Ethylenediaminedissuccinate as a new chelate for environmentally safe enhanced lead phytoextraction

Direct analysis of biodegradable chelating agents based on liquid chromatography/electrospray ionization mass spectrometry using a metal-free hydrophilic interaction liquid chromatographic column

Recently, biodegradable aminopolycarboxylic acid chelating agents have attracted attention as an alternative to environmentally persistent chelating agents such as ethylenediamine-N,N,N',N'-tetraacetic acid. However, the detection of chelating agents requires complexation with metals or derivatization by esterification reagents, and their direct detection using the currently available analytical methods still represents a challenge. Herein, we describe a direct analytical method for the biodegradable chelating agents ethylenediamine-N,N'-disuccinic acid, 3-hydroxy-2,2'-iminodisuccinic acid, methylglycine-N,N'-diacetic acid, and N,N-bis(carboxymethyl)-L-glutamic acid, via ultra-performance liquid chromatography/electrospray ionization quadrupole/time-of-flight mass spectrometry. Satisfactory retention and separation with a good peak shape were successfully achieved using a metal-free hydrophilic interaction liquid chromatographic column. The calibration curves showed good linearity in the range of 1.0-50 μM with correlation coefficients greater than 0.9988. The detection limits ranged from 0.04 to 0.12 μM. Furthermore, the developed method could be applied to the quantitative analysis of the four chelating agents in biodegradation and photodegradation experiments at the laboratory level. The proposed method, which offers the advantages of quickness, sensitivity, and requiring no complicated pretreatment steps, is expected to contribute significantly to the practical analysis of chelating agents in environmental water samples.

Effects of chelates (EDTA, EDDS, NTA) on phytoavailability of heavy metals (As, Cd, Cu, Pb, Zn) using ryegrass (Lolium multiflorum Lam.)

This paper summarises a study of the application of the synthetic chelate ethylenediaminetetraacetic acid (EDTA), and the natural chelates ethylenediamine-N,N'-disuccinic acid (EDDS) and nitrilotriacetate (NTA) to enhance ryegrass (Lolium multiflorum Lam.) uptake of the heavy metal(oid)s (HMs) (As, Cd, Cu, Pb and Zn) from contaminated soils in mining sites. The study compares the effects of these chelates (EDTA, EDDS and NTA) on the phytoavailability of HMs (As, Cd, Cu, Pb, Zn) using ryegrass (Lolium multiflorum Lam.) through the single addition and sequential addition methods. The results show that application of EDTA, EDDS and NTA significantly increases ryegrass (Lolium multiflorum Lam.)'s shoot uptake of some HMs when compared with no EDTA, EDDS or NTA application, particularly through sequential chelate treatment (EDTA 0.5:1+0.5:1; NTA 0.5:1+0.5:1; EDDS 0.5:1+0.5:1). EDTA 0.5:1+0.5:1 was more effective at increasing the concentration of Pb in shoots than were the other chelates (EDDS and NTA) and controls. Moreover, the concentrations of Zn in the shoots of ryegrass (Lolium multiflorum Lam.) in Hich Village significantly increased with the application of split dose (0.5:1+0.5:1). The plants displayed symptoms of toxicity including yellow and necrotic leaves at the end of the experiment. The selected chelates (EDTA, EDDS and NTA) led to a significant decrease in plant biomass (yield) 28 days after transfer with a maximum decrease in EDTA treatment (0.5:1+0.5:1) soils. This decrease was 3.43-fold in Ha Thuong, 3-fold in Hich Village and 1.59-fold in Trai Cau, respectively, relative to the control. HM concentration and dissolved organic carbon (DOC) in pore water provided an explanation for why fresh weight was significantly reduced with application of chelates in sequential dose (EDTA 0.5:1+0.5:1 and NTA 0.5:1+0.5:1).

Phytoremediation of nitrate contamination using two halophytic species, Portulaca oleracea and Salicornia europaea

Nitrate is a common form of nitrogen fertilizer, and its excess application combined with easy leaching from agricultural fields causes water and soil contamination, hazards on human health, and eutrophication of aquatic ecosystems. Compared to other pollutants, the application of phytoremediation technology for nitrate-contaminated sites has received less attention. Nitrophilous halophyte species are suitable candidates for this purpose particularly by application of additional treatments for assisting nitrate accumulation. In this work, two annual halophyte species, Portulaca oleracea and Salicornia europaea were studied for their phytoremediation capacity of nitrate-contaminated water and soils. Plants were treated with three nitrate levels (2, 14, and 50 mM) combined with either selenium (10 µM as Na₂SeO₄) or salt (100 mM NaCl) in the hydroponics and sand culture medium, respectively. A fast growth and production of higher biomass enables P. oleracea for higher nitrate removal compared with S. europaea in both experiments. In S. europaea, both selenium and salt treatments enhanced nitrate removal competence through increasing the biomass and nitrate uptake or assimilation capacity. Salt treatment, however, reduced these parameters in P. oleracea. Based on data, selenium-assisted phytoremediation of nitrate contamination is a feasible strategy for both species and S. europaea is better suited to nitrate-contaminated saline water and soils. Nitrate accumulation in both species, however, exceeds that of the permitted nitrate level in the forage crops suggesting that the phytoremediation byproducts could not be consumed and other management strategies should be applied to the residual biomass.

Exploring a library of water-soluble polymers as abiotic phytoremediation agents for treating (Pseudo)metal ion-contaminated soil

Herein, we investigate the effect of eleven water-soluble polymers on the growth of Sedum alfredii and its uptake of As, Cd, or Pb in polluted soil in a pot experiment. The polymers selected are generally non-toxic, metal-chelating, and hygroscopic. They also range from acidic (carboxylate-containing polymers) to neutral (e.g. polyacrylamide, polyvinyl alcohol) and to basic (polyethylene imine). It has been found that sodium alginate exhibits a significant growth-promoting effect (as much as ∼8-fold) as determined by plant total dry weight, while all other tested polymers exert either minor growth promotion or a negative effect. To examine the absorption of heavy (pseudo)metals, the pollutant content in above- and below-ground portions of the plant were separately studied by inductively coupled plasma mass spectrometry. Among the tested polymers, sodium alginate emerges as the strongest absorption accelerator for all three metal pollutants in the above-ground part of the plant (∼3-4-fold increase over blank), mainly due to promotion of plant growth. On the other hand, polyethylene imine is the most potent inhibitor of metal absorption (10%-51% of blank) due to a combination of plant growth inhibition and absorption deactivation. Polymers with such effects may be used to reduce the contamination of (pseudo)metals in crops.

