Bioaccumulation of zinc and cadmium in freshwater alga, Chlorella vulgaris. Part I. Toxicity and accumulation

Abstract The essential trace metallic element, zinc, and the non-essential metal, cadmium, were investigated for toxicity and accumulation in a freshwater alga, Chlorella vulgaris , which has been isolated from natural water and which has a very large resistance to arsenic. Above 80 mg Zn L −1 in medium, the lag phase in the growth curve appeared, but the growth was recovered in a few days. Above 25 mg Cd L −1 in medium, the cells were killed. Zinc and cadmium were accumulated by the cells from the aqueous medium containing 100 and 10 mg metal L −1 , to the extents of 35 × 10 4 mg Zn and 1.8 × 10 4 mg Cd kg −1 of dry cells, respectively. Accumulation of zinc by the cells was affected by NaN 3 (photosynthesis inhibitor) treatment. Accumulation of cadmium was affected both by NaN 3 and dinitrophenol (respiratory inhibitor). Zinc and cadmium were predominantly accumulated by biological processes and physicochemical processes, respectively.