FOOD
SAFETY ASSESSMENT AND STARLINK CORN
Many controversies exist over
the use of genetically modified crops. The first point to make is that all
crops have been genetically modified in some way. Even the oldest variety of
edible corn bears no resemblance to its ancestor, teosinte. These changes have
occurred through cross-pollination and selective breeding. Thus, using the term
transgenic crop instead of genetically modified crop is more
accurate.
A main concern with
transgenic crops is the health issue. Does the transgenic crop include toxins
or allergens, change the nutrient level of the food, or promote antibiotic
resistance in humans or cattle? The spread of antibiotic resistance due to
reporter genes or selective markers is no longer an issue because new
transgenic varieties no longer contain these marker genes. The nutrient level
of transgenic food is strictly controlled and evaluated before any transgenic
crop is released to the public.
The allergenic potential of
transgenic crops has caused much controversy. In 2000, an unapproved transgenic
corn called Starlink was detected in
taco shells found in the grocery store. Starlink corn has two transgenes. One
makes it resistant to the European corn borer by encoding the toxin from Bacillus thuringiensis (see earlier
discussion). This Bt transgene is the Cry9C isoform. The second transgene, from
Streptomyces hygroscopicus, makes the
corn resistant to a commonly used broad-spectrum herbicide.
The Cry9C isoform of Bt toxin
is much more resistant to stomach acid. Also, after cooking and processing,
Starlink corn had a higher concentration of Cry9C protein than expected,
suggesting that this protein is more stable than other isoforms of Bt toxin.
(In contrast, cooking, processing, and digestive enzymes readily break down the
Cry1A isoform of Bt toxin.) Because the findings for Cry9C protein came from
only one study, the EPA demanded more tests to ensure that it would not cause
an allergic reaction if consumed by the public. The companies that developed
Starlink corn pushed the EPA for some sort of approval. The EPA responded by
giving split approval—that is, Starlink corn could be grown, as long as it was
only used to feed livestock. What the EPA failed to realize is that after corn
is grown, it is hauled to the nearest grain elevator. The corn is then mixed
with all the other corn in the region and shipped to processing centers. So the
company and farmers were following the EPA guidelines in good faith, but the
next step in the process made it impossible to keep the Starlink corn separate
from all the other varieties.
In September of 2000, a
coalition of groups opposed to genetically modified foods announced they had
detected traces of Starlink in taco shells. Further studies confirmed this and
all the products were taken off the shelves. The Centers for Disease Control
(CDC) examined all the people who complained of an allergic reaction to the
contaminated taco shells. They first determined the type of antibody that the
body would produce in response to Cry9C protein. Next they took blood samples
and coded them. The blood samples were examined for the presence of Cry9C
antibodies by both the CDC and an outside lab. Both concluded that none of the
samples contained antibodies to Cry9C. This suggested that any allergic
reactions were to some other component in the meals eaten.
After this, the company
offered to buy back all remaining Starlink corn, providing the farmer with a
premium price, so that no more food became contaminated. In addition, all
Starlink seed was pulled from the market to prevent its future growth. In all,
Starlink was on the market for only 2 years, 1999 and 2000. In 1999, the amount
of Starlink grown in the United States represented only 0.4% of the corn crop
and in 2000, 0.5%. Because this was such a small percentage of the overall
crop, the Cry9C in the taco shells was massively diluted by other varieties of
corn. Starlink is no longer grown anywhere in the world, and the EPA has
revoked all approval.
Assaying allergic potential
is critical to development of transgenic crops. In another example, soybean
plants were transformed with a gene from the Brazil nut. The gene was intended
to increase the methionine content of soybeans, which would improve them as
cattle feed. Because many people are allergic to Brazil nuts, the FDA ordered
tests for allergenicity by skin prick tests and immunoassays. This transgene
was found to cause allergic reactions. The work was discontinued, and none of
the transgenic plants were ever released to the public.
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