Pb In Soil Solution Research Articles

Speciation, bioaccumulation, and toxicity of the newly deposited atmospheric heavy metals in soil-earthworm (Eisenia fetida) system near a large copper smelter

The speciation, bioaccumulation, and toxicity of the newly deposited atmospheric heavy metals in the soil-earthworm (Eisenia fetida) system were investigated by a fully factorial atmospheric exposure experiment using soils exposed to 0.8-year and 1.8-year atmospheric depositions. The results shown that the newly deposited metals (Cu, Cd, and Pb) primarily accumulated in the topsoil (0–6 cm) and were present as the highly bioavailable speciation. They can migrate further to increase the concentrations of Cu, Cd, and Pb in soil solution of the deeper layer (at 10 cm) by 12 %–436 %. Earthworms tended to preferentially accumulate the newly deposited metals, which contributed 10 %–61 % of Cu, Cd, and Pb in earthworms. Further, for the unpolluted and moderately polluted soils, the newly deposited metals induced the significant oxidative stress in earthworms, resulting in significant increases in antioxidant enzyme activities (SOD, CAT, and GSH-Px). No significant differences were observed in the levels of heavy metals in soil solutions, bioaccumulation, and enzyme activities in earthworms exposed to 0.8-year and 1.8-year depositions, indicating the bioavailability of atmospheric metals deposited into soils was rapidly decreased with time. This study highlights the high bioaccumulation and toxicity of heavy metals to earthworm from the new atmospheric deposition during the earthworm growing period.

Chemical Soil-Biological Engineering Theoretical Foundations, Technical Means, and Technology for Safe Intrasoil Waste Recycling and Long-Term Higher Soil Productivity

The amelioration and remediation technology was developed on the basis of research of phosphogypsum and utilization in the Haplic Chernozem of South-European facies (Rostov Region). Phosphogypsum was utilized via dispersed application into a soil layer of 20–45 cm with intrasoil milling of this layer. The phosphogypsum utilization doses were 0, 10, 20, and 40 t ha–1. The Pb analytical content in soil solution was studied in the model experiment. The soil solution Pb thermodynamic forms were calculated. The mathematical chemical–thermodynamic model ION-2 was developed to calculate the real soil solution (water extract) calcium-carbonate equilibrium (CCE) ion forms, considering the ion pair association. The associated ion pairs CaCO30, CaSO40, MgCO30, MgSO40, CaHCO3+, MgHCO3+, NaCO3–, NaSO4–, CaOH+, and MgOH+ were accounted for in soil solution equilibrium macroion form calculation. The procedure for the microelement ion [including heavy metals (HMs)] equilibrium concentration in the soil solution coefficient kas calculation was proposed to account for the real soil solution CCE, macroions, and HM (including Pb) association. The Pb2+ ion in soil solution was mostly bound to associates PbOH+, Pb(OH)20, PbCO30, Pb(CO3)22–, and PbHCO3+. The calculation of CCE and ion association in soil solution revealed 14.5–21.5 times HM passivation compared to HM water-soluble values. The calculated HM activity in the soil solution in the example of the Pb2+ ion was less than 4% after phosphogypsum application in the target amelioration layer of 20–45 cm. The studied phosphogypsum doses were substantiated as environmentally safe. This was because the real soil solution CCE provided HM ion form association and consequent passivation. The dry steppe soil remediation after phosphogypsum application was justified as highly probable. The intrasoil milling chemical soil-biological engineering technology was developed for simultaneous soil amelioration and remediation on the basis of the biogeosystem technique (BGT*) transcendental methodology. The BGT*-based technology was tested in the long-term field experiments and is capable of ensuring the priority geophysical micro- and macroaggregate structure via intrasoil milling and mixing of soil illuvial and transitional horizons. This helps synthesize soil multilevel architecture, providing intrasoil-dispersed environmentally safe recycling of wastes of different origin. Addressing the environment safety concerns, a new decision of the intrasoil milling device was proposed for phosphogypsum and other substance application to soil.

