The discovery of a mysterious chemical that kills coho salmon in urban streams is expected to spawn new research throughout the world while possibly inspiring new demands for protective regulations.
The deadly chemical, associated with automobile tires, was identified by researchers at the University of Washington’s Center for Urban Waters, which is affiliated with the Puget Sound Institute. The findings were published yesterday in the journal “Science.” I wrote about this discovery and more than 20 years of related scientific investigations in PSI’s online magazine “Salish Sea Currents.”
“This is an important finding,” said Erik Neatherlin, executive coordinator of the Governor’s Salmon Recovery Office. “We have known that stormwater is an issue. Now we can talk about the specific culprit (affecting coho).”

A chemical known as 6-PPD is often added to tires to extend their useful life. The additive works by reacting with ground-level ozone before the ozone can damage the tire’s rubber. The chemical reaction produces 6-PPD-quinone, a compound apparently never studied until now. The newly discovered compound is estimated to be more than 100 times as toxic as the parent compound, 6-PPD.
Neatherlin said the logical course toward solving the problem for coho involves strategies to reduce stormwater pollution and finding safer alternatives to 6-PPD. State and federal agencies, Indian tribes, salmon-recovery groups and industry should work together on this, he said.
“I see this as an opportunity to work directly with industry and to find alternatives to this preservative,” Neatherlin said. “We will need to do follow-up scientific studies. I don’t think we need to pit folks against each other right now.”
The findings reported in the new scientific paper are being reviewed by chemists working for tire manufacturers, according to Sarah Amick of the U.S. Tire Manufacturers Association. The tire scientists are already working with the UW researchers and regulatory agencies, she said.
“We welcome the continued opportunity to work with them,” said Amick, who is vice president of environment, health, safety and sustainability for the association. Findings from the latest study must be validated before moving forward, she said, adding that it is “premature” to discuss alternative chemicals that could protect tires from ozone.
The association, which represents 13 major tire companies, is committed to not only the safety of tires but also the protection of human health and the environment, Amick said. An industry-funded research effort, known as the Tire Industry Project, has been studying the environmental effects of tires, including tire-wear particles.
“It is our obligation to understand our products’ impacts on the environment,” she said.
[iframe align=”right” width=”560″ height=”315″ src=”https://www.youtube.com/embed/vxmojuC_dJE”%5D
Ed Kolodziej, a UW associate professor and a senior author of the new paper, said he expects the findings to inspire other researchers to launch investigations into numerous issues raised by the research. They range from basic questions about how long 6-PPD-quinone persists under various environmental conditions to how the chemical affects lesser-known species.
Nat Scholz, a marine zoologist with NOAA’s Northwest Fisheries Science Center, said tires are used in automobiles throughout the world, and stormwater is a problem everywhere. It is important to learn what other species might be affected by tire chemicals, he said. Another big question is whether toxic compounds can accumulate in animal tissues and whether greater concentrations are found in species higher on the food web, a process called bioaccumulation.
Tire chemistry, which has been of interest in several European countries, also plays a role in human health. Artificial turf and crumb rubber used on playfields typically are made with ground-up tires, and researchers say they expect ongoing studies into the health effects of such uses on athletic fields.
Coincidentally, while the new study on tire chemicals was undergoing formal review, artificial turf containing ground-up tires was washing downstream in the Puyallup River from the Electron Dam in Pierce County. The artificial turf had been installed as part of a temporary water-diversion structure during reconstruction of the dam. During late July and August, high flows damaged a plastic liner, allowing pieces of artificial turf and tire particles to wash downstream. That unpermitted use of artificial turf has come under heavy criticism. Long-term effects of that incident remain under investigation, and the latest study reported in “Science” could raise new implications about the extent of the damage.
While 6-PPD-quinone produces dramatic and deadly effects for coho salmon, as reported yesterday, stormwater exposure seems to have little effect on chum or sockeye, based on previous studies. Steelhead and Chinook may be affected but to a lesser degree than coho.
