Ethylene Diamine Disuccinate Research Articles

Interactions of chelating agents with Pb-goethite at the solid–liquid interface: Pb extraction and re-adsorption

The use of ethylenediaminetetraacetic acid (EDTA) for soil remediation is under concern due to its non-biodegradability and toxicity; thus, its biodegradable structural isomer, [S,S]-ethylenediamine disuccinate ([S,S]-EDDS), has been proposed as an emerging substitute. In this study, batch experiments were performed to quantify the Pb extraction from goethite by EDTA and EDDS, respectively, and attenuated total reflectance-Fourier transform infrared (ATR/FT-IR) spectroscopy was used to investigate the corresponding mechanisms at the solid–liquid interface at different pH and reaction times. The Pb extraction was pH-dependent for both chelating agents; mildly alkaline condition was favorable for EDDS, while mildly acidic condition for EDTA. The discrepancy between two structural isomers might be caused by their pH-dependent zwitterionic structures. The ATR/FT-IR results revealed that under acidic conditions, hydrogen-bonded carboxyl groups were present in both zwitterionic EDDS and EDTA. However, ring structure of zwitterionic EDDS formed with stable intramolecular hydrogen bond might limit the availability for EDDS to extract Pb from goethite. On the other hand, each protonated amine of zwitterionic EDTA could form hydrogen bonds with two neighbouring carboxyl groups, intensifying the negative charge of carboxyl groups and enhancing the Pb extraction efficiency. However, there was a higher amount of re-adsorption of PbEDTA than PbEDDS, because zwitterionic EDTA resulted in a greater Pb extraction and facilitated iron dissolution which significantly altered the goethite morphology, particle size, and surface area. These results suggested that, despite being structural isomers, EDDS and EDTA resulted in varying extents of Pb extraction and re-adsorption due to their different zwitterionic properties.

Metal contents and fractionation in contaminated soil after column leaching using [S, S]-EDDS

Column leaching using [S, S]-ethylene diamine disuccinate ([S, S]-EDDS) on copper tailing soils was carried out to investigate metal content and fractionation after leaching. The soil column was divided into four layers after leaching. Fractionation of Cu, Pb, Zn, and Mn in soil was analyzed using a modified BCR sequential extraction method. Metal contents (Cu, Pb, Ca, Mn) in soil layers increased with the depth of the soil column after leaching in the [S, S]-EDDS treatment. The cumulative extraction efficiency was approximately 43.1% for Cu, 26.8% for Zn, 19.5% for Pb, 10.5% for Ca, 2.07% for Mg, 58.5% for Mn, and 7.92% for Fe. The removal of the reducible fractions of Cu and Mn and the exchangeable fraction of Zn was the most significant in the treatment with [S, S]-EDDS. The exchangeable fraction of Pb was the main fraction that was affected by leaching using [S, S]-EDDS. Distribution of Cu and Mn were severely modified by leaching with [S, S]-EDDS. Percentages of residual fractions of the tested heavy metals in the treatment with [S, S]-EDDS after leaching were much higher than that in the control. Although column leaching using [S, S]-EDDS could remove target metals effectively and impaired their availability, it also dissolved large amounts of major elements and modified the distribution of Mn appreciably.

Chelators enhanced biocide inhibition of planktonic sulfate-reducing bacterial growth

Biocides are currently the primary mitigation method to control sulfate-reducing bacteria (SRB) in biofouling, reservoir souring and microbiologically influenced corrosion. Increasingly restrictive environmental regulations and safety concerns on biocide uses demand more efficient dosing of biocides. Chelators have been known to enhance antibiotics because of their properties such as increasing the permeability of the outer cell membrane of Gram-negative bacteria. Two readily biodegradable chelators, ethylenediaminedisuccinate (EDDS) and N-(2-hydroxyethyl)iminodiacetic acid (HEIDA) disodium salts that are touted as potential replacements of ethylenediaminetetraacetic acid (EDTA), were evaluated as potential biocide enhancers for glutaraldehyde and tetrakis hydroxymethyl phosphonium sulfate (THPS) in their inhibition of planktonic SRB growth. Desulfovibrio vulgaris ATCC 7757 and Desulfovibrio desulfuricans ATCC 14563 were grown in modified ATCC 1249 medium and in enriched artificial seawater, respectively. Laboratory tests in 100 ml anaerobic vials showed that EDDS or HEIDA alone did not inhibit SRB growth. However, when EDDS or HEIDA was combined with glutaraldehyde or THPS, each of them enhanced the biocide inhibition of planktonic SRB growth.

