Structure and fertilizer properties of byproducts formed in the synthesis of EDDHA

The synthesis of commercial EDDHA produces o,o-EDDHA as the main reaction product, together with a mixture of regioisomers (o,p-EDDHA and p,p-EDDHA) and other unknown byproducts also able to complex Fe3+. These compounds have been obtained by direct synthesis, and their structures have been determined by ESI-MS analysis as oligomeric EDDHA-like products, formed by polysubstitution in the phenolic rings. Short-term experiments show that the iron complexes of samples enriched in these oligomeric byproducts have adequate stability in solution, but a significant amount of them is lost after interaction with soils and soil materials. Mildly chlorotic cucumber plants are able to reduce iron better from o,p-EDDHA/Fe3+ than from the iron complexes of the oligomeric byproducts. In hydroponics, the chlorotic soybean susceptible plants have a lower potential for Fe absorption from these byproducts than from o,o-EDDHA/Fe3+ and from o,p-EDDHA/Fe3+. In the studied conditions, the iron chelates of EDDHA byproducts do not have the long-lasting effect shown by o,o-EDDHA/Fe3+ and present a less efficient fast-action effect than the o,p-EDDHA/Fe3+.     

Kinetic behavior of Fe(o,o-EDDHA)-humic substance mixtures in several soil components and in calcareous soils

Ferric ethylenediamine- N, N'-bis-(o-hydroxyphenylacetic)acid chelate (Fe(o, o-EDDHA)) is one of the most effective Fe fertilizers in calcareous soils. However, humic substances are occasionally combined with iron chelates in drip irrigation systems in order to lower costs. The reactivity of iron chelate-humic substance mixtures in several soil components and in calcareous soils was investigated through interaction tests, and their behavior was compared to the application of iron chelates and humic substances separately. Two commercial humic substances and two Fe(o, o-EDDHA) chelates (one synthesized in the laboratory and one commercial) were used to prepare iron chelate-humic substance mixtures at 50% (w/w). Various soil components (calcium carbonate, gibbsite, amorphous iron oxide, hematite, tenorite, zincite, amorphous Mn oxide, and peat) and three calcareous soils were shaken for 15 days with the mixtures and with iron chelate and humic substance solutions. The kinetic behavior of Fe(o, o-EDDHA) and Fe non-(o,o-EDDHA) (Fe bonded to (o,p-EDDHA) and other polycondensated ligands) and of the different nutrients solubilized after the interaction assay was determined. The results showed that the mixtures did not significantly reduce the retention of Fe(o, o-EDDHA) and Fe non-(o,o-EDDHA) in the soil components and the calcareous soils compared to the iron chelate solutions, but they did produce changes in the retention rate. Moreover, the competition between humic substances and synthetic chelating agents for complexing metal cations limited the effectiveness of the mixtures to mobilize nutrients from the substrates. The presence of Fe(o, p-EDDHA) and other byproducts in the commercial iron chelate had an important effect on the evolution of Fe(o, o-EDDHA) and the nutrient solubilization process.     

Influence of the soil/solution ratio, interaction time, and extractant on the evaluation of iron chelate sorption/desorption by soils

Synthetic Fe chelates are the most efficient agricultural practice to control Fe deficiency in crops, EDTA/Fe3+ and o,o-EDDHA/Fe3+ being the most commonly used. Their efficacy as Fe sources and carriers in soils can be severely limited by their retention on it. The aim of this work is to evaluate the possible bias introduced in the studies of the iron chelate retention by soils. For that purpose, results obtained for EDTA and EDDHA iron chelates from two batch studies with different soil/solution ratios were compared with data obtained for a leaching column experiment. Moreover, different extractants were tested to study the o,o-EDDHA/Fe3+ and o,p-EDDHA/Fe3+ desorption from a calcareous soil, and also the effect of the interaction time in their retention process has been evaluated. In summary, the mobility through a calcareous soil of the studied iron chelates differs greatly depending on the type of iron chelate and also on the procedure used to evaluate the retention and the soil/solution ratio used. In general, the leaching column method is preferred because the achieved conclusions are more representative of the natural conditions, but batch methods are very useful as a preliminary experiment, especially one with a high soil/solution ratio. The iron chelate desorption could be quantified by using a sequential extraction with water, sodium sulfate, and DTPA as extractants. Under the experimental conditions used in this study, o,o-EDDHA/Fe3+ retention increased with interaction time.     

