In this study, a green adsorbent was successfully applied to remove toxic metals from aqueous solutions. Dried minced castor leaves were fractionated into 63-mu m particles to perform characterization and extraction experiments. Absorption bands in FTIR (Fourier Transform Infrared Spectroscopy) spectra at 1544, 1232 and 1350 cm(-1) were assigned to nitrogen-containing groups. Elemental analysis showed high nitrogen and sulfur content: 5.76 and 1.93%, respectively. The adsorption kinetics for Cd(II) and Pb(II) followed a pseudo-second-order model, and no difference between the experimental and calculated N-f values (0.094 and 0.05 mmol g(-1) for Cd(II) and Pb(II), respectively) was observed. The N-s values calculated using the modified Langmuir equation, 0.340 and 0.327 mmol g(-1) for Cd(II) and Pb(II), respectively, were superior to the results obtained for several materials in the literature. The method proposed in this study was applied to pre-concentrate (45-fold enrichment factor) and used to measure Cd(II) and Pb(II) in freshwater samples from the Parana River. The method was validated through a comparative analysis with a standard reference material (1643e). (C) 2013 Elsevier B. V. All rights reserved.