Words by Simon Drew and Caitlin Lichimo.
Coho salmon are vital players in our ecosystems due to their key role in the marine environment, the food security and economic value they provide, and the cultural meaning they bring for Indigenous peoples.
The deadly impacts of 6PPD-q rain runoff on Coho salmon populations
For many years, Pacific coast salmon hatcheries have been reporting incidents of newly released salmon (especially Coho salmon) dying almost immediately along the banks of rivers and streams running nearby leading to reduced spawn, especially after rain events.
“This is a significant problem in our corner of the world, and we are looking to find out where the problem is worst in Vancouver before creating new ways in which we can protect our salmon.”
- Dr Rachel Scholes, Assistant Professor, UBC Civil Engineering.
After years of unprecedented salmon mortalities, the University of Washington published a research study that finally found the culprit: 6PPD-quinone, also known as 6PPD-q, an oxidation product of an additive used by car manufacturers to prevent damage to tire rubber from ozone exposure.
When it rains, microscopic particles containing 6PPD-q shed from the car tires, leaching into urban drainage systems later. Once making their way into nearby streams, these toxic particles get ingested and absorbed by the fish and kill them.
Car tire industry slow to change
Researchers, local stream keepers, and environmental activists have been urging federal agencies to implement harsher regulations to more effectively protect aquatic wildlife from 6PPD-q. However, even if 6PPD-q toxins are omitted in the manufacturing of new tires, old tires will still be used on our roads for many years to come. Regulatory changes also tend to be quite slow, making it reasonable to assume that it will take several years before any changes are implemented.
The STREAM (Salmonid Toxic Runoff Exposure and Mitigation) group, led by the Scholes Lab in Civil Engineering at UBC, took this regulatory problem as an opportunity to identify which species are most vulnerable to 6PPD-q to locate the most efficient ways to mitigate the problem.
The STREAM project: A government-funded research collaboration between UBC, SFU, and A Rocha conservation group
The STREAM group, consisting of chemists, engineers, ecotoxicologists, modelers, conservationists, and hydrologists, has begun a period of intensive field work, traveling to sites around Metro Vancouver and collecting water samples from affected streams and rivers before, during, and after rainstorms. The data collected will be used to create a model showing the relationship between levels of 6PPD-q in salmon waters and traffic on local roads.
By sampling specifically at locations where preexisting green infrastructure —such as rain gardens and ponds — may be reducing 6PPD-q levels in the receiving waters, researchers can generate results that will help environmental managers identify which salmon streams and rivers are most vulnerable to this toxin, based on concentrations, water flow rates, and volumes.
Nature-based infrastructure as a potential solution to filtering 6PPD-1
Once the field sampling section of the project is finished, the team will turn its attention to designing ways of removing 6PPD-q from road run-off before it gets into salmon waters. The STREAM project grew out of an earlier study by Dr. Rachel Scholes’ team which showed that some features designed to prevent flooding, such as rain gardens, can be effective in removing 6PPD-q from rainwater runoff.
“We have good reason to believe that some materials can help us mop up 6PPD-q. Adding these to the soil of these constructions may help them remove 6PPD-1 from water moving through it, and maybe other pollutants as well, much more efficiently.”
- Dr. Rachel Scholes, Scholes Lab Principal Investigator
Learn more about the Salmonid Toxic Runoff Exposure and Mitigation (STREAM) project, investigating the transport and fate of 6PPD-quinone and other toxic road runoff compounds (TRRCs) to water courses used by salmonids, its impacts, and potential mitigation measures to reduce levels in streams.