Quality reference values for heavy metals in soils developed from basic rocks under tropical conditions

Soil Quality Reference Values (QRV) refer to the natural heavy metal concentrations that is not influenced or is minimally influenced by anthropogenic activities. Such values are unique of each environment, and their extrapolation to different locations becomes inadequate. This research aimed to determine the natural concentrations of metals in soils (QRV) developed on essentially basaltic lithology and tropical conditions in the south of Brazil. Seventy-two soil samples from the Forest Conservation Areas in the west of the state of Parana, Brazil, were obtained. The extraction and dosage of Ag, As, Ba, Cd, Cr, Cu, Mo, Ni, Pb, Sb, V, and Zn were carried out employing methods USEPA 3051a and ICP-OES. The QRV was set to 75th percentile of each element, from the detection and exclusion of the outliers. The natural concentration of all heavy metals was related to the geological context of the basaltic area in Brazil. There was no influence of the pedogenetic degree of soils on the natural heavy metal concentration. The only relevant process for reducing the natural heavy metal levels was the Fe and Mn oxide solubility promoted by hydromorphic conditions. Fe oxides had a significant role in the maintenance of structural and adsorbed heavy metal forms in soils. The results may help the research and monitoring of environmental heavy metals in soils developed from basalt under tropical conditions.