A stormwater priority: Protecting coho salmon from tire chemicals

Coho salmon in urban areas were dying from stormwater runoff, but scientists didn’t know why until a few years ago.

A team of researchers from Washington State University and University of Washington identified a chemical found in tires as the culprit. 

Tires contain 6PPD, which keeps the rubber from cracking after exposure to ozone in the atmosphere. But 6PPD also reacts with ozone, forming the organic chemical 6PPD-quinone. 

During rainstorms, tire dust washes into rivers and streams, where 6PPD-quinone is lethal to juvenile and adult coho in small doses. It’s a complex issue—with no easy fix.

Caitlin Lawrence and Nathan Ivy are master’s students studying aquatic toxicology at WSU’s School of the Environment. Washington State Magazine science writer Becky Kramer talked with them about their separate research projects related to coho and 6PPD-quinone.

Links and resources mentioned in this episode

Puget Sound Starts Here

Washington Stormwater Center

The podcast music is by WSU emeritus professor of music and composer Greg Yasinitsky.

Transcript

Ep 32 WSM Podcast – salmon and tires

Larry Clark  00:00

Coho salmon in urban areas were dying from stormwater runoff, but scientists didn't know why. Until a few years ago, the team of researchers from Washington State University and University of Washington identified a chemical found in tires as the culprit. 

Welcome to the Washington State Magazine Podcast. I'm Larry Clark, editor of the magazine. We connect you to Washington State University research, campus life, outreach, and fascinating alumni.

Tires contain 6PPD, which keeps the rubber from cracking after exposure to ozone in the atmosphere. But 6PPD also reacts with ozone, forming the organic chemical 6PPD-quinone, during rainstorms, tire dust washes into rivers and streams, where the chemical, even in small doses, is lethal to juvenile and adult coho. It's a complex issue with no easy fix. 

Caitlin Lawrence and Nathan Ivy are master’s students studying aquatic toxicology at WSU School of the Environment. Washington State Magazine science writer Becky Kramer talked with them about their separate research projects related to coho and tire dust.

Becky Kramer  01:19

So Caitlin and Nathan welcome to the Washington State Magazine podcast. Thank you. Thanks. What is 6PPD and why is it used in tires?

Caitlin Lawrence  01:33

Yeah, so 6PPD is an antiozonant that's used in almost every single tire on market, probably all the tires, but we can't say for sure, and an antiozonant simply means that it reacts with ozone at very quick rates and very easily. And so a lot of people are familiar with antioxidant. Antioxidants react with oxygen. Antiozonants react with ozone. And so 6PPD is used in tires because rubber is very sensitive to ozone attack, so it can very easily be attacked by ozone, the bonds broken, and cracks can form. So this is especially a problem in stretched rubber, such as tires. So they add this chemical 6PPD, which is an antiozonant, to tires to offer a protective effect. And so when 6PPD is added to the rubber, the ozone in the atmosphere then wants to react with something that's super easy to react with. And since the 6PPD is there and easier to react with than the rubber, it chooses to react with that rather than the tire itself, and so that prevents cracks from forming in rubber. And so this is probably one of the most important components of tires, chemically wise, and without it, tires would not meet safety standards set by the federal government. So it's not something that can just be taken out, since it is such an integral component of how tires perform.

Becky Kramer  03:04

So we talked a little bit about how 6PPD interacts with the ozone, and how does that chemical 6PPD-q, how does that get into streams?

Nathan Ivy  03:18

That's a great question. Well, so whenever you're driving on the road, whether you're braking or accelerating or cornering in your vehicle, small particles of material are gradually shed from your tires, forming tire dust. These particles accumulate on road surfaces and mix with particles from all the other vehicles that we've shared the road with. And when it rains, as it often does in Seattle, stormwater carries these particles into nearby streams.

Becky Kramer  03:49

Is this primarily a problem in Seattle, or is it also a problem that other parts of the state?

Caitlin Lawrence  03:57

It's a problem in other parts of the state country and in other countries too. So a lot of people in like British Columbia, Canada, are also very focused on this. So yeah, essentially anywhere where there's tires, stormwater, it's an issue.

Becky Kramer  04:15

What happens when coho encounter 6PPD-q? And Caitlin, how toxic is it?

