Comparative study on bioaccumulation of lead and cadmium by the cyanobacterium Synechocystis sp. PCC 6803 under laboratory conditions

Abstract

Bioremoval techniques have been employed in cleaning water bodies that suffer from detrimental effects of heavy metal pollution. In the present laboratory study, bioaccumulation of Pb²⁺ and Cd²⁺ was assessed using the unicellular cyanobacterium Synechocystis sp. PCC 6803, a model organism widely used in genetic, physiological and morphological studies. Growth was measured as cell counts and showed that Pb²⁺, at low exposure concentrations (0.5 and 1 µg mL^–1), had a positive influence on Synechocystis sp. PCC 6803, resulting in slight growth stimulations; however, the species could not withstand long periods of exposure to both metals at higher concentrations (2, 4, 6 and 8 µg mL^–1). The highest inhibitions (53.14% and 70.07% for Pb²⁺ and Cd²⁺, respectively, at 8 µg mL^–1) were recorded after six days. Rapid metal removal was observed during the first two days of incubation, followed by a gradual reduction. Though the differences in accumulated amounts seemed to be narrow, the percentage of Pb²⁺ removed from the solution was always higher than that of Cd²⁺ in all the treatments. Accumulated amounts increased in a dose-dependent manner for both metals. The maximum accumulations (155.63 and 199.83 mg g^–1dry weight for Pb²⁺ and Cd²⁺, respectively) were recorded at the end of six days. The species can be considered a good accumulator of metals, with high bioconcentration factor values of 20 657 and 24 980 for Pb²⁺ and Cd²⁺, respectively.