Cd In Soil Solution Research Articles

Modelling the complexation of Cd in soil solution at different temperatures using the UV-absorbance of dissolved organic matter

It is well established that the soil temperature impacts on the mobility of Cd in soil but the role of dissolved organic matter (DOM) quality in this process is still unclear. During a 42-day period, soil solutions were sampled from a Cd-contaminated soil incubated at 10, 20 or 30 °C. The quantity and the quality of DOM were monitored over time as well as the concentration and the speciation of dissolved Cd. The fraction of Cd complexed by ligands ( f CdL) increased over time and with the rise in soil temperature and exhibited a significant correlation with the absorbance of DOM at 254 nm. In contrast, the quantity of DOM did not much vary between soil solutions. These results suggest that, during incubation, the composition of DOM shifted to more aromatic compounds, assimilated to humic substances (HS), with higher Cd affinity. The kinetics of DOM aromatization and Cd complexation were described using thermal time. A first order model adequately fitted all the experimental data, suggesting that similar microbial processes responsible for the aromatization of DOM occurred at 10, 20 and 30 °C. The fraction of Cd complexed by ligands was predicted by Visual MINTEQ using the solution properties measured at 140 day-degrees and the specific UV-absorbance of DOM ( SUVA) monitored over thermal time. SUVA values were used to adjust the reactivity ratio of DOM ( R). The model predictions were highly correlated with the measured values but they overestimated f CdL. It is concluded that the aromaticity of DOM should be taken into account to predict the impact of soil temperature on the complexation of Cd in rewetted soils. The relation between SUVA values and the HS fraction of DOM still needs, however, to be worked out.

Soil solution dynamics and plant uptake of cadmium and zinc by durum wheat following phosphate fertilization

A growth chamber study was conducted to evaluate the effect of application of phosphate fertilizer on soil solution dynamics of cadmium (Cd) and Cd accumulation in durum wheat (Triticum turgidum L. var. durum). Treatments consisted of three phosphate fertilizer sources containing 3.4, 75.2, and 232 mg Cd kg−1 applied at three rates (20, 40 and 80 mg P kg−1) plus a no fertilization control. An unplanted treatment at 40 mg P kg−1 was included to separate the effects on soil solution Cd dynamics of the crop from that of the fertilizer. Soil solution samples were obtained using soil moisture samplers every 10 days after germination. The experimental results indicated that plant biomass significantly increased with P application rates and decreased with increased Cd concentration in the phosphate fertilizers. Total cadmium concentration in soil solution was not consistently affected by phosphate fertilization rate and fertilizer sources, and therefore Cd concentration in the fertilizer. Application of phosphate fertilizer, however, increased the concentration and accumulation of Cd and shoot Cd/Zn ratio, and decreased shoot Zn concentration in durum wheat. Phosphate sources had a marginally significant effect (P = 0.05) on shoot Cd concentration and did not affect Cd accumulation in durum wheat. Concentration of Cd in soil solution was unrelated to Cd concentration in durum wheat. These results suggest that the immediate increase in Cd concentration and Cd accumulation in durum wheat with phosphate application is due more to competition between Zn and Cd for absorption into plants, enhanced root to shoot translocation and enhanced root development, than to a direct addition effect from Cd contained in phosphate fertilizer. In the short term, application of phosphate fertilizers can increase Cd concentration in the crops, regardless of the Cd concentration of the fertilizer. An optimal P fertilization, possibly in combination with Zn application, may offer an important strategy for decreasing Cd concentration and accumulation in crops.

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 μg l−1 beside Zn (<1200 μg 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–solution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. In the mineral soil horizons, Kd values derived from field measurements were substantially larger than those predicted with empirical regression equations from Sauvé et al. (Environ Sci Technol 34:1125–1131, 2000; Environ Sci Technol 37:5191–5196, 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–solution 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.

