Marta Susana Zubillaga

Heavy metals in soils of Argentina: Comparison between urban and agricultural soils

Abstract Trace metals, including heavy metals, can be harmful to the biota and human beings. This leads to study the accumulation of those elements in soils. In the Pampean region (Argentina) this knowledge is scarce. Our objectives were to (i) determine the trace metal concentration in soils of Buenos Aires City and agricultural areas, (ii) start to establish the soil trace metals baseline concentration, and (iii) find relationships between soil properties and those elements Topsoil samples were taken in Buenos Aires City and on farms along an arc 50 to 250 km away from the metropolis. All studied soils were Mollisols. Soil samples were analyzed for their cadmium (Cd), copper (Cu), zinc (Zn), chromium (Cr), cobalt (Co), lead (Pb), and nickel (Ni) contents by acid extraction. Soil properties were determined using standard methods. The soils of Buenos Aires City show the highest average concentrations of Cd, Cu, Pb, and Zn. The further the sampling sites were from Buenos Aires, the lower the metal concentr...

Baseline Levels of Potentially Toxic Elements in Pampas Soils

The soils of the Pampas are thought to be generally non-contaminated but there is growing evidence of trace element accumulation at some specific sites. The goal of this study was to measure the current levels of the main Potentially Toxic Elements (PTE) in the top horizon and in specific soil profiles so that we would establish the baseline concentrations of these elements. Eighty-eight top soils and three soil profiles were sampled. The samples were acid digested. Arsenic, boron, barium, cadmium, cobalt, chromium, copper, lead, manganese, mercury, molybdenum, nickel, silver, selenium and zinc were determined with inductively coupled argon plasma emission spectrometry (ICPES). All of the values found are within the normal range for uncontaminated soils as reported from several continents. Elements with high environmental risk potential are lower than the admissible range of the European Union and some of them are orders of magnitude lower than those of the United States Environmental Protection Agency (US-EPA) 501 levels. Potentially Toxic Elements contents increased with depth or showed a maximum concentration at the B2 horizon. This is related to the parent material and the pedogenetic processes but not to recent contamination. Soil profiles showed higher concentrations of PTE in clayey horizons. However, these relationships did not appear in top soil samples in any soil Great Group studied. The shown data establishes a baseline for PTE concentrations for Pampas soils.

Phytotoxicity of Biosolids Compost at Different Degrees of Maturity Compared to Biosolids and Animal Manures

Biosolids compost is a good organic amendment but immature compost can exhibit phytotoxic behavior which can be attributed to different toxic substances. Our objective was to determine the phytotoxicity of: i) Biosolids; ii) Mix of biosolids and wood sawdust sampled a day after composting started; iii) The same material sampled at the end of the thermophilic stage; iv) cured compost; v) cow manure and vi) horse manure A germination bioassay was carried out using Lolium perenne (ryegrass) seeds: germination and root growth percentage were determined as well as electrical conductivity, pH, phenol content and volatile organic acids. In three treatments, Ni, Pb, Zn, Cu and Cd were also determined. Ammonia volatilization was determined during biosolids composting. The germination percentage varied from 67% to 95% but the inhibition of root growth appears to be a more sensitive phytotoxicity indicator (18% to 74%. Phytotoxic effects on germinating ryegrass were mainly related to extract pH and electrical conductivity. Potentially toxic elements, volatile organic acids, phenolic compounds and ammonia were not related to germination.

Stability Indexes of Sewage Sludge Compost Obtained with Different Proportions of a Bulking Agent

The aim of using wastes in agriculture is to achieve a sustainable cycle in which these wastes will turn into organic sources in agricultural production. The specific objective was to study the composition of compost made with different sewage sludge/bulking agent ratios and to establish the most suitable stability or maturity analytical index for the compost. Three compost piles with different volume proportions (biosolids:sawdust) were performed. Measurements of pH, cationic-exchange capacity (CEC), total carbon (Ct), total nitrogen (Nt), ignition losses (IL), dissolved organic carbon (DOC), humic (HA), and fulvic acids (FA) were conducted. Microbial respiration was measured in the first and last thermophilic stage. Heavy metals [chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), copper (Cu), mercury (Hg), silver (Ag), arsenic (As), barium (Ba), selenium (Se), and cadmium (Cd)] were determined at the end of composting. The ratios used did not influence the compost properties since no differences were found either in the composition of final product or in the time required to achieve a mature compost. The pH, CEC/Ct, Ct/Nt, and IL% did not indicate degree of stability or maturity of compost. The HA and FA trials did not allow to establish the degree of the humification process. The Ct, Nt, and DOC clearly indicated the end stage in the compost piles maturity. These assessments were achieved after two months of processing, reaching stability with the following values: 3.5 and 5 g kg−1 for the Ct, 0.25 and 0.38 g kg−1 for Nt and 0.03 g kg−1 for DOC. The respiration activity decreased by 70% to 80% at the end of the thermophilic stage. The level of heavy metals, measured when the study was over, did not reach the highest values permitted by current regulations.

