Chemical speciation used to assess [S,S']-ethylenediaminedisuccinic acid (EDDS) as a readily-biodegradable replacement for EDTA in radiochemical decontamination formulations

EDDS and polystyrene interactions: implications for soil health and management practices

Ethylenediamine-N,N'-disuccinic acid (EDDS) has been studied extensively for its potential use as an amendment in agriculture due to its numerous beneficial properties. The widespread usage of microplastics (MPs) poses a growing threat to plant growth. This study investigated the effects of Polystyrene MPs (PSMPs) and EDDS on soil pH, EC, organic matter (OM), available nutrients, and maize (Zea mays L.) growth in a calcareous soil. Results showed that both PS and EDDS had significant effects on soil pH, with higher concentrations leading to a decrease in pH. PSMPs negatively impacted soil health by increasing EC and decreasing OM, nitrogen (N), phosphorus (P), and potassium (K). EDDS had potential applications in soil remediation and phytoremediation by decreasing EC and increasing N, P, and K. The interaction between EDDS and PSMPs suggests that their effects on soil pH may be modulated by each other. The study highlights the potential negative impacts of high concentrations of PS on soil health and the potential benefits of using EDDS at lower concentrations in soil remediation and phytoremediation. However, further research is needed to understand the mechanisms and environmental impacts of EDDS and the combined effects of EDDS and PSMPs on soil properties and plant growth.

Utilization of Fe-Ethylenediamine-N,N'-Disuccinic Acid Complex for Electrochemical Co-Catalytic Activation of Peroxymonosulfate under Neutral Initial pH Conditions

The ethylenediamine-N,N'-disuccinic acid (EDDS) was utilized to form Fe-EDDS complex to activate peroxymonosulfate (PMS) in the electrochemical (EC) co-catalytic system for effective oxidation of naphthenic acids (NAs) under neutral pH conditions. 1-adamantanecarboxylic acid (ACA) was used as a model compound to represent NAs, which are persistent pollutants that are abundantly present in oil and gas field wastewater. The ACA degradation rate was significantly enhanced in the EC/PMS/Fe(III)-EDDS system (96.6%) compared to that of the EC/PMS/Fe(III) system (65.4%). The addition of EDDS led to the formation of a stable complex of Fe-EDDS under neutral pH conditions, which effectively promoted the redox cycle of Fe(III)-EDDS/Fe(II)-EDDS to activate PMS to generate oxidative species for ACA degradation. The results of quenching and chemical probe experiments, as well as electron paramagnetic resonance (EPR) analysis, identified significant contributions of •OH, 1O2, and SO4•- in the removal of ACA. The ACA degradation pathways were revealed based on the results of high resolution mass spectrometry analysis and calculation of the Fukui index. The presence of anions, such as NO3-, Cl-, and HCO3-, as well as humic acids, induced nonsignificant influence on the ACA degradation, indicating the robustness of the current system for applications in authentic scenarios. Overall results indicated the EC/PMS/Fe(III)-EDDS system is a promising strategy for the practical treatment of NAs in oil and gas field wastewater.

Chelation-Assisted Ion-Exchange Leaching of Rare Earths from Clay Minerals

The effect of biodegradable chelating agents on the recovery of rare earth elements (REE) from clay minerals via ion-exchange leaching was investigated, with the aim of proposing a cost-effective, enhanced procedure that is environmentally benign and allows high REE recovery while reducing/eliminating ammonium sulfate usage. A processing route employing a lixiviant system consisting of simulated sea water (equivalent to about 0.5 mol/L NaCl) in conjunction with chelating agents was also explored, in order to offer a process alternative for situations with restricted access to fresh water (either due to remote location or to lower the operating costs). Screening criteria for the selection of chelating agents were established and experiments were conducted to assess the efficiency of selected reagents in terms of REE recovery. The results were compared to extraction levels obtained during conventional ion-exchange leaching procedures with ammonium sulfate and simulated sea water only. It was found that stoichiometric addition of N,N′-ethylenediaminedisuccinic acid (EDDS) and nitrilotriacetic acid-trisodium form (NTA-Na3) resulted in 10–20% increased REE extraction when compared to lixiviant only, while achieving moderate Al co-desorption and maintaining neutral pH values in the final solution.

Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review

Persistent organic contaminants affecting soil and groundwater pose a significant threat to ecosystems and human health. Fenton oxidation is an efficient treatment for removing these pollutants in the aqueous phase at acidic pH. However, the in-situ application of this technology for soil remediation (where pHs around neutrality are required) presents important limitations, such as catalyst (iron) availability and oxidant (H2O2) stability. The addition of chelating agents (CAs), forming complexes with Fe and enabling Fenton reactions under these conditions, so-called chelate-modified Fenton process (MF), tries to overcome the challenges identified in conventional Fenton. Despite the growing interest in this technology, there is not yet a critical review compiling the information needed for its real application. The advantages and drawbacks of MF must be clarified, and the recent achievements should be shared with the scientific community. This review provides a general overview of the application of CAs to enhance the Fenton process for the remediation of soils polluted with the most common organic contaminants, especially for a deep understanding of the activation mechanisms and influential factors. The existing shortcomings and research needs have been highlighted. Finally, future research perspectives on the use of CAs in MF and recommendations have been provided.

Process design and validation of a new mixed eluent for leaching Cd, Cr, Pb, Cu, Ni, and Zn from heavy metal-polluted soil

Chemical leaching, an emerging technology for treating heavy metal-polluted soils, requires a design for reasonable and new eluent and an evaluation of its efficiency on the simultaneous removal of different elements. In this study, the leaching effect and biodegradability of chelating agents were compared, and ethylenediamine disuccinic acid (EDDS) was selected to combine with ferric chloride (FeCl₃) for the design of a mixed eluent (EDDS + FeCl₃). Through batch experiments, the influences of the eluent concentration and solution pH on leaching were revealed, and leaching efficiencies of EDDS, FeCl₃, and EDDS + FeCl₃ on six heavy metals Cd, Cr, Pb, Cu, Ni, and Zn in the soil were separately analyzed. Results indicated that EDDS + FeCl₃ showed advantages over both EDDS and FeCl₃ alone, and it presented an excellent effect, especially for simultaneously leaching multiple heavy metals from the soil. The highest leaching efficiencies for Cd, Cr, Pb, Cu, Ni, and Zn reached up to 71.36%, 21.29%, 31.14%, 30.25%, 34.05%, and 4.96%, respectively. According to different soil types and target elements, the concentration, pH condition, and mass ratio of EDDS + FeCl₃ could be adjusted for soil remediation. Fourier transform infrared spectroscopy proved that the better leaching effect of EDDS + FeCl₃ was attributed to changes in the number and strength of functional groups in the solution, which enhanced the chelating ability of the mixed eluent and heavy metal ions. Therefore, chemical leaching by EDDS + FeCl₃ for the remediation of multiple heavy metal-contaminated soil is a potential feasible strategy.

A critical review of the application of chelating agents to enable Fenton and Fenton-like reactions at high pH values

To overcome the drawback of low pH requirement of the classical Fenton reaction, researchers have applied chelating agents to form complexes with Fe and enable Fenton reaction at high pHs, which is reviewed in this article. The chelating agents reviewed include humic substances, polycarboxylates, aminopolycarboxylic acids, and polyoxometalates. Ligands affect the reactivity of Fe-complexes by changing their redox potentials, promoting their reaction with H₂O₂, and competing with target contaminants for the oxidative species. Fe(III)-complexes are reduced to Fe(II)-complexes by O₂^- not H₂O₂, as indicated by their redox potentials. The stability constants of Fe-complexes increase with increasing pK_a values of the corresponding ligands and also with increasing charge density of the metal ions. A higher stability constant of Fe(III)-complex indicates higher reaction rate of corresponding Fe(II)-complex with H₂O₂ and lower reduction rate of Fe(III)-complex to Fe(II)-complex. OH, O₂^-, and ferryl species were reported to be the reactive species on the contaminant removal in the chelate-modified Fenton process. The generation of these species depends on the chelating agents and reaction conditions. The process is very efficient in degrading contaminants, indicating a potential treatment approach for the pollution remediation at natural pH.

