Modeling sorption behavior of atrazine on intact soil columns

The sorption behavior of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s -triazine), 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 int raparticle diffusion of pesticide into the soil matrix (also sometimes know n as bound residues), the sorption capacity of soil, and a variable pestici de distribution coefficient K-d. The modified model's performance was verif ied by comparing simulated values with those obtained from an intact column study in the laboratory. The two-stage mechanism was also compared and con trasted with the conventional adsorption approach based on a constant K-d. Simulations with the two-stage mechanism indicated a closer agreement with measured values (deviations in the range of 5-65%) than that of the convent ional adsorption approach (deviations in the range of 10-700%). Furthermore , it was found that simulated values were particularly sensitive to soil to rtuosity tau, soil bulk density rho, soil moisture content theta(w), labile sorption capacity theta(c), and intraparticle diffusion parameters.