Trace Elements in Areas of Intensive Agriculture in Mato Grosso, Brazil.

The state of Mato Grosso (MT) is the largest producer of soybeans, corn, and cotton in Brazil and also the greatest consumer of agricultural inputs such as fertilizers, lime, and pesticides, which are applied to ensure high crop yields. Some of these inputs may represent a diffuse source of trace elements (TE) to agricultural ecosystems. This study evaluated the contents of selected TEs (Cr, Mn, Ni, Zn, Cu, As, Se, Hg, and Pb) in soils cultivated under intensive agriculture in 12 representative municipalities of MT. A total of 144 composite soil samples were collected from cultivated areas and areas under native vegetation at two depths: 0-20, 20-40 cm. Trace elements were analyzed using the USEPA 3051A procedure, and quantified by either atomic absorption spectroscopy or total X-ray fluorescence spectroscopy, using standard reference materials for QA/QC protocols. The average contents of TEs (mg kg^-1) in native and cultivated areas were, respectively: Cr 31.3 and 31.5; Zn 7.8 and 3.2; Pb 13.2 and 11.1; Mn 17.5 and 16.2; As 5.2 and 4.4; Cu 5.6 and 3.6; Ni 2.1 and 2.1; Se 0.88 and 0.59; Hg 0.03 and 0.03. It appears that the intensive cultivation, with the use of high inputs, of soybeans, corn, and cotton in the state of Mato Grosso has not resulted so far in increasing contents of the selected TEs in the soils. The few exemptions include Zn in Primavera do Leste and Sapezal, Pb in Campos de Julho, and Cu in Campos de Julho, Primavera do Leste, and Sapezal, whose levels were higher in cultivated areas. Still, the contents of such elements presented in these areas are similar to those reported for uncontaminated soils. Sponsored by CNPq and FAPEMIG.