Studies into how the toxic chemical affects the physiology of salmon are underway, and experts expect that other studies will be proposed to better understand the toxic effects of 6-PPD-quinone exposure on a variety of species, including humans.
In portions of California and Oregon, coho salmon are listed as threatened or endangered under the Endangered Species Act. The new findings on this toxic chemical in tires could bring more funding to answer questions about the threats to salmon. A need to better understand subtle effects of tire chemicals on steelhead and Chinook as well as other species could lead to increased research attention, as federal and state authorities develop recovery plans for threatened and endangered salmon along the West Coast.
Michelle Chow, who worked on the coho mortality studies as a UW graduate student, now serves as stormwater and toxics policy manager for Washington Environmental Council.
The recent identification of the deadly chemical related to tires is “a huge step forward,” Chow said, but it is essential not to lose track of the big picture.
“We know that stormwater has this effect,” she said, “but we don’t know what the other effects might be on the food web — from insects up to southern resident orcas. It is important to remember that we have found one chemical for this particular issue, but there are so many other chemicals in stormwater.”
Studies have shown that filtering stormwater through natural soils and vegetation can significantly reduce the overall toxicity. While it would be impossible to install such “green infrastructure” everywhere, things can be done in strategic locations, Chow said. Meanwhile, minimizing impervious roads and driveways throughout the region can reduce the amount of stormwater going into salmon streams.
Now that researchers have identified the chemical responsible for killing coho, Chow would like to see the Washington Department of Ecology gather all available information about tire chemistry from the tire manufacturers. The state agency can demand such information under a 2019 law that created the Safer Products for Washington program.
“We have to start thinking about the different possibilities,” she said. “We need to find out if a safer alternative exists. We are hoping that (industry officials) are thinking about how they can work quickly to start solving this problem.”
Safer Products for Washington involves designating chemicals of highest concern, determining if alternative chemicals are available and deciding if regulations are needed to protect people and the environment. Five classes of chemicals are currently in the second year of a four-year review. A new round of review for new priority chemicals will begin in 2022, and anyone can offer suggestions about what chemicals should be considered for study, said Lauren Tamboer, spokeswoman for the program.
Officials can be expected to debate whether the tire chemical 6-PPD should be considered a priority chemical under the Safer Products program. Another approach, if alternative chemicals are available, is for the Legislature to simply ban 6-PPD from tires at a future date.
That was the approach used to eliminate copper in automobile brake pads, after it was found that copper affects the sense of smell in coho salmon, potentially disrupting their ability to avoid predators and find their way home. The Washington Legislature approved the ban in 2010. California quickly followed, paving the way for new national standards. That was nine years before the Safer Products law was approved. Although it took time to implement, the ban on copper has proven successful, and several alternative brake materials are now on the market. Check out Water Ways, Nov. 6.
The 20-year effort to figure out what was killing the coho makes for a compelling story, one that has already captured the attention of news reporters across the U.S. and in Europe. Here are some of the stories published so far:

• New York Times: “How Scientists Tracked Down a Mass Killer (of Salmon)”
• Los Angeles Times: “Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires”
• Seattle Times: “Tire dust killing coho salmon returning to Puget Sound, new research shows”
• Marin Independent Journal: “Study finds California salmon face deadly threat from car tires”
• CNN: “Salmon have been dying mysteriously on the West Coast for years. Scientists think a chemical in tires may be responsible”
• UPI: “Toxic tire additive blamed for massive coho salmon die-offs”
• The Guardian: “Pollution from car tires is killing off salmon on US west coast, study finds”
• Science magazine: “Common tire chemical implicated in mysterious deaths of at-risk salmon”
• The Daily Mail: “Toxic chemicals used to stop car tyres wearing out too fast are leaching into rivers and killing off salmon, researchers warn”
• Chemistry World: “Tyre chemical drives mystery salmon deaths”

The discovery of a mysterious chemical that kills coho salmon in urban streams is expected to spawn new research throughout the world while possibly inspiring new demands for protective regulations.
