Hope Not Hype - Third World Network

Pesticides
69
Preparations of B. thuringiensis have been used as insecticides for many years. In
general, Bt is considered far more benign to humans than chemical insecticides. However,
this confidence does not extend automatically to the cry toxin proteins when they are
expressed in plants for several reasons.
First, it is reasonably clear that Bt sprays do cause allergic symptoms, as detailed at the
beginning of this case study. Expert advisers to the [US Environmental Protection Agency]
EPA told the Agency that more studies are needed to determine the allergenic risk posed by
Cry proteins in general – whether from Bt sprays or crops. Secondly, there is likely much
greater chronic exposure to Cry proteins in Bt crops than in sprays. Cry proteins in Bt sprays
break down within several days to two weeks upon exposure to UV light, while this is obviously
not the case with Bt crops, which produce the toxin internally in grains and other plant tissues.
Thirdly, Bt sprays are composed primarily of endotoxins in an inactive crystalline form. They
are only toxic to insects with alkaline gut conditions that permit solubilization of the crystal
to the protoxin, followed by proteolytic cleavage to the active toxin. Bt crops, on the other
hand, are generally engineered to produce the Bt toxin (e.g. Bt11), which is active without
processing, or a somewhat larger fragment (e.g. MON810). There is also evidence indicating
that Cry toxins are more immunoreactive than Cry protoxins. Finally, the trend to increased
Cry protein expression fostered by the EPA’s “high-dose” strategy to slow development of
pest resistance to Bt crops may result in an increase in consumers’ dietary exposure to Bt
proteins…Thus, even if one ignores the evidence of allergenicity and concedes that Bt sprays
have a history of safe use, this is clearly not adequate grounds on which to judge Bt crops and
their incorporated plant pesticides as safe (Freese and Schubert, 2004, pp. 312-313).
In addition, proteins are modified differently in plants and this kind of modification
creates the potential for new activities or the potential for a protein to become an allergen
(Heinemann, 2007). Finally, the concentration and context of the Cry toxin proteins in
food plants subjects humans to new ways of exposure which never materialized when
these proteins were only in bacteria (Appendix Three).
A whole-plant study, which was not conducted with GM-Maize MON810, would also consider
other important exposure routes that have been previously dismissed by GMO panel (inhalation
of pollen as well as dust e.g. during handling and processing of the plants). GM crops may,
however, exhibit allergenic activity also via other routes, particularly in case of large scale
cultivation and processing. For example, pollens represent much more potent and frequent
allergen sources than plant-derived food and it should, therefore, be considered that GM
crops may also release allergens via pollen production and hence cause respiratory sensitization.
Furthermore, processing of maize may lead to respiratory sensitization in bakers who are
exposed to flour. In this context it has been reported that soybean dust caused severe outbreaks
of asthma in Barcelona, Spain when the soybeans were unloaded in the city harbour (Dolezel
et al., 2006, p. 39).
In summary, there is conflicting data on environmental harms and benefits of GM
insecticidal crops in the sense that measured benefits are crop type- and environment-