Are Alaska’s silver salmon at risk? UAA researchers investigate contamination from tires

Coho salmon - known to Alaskans as silver salmon or "silvers" - are a popular fish species for the commercial fishing industry, subsistence users and anglers. While silver salmon populations in Alaska are currently considered healthy, according to the Alaska Department of Fish and Game, "coho salmon on the West Coast of the United States have experienced dramatic declines in abundance during the past several decades as a result of human-induced and natural factors."

In 2021, a publication in the academic journal Science concluded that a chemical found in tire rubber is likely responsible for "acute mortality in coho salmon" in urban creeks in the U.S. Pacific Northwest. The chemical compound, 6PPD-quinone, is formed from the degradation of a common tire additive which is added by tire manufacturers to prevent damage from ozone. As tire treads wear along roadways, small traces of the chemical compound can wash into nearby waterways, especially after rain, and pose a lethal threat to silver salmon.

The extent to which 6PPD-quinone poses a threat to Alaska's silver salmon remains an open question. Brian DiMento, Ph.D., a research professional in the UAA Department of Chemistry, is determined to find out.

"We have lots of salmon, but not necessarily lots of roads," said DiMento about the risks of 6PPD-quinone runoff in Alaska's streams. "So how bad is it? We still would like to know."

Shortly after the publication in Science in 2021, researchers at UAA's Applied Science, Engineering and Technology (ASET) Lab were able to identify 6PPD-quinone in local streams, though a thorough study was not conducted. DiMento, who joined UAA in 2023, has been working to gather more data.

"Given that I'm paid by other grants to do other work, I can't dedicate a lot of my own time to it," said DiMento. Fortunately, DiMento had assistance this summer from Research Experiences for Undergraduates (REU) intern Elizabeth Gruen.

Gruen and DiMento collected water samples from Chester Creek and other streams near UAA's Anchorage campus, including Campbell Creek and Ship Creek. Gruen's work "vastly improved the amount of data we have on 6PPD-quinone in the local watersheds," said DiMento. "She's been getting lots of great data - great, but bad, in that we're finding [6PPD-quinone] in lots of places, especially during rain events."

Even trace amounts of 6PPD-quinone can be lethal to silver salmon; researchers at UAA found that salmon died when exposed to concentrations of only 67 parts per trillion. "One part per trillion is roughly equivalent to a single drop in 20 Olympic-sized swimming pools," said DiMento. "We have now measured concentrations in Chester Creek over 200 parts per trillion, and far higher concentrations in storm drains pouring into the streams." The presence of the compound in streams around campus may be a sign of a larger threat to silver salmon in other parts of Alaska.