Lead was mobilized in acid silty clay loam paddy soil with potassium dihydrogen phosphate (KDP) amendment

The immobilization effectiveness between Pb and phosphorus in soil varies with soil types. To clarify the effect of phosphate on the availability of Pb in agricultural soil, a culture experiment with three types of paddy soil was performed with potassium dihydrogen phosphate (KDP) added. EDTA, DGT and in-situ solution extraction methods were used to represent different available Pb content. Results showed that the concentration of EDTA-Pb in HN soil was slightly elevated after exogenous KDP added. The supplement of 300 mg/kg KDP significantly increased the content of soluble Pb in both acid silty clay loam soil and neutral silty loam soil (increased by 104.65% and 65.12%, respectively). However, there was no significant influence of KDP on the concentration of DGT extracted Pb. XANES results showed that Pb(OH)2, PbHPO4, humic acid-Pb and GSH-Pb were the major speciation of Pb in soil colloids. The proportion of Pb(OH)2 and humic acid-bounded Pb in soil colloids were elevated after exogenous KDP added. Our results indicated that there was a mobilization effect of KDP on Pb by increasing the amount of colloidal Pb in soil solution, especially in acid silty clay loam paddy soil. Such colloid-facilitated transport might promote the uptake of Pb in rice and pose a potential threat to human health.

Comparing the risk of metal leaching in phytoremediation using Noccaea caerulescens with or without electric field

Hyperaccumulators can mobilize all metals in soil through secreting exudates to form soluble compounds but only hyperaccumulate part of them. Metals that cannot be accumulated are defined as non-hyperaccumulated metals and can increase the leaching risk in phytoremediation. Cd and Zn hyperaccumulator Noccaea caerulescens (formerly Thlaspi caerulescens) was utilized to remediate multi-metal polluted soil in the present study, and the leaching risk of non-hyperaccumulated metals including Cu and Pb was investigated during the phytoremediation process. Comparing with Thlaspi arvense, a non-hyperaccumulator, N. caerulescens significantly decreased the concentrations of Cd and Zn in leachate gathered from precipitation simulation experiments without electric field, but meanwhile dramatically increased the concentrations of Cu and Pb in soil solution. Electric field with low (2 V) and moderate (4 V) voltages increased the biomass yield and metal uptake capacity of N. caerulescens simultaneously and therefore further reduced the concentrations of Cd and Zn in the leachate. Although the volume of leachate decreased significantly in pots with electric field, the leaching risk of Pb and Cu was deteriorated. Thus, decontaminating multi-metal polluted soil with electric field and hyperaccumulator should be conducted with caution due to potential secondary environmental risk caused by activated non-hyperaccumulated metals.

Lead Uptake and Accumulation in Rice (Oryza sativa L.) with Water Management and Selenite Fertilization

Lead (Pb) accumulation in rice grains has been identified as a potential threat to human health. Our study investigated the effects of varied rates of selenite fertilization (0, 0.5 and 1.0 mg·kg-1) on the dynamics of Pb in soil solutions, and its uptake and translocation by rice under different water management scenarios (aerobic and flooded) in pot experiments. Plants were harvested at seedling stage and at maturity to determine the Pb contents, and soil solutions were extracted during the growing season to monitor the Pb dynamics. Results showed that flooding the soil significantly increased Pb concentrations in DCB extracts and rice roots both at seedling stage and maturity. Root Pb contents in flooded treatments were 4.2-8.5 and 1.4-1.5 times higher than those under aerobic conditions at rice seedling stage and maturity. Flooding also decreased the percentage of Pb in rice shoots. The Pb content in soil solutions, rice seedlings, rice roots and stems at maturity were significantly decreased by selenite additions. Relative to the control treatment, selenite additions decreased the rice root Pb contents by 5.4%-24.3% and 2.7%-61.7% under flooding and aerobic conditions at seedling stage, respectively; while decreased Pb in rice root by 56.1%-64.1% and 53.8%-63.2% respectively, at maturity. No significant differences existed in grain Pb levels among the treatments. Results demonstrated that water management regimes and selenite additions affected Pb uptake by rice roots significantly, but had no significant influence on Pb accumulation in rice grains.

