Absence Of Ethylenediaminetetraacetic Acid Research Articles

The study of EDTA enhanced Cd accumulation and formation in Napier grass using synchrotron μX-ray fluorescence imaging and X-ray absorption spectroscopy

In this study, Pennisetum purpureum, a fast growing and highly tolerant plant, was used as a Cadmium (Cd) hyperaccumulator associated with Ethylenediaminetetraacetic acid (EDTA). It was found that P. purpureum's shoots and roots grown in the presence of EDTA accumulated significantly higher Cd than those grown in the absence of EDTA. Synchrotron μX-ray fluorescence imaging demonstrated the significant Cd accumulation in the internal tissues of root: endodermis, xylem and phloem, while at stem, it was found at the external tissues: epidermis and phloem. Synchrotron X-ray Absorption Spectroscopy was used to characterize the Cd speciation in plant cells. P. purpureum was discovered to accumulate Cd (II) form. In order to determine the possibilities of Cd bonding in chemical compounds, linear combination fitting of Cd K-edge XANES spectra was carried out. The EDTA-free condition as a control revealed mainly Cd–N/O bonding ligand, while the EDTA-treated condition mostly showed Cd–N/O and Cd–S bonding. The overall results suggested that EDTA is a potential substance to enhance the efficiency of Cd absorption in P. purpureum.

Antioxidant and Prooxidant Effects of Thymoquinone and Its Hydroquinone Metabolite.

Thymoquinone is a popular health-promoting antioxidant supplement, but it may induce toxicity to cells and organs because of its propensity to promote oxidation of biomolecules under some conditions. Furthermore, as hydroquinones have been found to exhibit more potent antioxidant and prooxidant activities than their parent quinones, the reduced metabolite thymohydroquinone may have stronger effects than thymoquinone. In this study, the antioxidant and prooxidant activities of thymoquinone and thymohydroquinone were assessed to determine whether they both act as antioxidants and induce oxidative damage to biomolecules as do other quinones. Using ESR spectroscopy, we demonstrated that thymohydroquinone exhibits more potent antioxidant activity than does thymoquinone. In addition, thymohydroquinone was found to act as a prooxidant to induce oxidative damage of isolated plasmid DNA in the presence of free Cu2+ or Fe2+-ethylenediaminetetraacetic acid (EDTA). Interestingly, the prooxidant effect of thymohydroquinone in the presence of Fe2+ was not observed in the absence of EDTA. Thymohydroquinone thus was demonstrated to have two biologically relevant activities: as an antioxidant and a prooxidant.

Effects of crushed mussel, Perna canaliculus, shell enrichment on seawater carbonate buffering and development of conspecific larvae exposed to near‐future ocean acidification

AbstractPerna canaliculus is an aquaculture species vulnerable to ocean acidification (OA). Returning shell waste to the sea after commercial processing has potential to provide localized buffering to OA. We investigated whether seawater enrichment with crushed shell buffers carbonate chemistry and improves P. canaliculus larval performance under current (400 μatm) and future (1,100 μatm) PCO2 conditions. Fertilized eggs from two parent pools were reared for 42 hr in seawater previously enriched with shell or non‐enriched. Aragonite saturation state (ΩA) decreased in high PCO2 seawater (ΩA 1.26, compared to 2.54 under present‐day conditions). This was partially mitigated by shell enrichment (ΩA 1.44). In high PCO2 ethylenediaminetetraacetic acid (EDTA)‐treated seawater, shell enrichment resulted in minor increases in the proportion of larvae developing into normal veligers (no shell = 3.7 ± 3.0%, shell = 9.6 ± 4.7%; mean ± SD). Larvae failed to develop normally in the absence of EDTA, with the exception of ambient PCO2 seawater enriched with shell, which yielded a pool‐dependent mean 2.3–17.8% normal veligers, possibly reflecting other properties of crushed shell including metal uptake. Non‐buffering effects of crushed shell, parental pool, and inclusion of a chelator (EDTA) in seawater appeared to have a greater influence upon larval performance than buffering per se, warranting further investigation.

