Bioacumulações de Cd, Ni, Pb e Zn durante os crescimentos de Salvinia minima e Lemna valdiviana

Abstract

Metals are dispersed easily in environments and are bioconcentrated in tissues of many organisms causing risks to the health and stability of aquatic ecosystems even at low concentrations. The use of plants in phytoremediation has been evaluated in order to mitigate environmental contamination since it has large capacity to adsorb and/or accumulate metals. This study evaluated the growth and phytoremediation of Salvinia minima and Lemna valdiviana grown in different concentrations of Cd, Pb, Ni and Zn. The growths were determined through measurements of leaf area by photographic images. The cultures were performed in a continuous flow (residence time = 2 days), under controlled temperature (23 ºC) and photoperiod (12/12h; radiation intensity: 4.31x10- 3 μmol sec-1 cm-2). The selected concentrations were 0.003 0.030 0.300 and 0.600 mg L-1 Cd; 0.020 0.200 and 0.400 mg L-1 Ni; 0.01 0.10 and 1.00 mg L-1 Pb and 0.10 1.00 10.0 100.0 and 1,000.0 mg L-1 Zn. The metals selection derived from the difficulty of its removal by conventional methods, and the selection of concentrations was based on values toxic to humans and on the maximum values allowed by Brazilian legislation for effluent discharge. None S. minima growth in concentrations of 0.300 mg L-1 Cd and 10.0 mg L-1 Zn were observed. L. valdiviana showed no growth when cultured at concentrations of 0.600 mg L-1 Cd; 0.10 and 1.00 mg L-1 Pb; and greater than 100.0 mg L-1 Zn. Individuals of S. minima bioaccumulated maximum 0.803 mg g-1 Cd; 0.677 mg g-1 Ni; 1.786 mg g-1 Pb and 10.464 mg g-1 Zn. L. valdiviana bioaccumulated maximum 1.15 mg g-1 de Cd; 0.045 mg g-1 de Ni e 62.465 mg g-1 de Zn. The metals content in plant tissues increased and the growth coefficients decreased when progressively increased the Cd, Pb and Ni concentrations. We conclude that, depending on the concentration, the two species of macrophytes can be used to phytoremediate effluents with metals and S. minima is more efficient on Ni, Pb and Zn removal and L. valdiviana on Cd removal. The Cd and Ni concentrations allowed by Brazilian law were toxic for both species and the allowed Pb concentration were toxic for Lemna valdiviana.