The influences of clay minerals and humic acids on the sorption and hydrolysis of alpha-endosulfan were studied. The batch experiments were conducted at pH 8 in dark. The Freundlich sorption coefficient, Kf, demonstrated a greater sorption of alpha-endosulfan on montmorillonite than kaolinite. Endosulfan diol showed less sorption by kaolinite and montmorillonite compared to alpha-endosulfan, demonstrating less hydrophobicity than its parent compound. For both minerals, sorption of alpha-endosulfan by the HA-mineral complex was greater than for sorption by the minerals alone, suggesting additional adsorption of alpha-endosulfan by HA associated with the mineral surface. The Kf values appeared to decrease in the order of EHA > PHA > SHHA, which was likely related to the polarity (O/C ratio) of each of the HA.; Comparing to the water only system at 25°C, montmorillonite surface likely catalyzed the hydrolysis of alpha-endosulfan whereas kaolinite surface delayed the hydrolysis of alpha-endosulfan. The presence of humic acids appeared to affect the catalytic activity of mineral surfaces. The PHA appeared to enhance the aqueous phase and surface-catalyzed hydrolysis of alpha-endosulfan in both kaolinite and montmorillonite systems. The SHHA did not appear to enhance the aqueous phase and surface-catalyzed hydrolysis of alpha-endosulfan in the montmorillonite system but appear to enhance the aqueous phase and surface-catalyzed hydrolysis of alpha-endosulfan in the kaolinite system. The EHA appeared to reduce the aqueous and surface-catalyzed hydrolysis of alpha-endosulfan in all systems studied.
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