Quantifying hysteresis of atrazine desorption from a sandy loam soil

Batch experiments were carried out to investigate the e ects of initial atrazine concentrations and consecutive desorption steps on the desorption characteristics of atrazine from a sandy loam soil. As initial atrazine concentration increased, the average percentage of atrazine desorption on the sandy loam soil ranged gradually from 23.1% to 38.5% after five consecutive desorption steps. The values of the Freundlich capacity parameter, kdes, derived from the initial concentration and time-dependent desorption isotherm were consistently higher than those associated with sorption. The opposite trend was observed only for the values of nonlinear parameter, ndes, from the initial concentration-dependent desorption isotherms. Atrazine hydrolysis to hydroxyatrazine and bound residue formation were mainly responsible for the observed hysteresis in its sorption and desorption isotherms. For the initial concentration-dependent desorption isotherms, as initial atrazine concentration increased, the values of hysteretic coe cients ! and decreased, and H values increased. However, the relationships between initial atrazine concentration and hysteretic coe cients were not pronounced for !, H, or . For the time-dependent desorption isotherms, and H values increased as the atrazine desorption step proceeded. The correlation between hysteretic coe cient and desorption step was highly significant for (P < 0.0001), but not for H.