Kinetics study on the degradation of a model naphthenic acid by ethylenediamine-N,N'-disuccinic acid-modified Fenton process

Naphthenic acids (NAs) are reported to be the main species responsible for the oil sands process-affected water (OSPW) toxicity. In this study, the degradation of cyclohexanoic acid (CHA) as a model compound for NAs by an ethylenediamine-N,N'-disuccinic acid (EDDS)-modified Fenton process was investigated at pH 8. Optimum dose for Fe-EDDS (EDDS:Fe=2:1) was 0.45mM, and 2.94mM for hydrogen peroxide (H2O2). The time profiles of the main species in the process were studied, including CHA, H2O2, Fe(II), total Fe, and Fe-EDDS (in the main form of Fe(III)EDDS). The second-order rate constant between EDDS and hydroxyl radical (OH) at pH 8 was obtained as 2.48±0.43×10(9)M(-1)s(-1). OH was proved to be the main species responsible for the CHA degradation, while superoxide radical (O2(-)) played a minor role. The consecutive addition of H2O2 and Fe-EDDS led to a higher removal of CHA compared to that achieved by adding the reagents at a time. The half-wave potential of Fe(III/II)EDDS was measured at pH 7-9. The EDDS-modified Fenton process is a promising alternative to degrade NAs.

Comparison of Nitrilotriacetic Acid and [S,S]-Ethylenediamine-N,N'-disuccinic Acid in UV-Fenton for the Treatment of Oil Sands Process-Affected Water at Natural pH

The application of UV-Fenton processes with two chelating agents, nitrilotriacetic acid (NTA) and [S,S]-ethylenediamine-N,N'-disuccinic acid ([S,S]-EDDS), for the treatment of oil sands process-affected water (OSPW) at natural pH was investigated. The half-wave potentials of Fe(III/II)NTA and Fe(III/II)EDDS and the UV photolysis of the complexes in Milli-Q water and OSPW were compared. Under optimum conditions, UV-NTA-Fenton exhibited higher efficiency than UV-EDDS-Fenton in the removal of acid extractable organic fraction (66.8% for the former and 50.0% for the latter) and aromatics (93.5% for the former and 74.2% for the latter). Naphthenic acids (NAs) removals in the UV-NTA-Fenton process (98.4%, 86.0%, and 81.0% for classical NAs, NAs + O (oxidized NAs with one additional oxygen atom), and NAs + 2O (oxidized NAs with two additional oxygen atoms), respectively) under the experimental conditions were much higher than those in the UV-H₂O₂ (88.9%, 48.7%, and 54.6%, correspondingly) and NTA-Fenton (69.6%, 35.3%, and 44.2%, correspondingly) processes. Both UV-NTA-Fenton and UV-EDDS-Fenton processes presented promoting effect on the acute toxicity of OSPW toward Vibrio fischeri. No significant change of the NTA toxicity occurred during the photolysis of Fe(III)NTA; however, the acute toxicity of EDDS increased as the photolysis of Fe(III)EDDS proceeded. NTA is a much better agent than EDDS for the application of UV-Fenton process in the treatment of OSPW.

Application of calcium peroxide activated with Fe(II)-EDDS complex in trichloroethylene degradation

This study was conducted to assess the application of calcium peroxide (CP) activated with Fe(II) chelated by (S,S)-ethylenediamine-N,N'-disuccinic acid (EDDS) to enhance trichloroethylene (TCE) degradation in aqueous solution. It was indicated that EDDS prevented soluble iron from precipitation, and the optimum molar ratio of Fe(II)/EDDS to accelerate TCE degradation was 1/1. The influences of initial TCE, CP and Fe(II)-EDDS concentration were also investigated. The combination of CP and Fe(II)-EDDS complex rendered the efficient degradation of TCE at near neutral pH range. Chemical probe and scavenger tests identified that TCE degradation mainly owed to the oxidation of HO while O2(-) promoted HO generation. Cl(-), HCO3(-) and humic acid were found to inhibit CP/Fe(II)-EDDS performance on different levels. In conclusion, the application of CP activated with Fe(II)-EDDS complex is a promising technology in chemical remediation of groundwater, while further research in practical implementation is needed.

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.

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.

