Effect Of Nitrilotriacetic Acid Research Articles

Enhanced removal of sulfamethoxazole by Mn(II)/bisulfite in presence of nitrilotriacetic acid: Role of Mn(III)

Currently, the research on bisulfite (BS) activation by Mn(II) is very limited probably because of the low catalytic efficiency of Mn(II). Adding ligands to Mn(II)/BS system is likely to improve the BS activation, but the relative information is very rare. Therefore, the effect of nitrilotriacetic acid (NTA) on Mn(II)/BS system was investigated in this work using sulfamethoxazole (SMX) as the target contaminant. The results showed that the addition of NTA enhanced SMX removal in Mn(Ⅱ)/BS system through forming Mn(Ⅱ/III)-NTA complexes driving Mn(III)/Mn(II) cycle and stabilizing Mn(III). Alcohol scavenging experiments and competitive kinetic experiments indicated that sulfate radical (SO4•−) and hydroxyl radical (HO•) were not the main reactive species in Mn(II)/NTA/BS system. Mn(Ⅲ) was the primary oxidant for SMX elimination in this system and its existence was proved by UV-Vis absorption spectrum of reaction solution. Mn(Ⅱ)/NTA/BS system could greatly degrade SMX in near-neutral conditions, while nearly no SMX removal was observed at pH 3.0. The decrease of dissolved oxygen concentration significantly inhibited BS autocatalytic stage, thus suppressing the removal of SMX. Due to the competitive complexation of HCO3− and FA with NTA for Mn(II), their addition in Mn(Ⅱ)/NTA/BS system obviously inhibited SMX degradation. Four intermediates were detected during SMX degradation in Mn(Ⅱ)/NTA/BS system, and the possible SMX transformation pathways were speculated as N-S bond breaking, hydroxylation, amino oxidation and coupling reaction.

Willow and Herbaceous Species' Phytoremediation Potential in Zn-Contaminated Farm Field Soil in Eastern Québec, Canada: A Greenhouse Feasibility Study.

Phytoremediation shows great promise as a plant-based alternative to conventional clean-up methods that are prohibitively expensive. As part of an integrated strategy, the selection of well-adapted plant species as well as planting and management techniques could determine the success of a long-term program. Herein, we conducted an experiment under semi-controlled conditions to screen different plants species with respect to their ability to phytoremediate Zn-contaminated soil excavated from a contaminated site following a train derailment and spillage. The effect of nitrilotriacetic acid (NTA) application on the plants and soil was also comprehensively evaluated, albeit we did not find its use relevant for field application. In less than 100 days, substantial Zn removal occurred in the soil zone proximal to the roots of all the tested plant species. Three perennial herbaceous species were tested, namely, Festuca arundinacea, Medicago sativa, and a commercial mix purposely designed for revegetation; they all showed strong capacity for phytostabilization at the root level but not for phytoextraction. The Zn content in the aboveground biomass of willows was much higher. Furthermore, the degree of growth, physiological measurements, and the Zn extraction yield indicated Salix purpurea ‘Fish Creek’ could perform better than Salix miyabeana, ‘SX67’, in situ. Therefore, we suggest implementing an S. purpurea—perennial herbaceous co-cropping strategy at this decade-long-abandoned contaminated site or at similar disrupted landscapes.

Effect of nitrilotriacetic acid and tea saponin on the phytoremediation of Ni by Sudan grass (Sorghum sudanense (Piper) Stapf.) in Ni-pyrene contaminated soil

Phytoremediation is commonly used in the remediation of soils co-contaminated by heavy metals and polycyclic aromatic hydrocarbons (PAHs) because of its economy and effectiveness. Sudan grass (Sorghum sudanense (Piper) Stapf.) has well-developed roots and strong tolerance to heavy metals, so it has been widely concerned. In this study, nitrilotriacetic acid (NTA) and tea saponin (TS) were used as enhancers and combined with Sudan grass for improving the remediation efficiency of Ni-pyrene co-contaminated soil. The results of the pot experiment in soils showed that enhancers promoted the enrichment of Ni in plants. With the function of enhancers, more inorganic and water-soluble Ni were converted into low-toxic phosphate-bonded and residual Ni, so as to reinforce the tolerance of Sudan grass to Ni. In the pot experiment based on vermiculite, it was found that enhancers increased the accumulation of Ni in cell wall by 49.71–102.73%. Enhancers also had the positive effect on the relative abundance of Proteobacteria, Patescibacteria and Bacteroidetes that could tolerate heavy metals at phylum level. Simultaneously, the study found that pyrene reduced the exchangeable Ni in soils. More Ni entered the organelles and transfer to more high-toxic forms in Sudan grass when pynere coexisted. The study manifested that enhancers improved the phytoremediation effect of Ni significantly, yet the co-existence of pyrene weakened the process. Our results provided meaningful references for remediating actual co-contaminated soil of heavy metals and PAHs.

