Translocation and accumulation of heavy metals in Ocimum basilicum L. plants grown in a mining-contaminated soil

Purpose

The evaluation of the ecotoxicity effects of some heavy metals on the plant growth and metal accumulation in Ocimum basilicum L. cultivated on unpolluted and polluted soils represented the objective of the present study.

Materials and methods

The basil aromatic herb was evaluated in a laboratory experiment using soil contaminated with Cd, Co, Cr, Cu, Ni, Pb, and Zn, similar to the one from a mining area. The soils and different organs of the basil plants were analyzed, the total contents of the added elements being determined using inductively coupled plasma optical emission spectrometry. The ability of basil plants to accumulate metals from soil and to translocate them in their organs was evaluated by transfer coefficient, translocation factor, enrichment factor, and geo-accumulation index determinations.

Results and discussion

The basil plants grown in the metal-polluted soil showed stimulation effects comparing with the plants from the control soil. At the end of the exposure period, the plants had a visible increase of biomass and presented inflorescences and the leaves’ green pigment was intensified. The metals gathered differently in plant organs: Cd, Co, Cr, and Pb were accumulated in roots, while Cu, Ni, and Zn in flowers. Cr and Pb exceeded the toxic levels in roots. Also, the heavy metal intake depends on the plant development stages; thus, Cd, Cr, and Pb were accumulated more in mature plant leaves. The Cd and Pb contents were higher than the World Health Organization and European Commission permissible limits.

Conclusions

The experimental results revealed that the basil plants exposed to a mixture of heavy metals have the potential to reduce the metal mobility from soil to plants. Translocation process from roots to flowers and to leaves was observed for Cu, Ni, and Zn, emphasizing a competition between metals. The calculated bioaccumulation factors were insignificant, but Cd and Pb concentrations exceeded the legal limits in the mature plants, being restricted for human or animal consumption.

     

Bean Plant Production of Dry Matter and Grain Related to Soil Citric Acid–Extractable Copper,Zinc, Cadmium,and Lead

Some knowledge concerning soil heavy‐metal content and its availability to plants is essential to evaluate the risk of potentially toxic elements in the alimentary chain. Assessment of heavy‐metal availability to plants was achieved by a simple extraction method. The goal of this work was to determine the contents of copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb), soluble in 2% citric acid solution (chelating agent), in dystrophic red latosol soil (RL_d) and humic red‐yellow latosol soil (RYL_h). We focused on relating the contents of Cu, Zn, Cd, and Pb to the production of dry matter and grains by bean plants cultivated in a glasshouse. Heavy‐metal contents extracted by citric acid increased with increasing dosage increments, mainly in RL_d; production of dry matter by bean plant was negatively affected by the studied metals. However, in some cases, grain production was increased.     

Plant uptake of metals,transfer factors and prediction model for two contaminated regions of Kosovo

The bioavailability and plant uptake of heavy metals (HM), as well as finding the most reliable methods for the prediction of availability, continues to be one of the most crucial problems in agricultural and environmental studies. In agricultural soils from two regions in Kosovo, known for its metal pollution, we collected 60 soil and plant samples (wheat, corn, potatoes, and grass). Heavy metals were extracted from soil with aqua regia (pseudototal concentration), NH₄OAc‐EDTA (potential bioavailable), and NH₄NO₃ (mobile fraction), plant samples were digested with HNO₃/H₂O₂ (microwave assisted extraction). The pseudo total content of Cd, Pb, and Zn showed high value in Mitrovice (mean: Cd–2.92, Pb–570.15, and Zn–522.86 mg kg^?1), whereas in Drenas region Ni and Cr showed high value with a mean 258.54 and 203.22 mg kg^?1. Also, the potential bioavailability and mobile form of these metals were increased in Mitrovice (mean: Cd–1.59, Pb–217.05, Zn–522.86 mg kg^?1, respectively Cd–0.17, Pb–0.64, and Zn–15.45 mg kg^?1), compared to Drenas. Cd and Pb were elevated in potato tubers (mean Cd–0.48 and Pb–0.85 mg kg^?1). The TF was higher for micronutrients (Zn and Cu) than for non‐essential metals (Cd and Pb). Multiple regression analysis showed a good model for prediction of Cd, Pb and Zn content in plant with significance 99.9%, whereas this model was not significant for Cu, Cr, and Ni. Soil pH played a significant role in the content of Cd and Zn in wheat and potato plants. Clay content also showed significance in Cd concentration in wheat and potato plants, while carbon content was significant for Cd in grass plants, as well as for Zn in wheat and grass plants.     

