Toxicity of metal mixtures to the Pacific white shrimp Litopenaeus vannamei postlarvae

According to the literature, the safe level of a toxic substance for any given organism may be calculated from its median lethal concentration multiplied by a suitable application factor (AF: usually 0.1 and 0.01). The medial lethal concentrations for Litopenaeus vannamei postlarvae exposed to the mixtures in equitoxic proportions of Cd–Hg, Hg–Zn and Hg–Pb were close to one order of magnitude lower than the values calculated from individual toxicity tests, indicating a synergistic effect, while the mixture Cd–Zn showed an antagonistic effect. Exposure to the mixture of Cu, Fe, Mn, Zn, Cd, Hg and Pb caused 63.3% and 100% mortality after 21 and 13 days for 0.05 and 0.1 AF, showing that environmental safe concentrations of toxicants should not be calculated from individual toxicity tests.