Effects of biochar in mitigating heavy metals toxicity in multicontaminated soils

Abstract

Heavy metals occur naturally in soils or can be increased due to human activities, mainly those associated with mining. Due to the high toxicity and accumulation in the food chain is of great importance to determine the behavior and fate of these elements in contaminated soils. Therefore, such information can help to minimize the ecotoxicological risk. With this proposal we aim to evaluate the effect of biochar (BC) on the mobility of Cd, Pb and Zn in contaminated soils at different pH values, as well as on growth and absorption of these elements, and the activity of some enzymes and structures of two plant species. In a first experiment five leaching columns will be installed with a contaminated soil by mining, with the following treatments: natural soil pH (6,0-7,0); acidified soil to reach pH H 4,0; natural soil pH with the application of BC (10 % m / m); acidified soil with application of BC (10% w/w); lime application to soil to raise pH H 8,0. The BC will be produced and characterized in a previous study from sugar cane straw. The leachate will be analyzed for Cd, Pb and Zn concentrations , water soluble carbon, electrical conductivity and pH. After leachings the soil will be sequentially extracted to study the distribution of these elements in different compartiments. In another experiment the effect of BC addition on the absorption and accumulation of Cd, Pb and Zn in ryegrass and tobacco will be evaluated. Besides, we will evaluate the dry mass yield, the activities of catalase and guaiacol peroxidase, lipid peroxidation, and the alterations in the structure and ultrastructure by using scanning electron microscope. BC will be applied to the soil at 0% (control), 2%, 5% and 10% (m / m) rates, with four replicates. The soils of this experiment will be extracted by DTPA pH 7,3 and 0,01 M CaCl2 to determine the available contents of heavy metals, which will be tested for correlation with the content in shoots. The obtained results will be analyzed by ANOVA, as significant (p <0,05) means will be compared by Tukey test (p <0,05), polynomial regression and correlation analysis to diferentiate the treatments.