Effects of ionic and complexed metal concentrations on plant uptake of cadmium and micronutrient metals from solution

Summary Uptake of Cd and micronutrient metals by intact tomato plants (Lycopersicon esculentum, cv. Wisconsin-55) from solution cultures was investigated by establishing four levels of Cd-ion activity in the presence or absence of a metal-complexing agent (±EDTA). Activity ratios of Cd, Cu, Mn, Ni, and Zn were controlled with chelating resin while activity ratios of K, Ca, and Mg were controlled with a strong-acid cation-exchange resin. Hydrogen ion activity was controlled with a weak-acid cation-exchange resin and P activity by a cation-exchange resin containing adsorbed polynuclear hydroxy-Al. The concentrations of all nutrients and Cd were maintained at concentrations similar to those occuring in solutions of sludge-amended soils. The EDTA treatments increased the concentrations of Cu and Ni in hydroponic solution by approximately four orders of magnitude, Zn by two orders of magnitude, Cd by a factor of 50, Mn by a factor of 2.4, and Fe by a factor of 1.6 Neither the Cd nor the EDTA treatments affected plant yield, and Cd treatments did not significantly affect uptake of other elements. EDTA treatments inhibited Fe uptake, enhanced Cu uptake, and had little effect on the uptake of Cd, Zn, and Mn. Accumulation of Cd, Zn, Mn, and Cu in plant shoots appears to be related to their respective ionic activities rather than their concentrations in hydroponic solution. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and by the United States Environmental Protection Agency through Grant CR807270010.     

Speciation of heavy metals in soils based on charge separation

Summary An experimental approach to the speciation of heavy metals in soil extracts has been developed. The proposed methodology differentiates between differently charged metal species in water and ammonium acetate soil extracts. Furthermore a distinction has been made between labile and stable metal species by using a Chelex 100 chelating ion exchange resin.Significant differences in heavy metal speciation were found between an untreated soil and the same soil treated with 100 ppm Zn-ions and 100 ppm Zn-EDTA-ions.     

Copper,Lead, Cadmium,and Zinc Sorption By Waterlogged and Air-Dry Soil

Competitive sorption of copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) was studied in three soils of contrasting chemical and physical properties under air-dry and waterlogged conditions. Competitive sorption was determined using the standard batch technique using six solutions, each with Cu, Pb, Cd, and Zn concentrations of approximately 0, 2.5, 5, 10, 20, and 50?mg L^?1Waterlogged soils tended to sorb higher amounts of added Cu, Pb, Zn and Cd relative to soils in the air-dry condition; however, this increase in sorption was generally not statistically (p<0.05) significant. The magnitude of sorption under both waterlogged and air-dry conditions was affected by the type and amount of soil materials involved in metal sorption processes, and competition between other metals for the sorption sites. Metal sorption was closely correlated with soil properties such as cation exchange capacity, organic carbon, and Fe and Mn hydrous oxides. Exchangeable Al may have markedly reduced metal sorption due to its strong affinity for the sorption sites, while increases in exchangeable Mn may have enhanced Zn and Cd sorption. Heavy metal sorption was best described as a combination of both specific and nonspecific interactions. The extractability of Cu, Pb, Cd, and Zn under waterlogged and air-dry conditions was also studied. Three solutions containing these metals were mixed with each soil to achieve a final concentration of 0, 50, and 500?mg kg^?1. Each soil was extracted every 7 days using 1?M MgCl₂ (pH 7) to determine metal extractability. Metal extractability initially decreased then increased due to waterlogging. The increased extractability of added metals was closely related to increased solubility of Fe and Mn suggesting that dissolution of Fe and Mn, oxides under reducing conditions caused a release of previously sorbed Cu, Pb, Cd, and Zn.     

