Acute toxicity of nonpolar versus polar narcosis: Is there a difference?

Narcosis I and II chemicals exhibit different lethal body burdens (LBBs) and acute toxicities (median lethal concentrations [LC50's]) in fish, when compared with their log n-octanol-water partition coefficient (K-ow), The higher toxicity of polar narcosis chemicals has often been suggested to be related to the polar group in these molecules. Recently we showed that membrane (L-alpha-dimyristoyl phosphatidyl-choline [DMPC])-water partition coefficients (log K-DMPC) are higher than log K-ow for narcosis II chemicals. Using log K-DMPC to model the acute toxicities to fish (log LC50) of the two classes of chemicals together, gives one high-quality quantitative structure-activity relationship (R-2 = 0.98, Q(2) = 0.97). In addition, assuming that the apolar fat-water partition coefficient behaves like the n-octanol-water partition coefficient, differences in LBB can also be explained. Thus, using log K(DMPC)s all earlier reported quantitative differences between narcosis I and II chemicals can be explained.