Zamzow et al. 1990; Curkovic et al. 1997), and converting zeolite to the homoionic sodium form also increases its cation exchange capacity (Zamzow et al. 1990; Malliou et al. 1994; Vaca Mier et al. 2000).
The iron waste was a byproduct from the steel-making industry based at the Glenbrook Steel Mill, South Auckland, New Zealand. The iron waste material used for this study is described as an iron slag or dust generally with particle size 5 mm-75 pro. The average composition (main constituents only) is 2.5% Fe, 10.4% Al, 6.0% Mg, 8.9% Ca, 5.8% Si, and 20.2% Ti.
Laboratory grade Ca[(OH).sub.2] (>99.8% purity) was used as the liming material in this study.
The aim of these experiments was to undertake a fairly rapid assessment of the potential of various soil amendment treatments to reduce metal concentrations in plants grown in metal-contaminated soils. A preliminary experiment demonstrated that sunflower seedlings were able to grow quickly in the biosolids-treated soils and take up higher concentrations of metals than several other plant species tested. Sunflower cv. Giant Russian, sourced from the Yates seed company (Australia/ New Zealand), was used for the glasshouse experiments. In addition, to maximise exploitation of the soil and produce enough plant dry matter for analysis in a short period of time, a large number of seedlings were grown in a relatively small volume of soil.
Two separate experiments were carded out. The first (Expt 1) examined the effect on plant metal concentrations of adding 5% and 10% by weight of treated zeolite or iron waste to the 2 soils. For practical and economic reasons, it would be very unlikely that rates > 5-10% would be used at field sites. Expt 2 examined the effects of the same treatments in the presence of low (0.33% by weight) and high (0.66% by weight) rates of Ca[(OH).sub.2] addition. These rates were determined in the laboratory to increase soil pH values to approximately 6.5 and 7.0. Both experiments included control soils with no zeolite or iron waste added and, in the case of Expt 2, soils with the Ca[(OH).sub.2] treatments alone added.
The various amendment treatments were well mixed into the soils (150g soil/pot, pot dimensions 100mm diameter by 150mm height) before the seeds were planted. All treatments were replicated 3 times. The sunflower seeds were pre-germinated by placing on wet paper towels for 3 days before being planted in the pots (15 per pot), which were then slightly covered with autoclaved sand, and the pots made up to field capacity with deionised water. The experiments were conducted in a glasshouse at ambient temperature (15-24[degrees]C) illuminated with natural light. Following germination, the pots were randomly arranged in the glasshouse and watered with deionised water as required.
Plants were grown for 3 weeks and then harvested. The plants were separated into roots and shoots and washed thoroughly with de-ionised water, placed in paper bags, and dried to constant weight at 65[degrees]C for 72 h in a forced-air oven.
Plant and soil analysis
The dried tissues were finely ground and placed in 10mL of 69.5% aristar grade nitric acid and digested on a heating block for 7 h. The maximum temperature of digestion was 140[degrees]C. The digests were analysed for Cu, Ni, and Zn, using a flame (FAAS) or graphite furnace atomic absorption spectrophotometer (GFAAS).
Soils sampled from the pots post-harvest were dried at ambient temperature (approx. 21[degrees]C) and then ground to pass a 2-mm sieve. The soil samples were analysed for Ca[(N[O.sub.3]).sub.2]-extractable metals as described by Jing and Logan (1992). Soil pH was determined as described by Blakemore et al. (1987).
Metal detection limits using FAAS were Cu 0.02 rag/L, Ni 0.10mg/L, and Zn 0.02 mg/L; and using GFAAS were Cu 0.001 mg/L and Ni 0.01 mg/L (GFAAS not required for Zn).
Statistical analyses were carried out using Minitab[R] 15. Results presented are the means of 3 replicates and were statistically analysed for main effects of treatments with a general linear model ANOVA. Individual means were compared using Tukey's method of comparisons.