The changes of rhizosphere characteristics contributed to enhanced Pb accumulation in Athyrium wardii (Hook.) Makino after nitrilotriacetic acid application.

Chelant-assisted phytoremediation may modify plant rhizosphere, which is closely related to heavy metal (HM) accumulation in plants. This work focused on the effects of nitrilotriacetic acid (NTA) on rhizosphere characteristics to investigate the mechanisms of lead (Pb) accumulation in Athyrium wardii (Hook.) Makino with exposure to 800 mg kg-1 Pb. After NTA application, Pb accumulation in the underground part of A. wardii increased by 14.3%, accompanying with some changes for the rhizosphere soils. Soil pH decreased by 0.37 units, and the dissolved organic carbon (DOC) content in the rhizosphere soils significantly increased by 7.6%. The urease, acid phosphatase, and catalase activities in the rhizosphere soils significantly increased by 104.8%, 19.7%, and 27.1%, respectively. However, a slight inhibition on microbial activities was observed in the rhizosphere of A. wardii after NTA application. Soil respiration decreased by 8.9%, and microbial biomass carbon decreased by 8.9% in the rhizosphere soils, indicating that NTA addition might recruit some microorganisms to maintain rhizosphere functions in Pb-contaminated soils while inhibiting others with low tolerance to Pb. Results suggest that lower pH, more DOC exudation, and higher soil enzyme activities after NTA application contributed to the increase of Pb accumulation in A. wardii. This study gave some preliminary evidence for NTA-assisted Pb remediation by A. wardii by modifying rhizosphere characteristics.

Effects of nitrilotriacetic acid and corrosion inhibitor on cobalt barrier chemical–mechanical polishing: Experimental and density functional theory analysis

Nitrilotriacetic acid (NTA) was used as a complexing agent for Co barrier chemical–mechanical polishing (CMP), and 2,2'-{[(methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol (TT-LYK) as a corrosion inhibitor. The mechanism of both the complexing agent and inhibitor—individually and combined—on the Co surface was comprehensively studied. Static etch rate (SER) experiments showed that NTA is an effective complexing agent for Co. After adding NTA, Co SER increases from ∼0 to ∼15 Å/min, and a complexing mechanism is proposed. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface state and species composition. The active site of TT-LYK was analyzed by density functional theory and the adsorption mechanism of TT-LYK on the Co (0001) plane. The calculations showed that TT-LYK molecules were vertically adsorbed through atoms N9 and N10 as well as O17–H··Co hydrogen bonds, and parallel adsorbed through benzene and triazole rings. CMP, atomic force microscopy (AFM), potentiodynamics, and electrochemical impedance spectroscopy (EIS) were used to study the mechanism of NTA and TT-LYK under polishing conditions. TT-LYK inhibits chemical corrosion of the concave surface, and NTA promotes removal of the oxide film on the convex surface. In combination, NTA and TT-LYK impart a high-quality Co surface.

Synergetic effects of DA-6/24-EBL and NTA on uptake, subcellular distribution and chemical form of Cd in Amaranthus hybridus L