Pyrophosphate coupling with chelant-enhanced soil flushing of field contaminated soils for heavy metal extraction

This study investigated the influence of flushing duration, [S,S]-ethylenediaminedisuccinic acid (EDDS) dosage, humic acid and various combinations of ethylenediaminetetraacetic acid (EDTA), EDDS and tetrasodium pyrophosphate (Na(4)P(2)O(7)) on metal extraction during soil flushing, through column experiments. A lesser extent of enhancement in metal extraction efficiencies was found when the flushing duration and the dosage of EDDS was doubled, compared to their efficiencies measured at pore volume 100. Metal extraction efficiency was mainly influenced by the initial metal distribution in the soils rather than the flushing duration and the EDDS-to-metal molar ratio. Humic acid of less than 10mg/L as dissolved organic carbon (DOC) posed an insignificant effect on metal extraction during EDDS enhanced soil flushing. The extraction rate of Ni by EDTA and EDDS was time dependent, and was initially fast in the case of EDDS, whereas it was slow for EDTA. However, the overall Ni extraction efficiency by EDTA was higher when the flushing time was longer. Na(4)P(2)O(7) promoted the mineral dissolution which enhanced the metal extraction as a result of soil disruption. The order of metal extraction by Na(4)P(2)O(7) was Ni>Cr>Cu, probably be due to the different affinities between metals and P(2)O(7)(4-).

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.

Ethyl lactate enhances ethylenediaminedisuccinic acid solution removal of copper from contaminated soils

A new approach using aqueous ethyl lactate-modified [S,S]-ethylenediaminedisuccinic acid (EDDS) washing solutions for the removal of Cu from field-contaminated soils was examined in the laboratory. At pH 7 the maximum extraction efficiencies of Cu were about 41% by EDDS solution (EDDS:Cu molar ratio=8), and <2% by ethyl lactate solution. However, greater extraction efficiencies of up to 50% were achieved by amending the EDDS solution with ethyl lactate (EDDS:Cu molar ratio=2, ethyl lactate:Cu molar ratio=25). The pH of the extraction solution did not have a significant effect on the extraction of Cu. The washing agent could also be regenerated quite effectively for economy of use. Sequential extraction results showed that the two most bioavailable Cu fractions, i.e., the acid extractable and reducible fractions, were significantly reduced. The mechanism responsible for the enhanced extraction efficiency in the presence of ethyl lactate is the increased the stability constant of Cu-EDDS complexes in the presence of ethyl lactate, which enhanced desorption of Cu from soil.

Effect of inorganic, synthetic and naturally occurring chelating agents on Fe(II) mediated advanced oxidation of chlorophenols

This study examines the feasibility and application of Advanced Oxidation Technologies (AOTs) for the treatment of chlorophenols that are included in US EPA priority pollutant list. A novel class of sulfate/hydroxyl radical-based homogeneous AOTs (Fe(II)/PS, Fe(II)/PMS, Fe(II)/H2O2) was successfully tested for the degradation of series of chlorophenols (4-CP, 2,4-CP, 2,4,6-CP, 2,3,4,5-CP). The major objective of the present study was to evaluate the effectiveness of three representative chelating agents (citrate, ethylenediaminedisuccinate (EDDS), and pyrophosphate) on Fe(II)-mediated activation of three common peroxide (peroxymonosulfate (PMS), persulfate (PS), and hydrogen peroxide (H2O2)) at neutral pH conditions. Short term (4 h) and long term (7 days) experiments were conducted to evaluate the kinetics and longevity of different oxidative systems for 4-chlorophenol degradation. Results showed that each of the iron-chelating agent couple was superior in activating a particular oxidant and consequently for 4-CP degradation. In case of Fe(II)/PMS system, the inorganic chelating agent pyrophosphate showed effective activation of PMS whereas very fast dissociation of PMS was recorded in the case of EDDS without any apparent 4-CP degradation. In Fe(II)/H2O2 system, EDDS was proven to be the most effective whereas pyrophosphate showed negligible activation of H2O2. Fe(II)/Citrate system showed moderate activation of all three oxidants. PMS was found to be the most universal oxidant, which was activated by all three iron-chelating agent systems and Fe(II)/Citrate was the most universal chelating agent system, which was able to activate all three oxidants to a certain extent.

