Chelate-assisted Phytoextraction Research Articles

PHYSIOLOGICAL RESPONSES AND TOLERANCE EFFICIENCY OF Spinacea oleracea L. UNDER HYDROPONIC Ni2+ STRESS CONDITION

An indoor EDTA and HNO3 enriched environment was created by an injection system with timing and varying concentration control. Spinacea oleracea was selected hydroponic plant exposed to various doses of Ni2+ (0, 1000, 2000 and 4000 mg/L) as Na2EDTA at (0, 500 and 3000 mg/L) and (0,500 and 3000 mg/L) HNO3 in different combinations for 6 days with 10-hour-treatment each day. This study used modified Hoagland nutrient culture in a screen house to provide an ideal environment for comparing the efficiency of chelate-assisted and unchelated phytoextraction of Ni2+ by S. oleracea. Changes in morphological characteristics including leaf damage rate to evaluate morphological resistance to Ni2+ uptake and proline contents was observed. Changes in fresh biomass were significant (p < 0.05) with respect to addition of EDTA and HNO3 at different concentration to different concentrations of Ni2+ compared to unchelated treatments of same concentrations of Ni2+. The Ni2+ induced proline accumulation in shoots increased significantly (P < 0.05) with increasing Ni2+ concentrations.

Plant growth regulators and EDTA improve phytoremediation potential and antioxidant response of Dysphania ambrosioides (L.) Mosyakin & Clemants in a Cd-spiked soil.

Soil pollution due to potentially toxic elements is a worldwide challenge for health and food security. Chelate-assisted phytoextraction along with the application of plant growth regulators (PGRs) could increase the phytoremediation efficiency of metal-contaminated soils. The present study was conducted to investigate the effect of different PGRs [Gibberellic acid (GA3) and indole acetic acid (IAA)] and synthetic chelator (EDTA) on growth parameters and Cd phytoextraction potential of Dysphania ambrosioides (L.) Mosyakin & Clemants grown under Cd-spiked soil. GA3 (10-7 M) and IAA (10-5 M) were applied four times with an interval of 10 days through a foliar spray, while EDTA (40 mg kg-1 soil) was once added to the soil. The results showed that Cd stress significantly decreased fresh biomass, dry biomass, total water contents, and photosynthetic pigments as compared to control. Application of PGRs significantly enhanced plant growth and Cd phytoextraction. The combined application of GA3 and IAA with EDTA significantly increased Cd accumulation (6.72 mg pot-1 dry biomass) and bioconcentration factor (15.21) as compared to C1 (Cd only). The same treatment significantly increased chlorophyll, proline, phenolic contents, and antioxidant activities (CAT, SOD, and POD) while MDA contents were reduced. In roots, Cd accumulation showed a statistically significant and positive correlation with proline, phenolics, fresh biomass, and dry biomass. Similarly, Cd accumulation showed a positive correlation with antioxidant enzyme activities in leaves. D. ambrosioides showed hyperaccumulation potential for Cd, based on bioconcentration factor (BCF) > 1. In conclusion, exogenous application of GA3 and IAA reduces Cd stress while EDTA application enhances Cd phytoextraction and ultimately the phytoremediation potential of D. ambrosioides.

Accumulation potential and tolerance response of Typha latifolia L. under citric acid assisted phytoextraction of lead and mercury

Chelate-assisted phytoextraction by high biomass producing macrophyte plant Typha latifolia L. commonly known as cattail, is gaining much attention worldwide. The present study investigated the effects of Lead (Pb) and Mercury (Hg) on physiology and biochemistry of plant, Pb and Hg uptake in T. latifolia with and without citric acid (CA) amendment. The uniform seedlings of T. latifolia were treated with various concentrations in the hydroponics as: Pb and Hg (1, 2.5, 5 mM) each alone and/or with CA (5 mM). After four weeks of treatments, the results revealed that Pb and Hg significantly reduced the plant agronomic traits as compare to non-treated plants. The addition of CA improved the plant physiology and enhanced the antioxidant enzymes activities to overcome Pb and Hg induced oxidative damage and electrolyte leakage. Our results depicted that Pb and Hg uptake and accumulation by T. latifolia was dose depend whereas, the addition of CA further increased the concentration and accumulation of Pb and Hg by up to 22 & 35% Pb and 72 & 40% Hg in roots, 25 & 26% Pb and 85 & 60% Hg in stems and 22 & 15 Pb and 100 & 58% Hg in leaves respectively compared to Pb and Hg treated only plants. On other hand, the root-shoot translocation factor was ≥1 and bioconcentration factor was also ≥2 for both Pb & Hg. The results also revealed that T. latifolia showed greater tolerance towards Hg and accumulated higher Hg in all parts compared with Pb.

