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Male coho salmon spawning colors. Illustration by award-winning watercolorist Thom Glace.

For 20 years, researchers tried to find out why many coho salmon were dying in West Coast streams whenever it rained

Scientists placed fish in water with particles from new and old tires to investigate. The salmon died, leading researchers to test hundreds of chemicals that had leaked into the water.

A 2020 study identified the cause of death: a chemical called 6PPD was added to tires to stop them from cracking and breaking down. When 6PPD mixes with ground-level ozone, it turns into other harmful substances, including 6PPD-quinone or 6PPD-q. This compound is highly toxic to four out of 11 tested fish species, including t

While the mystery is solved, the problem remains

All major tire manufacturers still use 6PPD on roads and in waterways worldwide. No one has studied how 6PPD-q affects human health, but it has been found in the urine of children, adults, and pregnant women in South China.

How this contamination affects health is still unknown

An estimated 78% of ocean microplastics are synthetic tire rubber. Now, there are calls for regulatory action. Recently, the nonprofit Earthjustice filed a notice to sue tire manufacturers for breaking the Endangered Species Act by using 6PPD.

A coalition of Indian tribes also urged the EPA to ban this chemical

The Puyallup Tribal Council stated, “We have witnessed the devastation to the salmon species we have always relied upon to nourish our people. We have watched as the species have declined to almost certain extinction if nothing is done to protect them.”

The analysis of 6PPD and 6PPD-q was just the start of a broader effort to understand the mix of toxic chemicals, tiny particles, and heavy metals in tires and brakes to a lesser extent. While scientists agree on the severe toxicity of 6PPD-q and where it comes from, tire rubber contains over 400 chemicals and compounds, many of which can cause cancer.

The chemical 6PPD is a rubber stabilizer that prevents tires from breaking down while driving and helps them last longer—photo from pexels.com.

Research is just beginning to reveal how widespread the issues from tire dust may be

Though tires may seem harmless—for example, one ad featured babies in tires—they are significant sources of air, soil, and water pollution that may harm humans, fish, and wildlife. About 2 billion tires are sold globally yearly, enough to reach the moon if stacked on their sides.

This market may grow to 3.4 billion tires yearly by 2030

Tires contain about 20% natural and 24% synthetic rubber, which uses five gallons of petroleum per tire. The remainder comprises other materials, including steel, fillers, and heavy metals like copper, cadmium, lead, and zinc. These are added to improve performance and durability and reduce fire risks. Both natural and synthetic rubber breaks down in the environment, but synthetic fragments last much longer.

According to the Pew Charitable Trust, 78% of ocean microplastics are synthetic tire rubber

Marine animals often ingest these fragments, which can cause various effects, from neurotoxicity to growth problems and behavioral issues. Tire emissions from electric vehicles are 20% higher than from fossil-fuel cars. Rebecca Sutton, an environmental scientist with the San Francisco Estuary Institute, studied runoff and found extremely high levels of microplastics in stormwater. “Our estimated annual discharge of microplastics into San Francisco Bay from stormwater was 7 trillion particles, and half of that was suspected tire particles.”

Tire wear particles, or TWP, are released continuously as vehicles drive

They can be visible pieces of rubber or plastic or tiny microparticles. According to the British firm Emissions Analytics, they represent one of the significant environmental impacts of tires.

A study revealed that a car’s four tires emit 1 trillion ultrafine particles (less than 100 nanometers) for every kilometer driven. These tiny particles pose unique health risks: they can pass through lung tissue into the bloodstream, cross the blood-brain barrier, or travel directly to the brain, causing various issues.   

Research from Imperial College London shows that tire wear particles and other materials may lead to adverse health effects, including heart, lung, developmental, reproductive, and cancer. Tires create 6 million tons of particles worldwide yearly, with 200,000 tons ending in oceans.

Chemist Joan Protasio explains the process for analyzing and measuring 6PPD-quinone in water samples to Gov. Jay Inslee—Dept. Of Ecology – State of Washington.

In the U.S., cars emit an average of 5 pounds of tire particles per year

European cars, which generally drive fewer miles, shed 2.5 pounds yearly. Tire emissions from electric vehicles are 20% higher than fossil-fuel vehicles because EVs are heavier and have greater torque, which wears out tires more quickly.

Unlike tailpipe exhaust, which is heavily studied and regulated, emissions from tires and brakes are harder to measure and control, allowing them to escape regulation.

Recently, new technologies have emerged to measure tire emissions, revealing the troubling discovery of 6PPD-q and bringing attention to this issue. Recent studies indicate that PM 2.5 and PM 10 emissions from tires and brakes far exceed emissions from tailpipes, especially in places with reduced emissions.

Tires release 100 times more volatile organic compounds than modern tailpipes, according to analysts

The problem includes rubber in its synthetic and natural forms and chemicals emitted when tires break down. Various companies are now seeking solutions for the tire emissions problem. The Tyre Collective, a clean-tech startup in the U.K., developed an electrostatic plate that attaches to car tires. These plates can remove up to 60% of particles from tires and brakes, storing them in a cartridge for reuse in other applications, including new tires.

Rain Gardens is a straightforward solution

Scientists studying stormwater pollutants in San Francisco discovered that rain gardens can effectively capture stormwater. These gardens trap 96% street litter and 100% black rubber particles. In Vancouver, researchers determined that rain gardens could keep more than 90% of 6PPD-q from running off roads into streams where salmon live.

Rain gardens, installed in yards to capture stormwater, were also trapping 96 percent of street litter and 100 percent of black rubbery fragments. In Vancouver, B.C., researchers found that rain gardens could prevent more than 90 percent of 6PPD-q from running off roads and entering salmon-bearing streams.—Dept. Of Ecology – State of Washington.

Tire manufacturers now face the same scrutiny that car manufacturers have had for decades.

NOTE: Featured Image—Dept. Of Ecology – State of Washington.




Sources:

A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon | Science

After Salmon Deaths, EPA Takes Aim at Toxic Chemical Issuing from Car Tires / 360

Saving Washington’s salmon from toxic tire dust / Dept. Of Ecology – State of Washington

 

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