The deadly chemical, associated with automobile tires, was identified by researchers at the University of Washington’s Center for Urban Waters, which is affiliated with the Puget Sound Institute. The findings were published yesterday in the journal “Science.” I wrote about this discovery and more than 20 years of related scientific investigations in PSI’s online magazine “Salish Sea Currents.”
“This is an important finding,” said Erik Neatherlin, executive coordinator of the Governor’s Salmon Recovery Office. “We have known that stormwater is an issue. Now we can talk about the specific culprit (affecting coho).”

A chemical known as 6-PPD is often added to tires to extend their useful life. The additive works by reacting with ground-level ozone before the ozone can damage the tire’s rubber. The chemical reaction produces 6-PPD-quinone, a compound apparently never studied until now. The newly discovered compound is estimated to be more than 100 times as toxic as the parent compound, 6-PPD.
Neatherlin said the logical course toward solving the problem for coho involves strategies to reduce stormwater pollution and finding safer alternatives to 6-PPD. State and federal agencies, Indian tribes, salmon-recovery groups and industry should work together on this, he said.
“I see this as an opportunity to work directly with industry and to find alternatives to this preservative,” Neatherlin said. “We will need to do follow-up scientific studies. I don’t think we need to pit folks against each other right now.”
The findings reported in the new scientific paper are being reviewed by chemists working for tire manufacturers, according to Sarah Amick of the U.S. Tire Manufacturers Association. The tire scientists are already working with the UW researchers and regulatory agencies, she said.
“We welcome the continued opportunity to work with them,” said Amick, who is vice president of environment, health, safety and sustainability for the association. Findings from the latest study must be validated before moving forward, she said, adding that it is “premature” to discuss alternative chemicals that could protect tires from ozone.
The association, which represents 13 major tire companies, is committed to not only the safety of tires but also the protection of human health and the environment, Amick said. An industry-funded research effort, known as the Tire Industry Project, has been studying the environmental effects of tires, including tire-wear particles.
“It is our obligation to understand our products’ impacts on the environment,” she said.
[iframe align=”right” width=”560″ height=”315″ src=”https://www.youtube.com/embed/vxmojuC_dJE”%5D
Ed Kolodziej, a UW associate professor and a senior author of the new paper, said he expects the findings to inspire other researchers to launch investigations into numerous issues raised by the research. They range from basic questions about how long 6-PPD-quinone persists under various environmental conditions to how the chemical affects lesser-known species.
Nat Scholz, a marine zoologist with NOAA’s Northwest Fisheries Science Center, said tires are used in automobiles throughout the world, and stormwater is a problem everywhere. It is important to learn what other species might be affected by tire chemicals, he said. Another big question is whether toxic compounds can accumulate in animal tissues and whether greater concentrations are found in species higher on the food web, a process called bioaccumulation.
Tire chemistry, which has been of interest in several European countries, also plays a role in human health. Artificial turf and crumb rubber used on playfields typically are made with ground-up tires, and researchers say they expect ongoing studies into the health effects of such uses on athletic fields.
Coincidentally, while the new study on tire chemicals was undergoing formal review, artificial turf containing ground-up tires was washing downstream in the Puyallup River from the Electron Dam in Pierce County. The artificial turf had been installed as part of a temporary water-diversion structure during reconstruction of the dam. During late July and August, high flows damaged a plastic liner, allowing pieces of artificial turf and tire particles to wash downstream. That unpermitted use of artificial turf has come under heavy criticism. Long-term effects of that incident remain under investigation, and the latest study reported in “Science” could raise new implications about the extent of the damage.
While 6-PPD-quinone produces dramatic and deadly effects for coho salmon, as reported yesterday, stormwater exposure seems to have little effect on chum or sockeye, based on previous studies. Steelhead and Chinook may be affected but to a lesser degree than coho.
