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

The soil organic partition coefficient (K_oc) is one of the most important parameters to depict the transfer and fate of a chemical in the soil-water system. Predicting K_oc 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 K_oc of hydrophobic organic chemicals (HOCs), over a log K_oc 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′) with various volume fractions of methanol (φ). The important effects of solute activity coefficients in water on k_W′ and K_oc were illustrated. Hence, the correlation between log K_oc and log k_W′ (and log k′) exists in the soil. The correlation coefficient (r) of the log K_oc vs. log k_W′ correlation for 58 apolar and polar compounds could reach 0.987, while the correlation coefficients of the log K_oc-log k′ correlations were no less than 0.968, with φ ranging from 0 to 0.50. The smaller the φ, the higher the r. Therefore, it is recommended that the eluent of smaller φ, such as water, be used for accurately estimating K_oc. Correspondingly, the r value of the log K_oc-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 K_oc indirectly from a correlation with k_W′ than the reversed-phase liquid chromatographic (RPLC) one.