The Toxicity of Copper to Microcystis and its Reduction by Complexing Agents

Abstract

Toxicity of copper, cadmium and cobalt on the growth of blue-green algae Microcystis aeruginosa K3A, Microcystis viridis (toxic algae). Anabaena affinis and green algae Chlorella ellipsoidea was determined in the liquid medium. The EC₅₀ (effective concentration, 50% inhibition of the specific growth rate of control) of copper for M. aeruginosa K3A, M. viridis, A. affinis, C. ellipsoidea were 0.019 μM, 0.023 μM, 0.018 μM and 0.58 μM, respectively. Copper showed the severest toxicity to the growth of these algae compared with cadmium and cobalt. The sensitivity to copper of three species of the blue-green algae was 30 times higher than that of the green algae C. ellipsoidea. Chelating agents such as EDTA and EGTA showed the strong reducing effect on the copper toxicity while NTA had the weak reducing effect. Copper concentration in the surface water of Lake Kasumigaura was 0.017 μM, which was the almost same to the value of EC₅₀ for blue-green algae. However, the EC₅₀ of copper for M. aeruginosa K3A in the lake water was found to be 3 times larger than in the liquid medium. From these facts, natural ligands in the lake water is assumed to stimulate the growth of blue-green algae to make algal bloom.