Soil washing with biodegradable chelating agents and EDTA: Effect on soil properties and plant growth

Soils contaminated with Pb, Zn and Cd are hazardous. Persistent EDTA and biodegradable GLDA, EDDS and IDS have been used as chelators in the ReSoil soil washing technology, which recycles chelator and curbs toxic emissions. The washed soils supported similar growth of buckwheat (F. esculentum) and better growth of Chinese cabbage (B. rapa) compared with the original (not-remediated) soil. The growth of buckwheat on EDDS-washed soil was an exception and was 67% suppressed. The activities of enzymes of the plant antioxidant preventive system were assessed in roots and leaves of Chinese cabbage on all soils. Similar activities were measured, confirming that washed soils are not harmful to the plants. Plant uptake of potentially toxic elements was reduced from all washed soils, i.e. buckwheat grown on GLDA-washed soils accumulated up to 27 and 83 times less Pb and Cd than in the original soil. The initial Pb emissions in leachate from GLDA and IDS washed soils were up to 89 and 92% higher than those of the original soil, respectively. The latter emissions ceased to the levels measured in original, EDTA and EDDS washed soils. Soil physical properties (water holding capacity, aggregate stability) and soil functionality, assessed as soil respiration and activity of enzymes indicative for soil C, N and P cycle, were similar in all soils after 10 weeks of plant growth experiment. The overall results indicate a low impact of the remediation on soil quality. Soils washed with EDTA performed slightly better compared to GLDA-, EDDS- and IDS-washed soils.

Effect of biodegradable chelators on induced phytoextraction of uranium- and cadmium- contaminated soil by Zebrina pendula Schnizl

This study investigated the effect of ethylenediamine-N,N'-disuccinic acid (EDDS), oxalic acid (OA), and citric acid (CA) on phytoextraction of U- and Cd-contaminated soil by Z. pendula. In this study, the biomass of tested plant inhibited significantly following treatment with the high concentration (7.5 mmol·kg-1) EDDS treatment. Maximum U and Cd concentration in the single plant was observed with the 5 mmol·kg-1 CA and 7.5 mmol·kg-1 EDDS treatment, respectively, whereas OA treatments had the lowest U and Cd uptake. The translocation factors of U and Cd reached the maximum in the 5 mmol·kg-1 EDDS. The maximum bioaccumulation of U and Cd in the single plants was 1032.14 µg and 816.87 µg following treatment with 5 mmol·kg-1 CA treatment, which was 6.60- and 1.72-fold of the control groups, respectively. Furthermore, the resultant rank order for available U and Cd content in the soil was CA > EDDS > OA (U) and EDDS > CA > OA (Cd). These results suggested that CA could greater improve the capacity of phytoextraction using Z. pendula in U- and Cd- contaminated soils.

Assessment of EDDS and vermicompost for the phytoextraction of Cd and Pb by sunflower (Helianthus annuus L.)

The effects of Ethylenediamine disuccinic acid (EDDS) (0 and 5 mmol·kg^-1) as a synthetic chemical amendment, vermicompost (0 and 5%w/w) as an organic amendment and their combined application were evaluated for the phytoextraction by sunflower (Helianthus annuus L.) of cadmium (Cd) and lead (Pb) at three artificial contamination levels in soils (0, 50, and 100 mg·kg^-1 for Cd and 0, 100, and 200 mg·kg^-1 for Pb). The results showed that the application of EDDS was the most effective method to increase Pb and Cd concentrations in both parts of the plant. The results also showed that the application of EDDS increased 9.27% shoot Pb content at 200 mg·kg^-1 but decreased 15.95% shoot Cd content at 100 mg·kg^-1 contamination level with respect to the respective controls. The bioavailable concentrations of Cd at 100 mg·kg^-1 and Pb at 200 mg·kg^-1 contamination level in the soil at the end of experiment increased 25% and 26%, respectively after the application of EDDS but vermicompost decreased 43.28% the bioavailable Pb concentration relative to their controls. Vermicompost increased the remediation factor index of Cd, thus making it the best treatment for the phytoextraction of Cd. The combined application of EDDS and vermicompost was the best amendment for Pb phytoextraction.

Screening of plant growth promoting traits in heavy metals resistant bacteria: Prospects in phytoremediation

Phytoremediation is considered as a novel environmental friendly technology, which uses plants to remove or immobilize heavy metals. The use of metal-resistant plant growth-promoting bacteria (PGPB) constitutes an important technology for enhancing biomass production as well as tolerance of the plants to heavy metals. In this study, we isolated twenty seven (NF1-NF27) chromium resistant bacteria. The bacteria were tested for heavy metals (Cr, Zn, Cu, Ni, Pb and Co) resistance, Cr(VI) reduction and PGPB characters (phosphate solubilization, production of IAA and siderophores). The results showed that the bacterial isolates resist to heavy metals and reduce Cr(VI), with varying capabilities. 37.14% of the isolates have the capacity of solubilizing phosphate, 28.57% are able to produce siderophores and all isolates have the ability to produce IAA. Isolate NF2 that showed high heavy metal resistance and plant growth promotion characteristics was identified by 16S rDNA sequence analysis as a strain of Cellulosimicrobium sp.. Pot culture experiments conducted under greenhouse conditions showed that this strain was able to promote plant growth of alfalfa in control and in heavy metals (Cr, Zn and Cu) spiked soils and increased metal uptake by the plants. Thus, the potential of Cellulosimicrobium sp. for both bioremediation and plant growth promotion has significance in the management of environmental pollution.

Improvement of the phytoremediation efficiency of Neyraudia reynaudiana for lead-zinc mine-contaminated soil under the interactive effect of earthworms and EDTA

Slow plant growth, low biomass, and low bioavailability of heavy metals in soil are important factors that limit remediation efficiencies. This study adopted a pot cultivation method to evaluate the phytoremediation efficiency of Neyraudia reynaudiana, planted in contaminated soil from a lead-zinc mining area. The soil was inoculated with earthworms (Eisenia fetida), and mixed with the chelating agent ethylenediaminetetraacetic acid (EDTA) one month after planting. The addition of earthworms significantly increased the aboveground biomass of N. reynaudiana and activated heavy metals in the soil, thus facilitating heavy metal uptake by N. reynaudiana. The addition of EDTA significantly increased the incorporation and transport of heavy metals, reduced the uptake of heavy metals by the plant cell wall, and increased the proportions of cellular soluble constituents. Especially with regard to lead, inoculation with earthworms and EDTA application significantly promoted the accumulation efficiency of N. reynaudiana, increasing it 7.1-16.9-fold compared to the control treatment without earthworms and EDTA, and 1.5-2.3-fold compared to a treatment that only used EDTA.

Effect of two biodegradable chelates on metals uptake, translocation and biochemical changes of Lantana Camara growing in fly ash amended soil

The present work had two purposes firstly to evaluate the potential of Lantana Camara for phytoextraction of heavy metals from fly ash amended soil and to assess the suitability of a proper biodegradable chelating agent for chelate assisted phytoextraction. Plants were grown in manure mixed soil amended with various concentration of fly ash. Two biodegradable chelating agents were added (EDDS and MGDA) in the same dose separately before maturation stage. Sampling was done at different growing stages. The plant took up metal in different plant parts in the following order: for Cu, and Zn leaf >root >stem, for Cr and Mn leaf>stem >root, for Ni root >leaf>stem and for Pb root≈leaf>stem respectively. For Cu, Zn, Cr and Mn Lantana camara acted as phytoextractor. Translocation factor and bioaccumulation coefficient was>1 signifying enrichment and translocation of metals in the plant. Morphological studies showed no toxicity symptom in the plant. Among biochemical parameters protein and nitrate reductase activity decreased, whereas, chlorophyll and peroxidise activity increased with the growth stages. Finally, it was evident from the results that Lantana Camara can be used as efficient phytoextractor of metals, with proper harvesting cycle and both chelate were proved as effective chelators for phytoextraction of metals.

Differential mobilization and metal uptake versus leaching in multimetal soil columns using EDTA and three metal bioaccumulators

Tannery waste is a major environmental concern that needs proper management. Tannery solid waste (TSW) can be added to the soil as an organic amendment but needs metal removal. Chelant-assisted phytoremediation hastens the process of metal removal but also poses risk of leaching at the same time. This research evaluates Ethylenediaminetetraacetic acid (EDTA)-assisted phytoextraction and associated leaching hazard using metal-tolerant plants. Greenhouse trials were carried out with sunflower, spinach, and marigold using columns of uniform diameter packed with field soil and multimetal contamination of TSW (5% and 10%) with four EDTA doses. The amounts of metal absorbed or leached conformed to amounts in the soil amendment and the dose of EDTA. The mobilization of metals by EDTA was however metal-specific. The metals that were extracted in greater amounts by the plants were leached less compared to Cr and Cu. A significant amount of other metals was leached down and thus less amount was phytoextracted by the plants e.g. Cd and Ni. A high correlation was observed between the amount of metal absorbed by the plant and the amount in leachate except for Cr in all the plants. Antioxidant activities like SOD and catalase were also found to be high in sunflower and spinach.

Leaching variations of heavy metals in chelator-assisted phytoextraction by Zea mays L. exposed to acid rainfall

Chelant-enhanced phytoextraction method has been put forward as an effective soil remediation method, whereas the heavy metal leaching could not be ignored. In this study, a cropping-leaching experiment, using soil columns, was applied to study the metal leaching variations during assisted phytoextraction of Cd- and Pb-polluted soils, using seedlings of Zea mays, applying three different chelators (EDTA, EDDS, and rhamnolipid), and artificial rainfall (acid rainfall or normal rainfall). It showed that artificial rainfall, especially artificial acid rain, after chelator application led to the increase of heavy metals in the leaching solution. EDTA increased both Cd and Pb concentrations in the leaching solution, obviously, whereas EDDS and rhamnolipid increased Cd concentration but not Pb. The amount of Cd and Pb decreased as the leaching solution increased, the patterns as well matched LRMs (linear regression models), with R-square (R ²) higher than 90 and 82% for Cd and Pb, respectively. The maximum cumulative Cd and Pb in the leaching solutions were 18.44 and 16.68%, respectively, which was amended by EDTA and acid rainwater (pH 4.5), and followed by EDDS (pH 4.5), EDDS (pH 6.5), rhamnolipid (0.5 g kg^-1 soil, pH 4.5), and rhamnolipid (pH 6.5).

EDTA and hydrochloric acid effects on mercury accumulation by Lupinus albus

The efficiency of white lupine (Lupinus albus) to uptake and accumulate mercury from a soil polluted by mining activities was assessed in a pot experiment with chemically assisted phytoextraction. The mobilizing agents tested were ethylenediaminetetracetic acid (EDTA) and hydrochloric acid (HCl). Two doses of each amendment were used (0.5 and 1.0 g of amendment per kg of soil), and unamended pots were used as a control. Addition of HCl to the soil did not negatively affect plant biomass, while the use of EDTA led to a significant decrease in plant growth when compared to that found for non-treated pots, with plants visually showing symptoms of toxicity. The addition of hydrochloric acid increased root, shoot and total plant Hg uptake of white lupine by 3.7 times, 3.1 times and 3.5 times, respectively, in relation to non-amended plants. The greatest efficiency was obtained for the highest HCl dose. EDTA led to higher concentrations of total plant Hg than that found with the control, but, due to the aforementioned decrease in plant biomass, the Hg phytoextraction yield was not significantly increased. These results were attributed to the capability of both amendments to form stable Hg complexes. The concentration of Hg in the water of the soil pores after the phytoextraction experiment was very low for all treatments, showing that risks derived from metal leaching could be partially avoided by using doses and chemicals suitable to the concentration of metal in the soil and plant performance.

Effects of heavy metals and chelants on phytoremediation capacity and on rhizobacterial communities of maize

Heavy metals (HMs) are one of the major ecological problem related to human activities. Phytoremediation is a promising "green technology" for soil and water reclamation, and it can be improved by means of the use of chelants. In the past particular attention was paid on the effects of HMs and/or chelants on plant health, but much less on their effects on rhizosphere communities. To shed light on the interaction among plant-HM-chelant-rhizobacterial community a pot experiment was set up. Maize plants were grown on uncontaminated, multi-metal (copper and zinc) contaminated and chelants artificially amended soils. A high concentration of HMs was detected in the different maize organs; chelants improved the accumulation capacity of the maize plants. The rhizosphere bacterial community isolated from control plants showed the largest biodiversity in terms of bacterial genera. However, the addition of HMs reduced the number of taxa to three: Bacillus, Lysinibacillus and Pseudomonas. The effects of HM treatment were counteracted by the addition of chelants in terms of the genetic biodiversity. Furthermore, several bacterial strains particularly resistant to HMs and chelants were isolated and selected. Our study suggests that the combined use of resistant bacteria and chelants could improve the phytoremediation capacity of maize.

Combining Nitrilotriacetic Acid and Permeable Barriers for Enhanced Phytoextraction of Heavy Metals from Municipal Solid Waste Compost by and Reduced Metal Leaching

Phytoextraction has the potential to remove heavy metals from contaminated soil, and chelants can be used to improve the capabilities of phytoextraction. However, environmentally persistent chelants can cause metal leaching and groundwater pollution. A column experiment was conducted to evaluate the viability of biodegradable nitrilotriacetic acid (NTA) to increase the uptake of heavy metals (Cd, Cr, Ni, Pb, Cu, and Zn) by L. in municipal solid waste (MSW) compost and to evaluate the effect of two permeable barrier materials, bone meal and crab shell, on metal leaching. The application of NTA significantly increased the concentrations and uptake of heavy metals in . The enhancement was more pronounced at higher dosages of NTA. In the 15 mmol kg NTA treatment using a crab shell barrier, the Cr and Ni concentrations in the plant shoots increased by approximately 8- and 10-fold, respectively, relative to the control. However, the addition of NTA also caused significant heavy metal leaching from the MSW compost. Bone meal and crab shell barriers positioned between the compost and the subsoil were effective in preventing metal leaching down through the soil profile by the retention of metals in the barrier. The application of a biodegradable chelant and the use of permeable barriers is a viable form of enhanced phytoextraction to increase the removal of metals and to reduce possible leaching.

