Chapter 39 - The Food Safety Assessment of Bt Crops

Abstract

The food safety of Bacillus thuringiensis (Bt) crops is supported by over 50years of history of safe use of Bt microbial pesticides in agriculture. Bt microbes produce a variety of crystal (Cry) proteins that work by acute mechanisms to control larval insect pests. Their effectiveness is limited when they are sprayed on plants. The introduction of genes coding for Cry proteins genes into plants (Bt crops) prolongs their effectiveness. Human dietary intake of Cry proteins from consumption of crops sprayed with Bt microbes and Bt crops is negligible. In Bt crops Cry proteins are present at parts per million levels, and processing (e.g., cooking) of crops (maize, soybeans, rice) into food inactivates them, further reducing exposure. Intact Cry protein that survives cooking is subject to degradation by gut digestive enzymes. Mammals and other nontarget organisms lack the high affinity Cry binding receptors on gut cells present in target insects. The Cry protein receptor complex in the gut of target insects forms pores in cell membranes which lyse, leading to insect death. Due in part to the absence of high affinity receptors on the gut cells of mammals and other nontarget organisms, no toxicity occurs following acute oral high dosing with Cry proteins. In approximately 20 longer-term feeding studies with Bt crops, no toxicity has also been observed. Growing Bt crops such as cotton can lower chemical insecticide use and reduce fumonisin mycotoxin contamination of maize by reducing insect feeding damage that facilitates fungal infection.