When returning adult coho salmon started dying before spawning in the Seattle area, scientists went into action. Polluted road run-off was the suspected culprit, but discovering what of the thousands of chemicals was the primary cause took years of research. We now know it is from tire particles- specifically, a chemical referred to as 6PPD-quinone, added to tires to slow degradation.
SPAWN has tested San Geronimo Creek for presence of the chemical and has found trace amounts, but so far we have not seen the die-offs being seen in more urban settings. We are also looking at ways to catch road-runoff and biofilter the water before it reaches the salmon-bearing creeks, see https://pubs.acs.org/doi/10.1021/acs.estlett.3c00203 .
California is taking action to eliminate 6PPD-quinone sold in California and other States are too. To read more about the actions of California, visit https://dtsc.ca.gov/scp/motor_vehicle_tires_containing_6ppd/