Phytoavailability Of Zn Research Articles

Stabilization of Sewage Sludge by Using Various By-products: Effects on Soil Properties, Biomass Production, and Bioavailability of Copper and Zinc

Stabilization of sewage sludge (SS) prior to its land disposal may help control the mobility of SS-borne contaminants, particularly potentially toxic metals. We examined the effects of stabilized SS application on soil properties, biomass production, and phytoavailability of Cu and Zn to plants grown in two contrasting soils, Entisol and Aridisol. Stabilized SS mixtures were created by mixing SS in a 3-to-1 ratio with bentonite (B), sugar beet factory lime (SL), brick factory fly ash (BFA), rice straw (RS), water hyacinth (WH), and 50:50 mixture of RS and SL. Mixtures were applied at 50 Mg ha−1, and Sorghum vulgare L. and Eurica sativa were grown in a pot experiment. All the amendments increased plant availability and uptake of both Cu and Zn compared to the unamended control. The application of stabilized SS increased dry plant biomass significantly and decreased DTPA-extractable elements compared to the non-stabilized SS treatment. We conclude that of the six amendments studied, especially sugar beet factory lime (SL) and bentonite (B), are promising for the stabilization of metal-contaminated biosolids and should be tested under field conditions.

Changes in Phytoavailability of Cadmium, Copper, Lead, and Zinc after Application with Eggshell in Contaminated Agricultural Soil

Agricultural soils surrounding mine areas in South Korea are often contaminated with multiple metals such as Cd, Pb and Zn. It poses potential risks to plants, soil organisms, groundwater, and eventually human health. The aim of this study was to examine the changes in phytoavailability of Cd, Cu, Pb and Zn after application with calcined eggshell (CES; 0, 1, 3, and 5% W/W) in an agricultural soil contaminated by mine tailings. The contents of Cd, Cu, Pb and Zn in soils were 8.79, 65.4, 1602, and <TEX>$692mgkg^{-1}$</TEX> (aqua regia dissolution), respectively. The experiments were conducted with lettuce (Lactuca sativa L. var. longifolia) grown under greenhouse conditions during a 30-d period. <TEX>$NH_4NO_3$</TEX> solution was used to examine the mobile fraction of these metals in soil. The application of CES dramatically increased soil pH and inorganic carbon content in soil due to CaO and <TEX>$CaCO_3$</TEX> of CES. The increased soil pH decreased the mobile fraction of Cd, Pb, Zn: from 3.49 to < <TEX>$0.01mgkg^{-1}$</TEX> for Cd, from 79.4 to <TEX>$1.75mgkg^{-1}$</TEX> for Pb, and from 29.6 to <TEX>$1.13mgkg^{-1}$</TEX> for Zn with increasing treatment of CES from 0 to 5%. In contrast, the mobile fraction of Cu was increased from 0.05 to <TEX>$3.08mgkg^{-1}$</TEX>, probably due to the formation of soluble <TEX>$CuCO_3{^0}$</TEX> and Cu-organic complex. This changes in the mobile fraction resulted in a diminished uptake of Cd, Pb and Zn by lettuce and an increased uptake of Cu: from 4.19 to < <TEX>$0.001mgkg^{-1}$</TEX> dry weight (DW) for Cd, from 0.78 to < <TEX>$0.001mgkg^{-1}$</TEX> DW for Pb, and from 133 to <TEX>$50.0mgkg^{-1}$</TEX> DW for Zn and conversely, from 3.79 up to <TEX>$8.21kg^{-1}$</TEX> DW for Cu. The increased contents of Cu in lettuce shoots did not exceed the toxic level of <TEX>$</TEX><TEX>></TEX><TEX>25mgkg^{-1}$</TEX> DW. The mobile contents of these metals in soils showed a strong relationship with their contents in plant roots and shoots. These results showed that CES effectively reduced the phytoavailability of Cd, Pb, and Zn to lettuce but elevated that of Cu in consequence of the changed binding forms of Cd, Cu, Pb, and Zn in soils. Based on these conclusions, CES can be used as an effective immobilization agent for Cd, Pb and Zn in contaminated soils. However, the CES should be applied in restricted doses due to too high increased pH in soils.