Influence of Indian mustard ( Brassica juncea) on rhizosphere soil solution chemistry in long-term contaminated soils: A rhizobox study

This study investigated the influence of Indian mustard ( Brassica juncea) root exudation on soil solution properties (pH, dissolved organic carbon (DOC), metal solubility) in the rhizosphere using a rhizobox. Measurement was conducted following the cultivation of Indian mustard in the rhizobox filled four different types of heavy metal contaminated soils (two alkaline soils and two acidic soils). The growth of Indian mustard resulted in a significant increase (by 0.6 pH units) in rhizosphere soil solution pH of acidic soils and only a slight increase (< 0.1 pH units) in alkaline soils. Furthermore, the DOC concentration increased by 17–156 mg/L in the rhizosphere regardless of soil type and the extent of contamination, demonstrating the exudation of DOC from root. Ion chromatographic determination showed a marked increase in the total dissolved organic acids (OAs) in rhizosphere. While root exudates were observed in all soils, the amount of DOC and OAs in soil solution varied considerably amongst different soils, resulting in significant changes to soil solution metals in the rhizosphere. For example, the soil solution Cd, Cu, Pb, and Zn concentrations increased in the rhizosphere of alkaline soils compared to bulk soil following plant cultivation. In contrast, the soluble concentrations of Cd, Pb, and Zn in acidic soils decreased in rhizosphere soil when compared to bulk soils. Besides the influence of pH and DOC on metal solubility, the increase of heavy metal concentration having high stability constant such as Cu and Pb resulted in a release of Cd and Zn from solid phase to liquid phase.

Solubility of Trace Elements and Heavy Metals from Stabilized Sewage Sludge by Fly Ash

Stabilized sewage sludge (SS) by fly ash (FA) and alkaline mine tailing as artificial soil, to be applied on the ecological rehabilitation at mining junkyard, offers a potential viable utilization of the industrial by-product, as well as solves the shortage of soil resource in mine area. In this study, trace element and heavy metal soil solution concentrations arising from fly ash, sewage sludge, mine tailing, and artificial soil mixtures were investigated in a laboratory incubation. It was found that total Cd, Pb, and Zn contents in artificial soils were significantly lower than the control standards for pollutants in sludges from agricultural use (GB 4284-84). Soil solution Cd and Pb concentrations were obviously reduced by mixing sewage sludge with alkaline fly ash. Initial soil solution Cd, Pb, and Zn concentrations in artificial soils were 1.773-14.672, 4.05-24.95, and 133-608 microg L(-1), respectively, and after 35-days incubation, soil solution Cd, Pb, and Zn concentrations gradually decreased and were approaching control levels by the end of the experiment, and finial soil solution were decreased to 0.037-0.365, 2.12-7.34, and 29-509 microg L(-1), respectively.

Cadmium speciation assessed by voltammetry, ion exchange and geochemical calculation in soil solutions collected after soil rewetting

Analytical techniques and speciation models have been developed to characterize the speciation of Cd in soil solution. They provide an estimate of operationally defined species of Cd that need to be compared, especially for soil solutions highly concentrated in organic matter as are the solutions collected after soil rewetting. This work deals with the comparison between the speciation of Cd measured by anodic stripping voltammetry (ASV) and ion exchange and the speciation of Cd calculated using Visual MINTEQ. The aim of this study was to quantify and explain the differences in Cd speciation observed between the three approaches. Cd speciation was assessed in soil solutions collected 4, 8, 24, 48, 96 and 144 h after the rewetting of an air-dried contaminated soil. To optimize the computed speciation of Cd, other physico-chemical parameters were followed ( e.g. pH, ionic strength and the concentrations of major anions, major cations and dissolved organic carbon) and a brief characterisation of dissolved organic matter (DOM) was performed. The discrepancy between model predictions and analytical measurements highlighted the need for caution in the interpretation of geochemical speciated data for Cd. The major result of this study was that a characterization of DOM based on its specific UV-absorbance at 254 nm improved the accuracy of model predictions. Another finding is that labile Cd complexes, even organic, may have been included in the electrochemically labile fraction of Cd measured by ASV.

Determination of speciation and bioavailability of Cd in soil solution using a modified soil column Donnan membrane technique

The concentration of free metal ion (Mz+) has a strong impact on bioavailability and toxicity. In this study, Cd2+ concentration in soil solution was measured by a modified soil column-Donnan membrane technique (S-DMT). Compared with the previously reported DMT, the equilibrium time was relatively short (8 hours) and the multiple metals in the solution can be determined using ICP-AES. This technique was successfully applied in a pot experiment to evaluate Cd speciation and availability to rice. The measured Cd2+ concentration in the soil solutions agreed with the model calculation and correlated very well with the rice growth and the Cd uptake in rice.

