Tire chemicals cause massive fish deaths

American biologists have found an answer to the question why every autumn more than half of the coho salmon that return to spawn in the rivers of Puget Sound, Washington, die before spawning.

The answer has been sought for a long time, and now a team of scientists from Washington State University has discovered that the killer is a mixture of chemicals found in tire particles. When it rains, storm water flushes tire debris off the roads into nearby rivers, and a toxic preservative is harmful to fish to prevent tire deterioration too quickly.

The study was published on December 3 in the journal Science.

“Most people think we already know which chemicals are toxic, and all we have to do is control the amount of these chemicals to ensure good water quality. But in fact, animals are exposed to a huge complex of substances in the water, and we do not even know what chemicals are there, ”said study co-author Edward Kolodziej, an assistant professor at the University of Washington. “We started out by identifying a mixture of 2,000 chemicals and ended up with one very toxic chemical that quickly kills large fish and we believe is found on every busy road in the world.”

The fish killer project began with a survey of water quality in streams and rivers. It was a collaborative effort by several agencies, including the US Wildlife Service. The researchers were able to determine that the mass death of fish cannot be explained by high temperatures, low levels of oxygen dissolved in water, or any known pollutants. The Puget Sound water samples were then found to contain tire-related substances.

But the micro-particles of worn tires, washed off the roads by the rains, are a mixture of hundreds of different chemicals, so the task of the accounting team was: how to find the specific culprit? Here long-term laboratory tests came to the rescue, which helped to determine the most toxic substances for fish contained in water from the roads. Eventually, a chemical called 6PPD was discovered, a preservative used to prevent ozone from degrading tires too quickly. When 6PPD is found to react with ozone, it is transformed into a variety of chemicals, including 6PPD-quinone, a toxic chemical that kills coho salmon.

Scientists have already discovered this substance not only in Puget Sound: they checked water drains from the Los Angeles roadway and the river near San Francisco, and found 6PPD-quinone there.