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Ecology of Transgenic Crops

Genetically engineered plants might generate weed problems and affect nontarget organisms, but measuring the risk is difficult

Michelle Marvier

On May 20, 1999, a short article in Nature called attention to a potential ecological problem with a genetically engineered, or transgenic, crop. John Losey and his colleagues at Cornell University reported that a variety of transgenic corn could kill the larvae of monarch butterflies. Opponents of transgenic crops held up the report as evidence of the potentially devastating environmental impact of this new technology. Proponents, on the other hand, largely dismissed this laboratory-based research as unrepresentative of conditions on real farms. Yet despite the disagreements, this study draws attention to the difficulty of determining the safety or danger of this new generation of crops.

Genetic engineering makes it possible to transfer genes from virtually any species—animal, bacteria, plant or virus—into almost any other species, no matter how unrelated the two species might be. Consequently, these revolutionary molecular techniques let scientists generate organisms with entirely new combinations of properties. For example, a jellyfish gene transferred to plants makes them luminescent, and the Monsanto Corporation is developing new varieties of grass that will produce colored lawns.

Beyond these more fantastic applications, genetically engineered crops might offer valuable benefits: increased yields, improved flavor or nutritional quality of foods and reduced pesticide use. On the other hand, transgenic crops also pose potential risks. Most public attention has focused on harmful effects to human health, including the production of novel allergens or carcinogens. But there is also a range of possible environmental impacts, including increased reliance on herbicides, the creation of new pests, harmful effects on non-target species and the disruption of ecosystem processes—concerns that have been the focus of my work. Unfortunately, scientists lack the necessary data to predict the consequences of widespread commercial planting of transgenic crops, largely because the technology itself remains so new. Nonetheless, transgenic crops are currently being planted on a commercial scale, and the area devoted to transgenic crops increased from 4.3 million acres in 1996 to 69.5 million acres in 1998. With such rapidly increasing use of transgenic crops, scientists and society must weigh whether the potential benefits outweigh the potential risks.

Scientists must ask: Do transgenic crops pose different risks from those common to crops created through traditional methods of plant breeding? After all, plant breeders used traditional methods for millennia to create organisms with quite novel traits. For example, varieties as distinct as broccoli, Brussels sprouts and cabbage came from a single species of mustard. Many scientists emphasize that the product—not the process—needs to be regulated and evaluated for risk. In other words, transgenic crops should not require regulation simply because they are genetically engineered. Instead, a transgenic crop should be regulated only if it is likely to pose elevated threats to human health or the environment. Nevertheless, genetic engineering can create many more combinations of genes and new traits than can traditional breeding. This greatly enhanced novelty diminishes anyone's ability to predict the safety of a transgenic organism on the basis of past experience.

Proponents of genetic engineering call attention to the lack of major trouble associated with transgenic crops, but that record does not guarantee that they are completely safe. As a case in point, scientists and manufacturers considered pesticides totally risk-free when first marketed in the late 1940s, and data that documented ill effects took nearly 20 years to surface. Similarly, major problems might result from transgenic crops over time. So far, few experiments have examined the safety of transgenic crops, especially the many ways that these modifications could affect the environment. Moreover, the companies that manufacture and market transgenic crops are responsible for assessing their safety, which results in a potential conflict of interest that could compromise the rigor of safety assessments. Finally, because some of the risks derive from rare, chance events—including hybridization between a crop and a weedy relative—it might take quite some time for troubles to emerge. Meanwhile, money and time for monitoring the environment after release of transgenic crops are limited, making it likely that no one would detect any sign of trouble until well after a problem developed.

To illustrate the challenges associated with assessing the risks and merits of this new technology, I shall focus on insect-resistant transgenic crops. The safety of crops engineered to be toxic or repellent to insects is a crucial concern, because such crops made up about one-quarter of the total cotton acreage and one-fifth of the total corn acreage in the United States in 1998. This rapidly increasing use of transgenic crops demands heightened rigor in testing these novel plants.

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