BATCH VERSUS COLUMN METHOD FOR DETERMINING DISTRIBUTION OF ORGANICS BETWEEN SOIL AND WATER PHASES

The batch equilibrium and a continuous flow (column) procedures were compared to determine if similar pesticide distribution coefficients could be obtained for the two methods. Using a low infiltration rate of 2.7 cm day-1, essentially identical values were obtained by the two methods for the distribution of napropamide and lindane between the sorbed and solution phases in a Pachappa sandy loam. Values for K(oc) of 421 and 1300 L kg-1 were measured for napropamide and lindane, respectively, at 20-degrees-C. Distribution coefficients decreased with increasing temperature. In the column experiments, similar values for the distribution coefficients were obtained regardless of whether the amounts of pesticide sorbed were determined by direct extraction of the soil or by the difference between quantities added to the columns and the quantities of solute in the effluent. Both linear and Freundlich isotherm models were used to calculate distribution coefficients. The soil column breakthrough curves were reproducible in duplicate runs for both napropamide and lindane. When distribution coefficients were estimated using a chemical retardation factor from the column experiments, the coefficients were consistently larger than those determined by the batch equilibrium method.