Leaching of heavy metals from sewage sludge through coastal plain soils

Abstract

Three types of sewage sludge are applied to the surface of soil columns of Coastal Plain soils and leached with distilled water. The Zn concentrations in leachate samples from a Sassafras loamy sand soil loaded with an industrial sludge increased with sludge loading rate. All leachate samples contained very low concentrations of Cd, Cr and Cu. Hazardous amounts of Cd, Cr, Cu and Zn would not be leached to the groundwater when recommended rates of the tested sludges are applied to Coastal Plain soils under most conditions.     

外来种互花米草对江苏省潮间带生物地球化学过程的影响研究

Spartina alterniflora Loisel, a species vegetating in intertidal flats along the eastern coast of the United States, was introduced in China almost 30 years ago and has become an urgent topic due to its invasiveness in the coastal zone of China. The impacts of this alien species S. alterniflora on intertidal ecosystem processes in the Jiangsu coastland were investigated by comparing the sediment nutrient availability and trace element concentration characteristics in a mud flat and those of a four-year old Spartina salt marsh that had earlier been a mudflat. At each study site, fifteen plots were sampled in different seasons to determine the sediment characteristics along the tidal flats. The results suggested that Spartina salt marsh sediments had significantly higher total N, available P, and water content, but lower pH and bulk density than mudflat sediments. Sediment salinity, water content, total N, organic C, and available P decreased along a seaward gradient in the Spartina salt marsh and increased with vegetation biomass. Furthermore, the concentrations of trace elements and some metal elements in the sediment were higher under Spartina although these increases were not significant. Also, in the Spartina marsh, some heavy metals were concentrated in the surface layer of the sediment. The Spartina salt marsh in this study was only four years old; therefore, it is suggested that further study of this allen species on a longer time frame in the Jiangsu coastland should be carried out.     

Heavy‐metal displacement in chelate‐treated soil with sludge during phytoremediation

Heavy metals (HMs) in domestic sewage sludge, applied to land, contaminate soils. Phytoremediation is the use of plants to clean‐up toxic HMs from soil. Chelating agents are added to soil to solubilize the metals for enhanced uptake. Yet no studies report the displacement of HMs in soil with sludge following solubilization with chelates. The objective of this work was to determine the uptake or leaching of HMs due to a chelate added to a soil from a sludge farm that had received sludge for 25 y. The soil was placed in long columns (105 cm long; ?? 39 cm) in a greenhouse. Columns either had a plant (hybrid poplar; Populus deltoides Marsh. × P. nigra L.) or no plant. After the poplar seedlings had grown for 144 d, the tetrasodium salt of the chelating agent EDTA was irrigated onto the surface of the soil at a rate of 1 g per kg of soil. Drainage water, soil, and plants were analyzed for three toxic HMs (Cd, Ni, Pb) and four essential HMs (Cu, Fe, Mn, Zn). At harvest, extractable and total concentrations of each HM in the soil with EDTA were similar to those in soil without EDTA. The chelate did not affect the concentrations of HMs in the roots or leaves. With or without plants, EDTA mobilized all seven HMs and increased their concentrations in drainage water. Lower concentrations of Cd, Cu, Fe, Ni, and Zn in leachate from columns with EDTA and plants compared to columns with EDTA and no plants showed that poplars can reduce groundwater contamination by intercepting these HMs in the soil. But the poplar plants did not reduce Pb and Mn in the leachate from columns with EDTA. Concentrations of Cd and Pb in the leachate mobilized by EDTA remained above drinking‐water standards with or without plants. The results showed that a chelate (EDTA) should not be added to a soil at a sludge farm to enhance phytoremediation. The chelate mobilized HMs that leached to drainage water and contaminated it.     

Bulk sediment bioassays with five species of fresh-water oligochaetes

The fluxes of metals (Na, K, Ca, Mg, Fe, Mn, Al, Cu, Zn, Pb, Cd, Cr, and Ni) in two spruce forest soils in S. Sweden were quantified using the lysimeter technique. Amounts in precipitation (dry and wet), throughfall, litterfall and annual accumulation in biomass were also quantified, as well as stores in soil and biomass. The metal concentrations of the soil solutions varied greatly according to season. The leaching of some metals (Fe, Cu, Pb, Cr, and organic forms of Al) was associated with the leaching of organic matter. These complexes were leached from the A horizon in considerable amounts. They were precipitated in the upper B horizon and only small amounts were transported further downward. By contrast, the leaching of Na, Mg, Ca, Mn, Cd, Zn, Ni, and inorganic forms of Al increased with increasing soil depth. The concentrations of these metals also increased with increasing soil solution acidity. The highest concentrations were often found at the transition to the C horizon. The amounts of Na, K, Mg, Ca, Mn, Al, Zn, Cd, Cr, and Ni leached from the rooting zone were found to be larger than the amounts deposited from the atmosphere, the main source of these metals being the mineral soil. The reverse was true of Ph, Cu, and Fe, the sink being the upper part of the B horizon.     

