Counter-Current Metal Leaching and Precipitation for Soil Remediation

Chemical acid leaching is an effective technique for extracting toxic metals from the finest fractions of polluted soils. Nevertheless, the use of large quantities of reagents and process water results in prohibitive operating costs. The purpose of this study was to evaluate the technical and economic advantages of recirculating water in a counter-current leaching process (CCLP). Five 1-h sulfuric acid extraction steps (at pH = 1.5) followed by three 5-min water-washing steps were applied to the fine particle fraction (<0.125 mm) of an industrial soil polluted by Cd (13.2 mg·kg^?1), Cu (3 100 mg·kg^?1), Mn (685 mg kg^?1), Pb (550 mg·kg^?1), and Zn (2 840 mg·kg^?1). The leaching experiments were carried out at ambient temperature using a 10% soil suspension and in 1-L working volume stirred tank reactors. This paper presents results of conventional and counter-current leaching process (CCLP) tests and shows that the CCLP yields removal results for Cu (85%), Zn (86%), Mn (75%), and Cd (90%) that are similar to those obtained using the conventional leaching process. Moreover, the CCLP uses half of the quantity of acid and one-eighth of the amount of water that the conventional process uses. Metal precipitation with NaOH and Ca(OH)₂ was applied to treat the acidic leachates, and good metal removal yields were achieved with both reagents. However, the large consumption of chemicals implies high operating costs. In addition, the precipitation causes considerable sludge production, particularly when using Ca(OH)₂. Overall, the CCLP coupled to metal precipitation using NaOH and water recycling appears to be the most attractive option for the removal of toxic metals from this industrial soil.     

Metal Distribution and Characterization of Cultivable Lead-Resistant Bacteria in Shooting Range Soils

Shooting ranges represent about 10% of polluted sites in Switzerland. This pollution, mainly consisting of lead (Pb) and antimony (Sb), can spread into the local groundwater, wildlife and plants. In this study, shooting range stop butt soils (elevated soil mount behind the target) of three sites (Versoix, Cartigny and Nyon, Western Switzerland) were investigated for metal contamination and culturable lead-resistant bacteria in contaminated soils. The inductively coupled plasma mass spectrometry analysis of surface stop butt soils (0–5 cm) indicated high metal concentrations especially for Pb and Sb, e.g., the Pb concentration ranging from 61,135 to 395,651, 23,821 to 201,268 and 120 to 27,517 mg kg^?1 in the soil from the sites of Versoix, Cartigny and Nyon, respectively. Molecular analysis of 16S rRNA gene demonstrates the presence of bacteria from diverse classes: Flavobacteriia, α-Proteobacteria, γ-Proteobacteria, Actinobacteria and Bacilli that exhibited high Pb minimum inhibitory concentration value from 1,036 to 2,694 mg kg^?1. The isolated strains could be the subject of further studies to evaluate their role in bioremediation of lead-contaminated soil.     

Effect of Phosphate Treatment on Pb Leachability in Contaminated Shooting Range Soils

A cost-effective way to reduce lead released into the environment is through immobilization with readily available soil amendments. Leaching of Pb from four shooting range soils treated with two phosphate sources was evaluated in soil columns. Phosphate was applied at a P/Pb molar ratio of 4:1 with two-thirds of the P supplied from phosphate rock (PR) and one-third from phosphoric acid (PA). The soils were incubated for 18 hr and leached with toxicity characterization leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) fluids, respectively. PR/PA treatment reduced Pb in TCLP leachate to below regulatory limit of 5 mg/L after 18 hr of incubation. Reduction of Pb leached was more dependent on clay content than total Fe. PR/PA treatment had no effect on pH of TCLP leached soils, while it led to a drastic lowering of pH that mobilized Pb in SPLP leached soils. However, leaching of Pb reduced with time in SPLP leached soils because pH increased gradually. PR/PA treatment was more effective in SPLP leached soils with low total soil Pb because they received lower amounts of PA. PR/PA treatment may be more efficient when applied as split applications in soils with a low to medium Pb loading and a high buffering capacity.     