Studies into how the toxic chemical affects the physiology of salmon are underway, and experts expect that other studies will be proposed to better understand the toxic effects of 6-PPD-quinone exposure on a variety of species, including humans.
In portions of California and Oregon, coho salmon are listed as threatened or endangered under the Endangered Species Act. The new findings on this toxic chemical in tires could bring more funding to answer questions about the threats to salmon. A need to better understand subtle effects of tire chemicals on steelhead and Chinook as well as other species could lead to increased research attention, as federal and state authorities develop recovery plans for threatened and endangered salmon along the West Coast.
Michelle Chow, who worked on the coho mortality studies as a UW graduate student, now serves as stormwater and toxics policy manager for Washington Environmental Council.
The recent identification of the deadly chemical related to tires is “a huge step forward,” Chow said, but it is essential not to lose track of the big picture.
“We know that stormwater has this effect,” she said, “but we don’t know what the other effects might be on the food web — from insects up to southern resident orcas. It is important to remember that we have found one chemical for this particular issue, but there are so many other chemicals in stormwater.”
Studies have shown that filtering stormwater through natural soils and vegetation can significantly reduce the overall toxicity. While it would be impossible to install such “green infrastructure” everywhere, things can be done in strategic locations, Chow said. Meanwhile, minimizing impervious roads and driveways throughout the region can reduce the amount of stormwater going into salmon streams.
Now that researchers have identified the chemical responsible for killing coho, Chow would like to see the Washington Department of Ecology gather all available information about tire chemistry from the tire manufacturers. The state agency can demand such information under a 2019 law that created the Safer Products for Washington program.
“We have to start thinking about the different possibilities,” she said. “We need to find out if a safer alternative exists. We are hoping that (industry officials) are thinking about how they can work quickly to start solving this problem.”
Safer Products for Washington involves designating chemicals of highest concern, determining if alternative chemicals are available and deciding if regulations are needed to protect people and the environment. Five classes of chemicals are currently in the second year of a four-year review. A new round of review for new priority chemicals will begin in 2022, and anyone can offer suggestions about what chemicals should be considered for study, said Lauren Tamboer, spokeswoman for the program.
Officials can be expected to debate whether the tire chemical 6-PPD should be considered a priority chemical under the Safer Products program. Another approach, if alternative chemicals are available, is for the Legislature to simply ban 6-PPD from tires at a future date.
That was the approach used to eliminate copper in automobile brake pads, after it was found that copper affects the sense of smell in coho salmon, potentially disrupting their ability to avoid predators and find their way home. The Washington Legislature approved the ban in 2010. California quickly followed, paving the way for new national standards. That was nine years before the Safer Products law was approved. Although it took time to implement, the ban on copper has proven successful, and several alternative brake materials are now on the market. Check out Water Ways, Nov. 6.
The 20-year effort to figure out what was killing the coho makes for a compelling story, one that has already captured the attention of news reporters across the U.S. and in Europe. Here are some of the stories published so far:

• New York Times: “How Scientists Tracked Down a Mass Killer (of Salmon)”
• Los Angeles Times: “Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires”
• Seattle Times: “Tire dust killing coho salmon returning to Puget Sound, new research shows”
• Marin Independent Journal: “Study finds California salmon face deadly threat from car tires”
• CNN: “Salmon have been dying mysteriously on the West Coast for years. Scientists think a chemical in tires may be responsible”
• UPI: “Toxic tire additive blamed for massive coho salmon die-offs”
• The Guardian: “Pollution from car tires is killing off salmon on US west coast, study finds”
• Science magazine: “Common tire chemical implicated in mysterious deaths of at-risk salmon”
• The Daily Mail: “Toxic chemicals used to stop car tyres wearing out too fast are leaching into rivers and killing off salmon, researchers warn”
• Chemistry World: “Tyre chemical drives mystery salmon deaths”