Pesticide 'causes frogs to change sex'

Amphibians: In decline globally for the last half-century

By Helen Briggs BBC News Online science staff

Frogs and toads are rapidly disappearing around the world and nobody knows why. Climate change, pollution, and unknown diseases have all been blamed.

What are the environmental costs of using atrazine? What diversity have we lost?

Dr Tyrone Hayes, University of California

Now, a US biologist has put forward another explanation - pesticides.

In the lab at least, one of the world's best selling weedkillers seems to cause male frogs to change sex.

Dr Tyrone Hayes of the University of California, Berkeley, claims atrazine could be a danger to amphibians in the wild.

Environmental campaigners are calling for a ban on the herbicide, amid concerns about human health.

'Environmental costs'

According to the study, the chemical can turn male tadpoles into hermaphrodites - frogs with both male and female sexual characteristics.

In adult males, the herbicide lowers levels of the sex hormone testosterone to below that of female frogs.

Frogs are changing colour and possibly sex

Dr Hayes says atrazine can be present in the environment at similar levels to those tested in the lab.

This suggests that frogs and other amphibian species exposed to atrazine in the wild could be at risk of impaired sexual development, he says.

"Atrazine is obviously affecting frogs," said Dr Hayes. "We have shown serious effects on their sexual development. We need to ask the questions, 'What are the environmental costs of using atrazine? What diversity have we lost?'"

'Serious concerns'

Atrazine is sprayed on corn (maize), soybeans and other crops - but it can run off into ponds where amphibians swim and breed.

Environmental groups have expressed concern that the herbicide is seeping into drinking water. They claim it may have implications for human health.

Even more alarming is the potential for these products to affect human health

Sandra Bell, Friends of the Earth

Friends of the Earth described the research, published in a leading scientific journal, the Proceedings of the National Academy of Sciences, as "alarming".

"Atrazine is just one of a long list of pesticides thought to have hormone disrupting effects and many of these turn up in our food as residues," pesticides campaigner Sandra Bell told BBC News Online.

"'Gender bending' effects on fish and frogs raise serious concerns about the impact such chemicals are having on our wildlife, especially as the effects were found at such low levels.

"But even more alarming is the potential for these products to affect human health."

Contradictory results

Atrazine is the most commonly used herbicide in the US and probably the world.

It has been in use in about 80 countries for 40 years. More recently, it has been banned in several countries, including France, Germany, Italy, Sweden and Norway. The weedkiller is still on sale in the UK.

Agrochemicals giant Syngenta, the main manufacturer of atrazine, said it had commissioned a panel of experts from several US universities to look at the possible effects of atrazine on frogs.

Dr Timothy Pastoor, head of global risk assessment at Syngenta, told BBC News Online they were unable to replicate Dr Hayes' work.

The panel's study would be passed to the US regulatory body, the Environmental Protection Agency, he added.