Adsorption of U(VI) on montmorillonite in the presence of ethylenediaminetetraacetic acid

The adsorption, diffusion and migration behaviors of uranium may be highly influenced by organics in natural environments. Ethylenediaminetetraacetic acid (EDTA) is one of the most important small organics in groundwaters, especially at the radioactive contaminated sites. In this work, we studied U(VI) adsorption on montmorillonite in the presence of EDTA with batch method. Our results indicated that U(VI) adsorption was significantly different in the presence and absence of EDTA. The equimolar EDTA inhibited the U(VI) adsorption at a wide pH range while only enhanced the adsorption at pH ˜7.0. The pseudo-second-order model showed the best fit for describing the adsorption kinetics in comparison with three other popular models. The influence of different addition sequences on adsorption of EDTA and U(VI) on montmorillonite was also investigated, and the results indicated that EDTA played the role as a bridge between montmorillonite surface sites and U(VI). The X-ray photoelectron spectroscopy and attenuated total reflectance Fournier-transform infrared spectroscopy also suggested the formation of EDTA-bridge inner-sphere surface complexes on montmorillonite. This work provides the valuable information of U(VI) adsorption on montmorillonite in the presence of EDTA, and helps us understand the diffusion and migration behaviors of uranium in natural environments.

Comparative effect of calcium and EDTA on arsenic uptake and physiological attributes of Pisum sativum

ABSTRACTIn this study, we determined the effect of ethylenediaminetetraacetic acid (EDTA) and calcium (Ca) on arsenic (As) uptake and toxicity to Pisum sativum. Plants were treated with three levels of As (25, 125, and 250 µM) in the presence and absence of three levels of Ca (1, 5, and 10 mM) and EDTA (25, 125, and 250 µM). Exposure to As caused an overproduction of hydrogen peroxide (H2O2) in roots and leaves, which induced lipid peroxidation and decreased pigment contents. Application of both Ca and EDTA significantly reduced As accumulation by pea, Ca being more effective in reducing As accumulation. Both Ca and EDTA enhanced As-induced H2O2 production, but reduced lipid peroxidation. In the case of pigment contents, EDTA significantly reduced pigment contents, whereas Ca significantly enhanced pigment contents compared to As alone. The effect of As treatment in the presence and absence of EDTA and Ca was more pronounced in younger leaves compared to older leaves. The effect of amendments varied greatly with their applied levels, as well as type and age of plant organs. Importantly, due to possible precipitation of Ca-As compounds, the soils with higher levels of Ca ions are likely to be less prone to food chain contamination.

Degradation of trichloroethene by nanoscale zero-valent iron (nZVI) and nZVI activated persulfate in the absence and presence of EDTA

This study investigated the degradation of trichloroethene (TCE) by nanoscale zero-valent iron (nZVI) w/o persulfate (PS) in the absence and presence of ethylenediaminetetraacetic acid (EDTA). In the absence of EDTA, the degradation of TCE obeyed the pseudo-first-order kinetics, and the rate constants increased exponentially with increasing molar ratio of PS and nZVI. Ethene was found to be the main reaction products in either the single nZVI system or nZVI/PS system. The presence of EDTA increased TCE degradation by nZVI in a short reaction period (within 360min), whereas the TCE degradation was almost ceased after 1day in a long-term (6days) experiment, resulting in a lower TCE degradation than that in the absence of EDTA. However, EDTA drastically decreased TCE degradation in nZVI/PS system. The positive effect of EDTA in the nZVI system should be attributed to its possible inhibition of the precipitation of Fe2+/Fe3+, which could reduce the surface passivation of nZVI. On the other hand, the adverse effect should be due to the rapid corrosion of nZVI by EDTA and the generation of a large amount of Fe2+ ions in short time, which could possibly lead to a rapid consumption of sulfate radicals originally for the degradation of TCE.

Antibacterial Activity of Stenotrophomonas maltophilia Endolysin P28 against both Gram-positive and Gram-negative Bacteria.

