Fe Ethylenediaminetetraacetic Acid Research Articles

Carbon zero-valent iron materials possessing high-content fine Fe0 nanoparticles with enhanced microelectrolysis-Fenton-like catalytic performance for water purification

Carbon-coated nanoscale zero-valent iron (Fe@C) is a robust active material in wastewater treatment. Small particle size and high content of zero valent iron nanoparticles (Fe° NPs) in Fe@C composites ensure their desired activity in Fenton-like reaction. We mechanochemically prepared Fe-ethylenediaminetetraacetic acid (Fe-EDTA), Fe-aminoterephthalic acid (Fe-ATA), and Fe-melamine (Fe-MA) complex as starting materials to synthesize Fe@C. The coordination ability between iron and ligands determines the particle size and distribution of Fe NPs. Fe@C derived from Fe-EDTA possessed 97.6 % of Fe° NPs (4 nm-in-diameter), exhibited strong catalytic ability for sulfamethazine removal with and without the addition of H2O2, but also encountered serious erosion and poor reusability. Fe@C generated from Fe-ATA manifested reasonable activity and excellent stability and reusability in Fenton-like reaction, which was contributed by the suitable particle size (6 nm) and special topological structure. Fe@C-MA produced from Fe-MA exhibited bad catalytic performance and reusability due to its larger Fe NPs size (300 nm).

Electrocatalytic ozonation process supplemented by EDTA-Fe complex for improving the mature landfill leachate treatment

The present study was to enhance catalytic ozonation process (COP) using ferric (Fe)- ethylenediaminetetraacetic acid (Fe-EDTA) integrated with an electrocoagulation (EC) process for landfill leachate pretreatment. For this purpose, the effect of operating parameters such as ozone and Fe-EDTA concentrations, current, initial pH, and reaction time were investigated. The findings revealed that the EC process and single ozonation process (SOP) could alone reduce chemical oxygen demand (COD) in landfill leachate by 23% and 39%; respectively. Moreover, integration of both processes at 100 mA current, 400 mg h−1 ozone concentration, and 3 h reaction time could significantly improve COD reduction to 70%. As well, current efficiency and ozone consumption in the proposed system could considerably develop compared with EC process and SOP. The integrated electro-catalytic SOP using Fe-EDTA could be operated at neutral pH value, which the COD removal efficiency was obtained 79.7%. Subsequently, biochemical oxygen demand (BOD5)/COD ratio of effluent increased to 0.64. Examining pseudo-first-order and pseudo-second-order kinetics, it was realized that constant rate in the system had augmented. These results also indicated that the modified process using Fe-EDTA was a promising landfill leachate pretreatment technique that could significantly enhance COD removal efficiency and BOD5/COD ratio, and ultimately decrease time and sludge production.

Effects of Fe fertilizer eluate on the growth of Sargassum horneri at the germling and immature stages

To aid in the restoration of coastal barren ground areas, it is important to clarify the effects of chelated iron on the growth of seaweed. In particular, for the further development of practical methods to promote seaweed growth, Fe-binding organic ligands, such as humic substances (HSs) composed of humus materials, rather than Fe-binding inorganic ligands, such as ethylenediaminetetraacetic acid (EDTA), should be investigated. In this study, the effects of an Fe fertilizer, made from HSs and steelmaking slag, on the growth of the brown alga Sargassum horneri at the germling and immature stages were examined. The addition of the Fe fertilizer eluate containing Fe organic ligand complexes clearly promoted the growth of S. horneri at the germling and immature stages. It was also clear that the effect of Fe concentration in the Fe fertilizer eluate on the growth rate was almost the same as that of Fe–EDTA. Moreover, the addition of the Fe fertilizer eluate had a great effect on the brown color of S. horneri thalli and promoted the increased content of photosynthetic pigments, such as chlorophyll a. Based on these experimental results, the application of the Fe fertilizer containing Fe organic ligand complexes is expected to become an effective method for the restoration of the barren ground phenomenon in Fe-deficient coastal areas.