Laboratory studies of effects of lime on soluble Al, Ca, Mg and Mn in a pelostagnogley soil

The cation composition of solutions and leachates from small-diameter laboratory soil columns was examined over a 23-week period after the addition of lime (0, 3 and 6 t ha^–1) and/or nitrogen fertilizer (0 or 200 kg N ha^–1) to an acid soil (pH 4.2). Water was applied at regular intervals to the surface of the columns and 17 leachate samples collected. Initially, the pH of the leachate was high (6.6) in all treatments (including those without lime) but fell rapidly to approach a steady value of 3.8. Large losses of calcium occurred from all columns; the total equivalent amounts of lime lost ranged from 0.88 (no addition) to 2.38 (with added lime) t CaCO₃ ha^–1 High concentrations of aluminium (181–325 μM) were present in leachates from all treatments; the addition of 200 kg N ha^–1 increased the leaching of Al by 94%; addition of lime also increased the amounts of Al leached (by 52%).
The pH of the soil solution (separated by centrifugation) was influenced by treatment, especially in the top 0–40 mm of the column. Aluminium concentration was related to pH, but the form of the relationship differed amongst the treatments.     

Heavy Metals Leachability as Affected by pH of Compost-Amended Growth Medium Used in Container-Grown Rhododendrons

The leaching of heavy metals from plant growth medium, admixed with different amounts of compost (prepared from sewage sludge and yard waste) at pH 5, 6 and 7 was determined over a six-month period. Twelve-week old rhododendron cuttings were planted in 2-L containers and rainfall was supplemented with irrigation to supply two centimeters of water per day. Leachates collected over each two to four week period were analyzed for Cd, Cr, Cu, Ni, Pb and Zn using atomic spectrometry. The concentrations of Cd, Cu, Ni and Zn in the leachates increased with increasing proportions of compost in the medium and decreased with increasing time of leaching. Decreasing media pH dramatically increased the concentrations of Cd, Ni and Zn in the leachates, but had no effect on the Cu concentrations. For example, as the proportion of the compost in the pH 5 medium increased from 0 to 100 percent, the concentrations of metals (μg L^?1) in the leachates collected during the first two weeks increased from 1 to 33 (Cd), 10 to 123 (Cu), 8 to 113 (Ni) and 300 to 24,000 (Zn). Corresponding increases at pH 7 were 0.4 to 0.8 (Cd), 14 to 141 (Cu), 8 to 28 (Ni) and 100 to 400 (Zn) μg L^?1. The concentrations of Cr and Pb in the leachates remained below the detection limits regardless of media pH and amounts of compost.     

煤矿区矸石山周边土壤重金属污染特征与规律

以山东某矿区为例,通过淋溶模拟实验,研究了煤矸石中重金属的淋溶规律,并探讨了煤矸石山周边土壤重金属污染特征.结果表明:风化矸石淋滤液中的Zn、Pb、Cr和Cu浓度较高,并很快稳定;新鲜矸石在淋溶初期检出Zn,其它重金属元素没有检出;风化矸石淋滤液中重金属的含量要高于未风化矸石.矸石山周边表层土壤中的Zn、pb、Cr和Cu较高,且浓度高出矸石淋溶液许多倍,表明煤矸石中重金属淋滤具有长期性,矿区土壤对重金属具有迁移性和富集性.表层土壤重金属含量随着距煤矸石堆的距离增加而呈明显的下降趋势,充分表明矸石山对周边土壤造成了严重的重金属污染,而且在土壤剖面上,重金属含量表现出随土壤深度的增加而降低的趋势.     

