Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces proteins active against certain insects. Beginning in the mid-1990s, crop plants expressing Bt genes were commercialized in the United States. Cry1Ab and Cry1F Bt corn are effective in controlling certain pests of corn (European corn borer, corn earworm and southwestern corn borer), and Cry1Ac Bt cotton is effective in controlling certain pests of cotton (tobacco budworm, cotton bollworm and pink bollworm). Beyond the economic benefits to growers, the use of Bt corn and Bt cotton result in less risk to human health and the environment than chemical alternatives.In 2001, the US Environmental Protection Agency (EPA; Washington, DC, USA) reassessed the four still registered, but expiring, Bt crops that had been accepted for agricultural use in the preceding six years (from 1995 to October 2001; Table 1). The Bt crop reassessment approvals included provisions to prevent gene flow from Bt cotton to weedy relatives, increase research data on potential environmental effects and strengthen insect resistance management.From this reassessment, the EPA has determined that Bt corn and Bt cotton do not pose unreasonable risks to human health or to the environment. In this article, we summarize the supporting data and conclusions of the EPA. The complete reassessment document 1 , Biopesticides Registration Action Document (BRAD)-Bacillus thuringiensis Plant-Incorporated Protectants, which describes in detail the reassessment process, along with extensive references, can be found on the EPA website at h t t p : / / w w w . e p a . g o v / p e s t i c i d e s / biopesticides/pips/bt_brad.htm. Federal oversight of Bt crops Consistent with the Coordinated Framework for Regulation of Biotechnology

This manuscript focuses on the toxicological evaluation of proteins introduced into GM crops to impart desired traits. In many cases, introduced proteins can be shown to have a history of safe use. Where modifications have been made to proteins, experience has shown that it is highly unlikely that modification of amino acid sequences can make a non-toxic protein toxic. Moreover, if the modified protein still retains its biological function, and this function is found in related proteins that have a history of safe use (HOSU) in food, and the exposure level is similar to functionally related proteins, then the modified protein could also be considered to be “as-safe-as” those that have a HOSU. Within nature, there can be considerable evolutionary changes in the amino acid sequence of proteins within the same family, yet these proteins share the same biological function. In general, food crops such as maize, soy, rice, canola etc. are subjected to a variety of processing conditions to generate different food products. Processing conditions such as cooking, modification of pH conditions, and mechanical shearing can often denature proteins in these crops resulting in a loss of functional activity. These same processing conditions can also markedly lower human dietary exposure to (functionally active) proteins. Safety testing of an introduced protein could be indicated if its biological function was not adequately characterized and/or it was shown to be structurally/functionally related to proteins that are known to be toxic to mammals.

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