Effect of panchakavya (organic formulation) on phytoremediation of lead and zinc using Zea mays.

Chelate-assisted phytoextraction is proposed to be an effective approach for the removal of metals from contaminated soil. Organic chelators can improve this biological technique by increasing metal solubility. The aim of this study was to investigate the possibility of improving the phytoextraction of lead (Pb) and zinc (Zn) by the application of panchakavya, a traditional Indian organic formulation. Panchakavya was prepared by fermentation process in open environment using cow dunk, cow ghee, cow urine, cow milk, cow curd, tender coconut water, crude jaggery, and mashed bananas. Soil metal fraction studies indicate that the panchakavya treatment decreased (73%) water-soluble fraction of Pb. Plant growth analysis indicated the application of panchakavya to increase Zea mays fresh root weight, shoot biomass and superoxide dismutase level in Zn contaminated soil. Similarly, a significant increase in the Zn accumulation (12% in shoots and 9% in roots) was observed in panchakavya treated plants. However, when compared to control plants, panchakavya treatment significantly decreased (32% in shoots and 37% in roots) Pb accumulation in Z.mays. Obtained results point out that panchakavya could potentially increase the phytoremediation of Zn in Z.mays.

Chelate-assisted phytoaccumulation: growth of Helianthus annuus L., Vigna radiata (L.) R. Wilczek and Pennisetum glaucum (L.) R. Br. in soil spiked with varied concentrations of copper.

Phytoextraction is an economic, environment-friendly and growing technology for clean-up of metal-contaminated soil. Several factors play pivotal role in making phytoextraction a successful technique. Soil fraction is an important parameter that may affect phytoextraction potential. There has been an increased realization on the role of chelates in accelerating metal uptake by plants. Thus, the present study examined the influence of different soil fractions, spikedmetal concentrations and chelate dosages on Cu accumulation by Helianthus annuus L. (common sunflower), Vigna radiata (L.) R. Wilczek (mung bean) and Pennisetum glaucum (L.) R. Br. (pearl millet). To mimic the mill tailings of various mined-out sites in India, five soil fractions containing different proportions of garden soil and silica were prepared (S1: 100% soil; S2: 75% soil + 25% silica; S3: 50% soil + 50% silica; S4: 25% soil + 75% silica; and S5: 100% silica) and each fraction was spiked with known Cu (100, 250, 500 and 1000mgkg-1) concentration. Upon maturity of the plant, EDTA and NTA in different dosages (0.25, 0.5, 1.0 and 2.0gkg-1) were applied to each pot. Bioconcentration factor (BCF), bioaccumulation coefficient (BAC) and translocation factor (TF) were estimated for each set. The accumulation of Cu by H. annuus, V. radiata and P. glaucum indicated direct relation between soil fractions and harvesting periods. Betterplant growth and Cu uptake were observed in pots with silica < 50% of fraction, whereas growth was arrested in pots with silica > 75%. The Cu accumulation varied significantly (p < 0.05) among the species, spiked metal concentration, chelate dosages and plant parts. Best accumulation was reported in pots with 50% soil and 50% silicaeither under 1.0gkg-1 EDTA or 2.0gkg-1 NTA. Irrespective of the combinations of various variables, the harvesting time affected Cu accumulation considerably. Among the species, H. annuus emerged out to be the most efficient for Cu translocation. Apparently, soil amendments facilitated enhanced uptake thereby playing an active role in improving theBAC and TF. Assisted phytoextraction is still a need until full-fledged alternatives are established in the market. The future of chelate-assisted phytoextraction seems to be limited to ex situ condition.