Effect of biosolid application to Mollisol Chilean soils on the bioavailability of heavy metals (Cu, Cr, Ni, and Zn) as assessed by bioassays with sunflower (Helianthus annuus) and DGT measurements

This study assessed the effect of biosolid application on the bioavailable fraction of some trace elements (Cu, Cr, Ni, and Zn) using a bioassay with sunflower (Helianthus annuus) and a chemical assay, diffusion gradient in thin films (DGT). Five surface soil samples (0–20 cm) were collected from an agricultural zone in Central Chile where biosolids are likely to be applied. Municipal biosolids were mixed with the soil at concentrations of 0, 30, 90, and 200 Mg ha−1. The experiment to determine the bioavailability of metals in the soil using the bioassay was performed using sunflower. The DGT technique and Community Bureau of Reference (BCR) sequential extraction were used to determine the bioavailable fractions of the metals. The application of biosolids increased the phytoavailability of Zn, Ni, and Cr in most of the soils, as indicated by the increasing concentrations in sunflower plants as the biosolid application rate increased. In two of the soils, Codigua and Pelvin, this increase peaked at an application rate of 90 Mg ha−1. Decreases in the bioavailable fractions of Zn, Ni, and Cr were observed with higher biosolid application rates. The bioavailability of metals was estimated through multiple linear regression models between the metals in the sunflower plants and the different chemical fractions of metals in the soils treated with different biosolid rates, which displayed a positive contribution of the labile (water soluble, carbonate, and exchangeable), oxide, and organic metal forms in the soil, particularly with respect to Ni and Zn at application rates of 30 and 90 Mg ha−1. The bioavailable fraction of metals was determined in soils using the DGT technique. The effective concentration (C E) results were compared with those in sunflower plants. The DGT technique could effectively predict the bioavailable fractions of Cr, Ni, and Zn in the Taqueral soil but only that of Zn in the Polpaico soil. The application of biosolids significantly increased the labile fraction of most of the metals in the studied soils, particularly at the highest biosolid application rate. C E increased as the concentration of biosolids increased for most of the metals. The effectiveness of the DGT technique for predicting the bioavailability of metals was dependent on the soil type and the metal. However, the C E for soil Cu was not related to plant Cu for all soils studied.

Effects of particle sizes of rock phosphate on immobilizing heavy metals in lead zinc mine soils

Abstract Phosphate-induced immobilization is recognized as one of effective in situ remediation methods for heavy metal contaminated soils. Phosphate-based minerals that adsorb, chelate, or complex heavy metals in soil were greatly concerned as effective heavy metals immobilizing materials. Effects of particle sizes of rock phosphate on immobilizing heavy metals in Pb-Zn mine soils by a greenhouse experiment was conducted. Rock phosphate was added to a Pb-Zn mine soil with four different particle sizes, D97<101.43 µm (UP), D97<71.12 µm (P1), D97<36.83 µm (P2) and D97< 4.26 µm (P3) (the diameters of 97% of the particles were less than 4.26 µm.), and 2 rates (2.5% and 5%). Lolium prenne , L. were grown in the treated soils. Compared to the control, addition of rock phosphate (RP) decreased metal contents in both roots and shoots significantly. Pb contents in shoots decreased by 19.59%-37.80% by different particle sizes at the rate of 5%, reaching lowest level at lowest particle size P3. Zn contents in shoots decreased by 13.47% -13.75 %, Cu in roots was decreased by 18.46%-67.98% and in shoots by 16.82%-32.61%, and Cd in roots decreased by 31.03%-74.23%. The results indicated that, RP can reduce the phytoavailability of Pb, Zn, Cu and Cd in soil significantly by immobilization and the effects strengthened with the decrease of particle size and increasing the rate of addition.