Synthesis of o,p-EDDHA and its detection as the main impurity in o,o-EDDHA commercial iron chelates

Ethylenediamine-N,N'bis(o-hydroxyphenyl)acetic acid (o,o-EDDHA) is one of the most efficient iron chelates employed to relieve iron chlorosis in plants. However, the presence of positional isomers of EDDHA in commercial iron chelates has been recently demonstrated, and among them, it has been claimed that ethylenediamine-N(o-hydroxyphenylacetic)-N'(p-hydroxyphenylacetic) acid (o,p-EDDHA) is the main impurity present in EDDHA fertilizers. Here we report the preparation of o,p-EDDHA, a compound whose synthesis had not been previously reported. The synthetic o,p-EDDHA is able to form ferric complexes, and it has been used as a standard in the analysis of the impurities of commercial iron fertilizers. The presence of o,p-EDDHA/Fe(3+) in commercial samples has been unambiguously demonstrated by HPLC.     

Chromatographic determination of Fe chelated by ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid in commercial EDDHA/Fe3+ fertilizers

EDDHA/Fe3+ chelates are the most common fertilizers used to solve Fe chlorosis in established crops. Commercial products contain two regioisomers, ethylenediamine-N,N'-bis(o-hydroxyphenylacetic) acid (o,o-EDDHA)/Fe3+ and ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA)/Fe3+. Although several chromatographic methods exist for the determination of Fe3+ chelated by the o,o-EDDHA isomer, no method has been described for the quantification of Fe3+ chelated by o,p-EDDHA. In this work, factors that affect the behavior of o,p-EDDHA/Fe3+ in ion pair chromatography are reviewed: pH, ion pair reagent, and organic modifier. The best chromatographic performance was obtained with an aqueous mobile phase at pH 6.0 containing 35% acetonitrile and 5 mM tetrabutylammonium hydroxide under isocratic elution conditions. This method was applied to the quantification of commercial samples.     

Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA) isomers by strategy I and II plants

One of the most efficient fertilizers to correct Fe deficiency in calcareous soils and waters with high bicarbonate content is based on ferric ethylenediamine-N,N'-bis(o-hydroxyphenylacetic) acid [Fe(o,o-EDDHA)]. Fe(o,o-EDDHA) forms two groups of geometric isomers known as meso and D,L-racemic. To determine the Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA), four iron-efficient plants, two plants representative of strategy I (tomato and pepper) and two plants representative of strategy II (wheat and oats), were grown in hydroponic culture. Results indicated that strategy II plants took up iron from both Fe(o,o-EDDHA) isomers equally. However, strategy I plants took mainly the iron associated with the meso form (the lowest stability isomer).     

Computer simulation of the interactions of glyphosate with metal ions in phloem

Essential nutrients such as trace metal ions, amino acids, and sugars are transported in the phloem from leaves to other parts of the plant. The major chelating agents in phloem include nicotianamine, histidine, cysteine, glutamic acid, and citrate. A computer model for the speciation of metal ions in phloem has been used to assess the degree to which the widely used herbicide glyphosate binds to Fe(3+), Fe(2+), Cu(2+), Zn(2+), Mn(2+), Ca(2+), and Mg(2+) in this fluid over the pH range of 8 to 6.5. The calculations show that glyphosate is largely unable to compete effectively with the biological chelating agents in phloem. At a typical phloem pH of 8, 1.5 mM glyphosate binds 8.4% of the total Fe(3+), 3.4% of the total Mn(2+), and 2.3% of the total Mg(2+) but has almost no effect on the speciation of Ca(2+), Cu(2+), Zn(2+), and Fe(2+). As the pH decreases to 6.5, there are some major shifts of the metal ions among the biological chelators, but only modest increases in glyphosate binding to 6% for Fe(2+) and 2% for Zn(2+). The calculations also indicate that over 90% of the glyphosate in phloem is not bound to any metal ion and that none of the metal-glyphosate complexes exceed their solubility limits.     

