Increased production of extra- and intracellular metal-ligands in phytoplankton exposed to copper and cadmium

Several diatom and dinoflagellate species isolated from the Adriatic Sea, grown in batch cultures in f/2 medium, were exposed to two different concentrations of Cu and Cd. The concentrations chosen caused a reduction of growth, but were not lethal. The species able to tolerate the highest Cu concentrations (in the order of 0.2-0.5 mg L-1) were diatoms, while some diatoms and all the dinoflagellates were inhibited by concentrations between 0.01 and 0.05 mg Cu L-1. Cadmium was less toxic in that it did not affect diatom or dinoflagellate growth up to a concentration of 0.2 mg L-1. Increased production of extracellular polysaccharides was found to be a general response to the presence of the pollutant. Cylindrotheca fusiformis, Achnanthes brevipes and Prorocentrum micans were investigated for their production of intracellular metal-ligands. Molecules with Cd-binding properties and having a molecular weight comparable with that of phytochelatins were found only in C. fusiformis, and their presence showed both a dose- and time-dependent response. The presence or absence of intracellular ligands in these algae is consistent with their ability to exclude the metal extracellularly.