Remediation of Cu-contaminated soil using chelant and EAOP

An electrochemical advanced oxidation process (EAOP) was used for treatment of the washing solution obtained during leaching of Cu (364 ± 2 mg kg−1) contaminated soil, with chelant S,S isomer of ethylenediamine disuccinate ([S,S]-EDDS). In the EAOP (constant current density 40 mA cm−2), a boron-doped diamond anode was used for the generation of hydroxyl radicals and oxidative decomposition of [S,S]-EDDS-metal complexes in the washing solution. The released Cu was mostly electro-deposited on the stainless-steel cathode. Three consecutive additions of 5 mmol kg−1 [S,S]-EDDS removed 46% of the Cu from the soil, mostly from carbonate and oxide soil fractions (87 and 99% Cu reduction). The soil Cu oral availability in the simulated stomach and intestinal phases (in vitro physiologically based extraction test) was reduced by 5.5 and 4.6-times. Cu plant availability (in vitro diethylenetriamine pentaacetate test) was reduced by 3.6-times. The discharge solution was clear, almost colorless, with pH 8.4, 0.45 mg L−1 Cu and 0.01 mM EDDS.

Interactions of EDDS with Fe- and Al-(hydr)oxides

The efficiency of EDDS ([S,S]-ethylenediaminedisuccinate) in metal (phyto) extraction has been discussed in many recent papers. This study demonstrated that the presence of Fe- and Al-(hydr)oxides in soils influences the speciation of EDDS and thus can decrease the extraction of the targeted metallic contaminants (e.g., Pb, Cu, Zn). Above all, amorphous and poorly crystalline oxides (e.g., ferrihydrite) seem to significantly control dissolved Fe and Al concentrations in soils in the presence of metal–EDDS complexes and especially uncomplexed EDDS. Metals released from these minerals compete for the chelating agent and the extraction efficiency of the targeted metals is lowered. The formation of stable Cu–EDDS complexes, which are preferentially formed in soils with high Cu concentrations, results into a lower dissolution of ferrihydrite and goethite compared to free EDDS and Al–EDDS. Information about the contents of amorphous and poorly crystalline oxides in the treated soils would thus be beneficial for choosing efficient EDDS dosages.

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)/H 2O 2) 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 (H 2O 2)) 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)/H 2O 2 system, EDDS was proven to be the most effective whereas pyrophosphate showed negligible activation of H 2O 2. 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.

Copper contamination of vineyard soils from small wine producers: A case study from the Czech Republic

This work focused on evaluating metal (Cd, Cu, Pb) contamination of vineyard soils from small wine producers from the Czech Republic. Copper, as the main contaminant originating mostly from the application of Cu-pesticides, was mainly concentrated in the superficial layers and close to the treated plants, which represents its tight binding to soil organic matter and Fe-, Mn-, Al-(hydr)oxides as proved by chemical fractionation analyses. Most of the studied vineyard soils did not meet the regulatory limits for Cu in agricultural soils set by the Ministry of the Environment of the Czech Republic and the warning limits set by the European Commission (EC). The highest Cu concentrations were found in the soil from the non-active vineyard, suggesting that contamination of soils from abandoned vineyards should be investigated before changing their use in agriculture. Total Cd concentrations, resulting probably from the application of fertilisers, exceeded the Czech regulatory limits in all soils. However, when the EC regulations would be used, soils only from two vineyards would not meet the warning limits. This fact calls for a unification of the Czech and European regulations. Furthermore, standardised single-step extraction procedures, 0.01 M CaCl 2; and 0.05 M EDTA (ethylenediaminetetraacetate) were carried in order to evaluate the potential availability of Cu in these soils. This study showed that the CaCl 2 extraction is not suitable for predicting Cu bioavailability in slightly alkaline vineyard soils and that the EDTA extraction is more suitable for predicting the potential availability of Cu in such soils. Furthermore, the 0.05 M EDDS (ethylenediaminedisuccinate) extraction was proposed for Cu-contaminated soils as an alternative to the 0.05 M EDTA extraction procedure.

