Comparison of the critical concentration and critical volume hypotheses to model non-specific toxicity of individual compounds

The critical concentration and critical volume hypotheses for non-specific toxicity require the molar concentration (CC) and volume fraction (VF) of toxicant in target tissue to be constant. Thus these factors should be independent of the octanol-water partition coefficient (K_ow) for individual compounds. CC and VF values were calculated based on acute sub-lethal, acute and chronic lethal toxicity data, K_ow and pure component molar volume (MV) data. When these values were plotted against log K_ow, the slopes of the regression equations were significantly different to zero but were not significantly different from each other. The observed slight increase in CC and VF with increasing log K_ow was attributed predominantly, to the use of K_ow values which overestimate the target tissue-water partition coefficient (K_ttw. An additional error associated with the volume fraction calculations was the use of the molar volume instead of partial molar volume. VF and CC values were calculated correcting for both these factors and regressed against log K_ow. The resulting for VF had a gradient not significantly different from zero, while that for CC was, thus indicating the superiority of the critical volume hypothesis in modelling non-specific toxicity of individual compounds.