Abstract
The toxicity of fourteen insecticides commonly used in Egypt to Ceriodaphnia quadrangula was investigated when mixtures of two of the pesticides were combined. The insecticides included organophosphates, carbamates, and synthetic pyrethroids. The concentration required to immobilize 50% of the crustaceans in one hour was determined for each pesticide individually (EC super(50). Next insecticides were paired so that the pyrethroids were grouped with either an organophosphate or a carbamate, making 45 mixtures that were applied at the EC super(25) rate for each individual pesticide in the single dose application test. Results were used to calculate a cotoxicity factor from the observed and expected percentage mortalities. In the multidose application, daphnids were exposed to a variety of concentrations of nine mixtures made from stock solutions containing half the EC super(50) of each pesticide in the pair. For the single dose test, potentiation, additivity, and antagonism were found for 32, 6, and 7 pairs, respectively. The test was adequate as a first screening method, which could be confirmed using the multiple dose test.