Efficiency of selected heavy metals accumulation by Salix viminalis roots

The efficiency of the absorption from the medium and accumulation by plant of ions of the heavy metals depends on many factors including plant age and its genotype. The heavy metals accumulation by 1-, 2- and 3-year-old plants was studied in the aspect of reclamation and revitalization effectiveness of demoted areas. Results of this study answer the question concerning the accumulation of seven heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) by willow cuttings (Salix viminalis) in environments with different concentrations of these elements. Cuttings used were originally grown on a substrate not contaminated with the metals and rich in nutrients. In order to eliminate the effect of soil physicochemical factors, the experiment was carried out using a hydroponic system. Results indicated significant effects of the investigated metal concentrations on their accumulation by willow. The extent of metal accumulation as an indicator of the remediation capacity of willow depended on the age of the cuttings used at planting.     

Plant uptake and the leaching of metals during the hot EDDS-enhanced phytoextraction process

Using pot experiments, the effect of the application of the biodegradable chelating agent S,S-ethylenediaminedisuccinic acid (EDDS) in hot solutions at 90 degrees C on the uptake of Cu, Pb, Zn, and Cd by corn (Zea mays L. cv. Nongda No. 108) and beans (P vulgaris L. white bean), and the potential leaching of metals from soil, were studied. When EDDS was applied as a hot solution at the rate of 1 mmol kg(-1), the concentrations and total phytoextraction of metals in plant shoots exceeded or approximated those in the shoots of plants treated with normal EDDS at the rate of 5 mmol kg(-1). On the other hand, the leaching of Cu, Pb, Zn, and Cd after the application of the hot EDDS solution at the rate of 1 mmol kg(-1) was reduced by 46%, 21%, 57%, and 35% in comparison with that from the application of normal EDDS at 5 mmol kg(-1), respectively. For treatment with 1 mmol kg(-1) of EDDS, the leached metals decreased to the levels of the control group (that without EDDS amendment) 14 d after the application of EDDS. The soil amendment with biodegradable EDDS in hot solutions may provide a good alternative to chelate-enhanced phytoextraction in enhancing metal uptake by plants and limiting metals from leaching out of the soil.     

Cadmium and zinc in plants and soil solutions from contaminated soils

In an experiment using ten heavy metal-contaminated soils from six European countries, soil solution was sampled by water displacement before and after the growth of radish. Concentrations of Cd, Zn and other elements in solution (K, Ca, Mg, Mn) generally decreased during plant growth, probably because of uptake by plants and the subsequent redistribution of ions onto soil exchange sites at lower ionic strength. Speciation analysis by a resin exchange method showed that most Cd and Zn in non-rhizosphere solutions was present as Cd2+ and Zn2+, respectively. The proportion of free ions was slightly lower in rhizosphere solutions, mainly due to an increase in dissolved organic carbon during plant growth. Solution pH increased during plant growth, although the bulk soil pH generally remained constant. Cd concentrations in leaves and tubers were more closely correlated with their total or free ionic concentrations in rhizosphere solutions (adjusted R2 0.90) than with their concentrations in soils (adj. R2 0.79). Cd concentrations in non-rhizosphere solutions were only poorly correlated with Cd concentrations in leaves and tubers. In contrast to Cd, there were no soil parameters that individually predicted Zn concentrations in leaves and tubers closely. However, multiple correlation analysis (including Zn concentrations in rhizosphere solutions and in bulk soils) closely predicted Zn concentrations in leaves and tubers (adj. R2 = 0.85 and 0.70, respectively). This suggests that the great variability among soils in the solubility of Zn affected the rate of release of Zn into solution, and thus Zn uptake. There was no such effect for Cd, for which solubility varied much less. Furthermore, the plants may have partly controlled Zn uptake, as they took up relatively less at high solution concentrations of Zn.Free ionic concentrations in soil solution did not predict concentrations of Cd or Zn in plants better than their total concentrations in solution. This suggests that with these soils, analysis of Cd and Zn speciation is of little practical importance when their bioavailability is assessed.     

