Chronic toxicity of a homologous series of linear alcohol ethoxylate surfactants to Daphnia magna in 21 day flow‐through laboratory exposures

Abstract

The chronic toxicity to Daphnia magna Straus in 21 day flow-through laboratory exposures was assessed for a homologous series of nonionic linear alcohol ethoxylate surfactants. Three primarily linear alcohol ethoxylate surfactants with alkyl chain distributions of C9-11, C12-13, and C14-15, and with respective average ethoxymer groups of 6, 6.5, and 7 were tested. Mean measured surfactant exposure concentrations agreed with nominal concentrations, with average recoveries of 93, 84, and 86% (R2=0.99, 0.99, and 0.98) for the C9-11EO6, C12-13EO6.5, and C14-15EO7 surfactants, respectively. Daphnia magna survival 21 day EC50s were 5.9, 2.2 and 1.2 mg L−1 for the C9-11, C12-13, and C14-15 surfactants, respectively. Data indicate a twofold increase in toxicity in terms of daphnid survival with each two carbon addition in alkyl chain length. Daphnid survival and reproduction were equally sensitive for the C9-11 and C14-15 surfactants, however, reproduction was more sensitive than survival for the C12-13 surfactant. Survival NOECs were 2.77, 1.75, and 0.79 mg L−1 while reproduction no observed effect concentrations (NOECs) were 2.77, 0.77, and 0.79 mg L−1 for the C9-11, C12-13, and C14-15 surfactants, respectively. For the surfactants studied, chronic laboratory NOECs for D. magna survival (21 day) were similar to NOECs obtained for cladoceran densities in stream mesocosm experiments (30 day exposures) indicating a direct relationship between laboratory chronic effects and field effect levels for similar organisms. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 293–300, 1999