What happens to the rubber that wears out of the tires as the cars, trucks roll down the road?

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Dear EarthTalk: What’s happening of all the rubber waste that wears off tires as cars and trucks roll down the road? Is it bad for the environment?
– Jack S., Marion, Ohio

Most people have heard of exhaust emissions, but there is another form of emissions emitted by vehicles known as unburned emissions (NEE). According to independent tests and data firm Emissions Analytics, they can be up to 1,000 times worse for the environment. NEE are defined as “particles released into the air from brake wear, tire wear, road surface wear and resuspension of road dust during the use of a road vehicle”.

Unfortunately, NEEs account for the majority of primary particulate matter emitted by road vehicles on a daily basis. In total, more than 1.5 million metric tons of tire wear particles are lost to the environment each year, which equates to 30 percent of the weight of each tire used in the U.S. NEEs account for up to 60 percent of particles that are less of 2.5 micrometers in size (PM2.5) and 73 percent of those below 10 micrometers in size (PM10), making them one of the biggest environmental threats from vehicles.

This is only exacerbated by the growing electric vehicle industry, as EVs weigh significantly more due to their batteries and also have a higher torque output. Putting these two characteristics together, tires used on EVs will inevitably wear faster. According to Scott Clark, Michelin’s executive vice president of automotive, motorsports and regions of the Americas, the difference in tire life can be as much as 20 percent less for an EV compared to a car with an internal combustion engine.

When it comes to the effects that NEEs have on the environment, the data is troubling to say the least. In a study on estuarine ecosystems led by postdoctoral researcher Samreen Siddiqui, it was found that inland silverside and mysid shrimp, when exposed to tire particles and a resulting pollutant known as leachate (a mixture of chemicals that are released from particles from tires) had a number of problems including significantly altered swimming behavior and reduced growth.

In a similar study led by graduate student Brittany Cunningham, a freshwater ecosystem was exposed to tire particles and leachate. The organisms in question—embryonic zebrafish and the crustacean Daphnia magna—suffered mortality and developmental abnormalities as a result of exposure. Leachate was considered a major driver of toxicity in both organisms, with particles themselves increasing toxicity compared to leachate alone. The researchers recommended some innovative solutions to prevent exposure to tire wear, including roadside rain gardens to catch tire particles, as well as more durable tires, encouraging greener transport alternatives and something known as capture devices of particles.

The Tire Collective, a research group that produces sustainable devices to remove particles from tires, has invented a device that is capable of capturing the particles themselves. Because the particles become positively charged when they are released due to friction, the device uses electrostatic plates to capture up to 60 percent of the released particles, preventing them from entering the environment at all!

CONTACTS: Emissions Analytics, emissionsanalytics.com; Tire dust is pollution, greencarreports.com/news/1129809_tire-dust-is-pollution-and-this-invention-will-help-vehicles-clean-up-as-they-go; Why don’t tires last as long on an EV? cleanfleetreport.com/tech-why-dont-tires-last-as-long-on-an-ev/.

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