This experiment examined the effect of incorporating 5% and 10% treated zeolite or iron waste alone into the soils at their existing pH values, which were reasonably acid (Table 1). Table 2 shows the plant yields and metal concentrations (Ni, Cu, and Zn) for the various treatments, and Table 3 shows the soil pH values and calcium-nitrate extractable soil metal concentrations in the post-harvest soils. Application of the treated zeolite clearly had a major effect on plant yields in both soils, significantly decreasing yields by up to 90% (Table 2). In contrast to the zeolite treatments, plant yields for the iron waste treatments were not significantly different from the controls for either soil.
Plant Cu concentrations appeared to be increased by the zeolite treatments (Table 2), possibly a result of the decreased dry matter production; however, the observed increases in Cu concentration were not statistically significant. There was no effect of the iron waste treatments on plant Cu concentrations, even though for both soils, the 10% iron waste treatment caused a significant reduction in soluble soil Cu concentrations as estimated by calcium nitrate extraction (Table 3).
Soluble soil Ni concentrations were significantly reduced by both zeolite and iron waste treatments applied to the moderately contaminated soil (Table 3). These decreases were mirrored by small, but non-significant, decreases in plant Ni concentrations (Table 2). For the highly contaminated soil, soluble soil Ni concentrations were decreased only by the zeolite treatments (Table 3). However, in this case, plant Ni concentrations were also significantly decreased by zeolite additions (Table 2).
Soluble soil Zn concentrations were decreased in both soils by applications of both zeolite and iron waste (Table 3). Plant Zn concentrations also appeared to generally decrease in both treatments, although only significantly so for the moderately contaminated soil (Table 2).
In addition to the effects on soluble metal concentrations, both the zeolite and iron waste treatments tended to produce small increases in soil pH. In the case of the moderately contaminated soil, these observed increases were not statistically significant, and for the highly contaminated soil, only the soil pH of the 5% zeolite treatment was significantly higher than that of the control soil (Table 3).
There are some differences in data for the control treatments between Expts 1 and 2, for example yields and plant metal concentrations, due to the fact that the experiments were not carried out at the same time and conditions in the glasshouse were not identical.
Treatment effects in Expt 2 on soil pH and soluble metal concentrations are shown in Table 4. As expected, the addition of Ca[(OH).sub.2] on its own to both soils increased soil pH significantly (P < 0.001), pH increasing with the rate of addition. The 2 amendments, zeolite and iron waste, also appeared to have a small additional liming effect, although this was significant (P < 0.01) only with the moderately contaminated soil (Table 4).
For both soils, all treatments tended to reduce soluble metal concentrations as assessed by extraction with calcium nitrate, although the effects were not always significant (Table 4). Ca [(OH).sub.2] had significant main effects (P < 0.001) on soluble Ni and Zn concentrations in both soils, and on soluble Cu in the highly contaminated soil. Zeolite had a significant (P <0.01) main effect on Ni in both soils, and iron waste on Cu (P < 0.001) in both soils. Neither zeolite nor iron waste had a significant main effect on soluble Zn.
Treatment effects on plant shoot yields are shown in Fig. 1, significance of main treatment effects in Table 5. There was no significant effect on plant yield due to Ca[(OH).sub.2] in either soil. However, in both soils, although plant yields in the zeolite treatments were much higher than when grown in the absence of Ca[(OH).sub.2] in Expt 1, overall they were still significantly lower than the controls. In contrast, the iron waste treatment had positive main effects (P < 0.05) on plant yield for both soils (Fig. 1).
Plant Ni concentrations were greatly reduced by all treatments relative to the controls in both soils (Fig. 2). There were highly significant main effects of Ca[(OH).sub.2] (P < 0.001) in both soils, and a significant main effect of zeolite (P < 0.05) in the highly contaminated soil, but no significant main effect of iron waste in either soil (Table 5). For the moderately contaminated soil, plant Ni concentrations in all treatments, apart from the control, were near or below detection limits. For the 2 soils overall there was a significant positive correlation between plant Ni concentration and soluble soil Ni concentration, and a significant negative correlation with soil pH (Table 6).
