Salmon deaths linked to chemical

Scientists in the Pacific Northwest say they’ve solved a long-running mystery behind the region’s dying salmon, a discovery that may explain what’s harming fish elsewhere around the globe, including California.

In research published Thursday, a team of university and government scientists identify a toxic material derived from tire treads that is washing into rivers and creeks as the killer of as many as 90% of the coho salmon in parts of the Puget Sound.

The finding is a welcome breakthrough for Washington state after decades of losing the revered fish without a full explanation. However, it also points to a bigger problem, one that’s both difficult to solve and not limited to a single part of the country, and possibly rampant in urban areas everywhere.

“Tires are obviously ubiquitous in our society,” said Jenifer McIntyre, one of the senior authors of the new study published in the journal Science and an assistant professor at Washington State University’s School of the Environment. “We expect to find this chemical in water bodies around the world.”

As part of the study, a handful of waterways in California were tested for the fish-killing compound, called 6PPDquinone. The scientists found the compound present at lethal levels in four of nine spots sampled along San Francisco Bay, including in Oakland, two areas in San Jose and near the Carquinez Strait.

While the bay no longer hosts migrating coho salmon, nearby rivers and creeks that flow to the ocean do. The toxic substance, the researchers say, could also be hurting other struggling fish that move through San Francisco Bay, such as chinook salmon and steelhead trout.

“There are signs that other salmonids have some sensitivity,” said Rebecca Sutton, a senior scientist at the San Francisco Estuary Institute who led the toxicity tests in the Bay Area and coauthored the new paper. “There will have to be follow-up to see what species are sensitive.”

Among the many future tests expected to come out of the study is looking at whether dangerous levels of the compound are present in the California rivers and streams that contain coho salmon, which include Pescadero Creek in San Mateo and Santa Cruz counties and Lagunitas Creek in Marin County. Larger populations endure in the Klamath and Eel rivers farther north.

The state’s coho salmon, once widespread in coastal waterways, have dwindled to less than 5% of their historical numbers and are now protected under the federal Endangered Species Act.

The fish generally live at sea, where they feed and grow before migrating to fresh water to spawn. The migrations, though, have faced numerous hurdles, from dams built across the rivers the fish swim up to destruction of their spawning grounds. But even as these issues have been addressed and fish habitats have been restored, the salmon continue to die in many places.

Scientists have long identified runoff from roads into rivers and creeks as a contributing problem for the coho. Recent studies have even implicated tire treads as potentially harmful. But past research hadn’t isolated the material that was hurting the fish or explained how damage was occurring.

After evaluating hundreds of chemicals found in tires and measuring their presence in waterways with dying coho, the authors of the new study determined that 6PPD, an industrial substance used to prolong tire life and often added to rubbers and plastics, was the culprit.

What made the discovery especially challenging was that 6PPD itself isn’t the problem but what happens to 6PPD when it encounters ozone, or smog, according to the researchers. The team found that when 6PPD reacts with the pollutant it breaks down into multiple chemicals, including the lethal 6PPD-quinone, and that’s washing into local waterways.

“There are a lot of studies on tires and microplastic,” said Zhenyu Tian, lead author of the new paper and research scientist at the Center for Urban Waters at the University of Washington at Tacoma. “This (new study) clearly shows the chain of evidence. We showed the connection. We showed evidence that this is harming the environment.”

Tian thinks it’s likely that fish other than coho and additional aquatic animals are being harmed by 6PPD-quinone and that many waterways, not just in Puget Sound, are contaminated.

“As far as we know, almost all tire manufacturers are using this in their tires,” he said.

Representatives of the tire industry said Thursday, after reviewing the study, that it was premature to blame 6PPD for killing fish.

“It’s important that we do additional research and look at this issue holistically,” said Sarah Amick, a vice president and senior counsel for the U.S. Tire Manufacturers Association.

Tire companies, Amick said, have invested heavily in making sure their products contain the most environmentally sustainable materials, and they’re continuing to improve, including adding plant-based substances like soybeans and dandelions to tires. At the same time, she said, the companies can’t compromise the safety of what they sell, meaning that 6PPD, which keeps tires strong, isn’t something they’ll needlessly give up on.

In the short term, the authors of the new study recommend that cities and public works agencies do more to keep streets clean and filter stormwater runoff before it flows into rivers and creeks. Long term, they’d like the tire industry to revisit the composition of its products.

In California, the Department of Toxic Substances Control regulates the harmful effects of such commercial items as tires. A proposal filed with the agency two years ago to reduce the amount of zinc in tires, also believed to harm wildlife, has yet to be addressed.

“This will probably take some time to change,” Tian said.

The study’s authors included researchers at the National Marine Fisheries Service and the U.S. Fish and Wildlife Service.

Tires are hardly the only thing that health and environment experts have sought to regulate to help clean up what runs into waterways. Copper and heavy metals have been phased out of automobile brake pads. The manufacturing of PCBs, once common in electronics and detrimental to marine life, have long been banned. And the application of pesticides has been increasingly subject to restrictions.

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander