Experimental study of octanol–water partition coefficients for2,4,6-trichlorophenol and pentachlorophenol: Derivation of an empirical model of chlorophenol partitioning behaviour

Abstract

The octanol–water partition coefficients (log Kow) of 2,4,6-trichlorophenol and pentachlorophenol were determined as functions of pH, ionic strength and aqueous metal content. For both chlorophenols, the log Kow exhibits pH dependence in the range pKa−1<pH<pKa+3. At lower and higher pH values, the behaviour of the chlorophenols is independent of pH. The present data, in conjunction with that of pre-existing data, indicate that a linear relationship exists between log Kow and log ionic strength of the aqueous solution for pentachlorophenol, and the data also suggest that aqueous metal–chlorophenolate complexation can significantly alter the partitioning behaviour. The data reported here was used to obtain an empirical model of the partitioning behaviour based on speciation of the aqueous chlorophenol. The model requires knowledge of the low pH partitioning behaviour, as well as the acidity constant for the particular chlorophenol of interest. Although Kow values have been measured as a function of pH and/or ionic strength for only pentachlorophenol, the input parameters for our empirical model are readily accessible in the literature for many chlorophenols. The model greatly expands our ability to quantify the hydrophobicity of chlorophenols, enabling accurate estimations of the pH and ionic strength dependencies of the partitioning behaviour over a wide range of pH and ionic strength values of environmental interest.