Fe(III)EDTA and Fe(II)EDTA-NO reduction by a sulfate reducing bacterium in NO and SO2 scrubbing liquor

A viable process concept, based on NO and SO2 absorption into an alkaline Fe(II)EDTA (EDTA: ethylenediaminetetraacetic acid) solution in a scrubber combined with biological reduction of the absorbed SO2 utilizing sulfate reducing bacteria (SRB) and regeneration of the scrubbing liquor in a single bioreactor, was developed. The SRB, Desulfovibrio sp. CMX, was used and its sulfate reduction performances in FeEDTA solutions and Fe(II)EDTA-NO had been investigated. In this study, the detailed regeneration process of Fe(II)EDTA solution, which contained Fe(III)EDTA and Fe(II)EDTA-NO reduction processes in presence of D. sp. CMX and sulfate, was evaluated. Fe(III)EDTA and Fe(II)EDTA-NO reduction processes were primarily biological, even if Fe(III)EDTA and Fe(II)EDTA-NO could also be chemically convert to Fe(II)EDTA by biogenic sulfide. Regardless presence or absence of sulfate, more than 87 % Fe(III)EDTA and 98 % Fe(II)EDTA-NO were reduced in 46 h, respectively. Sulfate and Fe(III)EDTA had no affection on Fe(II)EDTA-NO reduction. Sulfate enhanced final Fe(III)EDTA reduction. Effect of Fe(III)EDTA on Fe(II)EDTA-NO reduction rate was more obvious than effect of sulfate on Fe(II)EDTA-NO reduction rate before 8 h. To overcome toxicity of Fe(II)EDTA-NO on SRB, Fe(II)EDTA-NO was reduced first and the reduction of Fe(III)EDTA and sulfate occurred after 2 h. First-order Fe(II)EDTA-NO reduction rate and zero-order Fe(III)EDTA reduction rate were detected respectively before 8 h.

Iron requirement for soybean [Glycine max (L.) Merrill] inoculated with selected exotic and native isolates of Bradyrhizobium sp. under irrigated conditions

A field and greenhouse experiments were conducted to determine the requirement of Fe nutrient supplied through foliar and soil application in soybean inoculated with different selected isolates of exotic and native Bradyrhizobium spp. in saline soils. Six soybean genotypes and three Bradyrhizobium spp. were used for the greenhouse experiments, whereas only two soybean genotypes, namely TGx-1336424 and GIZA, were selected for further study under field conditions. Two levels of FeSO4 (0 and 4 mg Fe kg−1 soil) directly supplied to the soil and three levels of Fe-ethylenediaminetetraacetic acid (0–2% of Fe) through foliar application were used for greenhouse and field experiments, respectively. The results of the greenhouse experiment indicated a non-significant effect of Fe application on nodulation and shoot biomass in soybean. Fe application did not improve the grain yield and total biomass yield in soybean inoculated with UK isolate and local isolate but showed remarkable improvement with TAL-379. High soil native N might be the cause for insignificant effect of Fe applied at 2% in highly effective inoculated plants. Therefore, it can be concluded that the symbiotic effectiveness of Bradyrhizobium sp. and the native soil N would affect the soybean Fe requirement supplied through foliar application.

Iron efficiency of different corn hybrids grown in nutrient solution culture

Growing Fe-efficient genotype(s) could be considered as a preferred genetic approach to tackle the widespread constraint of Fe-deficiency-/lime-induced chlorosis in crop grown on alkaline soil. This study aimed to investigate morphological and physiological traits linked to expression of Fe deficiency among four corn (Zea mays) including sweet (Z. mays sacchrata cvs. H403 and H404) and grain (Z. mays indentata cvs. H500 and H700) hybrids grown in nutrient solution using two Fe concentrations (5 and 50 µM Fe-ethylenediaminetetraacetic acid (Fe-EDTA)). Significant variation was found among studied hybrids in their tolerance to Fe-deficiency stress. Sweet corn hybrids were more sensitive to Fe deficiency as compared with grain corn hybrids and greater reduction was observed in their shoot dry matter at the 5 µM Fe-EDTA treatment. The greatest decrease in plant height, leaf area, and root and shoot dry matter weight under Fe-deficiency condition was found for H403 hybrid. No significant correlation was found between shoot and root Fe concentration with crop tolerance to Fe deficiency. Furthermore, different response of corn hybrids to Fe deficiency is an important factor, which has to be considered in Fe fertilizer recommendation as well as breeding programs.