Simultaneous enhanced removal of Cu, PCBs, and PBDEs by corn from e-waste-contaminated soil using the biodegradable chelant EDDS

We evaluated the influence of the biodegradable chelant ethylenediamine disuccinic acid (EDDS) on plant uptake of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and Cu by corn from electronic waste (e-waste)-contaminated soil. The highest concentration and highest total uptake of Cu in corn were observed in the treatment with 5 mM EDDS, which resulted in a 4-fold increase of the Cu translocation factor (C(shoot)/C(root)) compared to the control. The concentrations of PCBs and PBDEs in shoots and roots increased with increasing application rates of EDDS, and 1.58- and 1.32-fold average increases in the concentrations of PCBs and PBDEs, respectively, were observed in shoots in the EDDS treatments. A significant positive correlation was observed between shoot Cu and shoot PCBs and PBDEs. We speculate that PCBs and PBDEs were activated by the EDDS-triggered dissolved organic carbon (DOC) and then indiscriminately taken up by roots and translocated to shoots following damage to the roots mainly by the increased extractable Cu resulting from the EDDS application.

Assessment of amendments for the immobilization of Cu in soils containing EDDS leachates

In this study, the effectiveness of six soil amendments (ferrihydrite, manganese dioxide, gibbsite, calcium carbonate, biochar, and organic fertilizer) was investigated to assess the feasibility of minimizing possible environmental contaminant leaching during S,S-ethylenediaminedisuccinic acid (EDDS)-enhanced phytoextraction process based on 0.01-M CaCl2 extraction. Results showed that the application of EDDS could significantly increase Cu concentrations in the leaching solution. Compared with control, incorporation of six amendments (excluding organic fertilizer) significantly decreased CaCl2-extractable Cu concentrations in both soils. When EDDS-containing solutions leached from the soil columns (mimicking the upper soil layers) were added to soils with different amendments (mimicking the subsoil), CaCl2-extractable Cu in the soils amended with ferrihydrite, manganese dioxide, gibbsite, and calcium carbonate was significantly lower than that in the control soil (no amendments) and remained relatively constant during the first 14 days. Incorporation of biochar or organic fertilizer had no positive effect on the immobilization of Cu in EDDS leachates in soils. After 14 days, CaCl2-extractable Cu concentration decreased rapidly in soils incorporated with various amendments. Integrating soil washing with biodegradable chelating agents or chelant-enhanced phytoextraction and immobilization of heavy metals in subsoil could be used to rapidly reduce the concentration of bioavailable metal fractions in the upper soil layers and minimize environmental risks of secondary pollution.

Effects of EDDS and plant-growth-promoting bacteria on plant uptake of trace metals and PCBs from e-waste-contaminated soil

The present study investigated the effects of the biodegradable chelant S,S-ethylenediaminedisuccinic acid (EDDS) and the plant-growth-promoting bacterium DGS6 on pollutant uptake by corn from e-waste-contaminated soils. The highest concentration and total uptake of Cu and Zn in corn shoots were observed in the presence of EDDS and DGS6+EDDS, respectively. The ΣPCB concentrations in shoots ranged from 0.53 to 0.72 ng g(-1), and the highest PCB concentration was observed in the presence of EDDS. This could be ascribed to the enhanced dissolved organic carbon, increased dissolution and efficient translocation of PCBs from roots to shoots, as well as potential root damage due to increased soluble metal levels in soil solution. In contrast, the highest total uptake of PCBs in shoots was observed in the presence of DGS6, likely due to enhanced shoot biomass and high levels of air deposition.

Changes in the spectral pattern of selenium accumulation in Coleus blumei and the effects of chelation

Chemically enhanced phytoremediation has been proposed as an effective approach to remove heavy metals from contaminated soil through the use of high biomass production plants. This study investigated changes in the spectral pattern of selenium (Se) accumulation in Coleus blumei Benth. (coleus) plants grown in hydroponics with 1.0 mg/l sodium selenite (Na2SeO3) and the effects of (S,S)-ethylenediamine disuccinic acid (EDDS) thereon through X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS) and Fourier transform infrared (FTIR) spectroscopy analyses. When EDDS concentrations were in the range of 0-1.0 mmol/l, Se content increased significantly; however, at EDDS concentrations above this range, the symptoms of Se toxicity were alleviated in coleus leaves. Application of EDDS over 1.0 mmol/l significantly decreased total Se uptake in the leaves and roots of the plants. The powder diffraction patterns of the roots and leaves displayed sharp crystalline peaks, which were characteristic of an organic molecule with crystallinity. Our results revealed the presence of high amounts of C, O, Mg, Al, Si, K and Ca in the roots and leaves under Se-induced stress with different concentrations of EDDS. There were no changes in the chemical compositions of the roots and leaves, but the contents were influenced by Se-induced stress and EDDS treatment. This study demonstrated the importance of applying XRD, EDXS and FTIR methods toward a more comprehensive understanding of the mechanisms of EDDS-induced Se accumulation in plants.

Metal partitioning in plant-substrate-water compartments under EDDS-assisted phytoextraction of pyrite waste with Brassica carinata A. Braun

Soil amendment with chelating agents can increase metal uptake and translocation in biomass species through increased metal bioavailability together with possible increases in metal leaching. In this study, we assessed the efficiency and environmental risk of the fast-degradable [S,S]-EDDS. Cu, Pb and Zn uptake in pot-cultivated Brassica carinata A. Braun, residual substrate metal bioavailability and leaching were investigated after one cycle of EDDS-assisted phytoextraction in mixed metal-contaminated pyrite waste, which is characterised by high Fe content. The chelator was supplied at doses of 2.5 and 5 mmol EDDS kg(-1) waste 1 week before harvest and 1 mmol EDDS kg(-1) waste repeated five times at 5- and 10-day intervals during the growing cycle. Here we demonstrate that EDDS generally increases shoot metal concentrations-especially of Cu-but only seldom improves removals because of markedly impaired growth. Considerable phytotoxicity and Cu leaching occurred under repeated EDDS treatments, although environmental risks may also arise from the single, close-to-harvest applications as Cu bioavailability in waste at plant harvest still remained very high (up to +67 % at 5 mmol EDDS kg(-1) vs. untreated controls). The residual bioavailability of Zn and Pb was instead generally reduced, perhaps due to shifts in cation exchange, whereas Fe mobility was not apparently affected. The amount of metals removed by plants represented a small fraction of the bioavailable pool (<1 %), and mobilised metals quickly reached deep layers in the substrate. We conclude that EDDS assistance can provide only some limited opportunities for improving phytoremediation of pyrite waste, major benefits being achieved by low doses to be traditionally applied shortly before harvest, with due attention to limiting groundwater pollution.

