REMOVAL OF CADMIUM IONS BY THE MARINE DIATOM PHAEODACTYLUM-TRICORNUTUM BOHLIN ACCUMULATION AND LONG-TERM KINETICS OF UPTAKE

The marine diatom Phaeodactylum tricornutum Bohlin was exposed to diff erent cadmium concentrations (1-100 mg l(-1)) for 4 days. The amount o f cadmium removed was recorded, with particular attention paid to long -term uptake kinetics, and to the cellular location of cadmium. Cadmiu m accumulation occurred at all concentrations assayed. The EC50 of cad mium to P. tricornutum was 22.39 mg l(-1) after 4 days of exposure. Ca dmium uptake followed a saturation kinetic at cadmium concentrations g reater than or equal to 25 mg l(-1). However, at lower cadmium concent rations, the uptake of this metal followed a linear trend for all days of culture. At cadmium concentrations in the medium lower than 25 mg l(-1), P. tricornutum removed cadmium mainly within the cell. At highe r cadmium concentrations, the amount of cadmium removed by adsorption to the cell surface was higher than intracellular cadmium, because of the toxic effects of cadmium on P. tricornutum cells. This toxicity re duced the cadmium accumulation within the cells. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.