Study: Pollution Causes Sex Change in Frogs

Frogs are more sensitive to hormone-disturbing pollutants than was previously thought, researchers said. Male tadpoles that swim in water with relevant levels of such substances become females, according to a new study from Uppsala University.

A great number of medicines that humans take are released through waste waters and end up in nature. The contraceptive pill estrogen ethynylestradiol has been found in waters in many countries, and this substance has been linked to disturbances in reproduction in wild fish. Researcher Cecilia Berg and doctoral candidate Irina Pettersson at the Department of Environmental Toxicology, Uppsala University, announced on Feb. 22 they found that low, environmentally relevant concentrations of ethynylestradiol cause sex reversal in frogs.

"This is the first clear evidence that estrogen in nature really can have a detrimental effect on frogs. Previous studies have used considerably higher concentrations than are normally found in nature," Berg said.

Under normal conditions, half of the frogs develop ovaries and the other half testicles. When tadpoles swim in water with low concentrations of ethynylestradiol, all of them develop ovaries. The research team has shown this in two species of frogs, the common frog (Rana temporaria) and the African clawed frog (Xenopus tropicalis). It is during the tadpole stage that reproductive organs begin to develop in frogs, a process that is regulated by the hormone system.

The study's findings will be published in the scientific journal Environmental Toxicology and Chemistry in May.

Cecilia Berg:

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