Characterization of Lead in Soils of a Rifle/Pistol Shooting Range in Central Florida,USA

The distribution of lead in soil samples collected from both surface (0 to 10?cm) and profile (O 0 to 10?cm, E 11 to 30?cm, Eb 31 to 50?cm, Bw 51 to 100?cm, and C 181 to 200?cm) at a 14-year-old rifle/pistol shooting range located in central Florida were determined using EPA Method 3051a (microwave, HNO₃/HCl=3:1, v/v). In addition to total lead analysis, Toxicity Characteristic Leaching Procedure (TCLP) analysis was performed on corresponding samples to determine whether the soils would require special handling as hazardous waste if the soils were to be removed from the range. Total lead in surface soils varied from 330 to 17 850?mg Pb kg^?1, with the greatest concentration in the middle of the backstop berm. The TCLP tests indicated that lead in all surface soils exceeded the 5?mg Pb L^?1 critical level of federal regulation for solid wastes and hazardous wastes provided by the Resource Conservation and Recovery Act (RCRA) and would be characterized as hazardous waste. Sequential fractionation and X-ray diffraction (XRD) analyses revealed that lead carbonate existed predominantly (91.3%) in the berm soil. The weathering of lead bullets in the soil environments formed primarily as hydrocerussite (Pb₃(CO₃)₂(OH)₂), with small amounts of massicot (PbO) and cerussite (PbCO₃). However, the elevated soil pH, caused by the oxidization and transformation process of elemental lead in lead bullets, could be a significant factor in limiting the migration of lead in the soil.     

Remediation of Gulf War Oil Spill Contaminated Soil by a Subcritical Water Extraction Process: Oil Removal,Recovery, and Degradation

Due to the unique properties of subcritical water (marked change in water's dielectric constant and viscosity), the extraction by subcritical water offers a great opportunity to remediate soil contaminated with organic pollutants as an alternative and green remediation method. In this study, subcritical water extraction is proposed as an efficient remediation technique for the Gulf War oil spill contaminated soil. The subcritical water extraction experiment was carried out in a lab-scale continuous flow apparatus. The three major operating factors, temperature, time and water flow rate, were evaluated in terms of optimum removal efficiency. The results show that crude oil removal depended largely on water temperature, whereas an extraction run time higher than 1 h and a water flow rate higher than 1.5 mL/min marginally or negatively affected removal efficiency. During subcritical water treatment at 300°C for 1 h at a flow rate of 1.5 mL/min, removal efficiency was almost 95%. Under these operating conditions, the subcritical water treatment demonstrated a similar removal efficiency to those of organic solvents like acetone. In contrast, the efficiency of oil recovery decreased with an increase in extraction temperature, due to degradation by a water self-oxidizing agent. Several degradation products identified in the treated soil and in the effluent sample (which initially were absent in the contaminated soil) were oxygen-containing aromatic compounds, confirming the oxidation-degradation.     

Counter-Current Attrition Process (CCAP) to Remove Metals,Pentachlorophenol (PCP), Dioxins and Furans (PCDDF) from the 1-4-mm Fraction of Contaminated Soil

The objective of this study was to evaluate the potential of a counter-current attrition process (CCAP) over 15 cycles for removing metals, pentachlorophenol (PCP) and polychlorinated dibenzo-p-dioxins and -furans (PCDDF) from contaminated soil. The CCAP, applied to the 1–4-mm fraction of a contaminated soil, included five attrition steps (pulp density (PD) = 40% (w w^?1), surfactant [BW] = 2% (w w^?1), t = 20 min, T = 20°C) followed by one rinsing step. The water emerging from the first attrition step was treated using flocculation in the presence of 0.04 g CMX 123 (commercial flocculent) L^?1 before being reintroduced into the CCAP. The CCAP including the treatment of attrition wastewater (ATW) by flocculation achieved a removal of 44 ± 5% As, 26 ± 6% Cr, 24 ± 5% Cu, 49 ± 4% PCP and 45 ± 3% PCDDF. Moreover, the CCAP enabled a significant reduction (78%) in the amount of water required (around 14.5 m³ of water per ton of the 1–4-mm soil fraction). The high removal yields obtained after 15 attrition cycles of the CCAP for PCP and PCDDF and the significant reduction of water consumption confirm that this CCAP can be considered for industrial applications.     

