Browsing by Author "Molina, Mauricio"

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    Impact of forest fire ash on surface charge characteristics of andisols
    (LIPPINCOTT WILLIAMS & WILKINS, 2007) Molina, Mauricio; Fuentes, Roxana; Calderon, Raul; Escudey, Mauricio; Avendano, Katherine; Gutierrez, Marlen; Chang, Andrew C.
    Forest fires are a common occurrence in central southern Chile where soils are mostly Andisols. The ash deposits may alter the chemical properties of the soils in the burned areas and nearby agricultural lands. In a column experiment, three Andisols found in this region were treated with 2-cm-thick ash deposit on the surface and leached with 12 pore volumes of water for 3 months. At the end of the leaching, the ashtreated and their respective control soils were sectioned, and the surface charge characteristics of each soil section were determined by electrophoretic mobility test and potentiometric titration. Chemical constituents released from the ash affected mainly the surface 0- to 5-cm section of the soils. The ash treatment and leaching caused the soil pH of the 0-to 5-cm section to increase from 2 to 3 pH units. Consequently, the negative surface charge and cation exchange capacity of affected soils both increased. The ash treatment changed the isoelectric point when the isoelectric point of respective control soil section was > 3. The point of zero salt effect and the point of zero net proton charge of the ashtreated soils were increased in the 0- to 5-cm section and the influences of the ash leachates gradually diminished with soil depths. The alkaline leachates dissolved and mobilized the soil organic carbon and associated soil constituents. The effects observed on the surface charge and dissociation constants are consistent with anion and/or dissolved organic carbon adsorption. The surface dissociation constants, estimated by the constant capacitance model, showed that the ash treatment caused modifications of the active sites on the soil particles. Although ash leachates increase the cation retention capacity, the adsorption of other cations may be adversely affected by the ash deposit that is rich in Ca2+ and K+.
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    Sorption and Selectivity Sequences of Cd, Cu, Ni, Pb, and Zn in Single- and Multi-Component Systems in a Cultivated Chilean Mollisol
    (TAYLOR & FRANCIS INC, 2010) Molina, Mauricio; Manquian Cerda, Karen; Escudey, Mauricio
    The heavy-metal sorption ability of soils is one of the most important factors that determine the fate of these contaminants in this medium of the biosphere. When heavy-metal containing soil amendments are land applied, a multi-component soil-solution equilibrium may occur in which various metals compete simultaneously for the sorption sites on the soil particles. In order to determine the effect of competition among Cd, Cu, Ni, Pb, and Zn on sorption characteristics and the selectivity sequence of those heavy metals in a cultivated Mollisol of central Chile, batch sorption experiments were carried out in single- and multi-component systems. Heavy metal sorption isotherms in both types of system were well described by the Langmuir's equation. For all the metals evaluated, competition among them (multi-component system) decreased both the maximum sorption capacity, obtained from the Langmuir's isotherm, and the partition coefficient (Kd) compared to the single-component system. In addition, the simultaneous presence of the five metals promoted the sorption of Cd, and to a lesser extent of Ni, on more specific sorption sites of soil particles. Either in single- or multi-component system, Pb and Cu showed a higher selectivity and retention compared to Cd, Ni and Zn, which indicates that the later heavy metals would present a higher mobility in the soil-plant-water system. Since Langmuir's parameters and Kd were highly affected by competition for all heavy metals evaluated, the use of single-component parameters in modeling assessment might lead to an incorrect description of the transport and fate of these contaminants in receiving Mollisols.
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    Trace Element Composition of Selected Fertilizers Used in Chile: Phosphorus Fertilizers as a Source of Long-Term Soil Contamination
    (TAYLOR & FRANCIS INC, 2009) Molina, Mauricio; Aburto, Fabian; Calderon, Raul; Cazanga, Marcia; Escudey, Mauricio
    Anthropogenic activities like agriculture have resulted in increased concentrations of some trace elements of toxicological and environmental concern in soils. Application of fertilizers has been one of the major inputs of these contaminants to agricultural soils in developing countries. Twenty-two fertilizers, including straight nitrogen (N), phosphorus (P), potassium (K), and NK fertilizers and micronutrient sources, were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES)for arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn). As expected, the trace element content of fertilizers was highly variable and related to the origin of the material. Phosphorus fertilizers, especially triple superphosphate, presented the highest As, Cd, Cu, Cr Ni, V and Zn concentrations. In some of these fertilizers, the Cr V and Zn contents reached values greater than 3475 mg kg(-1) of P, and the Cd content (up to 288 mg kg(-1) of P) was several times higher than the regulatory limits of different countries. Some micronutrient sources presented the highest concentrations of Mn and Pb. In the cases of N, K, and NK fertilizers, the trace element concentration was very low, sometimes below the detection limits. In some agricultural systems the input of trace elements such as As and Cd to the soil through P fertilizers application may be higher than the outputs through plant uptake and leaching; therefore the long-term use of these fertilizers may cause the trace element concentration to increase in the plow layer of agricultural soils.