Effect of solid-phase speciation on metal mobility and phytoavailability in sludge-amended soil

Sequential extraction was utilized for partitioning Cd, Cr, Ni, and Zn, in soil and sludge samples into five operationally-defined fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The highest amounts of Cd, Ni, and Zn, expressed as per cent of the total, were found in the Fe-Mn oxide fraction of the sewage sludge. Chromium was significantly associated with the organic fraction of the sludge. The residue was the most abundant fraction for all metals studied in the untreated soil, and for Cd and Ni in the sludge-treated soil. The concentration of exchangeable Cd and Cr was relatively low in the untreated soil and did not change much after sludge application, whereas the concentrations of exchangeable Zn increased about 50 times and the concentrations of exchangeable Ni doubled in the sludge-treated soil. The lysimetric experiment revealed an increase in Zn and Ni uptake by ryegrass and in the percentage of metals leached from the soil profile after massive sludge application. In contrast only negligible changes were observed for Cd and Cr. The assumption that mobility and biological availability are related to metal speciation was confirmed by the agreement between the distribution pattern of Cd, Cr, Ni and Zn in the soils, the uptake of the metals by plants and their capacity for leaching out from the soils.     

Mobilization of Cu and Zn in contaminated soil by nitrilotriacetic acid

Batch and upflow column leaching experiments were used to evaluate the nature and extent of Cu and Zn solubilization from contaminated soil by nitrilotriacetic acid (NTA) in 0.025 M NaClO₄. In batch soil suspensions, NTA levels of 10^?5 to 10^?3 M substantially promoted Cu and Zn release from the metal-enriched soil. The ability of NTA to enhance Cu and Zn solubility decreased with increasing solution acidity probably due to competitive binding of NTA by protons and Fe released by hydrous oxide dissolution. However, in the pH range typically encountered in northeastern U.S. soils, soluble metal levels were nearly constant for a given NTA concentration. Leaching soil columns with NTA solutions enhanced Cu release more than Zn, as the enrichment ratio (cumulative metal leached by NTA compared to the 0.025 M NaClO₄ control leachate) after 85 pore volumes displacements was 23.6 and 4.3 for Cu and Zn, respectively. While Cu release by 0.01 M CaCl₂ differed little from the control, 0.01 M CaCl₂ was substantially more effective than 10^?5 M NTA in displacing bound Zn. The data reflect different retention mechanisms for Cu and Zn in this soil.     

Relationship between Metals Leached and Soil Type from Potential Acid Sulphate Soils under Acidic and Neutral Conditions in Western Australia

Metal contaminants are likely to be mobilised from soil when in contact with acidic drainage. Soils containing sulphide are often associated with significant quantities of trace metals. Understanding the source of metal pollution is of significant concern for management because sulphide-containing soils are found in close proximity to estuaries, lowland rivers and lakes. This study focuses on Western Australian soils, which are typically sandy and well weathered. Two leachate trials, a batch and a column method, investigated the possibility of characteristic leachate signatures with respect to future traceability of metal contamination from soil drainage. Leaching signatures were assessed for four soil types (grey sand (GS), iron-rich sand (FeRS), silty sand (SS) and peat) found coastally between Perth and Albany, in Western Australia. Trace metals leached from the four soil types showed significant differences for both the metals leached and the concentrations for the column leaching trial. No nickel (<1.0 µgL^?1) but relatively high concentrations of arsenic were leached from the peat site. The FeRS leachates contained chromium, copper, high aluminium and relatively high iron. The GS leached extremely high iron and relatively high manganese concentrations. In comparison, only small concentrations of nickel, iron, aluminium, arsenic and manganese leached from the SS columns. Selenium did not leach above reporting limits (<1.0 µg L^?1) from any of the soil types. This work suggests that leachate signatures from different soil types exist and that soil type should be considered when determining the risk of aquatic impact associated with acidic drainage.     

Mobility of lead in mine tailings due to landfill leachate

An old lead mine tailings pile in Southeast Missouri is being used as a sanitary landfill. The tailings were found to consist of 60–70% dolomite, 20–30% mascovite/illite and trace amounts of quartz, galena, and calcite. The pH was 8.1 and the lead concentrations were 810-3200 mg/kg. Several samples at the site were found hazardous using the EPA toxicity characteristic leaching procedure (TCLP). Since little was known about the mobility of the lead under these conditions, laboratory scale column experiments were conducted to determine if the lead in the tailings might be mobilized with a landfill leachate. Total lead was determined and lead availability was determined using sequential extraction. The lead associated with Fractions 1 (MgC1₂), 2 (NH₄OAc), and 3 (Na₄P₂O₇) of the sequential extraction leached rapidly and immediately produced a leachate after 1 hr of 440 mg/L before decreasing to 40 mg/L after 12 hr. Fraction 4 (EDTA) and Fraction 5 (HNO₃), were unaffected by the leachate.     

