Characterising the emissions, occurrence and fate of tyre wear particles in urban rivers

Tyre and road wear particles (TRWP), generated from the interaction between road surfaces and tyres, are increasingly recognized for their role in microplastic pollution of freshwater systems. The release of these particles into the environment poses potential toxicological risks to aquatic organisms due to both the chemicals added during manufacturing and the adsorption of environmental contaminants. Although annual TRWP emissions have been estimated for various countries, studies simulating TRWP transport through surface runoff to freshwater systems, particularly at high spatial and temporal resolutions, remain limited.
This thesis aims to determine the emissions and exposure of urban aquatic systems to TRWPs at high spatial and temporal resolutions. Firstly, a temporally and spatially resolved model was used to estimate TRWP emissions in the City of York, UK. The exposure modelling used data on tyre particle generation rates, local weather patterns, land cover composition, and wastewater treatment plant characteristics to estimate emissions to different points in York’s river system at a daily resolution.
Secondly, a method was developed for the analysis of TRWPs in environmental samples using Py-GC-MS, focusing on pre-treatment procedures to mitigate matrix interferences. The method involved organic matter digestion and TRWP extraction by density separation, which was then tested by analysing sediment samples collected from regions characterized by significant traffic influence.
Lastly, the proposed methodology was employed to investigate the spatio-temporal distribution of TRWP concentrations in York’s river sediments. The analysis of sediment samples revealed a wide range of TRWP concentrations attributed to differences in river size, depositional characteristics, and monthly precipitation fluctuations. This study underscores the significance of extended sampling periods for a comprehensive assessment of TRWP and microplastic contamination in the environment, as well as the value of employing multiple methods for the analysis of TRWPs (i.e., microscopy and Py-GC-MS) to cross-reference results and reduce uncertainties.