FEATURE ARTICLE
Ecology of Transgenic Crops
Genetically engineered plants might generate weed problems and affect nontarget organisms, but measuring the risk is difficult
Michelle Marvier
Dealing with Uncertainty
The public knows that some past technologies—including DDT, PCBs and others—caused major environmental problems, despite repeated assurances of safety from scientists. Undoubtedly, that history contributed to the public's current concern over transgenic crops. Those who stand to profit from transgenic technologies view this heightened public vigilance as unfounded, even hysterical, and caution that increased regulatory oversight would hinder progress. Nevertheless, the public stands to lose if transgenic crops cause damage to the environment.
Risk analysis should reveal how the public good might suffer if new technologies backfire. Nevertheless, transgenic crops offer some special challenges in applying ecological-risk analysis. Currently, investigators evaluate risks by analogy or by direct experiments. Analogies to exotic, invasive plants fall short, because transgenic crops are not entirely new to an area, but rather are modifications involving only a few traits. Analogies to familiar crops also fail, because the mingling of genes in transgenic crops can produce completely novel traits. This leaves direct experimentation and monitoring as the primary tools for risk assessment. To be completely assured of the ecological safety of a transgenic crop, however, would require many experiments: testing the transgenic plant in different environmental conditions, at different times of year, in combination with different farming practices, and examining the effects of the plants and plant by-products on an enormous number of species that could potentially be affected by the transgenic traits. Clearly, attaining this level of certainty is neither reasonable nor possible.
Consequently, we must decide how we will deal with the unavoidable uncertainty that accompanies transgenic crops. In essence, current regulations assume that a transgenic crop is safe unless it is shown otherwise. Alternatively, we could assume that a transgenic product is unsafe until the manufacturer demonstrates its safety. Despite recent studies that highlight possible risks, plants engineered to express Bt toxin are almost certainly safer than most chemical pesticides, which generate well-established dangers for nontarget arthropods. Nevertheless, an extraordinary variety of novel traits will be incorporated into tomorrow's transgenic plants, and the safety of those plants will vary substantially. If the assumption remains "safe until proven otherwise," regulators must boost the rigor of testing. Experiments with a handful of replicates and low statistical power could fail to expose the environmental risks associated with particular transgenic varieties.
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