Distribution and Accumulation of Copper and Cadmium in Soil–Rice System as Affected by Soil Amendments

The effects of seven amendments on the distribution and accumulation of copper and cadmium in a soil–rice system were investigated using a pot experiment. Results showed that application of limestone, calcium magnesium phosphate (Ca–Mg–P fertilizer), calcium silicate (silicon fertilizer), Chinese milk vetch, pig manure, and peat significantly decreased the concentrations of Cu and Cd in rice roots by 24.8–75.3% and 9.7–49.9%, respectively. However, no significant difference was observed between zinc sulfate (zinc fertilizer) and the control treatment. The concentrations of Cu and Cd in different parts of rice followed the order: root > straw > grain, and all amendments restrained the transfer of Cu and Cd from rice root to stem. Copper and Cd concentrations in rice stems at the tillering stage were the highest, and then decreased from the tillering stage to the heading stage. However, they increased again at the ripening stage. The results also showed that application of amendments changed Cu and Cd solubility in soil and decreased their bioavailability, which resulted in the reduction of Cu and Cd uptake by rice. Significant correlations between the concentrations of Cu and Cd in soil solutions and in rice stems were found. The result demonstrated that limestone has the best efficiency among all the amendments used in reducing Cu and Cd contamination to rice production.

Temporal variability of solution Cd2+ concentration in metal-contaminated soils as affected by soil temperature: consequences on lettuce (Lactuca sativa L.) exposure

The aim of this study was to assess how the solubility and the speciation of Cd in soil solution were affected over time by the soil temperature for three metal-contaminated soils. The changes of solution Cd concentration (either total or free ionic) and other physico-chemical parameters (e.g. pH, ionic strength, the concentrations of \({\text{NO}}_3^ - \), \({\text{SO}}_4^{2 - } \), Ca, Mg and dissolved organic carbon) were monitored over a 28-day culture of lettuce (Lactuca sativa L.) in soils incubated at 10°C, 20°C or 30°C. The major result of this study was that Cd2+ concentration greatly varied over time in soil solution. The Cd2+ concentration declined over time in soil solution as did the concentration of cations that may compete for adsorption (Ca2+, Mg2+). The rise in soil temperature primarily impacted on the concentration of Cd2+ via promoting the microbial C-degradation and, thus, the complexation of Cd in soil solution. The integration of the temporal variations in Cd2+ concentration through the calculation of the root exposure to solution Cd (ECd) provided a fairly close and robust prediction of Cd concentration in lettuce roots. The present work thus provided new insights on the fate of Cd in contaminated soils that may be relevant for predicting the root uptake of Cd.

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.

Temporal evolution of redox processes and free Cd dynamics in a metal-contaminated soil after rewetting

Soil testing procedures to address metals bioavailability currently use air-dried soil rewetted almost until saturation. Such practices may influence the redox state of soil and the related dynamics of metals. To assess this potential impact, a metal-contaminated soil was air-dried and rewetted to 90% water holding capacity. We monitored over a 21-day incubation period the temporal changes of soil redox potential and solution Cd concentration (either total or free). Other physico-chemical parameters were followed notably pH, ionic strength ( I) and the concentrations of NO 3 - , Mn, Fe and SO 4 2 - in solution. Soil redox potential showed the progressive establishment of strong reducing conditions in soil, in agreement with the temporal changes of NO 3 - , Mn, Fe and SO 4 2 - concentrations. It decreased by 13 pe units over the culture period leading to sulphate-reducing conditions (pe < −3) within only 21 days. Solution Cd concentration increased transitorily over the first 100–150 h of incubation (2-fold increase) in relation with the parallel increase in the concentration of competing cations for adsorption (Ca, Mg). It steeply decreased over the last 300 h of incubation (30-fold decrease) as a result of Cd precipitation as Cd sulphides. This biphasic evolution of Cd dynamics was related to the temporal changes of Cd resupply from the solid phase. Using the technique of DGT we described the kinetics of Cd resupply over time and needed to invoke the existence of two pools of Cd.

Elevated Cadmium Concentrations in Potato Tubers Due to Irrigation with River Water Contaminated by Mining in Potosí, Bolivia

