Pesticides Causing Sex Changes in Frogs

>From Grist Magazine <www.grist.org> March 2, 2005

SEX AND THE SINGLE FROG
High rate of frog hermaphroditism linked to pesticides

An examination of the sex organs of cricket frogs collected in
Illinois between 1852 and 2001 is presumably its own reward.
However, in this case it's also led researchers to a notable
conclusion: Heavy use of chemicals such as DDT and PCBs may cause
higher rates of hermaphroditism in frogs. In a study published in
the journal Environmental Health Perspectives, scientists noted that
the number of cricket frogs born with both male and female sex organs
was highest during the 1950s when the chemicals were used most
heavily, before being outlawed in the U.S. In the 1960s, the
once-abundant cricket frogs quickly dropped in number, presumably
because the chemicals affected female hormone production, leading to
an unhealthy male/female ratio and eventually a population crash.
The research also suggested that atrazine, the most popular herbicide
in use today, may be causing similar effects. Val Beasley, coauthor
of the study, says it's hard to determine how serious the current
problem is "because you can't collect where the intersex rate was
high. There aren't any frogs left in those areas to collect."

straight to the source: Los Angeles Times, Marla Cone, 02 Mar 2005
<http://grist.org/cgi-bin/forward.pl?forward_id=4454>
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www.latimes.com/news/printedition/asection/la-na-frogs2mar02,1,6895430.story
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THE NATION

Hermaphrodite Frogs Linked to Pesticide Use

Study finds more sex organ abnormalities in 1950s, when chemicals were more
widespread.
By Marla Cone
Times Staff Writer

March 2, 2005

Scientists who compared frogs collected over the last 150 years have
discovered a dramatic increase in hermaphrodites during the times when
contamination from the pesticide DDT and other chlorinated compounds was
widespread.

Frogs with both male and female reproductive organs were rare in the 19th
and early 20th centuries but more common during the 1950s, when the largest
volumes of the chemicals were used.

The findings, reported Tuesday in the journal Environmental Health
Perspectives, add to the growing evidence that an array of pesticides and
industrial chemicals can alter the sex hormones of animals.

The ability of certain chemicals to mimic or block estrogen and
testosterone, which are key in sexual organ development and reproduction, is
considered one of the most disturbing discoveries in environmental science
of the last decade.

Scientists suspect that the phenomenon has been occurring for decades but
it wasn't documented in wildlife until the early 1990s when it was first
observed in Florida alligators and then among many other species.

Toxicologists and veterinarians at the University of Illinois at
Urbana-Champaign, led by Amy Reeder, examined the reproductive organs of 814
cricket frogs collected in Illinois between 1852 and 2001 and stored at
natural history museums.

Studying endocrine disruption of animals dating back more than a century
has not commonly been done.

"It's a wonderful approach, and appropriate, because museums have this
great collection of data that goes back through time," said Louis Guillette,
a reproductive zoologist at the University of Florida and an expert on
hormone disruption. "This is a very, very important study that suggests to
us that some of the things we're seeing, even today, in frog populations may
have a historical basis dating back to when we were using large amounts of
these compounds." Guillette, who was not involved in the study, has linked
hermaphroditic alligators to DDT.

Cricket frogs, once abundant, declined dramatically around Chicago and in
other regions in the 1960s. Scientists found that the times and places with
high rates of hermaphrodites, also called intersexes, overlapped with when
and where the frog numbers dropped in Illinois.

The scientists theorize that DDT, industrial compounds called PCBs
(polychlorinated biphenyls) and other contaminants had an antiestrogenic
effect, reducing the proportion of females and causing them to develop
abnormal sex organs, triggering a population crash, particularly in the
Chicago region.

"I'm sure it's not the only stressor that affected cricket frogs, but the
intersexes did come along and the species did disappear," said Val Beasley,
a coauthor of the study and a professor of ecotoxicology at the University
of Illinois' College of Veterinary Medicine.

Frogs and other amphibians have been vanishing worldwide over the last few
decades.

"These guys have been around a long time, since before the dinosaurs, and
they are declining all over the place," Beasley said. "Endocrine disruptors
seem to be a factor, but certainly not the only factor."

Frogs are considered key specimens for studying effects of environmental
degradation because they undergo a vulnerable time of metamorphosis and
spend most of their time in water, where pollutants accumulate.
Environmental Health Perspectives science editor Jim Burkhart said frogs
"may show the effects of ecological change more quickly or more obviously
than other species."

The new study has limitations. The team did not measure individual animals
for contaminants because archived samples could not be reliably tested. As a
result, there could be other explanations for the hermaphrodites, such as
factory and vehicle emissions or other environmental changes. Also, the
scientists could not compare frogs from the same lakes or ponds over time.

The highest rates of intersexes were found in frogs collected from 1946 to
1959, when larger volumes of DDT were used for mosquito control in Illinois.
Some frogs had complete ovaries as well as complete testes. The proportion
of females also was greatly reduced during that period. The area around
Chicago had four times more intersex cricket frogs than southern Illinois.

From 1852 to 1929, one intersex frog was found in the 84 collected. In the
1930s, the intersex rate began to increase. Between 1946 and 1959, 17 out of
153, or 11%, were intersex.

Recent rates of hermaphrodites were the lowest of any period studied except
for 1852 to 1929. Out of 339 collected from 1980 to 1996, there were nine
intersex frogs, or less than 3%. DDT and PCBs were banned in the 1970s in
the United States and although they remain in the environment, levels are
low in most areas.

But, the scientists reported, "we cannot conclude that the era of endocrine
disruption in cricket frogs has come to an end." The severity of the current
problem is unknown, Beasley said, "because you can't collect where the
inter-sex rate was high. There aren't any frogs left in those areas to
collect." Also, males still outnumber females, while it was the opposite
before 1930.

Atrazine, an herbicide widely used on corn, might also contribute to the
sex organ abnormalities and decline of the frogs, the report says. The
intersex rate in central Illinois, where atrazine is used, is twice as high
as in the southern areas, where atrazine use is low, Beasley said.

The possibility that atrazine alters hormones is controversial because it
is the most popular herbicide in use today and the U.S. Environmental
Protection Agency decided in 2003 to allow its continued use. Some studies
have found reproductive or hormonal effects from atrazine while other
studies have found no effects at levels found in the environment.

Wildlife biologists agree that environmental contaminants have altered
hormones of wild animals, including polar bears in the Norwegian Arctic,
fish in the Potomac River and otters in the Columbia River.

But the experts don't agree on what doses are harmful and whether
populations have been substantially reduced. Scientists do not know if there
are human effects, although some theorize that chemicals cause reduced sperm
counts, reproductive diseases and premature puberty in girls.