ABSTRACT Plant growth regulators(PGR)-assisted phytoremediation is a technique which could improve the efficiency of heavy metal accumulation in hyperaccumulator plants. The aim of this study was to explore the effects of PGR combination with nitrilotriacetic acid (NTA) on Cd extraction and distribution in Cd hyperaccumulator. To achieve this objective, a pot experiment was carried out to investigate the effects of the diethyl aminoethyl hexanoate (DA-6) and 24-epibrassinolide (24-EBL) and/or NTA on Cd phytoextraction, subcellular distribution and chemical forms in Amaranthus hybridus L. Results showed that NTA significantly decreased plant biomass production, but increased shoot and root Cd concentrations. Foliar spray containing DA-6 and 24-EBL alone increased both plant biomass and shoot and root Cd concentrations, the most pronounced effects observed were with 1 μM of DA-6. The combination of DA-6 and NTA inhibited toxicity and synergistically affected Cd uptake/accumulation. The addition of NTA alone enhanced Cd levels in soluble and cellular organelle fractions, whilst DA-6 and 24-EBL counteracted the toxic effects of Cd by promoting Cd retention in the cell walls, with 1 μM of DA-6 being the most effective dose. The NTA promoted metal mobility in shoots, resulting in increased Cd toxicity and stunted plant growth. In contrast, DA-6 and 24-EBL significantly reduced Cd mobility in plants. These results demonstrate that DA-6/24-EBL with NTA overcomes the detrimental effects of NTA on plant growth. Of the concentration ranges assessed, NTA + 1 μM DA-6 was optimal for the improving the remediation efficiency in A. hybridus.

Effects of NTA on Pb phytostabilization efficiency of Athyrium wardii (Hook.) grown in a Pb-contaminated soil

Chelate-assisted phytoremediation with biodegradable chelates has been considered to be a promising technique to enhance phytoremediation efficiency, while little information is available on phytostabilization. This study aims to assess NTA-assisted phytostabilization of Pb-contaminated soils by Athyrium wardii (Hook.). A pot experiment was carried out to investigate the effects of different application days (1, 3, 5, 7, 10, 14, 21) of nitrilotriacetic acid (NTA) on plant growth, Pb accumulation, and Pb availability in rhizosphere soils of A. wardii grown in soils contaminated with low (200 mg kg−1) and high (800 mg kg−1) concentrations of Pb. With the application of NTA, better growth for A. wardii was observed when treated with NTA for 5–14 days for both low and high Pb soils, suggesting potential harvest time. Pb concentrations and Pb accumulation in underground parts of A. wardii grown in low and high Pb soils increased with increasing application time of NTA generally. Similar changes were also found for bioaccumulation coefficients (BCFs) of A. wardii. The greatest remediation factors (RFs) for underground parts and whole plant of A. wardii were observed for NTA application time of 7 and 5 days for low and high Pb soils, suggesting the greatest remediation efficiency. Furthermore, plant growth, BCF, and RF of A. wardii grown in low Pb-contaminated soils were greater than those grown in high Pb-contaminated soils. Pb availability in rhizosphere soils of A. wardii grown in low Pb soils was lower than those in high Pb-contaminated soils. It seems to be the optimum for A. wardii to phytostabilize slightly Pb-contaminated soils with the application of NTA for 7 days as taking plant growth, Pb remediation efficiency, and environmental risk into consideration.

Global overexpression of divalent metal transporter 1 delays crocidolite-induced mesothelial carcinogenesis in male mice

Exposure to asbestos fiber is central to mesothelial carcinogenesis, for which iron overload in or near mesothelial cells is a key pathogenic mechanism. Alternatively, iron chelation therapy with deferasirox or regular phlebotomy was significantly preventive against crocidolite-induced mesothelial carcinogenesis in rats. However, the role of iron transporters during asbestos-induced carcinogenesis remains elusive. Here, we studied the role of divalent metal transporter 1 (DMT1; Slc11a2), which is a Fe(II) transporter, that is present not only on the apical plasma membrane of duodenal cells but also on the lysosomal membrane of every cell, in crocidolite-induced mesothelial carcinogenesis using DMT1 transgenic (DMT1Tg) mice. DMT1Tg mice show mucosal block of iron absorption without cancer susceptibility under normal diet. We unexpectedly found that superoxide production was significantly decreased upon stimulation with crocidolite both in neutrophils and macrophages of DMT1Tg mice, and the macrophage surface revealed higher iron content 1 h after contact with crocidolite. Intraperitoneal injection of 3 mg crocidolite ultimately induced malignant mesothelioma in ∼50% of both wild-type and DMT1Tg mice (23/47 and 14/28, respectively); this effect was marginally (p = 0.069) delayed in DMT1Tg mice, promoting survival. The promotional effect of nitrilotriacetic acid was limited, and the liver showed significantly higher iron content both in DMT1Tg mice and after crocidolite exposure. The results indicate that global DMT1 overexpression causes decreased superoxide generation upon stimulation in inflammatory cells, which presumably delayed the promotional stage of crocidolite-induced mesothelial carcinogenesis. DMT1Tg mice with low-stamina inflammatory cells may be helpful to evaluate the involvement of inflammation in various pathologies.

