ANOMALIES IN THE LOG FREUNDLICH EQUATION RESULTING IN DEVIATIONS IN ADSORPTION K VALUES OF PESTICIDES AND OTHER ORGANIC COMPOUNDS WHEN THE SYSTEM OF UNITS IS CHANGED KEY WORDS: Isotherm, distribution coefficient, adsorption coefficient

Freundlich K values cannot be directly converted from one set of units to another unless the slope, N, is unity. Dimensional analysis of the Freundlich equation shows the units of K to be moles L g, instead of the commonly used units, moles/g. A mathematical relationship exists between the ratio of K values in two different sets of units, and N. The magnitude of K does not change by the same factor as the adsorption data (x/m, C) from which it was calculated, when units are changed, unless N=1.0. To avoid problems associated with units of K, it is recommended that mole fraction (a unitless quantity) be used to express equilibrium concentration, and that K no longer be used as an indicator of relative adsorption. An alternate means of assessing relative adsorption among pesticides is proposed. INTRODUCTION Recently there has been an increasing demand by regulatory agencies to quantify pesticide adsorption in soil-water systems. Although octanol-water partition coefficients have