Metais pesados e sílico-fitólitos em Setaria vulpiseta cultivada em área de mineração em Riacho dos Machados-MG

Abstract

The heavy metal contamination is a major concern nowadays, since it can cause public health problems. Currently, one of the main problems due to mining is changing the geochemical flow and natural flow of heavy metals, thus increasing their release in the biosphere. The use of plants to remediate soils contaminated by heavy metals is an alternative to conventional methods, when used correctly. In contaminated areas, plants of the family Poaceae play an important role in soil remediation, as they can forme large amounts of sand-phytolith (opal-gene), which sequester heavy metals. The phytolith are amorphous silica particles with size between 10 and 200 microns, which result of absorption of silicic acid Si (OH4) from soil by the plants. They are formed by polymerising processes of silicic acid, which causes the amorphous silica to precipitate with metals in the cells of various plants. The formed phytolith have great stability, may require thousands of years for its decomposition, thus eliminating the risk of contamination of the food chain. Thus, this study aimed to evaluate the phytoremediation potential of metals on the grass of Setaria vulpiseta species and in the soil from mining areas in Riacho dos Machados-MG. We collected 56 soil samples, 28 samples collected at depth of 0-5 cm and 28 samples at depth of 5-20 cm, and 28 plant samples in areas with high levels of metals. The analyses were conducted in Agrochemical Laboratory and Laboratory of Solid Residue at the ICA/UFMG. In these laboratories we made the extraction, identification and quantification of phytoliths and heavy metals. The heavy metals also were quantified in the soil and in the organic tissues of the plants. For analysis of the variables, we calculated the average confidence intervals using the t test at 10% probability. Thus, it was concluded that the area presents a risk of increase heavy metals As, Cu, Zn and Cr, being the Cr already at level of agricultural intervention. It was observed that plants absorb As, Cu e Zn; however, part of these metals is sequestrated by sand-phytolith. Though these metals are retained in phytolith, Cu is at a level that may be toxic to plants. The studied soils have good fertility and pH suitable for the growth and development of Setaria vulpiseta, requiring only correction of phosphorus levels and of irrigation to achieve greater productivity throughout the year.