Biodegradation and Ecotoxicity of Branched Alcohol Ethoxylates: Application of the Target Lipid Model and Implications for Environmental Classification

With the advent of global regulations for safer detergent and an emphasis on a shift toward more environmentally friendly formulations, the environmental profile of surfactant chemistries have moved to the forefront of product formulation and design. The two cornerstones of surfactant environmental profiles are the ability to biodegrade in the natural environment and the ecological hazard profile. The objectives of this article are to describe biodegradation and aquatic toxicity data for a series of branched oxo-alcohol ethoxylate (AEO) surfactants; to apply the target lipid model (TLM) for deriving model-based threshold hazard concentrations (HC5) of AEO; and, finally, to accurately determine aquatic classifications for AEO surfactants for use in regulatory classification frameworks. Biodegradation results indicate a high level of biodegradability of branched AEO, with C8-C13-rich oxo-alcohols with 1-20 mol of ethoxylate meeting the readily biodegradable criteria. Results from acute and chronic toxicity tests indicated comparable or lesser aquatic toxicity versus linear AEO structures previously reported in the literature. The TLM model, applied a priori, resulted in good agreement with acute toxicity data (RMSE = 0.49) and is comparable to the root mean square errors (RMSE) previously determined for other narcotic chemicals (RMSE = 0.46-0.57). Model errors for invertebrates and fish were smaller than those for algae, with the TLM systematically overpredicting acute and chronic classification of two of seven branched AEO. Furthermore, TLM-predicted HC5 values were determined to be sufficiently conservative, with 100% of observed chronic data (N = 79) falling above the HC5 threshold values, providing a useful tool for the risk assessment of AEO.