“Coho are enormous and brightly colored, so people can readily see them suffering,” says Sutton, who notes that salmon’s troubles could signal other systemic problems. “A smaller fish,” she says, “could experience the same impacts, but you wouldn’t see it [if you were] walking through a rainy creek.”
One potential, and potentially problematic, solution for reducing tire-shedding involves changing the texture of pavement. California’s concrete and asphalt highways act like cheese graters on tires. On a Thursday in February, shortly before the coronavirus lockdown, I join Matthew Souterre and Marissa Padilla to check out an alternative way to surface roads in Escondido, a bedroom community north of San Diego where the pair work in the city’s engineering-services department.
Souterre looks in his rearview mirror. “Marissa, where do you have us going to next?” he asks.
Padilla, in the back seat, shuffles some papers. “The Miller-Alexander area,” she says.
“The Miller area…” Souterre repeats absently until his memory jogs. He executes a silent U-turn, passing bungalows painted in neutral desert tones.
Less than a year earlier, Souterre and Padilla used a grant from the state’s recycling agency, CalRecycle, to divert 15,198 tires from landfills. The tires were processed into hot asphalt to form rubberized pavement, which reduces traffic noise and tire-shedding, and speeds water drainage due to its porosity.
We arrive at a quiet residential street, and I climb out to take a closer look at the road surface. It looks like … pavement. Souterre and Padilla point out its highlights: no weeds sprouting and no “alligatoring”—where pavement splits into slabs like reptile skin.
Mixing old tires into new roads is a full-circle solution that California—burdened with diverting tens of millions of junked tires from landfills annually—has embraced. In 2005, the California State Legislature mandated recycling waste tires in state pavement and aimed to rubberize 35 percent of new pavement projects beginning in 2013. Experts hoped that this would also lessen air pollution, as tire wear contributes to airborne particulate matter—increasing it by up to 30 percent in some high-traffic areas—and the dust can inflame human lungs. But Sutton, of the SFEI, worries that paving streets with ground-up car tires may be unloading their heavy metals and chemicals into sensitive aquatic ecosystems.
“To be honest,” she says, “the concerns we’re now having about tires are brand-new concerns. I’m not sure those have been part of the strategy as CalRecycle was trying to come up with new uses for tires. We want to fix the issue. But reuse needs to be wise—or we’re just going to create a new problem.”
CalRecycle recently funded a study on whether zinc oxide in rubberized pavement was leaching into California waterways, dozens of which occasionally exceed the Clean Water Act’s standards for the heavy metal. The study found that rubberized pavement does indeed leach 40 percent more zinc oxide than non-rubberized pavement, but it reached the unsatisfying conclusion that other sources of zinc oxide—including tire fragments—could also be at play, so it wasn’t possible to definitively pin the blame on recycled tires.