Caitlin Lawrence  04:24

Yeah. So we don't exactly know what happens inside coho bodies when this chemical enters them, and that's because this chemical is so new, and there's tons of research being done on that, and many different pathways being looked at that. But what we do know is that 6PPD-quinone acts very rapidly. So hours after a storm, we can find symptomatic coho in streams. And so this looks like fish surfacing, swimming much closer to the surface than they normally do, gasping for air, spiraling, and then towards the end, they'll have a complete loss of equilibrium, which means that they just can't keep themselves upright, so they'll be flipping over, belly up and trying to right themselves until, eventually, they unfortunately die. And we know also that this affects adults as well as juveniles, which is super important, because originally we thought maybe it was just something happening with adults, because it's much easier to see dead adult salmon that are very large in streams acting unusual, rather than juveniles, which are very hard to see in streams. We didn't know what was happening to them, but research has shown that they're almost equally as sensitive, which is very important since juvenile coho rear in streams before they go to the ocean, which means they're sensitive at all parts of their life cycle that they're in freshwater, especially near urban areas. 

And for how toxic it is, it's really one of the most toxic aquatic chemicals known to man, up there with some very toxic pesticides. As far as concentration goes, we talk in LC 50 as toxicologists. So LC 50 is an easy way to compare chemicals to each other. So an LC 50 is a concentration at which half the test organisms die during an experimental test. And this is the concentration that has the least error with our statistical analysis. That's why we choose that. 

But in our lab environment, coho are sensitive at around 100 nanograms per liter, or 100 parts per trillion, and this can be very difficult to wrap your mind around, just how little of this it takes to kill the salmon to get an LC 50. And so an analogy that was very striking is if you were to think of the world population, which has 8 billion people, around 8 billion people, 100 parts per trillion, if we were to do it in terms of humans, would be less than one person out of the entire world population. So parts per trillion, extremely toxic, a very hard number to wrap your mind around, but yeah, it would be fractions of a human out of our entire population. So it's a very, very toxic chemical.

Becky Kramer  07:11

That's quite a visualization. We hear a lot about coho, but does 6PPD-q affect other salmon species or other fish, and what about humans?

Nathan Ivy  07:26

Well, let me emphasize that our research focuses primarily on coho salmon. However, there is research that indicates that rainbow trout and their sea-running form steelhead are also sensitive to 6PPD-q. Brown trout are in there too. Now these species experience acute mortality at extremely low concentrations of this toxicant, as Caitlin mentioned already, and this region's seasonal precipitation pattern coincides with the most vulnerable life stages of these salmonids. So we know that the acute mortality is a major concern, and historic coho and steelhead populations have declined by approximately 90 and 95% respectively. Now it should be noted that we've primarily studied the acute toxicity of 6PPD-q. However, the sublethal effects of this toxin are still under investigation. 6PPD-q has also recently been detected in human urine, which suggests that we experience some level of exposure as humans. And this discovery has prompted additional research into its potential health effects. But it's very crucial to emphasize that the research is still in its early stages, and we don't really have conclusive understanding of the actual impacts on human health. That's why ongoing investigations like this are so important. We need more comprehensive studies to determine the real-world risk and what levels of exposure might be harmful to humans.

Becky Kramer  08:59

Why is it important to control 6PPD at the source versus trying to filter it out of storm water?

Caitlin Lawrence  09:07

Yeah, this is a great question, because a lot of people ask, well, we can just clean it up out of the environment, right? And, well, that's sort of true. We have green stormwater infrastructure, low-impact development and stormwater treatment. These are all very costly, take up a lot of land space and require constant maintenance throughout time. So although it is very important to mitigate the effects of 6PPD-quinone that we can in areas that might have the most impact, such as areas in Seattle where there's a lot of traffic, it's pretty much impossible to ensure that all 6PPD-quinone is not going to be entering streams. So it's important to think about source control, which just means, how can we keep this chemical from entering the environment in the first place? And this is important, especially when we're thinking of, okay, this research is very new. You know, coho are extremely sensitive. But what other species are sensitive? You know, there's populations of fish declining all across the country, different species. Could it be because of 6PPD-quinone or other issues? So if this becomes a countrywide issue or a worldwide issue, we're not going to be able to clean up all the 6PPD-quinone in the environment, so we want to stop it from entering the environment by replacing it with an alternative that is safer and less toxic.

