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Environment
Tire dust killing coho salmon returning to Puget Sound, new research shows
Dec. 3, 2020 at 11:00 am Updated Dec. 3, 2020 at 3:53 pm
A team led by researchers at the University of Washington Tacoma, UW and Washington State University Puyallup have discovered a chemical that kills coho salmon in urban streams before the fish can spawn. (Kiyomi Taguchi/University of Washington)
By Lynda V. Mapes
Seattle Times environment reporter
First they circle. Then they gasp at the surface of the water. Soon they can’t swim. Then they die.
For decades now, scientists have known something was killing beautiful, adult coho salmon as soon as they hit Seattle’s urban waters, ready to spawn. They had escaped the orcas, the fishermen, traveled thousands of miles, only to be mysteriously killed as soon as they finally reached home.
In a breakthrough paper published in the Dec. 3 issue of Science, a team of researchers revealed the culprit behind the deaths of coho in an estimated 40% of the Puget Sound area — a killer so lethal it takes out 40 to 90% of returning coho to some urban streams before they spawn. It is a killer hidden in plain sight.
Tires.
More specifically, a single chemical, 6PPD-quinone, derived from a preservative that helps tires last longer.
Through painstaking analysis and building on years of prior research, the team, including researchers from the Center for Urban Waters in Tacoma, the University of Washington and Washington State University, isolated the killer from a witch’s brew of some 2,000 chemicals in roadway runoff.
The chemical is a globally common tire rubber antioxidant. But when it does its job, interacting with ozone in the atmosphere, the chemical transforms to a substance that is highly toxic to coho.
Bound up in the rubber, this chemical taints tire-wear particles shed by tires onto roads. The tire dust is in roadway runoff that seeps, trickles and pours into water bodies, including urban streams, every time it rains. The more traffic on the road, the higher the dose.
Zhenyu Tian, a research scientist at the Center for Urban Waters at UW Tacoma, holds a sampling pole, which is used to collect creek water for future tests. (Mark Stone / University of Washington)
A preservative in vehicle tires keeps them from breaking down too quickly. 6PPD reacts with ozone and is transformed into multiple chemicals, including the toxic chemical the researchers found that is responsible for killing coho salmon. (Mark Stone / University of Washington)
Jenifer McIntyre (left), an assistant professor at WSU School of the Environment in Puyallup; Edward Kolodziej (center), an associate professor in both the UW Tacoma Division of Sciences & Mathematics and the UW Department of Civil & Environmental Engineering; and Zhenyu Tian (right), a research scientist at the Center for Urban Waters at UW Tacoma; at Longfellow Creek, an urban creek in the Seattle area. (Mark Stone / University of Washington)
Jenifer McIntyre (left), an assistant professor at WSU School of the Environment in Puyallup; and Zhenyu Tian (right), a research scientist at the Center for Urban Waters at UW Tacoma, at Longfellow Creek, an urban creek in the Seattle area. (Mark Stone / University of Washington)
1 of 4 | Zhenyu Tian, a research scientist at the Center for Urban Waters at UW Tacoma, holds a sampling pole, which is used to collect creek water for future tests. (Mark Stone / University of Washington)
Coho salmon, returning with the first fall rains, take the hit. They usually die within hours.
The pollutant is particularly problematic for waters near busy roads. Translation: most of central Puget Sound and its sprawl. Ironically, the millions of dollars spent to make these areas more salmon friendly and boost fish populations have created ecological traps for coho coming back to toxic waters.
Some of the scientists who published the paper were both exhilarated at the breakthrough and concerned by the findings.
“I find it incredibly sad to watch the adults when they are sick,” said co-senior author on the paper, Edward Kolodziej, an associate professor in both the UW Tacoma Division of Sciences & Mathematics and the UW Department of Civil & Environmental Engineering.
Every fall he’d make a visit to Longfellow Creek in West Seattle and mourn what he saw.
“When you see a fish in the field, and know something is happening that is not understood, you just have to take that very seriously. … It was just so evident to everyone we were working on a real problem.”
It was the cross-disciplinary approach of bringing together experts in the biology and chemistry of the problem that finally cracked the mystery. Dogged determination helped, too.
Lead author Zhenyu Tian, a research scientist at the Center for Urban Waters at UW Tacoma said there were times when he wondered if they would ever figure out just what chemical was the killer.
He finally had the idea it might be not the tire itself but something related to it — and hit on the preservative. They figured out that the preservative, 6PPD, goes through an environmental transformation that turns it into 6PPD-quinone — a coho killer.
“This is the smoking gun. You go through all the lines of evidence and it lines up.”
Tian modestly makes it sound easier than it was, Kolodziej said. “It looks so nice and tidy in the paper. They went above and beyond,” he said of Tian and Jenifer McIntyre, an assistant professor at WSU’s School of the Environment.
“If you are a scientist, you are among the people most familiar with failure; you have to be so comfortable with not succeeding,” Kolodziej said. After all, most research is a product of figuring out what doesn’t work, what doesn’t answer the question pursued, Kolodziej said. “It is slow and difficult and positive reinforcement is rare,” he said of scientific research. “You have to trust the scientific process. You put in the work, like so many things in life, it is about putting in the work. “
It has taken decades to solve this problem, noted McIntyre, who is based in Puyallup and is among scientists who have been sleuthing out the coho killer for years.
Nat Scholz of the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center in Seattle was the lead author in a 2011 paper with McIntyre and other authors that showed that coho pre-spawn mortality was routine in urban streams. They joined with other scientists who documented that bio-filtration through soil solves the problem, purifying the water.
