Salmon deaths may be linked to dangerous chemical found in tires: experts

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After years of extensive research and not understanding why coho salmon were dying after heavy rains, scientists believe it's linked to a chemical found in automotive tires.

The study, published in Science, links the massive number of deaths of the West Coast-based coho salmon to a chemical known as 6PPD, which is used to make tires last longer.

“Most people think that we know what chemicals are toxic and all we have to do is control the amount of those chemicals to make sure water quality is fine," the study's co-author, Edward Kolodziej, said in a statement. "But, in fact, animals are exposed to this giant chemical soup and we don’t know what many of the chemicals in it even are.” 

A team led by researchers at the University of Washington Tacoma, UW and Washington State University Puyallup have discovered a chemical that kills coho salmon in urban streams before the fish can spawn. Shown here Zhenyu Tian (left), a research scientist at the Center for Urban Waters at UW Tacoma; Jenifer McIntyre (right), an assistant professor at WSU School of the Environment in Puyallup; and Edward Kolodziej (right, background), an associate professor in both the UW Tacoma Division of Sciences & Mathematics and the UW Department of Civil & Environmental Engineering, are at Longfellow Creek, an urban creek in the Seattle area. (Credit: Mark Stone/University of Washington)

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“Here we started with a mix of 2,000 chemicals and were able to get all the way down to this one highly toxic chemical, something that kills large fish quickly and we think is probably found on every single busy road in the world," Kolodziej, an associate professor at the University of Washington, added.

As the tire treads break down over time, the 6PPD, which lead author Zhenyu Tian described as a "preservative for tires," reacts with the ozone to become a byproduct known as 6PPD-quinone, and becomes toxic to the fish.

“There were periods last year when we thought we might not be able to get this identified," Tian explained. "We knew that the chemical that we thought was toxic had 18 carbons, 22 hydrogens, two nitrogens and two oxygens. And we kept trying to figure out what it was. “Then one day in December, it was just like bing! in my mind. The killer chemical might not be a chemical directly added to the tire, but something related.”

According to the research, approximately 0.1% of coho salmon return to their homes and lay eggs before dying. In a healthy area, less than 1% of them die before laying eggs, but with the presence of 6PPD-quinone, the percentage jumped to anywhere between 40% and 90%.

The researchers found the presence of 6PPD-quinone in several spots along the West Coast, including Los Angeles, urban creeks near San Francisco, as well as the Puget Sound region. 

With the near-ubiquitous presence of 6PPD-quinone, the experts say they need additional research to understand why it's so toxic and what can be done about it.

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“How does this quinone lead to toxicity in coho? Why are other species of salmon, such as chum salmon, so much less sensitive?” study co-author and Washington State University aquatic toxicologist Jen McIntyre asked. “We have a lot to learn about which other species are sensitive to stormwater or 6PPD-quinone within, as well as outside, of the Puget Sound region.”

Given that there are more than 3 billion tires sold every year, according to research firm Freedonia Group, the presence of 6PPD and a substitute for it is of extreme importance, the scientists explained.

“Tires need these preservative chemicals to make them last,” Kolodziej said. “It’s just a question of which chemicals are a good fit for that and then carefully evaluating their safety for humans, aquatic organisms, etc. We’re not sure what alternative chemical we would recommend, but we do know that chemists are really smart and have many tools in their toolboxes to figure out a safer chemical alternative.”

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