Enhancement of phytoextraction of Pb by compounded activation agent derived from fruit residue

Chelate-assisted phytoextraction is an attractive strategy to remove toxic metals from soil. However, there is lack of an effective and sustainable chelating agent. In this study, 11 kinds of fruit residue were extracted and selected to combine with N, N-bis (carboxymethyl) glutamic acid (GLDA) (0.7%) and tea saponin (4%) for the compounded activation agent (CAA), and its enhancement on Pb phytoextraction by Sedum alfredii was further evaluated by pot experiment. Among 11 fruit residue extracts, lemon residue showed the highest ability (34.7%) to extract Pb from soil. Through combining with GLDA (0.7%) and tea saponin (4%) at the optimal volume ratio of 15:2.5:2.5, the CAA removed Pb most effectively (57.1%) from soil and increased the solubility of three Pb mineral (PbS, PbCO3 and PbSO4) by 8.7–56.4 times. In pot experiment, the addition of high dosage (15 mL) CAA increased the biomass of S. alfredii by 52% and doubled the Pb accumulation. In addition, CAA-assisted phytoextraction also increased both water-soluble and acid-soluble Pb in soil, while reduced the proportion of the immobile Pb (oxidizable and residual). Generally, the compounded activation agent derived from lemon residue could be considered as-a promising enhancer for Pb phytoextraction.

Chelate-assisted phytoextraction: Growth and ecophysiological responses by Salix schwerinii E.L Wolf grown in artificially polluted soils

The present study investigated the phytoextraction ability of Salix schwerinii E.L. Wolf enhanced with an application of the chelate N10O. Salix schwerinii were grown in garden soil that was also amended with Cu (400 mg kg−1), Ni (30 mg kg−1) and Zn (200 mg kg−1). Multiple doses of N10O were applied to the treatments as follows: Cu (3.45 g and 6.9 g), Ni (1.2 g and 2.4 g), and Zn (1.45 g and 2.9 g). Furthermore, N10O doses were also repeated with the control soil. The effect of N10O on height growth, biomass production, ecophysiological attributes, and the accumulation of metals (Cu, Ni, and Zn) in Salix in polluted soils was studied. Compared to the control, the total metal concentrations in S. schwerinii growing in the soils amended with N10O increased substantially by up to 895% for Cu, 324% for Ni and 722% for Zn. The translocation factor (TF) and bioconcentration factor (BF) values for S. schwerinii increased with the application of N10O and varied from 0.30–1.01 for Cu, 0.45–1.25 for Ni, and 4.40–5.89 for Zn, whereas, BF values varied from 0.60–1.15 for Cu, 0.80–1.50 for Ni, and 4–8 for Zn. This study indicated that S. schwerinii can be used for phytoextraction of Cu, Ni and Zn from contaminated soils. However, further research is needed to examine the phytoextraction potential of other Salix species using N10O to remediate soils polluted with various toxic metals.

Chelate-assisted phytoextraction of lead using Fagopyrum esculentum: laboratory vs. field experiments

The development of more sustainable remediation techniques has been receiving greater attention, as an alternative to soil excavation plan in urban gardens. An in situ phytoextraction experiment with buckwheat (Fagopyrum esculentum) was performed with a 5 mmol kg−1 citric acid (CA) application. Joint experiments under laboratory conditions were conducted using various cultivars of F. esculentum in two soils with a Pb contamination of either geogenic or anthropogenic origin and various chelate concentrations. Results show that a minimum dose of 50 mmol kg−1 of CA is required to lower soil pH and raise the concentration of mobile Pb–CaCl2 for both soils. Consequently, Pb shoot uptake is increased from 6.3 to 8.9 times depending on soil type. Phytoextraction efficiency is found to be 1.3 to 2.0 times higher in the anthropogenic contaminated soil than in the soil with geogenic Pb. A scale effect has also been identified since Pb root accumulation under laboratory conditions was 2.4 times higher than in the field experiment. Despite an increase in the Pb extraction rate with CA, buckwheat appears to lack the efficiency needed to remove Pb in moderately contaminated soils. The calculated remediation period would last 166 years to remove the mobile Pb fraction.

