Every time it rains, fish living downstream of storm drains are exposed to pollutants, including the tire-derived compound 6PPD-quinone, in the runoff. Recently, this substance has been linked to massive die-offs of coho salmon across the US West Coast. Now, researchers in Canada report that exposure to 6PPD-quinone at environmentally relevant levels can also be deadly for rainbow and brook trout, though not for Arctic char or white sturgeon.

Their findings appear in ACS’ Environmental Science & Technology Letters.

Rubber tires are fortified with protectants, such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine or simply 6PPD. 6PPD is an antioxidant and antiozonant that helps prevent the degradation and cracking of rubber compounds caused by exposure to oxygen, ozone and temperature fluctuation.

6PPD is used industry-wide to help tires resist degradation and cracking. There are no known alternatives to 6PPD that provide the same safety and performance characteristics in a tire, according to the US Tire Manufacturers Association.

However, as the treads wear down and pieces flake off over time, small rubber particles (tire wear particles, TWPs) scatter across roads. There, the particles react with oxidants such as ozone in the air, converting 6PPD to 6PPD-quinone, which washes into waterways along with the source tire particles in stormwater runoff.

Previous studies reported that exposure to small amounts of 6PPD-quinone (median lethal concentration (LC₅₀) of <0.1 μg/L) is toxic to coho salmon—a popular fish among recreational fishers and an environmentally important species—and likely caused the phenomenon in urban streams called urban runoff mortality syndrome.

Conversely, another study indicated that zebrafish and Japanese medaka can withstand even very high amounts of 6PPD-quinone. So, Markus Brinkmann, Markus Hecker, Steve Wiseman and colleagues wanted to see whether this contaminant poses a risk to a broader range of commercially, culturally and ecologically important fish species.

The researchers exposed juvenile brook trout, rainbow trout, Arctic char and white sturgeon to varying levels of 6PPD-quinone. They found that even small concentrations, such as those regularly occurring in surface waters after stormwater runoff events, were fatal to brook and rainbow trout. The LC₅₀s in brook trout (24 h) and rainbow trout (72 h) were 0.59 and 1.00 μg/L, respectively.

For both trout species, the researchers observed an increased blood glucose level after 6PPD-quinone exposure, suggesting it affected the fish’s energy metabolism pathways. However, none of the Arctic char and white sturgeon died after four days of exposure to a high level of the contaminant that was similar to the maximum amount previously observed in stormwater runoff (14.2 μg/L).

The results indicate mortality from exposure to 6PPD-quinone varies among fish species, but for animals that don’t die, possible non-lethal effects could be occurring and need further examination, the team says.

This project was supported partially by a financial contribution from Fisheries and Oceans Canada. The authors acknowledge additional funding from the Discovery Grants program of the Natural Sciences and Engineering Research Council of Canada (NSERC), Western Economic Diversification Canada (WED), the Canadian Foundation for Innovation, the Banting Postdoctoral Fellowship program of NSERC, the Canada First Research Excellence Funds (CFREF) and the Canada Research Chairs Program.

Resources

• Markus Brinkmann, David Montgomery, Summer Selinger, Justin G. P. Miller, Eric Stock, Alper James Alcaraz, Jonathan K. Challis, Lynn Weber, David Janz, Markus Hecker, and Steve Wiseman (2022) “Acute Toxicity of the Tire Rubber-Derived Chemical 6PPD-quinone to Four Fishes of Commercial, Cultural, and Ecological Importance” Environmental Science & Technology doi: 10.1021/acs.estlett.2c00050