EVALUATION OF DIFFERENT IRON SOURCES FOR IRON CHLOROSIS RECOVERY IN LOW-CHILL PEACH CULTIVARS

An experiment was conducted with iron chlorosis affected low-chill peach cultivars such as ‘Shaharanpur Prabhat’, ‘Shan-e-Punjab’, and ‘Pratap’ to examine the recovery upon foliar application of three iron sources namely iron (Fe)-sulfate, Fe-citrate and Fe ethylenediaminetetraacetic acid (EDTA). All the iron sources significantly increased the SPAD meter value, physiologically active (Fe2+) iron and total iron content of the leaves over control. However, highest values were noted with foliar spray of 1.0% Fe-sulfate. The low-chill peach cultivar ‘Saharanpur Prabhat’ responded best with iron resupply treatment. Significant correlations (at P ≤ 0.01) were obtained between SPAD meter readings with both physiologically active iron (Fe2+) and total iron content of leaves in all peach cultivars. Among the sources, the correlations between SPAD meter readings, physiologically active iron (Fe2+) and total iron contents were significant at P ≤ 0.01 for only Fe-sulfate and Fe-citrate. The regression analysis showed that the SPAD meter reading accounted 78.2 to 88.0% variation in physiologically active iron (Fe2+) and 65.0 to 73.7% variation in the total iron content in the low-chill peach cultivars. The SPAD readings could be used for management of iron chlorosis in peach orchard.

Evaluation of sustainable management techniques for preventing iron chlorosis in the grapevine

Background and Aims The control of iron (Fe) chlorosis by synthetic Fe chelates is costly and their application can have adverse environmental impacts. We investigated the effectiveness of alternative vineyard strategies to prevent Fe chlorosis in grapevines. Methods and Results An experiment was conducted over two consecutive seasons on Vitis vinifera L. cv. Cabernet Sauvignon grafted on the Fe-chlorosis susceptible Vitis riparia grown in pots filled with calcareous soil. Intercropping with Festuca rubra enhanced leaf chlorophyll index and reduced the root activity of phosphoenolpyruvate carboxylase enzyme, a physiological marker of Fe deficiency. This response was similar to that of supplying Fe-ethylenediamine-N,N'-bis(2-hydroxyphenyl)acetic acid to soil. Application of ammonium with 3,4-dimethylpyrazole phosphate (a nitrification inhibitor) increased leaf chlorophyll index and stomatal length, and induced root biochemical responses similar to those with Fe-ethylenediamine-N,N'-bis(2-hydroxyphenylaceticacid) application. Leaf-applied Fe-ethylenediaminetetraacetic acid induced a high root citric acid concentration, suggesting a limited translocation of Fe from leaves to roots. Intercropping with Festuca rubra decreased the leaf fluorescence-derived parameters in the first year and increased the leaf stomata conductance in the second year of the experiment. Conclusions The results demonstrate the potential for preventing grapevine Fe chlorosis more sustainably through managing ammonium nutrition and adopting intercropping with Fe-efficient grasses. Significance of the Study The data provide evidence of the effectiveness and physiological responses of agronomic strategies, alternative to synthetic Fe chelates, for preventing Fe deficiency in the grapevine.

Three-Liquid-Phase Extraction and Separation of Ti(IV), Fe(III), and Mg(II)

Three-liquid-phase extraction has been considered to be a promising method for isolation and separation of multicomponents. Selective extraction-separation of Ti(IV), Fe(III), and Mg(II) in the three-liquid-phase system containing trialkylphosphine oxide (TRPO), poly(ethylene glycol) with an average molecular mass of 2000 (PEG 2000), and (NH(4))(2)SO(4) was achieved by adding a water-soluble complexing agent, ethylenediaminetetraacetic acid (EDTA). The simple and environmentally benign complexing method was proved to be an effective strategy for enhancing the selectivity of the PEG-2000-rich middle phase for Fe(III) without reducing the affinity of the TRPO-rich top phase to Ti(IV). The related chemistry was detailed, and effects of some important parameters such as the aqueous phase pH, EDTA amount, mixing time, and temperature were examined. It revealed that Ti(IV) and Fe(III) could be enriched respectively into the TRPO-rich top phase and the PEG-2000-rich middle phase through optimization of the aqueous pH and the EDTA amount. Ti(IV) was extracted into the top phase with a slow kinetics and a positive enthalpy change (Delta H), whereas Fe(III) was rapidly transferred to the middle phase as Fe(III) EDTA complexes formed by an exothermic reaction. Mg(II) tended to remain in the bottom phase.

