What is 6PPD? How a Tire Chemical Harms Salmon — and Possibly Your Health

In 2020, scientists discovered the culprit behind decades of mass salmon deaths in the Pacific Northwest: 6PPD, a chemical used in every tire vehicle in America that creates a toxic byproduct once it’s exposed to the environment.

Known as 6PPD-Q, this toxic byproduct has been killing salmon for decades, decimating populations that support entire ecosystems, tribal lifeways, and the fishing industry economy. The tire industry knows that 6PPD-Q is a coho salmon killer yet has failed to commit to replacing it. In response, Earthjustice sued the tire industry, and we won’t back down until salmon are protected, as the law demands.

What is 6PPD-Q?

For decades, the tire industry has added the chemical 6PPD to its tires to help slow tire degradation. Once 6PPD is exposed to ozone in the air, it forms the chemical byproduct 6PPD-Q. Every time you go for a drive, your tires are shedding 6PPD-Q onto the road, which may eventually make its way into nearby streams that salmon use for spawning.

Almost 300 million vehicles are registered in the U.S., each of them equipped with multiple tires that continuously shed tire waste particles when driven. Researchers estimate that each person in the U.S. creates roughly a bowling-ball’s weight of tire waste each year.

Why is 6PPD-Q a problem for salmon?

6PPD-Q is extremely toxic to salmon. In fact, just a few drops of 6PPD-Q in an Olympic-sized swimming pool can cause mass coho salmon deaths in a few hours, and scientists believe it’s likely that 6PPD-Q is harming aquatic species worldwide.

Salmon populations are already struggling from a combination of habitat degradation, excessive harvest, and harmful dams. 6PPD-Q only adds to those stressors, and scientists believe we cannot fully protect salmon from further decline without addressing 6PPD in tires.

Is 6PPD-Q dangerous to me?

Researchers have found widespread 6PPD-Q contamination in humans, in everything from urine and blood to spinal fluid. What that means for our health is still emerging, but early scientific findings are concerning. Research on human health effects from the chemical is still ongoing, but early studies have linked 6PPD-Q to reproductive impairment, potential carcinogenicity, and even potentially Alzheimer’s.

Tire waste particles and dust are the main contributors to human exposure to 6PPD-Q, with 6PPD-Q contamination even found on foods like lettuce and eggs. Scientists are still figuring out what exposure levels of 6PPD-Q are harmful to humans, and there is still much we don’t know about this toxic chemical.

How is Earthjustice fighting to end 6PPD and 6PPD-Q contamination?

• Suing the tire industry. Tire manufacturers have known for years that 6PPD harms salmon. In November 2023, we sued 14 tire companies, representing roughly 80% of the U.S. tire market. Our lawsuit alleges that tire companies are violating the Endangered Species Act (ESA) by continuing to use a chemical in their product that kills and injures critically imperiled salmon and trout protected under the ESA. Our clients are commercial fishing families up and down the West Coast.
• Pushing for federal regulations. In 2023, the Environmental Protection Agency (EPA) granted a petition that we submitted on behalf of the Yurok, Port Gamble S’Klallam, and Puyallup Tribes recognizing that 6PPD in tires poses an unreasonable risk to the environment. Now, the agency must take the next step in regulating this toxic chemical under the Toxic Substances Control Act.