For decades, coho salmon have been dying before they could spawn in watersheds in Seattle and elsewhere. Now we know specifically why—new research results point to a contaminant derived from vehicle tires, and the news media have been all over the story this month.
In the late 1990s, I got a call from a foreman for the construction of Meadowbrook pond, alerting me to his discovery of several dead salmon on the site. As part of a volunteer team monitoring for salmon spawning in the local vicinity, I had access to the site, and went down to let myself in. I found the salmon—coho as it turned out—bright silver, not in spawning coloration, and killed by something unknown. It turned out to be a problem, especially for coho, in urban watersheds up and down the west coast.
TCA has been following the research that ensued from that and similar incidents—a search for a “smoking gun.” Contaminants in stormwater runoff were suspected, and in collaboration with the environmental scientists, TCA-led Community Scientists have sampled stormwater runoff for chemical analysis by UW Tacoma, a leading lab in the research.
Before researchers knew what chemical or combination of chemicals they were looking for, they did determine that biofiltration of stormwater through a soil and organics matrix could mitigate against the mortality. That helps establish the benefits of natural drainage systems, or green stormwater infrastructure—the swales for groundwater infiltration that SPU has been installing in areas of the city such as Pinehurst. More of those are on the way.
Now, in a culmination of decades of research. a team of researchers including scientists at UW, WSU, and the National Marine Fisheries Service (popularly known as NOAA Fisheries) have published results on the identification of a specific chemical culprit in the coho prespawn deaths.
And, TCA’s Community Scientists got an acknowledgment in the Science Magazine publication on this discovery.
The contaminant was identified through a complex series of chemical separations of thousands of chemical compounds. It’s called 6PPD-quinone (or C18H22N2O2, where C is carbon, H is hydrogen, N is nitrogen, and O is oxygen), and is a product of the reaction of a component in tires called 6-PPD with atmospheric ozone (an oxygen compound), against which 6PPD is intended to protect the tires. As tires wear, tiny particles of rubber end up on streets and roads. 6PPD-quinone becomes a constituent in runoff entering streams, lakes and Puget Sound, and is about 100 times more toxic than 6PPD. Even small amounts of 6PPD-quinone were lethal to coho salmon (juveniles, used as a proxy for adult salmon) in lab studies.
The detailed Science Magazine article is here: https://science.sciencemag.org/content/early/2020/12/02/science.abd6951
A summary is here: https://science.sciencemag.org/content/sci/370/6521/1145.full.pdf
However, nonsubscribers may have difficulty accessing those articles; here is a good translation:
https://www.eopugetsound.org/magazine/IS/coho-and-tires
So it’s good news that this contaminant has been singled out and a mystery has been solved. The bad news is that it’s in tires worldwide, and at this point, there is no plan to begin eliminating it. That’s in part due to the fact that discovery is so new, but the tire industry has come out calling for more research as well as efforts to divert and treat stormwater. Even if action were to be taken now to eliminate the chemical from tires, the vast number of them already on the road will continue to cause problems for the foreseeable future.
Of course, there are many contaminants in road runoff that are unhealthful for aquatic organisms, so efforts must continue to address them. Also, it will be worth exploring what damage this contaminant may be associated with in other types of aquatic systems. Lots of work remains.
