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.
annual Adjective for something that happens every year. (in botany) A plant that lives only one year, so it usually has a showy flower and produces many seeds.
aquatic An adjective that refers to water.
carbon dioxide (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
constant Continuous or uninterrupted.
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.
electron A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.
electron microscope A microscope with high resolution and magnification that uses electrons rather than light to image an object.
exhaust (in engineering) The gases and fine particles emitted — often at high speed and/or pressure — by combustion (burning) or by the heating of air. Exhaust gases are usually a form of waste.
fuel Any material that will release energy during a controlled chemical or nuclear reaction. Fossil fuels (coal, natural gas and petroleum) are a common type that liberate their energy through chemical reactions that take place when heated (usually to the point of burning).
geological Adjective to describe things related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.
microplastic A small piece of plastic, 5 millimeters (0.2 inch) or smaller in size. Microplastics may have been produced at that small size, or their size may be the result of the breakdown of water bottles, plastic bags or other things that started out larger.
microscope An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.
particle A minute amount of something.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
scanning electron microscope A scientific instrument in which the surface of a specimen is scanned by a beam of electrons that are reflected to form an image.
society An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.
synthetic An adjective that describes something that did not arise naturally, but was instead created by people. Many synthetic materials have been developed to stand in for natural materials, such as synthetic rubber, synthetic diamond or a synthetic hormone. Some may even have a chemical makeup and structure identical to the original.
toxicologist A scientist who investigates the potential harm posed by physical agents in the environment. These may include materials to which we may be intentionally exposed, such as chemicals, cigarette smoke and foods, or materials to which we are exposed without choice, such as air and water pollutants. Toxicologists may study the risks such exposures cause, how they produce harm or how they move throughout the environment.
X-ray A type of radiation analogous to gamma rays, but having somewhat lower energy.
Meeting: R. Gieré et al. Tire-wear particles as a major component of microplastics in the environment. Geological Society of America Meeting. November 6, 2018. Indianapolis, Ind.
Journal: F. Sommer et al. Tire abrasion as a major source of microplastics in the environment. Aerosol and Air Quality Research. Vol. 18, August 2018, p. 2014. doi:10.4209/aaqr.2018.03.0099.