A comparison of physiologically based extraction test (PBET) and single-extraction methods for release of Cu, Zn, and Pb from mildly acidic and alkali soils

In vitro digestion test can be applied to evaluate the bioaccessibility of soil metals by measuring the solubility of the metals in synthetic human digestive tract. Physiologically based extraction test (PBET), composed of sequential digestion of gastric and intestinal phase, is one of the frequently used in vitro digestion tests. In this study, the PBET was chosen to determine the bioaccessibility of Cu, Zn, and Pb in 14 mildly acidic and alkali (pH 5.87-8.30) soils. The phytoavailability of Cu, Zn, and Pb in the same soils was also measured using six single-extraction methods (0.1 M HNO₃, 0.4 M HOAc, 0.1 M NaNO₃, 0.01 M CaCl₂, 0.05 M EDTA, and 0.5 M DTPA). The extraction efficiencies of the methods were compared. The PBET had a strong ability to extract metals from soil, which was much greater than neutral salt extraction and close to dilute acid and complex extraction in spite of the last 2 h neutral intestinal digestion. The amounts of bioaccessible Cu, Zn, and Pb in the gastric phase and in the gastrointestinal phase were both largely determined by the total content of soil Cu, Zn, and Pb. But the results of gastrointestinal digestion reflected more differences resulting from element and soil types than those of gastric digestion did. It was noticed that most of variations in the amounts of soil Cu, Zn, and Pb extracted by EDTA were well explained by the total soil Cu, Zn, and Pb, as same as the PBET. Moreover, the solubility of Cu, Zn, and Pb in the gastric phase and gastrointestinal phase were all positively linearly correlated with the results of EDTA. It was suggested that EDTA extraction can be used to predict the bioaccessibility of Cu, Zn, and Pb in mildly acidic and alkali (pH > 5.8) soils, and the PBET and EDTA could be applied to measure, in a certain extent, the bioaccessibility and phytoavailability of Cu, Zn, and Pb in mildly acidic and alkali (pH > 5.8) soils at the same time.

CRITICAL DEFICIENCY LEVEL OF ZINC FOR CORN ON CALCAREOUS SALT-AFFECTED SOILS IN CENTRAL IRAN

A greenhouse experiment with 11 soil series and two zinc (Zn) rates (0 and 15 mg Zn kg−1 as zinc sulfate) was performed to determine critical deficiency level of Zn for corn (Zea mays L.) on calcareous salt-affected soils in central Iran. In addition, the most important soil properties affecting Zn phytoavailability were determined. Critical Zn deficiency levels were determined using the Cate-Nelson and Mitscherlich procedures. In most soils, application of Zn increased the dry matter yield, and Zn concentration and content in the shoot and root of corn. A positive correlation was observed between the soil electrical conductivity (EC) with Zn concentration in shoots, roots and whole plant while shoot Zn content was negatively correlated with buffer capacity of Zn in soil. Critical deficiency levels of Zn in soil for corn based on the Cate-Nelson and Mitscherlich method were 1.35 and 1.23 mg kg−1 for diethylenetriaminepentaacetic acid (DTPA)-extracted soil Zn, respectively.

Prediction of phytoavailability of trace metals to plants: Comparison between chemical extractions and soil-grown radish

One of the major routes of human exposure to toxic metals is the consumption of vegetables grown on contaminated soils. Radishes were grown in three different soils (kitchen garden, agricultural and industrial soils), presenting various contamination levels. A sequential extraction procedure was compared with EDTA and HCl simple extractions methods in order to predict the metals phytoavailabilty to radish. The analysis of the results shows that the simple HCl and sequential chemical extractions bring complementary results, since HCl is correlated in the phytoavailability of Cd, Mn and Zn, whereas the sequential extraction is correlated in the phytoavailability of Cr, Fe, Mn, Ni. EDTA simple extraction brings here less interesting results than the two other tested extractions.

