Effects of heavy metals on the morphology of some marine phytoplankton

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Abstract
The effects of eleven heavy metals on the morphology of several marine diatoms and a silicoflagellate were compared. With Thalassiosira aestivalis the main effects of metals that were toxic were granular, yellowed cytoplasm; a disruption of chloroplast integrity and dispersion; and more delicate spines extruded from the marginal processes. The metals could be divided into three groups on the basis of other toxic effects. Cu, Zn, Ge, and a metal mixture increased the chain length and did not allow the normal separation of cells, although complete frustules were formed. With these metals there was an inability to form the central chitinous threads that separate normal cells. With Hg, Cd, and Pb, there was some disruption of cell separation, so that cell clumps were formed, but the main effect was the formation of elongated, bent, out-of-column cells. These metals seemed to interfere with cell division. Cr, Ni, Se, Sb, and AsIII were without effect (except for lysis of cells exposed to AsIII) at a concentration of 1 μM, well above the concentrations that showed effects with the toxic metals. The similarity of morphological effects of Cu, Zn and Ge suggests that at least one biochemical pathway of Si metabolism was affected by these metals. Other marine diatoms and a silicoflagellate were also affected by Cu and Hg but were not studied as extensively as Thalassiosira aestivalis.