Extractability and plant uptake of heavy metals in alum shale soils

Abstract

Fifty soil samples (0–20 cm) with corresponding numbers of grain, potatoes, cabbage, and cauliflower crops were collected from soils developed on alum shale materials in Southeastern Norway to investigate the availability of [cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and manganese (Mn)] in the soil and the uptake of the metals by these crops. Both total (aqua regia soluble) and extractable [ammonium nitrate (NH₄NO₃) and DTPA] concentrations of metals in the soils were studied. The total concentration of all the heavy metals in the soils were higher compared to other soils found in this region. Forty‐four percent of the soil samples had higher Cd concentration than the limit for application of sewage sludge, whereas the corresponding values for Ni, Cu, and Zn were 60%, 38%, and 16%, respectively. About 70% the soil samples had a too high concentration of one or more of the heavy metals in relation to the limit for application of sewage sludge. Cadmium was the most soluble of the heavy metals, implying that it is more bioavailable than the other non‐essential metals, Pb and Ni. The total (aqua regia soluble) concentrations of Cd, Cu, Zn, and Ni and the concentrations of DTPA‐extractable Cd and Ni were significantly higher in the loam soils than in the sandy loam soils. The amount of NH₄NCyextractable metals did not differ between the texture classes. The concentrations of DTPA‐extractable metals were positively and significantly correlated with the total concentrations of the same metals. Ammonium nitrate‐extractable metals, on the other hand, were not related to their total concentrations, but they were negatively and significantly correlated to soil pH. The average concentration of Cd (0.1 mg kg^‐1 d.w.) in the plants was relatively high compared to the concentration previously found in plants grown on the other soils. The concentrations of the other heavy metals Cu, Zn, Mn, Ni, and Pb in the plants were considered to be within the normal range, except for some samples with relatively high concentrations of Ni and Mn (0–11.1 and 3.5 to 167 mg kg‘¹ d.w., respectively). The concentrations of Cd, Cu, Zn, Ni, and Mn in grain were positively correlated to the concentrations of these respective metals in the soil extracted by NH₄NO₃. The plant concentrations were negatively correlated to pH. The DTPA‐extractable levels were not correlated with plant concentration and hence DTPA would not be a good extractant for determining plant availability in these soils.     

不同城市功能区绿地土壤重金属分布及其生态风险评价

对山东中部某典型城市9个城市功能区64个绿地土壤样品中的Cu,Zn,Pb,Cd 4种重金属元素含量进行了测定,评价了土壤重金属污染特征及其生态风险。结果表明:各功能区绿地表层土壤Cu,Zn,Pb和Cd的平均含量均高于当地自然植被土壤背景值,已表现出富集状态,其中Cd平均含量超标严重;工业区、风景名胜区、商业区和居民区等绿地土壤污染程度居前;单因子污染评价表明,该市绿地土壤中Cu,Zn和Pb已处于潜在污染状态,而Cd已经处于重污染状态;综合污染评价研究表明,处于“中度污染”污染级别的绿地类型有工业绿地、商业区绿地、风景名胜区和居住区绿地,而且苗木生产区和道路绿地也接近“中度污染”级别;潜在生态危害评价表明,该市绿地土壤处于轻微生态风险,但Cd潜在生态危害指数已经处于中等生态风险;土壤中Cu-Zn,Cu-Cd,Pb-Cd显著相关,Cu-Pb,Zn-Cd极显著相关,重金属之间存在一定复合污染现象,表明这些重金属元素的来源可能相同。该市绿地土壤Cd污染的防治应该引起重视。     

Effect of pH on Potentially Toxic Trace Elements (Cd,Cu, Ni,and Zn) Solubility in Two Native and Spiked Calcareous Soils: Experimental and Modeling

