TACOMA, WASHINGTON — For decades, after heavy autumn rainstorms, coho salmon returning from the Pacific Ocean to the West Coast have been dying in huge numbers before they spawn.
Now scientists believe they have found the primary cause.
A powerful antioxidant present in runoff called 6PPD, used in tires to make them last longer, is poisoning the fish.
Researchers from the University of Washington Tacoma found that 6PPD reacts with ozone to form a previously unknown byproduct called 6PPD-quinone.
The findings were published on Dec.
3, in the journal Science.
According to the study, less than 1 percent of adult coho typically die before spawning.
But in the mass die-off autumn events along the West Coast, 40 percent to 90 percent of the salmon have died.
It is unlikely 6PPD-quinone is toxic only to coho salmon, the researchers said, but 6PPD-quinone is a ubiquitous pollutant.
There are more than 1.4 billion vehicles on the planet, for which roughly 3.1 billion tires are produced annually, and 6PPD appears to be in all of them.