Potential for CO2 Fixation by Chlorella pyrenoidosa Grown in Oil Sands Tailings Water

Discharge of process water into tailings ponds is associated with many mining operations, including that of bitumen. These tailings ponds can be used to grow organisms, such as algae, which, in turn, fix CO2 and degrade unwanted dissolved components. After processing, algae can be used for the production of fuels (for example, biodiesel or methane). In this work, we explored the potential for growth of a unicellular algae, Chlorella pyrenoidosa, in tailings water from an oil sands mining and upgrading operation. Once we determined that it was possible to grow algae in the tailings water, we designed and optimized minimal growth media for biomass (algae) production and did a preliminary engineering estimate of the potential for CO2 fixation. The medium components required for growth of C. pyrenoidosa in 95% oil sands tailings water (OSTW) were screened using a two-level full factorial experiment. Sodium nitrate, phosphate, and Fe-ethylenediaminetetraacetic acid (EDTA) were the most important medium compone...

INFLUENCE OF IRON-CHELATES ON TRACE ELEMENT UPTAKE FROM TWO CALCAREOUS SOILS AND THE ACTIVITY OF OXYGEN-SCAVENGING ENZYMES IN LETTUCE

A pot experiment was carried out to determine the ability of lettuce (Lactuca sativa cv. ‘Waldmann's dark green’) to acquire iron (Fe) from Fe-ethylenediaminedisuccinic acid [EDDS, both as an isomeric mixture, EDDS(mix), and (S,S)-EDDS], Fe-ethylenediaminetetraacetic acid (EDTA) and Fe-ethylenediimonobis(2-hydroxyphenyl)acetic acid (EDDHA) in two calcareous soils and consequent effect on the activity of reactive oxygen species scavenging enzymes. Probably due to the rapid biodegradation of [S,S]-EDDS, EDDS(mix) provided Fe to lettuce more efficiently. Iron-EDDS(mix) and Fe-EDDHA were equally efficient in increasing Fe concentration in lettuce. The activity of superoxide dismutase (SOD) was not affected by Fe deficiency and the activity of copper (Cu) and zinc (Zn) containing SOD (Cu/ZnSOD) was dependent on lettuce Zn concentration. Ascorbate peroxidase and guaiacol peroxidase activities were increased by Fe-EDDHA, probably due to the steady supply of Fe. Physiologically active Fe pool for lettuce was equally provided by Fe-EDDS(mix) and Fe-EDTA.

Oxidation of EDTA with H2O2 catalysed by metallophthalocyanines

The oxidation of ethylenediaminetetraacetic acid (EDTA) and Na, Ca, Zn, Fe, and Mn EDTA complexes with hydrogen peroxide was studied in aqueous solution with the use of several metallophthalocyanines (MePcS) as catalysts. The impact of pH, temperature, and catalyst/substrate ratio were investigated. The most effective catalytic system under neutral conditions was FePcS–H2O2. In these laboratory‐scale experiments, a catalyst/substrate/H2O2 molar ratio of 4:100:2000 was found to be optimal, while the effective reaction temperature was 40–60 °C. When the impact of metal speciation was studied, metal‐specific degradation rates in the removal of these compounds were observed: all EDTA–metal complexes except Zn–EDTA were efficiently oxidized within three hours. The most degradable species was Fe(III)–EDTA. Among the catalysts, FePcS was found to be the most active in EDTA degradation. Over 90% of EDTA was removed in the presence of FePcS as catalyst within three hours of reaction time.

Effects of NO2− and NO3− on the Fe(III)EDTA reduction in a chemical absorption–biological reduction integrated NOx removal system