The effect of soil pH on solubility of the potentially toxic trace elements (PTEs) [cadmium (Cd), copper (Cu), nickel (Ni), zinc (Zn)] was assessed using two native and spiked calcareous soils. Multiple PTEs solutions were added to soils and equilibrated (aged) for 40 days. Then, PTEs solubility was measured at different pH level (1–3 units below and above the pH of native soils). In native soils, all PTEs displayed a V-shaped pH-dependent solubility pattern with important releases at pH 4 and 10 (native soil 1) and 5 and 11 (native soil 2). In spiked soils, the general tendency for the pH where solubility started was in the order Cd > Ni > Zn > Cu. Solubility of added trace elements increased with a decrease in pH. Solubility of PTEs occurred at a lower pH in the soil with a higher carbonate content than the other soil (both native and spiked). In order to predict the effect of soil pH on solubility of PTEs, surface complexation and ions exchange models of PHREEQC program were used. The model simulated the PTEs solubility in soils very well. Comparison of experimental and simulated data indicated that ions exchange and surface complexation were the main mechanisms for predicting PTEs solubility in soils. Environmental implications concerning PTEs mobility might be derived from these findings.     

Arsenic and Heavy Metal Uptake and Accumulation in Native Plant Species from Soils Polluted by Mining Activities

Arsenic and heavy metal (specifically Cd, Cr, Cu, Ni, Pb, and Zn) uptake, translocation, and accumulation in ten native plant species spontaneously growing in soils polluted by mining activities were studied, with a focus on future phytoremediation work in polluted soils. Plant and soil samples were collected in the vicinity of the Mónica mine (NW Madrid, Spain). Soil analysis showed the ability of native plants for growing in soils with high concentration levels of Cd, Cu, Pb, Zn, and especially As. From these elements, the highest percentage of extractable elements was found for Cd and the lowest for Pb. A highly significant correlation was observed between total and extractable element concentrations in soils, except for Cu, indicating that total concentration is the most relevant factor for element mobility in these soils. Extractable elements in soils were better correlated with concentrations in plants than total elements in soils; thus, extraction methods applied are suitable to estimate the element phytoavailable fraction in soils, which depends on the plant species and not only on the element mobility in soils. High element concentrations were found in the aboveground parts of Corrigiola telephiifolia (As and Pb), Jasione montana (Cd and Zn), and Digitalis thapsi (As, Cd, Cu, Pb and Zn). However, considering the translocation and accumulation factors, together with the concentration levels found in roots and aboveground parts, only C. telephiifolia could be considered a Pb accumulator and an As hyperaccumulator plant, which could be used for future phytoremediation work in soils polluted with As.     

Does returning sites of historic peri‐urban waste disposal to vegetable production pose a risk to human health? – A case study near Manchester,UK

Urban waste disposal occurred on fenland to the west of Manchester, England, between 1900 and 1964. The reclaimed fenland, Chat Moss, is now used for mixed arable farming. A total of 1.92 Mt of waste including privy midden, street sweepings, clinkers and slaughterhouse refuse was incorporated into the moss resulting in a modified topsoil with raised pH and reduced organic matter content compared with the subsoil. Elevated levels of potentially toxic elements (PTEs) are observed in the topsoil beyond the typical depth of atmospheric contamination; Cd and As concentrations exceed soil guideline values (SGVs) at 1.8 and 43 mg/kg, respectively. Sequential extraction indicates that waste‐derived Pb, Zn and Ni remain predominantly in the residual fraction, whereas Cu was mainly organically bound. Arsenic was predominately found in oxide and organic matter fractions with Cd in carbonate, oxide, organic matter and residual fractions. Pot trials indicated limited uptake of PTEs by vegetables grown on the waste‐amended soil, with the exception of Cd uptake by lettuce (0.22 mg/kg FW) and Pb uptake by radish (0.16 mg/kg FW), which exceeded current EU limits of 0.2 and 0.1 mg/kg FW, respectively. Hazard quotients (HQs) identified no risks to adults from consumption of vegetables grown in these soils with the exception of lettuce consumption with a HQ of 1.4. Risks to children were slightly greater with HQs >1 for Cd in lettuce, spinach, carrots and onion, As in lettuce, parsley and onion and for Zn in spinach.     

