How Much Bt Toxin Do Genetically Engineered MON810 Maize Plants Actually Produce?
By Antje Lorch & Christoph Then
May 11, 2007
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 unpredictable effects.
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 published.
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 toxin doses.
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 monitoring.
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.