DEFUR, Peter L.; FOERSOM, Lisa L.; TUBERTY, Shea; Virginia Commonwealth Univ; Virginia Commonwealth Univ; Appalachian State Univ
We examined the effects of endosulfan exposure on molting in juvenile crayfish, Procambarus clarkii, common inhabitants of southeastern freshwater wetlands where endosulfan is used agriculturally. Endosulfan is estrogenic based on binding affinity for the estrogen receptor. Researchers recently found that endosulfan inhibits the molting enzyme chitobiase.Acute toxicity testing with three concentrations of endosulfan (0.65 ppb, 0.065 ppb, 0.0065 ppb) determined a sublethal concentration for juveniles. The toxicity testing produced an inverted U-shaped dose-response curve with the highest mortality (79%) at the intermediate concentration (0.065 ppb), 53% mortality at the highest concentration (0.65 ppb) and 21% at 0.0065 ppb. Animals in early premolt, stage D0-D1, were the most sensitive to endosulfan exposure at all three concentrations. A lower percentage of premolt exposed animals molted compared to controls, indicating molt inhibition. Molt stage specific ecdysone (Ecy, molting hormone) titers were measured by radioimmunoassay. Oxygen consumption was measured as an indicator of metabolic activity in freshwater and 0.0065 ppb using flow-through respirometers. Oxygen consumption in controls decreased over time and increased during endosulfan exposure. The lowest exposure concentration resulted in high mortality and reduced molt rate - while the middle concentration (0.065 ppb) produced the greatest effect. Ecdysone titers did not seem to be affected by 96 hr endosulfan exposure of 0.065 ppb in adult or juvenile crayfish, although there were some elvated Ecy titers in adult animals that do not molt. We are continiuing this research on blue crabs, horseshoe crabs and crayfish with several known or suspected endocrine disruptors.
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