“When contemplating the emissions from road vehicles, our first thought is often about the various gases coming out of the tailpipe,” Lewin Day writes for The Drive. However, new research shows that we should be more concerned with the harmful particles that are shed from tires and brakes.”
“Scientists have a good understanding of engine emissions, which typically consist of unburnt fuel, oxides of carbon and nitrogen, and particulate matter related to combustion. However, new research shared by Yale Environment 360 indicates that there may be a whole host of toxic chemicals being shed from tires and brakes that have been largely ignored until now. Even worse, these emissions may be so significant that they actually exceed those from a typical car’s exhaust output,” Day wrote in his article, entitled “Tire Dust Makes Up the Majority of Ocean Microplastics, Study Finds.”
6PPD is an organic chemical widely used as stabilizing additive in rubbers, especially those common in vehicle tires. Although it is an effective antioxidant it is primarily used because of its excellent anti-ozonant performance can form when car tires interact with the atmosphere. (An anti-ozonant, is an organic compound that prevents or retards damage caused by ozone.)
Like road salt, 6PPD-quinone it enters rivers and streams when rain runs off roads into waterways. The 6PPD-quinone (6PPD-Q, CAS:2754428-18-5) has been shown to be toxic to coho salmon, brook and rainbow trout and has led to substantial concern regarding the toxicity of this contaminant for other aquatic species.
It has been shown to kill coho salmon before they spawn in freshwater streams. A 2022 study also identified the toxic impact on species like brook trout and rainbow trout, fish widely prized by anglers in New York State. The published lethal concentrations are:
- coho salmon: LC50 = 95 ng/L
- brook trout: LC50 = 0.59 μg/L
- rainbow trout: LC50 = 1.0 μg/L
Specially designed gardens and natural areas could reduce the amount of a toxic chemical associated with tires entering our waterways by more than 90 per cent, new research shows.
With the City of Vancouver, University of British Columbia researchers Drs. Timothy Rodgers and Rachel Scholes tested a Vancouver rain garden at 8th and Pine Streets, pumping about 3700 gallons (14,000 litres) of water spiked with 6PPD-quinone onto the garden for four hours and testing the water draining from beneath the garden at frequent intervals.
They found only about two to five per cent of the chemical made it through, with about 75% captured by the soil and plants. Their research was published in Science Daily in June, 2023.
Extrapolating their results using a computer model, the team predicted the garden would prevent more than 90% of the chemical from directly entering salmon-bearing streams in an average year.
Vancouver’s Rain City Strategy will build more “green infrastructure” including rain gardens, and municipalities could use the research to plan where and how to place these, the researchers say. This could include targeting areas with large highways that runoff into salmon and trout-bearing streams and such systems could help meet multiple municipal environmental goals simultaneously.
“Anywhere where you know there’s salmon, you should be trying to direct that runoff as much as possible into systems like this,” says Dr. Rodgers.
Photos, from above: Vehicle tire road wear particles (courtesy World Business Council for Sustainable Development); and a vehicle tire showing uneven tread wear to the point of exposing the casing (courtesy Wikimedia user CZmarlin).