Jorge Mendoza

Sequential extraction of heavy metals in soils irrigated with wastewater

Abstract Different chemical forms of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) were determined in agricultural soils cultivated with lettuce and celery. These soils have been irrigated for several decades with nontreated wastewaters. The chemical forms of the metals were characterized by sequential extraction analysis in five steps, the extracting solutions of which contained 200 mg L‐1 nitrilotriacetic acid (NTA). The results showed that Cd, Pb, and Cu exhibited the highest values of extracted metal, and Cr exhibited the lowest value. Almost all of the metals in these soils are bound to iron oxides, followed by the metal complexed to organic matter. The form bound to manganese oxides is equally important to Co. Cadmium is the most mobile metal and its available forms account for 40% of the total extracted. When these metals were determined in plants, both shoots and roots, a greater concentration of Cr, Zn, and Cu was found in celery, and Cu, Ni, and Zn ...

Extractability of arsenic, copper, and lead in soils of a mining and agricultural zone in central Chile

Abstract Copper (Cu) mining activities are very important in central Chile. The present study consists in determining the distribution and availability of copper, arsenic (As), and lead (Pb) in soils near a smelting facility, in the VI Administrative Region of Chile, which are subjected to risk of contamination by emissions and by irrigation with contaminated water. In order to determine the distribution of these elements in their various chemical forms in soils, two sequential extraction methods (SEM) were applied. A five stage SEM was used for Cu and Pb, and a four stage one for As. Single extraction methods were also carried out using 1 M HCl, 0.005 M DTPA and 0.005 M EDTA for As, Cu, and Pb, respectively. Furthermore, a 0.1 M malic-citric acid solution (MC) was used as simple extractant for the three elements to simulate the conditions of root environment of the plant. The soils showed the following order of total metal concentration: Cu > As > Pb. Copper was extracted in higher amount than the other metals, both with the sequential and with the simple extraction method. Single correlation analysis was applied between the amount of metal in the single extraction method and the different fraction obtained with the sequential technique. Significant positive correlations were obtained, especially for copper and lead.

EFFECT OF ACETATE, CITRATE, AND LACTATE INCORPORATION ON DISTRIBUTION OF CADMIUM AND COPPER CHEMICAL FORMS IN SOIL

Some organic acids of low molecular weight, generated through breakdown of plant wastes or root exudation, increase the solubilization of heavy metals, such as cadmium (Cd) and copper (Cu) through complexation reactions and may affect the distribution of their chemical forms in soil. By using natural soil and soil spiked with Cd or Cu, the effect of acetate, citrate, and lactate incorporation on the solubilization of these metals and the distribution of their chemical forms was assessed. To this end, four concentration levels of organic acids were incorporated to soil: 0, 0.4, 0.8, and 1.6 mM at constant ionic strength in 0.02 M potassium chloride (KCl) at pH 5.5 at a soil to solution ratio of 1:20. After 24 h equilibrium, the supernatant was separated and used to determine the concentration of organic acid not retained by soil through the technique of Zone Capillary Electrophoresis and the metal concentration through inductively coupled plasma-mass spectrometry (ICP-MS). The residue was fractionated to determine Cd and Cu chemical forms through a sequential extraction method of five steps. Results showed that acetate and lactate retention is higher in non-sterilized soils which would indicate that anion retention would partly correspond to consumption by microorganisms rather than to anion adsorption by soil particles. It was also found that a higher metal content has a negative effect on acetate retention. The presence of lactate and citrate increases the solubility of both metals, and treatment with these acids in some cases affect the distribution of their chemical forms. Acetate incorporation increased the amount of Cu associated to organic matter, and the presence of citrate affected the fractions of exchangeable Cu, carbonate, and associated to manganese oxides. The fraction of both metals associated to iron oxides was the least affected by the incorporation of organic acid anions.

Effect of Glomus etunicatum inoculation on aluminum, phosphorus, calcium, and magnesium uptake of two barley genotypes with different aluminum tolerance

Abstract This study was conducted to evaluate the effect of vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus etunicatum on growth, absorption, and distribution of calcium (Ca), magnesium (Mg), phosphorus (P), and aluminum (Al) in one Al‐tolerant and one Al‐sensitive barley cultivar. The plants were grown in sand daily irrigated with nutrient solution containing 0 or 600 μM Al at pH 4.8. Significant interaction (P=0.05) among variety, mycorrhiza, and aluminum (VxMxAl) were noted for both shoot and root dry matter (DM); shoot concentration and content of Al, P, Ca, and Mg; root concentration of Al, P, and Mg; and root content of Al, P, Ca, and Mg. With VAM inoculation: i) root colonization degree was about 50% in all treatment, ii) shoot DM yield increased between 30 and 70%, iii) Al concentration and content decrease down to a half both in shoots and roots of sensitive barley, iv) Ca concentration in shoots of sensitive barley showed a high increase at 600 μM Al, and v) P concentration and content in s...

