Inés Ahumada

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 ...

Determination of pesticides in river water using rotating disk sorptive extraction and gas chromatography-mass spectrometry.

The rotating disk sorptive extraction (RDSE) technique was applied to the determination of pesticides in aqueous samples. Pesticides of different polarities were considered in this study: chlorpyrifos, diazinon, fenvalarate, cyhalothrin, cypermethrin, lindane and malathion. The sorptive/desorptive behavior of the pesticides was studied using a rotating disk containing a polydimethylsiloxane (PDMS) phase on one of its surfaces. The analyte polarity was a significant factor in the extraction time; shorter extraction times were required for the more apolar pesticides. The optimum variables for the extraction of all analytes were: extraction time of 3h, sample volume of 25 mL, rotational velocity of the disk 1250 rpm, desorption time of 30 min using methanol. For pesticides with values of Log K(ow)>4, the extraction time can be reduced to 30 min for a quantitative extraction. Under these conditions, recoveries between 76% and 101% were obtained for the target pesticides, and the repeatability of the methodology, expressed as relative standard deviation, was determined to be between 10% and 20%. Additionally, the limits of detection of the analytes were lower than 3.1 μg L(-1). The extraction method developed using the RDSE was compared to a stir bar sorptive extraction (SBSE) under the same conditions. It can be observed that the extraction using the rotating disk offers higher recoveries because of its higher PDMS volume and its higher surface area to volume ratio that allows for improved mass transfer.

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.

Rotating disk sorbent extraction for pre-concentration of chromogenic organic compounds and direct determination by solid phase spectrophotometry

A novel and very simple microextraction approach for pre-concentration and direct solid phase spectrophotometric measurement has been developed for the determination of chromogenic analytes. The model analyte to assess this approach was the chromophore malachite green (MG). The analyte was extracted from water samples onto a small rotating disk made of Teflon containing a sorbent phase of polydimethylsiloxane (PDMS) on one of its surfaces. We refer to the extraction procedure as rotating disk sorptive extraction (RDSE). After extraction, the sorbent phase with the concentrated analyte was separated from the Teflon disk and used directly for MG determination by solid phase spectrophotometry at 624 nm, without the necessity of a desorption step. Chemical and extraction variables such as concentration of sodium sulfate, pH, disk rotational velocity, extraction time, and temperature were studied in order to establish the best conditions for extraction. Under optimum conditions, the extraction of MG was carried out in 18 min and 90 min, for sample volumes of 100mL or 1000 mL, respectively. The detection limit, based on three times the standard deviation of the blank phase (3σ(b)), was 1.4 μg L⁻¹ and the repeatability, expressed as relative standard deviation (RSD), for 20 μg L⁻¹ MG was 8.1%. This study also applied the method to real samples, obtaining quantitative recovery (mean recovery of 99.3%). The PDMS phases could be reused after desorbing the MG into methanol for 3h. Replacement of the PDMS film onto the disk is very easy and low cost.

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.

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.

Determination of polychlorinated biphenyls in biosolids using continuous ultrasound-assisted pressurized solvent extraction and gas chromatography-mass spectrometry.

An efficient continuous pressurized solvent extraction (PSE) method assisted by ultrasound energy was developed for the extraction of polychlorinated biphenyls (PCBs) from biosolids. Analytes were determined in the extracts by gas chromatography-mass spectrometry in selected ion monitoring (SIM) mode. A screening-type experimental design pointing to dynamic extraction time as the only significant variable in the extraction process was carried out to optimize PCB extraction from the biosolids. Final selected conditions for PSE were extraction temperature, 50 degrees C; static extraction time, 0 min; and dynamic extraction time, 30 min. Recovery of the PSE method was 73%, which was significantly improved (103%) when PSE was assisted with 30-min ultrasound (US-PSE). Precision of the overall method, expressed as relative standard deviation, was 3.6% and the detection limit was 0.037 mg/kg. The method was applied to the determination of PCBs in biosolids from different water treatment plants from central Chile.

Chemical forms and sorption of copper and zinc in soils of central Chile

Abstract Soil samples from a field irrigated with untreated industrial and municipal wastewater for several decades and from a field not receiving wastewater (control) were analyzed for total copper (Cu) and zinc (Zn) and for the amount of these elements removed in sequential extractions with MgCl2, NaOAc, NH2OH#lbHCl, 6H2O2‐HNO3‐NH4OAc, and HNO3‐HF‐HCl. Organically‐bound Cu forms predominated in the wastewater‐affected soil while in the control soil both residual and organic forms yielded the same proportion of Cu. Distribution of Zn was different in the diverse fractions, and in the polluted soil the reducible and the residual forms predominated while in the control soil the residual form accounted for the highest proportion of recovered Zn. Sequential extraction of Cu from a copper sulfate‐treated soil incubated for 32 days at constant temperature resulted in the same proportional distribution of Cu forms in the polluted soil. In the control soil the oxidizable form decreased and the residual one incre...