Loreto Ascar

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 ...

Influence of redox potential (Eh) on the availability of arsenic species in soils and soils amended with biosolid.

A study was done on the influence of redox potential on the mobility and availability of the various arsenic chemical forms in a Mollisol soil from central Chile amended with biosolid. Arsenic availability was strongly dependent on the applied redox potential. As expected, under reducing conditions (-200 mV vs Hg/Hg(2)Cl(2)) arsenic availability increased significantly, and arsenic was found mainly as arsenite. On the contrary under oxidizing conditions (200 mV vs Hg/Hg(2)Cl(2)) arsenic solubility decreased markedly and was governed by the presence of arsenate. The greatest concentration of organic arsenic species was found under reducing conditions, which would indicate that methylated species may participate in the transformation of arsenate to arsenite. In biosolid-amended soils the concentrations of methylated species increased as a function of time under reducing conditions, which can be attributed to the greater microbial activity resulting from the organic matter supply from the biosolid to soil. In all the systems, a high concentration of As(V) was found under reducing conditions, indicating that the chemical kinetics for the conversion of arsenate to arsenite is slow. Along time, the content of As(V) increased in the control soils, which may be attributed to the possible dissolution of iron oxides and hydroxides under reducing conditions.

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.

Use of sequential extraction to assess the influence of sewage sludge amendment on metal mobility in Chilean soils

In Chile, the increasing number of plants for the treatment of wastewater has brought about an increase in the generation of sludge. One way of sludge disposal is its application on land; this, however involves some problems, some of them being heavy metal accumulation and the increase in organic matter and other components from sewage sludge which may change the distribution and mobility of heavy metals. The purpose of the present study was to determine the effect of sewage sludge application on the distribution of Cr, Ni, Cu, Zn and Pb in agricultural soils in Chile. Three different soils, two Mollisols and one Alfisol, were sampled from an agricultural area in Central Chile. The soils were treated with sewage sludge at the rates of 0 and 30 ton ha(-1), and were incubated at 25 degrees C for 45 days. Before and after incubation, the soils were sequentially extracted to obtain labile (exchangeable and sodium acetate-soluble), potentially labile (soluble in moderately reducing conditions, K4P2O7-soluble and soluble in reducing conditions) and inert (soluble in strong acid oxidizing conditions) fractions. A two-level factored design was used to assess the effect of sludge application rate, incubation time and their interaction on the mobility of the elements under study. Among the metals determined in the sludge, zinc has the highest concentration. However, with the exception of Ni, the total content of metals was lower than the recommended limit values in sewage sludge as stated by Chilean regulations. Although 23% of zinc in sludge was in more mobile forms, the residual fraction of all metals was the predominant form in soils and sludge. The content of zinc only was significantly increased in two of the soils by sewage sludge application. On the other hand, with the exception of copper, the metals were redistributed in the first four fractions of amended soils. The effect of sludge application rate, incubation time and their interaction depended on the metal or soil type. In most cases an increase in more mobile forms of metals in soils was observed as the final effect.

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.

Microextraction of non-steroidal anti-inflammatory drugs from waste water samples by rotating-disk sorptive extraction.

In this study, six non-steroidal anti-inflammatory drugs (NSAIDs) were extracted from water samples using the rotating-disk sorptive extraction (RDSE) technique. The extraction disk device contains a central cavity that allows for the incorporation of a powdered sorbent phase (Oasis™ HLB). The analytes were extracted from water and pre-concentrated on the sorbent to reach the extraction equilibrium, and then they were desorbed with solvent, derivatized and determined by gas chromatography-mass spectrometry (GC-MS). The variables for the extraction were studied using high performance liquid chromatography with a diode array detector (HPLC-DAD) to avoid the derivatization step, and the optimum values were as follows: 60 mg of Oasis™ HLB, a rotation velocity of 3,000 rpm, a pH of 2, a sample volume of 50 mL, and an extraction time of approximately 90-100 min. The recoveries ranged from 71 to 104%, with relative standard deviations (RSD) between 2 and 8%. The detection limits ranged from 0.001 to 0.033 µg L(-1). The described method was applied to the analysis of influents and effluents from wastewater treatment plants (WWTP) in Santiago, Chile. The concentrations of the detected drugs ranged from 1.5 to 13.4 µg L(-1) and from 1.0 to 3.2 µg L(-1) in the influents and effluents, respectively. The samples were extracted by solid phase extraction (SPE). No significant differences were observed in the determined concentrations for most of the NSAIDs, indicating that RDSE is an alternative method for the preparation of water samples.

