Prediction of soil organic partition coefficients by a soil leaching column chromatographic method

The soil organic partition coefficient (Koc) is one of the most important parameters to depict the transfer and fate of a chemical in the soil-water system. Predicting Koc by using a chromatographic technique has been developing into a convenient and low-cost method. In this paper, a soil leaching column chromatograpy (SLCC) method employing the soil column packed with reference soil GSE 17201 (obtained from Bayer Landwirtschaftszentrum, Monheim, Germany) and methanol-water eluents was developed to predict the Koc of hydrophobic organic chemicals (HOCs), over a log Koc range of 4.8 orders of magnitude, from their capacity factors. The capacity factor with water as an eluent (k'w) could be obtained by linearly extrapolating capacity factors in methanol-water eluents (k'w) with various volume fractions of methanol (symbol in text). The important effects of solute activity coefficients in water on k'w and Koc were illustrated. Hence, the correlation between log Koc and log k'w (and log k') exists in the soil. The correlation coefficient (r) of the log Koc vs. log k'w correlation for 58 apolar and polar compounds could reach 0.987, while the correlation coefficients of the log Koc -log k' correlations were no less than 0.968, with (symbol in text)ranging from 0 to 0.50. The smaller the (symbol in text), the higher the r. Therefore, it is recommended that the eluent of smaller (symbol in text), such as water, be used for accurately estimating Koc. Correspondingly, the r value of the log Koc -log k'w correlation on a reversed-phase Hypersil ODS (Thermo Hypersil, Kleinostheim, Germany) column was less than 0.940 for the same solutes. The SLCC method could provide a more reliable route to predict Koc indirectly from a correlation with k'w than the reversed-phase liquid chromatographic (RPLC) one.