Camila Dominovsky
Appearances
Short Wave
The Mystery of the Dead Coho Salmon
You're listening to Shortwave from NPR. Hey, Shortwavers. Camila Dominovsky here in the host chair with a mystery. A decades-long puzzle centering on a string of inexplicable deaths. The victims were coho salmon showing up dead in urban streams in Puget Sound around Seattle today. in very suspicious circumstances.
Short Wave
The Mystery of the Dead Coho Salmon
Traffic. It's something to do with the roads, the urban runoff. So after years of work, the list of suspects is narrowing, but what part of the runoff? Enter another team of scientists from the University of Washington, including Zhen Yu. They're testing chemicals in runoff.
Short Wave
The Mystery of the Dead Coho Salmon
Smoking gun. It's coming from tire particles. But tires have tons of chemicals in them, and they need to find which one is the culprit. So today on the show, how a team of researchers finally cracked the case of the coho salmon, and how their discovery is having ripple effects. I'm Camilla Dominovsky, and you're listening to Shortwave, the science podcast from NPR.
Short Wave
The Mystery of the Dead Coho Salmon
So knowing that tires have tons of chemicals in them that would need to be narrowed down, Zhenyu and his team step in and start testing batches.
Short Wave
The Mystery of the Dead Coho Salmon
And one by one, they narrowed down the options until they found the deadly chemical. But that chemical, whatever was killing the salmon, it wasn't a tire additive. It didn't match anything put into tires. They still had no idea what it was. So Zhenyu and his team were stuck. They'd zeroed in on this chemical killing the salmon.
Short Wave
The Mystery of the Dead Coho Salmon
They knew it came from the tires somehow, but it just didn't match any tire additive. Zhenyu says, yeah, that's the scientific process for you.
Short Wave
The Mystery of the Dead Coho Salmon
Okay, new assumption. If this wasn't a chemical added to tires, maybe it's a chemical that's produced when a tire additive reacts with something. Chemists call that a transformation product. But how do you find that? They were kind of stuck for months until Genu had an idea. Now, at this point, it was 2020. The pandemic had started.
Short Wave
The Mystery of the Dead Coho Salmon
Genu's boss, if you're listening, give this dude some more time to take runs. But anyway, this was his eureka moment. During his post-run shower, the location of so many great ideas, he realized how to find the additives.
Short Wave
The Mystery of the Dead Coho Salmon
They knew their mysterious murderous chemical, the product after a transformation, was made of very specific amounts of carbon, nitrogen, hydrogen, and oxygen. So he searches for a tire additive with the same carbon and nitrogen makeup as their murderous chemical. And they found it, a tire additive called 6-PPD that helps tires last longer because it's an antioxidant.
Short Wave
The Mystery of the Dead Coho Salmon
It reacts with ozone to make 6-PPD-Quino. That has more oxygen bonds and it kills the coho. This breakthrough got a lot of attention because, well, everyone knew, yeah, probably not great that all these tire particles are full of all these chemicals.
Short Wave
The Mystery of the Dead Coho Salmon
Changing the way people like Nick Malden think. He's with a company called Emissions Analytics in the UK. They used to study tailpipe emissions. These days, they do a lot of work on tire emissions. All the particles that go into the air and waterways as your tires wear away.
Short Wave
The Mystery of the Dead Coho Salmon
Now, to be clear, some researchers into air and water quality have always been worried about tire emissions. But the general public, regulators, the auto industry were much more focused on tailpipes. And regulations to cut tailpipe emissions have, in fact, been super effective. They've come down a lot.
Short Wave
The Mystery of the Dead Coho Salmon
So much that Nick's company, as well as peer-reviewed research, have found that tire emissions are now on some metrics a bigger problem than tailpipe emissions.
Short Wave
The Mystery of the Dead Coho Salmon
Five versus a hundred. And to add a wrinkle, this realization is coming right as electric vehicles are becoming more popular. And they're heavier. Heavier vehicles mean more tire emissions as you drive. One researcher told me, just picture using a rubber eraser. The harder you press, the more you wear it down.
Short Wave
The Mystery of the Dead Coho Salmon
when he was called in to the case. These fish spawn in freshwater, strike off for the open seas, trek back to the place of their birth, but then they die before they can spawn. And this keeps happening for years.
Short Wave
The Mystery of the Dead Coho Salmon
Now, he is not saying that EVs are worse than gas cars overall. Tailpipes produce different kinds of pollution. We're just talking about one kind here, particulates. And the biggest benefit of EVs is that they reduce carbon emissions to reduce climate change. That benefit is clear, even if you factor in making batteries and charging vehicles.
Short Wave
The Mystery of the Dead Coho Salmon
And when it comes to tire emissions specifically, it's complicated. EVs have pros and cons. While EVs are heavier, which makes these emissions worse, they also have regenerative braking.
Short Wave
The Mystery of the Dead Coho Salmon
So like I said, complicated. But suffice to say, tire wear pollution is a problem for all road vehicles, including EVs. So what's the solution? There are lots of ways to help, like start with the tires. We can change the chemicals in them to be less toxic. We can get fewer particles in the first place, tweak the way roads are designed, or encourage people to drive less aggressively.
Short Wave
The Mystery of the Dead Coho Salmon
That makes a huge difference, actually. Or, of course, drive less. Or after we've made particles, street sweeping and filtering runoff can help animals like the salmon. And then there are ideas, like the one they're working on at the Korea Institute of Machinery and Materials. I reached out to ask about some testing that they've done.
Short Wave
The Mystery of the Dead Coho Salmon
And Seo Kwon Lee told me they're also 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.
Short Wave
The Mystery of the Dead Coho Salmon
We'll see where that goes. In the meantime, the world makes billions of tires every year. Producing them, using them, and disposing of them are all sources of pollution. And as tailpipes get cleaner and electric vehicles get more popular, this is kind of the new frontier for reducing emissions on roads, cutting down on pollution that doesn't come from tailpipes.
Short Wave
The Mystery of the Dead Coho Salmon
Before we head out, if you liked this episode, make sure to follow us if you haven't already. That way you never miss a new episode. And if you liked this episode, check out our episodes on satellites, monitoring emissions, and how air pollution could create superbugs. We'll link to them in our show notes. This episode was produced by Jessica Young and edited by our showrunner, Rebecca Ramirez.
Short Wave
The Mystery of the Dead Coho Salmon
It was fact-checked by Tyler Jones, and Kwesi Lee was the audio engineer. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Camilla Dominovsky. Thanks for listening to Shortwave from NPR.
Short Wave
The Mystery of the Dead Coho Salmon
And we was a lot of people. Biologists, modelers, community scientists, environmental chemists. Some researchers rule out all the obvious culprits. Temperature, oxygen, known toxins. It's none of those. They need a lead.
Short Wave
The Mystery of the Dead Coho Salmon
They look through the data about where fish were dying and started running models.