Rubber in the Runoff
The toxic chemical 6PPD-Q has leached into our waterways and impacted marine life. One scientist might have a solution.
A dead female coho salmon found along the banks of a river with its eggs still inside. Salmon dying in polluted streams and rivers before they could have a chance to spawn has come to be known as Urban Runoff Mortality Syndrome. // Photo courtesy of Miller and Walker Community Salmon Investigation
Story by India Rahmani
March 15, 2024
The rush of cars along the sopping highway during storm season in King County has toxicology scientists biting their nails. As rubber tires circle round and round, tiny toxic particles make their way onto the sides of our roads. When rain pours down it carries the tire particles into our nearby streams, creating health problems for our fish. Coho salmon in particular are gasping for air, disoriented, swimming on their sides and dying before laying their eggs. The culprit: 6PPD-Q.
Used to prevent tires from cracking, 6PPD is a chemical anti-degradant that protects rubber from ozone exposure. Ozone and friction degrade tires over time, creating dangerous cracks that could lead to drivers losing control of their vehicles..
When a tire starts to wear down, 6PPD is exposed to ozone, changing it into a new toxic compound called 6PPD-Q. Rain and snow storms flush the chemicals from roadways into nearby creeks and rivers.
6PPD-Q is one of the most destructive chemicals to the health of Washington’s Ecosystem, according to Tanya Williams, 6PPD lead agency planner for the Washington State Department of Ecology.
“I would say it is the second most toxic aquatic chemical ever found,” Williams said.
Although not a lot of research has been conducted on how 6PPD-Q affects humans, possible impacts of the chemical include skin irritation, cell and tissue damage and possible reproductive harm. 6PPD-Q has been a silent killer of fish since the 1960s when it first was used in tires. Coho salmon, trout and char fish are all extremely sensitive to 6PPD-Q and are bearing the brunt of the chemical’s impacts.
Rainwater falls mixing with 6PPD-Q and other pollutants before washing into a storm drain. Left as a byproduct of the chemical that protects rubber from ozone exposure being exposed to ozone itself, 6PPD-Q is one of the most toxic aquatic chemicals. // Photo courtesy of Wild Fish Conservancy and taken by Tyrone Turner
Coho salmon start their lives as small and vulnerable baby fish, called fry. Throughout their adolescence these fry eat their way to the ocean. There, the salmon grow and fatten up in preparation for the treacherous journey back into freshwater. As spawning adults these salmon swim upstream to the same spot where they were hatched to lay their eggs. Many of them will die along the way.
Fish have tightly linked cells in the brain called the blood-brain barrier that defend their neurons from harmful substances. As 6PPD-Q passes through coho salmon it disrupts the blood-brain barrier, and can lead to death in just hours.
In 2020, scientists discovered that 6PPD-Q was a partial contributor to the 80% to 100% death rate of coho salmon in watersheds around the Pacific Northwest. Since then scientists and researchers are dedicated to finding a solution.
In 2022, King County received a grant to conduct experiments to determine how well new high-performance bioretention soil media (HPBSM), adopted by Ecology, can filter 6PPD-Q. Made out of soil and plants, bioretention media is a type of living filter that captures metals and chemicals that could be harmful to the environment and introduces much healthier water to our ecosystem. The bioretention media is made out of sand, coir (coconut fiber) and biochar, and can be combined with a polishing layer consisting of iron and alumina.
King County asked Curtis Hinman, a green stormwater scientist, to test the HPBSM at Western Washington University. He works in the lab in partnership with the Institute of Environmental Chemistry and Western students.
The filter has been tested against 6PPD-Q at the Western toxicology lab and sent to King County for further examination. The county is currently testing young coho salmon in tanks with water filtered by the HPBSM to determine its effectiveness.
Thus far the results have been promising, according to Hinman.
Rivers have always been a part of Hinman's life. His work is a way for him to give back to the water.
Hinman first encountered bioretention media on the East Coast. In 1999, Hinman began working on management designs for stormwater within Puget Sound. Twenty-four years later Hinman is still working to find better ways to filter harmful substances out of the water.
In the basin of Lake Whatcom, Hinman led the research to create high performance bioretention media meant to catch pollutants before they enter the lake. This version has been installed to help the City of Bellingham meet regulations to reduce phosphorus entering the lake through stormwater runoff. The filter is located on North Shore Drive and Britton Road.
It wasn’t until the late 1980s that scientists started to find fish dying from polluted stormwater.
The phenomenon was first called Pre-Spawn Mortality Syndrome because the female salmon would die with all their eggs before they could have a chance to spawn. After discovering the link between polluted stormwater and pre-spawn mortality, scientists renamed it Urban Runoff Mortality Syndrome.
“Some of the carcasses were really bright and looked like they were fresh from the ocean but they were dead on the banks,” Jamie Glasgow, the director of science and research at Wild Fish Conservancy, said. “When we cut them open, sure enough, the females were still carrying all of their eggs so they had died before they spawned.”
If an Olympic Swimming Pool filled with 5,000 cubic yards of water held 1,000 coho salmon, it would only take one-tenth of a tablespoon of 6PPD-Q to kill 500 of them in about four hours, according to Larry Franks, a board member of Friends of the Issaquah Salmon Hatchery.
“This is the chemical that at environmentally relevant concentrations and very low concentrations is killing fish,” Ruth Sofield, the director of the Institute of Environmental Toxicology and Chemistry at Western, said.
Steamrolling its way up the West Coast, a large section of I-5 cuts through Seattle, and is hugged on either side by Puget Sound and Lake Washington, two large bodies of water that hold coho salmon. Over 70,000 vehicles commute on this section of I-5 a day. Although unable to quantify the exact amount of 6PPD-Q coming off of this many tires, the scientific community is concerned about the effects it will have on aquatic life.
Cross section showing the layers of High Performance Bioretention Soil Media (HPBSM). // Photo courtesy of Washington State Department of Ecology
Biofiltration media could be an effective solution to stop 6PPD-Q from getting into our waters but there is concern that price will pose a problem. The cost of infrastructure, maintenance and permits for the filtration systems could potentially be billions of dollars, according to Williams, the lead agency planner for Ecology.
Hinman argues that although there is not a set price on the media it can be cost-effective and some of the cheapest filter media given how well it captures pollutants.
“Even if we had a replacement tomorrow for 6PPD, you would still have everybody's tires emitting 6PPD-Q for at least another several years,” Williams said.
This is why solutions like Hinman’s filter are crucial to eliminating 6PPD-Q from the environment while simultaneously finding a replacement for the chemical.
“Where salmon goes humankind will follow,” Franks said.
India Rahmani is an environmental studies student at Western concentrating in sustainability and design.