Effects of atmospheric deposition,soil pH and acidification on heavy metal contents in soils and vegetation of semi-natural ecosystems at Rothamsted Experimental Station,UK

The effects of acidification on the soil chemistry and plant availability of the metals Pb, Cd, Zn, Cu, Mn and Ni in new and archived soil and plant samples taken from the >100-year-old experiments on natural woodland regeneration (Geescroft and Broadbalk Wildernesses) and a hay meadow (Park Grass) at Rothamsted Experimental Station are examined. We measured a significant input of metals from atmospheric deposition, enhanced under woodland by 33% (Ni) to 259% (Zn); Pb deposition was greatly influenced by vehicle emissions and the introduction of Pb in petrol. The build up of metals by long-term deposition was influenced by acidification, mobilization and leaching, but leaching, generally, only occurred in soils at pH<4. Mn and Cd were most sensitive to soil acidity with effective mobilization occurring at pH 6.0–5.5 (0.01 M CaCl₂), followed by Zn, Ni and Cu at pH 5.5–5.0. Pb was not mobilized until pH<4.5. Acidification to pH 4 mobilized 60–90% of total soil Cd but this was adsorbed onto ion exchange surfaces and/or complexed with soil organic matter. This buffering effect of ion exchange surfaces and organic matter in soils down to pH 4 was generally reflected by all the metals investigated. For grassland the maximum accumulation of metals in herbage generally corresponded to a soil pH of 4.0. For woodland the concentration of Pb, Mn and Cd in oak saplings (Quercus robur) was 3-, 4- and 6-fold larger at pH 4 than at pH 7. Mature Oak trees contained 10 times more Mn, 4 times more Ni and 3 times more Cd in their leaves at pH 4 than at pH 7. At pH values <4.0 on grassland the metal content in herbage declined. Only for Mn and Zn did this reflect a decline in the plant available soil content attributed to long-term acid weathering and leaching. The chief cause was a long-term decline in plant species richness and the increased dominance of two acid-tolerant, metal-excluder species     

A novel strategy using biodegradable EDDS for the chemically enhanced phytoextraction of soils contaminated with heavy metals

For the sake of cost and potential environmental risk, it is necessary to minimize the amount of chelants used in chemically enhanced phytoextraction. In the present study, a biodegradable chelating agent, EDDS was added in a hot solution at 90°C to the soil in which garland chrysanthemum (Chrysanthemum coronarium L.) and beans (Phaseolus vulgaris L., white bean) were growing. The application of hot chelant solutions was much more efficient than the application of normal chelant solutions (25°C) in improving the uptake of heavy metals by plants. When 1 mmol kg⁻¹ of EDDS as a hot solution was applied to soil, the concentrations of Cu, Zn and Cd and the total phytoextraction by the shoots of the two plant species exceeded or approximated those in the shoots of plants treated with 5 mmol kg⁻¹ of normal EDTA solution. The concentrations of metals in the shoots of beans were significantly correlated with the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the hot solution might play an important role in the process of chelant-enhanced metal uptake. The soil leaching study demonstrated that decreasing the dosage of chelant resulted in decreased concentrations of soluble metals in soils. On the 28th day following the application of chelant, the concentrations of soluble metals in the EDDS treated soil were not significantly different from the concentrations in the control soil to which chelants had not been applied. The application of biodegradable EDDS in hot solutions to soil may be an efficient alternative in chemically-enhanced phytoextraction to increase metal removal and to reduce possible leaching.Section Editor: J. Barcelo     

Extraction,Recovery, and Biostability of EDTA for Remediation of Heavy Metal-Contaminated Soil

Chelation removal of heavy metals from contaminated soil is seen as a viable remediation technique. A useful chelating agent should be strong, reusable, and biostable during metal extraction and recovery operations. This work tested the extraction, recovery, and biostability of EDTA as a potential remediating agent. Parameters, including EDTA concentration, soil type, soil content, washing cycle, precipitant concentration and type, and pH, were varied and tested during metal extraction and recovery operations. Factors, including EDTA concentration, aqueous and 5% soil slurry, presence of Pb, acclimated and unacclimated activated sludges, along with abiotic control, were varied and studied in the biodegradation of EDTA. The results showed that EDTA was able to extract lead completely from the tested soils, amenable to recovery by addition of cationic and anionic precipitants in the alkaline pH range, relatively biostable even under conditions very favorable toward biodegradation. Thus, EDTA is a strong, recoverable, and relatively biostable chelating agent that has potential for soil remediation application.     

