Endocrine-disrupting compounds and mixtures: unexpected dose-response.
The current study examined the effects on the red-eared slider turtle of extremely low doses of three endocrine-disrupting compounds (EDCs)--trans-Nonachlor, chlordane, and p,p'-DDE-singly and in mixtures. Previous studies using the red-eared slider turtle have proven its value as an organism for obtaining information about the effects of endocrine-disrupting compounds. The sex of the turtle, easily manipulated by exposure during embryogenesis, continues to be a marker of effects. When red-eared slider turtle embryos incubating at a temperature that normally produces a male-biased sex ratio are exposed to these compounds singly, the sex ratio of the resulting hatchlings shifts significantly to a female bias. The current work offers further evidence that the red-eared slider turtle provides a way to quantify the effects of mixtures and has the potential as a model for evaluating additivity and synergy. The results provide information about how very low doses (parts per billion) of these compounds behave in mixtures. The dose ranges were 0.125-0.5 ng/egg for trans-Nonachlor and chlordane and 7-28 ng/egg for p,p'-DDE. Results suggest the possibility that two of the compounds may exert effects in mixtures via complementary pathways; when applied singly, the effects of chlordane and p,p'-DDE were inversely related to dose, but in mixtures, which were essentially a greater dose of EDC, the compounds had an increased effect. In all cases, mixtures resulted in 100% females.
Willingham
Emily
E
Department of Biology, Texas State University, 316 Science, 601 University Dr., San Marcos, TX 78666, USA. willingham@swt.edu
D000818:Animals; D045424:Complex Mixtures / Q000633:toxicity*; D012734:Disorders of Sex Development; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian / Q000002:abnormalities / Q000187:drug effects*; D005260:Female; D006727:Hormone Antagonists / Q000633:toxicity*; D006843:Hydrocarbons, Chlorinated; D007306:Insecticides / Q000633:toxicity*; D008297:Male; D019849:Sex Determination Processes; D012733:Sex Differentiation / Q000187:drug effects*; D012744:Sex Ratio; D014426:Turtles
D045424:Complex Mixtures; D006727:Hormone Antagonists; D006843:Hydrocarbons, Chlorinated; D007306:Insecticides