Becky Kramer  10:29

So Caitlin, some of your research involves alternatives to 6PPD. Tell me about your work with testing alternatives.

Caitlin Lawrence  10:40

I test alternatives to 6PPD to see if they're they are less toxic to coho salmon. My work is funded by the Washington Department of Ecology. Ecology along with tire manufacturers at the beginning of my project combined to figure out, okay, what chemicals are potential alternatives, and from there, I received that list, and then am working through some of these chemicals to test. And I will say that was very helpful for the tire industry to do that, since we're not like, okay, what chemicals would they use? What chemicals wouldn't they use? They kind of just gave us a list, and we're like, okay, here are some alternatives that we would potentially use in tires. Now, can you test them? And so I take these chemicals, which are all PPDs, so they're all in the PPD family the same as 6PPD, the tire industry chose to add those to the list, mostly because they have the same function. So they have the same like chemical core, so they'll react the same way to ozone, which is very important. All of the chemicals that were listed have no current toxicity information for any aquatic species. So it is very important to start filling these data gaps. And we use coho to do this, because they are really an important species and the most sensitive that we have seen. So what I do is I get parent compounds. We call them parent compounds. It's the pure parent chemical. And we test this on coho, so 6PPD along with some other PPDs. And then we see how those toxicity compares to each other with the parent compounds. Then we take those chemicals and ozonate them. This is an important part of the process, because, as we know earlier, 6PPD, when it reacts with ozone, forms 6PPD-quinone, which is a super toxic part. So by ozonating the other parent compounds, we are hoping that we would form any transformation products that we would see in the environment. And so then we, after ozonation, expose those chemicals to the coho again, and we're seeing if any of those are less toxic, the other chemicals have been a little bit more promising. So yeah, that's a step in the right direction.

Becky Kramer  12:53

In terms of discovering an alternative, is that still a ways out?

Caitlin Lawrence  12:58

Yes, for sure. In the grand scheme of things, finding something that's less toxic to coho doesn't mean that it could be less toxic to all the other organisms. So there's a lot of testing on other organisms that needs to be done, aquatic, terrestrial, everything, basically. And then is the research and development in the tire industry. So how does replacing the 6PPD with something else? How does that influence the tire's performance and life, which are very important things. So all in all, we've heard some estimates from the tire industry on how long it could take, and it could be up to 20 years, you know, to completely switch over and roll out to a new chemical, although we're really pushing for a quicker timeline.

Becky Kramer  13:46

Wow, 20 years. Okay, so, Nathan, you're also involved in research related to this issue. Tell me what you do at the Miller Creek field lab. 

Nathan Ivy  13:59

So Miller Creek, it runs through Burien and Normandy Park. It's a small watershed with significant inputs of untreated stormwater runoff, and it does have a coho salmon run. And over the past 25 years, population declines and anecdotal evidence of pre-spawn mortality has prompted some significant scientific research. My research specifically focuses on understanding the real-time storm events in the spring, when 6PPD-q is being pulsed into the creek, and how urban runoff impacts the survival of juvenile coho salmon. Now the Miller Creek field Lab is a small hatchery facility owned by the Southwest Suburban Sewer District. It's been made available to use for fish exposure studies to creek water. Now, earlier this year, we conducted a study where we observed approximately 80% mortality among juvenile coho salmon exposed to unfiltered water during three representative spring storm events. The Miller Creek project aims to ground-truth the findings from our controlled lab studies by observing how 6PPD-q behaves in real world conditions. Now in the lab, we can tightly control exposure levels and time frames. But in nature, these contaminants enter the ecosystem through complex pathways, and these storms act as a trigger and watch the accumulated roadway contaminants into the creek that's creating this kind of pulsing effect of 6PPD-q by capturing real-time data during the storm events. We can see how well our lab results translate to real conditions, and this real-world validation helps better understand the timing concentration spikes and persistence of 6PPD-q in the natural environment, which is absolutely critical for understanding the actual risk to coho populations. This will help us better predict when streams are most likely to be contaminated with this information, hatchery managers can avoid releasing fish into streams during high-risk periods, and that could potentially improve the survival rate of fish themselves.

