Heavy metal tolerance of marine phytoplankton. IV. Combined effect of zinc and cadmium on growth and uptake in some marine diatoms

Abstract

Combinations of zinc and cadmium ions acted synergistically on the growth of the marine diatoms Thalassiosira pseudonana (Huds.) Hasle and Skeletonema costatum (Grev.) Cleve, clone Skel-5. Mixtures of the metals behaved less than additively on Phaeodactylum tricornutum Bohlin, and antagonistically on Skeletonema costatum, clone Skel-0. Sorption studies supported the hypothesis that the two latter algae gained their relative resistance to heavy metal ions from competition for uptake sites by the zinc and cadmium species involved. In the more resistant alga, Phaeodactylum tricornutum, the sorption of cadmium and zinc was also dependent on the magnesium concentration of the medium, in a way which indicated a common uptake route for several divalent cations in this species. Cadmium was found to be more toxic than zinc to Skeletonema costatum, clone Skel-0 and to Thalassiosira pseudonana, while zinc was slightly more toxic than cadmium to Phaeodactylum tricornutum and Skeletonema costatum, Skel-5.