Cr, Cu, Pb and Zn in soils near a red mud basin in the Brazilian Amazon

The environmental impacts caused by the actions of industriesin the Amazon have been the object of investigation in several areas of knowledge. Red mud is the name given to the insoluble residue that remains after the digestion of bauxite by NaOH solutions, in the manufacture of alumina by the Bayer process. Barcarena, one of the largest alumina industries in the world, over the years, has caused a series of environmental problems in local ecosystems due to the constant leakage of effluents from a red mud deposit. In this study, the presence and contamination factor of potentially toxic elements (Cr, Cu, Pb, and Zn) in the soil of areas close to the red mud sedimentation basin of an alumina-producing company was evaluated. Twelve soil samples were collected at three depths (surface, 50 cm, and 100 cm) of the impacted area. The elements were analyzed using inductively coupled plasma optical emission spectrometry. The results showed that Pb was twice (571 mg.kg-1) above the limit established by Brazilian legislation (300 mg.kg-1) ranging from 102 to 967 mg.kg-1 with a contamination factor ranging from 1.66 to 2.10, which represents medium to moderate contamination at all depths of the evaluated soil. Zn was 1.4 (1379 mg.kg-1) times above the limit (1000 mg.kg-1) ranging from 315 to 6502 mg.kg-1. The contamination factor for Zn ranged from 0.800 to 2.06 with medium to moderate contamination.