We have tried to assess the effects of chromium(VI) in four freshwater green algae (Coccomyxa minor, Scenedesmus armatus, S. dimorphus, and Haematococcus lacustris) and two freshwater macrophytes (Lemna minor and Pistia stratiotes). The algae were kept in liquid or solid culture medium containing 1, 2, 5 and 10 mg/L of chromium (VI) supplied as K2Cr2O7. Lemna and Pistia were grown in nutrient solution to which chromium was added as K2Cr2O7 to give final concentrations of Cr(VI) from 0.1 to 20 mg/L.
Coccomyxa and S. dimorphus seem to be less tolerant than the other algae because 1 mg/L Cr(VI) is sufficient to induce alterations of chloroplasts and cell wall. S. armatus and the quiescent spores of Haematococcus show alterations if Cr(VI) concentration is at least 5 mg/L. With 10 mg/L spore germination is completely inhibited. All the algae show loss of chlorophyll and other pigments and cell vacuolation. The chloroplasts appear damaged, and electronopaque deposits are visible in the cytoplasm and vacuoles.
In Lemna and Pistia the main macroscopical effects are retardation of growth, chlorosis, and wilting. Ultrastructural alterations consist in convolution and retraction of the plasma membrane, thylakoid disarrangement and swelling, transient increase of the number of mitochondria. Chlorophyll content diminishes, while protein content at first increases, then returns to average control values. These alterations are caused by even low doses of the metal (0.1 mg/L in Lemna and 1 mg/L in Pistia).