In spite of striking cultural differences regarding willingness to accept risk, countries around the world have converged on three general principles of risk assessment for transgenic crops: containment, the principle of familiarity, and a reliance on small-scale experiments. We discuss each of these approaches and their limitations. Finally, in recognition of the shortcomings of existing screening procedures, we end with a recommendation that greater consideration be given to postrelease monitoring of transgenic plantings.

CONTAINMENT

The most straightforward way to manage the risk of a biological organism would be to simply contain the organism, to somehow prevent it from spreading beyond its intended release site. For instance, the initial experiments with genetically engineered ice-minus bacteria in Northern California were subjected to elaborate security measures, including fences and broad isolation zones. In its 1989 report on the field testing of genetically modified organisms, the National Research Council (NRC) offered the optimistic conclusion that "routinely used methods for plant confinement offer a variety of options for limiting both gene transfer by pollen and direct escape of the genetically modified plant" (NRC, 1989, p. 36). If transgenic plants and genes could in fact be contained, decisions regarding their risks would be greatly simplified. Yet, on the contrary, data from field trials clearly demonstrate that this initial faith in the feasibility of containment was overly optimistic. For some species hybridization and transfer of genes to wild relatives can occur very rapidly (e.g., Mikkelsen et al., 1996). In addition, direct field experiments indicate that, although most pollen moves only short distances from source plants, a measurable quantity of pollen travels vast distances, making containment of transgenic pollen highly unlikely (e.g., Kareiva et al., 1991; Kareiva et al., 1994; Lavigne et al., 1998).

Potential methods of containment include the use of barren zones around crops and plantings of trap plants into border rows. Unfortunately, barren zones may actually cause increases in the mean distance or amount of gene flow out of plots (Manasse, 1992; Morris et al., 1994). Although the use of border rows to trap pollen has proven more successful in reducing the extent of gene movement, the borders must be substantially larger than the transgenic fields, making their use impractical for agronomic-scale plantings (Hokanson et al., 1997).

Even in cases where gene transfer is an extremely infrequent event, the notion that transgenes could ever be completely contained remains indefensible. Furthermore, with large-scale commercial production, the sources of transgenes are so plentiful and opportunities for exchange so widespread, containment can not possibly be considered as a tenable risk management procedure. It is noteworthy that regulations in the United States and in the European Union do not in any way rely on containment as part of their risk management procedure for commercial products. In these countries, containment practices are only required for small-scale experiments during the research and development stage of novel cultivar breeding and genetic modification.



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