Relative Toxicity of Three Homologous Series of Nonionic Surfactants in the Planarian

Abstract

An investigation on the toxicity of three homologous series of nonionic surfactants was carried out using planarian Dugesia lugubris (O. Schmidt). The surfactants used in this study were polyoxyethylene stearic acid esters, polyoxyethylene sorbitan fatty acid partial esters, and polyoxyethylene alkyl ethers. The effect of surfactant concentration (C) on time of death (T) of planarian can be described by a regression equation, where 1/T is linearly related to C. Analysis of variance of 1/T showed that each regression was highly significant and that deviations from linearity were not significant. The behavior of the polyoxyethylene stearic acid esters and polysorbates was in good agreement with the Levy-Gucinski theory, which describes the effect of toxic agents on goldfish. No agreement with the same theory was shown by surfactants of the polyoxyethylene alkyl ethers, whose regression lines, in the C range 0.05-1.0%, failed to intersect the origin. Statistical differences in relative toxicity between the members of each series were assessed. In the polyoxyethylene stearic acid esters, a linear relationship between the length of the polyoxyethylene chain and lethal time was detected. Relative toxicity in the polysorbates decreases in the order of the 20, 40, 60, and 80 esters, thereby depending on the nature of the esterifying acid (lauric, palmitic, stearic, and oleic, respectively). No clear-cut pattern was found with the polyoxyethylene alkyl ethers; differences in relative toxicity between the ethers of the series were not statistically significant. The present study is indicative of the utility of the planarian in biopharmaceutical research.