Research out of Washington State University is bringing scientists closer to preventing roadway runoff from killing coho salmon.
For years, researchers have wondered which chemical was making salmon suffocate in the water of urban creeks near high-traffic areas.
"You can see a bright, beautiful, healthy-looking salmon that obviously had just come in from the saltwater is migrating up these urban creeks and starts to exhibit these really strange symptom: sticking their nose out of the water, gasping at the surface as if it's suffocating in these streams that are surrounded with plenty of oxygen," WSU researcher and PhD candidate Negonnekodoqua Blair said. "It was really obvious that these fish were under severe distress and that they were dying very quickly."
In 2020, they identified 6PPD-quinone as the culprit. It's a byproduct of 6PPD, a preservative in almost all tires, Blair told SPR News.
But her recent study shows how that chemical kills fish: It causes plasma—and therefore oxygen—to leak out of a salmon’s blood.
This new information is a big step toward finding a replacement, Blair said.
"We have a lot of gratitude to show towards the coho salmon, towards our other species that really are here to let us know whether or not our systems are healthy to live in, whether or not we can give our future generations a healthy environment to live in," she said.
As scientists search for a chemical that does the same job in tires, Blair said they can check to see if it has the same properties that make it toxic to coho.
Blair, an enrolled member of the Sault Ste. Marie Tribe of Chippewa Indians who works as the environmental toxicologist for the Confederated Tribes of the Umatilla Reservation, told SPR News she hopes her research will contribute to upholding tribal treaty rights to salmon habitat protection—which she says will benefit not just tribes but all Northwest residents.
"I think the core message for non-tribal audiences, especially in the scientific world working with tribes, is that the treaties really guaranteed that salmon habitat would be protected for everyone, not just tribal people, but in common with citizens of the territory," she said. "That's the language of the treaties. So, this was a promise that was made since that founded this country.
"And I think it's important for people to know that, that this is not just about caring for our environments and making our habitats more hospitable to salmon. This was a promise that was made when this country was founded, this agreement with tribes that still exist today. And it's also about upholding those promises."
Blair spoke with SPR's Owen Henderson about her research.
This interview has been edited for length and clarity.
OWEN HENDERSON: Let's start with your most recent findings. What's the thrust of the paper that you published this summer?
NEGONNEKODOQUA BLAIR: Our research paper was investigating mechanisms of toxicity in the acute mortality response of coho salmon to 6PPD-quinone, and that's very technical speak for we want to know why coho are dying when they're exposed to urban stormwater and especially roadway runoff.
And so when I started in 2016, I was starting my master's, that's when they were just finding out that roadways and high traffic areas were a strong predictor of where these coho die-offs were happening.
And we were looking at different sources. We had an idea it was roadway runoff and looking at vehicles as sources, but there's many different types of sources when you look at vehicles. At that time, no one really knew what was driving the recurrent die-offs, but we knew that the usual suspects of known contaminants that were ending up in urban waterways were not causing it.
Those had been ruled out. So we had a pretty good team kind of looking at the question of what could be causing it, narrowing down the sources.
The biggest mystery was really why. How was this unknown chemical killing coho so quickly?
So it wasn't an easy question at all for a new graduate student to tackle, but what was great about it is it was so open-ended, and there was this huge need for generating new hypotheses and building on a lot of this work that these amazing researchers had done a lot of studies on.
So we had some clues to build on and that's what led to the development of testing the blood-brain barrier and blood-gill barriers as a reason for driving these cardiorespiratory distress symptoms that we've been seeing for such a long time.
OH: Expand on that a little bit for me. How exactly did you test this to determine how the chemical killed the salmon?
NB: I talked about the behavioral symptoms that the fish were exhibiting. They look like they were suffocating. Now in any organism, any vertebrate, you have a vascular system, and you have blood that carries oxygen from your lungs—or in a fish it's from the gills and carries it to the tissues and delivers that oxygen to those tissues.