Colloid mobilization and heavy metal transport in the sampling of soil solution from Duckum soil in South Korea.

Colloid mobilization is a significant process governing colloid-associated transport of heavy metals in subsurface environments. It has been studied for the last three decades to understand this process. However, colloid mobilization and heavy metal transport in soil solutions have rarely been studied using soils in South Korea. We investigated the colloid mobilization in a variety of flow rates during sampling soil solutions in sand columns. The colloid concentrations were increased at low flow rates and in saturated regimes. Colloid concentrations increased 1000-fold higher at pH 9.2 than at pH 7.3 in the absence of 10mM NaCl solution. In addition, those were fourfold higher in the absence than in the presence of the NaCl solution at pH 9.2. It was suggested that the mobility of colloids should be enhanced in porous media under the basic conditions and the low ionic strength. In real field soils, the concentrations of As, Cr, and Pb in soil solutions increased with the increase in colloid concentrations at initial momentarily changed soil water pressure, whereas the concentrations of Cd, Cu, Fe, Ni, Al, and Co lagged behind the colloid release. Therefore, physicochemical changes and heavy metal characteristics have important implications for colloid-facilitated transport during sampling soil solutions.

Speciation of Cu, Zn, and Pb in Soil Solutions Extracted from Strongly Polluted Soils Treated with Organic Materials

Speciation of Cu, Zn, and Pb in Soil Solutions Extracted from Strongly Polluted Soils Treated with Organic Materials

Use of Energy Crop (Ricinus communis L.) for Phytoextraction of Heavy Metals Assisted with Citric Acid

Ricinus communis L. is a bioenergetic crop with high-biomass production and tolerance to cadmium (Cd) and lead (Pb), thus, the plant is a candidate crop for phytoremediation. Pot experiments were performed to study the effects of citric acid in enhancing phytoextraction of Cd/Pb by Ricinus communis L. Citric acid increased Cd and Pb contents in plant shoots in all treatments by about 78% and 18–45%, respectively, at the dosage of 10 mM kg−1 soil without affecting aboveground biomass production. Addition of citric acid reduced CEC, weakened soil adsorption of heavy metals and activated Cd and Pb in soil solutions. The acid-exchangeable fraction (BCR-1) of Pb remained lower than 7% and significantly increased with citric acid amendment. Respective increases in soil evaluation index induces by 14% and 19% under the Cd1Pb50 and Cd1Pb250 treatments upon addition of citric acid resulted in soil quality improvement. Ricinus communis L. has great potential in citric acid-assisted phytoextraction for Cd and Pb remediation.

Effect of dissolved organic matter composition on metal speciation in soil solutions

Knowledge of the speciation of heavy metals and the role of dissolved organic matter (DOM) in soil solution is a key to understand metal mobility and ecotoxicity. In this study, soil column-Donnan membrane technique (SC-DMT) was used to measure metal speciation of Cd, Cu, Ni, Pb, and Zn in eighteen soil solutions, covering a wide range of metal sources and concentrations. DOM in these soil solutions was also fractionated into humic acid (HA), fulvic acid (FA), hydrophilic acid (Hy), and hydrophobic neutral organic matter (HON) by a rapid batch technique using DAX-8 resin. Our results show that in soil solution Pb and Cu are dominant in complex form, whereas Cd, Ni and Zn mainly exist as free ions; for the whole range of soil solutions, only 26.2% of DOM is humic substances and consists mainly of fulvic acid (FA). The metal speciation measured by SC-DMT was compared to the predicted ones obtained via the NICA-Donnan model using the measured FA concentrations. The free ion concentrations predicted by speciation modeling were in good agreement with the SC-DMT measurement. Moreover, we show that to make accurate modeling of metal speciation in soil solutions, the knowledge of DOM composition, especially FA fraction, is the crucial information, especially for Cu and Cd; like in previous studies the modeling of Pb speciation is not optimal and an update of Pb generic binding parameters is required to reduce model prediction uncertainties.