Effects of Nitrilotriacetic Acid on Anaerobic Co-Digestion of Food Waste and Sludge

The role of nitrilotriacetic acid (NTA) with the addition of four trace elements on mesophilic anaerobic co-digestion of food waste and sludge was investigated in batch reactor. Five different NTA concentrations (0, 8, 80, 800 and 8000 μM) were evaluated. The greatest coenzyme F420 content of five digester were 1.210 ± 0.210, 1.286 ± 0.179, 1.547 ± 0.187, 1.400 ± 0.222 and 0.955 ± 0.146 μmol L−1 during whole digestion process. The ultimate biogas yield of five digester were 198.1, 200.7, 239.7, 219.5 and 174.8 mL g−1-VSadded, respectively. The results indicated that the addition of NTA increased the biogas yield of anaerobic digester at an adequate concentration (around 80 μM).

Sorption behaviour of Co(II) and Cu(II) on chitosan in presence of nitrilotriacetic acid

Separation and isolation of radioactive cobalt ( 60Co), one of the main contributors towards the activity build up in nuclear reactors, is essential for radioactive waste volume reduction during nuclear reactor decontamination procedures. In this context, sorption of free and complexed Co(II), Cu(II) and nitrilotriacetic acid (NTA) on the biosorbent, chitosan was studied. A detailed investigation on the role of pH on sorption of Co(II), Cu(II) and NTA was done. Uptake capacities of the metal ions and NTA were measured within pH range of 2.0–7.0. At pH above 5, the NTA uptake capacities were found to be higher in presence of the metal ions than in their absence. Effect of NTA was found to be more pronounced on copper uptake than on cobalt uptake. Significant change in selectivity of chitosan towards metal ion uptake from NTA medium was observed with respect to change in pH. At pH 2.9, the uptake of cobalt was found to be more than that of copper, while the selectivity was reversed at pH 6.0. The respective selectivity coefficient ( k Co/Cu) values were found to be 2.06 and 0.072.

Effect of nitrilotriacetic acid on batch methane fermentation of sulfate-containing wastewater

The effects of nitrilotriacetic acid (NTA) on methane production and sulfate reduction during the treatment of sulfate laden organic wastewater were investigated in batch assays. The results showed that the methane fermentation was stimulated, while the sulfate reduction was inhibited. At a sodium acetate concentration of 7.0 g/L, temperature of 35 °C, and 0.9–15.0 of COD/SO 4 2− ratio, the methane production was increased by 20.8–42.4% and sulfate reduction rate was decreased by 33.0–76.0%, in the presence of 100 μM NTA. Also, the coenzyme contents of the biomass went up from 0.12 μmol Ni/g to 0.20 μmol Ni/g (volatile suspended solids) VSS for F 430 and from 0.30 μmol/g VSS to 1.06 μmol/g VSS for CoM. COD removal was also enhanced. Lack of nutrients for MPB greatly affected methane fermentation. By the addition of NTA, NTA-metal complexes formed and speciation of the trace metals in biomass changed. The amount of Co and Ni in the sulfides fraction in the biomass decreased from 145.9 and 50.0 μg/g (total suspended solids) TSS to 86.3 and 42.9 μg/g TSS, and their residual fraction increased by 4.4- and 9.0-fold, respectively. NTA boosted the internalization of Co and Ni, consequently enhancing the availability of trace metals for MPB and promoting the methane production. The results indicate that bioavailability of adequate nutrients is an important factor for MPB to compete with SRB (sulfate-reducing bacteria) in methane fermentation of sulfate-containing wastewater.

Effect of nitrilotriacetic acid on bioavailability of nickel during methane fermentation

In the case of anaerobic reactors for the treatment of wastewaters, the ubiquitous presence of sulfide and carbonate leads to extensive precipitation of metals like nickel, which are essential for the metabolism of the anaerobic microorganisms that carry out the mineralization of the pollutants present in the wastewater. This study is concerned with the complexation of nickel with nitrilotriacetic acid (NTA) and its effect on the biogas production by methanogenic archaea in the presence of sulfide. Methane production was enhanced 10, 30 and 48%, at sulfide concentration of 0.25, 0.5 and 1 mM, respectively, by the addition of 10 μM NTA. Accompanying with that, substrate degradation and methane production were accelerated and the carbonate and sulfide fraction of nickel in the biomass decreased 28.8 and 58.0%. NTA boosted the internalization of Ni, consequently enhancing the bioavailability of Ni for methanogenic archaea and promoting the methane production.

