Scientists seek funding to look for toxic tire chemical in Minnesota waters

Three people stand near a bridge over a stream
A team led by researchers at the University of Washington Tacoma, UW and Washington State University Puyallup have discovered a chemical that kills coho salmon in urban streams before the fish can spawn. Shown here Zhenyu Tian (left), a research scientist at UW Tacoma; Jenifer McIntyre (right), an assistant professor at WSU's School of the Environment; and Edward Kolodziej (right, background), an associate professor at the UW, are at Longfellow Creek, an urban creek in the Seattle area.
Mark Stone | Courtesy of University of Washington

Minnesota scientists are seeking funding to investigate if a toxic chemical from tires is harming popular fish species.

Scientists in Washington spent years unraveling the mystery of unexplained deaths of coho salmon in urban streams.

They eventually linked the fish kills to a previously unknown chemical that enters the environment from tire rubber.

"The toxicity data in coho salmon says this is among the five or six most toxic compounds yet known,” said Ed Kolodziej, a University of Washington researcher.

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A chemical called 6PPD has been used in tires for decades to protect them from oxidation, essentially keeping the rubber from cracking and crumbling.

a car tire next to a storm drain
Researchers say vehicle tires shed a chemical toxic to some aquatic life when rain or snowmelt carries it into streams.
Dan Gunderson | MPR News

But when exposed to oxygen and ozone in the environment, that tire protecting chemical transforms into another, called 6PPD-quinone, and that's what researchers in Washington found is highly toxic to the salmon.

"So we have this combination of incredibly high toxicity and incredibly widespread use. And to me, those factors together are pretty substantial cause for concern," said Kolodziej.

Scientists still have more questions than answers about how widespread the chemical is, and what aquatic species are most susceptible to it.

But many agree on the potential risk.

"I would actually place this [as] one of the priority contaminants of concern right now,” said Markus Hecker, professor and Canada Research Chair at the University of Saskatchewan.

"I haven't seen a chemical with similar dramatic effects over such a short period of time in such low concentrations, for quite some time," he said.

Researchers in Saskatchewan found the toxic chemical in stormwater runoff and in snowmelt in 2019 and 2020 at levels similar to those that were toxic to the coho salmon in Washington.

Research also found the chemical in runoff in a highly urbanized watershed near Toronto.

Hecker has tested the toxicity of 6PPD-quinone on trout species related to salmon.

The research is under review prior to publication.

two people stand in a forest
A team led by researchers at the University of Washington Tacoma, UW and Washington State University Puyallup have discovered a chemical that kills coho salmon.
Mark Stone | Courtesy of University of Washington

"It seems that there actually are other salmonid species that are relatively sensitive at comparable or at slightly higher levels than the coho salmon, so there may be other species we are concerned about," said Hecker.

But scientists in Washington also found puzzling differences in response among fish to the chemical during stormwater runoff events.

“Sometimes there was chum salmon right there in the same storm, and the chum were apparently totally fine,” said Kolodziej. “And yet the coho salmon died. And so we know there's the substantial differences in their sensitivity.”

“So this is unique from my perspective that you have such a vast difference between toxic or not toxic,” said Hecker. “It's almost like a switch to turn on and off and say it's toxic or it's not toxic.”

It also appears the chemical is not persistent at toxic levels, but is directly related to stormwater runoff in rain events.

“It's not present at high concentrations all the time. We see concentrations pretty low before a storm, and then the storm happens and then the concentrations shoot way up within an hour or two,” explained Kolodziej. “And then a few hours later, they drop back down. Concentrations go up and down quickly in storms. And that always makes sampling hard.”

Much of the limited research done so far has focused on salmon species. Minnesota has three salmon species that have been introduced over the years in Lake Superior and its tributaries, including coho salmon.

At a congressional hearing in July, a tire industry official said the U.S. Tire Manufacturers Association supported additional research to learn more about the recently discovered transformation chemical.

University of Minnesota associate professor Nick Phelps wants to find out if more prominent Minnesota species like walleye, bass or bluegill are susceptible to the chemical.

"Given the acute toxicity at very low concentrations, it got a lot of people’s attention. And I think it's well-deserved,” said Phelps. “I am very confident we will find the chemical here in Minnesota. The extent of the problem is still unknown. And the impact it might have on our local species is a question."

Phelps and a team of scientists submitted a proposal for research funding to the Legislative-Citizen Commission on Minnesota Resources to first test for the chemical in urban waterways, and establish the level of sensitivity for ecologically and economically important fish species in the state.

A fish with a hook in its mouth leaps out of the water.
A brook trout leaps out of the water after biting a fly in a creek down the Gunflint Trail near Grand Marais, Minn.
Evan Frost | MPR News 2019

Phelps has studied fish kills across the state and he found many that are unexplained.

He said it's important to understand if the toxic tire chemical might be responsible for some of those events.

"We're primarily concerned about these urban areas and massive impulses of water from road runoff. The lake that has the most fish kills over the timespan that we have data is Lake Calhoun (renamed Bde Maka Ska). Those are the types of places where we're probably going to focus this study," said Phelps.

The Legislative-Citizen Commission on Minnesota Resources did not recommend a package of research projects for this legislative session, leaving the fate of the request and dozens of other research proposals in doubt.