Not All Phosphate Fertilizers Immobilize Lead in Soils

The effects of six phosphate (P) fertilizers in mobilizing and immobilizing water-soluble lead (Pb) were determined in a contaminated soil (Alfisol from Shaoxing) from China and four Australian soils (an Oxisol from Twonsville Queensland and three South Australian soils from Cooke Plains (Typic Palexeralf)), Inman Valley (Vertisol), and Two Wells (Natric Palexeralf). The fertilizers tested were single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), monocalcium phosphate (MCP), and dicalcium phosphate (DCP) to produce an initial P concentration of 1,000 mg/L. The Chinese soil contained 16,397 mg/kg total Pb, but the Australian soils were uncontaminated. The four Australian soils were each spiked with 1,000 mg Pb/kg soil (as Pb(NO3)2) and incubated for a month. Single superphosphate treatments decreased total soluble Pb in soil solution to 2–14 % of those of the nil-P (0P) treatment in the four Pb-spiked soils and to 48 % in the Chinese Pb-contaminated soil. The DAP treatment followed by the MAP treatment greatly increased the total soluble Pb in soil solution up to 135–500 % of the 0P treatment, except in the Two Wells soil. MCP could decrease the total soluble Pb in Cooke Plains, Inman Valley, Shaoxing, and Two Wells soils while increase it in the Queensland soil; DCP decreased the total soluble Pb in Cooke Plains and Queensland soils while increased it in the Shaoxing and Inman Valley soils. There were close relationships between the total soluble Pb, total soluble Al, and total soluble Fe in the water extracts of each. Soluble Al and Fe ions in soil solution increased soluble Pb concentrations. We conclude that not all phosphate fertilizers immobilize Pb in soils equally well. SSP and TSP are excellent Pb-immobilizing fertilizers, while MAP and DAP are strong Pb-mobilizing fertilizers. MCP and DCP are either Pb-immobilizing fertilizers or Pb-mobilizing fertilizers depending on their reactions with individual soils.

Lead phytotoxicity in soils and nutrient solutions is related to lead induced phosphorus deficiency

This study was set up to relate lead (Pb) bioavailability with its toxicity to plants in soils. Tomato and barley seedlings were grown in six different PbCl2 spiked soils (pH: 4.7–7.4; eCEC: 4.2–41.7 cmolc/kg). Soils were leached and pH corrected after spiking to exclude confounding factors. Plant growth was halved at 1600–6500 mg Pb/kg soil for tomato and at 1900–8300 mg Pb/kg soil for barley. These soil Pb threshold were unrelated to soil pH, organic carbon, texture or eCEC and neither soil solution Pb nor Pb2+ ion activity adequately explained Pb toxicity among soils. Shoot phosphorus (P) concentrations significantly decreased with increasing soil Pb concentrations. Tomato grown in hydroponics at either varying P supply or at increasing Pb (equal initial P) illustrated that shoot P explained growth response in both scenarios. The results suggest that Pb toxicity is partially related to Pb induced P deficiency, likely due to lead phosphate precipitation.

Labile pools of Pb in vegetable-growing soils investigated by an isotope dilution method and its influence on soil pH