Heavy Metal Content in Lettuce Plants Grown in Biosolids Compost

The objective of this work was to evaluate the affects of the application of composted biosolids on the accumulation of heavy metals (Cd, Cu, Ni, Pb and Zn) in lettuce leaves. Pots containing different proportions (0 to 100%) of composted biosolids were used to grow lettuce plants under greenhouse conditions. Dry and fresh weight, leaf area and Cd, Cu, Ni, Pb and Zn uptake were determined after harvest. It was found that the dry and fresh matter productions of the plants were significantly lower in the control treatment. The addition of composted biosolids caused a 20 and 40% increase in biomass accumulation. Cd and Pb concentrations in leaves were below detection limits (0.05 mg kg−1) in all treatments. Zn concentration in leaves increases as compost proportion decreases, ranging from 57.2 to 80.4 mg kg−1. Composted biosolids application increased the Cu and Ni plant concentrations, ranging from 5.1 to 9.8 mg Cu kg−1 and 2.3 to 3.7 mg Ni kg−1. In all treatments the proportions of heavy metals in plants were below the international standards of toxicity. The results allow us to suggest that, in short-term applications, composted biosolids could be used as soil amendment for lettuce production, without toxic effects in the chemical composition of the plant.

Assessing phytotoxicity of heavy metals in remediated soil.

Copper (Cu), zinc (Zn) and chromium (Cr) are pollutants that usually are accumulated in soils. Their toxicity can be decreased by applying amendments. We proposed to evaluate changes in Cu, Zn, and Cr availability, due to the application of amendments, through chemical analysis and phytotoxicity tests. The phytotoxicity test was carried out using species belonging to Sesbania genus; plant parameters were measured 48, 72, 96, and 168 hours after the start of incubation. The treatments included enriched soil, in addition to biosolid compost and triple superphosphate. Cu and Zn amounts were higher in treatments without amendments, indicating immobilization on the part of these. The amounts of Cr tended to decrease with amendments application. The amendments increased pH values and decreased EC; however, this had no impact on the results. No relationship was found among pH, EC, and plant parameters. Different behaviors were observed. S. virgata showed germination seed delay. In addition, while in S. virgata the IG increased during the assay, in S. punicea it diminished. The application of compost, fertilizer or both combined could be of interest for contaminated soils remediation. The use of chemical analysis and phytotoxicity tests allowed to estimate heavy metal availability and the effect on both Sesbania species.

Comparative Use of Soil Organic and Inorganic Amendments in Heavy Metals Stabilization

Remediation strategies are capable to mitigate negative effects of heavy metals (HMs) on soils. The distribution of cooper (Cu), zinc (Zn), and chromium (Cr) was evaluated in a contaminated soil after adding biosolid compost (BC) and phosphate fertilizer (PF). A greenhouse assay and sequential extraction procedure were performed to determine the fractionation of HM in contaminated and remediated soil. In BC treatment, among 4 to 6% of Cu was associated with soil humic substances. Without amendments and with fertilizer application, Zn solubility increased by 15.4 and 8.4%, respectively, with experiment time. Although Cr was significantly adsorbed to the inorganic fraction, with compost application there was a transfer to organic fraction. A single amendment application is not suitable for immobilizing all metals of concern, because there are diverse union’s behaviors between HM and soil matrix. As the organic matter and phosphate fertilizer were effective in reducing mobility of Cu, the organic matter was more effective in the immobilization of Cr, and inorganic amendment induced the Zn precipitation, results from this pilot study suggest a combined use of these two amendments for soil remediation strategies. However, liming may be further needed to prevent soil acidification on longer time scales. Also, we propose the use of chemical and biological remediation strategies for potential improvement of effectiveness.

Effects of phytoremediation and application of organic amendment on the mobility of heavy metals in a polluted soil profile.