Effect of biodegradable amendments on uranium solubility in contaminated soils

Chelate-assisted phytoextraction has been proposed as a potential tool for phytoremediation of U contaminated sites. In this context, the effects of five biodegradable amendments on U release in contaminated soils were evaluated. Three soils were involved in this study, one with a relatively high background level of U, and two which were contaminated with U from industrial effluents. Soils were treated with 5 mmol kg(-1) dry weight of either citric acid, NH(4)-citrate/citric acid, oxalic acid, S,S-ethylenediamine disuccinic acid or nitrilotriacetic acid. Soil solution concentration of U was monitored during 2 weeks. All amendments increased U concentration in soil solution, but citric acid and NH(4)-citrate/citric acid mixture were most effective, with up to 479-fold increase. For oxalic acid, S,S-ethylenediamine disuccinic acid and nitrilotriacetic acid, the increase ranged from 10-to 100-fold. The highest concentrations were observed 1 to 7 days after treatment, after which U levels in soil solution gradually decreased. All amendments induced a temporary increase of soil solution pH and TOC that could not be correlated with the release of U in the soil solution. Thermodynamic stability constants (log K) of complexes did not predict the relative efficiency of the selected biodegradable amendments on U release in soil solution. Amendments efficiency was better predicted by the relative affinity of the chelate for Fe compared to U.

Extraction of copper from sewage sludge using biodegradable chelant EDDS

[S,S]-Ethylenediaminedisuccinic acid (EDDS), a biodegradable chelant, was used to separate the heavy metals from the sewage sludge based on chemical extraction technology. Under various conditions, the extraction experiments were carried out for the sewage sludge from Shanghai Taopu Municipal Wastewater Plant, China. The influences of pH and the concentration of EDDS on the extraction efficiency for copper (Cu) were discussed. The results showed that EDDS had higher extraction efficiency for Cu from the sewage sludge than other heavy metals. The system pH and the concentration of EDDS had a significant effect on the extraction efficiency. The extraction efficiency of Cu increased gradually with the increase of system pH and reached a higher efficiency within pH range of 3-10. The extraction efficiency maintained at approximately 70% when the pH > or = 4.5 and the molar ratio of EDDS to total heavy metals was 10:1. From the fractional analysis of the heavy metals in sewage sludge before and after the extraction, it was found that the extracted Cu mainly came from the following four fractions, i.e. water soluble, acid-soluble, reducible, and oxidizable fractions.

An evaluation of the green chelant EDDS to enhance the stability of hydrogen peroxide in the presence of aquifer solids

Hydrogen peroxide is a widely used in situ chemical oxidation reagent which relies on catalysts to generate the suite of reactive species that are required to aggressively remediate contaminated soils and groundwater. In the subsurface environment these catalysts are usually transition metals that are added to the injected solution, or are naturally occurring. Chelating agents are widely used to maintain an adequate dissolved transition metal concentration in near-neutral pH conditions; however, they can also be used to improve the persistence of H(2)O(2) in situations when the aquifer solids have sufficient transition metal content. Ethylenediamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) have been considered to be the most effective chelants and therefore are the most widely used. While previous research efforts have focused on the chelating agent efficiency, the long-term fate of these chelants in the natural subsurface environment is a concern since both EDTA and NTA are non-readily biodegradable. The focus of this investigation was to evaluate the potential of using the environmentally friendly or green chelating agent ethylenediaminedisuccinate (EDDS) as an alternative to EDTA or NTA to suppress the catalytic activity of naturally-occurring transition metals. A series of batch reactor and column experiments were performed using five different aquifer materials and the results demonstrate that EDDS has a comparative chelating efficiency to that of EDTA. The addition of EDDS was able to reduce the H(2)O(2) decomposition rates in the presence of the aquifer materials used in this investigation by 24-97% in well-mixed batch systems, and by 20% and 38% in the column trials where H(2)O(2) was detected in the effluent.

