ASSESSMENT OF A SIMPLE EXTRACTION METHOD TO DETERMINE THE BIOACCESSIBILITY OF POTENTIALLY TOXIC Tl, As, Pb, Cu, Zn AND Cd IN SOILS CONTAMINATED BY MINING-METALLURGICAL WASTE

The potential to determine the gastric bioaccessibility (BA) of Tl, As, Pb(II), Cu(II), Zn(II) and Cd(II) using a simple extraction method was evaluated in selected samples from soils contaminated by mining and metallurgical wastes. The SBRC (Solubility and Bioavailability Research Consortium) test was used as a gastric BA comparative method versus a simple extraction method using HCl solution at pH 1.5. High correlations (r >= 0.98, p < 0.01) were obtained between the two extraction methods for Cd(II), Cu(II), Tl and Zn(II), in all samples investigated. Bioaccessible As, however, only showed a high correlation in the metallurgical area (r = 0.99, p < 0.01), but not in the mining area (r = 0.88, p < 0.01). Conversely, Pb(II) showed a better correlation in samples from the mining area (r = 0.99, p < 0.01) than in those of the metallurgical area (r = 0.92, p < 0.01). Three experimental conditions of the extraction procedures ensured the high correlations observed: (1) Maintaining a strict pH control of 1.5 (+/- 0.1), (2) a stirring time of 1 h (+/- 1 min), and (3) filtration of the extraction mixture through a membrane of small pore size (0.05 mu m). Bioaccessible Tl was detected in all samples, a fact that has not been reported before in these enviromnents, and alerts to potential health risks not previously identified.