In a healthy ecosystem, salmon provide food for orcas and spawn in urban creeks. Their decomposing corpses also provide nourishment for soil and forests.

It’s this critical role that led scientists on a journey of searching for the mystery killer and one that ended in western Washington.

With more than 2,000 chemicals found in the water, it took researchers three years to narrow those thousands of chemicals to one.

Jen Mcintyre.

A few months after the initial discovery, the team brought a sample of the chemical to Jen McIntyre over at Washington State University in Puyallup where it was put to the test.

“The fish would start to come to the surface of the water, they’d start swimming at the surface of the water, they would start to lose equilibrium and swim on their side and then upside down and eventually settle to the bottom of the tank and die,” said McIntyre who also explained how much testing was done to ensure accurate reporting and data.

What they discovered was a toxin called 6PPD-quinone produced when the common tire preservative 6PPD mixes with oxygen. As tires age, the rubber starts to peel off leaving bits and pieces in their path.

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