Changes in the sorption, desorption, distribution, and availability of copper, induced by application of sewage sludge on Chilean soils contaminated by mine tailings

The effect of mine tailings and sewage sludge was evaluated on sorption, desorption, availability and distribution of copper in two soils, one high (sandy soil) and one low in copper (clay soil). In both soils contaminated by mine tailings the copper sorption capacity and the affinity of the substrate for the metal decreased substantially compared to the uncontaminated soils, however, the sorption remained always high in the clay soil substrates. In the substrates with sandy soil, the high Cu content and lower clay content were determining factors in the lower magnitude of the sorption. Similarly, metal desorption was closely related to these two parameters, and it was higher in clay soil with lower pH. In general, the application of sewage sludge favored the sorption of Cu in soils contaminated and uncontaminated with mine tailings, and in all cases desorption decreased, an effect that remained for at least 30 days. Simple extraction of Cu with CaCl2 and diethylenetriaminepentaacetic acid gave contradictory results, so a careful choice of the procedure is required, depending on the level of metal in the soil and on the acting principle of the extracting agent. In that relation, more complete information on the changes in the metal forms was obtained by application of the sequential extraction procedure proposed by the European Community Bureau of Reference.

Rapid capillary electrophoresis analysis of glutathione and glutathione disulfide in roots and shoots of plants exposed to copper

INTRODUCTION Glutathione and glutathione disulfide can be determined by capillary zone electrophoresis; however, the frequent use of acidic precipitation of protein from samples prior to analysis generates an acidic matrix of strength and pH that may cause changes in the method sensitivity, comigration of species or changes in the equilibria that relate both species in cells or fluids. OBJECTIVE To optimise electrophoretic conditions for glutathione and glutathione disulfide determination, and to improve pre-analytical treatment for better visualization of the signals of both peptides in an acidic matrix. METHODOLOGY The method consisted of direct photometric detection at 185 nm and 300 mm borate at pH 7.6 as background electrolyte. The variables under study were voltage applied, injection time, capillary length and electrolyte pH. Seedlings were hydroponically grown and the peptides were extracted with metaphosphoric acid. RESULTS The resulting acidic matrix was previously treated with the same background electrolyte to prevent comigration and to improve signal resolution. The optimised method showed good reproducibility and linearity, with correlation coefficients above 0.999 and detection limits below 3 microM, and determination of both analytes in less than 3 min. Analyte recovery in the process was in the 88-104% range. The concentration range found in hydroponically grown tomato plants, irrespective of copper level, was 45-100 nmol/g fresh weight for glutathione and below 56 nmol/g fresh weight for glutathione disulfide. CONCLUSION The results obtained here support the applicability of the method to the fast and simultaneous determination of glutathione and glutathione disulfide in tissue of shoots and roots of plants grown under either normal or stressful conditions.

Determination of organic acids and phosphate in soil aqueous extracts by capillary zone electrophoresis

Abstract Organic acids and phosphate were determined in soil aqueous extracts by capillary zone electrophoresis using indirect UV detection. The electrolyte system was 10 mM sodium benzoate with 0.5 mM tetradecyltrimetyl‐ammonium bromide as flow modifier at pH 4.0, pH 4.5, or pH 5.0. This methodology was adequate to determine organic acids and phosphate in soil samples, but the major inorganic anions interfered in the determination. In all the samples of soil extracts, the presence of phosphate was detected. Acetate was found in most of the samples and lactate and formate in some of them.

SIMULTANEOUS DETERMINATION OF GLUTATHIONE AND GLUTATHIONE DISULFIDE IN AN ACID EXTRACT OF PLANT SHOOT AND ROOT BY CAPILLARY ELECTROPHORESIS

This study describes the fast and simultaneous determination of glutathione and glutathione disulfide by Capillary Zone Electrophoresis in plant extracts of shoot and root of tomato plants. Frequent use of acidic precipitation of protein generates an acidic matrix of strength and pH that may cause changes in the method sensitivity, comigration of species or changes in the equilibria that relate both species in cells or fluids. In this study, the resulting acidic matrix was previously treated with the same background electrolyte to prevent comigration and to improve signal resolution. Optimization of some parameters of the technique allowed the determination of both analytes in less than three minutes. The optimized method showed good reproducibility and linearity, with correlation coefficients above 0.999 and detection limits below 3 µM for both peptides. Analyte recovery in the process was in the 88-104% range. The concentration found in tomato plants hydroponically grown in the absence of stress factors was in the 51-100 nmol g-1 range, fresh weight for GSH and 5-32 nmol g-1 range, fresh weight for GSSG.

ENANTIOSELECTIVE ADDITION OF DIETHYL ZINC TO BENZALDEHYDE CATALYZED BY TI(IV) AND GLUCOSE DERIVATIVES

D-Glucose derivatives 1,2:5,6-di-O-isopropyline-a-D-glucofuranose (1) and 1,2-O-isopropyline-a-D-glucofuranose (2) with Ti(IV) are chiral catalysts in the addition of diethylzinc to benzaldehyde. The Ti(IV)-carbohydrate catalytic system is optimal with excess Ti(IV) and substoichiometric carbohydrate and 2 is the more active chiral catalyst probably because this derivative acts as a bidentate ligand in the proposed reaction. The arrangement of OH groups is crucial in determining the configuration of the alcohol product.

ISOLATION AND CHARACTERIZATION OF COBALT (III) TRIS-D-AMINOSUGARS

Mixed complexes of aminosugars and 1,10-phenanthroline (phen) with cobalt(III), with the composition Co(III)(phen)2sugar, disproportionate in aqueous solution in approximately one month, giving non ionic tris-aminosugar complexes. The complexes with a-D-glucosamine, a-D-galactosamine and b-D-mannosamine have the L-configuration at Co(III) with facial isomerism, on the bases of molecular composition and absorption and circular dichroism spectra