Leaching of Cd,Zn, Pb,and Cu in Packed and Undisturbed Columns of Soils Affected by the Spill from a Pyrite Mine in the South of Spain

A study has been made of the leaching of Cd, Zn, Pb, and Cu in three representative soils within the zone affected by the spill from a pyrite mine in Aznalcollar (Sevilla, Spain) employing packed soil columns. According to the breakthrough and cumulative leaching curves, the relative mobilities of the different toxic elements in the columns are as follows: Cd> Zn> Cu> Pb. The effect of leaching on the distribution of metals as a function of depth using intact soil cores was also studied. The results showed that the soils themselves have a good capacity for immobilizing the soluble fraction of the elements from the spilled mud. This capacity varied as follows: clayey soil with a high carbonate content > clayey soil with a moderate carbonate content > sandy-clay loam soil with a low carbonate content. However, sandy soils with a low carbonate content could pose a risk to groundwater if initial contamination was high. These results could be considered during the evaluation of remedial technologies for the immobilization of soil metals.     

A Comprehensive Approach to Speciation of Lead and Its Contamination of Firing Range Soils: A Review

Lead pollution of shooting range soils has received tremendous attention in the past few years due to its adverse effects to the environment. High total Pb concentrations have been reported in shooting range soils. Soil physicochemical properties such as pH, organic matter, cation exchange capacity (CEC) and soil moisture have been found to have a strong influence on the transformation of Pb shots. Therefore, it is imperative that the soil physicochemical properties are well understood when investigating the environmental effects of Pb. Total Pb concentration gives a measure of the amount of Pb stored in soil but does not give a true picture of the environmental pollution risk. In their quest to control pollution of shooting range soils from Pb, scientists have applied soil remedial methods such as soil washing, chemical stabilisation and phytoremediation. This review examines the pollution status of shooting range soils from Pb, the effect of soil properties on Pb mobility and bioavailability, the importance of Pb chemical speciation in understanding Pb mobility and shooting range management strategies applied in the control and management of Pb pollution of shooting range soils. This is a holistic review covering literature from 1983 to 2018, a period of 35 years.     

Remediation of Copper from Copper Mine Wastes and Contaminated Soils Using (S,S)-Ethylenediaminedisuccinic Acid and Acidophilic Bacteria

The biodegradable chelating agent (S,S)-Ehylenediaminedisuccinic acid (EDDS), autochthonous acidophilic bacteria, and a combination of the two means were investigated for the removal of pseudo-total and ethylenediaminetetraacetic acid (EDTA)-available content of Cu from surface layers of three soil categories in the Bor copper mining area. Their efficiencies were compared at mine overburden, flotation tailings, and agricultural land sites in order to determine the potential role of these approaches in the soil remediation process. The most effective removal of Cu was achieved on flotation tailings, where combined treatment showed significant reduction of pseudo-total and EDTA-available concentrations of Cu (40.5?±?27.3% and 99.6?±?0.2%, respectively). Acidophilic bacteria treatment showed high efficiency on flotation tailings, removing 94.1?±?1.2% of EDTA-available Cu. EDDS treatment showed discernible results in the removal of EDTA-available Cu from agricultural land soil (44.4?±?13.9%). In the case of overburden soil material, selected agents did not have statistically significant results in the removal of pseudo-total or EDTA-available fraction of Cu. Chosen remediation approaches showed diverse efficiency for soil categories on investigated sites. Combined approach showed synergistic results in the case of EDTA-available Cu removal from flotation tailings soils, suggesting that this combination deserves further attention as a potentially promising environmentally friendly remediation option.     

Biological Responses in the Earthworm Eisenia fetida Exposed to Soils near a Typical Lead Acid Battery Plant

There are increasing concerns over the environmental implications involved in battery plant due to the elevated metal concentrations in the surrounding soils. Earthworms are regarded as a model organism for evaluation of terrestrial environmental pollution. The biochemical responses in the earthworms, Eisenia fetida, exposed to polluted soils were investigated. Soil samples at 0, 50, 100, 200, 500 and 1000 m from a battery plant were collected and used to assess the relationship between sampling distance and biochemical responses in E. fetida. Biochemical alterations were carried out on 1, 3, 7 and 14 d of exposure. The metallothionein (MT), malondialdehyde (MDA) and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) were measured. The results demonstrated that concentrations of heavy metals, especially Pb, decreased sharply with increase in distance, which may be due to the leaching and accumulation of Pb in soil during production processes. The concentrations of MT and MDA increased with exposure (dosage and time), indicating that E. fetida presented dose and time dependence after heavy metal exposure. The activities of SOD and CAT increased after heavy metal induction, while the activity of POD was lower than that of the control group. The SOD, CAT and POD present a cooperative effect for the protection of lipids and enzymes due to the pollution. The soils around the battery plant were polluted with metals giving rise to adverse biological effects.     

