Three element were chosen for this investigation, radioactive carbon ¹⁴C  in form of ¹⁴C-urea and two element; chromium III and cobalt to study their biosorption and desorption mechanisms by two algal species;  Sargassum linifolium and  Dunaliella salina, in relation to their surface area. Active transport was the mechanism for ¹⁴C, Co and Cr uptake by the two algal species. Sargassum showed higher accumulation ratios than living algal cells; the reverse was true for Dunaliella. The antagonistic action between metal ions (radionuclide) binding to different algal cell surface was obtained by mixing ¹⁴C with Cr and ¹⁴C with Co in living algal cells of the two tested algae, while synergistic action was obtained by mixig Cr and Co in the living algal species. Non-interactive action was shown by mixng ¹⁴C with Cr or Co in dried algal material. ¹⁴C-uptake by living cells of Sargassum and Dunaliella ameliorated cell vitality; this effect was higher in Dunaliella than in Sargassum. Chromium showed adverse effect than cobalt, both Co and Cr altered the metabolic pathway of chlorophyll formation. Siderophore formation increased the adsorption power of algal cell-wall especially Sargassum alga. The biosorption effect of these radionuclides was due to surface characteristics. Desorption mechanism was fast from Sargassum surfaces, while it was slower in Dunaliella. Dried Sargassum can be used successfully for bioremediation of ¹⁴C, Co and Cr from the contaminated sea water (even, at low concentration) up to five elution times, while living Dunaliella could be used for the removal of these elements from lakes. To ameliorate the adsorptive power of dried Sargassum, its surface area must be increased and the media must be iron-free.