Over the last years, algal blooms occurrences have increased on the Romanian Black Sea coast. In this study, Ulua rigida and Cladophora sericea green algae were used to investigate the removal of As(III), As(V), Sb(III), Se(IV) and Se(VI) in aqueous solution. In virgin forms, both macroalgae showed good perspectives for application on antimony and selenium uptake from water, although no significant efficiency towards arsenic was observed. Several treatments were applied to the algae to eventually enhance their adsorption capacity. Potentiometric titrations and infrared spectroscopy confirmed favorable chemical modifications in algae surface due to HDTMA and ammonium treatments, although no considerable increase in the biosorption ability was found. C. sericea, in virgin form, was selected for further studies on the uptake of Se(IV) and Se(VI). The best results for Se(IV) removal (0.5 mg/g) were found at pH 2-4 and for Se(VI) (0.2 mg/g) at pH 2-3. The equilibrium isotherm for the adsorption of Se(IV), at pH 2 and 20 degrees C, reported a maximum experimental adsorbed amount of 0.74 mg/g and a Langmuir monolayer capacity of 4 mg/g, which are substantial values considering that the biosorbent (dead marine seaweeds) is a residue and requires no significant processing before use. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.