Metal Uptake in Plants and Health Risk Assessments in Metal‐Contaminated Smelter Soils

Metal pollution is an important concern because of its potential to affect human health. Metals such as lead and cadmium can enter soil via the food chain and exceed normal limits, producing harmful effects. In this study, six common garden and residential plant species were grown in soils from Spelter, WV, USA, contaminated with a variety of metals including lead (Pb), zinc (Zn), cadmium (Cd), and copper (Cu). Plant species included radish, carrot, chicory, spinach, lettuce, and clover. Metal concentrations in plant tissues were compared with metal concentration in soil by a multi‐step chemical extraction. The largest accumulation of Pb (126 mg kg⁻¹) and Zn (1493 mg kg⁻¹) was seen in radish roots, with Cd (40 mg kg⁻¹) having the largest accumulation in carrot roots. Comparisons of plant availability with soil chemical extractions indicated that the combined soluble and exchangeable fractions could estimate available Zn and Cd for all six plant species. For Pb and Cu, however, the comparisons indicate that these two elements were not readily available in Spelter soils. A health risk assessment was carried out for residents at Spelter on the basis of edible tissue concentrations and publicly available consumption data. Uptake of Cd by carrot roots was about five times more than the regulatory limits for men, eight times more for women, and 12 times more for children. On the basis of the results, carrot and lettuce grown in these soils have the potential to cause toxicological problems in men, women, and young children resulting from Cd and Zn accumulation. Copyright © 2013 John Wiley & Sons, Ltd.     

Heavy‐metal mobilization and uptake by mycorrhizal and nonmycorrhizal willows (Salix × dasyclados)

Ectomycorrhizal fungi have been shown to affect metal transfer from the soil to the host plant, but the use of these fungi for increased phytoextraction of heavy metals has been scarcely investigated. Therefore, a two‐factorial pot experiment was conducted with Salix × dasyclados and (1) two contaminated soils with different concentrations of NH₄NO₃‐extractable metals and (2) two strains of the ectomycorrhizal fungus Paxillus involutus (one strain originating from a noncontaminated site—Pax1, and another from a contaminated site—Pax2). The inoculation with Pax2 increased the phytoavailability of Cd in the soils. Inoculation with both fungal strains increased the stem and root biomass, but had no effect on metal concentrations in the stems. Decreased Cd and increased Cu concentrations were observed in the roots of inoculated willows. The inoculation with P. involutus increased Cd (up to 22%), Zn (up to 48%), and Cu content in the stems. Decreased Pb content (Cu and Pb content were always <1 mg per plant) occurred in the stems from plants at the soil with the higher concentration of NH₄NO₃‐extractable metals. Contrary to this, in the soil with lower concentrations of NH₄NO₃‐extractable metals, the inoculation had no significant effects on the total uptake of Zn and Cu and even caused decreased Cd (Pax2) and Pb (Pax1) contents in the stems. Strain Pax2 had higher colonization densities, but the plants had lower mycorrhizal dependencies in the contaminated soils than after inoculation with the strain Pax1. Generally, metal extractability in the soils substantially affected the mycorrhizal dependency and heavy‐metal uptake of the willows. We concluded, that the inoculation with P. involutus offers an opportunity to particularly increase the phytoextraction of Zn, but the metal extractability and fungal strain effects have to be tested.     

Trace elements in some Northern Nigerian soils

Abstract

The concentrations of the more‐or‐less strongly retained trace elements present in the root zone of some northern Nigerian soils were determined. The soils were chosen to represent some of the more extensively distributed soil orders under cultivation in the Nigerian savanna zone. Extraction by concentrated HNO₃ was used to determine the so‐called “total”; amount of retained Cu, Zn, Pb, Ni, Cd, and B in the soils. Aqueous solutions of the chelating agents, EDTA and DTPA, were used to extract the more weakly retained Cu, Zn, Pb, Ni, and Cd; whereas, hot water was used to extract the weakly retained B. The “total”; and the more‐weakly‐retained contents of these trace elements were significantly correlated with the amount of clay, silt, and the oxalate‐extractable oxyhydroxides present in the soils; whereas, only the weakly retained elements were significantly correlated with the content of organic matter in the soil. Both the “total”; concentrations and weakly‐retained Cu, Zn, and B were so low that deficiency problems may develop in these sandy soils if cultivated more intensively on a commercial scale without due precautions. The concentrations of the weakly‐retained toxic elements, Pb, Ni, and Cd, were low indicating that industrial pollution has not yet occurred.     