Phytoavailability of Copper, Zinc and Cadmium in Sewage Sludge-Amended Calcareous Soils

The toxicity of trace elements (TEs), such as copper (Cu), zinc (Zn), and cadmium (Cd), often restrict land application of sewage sludge (SS) and there was little information about soil-plant transfer of TEs in SS from field experiments in China. In this study pot and field experiments were carried out for 2 years to investigate the phytoavailability of TEs in calcareous soils amended with SS. The results of the pot experiment showed that the phytoavailability of Zn and Cu in the SS was equal to 53.4%–80.9% and 54.8%–91.1% of corresponding water-soluble metal salts, respectively. The results from the field experiment showed that the contents of total Zn, Cu, and Cd in the soils increased linearly with SS application rates. With increasing SS application rates, the contents of Zn and Cu in the wheat grains initially increased and then reached a plateau, while there was no significant change of Cd content in the maize grains. The bioconcentration factors of the metals in the grains of wheat and maize were found to be in the order of Zn > Cu > Cd, but for the straw the order was Cd > Cu > Zn. It was also found that wheat grains could accumulate more metals compared with maize grains. The results will be helpful in developing the critical loads of sewage sludge applied to calcareous soils.

Phytoavailability of heavy metals in tidal flat soils after fresh water leaching

The phytoavailability of Cd, Pb, Cr, Zn, Cu, and Ni, retained in tidal flat soil after fresh water leaching during reclamation was investigated. Two salt-tolerant varieties of tomato (Lycopersicon esculentum) and edible amaranth (Amaranthus mangostanus L.) were planted in soils having eight different desalination levels (from 6.7 to 1.4gkg−1 salinity) using pot experiments. Soil leaching significantly decreased the uptake of all metals by crop roots except for Ni. The reduction of soil salinity and exchangeable fraction content of Cd and Pb after leaching contributed to the decrease of uptake of metals by roots. All heavy metal concentrations in the edible parts of both crops in the two lowest salinity level treatments were lower than their maximum allowable levels in food. Results suggest that reclamation of tidal flats can reduce the phytoavailability of the heavy metals retained in soil. But the soil heavy metals may still pose health risks in the cultivation of root food crops.

Mudanças químicas e fitodisponibilidade de zinco estimada por método isotópico, em solo tratado com lodo de esgoto

Zn availability in Red Latossol (Rhodic Ferralsol) of different pH amended with different rates of sewage sludge was studied by the isotopic 65Zn L value method. Soil chemical properties were found to be altered by SS addition. Zn concentration and Zn derived from SS (ZnpfSS) in plant, and Zn phytoavailability (L value), were increased with increasing SS rates. The linear correlation coefficient of plant Zn with SS rates and with L value was significant at 1% probability. The L value proved an efficient method for predicting Zn phytoavailability in sewage sludge-amended soil with different pH under the soil conditions studied.

Wheat-Exuded Organic Acids Influence Zinc Release from Calcareous Soils

Rhizosphere drives plant uptake of sparingly soluble soil zinc (Zn). An investigation with three experiments was conducted to study organic acid exudation by two contrasting wheat genotypes (Sehar-06 and Vatan), Zn fractions in 10 different calcareous soils from Punjab, Pakistan, and release of different soil Zn fractions by organic acids. The two genotypes differed significantly in biomass production and Zn accumulation under deficient and optimum Zn levels in nutrient solution. At a deficient Zn level, Sehar-06 released more maleic acid in the rhizosphere than Vatan. Ten soils used in the present study had very different physicochemical properties; their total Zn and Zn distribution among different fractions varied significantly. Zinc release behaviour was determined by extracting the soils with 0.005 mol L −1 citric acid or maleic acid. The parabolic diffusion model best described Zn release as a function of time. Parabolic diffusion model fitting indicated more maleic acid-driven than citric acid-driven soil Zn mobility from different fractions. Cumulative Zn release in six consecutive extractions during 24 h ranged from 1.85 to 13.58 mg kg −1 using maleic acid and from 0.37 to 11.84 mg kg −1 using citric acid. In the selected calcareous soils, the results of stepwise linear regression indicated significant release of Fe-Mn oxide-bounded soil Zn by maleic acid and its availability to the Zn-efficient genotype. Hence, release of maleic acid by plants roots played an important role in phytoavailability of Zn from calcareous soils.