Effects of cover materials on leaching of constituents from dolomitic lead mine tailings

Five raised-bed test plots were used to study the effects of cover materials on the leaching of constituents from dolomitic Pb mine tailings over a 2-yr period. The cover materials studied were a fertilizer and seed mixture, anaerobically digested sewage sludge, loam and sod, and fallen leaves from silver maples (Acer Saccharinum); one plot was not covered. Fresh leachates and receiving pool waters were analyzed for ten metals, Si, P, inorganic anions, filterable organic carbon (FOC), and alkalinity. The mixture of fertilizer and seed decreased leaching of Pb and Zn during the first year. The leaf cover increased leaching of Pb during both years; this effect decreased as the leaves weathered. Sludge caused some increase in Pb leaching during the first year, and increased Cd leaching during both years. Concentrations of most leachate constituents decreased, and pH increased in the receiving pools. Concentrations of Pb remained higher in the receiving pool for the leaf-covered plot than in the other pools. Increases in leaching of Pb and Cd with a sludge cover were moderate, and the ability of the material to support plant growth on the tailings suggested that it may be a good medium for inducing growth of vegetative cover on the dolomitic tailings. Other organic materials may cause pronounced increase in the concentration of toxic trace metals in leachate from the tailings.     

Heavy Metals in Water Percolating Through Soil Fertilized with Biodegradable Waste Materials

The influence of manure and composts on the leaching of heavy metals from soil was evaluated in a model lysimeter experiment under controlled conditions. Soil samples were collected from experimental fields, from 0- to 90-cm layers retaining the layout of the soil profile layers, after the second crop rotation cycle with the following plant species: potatoes, spring barley, winter rapeseed, and winter wheat. During the field experiment, 20 t DM/ha of manure, municipal sewage sludge composted with straw (SSCS), composted sewage sludge (SSC), dried granular sewage sludge (DGSS), “Dano” compost made from non-segregated municipal waste (CMMW), and compost made from municipal green waste (CUGW) was applied, i.e., 10 t DM/ha per crop rotation cycle. The concentrations (μg/dm³) of heavy metals in the leachate were as follows: Cd (3.6–11.5)?<?Mn (4.8–15.4)?<?Cu (13.4–35.5)?<?Zn (27.5–48.0)?<?Cr (36.7–96.5)?<?Ni (24.4–165.8)?<?Pb (113.8–187.7). Soil fertilization with organic waste materials did not contaminate the percolating water with manganese or zinc, whereas the concentrations of the other metals increased to the levels characteristic of unsatisfactory water quality and poor water quality classes. The copper and nickel content of percolating water depended on the concentration of those metals introduced into the soil with organic waste materials. The concentrations of Cd in the leachate increased, whereas the concentrations of Cu and Ni decreased with increasing organic C content of organic fertilizers. The widening of the C/N ratio contributed to Mn leaching. The concentrations of Pb, Cr, and Mn in the percolating water were positively correlated with the organic C content of soil.     

Leaching Behavior of Heavy Metals In Biosolids Amended Sandy Soils

Use of biosolids in agriculture to improve crop production and soil quality have created concerns due to content of heavy metals that may affect surface or ground water quality. A column leaching study was conducted to evaluate the leaching potential of copper (Cu), lead (Pb), zinc (Zn), cdmium (Cd), cobalt (Co), chromium (Cr), and nickel (Ni) from two typical agricultural sandy soils in South Florida (Spodosol and Alfisol) with increasing application of pelletized biosolids (called PB) at the rates of 0, 1.25, 5.0, 10.0 g kg^?1, respectively together with chemical fertilizer (CF). Elevated PB rate resulted in reduced leaching loss of Cu, Pb, Zn, Cd, Co, Ni from Spodosol, but resulted in increased loss of Pb, Zn, Cd, and Co from Alfisol. Significant reduction in Cu loss occurred in both soils, which can be attributed to the strong binding of Cu with organic matter from the applied PB. Percentage of Cd loss as of total Cd was 13% – 41%, the highest in all the heavy metals, whereas loss of Pb as of total Pb was less than 6.6%, though the concentrations of Pb, Cd, Co, and Ni in leachate were mostly above the limits of U.S. EPA drinking water standards or the national secondary drinking water standards. These results indicate that soil properties, PB application rates, and chemical behavior of elements jointly influence the leachate total loads of heavy metals in sandy soils applied with biosolids. Application of CF together with BP at a rate higher than 10.0 g kg^?1 for sandy soils may pose potential threats to water quality due to enhanced leachate loads of Cr and Ni in Spodosol and Pb, Zn, Cd, Co and Ni in Alfisol.     