Maltocin P28 is a phage-tail like bacteriocin produced by Stenotrophomonas maltophilia P28. The ORF8 of maltocin P28 gene cluster is predicted to encode an endolysin and we name it endolysin P28. Sequence analysis revealed that it contains the lysozyme_like superfamily conserved domain. Endolysin P28 has the four consensus motifs as that of Escherichia coli phage lambda gpR. In this study, endolysin P28 was expressed in E. coli BL21 (DE3) and purified with a C-terminal oligo-histidine tag. The antibacterial activity of endolysin P28 increased as the temperature rose from 25 to 45°C. Thermostability assays showed that endolysin P28 was stable up to 50°C, while its residual activity was reduced by 55% after treatment at 70°C for 30 min. Acidity and high salinity could enhance its antibacterial activity. Endolysin P28 exhibited a broad antibacterial activity against 14 out of 16 tested Gram-positive and Gram-negative bacteria besides S. maltophilia. Moreover, it could effectively lyse intact Gram-negative bacteria in the absence of ethylenediaminetetraacetic acid as an outer membrane permeabilizer. Therefore, the characteristics of endolysin P28 make it a potential therapeutic agent against multi-drug-resistant pathogens.

Colorimetric detection of Cr3+ using gold nanoparticles functionalized with 4-amino hippuric acid

A facile and effective technique for monitoring Cr3+ concentration based on 4-amino hippuric acid (PAH) decorated Au nanoparticles (PAH-AuNPs) is introduced. The modified AuNPs were easily aggregated in the presence of Cr3+, resulting in the color change from red to violet or blue, which is in response to the surface plasmon absorption of dispersed or aggregated nanoparticles. Under the optimized conditions, a good linear relationship (correlation coefficient r = 0.998) was obtained between the ratio of the absorbance at 635 nm to that at 520 nm (A 635 nm/A 520 nm), and the concentration of Cr3+ was over the range of 5.0–120 µM with detection limit of 1.17 µM. This method exhibited excellent selectivity for Cr3+ over other tested heavy metal ions. Furthermore, there was no significant difference for the parameters of calibration equation between the presence and absence of ethylenediamine tetraacetic acid (EDTA), which suggests that the method can be applied in various real samples owing to the strong masking ability of EDTA. The assay was used to detect the concentrations of Cr3+ in liquid milk, milk power, and lake water samples with recoveries ranging from 93.5 to 114 %, indicating that the method could be used for extensive practical application. A facile and effective technique for monitoring Cr3+ based on 4-amino hippuric acid decorated Au nanoparticles is introduced. The modified AuNPs were aggregated in the presence of Cr3+ resulting in the color change from red to violet or blue, which is in response to the surface plasmon absorption of dispersed or aggregated nanoparticles.

Hydrothermal preparation of BiVO4 photocatalyst with perforated hollow morphology and its performance on methylene blue degradation

Monoclinic scheelite type BiVO4 samples with high photocatalytic activity were successfully synthesized by a hydrothermal method in the presence of ethylenediamine tetraacetic acid (EDTA). Monoclinic scheelite structure was obtained at a hydrothermal temperature as low as 140°C, which was much lower than 210°C in the absence of EDTA. Experimental results indicate that the morphology of the BiVO4 changed from sphere, polygon with hole, perforated hollow polygon, to particle with fragment with the increase of EDTA amount, and the particle size also decreased. On the conditions of the hydrothermal temperature of 170°C, pH of 7.0, hydrothermal time of 4h and the amount of EDTA of 3.0mmol, BiVO4 samples with perforated hollow polygon structure and low band gap of 2.48eV were obtained. Catalyzed by the perforated hollow polygon BiVO4, the discoloration rate of methylene blue (MB) reached 90.84% in simulated sunlight. The high discoloration rate of BiVO4 was successfully explained by the experiment results of crystal structure, morphology, UV–vis diffuse reflectance spectroscopy and band gap.