Removal of heavy metal species from industrial sludge with the aid of biodegradable iminodisuccinic acid as the chelating ligand

High level of heavy metals in industrial sludge was the obstacle of sludge disposal and resource recycling. In this study, iminodisuccinic acid (IDS), a biodegradable chelating ligand, was used to remove heavy metals from industrial sludge generated from battery industry. The extraction of cadmium, copper, nickel, and zinc from battery sludge with aqueous solution of IDS was studied under various conditions. It was found that removal efficiency greatly depends on pH, chelating agent's concentration, as well as species distribution of metals. The results showed that mildly acidic and neutral systems were not beneficial to remove cadmium. About 68 % of cadmium in the sample was extracted at the molar ratio of IDS to heavy metals 7:1 without pH adjustment (pH 11.5). Copper of 91.3 % and nickel of 90.7 % could be removed by IDS (molar ratio, IDS: metals = 1:1) with 1.2 % phosphoric acid effectively. Removal efficiency of zinc was very low throughout the experiment. Based on the experimental results, IDS could be a potentially useful chelant for heavy metal removal from battery industry sludge.

Chelant-enhanced heavy metal uptake by Eucalyptus trees under controlled deficit irrigation

We tested the hypothesis that controlled deficit irrigation (CDI) of the fast growing, salinity resistant Eucalyptus camaldulensis tree with timely EDTA application can enhance sediment clean-up while minimizing leaching of metal complexes. 220-L lysimeters containing a sand-metal-polluted sludge mixture. Established saplings were irrigated with tap or desalinized (RO) water with/without 4-times daily addition of EDTA, EDDS and citric acid. In the 2nd season (2008/9) the chelates were added at 2 mM for ≈ 70 summer days. Diagnostic leaves and soil solution compositions were regularly monitored, the latter by applying prescribed leaching at an overall leaching percentage of ≈ 0.4%. While the three chelants solubilized sludge metals in batch extraction, EDDS often being the more efficient chelant, EDTA only was effective in the soil system. Leachate and leaves peak average concentrations in EDTA treatment vs. the control treatments were: Cd: 200 mg L(-1) vs. 1.0 and 67 vs. 21 mg kg(-1); Cu: 90 vs. 1.5 mg L(-1) and 17 vs. 3.0 mg kg(-1); Ni: 60 mg L(-1) vs. 14 and 20 vs. 6.0 mg kg(-1); Pb: >44 vs. 0.1 mg L(-1) and 9.0 vs. 1.0 mg kg(-1); and Zn: 650 vs. 4.0 mg L(-1) and 200 vs. 70 mg kg(-1), all respectively. Peak average leachate EDTA concentration was >60 mM, yet acclimating soil microflora gradually degraded most all the EDTA. In incubation study, EDDS and EDTA half-lives in acclimated lysimeter media were 5-11 days and ≥ 27 days, respectively. It suggests that sustainable phytoextraction of heavy metals is feasible under careful CDI with EDTA (yet not with biodegradable chelants) augmentation at low doses. Despite that the eucalypt was highly salinity (and EDTA) resistant, CDI using RO water further reduces soil solution salinity, thus increasing the usefulness of this remediation technique.

Remediation of heavy metal(loid)s contaminated soils--to mobilize or to immobilize?

Unlike organic contaminants, metal(loid)s do not undergo microbial or chemical degradation and persist for a long time after their introduction. Bioavailability of metal(loid)s plays a vital role in the remediation of contaminated soils. In this review, the remediation of heavy metal(loid) contaminated soils through manipulating their bioavailability using a range of soil amendments will be presented. Mobilizing amendments such as chelating and desorbing agents increase the bioavailability and mobility of metal(loid)s. Immobilizing amendments such of precipitating agents and sorbent materials decrease the bioavailabilty and mobility of metal(loid)s. Mobilizing agents can be used to enhance the removal of heavy metal(loid)s though plant uptake and soil washing. Immobilizing agents can be used to reduce the transfer to metal(loid)s to food chain via plant uptake and leaching to groundwater. One of the major limitations of mobilizing technique is susceptibility to leaching of the mobilized heavy metal(loid)s in the absence of active plant uptake. Similarly, in the case of the immobilization technique the long-term stability of the immobilized heavy metal(loid)s needs to be monitored.

Pollution due to hazardous glass waste

Pollution resulting from hazardous glass (HG) is widespread across the globe, both in terms of quantity and associated health risks. In waste cathode ray tube (CRT) and fluorescent lamp glass, mercury and lead are present as the major pollutants. The current review discusses the issues related to quantity and associated risk from the pollutant present in HG and proposes the chemical, biological, thermal, hybrid, and nanotechniques for its management. The hybrid is one of the upcoming research models involving the compatible combination of two or more techniques for better and efficient remediation. Thermal mercury desorption starts at 100 °C but for efficient removal, the temperature should be >460 °C. Involvement of solar energy for this purpose makes the research more viable and ecofriendly. Nanoparticles such as Fe, Se, Cu, Ni, Zn, Ag, and WS2 alone or with its formulation can immobilize heavy metals present in HG by involving a redox mechanism. Straight-line equation from year-wise sale can provide future sale data in comparison with lifespan which gives future pollutant approximation. Waste compact fluorescent lamps units projected for the year 2015 is 9,300,000,000 units and can emit nearly 9,300 kg of mercury. On the other hand, CRT monitors have been continuously replaced by more improved versions like liquid crystal display and plasma display panel resulting in the production of more waste. Worldwide CRT production was 83,300,000 units in 2002 and can approximately release 83,000 metric tons of lead.

Effect of compost and biodegradable chelate addition on phytoextraction of copper by Oenothera picensis grown in Cu-contaminated acid soils

Oenothera picensis plants (Fragrant Evening Primrose) grow in the acid soils contaminated by Cu smelting in the coastal region of central Chile. We evaluated the effects of compost, at application rate of 5 kg m(-2), and biodegradable chelate MGDA (methylglycinediacetic acid), at application rate of 6 mmol plant(-1), on Cu phytoextraction by O. picensis, in field plots. No significant differences were found between treatments regarding aboveground biomass, shoot Cu concentrations and Cu phytoextraction of O. picensis. This lack of effects of the treatments was provoked by the large variability of soil properties, prior to applying of the treatments. The shoot Cu concentration in O. picensis positively and significantly correlated to exchangeable Cu concentration in the soil. Likewise, the aboveground biomass of O. picensis positively and significantly correlated to soil organic matter content. The Cu phytoextraction by O. picensis, in turn, positively and significantly correlated to both variables, i.e. exchangeable Cu concentration and organic matter content. The average Cu phytoextraction was 1.1 mg plant(-1), which is equivalent to 90 g ha(-1) at planting rate of 8 plants m(-2). In the chelate treatment, Cu phytoextraction was 2.6±2.1 mg plant(-1), which is equivalent to 212±171 g ha(-1) at planting rate of 8 plants m(-2).