Efficacy of Fe(o,o-EDDHA) and Fe(o,p-EDDHA) isomers in supplying Fe to strategy I plants differs in nutrient solution and calcareous soil

The FeEDDHA [iron(3+) ethylenediamine di(o-hydroxyphenylacetic) acid] is one of the most efficient iron chelates employed in the correction of iron clorosis in calcareous soils. FeEDDHA presents different positional isomers: the ortho-ortho (o,o), the ortho-para (o,p), and the para-para (p,p). Of these isomers, the p,p cannot chelate Fe in soil solution in a wide range of pH values, while both o,o and o,p can. The objective of this work was to compare the efficiency of both isomers (o,o and o,p) to provide Fe to two Strategy I plants (tomato and peach) in nutrient solution (pH approximately 6.0), as well as in calcareous soil (pH approximately 8.4; CALCIXEREPT). For this, chelates of both o,o-EDDHA and o,p-EDDHA with 57Fe (a nonradioactive isotope of Fe) were used, where the 57Fe acts as a tracer. The results obtained showed that the o,o isomer is capable of providing sufficient Fe to plants in both nutrient solution and calcareous soil. However, the o,p isomer is capable of providing sufficient Fe to plants in nutrient solution but not in calcareous soil.     

Demetalation of Fe, Mn, and Cu chelates and complexes: application to the NMR analysis of micronutrient fertilizers

The application of nuclear magnetic resonance (NMR) for the quality control of fertilizers based on Fe(3+), Mn(2+), and Cu(2+) chelates and complexes is precluded by the strong paramagnetism of metals. Recently, a method based on the use of ferrocyanide has been described to remove iron from commercial iron chelates based on the o,o-EDDHA [ethylenediamine-N,N'bis(2-hydroxyphenylacetic)acid] chelating agent for their analysis and quantification by NMR. The present work extended that procedure to other paramagnetic ions, manganese and copper, and other chelating, EDTA (ethylenediaminetetraacetic acid), IDHA [N-(1,2-dicarboxyethyl)-d,l-aspartic acid], and complexing agents, gluconate and heptagluconate. Results showed that the removal of the paramagnetic ions was complete, allowing us to obtain (1)H NMR spectra characterized by narrow peaks. The quantification of the ligands by NMR and high-performance liquid chromatography showed that their complete recovery was granted. The NMR analysis enabled detection and quantification of unknown impurities without the need of pure compounds as internal standards.     

Nature of impurities in fertilizers containing EDDHMA/Fe(3+), EDDHSA/Fe(3+), and EDDCHA/Fe(3+) chelates.

Iron chelates derived from ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA), ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid (EDDHMA), ethylenediaminedi(2-hydroxy-5-sulfophenylacetic) acid (EDDHSA), and ethylenediaminedi(5-carboxy-2-hydroxyphenylacetic) acid (EDDCHA) are remarkably efficient in correcting iron chlorosis in plants growing in alkaline soils. This work reports the determination of impurities in commercial samples of fertilizers containing EDDHMA/Fe(3+), EDDHSA/Fe(3+), and EDDCHA/Fe(3+). The active components (EDDHMA/Fe(3+), EDDHSA/Fe(3+), and EDDCHA/Fe(3+)) were separated easily from other compounds present in the fertilizers by HPLC. Comparison of the retention times and the UV-visible spectra of the peaks obtained from commercial EDDHSA/Fe(3+) and EDDCHA/Fe(3+) samples with those of standard solutions showed that unreacted starting materials (p-hydroxybenzenesulfonic acid and p-hydroxybenzoic acid, respectively) were always present in the commercial products. 1D and 2D NMR experiments showed that commercial fertilizers based on EDDHMA/Fe(3+) contained impurities having structures tentatively assigned to iron chelates of two isomers of EDDHMA. These findings suggest that current production processes of iron chelates used in agriculture need to be improved.     