Effects of [S,S]-ethylenediaminedisuccinic acid and nitrilotriacetic acid on the efficiency of Pb phytostabilization by Athyrium wardii (Hook.) grown in Pb-contaminated soils

Chelate-assisted phytoextraction with biodegradable chelants has been demonstrated as an efficient method to enhance heavy metal remediation efficiency by plants, while there is little available information on phytostabilization. A pot experiment was conducted to investigate the effects of biodegradable [S,S]-ethylenediaminedisuccinic acid (EDDS) and nitrilotriacetic acid (NTA) on plant growth and Pb accumulation of Pb phytostabilizer Athyrium wardii (Hook.) grown in Pb contaminated soils and to explore the feasibility of chelate-assisted phytostabilization. Greater adverse effects on plant biomass under high EDDS treatments were observed than NTA treatments. Significant increase of shoot Pb concentrations of A. wardii was noticed with increasing NTA and EDDS dosages, while EDDS induced higher shoot Pb concentrations than NTA. Moreover, root Pb concentrations of A. wardii under NTA treatments were 1.18–1.28-time higher than EDDS treatments, and a peak value of root Pb concentrations was observed at 2 mmol kg−1 of NTA. Shoot Pb accumulations significantly increased with increasing dosages, and EDDS treatments caused a 1.44–1.6-time increase of shoot Pb accumulation than NTA. Root Pb accumulations under NTA treatments were 1.18–1.28-time higher than EDDS treatments. Maximum root Pb accumulation (155.5 mg plant−1) was found at 2 mmol kg−1 of NTA on the 14th day. Higher BCF values and lower TF values were found under NTA treatments as compared to EDDS treatments. Available Pb concentrations in soil significantly increased on the 7th day with increasing NTA and EDDS dosages, then gradually decreased on the 14th day. Soil pH slightly decreased with increasing NTA and EDDS dosages. Therefore, chelate-assisted phytostabilization could be a feasible way to enhance the efficiency of Pb phytostabilization by A. wardii.

The Potential of Abelmoschus esculentus in EDTA-Asssisted Phytoextraction of Heavy Metals from Soil of Bashiri Dumpsite, Ado Ekiti, Nigeria

The use of fast-growing tropical plants in planning phytoextraction strategies has been documented by several researchers. The work presented here examines the effect of germination on chelate-assisted phytoextraction of heavy metals by Abelmoschus esculentus cultivated on the Bashiri dumpsite Ado Ekiti. Topsoil (0 – 15 cm) samples were randomly collected from the dumpsite, control samples were collected in similar manner at 200 m away from the dumpsite. The pH, content of organic matter, cation exchange capacity as well as heavy metals concentrations of the soil samples were determined after the soil samples were treated properly. The seedlings of Abelmoschus esculentus was cultivated in different pots (for soil with EDTA) and control pots (for soil without EDTA), these plants were subsequently nurtured maturity by daily irrigation. The plants were harvested into parts at different germination stages, after which heavy metals concentrations (Cd, Cr, Pb, Zn, Co, Cu,Fe, Mn, and Ni) were determined. The result revealed the mean pH, content of organic matter and cation exchange capacity on dumpsite of 7.50 ± 0.12, 7.8 ± 0.12%, 40.10 ± 0.11 mmol/kg, respectively. The values for pH and the organic matter were higher than those obtained from control sites. Though, heavy metals concentrations on the dumpsite were higher than control site, their values reduced considerably to maturity. Early symptoms of phytotoxicity were noticed with an application of 0.2 g/kg EDTA of soil, which only affected the biomass levels of the experimental Abelmoschus esculentus but increased the concentrations of heavy metals in the plant shoot when compared with nonchelate assisted process. However, TF, BF and RR values greater than one measure phtoextraction efficiency, an indication of the possible application Abelmoschus esculentus for phytoextraction strategies. KeywordsEffect; Chelate Assisted; Heavy Metals; Phytoextractio; Basiri Dumpsite

Improving the efficiency of phytoremediation using electrically charged plant and chelating agents.

The low efficiency of phytoremediation is a considerable problem that limits the application of this environmentally friendly method on heavy metal-polluted soils. The combination of chelate-assisted phytoextraction and electrokinetic remediation could offer new opportunities to improve the effectiveness of phytoextraction. The current experiment aims to investigate the effects of electrical fields and chelating agents on phytoremediation efficiency. In a pot experiment using mine soil, poultry manure extract (PME), cow manure extract (CME), and ethylenediaminetetraacetic acid (EDTA) were applied to soil as chelating agents (2 g kg(-1)) at the beginning of the flowering stage. A week later, Helianthus annuus (sunflower) was negatively charged by inserting a stainless steel needle with 10 and 30 V DC electricity in the lowest part of the stems for 1 h each day for a 14-day period. At the end of the experiment, the shoot and root dry weight, lead (Pb) concentration in plant organs, translocation factor (TF), metal uptake index (UI), and soil available Pb (diethylene triamine pentaacetic acid (DTPA) extractable) were detected. Results indicated that the application of electrical fields had no significant impact on the shoot and root dry weights, while Pb concentration and UI increased in the 10-V EDTA treatment by 500 % compared to control. There was no significant difference between UI in 30- and 10-V EDTA treatments. Soil available Pb significantly increased in the 30-V treated soil. A positive correlation was observed between the available Pb in soil near the root and Pb concentration in shoot, its TF, and UI. In conclusion, a negatively charged plant along with the application of EDTA significantly increased the phytoremediation efficiency.