Hydrolysed wool: A novel chelating agent for metal chelant-assisted phytoextraction from soil

Phytoextraction has revealed great potential, however it is limited by the fact that plants need time and nutrient supply and have a limited metal uptake capacity. Although the use of synthetic chelators, such as EDTA, enhances heavy metal extraction, it also produces the negative side effects of high phytotoxicity, as well as leaching of essential metals. The aim of this research was to investigate the application of wool, in mobilising metals and in improving the phytoextraction of metals-contaminated soil. We performed column experiments with 14 d and 7 d partially hydrolysed wool as chelating agent on a silty-loamy sand agricultural soil. In the column experiment the 14 d wool hydrolysate mobilised 68% of Cu in soil, whereas in the case of Cd it mobilised 5.5%. The model plant selected for the phytoextraction experiments was tobacco ( Nicotiana tabacum). The plant uptake of Cd and Cu, assisted by the application of 6.6 g kg −1 wool hydrolysate was increased by 30% in comparison to the control plants. The application of 13.3 g kg −1 wool hydrolysate enhanced the Cu uptake by up to 850%. Moreover, high leaching probability frequently observed when applying chelating agents, such as EDTA or ethylene diamine disuccinate (EDDS), were not detected. The use of hydrolysed wool therefore merits further investigation.

Degradability of ethylenediaminedisuccinic acid (EDDS) in metal contaminated soils: Implications for its use soil remediation

Previous research has identified ethylenediaminedisuccinate (EDDS) as a promising biodegradable alternative for persistent compounds such as EDTA for application in soil washing or enhanced phytoextraction of heavy metals. This study examines heavy metal mobilization in three polluted soils varying in soil composition, with specific attention for competitive behaviour for complexation between the various metals and major elements, such as Al, Fe, Mn, Ca and Mg. In addition, amendment biodegradability was compared between the different soil types. The selected soils included a moderately contaminated calcareous clayey soil, a dredged sediment derived surface soil with similar soil characteristics yet more heavily polluted with Cd, Cr and Zn, and a sandy soil moderately contaminated by historical smelter activity (atmospheric deposition). Biodegradability of EDDS in the three soils varied distinctly. This was mainly expressed in the duration of the lag phase prior to metal complex degradation, and not so much in the half life when degradation effectively did set in. Differences in the lag phase were attributed to differences in soil pollution. However, EDDS was fully degraded within a period of 54 d in all soils regardless of initial delay. Assessment of the cation mobilisation patterns in the three soils under study revealed that mainly Ca, Fe and Al can reduce effectiveness of heavy metal mobilisation by competition for complexation.

Fate of DTPA, EDTA, and EDDS in Hydroponic Media and Effects on Plant Mineral Nutrition

ABSTRACT Synthetic chelators are commonly used in hydroponic media to solubilize iron (Fe); however, the fate of these chelators is unknown. This study examined the persistence of three synthetic chelators, ethylenediaminetetraacetate (EDTA), diethylenetriaminepentaacetate (DTPA), and ethylenediaminedisuccinate (EDDS) in a bench-scale lettuce production system. The EDDS concentration decreased rapidly within 7d, most likely due to biodegradation. The EDTA and DTPA concentrations stayed steady throughout the experiments despite additions to maintain a constant volume and loss of chelator may have been due to either plant uptake or photodegradation of the chelator. Despite large differences in solution chemistry, the final shoot concentrations of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) were similar among chelator treatments, whereas root concentrations of these same elements were highly variable. The concentration of DTPA in a commercial lettuce production system was measured and highly variable concentrations were found.

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 2O 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 2O 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 2O 2 was detected in the effluent.

Mobilization of heavy metals from contaminated paddy soil by EDDS, EDTA, and elemental sulfur

