Estimation of Organic Carbon Normalized Sorption Coefficient (KOC) for Soils Using the Fragment Constant Method

A fragment constant model for prediction of KOC was developed and evaluated with a diverse database of 592 chemicals belonging to 17 classes. The range of experimental KOC covered 7.65 log-units. The 592 chemicals were randomly divided into a training set and a testing set for model development and validation. A general model was then established using the entire database having 74 fragment constants and 24 structural factors. Statistically, the regression model accounted for as much as 96.96% of the variation in the measured log KOC. The mean residual between the experimental and predicted KOC values was 0.366 log-units. In more than 74% of the chemicals studied the residual values were less than 0.5 log-units. The robustness of the regression model, with respect to either specific individual chemicals or particular compound classes, was evaluated through use of jackknife tests. The experimental results confirmed the ability of the fragment model to predict KOC for a wide variety of untested chemicals.