Uptake and distribution of cd in sweet maize grown on contaminated soils: a field-scale study

Maize is an economic crop that is also a candidate for use in phytoremediation in low-to-moderately Cd-contaminated soils, because the plant can accumulate high concentration of Cd in parts that are nonedible to humans while accumulating only a low concentration of Cd in the fruit. Maize cultivars CT38 and HZ were planted in field soils contaminated with Cd and nitrilotriacetic acid (NTA) was used to enhance the phytoextractive effect of the maize. Different organs of the plant were analyzed to identify the Cd sinks in the maize. A distinction was made between leaf sheath tissue and leaf lamina tissue. Cd concentrations decreased in the tissues in the following order: sheath > root > lamina > stem > fruit. The addition of NTA increased the amount of Cd absorbed but left the relative distribution of the metal among the plant organs essentially unchanged. The Cd in the fruit of maize was below the Chinese government's permitted concentration in coarse cereals. Therefore, this study shows that it is possible to conduct maize phytoremediation of Cd-contaminated soil while, at the same time, harvesting a crop, for subsequent consumption.

Uptake and distribution of cd in sweet maize grown on contaminated soils: a field-scale study

Maize is an economic crop that is also a candidate for use in phytoremediation in low-to-moderately Cd-contaminated soils, because the plant can accumulate high concentration of Cd in parts that are nonedible to humans while accumulating only a low concentration of Cd in the fruit. Maize cultivars CT38 and HZ were planted in field soils contaminated with Cd and nitrilotriacetic acid (NTA) was used to enhance the phytoextractive effect of the maize. Different organs of the plant were analyzed to identify the Cd sinks in the maize. A distinction was made between leaf sheath tissue and leaf lamina tissue. Cd concentrations decreased in the tissues in the following order: sheath > root > lamina > stem > fruit. The addition of NTA increased the amount of Cd absorbed but left the relative distribution of the metal among the plant organs essentially unchanged. The Cd in the fruit of maize was below the Chinese government's permitted concentration in coarse cereals. Therefore, this study shows that it is possible to conduct maize phytoremediation of Cd-contaminated soil while, at the same time, harvesting a crop, for subsequent consumption.

Influence of the application of chelant EDDS on soil enzymatic activity and microbial community structure

The present study evaluated the effects of a biodegradable chelant, S,S-ethylenediaminedisuccinic acid (EDDS), on enzyme activities and microbial community composition in copper (Cu)-contaminated soils, planted with either corn or beans. Results showed that the application of EDDS did not affect urease and acid phosphatase activities in the soil, but greatly reduced catalase and saccharase activities, and increased β-glucosidase activity on the seventh day after EDDS application. On the 28th day, no significant difference was observed in the enzyme activities (except for β-glucosidase) of EDDS-treated soils compared to the controls. Analysis of phospholipid fatty acids (PLFAs) showed that the application of 3 mmol kg(-1) EDDS did not cause significant stress to soil microbial communities. However, PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprint revealed that EDDS influenced the bacterial communities in the soils, and the effects on bean soils were more significant than that with corn. In general, the enzyme activities and bacterial communities were influenced by the application of EDDS, but the impact became weaker or even disappeared with the biodegradation of EDDS.

Influence of chelation on Cu distribution and barriers to translocation in lolium perenne

Strong chelating agents are reported to enhance Cu translocation in plants; however, the mechanisms responsible have not yet been fully established. In this study, both ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid (DTPA) were found to increase Cu translocation to shoot tissue, while citric acid did not. Although all three amendments decreased Cu sorption to roots, which should cause greater Cu mobility within plants, this did not correspond with translocation. Energy-dispersive X-ray analysis of root cell walls showed that the endodermis presented a barrier (albeit partial) to the movement of free Cu ions, but this effect was negated by amendment addition. With EDTA, Cu levels in the stele were higher than those in the cortex after 1 week of exposure. Using Si deposition as an indicator, the presence of free Cu increased endodermal development, while amendments prevented this effect. Confocal microscopy and lipid peroxidation observations show that Cu and citric acid increased membrane damage, while EDTA and DTPA had transient effects. Strong chelating agents are less damaging alone than when present in conjunction with elevated Cu levels. Chelating amendments are proposed to enhance Cu phytoextraction by facilitating transport across the endodermis, ostensibly by influencing both membrane integrity and endodermal development.

Factors affecting chelating extraction of Cr, Cu, and As from CCA-treated wood

The disposal of chromated copper arsenate (CCA)-treated waste wood is becoming a serious problem in many countries due to potential leaching of hazardous elements from in-service use in the environment or disposal of solutions after remediation; therefore, it is necessary to develop proper remediation techniques. The effects of concentration, extraction period, temperature, and sequential extraction on the extraction of Cr, Cu, and As from CCA-treated wood using [S,S]-ethylenediaminedisuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), and nitrilotriacetic acid (NTA) were studied. Mobility of metal in the samples was evaluated by using a sequential extraction scheme that could give the information needed to explain different extraction efficiencies for different metals. Results of long-term leaching tests of CCA-treated wood before and after EDDS extraction were used to evaluate Cr, Cu, and As leachability. Kinetic experiments showed that 6 h was the optimum extraction time for all metals and CCA-treated wood. Experimental results showed that EDDS is a very effective chelating agent for the extraction of Cr, Cu, and As from CCA-treated wood. Increased temperature significantly enhanced the extraction efficiency of CCA metals, especially Cr and As. The much better extractability of Cu compared to Cr and As by chelating agents can be attributed to the presence of larger weakly bound fractions. The CCA-treated woods after EDDS extraction have met the EPA's TCLP regulatory limit and could be classified as a non-hazardous waste according to identification standard of hazardous wastes.

Efficiency of biodegradable EDDS, NTA and APAM on enhancing the phytoextraction of cadmium by Siegesbeckia orientalis L. grown in Cd-contaminated soils

Chelant assisted phytoextraction has been proposed to enhance the efficiency of remediation. This study evaluated the effects of biodegradable ethylene diamine tetraacetate (EDDS), nitrilotriacetic (NTA) and anionic polyacrylamide (APAM) on the tolerance and uptake of Siegesbeckia orientalis L. at 10 and 100 mg kg(-1) Cd-contaminated soils. On the 80th and 90th days of transplanting, pots were treated with EDDS and NTA at 0 (control), 1 and 2 mmol kg(-1) soils, and APAM at 0 (control), 0.07 and 0.14 g kg(-1). Generally, the root and shoot biomass of S. orientalis in all treatments reduced not significantly compared with the control, and the activities of peroxidase and catalase in leaves generally increased by the application of chelants (P<0.05). The concentrations of Cd in the shoots were increased significantly by addition of all chelants. As a result, the Cd accumulation of S. orientalis under treatments with higher dosages of the three chelants on the 80th day were 1.40-2.10-fold and 1.12-1.25-fold compared to control at 10 and 100 mg kg(-1) Cd, respectively. Under the addition of 2 mmol kg(-1) NTA on the 80th day, the highest metal extraction ratio reached 1.2% and 0.4% at 10 and 100 mg kg(-1) Cd soils, respectively. Therefore, the applications of EDDS, NTA and APAM may provide more efficient choices in chemical-enhanced phytoextraction.

