Relation between physicochemical properties of phenols and their toxicity and accumulation in fish.

The 96-hr LC50 values of 21 substituted phenols for the guppy (Poecilia reticulata) were determined at pH levels 6-8 and related to the lipophilicity defined as log P from the 1-octanol/water system, and to the delta pKa value (pKa of phenol-pKa). Log P was the more important parameter and exhibited a good correlation with log(1/LC50) at pH levels. The contribution of delta pKa when introduced as a second parameter into the regression equation was dependent on the pH of water: at pH 6 it was positive but turned negative as the pH was raised to 8. If the LC50 values were corrected for ionization using an empirically formulated relation between toxicity and pH, the resulting regression equation could be used to predict the toxicity at any pH from 6 to 8. When corrected for ionization, log BCF (the bioconcentration factor) of 8 phenols was highly correlated with log P but not with delta pKa. The regression of log BCF on log P sufficed to explain the regression of toxicity on lipophilicity.