Dispersion of contaminants from a lead processing industry in a toposequence dominated by vertisol

In 1997, 500,000 MG of mine tailing materials containing 3% lead (Pb), 21% cadmium (Cd), and 13% zinc (Zn) were buried at a site in Santo Amaro, Bahia, Brazil. The present study evaluated the dispersion of contaminants in a toposequence classified by the FAO system: Pellic Vertisol (hilltop, P1), Leptic Vertisol (upper third of the slope, P2), Leptic Endospolic Technosol (middle third, P3), Haplic Vertisol (lower third, P4), and Eutric Fluvisol (footslope, P5). The P1, P2, and P3 soil profiles were located within the processing plant boundary, whereas P4 and P5 were located outside the plant. According to the Brazilian Environmental Agency, the maximum concentrations of Pb and Cd were detected to be 26.4 and 2.6 times higher than the industrial intervention value, respectively, whereas Zn concentration was 1.9 times higher than the residential intervention limit. In the Technosol P3 region, the concentrations of Pb and Cd were above or around the industrial value, whereas Zn concentration ranged from agricultural to industrial values. The metal concentration in the Fluvisol (P5) region was lowest among all soil profiles; however, the concentration of Pb remained above the agricultural intervention limit. The high concentrations of metals, especially Pb, in the P4 and P5 regions are an evidence that after almost two decades, the contaminants still continue to sediment from the top to the lowland area of the toposequence.