Siderophores,NTA, and Citrate: Potential Soil Amendments to Enhance Heavy Metal Mobility in Phytoremediation

Phytoremediation of heavy metal-contaminated sites is often limited by the low bioavailability of the contaminants. Complexing agents can help to improve this technique by enhancing heavy metal solubility. We investigated the effect of three organic chelating agents, that is, the siderophore desferrioxamine B (DFOB), nitrilotriacetate (NTA), and citrate on binding of Cu, Zn, and Cd by either Namontmorillonite, kaolinite, or goethite. The different effects of the complexing agents on metal sorption can mainly be explained by the differences in stability constants and surface charge characteristics. In the presence of clay minerals, NTA was the most efficient ligand with respect to mobilization of heavy metals. In goethite suspensions, the effect of DFOB was more pronounced. In all systems, Cu proved to be the most affected element by the presence of the ligands. In batch experiments with heavy metal-contaminated soils from field sites, NTA was the most efficient metal mobilizer.     

DGT-measured fluxes explain the chloride-enhanced cadmium uptake by plants at low but not at high Cd supply

The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal uptake by plants in a wide range of soils. With the DGT technique, diffusion fluxes of trace metals through a diffusion layer towards a resin layer are measured. The DGT technique therefore mimics the metal uptake by plants if uptake is limited by diffusion of the free ion to the plant roots, which may not be the case at high metal supply. This study addresses the capability of DGT to predict cadmium (Cd) uptake by plants at varying Cd supply. To test the performance of DGT in such conditions, we used the chloride (Cl^?) enhancement effect, i.e. the increase in Cd solution concentrations—due to chloride complexation of Cd—and Cd uptake with increasing Cl^? concentrations, as previously characterized in pot, field and solution culture experiments. The uptake of Cd by spinach was assessed in soil amended with Cd (0.4–10.5 mg Cd kg^?1) and NaCl (up to 120 mM) in a factorial design. Treatments with NaNO₃ were included as a reference to correct for ionic strengths effects. The effect of Cl^? on the shoot Cd concentrations was significant at background Cd but diminished with increasing soil Cd. Increasing Cl^? concentrations increased the root area based Cd uptake fluxes by more than a factor of 5 at low soil Cd, but had no significant effect at high soil Cd. Short-term uptake of Cd in spinach from nutrient solutions confirmed these trends. In contrast, increasing Cl^? concentrations increased the DGT measured fluxes by a factor of 5 at all Cd levels. As a result, DGT fluxes were able to explain soil Cl^? effects on plant Cd concentrations at low but not at high Cd supply. This example illustrates under which conditions DGT mimics trace metal bioavailability. If biouptake is controlled by diffusive limitations, DGT should be a successful tool for predicting ion uptake across different conditions.     

Simultaneous extraction of soil phytoavailable cadmium,copper, and lead by chelating resin membrane

