Acute toxicity and structure-activity relationships of nine alcohol ethoxylate surfactants to fathead minnow and Daphnia magna

Aquatic toxicity of nine commercial-grade alcohol ethoxylate surfactants was studied in acute exposures to fathead minnow (Pimephales promelas) and Daphnia magna. All studies were conducted in accordance with USEPA TSCA Good Laboratory Practice Standards. Mean measured surfactant concentrations in the exposure solutions showed good agreement with nominal concentrations for both fathead minnow (R-2 = 0.98, p = 0.05) and daphnid (R-2 = 0.99, p = 0.05) tests. Surfactant recoveries ranged from 59 to 97% and 67 to 106% in the fathead minnow and daphnid solutions, respectively. Response of both species to the surfactants was generally similar. Surfactant toxicity tended to increase with increasing alkyl chain lengths. The effect of low average ethylene oxide (EO) groups on increased surfactant toxicity was more evident in the daphnid exposures. Quantitative structure-activity relationship (QSAR) models were developed from the data, which relate surfactant structure to toxicity. The models predict increasing toxicity with decreasing EO number and increasing alkyl chain length. The models also indicate that average alkyl chain length has a greater effect on toxicity than average EO groups. Further, the models indicate that both species did not differ markedly in their response to alkyl chain length effects, while the number of EO groups had a stronger effect on daphnids than fathead minnow. Model-predicted toxicity agreed well with toxicity estimated from USEPA alkyl ethoxylates SARs and with toxicity values reported in the literature for several surfactants previously studied.