31 December 2002
study finds deformed frogs
UC Berkeley prof's research links pesticide to abnormalities
T. Hall, Chronicle Science Writer
most widely used pesticide in the United States appears to be causing
developmental defects in a common Midwestern frog, according to
a new study that has sparked a high-stakes debate over a chemical
long considered environmentally safe.
by UC Berkeley biologist Tyrone B. Hayes, the study is the first
evidence from field studies to show a link between the controversial
weed killer, called atrazine, and health problems in a native species
of amphibian in the United States.
research, a summary of which appears today in the journal Nature,
is generating some fierce reactions from other scientists in the
an unusual step, scientists on an industry-financed panel assembled
to asses the latest research issued a written challenge this week
to a longer version of Hayes' study appearing in the journal Environmental
his part, Hayes said scientists who had been criticizing his work
were motivated in part by their own financial interests, because
many work as paid consultants or have had research financed by atrazine's
manufacturer, the Swiss agribusiness giant Syngenta.
say the battle may just be getting started and could seriously complicate
a federal regulatory review of atrazine's safety.
is a classic scientific debate where the stakes are kind of high,"
said Richard Wenning, senior manager at Environ, a risk-assessment
consulting firm in Emeryville that has advised the Swiss company.
"Atrazine is such a huge product. So people are shooting at
KILLER WIDELY USED
Atrazine has been used commercially in the United States since the
late 1950s. In 1999, an estimated 80 million pounds were applied
to U.S. corn and soybean crops, as well as golf courses, orchards
long line of research suggests the chemical breaks down quickly
in the environment and posed no particular danger, when used properly,
to humans or animal health. Now, environmentalists are questioning
the consensus view that atrazine is safe. The U.S. Environmental
Protection Agency is reviewing the technical and regulatory issues.
an associate professor of integrative biology at UC Berkeley, first
gained wide attention in April when he reported laboratory findings
that atrazine could disrupt hormones and alter the sexual traits
of certain male frogs.
that evidence, Hayes said the popular farm chemical might be causing
some of the widely observed declines in U.S. amphibian populations.
But other scientists noted that Hayes had only looked at one species
of African clawed frog, which is not native to North America.
the latest study, Hayes and colleagues went out into the field.
They drew a straight line on the map from Iowa to Utah, sampling
for atrazine levels in the environment and testing native leopard
frogs (Rana pipiens) taken from eight locations along the line.
researchers say they found high numbers of feminized male frogs
in watersheds even lightly contaminated with atrazine. In the most
extreme case, 92 percent of the male frogs had abnormal gonads in
water with just 0.1 part per billion of the farm chemical. The EPA
allows 3 parts per billion in drinking water.
speculates that lower doses of the chemical may actually be more
harmful than higher doses. Heavy exposures may trigger biological
defenses, he said, that allow the frogs to adapt, and in some cases
thrive in watersheds contaminated with concentrated farm runoff.
makes it difficult to find a conclusive cause-and-effect pattern
in Hayes' data. Other scientists appear to be having difficulties
replicating the Berkeley scientist's experiments.
Some independent experts say Hayes deserves credit for pioneering
research into the role of chemicals in aquatic environments -- even
though his studies leave many important questions unanswered.
example, natural hermaphrodites have been identified in some species
of amphibians as early as the 1920s, decades before atrazine was
introduced. And there is no clear evidence yet to show that the
defects Hayes reported cause reproduction problems and population
are preliminary papers that are setting the tone for other studies,"
said Andrew Blaustein, an ecologist at Oregon State University.
"This is a wake-up call, one of the early wake-up calls. But
his experiments are very well done and backed up with really good
field survey data."
biologist James A. Carr of Texas Tech University in Lubbock, Texas,
and others on the industry-financed panel raised "serious concerns"
about the Hayes study design and conclusions, including flawed statistical
analysis and "major inconsistencies in the data."
for comment on the latest study, a Syngenta spokeswoman said, "We
concur with the panel's opinions."
EPA official, who spoke on condition of anonymity, said the Hayes
study was being examined along with continuing, mostly unpublished
research at eight other universities. A special EPA science advisory
panel is being convened sometime next year to examine all the evidence.
in the middle of it," the EPA official said. "The Hayes
study isn't the only thing we are looking at."
Carl T. Hall at email@example.com.