For enhanced phytoextraction, mobilization of heavy metals (HMs) from the soil solid phase to soil pore water is an important process. A pot incubation experiment mimicking field conditions was conducted to investigate the performance of three soil additives in mobilizing HMs from contaminated paddy soil (Gleyi-Stagnic Anthrosol): the [S, S]-isomer of ethylenediamine disuccinate (EDDS) with application rates of 2.3, 4.3, and 11.8 mmol kg(-1) of soil, ethylenediamine tetraacetate (EDTA; 1.4, 3.8, and 7.5 mmol kg(-1)), and elemental sulfur (100, 200, and 400 mmol kg(-1)). Temporal changes in soil pore water HM and dissolved organic carbon concentrations and pH were monitored for a period of 119 days. EDDS was the most effective additive in mobilizing soil Cu. However, EDDS was only effective during the first 24 to 52 days, and was readily biodegraded with a half-life of 4.1 to 8.7 days. The effectiveness of EDDS decreased at the highest application rate, most probably as a result of depletion of the readily desorbable Cu pool in soil. EDTA increased the concentrations of Cu, Pb, Zn, and Cd in the soil pore water, and remained effective during the whole incubation period due to its persistence. The highest rate of sulfur application led to a decrease in pH to around 4. This increased the pore water HM concentrations, especially those of Zn and Cd. Concentrations of HMs in the soil pore water can be regulated to a large extent by choosing the proper application rate of EDDS, EDTA, or sulfur. Hence, a preliminary work such as our pot experiment in combination with further plant experiments (not included in this study) will provide a good tool to evaluate the applicability of different soil additives for enhanced phytoextraction of a specific soil.

Chelate assisted phytoextraction of heavy metals from soil. Effect, mechanism, toxicity, and fate of chelating agents

The low-cost, plant-based phytoextraction technique has often been described as a promising technique to remediate heavy metal contaminated agricultural land. The application of chelating agents has shown positive effects in increasing the solubility of heavy metals in soil and therefore in enhancing phytoextraction. This paper gives an overview of the chelating agents applied in recent studies. Various synthetic aminopolycarboxylic acids, such as ethylene diamine tetraacetic acid, and natural ones such as, ethylene diamine disuccinate and nitrilotriacetic acid, are described. Additionally, results of the application of natural low molecular weight organic acids, such as citric and tartaric acid are given. The effectiveness of these different chelating agents varies according to the plant and the heavy metals used. Furthermore, a focus is laid on the chelating agents fate after application and on its toxicity to plants and soil microorganisms, as well as it degradation. The rate of degradation is of great importance for the future of chelate assisted phytoextraction as it has a direct impact on the leaching probability. An effective prevention of leaching will be crucial for the acceptance and the economic breakthrough of enhanced phytoextraction, but a satisfactory solution to this key issue has so far not been found. Possibly further experiments in the field of enhanced phytoextraction will be able to solve this major problem, but over decades various greenhouse experiments and recently field experiments have resulted in different observations. Therefore, it is questionable if further research in this direction will lead to a promising solution. Phytoextraction has possibly reached a turning point in which it should distance itself from chelate assisted phytoextraction and focus on alternative options.

The influence of EDDS and EDTA on the uptake of heavy metals of Cd and Cu from soil with tobacco Nicotiana tabacum

Phytoextraction, the use of plants to extract contaminants from soils and groundwater, is a promising approach for cleaning up soils contaminated with heavy metals. In order to enhance phytoextraction the use of chelating agents has been proposed. This study aims to assess whether ethylene diamine disuccinate (EDDS), a biodegradable chelator, can be used for enhanced phytoextraction purposed, as an alternative to ethylene diamine tetraacetate (EDTA). EDDS revealed a higher toxicity to tobacco (Nicotiana tabacum) in comparison to EDTA, but no toxicity to microorganisms. The uptake of Cu was increased by the addition of EDTA and EDDS, while no increase was observed in the uptake of Cd. Both chelating agents showed a very low root to shoot translocation capability and the translocation factor was lower than the one of the control. Heavy metals where significantly more phytoavailable than in the control, even after harvesting, resulting in a high heavy metal leaching possibility, probably owing to a low biodegradation rate of EDDS. New seedlings which were transplanted into the EDDS treated pots 7d after the phytoextraction experiment, showed signs of necrosis and chlorosis, which resulted in a significantly lower biomass in comparison to the control. The seedlings on the EDTA treated pots showed no toxicity signs. Contrary to previous opinions the results of this study revealed the chelating agents EDTA and EDDS as unsuitable for enhanced phytoextraction using tobacco.

