Comparison of toxicities and mechanism of action of n‐alkanols in the submitochondrial particle and the Vibrio fischeri bioluminescence (Microtox®) bioassay

Many studies on the toxicity of n-alkanols have been conducted and quantitative structure-activity relationships (QSARs) established comparing bioassay toxicity data to carbon number. The results typically indicate increasing toxicity with increasing n-alkanol chain length, but often higher homologues are not assessed, where toxicity no longer increases with carbon number—a phenomenon commonly called the cutoff effect. The mode of toxic action of these compounds has been designated narcosis I; however, the specific mechanism is unknown and widely debated. This study compares results for two commonly used bioassays, the submitochondrial particle (SMP) and the Microtox® bioassay, for the homologous series of n-alkanols ranging from methanol (C1-OH) to stearyl alcohol (C18-OH). Analysis of dose-response curve slopes indicates that the SMP assay exhibits a general mechanism of toxicity, whereas the Microtox assay exhibits this general mechanism to short-chain alkanols, but subsequently switches to specific interaction with the higher alkanols. This specific interaction is likely competitive inhibition of the bacterial luciferase. Comparison of the toxicities in these assays with octanol/water partition coeffients (Kow), the results of whole-organism tests, and a bacterial luciferase assay further substantiate this claim and indicate that the SMP is a better model of toxicity in whole organisms.

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