Assessing the Distribution and Concentration of Heavy Metals in Soils of an Agricultural Frontier in the Brazilian Cerrado

Abstract

The continuous use of agricultural inputs for grain, fiber, and energy production in the Brazilian savannah can increase heavy metal (HM) concentrations in the soils. In this context, we aimed to determine the natural concentrations and establish the quality reference values (QRVs) of HMs in reference soils of a sedimentary watershed under native vegetation in one of the latest agricultural frontiers of Brazil in order to assess the impact of cultivation on the metal concentrations in cropped soils. Additionally, we studied the spatial variability of HMs and the efficiency of the multivariate analyses to distinguish between natural and anthropogenic sources of metals in the soils. Thirty-two and 30 composite soil samples were collected in areas under agricultural exploration and natural vegetation with minimal anthropic interference (low impact areas), respectively. The QRVs established could be ranked as follows (mg kg−1): Fe (18,700) > V (47.83) > Cr (43.44) > Ba (9.11) > Pb (2.73) > Ni (0.80) > Cu (0.74) > Zn (0.46) > Mo (0.34) > Cd (0.05) > Sb ( Co (< 0.00008). Natural concentrations observed in non-anthropogenic soils are lower than those found in other regions, with the exception of Cr. Also, we found that the mean concentrations of Cd, Cu, Cr, Mo, Mn, Ni, Sb, V, and Zn in agricultural soil were far higher than their background values of the watershed topsoil. Based on our findings, the increased metal concentration in the agricultural soils increases the ecological risk. On the other hand, the mean metal concentrations remain close to the prevention value for soils established by the Brazilian Council for the Environment for agricultural land, which indicates that these areas require monitoring to guarantee foodstuff safety. Our results are useful for public policies not only in the studied area but also worldwide where soils are derived predominantly from sedimentary rocks such as sandstones, siltstones, shales, and limestones.