In this study, the absorption capacity of active and inactive biomass of the microalgae Microcystis novacekii to remove Pb2+ from aqueous solutions was investigated. This is the first reported study of biosorption by a cyanobacterium species, which is abundant and easily found in eutrophic lakes and ponds in tropical areas of the world. We also evaluated the effects of different concentrations of Pb2+ on growth rates of M. novacekii. Inactive biomass was characterized by elemental composition, surface area, potentiometric titration, infrared spectroscopy and thermogravimetric analysis (TGA). The biosorption data of Pb2+ by inactive biomass were analyzed using the Langmuir and Freundlich isotherms. Pb2+ concentrations higher than 0.5 mg L-1 inhibited species growth. Potentiometric titrations showed a significantly higher negative surface charge (1.48 +/- 0.22 mmol g(-1)) with two acidic groups (pKa(1) = 3.74 +/- 0.12 and, pKa(2) = 7.25 +/-0.30). Analysis of inactive M. novacekii cells by infrared spectroscopy suggests that the cell wall carboxyl and amide groups participate in Pb2+ biosorption. The maximum Pb2+ adsorbed was found to be 70 mg g(-1), and the biosorption of Pb2+ on inactive M. novacekii correlated well (R-2 = 0.931) with the Langmuir equation compared to the Freundlich isotherm equation (R-2 = 0.823) in the concentration range studied. (C) 2010 Elsevier B.V. All rights reserved.