With all our perceived improvement in environmental sensibilities, I'm quite sure we send far more bad stuff to the landfills now than they tossed in the ground back then. Glass bottles in particular are pretty much inert and do little harm, as does most of the modern "litter" we pick up during clean-ups, being more of an aesthetic and symbolic issue than a major environmental one. Ask the pine snake living under a tire what he thinks about it. It's the stuff you don't see that is usually the most dangerous, as well as with habitat lost to over-development.