In this study, cabbage [Brassica rapa L. subsp. chinensis (L.) Hanelt cv. Xinza No 1], mung bean [Vigna radiata (L.) R. Wilczek var. radiata cv. VC-3762], and wheat (Triticum aestivum L. cv. Altas 66) were grown in Pb-contaminated soils. Application of ethylenediaminetetraacetic acid (EDTA) (3.0 mmol of EDTA/kg soil) to the soil significantly increased the concentrations of Pb in the shoots and roots of all the plants. Lead concentrations in the cabbage shoots reached 5010 and 4620 mg/kg dry matter on Days 7 and 14 after EDTA application, respectively. EDTA was the best in solubilizing soil-bound Pb and enhancing Pb accumulation in the cabbage shoots among various chelates (EDTA, diethylenetriaminepentaacetic acid [DTPA], hydroxyethylenediaminetriacetic acid [HEDTA], nitrilotriacetic acid [NTA], and citric acid). Results of the sequential chemical extraction of soil samples showed that the Pb concentrations in the carbonate-specifically adsorbed and Fe-Mn oxide phases were significantly decreased after EDTA treatment. The results indicated that EDTA solubilized Pb mainly from these two phases in the soil. The relative efficiency of EDTA enhancing Pb accumulation in shoots (defined as the ratio of shoot Pb concentration to EDTA concentration applied) was highest when 1.5 or 3.0 mmol EDTA/kg soil was used. Application of EDTA in three separate doses was most effective in enhancing the accumulation of Pb in cabbage shoots and decreased mobility of Pb in soil compared with one- and two-dose application methods. This approach could help to minimize the amount of chelate applied in the field and to reduce the potential risk of soluble Pb movement into ground water.
Available from: Int. J. Chem. Mater. Environ. Res. (ISSN 2410-5945)
"The intense and inadequate use of fertilizers and pesticides in the soil, coupled with the increase in industrial activity and mining are the main reasons for the contamination of soil, waterways and the water table by heavy metals . Among the existing pollutants, Pb is the major contaminant of the soil  posing significant environmental problems , including the risk of poisoning to human beings and especially the children . Pb absorption is regulated by pH, cation exchange capacity of the soil, as well as by exudation and physicochemical parameters  . "
[Show abstract][Hide abstract] ABSTRACT: The levels of lead (Pb) in soils (S), and eight (8) plants (P) growing naturally in a main agricultural activity, semi-arid zone and where there has been a long-term activity of heavy machineries carrying out construction works in the area were de-termined using atomic absorption spectrophotometer (AAS). Their concentration factors (CF) were also calculated. Whole plant parts were used, these include: calotropis procera (P = 4.6012 µg/g, S = 4.8611µg/g, CF = 0.9465). Commelina sp (P = 1.7053 µg/g, S = 1.479 µg/g, CF = 1.153), Colocynthis bulgaris (P = 1.4971 µg/g, S = 1.4231 µg/g, CF = 1.052), cucur-bita pepo (P = 1.754 µg/g, S = 1.342 µg/g, CF = 1.307), haemanthus sp (P = 0.1645 µg/g, S = 0.0164 µg/g, CF = 1 0.03), hibiscus esculenta (P = 0.5357 µg/g, S=0.1759 µg/g, CF = 3.045), mitracarpus scaber (P = 0.3313 µg/g, S=0.85 µg/g, CF = 0.3898) and lactuca taraxacifolia (P = 4.1067 µg/g, S = 4.8913 µg/g, CF = 1.63). The study is important considering the harmful effects of Pb in human and animal physiological systems. Results were significant at 0.05 level.
