Herbicide tolerance (HT) is a common trait in roughly 71 percent of all GM crops, which are mostly comprised of corn, soy, cotton and canola. HT crops tend to make a lot of money for biotech companies, since farmers who buy HT seeds are required to purchase that company's brand of herbicide as well.
The herbicide used in many GE crops is derived from a natural antibiotic found in soil, which produces specialized enzymes that transform from an antibiotic to a non-toxic form called NAG (N-acetyl-L-glufosinate). The enzymes are then inserted into the DNA of GM crops, so that when the crop is sprayed with herbicides, the plant transforms the herbicide into non-toxic NAG -- essentially, the plant is able to protect itself from the toxic chemicals that kill the weeds surrounding it.
However, recent animal studies have shown that after GM crops -- which have accumulated high levels of NAG after several herbicide sprays -- are consumed, stomach bacteria can re-transform NAG back into the toxic herbicide. Two rat studies found a 10 percent and a 1 percent rate of NAG conversion after consumption of HT crops.
According to a January 2006 report by the Environmental Protection Agency's Office of the Inspector General, certain pesticides easily enter the brains of young children and fetuses, where they then destroy cells. Studies of mice embryos exposed to glufosinate resulted in reduced numbers of vital brain receptors, growth retardation, increased death rates and incomplete development of the forebrain.
Critics of GM crops urge the public to call on the EPA for more rigorous testing of genetically engineered crops, and for stricter labeling laws on GM products so consumers can more easily avoid them.