According to https://hashilthsa.com/news/2026-03-23/tire-chemicals-rain-run-proving-toxic-coho-salmon, researchers have tied a breakdown product from a common tire additive to lethal pulses of toxicity in urban streams that kill juvenile Coho salmon.
The work, led by Dr. Erik Krogh of Vancouver Island University with support from the BC Conservation Foundation, zeroes in on 6PPD-quinone, or 6PPDQ. That molecule forms when the tire antiozonant 6PPD reacts with oxidants in air, and it leaches off tire wear particles on roads.
When rain hits pavement, those particles are flushed into storm drains and carried into creeks. The surprising and grim finding is how potent 6PPDQ is: concentrations measured at parts-per-trillion can be acutely toxic to Coho, producing rapid die-offs in small urban streams.
This is not a small pilot study. Thirty-five local groups, citizen scientists, and First Nations sampled more than 60 waterways at 140 sites, spanning from Victoria to Campbell River. The largest concentrations showed up in heavily trafficked, paved urban areas where tire dust is swept quickly into storm systems.
VIU graduate students developed a rapid testing protocol that allowed the team to process more than 100 samples a day. By November 2025 the project had analyzed over 6,400 samples. Results showed 6PPDQ above lethal thresholds for juvenile Coho in 26 waterways, and exceeding B.C. acute water quality guidelines in 36 waterways.
The data reveal a clear pattern: spikes in 6PPDQ during storms, most pronounced in small streams draining catchments with lots of impervious surface. Those flash pulses coincide with the timing of documented urban salmon die-offs, often described as urban runoff mortality syndrome.
Researchers say the problem reaches beyond Coho. Field observations and other studies point to impacts on Chinook, trout, and steelhead, all vulnerable to the same toxic pulses carried in stormwater.
Addressing the issue requires two lines of action. First, green infrastructure can intercept and filter runoff before it reaches streams. Tools include rain gardens, bio-retention ponds, and other stormwater controls designed to capture road-derived particulates.
Second, the tire industry needs to move toward safer chemistries. The current focus is on finding 6PPD alternatives that preserve tire performance and safety while not producing toxic oxidation products. Regulators are taking notice, and the U.S. EPA is assessing potential actions after tribal petitions.
The immediate goal of the VIU and BC Conservation Foundation effort is pragmatic mapping. By identifying hotspots and timing of pulses, the team aims to guide municipal stormwater management, prioritize green infrastructure, and reduce the acute die-offs linked to urban runoff.
For drivers and tire professionals the report is a reminder that tire wear is not just a maintenance or performance issue, it is an environmental source term. Managing where and how that dust enters waterways, and moving to safer chemical choices in tires, are both part of the solution to protect salmon populations in urban watersheds.