Enhancing radium solubilization in soils by citrate, EDTA, and EDDS chelating amendments

The effect of three chelating agents (citrate, EDTA, and EDDS) on the solubilization of radium from a granitic soil was studied systematically, considering different soil pH values, chelating agent concentrations, and leaching times. For all the chelating agents tested, the amount of radium leached proved to be strongly dependent on the pH of the substrate: only for acidic conditions did the amount of radium released increase significantly relative to the controls. Under the best conditions, the radium released from the amended soil was greater by factors of 20 in the case of citrate, 18 for EDTA, and 14 for EDDS. The greatest improvement in the release of radium was obtained for the citrate amendment at the highest concentration tested (50 mmol kg(-1)). A slightly lower amount of radium was leached with EDTA at 5 mmol kg(-1) soil, but the solubilization over time was very different from that observed with citrate or EDDS. With EDTA, a maximum in radium leaching was reached on the first day after amendment, while with citrate, the maximum was attained on the fourth day. With EDDS, radium leaching increased slightly but steadily with time (until the sixth day), but the net effect for the period tested was the lowest of the three reagents.

The use of a biodegradable chelator for enhanced phytoextraction of heavy metals by Festuca arundinacea from municipal solid waste compost and associated heavy metal leaching

In a column experiment with horizontal permeable barriers, the effects of a biodegradable chelator-nitrilotriacetic acid (NTA) on the uptake of heavy metals from municipal solid waste (MSW) compost by Festuca arundinacea and metal leaching were investigated. The use of NTA was effective in increasing Cu, Pb, and Zn uptakes in shoots of two crops of F. arundinacea. In columns with barriers and treated with 20 mmol NTA per kg MSW compost, metal uptakes by the first and second crop of F. arundinacea were, respectively, 3.8 and 4.0 times for Pb, and 1.8 and 1.7 times for Zn greater with the added NTA than without it. Though NTA application mobilized metals, it caused only slight leaching of metals from MSW compost. Permeable barriers positioned between compost and soil effectively reduced metal leaching. NTA-assisted phytoextraction by turfgrass with permeable barriers to cleanup heavy metal contaminated MSW compost should be environmentally safe.

Residual effects of EDDS leachates on plants during EDDS-assisted phytoremediation of copper contaminated soil

In this study, a novel experimental setup (one pot placed above another) was used to investigate the residual effects of EDDS application on plant growth and metal uptake. Two plant species, garland chrysanthemum and ryegrass, were grown in the upper pots (mimicking the upper soil layers) and were harvested 7 days after EDDS application. During this period the upper pots were watered twice. The lower pots (mimicking the subsoil under the upper soil layers) served as leachate collectors. Thereafter, the two pots were separated, and the same plants were grown in the upper and lower pots in two continuous croppings. Results showed that EDDS application restrained the growth of the first crop and resulted in a dramatic enhancement of Cu accumulation in plants grown in the upper pots. However, no negative growth effects were identified for the second and third crops, which were harvested 81 and 204 days after the EDDS application, respectively. In the lower pots, the leachate from the upper pots after EDDS application exhibited the increased total and CaCl(2)-extractable Cu concentrations in the soil. However, the growth of garland chrysanthemum and ryegrass, and their shoot Cu concentrations were unaffected. These data suggest that the residual risk associated with EDDS application was limited, and that subsoil to which EDDS leachate was applied may exhibit reduced Cu bioavailability for plants due to the biodegradation of EDDS.

Metal leaching along soil profiles after the EDDS application--a field study

One concern about the chelant-enhanced phytoextraction is the potential metal leaching associated with chelant application. A field study was carried out and the metal leaching along the 60-cm depth soil profiles were evaluated within 36 days after the biodegradable chelant EDDS was applied. Results showed EDDS significantly increased soluble Cu in the top 5 cm soil layer 1 day after the application, and the increase of soluble metals was generally limited in the top 20 cm soil. Metal speciation analysis indicated all Cu and Zn were in forms of Cu-EDDS and Zn-EDDS complexes in soil solution, and Ca was the major competitor with trace metals to EDDS. The soluble metals decreased quickly with time, and no significant difference was observed in the extractable Cu between EDDS treatments and the controls 22 days after the EDDS addition. The potential leaching associated with biodegradable EDDS addition may be controlled under field conditions.

Extraction of heavy metals from e-waste contaminated soils using EDDS

Environmental contamination due to uncontrolled e-waste recycling activities is drawing increasing attention in the world. Extraction of these metals with biodegradable chelant [S,S]-ethylenediaminedisuccinic acid (EDDS) and the factors influencing extraction efficacy were investigated in the present study. Results showed that the addition of EDDS at low pH (5.5) produced higher metal extraction than that at high pH (8.0) solution. Metal speciation analysis indicated that Cu was completely complexed with EDDS at different pH conditions with various amounts of EDDS applied. For Pb and Zn, at low EDDS dose of 0.304 mol/kg soil, they were present as Pb- and Zn-EDDS. However, at high EDDS dose of 1.26 mol/kg soil, most of Pb was bound with dissolved organic matter. Ca and Al were found to be strong competitors for trace metals to EDDS at low application dose and low pH condition.

Effects of amendments on copper, cadmium, and lead phytoextraction by Lolium perenne from multiple-metal contaminated solution

Chemical amendments can increase metal uptake by plant roots and translocation to shoots, however their effectiveness can be influenced by the presence of other amendments and metal ions in a multiple-metal environment. A range of amendments and combinations were tested to explore their effect on phytoextraction of Cu, Cd, and Pb by perennial ryegrass (Lolium perenne) from solutions containing one or more of these metals. The amendments studied included EDDS (an aminopolycarboxylic acid), histidine (an amino acid), citric acid (an organic acid), rhamnolipid (a biosurfactant) and sulfate (an inorganic ligand). For all amendment treatments, the presence of multiple metals in solution reduced shoot concentrations of Cd and Cu, while Pb levels in shoots were generally enhanced by the presence of Cu. Although slightly toxic to the plants, EDDS (1 mM) was the most effective individual amendment for enhancing shoot metal uptake and translocation from solution without significantly reducing biomass yield. The combination Rhm+Cit+EDDS resulted in the highest shoot metal concentrations of all the treatments but also caused severe phytotoxicity. Amendment combinations Rhm+His and Sulf+Cit were less toxic for plant growth while moderately enhancing metal mass accumulation in shoots and thus could be considered as alternative treatments for enhanced phytoextraction.

Effects of iron(III)chelates on the solubility of heavy metals in calcareous soils

In this study I evaluated the effects of complexing agents on the solubility of heavy metals in an incubation experiment up to 56 days when complexing agents were applied as Fe-chelates (Fe-EDDS(S,S), Fe-EDDS(mix), Fe-EDTA and Fe-EDDHA) on calcareous soils at a level sufficient to correct Fe chlorosis (0.1 mmol kg(-1)). Of these ligands, EDDHA was the most efficient in keeping Fe in water-soluble form, and EDDS increased the solubility of Cu and Zn most, and only EDTA increased the solubility of Cd and Pb. EDTA increased the solubility of Ni steadily during the incubation period, equalling about 5-8% of the added EDTA concentration. [S,S]-EDDS was biodegraded within 56 days, whereas EDDS(mix) was less biodegradable. Ni-chelates were the most recalcitrant against biodegradation. The study shows that even a moderate input of chelates to soil increases the solubility of toxic heavy metals and their risk of leaching.

