Dutch Precaution Keeps Bt Crops At Bay
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 complete document with references, is available in the ISIS members site. Full details here
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 [1], 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:
- Identifying the key species participating in food web interactions,
and elucidating their ecological function(s).
- Exposing these key species to Bt toxins, and monitoring the effects
on both below- and above-ground trophic levels.
- Identifying effects of Bt plants at the community level, which
require population studies and analysis of interactions with adjacent
ecosystems.
- Developing models to describe these processes ranging from organism
to population level, to provide insights into potential ecological effects over
larger temporal and spatial scales.
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
[6].
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.
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