Dutch ecologists outline risk-assessment strategy for Bt-crops based on the precautionary principle, highlighting special concerns associated with small farms in Europe as opposed to much larger farms in the United States. Dr. Mae-Wan Ho and Prof. Joe Cummins report.
The Dutch take the precautionary principle very seriously. In the matter of approving GM crops, "the mere conception of a possible ecological hazard, even in the absence of scientific evidence, requires precautionary interim measures until research enables full risk management." That's the position stated by Bart Knols and Marcel Dicke, entomologists from Wageningen University in the Netherlands, in their correspondence to Nature Biotechnology in September 2003 , and they may be right.
Over the past eight years, the Dutch Parliament has mostly prevented cultivation of GM crops on Dutch soil, and it remains to be seen whether the new government will stick to this policy.
The Committee on Genetic Modification (Cogem) is responsible for regulating GM crops in the Netherlands. A recent Cogem-sponsored survey of nine prominent Dutch ecologists indicated that, in line with adherence to the precautionary principle, answers to ecological issues too important to be ignored are still lacking. These include outcrossing of transgenes to related plant species, effects on soil ecosystems and, in particular, impacts on multiple layers of the food web.
The plants as primary producers are eaten by primary consumers or herbivores, which are in turn consumed by and secondary consumers, or carnivores. These feeding relationships form an intricate web of inter- and intraspecific interactions. Incorporating Bt transgenes in a plant genome results in production of delta-endotoxins, thereby reducing feeding by herbivores. But effects on other levels remain largely unknown.
Knols and Dicke point out that accumulation of toxins in non-target herbivores may affect natural enemies, yielding secondary pests that may require chemical-based interventions to reduce crop losses. Persistence of toxins in the soil may affect soil arthropods, and disturbance of below-ground interactions may in turn impact on the above-ground food web.
Furthermore, how a plant allocates resources towards producing toxin affects its metabolism, and that may impact on herbivores and carnivores. These higher level disturbances may favour evolution of Bt resistance in pests.
Farming in the Netherlands is predominantly small-scale. And that raises additional concerns, as the interaction between Bt crops and surrounding natural or semi-natural ecosystems will be orders of magnitude greater than in countries with large-scale Bt-crop cultivation like the United States. For example, even though the Monarch butterfly may only be harmed by high-expressing genotypes in laboratory experiments, Bt pollen may have much larger impacts on vulnerable and/or endangered Dutch lepidopteran species, several of which are already on the verge of extinction and survive only in isolated refuge areas.
The presence and persistence of Bt toxins in soil and resulting effects on the below-ground ecosystem may actually affect the succession of plant species and thus result in changes in floral composition in the natural vegetation. Finally, cultivating crops expressing different Bt toxins in adjacent areas may enhance development of cross-resistance, a risk that, again, should be considered relatively high in the Dutch landscape with small-scale crop production.
These considerations have prompted the researchers to define a four-pronged approach in risk assessment of Bt crops:
These goals are ambitious and will require lengthy and costly studies. Dutch environmental policy advocates crop intensification through environmentally sound means, including nonchemical pest control strategies.
"Whether or not Dutch postcards will ever feature windmills surrounded by fields of bright yellow transgenic oilseed rape remains to be seen," the authors wrote, "but that it will take a long time is certain."
There can be no greater contrast between the Dutch approach to risk assessment and that of the United States. In the United States, GM crops with pesticidal genes are regulated by the Environmental Protection Agency (EPA) under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The actual evaluations are done by Scientific Advisory Panels (SAPs) chosen from academia, corporations and bureaucratic scientific professionals. The evaluation of Bt crops is published as Biopesticide Registration Documents [2-9].
The underlying principle of the SAPs appears to be that the Bt crops should be considered safe until proven otherwise. Furthermore, the SAPs consider each form of the Bt toxin (for example Cry1Ab, Cry1Ac, Cry1F , etc.) as an independent and separate pesticide from the other forms. But the actual transgenes for a single toxin, say, for example, Cry1Ab, may differ from one crop to another. Some are completely synthetic, with regulatory inserts and radically altered DNA codes, and the final product, the protein toxin, may be considerably shorter than the original native toxin. Nevertheless, these are not considered separately. The SAP process, with its insistence on evidence of harm for each and every variant of the toxin genes seem to assume that fundamental differences in the transgenes of a particular toxin are insignificant even though they are bound to greatly influence activity of production of a toxin, as well as the stability and motility of the genes.
Some of the EPA assessments appear to depend on selection of evidence rather than full and truthful reporting of all evidence. For example, the SAPs proclaim that "there is no significant risk of gene capture and expression of any Bt endotoxin by wild or weed relatives of corn, cotton or potato" [4,5].
The resistance management strategy approved by EPA allows the use of pesticide spray in the refuge as well as on the transgenic crop. It assumes that resistance appearing in a particular transgenic crop will not affect another that produces a different Bt toxin, and finally, a resistant mutant in the target pest is necessary, but not sufficient to trigger regulatory action; only in the case of a substantial outbreak is regulatory action required .
The benefit assessment by SAPs predicted a reduction in chemical pesticides with the use of Bt crops, but noted "environmental benefits were difficult to quantify".
The Dutch approach to Bt risk assessment is based on the precautionary principle and thorough scientific investigation prior to widespread release of transgenic crops. In contrast, the US EPA use SAPs to approve widespread release of transgenic crops presuming they are safe, and dismiss contrary evidence that comes to light.
Article first published 10/10/03
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