Washington, DC
October 9, 2007
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Genetically
modified corn, commonly called Bt corn, is
engineered to kill pests such as the European
corn borer. However, a new study shows that Bt
corn may also harm the caddisfly, which serves
as food for fish and amphibians. The new study
also shows that parts of Bt corn, such as
leaves, cobs and pollen, can travel as far as
2000 meters away from source areas--a phenomenon
that was not considered when Bt corn was
licensed.
Credit: Zina Deretsky, National Science
Foundation |
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Source:
Source:
The National Science Foundation
Ecological impacts of
genetically engineered corn are particularly important because
of increased corn demand created by biofuels production
A new study* indicates that a popular type of genetically
engineered corn--called Bt corn--may damage the ecology of
streams draining Bt corn fields in ways that have not been
previously considered by regulators. The study, which was funded
by the National Science Foundation,
appears in the Oct. 8 edition of
The Proceedings of the National Academy of Sciences.
This study provides the first evidence that toxins from Bt corn
may travel long distances in streams and may harm stream insects
that serve as food for fish. These results compound concerns
about the ecological impacts of Bt corn raised by previous
studies showing that corn-grown toxins harm beneficial insects
living in the soil.
Licensed for use in 1996, Bt corn is engineered to produce a
toxin that protects against pests, particularly the European
corn borer. Bt corn now accounts for approximately 35 percent of
corn acreage in the U.S., and its use is increasing.
"As part of the licensing process for genetically modified
crops, the U.S. Environmental Protection Agency (EPA) was
responsible for testing and identifying potential environmental
consequences from the planting of Bt corn," says Jennifer Tank,
who is from the University of Notre Dame and is a member of the
team studying Bt corn.
To fulfill this requirement, EPA completed studies that assumed
that plant parts would remain in fields without being carried
away by streams draining agricultural lands, says Tank. In
addition, EPA only tested the impacts of Bt corn on small lake
organisms that are typically used to test the impacts of
chemicals on aquatic ecosystems.
The agency did not evaluate the impacts of Bt corn on organisms
that live in streams--even though Midwest agricultural lands
where Bt corn is grown are heavily intersected by streams
draining the landscape. But despite the limitations of its
tests, EPA concluded that Bt corn "is not likely to have any
measurable effects on aquatic invertebrates."
To more comprehensively evaluate the ecological impacts of Bt
corn than did the EPA, the research team did the following:
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Measured the
entry of Bt plant parts--including pollen, leaves and
cobs--in 12 streams in a heavily farmed Indiana region. The
research team's results demonstrate that these plant parts
are washing into local steams. Moreover, during storms,
these plant parts are carried long distances and therefore
could have ecological impacts on downstream water bodies,
such as lakes and large rivers.
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Collected
field data indicating that Bt corn pollen is being eaten by
caddisflies, which are close genetic relatives of the
targeted Bt pests. Todd V. Royer, a member of the research
team from Indiana University, says that caddisflies "provide
a food resource for higher organisms like fish and
amphibians."
-
Conducted
laboratory tests showing that consumption of Bt corn
byproducts increased the mortality and reduced the growth of
caddisflies. Together with field data indicating that the
caddisflies are eating Bt corn pollen, these results
"suggest that the toxin in Bt corn pollen and detritus can
affect species of insects other than the targeted pest,"
Tank said.
Royer says that "if our goal is to
have healthy, functioning ecosystems, we need to protect all the
parts. Water resources are something we depend on greatly."
"Overall, our study points to the potential for unintended and
unexpected consequences from the widespread planting of
genetically engineered crops," Tank said. "The exact extent to
which aquatic ecosystems are, or will be, impacted is still
unknown and likely will depend on a variety of factors, such as
current ecological conditions, agricultural practices and
climate/weather patterns."
James Raich, a National Science Foundation program director,
adds that "increased use of corn for ethanol is leading to
increased demand for corn and increased acreage in corn
production. Previous concerns about the nutrient enrichment of
streams that accompany mechanized row-crop agriculture are now
compounded by toxic corn byproducts that enter our streams and
fisheries, and do additional harm."
The Bt corn researchers stress that their study should not be
viewed as an indictment of farmers."We do not imply that farmers
are somehow to blame for planting Bt corn, nor are they
responsible for any unintended ecological consequences from Bt
corn byproducts," Tank said. "Farmers are, to a large extent,
required to use the latest technological advances in order to
stay competitive and profitable in the current agro-industrial
system."
* Toxins in transgenic crop
byproducts may affect headwater stream ecosystems
E. J. Rosi-Marshall, J. L. Tank, T. V. Royer, M. R. Whiles, M.
Evans-White, C. Chambers, N. A. Griffiths, J. Pokelsek, and M.
L. Stephen
ABSTRACT
Corn (Zea mays L.) that has been genetically engineered to
produce the Cry1Ab protein (Bt corn) is resistant to
lepidopteran pests. Bt corn is widely planted in the midwestern
United States, often adjacent to headwater streams. We show that
corn byproducts, such as pollen and detritus, enter headwater
streams and are subject to storage, consumption, and transport
to downstream water bodies. Laboratory feeding trials showed
that consumption of Bt corn byproducts reduced growth and
increased mortality of nontarget stream insects. Stream insects
are important prey for aquatic and riparian predators, and
widespread planting of Bt crops has unexpected ecosystem-scale
consequences.
http://www.pnas.org/cgi/content/abstract/0707177104v2?etoc |
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