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Surface-Catalyzed Transformations of Aqueous Endosulfan

2002; American Chemical Society; Volume: 36; Issue: 22 Linguagem: Inglês

10.1021/es0256257

1520-5851

Spencer S. Walse, Ken D. Shimizu, John L. Ferry,

Environmental Toxicology and Ecotoxicology

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 NaHCO3 buffer (pH 8.15). Suspensions of sea sand, TiO2, α-Fe2O3, α-FeOOH, Laponite, and SiO2 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.