Salmon deaths bring new attention to a longstanding problem

A few years ago, scientists cracked a murder mystery -- they figured out what's been killing Coho salmon in urban streams in the Pacific Northwest. The culprit: particles from tires.

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Next, a decades-long mystery. Coho salmon in urban streams of the Pacific Northwest would swim like they were drunk. Then within a few hours, they would die, and they were doing it before they could spawn new fish, putting them at risk of extinction. After years of investigating, researchers found their smoking gun - tire particles. But tires have tons of chemicals in them, so the researchers needed to find which one was the culprit. That's where NPR's Camila Domonoske picks up the mystery for NPR's Short Wave podcast.

CAMILA DOMONOSKE, BYLINE: To narrow down the list of suspects, Zhenyu Tian, a researcher at the University of Washington at the time, steps in and starts testing batches of chemicals.

ZHENYU TIAN: You can think of this as cutting a loaf of bread, right? Like, you have something abnormal in the bread, but you don't know where it is. So by cutting into slices, you can test each slice individually so that you can narrow down the scope from, like, hundreds to tens to ones. That's the logic.

DOMONOSKE: One by one, he and his team narrowed down the options until they found the deadly chemical. But that chemical, it didn't match any known tire additive. So Zhenyu and his team focused on a new hypothesis - maybe it's a chemical that's produced when a tire additive reacts with something. They looked for an additive that was similar to their mysterious, murderous chemical and found it - an antioxidant that helps tires last longer and that creates 6PPD-quinone when it reacts with ozone, and 6PPD-quinone kills the coho. This breakthrough got a lot of attention because its effects are not a slow creep.

TIAN: This thing is, like, killing a big fish in hours. So that is why it's kind of, like, getting more attention and, like, changing the way people think.

DOMONOSKE: Changing the way people like Nick Molden think. He's with a company called Emissions Analytics in the U.K. After the coho salmon discovery, they started doing a lot of work on tire emissions - all the particles that go into air and waterways as your tires wear away.

NICK MOLDEN: Now that people have started looking, we're realizing the problem all along has been much bigger than expected.

DOMONOSKE: Some researchers into air and water quality have always been worried about tire emissions. But the general public, regulators, the auto industry, we're much more focused on tailpipes. And regulations to cut tailpipe emissions have, in fact, been super effective, so much so that tire emissions are now, by some metrics, a bigger problem than tailpipe emissions. And they're also a big problem for electric vehicles. EVs don't have tailpipes, but they do have tires. And they're heavier than similar gas cars, which can make these emissions worse.

So what's the solution? There are lots of ways to help. To name a few, you can change the chemicals and tires to be less toxic or tweak the way roads are designed and encourage people to drive less aggressively and less, period. And then there are ideas like the ones they're working on at the Korea Institute of Machinery and Materials. Seokhwan Lee, a researcher there, told me they're working on collection systems to suck up and store road dust and tire particles a car would otherwise send into the air. He said it's a two-part system.

SEOKHWAN LEE: The first part is ingesting system. The second part is the collector.

DOMONOSKE: Is it like taping a vacuum cleaner on the back?

LEE: Yeah, it's similar. The big principle is the same for the vacuum cleaner. Yeah, that's right.

DOMONOSKE: This is kind of the new frontier for reducing emissions on roads - cutting down on pollution that doesn't come from tailpipes.

Camila Domonoske, NPR News. Transcript provided by NPR, Copyright NPR.