Nonlinear Dependence of Bioconcentration Factors on n-Octanol-Water Partition Coefficients of Chlorinated Dibenzofurans and Dibenzo-p-Dioxins

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Abstract
A nonlinear thermodynamic model is applied to the prediction of both the bioconcentration factor (Kbw) in the guppy (Poecilia reticulata) and the n-octanol-water partition coefficient (Kow) of chlorinated dibenzofurans and dibenzo-p-dioxins. To this end molar liquid volumes, heats of vaporization and empirically fitted parameters of the pertinent solute and solvents are used. Calculated log Kbw and log Kow values are obtained with correlation coefficients (r = 0.85 and 0.992) and mean deviations (< dev > = 0.19 and 0.17), which compare favourably with experimental data. In addition the model enables an explanation of the well-known nonlinear log-log relationship between the two properties for compounds with high Kow values on the basis of differences between the properties of biotic lipid and n-octanol. It is suggested that the breakdown of the linear relationship is caused by entropic effects related to the number of chlorine atoms in the solute molecules and to the structures of the lipid and n-octanol.

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