Index of geoaccumulation and spatial distribution of potentially toxic elements in the Serra Pelada gold mine

Abstract

The concentration and spatial distribution of many potentially toxic elements (PTEs) have not been studied in the mining areas of tropical soils in the Amazon. The objective of this study was to evaluate the concentrations and spatial distribution of Al, Bi, Fe, Li, Sn, Sr, Te, Ti, and V in an area influenced by artisanal gold (Au) mining and chemical attributes related to soil fertility. The study area is located in Serra Pelada, on the east bank of the Brazilian Amazon, in the state of Para. A total of 104 soil samples were collected with different forms of use: residential areas, agricultural, forest, and mining areas. 0.5 g of soil previously sieved at 0.15 mm was weighed to determine the pseudo total contents of the PTEs. The soil was mixed to 9 mL of concentrated HNO3 and to 3 mL of concentrated HCl; then, this solution was digested in microwave according to the EPA method 3051A (Test Methods for Evaluating Solid Waste 1–30, 2007). The digested extracts were filtered on blue filter paper and diluted with ultrapure water to the final volume of 50 mL. The pseudo total contents of Al, Bi, Fe, Li, Sn, Sr, Te, Ti, and V were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The pseudo total concentrations of Al, Bi, Fe, Li, Sn, Sr, Te, Ti, and V were high, considering the natural occurrence in the soils. The levels of Li, Sn, Sr, Te, and V did not differ between them as forms of soil use, while the levels of Al, Bi, Fe, and Ti were higher in residential and/or agricultural areas. The spatial distribution maps of the elements showed that the material removed from the pit is not a major source of contamination. In the residential areas, the exploitation of the Au in the backyards provided greater surface accumulation. The accumulated geography index shown by Bi, Li, Sn, Sr, and Te varied from moderately contaminated to highly contaminated. The pseudo total contents of the potentially toxic elements (PTEs) are high, characterizing a scenario of diffuse contamination and geoaccumulation of Bi, Li, Sn, Sr, and Te caused by anthropogenic activities. The mine pit opened during the initial exploration of the mine is not the only one contaminated by PTEs, the exploitation of tailings, backyards, and agricultural areas were other forms of environmental contamination.