[FIGURE 1 OMITTED]
Plant Zn concentrations were also greatly reduced by all treatments relative to the controls in both soils (Fig. 3). For the moderately contaminated soil, there were highly significant main effects (P < 0.001) of Ca[(OH).sub.2] and iron waste but no significant main effect for zeolite. For the highly contaminated soil there were significant main effects of Ca[(OH).sub.2], zeolite, and iron waste (Table 5). Similarly to Ni, for the 2 soils overall there was a significant positive correlation between plant Zn concentration and soluble soil Zn concentration, and a significant negative correlation with soil pH (Table 6).
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
In contrast to Ni and Zn, there were no significant effects of any treatment on plant Cu concentrations in either soil.
The large decreases in plant yield observed with the zeolite treatments in Expt 1 were not expected, although Rebedea et al. (1997) reported deleterious effects on plant growth when some synthetic zeolites were added to soils on a 5% w/w basis. Those researchers attributed the poor plant growth to the zeolite reducing the plant availability of essential nutrients by the same ion exchange process intended to reduce metal phytoavailability. In the current study, the presence of residual NaCl used in the zeolite treatment process may also have had an adverse effect. High Na concentrations are known to adversely affect plant growth (e.g. Bernstein 1975), possibly by causing nutrient imbalances. This could have been exacerbated by relatively low Ca concentrations in the 2 acidic soils. Although sunflowers are considered to be moderately salt-tolerant (Jeschke 1984), calculations based on the amounts of NaCl used in the zeolite treatment process suggest that Na concentrations in the soil solutions of the zeolite-amended soils could well have exceeded concentrations at which adverse effects on sunflower growth have been previously observed (e.g. Benlloch et al. 1994). However, no measurements of salinity were made in the current study. In Expt 2, the negative effects of zeolite on plant yield in both soils were overcome by the addition of Ca[(OH).sub.2], suggesting that the addition of Ca had reversed a nutrient imbalance. There were, however, still significant (P < 0.05) adverse main effects of zeolite treatment for both soils (Table 5).
In contrast to the addition of zeolite, addition of iron waste with Ca[(OH).sub.2] in Expt 2 resulted in significant positive main effects on plant yield in both soils. Plant yields were generally highest in the iron waste plus Ca[(OH).sub.2] treatments (Fig. 1).
As expected, the addition of Ca[(OH).sub.2] lime increased the pH of both soils but effects on plant yield were small and not significant (Tables 4, 5 and Fig. 1). Applications of treated zeolite or iron waste to the soils also tended to increase soil pH, although the effects were significant only with the moderately contaminated soil (Table 4). The addition of zeolite is expected to raise the pH due to the release of alkali metal ions (Na in this case) from the mineral by exchange with [H.sup.+] ions (Pitcher et al. 2004), thus lowering the [H.sup.+] ion concentration in the soil solution. Iron wastes can often be alkaline due to their composition, which may contain of oxides of Ca and Mg.
The results of Expt 1 suggested that both the zeolite and iron waste treatments could result in some decreases in both soluble soil metal and plant metal concentrations; however, the responses were not particularly large or clear-cut. Both types of amendment should have increased the metal sorption capacity of the soils, but the amendments had relatively small, and not always significant, effects on soil pH, a major controlling factor of metal solubility. In Expt 2, however, the zeolite and iron waste treatments appeared to have small effects on soil pH additional to the effect of Ca[(OH).sub.2] on its own (Table 4). These effects were significant (P < 0.01) only for the moderately contaminated soil. This can be attributed to the higher soil organic matter content and finer texture of the highly contaminated compared with the moderately contaminated soil (Table 1), and therefore a higher buffer capacity.
In addition to the effect on soil pH, addition of Ca[(OH).sub.2] in Expt 2 also had substantial effects on soluble metal concentrations as assessed by extraction with calcium nitrate (Table 4). There were also significant main effects on soluble metal concentrations of the zeolite and iron waste treatments in some cases. However, it is clear from the data in Table 4 that different metals are affected to different degrees by the same amendment.
