Scientists point to a toxic chemical produced from tires, which is causing a serious decline in stream salmon.

Each fall, half of the coho salmon (scientific name Oncorhynchus kisutch, also known as silver salmon), goes back on its stomach before they can spawn. Salmon is completely absent from some streams. Scientists have not found a valid explanation.

It wasn’t until a team of researchers from the University of Washington in Tacoma and Washington State University located in Puyallup found the answer: when it rains, the big water pushes pieces of old tires on their way down the stream. The life-choking thing in salmon is a substance in a chemical compound leaking out of the tire molecule, a preservative that prevents the tire from degrading rapidly. The new research has been published in the journal Science.

“Many people think that we already know what harmful substances are, and all we have to do is control excess amounts to ensure water quality. But in fact, animals are constantly interacting with this ‘chemical soup’ and we don’t even know what some substances are.“, Study co-author Edward Kolodziej, associate professor working at the Institute of Science and Mathematics of the University of Washington Tacoma, said.

“Here, we started with a combination of 2,000 chemicals and identified this toxic chemical by itself, which is what can quickly kill large fish and we think this is possible. on most of the world’s most crowded roads“.

Coho salmon grow in freshwater springs. After the first year of living in the stream, these powerful animals find their way to the great sea and live for the rest of their lives in the ocean. Only a few of them (about 0.1%) find the spring where they were born to lay eggs before they die. But scientists noticed a strange point: it rained heavily, the salmon “returned” to die before giving birth. The journey to find the cause comes from studying water quality in small streams.

“We confirmed that the reason could not be from high temperatures, low oxygen levels or some contaminated water, for example the sudden increase in zinc.“, Study co-author Jenifer McIntyre, assistant professor working at the Environment Department of Washington State University, said. “And then we found out that flood waters can cause disease symptoms and increase mortality in fish. This is the time when Ed’s team is proposing to assist us in our research on chemicals in water“.

First, the group zoning off where flood waters originate. They compared the water in the stream, where salmon died massively, and found a common pattern: all the spring water samples contained chemicals related to degenerated tires. Furthermore, a study led by Ms. McIntyre found that a compound containing a tire molecule has a toxic response to salmon.

But tire molecules contain hundreds of chemicals. The team in front of the team makes a big comeback: finding out what affects the salmon.

Scientists divide the chemical combination of tire molecules into parts according to each chemical property, such as separating metals into separate components. Then they tried each of them, see which compounds caused salmon poisoning. Continuously dividing and testing each part, the team distilled the suspect, and found a substance with a concentrated concentration that did not appear on the list of substances that were found.

“In 2019, there were times when we thought we couldn’t find the reason. We know that the toxic chemical complex contains 18 units of carbon, 22 units of hydrogen, 2 nitro and 2 oxygen. We are constantly searching for substances with similar structures“, Said Zhenyu Tian, ​​lead author of the study. “And then one day in December, I put the number in my head! The chemical that causes poisoning in salmon is not necessarily chemically directly related to the tire, but it is just a related by-product.“.

Tian searched the list of known substances that make up rubber tires with properties similar to the suspect, plus and minus some hydrogen, oxygen and nitro, and found 6PPD, a chemical that helps the tire to keep the tire from eating longer. more worn out.

“Like a tire preservative. Similar to how food preservatives help foods last longer, 6PPDs help tires stay in shape by preventing them from interacting with ozone present in the air.“, Researcher Tian confirmed.

Ozone, a gas produced during vehicle operation as well as when many chemicals interact with the sun, break the tire’s topology. 6PPD present in the tire compound will interact with ozone before the gas reaches the rubber part. But the scientists found that when 6PPD is exposed to ozone, they change into many other substances, including 6PPD-quinone, the poison that prevents salmon from continuing to grow.

This chemical is not only present in the South Puget area, where there are no trout streams. The team also tested water coming out of a highway in Los Angeles, a small stream near San Francisco: the results showed that the water at these points also contained 6PPD-quinone. This discovery did not surprise the scientists, who thought that salmon poison would be present in any country near the road with many traffic vehicles.

Once the 6PPD has been named, the team will continue to find out why it is so toxic.

“Why does it cause salmon coho poisoning? Why are other salmon species, such as jum trout, less affected?”Asked researcher InMcTyre. “There are many aspects to understanding, whether there are still species affected by rainwater or 6PPD-quinone, and to survey other areas outside of South Puget.“.

One effective way to protect salmon or any other organism that lives near streams is to treat the rainwater before it reaches the water source. Although we are holding onto 6PPD-quinone filtration technology out of water, it is almost impossible to install a filtration system in every street in the world. Another option was introduced, which is to change the tire construction formula, making them “salmon-friendly“More.

“Tires need these preservatives to last longer“, Researcher Kolodziej said. “The question is, which chemicals can effectively and safely replace, considering toxicity in humans, aquatic animals and other organisms. We do not know what will be a viable alternative, but we do know that chemists are extremely intelligent, with many tools in hand to find a safe alternative.“.

According to Washington.edu