THE ENVIRONMENTAL CONTAMINANT DDE FAILS TO INFLUENCE THE OUTCOME OF SEXUAL-DIFFERENTIATION IN THE MARINE TURTLE CHELONIA-MYDAS

In many turtles, the temperature experienced during the middle of egg incubation determines the sex of the offspring. The implication of ste roid sex hormones as the proximate trigger for sex determination opens the possibility that endocrine-disrupting contaminants may also influ ence the outcome of sexual differentiation. In this study we investiga te the potential effects of DDE (a common DDT metabolite) on sexual di fferentiation of Chelonia mydas (green sea turtle). Four clutches of e ggs collected from Heron Island, Queensland, Australia: were treated w ith DDE at the beginning of the thermosensitive period for sexual dete rmination. An incubation temperature of 28 degrees C or less produces male hatchlings in this species, whereas 30 degrees C or more produces female hatchlings. Dosed eggs were consequently incubated at two temp eratures (27.6 degrees C and 30.4 degrees C) on the upper and lower bo undaries of the sex determination threshold for this species. DDE, ran ging from 3.3 to 66.5 mu g, was dissolved in 5, 10, and 25 mu l ethano l and applied to eggshells above the embryo. Less than 2.5 ng/g DDE wa s present in eggs prior to dosing. Approximately 34% of the applied DD E was absorbed in the eggs, jut only approximately 8% of applied DDE w as found in embryos. Thus, treated eggs, corrected, for background DDE , had up to 543 ng/g DDE. The sex ratio at these doses did not differ from what would be expected on consideration of temperature alone. Inc ubation time, hatching success, incidence of body deformities, hatchin g size, and weight were also within the limits of healthy developed ha tchlings. This indicates that the eggs of C. mydas in the wild with co ncentrations of DDE less than 543 ng/g should produce hatchlings with relatively high hatching success, survival rate, and normally differen tiated gonads.