Tire Chemical 6PPD-Quinone Spikes 240% in Santa Cruz Salmon Creeks

Rainstorms are washing the toxic tire-rubber byproduct 6PPD-quinone into Santa Cruz County creeks at sharply higher concentrations, with water testing showing jumps of roughly 240% at Felton and Zayante Creek and about 230% at Branciforte Creek following heavier storms, according to a report by Hoodline citing sampling reported by Good Times.

The chemical poses an acute threat to coho salmon, which have been listed as endangered in Santa Cruz County since 2005.

Sampling Results Across Four Coho Recovery Waterways

According to the water testing data, crews sampled four coho recovery waterway locations—including Zayante Creek, Felton, Branciforte Creek, and the San Lorenzo River—first on Nov. 8, 2022, shortly after early-season rains, and again on Feb. 3, 2023, following heavier flooding.

Concentrations of 6PPD-quinone more than doubled at three of the four sites, with Branciforte Creek recording the highest levels. The lone exception was the San Lorenzo River near downtown Santa Cruz, where measured concentrations declined from 6.2 nanograms per liter to less than 2 nanograms per liter between the two sampling events.

How 6PPD Oxidizes Into a Lethal Salmon Toxin

The compound originates as 6PPD, an antiozone chemical additive blended into motor-vehicle tires to prevent rubber from degrading. As tires wear against pavement, 6PPD reacts with ozone and oxidizes into 6PPD-quinone, which washes into storm drains and spawning streams during rain events.

Laboratory research published in Science found that tire-tread leachate caused 98.5% mortality among juvenile coho salmon within 24 hours of exposure (with a median lethal concentration of 0.8 ± 0.16 micrograms per liter), while Good Times noted separate thresholds showing 50% mortality at 95 nanograms per liter for adult coho and 41 nanograms per liter for juveniles.

California’s Department of Toxic Substances Control began the process of listing motor-vehicle tires containing 6PPD as a Priority Product under the Safer Consumer Products program in May 2022, requiring tire manufacturers to evaluate safer alternatives while the U.S. Environmental Protection Agency develops standardized water testing methods and watershed hotspot mapping for green stormwater infrastructure.