James R. Mihelcic Dean C. Luehrs James P. Hickey James R. Baker 1997 <p>A critically evaluated set of 94 soil water partition coefficients normalized to soil organic carbon content (<i>K_oc</i>) is presented for 11 classes of organic chemicals. This data set is used to develop and evaluate <i>K_oc</i> estimation methods using three different descriptors. The three types of descriptors used in predicting <i>K_oc</i> were octanol/water partition coefficient (<i>K_ow</i>), molecular connectivity (^mX_t) and linear solvation energy relationships (LSERs). The best results were obtained estimating <i>K_oc</i> from <i>K_ow</i>, though a slight improvement in the correlation coefficient was obtained by using a two-parameter regression with <i>K_ow</i> and the third order difference term from ^mX_t. Molecular connectivity correlations seemed to be best suited for use with specific chemical classes. The LSER provided a better fit than ^mX_t but not as good as the correlation with <i>K_oc</i>. The correlation to predict <i>K_oc</i> from <i>K_ow</i> was developed for 72 chemicals; log <i>K_oc</i> = 0.903* log <i>K_ow</i> + 0.094. This correlation accounts for 91% of the variability in the data for chemicals with log <i>K_ow</i> ranging from 1.7 to 7.0. The expression to determine the 95% confidence interval on the estimated <i>K_oc</i> is provided along with an example for two chemicals of different hydrophobicity showing the confidence interval of the retardation factor determined from the estimated <i>K_oc</i>. The data showed that <i>K_oc</i> is not likely to be applicable for chemicals with log <i>K_ow</i> &lt; 1.7. Finally, the <i>K_oc</i> correlation developed using <i>K_ow</i> as a descriptor was compared with three nonclass-specific correlations and two 'commonly used' class-specific correlations to determine which method(s) are most suitable.</p> application/pdf 10.2175/106143097X125281 en Water Environment Federation Evaluation of estimation methods for organic carbon normalized sorption coefficients article