Estimating the organic carbon partition coefficient and its variability for hydrophobic chemicals

Numerous correlations have been developed between the organic carbon/water partition coefficient K-OC and various molecular properties and descriptors , bur most notably the octanol/water partition coefficient K-OW and water s olubility. From an analysis of the theory underlying in this partitioning a nd an examination of the existing database, it is suggested that The prefer red approach is to correlate the quantity log(K-OC/K-OW), which is essentia lly the ratio of activity coefficients in octanol and organic carbon, with a molecular property or with log K-OW rather than lag K-OC with log K-OW. S uch an approach is presented for estimating K-OC for hydrophobic chemicals, including an expression of uncertainty limits, based on a correlation deri ved between log(K-OC/K-OW) and log K-OW. In its simplest form the correlati on is that K-OC = 0.35K(OW) subject to variation by a factor of 2.5 in eith er direction. It is suggested that new experimental data be assessed for co nsistency and achievement of true equilibrium by comparison with this corre lation.