Research has shown that the insecticidal proteins produced by insect-protected GM crops can be released into the soil. The proteins are released from the roots as they develop and from plant tissues and pollen in the soil as they decay. Therefore, assessment of the potential effects of these proteins on soil organisms is an important component of the regulatory review of insect-protected GM crops. Direct testing is conducted against earthworms and springtails, both of which are important in processing organic matter and maintaining a healthy soil. No effects of the insecticidal proteins have been seen on these organisms. Other studies have shown a lack of effect on nematodes, protozoa, bacteria, and fungi. Research is also routinely conducted on the stability of the insecticidal proteins in soil. This research shows that these proteins, just like other proteins, rapidly break down in agricultural soils. In addition to this, the EPA has required data on the potential for the insecticidal proteins to accumulate in fields where the GM crops have been grown over multiple growing seasons. Again, this research shows that the proteins are not present once the plant matter has decayed after harvest. Finally, studies have been conducted on soil structure and function with GM and non-GM crops. These studies again show that growing GM crops does not affect the ability of the soil to process organic matter and support a healthy crop.
It is important to remember that the source of these insecticidal proteins is itself a common soil-dwelling bacterium, Bacillus thuringiensis. This means that exposure of soil and soil organisms to these proteins is not unique to GM crop fields, but occurs in every field.