In order to estimate plant available fraction of metals in three soils, three vegetable samples: Amaranthus viridis, Celosea argentea and Corchorus olitorius were grown on contaminated soils. Matured plants were harvested and analyzed for their metal concentration. The soil samples were collected before and after planting, acid digested and analyzed to determine the pseudo total metal concentration, and quantification was done using flame - atomic absorption spectroscopy (FAAS). To correlate metal accumulation by these plants with potential bioavailability of metals in soils, sequential extraction (SE) using the modified BCR technique was performed on the soils. A secondary soil reference material (GLAURM) was used for quality control. The results of the reference material showed that the found values were within three standard deviations of the target values for the elements determined in the aqua regia digests and for most steps of the SE. It was observed that each metal differed considerably in uptake. Of the plants investigated, A. viridis had the highest tissue concentration of Cd, Cr, Pb and Zn from the soils with concentration of 1.4, 5.2 and 3.2 mgkg-1 of Cd, 76.5, 96 and 43.0 mgkg-1 of Cr, 49.5, 20.0 and 27.4 mgkg-1 of Pb and 78.1, 112 and 96.9 mgkg-1 of Zn in the soil from sites A, B and C respectively. Results of SE showed that Cd and Zn were mostly present in the acid exchangeable and reducible fractions, where these metals were mostly taken up. Soil–to-plant transfer factor values decreased in the order Zn > Cd > Cr > Pb.
Key words: Potentially toxic metals, plant uptake, bioavailability, phytoremediation, sequential extraction.
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