Coho salmon deaths linked to chemical from tires

For years, researchers have worked to solve the mysterious cause of extreme coho salmon mortality in the Pacific Northwest. A recent study by the San Francisco Estuary Institute and the University of Washington has finally identified the microscopic culprit as a highly toxic contaminant associated with tire particles.

Coho salmon are especially vulnerable to environmental stressors and are considered to be an endangered species throughout the Pacific Northwest. The study focused on water samples from the San Francisco Bay area and the Puget Sound in Washington state, but scientists fear the contaminant could affect coho salmon in the Eel and Klamath rivers as well.

“It’s been observed for decades now that these healthy adult coho salmon would come into urban streams to spawn and if there was a storm going on and stormwater rushing into a creek near a roadway, the fish would experience a really dramatic assault. They basically start gasping and they can die within hours,” said Rebecca Sutton, a senior scientist at SFEI and a co-author of the study. “Each year, hundreds to thousands are killed.”

Researchers looked for the usual suspects, toxic metals or pesticides, but were unable to identify the culprit.

“We ended up identifying a preservative in tires that can transform into this particular chemical that’s super lethal to these salmon,” Sutton said.

Sutton said her team sampled a mix of 2,000 chemicals found in road runoff and found something called 6PPD, a chemical used to keep tires from breaking down too quickly.

According to the study, “When 6PPD reacts with ozone, the researchers found that it was transformed into multiple chemicals, including 6PPD- quinone, the toxic chemical that is responsible for killing the salmon.”

The chemical doesn’t seem to have the same effect on other fish like steelhead trout or Chinook salmon, but Sutton said it’s too early to tell.

“It does seem to vary but we just discovered this chemical so we really need to do more testing before we can say for sure how different species of salmon react,” Sutton said. “I can say that there’s been some preliminary work to already show that the steelhead exhibit some sensitivity to chemicals in tire rubber. Until now we didn’t know this specific chemical, so we have to start figuring out whether other salmonids are sensitive and just how sensitive compared to the coho.”

Sutton said she’s concerned about coho salmon in the Eel and Klamath rivers but admitted neither river had been tested for the study.

“I do not think contamination from road runoff is causing the same issue for coho salmon in our local streams,” said Darren Ward, a fisheries biologist and assistant professor at Humboldt State University. “We do not see the same high levels of mortality for migrating adults as reported from the Seattle streams.”

However, Ward said the study makes a good case that the contaminant is killing coho salmon in urban streams.

“After rainstorms, they found concentrations of the contaminant in Seattle streams that were higher than the concentrations that killed coho salmon in their experiments. They also found the same contaminant at high concentrations in runoff from highways in Los Angeles and San Francisco,” Ward said. “It is worth paying attention to road runoff as a potential issue, but for now I think we can benefit our local coho salmon populations more by focusing on protecting and restoring complex habitats in our local streams.”

Eel River Recovery Project executive director Patrick Higgins agreed that urban pollution has many components that are harmful to fish.

“With regard to concerns about coho salmon in the Eel River, the only urbanized areas with significant related non-point source pollution are Fortuna and Willits,” Higgins said. “Although U.S. Highway 101 does follow the South Fork of the Eel, dilution from the whole watershed makes the likelihood of adult coho mortality low.”

The main impacts to salmon and steelhead in the Eel River are sediment, temperature and flow, Higgins said.

“These salmon need healthy habitat in terms of water quality, actual habitat and chemistry, so this is just one of many things that they are dealing with,” Sutton said. “I couldn’t say, ‘Forget about that one stressor we used to worry about.’ I think they’re all impacting the salmon.”

Sutton said her team plans to expand their research and work on solutions to remove the chemical from water sources. “There’s plenty of research that the science community can do, but I think what really needs to happen is for the tire industry to assess the preservatives they’re currently using in their tires and see if they can come up with some safer alternatives,” she said.

The study, “Using HighResolution Mass Spectrometry to Identify Orga nic C o n t a mi n a n t s Linked to Urban Stormwater Mortality Syndrome in Coho Salmon” can be found at https:// pubs. acs. org/doi/ 10.1021/acs. est.8b03287.