Mineralogia e teores naturais de metais pesados em solos da Bacia do Rio Juruá, na Amazônia Brasileira

Abstract

The Amazon region stands out not only in the national scenario, but also internationally because it houses the largest humid equatorial forest, the Amazon Forest being economically and socially relevant to the region. Human activities such as deforestation, burning, livestock, urban and industrial expansion, have contributed to the reduction of the forest. These practices are responsible for the emission of organic and inorganic substates in the environment, among them the heavy metals, which are naturally found in the environment, but may also have their levels influenced by anthropogenic actions. The determination of the natural contents of heavy metals is aimed at distinguishing the levels of anthropogenic origin from the elaboration of Quality Reference Values (VRQ's), intending to contribute to the strengthening of public policies of environmental nature, aiming at the protection of soils. The present study has the objective of determining the natural levels of heavy metals in soils of the states of Acre and Amazonas, with the prorpose to subsidize the environmental bodies to elaborate the VRQ's. Samples of 73 soils were used to determine the natural metal contents, which were extracted in acidic disgestion (HNO3 + HCl). The results indicate that the soils of these states present lower levels of metals than the soils of other parts of Brazil and the world. The highest levels were found in soils and várzea (Gleissols and Neosols), and the lowest levels were observed in Spodosols. With the use of multivariate analysis, it was possible to identify two groups of metals in these soils, where the soils of the floodplain presented the highest average levels of As, Cd, Hg, Co, Zr, Ti and V. The elements Ba, Mn, Pb, Cr, Cu and Zn presented their highest levels in the terra firme soils. The natural levels of heavy metals in soils of the states of Acre and Amazonas followed the following order: Mn > Ti > Ba > V > Zn > Co > Pb > Cu > Zr > Cr > Ni > As > Hg > Cd.