Magnetic association of microplastics in urban road dust: Size distribution and ecological risk

Urban road dust represents a complex reservoir of microplastics (MPs) and anthropogenic magnetic particles, reflecting diverse emission sources and environmental processes. This study investigates the distribution, magnetic properties, and polymer composition of MPs in road dust collected from seven urban sites in Vienna, focusing on particle size fractions (0.2-0.1 mm, 0.1-0.05 mm, and <0.05 mm) and magnetic separation. Magnetic susceptibility (χ), frequency-dependent susceptibility (χ_fd%), anhysteretic remanent magnetization (χ_ARM), and hysteresis parameters were measured to characterize magnetic minerals, while MPs were quantified and identified by polymer type. The finest fraction was strongly magnetic, enriched in superparamagnetic and ferrimagnetic particles, whereas the intermediate and coarse fractions contained both magnetic and nonmagnetic components. The magnetic fraction contained up to seven times more MPs than the nonmagnetic fraction, with the highest concentration of 3500 particles g^-1. Dominant MPs were polyurethane, polyvinyl chloride, and polyethylene, while <0.05 mm exhibited 100% magnetic share, leaving no nonmagnetic material for identification. Sankey diagrams revealed clear flows of polymers across particle sizes and magnetic subfractions. The MP pollution load index showed that magnetic fractions dominate overall contamination, particularly in coarser particles, whereas nonmagnetic fractions contribute primarily to intermediate sizes. Hierarchical cluster analysis highlighted co-varying patterns among MPs, magnetic parameters, and traffic intensity, suggesting that local environmental factors influence MP distribution beyond direct traffic load. These findings underscore the utility of combined granulometric and magnetic fractionation for tracing MPs in urban dust, providing insights into the sources, distribution, and potential risks of MP pollution in urban ecosystems.