We report the effect of suspended solids on the oxidation and hydrolysis of the insecticide endosulfan (α and β isomers) and its degradation products: endosulfan diol, endosulfan sulfate, endosulfan ether, and endosulfan lactone in 0.001 M NaHCO{sub}3 buffer (pH 8.15). Suspensions of sea sand, TiO{sub}2, α-Fe{sub}2O{sub}3, α-FeOOH, Laponite, and SiO{sub}2 all catalyzed the hydrolysis of endosulfan to the less toxic endosulfan diol. Suspended creek sediment (Bread and Butter Creek SC, 4 OC) inhibited endosulfan hydrolysis. Heterogeneous and homogeneous rate constants of endosulfan hydrolysis were measured and indicate that β-endosulfan hydrolyzes faster than α-endosulfan. This observation was explained by a more stable transition state for β-endosulfan that was confirmed with ab initio molecular orbital calculations (STO-6G) on the anionic intermediates of endosulfan hydrolysis. Rates of endosulfan hydrolysis over the different surfaces corresponded to their tritium-exchange site-density and suggest a mechanism involving surface coordination prior to nucleophilic attack. The oxidation of α-endosulfan and β-endosulfan to the persistent pollutant endosulfan sulfate was not observed in this study.
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