MODELING SORPTION BEHAVIOR OF ATRAZINE ON INTACT SOIL COLUMNS

The sorption behavior of atrazine (2-chloro-4-ethylamino-6-isopropylamino-j-triazme), a commonly used herbicide for corn, on intact soil columns was studied by incorporating a new two-stage sorption mechanism into PESTFADE, a pesticide fate and transport model. This mechanism takes into account intraparticle diffusion of pesticide into the soil matrix (also sometimes known as bound residues), the sorption capacity of soil, and a variable pesticide distribution coefficient Kd The modified modelʹs performance was verified by comparing simulated values with those obtained from an intact column study in the laboratory. The two-stage mechanism was also compared and contrasted with the conventional adsorption approach based on a constant Kd. Simulations with the two-stage mechanism indicated a closer agreement with measured values (deviations in the range of 5-65%) than that of the conventional adsorption approach (deviations in the range of 10-700%). Furthermore, it was found that simulated values were particularly sensitive to soil tortuosity T, soil bulk density p, soil moisture content teta(w) labile sorption capacity teta(c) and intraparticle diffusion parameters.