Q&A: Ecotoxicity of Tire Chemical 6PPD-Quinone
Q: What causes tire chemical toxicity and why is it a concern?
A: 6PPD [N-(1,3-Dimethylbutyl)-N’-phenyl-p-phenylenediamine] is added to a variety of rubber products so the rubber doesn’t break down over time. One of those products is vehicle tires. As vehicles are driven, tiny tire crumbs fall off, causing the 6PPD in the tire particles to come into contact with the ozone. This transformed compound—6PPD-quinone (C18H22N2O2)—is extremely toxic to coho salmon, at concentrations as low as 0.1 parts per billion.
Q: How did this concern “emerge”?
A: In the 1990s, researchers in Washington State noticed that a mass die-off of coho salmon in rivers and streams would occur after it rained, specifically in spaces where roadway runoff discharged into the waterways. Since 2011, the National Oceanic and Atmospheric Administration has studied this widespread and recurrent phenomenon. A group of researchers set out to determine what was causing the die-offs by collecting stream water samples and going through the painstaking process of fractionation, or separating the components. Ultimately, they isolated the toxic compound, but still needed to figure out what the unknown compound was.
Q: Are any other fish species affected?
A: This remains to be explored. So far, we know 6PPD-quinone is toxic to adult spawners as well as juveniles and alevin (recently hatched salmon), while chum salmon seem to be unaffected.
Q: How have regulatory agencies responded?
A: The response has been fairly limited so far. However, in May 2022 California’s Department of Toxic Substances Control filed notice to place vehicle tires on the Priority Products list under the state’s Safer Consumer Products regulations. Additionally, it seems tire manufacturers have opted to look for an alternative compound to 6PPD-quinone. The tire industry is also working collaboratively with Washington State regulators, U.C. Berkeley researchers, and others.
Q: It may take time to find an alternative and incorporate it into the manufacturing process. What can be done to protect coho salmon in the meantime?
A: Filtration, in the form of green infrastructure. Researchers have found that conventional methods such as sand filtration are ineffective, because 6PPD-quinone dissolves in water and there needs to be organic matter present. Bioswales, which rely on horizontal flow over vegetation and compost, remove a majority of the 6PPD-quinone present, while bioretention basins, which rely on infiltration, remove 6PPD-quinone to below-detectable levels.
About Sigrida Reinis, PhD, PE
Sigrida Reinis has 25 years of experience in environmental engineering and construction management, specializing in complex remediation projects, including commercial and residential redevelopment. Reinis has designed vapor mitigations systems for properties to be built on closed landfills and brownfield sites, as well as existing buildings undergoing remediation.