Thermodynamics of fish/water and octan-1-ol/water partitioning of some chlorinated benzenes

The thermodynamic properties of the partitioning of chlorobenzenes between fish and water have been investigated. It is shown that bioconcentration by fish of polychlorobenzenes is accompanied by positive enthalpy and entropy changes. The free energy of this transfer process at room temperature is dominated strongly by the favorable entropy contribution. In contrast, the partitioning of these compounds between octan-1-ol and water is accompanied by negative enthalpy and by small negative or positive entropy changes. These results demonstrate that octan-1-ol is a poor model of the fish lipids and that generally octan-1-ol/water partition coefficients will not give reliable predictions of bioconcentration factors. In particular, the slopes of plots of octan-1-ol/water partition coefficients against bioconcentration factors will not be the same for different compounds.