Probing tyre microplastic toxicity

The first phase of a study into the toxicity of tyre-particle compounds and how readily they are absorbed by living organisms has just been completed by EPFL and two other Swiss research institutes.

The significance of this study relates to the fact that tyre and road wear particles are one of the biggest sources of microplastics released into the environment.

The research seeks to shed light on the compounds of those particles as they affect the environment and has implications for the study of tyre microplastics globally. The work is sponsored by leading tyre manufacturers.

It looks specifically at the solubilisation and bio-accessibility of tyre-particle compounds in the digestive systems of rainbow trout.

To conduct their research, the scientists have used an in vitro approach based on simulated gastric and intestinal fluids. 

They have analysed 11 compounds and find that the solubilisation rate in gastrointestinal fluids ranges from 0.06% to 44.1%, and that this rate can vary depending on whether food is co-ingested. 

A particular compound of study was 6PPD-quinone (6PPD-Q), which is a toxic by-product of the oxidation of 6PPD – an antioxidant used widely in the tyre industry. If tyre particles containing 6PPD-Q are ingested, alongside amphipods, the compound solubilised in the fish gut increases. 

However, co-ingestion has the opposite effect with other chemical compounds. 
Additional experiments are under way to evaluate the toxicity of many other tyre-particle substances. The goal is to determine the bio-accessibility, bioaccumulation and toxicity of tyre-particle compounds and related additives. 

Now phase one is complete, phase two will begin and will involve examining how the compounds are passed up the food chain.

'These compounds are more complicated than standard polymers like polystyrene and PET – and there are probably hundreds of them,' says Florian Breider, Head of EPFL’s Central Environmental Laboratory (CEL) and the corresponding author of two papers on the topic. 

'Most research today focuses on microplastic pollution from packaging and waste, but microplastics from tyres account for 30-40% of plastic pollution in the environment. So, this kind of pollution is worth studying too,' says Thibault Masset, a Postdoctoral Student at CEL, and lead author of both papers.