Studies Conflict on Common Herbicide's Effects on Frogs -NY Times Science
By CAROL KAESUK YOON
Despite the release of a flurry of new results in what is becoming an
increasingly intense debate, scientists still have not reached a consensus
as to whether the nation's most commonly used herbicide is harming
amphibians in the wild.
The new studies raise questions about whether atrazine, used primarily for
killing weeds in cornfields, is acting as an endocrine disrupter in
amphibians, interfering with normal hormonal functions, and causing males to
become hermaphrodites, producing eggs in their testes. Some 60 million to 70
million pounds of atrazine are applied each year in the United States, and
it has been found in rivers, ponds, snowmelt and rainwater.
Scientists have taken a particular interest in the new studies because such
a widespread endocrine disrupter could help explain worldwide declines of
The studies could also affect continued use of atrazine. The Environmental
Protection Agency is reviewing the herbicide's environmental risks as part
of the periodic reregistration process required for continued sale of such
Much of the newest research was presented yesterday at the Society of
Environmental Toxicology and Chemistry in Salt Lake City.
The controversy began in April when Dr. Tyrone Hayes, an endocrinologist at
the University of California at Berkeley, and colleagues published results
in The Proceedings of the National Academy of Sciences indicating that very
low concentrations of atrazine, similar to those seen in the wild, could
turn males of the African clawed frog into hermaphrodites in the laboratory.
Then last month in Nature, Dr. Hayes and colleagues published studies
showing that males of the leopard frog, a native species, could also be
feminized by exposure to low levels of atrazine in the laboratory. More
worrisome, the researchers found that in the seven field sites from Utah to
Iowa where they could detect atrazine, they also found hermaphroditic frogs.
At the one site without detectable atrazine, there were no hermaphrodites.
Two industry-sponsored studies, carried out by a team that has been critical
of Dr. Hayes's work, have failed to replicate the findings with the clawed
frog. The work was paid for by Syngenta, a maker of atrazine. Yesterday the
team also reported that it had examined wild-caught males of the clawed frog
where it is native in Africa and where atrazine is widely used and found no
"Validated information should be replicable," said Dr. Ronald Kendall, an
environmental toxicologist at Texas Tech University and a leader of the
Dr. Hayes said he was surprised by the high levels of hermaphroditism caused
by sometimes minute levels of atrazine, with sometimes as many as one-third
of the males affected. The effects were less severe at higher levels of the
herbicide. But while that might seem counterintuitive, Dr. Hayes said it was
typical for chemicals affecting hormones to have highly different, even
opposite effects at increased levels.
Dr. Kendall said his team's work had been wrongly impugned as biased because
of its industry financing, and he pointed out that Dr. Hayes also formerly
received Syngenta financing. Dr. Hayes said his original research showing
that atrazine could create hermaphroditic frogs was sponsored by Syngenta,
which never published the work. The April publication in which he replicated
that research was sponsored by the National Science Foundation; the Nature
study was paid for by the W. Alton Jones Foundation, which finances
environmental work, and the conservation group WWF.
It remains unclear why the studies conflict.
Dr. Hayes, when interviewed, had seen only one of the Kendall team's
unpublished studies. Based on the methods, Dr. Hayes said he was not
surprised they had not replicated his results. He said that the researchers
had raised the frogs under unhealthy conditions and that they did not
properly control levels of atrazine in the frogs' water.
"Even if their animals were healthy, you can't compare them to our study,"
But Dr. Jim Carr, comparative endocrinologist at Texas Tech and a member of
Dr. Kendall's team, said that in another study team members had mimicked Dr.
Hayes's experimental conditions more closely but still did not produce his
results. Dr. Carr and colleagues have also criticized Dr. Hayes's omission
of certain experiments considered standard.
"There are not a lot of details published in the Hayes work," said Dr. Carr.
"So it's hard to compare."