Concentrations of Ni and Zn in sunflowers grown in both of the control soils in both experiments are certainly indicative of contaminated soils. According to Kabata-Pendias and Pendias (2001) the Ni content of plants growing on uncontaminated soils are generally < 1-2 mg/kg DW, and for Zn generally < 100 mg/kg DW. In the case of Zn, plant shoot concentrations for sunflowers grown in the control soils were well above the 240mg/kg observed to be toxic to sunflowers in sand culture studies (Khurana and Chatterjee 2001). As noted above, the effects of the zeolite and iron waste treatments on plant metal concentrations in Expt 1 were relatively small, and plant Zn concentrations remained > 240mg/kg (Table 2). However, in Expt 2, the addition of Ca[(OH).sub.2] on its own or in combination with zeolite or iron waste had substantial effects on both plant Ni and Zn concentrations (Figs 2 and 3). In particular plant Zn concentrations for the Ca[(OH).sub.2] plus Fe waste treatments were generally < 240mg/kg. It is therefore suggested that sunflower growth was restricted in the control soils by Zn toxicity, and the increased growth observed in the iron waste plus Ca[(OH).sub.2] treatments (Fig. 1) was due to a substantial reduction in Zn phytoavailability brought about by these treatments.
Both plant Ni and Zn concentrations were strongly correlated with both soluble soil metal concentrations and, negatively, with soil pH (Table 6). Correlations between soil pH and soluble metal concentrations were also very strong. Such relationships clearly result from the fact that the sorption of metals by soils, zeolites, and iron oxide minerals increases strongly with increased soil pH (e.g. Shuman 1977; McLaren 2003; Cabrera et al. 2005). Thus, treatments involving both addition of metal sorptive materials (zeolite or iron waste), and increases in soil pH, are most likely to result in the greatest reductions in the phytoavailability of metals to plants.
In contrast to Ni and Zn, the control plant Cu concentrations are at the upper end of the range found for uncontaminated soils (Kabata-Pendias and Pendias 2001), and well below concentrations shown to adversely affect the growth of sunflowers (Lin et al. 2003). The lack of effects of treatments on plant Cu concentrations in both experiments is not surprising, since neither soil soluble Cu concentrations nor plant Cu concentrations were particularly high to begin with. Copper is known to be one of the least mobile metals in soil (Adriano 2001) and is bound strongly by soil organic matter (Stevenson 1991). Both of the soils used in this study had relatively high soil organic matter contents (Table 1). Although reductions in calcium nitrate-extractable Cu concentrations were observed with some treatments, increased soil pH may also have resulted in increased complexing of soil solution Cu by soluble organic matter (McBride and Blasiak 1979), which can reduce phytoavailability (Stevenson 1976; Baker and Senft 1995).
Significant reductions in extractable Cu were observed due to application of iron waste combined with Ca[(OH).sub.2] (Table 4). This is most likely caused by a combination of higher pH and the adsorptive properties of the iron waste. This material contains substantial amounts of Si, Al, and Fe oxides which could enable the immobilisation of Cu by the formation of stable surface complexes (Wu et al. 2003).
In this study, although iron waste, and to a lesser extent zeolite, did have some additional effects on reducing Ni and Zn concentrations in sunflowers, it is clear that Ca[(OH).sub.2] on its own had the major effect. However, it has been argued that if in situ remediation materials exert their effect through changes in soil pH only, then acidification of the soil will return metal phytoavailability to its previous and possibly phytotoxic level (e.g. Hamon et al. 2002). In contrast, adding remediation materials that sorb metals strongly could conceivably produce a more enduring effect. The long-term effects of such remediation treatments clearly require further examination.
