Title: Herbicide threatens frog masculinity

[The Age, March 3, 2010 - By David Fahrenthold] MALE frogs exposed to the herbicide atrazine - commonly found in US rivers and streams - can make a startling developmental U-turn, turning female so completely that they can mate and lay viable eggs. A study will focus new attention on concerns about atrazine, which is applied to an estimated 75 per cent of American maize fields. Its manufacturer, Swiss agricultural giant Syngenta, says the product is safe for wildlife, and for people exposed to small amounts of it in drinking water.

But in recent years, some studies have seemed to show that atrazine can drive natural hormone systems haywire in fish, birds, rats and frogs. In some cases, male animals exposed to the chemical developed female characteristics.

The study which made this finding was led by Tyrone Hayes, a professor at the University of California, and published in the Proceedings of the National Academy of Sciences. It showed an even starker transformation: Among a group of male African clawed frogs raised in water tainted with atrazine, he said, a fraction grew up to look and act like females.

''Ten per cent of the chromosomal males become completely, functionally female,'' Professor Hayes said. ''They can lay eggs [and] mate with other males.'' Offspring of those unions survived, he said, but were all male, since both parents were genetically male. No female frogs were treated with atrazine in the study.

The other 90 per cent of the exposed frogs retained some male features, he said, but often showed signs of ''feminisation'', including lower testosterone levels and fertility.

When pitted against males that had not been exposed to atrazine, the atrazine-treated males frequently lost out in competition for female frogs.

Professor Hayes said the reason for these changes could be that atrazine, when absorbed through a frog's skin, helps produce an enzyme that converts an unusual amount of testosterone into estrogen. Those high estrogen levels could then trigger developmental changes.

Professor Hayes, who has written several previous papers examining atrazine's effects on wildlife, said the findings should raise alarms about human health.

''It's a chemical … that causes hormone havoc,'' he said. ''You need to look at things that are affecting wildlife and realise that, biologically, we're not that different.''

Those findings contradict a US Environmental Protection Agency's pronouncement in 2007 that atrazine causes no problems in amphibian development.

In a telephone interview on Monday, Syngenta's principal scientist said the EPA's conclusion should settle concerns about the product.

WASHINGTON POST



From http://www.theage.com.au, see original source.



Article: WeedsNews319 (permalink)
Categories: :WeedsNews:herbicides
Date: 3 March 2010; 11:55:16 AM AEDT

Author Name: David Low
Author ID: adminDavid