Coastal Cutthroat Trout Also Strongly Affected By Coho-killing 6PPD-q

A new study found that coastal cutthroat trout are nearly as sensitive to a tire preservative byproduct that gets washed into streams during rainstorms as coho salmon are.

The laboratory findings, performed by scientists at the U.S. Geological Survey’s Western Research Center, add to a growing body of literature around the aquatic effects of 6PPD-quinone, an “emerging contaminant of concern” that is most strongly associated with stormwater runoff in urban waters in Pugetropolis and the Portland area.

6PPD-q is the result of a tire preservative reacting with ozone at ground level. As one environmental specialist put it earlier this year, when the compound gets into creeks and is taken in by fish, it essentially can degrade the blood-brain barrier and allow other toxins to then get into the fish’s head. In coho, exposure leaves them gasping, per se, for air on the surface, and they soon die.

Now, mortality from the same cause is being shown in another Northwest native fish.

“Overall, [coastal cutthroat trout] are the second most sensitive species tested to date for 6PPDQ sensitivity which further emphasizes the need for identifying alternatives to 6PPD,” the researchers state in the abstract of their new paper, published this week in the journal Environmental Science & Technology.

The authors acknowledge that the effect, known as urban runoff mortality syndrome, or URMS, hasn’t been observed in coastal cutthroat in the wild like it has with coho – which are naturally far more obvious, given their concentrated fall spawning runs up city and other streams – but they say other studies do show cutthroat population declines in streams where environmental contaminants, along with habitat degradation and predation also occur.

The colorful slash-jawed trout are widespread west of the Cascade Mountains, and they’re a ready biter for anglers prowling small streams with spinners or flies or fishing in the myriad lakes with bait or trolled offerings. They feed on bugs, crustaceans and other fish.

Just as with rainbow trout/steelhead, coastal cutthroat have several different life histories, including a sea-going one. The cutts used in the USGS study came from two WDFW trout hatcheries: Eells Springs, which raises the resident form, and Cowlitz, which rears the anadromous version.

The researchers looked at how 6PPD-q affected four different ages of coastal cutthroat – alevin, fry, parr and juvenile.

“Our CCT results mirror the life-stage sensitivity differences identified in previous studies, including in coho salmon, lake trout, and brook trout, where fry appear to be more sensitive than either age 1+ year juveniles or alevins. While previous studies did not compare more than two life stages within the same study, we found that CCT fry were over seven times more sensitive than alevin, and over 4.5 times more sensitive than the 13-month juveniles from the same fish cohort. The 2–5-week swim-up CCT fry were similarly sensitive to 3–4 week swim-up coho salmon fry in a previous study. Variation in individual fish sensitivity to 6PPDQ was also observed in CCT similar to other species; higher exposure concentrations in all life stages sometimes had fewer mortalities compared to lower exposure concentrations,” their paper states.

They found that the sea-going coastal cutthroat raised at the Cowlitz Trout Hatchery “are likely equally or more sensitive than the Eells State CCT, confirming high 6PPDQ sensitivity of CCT across two different populations.”

The study also compared coastal cutts with westslope cutthroat sourced from a Northwest Montana hatchery. Interestingly, the latter trout were “largely insensitive” to 6PPD-q. That echoes previous studies on the genus Oncorhynchus that found while coho are highly sensitive, sockeye and chum salmon are much less so.

The researchers also investigated the effect sublethal 6PPD-q exposure had on coastal cutthroat’s ability to swim, finding it “negatively affects swimming performance, specifically reducing critical swimming velocity.”

“Overall, this study provides further evidence for the toxicity of 6PPDQ to aquatic animal species. While the long-term ecological impacts of 6PPDQ exposure in CCT remain unknown, these results along with others highlight the potential for population-level effects in Pacific salmonids, particularly across multiple vulnerable life stages in urban-impacted streams. Identifying safer alternatives to 6PPD in tire manufacturing could help protect aquatic ecosystems,” the authors conclude.

So, what can be done about mitigating 6PPD-q? That was one of the topics of a workshop organized by members of the Oregon Fish and Wildlife Commission earlier this year.

While there is no replacement for the tire preservative on the horizon – and the leading contender “still has just as bad effects on the aquatic life” – the problem is still thought to be workable, at least compared to contamination from so-called forever chemicals. That’s because the primary source of contamination is “pretty much just high-traffic roads that drain to streams,” and there are known treatments available, according to Katie Holzer, a senior environmental specialist with the city of Gresham.

Those include structures already in place – bioretention swales, proprietary filters and porous pavements. Initially meant to filter heavy metals, pesticides and other chemicals out of runoff, it turns out they are also helpful in dealing with 6PPD-q, and the mix for runoff ponds is pretty simple.

Earlier this year, scientists at King County’s Water and Land Resources Division as well as researcher Curtis Hinman confirmed that running stormwater through a mix of roughly 70 percent sand, 20 percent coconut fiber and 10 percent biochar, with a small proportion of engineered sand, iron aggregate and aluminum thrown in, filtered out 6PPD-quinone in a laboratory setting, rendering treated water safe for coho They now plan to try it in the wild on Whatcom Creek by the end of 2025.

Another presenter at the Oregon commission workshop pointed to targeted street sweeping as a potential way to help keep the toxin out of drains dumping into streams.

Tires aren’t going away anytime soon, if ever, but identifying species impacted by 6PPD-q rolls on.