Determining soil enzyme activities for the assessment of fungi and citric acid-assisted phytoextraction under cadmium and lead contamination.

Microorganism or chelate-assisted phytoextraction is an effective remediation tool for heavy metal polluted soil, but investigations into its impact on soil microbial activity are rarely reported. Consequently, cadmium (Cd)- and lead (Pb)-resistant fungi and citric acid (CA) were introduced to enhance phytoextraction by Solanum nigrum L. under varied Cd and Pb pollution levels in a greenhouse pot experiment. We then determined accumulation of Cd and Pb in S. nigrum and the soil enzyme activities of dehydrogenase, phosphatase, urease, catalase, sucrase, and amylase. Detrended canonical correspondence analysis (DCCA) was applied to assess the interactions between remediation strategies and soil enzyme activities. Results indicated that the addition of fungi, CA, or their combination enhanced the root biomass of S. nigrum, especially at the high-pollution level. The combined treatment of CA and fungi enhanced accumulation of Cd about 22-47 % and of Pb about 13-105 % in S. nigrum compared with the phytoextraction alone. However, S. nigrum was not shown to be a hyperaccumulator for Pb. Most enzyme activities were enhanced after remediation. The DCCA ordination graph showed increasing enzyme activity improvement by remediation in the order of phosphatase, amylase, catalase, dehydrogenase, and urease. Responses of soil enzyme activities were similar for both the addition of fungi and that of CA. In summary, results suggest that fungi and CA-assisted phytoextraction is a promising approach to restoring heavy metal polluted soil.

Comparative Chelate-assisted Phytoextraction ofHeavy Metals by Jatropha curcas, Jatropha gossypifolia and Jatropha multifida Cultivated onSoil Collected from Selected Dumpsites in Ekiti State, Nigeria

Comparative Chelate-assisted Phytoextraction ofHeavy Metals by Jatropha curcas, Jatropha gossypifolia and Jatropha multifida Cultivated onSoil Collected from Selected Dumpsites in Ekiti State, Nigeria

Effect of EDTA and DTPA on Phytoremediation of Pb-Zn Contaminated Soils by Eucalyptus camaldulensis Dehnh and Effect on Treatment Time

In this research a pot experiment was carried out to investigate the remediation ability of E. camaldulensis Dehnh in Lead-Zinc (Pb-Zn) contaminated soil. The study also investigated the effects of ethylenediaminetetraacetic acid (EDTA) and diethylenetrinitrilopentaacetic acid (DTPA) on the phytoremediation efficiency of the plant species, and harvest time as a suitable dose of chelating agents was considered. When the plants had grown for 30 days, the seedlings were harvested to determine the concentration of metals in plant tissues and soil. In general, Pb level decreased in the order of: shoot > soil > root, whilst Zn content decreased in the sequence shoot > root > soil. As a second step, contaminated soils were treated with EDTA (1.5, 3, 6, 9mmolkg -1 ) and DTPA (1.5, 3, 6, 9mmolkg -1 ). The results demonstrated that chelating agents enhance metal content in E. camaldulensis. The greatest bioconcentration factor in EDTA treatments (3.94) was observed in 9EDTA treatment followed by 6EDTA treatment (3.41). Similarly this was observed for 9DTPA (2.30) and 6DTPA (2.23) respectively. With respect to non-significant difference between 9EDTA and 6EDTA treatments and between 6DTPA and 9DTPA, low doses (6mmolkg -1 ) were used in the third step for the highest heavy metal uptake over 30, 60 and 90 days. Results reveal that the concentration of metal soil solution decreases gradually with the passage of time. The results indicate that E. camaldulensis has the potential for the phytoextraction of metal-contaminated soils but should not be used unless the biomass containing such accumulated metals is removed for disposal. Significant improvement over current chelate-assisted phytoextraction of metals may be possible but should be implemented cautiously because of the environmental risks.