The Use of Conocarpus lancifolius Trees for the Remediation of Oil-Contaminated Soils

The role of the Conocarpus lancifolius tree in remediaitng oil-contaminated soil, which was bioremediated using conventional methods, was investigated. The selected tree was used to phytoremediate bioremediated oil-contaminated soil for three successive growing seasons. At the end of the phytoremediation experiment, 85.7% of measurable total petroleum hydrocarbon (TPH) was degraded in Conocarpus lancifolius rhizosphere, and the detectable concentrations of some poly aromatic hydrocarbons (PAHs) were less than 0.02 ppm. A number of hydrocarbon degrading microorganisms (HDMs) were isolated at 35°C under aerobic conditions, and were identified using 16S rRNA gene sequencing and fatty acid methyl ester (FAME) analysis. The efficiency of the isolated HDMs in degrading a mixture of hydrocarbon compounds (HC) was assessed. Among the bacterial isolates, Rhodococcus equi was distinguished from the other isolates because of its efficient degradation of some compounds in the HC mixture.

Samples were also collected from Conocarpus lancifolius vegetative parts and were analyzed for heavy metal and mineral accumulation. The results demonstrated that the Conocarpus lancifolius tree was able to uptake high levels of chromium (Cr), vanadium (V), and nickel (Ni) and accumulate them in the tree's roots. Additionally, Conocarpus trees tolerated high concentration and accumulated several metals in all plant tissues. These metals included aluminum (Al), calcium (Ca) and iron (Fe).     

Comparison of Extractants for Removing Heavy Metals from Contaminated Clayey Soils

This article describes the removal of heavy metals from contaminated clayey soils by soil washing using various extractants. Two clayey soils, kaolin, a low buffering soil with pH of 5, and glacial till, a high buffering soil with pH of 8, were used to represent various soil conditions. These soils were spiked with chromium (Cr), nickel (Ni), and cadmium (Cd) to simulate improper disposal of typical electroplating waste constituents. The following extracting solutions were investigated for the removal of heavy metals from the soils: deionized water, distilled water, and tap water; acetic acid and phosphoric acid; chelating agents ethylenediaminetetraacetic acid (EDTA) and citric acid; and the oxidizing agents potassium permanganate and hydrogen peroxide. The effect of extractant concentration on removal of heavy metals was also investigated. Complete removal of Cr was achieved using 0.1?M potassium permanganate for kaolin, while a maximum of 54% was removed from glacial till. A maximum Ni removal of 80% was achieved using tapwater for kaolin, while a maximum removal of 48 to 52% was achieved using either 1?M acetic acid or 0.1?M citric acid for glacial till. A maximum Cd removal of 50% was achieved using any of the extractants for kaolin, while a maximum removal of 45 to 48% was obtained using either acids or chelating agents for glacial till. Overall, this study showed that complete removal of Cr, Ni, and Cd from clayey soils is difficult to achieve using the soil-washing process, and also the use of one extractant may not be effective in removing all metals. A sequential extraction using different extractants may be needed for the removal of multiple metal contaminants from clayey soils.     

Metal(loid)-Contaminated Soils as a Source of Culturable Heterotrophic Aerobic Bacteria for Remediation Applications

Heavy metal–contaminated soils are a serious environmental problem. Herein, the culturable heterotrophic bacterial community present on two metal(loid)-contaminated sites in the Northern Portugal was investigated. The bacterial counts ranged from 5.96 to 7.69 and 7.04 to 7.51 (log CFU g^?1 soil) in Sites 1 and 3, respectively. The bacterial population was predominantly composed of Firmicutes, Proteobacteria, and Actinobacteria on both sites. The most represented genera in Site 1 were Bacillus (41%) and Pseudomonas (27%), whereas Arthrobacter (21%) and Pseudomonas (13%) were the most represented genera in Site 3. Several bacterial isolates showed tolerance to high concentrations of metal(loid)s, suggesting that both contaminated sites are a valuable source of metal(loid)-tolerant bacteria, which may be further used in bioremediation and/or phytoremediation processes.     

