Impact of phase behavior on aquatic toxicity testing of alcohol ethoxylates

Due to the large quantity of alcohol ethoxylate surfactants used in both household and institutional cleaning applications and their discharge down-the-drain after use, the toxicity properties of alcohol ethoxylates (AE) in aqueous environments have received considerable attention. However, the potential effects of surfactant phase behavior have often not been considered when developing test procedures for ecotoxicity and interpreting test results. These effects are particularly important for studies of sparingly-soluble commercial AEs which are mixtures containing a broad distribution of ethoxylated species and alkyl chain lengths. In this regard, it has been determined that stock solutions containing 0.1–5 wt% AE should be prepared and stored in a single-phase micellar regime, i.e. between a lower crystallization temperature and the cloud point, to ensure that the test surfactant is dosed accurately. Turbidity and videomicroscopy measurements have been used to determine this temperature regime for a variety of ethoxylates. Also, the potential for phase separation of insoluble components as a broad distribution AE is diluted to below its critical micelle concentration has been examined using a variety of physical and analytical chemistry methods.