Physicochemical and functional properties of beany flavour‐free bambara groundnut protein isolate

Off-odour/flavour (beany) associated with bambara groundnut protein isolate (BGPI), due to oxidative degradation of lipids during either storage or processing, is a major problem limiting its application in foods. In this study, effects of heat treatment (50-80 °C) in combination with ethylenediaminetetraacetic acid (EDTA) on functional and sensory properties of BGPI were investigated. BGPI prepared in the presence of EDTA had lower lipoxygenase and trypsin-inhibitory activities than BGPI prepared in the absence of EDTA, regardless of the heating temperature used (P < 0.05). Inactivation of lipoxygenase was associated with lowered peroxide value, thiobarbituric acid-reactive substances and beany odour/flavour intensity in BGPI stored at room temperature for 30 days. BGPI with heat treatment at temperatures lower than 70 °C had similar protein patterns to BGPI prepared by the typical process, except for the occurrence of proteins with molecular weight 70-82 kDa. BGPI with heat treatment showed decreased protein solubility but increased surface hydrophobicity and sulfhydryl group content. BGPI prepared in the presence of EDTA exhibited higher emulsion activity and stability indices as well as higher foam expansion and stability than BGPI prepared in the absence of EDTA, regardless of heating temperature (P < 0.05). Heat treatment at 70 °C in the presence of 100 mmol L(-1) EDTA effectively reduced beany flavour development and enhanced the functionality of BGPI.

Purification and characterization of an exo-polygalacturonase secreted by Rhizopus oryzae MTCC 1987 and its role in retting of Crotalaria juncea fibre

An acidic polygalacturonase (PG) secreted by Rhizopus oryzae MTCC-1987 in submerged fermentation condition has been purified to electrophoretic homogeneity using ammonium sulphate fractionation and anion exchange chromatography on diethylaminoethyl cellulose. The purified enzyme gave a single protein band in sodium dodecyl sulphatepolyacrylamide gel electrophoresis analysis with a molecular mass corresponding to 75.5 kDa. The K m and k cat values of the PG were 2.7 mg/mL and 2.23 × 103 s−1, respectively, using citrus polygalacturonic acid as the substrate. The optimum pH of the purified PG was 5.0 and it does not loose activity appreciably if left for 24 hours in the pH range from 5.0 to 12.0. The optimum temperature of purified enzyme was 50°C and the enzyme does not loose activity below 30°C if exposed for two hours. The purified enzyme showed complete inhibition with 1 mM Ag+, Hg2+ and KMnO4, while it was stimulated to some extent by Co2+. The purified PG exhibited retting of Crotalaria juncea fibre in absence of ethylenediaminetetraacetic acid.

Polymorphism in CaCO3 — Effect of temperature under the influence of EDTA (di sodium salt)

Crystallization behavior and polymorphism of CaCO3 were studied at different temperatures (from 60 to 240°C) under the influence of ethylenediaminetetraacetic acid (EDTA). The samples were characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and field emission scanning electron microscopy (FESEM). In the absence of EDTA, a calcite–aragonite binary mixture was resulted between 60 and 170°C above which calcite alone was formed. The presence of EDTA significantly influenced the crystallization behavior and composition of different polymorphs of CaCO3 varied with temperature. Formation of a binary calcite–aragonite mixture at 60°C, ternary calcite–vaterite–aragonite mixture at 100°C, a binary aragonite–vaterite mixture at 130°C, a binary calcite–aragonite mixture at 170°C, purely aragonite at 200°C and vaterite with very little aragonite at 230°C confirmed that temperature affects the crystallization process in the presence of EDTA. Rhomboidal calcite, needle/rod like aragonite and flower like vaterite were obtained under different conditions. At 230°C, a unique flower like morphology was observed for vaterite. The efficacy of EDTA on CaCO3 scale inhibition between 60 and 230°C is discussed.

Weak Organic Ligands Enhance Zinc Uptake in Marine Phytoplankton

A recent study of the effect of pH on Zn and Cd bioavailability shows that binding to weak organic ligands can increase the pool of metals available to phytoplankton in the presence of strong chelating agents. We explore the underlying mechanism in laboratory experiments with the model species Emiliania huxleyi and Thalassiosira weissflogii. Additions of L- and D- isomers of cysteine (Cys) result in similar increases in Zn uptake rates in the presence of the strong chelator ethylenediaminetetraacetic acid (EDTA) but decrease it in the absence of EDTA, ruling out uptake by a specific Zn-Cys transporter. The effect of Cys does not result from alleviating diffusion limitation of inorganic Zn. The enhancement of Zn uptake kinetics by weak ligands is consistent with a mechanism involving formation of a transient ternary complex with uptake molecules: (1) the enhancement is most dramatic in Zn limited cells whose high affinity transporters should be most effective at extracting Zn from weak ligands; (2) the enhancement occurs with a variety of weak ligands, demonstrating that the underlying mechanism has little chemical specificity; and (3) no enhancement of uptake is seen when Zn is bound in complexes that would make formation of multiligand complexes with uptake molecules difficult. Weak complexing agents which have received heretofore little attention may play a key role in the bioavailability of metals in natural waters.