Cadmium, copper, and lead were extracted from suspensions of contaminated soils using metal chelating exchange resin membranes. Nine soils with widely varying properties and Cd, Cu and Pb levels were tested. Soil suspensions made up with 4 g in 40 mL deionized water were equilibrated with 5 cm² Ca-saturated Chelex exchange resin membrane which was retained inside a polypropylene bag and shaken at 150 rpm for 24 hrs. Resin membrane extractable Cd, Cu and Pb of the soils were correlated with Cd, Cu, and Pb uptake by young wheat seedlings grown in these soils and compared with soil Cd, Cu, and Pb extracted by 0.1 M HCl, 0.01 M CaCl₂, and 0.005 M Diethylenetriamine pentaacetic acid (DTPA). The amounts of Cd, Cu and Pb extracted by the Ca-saturated Chelex membrane from all tested soils correlated well with those absorbed by young wheat seedlings. The Ca-saturated Chelex membrane extractable Cd, Cu and Pb of the soil had the strongest correlation with plant uptake Cd, Cu and Pb among the extraction methods we tested. It was demonstrated that the Ca-saturated Chelex membrane extraction is an appropriate method in simultaneously estimating Cd, Cu and Pb phytoavailability of soil and is applicable to a wide range of soils.     

The choice of a masking agent in the histochemical staining of metals

Summary The masking effects of standard masking agents (aminopolycarboxylic acids, carboxylic acids and phosphates) have been investigated in both test-tube experiments and tissue sections in order to ascertain the factors which must be considered when choosing a masking agent for the histochemical staining of a metal. The masking effectsin vitro were determined by spectrophotometry through the complexing of the dye Chrome Azurol S with aluminium, beryllium, and iron at pH 5 and 7. The effects were also examined by staining metal-containing tissue sections in a Chrome Azurol S masking agent system at the same pH values. In many cases, the masking effects observed in sections did not agree with those obtained in the test-tube experiments. This means that the published values of stability constants are not a sufficient guide for choosing a suitable masking agent for the staining of metals. The discrepancy is mainly attributable to the presence of protein in a solid state when metals are stained in sections. Therefore, in the future, consideration should be given to a metal-protein or masking agent-protein interaction using a model compound such as a chelate resin. The polyphosphates are among the most useful masking agents for metal staining in acidic solutions from a practical standpoint.     

基于GIS和地统计学的稻田土壤养分与重金属空间变异

以湖南省长沙县北山镇3.56 hm²的水稻田为研究区域,基于网格法(25 m×25 m)等距离取样,采用GIS和地统计学相结合的方法,对研究区土壤耕作层(0～20 cm)的pH值、有机质、全氮、速效磷、阳离子交换量(CEC)与3种典型重金属元素Cd、As、Pb的空间变异特征进行了定量分析.结果表明: 研究区内土壤pH值和Pb含量表现为弱变异,其他各项指标均表现出中等强度变异,变异顺序的大小为:速效磷＞Cd＞全氮＞有机质＞CEC＞As＞Pb＞pH.半方差检验结果表明,有机质、速效磷、As的半方差函数的最佳拟合模型为指数模型;pH、全氮、CEC、Cd和Pb的最佳拟合模型为球状模型;除CEC呈中等空间相关外,其余指标均表现出强烈的空间相关.克里格插值分析表明: pH、全氮、CEC、Pb呈斑块状分布;有机质、速效磷、Cd、As呈块状和带状分布.植被、地形和人类活动是造成研究区土壤养分与重金属格局差异的主要因素.相关性分析表明,部分土壤养分与重金属含量的相关性达到显著水平,其中pH与有机质、Cd与Pb的相关性达到了极显著相关水平.     

