Are Bt crops safe?

Abstract

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

Reduced Fitness of Daphnia magna Fed a Bt-Transgenic Maize Variety

“…For the environment, the purported selectivity and localized effect of Bt-plants might be an improvement over the use of sprayed pesticides. According to the US Environmental Protection Agency, Bt-crops pose no significant risk to the environment or to human health (Mendelson et al 2003). However, the specificity of Bt-plant defense has yet to be established (Dutton et al 2003(Dutton et al , 2005, especially because the mode of action of Cry proteins, both in target and nontarget organisms, is not fully understood (Brandt et al 2004;Bravo et al 2007;Crickmore 2005;Hilbeck and Schmidt 2006).…”

“…D. magna feed nonselectively on a broad range of particles in the size range 1-50 lm, and where transgenic Bt-plants are grown, they might receive this in their diet in the form of detrital particles and pollen. The clonal D. magna is commonly used in toxicological and ecotoxicological research (Atienzar et al 2001;Barry 1996;Kramer et al 2004) and has shown no treatmentrelated adverse effects to acute toxicity tests on transgenic Cry1Ab-maize pollen (Mendelson et al 2003). However, a 48-h acute toxicity is only a first step in testing a GM crop plant because sublethal effects are precluded.…”

Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape

“…A commonly planted transgenic maize variety has been engineered to express the insecticidal Cry1Ab protein from Bacillus thuringiensis (Bt) to resist crop damage by the European corn borer (Ostrinia nubilalis); planting of insect-resistant transgenic maize represented an estimated 63% of the 2009 maize crop in the United States (1). Cry1Ab protein is expressed throughout the tissues of Bt maize (2,3), and after maize is harvested, the protein is detectable in terrestrial detritus left on agricultural fields for at least 7 mo (4,5). Recent work established that maize detritus enters, is processed, and can be transported within streams (6,7), and laboratory trials suggested that consumption of Bt maize detritus may affect stream-dwelling invertebrates (7,8) but some studies have shown little or no effect if detritus is leached prior to consumption (9).…”

Ecological Impacts of Genetically Modified Crops: Ten Years of Field Research and Commercial Cultivation

“…The toxin input from senescent plant tissue varies, depending on initial expression levels of the transgenic protein in different plant tissues, the progression of decay of the plant cells and the biomass remaining in the field. Expression levels in the Bt-maize variety MON810 are estimated to be around 4-7 times higher in leaves than in roots [71].…”