"The variations are within a biologically explainable range."
The Bt concentration in insect-resistant maize is not the same in every plant. Greenpeace has carried out measurements to check this and found that the Bt levels varied considerably. Greenpeace claims that the legal basis for the EU approval has not been fulfilled. Johannes Jehle of the Dienstleistungszentrum ländlicher Raum (DLR) in Neustadt an der Weinstrasse does not agree with either the results or the conclusions of the study. He led a three-year research project in which Bt levels in genetically modified MON810 maize were measured. GMO Safety asked him about it.
When genetically modified Bt maize is grown, not all plants produce exactly the same amount of the Bt toxin , a substance that is effective against pests. Like most plant substances, the Bt concentration is subject to certain natural variations. This has been known for a long time. Yet last year Greenpeace took a total of 600 leaf samples from several fields of MON810 Bt maize in Germany and Spain and asked a laboratory in Switzerland (Ecostrat) to examine the Bt concentrations in them.
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Greenpeace presented the results publicly on 11 May 2007. They claim that the Bt content varies by a factor of as much as a 100 between individual plants. Although even Greenpeace had to admit that the levels of Bt in the leaves were "surprisingly low" and considerably lower than the value given by Monsanto in the approval documentation. But since the "reasons for such differences and the range of variation cannot be identified", Greenpeace concludes from its research that “the commercial cultivation of the crops should be stopped.” A project funded as part of the biological safety research programme of the Federal Ministry of Education and Research (BMBF) also dealt in depth with the measurement of Bt levels in MON810. In April 2007 Johannes Jehle and Hang Thu Nguyen of the DLR in Neustand/Weinstrasse published their results in a scientific journal. GMO Safety: In the BMBF-funded safety research project you also found significant variations in the Bt toxin concentrations in the plants. What do you believe was the cause of the variations? Johannes Jehle: We were able to demonstrate that Bt expression varies depending on the plant organ under investigation, the stage of development, the location and therefore the weather. Many of these differences are statistically significant. In addition, varietal variations cannot be ruled out, although this is not something we examined. |
GMO Safety: In the Greenpeace study they found variations of between 0.1 and 10 µg/g fresh weight in some cases (factor of 100). Were the variations you found equally great? Do you view such variation ranges as agronomically significant?
Johannes Jehle: In our three years of measurements, the maximum variation range (ratio of maximum expression to minimum expression depending on the development stage) was a factor of between 3 and 5; in extreme cases as much as 14. However, the variation coefficients derived from the ratio of standard deviation to mean value are far more meaningful than a comparison of these extreme values. The variation coefficients in our investigations were between 20 and 60 per cent. In the Greenpeace study they were over 200% in some cases. This means that over a period of three years with extreme weather differences, the variations we measured were 3-10 times smaller overall than those in the one-year Greenpeace measurements. This means that we are unable to corroborate the Greenpeace measurements with our research.
A variation range such as that measured by Greenpeace in some cases would of course have a different significance in agronomic terms than the variability we measured. In the DLR study we used a standard commercial Bt detection test that had been validated again at DLR Rheinpfalz. Greenpeace evidently used a different detection method that they had developed themselves. Because of the different measurement methods, the DLR and Greenpeace measurements are almost certainly not directly comparable.
GMO Safety: In your view, do the observed variations between plant individuals and locations present problems for the safety assessment?
Johannes Jehle: No. We saw no grounds for this based on our data, since the variations were within a natural, biologically explainable range.
GMO Safety: As with the Greenpeace study, the average values were below the Bt concentrations given by Monsanto in its application documentation. How do you explain this?
Johannes Jehle: Our measurements were on average around 30 to 40 per cent below published data from the 1990s. It would certainly be useful to have more published comparable data from other growing regions. Our work is an important step in this direction. As I mentioned, the location and stage of development are the most important factors in the level of expression, and possibly also the varietal background. Certain differences in measurements can also arise from different extraction methods and different protein detection standards. But we definitely see no direct indication of genetic instability – the variability would have to be much higher for that.
GMO Safety: What impacts could the lower Bt concentration have on the safety assessment?
Johannes Jehle: The safety assessment is not performed by us, although the responsible authorities can make use of our data. However, in terms of the Bt concentrations we observed, I see no reason to cast doubt on the safety assessment. Despite the lower Bt concentrations and the observed variations between plant individuals, our results largely corroborate the known findings of earlier studies and do not tally with the Greenpeace measurements.
GMO Safety: Thank you for talking to us!
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