The biological reduction of Fe(III) ethylenediaminetetraacetic acid (EDTA) is a key step for NO removal in a chemical absorption-biological reduction integrated process. Since typical flue gas contain oxygen, NO(2)(-) and NO(3)(-) would be present in the absorption solution after NO absorption. In this paper, the interaction of NO(2)(-), NO(3)(-), and Fe(III)EDTA reduction was investigated. The experimental results indicate that the Fe(III)EDTA reduction rate decrease with the increase of NO(2)(-) or NO(3)(-) addition. In the presence of 10 mM NO(2)(-) or NO(3)(-), the average reduction rate of Fe(III)EDTA during the first 6-h reaction was 0.076 and 0.17 mM h(-1), respectively, compared with 1.07 mM h(-1) in the absence of NO(2)(-) and NO(3)(-). Fe(III)EDTA and either NO(2)(-) or NO(3)(-) reduction occurred simultaneously. Interestingly, the reduction rate of NO(2)(-) or NO(3)(-) was enhanced in presence of Fe(III)EDTA. The inhibition patterns observed during the effect of NO(2)(-) and NO(3)(-) on the Fe(III)EDTA reduction experiments suggest that Escherichia coli can utilize NO(2)(-), NO(3)(-), and Fe(III)EDTA as terminal electron acceptors.

Evaluation of complexed NO reduction mechanism in a chemical absorption–biological reduction integrated NOx removal system

Biological reduction of nitric oxide (NO) from Fe(II) ethylenediaminetetraacetic acid (EDTA)-NO to dinitrogen (N(2)) is a core process for the continual nitrogen oxides (NO(x)) removal in the chemical absorption-biological reduction integrated approach. To explore the biological reduction of Fe(II)EDTA-NO, the stoichiometry and mechanism of Fe(II)EDTA-NO reduction with glucose or Fe(II)EDTA as electron donor were investigated. The experimental results indicate that the main product of complexed NO reduction is N(2), as there was no accumulation of nitrous oxide, ammonia, nitrite, or nitrate after the complete depletion of Fe(II)EDTA-NO. A transient accumulation of nitrous oxide (N(2)O) suggests reduction of complexed NO proceeds with N(2)O as an intermediate. Some quantitative data on the stoichiometry of the reaction are experimental support that reduction of complexed NO to N(2) actually works. In addition, glucose is the preferred and primary electron donor for complexed NO reduction. Fe(II)EDTA served as electron donor for the reduction of Fe(II)EDTA-NO even in the glucose excessive condition. A maximum reduction capacity as measured by NO (0.818 mM h(-1)) is obtained at 4 mM of Fe(II)EDTA-NO using 5.6 mM of glucose as primary electron donor. These findings impact on the understanding of the mechanism of bacterial anaerobic Fe(II)EDTA-NO reduction and have implication for improving treatment methods of this integrated approach.

The role of Fe- and Mn-oxides during EDTA-enhanced phytoextraction of heavy metals

In several cases ethylenediaminetetraacetic acid (EDTA) proved to be an efficient mobilising amendment during chemically enhanced phytoextraction of heavy metals. The presence of Fe-(hydr)oxides and their dissolution after the addition of EDTA can limit the phytoextraction of the targeted heavy metals due to the high stability of the formed Fe(III)EDTA complexes. This study has focused on the influence of Fe- and Mn-oxides and hydroxides dissolution on heavy metal uptake by <i>Zea mays</i> in a two-year EDTA-enhanced phytoextraction process. Incubation experiments and speciation modelling proved the increased concentrations of Mn and Fe through the dissolution of Mn-and Fe-(hydr)oxides. Furthermore, increased Fe and Mn accumulation was observed in maize plants after the second year of the phytoextraction process. Therefore, the presence of Mn- and especially Fe-(hydr)oxides proved to be a limiting factor during EDTA-enhanced phytoextraction of heavy metals from contaminated soils.

Kinetics of Chemoheterotrophic Microbially Mediated Reduction of Ferric EDTA and the Nitrosyl Adduct of Ferrous EDTA for the Treatment and Regeneration of Spent Nitric Oxide Scrubber Liquor

