Modelling tyre particles in the aquatic environment

Published: 11 September 2018

Every car owner knows that tyres wear down and need to be replaced for new ones every now and then . But what happens with the rubber that our tyres lose while driving ? Are tyre particles ending up in our marine environment? And if so how much?

Source of microplastics

Tyre particles have recently been recognized as a source of microplastics present in our environment.  assenger vehicle tyres contain styrene-butadiene rubber and truck tyres natural rubber. But it is not only tyre particles that are released to the environment. Up to 50% of abrased material consists of road wear encrustastions. The European Tyre and Rubber Manufacturing Association (ETRMA) initiated a modelling study by Cardno Chemrisk and Deltares to investigate the fate and transport of tyre and road wear particles (TRWP) into the aquatic environment. A fate and transport model for the Seine catchment (France) and the Scheldt catchment (France/Belgium) has been set up as a case study.

Modelling shows that 2% of TRWP generated at source is released to the estuaries

The modelling study shows that for both catchments about 18% of the TRWP produced is released to the aquatic environment. Of that export a large portion (90% of the TRWP that enter the aquatic environment) is captured in the aquatic sediment as it settles out before reaching the estuaries. A smaller portion (2%) of the overall TRWP generated at source  is eventually exported to the estuaries. The likely range of the uncertainty is within 1.4% to 4.9% export to the estuary (25th and 75th percentile) and in extremes to 0.97% to 13% export to the estuary (10th to 90th percentile). This uncertainty is primarily influenced by the characteristic of the TRWP occurring, in particular the TRWP diameter and TRWP density.

Fig. Conceptual model describing the terrestrial generation and transport of TRWP to the estuary (Unice et al., 2018A).

First integrated watershed-scale mass balance assessment for TRWP

To date there has never been a watershed-scale mass balance assessment for TRWP that also includes the amount that remains in soil, water or the aquatic sediment.  By setting up such a model Cardno Chemrisk and Deltares were able to give insight in the likely amount of TRWP that is exported through the rivers towards the estuaries and how much remains in the fresh water environment, on land or is even captured earlier by waste water treatment or road cleaning. By taking the uncertainty about the actual characteristics of the TRWP into account (for example size, density, shape) the likely range and not just a single estimate was quantified.

Fig. Result for the Seine catchment of the central estimate scenario (most likely scenario) (Unice et al., 2018A).

Results used to discuss mitigation options

The results of this study are a key input to the work by the European TRWP Platform, recently initiated by ETRMA. This platform aims to  share knowledge on the generation and fate and transportation of TRWP in the environment and to explore potential mitigation options for a balanced and holistic approach to  reduce the generation and transportation of TRWP into the environment. Among the participants are European and National governmental bodies,  Joint Research Centre, Road Authorities, as well as representatives from industry, science, water management and NGO’s.

References:

Unice, K.M., Weeber, M.P., Abramson, M.M., Reid, R.C.D., van Gils, J.A.G., Markus, A.A., Vethaak, A.D., Panko, J.M., 2018AI Characterizing export of land-based microplastics to the estuary – Part I: Application of integrated geospatial microplastic transport models to assess tire and road wear particles in the Seine watershed. Science of the Total Environment.

Unice, K.M., Weeber, M.P., Abramson, M.M., Reid, R.C.D., van Gils, J.A.G., Markus, A.A., Vethaak, A.D., Panko, J.M., 2018B. Characterizing export of land-based microplastics to the estuary – Part II: Sensitivity analysis of an integrated geospatial microplastic transport modeling assessment of tire and road wear particles. Science of the Total Environment.