Binding of Cu, Pb, Zn and Cd to the cell surface of the marine diatomPhaeodactylum tricornutum

Abstract

The binding of Cu, Pb, Zn and Cd to the cell surface of the marine alga Phaeodactylum tricornutum was studied in organic-free seawater to obtain the adsorption capacity (F max ) and the adsorption equilibrium coefficient (K MES ,) for the metal ion on the algal cells. The experimental data can be fitted by a two-site Langmuir isotherm which considers the presence of high and low affinity binding sites on the cell surface. The maximal adsorption capacity for Cu, Pb, Zn and Cd on the algal surface was 0.8,0.6, 1.3 and O.5 x 10 -16 molcell -l, respectively. Cu exhibits the higher affinity, owing to the higher values of both the adsorption equilibrium coefficient and the maximal adsorption capacity of the stronger Cu-binding sites. The capability of cell exudates of Phaeodactylum tricornutum to bind Cu, Pb, Zn and Cd was also measured, and the effect of algae as competing ligand for the metal ion bound to exudates was investigated. The results show that the metal-exudates complexes can be available for the adsorption process on the cell surface.