In the 1980s, sport fishers in North America began to notice that coho salmon were dying after rainfall during the salmon run, often before they could spawn.
According to Professor Hui Peng, an environmental chemistry specialist at the University of Toronto, many of these salmon populations are now considered endangered in Canada and the US.
“Over the past several decades, mass amounts of these fish populations have been dying. In some cases, half the fish were found dead before spawning, and for years, the reason why had kind of been a mystery.”
While the die-off shows no signs of abating at present, the cause of the fish mortality was recently identified. Scientists from the University of Washington traced the fish deaths back to the watershed, and from there back to a ubiquitous human product—rubber motor vehicle tires.
The key clue turned out to be the weather.
“Every time it rained, the runoff went into the environment,” Peng explained, “and then that killed these salmon. Even more precisely, the element of rubber that is killing the fish is the transformation product of a tire additive that works as an antioxidant, 6PPD. "
Antioxidants are a necessary component in rubber, but the chemicals currently used to prevent tire degradation can form tire-wear particles, especially on highways. "This chemical can then react with atmospheric ozone to form a new chemical, 6PPD-Quinone, which is extremely toxic to fish even at concentrations of 0.095 microgram per liter of water.”
With the toxic puzzle unlocked, the Peng group has moved on to finding solutions to the problem.
The result of this search is a new paper by Peng, Professor Jonathan Abbatt and others: Structurally Selective Ozonolysis of p-Phenylenediamines and Toxicity in Coho Salmon and Rainbow Trout, which proposes an alternative to the chemical currently in use.
Human use of tires is unlikely to decrease anytime soon, and in the near future governments are looking at regulations to limit the toxins, which inevitably end up in the salmons’ habitat when it rains. But while the US and Canadian governments can potentially ban 6PPD, regulations will not feasible until a less harmful alternative is available. At present, 50 to 100 million tons of the oxidizing chemical are produced annually in the US alone.
The problem is a significant challenge... but within that challenge lies a potentially lucrative opportunity. The Peng group has been working to find a replacement for 6PPD, a substance whose production currently has an annual market value of $1billion.
“The tire industry is currently testing our suggested replacement compounds for applications," Peng said. “The U.S. Tire Manufacturers Association is extremely excited by our results.”
He added, “I have been regularly meeting with them to update them on our research. And currently, they are using our suggested chemicals to test their tire protection efficiency.”
If testing works out as hoped, it is possible industry will embrace the new anti-oxidation chemicals in production of new tires even before governments can legislate bans on 6PPD.
With the coho salmon fishery and related species, such as rainbow trout facing significant threats, Peng says, there is strong hope that this initiative will succeed.