ADSORPTION-DESORPTION EQUILIBRIA OF 14C-FLURIDONE AT LOW SOLUTION CONCENTRATIONS AND SOIL:WATER RATIOS

The adsorption and desorption of 14C-fluridone (1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1 H)-pyridinone) were investigated at 1:1 and 1:5 soil:water ratios at solution concentrations ranging from 11.9 to 1190 ng mL−1, simulating herbicide concentrations under field conditions from recommended rates of application. Freundlich adsorption isotherms were developed for a sandy loam, sandy clay loam and silty clay soil. At 1:1 soil:water ratio, as initial herbicide concentration in the system increased 20 fold, the soil solution concentration at adsorption equilibrium increased by 86, 87 and 76 times for the sandy loam, silty clay and sandy clay loam, respectively. The mean equilibrium concentrations at adsorption were 1.8, 9.5 and 3.4 times higher than those at desorption for the sandy loam, silty clay and sandy clay loam, respectively. For each soil type, the adsorption coefficient (K) values were higher at 1:1 compared to 1:5 soil:water ratio. Slope constants (1/n) for the isotherms indicated that the intensity of adsorption was affected by soil:water ratio. Key words: Herbicide, fluridone, adsorption, desorption, soil:solution ratio, isotherm