Risk of cadmium (Cd) in the human food chain in Cd-contaminated areas is often limited by phytotoxicity from zinc (Zn) that is associated with the Cd contamination. A semiarid area, 60 km downstream of a tin mine in Bolivia, was surveyed where irrigation with Cd-contaminated river water (65-240 microg Cd L(-1)) has increased median soil Cd to 20 mg kg(-1) while median soil Zn was only about 260 mg kg(-1). Cadmium concentrations in potato tubers increased from background values (0.05 mg kg(-1) dry wt.) in soils irrigated with spring water to a median value of 1.2 mg kg(-1) dry wt. in the affected area. Median concentration of Cd in soil solutions was 27 microg L(-1) and exceeded the corresponding value of Zn almost twofold. Soil-extractable chloride ranged from 40 to 1600 mg Cl(-) kg(-1) and was positively correlated with soil total Cd. Increasing soil solution Cl(-) decreased the solid-liquid distribution coefficient of Cd in soil. Soil total Cd explained 64% of the variation of tuber Cd concentration while only 3% of the variation was explained by soil extractable Cl(-) (n = 49). The estimated dietary Cd intake from potato consumption by the local population is about 100 microg d(-1) which exceeds the WHO recommended total daily intake. It is concluded that the food chain risk of Cd in the irrigation water of the semiarid area is aggravated by the association with Cl(-) and, potentially, by the relatively large Cd/Zn ratio.

Effect of Sodium Chloride-induced Salinity on Phyto-availability and Speciation of Cd in Soil Solution

A greenhouse experiment with two levels of Cd (0.5 and 10 mg Cd kg−1, in the form of CdCl2), and five salinity levels of irrigation water (0, 8.6, 17.1, 34.2 and 68.4 mM NaCl) in triplicate was conducted to determine the effect of NaCl-induced salinity on the solubility and availability of Cd in clay loam and sandy calcareous soils. Corn seeds (Zea mays L.) were sown in pots. Forty-five days after planting, the shoots were harvested, and their Cd concentration was determined. The post-harvest electrical conductivity (ECe), pH, and concentrations of cations and anions were determined in soil saturation paste extracts. Increasing irrigation water salinity resulted in significant increases in the total soluble Cd concentration in both studied soils. A positive correlation was found between the total soluble Cd and the chloride concentration in the soil solution.Solution speciation, calculated with MINEQL+ (a chemical equilibrium modeling system), predicted that Cd was present mainly as free Cd2+ ions followed by CdCl+ and $$ {\text{CdSO}}^{0}_{4} $$ in the soils irrigated with deionized water. However, Cd species in the soil solution were significantly altered by increasing chloride concentration, with Cd–chloro complexes becoming the dominant Cd species in the soil solution. Increasing the salinity level resulted in significant decreases in the shoot dry matter and increases in the shoot Cd concentration. Shoot Cd concentration was positively correlated with both the total Cd and Cd–chloro complexes in the soil solution.

Validation of Transfer Functions Predicting Cd and Pb Free Metal Ion Activity in Soil Solution as a Function of Soil Characteristics and Reactive Metal Content

According to recent insight, the toxicity of metals in soils is better related to the free metal ion (FMI) activity in the soil solution than to the total metal concentration in soil. However, the determination of FMI activities in soil solution is a difficult and time-consuming task. An alternative is to use empirical equations (so called transfer functions (TFs)) that relate FMI activity in solution to the reactive metal concentration in the solid phase and to soil properties (pH and organic matter content). Here we test the applicability of two sets of TF for Cd and Pb using independent data from a wide range of soil types and regions that are not represented in the datasets used to derive the TFs. From these soils, soil solution was extracted using four different methods. For all these extracts, FMI activities were calculated from total concentrations in solution using the speciation program WHAM VI. In some of the soils, Cd and Pb FMI activities were also measured using a Donnan membrane technique. Most of these FMI activities deviated from the TF predictions by less than one order of magnitude and were within the 95% confidence interval of the TFs, irrespective of the method used to extract soil solution. Predictability was higher for Pb than for Cd and differed also between the two TF sets.

Cadmium and Nutrient Heavy Metals Uptake by Rice, Barley, and Spinach as Affected by Four Ammonium Salts

ABSTRACT This experiment was conducted to investigate the influence of ammonium salts on the uptake of cadmium (Cd) and nutritional heavy metals (copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe)) by rice, barley, and spinach. These plants were grown in Cd, Cu, and Zn contaminated entisol (ES) or andisol (AS). The following ammonium salts were used: ammonium nitrate (NH4NO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), and ammonium dihydrogen phosphate (NH4H2PO4). In ES, the Cd concentrations in three plant shoots were higher with NH4Cl than with the other salts. The concentrations of Cd in soil solutions collected from ES were higher with NH4Cl. Thus, the increase of Cd uptake by three plants with NH4Cl treatment would be caused by the increased concentration of Cd in the soil solution. In contrast, in AS, the concentrations of the heavy metals in the shoots of all plants were not different among NH4 applications, with one exception, the Mn concentration in rice increased with NH4Cl in both ES and AS.

