DRBC to study chemical from rubber tire particles as source of water contamination

Researchers in the Delaware River watershed are gearing up to study what they consider an emerging water pollutant of concern: the flecks of rubber and dust that flake from worn car tires.

Scientists have long known that the flecks themselves, called tire wear particles, are one of the most prevalent microplastics in the ocean — one recent estimate from the Pew Charitable Trust said that tire particles make up around 78 percent of microplastic mass in the planet’s oceans. 

But there’s new buzz about the chemicals that these particles leach into the water since a 2020 paper found that one of the chemicals — 6PPD-q — was responsible for decades of coho salmon deaths in waterways in the U.S. Pacific Northwest. 

6PPD is a chemical that’s been used in tires since the 1960s, when manufacturers found that it acted as a sort of rubber preservative and kept tires from drying out and cracking when exposed to ozone, an odorless, colorless gas that occurs naturally in the environment. 

6PPD caught on in the global tire market, and it’s been in tire rubber everywhere ever since.  

“As far as I know, it’s in almost every tire produced in the U.S., if not the world,” said Jeremy Conkle, a senior chemist and toxicologist with the Delaware River Basin Commission.

6PPD is also found in footwear, synthetic turf and playground equipment. 

On its own, 6PPD isn’t toxic. But when rubber flakes and comes into contact with ozone, 6PPD transforms into a byproduct called 6PPD-quinine, or 6PPD-q, and it’s now known to have negative to lethal effects on several salmonid species.

(So, in a twist, the very compound that the industry uses in tires (6PPD) to keep the rubber preserved from ozone becomes a potentially lethal byproduct when itself is exposed to ozone.)

The 2020 paper on coho salmon found that tire particles collect in stormwater drains and leach 6PPD-q into the water. 

Heavy rainfalls can flush those chemical-laden particles out and into waterways, and coho salmon can die shortly after coming into contact with 6PPD-q. Within 90 minutes, the fish start experiencing its effects — losing their equilibrium, swimming in circles and succumbing to neurological changes that leave them gasping for air at the water’s surface.

Scientists have since found that other salmonids can experience more sublethal, subdued toxicity from 6PPD-q, according to Conkle, though scientists aren’t yet sure why responses to the chemical are so varied among fish species.

Scientists found in 2022 that 6PPD-q can be deadly to rainbow and brook trout, with brook trout dying as rapidly as the coho salmon and with the rainbow trout dying over the course of a few days. 

That news caught the DRBC’s attention.

Trout susceptible to exposure

Trout species are considered salmonids, according to Conkle, and three wild species of trout — the rainbow, brown and the native brook trout — all populate the upper basin of the Delaware River watershed. 

Conkle said brown trout is among the species that scientists believe suffer sublethal effects from 6PPD-q.

“The Upper Delaware is a world-class trout fishery, so it’s a resource that is very important regionally,” said John Yagecic, water quality assessment manager at the DRBC. “When we became aware that this pollutant was tied to negative impacts on salmonids, we thought that it was prudent to look and see if we saw that in our basin — in particular in the area where we have this world-class trout fishery.”

This past August, the DRBC won a grant for what will likely be the first large-scale, grant-supported effort to research 6PPD-q in the Delaware River basin.

Starting in the spring, three or four water samples will be collected from wild trout streams, with at least one sampling session taking place before and after a major stormwater runoff event. 

Conkle said these samples, which will be done by Temple University’s Water and Environmental Technology Center, should show whether 6PPD-q is present in the streams and, if so, how heavy rainfall affects those concentrations.

The DRBC’s initial study will focus only on measuring 6PPD-q concentrations in the upper basin’s wild trout streams, not effects on the fish or human populations.

“We’re just going to do some baseline monitoring to see if we find it,” Conkle said.

Assessing the urgency of the problem

The findings of the DRBC’s initial study will inform the level of urgency with which scientists continue studying 6PPD-q, Conkle said.

If scientists find the chemical is present in the basin, there’s potential for additional research on its effects on specific trout species and the presence of tire microplastics in the watershed.

The DRBC has studied microplastics in the Delaware River watershed since 2019, finding that microplastics were fairly ubiquitous in all of the water samples collected.

But most of these samples were taken from surface waters, where more lightweight microplastics, like microfibers, can collect, according to a DRBC scientist, Jacob Bransky. 

To find concentrations of microplastics from tire particles, the DRBC would need to take samples far beneath the water’s surface, where the heavier rubber particles are more likely to settle. 

For now, the trout populations seem healthy. But wildlife, recreation, economies and residents’ health could all be on the line in 6PPD-q studies like these. 

Search for solutions

The Delaware River basin supplies drinking water for more than 14 million people. Though the effects of 6PPD-q on humans are largely unknown for now, a South China study suggests that we are absorbing the chemical, too. 

The 2024 DRBC study is funded through a $14.9 million Delaware Watershed Conservation Fund grant from the U.S. Fish and Wildlife Service and the National Fish and Wildlife Foundation. The DRBC got a $498,200 grant from this year’s pot for three water quality studies, including the 6PPD-q research. 

As the science on 6PPD-q emerges across the globe, the tire market is booming.

Around 2.2 billion tires were sold globally in 2022, and sales are predicted to reach 3.4 billion by 2030. 

Tire manufacturers haven’t found a replacement for 6PPD that they say affords the same safety for drivers. But after an outcry from nonprofits, environmental advocates and Native American communities for alternatives, state and federal governments and agencies say they’re taking action. 

Tire manufacturers say they are working with federal agencies to present initial research on three possible 6PPD alternatives by March.

The U.S. Tire Manufacturers Association also put together a 16-member tire manufacturer consortium to perform an 6PPD alternative analysis under new directives from the state of California’s Safer Consumer Products Regulations.

“USTMA and its members have been working and will continue to work closely with federal and state regulators, materials suppliers, academic and government research teams, industry associations and other partners,” USMTA Vice President of Public Affairs Kim Kleine told Delaware Currents in an email.

Tire manufacturers will also have until the end of 2024 to turn in any previously unpublished 6PPD studies to the U.S. Environmental Protection Agency, which just granted a petition from three West Coast Native American tribes asking the EPA to make rules against the use of 6PPD in tires.

The EPA released its first draft of a 6ppd-q water sampling method on Jan. 30, the agency’s first steps toward regulating the toxin after pledging this past November to answer the widespread call for action against the chemical.

While the draft method won’t regulate 6ppd’s use, it will give government agencies and tribes clearcut sampling procedures and health and safety protocols when testing water for 6ppd-q. The method could help the agency to map the prevalence of 6ppd-q in what’s now a sparse field of data.

“The faster we can identify where problems exist, the faster we can correct them,” said Casey Sixkiller, the EPA’s regional administrator in Seattle.