Potential of five willow species ( Salix spp.) for phytoextraction of heavy metals

The potential of short rotation coppice (SRC) for phytoremediation of contaminated sites and simultaneous generation of bio-energy by conversion of the produced biomass has been discussed in previous publications. The current study compares five species of Salix spp. in their ability to extract and accumulate heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in harvestable plant parts. The species used in this study were: Salix dasyclados ‘Loden’, Salix triandra ‘Noir de Villaines’, Salix fragilis ‘Belgisch Rood’, Salix purpurea × Salix daphnoides ‘Bleu’, Salix schwerinii ‘Christina’. The comparison was conducted in a pot experiment in open air over the course of a growing season on three different soil types: a moderately contaminated dredged sediment derived surface soil (A1), a heavily polluted sediment derived surface soil (A2) and a sandy soil with moderately elevated concentrations due to atmospheric deposition by historic smelter activities (A3). In addition, the effects of soil treatment with 2.5 mmol kg −1 ethylene diamine disuccinate (EDDS) on metal accumulation in stems and leaves were evaluated for one Salix clone (Loden). Of the five clones tested, Christina, Loden and Belgisch Rood exhibited the highest Cd and Zn concentrations and therefore deserve further attention in field validation. A first estimation of the order of magnitude of Cd and Zn that could potentially be annually extracted with these clones, resulted in 5–27 kg ha −1 for Zn and 0.25–0.65 kg ha −1 for Cd, based on the soil type. However, biomass production in field situations will mainly determine metal removal. Treatment with EDDS exhibited distinct differences in inducing metal removal on the various soils. Uptake of Cd and Zn could not be enhanced in A1, whereas in A2 and A3 removal of these metals could be increased by 50–100% after treatment. In all soils EDDS treatment also had a distinct effect on Cu uptake.

Bioavailability and mobility of Pb after soil treatment with different remediation methods

The risk of Pb contaminated soil after treatment with different remediation techniques was assessed. Soil vitrification (microwaves) reduced Pb orally available from the stomach and intestinal phase measured by a physiologically based extraction test. Solidification of Pb (Slovakite) did not reduce the concentration of orally available Pb and increased the Pb uptake by Thlaspi goesingens for 2-times compared to plants grown on the original soil. Soil extraction with 40 mmol/kg EDTA removed 57.6% of Pb. However, the concentration of orally available Pb and Pb uptake by T. goesingens increased. The concentration of mobile soil Pb also increased for 14-times measured by a toxicity characteristic leaching procedure. Soil leaching with 10 mmol/kg biodegradable chelator [S,S] ethylenediamine disuccinate and using a horizontal permeable reactive barrier for Pb accumulation from the washing solution removed 17.8% of Pb, but increased Pb uptake by T. goesingens by 3-times and slightly increased the concentration of Pb in the intestinal phase. Leaching did not significantly effects Pb availability from the stomach phase or Pb mobility.

Heap leaching of Cu contaminated soil with [ S, S]-EDDS in a closed process loop

Heap leaching of Cu contaminated soil (412 ± 11 mg kg −1) with 5 mmol kg −1 ethylenediamine disuccinate [ S, S]-EDDS as a chelator was tested in a laboratory-scale soil column study. The washing solution was recycled in a closed process loop after microbial (using a microbially active permeable bed, composed of substrate and absorbent) and oxidative chemical (using combined ozonation and UV irradiation) degradation of metal–[ S, S]-EDDS complexes and retention of released Cu on a commercial absorbent Slovakite. Heap leaching using the permeable bed removed 25.5 ± 3.6% of initial total Cu from the soil. Ozone/UV treatment of the [ S, S]-EDDS washing solution removed much more, 47.5 ± 7.4%, of Cu. Both methods yielded a clear and colorless final (waste) washing solution, with 7.0 ± 10.0 and 2.6 ± 0.7 mg L −1 Cu (permeable bed and ozone/UV method, respectively). The results of our study indicate that chemical treatment of chelator washing solution with ozone/UV in a closed process loop could lead to the development of a new, efficient and environmentally safe remediation method with controllable Cu emissions.