Zinc availability of two wheat cultivars in soil amended with organic and inorganic Zn sources

-1 ) was applied to the soil at three rates of 25 (V 1), 50 (V 2), and 100 Mg ha - 1 (V 3). To compare the effects of organic and inorganic sources, similar rates of Zn as zinc sulphate (ZnSO 4) were also applied (Zn 1, Zn 2 and Zn 3, respectively). An untreated soil sample was considered as control soil (V 0). In general, cultivation of wheat plant (cv. Backcross) resulted in a lower Zn uptake relative to the Alvand cultivar. However, the plants Zn concentration of both cultivars depended on the rate and type of the applied manure (organic or inorganic sources). Both cultivars showed that plants grown in soil treated with ZnSO 4 accumulated significantly greater Zn in their root tissue compared to those grown in soil treated with cow manure. A significant increase in the shoot, spike and root Zn concentration was observed as the loading rate of cow manure increased. The results of this experiment point to the fact that the source of fertilizer, type of the plant and the loading rate of Zn are important factors in determining Zn phytoavailability.

Effects of a phosphorus amendment and the pH of water used for watering on the mobility and phytoavailability of Cd, Pb and Zn in highly contaminated kitchen garden soils

Studies on two lead and zinc smelters in Northern France (Metaleurop Nord and Umicore) showed that the level of metallic contamination of kitchen garden soils is higher than the agricultural soils located in the same environment. This results most particularly from cropping practices and the addition of various products. Due to the physical and chemical parameters of these soils, the behaviour and transfer of pollutants towards various plants (grass, trees, and vegetables) may be perceptibly different than what is observed on agricultural soils. For a better understanding of pollutant behaviour in kitchen garden topsoils, the Cd, Pb and Zn was fractionated using the SM&T protocol and various extracting solutions (CaCl 2, acetic acid, and citric acid) to evaluate their mobility in two highly contaminated soils chosen in the area affected by the past atmospheric emissions of the two smelters. In addition, agricultural topsoil was sampled in a non-massively contaminated area and was therefore chosen as the control soil. The three soils were amended with a mixture of hydroxyapatite (HA) and diammonium phosphate (DAP). At 6 months, extracting procedures were carried out to evaluate the effects of the amendment on the mobility of Cd, Pb and Zn. This step was then supplemented by an evaluation of the impact of the amendment on the phytoavailability of pollutants, which was determined in plant uptake studies with ryegrass ( Lolium perenne L.) by considering only the pollutant concentrations in their shoots. Two experiments were carried out. In the first one, unamended and amended soils and ryegrass were watered with distilled water (pH = 7). In the second one, osmosed water (pH = 5.5) was used to evaluate the effects of the acid water–phosphate amendment system on the mobility and phytoavailability of Cd, Pb and Zn. Six months after the start of the experiments, the selective extractions showed that the effectiveness of the amendment studied depended on the element, the soil and the water's pH. Reductions of metal eluted from the contaminated soils were 1.5–37.9% for Cd, and 9.1–80.9% for Pb. Application of P amendment to the combination of osmosed water was generally the most effective for immobilising Cd and Pb elution. In contrast, the mixture of HA and DAP was ineffective for reducing Zn elution. The plant-fresh biomass yield was significantly ( p < 0.05) increased by the combination of P amendment and distilled water, whereas a reduction of biomass was recorded with the combined amendment and osmosed water. Addition of P amendment generally reduced Pb uptake in ryegrass shoots (1–47%), while both Cd and Zn were increased by 17.9–79% and 0.45–100%, respectively.

Zinc Transformation in a Calcareous Soil as Affected by Applied Zinc Sulfate, Vermicompost, and Incubation Time

An experiment was conducted to evaluate the effect of zinc (Zn) rates and vermicompost levels on distribution of Zn forms of a calcareous soil. After incubation periods, soil samples were air dried, and a sequential extraction scheme was used to fractionate Zn into soluble and exchangeable, bound to carbonate, organically bound, bound to manganese (Mn) oxide, bound to amorphous iron (Fe) oxide, bound to crystalline Fe oxide, and residual forms. In untreated soil, Zn was mainly in the residual fraction. Increasing rates of applied Zn significantly increased all forms of Zn. Carbonate and residual forms showed the greatest increase. Application of vermicompost significantly increased all fractions except Mn-oxide form. This increase was more pronounced for organically bound, soluble, and exchangeable forms, indicating an increase in bioavailability of soil Zn. Incubation time significantly decreased soluble, exchangeable, and organically bound forms but increased other forms of Zn, meaning a significant reduction in Zn phytoavailability in soil with time.