Tissue iron distribution and urinary mineral excretion vary depending on the form of iron (FeSO4 or NaFeEDTA) and the route of administration (oral or subcutaneous) in rats given high doses of iron

Sodium iron ethylenediaminetetraacetate (NaFeEDTA) has considerable promise as an iron fortificant in food. However, effects of administering high levels of NaFeEDTA on tissue iron distribution and mineral excretion are not well understood. The objectives of this study were to assess nonheme iron distribution in the body and urinary excretion of Ca, Mg, Cu, Fe, and Zn after daily administration of high levels of iron to rats over 21 days. Iron was either given orally with food or injected subcutaneously, as either FeSO 4 or NaFeEDTA. Selected tissues were collected for nonheme iron analysis. Estimated total body nonheme iron levels were similar in rats fed NaFeEDTA or FeSO 4, but the tissue distribution was different: it was 53% lower in the liver and 86% higher in the kidneys among rats fed NaFeEDTA than among those fed FeSO 4. In contrast, body nonheme iron was 3.2-fold higher in rats injected with FeSO 4 than in rats injected with NaFeEDTA. Administering NaFeEDTA orally elevated urinary Cu, Fe, and Zn excretion compared with FeSO 4 (1.41-, 11.9-, and 13.9-fold higher, respectively). We conclude that iron is dissociated from the EDTA complex prior to or during intestinal absorption. A portion of intact FeEDTA may be absorbed via a paracellular route at high levels of intake but is mostly excreted in the urine. Metal-free EDTA may be absorbed and cause elevated urinary excretion of Fe, Cu, and Zn.     

Recovery and characterization of the metal polymeric organic fraction (polymerin) from olive oil mill wastewaters

A dark and complex metal polymeric organic mixture, named polymerin, was recovered from olive oil mill wastewaters (OMWW) and characterized by chemical analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and atomic absorption spectrometry (AAS). Polymerin proved to be composed of carbohydrates (52.40 mg 100(-1), w/w), melanin (26.14 mg 100(-1)), and proteins (10.40 mg 100(-1)), and the respective composition of monosaccharides, phenols, and amino acids was determined. It also contained metals (11.06 mg 100(-1)), mainly K(+) and, to a lesser extent, Na(+), Ca(2+), Mg(2+), Zn(2+), Fe(3+), and Cu(2+), which were naturally bound and chelated through carboxylate anions and other characteristic nucleophilic functional groups naturally occurring in polymerin. The distribution of polymerin relative molecular size was assessed to be approximately between 500.0 and 2.0 kDa by calibrated molecular weight gel filtration chromatography, indicating also that a fraction consisted of protein, melanin, and polysaccharide, strongly aggregated to each other in a supramolecular status by a combination of covalent and hydrogen bonds and CH/Pi interactions, and another fraction of only free polysaccharide. Polymerin was transformed into a potassium salt deglycosylated derivative, named KSDpolymerin, which was also characterized by chemical analysis, DRIFTS, and AAS. KSDpolymerin consisted of carbohydrates (6.00 mg 100(-1)), melanin (52.49 mg 100(-1)), and proteins (35.40 mg 100(-1)), and the composition of monosaccharides, phenols, and amino acids was determined. It also contained metals (6.11 mg 100(-1)), mainly K(+) and to a lesser extent Na(+), Ca(2+), Mg(2+), Zn(2+) and Fe(3+), bound as in polymerin. All the organic components were strongly linked in a supramolecular aggregate status and the relative average molecular size proved to be 6.3 kDa. Finally, we briefly discuss the possible use of such polymerins in agriculture as bioamendments and macro- and microelement biointegrators and as a biofilter for toxic metal removal, in light of their similarity with humic acids.     