Heap Leaching of Lead Contaminated Soil Using Biodegradable Chelator [S,S]-ethylenediamine Disuccinate

The feasibility of heap leaching Pb contaminated soil using biodegradable chelator [S,S]-ethylenediamine disuccinate ([S,S]-EDDS) in concentrations ranging from 10 to 40 mmol kg−1 was assessed in a laboratory study. Treatment with 40 mmol kg−1 [S,S]-EDDS was the most efficient, removing 31.3% of soil Pb and producing a waste washing solution with a peak Pb concentration slightly exceeding 10 mM. The removal of Pb from simulated washing solution containing 10 mM Pb by biodegradation of the Pb-[S,S]-EDDS complex and sorption of the released Pb on a vermiculite/soya meal/Slovakite based permeable bed was completed in 7.5 days. Lead recovery from washing solutions with higher molarity was significantly slower. Lead fractionation and bioavailability were assessed 6-months after soil treatment. Heap leaching removed Pb proportionally from carbonates (approx. 25% Pb) and organic matter (>50% Pb), the two main Pb-bearing soil fractions, and increased the small pool of Pb soluble in the soil solution. The latter had no effect on Pb phytoavailability. Accumulation of Pb in leaves of the reported hyperaccumulator species Thlaspi goesingense was <20 mg kg−1 in all treatments, comparable to the Pb concentration in lettuce (Latuca sativa). Soil treatment with 40 mmol kg−1 [S,S]-EDDS reduced concentrations of Pb orally-accessible in the stomach and intestine phase from initial 234.0 and 52.5 mg kg−1 to 157.8 and 29.7 mg kg−1, respectively, according to Ruby's test. Our results indicate that heap leaching of Pb with [S,S]-EDDS is not a viable remediation option for the tested soil and conditions used.

Comparison of EDTA and EDDS as potential soil amendments for enhanced phytoextraction of heavy metals

Phytoextraction has been proposed as an alternative remediation technology for soils polluted with heavy metals or radionuclides, but is generally conceived as too slow working. Enhancing the accumulation of trace pollutants in harvestable plant tissues is a prerequisite for the technology to be practically applicable. The chelating aminopolycarboxylic acid, ethylene diamine tetraacetate (EDTA), has been found to enhance shoot accumulation of heavy metals. However, the use of EDTA in phytoextraction may not be suitable due to its high environmental persistence, which may lead to groundwater contamination. This paper aims to assess whether ethylene diamine disuccinate (EDDS), a biodegradable chelator, can be used for enhanced phytoextraction purposes. A laboratory experiment was conducted to examine mobilisation of Cd, Cu, Cr, Ni, Pb and Zn into the soil solution upon application of EDTA or EDDS. The longevity of the induced mobilisation was monitored for a period of 40 days after application. Estimated effect half lives ranged between 3.8 and 7.5 days for EDDS, depending on the applied dose. The minimum observed effect half life of EDTA was 36 days, while for the highest applied dose no decrease was observed throughout the 40 day period of the mobilisation experiment. Performance of EDTA and EDDS for phytoextraction was evaluated by application to Helianthus annuus. Two other potential chelators, known for their biodegradability in comparison to EDTA, were tested in the plant experiment: nitrilo acetic acid (NTA) and citric acid. Uptake of heavy metals was higher in EDDS-treated pots than in EDTA-treated pots. The effects were still considered insufficiently high to consider efficient remediation. This may be partly due to the choice of timing for application of the soil amendment. Fixing the time of application at an earlier point before harvest may yield better results. NTA and citric acid induced no significant effects on heavy metal uptake.

Washing of Pb contaminated soil using [ S, S] ethylenediamine disuccinate and horizontal permeable barriers

The feasibility of in situ washing of soil contaminated with Pb (6.83 mmol kg −1) using biodegradable chelator, [ S, S] stereoisomere of ethylenediamine disuccinate ([ S, S]-EDDS) and horizontal permeable barriers was examined in soil columns. After 4-cycles of 10 mmol kg −1 soil [ S, S]-EDDS applications, followed by irrigation, 24.7% of total initial Pb was washed from the contaminated soil and accumulated into the barrier. Sequential extractions indicated that washing removed most of the Pb from the organic soil fraction. Barriers were positioned 20 cm deep in the soil and consisted of a 2 cm layer of nutrient enriched vermiculite. Barriers reduced leaching of Pb in the first cycle of [ S, S]-EDDS addition by more than 500-times compared to columns with no barrier. After four cycles of chelator addition, a total of 0.24% of the initial Pb was leached from the columns with barriers. Four cycles of in situ soil washing in soil columns were less effective than simulated ex situ soil washing with 40 mmol kg −1 [ S, S]-EDDS, where 51.0% of the Pb was removed after 48-h extraction. Ex situ soil washing with 10 mmol kg −1 [ S, S]-EDDS was equally effective as the first cycle of in situ soil washing (15.5% and 14.5% of removed Pb, respectively).