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

The acute toxicities of cadmium chloride (CdCl2.H2O), arsenic trioxide (AS2O3), 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 LC50 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 LC50 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.