Scientific review says health impacts of tire wear emissions remain 'inconclusive'

Geneva – A major scientific review of global research on tire wear emissions has concluded that current evidence remains insufficient to quantify potential human health impacts specifically linked to tire wear particles.

Published in April, the third and final paper in the “state of knowledge” (SoK) series reviewed existing studies on tire and road wear particles (TRWP) and tire-related chemicals.

The review found that "differences in sampling approaches, detection techniques and analytical methodologies limit reliable comparison across studies and prevent robust risk assessment."

The SoK series was supported by the Tire Industry Project (TIP) and reviewed more than 850 peer-reviewed scientific publications on tire wear emissions, said TIP in a statement.

The latest paper, authored independently by Kathrin Mueller, Julie Panko, Kenny Unice and Dr Stephan Wagner, found that TRWPs account for "only a small part of" the overall airborne particulate matter in urban environments.

The particles, the study found, generally represent less than 5% of PM2.5 and PM10 levels.

The review also stated that toxicological studies conducted so far do not indicate that TRWP are more harmful than general ambient particulate matter.

Available "in vivo and in vitro data" showed effects that were "similar to, or less potent than, other airborne particle types," it added.

"Despite growing interest, scientific evidence on human exposure to TRWP remains limited and inconclusive," said the study.

Chemicals that are used in tire manufacturing "are detectable in human body fluids, but their sources and exposure pathways have not been clearly linked specifically to tires," it added.

The study noted that many of such chemicals are used in a range of other applications and could not be directly linked to tires.

The paper identified the lack of globally harmonised methods for sampling and analysing tire wear emissions as a major obstacle to drawing firm scientific conclusions.

The authors called for "more coordinated research efforts" and greater standardisation of methodologies to improve the identification, measurement and attribution of tire wear emissions.

Future studies, they said, should "identify potential exposure pathways and examine relevant health outcomes, including potential chronic effects, under realistic exposure conditions covering urban and suburban populations across different regions worldwide."

“Tire wear emissions are a complex topic that we still only partly understand, especially in relation to human health,” said Dr Stephan Wagner, one of the paper’s lead researchers.

While research has advanced our understanding of TRWP, Wagner said the current data "simply isn’t robust enough to quantify any potential health risks specifically linked to tire wear.” 

He said cross-sector collaboration and improved data sharing would be important to develop “a stronger, more consistent evidence base to inform future decisions.”