A pilot study conducted at the University of Missouri showed that the synthetic chemical bisphenol A — or BPA, which is known to mimic estrogen and disrupt hormone levels in animals — can alter a turtle’s reproductive system after exposure in the egg. Turtles are perfect creatures for this type of study, because their sex is determined by the temperature of the environment during their development in the egg.

“Cool dudes or hot babes,” explained Sharon Deem, director of the St. Louis Zoo’s Institute for Conservation Medicine and a lead investigator on the study.

The researchers dropped a liquid form of the chemical onto hundreds of eggs that were incubated at cooler temperatures required to produce male turtles. A few months after they hatched, the turtles’ sex organs were removed and studied. The male turtles had developed gonads that were closer to ovaries than testicles.