Becky Kramer  16:21

The Miller Creek field lab, you mentioned that was in the Burien Normandy Park area. So that's South King County.

Nathan Ivy  16:29

Yeah, it's pretty close to the Seattle airport.

Becky Kramer  16:34

Oh, okay, that's a good landmark. And how, how is having that real-time information important to a place like the Seattle, King County area, which is experiencing rapid development and also high traffic volumes?

Nathan Ivy  16:55

Over the past 20 years, there's been a pretty exponential growth in the population and the 2020 pandemic really changed the way that we work as a nation, too. And according to a recent survey, approximately like 36% of the Seattle workforce now works remotely because of that population growth and the increase in goods transportation and the rise of hybrid commuting and e-commerce, traffic volumes have surged past pre-pandemic levels. And so to kind of give you some numbers to consider, in that Miller Creek area traffic volume, from Washington DOT, has increased 37% since 2020 and more traffic in that area equals more opportunity for particle accumulation on roadways, which translates to higher concentrations of toxicants and ultimately leading to higher rates of mortality.

Becky Kramer  17:55

So this is a pretty big, complex issue. Do you each have a parting thought?

Caitlin Lawrence  18:02

Yeah, I guess I can go first. So when we're thinking of like 6PPD-quinone and like the stormwater issue, it can become like all we think about in some ways when it relates to coho salmon. But I think it's also important to say that 6PPD-quinone is not the only threat that coho salmon face, and even this applies to all salmon, like there's many issues such as culverts and dams, overfishing, habitat loss and fragmentation, rising temperatures, so many things that need to be considered when looking at salmon recovery. And it just shows that salmon recovery is a complex issue, it can be easy to get caught. You know, this new flashy chemical is the reason why all the salmon are dying. But, in reality, if we fix one problem and don't fix the others, we're still not going to see any progress. So we need to advocate for all aspects of salmon recovery. And if we fix habitat but not water quality, the salmon will suffer. If we fix water quality, but not habitat, it also won't help. So thinking about salmon recovery as a whole big picture is definitely something that's important. And I think it's also important to note that us as individuals can have some sort of impact on stormwater and salmon recovery. So like action items, like talking to your representatives and making sure that your voices are heard, and advocating for stormwater treatment, stormwater planning, also public transportation, along with maybe going to PugetSoundStartsHere.org website that has a ton of information about things you can do, like keeping your tires inflated so that you have less resistance when you're driving, and therefore maybe less tire particles coming off of your tires. And also the Washington Stormwater Center website is a good place to get information if you're wondering what you can do. 

Becky Kramer  20:01

What again was the first reference? 

Caitlin Lawrence  20:05

PugetSoundStartsHere.org, and then the Washington Stormwater Center website, I believe, is wastormwatercenter.org.

Becky Kramer  20:16

And Nathan, do you have a parting thought?

Nathan Ivy  20:20

Yeah, absolutely. You know, the discovery of 6PPD-quinone and its lethal effects on salmonids has really fundamentally shifted how we understand stormwater's impact on our environment, our research. It serves as a call to action, not just for scientists, but also for city planners, policymakers, and the public through citizen science groups. As Seattle continues to grow and traffic increases, addressing stormwater contaminants like 6PPD-q becomes an urgent environmental and public health priority, and the public can get involved through these citizen science groups that have been extremely valuable in the research that we're doing. For example, the Miller Walker community salmon investigation group. They've been crucial to our research here at Miller Creek, and by protecting watersheds like Miller Creek. It's not solely about salmon; it's about preserving the integrity of the entire ecosystem that supports biodiversity, community health, and overall quality of life for future generations in this region.

Becky Kramer  21:33

Thank you both for being here with me today.

Caitlin Lawrence  21:35

Yeah, thank you. This was fun. 

Nathan Ivy  21:38

Yeah, thanks for having us.

Larry Clark  21:40

Thanks for listening. You can find links in the show notes to resources about stormwater and salmon that are mentioned in this episode. 

If you enjoy the Washington State Magazine podcast, please like us on Apple Podcasts, Spotify, or wherever you listen, and tell your friends about the podcast. 

If you have ideas for a future podcast episode, let us know@magazine.wsu.edu. You can also find more episodes and WSU stories there. 

Thank you to WSU emeritus music professor and composer Greg Yasinitsky for the podcast music.