The application of treated zeolite or iron waste alone to biosolids-amended soils had relatively small effects on metal solubility and phytoavailability to sunflowers under moderately acidic soil conditions. The results with the treated zeolite in particular were complicated by the adverse effect on plant growth caused by this material. However, in the presence of Ca([OH).sub.2], both materials showed some potential for reducing Ni and Zn concentrations in sunflowers relative to that shown by Ca[(OH).sub.2] on its own. Combinations of iron waste and Ca[(OH).sub.2] in particular resulted in substantial decreases in soil soluble Zn concentrations and increases in plant yield, attributed to the remediation of Zn toxicity. The effects of treatments involving zeolite or iron waste are considered to result from a combination of increased soil pH and increased metal sorption capacity. However, further research is required to examine the long-term effects of such treatments.
Manuscript received 23 April 2008, accepted 28 July 2008
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Z. Talebi Gheshlaghi (A,B), R.G. McLaren (A), and J.A. Adams (A)
(A) Soil and Physical Sciences Group, Agricultural and Life Science Division, P.O. Box 84, Lincoln University, Lincoln 7647, Canterbury, New Zealand.
(B) Corresponding author. Email: email@example.com
Table 1. Properties of the experimental soils Property Moderately Highly contaminated soil contaminated soil Soil pH 5.72 5.36 Total C (%) 4.51 6.67 Total N (%) 0.42 0.69 Oxide Al (%) 0.14 0.15 Oxide Fe (%) 0.34 0.38 Clay (%) 3.7 9.0 Silt (%) 15.1 40.7 Sand (%) 81.2 50.3 Texture Loamy sand Loam Total Cu (mg/kg) 83.3 177.3 Total Ni (mg/kg) 23.7 31.9 Total Zn (mg/kg) 322.6 434.5 Table 2. Expt 1: Shoot yields and metal concentrations in sunflowers For each soil, values followed by the same letter are not significantly different at P = 0.05. * P < 0.05; ** P < 0.01; *** P < 0.001; n.s., not significant Treatment Shoot yield Ni Cu Zn (g) (mg/kg) Moderately contaminated soil Control 1.03ac 13.16 13.98 342.7a 5% Treated zeolite 0.19b 7.29 20.05 270.6a 10% Treated zeolite 0.22b 8.20 21.56 278.7a 5% Fe waste 0.83a 7.59 15.69 312.9a 10% Fe waste 1.22c 7.85 12.69 240.4b Significance *** n.s. n.s. * Highly contaminated soil Control 1.17a 20.18a 18.11 490.10 5% Treated zeolite 0.37b 11.78b 28.91 328.80 10% Treated zeolite 0.09b 9.73b 50.58 589.00 5% Fe waste 0.92a 15.07ab 17.54 394.20 10% Fe waste 1.25a 17.79ab 17.33 370.90 Significance *** ** n.s. n.s. Table 3. Expt 1: Soil pH and calcium nitrate extractable metal concentrations (mg/kg) in post-harvest soils For each soil, values followed by the same letter are not significantly different at P = 0.05. * P < 0.05; ** P < 0.01; *** P < 0.001; n.s., not significant Treatment Soil pH Ni Cu Zn Moderately contaminated soil Control 5.72 2.34a 0.45a 39.67a 5% Treated zeolite 6.46 1.18b 0.63a 19.84b 10% Treated zeolite 6.38 1.34b 0.50a 23.07b 5% Fe waste 5.80 2.06ac 0.62a 32.22c 100% Fe waste 6.05 1.94c 0.00b 31.88c Significance