I would guarantee you that the backyards of most rural (and maybe even non-rural)Americans would be declared Superfund sites by the EPA from all of the used motor oil and solvents from house paintings dumped in the ground.
Even so, biodegradation over a few decades should eat up most of the toxics from common “household hazardous waste” backyard pollution.
Ever wonder why there aren’t little hills of powdered rubber along the sides of highways, representing what has gotten worn off of vehicle tires? Mother Nature has digested it through her microbes, and turned it into that awful global warming carbon dioxide and water.