Are Toxic Tires Killing Salmon?


Coho Salmon Spawner. Photo by K. King, USFWS.


A new study published in the journal Science may help explain why California’s coho salmon runs continue to decline. The study examined “urban runoff mortality syndrome,” a disconcerting phenomenon where stormwater runoff produces large mortality events. Clearly there was something in the water. But what? Researchers started by looking at over 2,000 chemicals routinely found in car tires and eliminated potential killers until one remained: 6PPD-quinone (pronounced “kwih-known”), a byproduct of a tire preservative. This chemical is now thought to be the primary driver in stormwater-related mortality events. EPIC’s podcast, the EcoNews Report, recently featured Warner Chabot from the San Francisco Estuary Institute to discuss the report. Listen here! (P.S. Subscribe to the EcoNews Report on your favorite podcast app!) You can also read the full report here

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Arriving at this conclusion took hard work and good science. First, scientists began with a list of chemicals found in stormwater runoff and noticed that all problem areas shared a common feature: chemicals found in tires. Then they began grouping chemicals together and testing. They were able to find that metals were not an issue, for example, by testing whether a concentrate with just metals found in tires killed the salmon. Through this repetitive process, they eliminated classes of chemicals and individual chemicals until just a few remained, including one that didn’t appear to be related to tires–at least at first. Scientists knew the constituent parts of the chemical–18 carbons, 22 hydrogens, two nitrogens and two oxygens–but nothing like that matched the known chemicals in tires. It then required an “a-ha!” moment to solve for the mystery chemical.

6PPD-quinone is produced when ozone reacts with 6PPD. This isn’t by accident, that is what is supposed to happen! Because 6PPD reacts with ozone, other parts of the rubber tire do not, helping to lengthen the life of the tire. Because we now know the problem, we can solve it. There is already a petition before the California Department of Toxic Substance Control to examine zinc, another toxic addition to tires. If the agency begins a regulatory process to address zinc, then 6PPD-quinone can be added to their list of things to consider as well. There is also interest from tire manufacturers, who worked cooperatively with researchers here, in addressing the issue.