n.s. *** *** *** Highly contaminated soil Control 5.40a 5.32a 1.21a 58.17a 5% Treated zeolite 6.43b 3.07b 0.90ab 43.47b 100/. Treated zeolite 6.19ab 2.39b 0.73ab 32.52c 5% Fe waste 5.63ab 4.60a 1.03ab 51.28a 10% Fe waste 5.69ab 5.03a 0.64b 53.92a Significance ** *** * *** Table 4. Expt 2: Soil pH and calcium nitrate extractable metal concentrations in post-harvest contaminated soils In each column, values followed by the same letter are not significantly different at P = 0.05. * P < 0.05; ** P < 0.01; *** P < 0.001; n.s., not significant Moderately contaminated soil Treatment Soil pH Ca[(N[O.sub.3]).sub.2]- extractable metals (mg/kg) Ni Cu Zn Control 5.70a 2.23a 0.46a 48.78a Low Ca[(OH).sub.2] 6.61bc 0.48c 0.31ab 9.28cd High Ca[(OH).sub.2] 7.02bc 0.16c 0.31ab 1.54e Low Ca[(OH).sub.2] 5% 6.36b 1.55b 0.29ab 22.66b zeolite Low Ca[(OH).sub.2] 10% 6.68bc 1.00bc 0.26abc 14.01c zeolite High Ca[(OH).sub.2] 5% 7.14e 0.31c 0.17bcd 0.00e zeolite High Ca[(OH).sub.2] 10% 7.29e 0.29c 0.27abc 0.00e zeolite Low Ca[(OH).sub.2] 5% Fe 6.74cd 0.35c 0.00d 5.58de waste Low Ca[(OH).sub.2] 10% Fe 6.74cd 0.25c 0.00d 4.92de waste High Ca[(OH).sub.2] 5% Fe 7.26e 0.13c 0.12bcd 0.30e waste High Ca[(OH).sub.2] 10% Fe 7.31e 0.06c 0.04cb 0.00e waste Main Effects Lime *** *** n.s. *** Zeolite ** ** n.s. n.s. Fe waste ** n.s. *** n.s. Highly contaminated soil Treatment Soil pH Ca[(N[O.sub.3]).sub.2]- extractable metals (mg/kg) Ni Cu Zn Control 5.52a 4.63a 0.88a 84.19a Low Ca[(OH).sub.2] 6.19bc 2.53bcd 0.55ab 37.67bc High Ca[(OH).sub.2] 6.46bc 0.33e 0.42bcde 19.89c Low Ca[(OH).sub.2] 5% 6.19bc 3.70ab 0.54abcd 56.00ab zeolite Low Ca[(OH).sub.2] 10% 6.27bc 2.89abc 0.52abcd 38.67bc zeolite High Ca[(OH).sub.2] 5% 6.58bc 1.84bcde 0.47bcd 23.52bc zeolite High Ca[(OH).sub.2] 10% 6.51bc 1.59cde 0.54abc 17.93c zeolite Low Ca[(OH).sub.2] 5% Fe 6.09b 2.10bcde 0.06ef 32.87bc waste Low Ca[(OH).sub.2] 10% Fe 6.29bc 1.62cde 0.09ef 22.44bc waste High Ca[(OH).sub.2] 5% Fe 6.67c 0.98de 0.17def 8.74c waste High Ca[(OH).sub.2] 10% Fe 6.59bc 0.57e 0.00f 4.46c waste Main Effects Lime *** *** *** *** Zeolite n.s. ** n.s. n.s. Fe waste n.s. n.s. *** n.s. Table 5. Expt 2: Treatment main effects on shoot yields and shoot metal concentrations * P < 0.05; ** P < 0.01; *** P < 0.001; n.s., not significant Treatment Shoot yield Ni Cu Zn (g) (mg/kg) Moderately contaminated soil Ca[(OH).sub.2] n.s. *** n.s. *** Zeolite * n.s. n.s. n.s. Fe waste * n.s. n.s. *** Highly contaminated soil Ca[(OH).sub.2] n.s. *** n.s. *** Zeolite ** * n.s. ** Fe waste * n.s. n.s. * Table 6. Coefficients of correlation (r) between plant Ni and Zn concentrations and soluble soil metal concentrations and soil pH (combined soils) *** P<0.001 Calcium nitrate-extractable Soil pH soil Ni/Zn Plant Ni conc. 0.705 *** -0.713 *** Plant Zn conc. 0.923 *** -0.865 ***
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|Author:||Gheshlaghi, Z. Talebi; McLaren, R.G.; Adams, J.A.|
|Publication:||Australian Journal of Soil Research|
|Date:||Sep 1, 2008|
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