MEMBRANE TOXICITY OF LINEAR ALCOHOL ETHOXYLATES

Abstract

The membrane toxicity of linear alcohol ethoxylates (AEO/single reference compounds and technical mixtures) was investigated with an in vitro method based on time-resolved spectroscopy on energy-transducing membranes. The nonspecific membrane perturbation of narcotic chemicals can be quantified by the degree of disturbance of buildup and relaxation of the membrane potential in membrane preparations of the purple bacterium Rhodobacter sphaeroides. The effect concentrations obtained for this narcotic effect correlated well with the results from various toxicity tests on whole organisms. In addition, the effect concentrations at the target site, the biological membrane, were derived from the nominal effect concentrations using membrane-water partition 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) units covering more than four orders of magnitude of hydrophobicity (expressed as octanol–water partition coefficient). All AEO exhibited their toxic effect 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 dependence on the number of EO units with a maximum at eight EO units. With the toxic effect expressed in terms of membrane concentrations, all AEO exhibited similar activity in the concentration range typical for narcotic chemicals. The toxic membrane concentrations of AEO with 5 and ≥8 EO units were 200 and 60 mmol/kg lipid, which correspond to the critical body residues of nonpolar and polar narcotics in fish, respectively. In addition, the toxic effects of mixtures of AEO were measured and could be modeled as the sum of activities of the single constituents, confirming the concept of concentration additivity of compounds with the same mode of toxic action.