Contrasting effects of pyoverdine on the phytoextraction of Cu and Cd in a calcareous soil

Enhanced metal phytoextraction by the use of siderophore-producing bacteria (SPB) has received a lot of attention in the past decade. Bacterial siderophores are able to bind a wide range of metals other than iron and thus should enhance their phytoavailability in contaminated matrices. However, the impact of bacterial siderophores in the soil–plant transfer of metals is not yet fully elucidated, as underlined by the opposing results reported in the literature regarding the efficiency of coupling phytoextraction with bioaugmentation by SPB. The present study focuses on one bacterial siderophore, the pyoverdine (Pvd), produced by Pseudomonas aeruginosa. The coordination properties of Pvd towards Cd(II) and Cu(II) were determined and the effect of Pvd supply was assessed on (i) the mobility (CaCl2 extractions), (ii) the phytoavailability (DGT measurements) and (iii) the phytoextraction of Cd and Cu, in a calcareous soil. The stability constant of Pvd-Cu (KL′Cu=1020.1) was found much higher than that of Pvd-Cd (KL′Cd=108.2). The major finding was the agreement observed between Pvd coordination properties and Pvd impact on metals phytoextraction. Pyoverdine, supplied at 250μmolkg−1 soil, enhanced the mobility, the phytoavailability and the phytoextraction of Cu while the fate of Cd was not affected. All these results were compared to those reported for chelate-assisted phytoextraction. Their relevance in using SPB for phytoremediation is discussed.

Chelate-assisted phytoextraction of cadmium from a mine soil by negatively charged sunflower

The effects of some chelating agents and electricity on cadmium phytoextraction from a mine soil were examined in pot culture of sunflower to achieve more remediation efficiency. At the beginning of the flowering stage, ethylene-diamine-tetra-acetic acid (EDTA) as a chemical chelator, cow manure extract (CME) and poultry manure extract (PME) as organic chelators were applied (2 g kg−1 soil) during irrigation. Seven days later, Helianthus annuus was negatively charged by inserting a stainless steel needle in the lowest part of the stem with 10 and 30 V direct current electricity for 1 h each day for 14 days. Afterward, concentration of cadmium in roots and shoots, cadmium translocation factor (TF), cadmium uptake index (UI) and soil available (diethylene-triamine-penta-acetic acid extractable) cadmium were measured. Results indicated that EDTA reduced roots dry weight while none of the roots and shoots was affected by other chelating agents and by electrical treatment as well. Highest concentration of cadmium in shoots was measured in 10 V-control with no significant differences with 30 V-PME and 30 V-EDTA. Utilization of chelating agents did not increase the cadmium TF and cadmium UI while highest values for cadmium TF and cadmium UI were observed in 10 and 30 V treatments, respectively. Available cadmium in the soil near root system treated with 10 and 30 V was relatively lower compared with the soil far from root system. Results of this experiment indicated that charging the plant with direct current electricity ameliorated the efficiency of cadmium phytoremediation.

Comparative study of natural phyto-extraction and induced phyto-extraction of lead using mustard plant (Brassica juncea arawali)

The objective of the present study was to assess the extraction efficiency of two different synthetic chelants [Ethelyne diamine tetraacetic acid (EDTA) and Salicylic acid (SA)] for desorbing Pb from Pb contaminated soil. Pot experiments were conducted in randomized block designing. First group of plants were treated with different Pb concentrations like 0, 100, 200, 400 and 800 mg/L. Second group of plants were treated with same Pb concentrations along with Chelant EDTA of 2.4 mM and third group of plants were also treated with same Pb concentrations along with Chelant salicylic acid (2.4 mM). EDTA and SA were applied after 6 weeks of growth i.e., at rosette stage. Different physical and biochemical parameters were studied. The concentrations of Pb in plant samples were determined by Atomic Absorption Spectrophotometer. It was found that Pb accumulation in mustard plant was significantly more enhanced by EDTA than that of SA. Chelants were found to improve Pb uptake by plants. In conclusion, chelate-assisted phytoextraction showed better results than continuous phytoextraction. B. juncea arawali is a suitable candidate for chelate-assisted phytoextraction of Pb.

Effects of Synthetic Chelators and Low-Molecular-Weight Organic Acids on Chromium, Copper, and Arsenic Uptake and Translocation in Maize (Zea mays L.)

