Multivariate quantitative structure-activity relationships for the aquatic toxicity of technical nonionic surfactants

The aquatic toxicity of 36 technical nonionic surfactants (ethoxylated fatty alcohols) was examined toward two freshwater animal species, the fairy shrimp Thamnocephalus platyurus and the rotifer Brachionus calyciflorus. Responses of the two species to the surfactants were generally similar. A multivariate-quantitative structure-activity relationship (M-QSAR) model was developed from the data. The M-QSAR model consisted of a partial least squares model with three components and explained 92.4% of the response variance and had a predictive capability of 89.1%. The most important physicochemical variables for the M-QSAR model were the number of carbon atoms in the longest chain of the surfactant hydrophobe (redC), the molecular hydrophobicity (log P), the number of carbon atoms in the hydrophobe (C), the hydrophilic-lipophilic balance according to Davis (Davis), the critical packing parameter with respect to whether the hydrophobe was branched or not (redCPP), and the critical micelle concentration. Surfactant toxicity tended to increase with increasing alkyl chain lengths.