Sorption potential of pretreated crab and area shell biomass for lead and copper from aqueous media was explored. The effects of pH, initial concentration, biosorbent dosage and contact time were studied in batch experiments. Effects of common ions like sodium, potassium, calcium and magnesium on the sorption capacity of pretreated crab and arca biomasses were also studied. At equilibrium, the maximum uptake by crab shell biomass was 19.83 +/- 0.29 and 38.62 +/- 1.27 mg/g for lead and copper, respectively. In case of arca shell biomass the maximum uptake capacity was 18.33 +/- 0.44 mg/g and 17.64 +/- 0.31 mg/g for lead and copper, respectively. Combined effect of all the common ions up to 50 mu g/ml concentration was negligible for both the metals using both biomasses. Sorption isotherms were studied to explain the removal mechanism of both elements by fitting isotherms data into Lagergren, Freundlich and Langmuir equations. (C) 2006 Published by Elsevier Ltd.