As the biotech industry and regulators cling to the notion that 'Bt' insecticide is toxic only to the target pests and is easily digested by mammals just like any other protein, science is throwing a few flies in their ointment.
GM crop plants have been created which generate one or several artificial versions of 'Bt' insecticides. These proteins, in their natural forms, are produced by soil bacteria, Bacillus thuringiensis.
It's disturbing to read in a recent scientific paper that:
"Bt toxins can be transferred via the food web and accumulate in organisms to different degrees".