Fractionation of Zn, Cd and Pb in a Tropical Soil After Nine-Year Sewage Sludge Applications

A long-term field experiment was carried out in the experiment farm of the Sao Paulo State University, Brazil, to evaluate the phytoavailability of Zn, Cd and Pb in a Typic Eutrorthox soil treated with sewage sludge for nine consecutive years, using the sequential extraction and organic matter fractionation methods. During 2005-2006, maize ( Zea mays L.) was used as test plants and the experimental design was in randomized complete blocks with four treatments and five replicates. The treatments consisted of four sewage sludge rates (in a dry basis): 0.0 (control, with mineral fertilization), 45.0, 90.0 and 127.5 t ha −1, annually for nine years. Before maize sowing, the sewage sludge was manually applied to the soil and incorporated at 10 cm depth. Soil samples (0-20 cm layer) for Zn, Cd and Pb analysis were collected 60 days after sowing. The successive applications of sewage sludge to the soil did not affect heavy metal (Cd and Pb) fractions in the soil, with exception of Zn fractions. The Zn, Cd and Pb distributions in the soil were strongly associated with humin and residual fractions, which are characterized by stable chemical bonds. Zinc, Cd and Pb in the soil showed low phytoavailability after nine-year successive applications of sewage sludge to the soil.

Eisenia fetida avoidance behavior as a tool for assessing the efficiency of remediation of Pb, Zn and Cd polluted soil

Remediation by means of soil leaching with ethylenediaminetetraacetic acid (EDTA) is capable of extracting the most labile soil fractions, leaving the residual metals in biologically non-available forms. We evaluated the feasibility of the standardized earthworm ( Eisenia fetida) avoidance test for assessing the efficiency of soil remediation of Pb, Zn and Cd polluted soil. Chemical extraction tests (six-step sequential extraction, toxicity characteristic leaching procedure, physiologically based extraction test, diethylenediaminepentaacetic acid extraction) indicated that the mobility, oral bioaccessibility and phytoavailability of Pb, Zn and Cd were consistently reduced. However, the avoidance test showed no significant avoidance of polluted soil in favor of that which had been remediated. Pb, Zn and Cd accumulation in E. fetida mirrored the decreasing pattern of metal potential bioavailability gained by leaching the soil with increasing EDTA concentrations. The calculated bioaccumulation factors indicated the possibility of underestimating the metal bioavailability in soil using chemical extraction tests.

Assessment of the Phytoavailability of Cd, Pb and Zn using Various Extraction Procedures(&lt;Special Issue&gt;International Symposium: Challenges to Soil Degradation Towards Sustaining Life and Environment, Tokyo Metropolitan University Symposium Series No.2, 2009)

Assessment of the Phytoavailability of Cd, Pb and Zn using Various Extraction Procedures(&lt;Special Issue&gt;International Symposium: Challenges to Soil Degradation Towards Sustaining Life and Environment, Tokyo Metropolitan University Symposium Series No.2, 2009)

Determination of Zinc Phytoavailability in Soil by Diffusive Gradients in Thin Films

Assessment of zinc (Zn) phytoavailability by the newly developed technique of diffusive gradients in thin films (DGT) has started gaining more importance because of some advantages over routine soil extractants. A greenhouse study was conducted to determine Zn phytotoxicity thresholds and the phytoavailability of Zn to sorghum sudan (Sorghum vulgare var. sudanese) grass by DGT, compared with calcium chloride (CaCl2) extraction. Treatments were five Zn levels and two soil pH (6.5 and 6). To obtain various amounts of Zn phytoavailability, soils having two different pH values were amended with zinc sulfate (ZnSO4) at rates of 0, 150, 300, 600, and 1200 mg Zn kg−1. Control soil (pH = 6.5) was treated with predetermined elemental sulfur to create different soil pH values (6). Shoot and root Zn concentrations ranged from 27 to 827 mg kg−1 and 101 to 2858 mg kg−1, respectively. In general, the Zn concentrations in shoots and roots were increased by increasing Zn concentrations and soil pH. Increasing applied Zn to soil decreased the plant biomass yield and increased adsorption of Zn by DGT. Calcium (Ca) to Zn ratios for all treatments except controls were <26 for shoots and <13 for roots. The CaCl2‐extractable Zn and effective concentration (CE) correlated well with plant Zn concentration. A critical shoot Zn concentration for 90% of the control yield was chosen as an indicator of Zn toxicity. The performance of DGT, CaCl2 extraction, Ca/Zn ratio and plant Zn concentrations were similar for assessing Zn phytoavailability.

