Someone once told me that if you have an ingredient that may have 0.3% toxins and you bought a cheap badge with 0.4% and a quality badge with 0.25% it is awfully tempting to mix them as close to 0.29% as possible. You might even convince the quality supplier to aim for 0.2% so that you can use the almost worthless 0.5% It isn't unthinkable that some would use the food supply to somewhat legally dispose of 100% toxic materials. Properly mixing is really hard and you cant really trust people who would do such a thing to mix in the poisons "properly".