Stormwater News

For over twenty years, environmental scientists battled a baffling mystery in the Pacific Northwest. Salmon who returned to urban streams and rivers in the Puget Sound were dying before they could lay their eggs. While the cause of their deaths was unknown, researchers hypothesize that toxic chemicals from roads and highways were to blame.

Identifying the culprit was of the utmost importance for scientists, as the salmon population plays a vital role in our local ecosystems. Salmon are the main food source of the endangered Southern Resident Orca Whales, whose population is the lowest it’s been in thirty years. Salmon are also linked with the culture of Indigenous communities, as well as the Washington State economy and food supply. This means that the health of the salmon population is closely intertwined with the prosperity of aquatic species as well as humankind.

University of Washington researchers made a breakthrough discovery in 2020 when they pinpointed the chemical culprit: 6PPD-quinone. 6PPD stands for the chemical N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine. This chemical prevents tires from breaking down. When 6PPD is exposed to air, it reacts with ozone (a naturally occurring gas) to create 6PPD-quinone. Due to friction on the road, driving causes tires to release small particles, which contain this harmful chemical. After rainfall, this chemical eventually makes its way into nearby streams and rivers, where it has deadly impacts on salmon.

In order to address an issue as widespread as tire dust, Washington state organizations are working hard to find a solution. Since tires are the main source of 6PPD-quinone, the long-term goal is to prevent tires from releasing this toxic chemical. However, removing 6PPD from tires altogether without an effective replacement would be dangerous for both humans and the environment. The ingredient prevents tires from breaking down quickly, which keeps passengers safe. In addition, the ingredient minimizes the amount of tires in landfills, since it prolongs the tire’s life and defers it being thrown away.

Anacortes Stormwater Manager Diane Hennebert shared her insights on this multifaceted issue. She explained, “If I didn’t work in the stormwater world, my knee-jerk reaction would be, ‘This stuff is bad! We’ve got to stop putting it in tires immediately!’ But, there’s a lot more to think about. What kinds of impacts would it have on safety if tires had an incredibly short lifespan? How many more tires would be sent to the landfill after only being used for short time? What other options do we have and what impacts might those options have?”

Researchers are hard at work searching for safer alternatives. In November of 2021, the WA Dept. of Ecology published an assessment of nine possible alternatives to 6PPD Unfortunately, their research concluded that all nine proposed alternatives were either equally toxic to fish, cancer-causing to humans, or ineffective in keeping tires safely intact. Scientists continue to strive for the discovery of an alternative that would keep both salmon and roadways safe.

The WA Department of Ecology is also testing how to prevent stormwater from transporting 6PPD-quinone from rivers, streams, and the Puget Sound. The department has identified three major pillars in the fight to protect salmon:

1. Capturing Tire Debris: Streets must be swept in order to prevent chemicals and debris from entering into stormwater drainage systems, as well as the water they drain to.
2. Detaining Water: Stormwater ponds could be used to hold large amounts of stormwater. This would slow down runoff and encourage rubber particles to settle. Using filtration areas would let stormwater soak into the ground before entering a body of water.
3. Treating Runoff: Stormwater runoff could be filtered through the soil and grasses in engineered channels, also known as swales. This would ensure that the concentration of pollutants is reduced before it enters a body of water and comes into contact with salmon.

The WA Dept. of Ecology continues to research the effectiveness of these methods, as well as meeting with local governments to incorporate these management practices into their infrastructure. The Department plans to release additional guidance in 2024 in order to assist local governments implement protective stormwater procedures.

Diane Hennebert explained more about how bioretention swales can be used to filter road water runoff. “A bioretention swale is a cross between a highly engineered rain garden and a drainage ditch,” she explained. “Swales consist of a gentle slope and a wide, flat bottom. A swale is designed to slow the water runoff down and allow it to infiltrate the soil, which will cleanse out the 6PPD-Quione compound from the water. The clean water will then be captured in an under-drain and channeled into the stormwater system.”

All drivers and vehicle owners can also take steps to be a part of the solution. Drivers can make an impact by inflating their tires at least every month, or when tire pressure gets low. Properly inflated tires will not shed as many tire particles that contain 6PPD-quinone, the chemical that is deadly to salmon. Click here to learn more about how to keep your tires properly inflated. A small task like inflating your tires has a significant impact on wildlife and your local community.

Want to learn more about the effects of tires on our environment? Check out these sources!

• Don’t Wait to Inflate.
• Saving Washington’s Salmon from Toxic Tire Dust
• Tire Anti-Degradant (6PPD) and 6PPD-Quinone
• Tire Chemicals and Coho Salmon – Washington Stormwater Center