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The degradation and corresponding product manifold for the pesticide fipronil was determined in three replicate estuarine mesocosms. Aqueous fipronil concentrations rapidly decreased over the 672 h timescale of the experiment (95% removal). Loss was apparently first-order in fipronil, although there appeared to be a change in the removal mechanism after 96 h that corresponded to a dramatic slowdown in its disappearance. The reduction product of fipronil, fipronil sulfide, was not detected in the water column; however, it formed rapidly in sediments and was identified as the major product of fipronil degradation in the system (20% yield at 672 h, with respect to initial fipronil concentration). Fipronil sulfone is thought to form primarily via biological oxidation; and, although it was generated rapidly in the water column (10% yield), only trace amounts were detected in the sediment (1% yield). The direct photolysis product of fipronil, fipronil desulfinyl, was present in all samples; it formed rapidly in the water column (4% yield) and partitioned into the sediment phase (7% yield) over the course of the experiment. The mass balance on fipronil and associated products was 42% at 672 h. 相似文献
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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. 相似文献
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