TOXICITY OF ZINC, CADMIUM AND COPPER TO THE SHRIMP CALLIANASSA-AUSTRALIENSIS .2. EFFECTS OF PAIRED AND TRIAD COMBINATIONS OF METALS

The acute toxicity of Zn, Cd and Cu to C. australiensis was assessed in paired and triad combinations in 14-day toxicity tests. Predicted mortalities following exposure to various mixtures of metals were evaluated according to 2 models proposed by Plackett and Hewlett (1967) for the noninteraction of toxicants: independent dissimilar action and simple similar action. Based on the rejection of these 2 models and analyses of experimental results for each metal alone, metals in all paired mixtures acted in an interactive manner. For the triad mixture, mortalities of shrimp were predictable by the independent dissimilar action model. Toxicities of mixtures of metals were also assessed using the toxic-unit concept. Mortalities in all mixtures were overestimated by this method. Some problems concerning the prediction of mortalities in mixtures of toxicants were discussed.