Soil solution Cd, Cu and Zn concentrations as affected by short-time drying or wetting: The role of hydrous oxides of Fe and Mn

Soil solution metal concentrations are affected, among others, by hydrous oxides of iron and manganese. In a greenhouse study, eight selected soils were subjected to different moisture regimes mimicking during 2 weeks (1) strongly oxidizing conditions of a completely dry surface soil; (2) moist, oxic conditions at field capacity; and (3) a short period of flooding and, hence, the establishment of temporarily low oxygen conditions. Hydrous oxides were characterized using selective extractions, X-ray diffraction and Mössbauer spectroscopy. The moisture regimes did not significantly alter the 0.25 M NH 2OH·HCl + 0.25 M HCl-extractable (“amorphous iron oxides”) nor the 0.04 M NH 2OH·HCl + 25% HOAc-extractable (“amorphous + crystalline iron oxides”) Fe, Mn and Al. X-ray diffraction and Mössbauer spectroscopy revealed that no major conversions or changes in degree of crystallization or redox state had occurred in any of the soils as a result of the 2-week events of flooding or drought. In sandy and acidic or poorly buffered soils that had been dried, soil solution metal concentrations were between 2 and 40 times higher than in the corresponding reference soils that had been kept at field capacity all the time. Soils that had been saturated tended to have slightly lower concentrations of metals in the soil solution. While the importance of iron oxides should not be neglected, it is clear that it is not the single dominant factor. Soil solution metal concentrations at one moment of time may significantly depend on previous soil moisture conditions.

Cadmium and Zinc in Saline Soil Solutions and their Concentrations in Wheat

Soil salinity and plant genotype may affect bioavailability of Cd and Zn to wheat. The aim of this study was to investigate the relationship between concentrations of Zn and Cd in saline soil solutions and in different wheat genotypes. A greenhouse experiment with four bread wheat genotypes (Triticum aestivum L. cv. Rushan, Kavir, Cross, and Falat), and a durum wheat (Triticum durum L. cv. Durum), at four salinity levels of irrigation water (0, 60, 120, and 180 mM NaCl) in triplicate was conducted. After 45 d of growth, the shoots were harvested, and Zn and Cd concentrations were determined in the shoots. Speciation of Cd and Zn in saturation paste extract was modeled using MINTEQA2. A significant (P &lt; 0.05) correlation was observed between model results and Cd and Zn species measured using Amberlite resin. Cadmium and Zn speciation in MINTEQA2‐calculated soil solution was affected by salinity but not by wheat genotype. The major Cd species present in MINTEQA2‐calculated soil solution were free Cd2+, CdCl+, and CdSO40, that increased with increasing salinity. Free Zn2+ was the dominant Zn‐species for all salinities and decreased with increasing salinity. Increasing salinity resulted in significant increases and decreases in shoot Cd and Zn concentrations, respectively, of the Zn‐inefficient genotypes. Cadmium concentrations in shoots of Durum and Kavir genotypes were best predicted by CdCl+ concentrations in solution. In contrast, free Zn2+ ion concentrations in MINTEQA2 calculated soil solution were best related to shoot Zn concentrations in Zn‐efficient genotypes. Under saline conditions, Zn and Cd speciation effects on bioavailability thus depend on both plant genotype and the metal of interest.

A voltammetric method for determining free metal activities in aqueous solutions. Part 2: anodic stripping voltammetry of Cd, Cu, Pb and Zn in synthetic and soil solutions

Theory and methodology for determining the free metal activity, (M2+), of Cd, Cu, Pb and Zn by anodic stripping voltammetry is presented. Metal-buffer solutions were prepared to control (M2+), which was varied by using different ligands and by changing pH. Total metal aqueous concentration of 10-6–10-7M and metal-ligand ratios of 1:20M, 0.010M acetate medium were used. Equations for reversible and irreversible systems were interpreted to explain the results. For Cd and Pb (pPb < 10), agreement was found among theory, experimental ASV and (M2+), calculated by using a speciation chemical equilibria programme and stability constants reported in the literature. Kinetic effects were observed for values of pPb > 10. For Cu and Zn, good agreement was found between the theory and calculated (M2+), and between experimental ASV results and calculated (M2+). Experimental ASV results showed Nernstian parallel shifts with regard to theory. Free metal activities in the order of pCd = 12, pCu = 18, pPb = 10 and pZn = 9 were measurable under the experimental conditions tested. Results too showed good agreement between Cu-ISE and Cu-ASV when measuring the free Cu2+ activity in aqueous extracts of four soils. Values of soil-(Cu2+) measured were in the order of 10-5–10-9.

