Car tires and brakes spew harmful microplastics

Car tires and brake pads wear down with use. Road surfaces wear down, too. All that spews synthetic rubber and other materials into the air. And they don’t just disappear. They linger in the form of tiny particles. Many are light enough to float in the air. Indeed, a new study found that almost nine in every 10 of the small particles sampled from the air around three busy highways came from vehicle tires, brake systems and roads themselves.

The researchers classify these particles as microplastics. (Actually, not all the materials are truly made of plastic.)

These particles get blown by wind and later washed by rain into waterways that lead to the ocean. There, the debris can harm aquatic animals and fragile ecosystems, says Reto Gieré. He’s an environmental scientist at the University of Pennsylvania in Philadelphia.

He presented the findings November 6 at the annual meeting of the Geological Society of America. It was held in Indianapolis, Ind. Previous research had estimated that about 30 percent of the microplastics (by volume) that pollute oceans, lakes and rivers come from tire wear.

When it comes to vehicle pollution, most people tend to think of what comes out of a car’s tailpipe. For instance, the carbon dioxide, or CO₂, emitted by burning fuel comes to mind. Those chemicals are major sources of environmental harm. So car makers are working on cutting how much of that pollution vehicles pump out. “We all want to reduce CO₂ emissions” from vehicle exhaust, Gieré says. “But you can’t stop tire abrasion.”

Traffic congestion makes the problem worse. Vehicles traveling at constant speeds don’t have to use their brakes much. That means they produce fewer particles, the researchers found.

Some materials that cars and roads give off can be hard to identify. That’s because they become coated in dust and other tinier bits of debris. “These [tire] particles are stealthy,” says John Weinstein, who was not involved in the study. An environmental toxicologist, he works at the Citadel in Charleston, S.C.

Gieré’s team analyzed more than 500 tiny particles in the air along German highways. To figure out what each was made of, the researchers used a scanning electron microscope. It scans the surface of a material with a beam of electrons. When the electrons hit the surface of the material, some of their energy is transferred to the material. The material reacts by giving off X-rays.

Different chemicals respond in different ways. So the pattern of X-rays tells researchers what chemicals the sample contained. This method revealed that the vast majority of particles along the German roadways were from tires, brake pads and the roads themselves.