Effect of Heavy Metals （Cd, Cu） on the Gametophytes of Laminaria japonica Aresch

Effects of various concentrations of two heavy metals, namely Cd and Cu, on gametophytes of Laminariajaponica Aresch were determined by recording morphological changes of gametophytes, determining pH values and the heavy metal content of the culture solution, calculating the germination rate of sporophytes, and observing heavy metal （Cd） distribution using a fluorescence microscope. The results showed that heavy metals damaged the gametophytes, and were even lethal, and that the higher the concentration of heavy metal ions, the greater the injury to gametophytes. Gametophytes could not survive in culture solutions containing more than 100 mg/L Cd and 50 mg/L Cu and were only able to survive in culture solution containing a mixture of Cd and Cu up to a concentration of 10 mg/L, which indicates that gametophytes have a higher tolerance to Cd than Cu and that multiple heavy metal ions in solution markedly aggravate the damage to gametophytes compared with individual heavy metal ions. With increases in the concentration of the heavy metal, the burgeoning rate of sporophytes decreased acutely, and solutions containing multiple heavy metal ions caused even more marked harm to sporophytes than solutions containing a single heavy metal ion, because most sporophytes died in mixed solutions. The pH value of the culture medium dropped immediately at the beginning （the first day） of treatment, increased over the following days, and then decreased again. The pH of culture media containing multiple heavy metal ions showed greater variation than media containing a single heavy metal ion, with the extent of the decrease in pH of culture media containing multiple ions being greatest during the last period of the experiment. With increases in the concentration of heavy metals, the capacity of gametophytes to accumulate these ions increased. The blue fluorescent light emitted by the Cd-and Cd-binding protein complex existing in gametophytes in media containing different concentrations of Cd showed clearly the distribution of the ion in gametophytes and the results obtained were consistent with distribution determined using other methods. All results of the present study showed that gametophytes of L. japonica play a remarkable role as heavy metal decontaminators, especially with regard to Cd.     

重金属镉在番茄及其害虫西花蓟马中的积累与传递

重金属镉(Cd)是农田土壤中的重要污染源,可在植物和植食性昆虫中积累与传递。本文采用水培法,研究了不同浓度的Cd在番茄Solanum lycopersicum不同组织和在其重要害虫西花蓟马Frankliniella occidentalis体内的积累量。结果表明,随着水培营养液中Cd浓度的增加,番茄植株的根、茎和叶中Cd含量呈增长趋势。根中Cd的积累量远高于茎和叶,当水培溶液中Cd含量为20 mg/L时,根、茎和叶中的积累量分别达19 333.67±233.38、122.67±6.84和147.33±2.96 mg/Kg(干重)。随着Cd浓度的增加,番茄根、茎和叶的鲜重和干重均显著下降。西花蓟马取食Cd处理的番茄叶片后,体内Cd显著积累,最高达1.95±0.36 mg/Kg。同时,Cd积累量的提高进一步影响了以番茄叶片为食的西花蓟马的适合度,降低了其存活率。除对照外,番茄茎-叶的转移系数和叶片对Cd的富集系数均大于1,叶片表现出较强的富集能力。而在所有的试验浓度处理中,西花蓟马对Cd的富集系数和转移系数均小于1,表明Cd未在其体内产生生物放大作用。研究结果明确了Cd在番茄各组织及其害虫中的积累和传递水平,为揭示重金属在农业生态系统食物链中的富集效应提供了基础数据。     

Effects of Cd or/and Pb on soil enzyme activities and microbial community structure

Heavy metals could have long-term hazardous impacts on the health of soil ecosystems and adverse influences on soil biological processes. A study of Cd or/and Pb effects on soil enzyme activities and microbial community structure was undertaken with brown soil in a greenhouse for a period of 10 weeks. The experiment results showed that urease, acid phosphatase and dehydrogenase activities were significantly lower (p < 0.05) in Cd or/and Pb treatments than in control. Three enzyme activities decreased with the increasing metal concentrations. The effects of Cd and Pb combined on enzyme activities were higher than Cd or Pb alone. The soil microbial populations were far lower in heavy metal treatments than in control, and soil microbial populations under different heavy metals levels showed a significant difference (p < 0.05). The PCR-DGGE banding patterns confirmed that the addition of metals had a significant impact on microbial community structure.     