Precipitation of secondary phases of iron and its role in controlling the mobility of potentially toxic elements in soils in a semiarid river basin in Northwest Mexico

Purpose

Soils have the ability to retain potentially toxic elements (PTEs) through different chemical processes that promote low mobility of these elements, such as the precipitation of secondary phases of Fe, which facilitate the adsorption/co-precipitation of PTEs. The main objective of this study was to evaluate the mobility of PTEs present in an acid solution in two soils with different concentrations of calcite, understanding the role of secondary iron phases in the retention of these elements.

Materials and methods

To evaluate this phenomenon, intact soil columns of two different types of soils from the Sonora River in Northwest Mexico were exposed to an acid solution with high concentration of dissolved PTEs (mainly Fe, Al, and Cu).

Results and discussion

The Tinajas soil was free of carbonates while the Bacanuchi soil had more carbonate content than the Tinajas soil. Secondary precipitates corresponding to secondary phases of iron (mainly ferrihydrite and jarosite) were identified by X-ray diffraction. Using scanning electron microscopy, the PTEs retained in the soils were identified. The presence of calcite favored the neutral pH values in the collected leachates in the Bacanuchi soil; consequently, the mobility of the PTEs present in the acid solution was nullified. Furthermore, this process facilitated the retention of the toxic elements in the Bacanuchi soil.

Conclusions

The retention of PTEs was 100% in the Bacanuchi soil where the natural acid-neutralizing capacity in this soil was associated with calcite. The formation of secondary phases of Fe, among them ferrihydrite, jarosite, and schwertmannite, mainly in Bacanuchi soil, promoted the retention of Al, As, Cd, Cu, Fe, Mn, and Pb (elements analyzed in this work). Results of this work can provide key insights to improve cleanup and conservation strategies in mining sites.

     

Field assessment of cadmium,lead and zinc contamination of soils and leaf vegetables under urban and peri-urban agriculture in northern Nigeria

Urban and peri-urban agriculture in dry semi-arid northern Nigeria relies on untreated wastewater for all-year irrigation and the production of vegetables for urban markets. Human and animal exposure to potentially toxic metals is attributed to the consumption of vegetables raised in metal-polluted soils. The objective of this study was to determine the bioavailability and soil–plant transfer of Cd, Pb and Zn to amaranthus (Amaranthus caudatus) and lettuce (Latuca sativa) raised in the garden fields and to assess their safety for human consumption. Ten farmers’ fields were selected per location for analysis of Cd, Pb and Zn in soils and vegetables. Whereas total concentrations of Cd and Zn were greater than the safe or permissible limits for agricultural soils, the Pb concentration was less than its maximum allowable concentration. However, the concentration of Pb and Cd in edible portions of amaranthus exceeded the safe limit for human consumption by 7–13 times, while lettuce exceeded the limit by 11–17 times. Cadmium was more rapidly transferred from soil through root to shoot than Zn > Pb. The plant tissue concentrations of the metals were not significantly correlated with the Diethylene triamine pentaacetic acid (DTPA) and dilute CaCl₂-extractable concentrations of the metals in the soils. Furthermore, permissible limit of Pb established as standards for agricultural lands may not be suitable to ensure produce safety in Urban and peri-urban agriculture (UPA) in the city of Kano.     

Long-term irrigation with zinc smelter effluent affects important soil properties and heavy metal content in food crops and soil in Rajasthan,India