Plant uptake and the leaching of metals during the hot EDDS-enhanced phytoextraction process

Using pot experiments, the effect of the application of the biodegradable chelating agent S,S-ethylenediaminedisuccinic acid (EDDS) in hot solutions at 90 degrees C on the uptake of Cu, Pb, Zn, and Cd by corn (Zea mays L. cv. Nongda No. 108) and beans (P vulgaris L. white bean), and the potential leaching of metals from soil, were studied. When EDDS was applied as a hot solution at the rate of 1 mmol kg(-1), the concentrations and total phytoextraction of metals in plant shoots exceeded or approximated those in the shoots of plants treated with normal EDDS at the rate of 5 mmol kg(-1). On the other hand, the leaching of Cu, Pb, Zn, and Cd after the application of the hot EDDS solution at the rate of 1 mmol kg(-1) was reduced by 46%, 21%, 57%, and 35% in comparison with that from the application of normal EDDS at 5 mmol kg(-1), respectively. For treatment with 1 mmol kg(-1) of EDDS, the leached metals decreased to the levels of the control group (that without EDDS amendment) 14 d after the application of EDDS. The soil amendment with biodegradable EDDS in hot solutions may provide a good alternative to chelate-enhanced phytoextraction in enhancing metal uptake by plants and limiting metals from leaching out of the soil.

Chelate-induced phytoextraction of metal polluted soils with Brachiaria decumbens

Chelate-induced phytoextraction with high biomass plant species has been proposed for the clean-up of heavy metal polluted soils. In the current work, the effect of the application of two different chelating agents, i.e. EDTA and EDDS, on the metal phytoextraction capacity of Brachiaria decumbens was studied. Although EDTA was, in general, more effective in soil metal solubilization, EDDS, a chelate less harmful to the environment, was more efficient inducing metal accumulation in B. decumbens shoots than EDTA. Indeed, in a moderately heavy metal polluted soil, EDDS caused a 2.54, 2.74 and 4.30-fold increase in Cd, Zn, and Pb shoot metal concentration, respectively, as compared to control plants. In this same soil, EDTA caused a 1.77, 1.11 and 1.87-fold increase in Cd, Zn, and Pb shoot metal concentration, respectively, as compared to control plants. EDDS was also more effective than EDTA in stimulating the translocation of metals from roots to shoots. B. decumbens plants were able to grow in the metal polluted soils showing no visible symptoms of phytotoxicity, which suggests their metal tolerance. Finally, B. decumbens, a fast-growing, high biomass, aluminum tolerant plant species, that has a well-established agronomic system, fulfills most of the requirements for chemically-induced phytoextraction.

Enhanced phytoextraction of Pb and other metals from artificially contaminated soils through the combined application of EDTA and EDDS

Chemically enhanced phytoextraction is achieved by the application of chelates to soils. Using pot experiments, the effect of the combined application of EDTA and EDDS on the uptake of Cu, Pb, Zn and Cd by Zea mays L. was studied. Among the tested application ratios of 1:1, 1:2, and 2:1 (EDTA/EDDS), 2:1 of EDTA:EDDS was the most efficient ratio for increasing the concentrations of Cu, Pb, Zn and Cd in the shoots. The combined application of 3.33 mmol kg(-1) soil of EDTA+1.67 mmol kg(-1) soil of EDDS produced 650 mg kg(-1) of Pb in the shoots, which was 2.4 and 5.9 times the concentration of Pb in the shoots treated with 5 mmol kg(-1) of EDTA and EDDS alone, respectively. The total phytoextraction of Pb reached 1710 microg kg(-1) soil, which was 2.1 and 6.1 times the total Pb from 5 mmol kg(-1) EDTA and EDDS alone, respectively. The combined application of EDTA and EDDS also significantly increased the translocation of Pb from the roots to the shoots. The mechanism of enhancing the phytoextraction of Pb by the combined application of EDTA+EDDS did not involve a change in the pH of the soil. The increase in the phytoextraction of Pb by the shoots of Z. mays L. was more pronounced than the increase of Pb in the soil solution with the combined application of EDTA and EDDS. It was thought that the major role of EDDS might be to increase the uptake and translocation of Pb from the roots to the shoots of plants.

