Biotechnology has nothing to do with heavy metals, so I’m going to focus on the question it appears you’re asking about Cry proteins (i.e., Bt proteins), which have been expressed in genetically modified (GM) crops to protect them from insect damage. You offer an interesting perspective, but remember that the soil is just soil (as it has always been) and it contains bacteria (just as it always has) and some of that bacteria is Bt, or Bacillus thuringiensis (just as it always was). These bacteria are ubiquitously distributed in the environment, and therefore, their Cry proteins also are ubiquitous. Thorough testing has shown that modifying a crop plant to express Bt proteins is safe. And in fact, these insect-resistant crops mean decreased use of chemicals that are used to protect against insect damage.
With regard to a Bt protein moving “up the food chain”―it will not happen. The human digestive system treats Bt proteins the same way it treats dietary proteins. In other words, it easily breaks them down into individual amino acids and small peptides that are absorbed for nutritive purposes. Bt proteins have long been used in agriculture without any effects on mammals, birds or other non- target (non-pest) species. They have a very narrow spectrum of activity because they have to bind to specific receptors on the lining of the gut of insects, and those receptors are not present in these other organisms.