QSPR Treatment of the Soil Sorption Coefficients of Organic Pollutants

In this study, general and class-specific QSPR models for soil sorption, logK OC , of 344 organic pollutants (0 < logK OC < 4.94) were developed using a large variety of theoretical molecular descriptors based only on molecular structure. Two general models were obtained. The first model was derived for a structurally representative set of 68 chemicals (R 2=0.76, s=0.44), whereas the second involved a total of 344 compounds (R 2=0.76, s=0.41). The first was validated using the data for the remaining 276 pollutants (R 2=0.70, s=0.45). An additional validation of both models was performed using an independent set of 48 pollutants. Both models predict the logK OC at the level of experimental precision, while the theoretical molecular descriptors appearing in the QSPR models give further insight into the mechanisms of soil sorption. The analysis of the distribution of the residuals of the logK OC values calculated by both general models indicated the need and possible advantages of modeling soil sorption for smaller data sets related to individual classes of chemicals. Accordingly, QSPR models were also developed for 14 chemical classes. The descriptors appearing in these models were discussed as related to the possible interaction mechanisms in soil sorption.