Atrazine--Environmental Toxicology of a Common Herbicide

Chuck Miller rellim at
Wed Apr 17 13:52:55 EST 2002

April 17, 2002  NY Times  Science Section

Weed Killer Deforms Sex Organs in Frogs, Study Finds


WASHINGTON, April 16 (AP) ‹ Male frogs exposed to very low doses of a common
weed killer can develop multiple sex organs, sometimes both male and female,
researchers in California have discovered.

The weed killer, atrazine, is the most commonly used one in North America
and can be found in rainwater, snow runoff and ground water, said Tyrone B.
Hayes of the University of California, who led the research.

"There is virtually no atrazine-free environment," Dr. Hayes said.

The Environmental Protection Agency permits up to three parts per billion of
atrazine in drinking water.

The University of California team found it affected frogs at doses as small
as 0.1 part per billion. As the amount of atrazine increased, as many as 20
percent of frogs exposed during their early development produced multiple
sex organs or had both male and female organs. Many had small, feminized

The research is reported today in The Proceedings of the National Academy of

Asked if atrazine might be a threat to people at low levels, Dr. Hayes said
he did not know, adding that, unlike frogs, "we're not in the water all the

"I'm not saying it's safe for humans," he said. "I'm not saying its unsafe
for humans. All I'm saying is it that it makes hermaphrodites of frogs."

Dr. Hayes's research team concluded that atrazine caused frog cells to
produce the enzyme aromatase, which is present in vertebrates and converts
the male hormone testosterone to the female hormone estrogen.

The effects on frogs in Dr. Hayes's study occurred at exposure levels
smaller than a 600th of the dose that induced aromatase production in human

Stanley I. Dodson of the University of Wisconsin called the work "the most
important paper in environmental toxicology in decades."

Asked if people should be worried, Dr. Dodson said, "We don't know," but he
added, "It's like a canary in the mine shaft sort of thing."

In his research, he said, he found that low exposures atrazine changes the
ratio of males to females among water fleas.

Besides atrazine's effects on developing frogs, the California researchers
found that testosterone levels in mature male frogs exposed to atrazine
decreased to the levels in female frogs.


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