"In another study, Shen et al. (2002) showed that the effectiveness of chelating agents for solubilization of Pb is based on the following order: EDTA > HEDTA > DTPA > NTA > citric acid. Each chelant usually has selective function for some metals. "
[Show abstract][Hide abstract] ABSTRACT: Phytoremediation is a naturally slow process limited by low availability of target metals in soils. Adsorption−desorption at the particle–solution interface are the most responsible reactions controlling heavy metal bioavailability in soil. Simply put, metal bioavailability and transport are mainly affected by iron and manganese oxides, clay minerals, carbonates, organic matters, and soil microorganisms. In the soils with higher clay content, cation exchange capacity (CEC), organic carbon (OC), biological activity, and amorphous and crystalline Fe and Al, a metal, e.g., Pb, is mostly observed in residual form followed by organic matter-associated and Mn–Fe-associated forms, respectively, whereas in the soils with higher sand content, pH, and equivalent carbonate calcium (EEC), the higher amount of this metal is reported to be in carbonate-associated form. It is worth noting that the existence and absence of soil microorganisms can alter the above distributions by different mechanisms. In order to increase the bioavailability of heavy metals in soil, application of chelating agents in soil is recommended. What chelating agents do is increasing the metal bioavailability and also increasing soil productivity through enhancing soil available nutrients; both result in a more efficient phytoremediation. Chelating agents are mainly categorized into synthetic (e.g., polycarboxylates, hydroxy carboxylates, etc.) and natural (e.g., organic acids, manures, siderophores, etc.) groups. Among all the other chelating agents, EDTA, which is a synthetic chelate, is frequently reported as the most efficient chelant to increase availability of metals in soil and enhance the translocation of them to aerial (harvestable) parts of plant. In terms of biomass production which is important for an efficient phytoremediation, EDTA cannot play its role as successfully as when it is used to enhance metal concentration. Toxicity of EDTA itself on the one hand and the toxicity of increased amount of heavy metals caused by EDTA on the other hand prevent plant from producing much biomass. It may be applied in soil during plant growth with lower concentration and different times. Natural chelating agents, nevertheless, noticeably enhance biomass production, although they are not so effective to improve metal concentration as EDTA is. On the other hand, electrokinetic is another technique used to increase available forms of heavy metals and their movement in soil toward plant roots. The most recent researches, interestingly, were designed based on the combination of electrokinetic and chelating agents, which significantly increases the uptake of metals by plants. Giving the negative charge to plant can lead to more cation taken up by plant roots because the electric field makes biomembranes more permeable, providing a transient exchange of metals across the perturbed membrane structure. More interesting results would be obtained when chelating agents provided more bioavailable metals for plant roots simultaneously. As a result, application of chelating agents along with electric fields amazingly raises the phytoremediation efficiency.
Heavy Metal Contamination of Soils, 1st edited by Irena Sherameti, Ajit Varma, 01/2015: chapter Chelating Agents and Heavy Metal Phytoextraction: pages 367-393; Springer International Publishing., ISBN: 978-3-319-14526-6
"Although heavy metals are naturally present in the soil, geologic and anthropogenic activities increase the concentration of these elements to amounts that are harmful to both plants and animals. Some of these activities include mining and smelting of metals, burning of fossil fuels, use of fertilizers and pesticides in agriculture, production of batteries and other metal products in industries, sewage sludge, and municipal waste disposal   . Growth reduction as a result of changes in physiological and biochemical processes in plants growing on heavy metal polluted soils has been recorded   . "
[Show abstract][Hide abstract] ABSTRACT: Soils polluted with heavy metals have become common across the globe due to increase in geologic and anthropogenic activities. Plants growing on these soils show a reduction in growth, performance, and yield. Bioremediation is an effective method of treating heavy metal polluted soils. It is a widely accepted method that is mostly carried out in situ; hence it is suitable for the establishment/reestablishment of crops on treated soils. Microorganisms and plants employ different mechanisms for the bioremediation of polluted soils. Using plants for the treatment of polluted soils is a more common approach in the bioremediation of heavy metal polluted soils. Combining both microorganisms and plants is an approach to bioremediation that ensures a more efficient clean-up of heavy metal polluted soils. However, success of this approach largely depends on the species of organisms involved in the process.
Applied and Environmental Soil Science 01/2014; 2014:1-12. DOI:10.1155/2014/752708
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