The issue is particularly acute after rainstorms, the paper's authors contend, when the death rate of salmon spawning upstream soars, according to decades of research into the subject.
The paper's authors link the presence of 6PPD in these rivers and streams to tire treadwear particles (ttp) that are part of roadway runoff.
"These results reveal unanticipated risks of 6PPD antioxidants to an aquatic species and imply toxicological relevance for dissipated tire rubber residues," the authors state in the paper's abstract.
The USTMA notes in its statement that 6PPD is used in tire production because it helps tires resist degradation and cracking, physical characteristics that are vital for passenger safety.
"The tire industry remains committed to safety and sustainability and understanding the impact of tire materials on the environment," the trade group said, noting it is reviewing the study and has contacted the University of Washington researchers to discuss their findings.
The study — "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon" — notes that 6PPD itself is not necessarily the problem. Instead the chemical transforms as it breaks down and reacts with ozone into what the study's authors describe as a more toxic and mobile "6PPD-quinone transformation product."
The study concludes that "environmental discharge of 6PPD-quinone is particularly relevant for the many receiving waters proximate to busy roadways. It is unlikely that coho salmon are uniquely sensitive, and the toxicology of 6PPD transformation products in other aquatic species should be assessed.
"If management of 6PPD-quinone discharges is needed to protect coho salmon or other aquatic organisms, adaptive regulatory and treatment strategies along with source control and 'green chemistry' substitutions (i.e., identifying demonstrably non-toxic and environmentally benign replacement antioxidants) can be considered."