Bt Toxin in GM maize

[img_assist|nid=174|title=|desc=|link=none|align=right|width=100|height=43]The report presented here shows the many ways Bt maize impacts the environment. Even after more then a decade of commercial growing of Bt maize crops, the risk assessment studies are still few and most of them tend to raise more open questions than solving concerns.

The cycle of the toxin in the environment

[img_assist|nid=163|title=|desc=|link=url|url=|align=right|width=250|height=351]Contrary to earlier assumptions Bt maize releases its toxin into the environment in many more ways than just by being taken up by the pest organisms or by animals using the Bt maize as feed after harvest. Bt toxin gets into the plant through living and degrading plant material but is also exudated from the plant roots. Evidence exists that the Bt toxin persists in the soil for as long as into the next growing season, but not sufficient methods exist to determine the actual amount, neither has it been determined until when the degrading Bt toxin has toxic effects on soil organisms.
Once taken up by any organism, the Bt toxin can be passed on to other organisms: either to predators or parasites or it can be released as faeces. In a number of cases the Bt have been found to be passed on in the food network without an apparent effect on the organism of the first level.

The mode of action of Bt toxins

A new study (Broderick et al. 2006) even shows that the assumed mode of action of the Bt toxin so far has not been understood, and that in fact gut bacteria might be required for the toxic effect. This however means that there is no simple dose-response relationship between toxin and effect.
It is also not clear whether the different versions of the Bt protein in the different Bt maize events have the same effects or whether the differences in size of the protein have different effects.
In general the concentration of the Bt toxin in specific parts of the plant is not determined or monitored.

Effects on soil organism

Effects on the soil have only been studied since the mid/late 1990s, after several Bt maize varieties were already approved for cultivation. Since then adverse effects could be observed on mycorrhiza, the symbiotic partner of a number of plants; fungus gnats, an important organism in soil ecology; nematodes, earthworms and predatory beetle larvae.

Effects on bees, butterflies and other organisms

Non-target studies are sketchy: some species get more attention while for other organisms whole groups are left unattended. The reasons why some species are chosen and others not remain often unclear. Nevertheless it becomes more and more evident that adverse effects can be both direct and indirect, and that they can on higher trophic levels in the food network, even if the first organism to take them up might not be affected.
Research on non-target butterflies only started after an accidental discovery that butterfly larvae could take up the anti-Lepidopteran Bt toxin from Bt maize pollen that was blown of the fields. Most studies since then have focused on the Monarch butterfly in the US, even though the butterfly fauna in European agricultural landscapes is very different. The few studies that were conducted about European butterflies revealed a number of potentially affected butterflies, a number of which are already threatened, and they also revealed that some of these are just as susceptible to the Bt toxin as the target pest Ostrinia nubilalis (ECB). Among them are for example Common Swallow tail, Small Tortoiseshelll or Peacock.
Studies with bees are often conducted in unrealistic conditions. A field study in Germany however came to the accidental findings that bee colonizes infected with a parasite were significantly more affected when they were feeding on Bt maize pollen. Bees treated with antibiotics in the next season however showed no effect. Besides the potential effects of Bt toxin on bees, this study also showed the differences between controlled lab studies, where common parasites can be excluded, even if they cannot in commercial growing. With new evidence however, that gut bacteria might be needed in order for the Bt toxin to unfold its toxicity, the lack of adverse effects on bees treated with antibiotics cannot be considered as a proof that the Bt toxin will not adversely affect bees.
Other affected non-target organisms also include the Green Lacewing or the beneficial insect Trichogramma that is used as biological pest control.

Basic technical information is missing

It is astonishing how much basic technical information about Bt GE maize is still missing:

  • It is not understood why different plant tissues produce different Bt concentrations and how environmental factors might influence the Bt plants.
  • There is not even a standard method available, evaluated by authorities and independent laboratories to determine Bt concentrations in plant material or in the soil.
  • Bt toxins differ from the original toxin produced by Bacillus thuringiensis, but they also differe from each other in size. It is therefore possible that these different proteins also have different effects.

Other open questions include that neither the number of gene sequences nor the location where the new genes are inserted can be controlled, that the interactions with other genes and the metabolism of the plants cannot be predicted, and that eco-systemic effects are complex and can only be partially assessed scientifically. Also health impacts cannot be ruled out, and pollen migration and contaminants in the harvest contaminate food products and seed.
All in all, the available studies on different Bt maize events (such as MON810, Bt176 or Bt11) show more questions then answers, and they show that the risks of Bt maize for the environment are real.
In this context, the European framework legislation (Directive 2001/18 and Regulation 1829/2003) gives high priority to the precautionary principle. Directive 2001/18, Article 4(1) states:
"Member States shall, in accordance with the precautionary principle, ensure that all appropriate measures are taken to avoid adverse effects on human health and the environment which might arise from the deliberate release or the placing on the market of GMOs."
In the light of the many uncertainties, the requirements for EU marketing approval are not in met. While the cultivation of these plants and their use for animal feed serves the financial interests of a few companies, the potential long-term effects make such cultivation unacceptable.