Effect of Metals on the Lytic Cycle of the Coccolithovirus, EhV86.

In this study we show that metals, and in particular copper (Cu), can disrupt the lytic cycle in the Emiliania huxleyi – EhV86 host–virus system. E. huxleyi lysis rates were reduced at high total Cu concentrations (> approximately 500 nM) in the presence and absence of EDTA (ethylenediaminetetraacetic acid) in acute short term exposure experiments. Zinc (Zn), cadmium (Cd), and cobalt (Co) were not observed to affect the lysis rate of EhV86 in these experiments. The cellular glutathione (GSH) content increased in virus infected cells, but not as a result of metal exposure. In contrast, the cellular content of phytochelatins (PCs) increased only in response to metal exposure. The increase in glutathione content is consistent with increases in the production of reactive oxygen species (ROS) on viral lysis, while increases in PC content are likely linked to metal homeostasis and indicate that metal toxicity to the host was not affected by viral infection. We propose that Cu prevents lytic production of EhV86 by interfering with virus DNA (deoxyribonucleic acid) synthesis through a transcriptional block, which ultimately suppresses the formation of ROS.

Miracle molecules of our age: ethylenediaminetetraacetic acid.

In his outstanding book, Power Aging (1), Gary Null spends much of the early part of the volume discussing the numerous man-made chemicals and components that constitute a major part of the problems with pollution and damage to human health. It is almost as though anything chemical which we manufacture and use in our world can damage us. Even the pharmaceuticals which have been designed and synthesised, especially to cure us, always have side-effects some of which appear to be at least as bad as the conditions that they were designed to abolish. In view of what Dr Null says, can we find any synthetic chemicals which are harmless to man and yet have useful and important health benefits for which they were not designed? Here I discuss one agent, namely ethylenediaminetetraacetic acid (EDTA) that seems, at present, to fit the above criteria. 1. EDTA as a bacterial permeabiliser It is as a permeabiliser, particularly of Gram-negative bacteria, that EDTA is best known. Numerous inhibitory agents are hydrophobic, and because these fail to enter Gram-negative organisms, they cannot kill them nor even inhibit their growth Le. they cannot have a bactericidal nor a bacteriostatic effect Generally, failure of hydrophobic agents to penetrate into the Gram-negative cell results from the outer membranes (OMs) being impenetrable to them, hence preventing their passage across the envelope (2,3). Outer membrane impenetrability as the basis of the above effects can be proven, for hydrophobic agents, by comparing their effects on normal strains and those (lps mutants) altered in the lipopolysaccharide (LPS) component of the OM; whereas unmutated strains are insensitive to hydrophobic agents, they readily cross the envelopes of the mutants with a lethal effect (2,3). Strikingly, the OMs of some Gram-negative bacteria can also be permeabilised by treatment with EDTA. This molecule is a chelator and its removal, by chelation, of magnesium, manganese and calcium ions from the OMs leads to permeabilisation. These ions are intimately involved in the LPS-LPS and LPS-protein interactions which stabilise the OMs, and so removal of them leads to loss of LPS from the envelopes and permeabilisation to the normally non-penetrating hydrophobic agents (2-4). The removal of these ions and the loss of LPS from the OMs, in the presence of EDTA, is particularly marked in pseudomonads, so that these organisms show the most marked sensitisation by EDTA (3,4). Hydrophilic antibacterials normally cross the OMs via the porins, provided that these antibacterials are less than ca 600 molecular weight (2). If this is so, then Gram-negatives show sensitivity to them in the absence of EDTA. Many such agents will, however, also show an increased effect on EDTA-treated organisms, as the hydrophilic molecules will use both entry routes i.e. entering via both the porins and the permeabilised OMs. Hydrophilic antibacterials above 600 molecular weight normally fail to affect Gram-negatives; after permeabilisation by EDTA, however, some of them will use the OM route and cause lethality (2). As a result of its permeabilising effect, EDTA generally sensitises Gram-negatives to an array of potentially lethal agents to which they are inherently resistant. Such agents can be divided into four classes namely disinfectants, antiseptics, preservatives and antibiotics (4). Many of these agents are hydrophobic, and therefore, cannot enter Gram-negatives, especially pseudomonads, without permeabilisation. The permeabilising effect of chelators such as EDTA is especially important for antiseptics and antibiotics, because organisms are more and more commonly becoming resistant to such agents that originally killed them. The ability of chelators such as EDTA to reverse this effect is of great importance. EDTA and enhanced lethal effects of disinfectants, antiseptics and antibiotics on organisms on inert surfaces, on wounds and on burns Because phenols and cresols are hydrophobic, they generally fail to kill Gram-negatives and therefore cannot be used to disinfect inert surfaces. …