This research aims to assess the effect of the application of biosolids compost and phytoremediation on the mobility of total and biodisponibles (DTPA) fractions of cadmium, copper, lead, and zinc from different horizons of a superficially contaminated soil. Leaching experiment in soil columns was proposed. Treatments contemplated application of compost biosolid and phytoremediation. Two destructive samplings were performed. Total and DTPA trace metals were identified in each horizon. The overall performance of the various elements in its total and DTPA forms show greater concentration in horizon A and fewer gradients between horizons Bt and BC, thus assuming that the high content of clay in horizon Bt (62.9%) limits its movement through the horizons. In the mobile nutrients, a greater mobility was evidenced in DTPA fractions if compared to Total fractions. In the horizon A, the more mobile metals, such as Zn and Cd, evidenced a greater percentage of DTPA/Total fractions in all treatments. The application of compost with or without plant diminished the mobilization of Zn, Cu, and Cd Total, thus limiting a potential leaching to inferior horizons. However, this effect was not observed in the DTPA fraction.

Potential of discaria Americana for metal stabilization on soils amended with biosolids and ash-spiked biosolids.

Biosolids (B) may contain various types of environmental pollutants, which can exert phytotoxic effects in plants. The effect of aqueous extracts on seed germination and the primary root growth of discaria (Discaria americana) obtained from different soil-application rates of B and a mixture of B and incinerated B were investigated. The objective was to evaluate the potential use of discaria for the stabilization of B-amended soils. Ryegrass (Lolium perenne L.) was used for comparison. Compared to ryegrass, relative seed germination (RSG) was significantly lower for discaria. RSG of discaria and rye grass was inversely correlated to the electrical conductivity of extracts, although a significant adverse effect was only observed for ryegrass with the highest dose of the mixture of B and incinerated B. This dose also produced a reduction in the germination index of discaria, which could not be correlated with the parameters studied. The B extracts did not exert any significant adverse effect on the relative root growth of both species. An increase in relative root growth and germination index was observed for discaria with a field application rate equivalent of 156 t DW ha−1 of B, suggesting a stimulating effect of the amendment. The results obtained in this study suggest that germinated seedlings of discaria might be used for the stabilization of B-amended soils. However, further greenhouse and field experiments should be performed to confirm these findings.

Soil phosphorus mobilization in different taxonomic orders

Changes in P fractions using Hedleys sequential fractionation of organic and inorganic soil P, were studied in soils covering a wide range of developmental stages and original materials. A greenhouse experiment was performed in order to make an exhaustive P uptake by Lolium perenne and to study soil phosphorus mobilization from different fractions. Samples were obtained at 30, 60 and 90 days from sowing, with two fertilization rates added as KH2PO4. The exhaustion produced by plants resulted in different patterns of mobilization according to soil characteristics. For control soils the contents of inorganic labile fraction (LIP) decreased at the end of the experience in Mollisol (31%), Vertisol (24%) and Andisol (17%). The mobilization of organic P was greater for Ultisol and Andisol (77 and 75% respectively) than for the other soils. Fertilization affected mainly inorganic P, with a significant increase in contents of LIP in Entisol (46%) and moderately resistant inorganic P (MRIP) in Andisol (15%). Inorganic P/organic P relationship tended to increase during the experiment, while labile P/moderately resistant P increased in Entisol and Mollisol. Mobilisierung von Phosphor bei verschiedenen taxonomischen Ordnungen Veranderungen von organischen und anorganischen Phosphorformen wurden nach der Hedleyschen sequentiellen Fraktionierung bei verschiedenen Bodenordnungen analysiert. Umfassende Gefasversuche wurden mit Weidelgras im Gewachshaus durchgefuhrt. Bodenproben wurden 0, 30 und 90 Tage nach dem Auflaufen der Keimlinge gesammelt. Aus der P-Aufnahme der Pflanzen ergaben sich in Abhangigkeit von den Bodeneigenschaften verschiedene Mobilisierungsmuster. Bei den Kontrollboden nahm der Gehalt an anorganischen labilen P-Formen beim Mollisol (31%), Vertisol (24%) und Andisol (17%) ab. Die Mobilitat organischer P-Formen waren beim Ultisol (77%) und beim Andisol (75%) am hochsten. P-Dungung beeinflust hauptsachlich den anorganischen P-Gehalt: Eine signifikante Erhohung der mobilen anorganischen P-Form wurden beim Entisol (46%) und der masig gebundenen anorganischen P-Form beim Andisol (15%) beobachtet. Das Verhaltnis anorganische/organische P-Fraktion zeigte wahrend des Experimentes eine zunehmende Tendenz, wohingegen sich das Verhaltnis mobile/masig gebundene P-Form beim Entisol und Mollisol erhohte.