Car Tire Chemicals Kill Salmon and Steelhead – Environmental Health News | CarTailz

Since the early 2000s, Barb French observed an unexplained phenomenon in coho salmon in Puget Sound in the Pacific Northwest.


When the fish returned to their natal waters to spawn, a point in their life cycle when they are usually in excellent health, they behaved strangely.

“They would swim into the banks of the creeks,” French, a researcher with the National Oceanic and Atmospheric Administration, told EHN. “They were very disoriented, even swimming sideways.” Losing their sense of direction, the fish opened their mouths at the surface and spread their fins. Within hours they would die.

Last year, a group of researchers in Washington pinpointed the cause of these mass fish die-offs: 6PPD, a chemical added to tires to keep them from failing. When 6PPD, which the US Tire Manufacturers Association says has been used in tires since the 1970s, reacts with ozone in the atmosphere to form 6PPD-quinone (6PPD-q), a compound that leachates into urban stormwater and watersheds. This derived chemical has proven difficult to identify and study, and even more difficult to regulate because the chemicals in tires are proprietary and not disclosed by tire manufacturers.

However, new research led by NOAA scientists found that 6PPD-q harms species other than Coho in the salmonid family, including the steelhead trout.

The team studied how different salmonids respond to undiluted urban rainwater contaminated with 6PPD-q, which is rarely treated before reaching larger bodies of water. Almost all coho salmon died immediately after exposure to the polluted water, and up to 42% of steelhead trout were also killed, although their deaths were delayed by a day or two.

French and her colleagues attempted to remove the steelhead from the contaminated water and place it in clean water, but once exposed to the chemical, they died anyway.

While research has focused on Pacific fish, impacts extend to other salmonids in the US and potentially other aquatic life. Even though human data is still sparse, some states are taking note of the potential effects and are beginning to regulate the chemical and source safer alternatives.

Much of this research is nascent and still ongoing, as scientists didn’t identify 6PPD and 6PPD-q until 2021, although scientists observed the effects for decades before knowing what was causing the mass fish die-off. “You can’t measure anything in rainwater unless you know what it is,” French said.

“A complete breakdown of the blood-brain barrier”

6PPD has been used in tires since the 1970s, according to the US Tire Manufacturers Association.

Credit: Corey/flickr

6PPD-q still puzzles scientists, but Washington State University researcher Stephanie Blair has made strides in understanding why the fish are dying. Blair observed that when coho salmon are exposed to the chemical, they swim to the surface of the water where the concentration of dissolved oxygen is highest – which she says was an extreme response to lack of oxygen, even though oxygen was abundant throughout the water.

Blair noticed that her blood thickened as the fish developed symptoms. Blair used a fluorescent tracer to visualize the fish’s circulatory system and found that plasma was leaking from the blood vessels and filling the brain tissue. “This is a complete breakdown of the blood-brain barrier, which shuts down neuronal function and leads to death very quickly,” Blair told EHN.

Many conservationists hope that 6PPD-q at a lower dilution will not be as dangerous to salmonids. But even in low concentrations, the chemical poses a high risk.

“We found quite high concentrations of 6PPD-quinone in our waters,” Ezra Miller, a research scientist at the San Francisco Estuary Institute, told EHN. In the San Francisco Bay and nearby watersheds, many coho salmon samples collected by the San Francisco Estuary Institute exceeded species LC50, a standard measure of toxicity that indicates the concentration of a chemical that is expected to affect half of the exposed population will kill. A sensitive population will have a low LC50, while a population that can tolerate a higher concentration will have a higher LC50.

The LC50 threshold for steelhead is higher than for coho, but Miller predicts that 6PPD-q values ​​in the Bay Area are high enough to harm steelhead, and the case is likely the same for every US waterway in near an urban area. Even if the concentration of 6PPD-q does not kill Steelhead, it could produce sublethal effects that limit their ability to reproduce and evade predators, or prevent the development of their cardiovascular system.

Researchers are just beginning to study the effects of 6PPD and 6PPD-q on humans and other organisms. But the ubiquity of 6PPD-q in our waters means it could potentially be passed down the food chain to humans. Salmon and steelhead are canaries in the coal mine, Blair explained; like many other organisms, including humans, have blood-brain barriers that 6PPD-q can potentially disrupt.

There are thousands of chemicals in urban rainwater, many from tires. French is concerned not only with these “source chemicals” but also with how they break down and interact with each other and the environment.

States act

Although 6PPD is present in tires nationwide, Washington and California are leading the nation in efforts to limit environmental levels. In October 2022, the Washington State Department of Ecology released a new report on stormwater management that aims to reduce runoff concentrations of 6PPD and 6PPD-q through source control (such as street sweeping and roadside cleaning) and flow control (such as soil filtration) in crevices that contain 6PPD filter out -q). Meanwhile, California’s Department of Toxic Substances Control is taking steps to designate 6PPD as a “priority product,” which would force companies to disclose their use of 6PPD and conduct analysis to find safer alternative chemicals.

“It’s going to be a long time before we can do product replacement or green chemistry,” Nat Scholz, NOAA’s ecotoxicology program manager and senior author of the French study, told EHN. Not only because it takes a long time to find a non-toxic alternative, but also because tire technology has to take human safety into account, Scholz added.

So, for now, scientists and engineers are treating the stormwater itself. Green infrastructure solutions like undergravel filter columns capture chemicals in urban stormwater before they reach watersheds. But it will require a tremendous amount of green infrastructure to ensure water quality for a fish population as sensitive to 6PPD-q as coho salmon.

6PPD-q has been polluting and killing salmon and steelheads for decades, long before we even knew the compound existed, Scholz told EHN. Since then, the scientific tools for detecting its pollution have evolved, such as B. molecular biology to understand how chemicals affect organisms and analytical chemistry to break down complex mixtures. And the complexity and scale of the problem has increased with urbanization. But our approach has not kept pace. “Most of our worldview on water quality and salmon habitats hasn’t really changed since the 1970s,” Scholz said. Fish will die until we adapt.

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