According to the book Simple Things You Can Do To...
According to the book "50 Simple Things You Can Do To Save The Earth," every two weeks, Americans wear almost 50 million pounds of rubber off their tires, enough to make more than three million new tires from scratch. Now, I dodge pieces of blown semi-trailer tire every day on the interstate, but I don't think that's what they're referring to. They're talking about normal wear. I'd really like to know what happens to all that WORN rubber. Is it embedded in the roadway in microscopic pieces, or does it gas-off into thin air? And is it harmful to the environment?
RAY: That's a very good question, isn't it Victor? That's a lot of rubber. And you don't see it on the road (except near high schools, where teen age boys peel out). So where is it going?
TOM: Well, it turns out that this is one of the great mysteries of the late 20th century.
RAY: We talked to the Rubber Division of the American Chemical Society. They confirmed that researchers really don't know exactly what happens to the rubber that comes off tires.
TOM: They told us an early concern was that it was coming off in a gaseous state--as air pollution. But all the research they've seen indicates that very little of the tire ends up in the air. And the amount that does represents much less of a pollution threat than the stuff that comes out of tailpipes.
RAY: Their best guess is that the majority of the rubber--which comes off in very small particles--ends up on or by the side of the road. And that it is broken down naturally--or converted back into the natural carbon cycle by oxidation, photoexcitation, and enzyme catalysis--aka "nature."
TOM: A German study recently claimed that not all tire residue disappears. It found that several pounds of heavy metals from tires are found by the side of highways each year. But that study is being disputed.
RAY: So what can you do vis a vis tires if you want to "save the earth?" I'd say you'd be best off encouraging the development of technologies that recycle USED tires that come off of cars. That represents far more rubber than what's being left by the side of the road.