Pollution of Pb in the surface of agricultural soils is of increasing concern due to its serious impact on the plant growth and the human health through the food chain. However, the mobility, activity and bioavailability of Pb rely mainly on its various chemical species in soils. In the present study, E and L values, the labile pools of isotopically exchangeable Pb, were estimated using the method of isotope dilution in three vegetable-growing soils. The experiments involved adding a stable enriched isotope ((206)Pb > 96%) to a soil suspension and to soils in which plants are subsequently grown, the labile pools of Pb were then estimated by measuring the isotopic composition of Pb in soil solutions and in the plant tissues, respectively. In addition, the correlation of E values and soil pH was investigated at the ranges of pH 4.5-7.0. The amount of labile Pb in soils was also estimated using different single chemical extractants and a modified BCR approach. The results showed that after spiking the enriched isotopes of (206)Pb (>96%) for 24 hours an equilibration of isotopic exchanges in soil suspensions was achieved, and the isotope ratios of (208)Pb/(206)Pb measured at that time was used for calculating the E(24 h) values. The labile pools of Pb by %E(24 h) values, ranging from 53.2% to 61.7% with an average 57%, were found to be significantly higher (p < 0.05) than the values estimated with L values, single chemical extractants and the Σ(BCR) values obtained with the BCR approach, respectively. A strong negative correlation (R(2) = 0.984) between E(24 h) values and soil pH was found in the tested soil sample. The results indicate that the %E(24 h) value can more rapidly and easily predict the labile pools of Pb in soils compared with L values, but it might be readily overestimated because of the artificial soil acidity derived from the spiked isotopic tracer and the excess of spiked enriched isotopes. The results also suggest that the amounts of Pb extracted with EDTA and the Σ(BCR) values extracted with the modified BCR approach are helpful to detect the labile pools of Pb in soils. In addition, the negative correlation between soil pH and the labile pools of Pb in soils may be useful for further remediation to reduce the bioavailability of Pb in contaminated soils.

Relative Value of Phosphate Compounds in Reducing the Bioavailability and Toxicity of Lead in Contaminated Soils

Lead forms stable compounds with phosphate and the immobilized Pb becomes less available to soil biota. In this study, we tested the bioavailabilty of Pb using earthworms (Eisenia fetida) and plants after immobilization of Pb by a soluble P compound and an insoluble rock phosphate compound in the presence of phosphate-solubilizing bacteria (Enterobacter sp.). Rock phosphate in the presence of phosphate-solubilizing bacteria and a soluble P compound enhanced Pb immobilization as measured by NH4NO3-extractable Pb concentration, thereby reduced its bioavailability as evaluated by earthworm Pb loading and sunflower (Helianthus annuus) Pb uptake under greenhouse conditions. However, soluble P treatment increased the concentration of Pb in soil solution thereby inhibited the root elongation of mustard (Brassica hirta) seedlings. Sunflower plants in the Pb-spiked soil without P amendments showed symptoms of necrosis and stunting because of Pb toxicity. Both soluble and insoluble P treatments significantly increased shoot and root weight and decreased Pb concentration in shoot by more than 50% compared to the control. However, high Pb concentration in soil solution was found in soluble P treatment, which can be attributed to dissolved organic carbon–Pb complex formation, thereby increasing Pb mobility. The inoculation of phosphate-solubilizing bacteria can facilitate phytostabilization of Pb-contaminated site.

Influence of plant roots on rhizosphere soil solution composition of long-term contaminated soils

Understanding the root mechanisms of hyperaccumulating or phytostabilizing plants in response to heavy metal exposure is important for the successful implementation of phytoremediation technologies. Root induced dissolved organic carbon (DOC) and organic acids (OAs) were investigated under greenhouse conditions in the rhizosphere after growing two plant species, Indian mustard ( Brassica juncea) and sunflower ( Helianthus annuus L.) in long-term heavy metal contaminated soils. Two alkaline soils (pH > 8) were highly contaminated while the other two acidic soils (pH < 6.5) were moderately contaminated with heavy metals. Cropping Indian mustard and sunflower on the alkaline soils increased the mean DOC concentrations in soil solution. Correspondingly, OAs which constituted a fraction of the total observed DOC, also increased due to plant cropping in these highly contaminated soils. The most marked increase was observed for lactate which increased 3–10 fold relative to the controls. Increased Cu and Pb solubility, through formation of metal–DOC complexes at soil pH > 8, was mainly attributed to increases in rhizosphere DOC. Soluble Cu increased from 47 (control) to 493 and 524 µg L − 1 and soluble Pb increased from 40 (control) to 149 and 148 µg L − 1 for sunflower and mustard, respectively in soil the most contaminated alkaline soil. MINTEQA2 speciation indicated that in this soil, the increased Cu and Pb in soil solution existed as metal–DOC complexes but soluble Zn existed mainly as a free ion (> 60% of the total Zn). In contrast, in a moderately contaminated acidic soil (380 mg kg − 1 Pb; pH < 6.5), Pb and Zn solubility was slightly decreased after plant culture and governed by soil solution pH rather than the DOC concentration, thus demonstrating that the influence of root induced DOC on metal solubility is a function of pH as well as total metal loading.

