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Whether they are orange, pink or red, salmon shares a common color: green. According to a study published earlier this year, salmon was the third most valuable type of fish, valued at $ 598 billion in 2018.
Salmon is not only good, but also good for us. These fish are nutritional powerhouses, loaded with omega-3 fatty acids and essential minerals. Eating a salmon-rich diet could help prevent cognitive decline, improve men’s reproductive health, and possibly even treat depression.
The demand is so high that some types of salmon struggle to keep up. But overfishing and human appetite aren’t the only danger to these fish – another human desire could drastically reduce their numbers, suggests a new study.
The danger comes when salmon return from the ocean to the rivers to spawn. Trapped in rivers, up to 40-90% of salmon can be killed not through fishing, but by driving.
The culprit, it seems, isn’t the exhaust fumes from the cars, the new research suggests. Rather, it’s the car itself – its tires.
Tires are universally made from a combination of natural rubber, synthetic rubber, steel and a variety of other materials. Inside fabrics and fillers is a little known chemical compound called 6PPD, the main antioxidant chemical used in tires. When combined with ozone, it forms what is known as 6PPD-quinone.
The study zoomed in on a species of salmon, coho salmon: these salmon commonly end up on American dishes, but some populations of coho salmon are considered endangered under the Endangered Species Act. The chemical 6PPD-quinone is deadly to salmon. coho, according to the new study.
Smoking gun – Edward Kolodziej is an associate professor at the University of Washington and the author of the study. He describes the study as “a classic detective story”, in which researchers turned to forensic techniques to “find the smoking gun” behind the salmon deaths.
Kolodziej and his team study what’s known as urban runoff mortality syndrome, which occurs when salmon returns from the ocean and encounters untreated rainwater from urban areas in rivers. Symptoms are not nice: The syndrome starts with the salmon acting lethargically, swimming on the surface of the water, appearing to pant and lose motor skills. Eventually, the salmon dies. No fish have ever been found to recover from the syndrome.
Urban runoff mortality occurs after rain or snow moves water through storm drains to larger bodies of water, such as lakes and rivers. When rain and snow fall on city streets, the water collects a wide variety of chemicals, which are what end up in rivers. Most frequently along the journey are those associated with cars. The chemicals range from engine oil to antifreeze, leaving scientists with a poisonous stew to sift through to find the exact killing mechanism.
“We’ve known for 30 or 40 years that there was something in the rainwater that was killing these fish, but we didn’t know what it was.” Kolodziej himself has been working on the problem for the better half of a decade.
Identifying the exact chemical killer was “definitely an interesting time”.
In the new study, Kolodziej and his colleagues used an imaging technique called high-resolution mass spectrometry to look for molecular clues as to what was killing the salmon.
“We’ve known for three or four years that the only thing that was killing Coho salmon was little bits of rubber and water. That was the only chemical source we looked at, from vehicle fluids and things like that, that could actually kill fish. ”Tiny pieces of rubber and plastic have become unavoidable on the planet.
There was only one way to determine if 6PPD-quinone was indeed the culprit: look inside the fish. The team obtained dead salmon from urban runoff mortality syndrome in the wild, carefully examining them for signs of the chemical. The team also took coho salmon from two local creeks and raised them at Washington State University’s Puyallup Research and Extension Center, where they were able to check the water supply with exact accuracy. Then, they were able to add small amounts of 6PPD-quinone and observe the reactions in a controlled environment. The results were the same as in the savage.
Tire change – Kolodziej states that the study presents “a difficult question. Because we can’t control what’s in our tires. ”
Changing the composition of tires would require large-scale changes in production. Ultimately, Kolodziej hopes the company can find “a way to find safer ingredients for tires.”
Meanwhile, Kolodziej says there are “obvious things” people can do now to improve the salmon’s prospects when swimming upstream.
“Don’t park your car in a river. Don’t throw your used tire in a river, “he says.
Coho salmon is unlikely to be uniquely affected by 6PPD-quinone. More studies are needed to fully understand how much damage this chemical causes in the ecosystem. It is also unclear whether the salmon we eat also contains 6PPD-quinone.
The history of the Coho salmon is intertwined with the history of America even before the country was born. The fish, which lives mainly in the Pacific Ocean, has been part of the indigenous mythologies and livelihoods between the Salish, Squamish and Spokane coast for centuries. Beyond the money salmon brings or the bellies they stuff around the world, salmon is a crucial part of American culture. Their survival may hinge on finding that safer ingredient.
Abstract: In the United States, Pacific Northwest coho salmon (Oncorhynchus kisutch), annual exposure to rainwater causes unexplained acute mortality when adult salmon migrate to urban creeks to reproduce. By studying this phenomenon, we identified a highly toxic quinone transformation product of N- (1,3-dimethibutyl) -N-phenyl-p-phenylenediamine) (6PPD), a globally ubiquitous tire rubber antioxidant. The retrospective analysis of the representative runway and stream runoff impacted by rainwater from the west coast of the United States indicated the widespread presence of 6PPD-quinone (<0.3-1.9 µg / L) at toxic concentrations. These results reveal unexpected risks of 6PPD antioxidants for an aquatic species and imply toxicological relevance for the rubber residues of dissipated tires.
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