Tolerance of the aquatic plants Pistia stratiotes and Eichhornia crassipes at hexavalent chromium in aqueous media

In the phytoremediation of media contaminated with heavy metals, the tolerance of plant species to metal plays an important role. In this research, the effect of hexavalent chrome [Cr(VI)] on the development of Pistia stratiotes and Eichhornia crassipes was evaluated through the monitoring of microcosms constituted by cylindrical glass containers containing 0.5 L of media enriched with 0.5 mL.L-1 commercial fertilizer Cathefoliar plus N:P:K (6:1:21) contaminated with Cr (VI): 5, 10, 25 and 50 mg.L-1, compared to a control without metal and one plant per container, maintained with artificial lighting (106 +/- 23 mu mol.quanto.m(2).s(-1)), photoperiod 12 h light and a temperature of 28 +/- 2 degrees C. The development of the plants was followed by their dry mass, wet mass, content of pigments (chlorophyll a and b, carotenoids) and proteins. The plants achieved a satisfactory growth under metal concentrations less or equal to 10 mg Cr (VI).L-1, for P. stratiotes, and up to 25 mg Cr (VI) for E. crassipes, without showing significant decreases in fresh, dry mass and pigments. The protein content was not affected, showing stimulation for both plants at concentrations of 50 mg Cr.L-1. The toxic effect on plants is evidenced by morphophysiological damages such as chlorosis, wilt or plasmolysis, apex burns, reduction and deformation of leaf area, necrosis and even death of the plant at high metal concentrations. P. stratiotes and E. crassipes demonstrated their tolerance to high concentrations of Cr (VI), making their potential use feasible in the treatment of water contaminated with this metal.