Bt corn May Harm Stream
October 10, 2007
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.
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.
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.
accumulations of debris from corn plants found in headwater streams
during floods in the U.S. corn belt. If such debris comes from corn that
has been genetically modified to contain insecticidal toxins (known as
Bt corn), it may harm stream organisms that consume it.
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:
- 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.
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,"
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."
typical headwater stream running through a corn field shown during
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
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