PLANTS: How much Bt toxin do genetically engineered MON810 maizeplants actually produce?
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------------------------------- GENET-news -------------------------------
TITLE: How much Bt toxin do genetically engineered MON810 maize plants
actually produce? - Executive Summary
SOURCE: Greenpeace Germany
AUTHOR: Antje Lorch & Christoph Then
How much Bt toxin do genetically engineered MON810 maize plants actually
Bt concentration in field plants from Germany and Spain
In the growing season 2006, Greenpeace took leaf samples of commercially
cultivated MON810 maize plants in Germany and Spain to determine the Bt
toxin (Cry1Ab) concentration. A total of 619 samples from 12 fields were
analysed using ELISA tests.
MON810 maize is genetically engineered to produce a modified insecticide
(Cry1Ab) that naturally occurs in the soil bacterium Bacillus
thuringiensis (Bt). The production of this toxin is supposed to protect
the maize plants from European corn borer larvae (ECB, Ostrinia nubilalis).
This Greenpeace study shows a surprising pattern of plants that
contained only very low Bt toxin levels. However, high levels could be
observed in some plants. The variation found on the same field on the
same day was considerable, and could differ by a factor of as much as
100. This is in agreement with the results of a new study published in
April 2007 that concludes that "the monitoring of Cry1Ab expression [of
MON810 plants] showed that the Cry1Ab concentrations varied strongly
between different plant individuals."
In total, the Bt concentrations were much lower than those available
from Monsanto for cultivation approval in the US and the EU, with a
arithmetic mean of 9.35 ?g Bt/ g fresh weight (fw; standard deviation
1.03; range 7.93-10.34 ?g Bt/g fw). Here, our data also corroborate the
results of Nguyen & Jehle (2007), who also found lower Bt concentrations
(with means between 2.4 and 6.4 ?g Bt/g fw) than those known from the
literature. The data recorded by Greenpeace, however, deviate even more
from the data published so far. The means ranged from 0.5 to 2.2 ?g Bt/g
fw, while Bt concentrations ranged from a minimum of no or 0.1 ?g Bt/g
fw to concentrations of about 14.8 ?g Bt/g fw.
The results presented here raise far-reaching questions about the safety
and the technical quality of the MON810 plants as well as some
fundamental methodological questions.
1. The variation of Bt concentrations
Since the Bt concentration on the field can vary greatly even between
neighbouring plants, the MON810 plants do not appear to be sufficiently
stable in their biological traits. The reasons for the high variation in
Bt contents could be related to genetic or environmental factors (e.g.
weather or soil conditions), or both. Nguyen & Jehle (2007) not only
found high variation between plants on a field, but also statistically
significant differences between different locations in Germany. Since
the reasons for such differences and the range of variation cannot be
identified, the commercial cultivation of the crops should be stopped to
avoid interactions with the environment that could lead to adverse and
To investigate these questions further, studies should be conducted
under contained conditions (such as glasshouse experiments) to study the
environmental effects (e.g. drought, moisture, temperature, soil,
nutrients) on the plants. Next to no studies of this type have yet been
2. The risk assessment of the plants
Risk assessment studies with non-target organisms or feeding studies in
which the actual Bt concentration has not been determined appear to be
of little use. Studies in which the toxin concentration is unknown
cannot be used to give approval for the commercial growing of these plants.
3. The actual Bt toxin concentrations
If the Bt toxin in GE Bt plants were more effective in considerably
lower concentrations than previously described, this would not be
identical with the naturally occurring Bt toxin. This would annul a
central aspect of the EU cultivation approval, which is based on the
assumption that the Bt toxin in plants could in general be equated with
the natural Bt protein from soil bacteria.
However, if the toxin is not effective in such low concentrations as we
have recorded, then serious concerns about the effectiveness of the
plants in controlling ECB larvae need to be raised.
Additional problems would then also concern insect resistance
management, as resistance development could be accelerated by sub-lethal
4. The methods for determining Bt concentrations
The methods used by Monsanto to determine the Bt concentration of their
original MON810 plants are not available from the publicly available
documents. In order to make a reliable comparison of new data with
Monsanto's data, it is essential that the test protocols as well as the
original data are published. All interested laboratories need
unrestricted access to relevant sample material. The authorities need to
define standardised and sufficiently reliable methods for determining Bt
concentrations in plants for risk assessment studies and for post-market
Until the open questions regarding risk assessment, monitoring and
product quality have been satisfactorily answered, the commercial
cultivation of MON810 needs to be stopped, because the legal basis for
approving MON810 for cultivation has not been fulfilled.
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