Cadmium effects and accumulation in cultures ofProrocentrum micans (dinophyta)

Abstract

Effects and accumulation of cadmium were studied in unialgal 10-1 batch-culture experiments with the dinoflagellateProrocentrum micans Ehrenberg. Tests were made using sterile filtered North Sea water enriched with nitrate and phosphate only in order to avoid disturbances by complex formation. Cadmium was added to the cultures in amounts of 100 to 0.13µg l⁻¹. In one series it was added at the start of the experiments and in a second one after a growth period of 1 week. Addition of only 1.2µg Cd l⁻¹ reduces multiplication rates and maximum cell densities of the algae. Not until 0.4µg Cd⁻¹ does growth correspond to that of the controls. Cadmium concentrations were measured, after filtration, in the culture medium and in the biomass by means of flameless AAS. The cadmium content in algae increased from 2.7µg g⁻¹ (dry weight) in controls to 500µg g⁻¹ (dry weight) in media containing 100µg Cd l⁻¹. Uptake occurred rapidly during the first few days of the experiments, slowed down somewhat during exponential growth stage, and increased during decay of the cultures. Cadmium content of culture media remained nearly constant (Series 1) or decreased only slowly during experimental time (Series 2). The highest concentration factor was measured in the controls. It decreased with increasing metal concentration in the medium and increased with experimental time. Structural modifications of the cells were visible after Lugol fixation only, indicating brittleness of the cell walls.P. micans has shown to be extremely sensitive to cadmium and to accumulate this metal.