Influence of graded EDTA applications on mobilization and translocation of trace elements—a soil column experiment

Increasing concerns about potential environmental effects of ethylenediaminetetraacetic acid (EDTA) accumulation in soils require better understanding of its behavior and its effect on trace element mobilization. In this study we investigated the effect of EDTA on soil trace element mobilization in undisturbed soil columns taken from a heavy metal contaminated field. The columns were leached by EDTA solutions of different concentrations under unsaturated, steady‐state conditions. The transport of trace elements (Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sn, Zn) and EDTA was monitored by regularly collecting the leachates. After the termination of the leaching experiment the soil columns were divided into 5 layers to determine trace elements and EDTA concentrations in the soil. The results revealed that the soil analysis alone was not suitable to infer mobilization or immobilization patterns in relation to the EDTA concentration, as the mobilized fraction was too small in relation to the total trace metal concentrations in the soil. Analysis of the leachates displayed that after 2–4 pore volumes the EDTA output concentration reached about 80% of the input concentration. The trace element concentrations in the leachates showed that some elements were mobilized by EDTA (Cd, Cu, Fe, Pb, Co, Ni, Zn) while others were immobilized (Mn, Cr, Mo, Sn) in the soil columns after EDTA application.     

Bioleaching of heavy metals from sewage sludge using indigenous iron-oxidizing microorganisms

Purpose

The objective of this study was to investigate the bioleaching of Cr, Cu, Pb, and Zn from sewage sludge using iron-oxidizing microorganisms. These conditions include the solid concentration, initial pH, ferrous iron concentration, inoculum concentration as well as the kinetics of solubilization of metals from sewage sludge to determine whether they impact on bioleaching efficiency.

Materials and methods

The sludge sample containing bacteria used in this study was collected from Fuzhou Jingshan sewage treatment plant. Indigenous iron-oxidizing bacteria were enriched from the sludge. Conditions affecting the bioleaching and application were conducted using batch experiments. The analysis of Cr, Cu, Pb, and Zn was carried out with an atomic absorption spectrophotometer, and the pH and ORP were measured using pH meter and ORP meter.

Results and discussion

The data show that 88.5 % of Zn, 79.9 % of Cu, 50.1 % of Pb, and 33.2 % of Cr can be removed from the sludge after 12 days of bioleaching at 30 °C, while only 80.2 % of Zn, 21.8 % of Cu, 10.9 % of Pb, and 10.5 % of Cr were leached out in the control without iron-oxidizing microorganisms. The leaching kinetics study shows that the rate of metal solubilization in bioleaching using iron-oxidizing microorganisms was more effective compared to chemical leaching.

Conclusions

The results suggest that the leaching of metals from sludge can be attributed to two leaching approaches: firstly, chemical leaching; and secondly, bioleaching. However, their effectiveness depends on metal species because of their different bindings in sludge. For example, the leaching of Zn from the sludge was dominated by chemical leaching while the removal of Cu, Pb, and Cr was dominated by bioleaching.     

Heavy Metals in Soil, Plants and Groundwater Following High-Rate Sewage Sludge Application to Land

The concentrations, solubility and mobility of Cr, Cu, Ni, Pb and Zn were measured over a four year period in soil from a site that had received over 1000 t ha^-1 wet, undigested, sewage sludge (on average, 15% dry solids). The pH of this light-textured sandy soil was markedly reduced after sludge application (to ≤4 in some samples), presumably as a result of breakdown of the unstable organic matter, nitrification of the NH₄ ⁺-N and sulphide oxidation. As a consequence, soil solution concentrations of Cu, Ni, and especially, Zn were initially elevated, and this was reflected in high plant uptake of Zn and elevated levels of all three metals in some groundwater wells. An extensive liming programme resulted in soil pH values generally between 5 and 6, more normal for this soil, in the following years. Soil solution metal concentrations were substantially lower, e.g., Zn from a high of 27 mg kg^-1 in 1995 to 0.04 mg kg^-1 in the equivalent sample in 1999. Herbage Zn concentrations declined accordingly and overall there was a strong relationship between plant metal uptake and soil solution concentration of this element (R² = 0.84), although not for any of the other metals. Our results suggested that, for this soil, pH was by far the greatest determinant of metal solubility and that the metal source, whether sewage sludge or geochemical, had little influence. Results from extractants that solubilise other metal phases, i.e., NaNO₃, EDTA and HNO₃, are also presented and discussed.     

