title: Stereoselective degradation of aqueous endosulfan in modular estuarine mesocosms: formation of endosulfan gamma-hydroxycarboxylate.
abstract: Solutions of alpha-endosulfan, beta-endosulfan, and technical grade endosulfan (70alpha:30beta) 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 alpha-endosulfan relative to beta-endosulfan. Beta-endosulfan hydrolyzed faster than alpha-endosulfan to endosulfan diol, which then rapidly degraded to endosulfan ether, endosulfan alpha-hydroxyether (major product), and endosulfan lactone. The ring-opened form of the lactone, endosulfan gamma-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 gamma-hydroxycarboxylate and endosulfan lactone is dependent on pH, as only the protonated form of the gamma-hydroxy acid undergoes ring-closure. The pKa of the gamma-hydroxy acid was determined to be 5.7, implying that the lactone will quickly open and deprontonate under environmentally relevant conditions.
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA.
authors.forename: Spencer S
authors.initials: SS
authors.lastname: Walse
authors.forename: Geoffrey I
authors.initials: GI
authors.lastname: Scott
authors.forename: John L
authors.initials: JL
authors.lastname: Ferry
mesh_terms: D001682:Biological Availability; D004726:Endosulfan / Q000737:chemistry / Q000378:metabolism*; D006843:Hydrocarbons, Chlorinated; D006868:Hydrolysis; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008962:Models, Theoretical; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D006843:Hydrocarbons, Chlorinated; D007306:Insecticides; D014874:Water Pollutants, Chemical; D004726:Endosulfan