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Fractioning and bioavailability of heavy metals in contaminated soil, incubated with organic and inorganic materials

M. R. Ribeiro-Filho J. O. Siqueira N. Curi J. B. P. Simão About the authors

Procedures based on modifications of chemical properties are potentially useful for mitigating phytotoxicity of heavy metals in soils. However, it is difficult to predict the effects of different ameliorating agents on the bioavailability of heavy metals in soil simultaneously contaminated with several metals. This study was developed in a soil from a dumping site of a zinc extraction and manufacturing industry-Companhia Mineira de Metais-CMM, located at Três Marias (MG), to assess content, fractioning and bioavailability of Zn, Cd, Cu and Pb in the soil, after incubation for six months using different doses of carbonate, gypsum, vermicompost, sawdust and Solomax, a commercial soil amendment. After incubation, samples were taken from each treatment for chemical analysis by means of single extractions or fractioning of the metals. Mimosa caesalpiniaefolia Benth. (sabiá) seedlings were transplanted into the soil and allowed to grow for ninety days, and then harvested and analyzed for metal content. Ameliorants were found to affect the main fractions of the elements in the soil. For Zn, which has the highest concentration in this soil, carbonate amendment reduced its exchangeable fraction from 842 mg kg-1 soil in the control to 32 mg kg-1 soil. Solomax also reduced this Zn fraction in the soil. Similarly to what occurs in the soil, Zn uptake by M. caesalpiniaefolia was also reduced from 544.85 mg kg-1 of dry matter in the control to 32.20 mg kg-1 for plants on carbonate-treated soil. Solomax reduced Zn in the plant by 87%. Other soil treatments exhibited no consistent effects on plant metal uptake. Organic amendments did not markedly affect metal bioavailability. Addition of gypsum enhanced bioavailability of all metals, except Pb. Contrary to what was found for other metals, Cd content in the plant was correlated with its extraction by DTPA (0.82**) and Mehlich-1 (0.60**), and Zn correlated with MgCl2 (0.49*) and DTPA (0.49*). Both sequential and single extractions showed differentiated treatment effects on metal availability in soil. Prediction of bioavailability was best attained for Cd for all extractants. It was concluded that carbonate is the most efficient amendment for reducing metal availability to M. caesalpiniaefolia plants.

soil analysis; soil pollution; sequential extraction; Mimosa caesalpiniaefolia; Mehlich-1; DTPA

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