Renewed conflict concerning the environmental risks of Bt maize

Bt toxin: Each maize plant is different – but is that a problem?

Genetically modified Bt maize does not contain a fixed concentration of Bt toxin. It varies depending on the plant, plant part and where it is grown. But does this imply an environmental risk? EU Commissioner for the Environment Dimas sees it as one reason for withholding approval of two Bt maize strains. And a new Greenpeace study takes the same line.

"GM maize cannot be controlled." Greenpeace did not mince its words when it presented its new report at the end of November. The environmental activists had once again commissioned the Swiss company EcoStrat to measure Bt toxin concentrations in maize plants. As with the first investigation, differences in concentration were found, although this time they were considerably smaller. EcoStrat used two different measurement methods in this latest study, and recorded different Bt values depending on which method was used. Greenpeace claims that there is "no reliable method of measurement", and that consequently a "key requirement for the risk assessment of genetically modified plants" has not been fulfilled. According to Greenpeace, the cultivation of GM maize should therefore be prohibited.

Dr Johannes A. Jehle: Agricultural Service Centre for Rhineland-Palatinate (DLR Rheinpfalz), Department of Phytomedecine, Biotechnical Plant Protection in Neustadt / Weinstrasse. His team measured the Bt toxin concentrations in maize plants as part of a research project spanning several years. Even though EU Commissioner Dimas and Greenpeace refer to his findings, he cannot understand their conclusions.

Bt maize: More Bt toxin in the leaves than in the kernels.

The recommendation of EU Commissioner for the Environment Stavros Dimas not to approve the two Bt maize strains Bt11 and 1507 for cultivation is also linked to the issue of Bt concentrations. According to Dimas’ draft resolution text, "more recent studies show a high variation of Bt toxin concentrations between individual plants in a single field, as well as statistically significant differences between different sites." Since the reasons for these differences have not been identified, Dimas maintains that "unforeseen interactions with the environment" could arise, which could have undesirable effects.

Dr Johannes Jehle from the Agricultural Service Centre for Rhineland-Palatinate (DLR Rheinpfalz)studied the Bt toxin contents of maize plants as part of a safety research project funded by the Federal Ministry of Education and Research (BMBF) and discovered that Bt expression varies depending on the plant organ under investigation, the stage of development, the location and the weather. Although many of these differences are statistically significant, in an interview with GMO Safety in May 2007 Jehle stressed that the findings cast no new doubts on the safety assessment of Bt maize (MON810). "We saw no grounds for this based on our data, since the variations were within a natural, biologically explainable range."

The interview with Jehle was brought about by the publication of the first Greenpeace study on Bt toxin concentrations in maize plants. In 2006, Greenpeace activists took samples from different fields in Germany and Spain and had them analysed. They found wide variations. However, the Greenpeace measurements were generally below the value given by the manufacturer, Monsanto, on which the ‘official’ risk assessments are based.

"There are no reliable methods of measurement."

Greenpeace has once again asked EcoStrat to examine Bt maize plants "collected" from fields in Germany by activists in June 2007. This time two different methods were used to determine the Bt toxin concentrations in the plant samples. Both methods are based on an ELISA test, in which antibodies are used to detect Bt protein. One method uses a commercially available test, whilst the other is broadly similar to the method used by Monsanto. In 1994 the company published Bt toxin values found in MON810 maize measured using this test.

The results vary depending on the method used – proof, in Greenpeace's view, that there is "no reliable method of measurement" and that the cultivation of Bt maize should therefore be prohibited. However, the findings are complex and it is not really possible to jump to conclusions.

The variation range in the EcoStrat results for the 2007 maize plants is significantly smaller than that for the 2006 maize plants. It now correlates with the variation range found by Jehle and his team.
EcoStrat’s 2007 measurements are significantly higher than those recorded by the same laboratory in 2006. No explanation has been given for this.
The values measured using the commercial method are generally above those obtained using the Monsanto-based method. However, the differences between the two methods are not consistent: in samples taken from the underside of the leaves and the kernels, the values obtained from the commercial method are higher but still within a ‘biologically explainable range’. Values obtained from samples of the upper side of the leaves and stalks are actually higher using the Monsanto method. In Johannes Jehle's view, this indicates that the two methods are "consistent and comparable".
Only samples taken from the root area produced striking differences. Here the concentrations found using the commercial method are twice as high on average. But even these deviations are not unusual, in Jehle’s view.
Monsanto specifies an average Bt toxin content of 9.4 μg/gram fresh weight for MON810 Bt maize. The values recorded by EcoStrat in 2007 in the kernels and stalks are considerably lower, but the findings for samples taken from the root area are close to those given by Monsanto. However, EcoStrat recorded values above the 9.4 mark in leaf samples. In general, the Bt toxin concentrations published by Greenpeace lie within the range specified by Monsanto, which forms the basis of safety assessments.

There is still no standardised method of measurement for Bt toxin, as there is for other transgenes . Differences in extraction methods and comparative protein detection standards, for example, can cause variations in results which overlap the natural variations in plant Bt toxin levels. Experts like Johannes Jehle are familiar with this problem, but they do not regard it as a safety risk.

Bt toxin: Each maize plant is different – but is that a problem?

"There are no reliable methods of measurement."

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