Copper and zinc bioavailabilities to ryegrass (Lolium perenne L.) and subterranean clover (Trifolium subterraneum L.) grown in biosolid treated Chilean soils.

The purpose of this study was assessing Cu and Zn availabilities in soils amended with a biosolid through the determination of their sequentially extracted chemical forms and their relationship with the contents of these metals in ryegrass (Lolium perenne L.) and subterranean clover (Trifolium subterraneum L.) plant tissues cultivated in a greenhouse using four soils classified as Aquic Xerochrepts and Ultic Haploxeralfs representatives of potential areas for biosolids application in the central zone of Chile. The soils were treated with sewage sludge at a rate of 0 and 30 Mg ha(-1). The greenhouse experiment was carried out through a completely randomized block design in a 2 x 4 (biosolid ratexsoil) arrangement, considering three repetitions per treatment. The soils used in the greenhouse experiment before and after cultivation, were sequentially extracted with specific reagents and conditions in order to obtain the following fractions: exchangeable, sodium acetate-soluble, soluble in moderately reducing condition, K(4)P(2)O(7)-soluble, soluble in reducing condition, and soluble in strongly acid and oxidizing condition. It was established that Cu and Zn were predominantly found in soils in less available forms, associated to organic matter, oxides and clay minerals. Zinc concentration in ryegrass plants was higher than that found in subterranean clover plants in biosolid-amended soils. Zinc contents in ryegrass shoot and root correlated with the exchangeable, bound-to-carbonate, and bound-to-FeOx metal forms in control soil. Copper and Zn bioavailabilities were estimated through satisfactorily fitted multiple linear regression models, with determination coefficients from 0.77 to 0.99, which showed a positive contribution of the labile metal forms in soils, especially in relation to Zn in both plant species.

Nonsteroidal anti-inflammatory drug determination in water samples by HPLC-DAD under isocratic conditions

Nonsteroidal anti-inflammatory drugs (NSAIDs) are a group of medications widely used by man to heal certain ailments. However, after consumption, they may be excreted in wastewaters with consequent environmental effects. NSAIDs are endocrine disruptors that can cause changes in animal physiology. The purpose of this study was to implement an analytical method that permits the determination of the presence of NSAIDs in water. Compound extraction was performed by solid-phase extraction (SPE) using an Oasis HLB cartridge. Analytes were analyzed by high-performance liquid chromatography with diode array detection (HPLC-DAD). The method was applied in water from the Maipo River and from a neighboring wastewater treatment plant in the Metropolitan Region of Pajaritos, Vina, Tuberia, Union and Gansos sampling points in Chile. This method turned out to be adequate for the determination of NSAIDs in water samples with recovery percentages above 80%. Naproxen and ibuprofen were mostly detected in the Maipo River water samples, with concentrations ranging from 0.33 to 0.83 µg L-1.

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.

Assessment of extractability of Cu, Cr, Ni, Pb and Zn in some chilean biosolid-amended soils by using BCR sequential extraction procedure

The effect of biosolid application on the distribution and extractability of Cr, Cu, Ni, Pb, and Zn was assessed in Mollisol soils from an important agricultural zone in central Chile. These were amended with biosolids at the amounts of 15 and 30 Mg ha-1 and incubated for 60 days under controlled conditions of moisture and temperature. Four domestic biosolids were obtained from the monofill at one of the Santiago wastewater treatment plants. Biosolid and soil sequential extraction was performed according to the procedure recommended by BCR, which considers four extractions to obtain an acid-soluble fraction (exchangeable, carbonates), a reducible fraction (iron/manganese oxides), an oxidizable fraction (organic matter and sulfides) and the residual one. Trace metals were determined by flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry. Among the metals determined in biosolids, Zn had the highest concentration. Total trace metal contents found, except for Ni in some biosolids, was below the limits allowed by the Chilean regulation for biosolids. In general, without considering the residual fraction, the metals were found predominantly as reducible and oxidizable fractions. A multifactorial design was applied to assess the effects of biosolid application amounts, biosolid type and incubation time. Biosolid incorporation at the amount of 30 Mg ha-1 produced an increase in Zn and Ni availability in all soils and Cu in most of them, while Cr, and Pb showed no significant variations. In general, the factors incubation and type of biosolid did not show remarkable effects compared with initial conditions.