Bt toxin is not taken up from soil or hydroponic culture by corn, carrot, radish, or turnip

The culture of transgenic Bt corn (Zea mays L.) has resulted in concern about the uptake of the Cry1Ab protein toxin by crops subsequently grown in soils in which Bt corn has been grown. The toxin released to soil in root exudates of Bt corn, from the degradation of the biomass of Bt corn, or as purified toxin, was not taken up from soil, where the toxin is bound on surface-active particles (e.g. clays and humic substances), or from hydroponic culture, where the toxin is not bound on particles, by non-Bt corn, carrot (Daucus carota L.), radish (Raphanus sativus L.), and turnip (Brassica rapa L.). The persistence of the toxin in soil for 90 days after its addition in purified form or for 120-180 days after its release in exudates or from biomass, the longest times evaluated, confirmed that the toxin was bound on surface-active particles in soil, which protected the toxin from biodegradation. The greater toxicity of the toxin in soil amended with 9% montmorillonite or kaolinite than in soil amended with 3% of these clay minerals indicated that the binding and persistence of the toxin increased as the clay concentration was increased.