Yes, I agree it's a very significant problem, and not one that's easy to deal with.
You can imagine, bringing it right back to the farm level, how surprised I was to find out 15 years ago, when the first semi trailer came onto our farm to pick up organic production, that the semi trailer had cleaned itself out by leaving the slide gates open at the bottom of the trailers, driving to my farm and hoping that any seeds in that trailer would drop out onto the road before they got to my farm.