pH Requirement for the Bioleaching of Heavy Metals from Anaerobically Digested Wastewater Sludge

Bioleaching has been demonstrated to be a feasible technology for removing heavy metals from sewage sludge, but the leaching medium needs to be pre-acidified to less than 4. The objective of the research presented in this paper was to investigate the pH requirement for isolated indigenous Thiobacillus ferrooxidans for bioleaching heavy metals from wastewater sludge in Hong Kong. Isolated sludge-indigenous iron-oxidizing bacteria were used for the bioleaching experiments to investigate the dissolution behaviour of heavy metals (Zn, Cu, Ni and Cr) from sludge set at an initial pH ranging from 3–7 with the purpose to reduce the acid consumption. The results showed that the inoculation of 15% of isolated indigenous iron-oxidizing bacteria and addition of 4.0 g L^-1 Fe²⁺ (in the form of FeSO⁴?7H₂O) resulted in a sharp decrease in sludge pH from an initial pH 3–7 to 2.1–2.4 and an increase in ORP (oxidation-reduction potential) from –200–38 mV to > 500 mV within the first 6 days. After 16 days of bioleaching, 50.2–78.4% of Cr, 63.7–74.1% of Cu, 74.9–88.2% of Zn and 15.5–38.6% of Ni can be leached out from the sludge at an initial pH range of 3–7. In contrast, only 1.5% of Cr, 1.7% of Cu, 15.3% of Zn and 15.5% of Ni was solubilized in the control run at pH 7.0. At the end of bioleaching, the dissolution of nutrients N and P from the organic matrix at pH 6 was significantly less than that at pH 3–5. Hence, the bioleaching efficiency could still be maintained at an initial pH of > 4 using the isolated indigenous T. ferrooxidans which would reduce the cost of operation.

     

砂质土壤积累的铜和锌的可提取性与移动性研究

An investigation was conducted to study problems of determining a reasonable percentage for ecological water-use in the Haihe River Basin of China. Three key aspects for the ecological water requirement （EWR） were analyzed, involving i） the EWR for river system, ii） the EWR for wetlands and lakes, and iii） the EWR for discharge into the sea to maintain the estuary ecological balance of the Haihe River. The Montana method and related water level-flow relationships, and the statistic approach based on hydrological records were applied to estimate different components of EWR. The results showed that the total ecological water demand in the region, was about 3.47-14.56 billion m^3. Considering flow regime change and uncertainty, the ecological water demand could be estimated by the hydrological frequency approach. Preliminary analysis showed that for different annual runoff under the frequencies of 20%, 50%, 75% and 95%, the ecological water demand approached 12%-50%, 18%-74%, 24%-103%, 35%-148% and 16%-66%, respectively. By further analysis to balance ecological water-use and socioeconomic water-use, the rational percentage of ecological water-use was estimated as 35%-74%, that provides useful information to judge whether the allocation of water resources is reasonable, and was proved to be satisfactory by comparing with the practical condition.     

Leaching of metals from the A-horizon of a spruce forest soil

The study quantifies the amount of metals (Na, K, Mg, Ca, Al, Fe, Mn, Ni, Cr, V, Cu, Zn, Cd, Pb) leached from the A-horizon of a podzolic spruce forest soil in southern Sweden during 2.5 yr, and offers statistical evidence of environmental conditions of importance to metal release. Considerable losses of Pb, Cr, Ni and V may occur from the A-horizon of forest soils under conditions favoring leaching of organic matter, Fe, and Al, i.e. during periods of comparably high soil temperature and moisture. Metals with a larger fraction present in exchangeable form (Na, Mg, Ca, Zn, Cd) are more susceptible to minor pH changes. An accelerated deposition or internal production of acidic matter therefore will reduce the retention times of these elements particularly.