Evaluation of the effect of small organic acids on phytoextraction of Cu and Pb from soil with tobacco Nicotiana tabacum

Phytoremediation, the use of plants to extract contaminants from soils and groundwater, is a promising approach for cleaning up soils contaminated with heavy metals. However its use is limited by the time required for plant growth, the nutrient supply and, moreover, by the limited metal uptake capacity. Synthetic chelators have shown positive effects in enhancing heavy metal extraction, but they have also revealed several negative side-effects. The objective of this study was to investigate the use of three natural low molecular weight organic acids (NLMWOA) (citric, oxalic, and tartaric acid) as an alternative to synthetic chelators. Slurry-, column-, toxicity- and phytoextraction experiments were performed. For the phytoextraction experiment the three NLMWOA were applied to a copper- and a lead-contaminated soil respectively. A significant increase in copper uptake was visible only in the citric acid treatment (67 mg kg-1) in comparison to the EDTA treatment (42 mg kg-1). The NLMWOA application showed no enhanced effect concerning the lead phytoextraction. A possible explanation for this lack of significance could be the rate of the degradation of NLMWOA. This rate might well be too high for these heavy metals with low mobility and bioavailability such as lead. The amounts of NLMWOA applied to the soil were very high (62.5 mmol kg-1 of soil) and the effect was too little. In this respect EDTA, which was applied in very small amounts (0.125 mmol kg-1) was more efficient. Thus making NLMWOA unsuitable to enhance phytoextraction of heavy metals from soil.

Enhanced phytoextraction of Cu, Pb, Zn and Cd with EDTA and EDDS

Chemically enhanced phytoextraction has been proposed as an effective approach to removing heavy metals from contaminated soil through the use of high biomass plants. Using pot experiments, the effects of the application of EDTA, EDDS and citric acid on the uptake of Cu, Pb, Zn and Cd by corn (Zea mays L. cv. Nongda 108) and bean (Phaseolus vulgaris L. white bean) plants were studied. The results showed that EDDS was more effective than EDTA at increasing the concentration of Cu in corn and beans. The application of 5 mmol kg-1 soil EDDS to soil significantly increased concentrations of Cu in shoots, with maximum levels of 2060 and 5130 mg kg-1 DW in corn and beans, respectively, which were 45- and 135-fold higher than that in the corresponding control plants to which chelate had not been applied. Concentrations of Zn in shoots were also higher in the plants treated with EDDS than in those treated with EDTA. For Pb and Cd, EDDS was less effective than EDTA. The maximum Cu phytoextraction was found with the EDDS treatment. The application of EDTA and EDDS also significantly increased the shoot-to-root ratios of the concentrations of Cu, Pb, Zn and Cd in both plant species. The results of metal extraction with chelates showed that EDDS was more efficient at solubilizing Cu and Zn than EDTA, and that EDTA was better at solubilizing Pb and Cd than EDDS.

Ethylenediaminedissuccinate as a new chelate for environmentally safe enhanced lead phytoextraction

Using a soil column experiment, we compared the effect of a single dose and weekly additions of ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedissuccinate (EDDS) on the uptake of Pb, Zn, and Cd by Chinese cabbage [Brassica rapa L. subsp. pekinensis (Lour.) Hanelt], and on the leaching of heavy metals through the soil profile. The analysis of plant material revealed that both chelates increased the concentrations of Pb and, to a lesser extent, also of Zn and Cd in the leaves of the test plant. The most effective applications were single doses of 10 mmol EDTA and EDDS kg(-1) soil, which caused the concentrations of Pb in the shoots to increase 94.2- and 102.3-fold, respectively, relative to the control. The same dose of EDTA increased the concentration of Zn and Cd in the leaves 4.3- and 3.8-fold and of EDDS 4.7- and 3.5-fold, respectively. In treatments with weekly additions and lower concentrations of both chelates, EDTA was more effective than EDDS in increasing the plant uptake of Pb. In soil columns treated with weekly additions of 10 mmol kg(-1) EDTA, on average 22.7, 7.0, and 39.8% of initial total Pb, Zn, and Cd in the soil were leached through the soil profile. The same amount of EDDS caused much lower leaching of Pb and Cd--only 0.8 and 1.5% of initial total concentrations. Leaching of Zn, 6.2% of the total concentration, was comparable with the EDTA treatment. A biotest with red clover (Trifolium pratense L.) indicated a greater phytotoxic effect of EDTA than EDDS addition. EDDS was also less toxic to soil fungi, as determined by phospholipid fatty acid (PLFA) analysis, and caused less stress to soil microorganisms, as indicated by the trans to cis PLFA ratio. Chelate addition did not prevent the development of arbuscular mycorrhiza on red clover.