Production, purification, and properties of an endoglucanase produced by the hyphomycete Chalara (Syn. Thielaviopsis) paradoxa CH32

The hyphomycete Chalara (syn. Thielaviopsis) paradoxa produces endoglucanase activity during the late trophophase. The low molecular mass (35 kDa) endoglucanase purified from cultured broths works optimally at 37 degrees C and pH 5.0. The enzyme inactivates at pH below 3.0 and also at temperatures of 50 degrees C or higher, but it is stable at lower temperatures, including refrigeration temperature and freezing. The enzyme is inhibited by detergents, by EDTA, and by the divalent cations Hg(2+) and Ag(2+). It is also inhibited to some extent by 10 mM Zn(2+), Fe(2+), and Mg(2+), but it is stimulated by Mn(2+). Enzyme activity is not affected by reducing agents. In the presence of low concentrations of water miscible organic solvents (20%) endoglucanase activity is inhibited by 7% (for methanol) to 50% (for acetonitrile), and it is totally inhibited at higher solvent concentrations (50%). Enzyme activity is not affected by the water immiscible solvent ethyl acetate. Carboxymethylcellulose is the preferred substrate (K(m(app)) = 8.3 g/L; V(max(app)) = 1.1 microM/min). Hydrolysis of crystalline cellulosic substrates is very limited, but it is greatly enhanced by phosphoric acid swelling. The purified enzyme shows no activity toward disaccharides or aryl-glucosides. Its activity is inhibited by cellobiose.     

β-Carotene Assay Revisited. Application To Characterize and Quantify Antioxidant and Prooxidant Activities in a Microplate

The β-carotene bleaching assay, a common method for evaluating antioxidant activity, has been widely criticized due to its low reproducibility, problematic quantification, complex reagent preparation, and interference of different factors (temperature, pH, solvents, and metals). In this work we have examined the effects of these factors and developed a highly reproducible procedure for microplate assay, evaluated the critical points of the method, and proposed a kinetic model for quantifying both antioxidant and prooxidant activities. The application of these tools produced very consistent results, which provide robust and meaningful criteria to compare in detail the characteristics of several well-known commercial antioxidants, as well as several predictable prooxidants, and can be easily applied to natural extracts, food samples, and many other type of compounds. As an example, we have tested a set of commercial antioxidants and some typical lipophilic prooxidants. The activity of the tested antioxidants decreased in the following order: ethoxyquin ? α-tocopherol > butylhydroxyanisole > butylhydroxytoluene ? propyl gallate. On the other hand, hemoglobin and Fe(2+), Fe(3+), Co(2+), and Cu(2+) showed a strong prooxidant effect, and the activity was null in Cd(2+), Ni(2+), and Sr(2+), slightly antioxidant in Mg(2+), and strongly antioxidant in Zn(2+) and Mn(2+).     

Effect of EDTA alone and in combination with polygodial on the growth of Saccharomyces cerevisiae

The antifungal activity of ethylenediaminetetraacetic acid (EDTA) against Saccharomyces cerevisiae was significantly affected by various conditions such as inoculum size, pH, and metal ions (Mg(2+), Ca(2+)). EDTA was found to be effective against this yeast at the inoculum size of 10(5) colony forming units (CFU)/mL with the minimum inhibitory concentration of 400 mug/mL and the minimum fungicidal concentration of 6400 mug/mL, but it was not effective at 10(7) CFU/mL up to 6400 mug/mL. The fungicidal activity of EDTA against S. cerevisiae was significantly enhanced in combination with polygodial. Isobolograms, fractional inhibitory concentration, and fractional fungicidal concentration indices were used for evaluating the interaction between combined compounds. This synergistic effect is likely due to polygodial's destructive action on the cellular membrane, which facilitates the transmembrane transport of foreign compounds (EDTA) into yeast cells. Once inside the cells, EDTA forms chelation with divalent metals such as Mg(2+) and Ca(2+), which are required by various essential enzymes.     