Control of lead solubility in soil contaminated with lead shot: effect of soil moisture and temperature

An incubation experiment was carried out to assess the rate of oxidation of lead (Pb) shot and subsequent transfer of Pb to the soil under different soil moisture and temperature regimes. Lead was readily released from Pb shot into the soil environment due to rapid corrosion of the Pb shot; however, the rate of Pb shot dissolution was slower at 70% than at 100% field moisture capacity. The corrosion and development of crust material on Pb shot, and corresponding increases in soil solution Pb and Pb associated with the soil solid phase, were also slower at 10°C than 25 or 30°C. Soil moisture and temperature also influenced the speciation of soil solution Pb as modelled using WHAM 6, mainly through the effects of moisture and temperature on soil pH, total soluble Pb, and dissolved organic C. The rate of approach to equilibrium of the Pb shot–soil–soil solution system will be much slower where soil moisture and temperature limit Pb shot corrosion. Calculated free ion Pb2+ concentrations suggest that after 6 months, almost all samples contaminated with Pb shot exceeded soil critical limits for Pb toxicity.

Effect of Organic Matter and Salinity on Ethylenediaminetetraacetic Acid–Extractable and Solution Species of Cadmium and Lead in Three Agricultural Soils

A study was conducted to investigate the chemical speciation of added cadmium (Cd) and lead (Pb) and their availability as influenced by fresh organic matter (OM) and sodium chloride (NaCl) in three agricultural soils. The soils were treated with 20 mg Cd/kg as cadmium nitrate [Cd(NO3)2 · 4H2O], 150 mg Pb/kg as lead nitrate [Pb(NO3)2], 20 g/kg alfalfa powder, and 50 mmol/kg of NaCl and then incubated for 3 months at 60% water‐holding capacity (WHC) and constant temperature (25 °C). Subsamples were taken after 1, 3, 6, and 12 weeks of incubation, and electrical conductivity (EC), pH, dissolved organic carbon (DOC), and concentrations of cations and anions were determined in the 1:2.5 soil/water extract. Available Cd and Pb were determined in 0.05 M ethylenediaminetetraacetic acid (EDTA) extract. Concentrations of organic and inorganic species of Cd and Pb in soil solution were also predicted using Visual Minteq speciation program. The most prevalent species of dissolved Pb and Cd in the soils were Pb‐DOC and Cd2+ species, respectively. Salinity application increased the available and soluble Cd significantly in the acid and calcareous soils. It, however, had little effect on soluble Pb and no effect on available Pb. Organic‐matter application decreased availability of added Pb significantly in all soils. In contrast, it raised soluble Pb in all soils except for the acid one and approximated gradually to the added Pb with time. Impact of OM on available Cd was somewhat similar to that of Pb. Soluble Cd increased by OM application in the calcareous soil, whereas it decreased initially and then increased with time in the other soils.

Control of lead solubility in soil contaminated with lead shot: Effect of soil pH

An incubation experiment was carried out to assess the rate of oxidation of Pb shot and subsequent transfer of Pb to the soil under a range of soil pH conditions. Lead shot corrosion was rapid, so that soil solution and fine earth (<1 mm) Pb concentrations increased rapidly within a few months. Corrosion products, dominated by hydrocerussite (Pb 3(CO 3) 2(OH) 2), developed in crusts surrounding individual Pb pellets. However, irrespective of pH, Pb 2+ activities in the soil solutions, modelled using WHAM 6, were much lower than would be the case if they were controlled by the solubility of the dominant Pb compounds present in the Pb shot crust material. In contrast, modelling of soil solid–solution phase distribution of Pb, again using WHAM 6, suggested that, at least during the 24 months of the study, soil solution Pb concentrations were more likely to be controlled by sorption of Pb by the soil solid phase.

