Tire Dust and 6-PPD-Q

What is 6-PPD-Q?

Scientists recently discovered a chemical in tire dust, called 6-PPD-Q, that is toxic to coho salmon and other aquatic life. This dust rubs off our tires when we drive, then gets washed to our creeks when it rains.

This chemical is added to our tires to help them last longer and keep our cars safe. The discovery of 6-PPD-Q and its effects on coho salmon are relatively new. This means there is still a lot of research to be done to understand its impacts, assess if there are safer alternatives, and find out how we can remove it from our rainwater runoff.

6-PPD-Q in Kirkland

Teams from King County Streams Monitoring recently released data documenting the presence of 6-PPD-Q in the upper reaches of Juanita Creek and in Yarrow Creek, as well as other places in the county.

Results indicate higher levels of 6-PPD-Q at sampling sites immediately next to busy roads like I-405 and NE 132nd St. Approximately 189,000 cars use I-405 through Kirkland every day.

What do we know about it?

6-PPD-Q is highly toxic to coho salmon. Research shows that 6-PPD-Q kills between 40-90% of coho salmon before they are able to spawn. Studies also show 6-PPD-Q is toxic to other fish like rainbow trout and brook trout. However, other fish like Chinook salmon appear to be less impacted. Further research is ongoing to understand more.

Is it harmful to humans? Impacts of 6-PPD-Q on human health are not well understood at this time. Further research is currently underway.

What is the City doing to keep our creeks clean?

City of Kirkland takes the health of our creeks seriously. Specific actions and projects include:

Installation of rainwater treatment projects like the 132nd Square Park vault, 100th Ave NE modular wetlands, and North Rose Hill infiltration wells.

Regular cleaning of our streets and stormwater system to remove pollutants. In 2023 we cleaned 2,500 storm drains and swept 1,700 miles of street. Read our Surface Water Utility Annual Progress Report(PDF, 3MB) .

Education and outreach efforts to encourage green driving behaviors, including our Don’t Wait to Inflate campaign to encourage proper tire inflation. Properly inflated tires help reduce toxic tire dust.

What can I do to keep our creeks clean?

Drive less - Choose talk walk, bike, carpool, or take transit to help reduce tire dust runoff.

Don’t Wait to Inflate – check your tires monthly and add air if needed. Properly inflated tires keep you safe, save gas money, and help salmon.

Only let rain down the storm drain. Learn more about keeping our creeks clean every day.

Additional Resources

Don't Wait to Inflate Tire Care Blog

Department of Ecology 6PPD Information

King County Streams Monitor