October 30, 1998
Pesticides and Amphibians
Strong evidence is emerging that reproduction and development
in aquatic animals is threatened by pesticides. A new study,
released jointly by researchers at the Canadian Wildlife
Service, the Redpath Museum at McGill University, and the
Ontario Veterinary College explores this connection further.
The researchers surveyed frog and toad populations in
agricultural areas in the St. Lawrence Valley, Canada, for
developmental defects such as limb deformities. They
compared amphibians that live in agricultural areas where
pesticides are applied regularly to those that live in areas
where little pesticide use has occurred. Many frogs had extra
legs growing from their stomachs and backs; other frogs had
only stumps for hind legs or fused hind legs. Some frogs were
missing eyes or had extra eyes; others were missing toes or
had extra ones. The scientists examined some frogs for
internal effects and found enlarged and diseased livers, as
well as female organs inside frogs that otherwise appeared to
be male.
After observing nearly 30,000 frogs and toads, they
determined that the incidence of limb deformities in animals
undergoing metamorphosis between tadpole and frog is
7% overall in agricultural habitats, but only 1.5% in the
non-agricultural areas. The prevalence of deformed tadpole-
frogs was between zero and 67% in pesticide-contaminated
sites but only between zero and 7.7% in the control sites.
The deformity rate of adult frogs from agricultural areas was
2.6%, just slightly higher than that for unexposed population
at 1.5%. This indicates that many of the deformed tadpole-
frogs did not survive to adulthood, a fact that is likely
responsible for the overall drop in frog and toad populations
in the area. Canada has 45 frog and toad species and of these
17 are in decline, largely due to human activities that
destroy habitat or contaminate water.
One of the researchers, Dr. Martin Oulette, is convinced that
the damage is due to pesticides. On a farm near St. Charles
in the St. Lawrence Valley, every frog he found was deformed.
"We have to know why the frogs are deformed and why they are
dying," says Oulette. "We're also living in the St. Lawrence
Valley and we put the food coming from there on our tables."
Researchers have been investigating deformities in amphibians
for a number of years. In 1994, Florida alligators were shown
to have been feminized by endocrine-disrupting pesticides
that interfere with normal development. In many species,
including amphibians, fish and humans, the endocrine and
thyroid hormones control the process of development. Exposure
to hormone-mimicking substances such as many commonly used
pesticides results in interrupted development, as in the case
of the Florida alligators, where the incidence of deformed
reproductive organs was extremely high due to exposure to the
pesticide dicofol. Because amphibians live in the water, it
is clear that they are the "front line" when it comes to
exposures.
More needs to be known about endocrine-disrupting substances
before we can fully evaluate their potential for
environmental damage. Scientists already suspect a link
between endocrine disruptors such as PCBs and declining sperm
counts, testicular cancer and genital defects in human males.
The World Wildlife Fund recently published a paper entitled
"Chemicals the Compromise Life: A Call to Action"
highlighting work on endocrine-disrupting chemicals that has
taken place since the "Our Stolen Future" was published in
1996 (see PANUPS Resource Pointer #184).
A comprehensive list of the chemicals that are responsible
for these problems is not yet available nor is there adequate
information about the specific effects of these chemicals on
different species. Based on the recommendations of the
Endocrine Disruptor Screening and Testing Advisory Committee
(EDSTAC) released in September 1998, the U.S. Environmental
Protection Agency is implementing an extensive testing
program to screen approximately 62,000 chemicals for their
endocrine-disrupting potential by the year 2000. The two-
tiered screening plan gives high priority to chemicals with
widespread exposure at the national level, as well as
those that cause high exposures in certain groups,communities
or ecosystems.
Sources: Martin Ouellet, et al., "Developmental abnormalities
in free-living anurans from agricultural habitats," Canadian
Wildlife Service, October 1998;
http://www.qc.ec.gc.ca/faune/faune/html/malformations_e.html.
The Ottawa Citizen Special Report: Science and the
Environment, Donna Jacobs, September 27, 1998.
U.S. Environmental Protection Agency EDSTAC recommendations:
http://www.epa.gov/opptintr/opptendo/.
Contact: PANNA.
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Fax (415) 981-1991
Email: panna@panna.org
web site www.panna.org/panna/
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