Scientists believe they have figured out why coho salmon are mysteriously dying in large numbers after heavy rain events.
The key factor that contributes to the deaths is a chemical antioxidant known as 6PPD, which is used in tires to make them last longer; however, according to scientists, the 6PPD in the bits of tires left on the roads react with ozone to become a byproduct called 6PPD-quinone.
"We believe that 6PPD-quinone is the primary causal toxicant for these observations of coho salmon mortality in the field," said the lead investigator for the study, Ed Kolodziej. "It's exciting to start to understand what is happening because that starts to allow us to manage these problems more effectively."
Coho salmon return from the Pacific Ocean each fall to spawn in streams and rivers and can be found from Alaska all the way down into California.
The central California coho population has been classified as endangered under the Endangered Species Act by the U.S. Fish and Wildlife Service.
Typically, fewer than 1% of adult coho die before spawning. Now, with the mass deaths, anywhere from 40% to 90% of the fish perish before spawning.
"We've been documenting these mortality events since the early 2000s," said Jen McIntyre, study co-author and aquatic toxicologist at Washington State University. "We suspect they've been going on for much longer than that, but nobody was looking for it."
Scientists previously reported that waterways where the mass deaths have occurred contained a chemical profile that was similar to roadway runoff. They say more research is needed to understand whether this chemical is toxic to other aquatic species and even humans.
"It would be surprising that these salmon are the only sensitive species of fish," Kolodziej said. "To me, it's a simple probability argument. There are over 30,000 species of fish, and it would just be really unlikely that coho salmon are the only one."
Even with this chemical identified, saving the fish will be difficult. Nearly 3.1 billion tires are produced annually, and the hazardous chemical is used in almost all of them.
"The tire manufacturing industry and our member companies design tires for safety and durability purposes. And every element, every material that goes into a tire is focused on the motorist's ability to drive safely on that tire," said Sarah Amick, the U.S. Tire Manufacturer's Association vice president of environment, health safety, and sustainability. "Our industry is deeply committed to sustainability and understanding our products' impacts not only on the environment and wildlife, but also on human health as well."