Microplastics (MPs) in urban roadside snowbanks: Quantities, size fractions and dynamics of release

The microplastics (MP) pollution has been receiving high attention in recent years, because of the massive amounts ofplastics it contributes to the environment.

Tyre wear and road wear particles (TWPandRWPs) were identified as majorsources of MPs, but the observed data on these particles in urban snow deposits and snowmelt is scarce.

To contributeto remediation of this situation, a study designed to quantify TWPs and RWPs in urban roadside snowbanks, and assessthe MP occurrence in three size fractions, was conducted in the Luleå and Umeå municipalities in Northern Sweden.

TWPs and RWPs were determined in three size fractions: 50–100 μm, 100–300 μm, and ≥300 μm, and their releasefrom melting snow was investigated in the laboratory under controlled conditions.

Among the MPs identified insnow and the associated snowmelt samples, a majority consisted of both types of particles (T&RWPs) with an averageof 20,000±48,000 number/L, whereas other MPs (fibres, fragments, flakes, and films of plastic) were much less plentifulwith an average concentration of 24±16 number/L. The largest proportion of T&RWPs was detected in the sizefraction 50–100 μm (around 80%), and the smallest proportion was in the fraction ≥300 μm (about 2%). Of theT&RWPs, about 85%were black bitumen particles (RWPs), composed of bitumen, mineral material and polymer modifiers,and 15% were tyre wear particles (TWPs) composed of rubber.

The laboratory snow melting experiments demonstratedthat urban snow stored MPs, which were eventually released during snowmelt. The ultimate fate of releasedMPs would depend on snowmelt drainage; it may either drain away from the road pavement and infiltrate into theground, or enter the road gutter and be conveyed to storm sewers discharging to the receiving waters.