There are some concerns regarding the safety of new proteins expressed in transgenic plants. Even low-level expression of a new transgene potentially may have an unintended, deleterious effect on other organisms including birds, insects, browsing animals, and soil organisms in the local environment. This is particularly the case when the protein has no prior history of being found in plants, or is not found at the levels expected in the GMO.

Proteins intended to control specifically targeted pests may be harmful to nontarget species. In terms of plant-produced insecticides, the only insecticidal compounds that currently are commercialized are the toxin proteins naturally produced by Bt. These proteins are highly specific in their toxic effects. One group of these proteins affects only certain species of caterpillars whereas others affect only a restricted set of beetles. None of these proteins has been shown to have a significant disruptive effect on predators of pest species or beneficial insects.

The toxicity issue (and any potential risk issue) can sometimes be inflated to alarming proportions. A report that pollen from Bt corn killed larvae of the monarch butterfly was taken to mean that Bt crops were harmful, prompting extensive negative press coverage. Numerous studies seeking to verify and clarify the reported findings all found that, under field conditions, monarch populations were not harmed. This episode may serve to underscore to biosafety reviewers the importance of carefully examining the quality and credibility of data relevant to biosafety decision making.

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