Membrane toxicity of linear alcohol ethoxylates

The membrane toxicity of linear alcohol ethoxylates (AEO/single reference c ompounds and technical mixtures) was investigated with an in vitro method b ased on time-resolved spectroscopy on energy-transducing membranes. The non specific membrane perturbation of narcotic chemicals can be quantified by t he degree of disturbance of buildup and relaxation of the membrane potentia l in membrane preparations of the purple bacterium Rhodobacter sphaeroides. The effect concentrations obtained for this narcotic effect correlated wel l with the results from various toxicity tests on whole organisms. In addit ion, the effect concentrations at the target site, the biological membrane, were derived From the nominal effect concentrations using membrane-water p artition coefficients. The test set of linear AEO comprised compounds with an alkyl chain length of 8 to 16 carbon units and 5 to 14 ethoxylate (EO) u nits covering more than four orders of magnitude of hydrophobicity (express ed as octanol-water partition coefficient). All AEO exhibited their toxic e ffect at concentrations well below the critical micelle concentration. When comparing aqueous effect concentrations, toxicity increased strongly with increasing length of the alkyl chain and showed a small parabolic dependenc e on the number of EO units with a maximum at eight EO units. With the toxi c effect expressed in terms of membrane concentrations, all AEO exhibited s imilar activity in the concentration range typical for narcotic chemicals. The toxic membrane concentrations of AEO with 5 and greater than or equal t o 8 EO units were 200 and 60 mmol/kg lipid, which correspond to the critica l body residues of nonpolar and polar narcotics in fish, respectively. In a ddition, the toxic effects of mixtures of AEO were measured and could be mo deled as the sum of activities of the single constituents, confirming the c oncept of concentration additivity of compounds with the same mode of toxic action.