Toxic pollutant from car tires reaching San Francisco Bay, scientists say

SAN FRANCISCO (KGO) -- It's no secret that the thousands of cars crisscrossing Bay Area roads and highways contribute to pollution, from air quality issues to CO2 in the atmosphere.

But now, a scientific research group here in the Bay Area is generating new evidence about another type of pollution caused not just by cars but by their tires. It's a chemical known as 6PPD-Q, which is so toxic to some species of fish, that it's believed that a single drop in a swimming pool could be fatal.

"It is a transformation product from an ingredient that's intentionally added to tires. So pretty much every tire on the market right now has this chemical," said Ezra Miller, Ph.D., senior scientist with the San Francisco Estuary Institute.

The organization monitors runoff from streams and creeks that empty into San Francisco Bay.

MORE: Commercial salmon fishing to open in CA for 1st time since 2022 as population rebounds

Miller said the institute was part of a team that first identified 6PPD-Q in the watershed roughly six years ago.

The chemical was already being blamed for the kill-offs of Coho Salmon, which is extinct in San Francisco Bay but still fighting for survival in other parts of California and the West Coast.

"So, there were lots of fish kills, the pre-spawn mortality events as well. They were called, and no one knew what was causing it," Miller said.

"So in Coho salmon specifically, which, you know -- sort of our canaries in the coal mine -- they tend to be the most sensitive of the salmon species," said Charlie Schneider, biologist with the environmental group, California Trout.

We followed along earlier this year, as the organization helped remove a creek barrier, which allowed a larger species of Chinook salmon to return to parts of the East Bay watershed for the first time in some 70 years. Schneider now worries about the longer-term effects of 6PPD-Q on multiple species, including native Steelhead.

MORE: Salmon spotted in Bay Area creek, marking return for 1st time in decades after restoration project

"It's sort of an emerging contaminant that those of us that care about salmon and Steelhead are paying attention to," he said.

Back at the Estuary Institute, Miller said the most recent data shows buildups around the Bay shoreline after winter storms. It's a time of year when Steelhead species return to spawn. Given the fact that the chemical is released as tires wear down during driving, Miller believes the long-term solution could include replacing 6PPDQ in car tires entirely.

"To try to find an alternative for 6PPD, so we can take 6PPD out of car tires," Miller said.

The state of California has begun regulating the chemical, which currently plays a significant role in extending the usable life of tires, a key economic benefit to drivers. And there are ongoing efforts to identify potential replacements that could do the same job, without the pollution risk.