A scenario-based risk assessment framework for tyre wear particles in European seas

Tyre wear particles (TWPs) are an emerging pollutant of concern due to their potential risks to ecosystems and human health, yet they remain absent from European pollution monitoring and risk assessment (RA) frameworks. This study introduces a novel scenario-based RA framework tailored to complex contaminants, using European regional seas as a case study. The framework applies three scenarios that reflect the availability of empirical data and guide when modelled exposure or hazard estimates must be used. This structured approach provides transparency and flexibility for emerging pollutants where conventional tools, such as species sensitivity distributions (SSDs), fail due to scarce, inconsistent, or non-comparable datasets. TWPs pose a dual challenge: they are both physical particles and carriers of tyre wear chemicals (TWCs), which leach into aquatic systems as tyre wear leachates (TWLs). Current evidence suggests TWCs drive most toxicity, but their quantification is hindered by overlapping sources, variable composition, and limited marine ecotoxicity data. To address these gaps, a riverine emission model estimated that 82 million-1.2 billion TWPs may enter European seas annually, with predicted concentrations of 0.0001-0.016 particles m³ . The Mediterranean receives the highest annual load, followed by the North-East Atlantic, Black Sea, and Baltic Sea. While modelled TWP concentrations fall below generic microplastic thresholds, TWCs may pose unaccounted ecological risks. This study highlights the innovation of the three-scenario framework, identifies critical data and regulatory gaps, and calls for harmonised monitoring, improved toxicity testing, and integration of TWPs and TWCs into EU policy to advance Zero Pollution goals.