Electron-transfer processes induced by the triplet state of pterins in aqueous solutions

Pterins (Pt) are heterocyclic compounds widespread in living systems. They participate in relevant biological processes, such as metabolic redox reactions, and can photoinduce the oxidation of biomolecules through electron-transfer mechanisms. We have investigated the electron-transfer pathways initiated by excited states of pterin (Ptr) and 6-methylpterin (Mep), selected as model compounds. The experiments were carried out in aqueous solutions under continuous UV-A irradiation, in the presence and in the absence of ethylenediaminetetraacetic acid (EDTA), used as an electron donor. The reactions were followed by UV/Vis spectrophotometry, HPLC, and an enzymatic method for H 2O 2 determination. The formation of the superoxide anion (O 2 •−) was investigated by electron paramagnetic resonance–spin trapping. The triplet excited states of Ptr and Mep are efficient electron acceptors, able to oxidize a Pt molecule in its ground state. The resulting radical anion (Pt •−) reacts with dissolved O 2 to yield O 2 •−, regenerating the pterin. In the presence of EDTA, this reaction competes efficiently with the anaerobic reaction between Pt •− and EDTA •+, yielding the corresponding stable dihydroderivatives H 2Pt. The effects of EDTA and dissolved O 2 concentrations on the efficiencies of the different competing pathways were analyzed.

Polar Anionic Metabolome Analysis by Nano-LC/MS with a Metal Chelating Agent

We have developed a practical method for the comprehensive analysis of polar anionic metabolites in biological samples with the use of a nano-LC/MS system. A polyamine-bonded polymer-based apHera NH2 column, which is compatible with ammonium carbonate buffer, effectively retained anionic polar metabolites, such as organic acids, sulfates, and phosphates, but multiply phosphorylated or carboxylated compounds showed highly distorted peak shapes on chromatograms. We found that addition of a trace amount of the metal chelating reagent ethylenediaminetetraacetic acid (EDTA) to the sample solution dramatically improved peak shapes of multiply charged anionic compounds, even though the mass spectra showed no trace of adduct ions in the absence of EDTA. The detection limits of typical polar anionic metabolites in the full-scan mode were from 0.19 to 2.81 pmol. After optimization of all the procedures from sample preparation to nano-LC/MS analysis, we applied our method to real biological samples: Hela cells, mouse brain, human cerebrospinal fluid (CSF), and human plasma. Our results indicated that phosphorylated metabolites were abundant in Hela cells and brain, while plasma and cerebrospinal fluid (CSF) mostly contained organic acids. Phosphorylated compounds might not be secreted into CSF/plasma or might be unstable in CSF/plasma. Finally, the method was used to examine the mode of action of the anticancer drug methotrexate (MTX), which inhibits purine de novo biosynthesis and thymidine biosynthesis. In addition of the expected changes of metabolite levels, we found that a previously unreported metabolite, probably a methylated uridine 5'-triphosphate (UTP), was produced by MTX-treated Hela cells.