Cadmium and zinc bioaccumulation by Phytolacca americana from hydroponic media and contaminated soils

Abstract

Hydroponic, greenhouse and field experiments were conducted to explore the potential of pokeweed (Phytolacca americana L.) to accumulate Zn and Cd from nutrient solutions and contaminated soils. The hydroponic results confirmed that this native species is a strong Zn and Cd bioaccumulator that does not experience severe phytotoxicity until quite high root and shoot concentrations, approaching 4000 and 1600?mg?kg^?1 of Zn, and 1500 and 500?mg?kg^?1 of Cd, respectively. These high Zn and Cd concentrations were accompanied by increased sulfur and lower manganese in both shoots and roots. However, in field and greenhouse trials with soils historically contaminated by a number of heavy metals including Zn and Cd, concentrations of Zn and Cd in shoots of P. americana reached concentrations less than 30% and 10%, respectively, of those achieved with hydroponics. The main constraint to phytoremediation of soils by P. americana was the low concentrations of Zn and Cd in soil solution. Pretreatment of the metal-contaminated soil by oxalic acid increased soluble Cd and Zn but failed to increase plant uptake of either metal, a possible result of higher solubility of competing metal ions (Cu, Mn) or low bioavailability of Cd and Zn-oxalate complexes.     

Fluxes and budgets of Cd, Zn, Cu, Cr and Ni in a remote forested catchment in Germany

The input of heavy metals by atmospheric deposition to forested watersheds substantially decreased during the last decades in many areas. The goal of our study was to identify the present sinks and sources of metals and factors influencing metal mobility at the catchment and soil profile scale. We determined concentrations and fluxes of Cd, Zn, Cu, Cr and Ni in precipitation, litterfall, soil solutions (Oi, Oe, Oa horizon percolates, 20 and 90?cm soil depth) and runoff in a forest ecosystem in NE-Bavaria, Germany for 1?year. The metal concentrations in solutions were mostly <10???g?l^?1 beside Zn (<1200???g?l^?1). The present total deposition was estimated at 1.0, 560, 30, 1.2 and 10.4?g?ha^?1?year^?1 for Cd, Zn, Cu, Cr and Ni, respectively. The mass balance (total deposition minus runoff) at the catchment scale indicated actual retention of Zn, Cu and Ni, but an almost balanced budget for Cr and Cd. Considering the soil profile scale, the Oi horizon still acted as a sink, whereas the Oe and Oa horizons were presently sources for all metals. The solid?Csolution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. In the mineral soil horizons, K_d values derived from field measurements were substantially larger than those predicted with empirical regression equations from Sauv?? et al. (Environ Sci Technol 34:1125?C1131, 2000; Environ Sci Technol 37:5191?C5196, 2003). The mineral soil acted as a sink for all metals beside Cd. Dissolved organic C and pH influenced the metal mobility, as indicated by significant correlations to metal concentrations in Oa percolates and runoff. The solid?Csolution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. Overall, the decreased deposition rates have obviously induced a source function of the Oe and Oa horizon for metals. Consequently, mobilization of metals from forest floor during heavy rain events and near surface flow conditions may lead to elevated concentrations in runoff.     

CEHIXM Extraction of Pb,Cd, Zn,and Mn from High Permeable Soils

A new method CEHIXM for extracting hea vy metals from high permeable soils under coupled electric-hydraulic gradient was investigated. Spent foundry sand, containing high levels of Pb, Cd, Zn, and Mn, was used as the contaminated source. A suitable ion-exchange resin was used for trapping and recovering the metals from the aqueous medium. Control experiments were conducted using hydraulic gradient alone to assess the leachability of the contaminants. The experiments were repeated with 50?V across the soil sample and without hydraulic gradient to evaluate ion migration under electric gradient. A number of CEHIXM experiments involving both hydraulic and electric gradients were conducted at a constant DC voltage of 50?V and a constant flow velocity of 0.0178?cm/ sec. With hydraulic gradient only, 3 to 8% metals were extracted, whereas with electric gradient only the metal removal rate was 0 to 0.7%. When the electric and hydraulic gradients were coupled, as much as 93% of Pb, 97% of Cd, 98% of Zn, and 94% of Mn were extracted, after 100?h of the processing.