Potential of Mauritius Hemp (Furcraea gigantea Vent.) for the Remediation of Chromium Contaminated Soils

The present study was conducted to evaluate the ability of a high biomass producing, drought tolerant succulent plant Mauritius hemp (Furcraea gigantea Vent.) for its tolerance to different levels of Cr (0, 25, 50, 100 and 200 mg Cr kg soil^?1) and its potential for phytoremediation purposes. Based on the data on inhibition of the growth of plants with Cr, tolerance index and grade of growth inhibition, it was observed that the plant could tolerate up to 50 mg Cr kg ^?1 soil. Absorption of Cr from soil to plant and its translocation into plant tissues were discussed in terms of bio concentration factor (BCF), transfer factor (TF), and translocation efficiency (TE%). Cr was mainly accumulated in the roots and exclusion of Cr was found to be the principal physiological tolerance mechanism followed by a marked increase in proline, ascorbic acid, total free amino acids in the leaf tissue and malic acid in the rhizosphere samples to counter Cr stress. Based on the tissue concentration of Cr (< 300 μg g^?1 in the leaves and TF<1), it was concluded that, Furcraea gigantea could not be considered a hyperaccumulator and therefore unsuitable for phytoextraction of Cr. Nevertheless, Furcraea gigantea could be a suitable candidate for phytostablization of Cr contaminated soils.     

Removal of Heavy Metals from Contaminated Soil and Sediments Using the Biosurfactant Surfactin

The feasibility of using a biodegradable surfactant, surfactin from Bacillus subtilis, for the removal of heavy metals from a contaminated soil (890?mg/kg zinc, 420?mg/kg copper, 12.6% oil and grease) and sediments (110?mg/kg copper, 3300?mg/kg zinc) was evaluated. Results showed that after one and five batch washings of the soil, 25 and 70% of the copper, 6 and 25% of the zinc, and 5 and 15% of the cadmium could be removed by 0.1% surfactin with 1% NaOH, respectively. From the sediment, 15% of the copper and 6% of the zinc could be removed after a single washing with 0.25% surfactin/1% NaOH. The geochemical speciation of the heavy metals among the exchangeable, oxide, carbonate, organic, and residual fractions was determined by selective sequential extraction procedure. For both matrices, the exchangeable fractions were minimal, while the carbonate and the oxide fractions accounted for over 90% of the zinc present and the organic fraction constituted over 70% of the copper. Results after washing indicated that surfactin with NaOH could remove copper from the organic fraction, zinc from the oxide, and cadmium from the carbonate fractions. The residual fraction remained untouched. These experiments indicate that the sequential extraction studies could be useful in designing soil-washing procedures.     

Applications of Citric Acid Industrial Wastewater and Phosphonates for Soil Remediation: Effects on Temporal Change of Cadmium Distribution

Citric acid industrial wastewater (CAIW) and phosphonates are potentially useful for enhancing remediation of metal-contaminated soil. This study aimed to investigate the effects of these enhancement agents on temporal change of Cd distribution in a clayey soil, which probably correlates with the metal lability and bioavailability in the environment. Sequential extractions were performed on the soil samples from batch desorption experiments between 5 and 4320 min. The CAIW primarily enhanced Cd extraction from weakly bound fractions (i.e., exchangeable and carbonate fractions), which was relatively fast and took place in the first 60 min. On the other hand, (nitrilotrimethylene)-triphosphonic acid (NTMP) and ethylene diaminetetra-methylenephosphonic acid (EDTMP) provided a more significant Cd extraction from exchangeable, carbonate, and oxide fractions, with the change of Cd distribution occurring over the first 300 min. The differences in the extent and temporal change of metal extraction reflected the weaker complexation strength of CAIW compared to that of NTMP and EDTMP. Moreover, an increase of pH from 4 to 10 shifted the remaining Cd from exchangeable fraction to carbonate and oxide fractions. These distribution changes indicated that both CAIW and phosphonates were efficient at removing weakly bound Cd fractions in a short period of time, but alkaline conditions could hinder their effectiveness.     

Pollution and ecological risk assessment of antimony and other heavy metals in soils from the world's largest antimony mine area,China

Xikuangshan is located in Lengshuijiang City, Hunan province, China. With intensive mining and metallurgical activities, large amounts of tailing containing heavy metals (in this study, the term “heavy metals” is used for both metals and metalloids) were introduced to the soils around the mine area. Those heavy metals including antimony and other heavy metals would pose huge risk to human health and ecological environment. With a view to providing information on the extent of contamination and potential ecological risk of heavy metals in the soils of this mine area, the total contents of antimony (Sb), manganese (Mn), zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb) in the soils were examined. The results revealed that the predominant pollutants in this area were Sb, Cd, and Zn with mean concentrations being 356.58, 9.98, and 486.42 mg kg^?1, 119.66, 117.41, and 5.17 times of the corresponding background values respectively. The pollution indices (Ps) indicated that the pollution levels of all sampling zones were serious including the control zones. The ecological risk levels of all heavy metals were very high on all the sampling zones except sampling zone 7 (as considerable), and Sb, Cd, and As were regarded as making great contribution to the risk indices (RI).     

