Throughout the lifetime of an average tire, 30 percent of it gets eroded away as cars zip around on city streets and brake for little old ladies. But the leftover particles don’t remain as streaks on a road. One study found that 1.5 million metric tons of this tire debris end up flowing out into the environment as microplastics or their diminutive cousins, nanoplastics.
Some of these tiny bits of tire—made up of synthetic rubber, oils, filling agents, etc.—end up in rivers and estuaries. And according to two new research papers, these bits can wreak havoc among the fish and invertebrates living in those bodies of water. According to Susanne M. Brander, an assistant professor at Oregon State University’s Fisheries, Wildlife, and Conservation Sciences Department, much of the current research on microplastics interacting with wildlife deals with the particles that come from a few different types of commercial plastics. Further, this field focuses more on microplastics—defined as anything under 5 millimeters—but “much less is known about nanoplastics,” she told Ars.
The researchers found that the presence of microplastics, nanoplastics, and the accompanying leachate—the chemicals released from them—hindered aquatic species’ ability to grow and impacted their swimming behavior, potentially making them more susceptible to predation.
“We know that they are out there”
Brander and her team began studying the effects of tire particles in rivers and coastal areas in 2019. One lab involved in the project focused on estuaries, looking at inland silverside fish and mysid shrimp for one paper. Another lab, which studies freshwater fish, used embryonic zebrafish and the crustacean Daphnia magna as the model organisms for the second paper.
The lab of Stacey Harper—one of the researchers—has the capacity to generate and isolate particles from different material. The lab can get the desired size on demand using a cryo-mill and various filtration processes. For the sake of the research papers, the team created microplastic particles between 1 and 20 microns in size and nanoparticles less than 1 micron. Though you can’t see the nanoparticles with the naked eye—and even seeing the microparticles would be a stretch—Brander said, “We know that they are out there.”
In the two labs, the team exposed organisms to the particles and the leachate that comes off of them. Brander noted that, because the organisms were in their young stage—and are just plain small to begin with—the team could introduce the particles to the subjects while they were swimming around in beakers.
In the freshwater tests, the researchers found that tire particles and leachate caused developmental abnormalities. Though the leachate was the main cause of toxicity in the two species, exposure to nanoparticles enhanced the problems.
In the saltwater tests, the team found that organisms had altered swimming behaviors after being exposed to concentrations of material regularly found in nature. The creatures tended to freeze in place more often, and their positioning changed compared to organisms that weren’t exposed. This, in turn, could make them easier prey. The subjects also experienced reduced growth—though the leachate didn’t seem to impact the growth of either species examined.
Brander noted that the team also recreated the experiments with different levels of salinity and found that more saline water tended to increase the amount of the particles the organisms ingested. This could be because things float better in saltier water, so the particles wouldn’t sink to the bottom. Another possibility is that the salt could cause the nanoparticles to clump together. This could mean the organisms ingest larger clusters of particles or, possibly, that the species might mistake a clump for a bit of food more often.
Don’t keep rollin’ rollin’ rollin’
Brander noted that, while the research focused on the US, it could hold true for other places around the world. She added that, in the case of the leachate, the chemicals could be ingested by smaller species and bioaccumulate up the food chain—though this may not hold true for the particles, as they can be excreted fairly quickly if they aren’t too large.
Plastics in waterways is a growing concern around the globe. Recently, nearly 200 UN member states have agreed to begin negotiating an international plastics treaty to tackle this issue. But dealing with plastics from tires is tricky, Brander said. However, she pointed to California’s statewide microplastics strategy as an example of what could be done in other jurisdictions. (Brander is a co-chair on one of the scientific advisory committees that helped develop the Golden State’s strategy.)
One tactic used in the state is simply creating better, more durable tires that don’t shed as much as their cheaper peers. Another is investing more in public transit to cut down on the number of cars on the road. California is also testing out catchment strategies—compartments around roads that fill up with the particles and the storm water that carries them, keeping them from the rivers and estuaries. However, these strategies have not been widely adopted in the US just yet. “I imagine those will be considered elsewhere—hopefully soon,” Brander said.