Acute Toxicities of Equimolar and Equitoxic Surfactant Mixtures to Daphnia magna and Lepomis macrochirus

Abstract

The acute toxicities of anionic, nonionic, and cationic detergent surfactants to Daphnia and bluegill were determined for individual surfactants and for binary and ternary surfactant mixtures. Data were analyzed using several models, including toxic units, the additive index, and concentration and response addition. The effects of the single surfactants, in decreasing order of toxicity, were as follows: in Daphnia, the effects were cationic, nonionic, and anionic; in bluegill, nonionic, anionic, and cationic. Approximately 72 percent of the binary and ternary mixtures were less than additive in response to either organism when analyzed by toxic units or by the additive index. Approximately 24 percent of the mixtures demonstrated simple addition using these methods. The anionic-cationic mixtures were synergistic to bluegill and in one case to Daphnia. The toxicities of the majority of mixtures fit response and concentration additive models; conformity to the response additive model was most common. Response addition, as applied and evaluated during the present investigation, offers an approach for early estimation and prediction of the toxicities of surfactant mixtures.