Use of wastewater for irrigating agricultural crops is on the rise, particularly in the developing countries. The present study was undertaken to assess the long-term effect of irrigation with zinc smelter effluent on important soil properties including heavy metal status. Metal concentration in the edible parts of the crops grown on smelter effluent-irrigated soils was also measured. For this purpose, the agricultural lands which have been receiving the zinc smelter effluent irrigation for about five decades at Debari, Udaipur, India were selected. The adjacent tubewell water-irrigated fields were selected as reference. Long-term irrigation with smelter effluent resulted into significant buildup of ethylenediaminetetraacetic acid extractable Zn (57.7 fold), Cu (4.51 fold), Fe (3.35 fold), Mn (1.77 fold), Ni (1.20 fold), Pb (45.1 fold), and Cd (79.2 fold) in soils over tubewell water-irrigated fields. Total Zn, Cu, Mn, Ni, Pb, and Cd content in effluent-irrigated soils was also increased by 27.0, 1.60, 1.40, 1.30, 26.2, and 167 fold, respectively. Risk assessment indicated a very high to moderate potential ecological risk due to Cd, Pb, and Zn in soils close to the immediate vicinity of the smelter plant. Cadmium and Pb concentrations in edible parts of almost all the crops grown on effluent-irrigated soils were above the safe limit of CODEX commission. On an average, soil pH dropped by 0.31 units due to smelter effluent irrigation. Smelter effluent irrigation resulted into significant increase in soil organic carbon, electrical conductivity, and CaCO₃ content. On an average, there was decrease in available N (21.0%) and P (20.8%) content in effluent-irrigated soils over the tubewell water-irrigated ones. An increase in available K (102%) and S (26.0 fold) was recorded in effluent-irrigated soils. Long-term irrigation with zinc smelter effluent resulted into reduced microbial activities in soil as evidenced from the level of microbial biomass carbon and dehydrogenase activity. In view of the buildup of heavy metals and subsequent imbalance in essential plant nutrients in smelter effluent-irrigated soils, appropriate remediation-cum-fertilization strategy needs to be adopted for better soil health and plant nutrition.     

Uptake of SigmaDDT, arsenic, cadmium, copper, and lead by lettuce and radish grown in contaminated horticultural soils

Horticultural soils can contain elevated concentrations of selected trace elements and organochlorine pesticides as a result of long-term use of agrichemicals and soil amendments. A glasshouse study was undertaken to assess the uptake of weathered SigmaDDT {sum of the p, p'- and o, p-isomers of DDT [1,1,1-trichloro-2,2- bis( p-chlorophenyl)ethane], DDE [1,1-dichloro-2,2- bis( p-chlorophenyl)ethylene] and DDD[1,1-dichloro-2,2- bis( p-chlorophenyl)ethane]}, arsenic (As), cadmium (Cd), copper (Cu), and lead (Pb) residues by lettuce ( Lactuca sativa) and radish ( Raphanus sativus) from field-aged New Zealand horticultural soils. Concentrations of SigmaDDT, DDT, DDE, Cd, Cu, and Pb in lettuce increased with increasing soil concentrations. In radish, similar relationships were observed for SigmaDDT, DDE, and Cu. The bioaccumulation factors were less than 1 with the exception of Cd and decreased with increasing soil concentrations. Lettuce Cd concentrations for plants grown on four out of 10 assayed soils were equivalent to or exceeded the New Zealand food standard for leafy vegetables of 0.1 mg kg (-1) fresh weight. Concentrations of As, Pb, and SigmaDDT did not exceed available food standards. Overall, these results demonstrate that aged residues of SigmaDDT, As, Cd, Cu, and Pb in horticultural soils have remained phytoavailable. To be protective of human health, site-specific risk assessments and soil guideline derivations for residential settings with vegetable gardens need to consider the produce consumption pathway.     

Extractors for barium,cadmium, copper,nickel, and zinc in tropical soils

ABSTRACT

The accumulation of potentially toxic elements (PTEs) in the soil can pose risks to human health, and precise risk assessment dealing with the production and consumption of plants is required. The 0.43 M of nitric acid (HNO?) solution was suggested by the International Organization for Standardization for reactive fraction of PTEs in the soil. The efficiency of some extractors was evaluated in tropical soils. Contents of barium (Ba), cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) were extracted in accordance with the methods of Environmental Protection Agency (EPA) 3051A, Aqua Regia, Diethylenetriaminepentaacetic acid (DTPA), Mehlich-1, Mehlich-3, 0.43 M HNO? and 0.01 M of calcium chloride (CaCl?), and these contents correlated with the contents of PTEs in roots, shoots, and fruits of vegetables. Mehlich-3 had the highest correlation with Ni and Zn contents extracted by the plants. Contents extracted with 0.43 M HNO? had high correlation with the amounts extracted by DTPA and Mehlich-3, as well as with the amounts of PTEs accumulated by plants.     