Effect of soil properties on lead bioavailability and toxicity to earthworms

Soil properties are important factors modifying metal bioavailability to ecological receptors. Twenty-one soils with a wide range of soil properties (USA; http://soils.usda.gov/technical/classification/taxonomy/) were amended with a single concentration of Pb (2,000 mg/kg) to determine the effects of soil properties on Pb bioavailability and toxicity to earthworms. Earthworm mortality ranged from 0 to 100% acute mortality following exposure to the same total concentration of Pb (2,000 mg/kg) in amended field soils. Internal Pb concentrations in earthworms ranged from 28.7 to 782 mg/kg, with a mean of 271 mg/kg. Path analysis was used to partition correlations in an attempt to discern the relative contribution of each soil property. Results of path analysis indicated that pH was the most important soil property affecting earthworm mortality (p < 0.01) and internal Pb (p < 0.05). Soil pH was related inversely to mortality and internal Pb, soil solution Pb, and Pb bioavailability. The most important soil property modifying reproduction was amorphous iron and aluminum oxides (FEAL). Because FEAL is rich in pH-dependent cation-exchange sites, several soil properties, including pH, FEAL, and cation-exchange capacity, have a causal effect on Pb adsorption and soluble Pb. Path analysis is useful for assessing contaminated soils with a wide range of soil properties and can assist in ecological risk assessment and remediation decisions for contaminated sites. Soil properties are important factors modifying metal bioavailability and toxicity and should be considered during the ecological risk assessment of metals in contaminated soils.

Effect of chemical amendments on the concentration of cadmium and lead in long-term contaminated soils

The availability of metal in contaminated soil can be reduced by the addition of soil amendments. The objectives of this study are to study the effects of applying different soil amendments on the concentration of Cd and Pb in soil solution, DTPA or EDTA extractable Cd and Pb, and the uptake of Cd and Pb by wheat ( Triticum vulgare) when growing in long-term Cd and Pb-contaminated soils, more than 20 years. The soil amendments, including check, compost, zinc oxide, calcium carbonate, calcium carbonate mixed with zinc oxide, and calcium carbonate mixed with compost, were conducted in a four replicates pot cultural study. The amended soils were incubated for six months under 60% of water holding capacity. Following incubation, wheat was grown for four months in greenhouse. Analyses of Cd concentration demonstrated a significant decrease in soil solution concentration and DTPA or EDTA extractable in soils amended with calcium carbonate or calcium carbonate mixed with ZnO (or compost) ( p < 0.01). These amendments can significantly reduce the Cd concentration in the grain, leaf and stem, or reduce the total Cd uptake in all parts of wheat species grown in highly contaminated soil amended with calcium carbonate or calcium carbonate mixed with ZnO (or compost) ( p < 0.01). The concentration of Cd in soil solution and extracted with DTPA or EDTA can predict the Cd concentration in wheat, especially for soil solution.

Assessment of lead availability in soils contaminated by mine spoil

The uptake of lead by two contrasting plant species, radish and red fescue, grown in soils contaminated by mine spoil was investigated. Uptake was found to be poorly correlated either with pH or total Pb concentration in the soils. By contrast, a good correlation was obtained, particularly for red fescue, between Pb uptake and Pb concentration in the solution of equilibrated soil suspensions over a wide range of soil pH, total soil Pb and soil solution Pb concentration. Calculations suggested a similar order of magnitude in the total amounts of Pb taken up by the plants and Pb in the soil solution of the root zone, justifying the latter as a good index of Pb-availability. ei]Section editor: A C Borstlap