Atrazine--Environmental Toxicology of a Common Herbicide
rellim at tulane.edu
Wed Apr 17 13:52:55 EST 2002
April 17, 2002 NY Times Science Section
Weed Killer Deforms Sex Organs in Frogs, Study Finds
By THE ASSOCIATED PRESS
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.
More information about the Toxicol