Chelate-assisted phytoextraction is a promising technique to remediate metal-contaminated soil. Batch and greenhouse experiments were conducted to assess the effects of synthetic chelators (ethylenediaminetetraacetic acid [EDTA], ethylenediaminedisuccinic acid [EDDS], and nitrilotriacetic acid) and low-molecular-weight organic acids (oxalic and citric acids) on the solubilization of copper, chromium, and arsenic (Cu, Cr, and As, respectively) in chromated Cu arsenate (CCA)-contaminated soil and on metal uptake and translocation in maize (Zea mays L.). Chelators significantly enhanced the solubilization of Cr, Cu, and As in the soil and markedly increased their accumulation in plant tissues. Applying 5 and 10 mmol kg EDDS increased plant Cu uptake by 2.8- and 3.5-fold greater than that in control soil (without chelate applications), respectively. EDTA and citric acid were more efficient for increasing Cr uptake by plant shoots, resulting in 5.0- and 5.5-fold increases, respectively, compared with that in the control. Maximum As uptake was observed in response to a treatment of 10 mmol kg citric acid, which was 1.9-fold greater than that in control soil. However, translocation factors, phytoextraction efficiencies, and remediation factors indicated that metal uptake was not high enough for successful phytoremediation of CCA–contaminated soil. Our results suggest that EDDS and citric acid as alternatives to EDTA may facilitate phytoextraction of contaminated soil.

Phytoextraction of Pb and Cu Contaminated Soil With Maize and Microencapsulated EDTA

Chelate-assisted phytoextraction using agricultural crops has been widely investigated as a remediation technique for soils contaminated with low mobility potentially toxic elements. Here, we report the use of a controlled-release microencapsulated EDTA (Cap-EDTA) by emulsion solvent evaporation to phytoremediate soil contaminated with Pb and Cu. Incubation experiments were carried out to assess the effect of Cap- and non-microencapsulated EDTA (Ncap-EDTA) on the mobility of soil metals. Results showed EDTA effectively increased the mobility of Pb and Cu in the soil solution and Cap-EDTA application provided lower and more constant water-soluble concentrations of Pb and Cu in comparison with. Phytotoxicity may be alleviated and plant uptake of Pb and Cu may be increased after the incorporation of Cap-EDTA. In addition phytoextraction efficiencies of maize after Cap- and Ncap-EDTA application were tested in a pot experiment. Maize shoot concentrations of Pb and Cu were lower with Cap-EDTA application than with Ncap-EDTA. However, shoot dry weight was significantly higher with Cap-EDTA application. Consequently, the Pb and Cu phytoextraction potential of maize significantly increased with Cap-EDTA application compared with the control and Ncap-EDTA application.

Chelate-assisted phytoextraction of mercury in biosolids

Mercury contaminated stockpiles of biosolids (8.4 mg kg − 1 Hg) from Melbourne Water's Western Treatment Plant (MW-WTP) were investigated to evaluate the possibility of their Hg chelate-assisted phytoextraction. The effects of ammonium thiosulphate (NH 4) 2S 2O 3, cysteine (Cys), nitrilotriacetic acid (NTA), and potassium iodide (KI) were studied to mobilize Hg and to increase its uptake in plant shoots. Three plant species were selected for this study, one herbaceous and two grasses: Atriplex codonocarpa, Austrodanthonia caespitosa and Vetiveria zizanioides. KI proved to be the best candidate for Hg phytostabilization in biosolids because it facilitated the concentration of this metal mainly in roots. (NH 4) 2S 2O 3 was shown to be the most effective chelating agent among those tested for Hg phytoextraction as it allowed the highest translocation of Hg into the above-ground tissues of the selected plant species. The phytoextraction conditions using A. caespitosa as the best performing plant species were optimized at an (NH 4) 2S 2O 3 concentration of 27 mmol kg − 1 and contact time with biosolids of seven day. Monitoring of the Hg concentration in biosolids and in leachate water during a 9-day treatment revealed that the biosolids Hg concentration decreased significantly after the first day of treatment and then it decreased only slightly with time reaching a value of 5.6 mg kg − 1 Hg at the end of the 9-day period. From the corresponding results obtained for the leachate water, it was suggested that a relatively large fraction of Hg (0.7 mg kg − 1 Hg) was promptly mobilized and consequently the plants were able to take up the metal and translocate it into shoots.