How car tires are decimating salmon populations

“Transportation agencies haven’t done anything about it,” claims new lawsuit aimed at protecting coho from a toxic chemical linked to rubber debris

Rough road: Debris from vehicle tires makes the spawning mission of salmon more perilous than it already is. Photo: ODFW

By Jordan Rane. June 29, 2023. It’s been over two years since the cause of a strange and devastating die-off of Pacific coho salmon was uncovered by clever scientific research—and a week since early signs of the first major lawsuit has rumbled in its wake.

On June 15, the Center for Biological Diversity filed a formal notice of an intent to sue several state and federal agencies for failing to act against the fatal impacts to salmon—from (no one had remotely guessed for decades) tire pollution.

Turns out, coho salmon have been dying en masse for years due to a specific chemical toxin leached from car tires into waterways after storm runoffs.

Identified by a team of Washington State University researchers in 2020, its devastating impacts remain unabated by state and federal agencies, according to the proposed lawsuit.

The ecological mystery ran unsolved for years. Endangered coho salmon along roughly 1,000-miles of Pacific coastal habitat were dying in droves in the immediate aftermath of storms.

The suspected connection—stormwater runoff—was as broad and hazy as it gets.

Something in this brew of thousands of chemicals was decimating salmon populations stretching from the mouth of the Columbia River in Oregon to the San Lorenzo River in Santa Cruz, California, and beyond.

The culprit, we now know, is car tires—specifically, a compound lethal to fish called 6PPD-quinone.

The oxidized form of a chemical (6PPD is an additive intended to prevent damage to tire rubber from ozone) leached from treated tire rubber onto roads by millions of cars and then washed into waterways via storms, 6PPD-quinone is especially toxic to certain anadromous fish.

This discovery from a WSU study led to a groundbreaking report in a December 2020 issue of Science pinpointing 6PPD-quinone as the “primary causal toxicant” for coho die-offs.

“For coho salmon in the U.S. Pacific Northwest, returning to spawn in urban and suburban streams can be deadly,” noted the WSU study’s abstract, entitled Tire Tread Particles Turn Streams Toxic. “Measurements from road runoff and immediate receiving waters show concentrations of 6PPD-quinone high enough to account for the acute toxicity events.”

Widespread overage of the study reported that up to 90% of coho salmon can be lost in streams contaminated by 6PPD-quinone—with fish, according to The New York Times “displaying strange behavior, listing to one side, rolling over, swimming in circles and dying within hours.”

“We’ve known for years now that tire pollution is killing Pacific salmon, but transportation agencies haven’t done anything about it,” said Emily Jeffers, a senior attorney at the Center for Biological Diversity in a June 15 press release. “Salmon are already threatened by drought and loss of habitat, and now it’s clear our commutes and road trips are making it even harder for the species to survive. To give coho salmon a fighting chance, we need action from the top to get this chemical off our roads and out of our waterways.”

Lawsuit targets government agencies

The Center’s 60-Day Notice of Intent to Sue cites violations of the Endangered Species Act regarding stormwater runoff in Oregon and Northern California.

Recipients of the notice include the federal and California Departments of Transportation (Caltrans), the Oregon Division of the Federal Highway Administration, the National Marine Fisheries Service (NOAA) and the Secretary of Commerce for violations of the Endangered Species Act—including “actions and inactions related to maintenance and management of roads affecting imperiled coho and chinook salmon and their critical habitat in California and Oregon,” according to the Notice of Intent.  

“The actions of Caltrans and the FHWA facilitate the ongoing pollution of waterways with 6PPD-quinone,” the Notice claims. “It is likely that maintenance projects will increase the flow of 6PPD-quinone.”

Further studies have determined that the tire chemical is toxic to other endangered fish, including chinook salmon, steelhead trout and even larger marine mammals such as orcas, which rely on coho as a primary food source and risk starvation when salmon populations decline.

Following the release of the initial study, 14 members of Congress sent a letter to the National Marine Fisheries Service in 2021 requesting the agency “take any necessary actions” to address the threat posed by 6PPD, and act with “great urgency.”

The service’s response seems to point to insufficient resources to adequately address the problem: “To better account for these issues, NOAA needs long-term funding to support a robust environmental health research program and to support management actions that consider water quality as a critical part of species habitats.”