Investigation of acute toxicity of cadmium-arsenic mixtures to Daphnia magna with toxic units approach

The acute toxicities of cadmium chloride (CdCl_2.H_2O), arsenic trioxide (AS_2O_3), and their mixtures to Daphnia magna were investigated by employing the statistical method of aquatic toxicity. The data obtained were statistically evaluated with probit analysis method (SPSS 17.0). The 24 h LC_{50} of Cd and As to Daphnia magna was estimated to be 44 µg L^{-1} for Cd, and 509 µg L^{-1} for As, respectively. With Behrens-Karber method the 24 h LC_{50} of these metals was found to be 46 µg L^{-1} and 509 µg L^{-1}, respectively. The 2 methods were in good agreement. The results suggested that D. magna is more sensitive to the 90% Cd + 10% As mixture than either metal alone. Toxic units (TUs) and additional index (AI) showed that all mixtures were synergistic.