Salmon have mysteriously been dying on the West Coast for years. Scientists believe chemical in tires may be responsible

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After heavy rains each fall, fish died in large numbers before spawning, a mysterious phenomenon that has been the subject of intense research for years.

Now scientists believe they have found a key piece of this morbid puzzle – and according to a new study it is prevalent on the roads of North America.

It starts with a chemical antioxidant called 6PPD, which is used in tires around the world to make them last longer.

However, as tire treads break down over time and leave chunks of microplastics on the roads, the 6PPD they contain reacts with ozone to become a different chemical – a chemical previously not reported. byproduct called 6PPD-quinone, say scientists.

This chemical is toxic to coho salmon. Researchers have found its presence in road runoff samples taken across the west coast, leading them to conclude that this is probably the main cause of the population decline.

A coho salmon is removed from the water to be tagged by a habitat manager in Washington State. Scientists have been studying the mass mortality of these fish for years.
The results were published in the journal Science on Thursday, marking a crucial step in ensuring the survival of these salmon, the scientists said.

“We believe that 6PPD-quinone is the main causative toxicant in these observations of coho mortality in the field,” said Ed Kolodziej, principal investigator of this study. “It’s exciting to start to understand what’s going on because it allows us to deal with these issues more effectively.”

Coho salmon return from the Pacific Ocean each fall to spawn in streams and rivers, and can be found from Alaska to California.

One of five species of salmon found in the forests of the Pacific Northwest, the coho is a favorite with sport fishermen and has enormous cultural significance to many Native American tribes in the region.

They are also an essential part of the food chain. The presence of healthy, breeding coho is a good indicator of the overall health of an ecosystem, said Kolodziej, associate professor of civil and environmental engineering. at the University of Washington.

These mysterious deaths are a clear sign that the coho salmon are in serious trouble.

The central California coho population is listed as Endangered, and three other populations are now listed as Threatened under the Endangered Species Act of the US Fish and Wildlife Service.

In a healthy stream, Kolodziej said less than 1% of adult coho typically die before spawning.

But in these mass death events, 40% to 90% of fish may perish in the most affected rivers, researchers say.

In mass mortality events that have occurred in streams along the west coast, between 40% and 90% of the salmon present have perished.

“We’ve been documenting these mortality events since the early 2000s,” said study co-author Jen McIntyre, aquatic toxicologist at Washington State University. “We suspect they’ve lasted much longer than that, but no one was looking for it.”

McIntyre has been working to unravel the mystery behind the deaths of the coho for decades.

Fish in the waterways closest to high traffic urban areas have often been the worst, Kolodziej said, leading scientists to suspect for years that road runoff was playing a role.

The waterways where these mortality events occurred, scientists had previously reported, contained a chemical profile similar to that of road runoff.

To focus on the likely culprit, scientists examined this leachate in the lab to isolate its chemical components and, through a careful removal process, said they found 6PPD-quinone to be the main cause of fish death. .

Kolodziej thanks study lead author Zhenyu Tian, ​​a researcher at the University of Washington-Tacoma, for playing a key role in the discovery.

Scientists said more research is needed to understand whether the chemical is toxic to other aquatic species – and even humans – given its prevalence in the environment.

“It would be surprising if these salmon were the only sensitive fish species,” Kolodziej said. “To me, that’s a simple argument of probability. There are over 30,000 species of fish, and it would be really unlikely that coho salmon were the only one.”

Even with this chemical identified, the scale of the problem could make it difficult to save the fish.

Microplastics in Your Tires Likely Reach the Farthest Places on Earth, Study Finds

About 3.1 billion tires for more than 1.4 billion vehicles on the planet are produced each year, according to the study, and this chemical appears to be used in almost all of them.

Previous studies have shown that tire abrasion is one of the world’s largest sources of microplastics in aquatic ecosystems and is responsible for about 30% of all microplastic particles in our oceans.

Better treatment and management of runoff before it enters coastal streams is part of the solution, the study authors say, but source control and the development of chemical substitutes ” greens’ for the 6PPD in the tires are also required.

Responding to these findings, Sarah Amick, vice president of the United States Tire Manufacturers Association, responsible for the environment, health safety and sustainability, called the study’s findings “ preliminary ‘, but said that friendly products.

“The tire manufacturing industry and our member companies design tires for safety and durability. And every element, every material that goes into a tire is focused on the motorist’s ability to drive safely. on that tire, ”Amick said. “Our industry is deeply committed to sustainability and understanding the impacts of our products not only on the environment and wildlife, but also on human health.”

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