At one point in my life I worked in a shop that formulated our own rubber compounds for retreading earthmover sized tires. The blends of different rubber and chemicals that make up a blend can be altered to accomplish different applications.
The raw rubber that you start with is put into a milling machine which has two giant rollers that will flatten and knead ( for lack of a better word) this hard rubber until it is pliable and then the other types of rubber is mixed in with a set amount of chemical to achieve the blend required. We used natural rubber and synthetic rubber to make a very hard but wearable type of tread rubber.
This blend left un cured for a length of time will leach oils and such. Therefore before curing this rubber into a finished product it needs to be re worked.
After this rubber is cured it is a finished product and after opening many tire carcasses whether they be car, truck or earthmover I have never seen a sign of rubber leaching anything.
Maybe when you bake a cake and leave it sit for a long period of time stuff will leach out. Tires are not cakes.
Dennis & Marcie & Hook The Jack Russell, 2001 HR Imperial 38wds 350 Cummins, 07 Chevy Trailblazer/Blue Ox/Ready Brake, 04 Dodge 3500 Cummins,