Adsorption characteristics of Fe(III) and Fe(III)–NTA complex on granular activated carbon

The adsorption of Fe 3+ ion on granular activated carbon has been studied in kinetic and equilibrium conditions taking into account the adsorbate concentration, temperature and solution pH as major influential factors. In addition, the effect of nitrilotriacetic acid on adsorption reaction as a complexing agent has been examined. Kinetic studies showed that the adsorption rate was increased as the initial Fe 3+ concentration was raised. The adsorption reaction was estimated to be first-order at room temperature. The adsorption rate and equilibrium adsorption of Fe 3+ increased as the temperature rose. The activation energy for adsorption was approximately 2.23 kJ mol −1, which implied that Fe 3+ mainly physically adsorbed on activated carbon. Coexistence of nitrilotriacetic acid with Fe 3+ resulted in a decrease of equilibrium adsorption and the extent of decrease was proportional to the concentration of nitrilotriacetic acid. In the presence of nitrilotriacetic acid, the adsorbability of Fe 3+ decreased with pH. However, the trend was reversed in the absence of nitrilotriacetic acid. When activated carbon was swelled by acetic acid, the specific surface area was increased and maximum swelling was achieved at approximately 48 h of swelling time. Thermodynamic parameters such as Δ G°, Δ H° and Δ S° for adsorption reaction were estimated based on equilibrium data and in connection with these results the thermodynamic aspects of adsorption reaction were discussed.

Comparison of NTA and Elemental Sulfur as Potential Soil Amendments in Phytoremediation

The effect of NTA (nitrilotriacetic acid) and elemental sulfur (S), two soil amendments suggested for the enhancement of metal phytoavailability in phytoextraction, on heavy metal uptake by Nicotiana tabacum (tobacco) and Zea mays (maize) were studied and compared in two Zn-, Cu-, Cd -, and Pb-contaminated soils from northern Switzerland. Experiments were performed in the greenhouse with topsoil (0 to 20 cm) material from two locations, Dornach and Rafz. The Dornach soil was calcareous and had been contaminated by dust emissions from a nearby brass metal smelter. The Rafz soil, free of carbonates, had been polluted by former sewage sludge application.Soil amendments with S increased the solubility (NaNO3 extraction) of Zn and Cd about 10-fold in Dornach soil and up to 30-fold in Rafz soil after 55 days. Zn and Cd removal by N. tabacum and Z. mays, however, increased only about 5.5- and 2.5-fold in these treatments in Rafz soil, respectively, while in the Dornach soil only a slight increase for Cd was found. Repeated NTA application increased soluble Zn, Cu, and Cd about 100-, 20-, and 19-fold in the Dornach soil and 13-, 4-, and 2-fold in the Rafz soil shortly after application. Soluble Pb was increased by NTA up to 50-fold in Rafz soil. After 90 days soluble heavy metal concentrations were only slightly elevated in both soils. Again, however, Zn, Cd, and Cu removal by N. tabacum and Z. mays increased only about 1.5- to 2.5-fold in the two soils, whereas Pb removal by N. tabacum increased about fivefold in the Rafz soil as a result of NTA application

Bioavailability of waterborne strontium to the common carp, Cyprinus carpio, in complexing environments