Methodology to Screen New Iron Chelates: Prediction of Their Behavior in Nutrient Solution and Soil Conditions

Abstract

Iron chelates analogous to ethylenediamino‐di(o‐hydroxyphenyl)acetic acid (EDDHA) are the fertilizers chosen to treat iron chlorosis of crops grown on calcareous soils. Characterization of these synthetic ligands should be made to establish their chemical behavior and efficiency as chlorosis correctors. The aim of this research was to develop an appropriate methodology to screen new iron chelates using analytical determinations and chemical equilibrium concepts. Fe‐EDDHA, Fe‐EDDH4MA, Fe‐EDDH5MA, and Fe‐PDDHA chelates, were compared to check the proposed methodology. Titrimetric purity, protonation and Ca, Mg, and Fe(III) stability constants, pFe and species distribution in nutrient solution and soil conditions were determined. The iron chelate stability constants were in order EDDHA > EDDH4MA > EDDH5MA > PDDHA. When pFe was calculated, the larger value corresponds to Fe‐EDDHA chelate at pH below 8; but at pH above 8 the Fe‐EDDH4MA shows the larger pFe values. When the species was plotted against pH, the dominant species was FeL^? at the physiological pH range in all cases. The pH at a FeL/L_T ratio of 80% in both Fe(OH)_3amorp and Fe_soil systems was considered as an iron chelate stability index. This index was EDDH4MA > EDDH5MA > EDDHA > PDDHA in both systems, but shows that all of the chelates tested were sufficiently stable in most soil and nutrient solution conditions. In conclusion, the proposed procedure is adequate for the preliminary evaluation of the synthetic chelating agents, using important parameters such as analytical and speciation properties to predict their chelating behavior and efficiency in nutrient solution and soil conditions.     

Plant tolerance to nickel toxicity: II nickel effects on influx and transport of mineral nutrients in four plant species

Nickel (Ni) is an essential micronutrient for higher plants but is toxic to plants at excess levels. Plant species differ extensively for mineral uptake and accumulation, and these differences often help explain plant tolerances to mineral toxicities/deficiencies. Solution culture experiments were conducted under controlled conditions to determine the effects of Ni on influx into roots (IN) and transport from roots to shoots (TR) of zinc (Zn), iron (Fe), copper (Cu), manganese (Mn), calcium (Ca), magnesium (Mg), phosphorus (P), and sulfur (S) in white clover (Trifolium repens L.), cabbage (ßrassica oleracea van capitata L.), ryegrass (Lolium perenne L.), and maize (Zea mays L.). Nickel decreased both IN and TR of Zn, Cu, Ca, and Mg, but only TR of Fe and Mn in white clover. Both IN and TR of Cu, Fe, Mn, Mg, and S were markedly decreased by Ni >30 μM in cabbage, whereas IN and TR of P increased with Ni treatment. For ryegrass, TR of Cu, Fe, Mn, Ca, and Mg was decreased, but IN of these elements except Mg was not affected by Ni. The IN and TR of P and S were increased in ryegrass with increasing external Ni levels. Nickel inhibited IN of Cu, Ca, and Mg, and TR of Zn, Cu, Fe, Mn, Ca, and Mg in maize. Plant species differed in response to Ni relative to IN and TR of mineral nutrients. Plant tolerance to Ni toxicity was associated with the influence of Ni on IN and TR of Cu, Fe, and Mn in white clover and cabbage but not in maize and ryegrass.     

