"Dust in the Fire" : First Investigation of Microplastics in Urban Road Dust via Magnetic Separation of Strong and Weak Components in Vienna, Austria

Urban road dust in Vienna, Austria’s capital, is a complex reservoir of microplastics (MPs) and anthropogenic magnetic particles, acting as a vector and source of environmental pollution. This study presents the first comprehensive analysis of road dust in Vienna using magnetic separation to investigate MPs and their association with magnetic properties. Seven urban sites were sampled, and dust was fractionated into 0.2–0.1 mm, 0.1–0.05 mm, and <0.05 mm particle sizes. Magnetic susceptibility (χ), frequency-dependent susceptibility (χfd%), anhysteretic remanent magnetization (χARM), and hysteresis parameters were measured to characterize magnetic minerals, while MPs were quantified and polymer types identified using laser direct infrared imaging (LDIR).

Results show that the finest fraction (<0.05 mm) is entirely magnetic, enriched in superparamagnetic and ferrimagnetic particles, whereas intermediate and coarse fractions contain both magnetic and non-magnetic components. Magnetic extracts contained the highest MPs concentrations, up to 25,423 particles/g, predominantly polypropylene (PP) and polyurethane (PU), indicating strong traffic-related sources such as brake dust and tire wear. Non-magnetic fractions were dominated by polyethylene (PE) and polyethylene terephthalate (PET), reflecting consumer waste contributions. Magnetic separation revealed hidden MPS patterns and enabled clear differentiation of polymer flows across particle sizes using Sankey diagrams.

Microplastic contamination was assessed with the Microplastic Contamination Factor (MCF) and Pollution Load Index (MPLI). The largest magnetic fractions showed dangerous to extremely dangerous MPLI levels (19.6–36.9), while medium fractions ranged from moderate to high contamination, and the finest fraction (<0.05 mm) was mostly uncontaminated except at one hotspot (27.4). Non-magnetic fractions exhibited moderate contamination primarily in the medium size fraction, confirming that traffic-related magnetic dust is the main contributor to urban MPs pollution. Hierarchical cluster analysis highlighted co-varying patterns among MPs, magnetic properties, and traffic intensity, indicating that local environmental factors influence MPs distribution beyond direct vehicular load.

These findings demonstrate that magnetic separation combined with granulometric analysis is a powerful tool for tracing microplastics in road dust and assessing their ecological significance. Fine, highly magnetic fractions concentrate MPSs from vehicular sources, representing the highest environmental risk due to potential atmospheric transport and runoff into soil and water systems. Coarser and non-magnetic fractions reflect additional inputs from infrastructure degradation and urban waste, emphasizing the multiplicity of sources. This study provides the first quantitative evidence linking magnetic properties of road dust with microplastic pollution in Vienna, Austria, and highlights the value of magnetic monitoring for rapid identification of high-risk dust fractions. Overall, this work establishes a baseline for urban MPs contamination in Vienna, showing strong size-dependent and magnetism-dependent patterns in road dust, and offers an effective methodology for future monitoring and risk assessment of microplastic pollution in urban environments.

This research was funded in whole by the National Science Centre, Poland under grant number 2021/43/D/ST10/00996.