Effect of Immobilizing Substances and Salinity on Heavy Metals Availability to Wheat Grown on Sewage Sludge-Contaminated Soil

The objective of the investigation was to evaluate the effect of immobilizing substances and NaCl salinity on the availability of heavy metals: Zn, Cd, Cu, Ni, and Pb to wheat (Triticum aestivum L.). In greenhouse pot experiment, a sewage sludge amended soil was treated with the following immobilizing substances: three clay minerals (Na-bentonite, Ca-bentonite and zeolite), iron oxides (goethite and hematite), and phosphate fertilizers (superphosphate and Novaphos). The pots were planted with wheat and were irrigated either with deionized or saline water containing 1600 mg L−1 NaCl. Wheat was harvested two times for shoot metal concentrations and biomass measurements. Metal species in soil solution were estimated using the software MINEQL+. The addition of metal immobilizing substances to the soil significantly decreased metal availability to wheat. The largest reduction in metal bioavailability was found for bentonites. The irrigation with saline water (1600 mg L−1 NaCl) resulted in a significant increase in metal chloride species (MCl+ and MCl2 0). The highest metal complexation with Cl occurred for Cd, which was about 53% of its total soil solution concentration. The total concentration of Cd (CdT) in soil solution increased by 1.6–2.8-fold due to saline water. The NaCl salinity caused a significant increase in uptake and shoot concentration of Cd for two harvests and small but significant increase in shoot Pb concentration for the second harvest. It was concluded that the use of bentonites is the most promising for the reduction of heavy metal availability to plants. Saline water containing 1600 mg L− 1 NaCl increased the availability of Cd and Pb to wheat and decreased the efficiency of bentonites to immobilize soluble Cd.

The EDTA effect on phytoextraction of single and combined metals-contaminated soils using rainbow pink ( Dianthus chinensis)

Rainbow pink ( Dianthus chinensis), a potential phytoextraction plant, can accumulate high concentrations of Cd from metal-contaminated soils. The soils used in this study were artificially added with different metals including (1) CK: original soil, (2) Cd-treated soil: 10 mg Cd kg −1, (3) Zn-treated soil: 100 mg Zn kg −1, (4) Pb-treated soil: 1000 mg Pb kg −1, (5) Cd–Zn-treated soil: 10 mg Cd kg −1 and 100 mg Zn kg −1, (6) Cd–Pb-treated soil: 10 mg Cd kg −1 and 1000 mg Pb kg −1, (7) Zn–Pb-treated soil: 100 mg Zn kg −1 and 1000 mg Pb kg −1, and (8) Cd–Zn–Pb-treated soil: 10 mg Cd kg −1, 100 mg Zn kg −1, and 1000 mg Pb kg −1. Three concentrations of 2Na-EDTA solutions (0 (control), 2, and 5 mmol kg −1 soil) were added to the different metals-treated soils to study the influence of applied EDTA on single and combined metals-contaminated soils phytoextraction using rainbow pink. The results showed that the Cd, Zn, Pb, Fe, or Mn concentrations in different metals-treated soil solutions significantly increased after applying 5 mmol EDTA kg −1 ( p < 0.05). The metal concentrations in different metals-treated soils extracted by deionized water also significantly increased after applying 5 mmol EDTA kg −1 ( p < 0.05). Because of the high extraction capacity of both 0.005 M DTPA (pH 5.3) and 0.05 M EDTA (pH 7.0), applying EDTA did not significantly increase the Cd, Zn, or Pb concentration in both extracts for most of the treatments. Applying EDTA solutions can significantly increase the Cd and Pb concentrations in the shoots of rainbow pink ( p < 0.05). However, this was not statistically significant for Zn because of the low Zn concentration added into the contaminated soils. The results from this study indicate that applying 5 mmol EDTA kg −1 can significantly increase the Cd, Zn, or Pb concentrations both in the soil solution or extracted using deionized water in single or combined metals-contaminated soils, thus increasing the accumulated metals concentrations in rainbow pink shoots. The proposed method worked especially well for Pb ( p < 0.05). The application of 2 mmol EDTA kg −1 might too low to enhance the phytoextraction effect when used in silty clay soils.