regulation of an adjacent gene. In this case, the regulatory regions of the transgene stimulate a nearby resident gene, and potentially cause increased expression of that gene. It has been argued that one unintended consequence of this process is up-regulation of genes for biosynthesis of plant toxins. The potential for overproduction of hazardous compounds by this random integration of transgenes is likely to be similar to that for mutations, transposable-element activation, and other processes that yield genomic variation. The potential for adverse effects can be minimized through characterization of the locus of transgene insertion. Plants with transgenes that insert relatively close to genes known to affect production of potentially toxic compounds can be avoided.

It is important to point out, however, that these pleiotropic effects are not peculiar to transgenic plants. Crops resulting from conventional breeding and other nontransgenic methods can contain potentially hazardous concentrations of naturally occurring toxic compounds, as has been documented in new or established varieties. The introduction of whole chromosomes or chromosome arms from wild, nonedible relatives presents risks that are proportional to the number of alien genes added to the commercial cultivar. With sufficient testing, the risks posed by the introduction of inadvertent, potentially hazardous concentrations of known or suspected toxins into commercial transgenic or conventionally bred cultivars can be reduced.

2.5 POTENTIAL HUMAN HEALTH EFFECTS

In the United States, the EPA proposes to assess the health effects of pest-protected plants under the FIFRA and FFDCA (section 1.5). The FDA will regulate food safety and quality under FFDCA (P.L. 104-170). This section discusses EPA's scientific review of potential human health effects and general scientific issues surrounding those effects.

Although human health risks associated with transgenic pest-protected plants tend to be potential rather than apparent, some regard these potential risks as important and have expressed their views on appropriate testing and controls (OECD 1993a; Goldburg and Tjaden 1990). Potential food safety concerns for transgenic pest-protected plants (and other transgenic plant products) have been identified and articulated by EPA and FDA (FDA 1992) and international organizations (OECD 1993; FAO/ WHO 1996; OECD 1997b). These key food safety considerations have served as a basis of the food safety reviews for the products currently in the market.

The potential risks of transgenic pest-protected plants to human health are generally related to the possibility of introducing new allergens



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