So if you have a circulatory system that collapses suddenly, that's definitely going to elicit these symptoms of suffocation. So that was the types of hypotheses that I was thinking about, is ‘How could oxygen be impaired?’
We had some studies that indicated that the blood was getting very thick suddenly before the fish were dying. Now that was an important clue because if you have blood that suddenly thickens, it's going to be really hard for your heart to pump that blood throughout the body and deliver that oxygen.
So that observation became the key observation that I used to say, ‘OK, what could be driving the severe blood thickening?’ And one of the drivers could be a loss of your blood plasma.
And in a fish, there are two regions of the vasculature that should definitely not be leaky. It shouldn't allow any blood plasma to leak out of them. And one of them is in the brain and the other one is in the gills. So if that region of the fish's blood vessels—if that suddenly becomes really porous and really leaky and you lose that blood plasma—well, that could be one explanation for why the blood thickens suddenly.
So to test for that, we took the juvenile coho salmon, we exposed them to roadway runoff, and we waited until they started to develop the symptoms of the surfacing and the loss of equilibrium, which we knew is always associated with the fish dying shortly after.
But before they die, and while their heart is still beating, we injected in these fluorescent tracers, and we looked at where they were ending up. And very quickly, we are able to see that not only were those fluorescent tracers accumulating in the brain, we were also seeing them just leak right out of the gills. And it was very obvious that the blood-gill barrier was being made to be very leaky by exposure to this chemical.
OH: So what are the implications moving forward, especially when it comes to salmon restoration efforts?
NB: Well, so our study confirms that indeed the blood-brain barrier and blood-gill barrier disruption is a key event in the rapid death response that that coho are showing when exposed to roadway runoff and this key chemical 6PPD-quinone. But we're interested in figuring out what drives the blood brain and blood gill barrier disruption. And that's still unknown.
We still don't have all of the answers to that yet, but this definitely focuses other toxicology research groups to start looking at what are those potential drivers. If we figure that out, we can create a way to screen for alternatives to 6PPD.
It's everywhere. Everywhere we have tire rubber, we have this tire preservative added to it called 6PPD. And then when it reacts with ozone in the atmosphere, it creates this transformation product, this toxic product called 6PPD-quinone.
So we know that it's so toxic at low and environmentally relevant concentrations. We need to replace it with [an] alternative that can still have the same performance and still protect the tire surface, but doesn't create this toxic product. And in order to do that, we need to have a way to screen and evaluate and to compare the toxicity between 6PPD-quinone and another potential replacement product.
And without knowing what those molecular initiating events are, it makes it really difficult to create these laboratory screening methods that could be used to look at not only a replacement for 6-PPD, but to look at effectiveness of green stormwater infrastructures.
We need to be able to test the water that gets filtered through those systems and be able to know whether or not it's going to be safe for salmon.
OH: Stepping back a bit for a moment, what drew you to this field of research?
NB: From my early childhood, we went out salmon fishing. This is much a part of my sense of place and identity and culture, just being from the Pacific Northwest, as it is about really protecting this important resource that's valuable, not just for society, but for the tribes, for the people of the Pacific Northwest.
And I feel a very strong responsibility as an Indigenous woman to give back to a place that has given me my whole life. And so that really narrowed my focus throughout my college education to look at water quality and to link that work with how can I use my education and my research ability to have the biggest impact to take care of people and take care of all of the things that people depend on, which very critically centers on salmon here in the Northwest.
I think what I've really come to realize is just how delicate and sensitive and at risk these systems that we live in every day really are.
I feel that the story of toxicology and of environmental chemistry really tells you that we are all connected.
We're not just what we eat: We are the things that we use. We are the things we consume. We are the things that we wear. We are the things that we throw away.
We have to pay close attention to our sensitive species in our environments. We have to take good care of them because if they aren't there to tell us that we have these toxic substances that are around us all the time, we won't even know how they're affecting our health and we'll continue to take them for granted.
OH: Neggonekodoqua Blair, thank you so much for your time.
NB: Yeah, thank you.