The uptake of strontium (Sr) and calcium (Ca) in the common carp, Cyprinus carpio, was studied in chemically defined freshwater in the presence of the complexing ligands, ethylenediaminetetraacetic acid (EDTA), and nitrilotriacetic acid (NTA). The uptake rates were measured in the whole body, gills, and blood of the fish after an exposure period of 3 h. The uptake rates were determined by using the radiotracers 85Sr and 45Ca, and analyzed as a function of the free-ion activity of Sr and Ca in water. Although Sr 2+ activity decreased, the uptake of Sr showed an increase at relatively low concentrations of EDTA and NTA, and a decrease at relatively high concentrations. This can be explained by the decreased competition between Sr 2+ and Ca 2+ at the gill uptake sites due to ∼30–140-fold higher affinity of EDTA and NTA for Ca 2+ than Sr 2+. With decreasing Ca 2+ activity, Ca uptake rates decreased in the presence of EDTA and NTA, but the effect of NTA was less pronounced. A Michaelis–Menten type competitive inhibition model was derived that could predict the whole-body Sr and Ca uptake rates, taking into account the ambient Sr 2+ and Ca 2+ activities in the presence of EDTA. In case of NTA, the uptake rates were found to be 1.5–3.2 times higher than what was predicted by the model. When the fish were exposed to complexing environments in the complete absence of Ca, an increased uptake of Sr was still observed in case of NTA, but not EDTA. The increased uptake in the presence of NTA is attributed to the direct uptake of SrNTA − and CaNTA − complexes from water. The results reveal that the uptake of Sr and Ca in carp is not merely a function of the free metal-ion activity but that certain complex species may contribute significantly to overall uptake.

XAFS study on the sulfidation mechanisms of Co-Mo catalysts supported on activated carbon and alumina: effect of complexing agent.

The effect of nitrilotriacetic acid (NTA) as a complexing agent on the sulfidation mechanisms of Co-Mo catalysts supported on activated carbon and alumina was examined by the XAFS technique. The XAFS results revealed that NTA interacted with Co atoms and formed the Co-NTA interaction, while it showed almost no influence on the local structures around Mo atoms. The Co-NTA interaction suppressed the aggregation of cobalt atoms and the interaction between cobalt and alumina during sulfiding, and consequently promoted the formation of the Co-Mo-S phase.

Influence de l'acide nitrilotriacetique (NTA) et de l'acide ethylene diamino‐tetracetique (EDTA) sur la dephosphatation biologique

Abstract This study examined the effects of nitrilotriacetic acid (NTA) and ethylenediamino‐tetracetic acid (EDTA) on the biological phosphorus removal. Batch tests indicated that exist perturbation levels (DD) of phosphorus removal which were situated at values of 40 mg g‐1 MVLSS for NTA and 45 mg g‐1 MVLSS for EDTA. A dynamic lab‐scale study showed a reduction of nitrogen and phosphorus removal efficiency, ten days after the introduction of NTA and EDTA in influent water in concentration lower than “DD”;.

Effects of nitrilotriacetic acid‐nickel complexes on activated sludge process

Abstract Effects of nitrilotriacetic acid (NTA), nickel ion (Ni2+) and their complexes on the efficiency of biological wastewater treatment, activated sludge process, were evaluated by determining the changes in physical and chemical parameters. Primary effects of these toxicants on microorganisms in the activated sludge process were evaluated by determining the change of in vivo dehydrogenase activity. The presence of 10 mg/L or higher of Ni2+ significantly affected the activated sludge process. Nitrification in the activated sludge process was more sensitive to the inhibition of Ni2+ . The presence of NTA, as high as 20 mg/L, didn't significantly affect the activated sludge process. Moreover, in the presence of 20 mg/L of NTA, the toxicity of Ni2+ on the activated sludge process was significantly reduced.

Technical note: Electrochemical and salt spray testing of zinc electrodeposits

AbstractThe corrosion resistance of six different zinc electrodeposits on steel was tested using potentiodynamic, weight loss, and salt spray techniques. Best results were obtained with coatings containing nitrilotriacetic acid (NTA) and it is recommended that further studies on the effects of NTA in coating baths should be conducted.

Induction of gene mutations insalmonellaandDrosophilaby soluble Cr(Vi) compounds: Synergistic effects of nitrilotriacetic acid

Abstract The interaction between NTA and soluble Cr(VI) (K2Cr2O7) was studied by the Ames test on S. typhimurium and the sex‐linked recessive lethal test on D. melanogaster. In both systems a synergistic effect of NTA on Cr(VI) mutagenicity took place at sub‐toxic doses of Cr(VI). The synergism could depend on the action of NTA on intracellular Cr(VI) reduction, as more Cr(VI) was reduced in vitro to Cr(III) by Salmonella and Drosophila protein extracts in the presence of NTA. A similar enhancement of soluble Cr(VI) mutagenicity was produced by low doses of EDTA.