Baseline Concentration of Heavy Metals in Brazilian Latosols

Abstract

Knowledge of baseline concentrations for heavy metals of environmental and agricultural concern in tropical soils is meager. Latosols are highly weathered soils that cover ∼40% of the Brazilian territory and are by far the most important agricultural soil order in Brazil. This paper aimed to compare two methods for heavy metal extraction from soils, and to provide baseline values of heavy metals for Brazilian Latosols. The soil samples came from the 0–0.2-m layer of 19 different Latosols from the various geographic regions of Brazil. The first experiment compared the USEPA method 3051A (microwave digestion with concentrated HNO3 in closed vessels) with the aqua regia extraction (hot plate digestion with concentrated HCl and HNO3, 3:1, in open vessels) regarding Pb determination. The second analyzed contents of Cd, Cu, Ni, Pb, and Zn, and for this the USEPA method 3051A was used. Heavy metal contents were assessed by flame atomic absorption spectroscopy. Although both methods were highly correlated, the USEPA-3051A rendered Pb contents 29% higher in average than the aqua regia. Average (n=57) and standard deviation values for heavy metals in Brazilian Latosols are 0.66±0.19 mg Cd kg−1, 65±74 mg Cu kg−1, 18±12 mg Ni kg−1, 22±9 mg Pb kg−1, and 39±24 mg Zn kg−1. Considerably variation is due to the inclusion of Latosols derived from a variety of parent materials. The values provided could be useful as reference baseline concentrations for heavy metals in Brazilian Latosols.