Ethyl lactate-EDTA composite system enhances the remediation of the cadmium-contaminated soil by autochthonous willow (Salix x aureo-pendula CL 'J1011') in the lower reaches of the Yangtze River

In order to explore a practical approach to the remediation of the cadmium (Cd)-contaminated soil in the lower reaches of the Yangtze River, we evaluated the effects of a local willow (Salix x aureo-pendula CL 'J1011') of absorbing, accumulating, and translocating Cd; and assessed the potential of chelator ethylenediaminetetraacetic acid (EDTA) in combination with ethyl lactate for enhancing the efficiency of the willow in removing Cd in two water-culture growth chamber trials and a field one. The willow showed a high tolerance to Cd in growth chamber trial 1 where the Cd concentration in the medium reached up to 25 mg L(-1) medium, and the bioaccumulation factors (BAFs) of the shoots for Cd rose from 3.8 to 7.4 as the Cd concentration in the medium was elevated from 5 to 25 mg L(-1) medium. In growth chamber trial 2, the average Cd removal rates in two treatments with EDTA and ethyl lactate (molar ratios of EDTA to ethyl lactate=68/39 and 53.5/53.5, respectively) reached 0.71 mg d(-1) pot(-1) for the duration of Day 5-8 and 0.59 mg d(-1) pot(-1) for that of Day 8-11, which were 5- and 4-fold of their counterparts in the control, respectively. In the field trial, for the remediational duration of 45 days, three treatments-willow alone, willow combined with EDTA, and willow combined with EDTA and ethyl lactate-led to decreases in the Cd concentration in soil by 5%, 20%, and 29%, respectively; increases in that in the leaves by 14.6%, 56.7%, and 146.5%, respectively; and increases in that in the stems by 15.6%, 41.2%, and 87.4%, respectively, compared to their counterparts on Day 0. These results indicate that EDTA combined with ethyl lactate significantly enhanced the efficiency of willow in removing Cd from the soil. Therefore, a phytoextration system consisting of the autochthonous willow, EDTA, and ethyl lactate has high potential for the remediation of the Cd-polluted soil in the lower reaches of the Yangtze River.

Effects of IDSA, EDDS and EDTA on heavy metals accumulation in hydroponically grown maize (Zea mays, L.)

Heavy metals contamination of soil is a widespread global problem. Chelant assisted phytoextraction has been proposed to improve the efficiency of phytoextraction which involves three subsequent levels: transfer of metals from the bulk soil to the root surfaces, uptake into the roots and translocation to the shoots. However, most studies focused on the first level. A hydroponic experiment, which addresses the latter two levels, was conducted to study the effects of EDTA, EDDS and IDSA on the uptake and the distribution of Pb, Zn, Cu and Cd in the apoplast and the symplast of roots of maize (Zea mays, L.). The concentrations of the metals (with exception of Zn) in the shoots were increased significantly by addition of all the chelants. EDTA was most effective for Pb uptake and IDSA was interestingly most effective for Cd uptake. Pb in the roots with EDTA was mostly distributed in the apoplast, while Zn, especially with IDSA, was mostly located in the symplast. The results indicated that, the capacity of chelant to enhance the nonselective apoplastic transport of metal may be most important for chelant enhanced phytoextraction.

Potential and drawbacks of EDDS-enhanced phytoextraction of copper from contaminated soils

Incubation and pot experiments using poplar (Populus nigra L. cv. Wolterson) were performed in order to evaluate the questionable efficiency of EDDS-enhanced phytoextraction of Cu from contaminated soils. Despite the promising conditions of the experiment (low contamination of soils with a single metal with a high affinity for EDDS, metal tolerant poplar species capable of producing high biomass yields, root colonization by mycorrhizal fungi), the phytoextraction efficiency was not sufficient. The EDDS concentrations used in this study (3 and 6 mmol kg(-1)) enhanced the mobility (up to a 100-fold increase) and plant uptake of Cu (up to a 65-fold increase). However, despite EDDS degradation and the competition of Fe and Al for the chelant, Cu leaching cannot be omitted during the process. Due to the low efficiency, further research should be focused on other environment-friendly methods of soil remediation.

Influence of EDDS-to-metal molar ratio, solution pH, and soil-to-solution ratio on metal extraction under EDDS deficiency

In situ biodegradable EDDS ([S,S]-stereoisomer of ethylenediaminedisuccinic acid) applications at low concentration may present conditions where applied EDDS is insufficient relative to sorbed metals in soils. This study investigated the influence of EDDS-to-metal molar ratios (MR), solution pH and soil-to-solution ratio on metal extraction under EDDS deficiency (i.e., MR<1). Batch kinetics experiments showed that Pb and Zn extraction exhibited different kinetic behaviors at MR 0.35-0.75, while Cu extraction was comparable. At MR 0.75 or below, newly extracted Pb was re-adsorbed onto the soil surfaces. Similar re-adsorption phenomenon, to a lower extent, was observed for newly extracted Zn at MR 0.5 or below, whereas this appeared to be marginal at MR 0.75, reflecting Zn extraction was less affected by EDDS deficiency than Pb extraction. Moreover, Pb extraction at an alkaline condition was preferable under EDDS deficiency because at MR 0.5 it was 30% higher at pH 8 and 9 than pH 5.5 and 7. The influence of varying soil-to-solution ratios (1:50-1:5) at MR 0.5 was marginal compared with that of MR and solution pH. These findings indicated that Pb extraction by deficient EDDS would be more difficult to accomplish compared to Cu and Zn extraction.

Symbiotic role of Glomus mosseae in phytoextraction of lead in vetiver grass [Chrysopogon zizanioides (L.)]

Lead (Pb) has limited solubility in the soil environment owing to complexation with various soil components. Although total soil Pb concentrations may be high at a given site, the fraction of soluble Pb that plants can extract is very small, which is the major limiting factor for Pb phytoremediation. The symbiotic effect of arbuscular mycorrhizal (AM) fungus, Glomus mosseae was examined on growth and phytoextraction of lead (Pb) by vetiver grass [Chrysopogon zizanioides (L.)]. A hydroponic study, Phase I (0, 1, 2, and 4mM Pb) was conducted followed by an incubation pot study, Phase II (0, 400, 800, and 1200 mg kg(-1) Pb) where vetiver plants were colonized with G. mosseae. The results obtained indicate that plants colonized by the AM fungi not only exhibit better growth (increase in plant biomass), but also significantly increase Pb uptake in root and higher translocation to the shoot at all given treatments. Moreover, plants colonized with AM fungi had higher chlorophyll content and reduced levels of low molecular weight thiols, indicating the ability to better tolerate metal-induced stress. Results from this study indicate that vetiver plants in association with AM fungi can be used for improved phytoextraction of Pb from contaminated soil.