Potential mobility and toxicity risk of metal pollutants in soils from a tropical area affected by industrial wastes

Abstract

The potential mobility of Cd, Cr, Cu, Ni, Pb and Zn in soils severely impacted by inadequate storage of industrial wastes in Rio de Janeiro State (Brazil) was evaluated by applying the Toxicity Characteristic Leaching Procedure (TCLP). This procedure allowed the estimation of toxicity risks for Cd, Cr and Pb. In a contamination hotspot within the study area, the following order of metal concentrations was observed: Pb > Zn > Cu > Ni > Cd > Cr, with significantly higher values than observed for a control site. Decades of soil exposure to wastes implied TCLP results for Pb above 300 mg/L in this hotspot, which exceed the TCLP regulatory threshold in two orders of magnitude, while Cd (up to 0.8 mg/L) and Cr (up to 0.3 mg/L) results were below the respective TCLP thresholds. Surface soil profile analysis (0-30 cm depth) indicates that Pb vertical migration occurs in the hotspot. TCLP concentrations of Pb were up to four orders of magnitude higher than the groundwater quality threshold preconized by Brazilian regulations for this metal (0.01 mg/L), suggesting that downward dispersion of large loadings of anthropogenic Pb is a major concern.