Effects of insoluble Zn, Cd, and EDTA on the growth, activities of antioxidant enzymes and uptake of Zn and Cd in Vetiveria zizanioides

A root-bag experiment was conducted to study the effects of insoluble Zn, Cd, and ethylenediaminetetraacetic acid (EDTA) on the plant growth, activities of antioxidant enzymes, proline, glutathione (GSH), water-soluble proteins and malondialdehyde (MDA) of Vetiveria zizanioides. The V. zizanioides uptake capacity of Zn and Cd also determined. The results showed that plant growth of V. zizanioides was inhibited by Zn and Cd. The shoot dry weight (SDW) and root dry weight (RDW) decrease by 14.2%, 14.1%, 17.0% and 17.3%, 32.5%, 35.7%, respectively, compared to the control without EDTA addition. After adding EDTA, shoot and root dry weight decreased over 10% and 15%, respectively. The toxicity from insoluble Zn and Cd in soil on SDW and RDW of V. zizanioides was in order: Zn+Cd > Cd > Zn. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and contents of MDA and proline increased significantly, while the contents of GSH and water-soluble proteins decreased markedly with increasing Zn and Cd toxicity. With EDTA, shoot and root Zn concentrations increased in the Zn treatment by 7.3% and 37.4%, and Cd concentrations in the combined Zn and Cd treatment increased by 18.6% and 391.9% compared to the treatment without EDTA. However, Zn and Cd concentrations in shoot and roots decreased in the Cd treatment compared to the plants grown in absence of EDTA, with exception of root Cd concentration in the presence of EDTA.

Influence of complex reagents on removal of chromium(VI) by zero-valent iron

The removal of Cr(VI) by zero-valent iron (Fe(0)) and the effect of three complex reagents, ethylenediaminetetraacetic acid (EDTA), NaF and 1,10-phenanthroline, on this reaction were investigated using batch reactors at pH values of 4, 5 and 6. The results indicate that the removal of Cr(VI) by Fe(0) is slow at pH ⩾ 5.0 and that three complex reagents play different roles in the reaction. EDTA and NaF significantly enhance the reaction rate. The zero-order rate constants at pH 5.0 were 5.44 μM min −1 in the presence of 4 mM EDTA and 0.99 μM min −1 in the presence of 8 mM NaF, respectively, whereas that of control was only 0.33 μM min −1, even at pH = 4.0. This enhancement is attributed to the formation of complex compounds between EDTA/NaF and reaction products, such as Cr(III) and Fe(III), which eliminate the precipitates of Cr(III), Fe(III) hydroxides and Cr x Fe 1− x (OH) 3 and thus reduce surface passivation of Fe(0). In contrast, 1,10-phenanthroline, a complex reagent for Fe(II), dramatically decreases Cr(VI) reduction by Fe(0). At pH = 4.0, the zero-order rate constant in the presence of 1 mM of 1,10-phenanthroline was 0.02 μM min −1, decreasing by 99.7% and 93.9%, respectively, compared with the results in the presence and absence of EDTA. The results suggest that a pathway of the reduction of Cr(VI) to Cr(III) by Fe(0) may involve dissolution of Fe(0) to produce Fe(II), followed by reduction of Cr(VI) by Fe(II), rather than the direct reaction between Cr(VI) and Fe(0), in which Fe(0) transfers electrons to Cr(VI).

Availability of iron from iron‐storage proteins to marine phytoplankton

We examined the bioavailability of iron‐storage proteins—including representatives of maxi‐ and miniferritins— to various species of marine phytoplankton. Both eukaryotic and prokaryotic species were able to grow rapidly with horse spleen ferritin (HoSF) or deoxyribonucleic acid (DNA)‐binding proteins from starved cells (Dps) from Trichodesmium erythraeum as the sole Fe source in the medium. In the presence of ethylenediaminetetra‐acetic acid (EDTA), cells grown with HoSF or Dps maintained exponential growth rates similar to those obtained at the same concentration of FeEDTA. Growth was also observed in the absence of EDTA, showing that a complexing agent is not necessary for Fe availability. The bioavailability of Fe in these storage proteins apparently results from a spontaneous release of Fe(III) to solution with an effective first‐order rate constant ~0.15 d−1. Genes coding for iron‐storage proteins are common in DNA samples from seawater. In iron‐deprived marine ecosystems, iron‐storage proteins may be important constituents of the recycled iron pool and modulate its availability to phytoplankton.