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Stereoselective degradation of aqueous endosulfan in modular estuarine mesocosms: formation of endosulfan γ-hydroxycarboxylate†
Abstract
Solutions of α-endosulfan, β-endosulfan, and technical grade endosulfan (70α∶30β) were added to modular estuarine mesocosms; the kinetics and degradation products from each mesocosm are reported. The persistent product endosulfan sulfate was generated in all cases; however, its yield was approximately a factor of three higher from α-endosulfan relative to β-endosulfan. β-endosulfan hydrolyzed faster than α-endosulfan to endosulfan diol, which then rapidly degraded to endosulfan ether, endosulfan α-hydroxyether (major product), and endosulfan lactone. The ring-opened form of the lactone, endosulfan γ-hydroxycarboxylate, is reported for the first time; it appears to be a terminal product, at least over the timescale of the experiment. The equilibrium between endosulfan γ-hydroxycarboxylate and endosulfan lactone is dependent on pH, as only the protonated form of the γ-hydroxy acid undergoes ring-closure. The pKa of the γ-hydroxy acid was determined to be 5.7, implying that the lactone will quickly open and deprontonate under environmentally relevant conditions.
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