Cadmium toxicity on synchronous populations of Chlorella ellipsoidea

Abstract

The primary phycotoxic effects of various concentrations (5–50 μM) of cadmium sulfate (CdSO₄) on synchronous cultures of Chlorella ellipsoidea were determined during a 14-h light and a 10-h dark incubation cycle. At a concentration of 5 μM CdSO₄ there was a slight stimulation in cell number, chlorophyll level, and dry weight whereas at higher concentrations (10–40 μM) a linear decrease in these parameters was evident. At even higher concentrations, 50 μM and above, cytolysis occurred. Inhibition of chlorophyll concentration and dry weight was greater the longer the cultures were exposed to cadmium. Cell division was completely arrested when toxic levels of cadmium were administered any time throughout the duration of the light phase. However, the severity of toxicity of cadmium, when applied during the dark phase, increased with the length of time of exposure. Cadmium toxicity also resulted in disturbances in cell division. Treated cells became larger than control cells. Unequal sporulation, microcolony and incipient microcolony formation, swelling, increased photolucence, and disruption of mitochondria occurred following treatment of cultures with toxic levels of cadmium. A further toxic effect of cadmium might relate to an increase in membrane permeability. Treatment of cultures with increasing concentrations of cadmium resulted in intracellular cadmium exceeding extracellular cadmium levels. The primary toxic effect of cadmium on synchronous cultures of C. ellipsoidea was attributed to a lack of cell division probably related to insufficient synthesis of chlorophyll and dry weight components as well as to a disruption of membrane integrity.