Cadmium and lead affect the status of mineral nutrients in alfalfa grown on a calcareous soil

ABSTRACT

Cadmium (Cd) and lead (Pb) are toxic trace elements which are not essential for plants but can be easily taken up by roots and accumulated in various organs, and cause irreversible damages to plants. A pot experiment was carried out to investigate the individual and combined effects of Cd (0, 10, 20 mg kg^?1) and Pb (0, 500, 1000 mg kg^?1) level in a calcareous soil on the status of mineral nutrients, including K, P, Ca, Mg, S, Fe, Mn, Cu, and Zn, in alfalfa (Medicago sativa L.) plants. Soil Pb level considerably (P ≤ 0.05) affected the concentrations of more elements in plants than soil Cd level did, and there were combined effects of soil Cd level and Pb level on the concentrations of some nutrients (Ca, Mg, and Cu) in plants. The effects of soil Cd level and Pb level on plant nutrient concentrations varied among plant parts. Cd and Pb contamination did not considerably affect the exudation of carboxylates in the rhizosphere. An increase in rhizosphere pH and exudation of significant amounts of carboxylates (especially oxalate) in the rhizosphere might contribute to the exclusion and detoxification of Cd and Pb. Neither shoot dry mass nor root dry mass was significantly influenced by soil Cd level, but both of them were considerably reduced (by up to 25% and 45% on average for shoot dry mass and root dry mass, respectively) by increasing soil Pb level. The interaction between soil Cd level and Pb level was significant for root dry mass, but not significant for shoot dry mass. The results indicate that alfalfa is tolerant to Cd and Pb stress, and it is promising to grow alfalfa for phytostabilization of Cd and Pb on calcareous soils contaminated with Cd and Pb.     

Adsorption isotherms of some heavy metals under conditions of their competitive adsorption onto highly calcareous soils of southern Iran

Recently, application of sewage sludge or effluents resulted in raising the concentrations of some heavy metals in some agricultural soils of Iran. Experiments were conducted to evaluate the competitive adsorption of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) on six calcareous soils. Adsorption characteristics were evaluated by equilibration of 1 g of each soil sample with 20 ml of 0, 10, 20, 30, 40, 50, 100, or 200 mg L^?1 of their nitrate solutions and 0.01 M NaNO₃ as background electrolyte. Furthermore, solid/liquid distribution coefficients (K_d) of studied metals, as an index of soil capacity to resist a change of the soil solution concentration, were calculated. Results indicated that amounts of adsorbed Pb, Cu, Zn, and Cd increased with increase in their concentrations in the contact solutions, but this trend was more pronounced for Pb and Cu than the others. For all studied soils and metals, Langmuir equation described the adsorption behavior fairly well. Furthermore, Langmuir and Freundlich equation parameters were positively correlated to cation exchange capacity (CEC) and smectite contents; whereas, they were negatively correlated to sand content. Considering K_d values, the selectivity sequence of the metal adsorption was Pb > Cu > Zn > Cd. Therefore, the risk of leaching and also plant uptake of Zn and Cd will be higher as compared to those of the other elements.     

Schwermetalle im Boden eines Klärschlamm-Versuchsfeldes

Heavy metals in soil of a sewage sludge experimental field The total amounts of Zn, Cd, Pb, Cu, Cr and Ni were determined in different depths of soils which have obtained sewage sludges in amounts between 180 and 1620 dt dry matter/ha. The elements Zn, Cd. Pb and Cu have been most enriched in the first twenty cm of the soils. The contents of Zn, Cd and Pb in the depth of 40–60 cm also showed a significant increase. The treshold values for Zn and Cd in soils were almost attained respectivly slightly exceeded in the first twenty cm of the soil which has obtained 1440 dt dry matter sewage sludge per ha.     

红壤重金属的复合污染

The effects of combined heavy metal pollution of red soil on the growth of wetland rice and the transfer of Pb,Cd,Cu and Zn from soil into plants were sudied by greenhouse pot experiment,The results showed that the plantyields were markedly affected by heavy metals,with the exception of Pb,in soils under the experimental conditions,without taking into consideration all the interactions among the elements.The concentrations of the elemets in plants were mainly affected by the specific element added to the soil.The effect of interactions among the heavy metals was very significant either on plant yields or on the concentration of the elements in plants.The risk assessment of a combined pollution by heavy metals in the soil is discussed preliminarily in terms of the relative pollution equivalent.