There isn't any question that lead and lots of other heavy metals are used in auto tires and plastics and have been for a very long time.
It ought not be a surprise the same heavy metals will be found in shredded tires. The studies I looked up in just a few minutes used xrf guns which are...
Interior Graphic Standards, second edition, published in 2010, a college text used to train architects and interior designers, you will find my name in the chapter author credits. I literally wrote the book on countertops...
Lead is used in a lot of PVC products as a stabilizer including garden hoses and those spiffy 4" PVC tube chicken feeders or the ports used in the bucket feeders. Without a stabilizer PVC, rubbers, and a lot of other polymers just decomposes quickly. There are relatively new PVC stabilizers...
Maybe once, until you clean the top, then not so much. Any sealer thick enough to provide a barrier would mark up with the slightest use.
Most, not all, granite tops are loaded with lead.