Endocrine-disrupting compounds and mixtures: unexpected dose-response

Area of Science:

• Environmental Toxicology
• Reproductive Biology
• Ecotoxicology

Background:

• The red-eared slider turtle is a valuable model organism for studying endocrine-disrupting compounds (EDCs).
• Turtle sex determination is sensitive to environmental factors during embryogenesis, making them useful for assessing EDC effects.
• Previous research demonstrated that EDCs can shift sex ratios in this species.

Purpose of the Study:

• To investigate the effects of extremely low doses of trans-Nonachlor, chlordane, and p,p'-DDE, individually and in mixtures, on red-eared slider turtle sex determination.
• To evaluate the potential of the red-eared slider turtle as a model for quantifying EDC mixture effects, including additivity and synergy.
• To understand the behavior of very low doses (parts per billion) of these EDCs in mixtures.

Main Methods:

• Red-eared slider turtle embryos were exposed to varying low doses of trans-Nonachlor, chlordane, and p,p'-DDE during embryogenesis.
• Exposure occurred at temperatures that typically yield a male-biased sex ratio.
• The sex ratios of resulting hatchlings were analyzed after single and mixture exposures.

Main Results:

• Exposure to single EDCs shifted the sex ratio towards a female bias.
• When trans-Nonachlor, chlordane, and p,p'-DDE were administered in mixtures, even at very low doses, they consistently resulted in 100% female hatchlings.
• The effects of chlordane and p,p'-DDE in mixtures appeared dose-dependent, contrasting with their inverse dose-relationship when applied singly.

Conclusions:

• The red-eared slider turtle is a sensitive indicator for EDC-induced sex ratio disruption.
• Mixtures of these specific EDCs exhibit potent feminizing effects, leading to complete sex reversal.
• The findings suggest complex interactions, potentially involving complementary pathways, in how EDC mixtures affect turtle sex determination.