ENVIRONMENT Study: Tire tread yields pollution

Tires leave behind a tiny trail of particles as they wear down.
LEWISBURG, Pa. (AP) -- It's a question that's stumped even Click and Clack, the "Car Talk" guys: What happens to the rubber that wears off a car's tires? Alison Draper thinks she knows the answer, and it's not a good one.
Draper, a professor of environmental chemistry at Bucknell University, is studying the effects of tire-wear particles on the environment with the hope of finding ways to make tires less polluting.
"The research is in a preliminary phase right now, but it seems to be pointing in the same direction, and that is that these particles have a negative effect in aquatic environments," Draper said.
Puzzling it out
Draper's research stems from a question that's so simple it's almost ridiculous. When the tread on a car's tire gets smaller, where did the rest of the tire go?
Three years ago, Tom and Ray Magliozzi, hosts of the National Public Radio show "Car Talk," were asked that question in their weekly newspaper column by a reader named Mike.
"That's a very good question, Mike. And we don't know the answer," Ray Magliozzi wrote. The Society of Automotive Engineers didn't know the answer, either. Neither did the American Chemical Society.
They guessed, though, that the "rubbed-off rubber" broke down into tiny particles, many of them suspended in the air like dust.
"Obviously the carbon and sulfur contribute somewhat to airborne pollution, but how much and whether that amount is significant, we don't know," Tom Magliozzi wrote.
That's one of the things Draper is trying to find out.
What she knows right now is that for every kilometer a car travels, about 90 milligrams of tread wears off in particles ranging in size from 10 microns or less to 75 microns.
The impact
Draper has just begun to test the effects of the smallest particles, which remain airborne. But she said her tests appear to show that a toxin or toxins in the larger particles leach out when exposed to water, harming both plant and animal life.
Draper soaked five grams of the particles in a liter of water for 10 days, then diluted that solution with an additional 100 liters of water. She then exposed both algae and fat head minnows to the leachate solution.
Algae exposed to the leachate stopped growing in her tests, Draper said, and the fish appeared to have serious, but not fatal reactions, including lesions and damage to their internal organs.
"Exposure to just a very small quantity of the tire leachate resulted in zero growth for the algae, and if you have population effects on algae, you're going to see them elsewhere in the food chain," Draper said.
Although she has not identified what is responsible for the damage, she said it could be zinc oxide or any of the sulfur-containing agents used in making tires.
Bob Amme, senior research physicist and director of the Environmental Materials Laboratory at the University of Denver, said he didn't know whether such effects would be seen in nature, though, because most of the tire particles probably would remain concentrated near roadways instead of polluting waterways.
"I think most of that rubber that she's talking about ends up near the roadways," Amme said. "I don't think it floats a long ways away unless it's washed away by water in a drainage system or something."