Biomass from a prototype reactor was used to investigate the kinetics of chemoheterotrophic reduction of solutions of ferric ethylenediaminetetraacetic acid (EDTA) and solutions containing the nitrosyl adduct of ferrous EDTA using ethanol as the primary electron donor and carbon source. A series of batch experiments were conducted using biomass extracted from the scrubber solution treatment and regeneration stage of a prototype iron EDTA-based unit process for the absorption of nitric oxide with subsequent biological treatment. Using a linear-sweep voltammetric method for analysis of the ferric EDTA concentration, iron-reducing bacteria were found to behave according to the Monod kinetic model, at initial concentrations up to 2.16 g chemical oxygen demand (COD) as ethanol per liter, with a half-velocity constant of 0.532 g COD as ethanol/L and a maximum specific utilization rate of 0.127 mol/L of ferric ethylenediamine-tetraacetic acid [Fe(III)EDTA]*(g volatile suspended solids [VSS]/L)d(-1). Based on batch analyses, biomass yield and endogenous decay values of iron-reducing bacteria were estimated to be 0.055 g VSS/g COD and 0.017 L/d, respectively. An average of 1.64 times the theoretical (stoichiometric) demand of ethanol was used to complete reduction reactions. Kinetics of the reduction of the nitrosyl adduct of ferrous EDTA are summarized by the following kinetic constants: half-velocity constant (Ks) of 0.39 g COD/L, maximum specific utilization rate (k) of 0.2 mol/L [NO x Fe(II)EDTA(2-)](g VSS/L)d(-1), and inhibition constant (K(I)) of 0.33 g COD/L, as applied to the modified Monod kinetic expression described herein. Based on batch analyses, the biomass yield of nitrosyl-adduct-reducing bacteria was estimated to be 0.259 g VSS/g COD, endogenous decay was experimentally determined to be 0.0569 L/d, and an average of 1.26 times the stoichiometric demand of ethanol was used to complete reduction reactions.

Sample Conservation Prior to Total EDTA and Fe(III)EDTA Measurements

Ethylenediamine tetraacetic acid (EDTA) is a potent chelating agent and has the potential to affect the environmental mobility of heavy metals. A reliable quantification of EDTA and its speciation is required in order to accurately estimate the actual impact of this compound on the aquatic environment. This study aimed to determine the optimal conservation conditions for samples in order to accurately measure EDTA speciation and total EDTA concentration. The results obtained by studying the effects of time elapsed between sampling, conditioning [i.e., addition of reagents to complex EDTA with Fe (III)], and analysis show that the determination of EDTA speciation needs to be carried out immediately after sampling. The measurement of total EDTA may be performed within 2 mo, as long as the sample is filtered and conditioned on the day of sampling.

Mobilisation of recently absorbed 59Fe in ex vivo perfused rat duodena and the influence of iron status and subsequently absorbed chelators

To investigate the effect of subsequently absorbed metal chelators on recently absorbed 59Fe, duodenal segments from iron-deficient and iron-adequate rats were perfused ex vivo until the 59Fe tissue load had reached a steady state. Subsequently, the segments were perfused with 3 model chelators and their iron complexes: nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and citrate. Of these, NTA and EDTA bind iron much tighter than citrate, and Fe–NTA complexes exchange iron within seconds while Fe-EDTA complexes need 48 h to reach equilibrium. Duodenal mucosa-to-serosa transport rates were comparable for all 3 chelators and correlated linearly with luminal concentration. Subsequent perfusion with increasing NTA, Fe–NTA(1:2) and EDTA concentrations mobilised increasing amounts of 59Fe from the duodenum. Mobilised 59Fe moved preferentially back into the luminal perfusate in iron-adequate segments. In iron-deficient segments, 59Fe preferentially continued the absorption process across the basolateral membrane. Fe–EDTA(1:1) hardly mobilised any 59Fe back into the lumen, though basolateral transfer increased at high concentrations. Citrate and Fe–citrate(1:1) mobilised 59Fe only at very high concentrations. This behaviour is in accordance with the rules of complex chemistry: strong, fast reacting ligands like NTA show most impact. Slowly reacting complexes like Fe–EDTA(1:1) have little mobilising impact in spite of strong affinity between EDTA and iron. The low affinity between iron and citrate can be compensated by large concentration. Moreover, iron-deficient segments show stronger re-uptake of mobilised 59Fe from the lumen and a stronger transfer of 59Fe from the tissue across the basolateral membrane. Both are compatible with the more marked expression of divalent metal transporter 1 (DMT-1) and IREG-1 at the brushborder and basolateral membrane of iron-deficient enterocytes. The data suggest that iron ions interact with food ligands during their passage from the apical to the basolateral side of duodenal enterocytes.

