It's common in many insecticides. Pyrethrum, widely regarded as natural and relatively safe, in fact is irreversibly absorbed into human nerve cells, of which the brain is built.
As an aside to that, no actual harm as a result has ever been demonstrated, but me, I don't use it in the house.
That's one of the beauties of some neonictiniods being hundreds of times stronger against insects than some of the old insecticides. It means that hundreds times less is used but still be effective, much better in many ways.