Strength and Leaching Characteristics of Magnesium Phosphate Cement-Solidified Zinc- Contaminated Soil under the Effect of Acid Rain

Long-term static leaching experiments were conducted to investigate characteristics of magnesium phosphate cement (MPC) solidified/stabilized Zn-contaminated soil under impact of acid rain. Effects of initial pH values of acid rain, binder agent types and compositions, as well as curing age on strength and leaching characteristics of the sample were analyzed. Standard sand was used as raw material, with the content of cement at 15%. Our study used two types of MPC with MgO/KH₂PO₄(M/P) ratio of 3:1 and 6:1 (respectively referred to as M3 and M6), and also ordinary Portland cement with content at 15% (referred to as C15) as test control. Experimental results show that acid rain with pH = 2 has the greatest weakening effect on unconfined compressive strength (q_u) of the sample, while with pH = 4 and 7 such weakening effects on q_u are similar. Research findings also indicate that M6 is the most effective in immobilizing Zn-spiked soils, M3 is next and C15 is the least. The effect of Zn²⁺ on hydration of MPC is much lower than that of C15. Precuring method can improve q_u of the MPC-solidified samples and its resistance to acid rain. Compared with non-renewal, replacing acid rain leachant at designated intervals decreases q_u of the sample.     

Chemical Extraction of Arsenic and Heavy Metals from Contaminated Soils Under High Temperature and Pressure Conditions in Abandoned Mines in South Korea

The chemical extraction of As and heavy metals from contaminated soils, sampled from the Geopoong and Keumpoong mines in South Korea, was investigated under subcritical conditions. Soil samples from the abandoned mines were heavily contaminated with As, Cd, Cu, Pb, and Zn. The extent of metal removed from the contaminated soils by extractants varied according to the chemical forms of the metals in the soils. When temperature increased, the extraction of As increased accordingly, showing 92-100% removal with 100 mM of NaOH at 300°C. In contrast, the extraction of cationic metals by citric acid and ethylenediaminetetraacetic acid (EDTA) decreased markedly at 200–300°C because their chelating ability was decreased via decarboxylation and dehydration at high temperatures. Furthermore, the extraction of cationic metals was significantly affected by solution pH. Our results suggest that chemical extraction of cationic metals under subcritical conditions may be affected by several factors, including character of metal, type of extracting reagent, existing forms of metal in the soil, temperature, and soil pH.     

Leaching of Zinc,Cadmium, and Lead in a Sandy Soil Due to Application of Poultry Litter

Dissolved organic matter in poultry litter could contribute organic ligands to form complexes with heavy metals in soil. The soluble complexes with heavy metals can be transported downward and possibly deteriorate groundwater quality. To better understand metal mobilization by soluble organic ligands in poultry litter, soil columns were employed to investigate the movement of zinc (Zn), cadmium (Cd), and lead (Pb). Uncontaminated soil was amended with Zn, Cd, and Pb at rates of 400, 8, and 200 mg kg ^{? 1} soil, respectively. Glass tubes, 4.9-cm-diameter and 40-cm-long, were packed with either natural or metal-amended soil. The resulting 20-cm-long column of soils had bulk density of about 1.58 g cm ^{? 3} . Columns repacked with natural or amended soil were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl ₂ , or poultry litter extract (PLE) solutions. Low amounts of Zn, Cd, and Pb were leached from natural soil with the solutions. Leaching of Zn, Cd, or Pb was negligible with distilled water. In the metal-amended soil, EDTA solubilized more Zn, Cd, and Pb than CaCl ₂ and PLE. The breakthrough curves of Zn and Pb in the PLE and CaCl ₂ were similar, indicating they have similar ability to displace Zn and Pb from soils. Compared with Zn and Cd the PLE had a small ability to solubilize Pb from metal-amended soil. Thus, the application of poultry litter on metal-contaminated soils might enhance the mobility of Zn and Cd.