CHELATOR EDTA IN NUTRIENT SOLUTION DECREASES GROWTH OF WHEAT

ABSTRACT Chelators have routinely been used to supply iron (Fe) in the nutrient solutions for growing plants. However, potential toxicity of these chelators to plants has not been assessed hitherto. In this study, wheat was grown in the presence or absence of EDTA (ethylenediaminetetraacetic acid) in the nutrient solution (with Fe supplied to plants as a foliar spray of Fe citrate). The effects of these treatments were compared with Fe(III)EDTA supplied to the nutrient solution. Plants grown in EDTA-containing nutrient solutions had lower biomass of roots, and especially shoots, in comparison to the plants grown in the EDTA-free solution. Greater accumulation of Fe in shoots occurred in the treatments with Fe foliar sprays compared to Fe supplied in the nutrient solution. In the treatments with foliarly-applied Fe, roots contained sufficient amounts of Fe, indicating good transport of Fe citrate in the phloem. Greater accumulation of zinc (Zn) and copper (Cu) occurred in roots and shoots of plants growing in the EDTA-free nutrient solution than in the EDTA-containing solutions. Such an effect was also observed for manganese (Mn), but to a smaller extent and only in 19-day-old shoots. In contrast, roots accumulated more Mn when grown in the Fe(III)EDTA solutions than in treatments where Fe was supplied to the foliage. The amount of Zn and Cu transported from roots to shoots was greater in plants grown in EDTA-free nutrient solution compared to EDTA-containing solutions, reflecting greater accumulation of these micronutrients by roots. In conclusion, EDTA in nutrient solutions can affect plant growth. Thus, for experimental work involving EDTA, it will be necessary to establish absence of interactions between EDTA-related growth reduction and the treatments under study.

Reactive transport of EDTA-complexed cobalt in the presence of ferrihydrite

Many low-level radioactive wastes, historically disposed in shallow land trenches, are illdefined mixtures of radionuclides and organic chelating agents. The observed migration of nuclides, such as 60Co, away from burial sites has been attributed, in part, to the formation of aqueous complexes with ethylenediaminetetraacetic acid (EDTA). The stability of Co-EDTA complexes, and thus the fate and transport: of 60Co in the subsurface, is strongly dependent on the oxidation state of cobalt (log K co(II)EDTA = 18.3; log K Co(III)EDTA = 43.9). The factors that control the oxidation of Co(II) to Co(III) in subsurface environments are not well understood. We conducted a series of column flow experiments to provide an improved understanding of the geochemical processes that control the reactive transport of cobalt in the subsurface. A solution of 0.2 mM Co(II)EDTA 2− in 5 mM CaCl 2 was passed through saturated columns that were packed with ferrihydrite (Fe(OH) 3)-coated Si0 2. During transport through the column, a portion of the Co (II) EDTA 2− was oxidized to Co (III) EDTA − ; the amount of oxidation reached a steady-state under oxic conditions. Transport of the oxidized species, Co(III)EDTA −, was substantially more rapid than the transport of Co(II) EDTA 2−. The retardation of both Co-EDTA species and the extent of cobalt oxidation increased as the pH decreased. These results are consistent with the hypothesis that the association of Co(H)EDTA 2− with the ferrihydrite surface is essential for the charge-transfer involved in the oxidation reaction. Co(III)EDTA- exhibited less retardation because this monovalent anion had a lower affinity for the surface than the divalent Co(II)EDTA 2−. At faster flow rate, the retardation of Co(II)EDTA 2− decreased whereas Co (III) EDTA — breakthrough occurred later; the amount of Co(III)EDTA − formed decreased with increasing flow rate. Under anoxic conditions, the oxidation of Co(II)EDTA 2− was decreased, but was not eliminated, suggesting that ferric iron may serve as an oxidant in the system. The loss of oxidative sites under continuous exposure to Co(II)EDTP 2− and the blocking of oxidative sites by ions residing on the ferrihydrite surface resulted in a slow decline in the amount of oxidation under anoxic conditions. The oxidation of Co(II)EDTA 2− effectively competed with other geochemical reactions such as the Fe(III)-induced dissociation of Co(II)EDTA 2− complexes under oxic and anoxic conditions. These results indicate that an iron mineral can be more important for the formation of Co(III)EDTA 2− in the subsurface than the mineral is important for the dissociation of Co(II)EDTA − and the concomitant formation of Fe(III)EDTA −. The results suggest that conditions of pH and flow rate that inhibit the formation of the very stable Co(III)EDTA − also promote the undesirable rapid transport of Co(II)EDTA 2− posing a challenge to the selection of future waste sites and the development of remedial strategies for existing sites impacted by EDTA-complexed 60Co.