Toxicity of tire wear particles rising up industry agenda

Hanover, Germany - Issues around tire wear are now topping the agenda of the tire manufacturing industry, with much effort among leading players and industry bodies to establish standarised measurement protocols to guide future regulation in this increasingly critical area.

But while much of the attention is on quantifying the rubber ‘dust’ and tire & road wear particles (TRWPs) generated by abrasion on road surfaces, and how driving behaviour affects this, another topic – toxicity – could soon take centre-stage.

According to Nick Molden, founder & CEO of UK-based Emissions Analytics, each car generates 4kg/year of abraded rubber, equivalent to 6 million tonnes per annum globally.

These ultrafine – below 100nm – particles are airborne before eventually settling around roadways, with larger particles being washed into drainage systems, said Molden, who is also an honorary research fellow at Imperial College London.

This, in turn, can lead to tire wear reaching land and marine environments, he added in a presentation, titled ‘Independent VOC analysis of European and American market tire particles’, at the Tire Technology Expo 2023, staged 21-23 March in Hanover.

There are then multiple vectors for human inhalation or ingestion, with some research estimating that there is on average 135ng of rubber chemical-derived 6PPD (n-(1,3-dimethylbutyl)-n’-phenyl-p-phenylenediamine) and 6PPD-quinone in the urine of every adult.

Molden also noted that 6PPD-quinone, formed by the oxidation of rubber antioxidant 6PPD, has recently been linked with deaths of coho salmon and trout in the US.

In a recent research programme, Emissions Analytics analysed 228 ‘light duty’ tires sourced from retail outlets across Europe and North America.

The results showed significantly less human toxicity potential in US tires, due to lower aromatic and alkanes content. The marine toxicity levels recorded were much less significant in scale.

In similar testing of 55 ‘heavy duty’ tires, less aromatics and alkanes were found in tires sourced in North America, compared to Europe, though Molden reported “high marine toxicity potential from US tires, but mixed effects on human health.”

Read the full report in the March/April issue of European Rubber Journal magazine or the online Featured content article under the 'Focus' tab on the ERJ homepage.