Effect of Composts, Lime and Diammonium Phosphate on the Phytoavailability of Heavy Metals in a Copper Mine Tailing Soil

Soil samples from a historic copper mine tailing site at the Parys Mountain, North Wales (UK) were amended with green waste compost (GC), GC+30% sewage sludge (GCS), lime and diammonium phosphate (DAP), to determine the effect of amendments on DTPA- and Ca(NO 3) 2-extractable metals in the mine tailing and on the phytoavailability of heavy metals by a lettuce ( Lactuca sativa L.). Both compost were added at the rate of 10% by weight, lime was added as calcium carbonate equivalent (pH = 7) and DAP at a 2 300 mg kg −1 soil level. The experiment was arranged in randomised complete design with three replicates in pots under control environment. Addition of lime resulted in the largest reduction in metal extractability with DTPA and Ca(NO 3) 2 and phytoavailability of Cu, Fe and Zn while DAP was effective in lowering Pb extractability and phytoavailability. With exception of Zn, all other metals extracted decreased with time after amendment applications. The distribution of heavy metals between and within the four procedures of potentially bioavailable sequential extraction (PBASE) varied significantly ( P < 0.001). Stronger relationships were noted between the metals extracted with PBASE SE1 and Cu, Pb ( P < 0.01) and Fe ( P < 0.001) in the lettuce. These results indicate that addition of lime is sufficient to restore the vegetative cover to a high metal mine waste while DAP is good for stabilizing Pb, but its detrimental role on plant growth and the risk associated with presence of N in DAP (through N leaching) may restrict its chances for remediation of contaminated sites.

A COMPARISON OF TESTS FOR EXTRACTABLE COPPER AND ZINC IN METAL-SPIKED AND FIELD-CONTAMINATED SOIL

Common soil test methods were compared with 0.01 M CaCl2 extraction to determine their relative abilities to extract and estimate phytoavailability of Cu and Zn. In aged metal-spiked soils, all soil tests evaluated (Mehlich 3, diethylenetriaminepentaacetic acid [DTPA], Morgan, modified Morgan, CaCl2) showed a linear relationship of extractable to total Cu and Zn for both soil types studied. The fraction of total Cu and Zn extracted by aggressive tests (Mehlich 3, DTPA) was much higher than the fraction extracted by CaCl2, with the Morgan tests being intermediate. Although all extraction methods revealed Cu and Zn to be more available in the coarse-textured soil than the fine-textured soil, this texture effect was greatest for the least aggressive test (CaCl2) and least for Mehlich 3. The texture effect on soil test Cu and Zn was also reflected in bioavailability, with greater plant tissue concentrations of both metals from the coarse-textured soil in a soybean assay. Although all soil test methods provided similarly strong correlations to plant tissue concentrations of Zn for soybeans grown in the two soils, the less aggressive soil tests seemed more reliable as predictors of Cu uptake. The efficiency of Cu and Zn extraction from field-contaminated soils was much lower than that from laboratory-spiked aged soils. For Mehlich 3 and DTPA tests, Cu and Zn in field-contaminated soils were less extractable by a factor of about 2 compared with the spiked soils. For less aggressive tests, the difference in extractability was even greater. This study suggests that soil extraction methods removing smaller pools of Cu and Zn are more responsive to soil properties affecting chemical lability of the metals. Therefore, chemically nonaggressive neutral salts may be the most appropriate extractants where phytotoxicity is the concern in metal-contaminated soils.