重金属污染土壤清洗导致几种营养元素流失的研究

通过HCl、柠檬酸、EDTA这3种提取剂对Pb、Cd、Cu、Zn污染土壤的漫提试验，研究了土壤清洗洗脱重金属的效果，并探讨了土壤清洗导致K、Ca、Mg、Fe、Mn这几种营养元素的流失和有效性的改变。试验结果表明，土壤清洗能有效地洗脱土壤中的Ph、Cd、Cu、Zn，伺时也造成了土壤中K、Ca、Mg、Fe、Mn的流失，降低了其中部分营养元素的有效性。EDTA对重金属的洗脱能力大于HCl和柠檬酸。HCl漫提造成的K、Ca、Mg的流失量大于柠檬酸和EDTA，柠檬酸浸提造成的Fe流失量大于HCl和EDTA，EDTA漫提造成的Mn流失量大于HCl和柠檬酸。HCl和柠檬酸浸提降低了土壤K、Ca、Mg的有效性EDTA浸提提高了土壤K的有效性。降低了土壤Ca的有效性。在高浓度时（50mmol／L），EDTA显著地降低了土壤Mg的有效性。HCl漫提导致土壤K的有效性下降比柠檬酸严重，高浓度的EDTA浸提导致土壤Ca的有效性下降比HCl和柠檬酸严重。HCl、柠檬酸、EDTA浸提都能提高土壤中Fe的有效性．且EDTA的效应大于其它2种萃取剂；在低浓度时，3种提取剂都能提高土壤中Mn的有效性，且以柠檬酸的作用最为明显，当提取剂浓度增加时，Mn的有效性有所回落。     

Sequestering Ability of Phytate toward Biologically and Environmentally Relevant Trivalent Metal Cations

Quantitative parameters for the interactions between phytate (Phy) and Al(3+), Fe(3+), and Cr(3+) were determined potentiometrically in NaNO(3) aqueous solutions at I = 0.10 mol L(-1) and T = 298.15 K. Different complex species were found in a wide pH range. The various species are partially protonated, depending on the pH in which they are formed, and are indicated with the general formula MH(q)Phy (with 0 ≤ q ≤ 6). In all cases, the stability of the FeH(q)Phy species is several log K units higher than that of the analogous AlH(q)Phy and CrH(q)Phy species. For example, for the MH(2)Phy species, the stability trend is log K(2) = 15.81, 20.61, and 16.70 for Al(3+), Fe(3+), and Cr(3+), respectively. The sequestering ability of phytate toward the considered metal cations was evaluated by calculating the pL(0.5) values (i.e., the total ligand concentration necessary to bind 50% of the cation present in trace in solution) at different pH values. In general, phytate results in a quite good sequestering agent toward all three cations in the whole investigated pH range, but the order of pL(0.5) depends on it. For example, at pH 5.0 it is pL(0.5) = 5.33, 5.44, and 5.75 for Fe(3+), Cr(3+), and Al(3+), respectively (Fe(3+) < Cr(3+) < Al(3+)); at pH 7.4 it is pL(0.5) = 9.94, 9.23, and 8.71 (Al(3+) < Cr(3+) < Fe(3+)), whereas at pH 9.0 it is pL(0.5) = 10.42, 10.87, and 8.34 (Al(3+) < Fe(3+) < Cr(3+)). All of the pL(0.5) values, and therefore the sequestering ability, regularly increase with increasing pH, and the dependence of pL(0.5) on pH was modeled using some empirical equations.     

Influence of herbicide structure,clay acidity,and humic acid coating on acetanilide herbicide adsorption on homoionic clays

Adsorption of chloroacetanilide herbicides on homoionic montmorillonite was studied by coupling batch equilibration and FT-IR analysis. Adsorption decreased in the order metolachlor > acetochlor > alachlor > propachlor on Ca(2+)- or Mg(2+)-saturated clays and in the order metolachlor > alachlor > acetachlor > propachlor on Al(3+)- or Fe(3+)-saturated clays. FT-IR spectra showed that the carbonyl group of the herbicide molecule was involved in bonding. For the same herbicide, adsorption of alachlor, acetachlor, and metolachlor on clay followed the order Ca(2+) approximately Mg(2+) < Al(3+) < or = Fe(3+), which coincided with the increasing acidity of homoionic clays. Adsorption of propachlor, however, showed an opposite dependence, suggesting a different governing interaction. In clay and humic acid mixtures, herbicide adsorption was less than that expected from independent additive adsorption by the individual constituents, and the deviation was dependent on the clay-to-humic acid ratio, with the greatest deviation consistently occurring at a 60:40 clay-to-humic acid ratio.